ATMOSPHERIC OZONE RESEARCH AND ITS POLICY IMPLICATIONS
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Studies in Environmental Science 35
ATMOSPHERIC OZONE RESEARCH AND ITS POLICY IMPLICATIONS Proceedings of the 3rd US-Dutch International Symposium, Nijmegen, The Netherlands, May 9- 13 , 1 9 8 8
Organized by the EnvironmentalProtectionAgency, United States of America, and the Ministry of Housing, Physical Planning and Environment, The Netherlands Edited by
T. Schneider National Institute of Public Health and Environmental Protection, 3 7 2 0 BA Bilthoven, The Netherlands
S.D. Lee Harvard University, Energy and Environmental Policy Center, Cambridge, M A 02 138, U.S.A. G.J.R. Wolters Ministry of Housing, Physical Planning and Environment, 2260 MB Leidschendam, The Netherlands L.D. Grant US Environmental Protection Agency, Research TrianglePark, NC 2 7 7 1 1, U.S.A.
ELSEVlEH Amsterdam - Oxford - New York -Tokyo
1989
ELSEVIER SCIENCE PUBLISHERS B.V. Sara Burgerhartstraat25 P.O. Box 21 1, 1000 AE Amsterdam, The Netherlands
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First edition 1989 Second impression 1990
ISBN 0-444-87266-3
0 Elsevier Science Publishers B.V., 1989 All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior written permission of the publisher, Elsevier Science Publishers B . V . 1 Physical Sciences & EngineeringDivision, P.O. Box 330, 1000 AH Amsterdam, The Netherlands.
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Other volumes in this series
1 Atmospheric Pollution 1978 edited by M.M. Benarie
2 Air Pollution Reference Measurement Methods and Systems edited by T. Schneider, H.W. de Koning and L.J. Brasser
3 Biogeochemical Cycling of Mineral- Forming Elements edited by P.A. Trudinger and D.J. Swaine
4 Potential Industrial Carcinogens and Mutagens by L. Fishbein
5 Industrial Waste Management by S.E. Jprrgensen 6 Trade and Environment: A Theoretical Enquiry by H. Siebert, J. Eichberger, R. Gronych and R. Pethig 7
Field Worker Exposure during Pesticide Application edited by W.F. Tordoir and E.A.H. van Heemstra-Lequin
8 Atmospheric Pollution 1980 edited by M.M. Benarie 9 Energetics and Technology of Biological Elimination of Wastes edited by G. Milazzo 10 Bioengineering, Thermal Physiology and Comfort edited by K. Cena and J.A. Clark 11 Atmospheric Chemistry. Fundamental Aspects by E. M6szBros
12 Water Supply and Health edited by H. van Lelyveld and B.C.J. Zoeteman 13 Man under Vibration. Suffering and Protection edited by G. Bianchi, K.V. Frolov and A. Oledzki 14 Principles of Environmental Science and Technology by S.E. Jprrgensen and I. Johnsen
15 Disposal of Radioactive Wastes by Z. Dlouhi, 16 Mankind and Energy edited by A. Blanc-Lapierre 17 Quality of Groundwater edited by W. van Duijvenbooden, P. Glasbergen and H. van Lelyveld
18 Education and Safe Handling in Pesticide Application edited by E.A.H. van Heemstra-Lequinand W.F. Tordoir 19 Physicochemical Methods for Water and Wastewater Treatment edited by L. Pawlowski 20 Atmospheric Pollution 1982 edited by M.M. Benarie 21 Air Pollution by Nitrogen Oxides edited by T. Schneider and L. Grant 22 Environmental Radioanalysisby H.A. Das, A. Faanhof and H.A. van der Sloot 23 Chemistry for Protection of the Environment edited by L. Pawlowski, A.J. Verdier and W.J. Lacy
vr 24 Determination and Assessment of Pesticide Exposure edited by M . Siewierski 25 The Biosphere: Problems and Solutions edited by T.N. Veziroglu 26 Chemical Events in the Atmosphere and their Impact on the Environment edited by G.B. Marini-Bettblo 27 Fluoride Research 1985 edited by H. Tsunoda and Ming-Ho Yu 28 Algal Biofouling edited by L.V. Evans and K.D. Hoagland 29 Chemistry for Protection of the Environment 1985 edited by L. Pawlowski, G. Alaerts and W.J. Lacy 30 Acidification and its Policy Implications edited by T. Schneider 31 Teratogens: Chemicals which Cause Birth Defects edited by V. Kolb Meyers 32 Pesticide Chemistry by G. Matolcsy, M. Nhdasy and V. Andriska
33 Principles of Environmental Science and Technology (second revised edition) by S.E. Jargensen 34 Chemistry for Protection of the Environment 1987 edited by L. Pawlowski, E. Mentasti, C. Sarzanini and W.J. Lacy
VII CONTENTS
Foreword The E d i t o r s
SESSION I
............................................
XVII
PLENARY SESSION: WELCOME AND OVERVIEW PAPERS
Opening Address P.J.Verkerk
............................................
3
Keynote Address V.A.Newil1
.............................................
11
Ozone Health E f f e c t s and emerging Issues i n Relation t o Standards s e t t i n g M.Lippmann
21
Photochemical Oxidant Formation: Overview o f c u r r e n t Knowledge and emerging Issues 6.Dimitriades
..........................................
35
Current Knowledge o f Ozone on Vegetation/Forest E f f e c t s and emerging Issues G.H.M.Krause and B.Prinz
45
Global elemental Cycles and Ozone J.van Ham
57
Changes i n atmospheric Composition and C1 imate C.J.E.Schuurmans
73
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SESSION II
TROPOSPHERIC OZONE, OXIDANTS AND PRECURSORS: SOURCES AND LEVELS
Motor Vehicles as Sources o f Compounds important t o tropospheric and stratospheric Ozone F.M.Black
..............................................
85
VIII
Emission Inventories for Europe C.Veldt ................................................
111
Sources and Levels of Background Ozone and its Precursors and Impact at Ground Level A.P.Altshuller .........................................
127
Trends in atmospheric Trace Gases S.A.Penkett ............................................
159
Concentrations and Patterns of Ozone in Western Europe R.Guicherit ............................................
167
Concentrations and Patterns of photochemical Oxidants in the United States B.E.Tilton and S.A.Meeks ...............................
177
Trends in ambient Ozone and Precursor Emissions in U.S. urban Areas T.C.Curran .............................................
195
Relationships among Ozone Exposure Indicators in the United States T.McCurdy ..............................................
205
SESSION I I I
EFFECTS ON VEGETATION AND ECOSYSTEMS
Analysis of Crop Loss for alternative Ozone Exposure Indices D.T.Tingey, W.E.Hogsett and E.H.Lee
219
Effects of Ozone on agricultural Crops S.V.Krupa and M.Nosa1
229
....................
..................................
Effects of Ozone and Ozone-acidic Precipitation Interaction on Forest Trees in North America W.J.Manning 239
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Evaluation of Ozone Effects on Vegetation in The Nether1 ands A.E.G.Tonnei jck
........................................
251
IX
Consequences of decreased atmospheric Ozone: Effects o f ultraviolet Radiation on Plants L.O.Bj8rn ..............................................
261
What are the Effects of UV-B Radiation on Marine Organisms? 269 R.C.Worrest ............................................
SESSION IV
EMERGING HEALTH STUDY METHODOLOGIES AND ISSUES
Critical Issues in Intra- and Interspecies Dosimetry of Ozone F. J .Mi 11 er and J .H.Overton .............................
281
Do functional Changes in Humans correlate with the Airway
Removal Efficiency of Ozone? T. R.Gerri ty and W. F .McDonnel 1
..........................
293
Extrapulmonary Effects of low Level Ozone Exposure E.Yokoyama, 1.Uchiyama and H.Ari to .....................
301
Responses of selected reactive and nonreactive Volunteers to Ozone Exposure in high and low Pollution Seasons J.D.Hackney, W.S.Linn, D.A.Shamoo and E.L.Avo1 ......... 311 Dosimetric Model of acute health Effects of Ozone and Acid Aerosols in Children M.E.Raizenne and J.D.Spengler ..........................
319
Is there a Threshold for human health Risk from Ozone? D.B.Menze1 and R.L.Wolpert .............................
331
Ozone-induced Changes in the Pulmonary Clearance of 99?c-DTPA in Man H.R.Kehr1, L.M.Vincent, R.J.Kowalsky, D.H.Horstman. J. J.O-Nei1, W.H.McCartney and P.A.Bromberg ............. 343
X SESSION V
GLOBAL ATMOSPHERIC CIRCULATION AND MODELING
Chemistry o f stratospheric Ozone Depletion i n c l u d i n g possible Mechanisms underlying the A n t a r c t i c Ozone Hole G.D.Hayman
.............................................
355
P o t e n t i a l E f f e c t s o f stratospheric Ozone Depletion and global Temperature Rise on urban Photochemistry M.W.Gery, R.D.Edmond and G.Z.Whitten
365
A Scenario Study o f t h e Greenhouse E f f e c t J.Rotmans
377
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SESSION V I
MOBILE SOURCE CONTROL TECHNOLOGIES
Motor Vehicle Contribution t o global and transported A i r Pol 1u t i o n M.P.Walsh and C.A.Moore
................................
387
Evaporative and r e f u e l i n g Emissions: Options f o r Control i n the U.S.A. R.A.Rykowski and J.F.Anderson 405
..........................
Evaporation and r e f u e l i n g Losses: Options f o r Control i n Europe A.Friedrich
423
Heavy Duty Diesel Emissions Control: I m p l i c a t i o n s f o r Fuel Consumption H.D.Freeman
431
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............................................
Effectiveness o f Control Technology i n Use and I m p l i c a t i o n s f o r a P o l i c y on T r a f f i c Emissions 443 L.C.van Beckhoven and Y.J.Zwalve
.......................
Overall P r o g r a m f o r Monitoring t h e Emission Behaviour o f new and I n - t r a f f i c Motor Vehicles K.Becker
455
Mobile Source Control Strategies i n The Netherlands M.Kroon
467
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................................................
XI
SESSION VII
MECHANISMS OF HEALTH EFFECTS
Persistence of Ozone-induced Changes in Lung Function and Ai m a y Responsiveness L. J.Fol i nsbee and M. J.Hazucha ..........................
483
Ozone-induced Lung Function Changes in normal and asthmatic Subjects and the Effect of Indomethacin W.L.Eschenbacher, R.L.Ying, J.W.Kreit and K.B.Gross .... 493 Effects of Ozone on the Production of active bactericidal Species by A1 veol ar Macrophages M.A.Amoruso, J. E. Ryer-Powder, J .Warren, G. W i tz and B.D.Goldstein ..........................................
501
Impact Mechanisms of Ozone at Cell Level I.Rientjens, L.van Bree, A.Konings, P.Rombout and G.Alink ................................................
513
Ozone-induced structural Changes in Monkey Respiratory System D.M.Hyde, C .G. P1 opper, J .R.Harkema, J .A. St .George, W.S.Tyler and 0.L.Dungworth ............................
523
SESSION VIII CHRONIC OZONE EXPOSURE HEALTH EFFECTS The Impact of a 12-Month Exposure to a diurnal Pattern of Ozone on pulmonary Function, antioxidant Biochemistry and Immunology E.C.Grose, M.A.Stevens, G.E.Hatch, R.H. Jaskot, M. J.K.Selgrade, A.G.Stead, D.L.Costa and J.A.Graham .... 535 Effects of repeated Exposure to 0.15 ppm O3 for four Months on bronchial Reactivity in Guinea Pigs (4 hrs/day; 5 days/wk) J.Kagawa, M.Haga and M.Miyazaki ........................ 545 Respiratory Tract Dosimetry of [18]O-labeled Ozone in Rats: Implications for a Rat-human Extrapolation of Ozone Dose 6.E.Hatch, M. J.Wiester, J .H.Overton and M.Aissa ........ 553
XI1
SESSION I X
ATMOSPHERIC CHEMISTRY AND MODELING
The Use o f Ozone Modeling i n t h e Design o f Control St r at eg ies E. L.Meyer Jr.
563
Ozone and Oxidants i n t h e planetary boundary Layer R.M.van A a l s t
573
Comparison o f chemical Mechanisms i n photochemical Models R.G.Dement and A.M.Hough
589
I n t e r a c t i o n o f planetary boundary Layer and f r e e Troposphere P J H Bui1tj e s
605
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...
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Development and Evaluation o f the regional Oxidant Model f o r the Northeastern United States 613 K. L. Schere and R.A.Way1 and
.............................
Evaluation o f Ozone Control Strategies i n t h e Northeastern Region o f the United States N.C. Possiel , J.A.Ti kvart, J.H.Novak, K.L.Schere and E. 1.Meyer
..............................................
623
Photochemical Oxidant Model A p p l i c a t i o n w i t h i n t h e Framework o f Control Strategy Development i n t h e Dutch/ German P r o g r a m PHOXA J.Pankrath
.............................................
633
C a l c u l a t i o n o f Long Term averaged Ozone Concentrations F.A.A.M.de Leeuw, H.J.van Rheineck Leyssius and P.J.H.Builtjes
.........................................
647
Model Calculations o f Ozone i n t h e atmospheric boundary Layer over Europe j3.Hov
657
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XI11
SESSION X
STATIONARY SOURCE CONTROL TECHNOLOGIES
Hydrocarbons 2000 N.Stenstra
667
VOC Control i n Storage and Process Industry J. J.Verhoog
675
NOx Control Technology f o r large Combustion I n s t a l l a t i o n s J.van der Kooij
681
Perspectives f o r 1ow-solvent Pal nts J.C.den Hartog
691
............................................. ............................................ ........................................
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SESSION X I
RECENT STUDIES ASSESSING THE NEED FOR AN ADDITIONAL LONG-TERM OZONE STANDARD
The Need f o r an eight Hour Ozone Standard P. J .A. Rombout , L. van Bree, S .H. Hei sterkamp and M.Marra
701
The Dynamics o f human Exposure t o tropospheric Ozone P.J.Lioy and R.V.Dyba
711
Pathobiochemical Effects i n Rat Lung related t o episodic Ozone Exposure L .van Bree, P. J .A. Rombout* I.M.C .M. Rientjens J.A.M.A.Donnans and M.Marra
723
Pulmonary Function Studies i n the Rat addressing Concentration versus Time Relationships o f Ozone D. L.Costa, G. E.Hatch, J.Highf 111, M.A.Stevens and J.S.Tepper
733
The i n f l a m a t o r y Response i n human Lung exposed t o ambient l e v e l s o f Ozone H.S.Koren, R.B.Dev1 in, D. E.Graham, R.Mann and W. F.McDonnel1
745
................................................ ..................................
............................
.............................................
..........................................
XIV
Changes i n pulmonary Function and Airway Reactivity due t o prolonged Exposure t o t y p i c a l ambient Ozone Levels D.Horstman, W.McDonnel1, L.Folinsbee, S.Abdu1-Salaam and 755 P.Ives
.................................................
SESSION XI1
SOURCE CONTROL FOR STRATOSPHERIC OZONE PROTECTION
Overview o f Controls f o r Chlorofluorocarbons D.L.Hamn and W.J.Rhodes
765
Moving Forward: Key Implications o f the Montreal Protocol D.Dul1, S.Seide1 and J.Wells
775
Prevention o f stratospheric Modification L.Rei jnders
785
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SESSION X I I I
HEALTH EFFECTS OF STRATOSPHERIC MODIFICATION
Health Effects o f stratospheric Ozone Depletion: An Overview M.L.Kripke
795
Effects o f increased UV-B on human Health J.C.van der Leun
803
Ozone Change and Melanoma F.R.de Grui j l
813
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SESSION X I V
RISK EVALUATION, CONTROL COSTS
AND ASSESSMENT
Application o f the NAAQS Exposure Model t o Ozone T.McCurdy and R.A.Pau1
825
Risk Analysis and Evaluation f o r Development o f an Ozone Control Strategy K.R.Kri jgsheld and S.Zwerver
837
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xv A health Risk primary Ozone S.R.Hayes, R.L.Winkler
Assessment f o r Use i n s e t t i n g the U.S. Standard A.S.Rosenbaum, T.S.Wallsten, R.G.Whitfield, and H.Richmond
.............................
851
Estimated economic Consequences o f Ozone on Agriculture: Some Evidence from the U.S. R.M.Adams
869
Estimating t h e Costs o f c o n t r o l l i n g ambient Ozone i n the United States T.McCurdy, W.Battye, M.Smith and M.Deese
881
Estimated Costs and Benefits o f c o n t r o l l i n g Chlorofluorocarbons D.Du11. S.Seide1 and J.Wells
891
Cost-effectiveness o f s p e c i f i c Control Options f o r VOC Emissions - A European O i l Industry Assessment R.J.Ellis
901
Options f o r VOC-Reduction i n t h e mechanical and e l e c t r i c a l engi neeri ng Industry J.Nobe1
911
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SESSION XV
POLICY ISSUES AND CONTROL STATEGIES
Emerging U.S. Pol i c y regarding stratospheric and Ground Level Ozone D.Clay
919
Ozone Control P o l i c y i n The Netherlands 6. J.R.Wo1 t e r s , S.Zwerver and K.R.Krijgsheld
931
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............
Conrnent on P o l i c y Issues and Control Strategies o f U.S. EPA, Ozone NAAQS M.A.Mehlman
943
The Ozone Layer Depletion and European P o l i c i e s M. J . Scoul 10s
949
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xv I Chairman-s concluding Remarks L.D.Grant
..............................................
953
POSTER SESSION Ozone Aggravates H i stopathology due t o a r e s p i r a t o r y I n f e c t i o n i n t h e Rat H.van Loveren, P. J.A.Rombout and J.G.Vos
967
Adaptation upon Ozone Exposure i n Mice and Rats T.S.Veninga
............................................
975
..............................................
981
......................................
983
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1009
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ORGANIZATION
LIST OF PARTICIPANTS
SUBJECT INDEX
PAPERS RECEIVED LATE
...................................... 1013
Stationary Source Characterization and c o n t r o l S t r a t e g i e s f o r r e a c t i v e v o l a t i l e organic Compounds G.B.Martin
.............................................
1015
Global Modeling o f Ozone and Trace Gases W.L.Grose, R.S.Eckman, R.E.Turner and W.T. Blackshear
... 1021
C a t a l y t i c Control o f Hydrocarbons i n autornative Exhaust H.S.Gandhi and M.Shelef
1037
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XVII
FOREWORD
The t h i r d US-Dutch I n t e r n a t i o n a l Symposium on Ozone Research and i t s P o l i c y Implications was h e l d i n Nijmegen, The Netherlands, from May 9-13, 1988, as one o f the a c t i v i t i e s under the Memorandum o f Understanding between t h e United States o f America and The Netherlands. The f i r s t Symposium i n t h i s series dealing with a i r p o l l u t i o n was held i n Maastricht, The Netherlands, May 1982 and addressed problems associated w i t h n i t r o g e n oxides p o l l u t i o n . The f o l l o w i n g Symposium held i n Williamsburg, V i r g i n i a USA, i n May 1985 discussed issues concerning a i r p o l l u t i o n by aerosols. The present Symposium covers the wide range o f issues concerning ozone p o l l u t i o n both i n t h e troposphere as w e l l as i n t h e stratosphere. Recent research r e s u l t s as w e l l as p o l i c y measures t o reduce t h e impact o f ozone o r secondary e f f e c t s caused by UV-B r a d i a t i o n , were discussed. These proceedings contain the t e x t s o f t h e opening statements made by US and Dutch Government o f f i c i a l s , t h e keynote sddress given by Dr.Vaun Newill, Assistant Administrator o f the United States Environmental Protection Agency and the technical papers presented a t t h e Symposium. I n a d d i t i o n t o the technical papers a number o f poster presentation were made during t h e Symposium. The successful conduct o f an i n t e r n a t i o n a l conference o f t h i s magnitude, depends on the cooperation and dedication o f numerous i n d i v i d u a l s and groups t o whom the e d i t o r s o f t h i s Symposium are deeply indebted. The organization o f t h e Ozone Symposium, e s p e c i a l l y t h e preparation o f the f i n a l p r o g r a m was made possible w i t h the a i d o f t h e members o f t h e US and Dutch Advisory C o n i t t e e s l i s t e d i n t h e present volume, t h e sessions' chairmen and i t s rapporteurs. The invaluable h e l p o f Mr.David S t r o t h e r o f the O f f i c e o f I n t e r n a t i o n a l A f f a i r s o f t h e US Environmental Protection Agency i s g r e a t l y appreciated as w e l l . It would be impossible t o acknowledge here a l l those i n d i v i d u a l s who have c o n t r i b u t e d i n many ways t o the organization o f t h e Symposium and i t s associated events as w e l l as t o the subsequent preparation f o r p u b l i c a t i o n o f t h e present proceedings. However, we would l i k e t o express our sincere appreciation t o a number o f s p e c i f i c i n d i v i d u a l s whose very hard work and cooperation contributed i n such a l a r g e way t o t h e f i n a l success o f t h e conference. We would l i k e t o recognize t h e e x c e l l e n t work p e r f o m d by J.van Ham o f TNO Study and Information Centre f o r Environmental Research who served as i n t e r n a t i o n a l secretary t o the Symposium, by S.Zwerver o f t h e M i n i s t r y o f Housing, Physical Planning and Environment and O t t e l i e n van Steenis o f t h e National I n s t i t u t e o f Public Health and Environmental P r o t e c t i o n as a c t i v e members o f t h e Organizing C o n i t t e e , t o Nel Venis-Pols from TNO Study and
XVIII
Information Centre for Environmental Research and Hanneke Brosi -Heymans from the National I n s t i t u t e of Public Health and Environmental Protection as members o f the Symposium Bureau, without whom the organization o f the Symposium and i t s successful conduct would not have been possible. We are also grateful f o r the excellent organization and conduct by Mrs.M.Schneider o f the partners programne. This programne involved not only the excursions during the conference week but also two well attended weekends before and the a f t e r the conference. Not only s i t e s i n Nijmegen and i t s surroundings were v i s i t e d but also other i n t e r e s t i n g parts o f The Netherlands. Especially the weekend t r i p t o the south-western p a r t o f the country was highly appreciated by the foreign guests. There were during the Symposium week also numerous social events, including the Symposium dinner and several receptions associated with the meeting. Thanks are due t o the M i n i s t r y o f Housing, Physical Planning and Environment, the Council o f the City o f Nijmegen and the Board o f Directors o f the National I n s t i t u t e o f Public Health and Environmental Protection for hosting the receptions during the conference. O f great value t o the Organizing Comittee was also the excellent help given by representatives o f the symposium hotels, Hotel Erica and Hotel Val Monte, both i n Berg en Dal near Nijmegen, Nessrs. Van V l i e t and t h e i r coworkers offered a very high standard o f Dutch h o s p i t a l i t y t o a l l our hosts a t the Symposium. F i n a l l y a special word o f thanks i s due t o O t t e l i e n van Steenis who took also care o f the preparations f o r these proceedings including corrections and adjustments i n the prepared papers, i n time t o meet the deadline f o r pub1ication. We hope t h a t these proceedings from the International Symposium on Ozone Research and i t s Policy Implications, w i l l be h e l p f u l as a reference volume, both f o r research s c i e n t i s t s and policymakers i n the environmental field. Preparations are already under way f o r the f o u r t h US-Dutch international symposium, which i s t o be hosted by the United States o f America i n 1991.
The Editors
T
SESSION I
PLENARY SESSION: WELCOME AND OVERVIEW PAPERS
Chairmen
G.J.R. Wolters L. Grant
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T. Schneider et aL (Editors),Atmospheric Ozone Research and ite Policy Zmplicotiona 1989 Elsevier Science Publishers B.V., Ameterdam Printed in The Netherlands
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3
OPENING ADDRESS
P. J. VEFMERK Ministry of Housing, Physical Planning and Environm8nt, P.O. Box 450, 2260 ME Leidschendam (The Netherlands)
INTRODUCTION On behalf of Minister Nijpels, the Dutch Minister of Housing, Physical Planning and Environment, it is my pleasure to welcome you here in Nijmegen on the ozone-symposium. Minister Nijpels regrets not being here. He has to accompany her majesty Queen Beatrix on a state visit to Canada. In particular I would like to welcome Mr. Newill, Assistant Administrator for Research and Development and Mr.Clay, Acting Assistant Administrator for Air and Radiation from the Environmental Protection Agency in the United States of America. This ozone symposium has been organized by the Environmental Protection Agency of the United States of America and the Ministry of Housing, Physical Planning and Environment of the Netherlands. The close co-operation between these two organizations stems from an agreement between our two countries regarding co-operation on environmental matters. A Memorandum of Understanding to this end was signed in 1980 by Dr. L. Ginjaar, former Dutch Minister of Health and Environmental Protection, and Mr. D.M. Costle, former Administrator of the U.S. Environmental Protection Agency. The first joint symposium, which dealt with air pollution caused by nitrogen oxides (NO,), was held by in Maastricht in 1982. It was one of the most important scientific events of the Dutch-American bicentennial, which celebrated 200 years of unbroken friendly relations between our two nations. Her majesty Queen Beatrix, who attended the opening of the first symposium, attaches great importance to a clean environment. She would most likely have attended this opening too, were it not for the fact that she is currently making a state visit to Canada. Bilateral co-operation between countries offers an opportunity to acquire and deepen knowledge together and to support one
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another in dealing with problems. The fruits of such co-operation can, in turn, provide an impulse for the broader international cooperation which is sorely needed. The problems associated with air pollution from ozone are a good illustration of the fact that environmental protection, preservation and management cannot be the business of one nation alone. This has been made painfully clear to us by the large scale ambient ozone pollution and especially by the damage being done to the ozone layer by CFC's in the stratosphere. A topic like this one, which does not stop at any national boundary but affects the whole world, is very appropriate to the co-operation between our countries in the context of the Memorandum of Understanding. This symposium, like the two earlier ones, is being held in the framework of the Memorandum of Understanding. The first symposium, which was held in Maastricht in 1982, was devoted to nitrogen oxides and was a great success. Since then, there has also been movement in NO, abatement policy internationally. Effective NO, control measures are starting to take shape. Hopefully, many countries will be ready to sign the NO, Protocol to the ECE Convention on Long Range Transboundary Air Pollution late this year; this Protocol will promote the reduction of NO, emissions. Standards are also being prepared for the European Community, including ones pertaining to NOI in vehicle exhaust. The Netherlands, together with the Federal Republic of Germany, Denmark, Portugal and Greece, is striving after stringent EC standards, comparable to those in force in the U.S. The second symposium in the series took place in Williamsburg in 1985 and dealt with the problem of aerosols. I had the opportunity to attend this aerosolsymposium and it is a great pleasure to recognize so many good friends among the audience today. This second symposium was also a succes. New particulate norms, based on the PM-10 standard, are now in effect in the U.S.. The World Health Organization Air Quality Guidelines, brought out late last year, also speak out for the PM-10 standard as the relevant health parameter. The Netherlands is trying to get the PM-10 standard accepted in Europe through the intended revision of the EC Directive on Sulfur Dioxide and Suspended Particulates. This would introduce harmonization on at least a trans-Atlantic, though not a worldwide, scale.
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The major focus of this third symposium, is both to address the problems of tropospheric pollution caused by ozone and other photochemical oxidants and to examine the possible consequences of projected changes in stratospheric ozone resulting from anthropogenic activities. The choice of ozone for this international symposium reflects the need for an international approach to evaluating and dealing with these problems. Air pollution, and especially the ozone problem, is a topic which is receiving a great deal of attention, certainly in the Netherlands. Environmental pollution in general, and air pollution in particular, have international dimensions. That is why the Netherlands considers international co-operation on environmental matters so vitally important. In addition to our existing bilateral agreements, with Poland and the U.S. among other, our country is also entering into an agreement with Canada for co-operation in the environmental field. Minister Nijpels of Environment and his Canadian colleague, Mr. T. MacMillan, will sign a Memorandum of Understanding this week, during Queen matrix's state visit to Canada. The EPA has also organized a workshop on polar ozone this week in Colorado. It is, of course, regrettable that various experts have had to choose between attending that workshop or this ozone symposium. But the fact of these two meetings occurring simultaneously does illustrate the enormous attention for the ozone problem which currently exists. EPA Administrator Lee Thomas underlined this once again most emphatically in a conversation that I had with him several weeks ago. Ozone will also be an important topic in the World Conference on "The Changing Atmosphere Implications for Global Security" to be held in Toronto late next month. In short, ozone is receiving ample international attention. But these events also illustrate the general recognition of the fact that environmental problems do not stop at national borders and that environmental management cannot be allowed to, either. SCALES OF ENVIRONMENTAL PROBLEMS Only 15 or 20 years ago, it was chiefly the local impact of pollution that was recognized. But today's environmental problems are presenting themselves on different scales.
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The lowest level of scale is that of local ecosystems like urban and industrial areas where man has disconnected himself from nature and the ecosystem is governed by technology and its buildings. The indoor environment is also part of this. The small-scale ecosystems of landscapes operate at the regional level. The processes occurring in the soil are the most distinctive ones of regional ecology. The fluvial scale has to do with river basins like those of the Rhine in Europe and the Mississippi in North America. The water cycle is characteristic of fluvial ecosystems: they are fed by moist air currents originating over the oceans to which the water ultimately returns. The continental scale, consisting of continents and oceans, comes above the fluvial scale. The prevailing air and ocean currents - such as the Atlantic Ocean's Gulf Stream - are salient features in these ecosystems. These, in turn, are determinant in the functioning of the smaller-scale ecysystems on the continents and in the oceans. At the global level, it is primarily the flows of energy and radiation which determine the earth's ecosystem. The ozone layer in the stratosphere protects the earth f r o m the harmful effects of the sun's ultraviolet. R6ntgen rays and radiant heat plays a major role in the troposphere. The lowest level of scale - that of local ecosystems - usually falls within the borders of a single country. The political and administrative structure for handling problems on this scale is the most well developed. Because of our country's small size, we in the Netherlands were rather rapidly confronted with the
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necessity of seeking political and administrative frameworks outside our borders. Frameworks which are suitable for dealing with the environmental problems occurring at the various higher levels of scale. Political and administrative structures like the Benelux, EC, OECD, ECE and UN can serve as platforms for solving problems occurring at the various higher levels of scale. New Structures have also been created where they used to be lacking. This has been the case, for example, at the fluvial scale of the Rhine. The International Rhine Commission, which is composed of representatives from the countries through which the Rhine flows, recently drew up the Rhine Action Plan and the environmental ministers of the countries involved formalized the plan on October la', 1987. Discharges of most priority substances will have to be reduced to 50 percent of their 1985 levels in 1995. It is just an exemple. Similar initiatives have been taken in relation to the pollution of the North Sea and the Mediterranean Sea.
A common feature of the environmental problems occurring at the various levels is that they make it painfully clear that the relationship between man and his environment has been distorted and that the resilience of the environment puts limits on our activities. In the highly developed, very densely populated Netherlands, it appears that we may have exhausted environmental resilience. The harmful effects of our activities are becoming manifest in scores of places. Damage to our forests, heathlands and fens, disintegration of our cultural heritage and threats to our drinking water from acidification and eutrophication, the waste problem and the wide diffusion of toxic substances into the food chain are all problems facing the Netherlands. These problems, but also higher scale problems such as climate impacts and damage to the ozone layer, require that measures to control pollution be taken internationally. A symposium like this one can be of great significance in this connection. In the early 19701s, the report of the Club of Rome confronted the world with limits to growth as a consequence of raw material shortage and environmental pollution. Nowadays, the report of the Brundtland Commission, "Our Common Future', is receiving a great deal of attention. This report, like that of the Club of Rome, also observes that equilibria continue to be threatened at various
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levels nearly twenty years later. The Commission concludes that the days of shifting environmental problems to future generations must be ended. Growth must be based on development that meets the needs of the present without compromising the ability of future generations to meet their own needs. They summarize this notion under the term "Sustainable development". The Commission recognizes, and the Netherlands agrees completely, that environmental management has to encompass more than just bailing out the boat to keep it from sinking. We must start now to plug the existing leaks and, more importantly, to ensure that no new ones develop. If we want to pass on a seaworthy boat, if we want to hand the world over to our children and grandchildren in good shape, we must take care that our activities do not lead to consequences which exceed the carrying capacity of our ecosystems. This will only be possible if there is a fundamental change in our attitude about the environment and if this changed attitude carries over into our behavior. SOCIETAL SUPPORT FOR ENVIRONMENTAL PROTECTION The desirability of sustainable development is not something that many people would refute: even stronger, all thoughtful people would endorse the notion that humanity should live in harmony with its surroundings. In short, such a general pronouncement about the environment is one which many people would be ready to make. But, as we all know, "talk is cheap". Even unanimous agreement with this statement worldwide will not mean much in the long run if behavior is not adjusted in a way which reflects this concern. Ultimately, the goal of our policies must be to change both attitudes and behavior. In fact, we are imposing a change in behavior when we promulgate regulations. Regulation is a logical and necessary step given the seriousness of the environmental problems confronting us. But regulations will not change attitudes in the long term. what we ultimately must have, if we are to achieve the goals of sustainable development, is environmentally favorable behavior which springs from personal conviction, not which is imposed from above. One of the things we can do to encourage a move in the direction of sustainable development is to use the price mechanism to reward environmentally favorable behavior. When push comes to
9 SOCIETAL SUPPORT FOR ENVIRONMENTAL PROTECTION
PUBLIC INFORMATION CAMPAIGNS
EDUCATION
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MEDIA
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ENVIRONMENTAL AWARENESS
PRICE MECHANISM
ENVIRONMENTALLY FAVOURABLE BEHAVIOUR
shove, the immediate effect on our pocketbook usually weighs more heavily in our decision-making than our awareness that our activities may affect the environment in a harmful way. For example, most Dutchmen are aware that driving a car is bad for the environment, but that knowledge doesn't seem to inhibit their behavior. There are currently about 5 million automobiles in our small country and we expect that this number will increase to 7 million before the year 2000. But, on the other hand, we have seen that we can achieve results by rewarding certain kinds of behavior financially. Lead free gasoline was introduced in the Netherlands through a government-induced price differential which led the oil companies to voluntarily withdraw normal octane, leaded gasoline from the market. We have also used fiscal measures to accelerate the introduction of "clean" cars. The result is that two out of three newly purchased cars already satisfy the EC standards which have not even entered into force yet.One out of four is equipped with a catalytic converter. But the price mechanism alone will not stimulate the fundamental change in attitude that is needed in the longer term. At least equally important is the diffusion of information. People must be made aware of the consequences that a failure to change behavior will have and of the alternative behavior possibilities open to them. This can be done via the schools, the media and public information campaigns initiated by the government and by environmental organizations. Public information is a policy tool which the Dutch government has used extensively in the past to stimulate changes in attitude and behavior with respect to various environmental issues. The
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role of cars in acidification and the possibilities for disposing responsibly of household items of chemical waste are just two exemples of this. Public information is a policy tool which we must also develop in our approach to dealing with the ozone problem in all its facets. But in order to do this, we must have access to good information. SIGNIFICANCE OF THE OZONE SYMPOSIUM This symposium can support the development of policy especially by providing well-ordered information about the ozone problem and what we can do about it. There are two aspects to the problem. Excessively high tropospheric ozone concentrations occur at the regional and continental scales, while in the stratosphere, we are threatened with an ozone shortage on a global scale. Neither of these problems can be solved at a national level any more, regardless of the size of the nation involved. The solutions will have to be found internationally. The Montreal CFC Protocol is an encouraging sign in this respect, but we in the Netherlands consider it far from adequate. Hopefully, an ECE protocol on NO, will be realized in the near future. But no matter what, the question of whether the emission reductions we are currently aiming at will be enough to prevent further damage to the environment, will be with us for a while. This ozone symposium will contribute to increasing our knowledge about this. And with prior knowledge, we will be able to increase support for the necessary measures through public information. It is important - although towards the end of the symposiumthat policy is also coming into the picture. Both scientists and policy-makers are grappeling with the ozone problem at this symposium. Scientists and policy-makers sometimes look at things somewhat differently, but hopefully these differences will generate interaction which will yield fruit that can lead to a good approach to the ozone problem in the future. I wish you a successful symposium. And I hope that this third symposium will live up to the high expectations that past experience with the previous US-Dutch air symposia has shown to be warranted.
T. Schneider et aL (Editors),Atmospheric Ozow Research and its Policy Implkatwns 1989 Elsevier Science Publishers B.V., Amsterdam -Printed in The Netherlands
KEYNOTE ADDRESS
Vaun A.Newil1 Assistant Administrator, Office o f Research and Development (RD-672), United States Environmental Protection Agency, 410 M Street SY, WASHINGTON DC 20460, USA
On behalf o f the United States Protection Agency, a cosponsor o f t h i s a l l o f you t o beautiful Nijmegen policy issues related t o ground level ozone.
delegation and the U.S.Environmenta1 Symposium, I am pleased t o welcome t o discuss new research findings and ozone p o l l u t i o n and stratospheric
EPA Administrator Lee Thomas has asked me t o express h i s best wishes f o r the success o f t h i s Symposium. He also sends h i s greetings t o the many individuals he enjoyed meeting a t the second U.S.-Dutch Syrpposium three years ago i n Williamsburg. The Williamsburg Symposium, which addressed a wide range o f issues concerning aerosols, followed an equally impressive f i r s t Symposium - held i n Maastricht i n 1982 - which focused on nitrogen oxides. Both o f these e a r l i e r symposia resulted i n proceedings that have been widely read and frequently cited. I n view o f these past successes, I am especially pleased t o help open this, the t h i r d Symposium i n the series. Here we w i l l focus on both tropospheric and stratospheric ozone. Tropospheric ozone, which i s sometimes referred t o as ambient o r "bad' ozone, r e f e r s t o ozone formed near the grounds as a r e s u l t o f photochemical oxidation. It i s a major component o f urban smog and presents a threat t o both human health and the environment
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I n contrast, stratospheric o r "good" ozone i s contained i n a t h i n layer w i t h i n the outer reaches o f the atmosphere, and i t benefits human health and environment. Many would argue t h a t t h i s t h i n layer o f stratospheric ozone has been essential i n the evolution o f l i f e as we know i t on earth, and t h a t i t s disruption o r depletion may have very serious consequences. This Symposium w i l l a r t i c u l a t e the s c i e n t i f i c bases f o r recent public concerns about these two types o f ozone. I would l i k e t o begin the process by i d e n t i f y i n g some o f the technical and p o l i c y issues we w i l l consider throughout t h i s meeting. The p o t e n t i a l l y serious human health e f f e c t s t h a t can be caused by tropospheric ozone have l e d the United States t o set a one-hour standard o f 0.12 ppm. As required by the U.S. Clean A i r Act, we p e r i o d i c a l l y reassess that standard i n l i g h t o f the most recent s c i e n t i f i c data. For example, recent studies indicate t h a t healthy exercising individuals breathing ozone concentrations a t o r s l i g h l y above the U.S. standard can experience reduced lung function, chest pain, and pulmonary congestion. New animal studies show that short- and long-term exposure t o high concentrations o f ozone can cause permanent structural damage t o animal lungs and/or impair lung inmune defense systems. Some o f these recent data have been generated by U.S.Dutch collaborative studies t h a t w i l l be reported l a t e r i n t h i s Symposium. O f p a r t i c u l a r note are new findings t h a t suggest changes i n lung function with more prolonged (6 - 8 hr) exposures t o ozone a t concentrations below the current 0.12 ppm one-hour standard. We are presently evaluating such new health data t o determine whether the e x i s t i n g ozone standard needs t o be adjusted e i t h e r i n terms o f allowable concentration o r averaging time. Any future adjustment w i l l depend l a r g e l y on what i s determined t o be an gdverse decrement i n lung function, as well as the relationship between transient acute e f f e c t s and more serious e f f e c t s frm chronic exposure. Our a b i l i t y t o define t h i s relationship i s closely l i n k e d t o dosimetry and health e f f e c t s modeling, by which we extrapolate from animals t o humans. This topic, which i s being researched a t EPA i n cooperation with researchers o f the National I n s t i t u t e o f Public Health and Environmental Protection (RIVM), Bilthoven, w i l l be addressed a t t h i s conference. I n addition t o health effects, we share w i t h our colleagues i n the Netherlands and many other countries concern about possible ozone damage t o crops, forests, and man-made materials. High ozone l e v e l s can a f f e c t not only c i t i e s , but r u r a l areas as w e l l , due t o large-scale regional d i s t r i b u t i o n o f a i r masses polluted with photochemical oxidants. Episodic accumulations o f such pollutants t h a t are formed over urban centers and then transported t o r u r a l areas have the potential t o reduce crop y i e l d s and t o seriously damage sensitive forest lands, including conmercially
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important plants. The U.S. experience with forest dieback in the Appalachian Mountains and recent European experiences with forest damage represent but two examples where ozone is suspected as a major contributor to forest damage. International cooperation is clearly needed to study and control such ozone damage. Because polluted air masses do not respect international boundaries, they have the potential to cause economic damage in neighbouring countries. In less developed countries, transboundary ozone could further exacerbate existing problems of deforestation and inadequate food production. Control1 ing tropospheric ozone adequately will not be easy, whether through domestic or international action. For example, many o f the major population centers in the United States do not meet the national ozone standard. A few cities experience ozone peaks twice as high as the current standard. Although the U.S. Clean Air Act called for national attainment of the standard by the end of 1987, EPA estimates that about 70 areas have not attained it, and that about 40 of those areas will not attain it in the near future. Some of the areas probably will require many years to achieve the standard, even if extraordinary control measures are taken. Nonattainment of the ozone standard presents one of the most difficult air pollution problems that we now face in the United States. Don Clay, EPA*s Acting Assistant Administrator for Air and Radiation, will discuss U.S. policies and strategies on the ozone non-attainment issue in the last session of this Symposium. Our failure to achieve widespread attainment of the ozone standard is especially disturbing in view of significant efforts undertaken to reduce ozone precursor emissions from both mobile and stationary sources in the United States. A number of factors contribute to the non-attainment experience in many U.S. urban areas, and those factors vary from area to area. Some of the possible reasons for non-attainment include: 1. incomplete implementation of state control strategies; 2. overly optimistic assumptions in state control strategies; 3. higher emissions of volatile organic compounds (VOC's) than assumed in state control strategies; 4. underestimates of VOC-control requirements due to inaccuracies in computer models used to plan control strategies; or 5. combination of all these factors. EPA research efforts that address these different factors, including improvement and validation of the regional oxidant model (ROM) and urban AIRSHED model, will be discussed later in this Symposium. EPA will be presenting recent data concerning hydrocarbon emissions inventories that will allow models to be adjusted for evaporative hydrocarbon emissions and
14 seasonal variations i n temperature. International cooperation t o improve these types o f models and inventories i s very important t o the control o f ground-level ozone. I shall conclude my coments on tropospheric ozone by noting t h a t the severity o f the ozone problem i n many c i t i e s i n the United States and elsewhere w i l l l i k e l y necessitate the implementation o f more stringent a i r p o l l u t i o n control programs. These new programs are expected t o be both c o s t l y and controversial. Unlike many other a i r p o l l u t i o n problems, ozone i s not caused by a few large and well-defined sources. Small, widely dispersed sources w i l l have t o be controlled i n order t o reduce ozone concentrations i n many areas. F o r example, everyday human a c t i v i t i e s such as d r i v i n g automobiles, refueling a t gas stations, drycleaning clothes, and using household products such as paints and cleansers a l l contribute t o the formation o f ozone. Reducing those kinds o f a c t i v i t i e s , o r f i n d i n g substitutes f o r those kinds o f products, may require substantial changes i n 1if e s t y l e. Now l e t me h i g h l i g h t several major points about stratospheric ozone depletion and the i n t e r r e l a t e d problem o f global warming, o r the so-called "greenhouse effect". These two problems are c l e a r l y international i n nature, both i n regard t o t h e i r sources and the scope o f t h e i r potential impacts on human health and the environment. Increased i n d u s t r i a l and agricultural a c t i v i t y during the past two centuries has resulted i n substantial atmospheric loadings o f c e r t a i n gases, such as carbon monoxide, methane, and chlorofluorocarbons (CFC-s) These and many other chemicals are causing important changes i n the chemical composition o f the atmosphere. O f p a r t i c u l a r concern i s the f a c t t h a t the continued o r increased use o f CFC-s may lead t o a substantial net depletion o f stratospheric ozone - an environmental degradation t h a t nay be more advanced than previously be1 ieved. Any s i g n i f i c a n t reduction o f ozone i n the upper atmosphere could mean long-term increases i n the frequency o f skin cancer and cataracts worldwide. It could also have s i g n i f i c a n t impacts on our t e r r e s t r i a l and aquatic ecosystems. In addition, the gases a f f e c t i n g ozone e x h i b i t greenhouse properties; because they t r a p solar energy i n the atmosphere, they could contribute t o future warming o f the earth. The adverse e f f e c t s o f global warming over the long-term extend well beyond higher temperatures. The greenhouse e f f e c t could also r e s u l t i n substantially altered r a i n f a l l patterns, increases i n sea level, l o s s o f s o i l moisture, and changes i n the movement o f storms. These s h i f t s could a l t e r agriculture, forests, wetlands, water resources, and coastal c i t i e s .
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As we look for solutions, we must recognize the unuasual nature of these
new challanges. Both the causes and effects of ozone depletion and global warming are distributed unevenly throughout the world - not just between two countries or within one region. Furthermore, in most cases the adverse environmental impacts in a particular country will not be proportional to its emissions of harmful air pollutants. Thus, traditional approaches to problem solving - domestic legislation, rulemaking, and enforcement - are inadequate to deal with these new problems. The United States has already taken some important domestic regulatory steps to control CFC’s, beginning with a ban on their use in aerosols in 1978. The United States Senate has ratified the Montreal Protocol. Even so, more needs to be done. More research is needed to delineate the full scope of expected impacts due to stratospheric ozone depletion and global warming, along with considerable international cooperation to develop and implement effective control strategies. There is good reason for all of us to be pleased with the Montreal Protocol on Substances that Deplete the Ozone Layer. That protocol was signed by the United States and 23 other nations in Montreal, Canada, on September 16, 1987. The signing of the Montreal Protocol was an historic event in both international relations and environmental protection. For the first time, concerted action has been taken by a group o f nations in anticipation of what could be a major global environmental problem. The Montreal Protocol is a truly international agreement. Signed initially by 24 nations, including Japan and the member countries of the European Community, it has since been signed by an additional seven countries, including the Sovjet Union. Together, these countries account for well over three-quarter of current global production of CFC-s and halons, two of the chemical compound families believed to cause depletion of the ozone layer. The protocol was also signed by many developing countries that do not now produce or use CFC’s and halons in significant quantities, but would be expected to increase use o f these chemicals as their economies develop. The fact that such nations are joining this effort to protect the environment should contribute greatly to the international community‘s ability to address this problem. The protocol would freeze the consumption of CFC*s 11, 12, 113, 114, and 115 at 1986 levels beginning in mid-1989 or six months after entry into force. Beginning in mid-1993, consumption would be reduced to 80% o f 1986 levels, followed by a reduction to 50% of the 1986 level in mid-1998. The protocol would also freeze the consumption of halons 1211, 1301 and 2402 at 1986 levels starting three years after entry into force.
16 I n addition, t h e protoqol contains special provisions t h a t apply t o developing countries. They are allowed an a d d i t i o n a l ten years before they must comply w i t h t h e same reduction schedule. It i s widely believed t h a t s u b s t i t u t e chemicals and technologies w i l l be a v a i l a b l e w i t h i n 10 years, and the protocol encourages major producing and consuming nations t o f a c i l i t a t e t h e access o f developing countries t o safe a l t e r n a t i v e s . The protocol a l s o provides a mechanism f o r change i n t h e reduction schedule. The p a r t i e s t o t h e protocol w i l l p e r i o d i c a l l y review t h e s c i e n t i f i c , technological, and economic data and then meet f o r m a l l y t o decide i f f u r t h e r o r d i f f e r e n t steps t o p r o t e c t the ozone l a y e r are required. The incorporation o f s c i e n t i f i c assessments i n t o the r i s k management process a t an i n t e r n a t i o n a l l e v e l i s a very p o s i t i v e step, and i t should be encouraged i n other areas o f i n t e r n a t i o n a l environmental concern where s c i e n t i f i c understanding can be a n t i c i p a t e d t o evolve. Other s i g n i f i c a n t provisions are also contained i n t h e protocol, b u t I w i l l defer t o Don Clay t o cover these and other aspects o f U.S. p o l i c y f o r addressing stratospheric ozone. I n t e r n a t i o n a l cooperation i s c r i t i c a l t o t h e long-term success o f t h e agreement. The world must now move forward t o implement t h e Montreal Protocol. EPA hopes t h a t meetings such as t h i s Symposium w i l l help f o s t e r r e g u l a t o r y programs t h a t support t h e goals o f t h e Montreal agreement. EPA urges favourable a c t i o n by a l l nations i n implementing i t as q u i c k l y as possible. Crucial t o e f f e c t i v e implementations o f t h e Montreal Protocol are c e r t a i n important research e f f o r t s , some o f which I would l i k e t o h i g h l i g h t today. Based on the r e p o r t from an Ozone Trends Panel f o n d by serveral U.S. and i n t e r n a t i o n a l organizations, t h e r e i s undisputed evidence t h a t t h e atmospheric concentrations o f source gases important i n c o n t r o l 1 i n g stratospheric ozone l e v e l s continue t o increase on a g l o b a l scale. A key challenge f o r EPA-s Stratospheric Ozone Research Progranne i s t o focus i t s e f f o r t s on those s c i e n t i f i c issues o f most concern t o policymakers. The Montreal Protocol can be successful on a g l o i a l scale o n l y i f t h e s c i e n t i f i c comnunity helps inform t h e p o l i t i c a l leaders i n developing and newly i n d u s t r i a l i z e d countries. Although we cannont acheve these r e s u l t s on our own, t h e Netherlands, t h e United States, and o t h e r nations, and other nations represented here can p l a y a c r u c i a l r o l e i n generating s c i e n t i f i c information t h a t i s c r e d i b l e and h e l p f u l t o various nations i n a r r i v i n g a t t h e i r own p o l i c y decisions.
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In the United States, EPA acts as the lead federal agency to: 1. set research goals in response to policy issues regarding stratospheric ozone; 2. coordinate "effects" research to accomplish those goals; 3. synthesize the results of the research which will take place within a number of agencies. For this part, EPA will continue to develop its international resources and research effort as necessary to fulfill its responsibilities under the Montreal Protocol and the U.S. Clean Air Act. According to the protocol, in 1990, again in 1994, and periodically thereafter, major risk assessments are scheduled to determine: 1. whether additional chemicals should be included in the protocol; 2. whether a faster or slower regulatory schedule is appropriate; and 3. whether current controls on chemicals regulated under the protocol are adequate. In light of the Ozone Trends report, EPA Administrator Lee Thomas has written Dr. Mustafa Tolba, Executive Director of UNEP, urging him to expedite the assessment and review process. For these risk assessments, we need to know the likely growth in the concentrations of gases that influence the column density of stratospheric ozone, and we need to understand the relationships between emissions and the potential impact on humans and the environment. EPA will compile and analyze data from both national and international sources to assess the effects of continued release of gases that deplete stratospheric ozone. These will include health effects, ecological effects, and welfare effects such as degradation of natural resources and materials damage. The data currently available for this assessment are incomplete and of highly variable quality. The cooperation of other national and international organizations is essential. EPA risk characterization and scientific assessment will address: 1. Predictions regarding the quantities and impact of continued release of ozone influencing substances into the stratosphere, and the concomitant increase in UV-B irradiation at the surface of the earth; 2. Trends in emissions of ozone influencing gases in the United States and around the world; and 3. The nature, extent, and severity of environmental impacts o f continued release of ozone depleting substances on the United States and other countries. Such impacts will be expressed in socially, institutionally, and economically relevant terms. These assesments will allow EPA to evaluate overall policy implications as new scientific information is developed.
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Five areas of further research or assessment are particularly important to understanding stratospheric ozone depletion. These include research on: 1. terrestrial ecosystems 2. aquatic ecosystems 3. human health 4. tropospheric oxidants and 5. mitigative solutions. As part of its terrestrial ecosystems research program, EPA is coordinating with the U.S. Department of Agriculture to provide preliminary dose-response data on important food crops and associated ecosystem processes. The integrated study will examine the effects o f UV-B radiation on interspecies competition and plant pathogen and pest interactions, the interaction between UV-B radiation and other stresses such as water and nutrient deficiency, and widespread anthrophogenic factors such as global climatic change and tropospheric ozone. These data will allow such factors to be considered in the overall risk assessment process. Little information currently exists regarding the effect of increased levels of UV-B radiation on long-lived or perennial species such as trees. These species are important from an economic as well as an ecological standpoint. EPA research has been initiated to study the effects of UV-B radiation on one commercial species of tree (Loblolly pine), but the impact of UV-B radiation on fores s in the United States and elsewhere also needs to be addressed. For aquatic ecosystems many of the projected results of increased levels of UV-B radiation are of acute concern. For coastal marine ecosystems in particular, where ecological impacts could be of consequence to many important fisheries, there is a pressing need to evaluate likely ecological change due to increased exposure to UV-B radiation. This issue is important not only for the United States and the Netherlands, but for most other seaboard nations as well. Using facilities already at its disposal, EPA will study the effects of UV-B radiation on one Atlantic coast and one Pacific coast fisheries ecosystem. Using fisheries models and food-web dynamics data generated in both areas, EPA will quantitatively'project the needs of UV-B radiation on select fisheries. * Also to be addressed among those critical aquatic ecosystems of recent concern is the Antarctic marine ecosystem. In the area of human health research, recent findings suggest that human exposure to UV-B radiation can lead to inmunological alterations and innnunosuppression, which implies an increased incidence of disease in people of all ethnic backgrounds. Research is needed to: 1. investigate the mechanisms of immunosuppression in animals and humans;
19 2. i d e n t i f y the i n f e c t i o u s diseases t h a t include a stage o r process t h a t could be worsened by exposure t o UV-B r a d i a t i o n and t o develop models t o
explain these diseases;
3 . i n v e s t i g a t e wavelength dependence and develop dose-response information f o r humans concerning the e f f e c t s o f UV-B exposure on t h e incidence o f i n f e c t i o u s diseases; and 4. determine the impact o f UV-B imnunosuppression on vaccination e f f i c a c y . I n addition, cataracts occur i n a l l societies, b u t because o f t h e l i m i t e d access t o surgical f a c i l i t i e s i n many countries, t h e r e are a major cause o f blindness i n l e s s developed countries. Additional EPA funded research on the biology and epidemiology o f cataracts and on methods t o reduce the r i s k o f eye diseases w i l l be pursued. Currently, only a preliminary assessment has been made r e l a t i n g UV-B i r r a d i a t i o n t o possible changes i n concentrations o f ozone p o l l u t i o n a t t h e surface o f the earth. Several f a c t o r s could increase tropospheric ozone p o l l u t i o n , including increased l e v e l s o f UV-B r a d i a t i o n and increased emissions o f methane and other hydrocarbons. This area o f research w i l l address the 1inkages between UV-B r a d i a t i o n and tropospheric ozone production, as w e l l as the s y n e r g i s t i c e f f e c t s o f oxidants and a c i d deposition. From t h i s , EPA w i l l determine some o f the i n d i r e c t e f f e c t s o f UV-B r a d i a t i o n on people, materials and ecosystems i n urban, r u r a l , and wilderness areas. While EPA w i l l conduct research o r assessments i n t h e f o u r areas I j u s t mentioned, a f i f t h area i s o f special i n t e r e s t . As w i t h tropospheric ozone, f i n d i n g new technologies t o m i t i g a t e t h e depletion o f stratospheric ozone i s a major challenge we a l l take. Many o f the p o t e n t i a l a l t e r n a t i v e s t o the current us o f CFC’s involve new o r modified technologies t h a t promise a v a r i e t y o f benefits. I f the claims are true, these a l t e r n a t i v e s would help reduce the upward pressure on p r i c e s t h a t r e s u l t from inadequate supplies o f CFC-s i n the future. Furthermore, new technologies have t o be s p e c i f i c t o t h e needs o f developing countries. The United States would l i k e t o be i n a p o s i t i o n t o present unbiased t e s t i n g data on new technologies i n order t o support f u t u r e negotiations and t o provide technology t r a n s f e r t o such nations. A t a minimum, EPA w i l l provide q u a l i t y assurance regarding these technologies, which w i l l allow the United States t o propose v i a b l e a l t e r n a t i v e s . These evaluations may even lead t o new i n s i g h t s i n t o b e t t e r ways t o achieve reduced dependency on e x i s t i n g CFC-s. It i s expected t h a t t h i s e f f o r t w i l l lead t o the f u t u r e t r a n s f e r o f engineering systems t h a t i s essential t o achieving worldwide solutions. We i n v i t e a l l nations t o j o i n in implementing so1utio;s f o r t h i s global problem, and we hope t h a t t h e present Symposium contributes movement toward t h e goal.
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Before closing, I wish t o thank the many people who have been involved i n t h e organization of an e x c e l l e n t technical program, and our Dutch hosts f o r t h e i r f i n e l o g i s t i c a l arrangements. The e f f o r t s o f t h e Organizing and Advisory Comittees, Session Chairmen and Rapporteurs, the Conference Secretariat, and other who are c o n t r i b u t i n g d u r i n g the next several days are a l l very much appreciated. I a l s o wish t o extend special r e c o g n i t i o n t o several key i n d i v i d u a l s who have l e d the organizational e f f o r t n o t o n l y f o r t h i s Symposium b u t a l s o f o r the previous two successful meetings i n Maastricht and Williamsburg. The e f f o r t s o f Drs.Toni Schneider and Joop van Ham from the Netherlands and Drs.Lester Grand and S i Duk Lee from the United States, along w i t h David S t r o t h e r and other s t a f f h e r s o f t h e i n t e r n a t i o n a l o f f i c e s from each country, are e s p e c i a l l y appreciated. Congratulations t o you a l l f o r p u l l i n g together what promises t o be y e t another superb Symposium.
T. Schneider et 01. (Editors),Atmospheric Ozone Research and its Policy Implications 0 1989 Elsevier Science PublishersB.V.. Amsterdam - Printed in The Netherlands
21
OZONE HEALTH EFFEepS AND EMEDGING ISSUES IN REXATICN TO STANDARDS SETTING
m r t o n LipFsMnn, Ph.D. I n s t i t u t e of Environmental W c i n e , Nar York University Medical Center, NY 10987 USA
TUX&,
ABSTRACT Our current knowledge of 0 exposure and health effects is growing rapidly. Transient respiratory functian effects accumulate throughout an exposure day, and ambient exposures have broad daily peaks. 0 exposures a l s o produce changes i n airway inflamation and p e m a b i l i t y . & l a y adults engaged f o r 1/2 hr i n outdoor exercise show greater responses than those observed i n chamber studies involving 1 o r 2 h r of exposure, indicating potentiation of
-
the 0 response by other environmental exposures. Acute animal studies show bioch&cal and structural responses t o O3 are potentiated by co-exposure t o NO and Chronic animal studies show that 0 effects on lung structure ac&mla2Y&d several recent epidemiological s t u h e s suggest that cumulative functional e f f e c t s are occurring in people. Recent research has a l s o shown: 1) a seasonal variation in functional responsiveness i n humans; 2) that a seasonal pattern of daily exposure in monkeys produces greater changes i n the lung than a continuous pattern of daily exposures at the same concentration; and 3) that transient exposures produce persistent responses.
OZONE HEALTH EFFECTS Ozone (03)exposure a f f e c t s the structure and function of the respiratory t r a c t i n a variety of ways. mst of the research on humans has focussed on its e f f e c t s on respiratory function, especially on transient responses t o acute exposures. Other lung functional responses t o acute and subacute exposures which have been studied, largely in animals, include m c o c i l i a r y and early alveolar zone particle clearance, functional responses in macrophages and e p i t h e l i a l cells, and changes i n lung cell secretions. Structural changes in the v i c i n i t y of the respiratory acinus have been associated with subchronic and chronic animal exposure protocols. However, the health significance of localized structural changes, and t h e roles of the transient functional and cellular responses, i f any, i n the pathogenesis of lung disease, remain speculative. The responses i n animals suggest possible links between O3 exposure and aggravation of asthma, bronchitis, and lung f i b r o s i s i n humans, but do not provide clear evidence f o r such ties. The following sunanarizes current knowledge on transient and chronic health effects produced by the inhalation of 03, and i d e n t i f i e s critical knowledge gaps i n the relationships between the observed e f f e c t s and lung disease.
22
Transient Effeds on Respiratory Function It is well established that the inhalation of O3 causes concentration dependent mean decrements in volumes and flow rates during forced expiratory maneuvers, and that the mean decrements increase with increasing minute ventilation [ref. 11, that there is a wide range of reproducible responsiveness among healthy subjects [ref. 21 , and that functional responsiveness to O3 is no greater, and usually lower, m n g cigarette smokers [refs. 3,4], older adults [refs. 5,6], asthmatics [refs. 7,81, and patients with allergic rhinitis [ref. 91 or chronic obstructive pulmonary disease (COPD) [refs. 10,111. It is also well established that repetitive daily exposures, at a level which produces a functional response upon single expcsure, results in an enhanced response on the second day but diminishing responses on days 3 and 4, with virtually no response by day 5 [refs. 12-141. This functional adaptation disappears about a week after exposure ceases [refs. 15,163. The current U.S. National Ambient Air Quality Standard ( W S ) for O3 uses a 1 hr averaging time, based primarily on a report of respiratory function inpainrent for exercising persons exposed for 1 hr at 0.15 ppn [ref. 171, and the expectation that ambient exposures are characterized by relatively sharp afternoon peaks. However, it has recently been shown that ambient O3 concentrations in the Netherlands and New Jersey often have broad daytime peaks, with maximum 8 hr averages close to 90% of peak 1 hr levels [ref. 181. In the ambient air in the U.S. as a whole, a 1 hr O3 peak at 0.12 ppn is, on average, associated with a maximum 8 hr average concentration of 0.10 p ~ m . Approximately half of the U.S. population lives in comnunities w h i c h exceed the current O3 NAAQS at least twice annually, and many comnunities in California frequently have concentrations exceeding 0.2 ppn [ref. 191. The first indications that the effects of O3 on respiratory function accumulate over more than 1 hr were the observations of M.3onnell et al. [ref. 201 and Kulle et al. [ref. 211 in chamber exposures to O3 in purified air for 2 hr. Significant function decrements observed after 2 hr of exposure were not present at measurements made after 1 hr. Spektor et al. noted that children at sumner camps with active outdoor recreation programs had greater lung function decrements than children exposed to O3 at comparable concentrations in chambers for 1 or 2 hr [ref. 221. Furthermore, their activity levels, although not measured, were known to be considerably lower than those of the children exposed in the chamber studies. Since it is well established that functional responses to O3 increase with levels of physical activity and ventilation [ref. 11, the greater responses in the carp children had to be caused by other factors, such as greater m l a tive exposure, or to the potentiation of the response to O3 by other pllu-
23 t a n t s in the ambient a i r . cumulative daily exposures t o O3 e r e generally greater for the camp children exposed all day long than for the children exposed i n chambers for a 1 or 2 hr period preceded and follow& by clean a i r exposure. Similar considerations apply t o the recent study of M e y et al. [refs. 23,241 of schml children i n Kingston and Harrirnan, TN whose lung function was measured i n school on up t o s i x occasions during a 2 mo period in the l a t e winter
and early spring.
Child specific regressions of function versus mix 1
hr O3 during the previous day indicated significant
associations between O3 and function, with Coefficients similar t o those seen i n the sumner camp studies of L i p p M n n et a l . [ref. 251 and -or et a l . [ref. 221. Since children i n school m y be expected t o have relatively low a c t i v i t y levels, the relatively high response coefficients m y be due t o potentiation by other p l l u -
or t o a low-level of seasonal adaptation. As shown by Spmgler et al. [ref. 261 , Kingston-Harrhan has higher annual average and peak acid aerosol concentrations than other cities studied, i.e., Steubemrille, OH, St. Louis, tants,
Alternatively, the relatively high response coefficients could have been due t o the fact that the W m t s were made i n the l a t e winter and early spring. Hackney [ref. 271 has shown evidence f o r a seasonal
M3, and Portage, W I .
adaptation, and children studied during the s~nrmermay not be a s responsive as children measured earlier in the year. In the study by Hackney [ref. 271 a t Rancho Los Amigos Hospital in Southern California, a group of subjects selected for their relatively high functional responsiveness t o O3 had much greater functional decrements following 2 hr of exposure t o O3 a t 0.18 p p n w i t h intermittent exercise in a chamber in the spring than t h e y did in the following autunm or winter, while their responses i n the
following spring were equivalent t o those in the preceding spring.
These findings suggest that some of the variability in response coefficients reported for earlier controlled human expsures t o O3 i n charr33ers could have been due t o seasonal variations i n responsiveness which, in turn, may be re-
l a t e d t o a long-term adaptation t o chronic O3 exposure. The observations from the f i e l d studies in the children's camps stimulated Folinsbee et a l . [ref. 281 a t the EPA Clinical Studies Laboratory i n chapel e of adult volunteers involving Kill, NC t o undertake a chamber e x ~ ~ s u rstudy
of O3 exposure @ 0.12 p. bbderate exercise was performed for 50 min/hr for 3 hr i n the morning, and again in the afternoon. They found that the function decrements become progressively greater a f t e r each hour of exposure, reaching average values of 400 mL for forced Vital capacity (EW) and 540 mL for forced expiratory volume i n one second (W1) by the end of the day. The effects were transient, w i t h no residual function decrements on the 6.6
-
hr
-
24
following day. The functional decrements after 6.6 hrs of exposure at 0.12 ppn were caparable to those seen previously in the same laboratory on similar subjects following 2 hr of intermittent heavier exercise at an interpolated concentration of 0.22 ppn. The total m u n t of O3 inhaled during 2 hr of intermittent heavy exercise @ 0.22 ppn would be 2.0 q 03. The corresponding amount of O3 inhaled during 6.6 hr of intermittent moderate exercise @ 0.12 ppn was 3.0 mg 03. Thus, the effect accumulates w i t h time, but there appears t o be a concurmt tanporal decay of effect. Follow-up studies in the same laboratory at 0.08, 0.10, and 0.12 ppn confirmed the previous findings, with the 0.08 and 0.10 ppn exposures producing lesser changes which also became progressively greater after each hour of exposure [ref. 291. Thus, it is now clear that the appropriate averaging time for transient functional decrements caused by O3 is 2 6 hr, and there is no scientific basis for a 1 hr health based exposure limit. Since O3 exposures in ambient air can have broad peaks with 8 hr averages equal to 90% of the peak 1 hr averages, the functional decrements associated with ambient concentrations are likely to be much greater than those predicted on the basis of the responses in the chamber studies following 1-2 hr exposures. To the extent that transient changes in respiratory function influence the selection of a W S , the case for a longer tern acute exposure standard is quite clear. The remaining question now has becaane whether there is any scientific rationale for retaining a 1 hr standard to supplement the clearly needed new standard with an averaging time on the order of 8 hr. A study which addressed the issue of the potentiation of the characteristic functional response to inhaled O3 by other e n v i r m t a l cofactors was performed at the NYU bdical Center in Tuxedo, NY on healthy adult nonsmkers engaged in a daily program of outdoor exercise. The ambient mixture contained low concentrations of acidic aerosols and No2 as well as 03. Each subject did the same exercise each day, but exercise intensity and duration varied widely between subjects. Spirametry was perfomid imnediately before and after each exercise period. O3 concentrations during exercise ranged fran 0.021 to 0.124
-
-
-
-
All measured functional indices showxi significant (~0.01)O3 associated man decrements. The functional decrenwts were sMlar, in praportion to lung velum, to those seen in children engaged in supervised recreational programs in sumnez camps, and about twice as large as those seen in controlled 1 and 2 hr exposures in chambers. Since the anbient exposures of the adults exercising out of doors were for 1/2 hr, it was concluded that ambient cofactors potentiate the responses to O3 [ref. 301. Thus, the results of the exposures in thankers to O3 in purified air can underestimate the O3 associated responses which occur among ppulations engaged in n o d outdoor recreational
ppn.
-
25
activity and exposedto O3 i n ambient a i r . The NYU study on exercising adults, and earlier studies on children a t sum-
mer camps [refs. 22,24,31] were not able t o demonstrate the specific effect of any of the measured environmental variables, including heat stress and acid aerosol concentration, on the 03-associated responses. The i n a b i l i t y t o show the individual effects of other environmental cofactors on the response t o ambient O3 m y be due t o inadequate knowledge on the apprapriate biological averaging t h e for these other factors. However, i n the study of functional responses of children t o ambient pollution in Mendham, NJ, a weeklong baselhe shift in PEFR was associated with both O3 and %SO4 exposures during a four day pollution episode which preceded it [ref. 311. A similar response t o a brief episode with elevated O3 and a mch higher peak 4 hr concentration of H2S04 (46 pg/m3) was seen among g i r l s attending a m r canp in 1986 a t Dunnv i l l e , Ontario, Canada, on the northeast shore of Lake Erie [ref. 321. Controlled human exposure studies i n chambers have not demonstrated synergism i n functional response &ween O3 and No2 or %SO4, although Stacy et a l . [ref. 331 reported m responses t o 0.40 ppn O3 and 100 pg/m 3 €$SO4 a f t e r 2 h r of exposure of -9.0% for FVC and -11.5% for E W l , carpared t o -5.7 and -7.7% for O3 alone, -1.4, and -1.2% f o r sham exposure, and t0.9 and +O.% for H2S04 alone. These mean differences, which appear t o indicate an e n h a n m t of the O3 response by %SO4, were not s t a t i s t i c a l l y significant because of the very high variability of the sham exposure results. Pollutant interactions w h i c h potentiate the characteristic O3 response have been reported for other effects, i n controlled exposure studies i n animals, as w i l l be discussed l a t e r i n the sections on lung defenses and lung structure. Exposure t o O3 can also alter the respansiveness of the airways t o other bronchoconstrictive challenges as measured by changes in respiratory mechanics. For example, Folinsbee et al. [ref. 281 reported that airway reactivity t o methacholine for the group of subjects as a whole was approximately doubled following 6.6 hr expsures t o 0.12 ppn 03. Airway hyperresponsiveness ( t o histamine) had previously been demonstrated, but only a t O3 concentrations 2 0.4 ppn [refs. 34,351. On an individual basis, Folinsbee et al. found no apparent relationship betwen the 03-associated changes in methacholine reae t i v i t y and those in FVC o r Wl. TNs d i f f e r s fran resporlSes t o inhaled €$SO4 aerosol, where changes in function correlated closely t o changes in reactivity t o carbachol aerosol [ref. 361. Perhaps the O3 associated changes in bronchia l reactivity predispose individuals t o bronchospasm f m other environmental agents such as acid aerosol and naturally cxxurring aeroallergens. Effects -- on Lung Defenses and Lung Structure Practical and ethical cansiderations limit the amoLlIlts and kinds of data
26
that can be collected on the effects of O3 on lung defenses and lung struc-
ture. Mst of the limited body of data on humans that are available relate t o the rate of particle clearance fmn the lungs and t o a l t e r a t i o n s i n the con: s t i t u e n t s of bronchoalveolar lavage (=) Foster et al. [ref. 371 s t d e d the effect of 2 h r exposures t o 0.2 o r 0.4 ppn O3 with intermittent light exercise on the r a t e s of tracheobronckial m a c i l i a r y particle clearance in seven healthy adult males, using y-tagged i n e r t p a r t i c l e s and external detection w i t h a )'-camera. The 0.4 ppn O3 exposure prcduced a marked acceleration in particle clearance from both central and peripheral airways, as ell as a 12% drop i n E'VC. The 0.2 ppn O3 exposure prcduced a significant acceleration of particle clearance only i n peripheral airways, and a small and nonsignificant reduction i n E'VC. The e f f e c t s of O3 on mucociliary particle clearance have a l s o been studied i n animals. Rats exposed f o r 4 h r t o O3 at 0.4 t o 1.2 ppn exhibited slowed clearance a t 1 0.8 ppn, but not a t 0.4 ppn [refs. 38,391 Rabbits exposed f o r 2 hr at 0.1, 0.25 and 0.6 ppn O3 showed a concentration dependent trend of reduced clearance rate with increasing concentrations, with the change at 0.6 ppn being 50%and significantly different from control [ref. 401 It is not known why t h e animal tests show only retarded mccciliary clearance i n response t o O3 exposure, while the human tests show accelerated clearance. In corresponding tests with other i r r i t a n t s , i.e., %SO4 aerosol and c i g a r e t t e smoke, both humans and animals have exhibited accelerated clearance a t lower exposures and retarded clearance a t higher exposures [ r e f . 411. Studies of the effects of O3 on alveolar macrophage mediated particle clearance during the f i r s t f e w weeks have a l s o been performed in rats and rabb i t s . Rats exposed f o r 4 h r t o 0.8 ppn O3 had accelerated particle clearance [refs. 38,391. Rabbits exposed t o 0.1, 0.6, o r 1.2 ppn O3 once f o r 2 hr had accelerated clearance a t 0.1 p%m and retarded clearance at 1.2 p ~ a n . Rabbits exposed f o r 2 hr/d f o r 13 days at 0.1 o r 0.6 ppn O3 had accelerated clearance for the f i r s t 1 0 days, with a greater e f f e c t at 0.6 ppn [ref. 421. The permeability of the respiratory epithelium can be determined by measuring the plasma concentration of horseradish peroxidase (HRP) a f t e r intratracheal i n s t i l l a t i o n [ r e f . 431. Miller et al. [ref. 441 showed that 2 hr exposures @ 1 ppn O3 affected permeability i n the guinea pigs using this technique. Permeability can a l s o be determined from the externally measured r a t e % ' diethylenetriminepntaacetate of clearance from the lung of Y-emitting c ('%c-DFA), inhaled a s a droplet aerosol o r i n s t i l l e d via the trachea. Bhalla et al. [refs. 45,461 reported increased t r a n s f e r of instilled tracers from the bronchoalveolar lumen t o blood following 2 hr exposure of r a t s t o 0.6 and 0.8 ppn 03. Bhalla et a l . [ref. 461 also examined the e f f e c t s of exercise
.
-
.
27
and -sure
t o other pollutants on tracheal and bronchoalveolar permeabil-
ity. Atmospheric mixtures inclukd: O3 + No2 at 0.6 ppn and 2.5 ppn, respec tively; and a 7-canponent particle and gas mixture (capla atmosphere) The effects representing urban air pollution in a photochemical.environment. of exercise during exposure w e r e evaluated by exposing additional groups in an
enclosed treahill. -sure of resting r a t s t o 0.8 ~ p O3 n increased tracheal permeability t o DTPA and bmnchoalveolar permeability t o DTPA and bovine serum allnrmin (BSA) a t 1 hr after the exposure. B r a n c h o a l v e o l ~ ,but not tracheal, permeability remained elevated a t 24 h r a f t e r the exposure.
Exercise during
exposure t o O3 increased permeability t o both t r a c e r s i n the tracheal and the bronchoalveolar zones, and prolonged the duration of increased permeability in
the tracheal zone from 1 h r t o 24 hr, and i n the bronchoalveolar zone fm 24 h r t o 48 hr. Exposure a t rest t o 0.6 ppn O3 plus 2.5 ppn NO2 significantly increased bronchoalveolar permeability a t 1 and 24 h r a f t e r exposure although exposure a t rest t o 0.6 ppn O3 alone increased branchoalveolar permeability only a t 1 h r a f t e r exposure. Fxposure t o O3 and No2 during exercise led t o significantly greater permeability t o DTPA than did exercising exposure t o O3 alone. Resting r a t s exposed t o the wnplex gas/aerosol atmosphere had increased permeability a t 1 and 24 hr a f t e r exposure. N i t r i c acid vapor was formed i n both the O3 + M2 a m s p h e r e and the ccrrplex gas/aerosol atmosphere. The particles in the l a t t e r also contained hydrogen ions equivalent in mcentration t o about 100 g/m3 of NI-I~HSO~,suggesting that acidic canponents in the atmospheres produced effects that were additive upon the e f f e c t of O3 i n prducing both increase and prolongation of permeability i n tracheal and bronchoalveolar zones of the respiratory tract. Intravenous injection of tracer molecules and xemvery of the label in lung lavage fluid can also be used t o identify lung injury and loss of integrity of air-blood barrier a f t e r expsures t o low levels of toxic agents [refs. 47,481. The increase in permeability fran blood t o air was carparable t o the haease
.
from a i r t o blood [ref. 451 Autoradiography by electron micrOscapy identified multiple pathways for BSA transfer frun blood t o the alveolar space. Although defects in t i g h t junctions of dlveolar type I cells were observed in lungs of r a t s exposed t o 03, autoradiographic grains also aFpeared i n intercellular spaces, with the intercellular junctions reMinFng intact. ry
Kehrl et a l . [ref. 491 have studied the effects of inhaled O3 on respiratoepithelial permeability in hunam. Perosolized '%C-DTPA was inhaled by
eight healthy, nonsnoking males following exposure f o r 2 hr t o purified air or 0.4 ppn O3 while performing intermittent high i n t a i t y exercise (minute ven-
.
t i l a t i o n = 66.8 L) Specific airway resistance ( S R A and Fvc Were measured before and a t the end of exgmsures. The pllmanary clearance of '%eDTPA was
28
measured 75 min after the q s u r e s by lung imaging with a Y-camera. O3 exposure caused respiratory symptans in all 8 subjects and was associated w i t h a 1 4 2 2.8% (mean 2 S.E.) decrement in Fvc (p < 0.001) and a 71 5 22% increase (p = 0.04). ccnpared w i t h the air exposure day, 7 of the 8 subjects i n saw showedincreasedg%c-mAclearanceafterthe o3 exposure w i t h the mean value increasing fran 0.59 2 0.08 t o 1.75 2 0.43%/& (p = 0.03). Thus, O3 exposure sufficient t o produce decrenwts in the respiratory function of human subjects a l s o caused increased '%c-D'FA clearance. The Overton and M i l l e r [ref. 501 model of O3 dosimetry w i t h i n the lungs predicts similar airway deposition patterns f o r O3 i n rats and humans, w i t h the greatest deposition in the Vicinity of the respiratory acinus. A recent extension of t h i s work, based upon differences i n O3 removdL i n the upper respiratory tract and fraction exhaled, suggests t h a t humans have about t w i c e the deposition rate at the respiratory a c b as rats [ref. 511. Thus, the e f f e c t s seen in the chronic animal inhalation studies are l i k e l y t o be conservative estimates of the effects that OCCUT i n humans i n areas w i t h high chronic exposure, such as Southern California. Mst of the inhaled O3 penetrates beyond the sites i n the airways which trigger the functional responses and produces e f f e c t s w h i c h are concentrated on the region at and j u s t beyond the terminal bronchioles. These include changes i n biochemical indices and lung structure. In this region, the eff e c t s of O3 exposure in terms of progressive epithelial damage and inflamnatory changes appear t o be cumdative and persistent, even in animals t h a t have adapted t o the exposure i n tenns of respiratory mecham'cs [ref. 521. In groups of mice exposed t o 0.2 ppn O3 f o r 1, 3, o r 6 hr, superoxide anion radical production decreased 8, 18, and 35%respebively, indicating a pro-
gressive decrease i n bacteriocidal capacity w i t h increasing duration of exposure [ref. 531. In inhalation studies in rats involving O3 exposures a t constant concentrations of 0.12 and 0.25 ppn f o r 12 hr/d f o r 6 and 12 wk, Barry et al. [ref. 541 found that hyperplasia of Type I alveolar cells i n the proxim a l alveoli was l i n e a r l y related t o the clnrmlative lifetime O3 q s u r e . For s aw chronic effects, intermittent e.qmsures can prcduce greater eff e c t s than those produced by a continuous exposure w h i c h results i n higher currmlative e.xpsures. For exanple, Tyler et al. [ref. 551 exposed two groups of 7 mo o l d male Rlonkeys t o 0.25 ppn O3 f o r 8 hr/d either daily or, i n the seasonal model, on days of alternate mths during a t o t a l exposure period of 18 mo. A control group breathed only f i l t e r e d air. W e y s fran the' seasonal exposure model, bA not those exposed daily, had significantly increased t o t a l lung collagen content, chest wall carpliance, and inspiratory capacity. A l l mankeys exposed t o O3 had respiratory bronchiolitis w i t h significant in-
29 creases i n related morphanetric parameters. The only significant moqhamtric difference between seasanal and daily groups was in the volume fraction of macrophages. Even though the seasonally exposed Inonkeys here exp3sed t o the s a m concentration of O3 for only half as many days, they had larger biochemical and physiological alterations and equivalent morphcmetric changes as those exposed daily. bng growth was not ccnpletely no& in either expsed group. Thus, long-term effects of oxidant air pollutants may be more dependent upon the sequence of polluted and clean air than on the t o t a l nLnrS3er of days of pollution, and estimations of the risks of hman exposure t o seasonal air pollutants frm effects observed in animals exposeddailymayunderestimate long-term pulmonary damage. Epidemiologic studies of popllations living in Southern California suggest that chronic oxidant exposures do affect baseline respiratory function. Detels et a l . [ref. 561 canpared respiratory function a t two times 5 yr apart in Glendora (a high oxidant ccmmity) andinLancaster (a lower oxidant comrmulity-but not low by M t i d standards). Baseline function was lower in Glendora, and there was a greater r a t e of decline Over 5 yr. Kilburn et a l . [ref. 571 reported that nonsnokhg and exgpokcng w i v e s of Long Beach shipyard workers had significantly lower values of FEvll mid expiratory flow, tenninal expiratory flow, and carbon monoxide diffusing Capacity than those in a matched population frcm Michigan. The oxidant exposures i n Long Beach and Michigan are not known, but those in Longeeach and Lancaster are similar, while those in Michigan are qenerallymch lower. Bothstudieshave scme serious methodologic deficiencies, but &serve citation because they suggest effects which are consistent with the chronic animal exposure findings. A variety of pollutant interactions which potentiate other characteristic O3 responses have been reported in studies i n animals. Last [ref. 581 reported significant synergistic interaction in rats, i n terms of increased lung 3 protein content, a f t e r 9 d exposures a t 0.2 ppn O3 with 20 or 40 m/m €$SO4, 3 and a non-significant increase for 9 d at 0.2 p p ~ l O3 with 5 pg/m €$So4. Kleinman e t al. [ref. 591 reported that 03-i"h"d lesions i n the lung parenchyma w e r e greater in s i z e in r a t s also exposedto either €$SO4 o r NO2. Graham et a l . [ref. 601 reported a synergistic interaction between O3 and NO2 i n terms of mortality i n mice challenged with streptococcal infection either hmediately or 18 h r a f t e r pollutant exposure. Pinkerton et al. [ref. 611 reported that asbestos fiber clearance fran the lungs of r a t s was reduced when the r a t s were also exposed t o 03. "his increased fiber retention could increase the fibrogenic and carcinogenic risks of asbestos. The a b i l i t y of O3 and other toxicants t o act synergistically indicates that exposure limits for O3 should include an extra w i n of safety t o acknowledge
30 that co-exposures m n g ubiquitous pollutants such a s 03, NO2, %SO4,
and as-
bestos are l i k e l y t o occur in anbient air and many work e n v i r o m t s .
EMERGING ISSUES I N RELATION TO STANDARDS SETTING The r e s u l t s of recent research have substantially expanded our knowledge of exposure-response f o r many of the various e f f e c t s of O3 on the respiratory t r a c t . They have a l s o provided a basis f o r e n h a n d appreciation of the fact o r s affecting delivered dose, t h e duration and progression of effects, and the variations i n responsiveness m n g individuals. A t the same t h , it is important t o recognize that we s t i l l have a primitive understanding of t h e biological mechanisms f o r most of the e f f e c t s of concern, and that we lack a consensus on the health significance and importance in the pathogenesis of disease of even the more completely described effects, such a s transient changes i n respiratory function. While the absence of an adequate mechanistic framework is unfortunate, there is still a need f o r public action on standards and measures t o protect the public health based on current knowledge. The issues related t o exposure standards which should and can be addressed effect i v e l y i n the next few years with carefully conceived and well executed exposure-response studies are:
on
The influence of patterns of g3 exposure patterns of response- extending from transient changes & respiratory and particle clearance functions through airway inflamnation, lung permeability, c e l l u l a r changes a t the respiratory acinus, t o persistent changes in lung architecture associated w i t h lung f i b r o s i s and enphysema. The influence of other environmental factors on responses tog3. We need t o know more about the influence of temperature, h d d i F y , and coexposures t o NO2, SO2, HN03, acidic aerosols, inert aerosols and other widespread components of ambient a i r on responses t o 03, and the extent t o which the sequence of the exposures a f f e c t the responses. -~ Host factors affecting responsiveness.
We need t o identify the host fac-
t o r s responsible f o r the very w i d e range of responsiveness t o O3 exposure among humm and animals. Specifically, we need a better appreciation of how factors such as airway s i z e and structure and respiratory patterns affect O3 uptake, and how biochemical and genetic variations m n g viduals affect the responses of exposed tissues and cells. Interspecies v a r i a b i l i t y jg responses.
indi-
W e need t o have a better appreci-
ation of the similarities and differences in responses between humans and laboratory animals, and the ventilatory,
structural,
biochemical and
31
studies i n animals can be i n t e r p r e t e d f o r their inplications t o human health, e s p e c i a l l y for the genetic factors which control them, so t h a t the results of
chronic changes resulting fran repetitive exposures. A(JK"TS
This research was supported by Coaperative Agreement No. CR 811563 between t h e U.S. Environmental Protection Agency and New York University Medical Center. It was p r f o r m d as part of a Center program a t NYU supported by the National I n s t i t u t e of Enviromental Health Sciences - Grant ES 00260 and as part of a Center program a t NYU supported by the National Cancer Institute G r a n t CA 13343. The research described i n t h i s report has not been reviewed by the Health Effects Research Laboratory of the Emrironmental Protection Agency and the contents do not necessarily r e f l e c t the views of the Agency. REFERENCES 1 M.J. Hazucha, J. -1. Physiol., 62 (1987) 1671-80. 2 W.F. WDomell, D.H. Horstman, S. Abdul-Salaam, D.E. House, Am. Rev. R e p . D i s . . 131 (1985) 36-40. 3 R.J..Shephard, B. U r c h , F. Silverman, P.N. Corey, Environ. Res., 31 (1983)
125-137. 4 J. Kagawa, Int. Arch. Occup. Emriron. Health, 53 (1984) 345-358. 5 D.M. Drechsler-Parks, J.F. Bedi, S.M. Horvath, Exp. Geront., 22 (1987) 91101. 6 C.S. Reisenauer, J.Q. K d g , M.S. WNanus, M.S. Smith, G. Kusic, W.E. Pierson, J. Air P o l l . Contr. Assoc., 38 (1988) 51-55. 7 W.S. L h , M.P. Jones, E.A. B a h y e r , C.E. Spier, S.F. Mazur, E.L. A w l , J.D. Hackney, Am. Rev. Resp. D i s . , 121 (1980) 243-252. 8 J.Q. Koenig, D.S. Covert, S.G. =shall, G. van Belle, W.E. Pierson, Am. Rev. Respir. D i s . , 136 (1987) 1152-7. 9 W.F. WDonnell, D.H. Horstman, S. Atxiul-Salaam, L.J. R a g g i O , J.A. Green, Toxicol. Indust. Health, 3 (1987) 507-517. 1 0 J.J. Solic, M.J. Hazucha, P.A. Brcaoberg, Am. Rev. Resp. D i s . , 125 (1982)
664-9. 11 W.S. Linn, D.A. Shamoo, T.G. Venet, C.E. Spier, L.M. Valencia, U.T. Anzar, J.D. Hackney, Arch. Emiron. Health, 38 (1983) 278-283. 12 J.D. Hackney, W.S. Linn, J.G. W e r , C.R. C o l l i e r , J. -1. Physiol., 43
(1977) 82-85. Young, Am. Rev. 13 B.P. F a r r e l l , H.D. Kerr, T.J. K u l l e , L.R. Sauder, J.L. Re-. D i s . , 119 (1979) 725-30. 14 L.J. Folinsbee, J.F. Bedi, S.M. Howth, Am. Rev. Resp. Dis., 121 (1980) 431-9. 15 S.M. Horvath, J.A. Glher, L.J. Folinsbee, Am. Rev. Resp. D i s . , 123 (1981) 496-9. 16 T.J. Kulle, L.R. Sauder, H.D. Kerr, B.P. F a r r e l l , M.S. B e r i I E l r D.M. Mth, Am. Ind. Hyg. Assw. J., 43 (1982) 832-837. 17 A.J. DeLucia, W.C. pdams, J. Appl. Physiol., 43 (1977) 75-81. 18 P.J.A. Fmbout, P. J. Lioy, B.D. Goldstein, J. A i r Pollut. Control Assoc. ,
36 (1986) 913-7. 19 EPA-OAQPS, U.S. EPA, Research Triangle Park, NC, NOv. 1987. 20 W.F. MZbnnell, D.H. Horstman, M.J. HaZuCha, E. sedl, E.D. Salaam, D.E. House, J. Appl. Physiol., 54 (1983) 1345-52.
Haakr
S.A.
32
2 1 T.J. K u l l e , L.R. Sauder, J.R. -1, M.D. chatham, Am. Rev. Resp. D i s . , 132 (1985) 36-41. James, 22 D.M. SpeMor, M. Upp~nn,P.J. Lioy, G.D. ThLrston, K. Citak, D.J. N. Bock, F.E. Speizer, C. Hayes, Am. Rev. Fesp. D i s . , 137 (1988) 313-20. 23 P.L. KFnney, J.H. ware, J.D. Spengler, Arch. Environ. Health (in press). 24 P.L. Kinney, J.H. W a r e , J.D. Spengler, D.W. Dockeq, F.E. Speizer, B.G. Ferris, Am. Rev. Resp. D i s . (sulmitted). 25 M. LippMnn, P.J. Lioy, G. Leikduf, K.B. Green, D. Baxter, M. Morandi, B. Pasternack, D. Fife, F.E. Speizer, Adv. in Modern Environ. TOxiCol., 5 (1983) 423-446. 26 J . D . Spengler, G.J. Keeler, P. Koutrakis, P.B. Ryan, Environ. Health Perspect. (inpress). 27 J.D. Hackney, Presentation at Conference on the Susceptibility t o Inhaled Pollutants, Williamsburg, VA, Sept. 30, 1987. 28 L.J. Folinsbee, W.F. McDonnell, D.H. Horstman, J. Air Pollut. Contr. Assm., 38 (1988) 28-35. 29 D.H. Horstman, Arlington, VA, Decenber 15, 1987. 30 D.M. SpeMor, M. L i p p ~ n n , G.D. Thurston, P.J. L h y , J. Stecko, G. O'Connor, E. Garshick, F.E. Speizer, C. Hayes, 31 P. J. Lioy, T.A. Vollmrth, M. L i w , J. air Pollut. Contr. Assoc., 35 (1985) 1068-1971. 32 M.E. Raizenne, R.T. Burnett, B. Stern, C.A. Franklin, J.D. Spengler, Environ. Health Persped. (in press) 33 R.W. Stacy, E. Seal Jr., D.E. House, J. Green, L.J. w r , L. Fbggio, Arch. Environ. Health, 38 (1983) 104-115. 34 M.J. Holtzman, J.H. tlmnhgham, J.R. Sheller, G.B. Irsigler, J.A. Nadel, H.A. Boushey, Am. Rev. Resp. D i s . , 120 (1979) 1059-1067. 35 J. Seltzer, B.G. Bigby, M. StuuWg, M.J. H o l t m , J.A. Nadel, I. Ueki, G.D. Leikauf, E.J. Goetzl, H.A. Bouskey, J. -1. Physiol., 60 (1986) 1321-6. 36 M.J. Utell, P.E. mrrow, D.M. Spers, J. D a r l i n g , R.W. Hyde, Am. Rev. Resp. D i s . , 128 (1983) 444-50. 37 W.M. Foster, D.L. Costa, E.G. Langenback, J. -1. Physiol. 63 (1987) 9961002. 38 N.B. Frager, R.F. Phalen, J.L. Kmoyer, Arch. mviron. Health, 34 (1979) 51-57. 39 J.L. Kaoyer, R.F. Phalen, J.R. Dads, Exp. Lung Res., 2 (1981) 111-120. 40 R.B. Schleshger, K.E. D r i s c o l l , J. Toxicol. Emriron. Health, 20 (1987) 125-134. 4 1 M. LippMnn, J.M. Gearhart, R.B. Schlesinger, Apl. Ind. Hyg., 2 (1987) 188-199. 42 K.E. D r i s c o l l , T.A. Vollmuth, R.B. Schlesinger, Fund. Apl. Toxicol., 7 (1986) 264-71. MDroz, J.C. Hogg, J. 43 R.C. Boucher, V. Ranga, P.D. Pare, S. Inoue, L.A. Appl. Physiol., 45 (1978) 939-48. 44 P.D. Miller, T. Gordon, M. W a r n i c k , M.O. Amchur, J. Tox. Endron. Health, 18 (1986) 121-32. R.C. Mmnix, M.T. Klehkm, T.T. Crocker, J. Toxicol. Emiron. 45 D.K. -la, Health, 17 (1986) 269-283. 46 D.K. Bhalla, R.C. Mannix, S.M. Lavan, R.F. Phalen, M.T. Kleinman, T.T. Crocker, J. Toxicol. Environ. Health, 22 (1987) 417-437. . 47 P.C. Hu, F.J. Miller, M.J. Daniels, G.E. Hatch, J.A. Graham, D.E. Gardner, M.K. Selgrack, Emiron. Res., 29 (1982) 377-388. 48 D.K. Bhalla, T.T. Crocker, J. ToXicol. Emdron. Health, 21 (1987) 73-87. 49 H.R. Kehrl, L.M. Vincent, R.J. -sky, D.H. Horstndn, J.J. O'Neil, W.H Am. T(ev. Resp. D i S . , 135 (1987) 1174-8. -y, P.A. B&rg, 50 J.H. Overton, F.J. Miller, P r e p r h t 87-99.4. 1987 Annual MeetOf Ai: Pollut. Cantr. Assoc., New York, June 1987. 1987 Zmnual bketing of ?d 51 T.R. Gerrity, M.J. Wiester, Preprint 87-99.3. Pollut. Contr. ASSIX., New York, June 1987.
.
~
33
52 J.S. Tepper, D.L. C o s t a , M.F. Weber, M.J. Wiester, G.E. Hatch, M.J.K. Selgrade, Amer. Rev. Resp. D i s . , 135 (1987) A283. 53 M.A. AmDruso, B.D. Goldstein, T o x i c o l o g i s t , 8 (1988) 197. 54 B.E. Barry, F.J. Miller, J.D. C r a p O r Lab. IIlvest., 53 (1985) 692. 55 W.S. Tyler, N.K. T y l e r , J.A. Last, M.J. G i l l e s p i e , T.J. Barstow, T o x i c o l o g y (in press). 56 R. Detels, D.P. Tashkin, J.W. S a p , S.N. Rokaw, A.H. Coulson, F.J. msey, D.H. m,Chest., 92 (1987) 594-603. 57 K.H. Kilburn, R. Warshaw, J.C. Thronton, Am. J. M., 79 (1985) 23-28. Health P e r s p e c t . ( i n press). 58 J.A. Last, &iron. 59 M.T. Kleinman, R.F. P h a l m , W.J. mutz, R.C. m, T.R. M X 3 r e , T.T. Crocker, Environ. Health P e r s p e c t . ( i n press). 60 J.A. Graham, D.E. Gardner, E.J. Blarmer, D.E. House, M.G. &ma&, F.J. Miller, J. T o x i c o l . Emriron. Wth, 21 (1987) 113-125. 61 K.E. P i n k e r t o n , A.R. Brody, F.J. M i l l e r , J.D. Crapo, Am. Rev. Resp. D i s . , 137 (1988) A b s t r a c t .
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T. Schneider et al. (Editors), Atmospheric Ozone Research and its Policy Zmplicatwns 0 1989 Elsevier Science Publishers B.V., Amsterdam -Printed in The Netherlande
PHOTOCHEMICAL OXIDANT FORMATION:
35
OVERVIEW OF CURRENT KNOWLEDGE AND EMERGING
ISSUES
Basil Dimitriades Atmospheric Sciences Research L a b o r a t o r y , U. S. Environmental P r o t e c t i o n Agency, Research T r i a n g l e Park, N o r t h C a r o l i n a 27711 (USA)
ABSTRACT D e s p i t e 1-1/2 decades o f c o n t r o l e f f o r t , t h e photochemical ozone p r o b l e m One reason a l l e g e d c o n t i n u e s t o p l a g u e human s o c i e t y and e c o l o g y i n t h e US. f o r t h e d i f f i c u l t y i n a c h i e v i n g t h e e s t a b l i s h e d ozone a i r q u a l i t y s t a n d a r d i s t h a t current understanding o f t h e science underlying t h e problem i s s t i l l insufficient S c r u t i n y o f e x i s t i n g empi r i c a l and theoretical/experimental evidence r e v e a l e d i m p e r f e c t i o n s i n ozone a i r q u a l i t y models and model a p p l i c a t i o n procedures. L a t e s t chemical mechanism developments e s t a b l i s h e d t h e CBM and CALL mechanisms as s u p e r i o r t o o t h e r s b u t s t i l l l a c k i n g i n some r e s p e c t s . P r e c u r s o r r e l a t e d u n c e r t a i n t i e s a r e o f consequence b o t h f o r models r e q u i r i n g e m i s s i o n r a t e i n p u t and f o r models r e q u i r i n g ambient c o n c e n t r a t i o n i n p u t . O t h e r f a c t o r s a f f e c t i n g model p r e d i c t i o n s a r e t h e c o m p o s i t i o n o f VOC e m i s s i o n s and t h e amount and makeup o f p o l l u t a n t s t r a n s p o r t e d i n t o t h e modeled atmosphere. Regional ozone a i r q u a l i t y models a r e now a v a i l a b l e and procedures a r e b e i n g developed f o r use o f such models i n f o r m u l a t i n g r e g i o n a l ozone c o n t r o l s t r a t e g i e s . The r e l a t i v e importances o f "hydrocarbons" (VOC) and n i t r o g e n o x i d e s (NO,) d i f f e r i n t h e urban and t h e r e g i o n a l ozone f o r m a t i o n phenomena.
.
INTRODUCTION I t has been some 3 1/2 decades s i n c e Haagen-Smit and co-workers
(ref.
1)
dernonstrated t h a t t h e smog symptoms e x p e r i e n c e d t y p i c a l l y i n Los Angeles and o t h e r urban areas a r e p r o d u c t s o f photochemical r e a c t i o n s o f o r g a n i c (VOC) and i n o r g a n i c (NO,)
pollutants.
Since then,
several
n o t a b l e developments have
taken place:
--
The s p e c i f i c chemical species r e s p o n s i b l e f o r t h e smog e f f e c t s (eye-
i r r i t a t i o n , p l a n t / m a t e r i a l s damage, etc.) aldehydes, H202, e t c . )
-
have been i d e n t i f i e d (e.g.
03, PAN,
(ref. 2).
Oryan'ic emissions, have been found t o d i f f e r w i d e l y i n ozone-forming
p o t e n t i a l , a f i n d i n g t h a t l e d t o t h e concept o f d i s c r i m i n a t e VOC c o n t r o l f o r ozone r e d u c t i o n ( r e f . 3).
-
Ozone and o t h e r p o l l u t i o n p r o b l e m have been f o u n d t o be a r e g i o n a l
r a t h e r t h a n an urban s c a l e phenomenon as a r e s u l t o f m u l t i - d a y p o l l u t a n t t r a n s p o r t ( r e f . 4).
36
-
The mechanism o f t h e atmospheric chemical process t h a t produces ozone
has been e l u c i d a t e d i n great d e t a i l ; i t now takes hundreds of elementary chemic a l r e a c t i o n steps t o describe t h e mechanism as now understood ( r e f s .
-
5-7).
Urban scale and regional scale ozone a i r q u a l i t y models capable of
p r e d i c t i n g s p a t i a l and temporal occurrence of ozone have been developed and are now i n use ( r e f . 8 ) . These remarkable advancements and t h e f a c t t h a t they r e q u i r e d more than 35 years of focused research e f f o r t appear t o suggest t h a t c u r r e n t understanding of t h e photochemical ozone problem i s adequate and a t t e n t i o n n a t u r a l l y s h i f t s t o " n e w ~ r " emerging a i r p o l l u t i o n problems (e.g.
t o x i c p o l l u t i o n , a c i d r a i n and
p r o b l e m a r i s i n g from changes i n stratosphere and global climate).
However,
t h e l a t e s t e f f o r t s t o evaluate mechanistic models and t h e d i s a p p o i n t i n g e x p e r i ences i n t h e US from a p p l i c a t i o n o f 33-related c o n t r o l s have a l l i n d i c a t e d t h a t t h e r e are s t i l l serious gaps i n our understanding o f the ozone problem.
Ozone
resedrch, and f u r t h e r advancement o f t h e theory u n d e r l y i n g t h e ozone problem, c l e a r l y , must
continue u n t i l t h e r e i s convincing evidence t h a t t h e o r e t i c a l
p r e d i c t i o n s agree w i t h r e a l world observations.
I n t h e discussion t h a t f o l l o w s ,
an attempt w i l l be made t o summarize t h e state-of-science i n t h e ozone problem area and t o i d e n t i f y and discuss outstanding s c i e n t i f i c issues. STATE-OF-SCIENCE AND ISSUES
I t i s now accepted t h a t t h e main reason f o r not having solved t h e ozone problem a f t e r 35 years o f research i s the enormous complexity o f t h e problem. This complexity stems from t h e f a c t s t h a t 03 i s an extremely r e a c t i v e p o l l u t a n t and t h a t i t can be scavenged by t h e very same p o l l u t a n t s t h a t produce i t .
It
i s f o r t h i s l a t t e r reason t h a t t h e ozone concentrations do not respond l i n e a r l y t o precursor
controls
or t o dilution.
Therefore,
the
key p r e r e q u i s i t e t o
s o l v i t i g t h e ozone problem i s a good, q u a n t i t a t i v e understanding o f t h e ozone-toprecursor r e l a t i o n s h i p s , which, i n t u r n , requires a good, d e t a i l e d understanding o f t h e atmospheric ozone-forming process. Ozone t o precursor r e l a t i o n s h i p s (ref.
2) a r e derived from basic labora-
t o r y , smog chamber, and modeling evidence, and t o a l e s s e r e x t e n t from empirical, f i e l d monitoring studies also.
U n l i k e i n past years, smog chamber data today
are n o t used d i r e c t l y t o d e r l v e such r e l a t i o n s h i p s .
Instead, such data a r e
used only f o r t h e purpose o f developing o r e v a l u a t i n g chemical mechanisms. t h i s reason,
For
smog chamber data, along w i t h l a b o r a t o r y k i n e t i c and mechanistic
data are now viewed as p a r t o f what i s commonly r e f e r r e d t o as modeling evidence, i n d i s t i n c t i o n t o empirical,
f i e l d monitoring evidence.
How do t h e modeling
evidence and empirical evidence r a t e r e l a t i v e t o each other?
37 Recent studies by t h e State of C a l i f o r n i a i l l u s t r a t e t h e t y p e and u t i l i t y of empirical evidence p e r t a i n i n g t o t h e ozone problem (ref. 9).
Notwithstanding
i t s non-causative nature and other l i m i t a t i o n s , such evidence i s believed by many t o have i n d i s p u t a b l e m e r i t because o f t h e i n t r i n s i c v a l i d i t y associated w i t h real world data.
For t h e evidence t o be conclusive, however, t h e r e must be an
abundance of data, and meteorology,
e.g.
multi-year h i s t o r i c a l data on emissions,
a i r quality
and t h e data must be o f documented r e l i a b i l i t y .
Based on
experiences t o date, these conditions o n l y r a r e l y can be met; f o r t h a t reason t h e amount o f acceptable empirical evidence i n existence i s r a t h e r l i m i t e d and can only be of suggestive nature.
I n contrast, t h e modeling evidence i s abun-
dant and extremely useful f o r d e r i v i n g q u a n t i t a t i v e ozone-to-precursor r e l a t i o n ships.
I n f a c t , t h e r e l a t i o n s h i p s we c u r r e n t l y accept and use have been derived
e n t i r e l y from modeling evidence and f o r t h a t reason, t h e next l o g i c a l question i s how r e l i a b l e and complete t h i s evidence i s . I n judging the r e l i a b i l i t y and completeness o f t h e modeling evidence, s p e c i f i c items of
i n t e r e s t are the accuracy o f t h e chemical and t r a n s p o r t /
dispersion mechanisms f o r t h e atmospheric ozone formation process, t h e accuracy of the r e q u i s i t e chemical k i n e t i c data, t h e accuracy of t h e precursor (ambient) concentration and emission inventory data, t h e d i s t i n c t i o n between " r e a c t i v e " versus "non-reactive"
VOC's, and the r o l e o f p o l l u t a n t transport.
I n 1981, we learned from s e n s i t i v i t y studies t h a t d i f f e r e n t chemical mechanisms appearing t o have equally good credentials,
when used t o compute VOC
c o n t r o l requirements, could g i v e widely d i f f e r e n t r e s u l t s ( r e f . 10).
This was
d i s t u r b i n g and underlined t h e need t o develop more r e l i a b l e methods f o r evaluat i n g chemical mechanisms. chamber data o r f i e l d data,
Such methods--e.g.
checking mechanisms against smog
o r against theory--do
e x i s t and,
i n concept can
give useful evaluations provided t h e r e q u i s i t e data and theory a r e s u f f i c i e n t l y accurate and comprehensive.
I n a 1986 workshop i n USA on Evaluation o f Chemical
Mechanisms, t h e p a r t i c i p a n t s agreed t h a t , despite c u r r e n t shortcomings o f smog chamber data, t e s t i n g o f a chemical mechanism against such data i s s t i l l t h e most r e l i a b l e and indispensable method f o r e v a l u a t i n g mechanisms ( r e f . Smog chamber data are not without shortcomings.
11).
The most important, w e l l known
shortcoming i s t h a t smog chambers e x h i b i t erroneously h i g h r e a c t i v i t y because o f chamber w a l l e f f e c t s . The question o f how t h e chamber w a l l s generate t h i s e x t r a r e a c t i v i t y has not been f u l l y and s a t i s f a c t o r i l y answered yet. r e c e n t l y (1987), Dr. Akimoto and h i s co-workers
Very
a t t h e Japanese I n s t i t u t e f o r
Environmental Studies reported evidence suggesting t h a t t h e e x t r a r e a c t i v i t y i s due t o a photoenhanced surface reaction between NO2 and H20 which r e s u l t s i n production o f n i t r o u s a c i d some 2-6 times more than o r i g i n a l l y thought ( r e f . 12). It would be very useful i f other smog chamber researchers would r e a c t t o o r
38 t e s t t h i s explanation so t h a t i t can be determined whether t h e Japanese theory has broad v a l i d i t y . From e f f o r t s t o date i n t h e US, two mechanisms have emerged as having t h e best c r e d e n t i a l s because o f t h e i r long h i s t o r y o f development and t e s t i n g . These are:
SAI's Carbon Bond Mechanism (CBM) ( r e f . 5), and t h e Carter-Atkinson-
Lurmann-Lloyd (CALL) mechanism developed by U. ( r e f . 6).
C a l i f o r n i a and ERT researchers
Ozone p r e d i c t i o n s by t h e two mechanisms agree w e l l w i t h each other
and they a l s o agree e q u a l l y well--or e q u a l l y badly--with e x i s t i n g smog chamber data.
The two mechanisms have undisputed strengths but they a l s o have imper-
f e c t i o n s ( r e f . 11).
For example, t h e p o r t i o n s o f t h e mechanisms t h a t describe
t h e r e a c t i o n o f OH w i t h most p a r a f f i n s , o l e f i n s and aldehydes have been shown t o be accurate.
The mechanisms, however, have u n c e r t a i n t i e s i n t h e areas of
aromatic hydrocarbon chemistry, t h e chemistry of heavy alkanes, and t h e ozoneo l e f i n r e a c t i o n chemistry.
U n c e r t a i n t i e s are a l s o caused by t h e lack o f photo-
l y t i c data f o r several carbonyl compounds, e.g. glyoxal, and methylglyoxal.
MEK, propionaldehyde, acetone,
One piece o f evidence a t t e s t i n g t o presence o f
imperfections i s t h e f a c t t h a t t h e 03 p r e d i c t i o n s o f t h e 2 mechanisms respond d i f f e r e n t l y t o changes i n VOC composition. One f a c t o r t h a t has been drawing i n c r e a s i n g a t t e n t i o n i n modeling s t u d i e s o f t h e ozone problem i s t h e precursor emissions o r ambient concentrations t h a t are i n p u t t o t h e models.
Use o f e x i s t i n g emission inventory data i n a i r q u a l i t y
models t o compare model-computed ambient VOC concentrations w i t h observations
o r t o compare VOC-to-NO,
emission r a t i o s t o respective ambient concentration
r a t i o s o r t o compare anthropogenic-to-biogenic VOC emission r a t i o s t o respective ambient r a t i o s r e s u l t e d i n inconsistencies t h a t suggest erroneously low emission i n v e n t o r i e s f o r anthropogenic VOC's ( r e f s .
13,14).
heretofore ignored anthropogenic VOC emissions ( r e f s .
More recent evidence on 15,16)
[e.g.
POTW's, f u g i t i v e emissions, higher evaporative auto emissions, etc.]
from TSDF, has v e r i -
f i e d t h i s emission problem and has cast a greater doubt on t h e accuracy o f model p r e d i c t i o n s regarding c o n t r o l requirements f o r ozone.
Another emission-
r e l a t e d problem i s t h e l a c k o f r e l i a b l e VOC emission composition data w i t h d e t a i l consistent w l t h t h e model ' s requirements.
Given t h e s e n s i t i v i t y o f model
p r e d i c t i o n s t o VOC composition, t h i s problem i s n o t i n s i g n i f i c a n t . Problems a l s o e x i s t
i n t h e cases f o r which the main precursor-related
i n p u t s t o t h e model are ambient concentrations. i s the 6:00-to-9:00-am presently measured--i .e. validity.
VOC-to-NOx
A key i n p u t t o t h e EKMA model
concentration r a t i o ,
an e n t i t y which,
as
a t c e n t e r - c i t y s i t e s d u r i n g 6-9 AM--is o f questionable
To explain, such r a t i o s vary widely from l o c a t i o n t o l o c a t i o n ( w i t h i n
t h e c e n t e r - c i t y area) and from day t o day both because o f measurement e r r o r and because of normal v a r i a b i l i t y o f t h e source and meteorology f a c t o r s . Because o f t h e l a t t e r reason, s e l e c t i n g t h e average o r mean r a t i o value (as i s c u r r e n t l y
39 done) f o r i n p u t i n g t o t h e EKMA model may o r may n o t be j u s t i f i e d .
In efforts
t o t e s t t h e v a l i d i t y o f t h e c u r r e n t method and t o s e a r c h f o r more v a l i d a l t e r n a t i v e s , a f i e l d s t u d y i s b e i n g c u r r e n t l y conducted b y USEPA i n w h i c h measurements o f VOC and NO,
a r e made i n t h e same a i r mass where t h e d a y ' s peak 03 Such VOC and NO,
c o n c e n t r a t i o n occurred.
measurements,
r e p r e s e n t t h e 6-9-AM concentrations--some VOC and NO,
of
course,
do n o t
must have r e a c t e d o u t and
must have mixed i n d u r i n g t h e t i m e i n which ozone reached
some f r e s h VOC and NO, i t s peak
concentration.
possible.
For example,
Some adjustment measurement
b a s i s f o r a d j u s t i n g t h e VOC/NO,
of
for
NO,
these
effects,
however,
are
r e a c t i o n p r o d u c t s can p r o v i d e a
r a t i o f o r reaction.
The d a t a f r o m t h i s s t u d y
w i l l be examined f o r e v i d e n c e on t h e m e r i t s o f t h i s method f o r o b t a i n i n g t h e r e q u i s i t e VOC/NO,
value.
The d i s t i n c t i o n between r e a c t i v e and n o n - r e a c t i v e VOC's has s i g n i f i c a n c e because o n l y r e a c t i v e VOC emissions a r e r e q u i r e d t o b e i n v e n t o r i e d and because r e a c t i v i t y must be c o n s i d e r e d i n j u d g i n g impacts o f VOC e m i s s i o n t r a d e - o f f s (e.9.
emissions
autos).
f r o m alcohol-powered
autos
versus
emissions
from
gasoline
Several r e a c t i v i t y c l a s s i f i c a t i o n schemes have been c o n c e i v e d t o date,
ranging from t h e simplest scheme t o a t e d XIS
b u t l e a s t e f f e c t i v e 2-Class
(reactive-unreactive)
t o use b u t more e f f e c t i v e 5-Class scheme ( r e f . 2).
Current
t h i n k i n g i n t h e US f a v o r s a 2-Class scheme t h a t uses t h e r e a c t i v i t y o f ethane
as t h e "border1 ne" s e p a r a t i n g r e a c t i v e f r o m n o n - r e a c t i v e VOC's. n o t a1 1--cases,
a VOC
measurement o f
t s r a t e o f r e a c t i o n w i t h t h e OH r a d i c a l ( r e f .
VOC's, however,
(e.g.
can
I n most--but
be r e a c t i v i t y - c h a r a c t e r i z e d t h r o u g h e x p e r i m e n t a l
17).
F o r some
h i g h m o l e c u l a r w e i g h t a l i p h a t i c s ) t h e OH r e a c t i o n r a t e
c o n s t a n t i s n o t a v a l i d i n d e x o f ozone-forming p o t e n t i a l ( r e f . 18). and use of more complex e x p e r i m e n t a l / m o d e l i n g t e c h n i q u e s i s r e q u i r e d . With respect t o p o l l u t a n t transport,
t h e phenomenon has been s t u d i e d t o
t h e p o i n t t h a t r e g i o n a l 03 a i r q u a l i t y models a r e now a v a i l a b l e . established t h a t
l o n g range ( i .e.
t h e 03-to-precursor transport conditions, formation ( r e f .
NO,
multi-day)
relationships drastically. f o r example,
It has been
pollutant transport
increasing
Under r e g i o n a l NOx
influences
o r multi-day
c o n s i s t e n t l y enhances
03
19) whereas under s i n g l e day t r a n s p o r t c o n d i t i o n s i n c r e a s i n g
may e i t h e r enhance o r i n h i b i t 03 f o r m a t i o n (depending on VOC/NO,
conditions ) ( r e f s
. 20.21).
and o t h e r
Regional 03 models have been developed ( r e f . 8) b u t have n o t been f u l l y evaluated yet.
I n f a c t , t h e modelers have n o t d e v i s e d y e t a t o t a l l y s a t i s f a c -
t o r y method f o r e v a l u a t i n g r e g i o n a l models.
Comparing r e g i o n a l model p r e d i c -
t i o n s and o b s e r v a t i o n s i n p a i r s , as commonly done w i t h u r b a n s c a l e models, i s much l e s s m e a n i n g f u l because o f t h e more s t r o n g l y s t o c h a s t i c n a t u r e o f t h e
40 r e g i o n a l model p r e d i c t i o n s .
S t a t i s t i c a l comparison of p r e d i c t i o n s and observa-
t i o n s ( r e f . 221, although somewhat l e s s u s e f u l , i s more r a t i o n a l and appears t o be t h e p r e f e r r e d e v a l u a t i o n approach a t t h i s time. While most o f t h e ozone i n problem areas o r i g i n a t e s from photochemistry of urban emissions, s i g n i f i c a n t c o n t r i b u t i o n s can a r i s e a l s o from s t r a t o s p h e r e troposphere exchanges,
from background t r o p o s p h e r i c chemistry,
from b i o g e n i c
emissions, and from photochemistry o f d i f f u s e anthropogenic emissions i n r u r a l areas ( r e f .
23).
ground ozone",
The sum t o t a l o f these c o n t r i b u t i o n s , r e f e r r e d t o as "backcan reach s i g n i f i c a n t
reason i t warrants
attention.
levels
i n c e r t a i n areas and f o r t h a t
Tropospheric chemistry has been r e p o r t e d t o
r e s u l t i n ozone formation only when t r o p o s p h e r i c NOx c o n c e n t r a t i o n s exceed a c e r t a i n t h r e s h o l d value;
otherwise,
destruction of
ozone occurs
(ref.
24).
Biogenic VOCls have been s t u d i e d and found t o be both p o t e n t producers and extremely e f f e c t i v e scavengers o f ozone ( r e f .
24).
There have been s t u d i e s
suggesting t h a t b i o g e n i c VOC's have an i n s i g n i f i c a n t r o l e i n urban ozone problems ( r e f . 24).
They may c o n t r i b u t e ,
however, t o r u r a l ozone--an e f f e c t which i s
supported by some b u t not enough evidence ( r e f . 25).
F i n a l l y , e x i s t i n g evidence
on t h e s i g n i f i c a n c e o f r u r a l anthropogenic emissions as a source o f background
ozone i s l i m i t e d and somewhat unclear.
Modeling estimates vary depending on
NO, assumptions and/or c a l c u l a t i o n techniques used ( r e f . 25). t i o n s o f magnitude,
Thus, t h e ques-
o r i g i n s and c o n t r o l l a b i l i t y o f background ozone a r e open
and important and c a l l f o r a d d i t i o n a l research. Next, t h e discussion w i l l address t h e c o n t r o l i m p l i c a t i o n s o f t h e recent advances i n 03 chemistry and modeling, and some c o n t r o l - r e l a t e d questions t h a t remain unanwered due t o unresolved s c i e n t i f i c issues. Recent modeling s t u d i e s have e s t a b l i s h e d t h a t t h e r e l a t i v e r o l e s o f VOC and NO,
i n urban 03 f o r m a t i o n vary considerably from c i t y t o c i t y depending on
a host o f f a c t o r s t h e most important o f which i s t h e VOC-to-NO, The r e l a t i v e m e r i t s o f VOC c o n t r o l and NO,
r a t i o ( r e f . 20).
c o n t r o l depend a l s o on whether t h e
c o n t r o l goal i s an immediate and modest r e d u c t i o n o f peak 03 c o n c e n t r a t i o n s o r t h e d r a s t i c 03 r e d u c t i o n r e q u i r e d t o meet t h e 03 a i r q u a l i t y standard. example, NO,
For
c o n t r o l can b r i n g about an immediate modest r e d u c t i o n o f peak 03
c o n c e n t r a t i o n i n urban areas b u t i t may also, under some, n o t uncommon condit i o n s , make i t more d i f f i c u l t t o u l t i m a t e l y achieve t h e 03 a i r q u a l i t y standard ( r e f . 20).
F i n a l l y , t h e evidence i n d i c a t e s t h a t whereas VOC c o n t r o l i s never
d e t r i m e n t a l , NO,
c o n t r o l can be d e t r i m e n t a l , p a r t i c u l a r l y ,
p a r t s o f the urban areas ( r e f . 20).
i n the center-city
U n l i k e urban 03, t h e r e l a t i v e e f f e c t s o f
NO, c o n t r o l s on r e g i o n a l 03 have n o t been w e l l s t u d i e d y e t . There i s suggestive evidence t h a t c o n t r o l o f NO, i n urban and r u r a l areas would reduce VOC and
r e g i o n a l 03 b u t more complete s t u d i e s are necessary b e f o r e such an e f f e c t can be a s c e r t a i n e d and q u a n t i f i e d .
41 The f i n a l
comnents p e r t a i n t o t h e modeling t o o l s c u r r e n t l y available.
From t h e discussion thus far, i t can be seen t h a t t h e 03 problem i s t o o complex f o r t h e c o n t r o l agencles t o design ozone c o n t r o l s t r a t e g i e s based on "comnon sense" o r on empirical evidence alone. Notwithstanding t h e i r imperfections and l i m i t a t i o n s , state-of-the-art physicochemical 03 a i r q u a l i t y models are t h e superior t o o l ,
indispensable i n 03 a i r q u a l i t y management p r a c t i c e s .
For t h e
urban 03 problem case, t h e r e are now a v a i l a b l e simple, EKMA-type models ( r e f s . 26,271 as w e l l as more sophisticated--but c o s t l i e r - - E u l e r i a n models ( r e f . 28). t h a t can be used by the s c i e n t i f i c comnunity w i t h i n t h e a i r p o l l u t i o n c o n t r o l agencies i n t h e US.
The EKMA models a r e acceptable f o r small,
i s o l a t e d urban
areas w i t h m i l d 03 problems whereas use o f t h e g r i d models i s g e n e r a l l y p r e f e r able i n t h e cases o f severe 03 problems i n urban areas w i t h i n densely populated regions.
I n e i t h e r case, t h e i n p u t information r e q u i r e d by t h e models i s a v a i l -
able o r can be measured, except f o r f u t u r e boundary conditions. The r e q u i s i t e data on t h i s l a t t e r i n p u t can be estimated only through use of p r e d i c t i v e regional models and t h i s i s one reason why regional 03 models have been developed.
Regional models are now a v a i l a b l e i n t h e US and Europe but, u n l i k e t h e
urban scale models, t h e i r use i s s t i l l q u i t e l i m i t e d .
Thus,
i n t h e US,
for
example, EPA's ROM has not been f u l l y evaluated y e t , t h e p r o b a b i l i s t i c nature o f i t s p r e d i c t i o n s complicates t h e use o f t h e model f o r 03 s t r a t e g y development, and l a s t l y but most importantly, i t s complexity and c o s t o f a p p l i c a t i o n make t h e model accessible t o only a few.
The model i s extremely demanding i n quan-
t i t y and q u a l i t y o f i n p u t and i n ADP resources. For example, t h e r e q u i s i t e emission inventory i n p u t should include biogenic emissions data, and t h e s t r o n g s e n s i t i v i t y o f model p r e d i c t i o n s t o the NOx emission f a c t o r makes i t c r u c i a l t h a t the NO, emission inventory i n p u t be extremely accurate.
Finally, there are
imperfections i n the chemistry and dispersion components o f t h e model. For example, the model ' s chemical mechanism does n o t i n c l u d e aerosol-related steps and, therefore,
sink processes such as l o s s o f H202 and o f N0,derived
products
on l i q u i d / s o l i d p a r t i c l e s , are ignored, and, as a r e s u l t , model-predictions f o r H202 and some NO,
species may be erroneously high.
While i t may t a k e several
years t o remove a l l o f these imperfections, i t i s expected t h a t i n a year o r so t h e current version o f USEPA's ROM w i l l be f u l l y evaluated and ready t o be used f o r development o f ozone c o n t r o l strategies. REFERENCES
1 Haagen-Smit, A. J. Ind. Eng. Chem., 44:1342 (1952). 2 U.S. Environmental Protection Agency. " A i r Qua1i t y C r i t e r i a f o r Ozone and Other Photochemical Oxidants", EPA-600/8-78-004, A p r i l 1978. EPA, C r i t e r i a and Assessment Office, Research T r i a n g l e Park, NC 27711.
42 3
4
5 6
7 8
9 10 11
12 13
14 15
16
17
18
19
U.S. Environmental P r o t e c t i o n Agency. " R e a c t i v i t y and I t s Use i n OxidantRelated Control". I n : Proceedings o f international Conference on Photochemical Oxidant P o l l u t i o n and I t s Control". EPA-600/3-77-001a, b, January 1977. E d i t o r , 8. Dimitriades, EPA, Environmental Sciences Research Laborat o r y , Research T r i a n g l e Park, NC 27711. Wolff, 6. T., P. J. Lioy, G. D. Wright, R. E. Meyers, and R. T. Cederwall. "An I n v e s t i g a t i o n o f Long Range Transport o f Ozone Across t h e Midwestern and Eastern United States". I n : Proceedings o f I n t e r n a t i o n a l Conference on Photochemical Oxidant P o l l u t i o n and I t s Control". EPA-600/3-77-001a, January 1977. E d i t o r , B. Dimitriades, EPA, Environmental Sciences Research Laboratory, Research T r i a n g l e Park, NC 27711. Whitten, 6. 2 . and M. W. Gery. EPA r e p o r t EPA-600/3-86;12, 1986. EPA, Atmospheric Sciences Research Laboratory, Research T r i a n g l e Park, NC 27711. Carter, W. P. L., F. W. Lurmann, R. Atkinson and A. C. Lloyd. EPA r e p o r t EPA-600/3-86-031, 1986, Atmospheric Sciences Research Laboratory, Research T r i a n g l e Park, NC 27711. Graedel, T. E., L. A. Farrow, and T. A. Weber. Atmospheric Environment, 10: 1095 (1976). Lamb, R. G. EPA reports EPA-600/3-83-035, September 1982, EPA-600/384-085, May 1984, and EPA/600-3-85-037, Apri 1 1985. EPA, Atmospheric Sciences Research Laboratory, Research T r i a n g l e Park, NC 27711. C a l i f o r n i a A i r Resources Board. "The E f f e c t s o f Oxides o f Nitrogen on C a l i f o r n i a A i r Q u a l i t y " . Report Number TSD-85-01, March 1986. State of C a l i f o r n i a , A i r Resources Board, 1102 Q Street, Sacramento, CA 95814. J e f f r i e s , H. E., K. G. Sexton, and C. N. Salmi. EPA report, EPA-450/481-034, November 1981, EPA, O f f i c e o f A i r Q u a l i t y Planning and Standards, Research T r i a n g l e Park, NC 27711. Atkinson, R., H. J e f f r i e s , G. Whitten, and F. Lurmann. Proceedings of Workshop on Evaluation/Documentation o f Chemical Mechanisms. E d i t o r , 6. Dimitriades. EPA-600/9-87-024, October 1987. EPA, Atmospheric Sciences Research Laboratory, Research T r i a n g l e Park, NC 27711. Akimoto, H., H. Tagagi, and F. Sakamaki. I n t . J. Chem. Kinet., 19:539 (1987). Ching, J. K. S., J. H. Novak, K. L. Schere, and F. A. Schiermeier. "Reconc i l i a t i o n o f Urban Emissions and Corresponding Ambient A i r Concentrations I n t e r n a l document. EPA, Atmospheric Using A Mass Flow Rate Technique". Sciences Research Laboratory, Research T r i a n g l e Park, NC 27711. EPA-600/3-85-013, 1985. EPA, Atmospheric Westberg, H. and B. Lamb. Sciences Research Laboratory, Research T r i a n g l e Park, NC 27711. "Area Source Documentation f o r t h e 1985 National Acid P r e c i p i t a Pahl, 0. t i o n Assessment Program Inventory". I n t e r n a l EPA Report, September 1986. EPA, A i r and Energy Engineering Research Laboratory, Research T r i a n g l e Park, NC 27711. "Motor Vehicles as Sources o f Compounds Important t o TropoBlack, F. spheric and Stratospheric Ozone". T h i r d US-Dutch I n t e r n a t i o n a l Symposium on Atmospheric Ozone Research and I t s P o l i c y I m p l i c a t i o n s , May 9-13, 1988, N i jmegen, Nether1ands. Proceedings i n press (1988). P i t t s , J. N., Jr., A. M. Winer, S. M. Aschmann, W. P. L. Carter, and R. Atkinson. "Experimental Protocol f o r Determining Hydroxyl Radical Reaction Rate Constants f o r Organic Compounds--Estimation of Atmospheric R e a c t i v i t y " . EPA Report 600/3-85-058, June 1985, EPA, Atmospheric Sciences Research Laboratory, Research T r i a n g l e Park, NC 27711. B u f a l i n i , J . J. and R. R. Arnts. "Review o f t h e UCR Protocol f o r Determinat i o n o f OH Rate Constants w i t h VOC's and I t s A p p l i c a b i l i t y t o P r e d i c t Photochemical Ozone Formati on". EPA Report 600/3-87-046, November 1987. EPA, Atmospheric Sciences Research Laboratory, Research T r i a n g l e Park, NC 27711. Carter, W. P. L., M. C. Oodd, W. D. Long, and R. Atkinson. EPA r e p o r t EPA-600/3-84-115, March 1985, EPA, Atmospheric Sciences Research Laboratory, Research T r i a n g l e Park, NC 27711.
43 20
21 22
23 24 25 26
27
28
Dimitriades, B. "The Role o f NOx i n t h e Urban Ozone Problem. Recent Developments i n Atmospheric Photochemistry". (Presented a t EPA-CARB ConferTiburon, CA., June 3-4, 1987). I n t e r n a l document, 1987, EPA, ence on NO, Atmospheric Sciences Research Laboratory, Research T r i a n g l e Park, NC 27711. P i t t s , J. N., Jr., A. M. Winer, R. Atkinson, and W. L. Carter. Env. Sci. Technol. 17:54 (1983). Schere, K. "Development and V a l i d a t i o n o f t h e Regional Ozone Model f o r t h e Northeastern United States". T h i r d US-Dutch I n t e r n a t i o n a l Symposium on Atmospheric Ozone Research and I t s P o l i c y Implications, May 9-13, 1988, N i jmegen, Netherlands. Proceedings i n press (1988). A l t s h u l l e r , A. P. JAPCA 37:1409 (1987). Dimitriades, B. JAPCA. 34:729 (1981). Trainer, M., E. J. Williams, 0. 0. Parrish, M. P. Buhr, E. J. Allwine, H. H. Westberg, F. C. Fehsenfeld, and S. C. Liu. Nature, 329:705 (1987). Dimitriades, B. "An A l t e r n a t i v e t o t h e Appendix J Method f o r C a l c u l a t i n g Oxidant and NO2 Related Control Requirements". In: " I n t e r n a t i o n a l Conference on Photochemical Oxidant P o l l u t i o n and I t s Control: Proceedings, Volume 11". Editor, B. Dimitriades. EPA-600/3-77-016, January 1977. EPA, Atmospheric Sciences Research Laboratory, Research T r i a n g l e Park, NC 27711. U.S. Environmental P r o t e c t i o n Agency. "Guideline f o r Use of C i t y - S p e c i f i c EKMA i n Preparing Post-1987 Ozone S I P ' S " . November 1987. I n t e r n a l OAQPS document. EPA, O f f i c e o f A i r Quality Planning and Standards, Research Triangle Park, NC 27711. U.S. Environmental P r o t e c t i o n Agency. "Guidelines f o r Applying t h e Airshed Model t o Urban Areas." NTIS P u b l i c a t i o n Number PB81-200529, 1980. U.S. National Technical Information Service, 5285 Port Royal Road, S p r i n g f i e l d , VA 22161.
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T.Schneider et al. (Editors),Atmospheric Ozone Research and its Policy Implications 0 1989 Elsevier Science PublishersB.V.,Amsterdam - Printed in The Netherlands
CURRENT KNOWLEDGE EMERGING ISSUES
OF
OZONE
ON
VEGETATIONfFOREST
EFFECTS
AND
G.H.M. KRAUSE and 8. PRINZ Landesanstalt ftr Immissionsschutz des Landes NRW, Wallneyer Strape 6, 4300 Essen 1, FRG
ABSTRACT In consequence of increased emissions of nitrogen oxides and reactive hydrocarbons as precursor substances as well as in respect of phytotoxicity, range of concentration and spatial distribution, ozone is today the most important phytotoxic component among photochemical oxidants and besides sulfur dioxide probably the most important air pollutant in Europe today. M i l e its importance to forest decline was first discovered in California 25 years ago, new impetus in effects research was caused by the appearance of novel forest decline in Europe and United States of America. Former research was emphasising more the acute effects, especially in connection with agricultural and horticultural crops. Now, the central point of discussion are chronic effects. By this, the problem has become increasingly difficult, since other environmental stresses, such as pathogenes, soil, and climate very often mimic ozone effects under field conditions.
INTRODUCTION Impact of air pollutants on vegetation and ecosystems is a well documented phenomenon, which has been observed for over 100 years in case of sulfur dioxide as shown by one of the first reviews prepared by Yislicenus (ref.1). With increasing efforts to reduce the air pollution burden, the pollution environment has changed considerably during the last decade. While sulfur dioxide emissions have stayed more or less constant and will be markedly reduced in the near future, secondary air pollutants such as photochemical oxidants have gained importance with respect to vegetation effects, due to increased emissions of nitrogen oxides and organic compounds as precursor substances and the long range transport of these pollutants. Effects of photochemical oxidants and their potential phytotoxicity though were discovered rather lately and observed first on vegetation during the fourties in the Los Angeles basin
(ref.2). Meanwhile, origins of ozone as the most prevalent com-
pounds within the group of photochemical oxidants have been subject to many
46
reviews in the past in respect to atmospheric chemistry, health effects, impact on vegetation, animals and materials as well as control strategies (refs.3-6). Especially recent decline phenomena observed in many forests throughout Europe, being first primarily related to 'acid rain' alone, are currently discussed to be associated with the impact of ozone in one or another way (refs.7-8), and recent research activities were focussed very effectively on this matter (ref.9). In the following, principle mechanisms of ozone impact on plants are discussed under consideration of external and internal growth factors. Special attention is given to the role of ozone in respect to novel forest decline and reference made to combinatory effects with other pollutants as well as dose-response relationships.
EFFECTS OF OZONE ON PLANT METABOLISM
The effects of
on plant metabolism can be described as follows: tree response to ozone starts with the diffusion of the gas from the atmosphere into the leaf through the stomata. Uptake is controlled by leaf resistances (ref.10) as well as stomatal density and conductance (refs.l1,12), and is generally dependent on physical, chemical, or biological factors involving the transition between gas phase and liquid phase movement into the cells (ref.13). In the liquid phase, ozone will readily undergo transformation, yielding a variety of free radicals which will then react with cellular components (ref.13). Sensitivity of plants is modified, therefore, by any factors influencing stomatal aperture such as light (refs.l4,15), relative humidity (ref.16), and soil moisture (ref.17). Besides genetic (refs.18,19) or developmental factors (ref. 2 0 ) , soil fertility (ref.21) or chemicals such as herbicides, fungicides (ref-22) etc. can also influence stomatal aperature. When plants are unable to repair or compensate oxidant induced perturbations, injury on above-ground plant parts occurs and.can be characterized for gymnosperms as destruction of the mesophyll cells leading to chlorotic bleaching of the needle tip or mottling of the youngest needles (ref.231, frequently accompanied by an unspecific needle cast (ref.24,25). Ozone injury in angiosperms starts with the decay of chlorophyll and the destruction of the palisade parenchyma cells, resulting in bleaching and minute necrotic stiples in the intercostal areas (ref.23). Similar injury patterns are observed in many broad-leaved agricultural and horticultural plants (ref.26), and since affected groups of cells are often minute but distributed over the whole leaf area, colour of leaves get a bronzing appearance. 03
41 Each leaf passes through phases of different sensitivity. As a general role, leaves are most sensitive, when unfolded and just developed to normal size. Conifer needles are most sensitive during elongation and susceptibility decreases after maturation. Chronic effects result eventually in changes at the cellular level. The primary site of action for ozone is to oxidize organic compounds, like specific enzymes and lipid compounds of cell membranes, leading to changes in membrane permeability of the plasmalemma as well as the chloroplasts, as shown by changes in flux of organic and inorganic plant metabolites (refs.13,2730). The peroxidation of lipids is deduced from the increase of antioxidants
like glutathions, vitamin E and C (refs.31,32), most likly as protective measure. Phenomena of increased membrane permeability have been associated with increased leaching of essential nutrients (refs.30,33), accompanied or even enhanced by ozone induced weathering of the cuticle (ref.34). Photosynthesis is very frequently reduced (refs.35-41) either indirectly by closure of the stomata1 aperture resulting in reduced COZ uptake (refs.42,43), or directly by damage to the chloroplasts (refs.44,45).
Another
effect is ozone induced reduction in assimilate translocation to roots with a resulting decrease in root size and fewer stored reserves, with the potential for increased sensitivity to frost, heat, and water stress (refs.20,46-48). Other effects, such as reduction in chlorophyll content (refs.39-41,43,49) or chlorophyll bleaching in the presence of light due to oxidation processes (refs.39,42) have been observed. Biochemical perturbations are a further expression of subtle injury reactions, frequently indicating premature ‘senescence which occurs under chronic
03
pollution stress (refs.50-52).
These
include the oxidation of sulfhydryl groups (ref.53). and changes in the content of soluble sugars, starch, phenols, ascorbic acid, amino acids, and protein, as well as interferences with enzymes such as the nitrate- or nitritereductase involved in nitrogen metabolism (refs.33,46,54).
EFFECTS OF OZONE ON FOREST ECOSYSTEMS Our knowledge is rather limited in terms of the many plant species indigenous to forest ecosystems (ref.55). Ozone effects are much more difficult to evaluate than those of SOZ, because there are no point sources to allow observations along a concentration gradient. Furthermore, it is difficult to determine if tree responses are cumulative and the result of a number of influencing chronic stress factors, unless they can be traced back to specific biotic diseases or pollution exposure. In areas with chronic ozone exposure
(and I think many areas of Europe should be ranked in this category), decline in vigor of trees and forest ecosystems is a commonly observed response (refs.51,55-57). Symptoms of chronic decline differ markedly from acute visible injury and include, according to HcLaughlin (ref.56): (1) premature senescence with cast of older needles in autumn, (2) reduced assimilate storage in roots at the end of the growing season and reduced resupply capacity in spring, ( 3 ) increased reliance of new needles on self support during growth, ( 4 ) shorter new needles and thus reduced assimilate production, (5) reduced
availability of photosynthates for homeostasis, and ( 6 ) premature cast of older needles. The most complete study of ozone effects on forest ecosystems was done within the San Bernardino National Forest near Los Angeles, California where, due to specific climatic, orographic, and emission characteristics, elevated ozone levels of up to 580 ug . r 3 were present (ref.58). Tree species sensitive to ozone were listed as: Pinus ponderosa, Pinus jeffrevi, Abies conco-
lor,
Quercus velutina, Librocedrus decurrens and Pinus lambertiana. Foliar
injury and premature leaf fall coincided with decreased rates of photosynthesis, reduced radial growth, tree height and seed production, as well as retarded nutrient retention (ref.57,69). Injury to Pinus ponderosa occurred even at concentrations of 100 to 120 ug.r3 for 24 h. However, sensitive tree species were not eliminated by the photooxidant burden, but by their 03 induced predisposition to insect infestations such as bark beetles. The other predominant tree species affected under ambient exposure of ozone is eastern white pine (Pinus strobus), as has been seen in many parts of the United States, such as the southern Sierra Nevada in Central California, Indiana and Wisconsin (refs.59-61). or the northeastern United States, such as the Appalachian region (refs.62-64). In eastern Tennessee for example, annual average growth was reduced between 1962 and 1979 by as much as 70% in sensitive species as compared to tolerant ones. The cause of these growth effects was attributed to chronic ozone exposure, frequently in the phytotoxic range 0 1 6 0 ~ g . m - ~ ) . In addition to growth reductions, premature senescence, and lower photosynthetic rate, perturbations in the processes of carbon allocation were also observed. In another field study with filtered versus non-filtered air using open top chambers, Duchelle et al. (ref.65) showed that summer mean concentrations of 86 ug.m-3 produced visible injury at the end of the growing season on species such as Liriodendron tulipifera, Liauidambur stvraciflua, and Fraxinus pennsvlvanica, while those in filtered chambers showed no effect. Betula ~ e n ,&d
Fraxinus excelsior, and some species of Fraxinus americana were found
49
to have ozone specific injury after one growing season in rural southeastern England using the same type of exposure system, while svlvatica and Quercus robur were more tolerant (ref.66). According to Ashmore et al. (ref.671, 0 3 concentrations were markedly below summer means of 100 ~ g . m - ~ measured at the Schauinsland station in the Black Forest in FRG (ref.68). On the other hand, fumigation experiments with Picea abies and Abies alba revealed that these major, European native species were relatively tolerant because only 03 fumigation with ,200 ug.m-3 for )40 days, produced visible injury in form of mottling as well as lead to an inhibition of photosynthesis, respiration, and transpiration (ref.39).
POLLUTANT INTERACTIONS The atmosphere usually contains a complex and dynamic mixture of pollutants occurring simultaneously or sequentially with great regional variation (ref.79). Therefore, it is difficult to evaluate vegetation response in a given experimental design, since only limited pollution regimes out of many potential ones are reflected. Plant response to air pollutant mixtures can be additive, less than additive (antagonistic) or greater than additive (synergistic). The last response type has particularly led to great concern for forest ecosystems. The pollution situation in remote areas is mostly characterized by the presence of SOX, NO2, and 0 3 , as well aa acidic deposition. Combinations of these pollutants are discussed briefely under reference of an excellent, recent review published by Guderian and Tingey (ref .70). Considering combined effects of SO2 and 0 3 it seems generally that injury symptoms are related more to ozone than to SOr (refs.71-73); however, exceptions are also reported (refs.74-76). While most herbaceous plants show additive or synergistic effects when exposed to SOr and Oa (refs.77-79). woody species show slightly less than additive or even antagonistic responses in plant growth (ref . 6 ) . Combined effects of NO2 and 0 3 resulted in chlorotic mottling in Pinus taand were occasionally accompanied by tip-burn Hight growth was reduced by two or three pollutant combination of S O I / N O P / O ~ in close to ambient concentrations It was shown that effects of the three pollutant combination were similar to two pollutant combinations of 0 3 + SOr or 03+ Nor, respectively (ref. 80). Low levels of NO2 and SO2 increased early senescence in poplar trees, accompanied by premature leaf drop, irrespective of the addition of ozone (ref.81). Cuderian (ref.82) reported that the combined effect of NOX, SOP, and 0 3 was yellowing of needles of Picea abies, and when nutrient
.
&I
.
50
deficiency was present at the same time, the symptoms showed remarkable similarity with those of the new forest decline (ref.7). Experiments carried out with poplar species fumigated with S 0 2 , N O z , and 03 singly and in combination revealed a less sensitive reaction to combinations of S 0 2 1 N 0 2 than to N O z / 0 3 or N 0 2 / S O ~ / 0 3 . It seems that combinations of N O z / 0 3 are more important with respect to leaf injury than N O z I S 0 2 (ref.82). Fumigation of Platanus occidentalis with a combination of S O z / N O 2 / 0 3 showed, greater effects than with two-gas-mixtures without foliar injury (ref.83) .' Other experiments revealed that growth reductions in Pinus strobus were more influenced by 0 3 and/or SO2 than NO2 alone or combinations of NO2 + 0 3 or NO? t SO2 (ref.84). These findings contradict those of Moo1 (ref.81) where a greater decrease in growth occurred with the combination of either N O 2 1 0 3 or all three pollutants, than with SOz/NOo (ref.82). Interactions of gaseous pollutants and acidic deposition and their impact on forest ecosystems is another important pollutant combination having been discussed only recently and, as yet, not many studies are available. So far most research has focussed on interactions between ozone and acidic deposition in the form of either rain or fog. Foliar leaching of essential nutrients such as magnesium, calcium, zinc, or copper, as well as nitrate and ammonium occurred in Picea abies when plants were fumigated consecutively with 200 or 600 ug m-3 0 3 and treated with acidic mist (pH 3.5) once a week (refs.30,39,85). For most cations, leaching was dependent on 03-dose, H*-ion concentration of fog solution, and was further enhanced by low nutrient content of soils or a reduction in plant vitality prior to exposure (ref.34). Although similar results were obtained in combined 0 3 fumigation and fogging experiments, foliar leaching was further modified by additional frost treatments (ref.86). Skeffington and Roberts (ref.871, however, using a different methodological approach, found only increased nitrate leaching in Pinus svlvestris, while leaching of cations was not enhanced by Oafacidic rain. Combined fumigation experiments with S O Z , 03, and acidic rain over two years in open top chambers, using Picea abies, Abies w, and F m svlvatica, revealed a marked increase in cation leaching when all three pollutants were supplied in concentrations approaching ambient levels (ref.88). Combinations of ozone and acidic rain, however, had no particular pronounced effect on leaching. There were marked effects on the photosynthesis of red oak, sugar maple, and white pine at various low concentrations of ozone close to the ambient, but no such effects occurred for acidic deposition, nor for the combination of the two (ref.89). However, there is given indication that leaching of cations and nitrate is enhanced
51
after ozone episodes, as shown by Fabig (ref.90) for an older Norway spruce stand. Waldman and Hoffmann (ref.91) also assume that cation leaching from pine trees in San Gabriel mountains in California is stimulated by earlier ozone episodes. It is clear that pollutant mixtures should be given high priority in future research because the conflicting results from mixture studies are so difficult to interpret. Although combined effects of pollutants can be synergistic, especially at low concentrations, the results from experiments using artificial pollutant combinations should be addressed with care (ref.70). It is absolutely essential, therefore, to produce more reliable information on mixtures, using exposure regimes which simulate the temporal and spatial variation of representative mean and peak concentrations which occur under ambient conditions.
CRITICAL OZONE LEVELS FOR PLANT PROTECTION Most of the sensitivity ranking was derived from short term exposure studies mostly with seedlings. Particularly for long living organisms like forst trees these results are questionable, if exposed chronically.
Furthermore,
judgement on visible injury can be of rather limited value for sensitivity ranking, when other indirect induced factors such as for example nutrient leaching determines actual injury, as pointed out earlier (ref .92) Thus these data should be adressed with caution for dose-effect relationships. This applies principally also for other parameters like yield and growth data gained under short term conditions of exposure. A further problem for the evaluation of proper ozone threshold values for plant protection is the very complicated ozone concentration time pattern, which is difficult to simulate in appropriate experiments. This is due to the pronounced diurnal variation in ozone concentration which varies furthermore with increasing distance from precursor sources as well as elevation. Contrary. to the other primary gaseous air pollutants, ozone does not vary that much in peak then in average concentration between industrialized and remote areas (refs.93,94). The probably best approach so far was made with the National Crop Loss Assessment Network (NCLAN) in the USA (ref.95). According to this study a mean seasonal ozone concentration of 56-72 can lead to growth reduction in sensitive agricultural crops. For protection of vegetation against longer lasting ozone episodes a threshhold value of 60 p g r 3 for a seasonal mean over 100 days was established by experts in a recent WXO-study WHO (ref .96). Ac-
cording to the Air Resource Board of California (ref. S O ) ,
this standard would
52
also be sufficient for sensitive pine forests. Under consideration of the NCLAN-results with very sensitive species and possible combinatory effects with other pollutants present at the same time or sequentionally, Guderian (ref.97) suggested at the most recent ECE Critical Levels Workshop in Bad Harzburg, FRG a standard of 50 pgm-3 as seasonal mean, derived from 7 hour daily average concentrations (9.00
-
17.00 hours). However, this value is
very low and may reach into the natural fluctuation of background concentration in future, when ambient ozone levels will increase further (refs.97,98).
REFERENCES 1 2 3
4
5
6 7 8 9
10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
H. Hislicenus (Ed.), Paul Parey Verlag, Berlin 1907, Reprint VDI-Verlag, DUsseldorf 1985. Environmental Protection Agency (EPA), Air Quality Criteria for Ozone and other Photochemical Oxidants. Document No.EPA-600/8-78-004, 1978. National Academy of Science (NAS), Ozone and Other Photochemical Oxidants, Washington,D.C., 1977. V.C. Runeckles, in A.H. Legge and S.V. Krupa (Eds.) Air Pollutants and their Effects on the Terrestrial Ecosystem, in J.O.Nriagu (Ed.) Advances in Environmental Science and Technology, Vo1.18, J.Wiley, NY, 1986, pp.265-303. NRCC, Photochemical Air Pollution: Formation, Transport, Effects, Report No.12: N.R.C.C.14096, National Research Council of Canada, Ottawa 1975. R. Guderian, D.T. Tingey and R. Rabe, in R.Guderian (Ed.) Air Pollution by Photochemical Oxidants, Springer Verlag, Berlin, 1985, pp. 129-333. B.Prinz, G.H.M. Krause and H. Stratmann, WaldschBden in der Bundesrepublik Deutschland, LIS-Berichte 28, 1982. FBW, Forschungsbeirat WaldschAden/Luftverunreinigungen der Bundesregierung und der Lander, 2.Bericht, KPZ-Karlsruhe GmbH, 1986. B. Prinz and I. Kath, Forschungsplan zum Forschungsprogramm des Landes NRW "Luftverunreinigungen und Waldschiiden", HURL, Dilsseldorf, 1987. C.R Krause and T.C Weidensaul, Phytopathology, 68, 1978, 301- 307. L.K.Butler and T.W. Tibbitts, J.Am.Soc.Hort.Sci., 104, 1979, 213-216. C.M. Gaselman and D.D. Davis, J.Am.Soc.Hort.Sci., 103, 1978, 489-491. D.T. Tingey and G.E. Taylor, Jr., in H . H . Unsworth and D.P. Ormrod (Eds.), Effects of Gaseous Air Pollution in Agriculture and Horticulture, Butterworth Scientific, London, 1982, pp.113-138. J.A. Dunning and W.W. Heck, Environ.Sci.Technol., 7, 1973, 824-826. J.A. Dunning and W.W. Heck, JAPCA, 27, 1977, 882-886. P.A. Miller and D.D.Davis, Plant Dis., 65, 1981, 750-751. D.M. Olszeyk and T.W. Tibbits, Plant Physiol., 67, 1981, 539-544. A.S. Heagle, Environ.Pollut., 19, 1979, 1-10. P.G. Hanson, D.H. Addis and L. Thorne, Can.J.Genet.Cytol., 18, 1976, 579-592. U.T. Blum and W.W. Heck, Environ.Exp.Bot., 20, 1980, 73-85. R. Harkov and E. Brennan, Phytopathology, 70, 1980, 991-994. J.A. Laurence, J.Plant Diseases and Protection, 87, 1981, 156-172. W.H. Smith, Air Pollution and Forest, Interactions between Air Contaminants and Forest Ecosystems. Springer Verlag, Berlin, 1981. M. Treshow, Environ.Pollut., 1, 1970, 155-161. L.S. Evans and P.R. Miller, Amer.J.Bot., 59, 1972, 297-304.
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26 27 28 29 30 31
32 33 34
35 36 37 38 39 40
41 42 43 44 45 46 47 48 49 50
51 52 53
54 55 56 57 58 59 60
APCA, Recognition of Air Pollution Injury to Vegetation: A Pictorial Atlas, (J.S. Jacobson, A.C. Bill (Eds.) Air Pollution Control Association, Pittsburgh, 1970 R.L. Heath and P.E. Frederick, Plant Physiol., 64, 1979, 455-459. R.L. Heath, Am.Rev.Plant Physiol., 31, 1980, 395-431. A. Keitel and U. Arndt, Angew. Botanik 57, 1983, 193-204. C.H.M. Krause, 8. Prinz and K.-D. Jung, (1983). in: D.D. Davis, (Ed.), Air Pollution and the Productivity of the Forest. Proc.of Symp. Izaak Walton League, Wash. 4.-5.10. 1983, pp. 297-332. K.J. Kunert and G. Hofer, In: 3, Statuskolloquium des PEF vom 10. bis 12. Marz 1987, Kernforschungszentrum Karlsruhe, 1987, pp- 177-188. H . G . Mehlhorn, C. Seufert, A. Schmidt and K.J. Kunert, Plant Physiol., 82, 1986, 336-338. G.H.M. Krause, Environ.Pollut., 48, 1988, in press. G.H.M. Krause, K.-D. Jung and B. Prinz, VDI-Berichte, 560, 1985, 627656. R.W. Carlson (1979). Environ.Pollut. 18, 1979, 59-170. R.L. Heath, P.E. Frederick and P.E. Chimiklis,. Plant Physical., 69, 1982, 229-233. V.J. Black, D.P. Ormrod and M . H . Unsworth, J.Experim.Bot., 33, 1982. 1302-1311. P.J. Coyne and G . E . Bingham, JAPCA, 31, 1981, 38-41. G.H.M. Krause and B. Prinz, Spezielle Berichte der Kernforschungsanlage Julich, 369, 1986, 208-221. Raba and R.C. Amundson, P.B. Reich, A.W. Schoettle, R . I . J.Environ.Qual., 15, 1986, 31-36. P.B. Reich, A.W. Schoettle and R.G. Amundson, Environ. Pollut.(Series A), 40, 1986, 1-15. H.D. Mohr, Biol. in unserer Zeit, 13, 1983, 74-76. A. Faensen-Thiebes, Angew.Botanik, 57, 1983, 181-191. T. Sakaki, N. Rondo and K. Sugahara, Physiol.Plant., 5 9 , 1983, 28-34. H.K. Lichtenthaler and C. Buschmann, Allg. Forst.Z., 39, 1984, 12-16. D.T. Tingey, R.G. Wilhour and C. Standley, Forest Sci., 22, 1976, 234-241. S.B. Mclaughlin and R.K. Hcconathy,. Plant Physiol.,73, 1983, 630635. D.C. Horsman, A.O. Nicholls and D.M. Calder, Aust. J. Plant.Physial., 7, 1980, 511-517. P.B. Reich, Plant Physiol. 73, 1983, 291-296. ARB (Air Resources Board), State of California, Effect of Ozone on Vegetation and Possible Alternative Air Quality Standards, Technical Rep. Doc., Sacramento, Calif., 1987. P.B. Reich and J.P. Lassoi, Environ.Pollut. (Series A ) . 39, 1985, 3951. P.B. Reich and R.C. Amundson, Environ.Pollut., 34, 1984, 345-355. J.B. Mudd, T.T. Hclanus, A. Ongun and T.E. IcCullough, Plant Physiol., 48, 1971, 335-339. R.L. Barnes, Can.J.Bot., 50, 1972, 215-219. J.M. Skelly, in P.R. Miller, (Ed.), Effects of Air/Pollutants on Hediterranean and Temperate Forest Ecosystems. Riverside, Calif. 22. 27.6.1980, 1980, pp. 38-50. S.B. McLaughlin, R.K. McConathy, D. Duvick and L.K. Mann, Por.Sci. 28, 1982, 60-70. P.R. Miller, O.C. Taylor and R.G. Wilhour, EPA-Report, Corvallis, OR: U.S. EPA-600/D-82/276, 1982, 10 pp. P.A. Hiller and H.J. Elderman, (Eds.), EPA-Report, Corvallis, OR.: U.S. EPA Report No. EPA-600/3-77-104, 1977. W.T. Williams, Environ.Pollut., 30, 1983, 59-75. R.W. Usher and W.T. Williams, Plant Dis., 66, 1982, 199-204.
54
61
62 63 64 65 66
67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90
91 92
C.L. Rezabek, J.A. Morton, E.C. Mosher, A.J. Prey and J.E. Cummings, Regional Effects of Sulfur Dioxide and Ozone on Eastern White Pine (Pinus strobus L.) in Eastern Wisconsin. Wisconsin Dept. of Nat. Resources, Rep. 78255, 2/1986, 20 p. C.R. Berry and L.A. Ripperton, Phytopath., 53, 1963, 552-557. C.R. Berry and C.H. Hepting, For.Sci., 10, 1964, 2-13. S.F. Duchelle, J.M. Skelly, J.L. Sharick, B.I. Chevonne, Y.S. Yang and J.E. Nelleson, J.Environ.Manag., 17, 1983, 299-308. S.F. Duchelle, J.M. Skelly and B.I. Chevonne,. WASP, 18, 1982, 363373. M.R. Ashmore, in P. Grennfeld, (Ed.), The Evaluation and Assessment of the Effects of Photochemical Oxidants on Human Health, Agricultural Crops, Forestry, Materials and Visibility. Swedish Environ.Res.Inst., Coteborg, 1984, pp.92-104. M.R. Ashmore, N. Bell and J. Rutter, Ambio, 14, 1985, 81-87. B. Prinz, C.H.M. Krause and K.-H. Jung, Waldschaden-Theorie und Praxis auf der Suche nach Antworten, Oldenbourg Verlag Miinchen, 1985, pp. 143-194. F.T. Last and D. Fowler, Forstw.Cbl., 103, 1984, 24-28. R. Cuderian and D.T. Tingey, Notwendigkeit und Ableitung von Grenzwerten far Stickoxide. UBA-Berichte 1/87, Umweltbundesamt Berlin, 1987. 96, D.T. Tingey, W.W. Heck and R.A. Reinert., J.Amer.Soc.Hort.Sci., 1971, 369-371. A.S.Heagle, D.E. Body and C.E. Neely, Phytopathology 64, 1974, 132136. T. Elkiey and D.P. Ormrod, Atmos.Environ., 13, 1979, 1165-1168. J.J. Crosso, H.A. Menser, G.H. Hodges and H.H. McKinney, Phytopathol., 61, 1971, 945-950. W.J. Render and F.H.F.C. Spierings, Neth.J.Plant Pathol., 81, 1975, 149-151. R.D. Shertz, W.J. Render and R.C. Musselman, J.Amer.Soc.Hort. Sci., 105, 1980, 594-598. D.T. Tingey, R.A. Reinert, C. Wickliff and W.W. Heck, Can.J.Plant Sci., 53, 1973, 815-879. A.S. Heagle, W.W. Heck, J.O. Rawlings and R.B. Philbeck, Crop.Sci., 23, 1983, 1184-1191. D.T. Tingey and R.A. Reinert, Environ. Pollut., 9, 1975, 117-125. L.W. Kress, J.M. Skelly and K.H. Kinkelman, Environ.Mon.Ass., 1, 1982, 229-239. J. Mooi, Forst- und Holzwirt, 39, 1984, 438-444. R. Guderian, K. Kiippers and R. Six, VDI-Berichte 560, 1985, 657-701. L.W. Kress and K.H. Hinkelman, Agric. Environ., 7, 1982, 265-274. Y.S. Yang, J.M. Skelly, B.I. Chevonne, Aquilo Ser. Bot., 19, 1983, 406-418. F. Jilttner, Spezielle Berichte der Kernforschungsanlage Jiilich, 369, 1985, 313-316. Chr. Bosch, E. Pfannkuch, K.E. Rehfuess, K.H. Runkel, P. Schramel and M. Senser, Forstw. Cbl., 105, 1986, 218-242. R.A. Skeffington and T.M. Roberts, Oecologia, 65, 1985, 201-206. G. Seufert and U. Arndt, Allg. Forst Z., 41, 1986, 545-549. P.B. Reich and R.C. Amundson, Science, 230, 1985, 560-570. W. Fabig, Chr. Boose, U. Fritsche, B. Crundmann, D. Hochrainer H. Kldppel, F.-J. Mdnig and H. Oldiges, In: Umneltforschungsplan des Bundesministers des Inneren, Forschungsvorhaben: 106070446 /01. Fraunhofer-Institut far Umweltchemie, Schmallenberg-Crafschaft, 1987, 241 p. J.M. Waldman and M.R. Hoffmann, WASP, in preparation. B. Prinz, in I.S.A. Isaksen (Ed.), Tropospheric Ozone, Reidel Publ. Comp., Dodrecht, 1988, pp. 161-184.
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H.U. Pfeffer, Staub-Reinhalt. Luft, 45, 1985, 187-193. B. Prinz, Environment, 29, 1987, 11-37. W.W. Heck, W.Y. Cure, J.O. Rawlings, L.J. Zaragoza, A.S. Heagle, H.E. Heggestad, R.J. Kohut, L.W.Kress and P.J. Temple, JAPCA, 34, 1984, 729-735, 810-8 17. WHO, Air Quality Guidelines for Europe, World Health Organization, Regional Publ., European Series No 23, 1987. R. Guderian, Critical Levels zum Schutz der Vegetation vor Ozon, ECE Critical Level Workshop, Bad Harzburg 14-18.3.1988. W. Warmbt, 2. Meteorol., 29, 1979, 24-31. W. Attmannspacher and R. Hartmannsgruber, P. Lang, Meteorol.Rdsch., 37, 1984, 193-199.
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T. Schneider et al. (Editors),Atmospheric Ozone Research and its Policy Implications 1989 Elsevier Science Publishers B.V., Amsterdam -Printed in The Netherlands
57
GLOBAL ELEMENTAL CYCLES AND OZONE
J . VAN HAM TNO Study and I n f o r m a t i o n Centre f o r Environmental Research, P.O. Box 186, 2600 AD D e l f t , The Netherlands
SUMMARY I n t h i s paper t h e way o u r atmosphere responds t o emissions f r o m t h e s u r f a c e i s e x p l o r e d f o r components o f t h e elemental c y c l e s o f c h l o r i n e , carbon and n i t r o g e n . M o d i f i c a t i o n o f t h e c y c l e s by man i s d e s c r i b e d and responses i n ozone budgets o f t h e s t r a t o s p h e r e and t h e f r e e t r o p o s p h e r e a r e discussed. P o s s i b l e i m p l i c a t i o n s o f t h e s t r o n g r e g i o n a l m o d i f i c a t i o n o f ozone l e v e l s i n t h e f r e e troposphere f o r p o l i c y a r e i n d i c a t e d .
INTRODUCTION T h i s paper i s n o t j u s t d e a l i n g w i t h n o v e l t i e s , "Ozone" was a l r e a d y known t o t h e Greeks and stands f o r odorous. And Greek philosophy, which i n c l u d e d science i n those days, i s known t o have brought f o r w a r d a k i n d o f atom t h e o r y which a l s o i m p l i e d t h e l a w o f mass c o n s e r v a t i o n . L u c r e t i u s , a Roman who l i v e d i n t h e f i r s t c e n t u r y B.C.
and who w r o t e s e v e r a l books ( r e f . 1) i n which he
e x p l a i n s t h e Greek p h i l o s o p h y t o h i s f r i e n d Memnius, acknowledges t h e f l u x e s between t h e e a r t h s u r f a c e and t h e a i r i n t h e upward as w e l l as t h e downward d i r e c t i o n . T h i s elemental c y c l i n g , though w i t h d i f f e r e n t elements, i s e x a c t l y t h e s u b j e c t o f my t a l k . I w i l l update t h i s c l a s s i c a l theme w i t h 20th c e n t u r y science i n t h e n e x t 25 minutes, though I may want t o make a few p h i l o s o p h i c a l remarks i n t h e Greek t r a d i t i o n as w e l l . We w i l l have a l o o k a t OZONE f i r s t and we w i l l s t a r t w i t h t h e good news: ozone i s a n a t u r a l component o f o u r atmospheric system and i s f o u n d t h e r e a t a l t i t u d e s between D and 90 km. I t i s formed and s p l i t c o n t i n u o u s l y under v a r i o u s photochemical regimes. Ozone t h r o u g h o u t our atmosphere, by i t s unique s p e c t r a l p r o p e r t i e s , complements t h e f i l t e r f o r t h e UV-part o f t h e s u n l i g h t . More f u n c t i o n s a r e w o r t h w h i l e o f mentioning. Ozone d r i v e s t h e s e l f c l e a n i n g
-
process i n t h e f r e e troposphere as t h e m a j o r source o f OH-radicals, v i a hu
O3
58
Also, ozone has s t r o n g b a c t e r i c i d a l p r o p e r t i e s and may b e i n s t r u m e n t a l i n t h e c o n t r o l o f epidemic diseases. It i s even b e l i e v e d t o have t h e r a p e u t i c a l v a l u e as w i t n e s s e d by a B e r l i n H o t e l : we a r e i n v i t e d t o improve o u r h e a l t h by exposing o u r s e l v e s d e l i b e r a t e l y t o an atmosphere c o n t a i n i n g some ozone. The c o n c e n t r a t i o n l e v e l may w e l l be d e c i s i v e i n r e c o n c i l i n g t h i s v i e w w i t h t h e s c i e n t i f i c d a t a base on t h e t o x i c i t y o f ozone. We can o n l y r e s p e c t N a t u r e f o r t h e i n g e n i o u s i d e a t o s t o r e t h e m a j o r p a r t of t h i s a i r t o x i c between 10 and 50 k i l o m e t e r up i n t h e s t r a t o s p h e r e . The n o t i o n t h a t t h i s and o t h e r o b s e r v a t i o n s do f i t w i t h i n a m a s t e r p l a n prompts me t o mention a modern v e r s i o n o f t h e c o m b i n a t i o n o f s c i e n c e and p h i l o s o p h y : Lovelocks Gaia-hypothesis ( r e f . 2). I t h o l d s t h a t l i f e i t s e l f has been c r e a t i n g t h e c o n d i t i o n s f o r l i f e on e a r t h and p r o v i d e s t h e c o n d i t i o n s f o r c o n t i n u i t y o f l i f e : t h e p r i n c i p l e o f homeostasis. I t w i l l be v i r t u a l l y i m p o s s i b l e t o p r o v e t h a t t h e Gaia-hypothesis i s c o r r e c t ; i t ' s u s e f u l n e s s as a w o r k i n g h y p o t h e s i s f o r l o o k i n g a t g l o b a l i s s u e s has been proven indeed, s i n c e i t i n s p i r e s many s c i e n t i s t s t o have a c l o s e r l o o k a t t h e mechanisms t h a t a r e o p e r a t i v e i n Gaia. Such a s t i m u l u s i s o f u t t e r importance now t h a t we have bad news on ozone as w e l l : we a r e c o n f r o n t e d w i t h a decrease o f ozone i n t h e s t r a t o s p h e r e and an i n c r e a s e o f ozone l e v e l s i n t h e f r e e troposphere. B o t h e f f e c t s a r e r e l a t i v e l y r e c e n t . They p r o b a b l y d a t e back f r o m a few decades ago and have been c o n f i r m e d by measurements i n t h e e i g h t i e s o n l y . The q u e s t i o n t h a t a r i s e s i s whether man i s p r e s e n t l y m o d i f y i n g l i f e on e a r t h t o such an e x t e n t t h a t t h e c o n t i n u i t y i s a t risk. ATMOSPHERIC SYSTEM G a i a ' s l a w o f c o n s e r v a t i o n o f mass r e q u i r e s an e f f i c i e n t system t o p r e v e n t any m a t e r i a l t o escape i n t o space. The c h a r a c t e r i s t i c l a y e r e d s t r u c t u r e o f o u r atmosphere i s w e l l known. 50 km stratopause
8-15 km
tropopause
1-2 km
NBL-Nocturnal Boundary Layer
surface
F i g . 1. G a i a ' s Mass C o n s e r v a t i o n system.
59 Emissions from the surface w i l l be trapped i n t h e boundary l a y e r s f i r s t and so on. The system i s c o n t r o l l e d by the sun: i t helps t o form t h e l a y e r s as they are and i t i s the d r i v i n g force i n most, i f not a l l , atmospheric chemical transformations which b r i n g the emitted components i n a form t h a t i s f i t f o r deposition. The layered structure, though not permanently there, functions as a powerful m u l t i t r a p f i l t e r . Mechanisms o f removal are:
-
by d i s s o l v i n g i n t o cloudwater and subsequent r a i n - o u t and by wash-out (wet
-
deposition) by deposition from the atmosphere on land, sea, vegetation o r other surfaces (dry deposition)
-
by (photo)chemical conversion, t o be followed by e i t h e r d r y o r wet deposition o f the r e s u l t i n g product(s).
The r a t e s o f these processes (rwet,r together determine the and rchem) dry f l u x from the atmosphere f o r an i n d i v i d u a l component: concentration x
(rwet rdry +
+
'them)
as w e l l as i t s residence time i n the atmosphere: T
1
=
rwet
+
‘dry
+
‘chem
Within the closed system o f our planet several c y c l i c processes are operational. The most obvious example i s the hydrological cycle: t h e continuous downward stream o f l i q u i d water towards sealevel i s balanced by an atmospheric inland vapor and cloud transport. For most elements s i m i l a r cycles e x i s t , though the f l u x e s from and towards the oceans may be f a r from balanced. I n the atmospheric compartment components w i t h short residence times are transported w i t h i n t h e planetary boundary l a y e r , and where necessary converted and deposited again. Components w ith long residence times are dispersed i n the f r e e troposphere f o r the major p a r t , i n order t o be converted i n t o depositable products. For a number o f compounds there i s no apparent removal from the troposphere (N20,CFC’s) and these a l l
w i l l reach the stratosphere. They have t o be converted i n t h e stratosphere and are removed a f t e r r e t u r n o f t h e i r products i n t h e troposphere. When the f l u x e s i n t o and from the atmosphere are equal the averaged concentration o f a component remains constant; f l u c t u a t i o n s may occur, however.
GO CHANGES I N THE TROPOSPHERE I n Table 1 c h a r a c t e r i s t i c v a l u e s f o r a number o f components i n t h e f r e e troposphere have been c o l l e c t e d . Measurements d u r i n g r e c e n t y e a r s have r e v e a l e d an i n c r e a s e o f v i r t u a l l y a l l these components. For those w i t h s h o r t r e s i d e n c e times, such t r e n d s have n o t been e s t a b l i s h e d , b u t s h o u l d be expected on t h e b a s i s o f i n c r e a s e d emissions. By t h i s change i n t r o p o s p h e r i c c o m p o s i t i o n o u r atmospheric system i s
s i g n a l l i n g an apparent unbalance: we a r e l e a v i n g b e h i n d an e r a w h e r e i n o u r atmosphere t h r o u g h s e l f c l e a n i n g processes m a i n t a i n e d a c o n s t a n t c o m p o s i t i o n and we do t h i s a t a speed which, i n g e o l o g i c a l sense, i s i n c r e d i b l y f a s t . It i s s a i d by some t h a t t h e s e l f c l e a n i n g c a p a c i t y o f t h e t r o p o s p h e r e i s a f f e c t e d . I t [ABLE 1.
C o n c e n t r a t i o n s o f t r a c e gases i n t h e f r e e t r o p o s p h e r e and e s t a b l i s h e d changes i n t h e l a s t decades. I f n o t s t a t e d o t h e r w i s e t h e f i g u r e s i n column 2 a r e f r o m r e f . 3 and i n columns 3 and 4 f r o m r e f . 4.
Component
Concentr a t ions around 1965
Concentrations i n 1985
Present per year
conc. r i s e
61
i s unclear whether t h i s i s true. The increased production o f ozone, the precursor o r OH, which i s the cleaning agent f o r the troposphere i s t h e adequate response; our conclusion should be t h a t the self-cleaning capacity has i n creased. On the other hand, i t i s apparent t h a t the response i s n o t strong enough, since trace gas concentrations continue t o increase. Trace gases i n the troposphere i n p r i n c i p l e are i n competition f o r r e a c t i o n w i t h OH. When the concentration o f trace component A increases because o f increased emissions, the r a t e o f removal f o r trace component B may decrease. As a consequence the concentration o f B w i l l a l s o r i s e . D i f f e r e n t i a t i o n between these two causes f o r accumulation o f trace gases w i l l be d i f f i c u l t because o f the u n c e r t a i n t i e s i n the emission rates. We w i l l now have a look a t a selected number o f elemental cycles. I w i l l be short w i t h respect t o the implications f o r stratospheric ozone and r e f e r t o chlorine only here. I w i l l comment a b i t more on the s i t u a t i o n w i t h ozone i n the f r e e troposphere. STRATOSPHERIC MOD I F I C A T l ON
Chlorine c y c l e There i s no doubt any longer t h a t stratospheric ozone d e p l e t i o n i s caused by the emission o f a number o f ha,locarbon compounds, notably CFC-11 and 12, CC14 and CH3CC13, which accumulate i n t h e troposphere and leak from there i n t o the stratosphere ( r e f . 4).
"1
0natural man-made
p p t , ~in~ troposphere
1000
0
CHsCI
Fig. 2. Burden o f long l i f e c h l o r i n e i n the troposphere. I f we look a t f i g u r e 2 we see t h a t the burden o f c h l o r i n e i n t h e troposphere t h a t i s non-reactive and i s not depositable i s p r e s e n t l y f o r 80% manmade. I n other words man has i n t e n s i f i e d a global elemental c y c l e by a f a c t o r 4
and i s now confronted w i t h a massive and serious response. The o t h e r components t h a t i n t e r a c t w i t h stratospheric ozone, V o l a t i l e Organic Components (VOC), mainly methane) and N20 are responsible f o r an i n t e n s i f i c a t i o n o f the stratospheric hydrogen, resp. n i t r o g e n c y c l e by f a c t o r s
62 o f approximately 2.5 and 1.75. We may hope t h a t UNEP's Convention f o r the Ozone Layer w i l l be i n time and e f f e c t i v e i n order t o prevent ecological disasters.
TROPOSPHERIC OZONE I n urban as w e l l as i n r u r a l areas we are s t i l l confronted w i t h elevated ozone concentrations. Urban ozone receives serious a t t e n t i o n since the f i f t i e s .
A s a t i s f a c t o r y s o l u t i o n has not been achieved, despite enormous e f f o r t s t h a t have been undertaken i n the United States and i n Japan and which are now underway i n Western Europe and A u s t r a l i a . We have seen t h a t i n t h e seventies the scale o f the photochemical smog problem s h i f t e d from urban i n t o r u r a l : elevated ozone concentrations were observed i n areas w i t h minimal anthopogenic emissions ( r e f . 11). The r o l e o f transport was demonstrated i n numerous back-trajectory f i e l d studies; also, modellers showed t h a t , during representative episodes, ozoneconcentrations over areas as wide as 50Ox500km2 are hardly influenced by emission reductions w i t h i n t h i s area ( r e f . 12). During the e i g h t i e s the l a r g e scale o f t h e phenomenon became more apparent from t r e n d measurements o f ozone i n the middle and higher troposphere: H Ikml12-
10-
06-
4-
2-
Fig. 3. Trends i n f r e e tropospheric ozone a t the Hohenpeissenberg, Federal Republic o f Germany ( r e f . 9). Measurements by the "Umkehr technique" a t t h e Hohenpeissenberg Observatory ( r e f . 9) i n West-Germany revealed t h a t the concentration o f ozone i n the f r e e troposphere has been increasing during the l a s t decennia. A t m i d - l a t i t u d e s i n the Northern Hemi sphere ozone concentrations above the planetary boundary 1ayer
63 tend t o annual averages o f 40 ppb and can be observed i n remote unpolluted areas as w e l l . Van A a l s t ( r e f . 10) observed concentration l e v e l s o f t h a t order i n the absence o f l o c a l ozone production i n The Netherlands a t a coastal monitoring s i t e . He concluded t o a net production o f ozone i n the f r e e troposphere as had been suggested e a r l i e r by Crutzen ( r e f . 13) and Logan ( r e f .
14). Ozone measurements i n Paris during the 19th century, which were r e d i s covered recently, reveal a background value o f 10 ppb a t t h a t t i m e ( r e f . 15).
2
8 1
1
b
5
8
7
I
0 1 I 1 1 1 2
MONRT
Fig. 4. Ozone concentration as measured i n Paris i n t h e lgth century (ref. 15). Though comparisons are d i f f i c u l t t o make we may f i n d some arguments f o r the statement t h a t the m o d i f i c a t i o n o f t h e tropospheric ozone budget i s a problem o f s i m i l a r size as t h a t o f the ozone layer. While the dreaded e f f e c t s o f increased UV-B r a d i a t i o n have n o t y e t materialized, the continents o f Europe and North America already s u f f e r from f o r e s t dieback, which i s , a t l e a s t p a r t l y , caused by ozone, notably i n mountainous areas. I n f l a t areas we have reason f o r concern as well. S t a r t i n g from average background l e v e l s o f 40 ppb and higher values on s p e c i f i c days, a small margin f o r production o f ozone i n the PBL i s l e f t , before no-effect l e v e l s w i l l be exceeded. I n f a c t , i n combination w i t h other p o l l u t a n t s , ozone concentrations o f 30 ppb already produce s p e c i f i c e f f e c t s w i t h s e n s i t i v e vegetation ( r e f . 16).
Also, we may f i n d t h a t i t w i l l be even more d i f f i c u l t t o c o n t r o l the ozone budget o f the f r e e troposphere, than t o r e s t o r e the stratospheric ozone layer. Ozone formation i n t h e f r e e troposphere i s i n i t i a t e d by the p h o t o l y s i s o f ozone i t s e l f :
03
hv +
01D t H20
0 2 + O 1D
-
20H'
64
-
f o l l o w e d by:
O2
OH' + CH4
CH300' + H20
02
OH' + CO
HOO'
-+
+ C02
I f t h e peroxy r a d i c a l s r e a c t w i t h NO t h e y produce NO2, t h e d i r e c t p r e c u r -
s o r o f ozone i n d a y l i g h t : H02/CH300' + NO
+HO'/CH30'
+ NO2
(4)
f o l l o w e d by r e a c t i o n ( 3 ) o r t h e b r a n c h i n g r e a c t i o n ( 5 ) : CH30' + O2
d
CH20 + H02'
(5)
The a c t u a l ozone f o r m a t i o n t a k e s p l a c e t h r o u g h t h e sequence:
NO^
hv,
3
0P+O2
NO + O ~ P
(6)
O3
(7)
M
A t low l e v e l s o f n i t r o g e n o x i d e s a t e r m i n a t i o n between two peroxy r a d i c a l s i s more probable, f.i.: CH300'
+
HOO'
+ CH300H +
O2
(8)
-
o r a t t a c k on ozone i t s e l f :
HOO' t O3
OH t 202
(9)
T h i s s e t o f r e a c t i o n s , though f a r f r o m complete, i l l u s t r a t e s t h e v i t a l r o l e o f NOx i n t r o p o s p h e r i c ozone f o r m a t i o n ( r e f . 17). M o d e l l i n g s t u d i e s by Crutzen ( r e f . 13) showed t h a t a c o n c e n t r a t i o n o f 5-10 p p t NOx t h r o u g h o u t t h e troposphere i s s u f f i c i e n t f o r b a l a n c i n g ozone f o r m a t i o n and d e s t r u c t i o n a t a l e v e l o f 20-40 ppb, g i v e n t h e p r e v a i l i n g l e v e l s o f methane and CO i n t h e remote atmosphere. However, t h e NOx-concentration i n t h e c o n t i n e n t a l t r o p o s p h e r e i s o f t e n w e l l above 100 p p t a t m i d - l a t i t u d e s ( r e f . 18) and i s accompanied b y p e r o x y a c e t y l n i t r a t e (PAN) l e v e l s o f 30-50 p p t . ( r e f . 7 ) .
The s i g n i f i c a n c e o f
PAN i s t h a t i t a c t s as a r e s e r v o i r f o r NO2 upon d e s t r u c t i o n by OH o r s u n l i g h t i n t h e upper troposphere and so c o n t r i b u t e s t o ozone p r o d u c t i o n . As soon as t h e NO,-concentration
exceeds t h e "break even" c o n c e n t r a t i o n of
5-10 p p t , any i n c r e a s e i n CH4- o r CO-levels w i l l a c c e l e r a t e r e a c t i o n ( 4 ) and promote t h e f o r m a t i o n o f ozone as w e l l .
65 Nitrogen c y c l e The n i t r o g e n c y c l e i s represented i n f i g u r e 5.
0natural
a man-made
Fig. 5. The c y c l e o f n i t r o g e n i n t h e g l o b a l atmosphere. F i g u r e s f o r NO a r e from r e f s . 17-19; f o r N 0 f r o m r e f s . 20 and 21; f o r NH f r o m r g f s . 17, 18, 20, 22 and 23. The atmosphehc burden o f these components 9 s : NO : 0.4 TgN; N 0: 1300 TgN; NH3: 0.4 TgN. An atmospheric accumulation o f 5 TgN asXN20 has b6en estimated.
Both, ammonia and n i t r o u s o x i d e c o n t r i b u t e t o t h e NOx-burden t h r o u g h conversion processes. Ammonia i s a l s o i n s t r u m e n t a l i n promoting t h e s o l u t i o n o f NO;
i n cloudwater and t h e f o r m a t i o n o f a e r o s o l s . The shaded area r e p r e s e n t s t h e
anthropogenic c o n t r i b u t i o n . Source s t r e n g t h s a r e g i v e n i n f i g u r e 6. It f o l l o w s from t h i s consensus diagram t h a t g l o b a l anthropogenic emissions
a r e one and a h a l f t o two t i m e s as h i g h as t h e n a t u r a l emissions, though t h e inaccuracy o f t h e i n d i v i d u a l e s t i m a t e s s t i l l a l l o w s a w i d e r range. On a r e g i o n a l s c a l e t h e r a t i o between anthropogenic and n a t u r a l NO,-emission
can be
q u i t e d i f f e r e n t , however. The source s t r e n g t h f o r a n t h r o p o g e n i c NOx i s h i g h e s t a t m i d - l a t i t u d e s o f t h e n o r t h e r n hemisphere. W i t h r e s p e c t t o i t s r o l e i n t h e f r e e troposphere i t i s o f i n t e r e s t t o know t h e f r a c t i o n o f t h e NOx-emissions t h a t may escape f r o m t h e boundary l a y e r . T h i s appears t o be a m a t t e r of considerable uncertainty.
66
50
r
20
10
0natural man-made Tg Ny-l
from NH3 lightning soil
Rn
tratosphere oceans
F i g . 6. Breakdown o f NOx-emissions i n t o m a j o r g l o b a l sources. Carbon c y c l e I n t h e carbon c y c l e , emissions, a p a r t f r o m C02, a r e grouped b y mass and r e a c t i v i t y i n t h r e e m a j o r c l a s s e s : CH4, CO and non-methane hydrocarbons (NMHC) (see f i g u r e 7 ) .
F i g . 7. The c y c l e o f carbon i n t h e g l o b a l atmosphere. F i g u r e s f o r CO a r e d e r i v e d f r o m r e f s . 17, 18 and 24-26; f o r CH f r o m r e f s . 27-35; f o r NMHC f r o m r e f s . 36-40. The atmosphpric burden o f these c8mponents i s : CO: 200 TgC, p r e s e n t accumulation 10 TgCy- ; CH : 2680 TgC, p r e s e n t a c c u m u l a t i o n 45 TgC; NMHC: 8 TgC, p r e s e n t accumulation 8.1 TgC.
Of these, CH4 and CO escape f o r a m a j o r p a r t f r o m t h e PBL, due t o t h e i r low ‘ r e a c t i v i t y ; f o r NMHC, o r V o l a t i l e Organic Components (VOC) a more d e t a i l e d
67 s i t u a t i o n can be sketched. Natural emissions c o n s i s t f o r the major p a r t o f
0natural 2000 r
man-made
1500 1000 -
500 -
0-
Fig. 8. Breakdown o f emissions i n the g l o b a l carbon c y c l e which a r e r e l e v a n t f o r t h e ozone-budget. isoprene and terpenes. These compounds a r e very r e a c t i v e and w i l l be trapped w i t h i n the PEL f o r the major p a r t . A f r a c t i o n may be converted i n t o CO, however. Oceans a r e sources o f C2-C4-alkanes and alkenes. O f these a considerable p o r t i o n may escape from the PBL. Anthropogenic VOC-emissions may have a range o f r e a c t i v i t i e s ; on t h e average, r e a c t i v i t y i s lower than f o r t h e mix o f n a t u r a l emissions. Estimates o f t h e emission f l u x e s on t h e g l o b a l s c a l e ( f i g u r e 8 ) show a dominating anthropogenic c o n t r i b u t i o n i n CO-emission. F o r t h e VOC-emission nature dominates man, w h i l e CH4 shows approximately equal shares o f man and nature. On a r e g i o n a l scale t h e p r o p o r t i o n s a r e again q u i t e d i f f e r e n t as i s shown f o r VOC-emissions i n Table 2. The reason i s t h a t t h e major source o f n a t u r a l hydrocarbon emissions are t r o p i c a l f o r e s t s w h i l e anthropogenic a c t i v i t i e s a r e concentrated a t t h e m i d - l a t i t u d e s o f t h e n o r t h e r n hemisphere. The d i s t r i b u t i o n p a t t e r n resembles t h a t o f NOx-emissions. VOC/NO_ r a t i o s n
,
I n numerous s t u d i e s o f photochemical a i r p o l l u t i o n i n t h e f i e l d , t h e
l a b o r a t o r y and i n s i m u l a t i o n models much a t t e n t i o n has ever been p a i d t o t h e e f f e c t o f t h e VOC/NOx r a t i o on t h e ozone f o r m a t i o n i n c o n j u n c t i o n w i t h s t u d i e s on VOC-reactivity. The body o f c o l l e c t e d i n f o r m a t i o n was a p p l i e d i n t h e development o f c o n t r o l s t r a t e g i e s , which i n t h e United States l a i d t h e emphasis on r e d u c t i o n o f VOC as w e l l as s u b s t i t u t i o n o f r e a c t i v e VOC by l e s s r e a c t i v e ; t h i s s t r a t e g y has been adopted by o t h e r c o u n t r i e s as w e l l . T h i s strategy, super-
GO imposed on autonomic developments has r e s u l t e d i n e x t r e m e l y l o w VOC/NOx emission r a t i o s , when compared w i t h emissions i n t h e n a t u r a l environment. (Tabel 2 ) . So f a r , i t has n o t been s e r i o u s l y e v a l u a t e d on i t s consequences f o r t h e f r e e t r o p o s p h e r e and f o r background areas. TABLE 2 . VOC and NOx-emissions, g l o b a l and r e g i o n a l and t h e i r r a t i o . Total VOC-1 (TgCy ) World ( t o t a l ) World ( n a t u r a l emissions o n l y i The Nether nds PHOXA-area OECD-Europeb) a) b) c)
930 880 0.435 9.2 10
% Natural of t o t a l VOC
T o t a l NOx
94% 100%
60aJ 20a)
8% 18% 50%
0.15 3.8 3.95
( T g NY-')
vocc) -
Ref.
NOX
16 44
2.9 2.42 2.53
41,42 43 42,44
I n c l u d e s atmospheric p r o d u c t i o n f r o m NH3 Base-year 1980 i n TgC/TgN; these r a t i o s a r e averages and may d i f f e r a p p r e c i a b l y f o r d i f f e r e n t a reas.
We have i n d i c a t i o n s f r o m t h e sparse measurements o f NOx and NOx-compounds i n t h e c o n t i n e n t a l f r e e troposphere t h a t t h e l e v e l s a r e i n t h e o r d e r o f t e n t i m e s p r e - i n d u s t r i a l c o n c e n t r a t i o n s . Though t h e e m i s s i o n growth as w e l l as t h e i n c r e a s e i n in s i t u emissions ( a i r c r a f t , h i g h s t a c k s ) may e x p l a i n t h i s t o a m a j o r e x t e n t , we should c o n s i d e r an a d d i t i o n a l reason: i t m i g h t be t h a t t h e f i r s t t r a p o f o u r atmospheric mass conservancy system, t h e boundary l a y e r , i s n o t f u n c t i o n i n g as good as i t used t o do. L e t us compare t h e urban plume w i t h a n atmosphere above and downwind a f o r e s t canopy. I n t h e u n d i s t u r b e d f o r e s t s i t u a t i o n , n i t r i c o x i d e e m i s s i o n f r o m t h e s o i I and hydrocarbon emissions f r o m t r e e s show a s i m i l a r temperature dependence. Terpenes a r e v e r y r e a c t i v e and quench h y d r o x y l r a d i c a l s as w e l l as any ozone formed p r o d u c i n g a b l u e haze, which i s a b l e t o scavenge subseq u e n t l y r e s i d u a l atmospheric NO,
and HN03 b y heterogeneous processes. Tempera-
t u r e f a l l a t t h e end o f a day induces p a r t i c l e g r o w t h by c o n d e n s a t i o n and uptake o f watervapour and enhances d e p o s i t i o n . I n t h e urban plume on a t y p i c a l photochemical-smogday most o f t h e NO,
will
be c o n v e r t e d i n t o n i t r a t e s a t t h e end o f t h e day, d e s p i t e o f t h e l o w VOC/NO,r a t i o . A p a r t f r o m p e r o x y a c y l n i t r a t e s , t h e y w i l l d i s s o l v e i n c l o u d w a t e r and w i l l be d e p o s i t e d subsequently. Anthropogenic NOx- and VOC-emissions show a s l i g h t l y o p p o s i t e temperature dependence. On a w i n t e r d a y o r even an "average" day, NOx-conversion may be i n c o m p l e t e a t t h e end o f a day; t h i s r e s u l t s i n a h i g h e r p r o b a b i l i t y o f escape i n t o t h e f r e e troposphere.
I am a f r a i d we cannot escape f r o m a s k i n g o u r s e l v e s a p h i l o s o p h i c a l q u e s t i o n now: does i t make sense t o work o u t c o n t r o l s t r a t e g i e s which r e s u l t i n atmospheric m i x t u r e s so d i f f e r e n t f r o m t h e mix i n t h e u n d i s t u r b e d f o r e s t e d area? I n o t h e r words: c o u l d we b e a t Nature? Has i t been r i g h t t o l a y t h e p r i o r i t y w i t h t h e r e d u c t i o n o f VOC-emissions and t h e i r r e a c t i v i t y ?
I w i l l n o t p r o v i d e t h e answers t o t h e s e q u e s t i o n s . Our p r e s e n t knowledge o f t h e troposphere w i l l be p r o b a b l y i n s u f f i c i e n t t o p r o v e o r r e j e c t d e f i n i t e l y any theory. I o n l y hope t h a t we w i l l s c r u t i n i z e o u r p r e s e n t s t r a t e g i e s and t a k e o u r r e s p o n s i b i l i t i e s . We c e r t a i n l y s h o u l d n o t l o s e o u r time, s i n c e mankind w i l l c o n t i n u e t o b r i n g about i m p o r t a n t changes i n o u r atmosphere i n t h e n e a r f u t u r e . FUTURE TRENDS I t i s c o n c e i v a b l e t h a t t h e r a t i o o f VOC t o NOx emissions w i l l d r o p f u r t h e r
i n t h e f u t u r e . The f o l l o w i n g t r e n d s a r e t o be expected o r r e c o g n i z a b l e :
-
F o r e s t dieback F o r e s t v i t a l i t y has dropped t o 50% and even l o w e r values i n a m a j o r p a r t of Europe ( r e f . 45). T h i s w i l l undoubtedly r e s u l t i n a r e d u c t i o n o f i s o p r e n e and terpene emission.
-
Deforestation T r o p i c a l r a i n f o r e s t s , which i n 1980 f i l l e d an a r e a o f 2970x10
6 ha, a r e
d i s a p p e a r i n g a t a r a t e o f 0.6% p e r annum ( r e f , 46). The e f f e c t o f t h i s change f o r t h e ozone budget i n t h e N o r t h e r n Hemisphere has n o t been assessed i n d e t a i l . I t seems c l e a r , however, t h a t t h e area where e f f i c i e n t scavenging o f ozone and NOx by i s o p r e n e and terpenes t a k e s p l a c e w i l l be 'developed"
i n t o r e g i o n s w i t h a n e t c o n t r i b u t i o n t o atmospheric ozone
production.
-
Coastal system We have i n d i c a t i o n s t h a t e u t r o p h i c a t i o n i n c o a s t a l seas has r e p e r c u s s i o n s f o r t h e source s t r e n g t h o f marine emissions. Each y e a r i n May and June N o r t h Sea beaches f r o m t h e Channel up t o Scandinavia a r e covered w i t h a foamy mass, caused b y a bloom o f t h e a l g a Phaeocystis bouchetii ( r e f . 47), which i s known as a d i m e t h y l s u l f i d e e m i t t e r . T o t a l emissions f o r t h e N o r t h Sea r e g i o n have been e s t i m a t e d t o amount t o 60.000 t o n s / y (CH3)$ which i s e q u i v a l e n t t o 20% o f t h e t o t a l S02-emissions i n The Netherlands! Veldhuis ( r e f . 48) o b t a i n e d s t r o n g i n d i c a t i o n s t h a t t h i s bloom i s connected w i t h e u t r o p h i c a t i o n o f t h e N o r t h Sea b y phosphorus. I r e f e r t o t h i s o b s e r v a t i o n because i t m i g h t be t h a t t h e i n t e n s i f i c a t i o n o f t h e P-cycle t r i g g e r s responses i n o t h e r elemental c y c l e s as w e l l . Obvious areas f o r f u r t h e r r e s e a r c h i n r e l a t i o n t o t r o p o s p h e r i c ozone a r e
t h e marine e m i s s i o n o f t h e l o w e r hydrocarbons. With r e s p e c t t o s t r a t o s p h e r i c ozone marine p r o d u c t i o n o f halomethanes, such as CH3C1 and CH3Br, s h o u l d be
70
watched
.
Methane emission from r i c e p a d i ' s which i s supposed t o be t h e major anthropogenic cause f o r t h e r i s e i n CH4-concentrations i s c o n t r o l l e d by t h e n u t r i e n t s t a t u s i n the padi. An assessment o f f e r t i l i z i n g p r a c t i c e s i n r e l a t i o n t o methane emission could be u s e f u l . CONCLUSIONS 1.
Man i s i n t e n s i f y i n g elemental cycles o f c h l o r i n e , carbon and n i t r o g e n by
f a c t o r s between 2 and 5 on a g l o b a l s c a l e and up t o a f a c t o r 10 on a continent a l scale (see Table 3 ) . The response i s a change i n t h e ozone budgets o f t h e stratosphere and t h e f r e e troposphere, which, on a c o n t i n e n t a l scale, i s s t r o n g i n b o t h l a y e r s : t h e A n t a r c t i c Ozone Hole corresponds t o an ozone drop by a f a c t o r 2-3 d u r i n g t h e s p r i n g season; i n t h e f r e e troposphere an increase by a f a c t o r 2-3 i s observed a t m i d - l a t i t u d e s over Europe and N o r t h America. 2.
Large-scale e f f e c t s i n t h e biosphere, a n t i c i p a t e d as a consequence o f
s t r a t o s p h e r i c m o d i f i c a t i o n , have caused a worldwide p o l i t i c a l a c t i o n i n o r d e r t o s t o p the t h r e a t . Large-scale e f f e c t s o f t r o p o s p h e r i c ozone increase, a1 ready v i s i b l e i n o u r f o r e s t s , deserve a s i m i l a r a c t i o n . TABLE 3. Factors o f int e n s if ic a t ion o f e 1eme nt a 1 cyc 1es
G1 oba 1 Chlorine ( w i t h -spheric residence t i m e ) Carbon
co CH4
co,
Continental (Europe o r N o r t h America)
4
irrelevant
a
20+ 1 - 2
2 - 3 1.2 2 - 3 1.5-2
3.
.
5 -10 1.5-2
NOx-emissions a r e h e l d p r i m a r i l y r e s p o n s i b l e f o r increase o f t r o p o s p h e r i c
ozone. Increases i n anthropogenic source s t r e n g h t s as w e l l as a reduced t r a p p i n g e f f i c i e n c y o f t h e p l a n e t a r y boundary l a y e r b o t h c o n t r i b u t e t o a h i g h e r NOx-burden i n t h e f r e e troposphere. Increases i n CH4- and CO-emission enhance t h e f r e e t r o p o s p h e r i c ozone production. 4.
Knowledge on ozone budgets and d e t a i l e d i n s i g h t i n t h e i n t e r a c t i o n o f
g l o b a l elemental c y c l e s has a b e a r i n g on t h e f e a s i b i l i t y o f m a i n t a i n i n g an a i r q u a l i t y standard f o r ozone and should be i n c o r p o r a t e d i n ozone c o n t r o l strategies.
71 ACKNOWLEDGMENT The a u t h o r would l i k e t o thank t h e C o u n c i l f o r Environment and N a t u r e Research i n The Netherlands which enabled him t o make an e x p l o r a t o r y s t u d y o f g l o b a l atmospheric issues. S t i m u l a t i n g c o n t r i b u t i o n s o f B e t t y G e r r i t s e n , P e t e r Heederik and D i c k van d e r Gugten who e x p l o r e d g l o b a l elemental c y c l e s w i t h him a r e g r a t e f u l l y acknowledged. Drs. R. G u i c h e r i t and M. Roemer gave v a l u a b l e comments on t h e manuscript. References
1 2
3 4 5
L u c r e t i u s , The Nature o f t h e Universe. A new t r a n s l a t i o n by R.E. Latham. P i n g u i n Books, 1951. J.E. Lovelock, Gaia, A new l o o k a t l i f e on Earth. O x f o r d U n i v e r s i t y Press, Oxford 1979. B.D. Tebbens i n : A i r P o l l u t i o n (A.C. S t e r n , Ed.), Vol.1, 27, Academic Press, 2d E d i t i o n (1968). W.M.O., Atmospheric ozone 1985. Global ozone r e s e a r c h and m o n i t o r i n g p r o j e c t , r e p o r t no. 16. V. Ramanathan, R.J. Cicerone, H.B. Singh, J.T. K i e h l , J. Geophys. Res. 90,
D3, 5547-66 (1985). 6 7a b
8 9
10
11 12 13 14
R.F. Weiss, J. Geophys. Res. 86, 7185-95 (1981). H.B. Singh, L.J. Salas, W. V i E e e , N a t u r e 321, 588-91 (1986). H.B. Singh, Env. Sci.Techn. 21, 320 (1987). R. B o j kov. These ProceedingsR. Hartmannsgruber, W. Altsmannspacher, H. Claude, i n C.S. Zerefos, A. Ghazi ( E d i t o r s ) , Atmospheric Ozone, Reidel, Dordrecht, 1984, pp 770-774. R..M. van A a l s t , i n R. G u i c h e r i t , J. van Ham and A.C.Posthumus ( E d i t o r s ) , Ozon: f y s i s c h e en chemische veranderingen i n de atmosfeer en de gevolgen, Kluwer, Deventer, 1987, p p 84-91. W. Warmbt, Z e i t s c h r i f t fiur M e t e o r o l o g i e 29 (l), 24 (1979). P.J.H. B u i l t j e s , K.D. van den Hout, S.D. Reynolds, i n C. de Wispelaere ( E d i t o r ) , A i r P o l l u t i o n Modeling and i t s A p p l i c a t i o n 111, Plenum Press, New York, 1984, pp. 507-523. P.J. Crutzen, i n 8. B o l i n and R.B. Cook, ( E d i t o r s ) , The m a j o r biogeochemical c y c l e s and t h e i r i n t e r a c t i o n s , SCOPE 21, Wiley, C h i c h e s t e r (1983), pp 67-103. J.A. Logan, M.J. P r a t h e r , S.C. Wofsy, M.B. McElroy, J.Geophys.Res. @
(C 8), 7210-54, 1981. 15 A. Volz, H.G.J. S m i t . D. Kley. Ber. von d e r Tagung d e r Arbeitsgerneinschaft d e r Grossforschungsanlagen (AGF), Dec. 1985, Bonn, pp. 5-13. 16 A.E.G. T o n n e i j c k , i n R. G u i c h e r i t , J. van Ham, A.C. Posthumus ( E d i t o r s ) , 17 18
19 20
Ozon: f y s i s c h e en chemische veranderingen i n de atmosfeer en hun gevolgen, Proc. Symp. Ede 1986, Kluwer, Deventer, 1987, pp. 60-65. P.J. Crutzen. i n R.Guicherit, J. van Ham, A.C. Posthumus, ( E d i t o r s ) , Ozon: f y s i s c h e en chemische veranderingen i n de atmosfeer en hun gevolgen. Proc. Symp. Ede 1986, Kluwer, Deventer, 1987, pp. 11-17. J.A. Logan, J. Geophys.Res. 88 ( C 15), 10.785-10.807, 1983. P.J. Crutzen and L.T. G i d e 1 , J . Geophys.Res. (C ll), 6641-6661, 1983. I . E . G a l b a l l y , i n : The biogeochemical c y c l i n g o f s u l f u r and n i t r o g e n i n t h e remote atmosphere (Galloway e t a l , e d i t o r s ) , NATO AS1 S e r i e s 159,
a
1985. 21 M. K e l l e r , J. Geophys.Res. 91 (D ll), 11.791-11.802, 1986. 22 E. Buijsman, H.F.M. Maas, W2.H. Asman, Atm.Environ. 21(5), 1009. 1987. 23 R. Soderlund, B.H. Svensson, i n : B.H. Svensson and R.-%derlund ( E d i t o r s ) , N i t r o g e n , Phosphorus and S u l f u r B u l l . , 1976.
-
Global c y c l e s , SCOPE Report 7, Ecol.
72
24 A. Marenco, J.C. Delaunay, J. Geophys. Res. 85, 5599-5613, 1980. 25 R. Conrad, W. S e i l e r , Geophys.Res. L e t t . 2 (E),1353-6, 1982. 26 P.R. Zimnerman, R.B. Chatfield, J. Fishman, P.J. Crutzen, P.L. Hanst, Geophys-Res. L e t t . 5 (8), 679-82, 1978. 27 W. S e i l e r , i n : M.J. Klug, C.A. Reddy ( E d i t o r s ) , Current perspectives i n microbial ecology, Amer.Soc. f o r Microbiology, Washington D.C., 1984, pp. 468-77. 28 D.R. Blake, V.H. Woo, S.C. Tyler, F.S. Rowland, Geophys.Res. L e t t . 11, 1211-14, 1984. 29 A. Holzapfel-Pschorn, W. S e i l e r , I n t . J. Biometeorol. 28 (suppl. dated 1984), 53-61, 1985. 30 J.C. Sheppard, H. Westberg, J.F. Hopper, K. Ganesan, P. Zimerman, J. Geophysics.Res. 87, 1305-12, 1982. 31 D.H. Ehhalt, Naturwissensch. 66, 307-11, 1979. 32 P.R. Zimnerman, J.P. Greenberg, S.O. Wandiga, P.J. Crutzen, Science 218, 563-5, 1982. 33 R.A. Rasmussen, M.A.K. K h a l i l , Nature 301, 700-703, 1983. 34 P.J. Fraser, R.A. Rasmussen, J.W. C r e f s l d , J.R. French, M.A.K. K h a l i l , J.Atm.Chem. 4, 295-310, 1986. 35 M.A.C. KhaliT, R.A. Rasmussen, J. Geophys.Res. & (C 9), 5131-44, 1983. 36 R.A. Duce, V.A. Mohnen, P.R. Zimmerman, D. Grosjean, W. Cautreels, 37 38 39 40 41 42 43
R. Chatfield, R. Jaenicke, J.A. Ogren, E.D. P e l l i z z a r i , G.T. Wallace, Rev. o f Geophys. and Space Phys. 21, 921-52, 1983. D.R. Blake, F.S. Rowland, Nature 321, 231-3, 1986. S.A. Penkett, i n E.G. Goldberg ( E d i t o r ) , Atmospheric Chemistry, Dahlem Konferenzen 1982, Springer, B e r l i n . S. Sawada, T. Totsuka, Atm. Environ. 20, 821-32, 1986. P.R. Zimmerman, R.B. C h a t f i e l d , J. Fixman, P.J. Crutzen, P.L. Hanst, Geophys.Res. L e t t . 5, 679-82, 1978. P.J.H. B u i l t j e s , Basisdocumenten koolwaterstoffen I V , Rapport TNO-CMP 85/04, J u l y 1985. OECD Environmental Data: Compendium 1987. I S B N 92-64-02960-5. C. Veldt e t a l , Emission Data Base. PHOXA-report I, D r a f t r e p o r t
1979. 44 Concawe. Report no. 2/86. The Hague, May 1986. 45 V D I , S c h r i f t e n r e i h e der VDI-Komnission Reinhaltung der L u f t Bd 1, 1985. 46 United Nations Environment Programme, The disappearing forests. UNEP Environment B r i e f No. 3, 1987. 47 C. Lancelot, G. B i l l e n , A. Sournia, T. Weisse, F. C o l i j n , M.J.W. Veldhuis, A. Davies, P. Wassman, Ambio 16, 38-46, 1987. 48 M.J.W. Veldhuis, The ecophysiXogy o f t h e c o l o n i a l alga Phaeocystis bouchetii, Thesis Groningen U n i v e r s i t y , 1987.
T. Schneider et al. (Editors),Atmospheric Ozone Research and its Policy Implications 1989 Elsevier Science Publishers B.V., Amsterdam -Printed in The Netherlands
73
CHANGES I N ATMOSPHERIC COMPOSITION A N D CLIMATE
C. J. E . Schuurmans
Royal Netherlands Meteorological I n s t i t u t e , P.O.
Box 201, 3730 AE
De B i l t , The Netherlands
ABSTRACT
Concentrations of some atmospheric t r a c e gases increase and enhance s u r f a c e temperature. Tropospheric ozone causes t h e same greenhouse warming e f f e c t . Changes of s t r a t o s p h e r i c ozone w i l l have complicated e f f e c t s on c l i m a t e , but i t s d i r e c t e f f e c t s on s u r f a c e temperature a r e probably small. In t h e paper the s u b j e c t is reviewed and conclusions f o r policy i m p l i c a t i o n s a s well a s f u r t h e r research a r e formulated.
CLIMATE PROBLEM
The climate problem has been with u s f o r some time. Even i f we r e s t r i c t our view t o t h e r e c e n t p a s t , not looking a t i c e ages and o t h e r long term and severe d i s r u p t i o n of c l i m a t e , we have t o explain such remarkable v a r i a t i o n s on a decadal time s c a l e a s f o r instance t h e world wide warming around t h e 4 0 - t i e s
of t h i s century and t h e subsequent cooling i n t h e 6 0 - t i e s , e s p e c i a l l y i n t h e Northern Hemisphere. I n f i g u r e 1 yearly averaged temperatures f o r De B i l t , The Netherlands c l e a r l y show t h e s e v a r i a t i o n s . Although such v a r i a t i o n s i n i t s e l f a r e r e l a t i v e l y small
-
and l o c a l l y sometimes a r e h a r d l y s t a t i s t i c a l l y
s i g n i f i c a n t , due t o t h e l a r g e interannual d i f f e r e n c e s
-
their large areal t o
even global extent suggests some e x t e r n a l cause, which f o r t h e v a r i a t i o n s considered, u p t i l l now is not known, or a t l e a s t not u n i v e r s a l l y accepted. C02 AND OTHER TRACE GASES The climate problem, a s y e t not s o l v e d , g r a d u a l l y merged with t h e so-called C02-problem.
In t h e 6 0 - t i e s already t h e atmospheric concentration of C02
s t e a d i l y increased by more than 1 ppm per year and t h e p o t e n t i a l c l i m a t i c e f f e c t s of l a r g e i n c r e a s e s of C02-concentration were s u f f i c i e n t l y known t o l e t t h e 1970 Study of C r i t i c a l Environmental Problems (SCEP) conclude t h a t t h e implications of f u r t h e r C02-increases should be u r g e n t l y i n v e s t i g a t e d (Ref. 1 ) . Curiously enough i n t h e same s t u d y , t h e paragraph
on c l i m a t i c e f f e c t s of
74
10.5"C -r
0 00
10.0
--
0 0
0
0
0
0
0
0
0
00
0
00
0
0
0 0
0
0
9.5
--
-
0
0
00
0
0
0
0
0 00
0 0
0
0
0 0
0
0
0
a5 --
0
0
0
0
0
0
0
0
0
0 0
0
0
0
8.0 -0
7.7
I
: -
Fig. 1 . Yearly averaged temperatures a t De B i l t , The Netherlands, 1901-1987. The curve shows non-overlapping 10-year averages.
o t h e r t r a c e g a s e s ends with: "We do not consider t h e s e gases t o have a g l o b a l s i g n i f i c a n c e except i n s o f a r a s they form p a r t i c l e s " . O t h e r t r a c e gases were added t o t h e climate-C02-problem only i n t h e l a s t 5-10 years. The s i t u a t i o n a t present seems t o b e more or l e s s t h e following:
75 TABLE I
Trace gas
Present concentration
(name)
(ppbv)
Increase p e r year
IR-absorp t ion
( i n %)
( A i n pm)
co2
345000
0.4
15
CH4
1650
1 .o
5-7.5
N20
O3 ( t r o p ) O3 ( s t r a t )
304 5 t o 500 10000
0.25
8,16
0.25?
-
9.6 9.6
?
CFC 1 1
0.23
5.0
10-1 2
CFC 1 2
0.4
5.0
10-12
GREENHOUSE EFFECT Changes of atmospheric composition may a f f e c t c l i m a t e i n a number of ways ( t h i n k of t h e r o l e of water vapor i n weather and c l i m a t e ) , b u t t h e primary e f f e c t is through changes of t h e earth-atmosphere r a d i a t i o n balance. Strangely enough the minor c o n s t i t u e n t s o r t r a c e g a s e s play a dominant r o l e i n t h e r a d i a t i o n balance. Short wave s o l a r r a d i a t i o n a s well a s long wave r a d i a t i o n from the e a r t h and atmosphere a r e a f f e c t e d by changing t r a c e gas concentratons. The l a t t e r however is much more important than t h e former, which i n o t h e r words means t h a t we have mainly t o consider t h e so-called change of t h e greenhouse e f f e c t . I t may b e noted from Table I t h a t C02 and t h e so-called o t h e r t r a c e gases d i f f e r i n the wave l e n g t h s of IR-absorption (and emission). While C 0 2 c o n t r i b u t e s t o t h e greenhouse e f f e c t a t 15
pm.
quite far
from t h e so-called atmospheric window a t about 10 pm ( t h e place i n t h e spectrum where most of t h e e a r t h ' s r a d i a t i o n can disappear uninteruptedly i n t o s p a c e ) , some of t h e o t h e r t r a c e gases have t h e i r absorption bands e x a c t l y i n s i d e t h i s window. CFC 1 1 and 1 2 t h e r e f o r e a r e s a i d t o d i r t y the atmospheric window. In physical terms i t means t h a t t h e a d d i t i o n o f 1 molecule of CFC 11 or 1 2 has t h e same e f f e c t on the r a d i a t i o n balance a s the a d d i t i o n of 1 04 C02molecules. The greenhouse e f f e c t of t h e atmophere under p r e s e n t c o n d i t i o n s amounts t o a downward I R - f l u x from t h e atmosphere t o t h e e a r t h s u r f a c e of 96% of t h e incoming s o l a r f l u x a t t h e top of t h e atmosphere. See f i g u r e 2. The l a t t e r being 350 W/m2, means t h a t a 1 % p e r t u r b a t i o n of t h e normal greenhouse backradiation involves a change of t h i s f l u x of some 3.4 W/m2. For comparison, t h e estimated increase of IR-backradiation a t tropopause l e v e l
due t o a doubled C02-concentration of t h e atmosphere is 4.2 W/m2. We may conclude t h e r e f o r e t h a t the i n i t i a l (without feed backs) p e r t u r b a t i o n of t h e r a d i a t i o n balance caused by C02 and o t h e r t r a c e gas concentration
76
i n c r e a se s seems t o be extremely small. However, a s we w i l l s e e l a t e r on, t h i s is only apparently so.
space
atmosphere
surface
F i g . 2. Radiation budget of t h e earth-atmosphere system. Left is s o l a r
incoming r a d i a t i o n , s e t a t 100%. Reflected s o l a r r a d i a t i o n is 30%. About 51% is absorbed a t t h e e a r t h s u r f a c e ; t h e remainder is absorbed i n t h e atmosphere.
The r i g h t p a r t g i v e s the emission of i n f r a r e d r a d i a t i o n b y the e a r t h s u r f a c e I, a n d by t h e atmosphere I,. RADIATIVE-CONVECTIVE MODELS
Computing t h e c l i m a t i c consequences of changes i n t h e r a d i a t i o n balance is i n p r i n c i p l e p o s s i b l e b u t i n p r a c t i c e l i m i t e d by t h e complexity of the e a r t h -
ocean-atmosphere system. A s i m p l e and yet powerful model however is t h e ra dia tive -c onve c tive model (RCM),
i n which only one
-
vertical
-
dimension is considered and a thermal
equilibrium s t r u c t u r e is computed t ak i n g i n t o account a l l r e l e v a n t feedbacks a c t i n g upon an i n i t i a l p er t u r b at i o n of t h e r a d i a t i o n balance. The point is t h a t t h e r e i s not a balance of r a d i a t i o n a l f l u x e s , n e i t h e r a t t h e earth s u r f a c e , nor a t any l ay er i n t h e troposphere. In t h e s t r a t o s p h e r e however thermal equilibrium sometimes may b e eq u i v al ent t o r a d i a t i v e e quilibrium . Needless t o say t h a t i n R C M ' s o t h e r v e r t i c a l t r a n s p o r t s of energy than b y r a d i a t i v e t r a n s f e r have t o be incorporated. The most obvious of them is convective t r a n s p o r t i n t h e troposphere which keeps the troposphe ric l a p s e r a t e of temperature a t a quasi-fixed value. Horizontal t r a n s p o r t s of h e a t and substances a r e not included i n a RCM implying t h a t the a p p l i c a t i o n of such a
77 model is l i m i t e d t o some kind of g l o b a l average p o s i t i o n . With these r e s t r i c t i o n s one must say t h e t h e RCM h a s given u s a g r e a t deal
of i n s i g h t i n t h e r e l a t i v e importance of a number of atmospheric processes and furthermore some q u a n t i t a t i v e e s t i m a t e s of t h e temperature e f f e c t s t o be expected from changes i n t h e atmospheric composition. A t a meeting on ozone i n t h e l a t e 8 0 - t i e s i t is good t o remember t h a t t h e RCM’s of the e a r l y 6 0 - t i e s already provided u s w i t h answers t o such v i t a l questions a s : 1 . Is i t ozone t h a t keeps t h e s t r a t o s p h e r e
warm? The answer turned out t o
be: yes. 2. Does t h e ozone l a y e r have an important e f f e c t on s u r f a c e temperature?
The answer was: no. Figure 3 shows t h e equilibrium p r o f i l e s of temperature a s computed. The s t r a t o s p h e r e warming by ozone is e v i d e n t . Addition of ozone does n o t apparently change s u r f a c e temperature. Nevertheless looking i n some d e t a i l l e a d s t o the conclusion t h a t from t h e 33 K temperature i n c r e a s e due t o the greenhouse e f f e c t some 0.8 K is d u e t o ozone (9 K is by C02 and t h e l a r g e s t p a r t by H20).
2.3
10
(30)
1000
100
140
180 27.0 280 temmraturs VK)
300
Fig. 3. Thermal equilibrium f o r atmospheres w i t h a d i f f e r e n t atmospheric composition, a s simulated by an RCM ( r e f . 2 ) . MODIFICATION OF TEMPERATURE RCM’s provided t h e f i r s t evidence t h a t p e r t u r b a t i o n s of t h e r a d i a t i o n
balance, although apparently s m a l l , could g i v e r i s e t o r e l a t i v e l y l a r g e changes i n s u r f a c e temperature. Feedback e f f e c t s , e s p e c i a l l y w i t h water vapor c o n t e n t , a r e mostly p o s i t i v e , which means t h a t t h e i n i t i a l greenhouse e f f e c t is magnified and equilibrium is reached a t much h i g h e r s u r f a c e temperature
than is needed t o compensate t h e i n i t i a l d i s turba nc e of t h e ba c kra dia tion. I n t h i s way R C M ' s some 20 y ear s ago p r ed i ct ed a 2.4 K inc re a se of s u r f a c e
temperature f o r a doubling of t h e C02 co n t ent of t h e atmosphere. This value i s s t i l l a g e n e r a l l y accepted order of magnitude, though s i n c e then numerous models of varying s o p h i s t i c a t i o n and s p a t i a l dimensions have been a pplie d t o t h i s s e n s i t i v i t y problem.
RCM's a l s o prove t e b e t h e r i g h t t o o l t o s t u d y t h e r e l a t i v e importance of
the various t r a c e g as p er t u r b at i o n s . In Table I1 some of the se results a r e compared (according t o Ref. 3 ) . TABLE I1
Trace gase (name)
Introduced
Surface temperature
change
response (K)
co2
300-600 ppm
2.8
CH4
1.6-3.2 ppm
0.2
0.28-0.56
N20
0.6
ppm
CFC 1 1
0-2 ppb
0.5
CFC 1 2
0-2 ppb
0.5
O3
-25%
-0.5
Comments on Table I1 a r e t h e following: a. r e a l i s t i c changes o f o t h e r t r a c e gas co n c e ntra tions toge the r may cause a modification of s u r f ace temperature which i s of t h e same orde r of magnitude
a s the e f f e c t of a doubling of t h e C02-concentration. b. s u r f a c e temperature e f f e c t s of changes i n ozone c onc e ntra tion strongly
depend on the v e r t i c a l d i s t r i b u t i o n of t h e ozone changes. A s i t u a t i o n a 8 i n d i c a t e d i n Table I1
-
a 25% decrease a t a l l l e v e l s
-
i s very unlike ly t o
occur i n n a t ur e. Decreases i n t h e s t r a t o s p h e r e a t pre se nt go along with i n c r e a se s of tropospheric ozone co n cen t r ation. The l a t t e r of course w i l l enhance t h e greenhouse e f f e c t of the atmosphere and thus lead t o a warming a t t h e s u r f a ce. SCENARIO T I L L 2050 A
l o g i c a l extension of s e n s i t i v i t y s t u d i e s i s t h e work on s c e n a r i o ' s :
educated guesses about f u t u r e developments. In one such sc e na rio the inc re a se i n concentration of C 0 2 , CH4, N20 and CFC's i s such t h a t around t h e year 2020
the p o i n t may be reached t h a t t h e b ack r ad i ation i s equal t o t h e p e r t u r b a t i o n caused by a doubling of t h e C02-concentration. See f i g u r e 4 . Some people mention t h i s the year of t h e e f f e c t i v e doubling of t h e C02-concentration. The
79 value of t h e p a r t i c u l a r s cen ar i o may be d i f f i c u l t t o judge, b u t i t anyhow makes c l e a r t h a t t h e time a v a i l a b l e t o avoid such a p o s s i b l e s i t u a t i o n has become l e s s than one generation of mankind.
-2
wm
I
I
I
1
I
PP"
600
Fig. 4 . Possible increase of greenhouse r a d i a t i o n based on a sc e na rio of the increase of t h e atmospheric concentration of C02 and some o t h e r trace gases (ref. 4). MODIFICATION OF CLIMATE
Estimates of t h e response of s u r f ace temperature t o p e r t u r b a t i o n s of t h e r a d i a t i o n balance or more g en er al l y t o p er t urba tions of the atmospheric composition a s indicated above, a r e poor i n d i c a t o r s of t h e r e l a t e d changes of climate. This has t o do w i t h a t l e a s t t h r e e things: a . climate is f a r t o complex t o d es cr i b e i n a 1-dimensional fashion. Fortunately, 3-D models of t h e earth-atmosphere system, so-called General C i r c u l a t i o n Models (GCM's), e x i s t which more o r l e s s confirm t h e responses computed b y 1 - D R C M ' s . Unfortunately, GCM's a r e a s ye t not s o p h i s t i c a t e d enough t o use t h e i r 3-D-specified
output a s a r e l i a b l e i n d i c a t i o n of
( r e g i o n a l ) c l i mat e change. In g en er al , GCM's a r e a b l e t o sim ula te the broad f e a t u r e s of present day cl i mat e, b u t simulations of a number a re giona l c l i m a t i c f e a t u r e s or as p ect s of t h e seasonal c yc le a r e s t i l l g r o s s l y in error. b. some processes a t work i n t h e cl i mat e system a r e s t i l l not s u f f i c i e n t l y
well understood t o have them r e l i a b l y incorporated i n the models. This
80 causes u n c e r t a i n t i e s i n t h e model e s t i m a t e s . For t h i s reason t h e formerly mentioned 2.5 K i n c r e a s e of g l o b a l average s u r f a c e temperature should be presented with i t s u n c e r t a i n t y range of 1.5-4.5
K.
I t i s believed t h a t a
l a r g e part of t h e u n c e r t a i n t y is caused by t h e u n c e r t a i n r o l e o f c l o u d s . I t has been known f o r q u i t e some time t h a t a few p e r c e n t i n c r e a s e of cloud amount by i n c r e a s i n g t h e albedo may o f f s e t t h e expected greenhouse warming. On t h e o t h e r hand t h e o r e t i c a l p o s s i b i l i t i e s e x i s t t h a t changes i n cloud amount may enhance t h e greenhouse e f f e c t ( p o s i t i v e feedback). c . e s t i m a t e s of temperature or c l i m a t e response published t h u s f a r i n most c a s e s p e r t a i n t o the e q u i l i b r i u m s i t u a t i o n . The t r a n s i e n t c l i m a t i c response
is what we a c t u a l l y w i l l f e e l . Due t o t h e l a r g e heat s t o r a g e i n t h e oceans an equilibrium response t o a c e r t a i n p e r t u r b a t i o n w i l l only be reached some decades or maybe a century a f t e r t h e i n t r o d u c t i o n o f t h e p e r t u r b a t i o n . (By p e r t u r b a t i o n we e.g. mean t h e year of the e f f e c t i v e doubling of t h e C02concentration a s mentioned above). Numerical s i m u l a t i o n of t r a n s i e n t c l i m a t e response is i n its beginning s t a g e . I t is very (computer)time consuming, p a r t l y because a coupled atmosphere-ocean GCM must be employed. Though s i m u l a t i o n s of t r a n s i e n t c l i m a t e response make t h e impression of climate p r e d i c t i o n s , they of course do not and cannot i n c o r p o r a t e e f f e c t s of f u t u r e volcanic e r u p t i o n s o r v a r i a t i o n s i n s o l a r o u t p u t .
CONCLUSIONS One might t h i n k of conclusions f o r ( p o l i t i c a l ) a c t i o n and c o n c l u s i o n s from t h e p o i n t of view of r e s e a r c h . I w i l l t r y t o look a t t h e problem from both s i d e s . Without f u r t h e r research I t h i n k we may conclude t h a t : 1 . Reduction of t h e increase o f atmospheric c o n c e n t r a t i o n s of o t h e r t r a c e
gases than C02 w i l l have a s i g n i f i c a n t e f f e c t i n delaying t h e greenhouse warming. I e s p e c i a l l y think of those g a s e s f o r which t h e r e l e a s e might be e a s i e r stopped than t h a t of C02 or w h i c h r e l e a s e s m u s t be stopped anyway f o r o t h e r reasons (e.g. CFC 1 1 and 12). 2 . The response of s u r f a c e temperature t o s t r a t o s p h e r i c ozone changes is
probably small. In general however t h e r e l a t i o n between ozone c o n t e n t o f t h e atmosphere and c l i m a t e is s o complicated t h a t t h e use of c l i m a t e response arguments i n t h e ozone debate i s e a s i l y misleading. Research i n t h i s f i e l d must be strengthened f o r some important reasons mentioned i m p l i c i t l y before. Our a b i l i t y t o s i m u l a t e p r e s e n t atmospheric s t r u c t u r e , composition and c l i m a t e must b e improved, f o r i n s t a n c e . In view of t h e present conference, two a s p e c t s of a research e f f o r t m u s t be s p e c i f i c a l l y stressed :
81 1 . I n t e r a c t i o n processes between s t r a t o s p h e r e and troposphere l a r g e l y belong
t o the f i e l d of present unknowns or i n s u f f i c i e n t l y knowns. Cooling or warming of t h e s t r a t o s p h e r e , due t o changing ozone concentrations i n d i r e c t l y may a f f e c t t h e l a r g e s c a l e tropospheric c i r c u l a t i o n , being a major component in determining regional climate. Unless such dynamic coupling mechanisms a r e b e t t e r s t u d i e d and properly simulated, climate simulations continue t o contain a l a r g e margin of uncertainty. 2 . Ozone depletion o r increases l i k e in the troposphere involve f i r s t of a l l
atmospheric chemical processes. Such processes in t u r n a r e s t r o n g l y influenced by atmospheric conditions (some people think t h a t t h e C02produced cooling of t h e Antarctic s t r a t o s p h e r e has stimulated t h e chemical reactions leading t o the ozone h o l e ) . This c r e a t e s some i n t i m i t e l y linked climate-chemistry processes which in t h e present generation of climate simulation models a r e lacking o r only very poorly developed. REFERENCES
Man's Impact on the Global Environment, Report of t h e S t u d y of C r i t i c a l Environmental Problems ( S C E P ) , MIT 162, Cambridge, Massachusetts, 1970, p. 54. S.
Manabe and R.F. S t r i c k l e r , Thermal Equilibrium of t h e Atmosphere w i t h a
Convective Adjustment, J . A t m . Sci., 21 (1964). 361-385. A. Henderson-Sellers and P . J . Robinson, Contemporary Climatology, Longman, Harlow, 1986. Wigley, Relative contributions of d i f f e r e n t t r a c e gases t o t h e greenhouse e f f e c t , Climate Monitor, 16 (19871, 14-28. T.M.L.
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83
SESSION It
TROPOSPHERIC OZONE, OXIDANTS AND PRECURSORS: SOURCES AND LEVELS
Chairmen
L.J. Brasser A.P. Altshuller
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T. Schneider et al. (Editors),Atmospheric Ozone Research and its Policy Implications 1989 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands
85
MOTOR VEHICLES AS STRATOSPHERIC OZONE
AND
SOURCES
OF
COMPOUNDS
IMPORTANT
F.M. BLACK U.S. Environmental P r o t e c t i o n Agency (MD-46) C a r o l i n a 27711
,
TO
TROPOSPHERIC
Research T r i a n g l e Park, N o r t h
ABSTRACT One o f t h e most r a p i d l y growing human a c t i v i t i e s i n t h e U.S. of importance t o atmospheric ozone i s t h e use o f highway m o t o r v e h i c l e s . T r a n s p o r t a t i o n sources a r e e s t i m a t e d t o have been r e s p o n s i b l e f o r about 34% o f 1985 U.S. a n t h r o p o g e n i c hydrocarbon emissions , 70% o f carbon monoxide emissions, 45% o f nitrogen oxide emissions, 24% o f nonaerosol c h l o r o f l u o r o c a r b o n emissions, and 14% o f carbon d i o x i d e emissions. Data i s presented d e s c r i b i n g p o s s i b l e u n i n v e n t o r i e d t r a n s p o r t a t i o n hydrocarbon emissions t h a t c o u l d i n c r e a s e t h e i r e s t i m a t e d c o n t r i b u t i o n t o 45 50% o f t h e anthropogenic t o t a l . Data i s a l s o p r e s e n t e d s u g g e s t i n g m o t o r v e h i c l e s t o be r e l a t i v e l y i n s i g n i f i c a n t sources o f a n t h r o p o g e n i c n i t r o u s o x i d e , b u t n o t i n g t h a t these emissions a r e i n c r e a s e d by t h e c o n t r o l t e c h n o l o g i e s used t o reduce hydrocarbon, carbon monoxide, and n i t r o g e n o x i d e s emissions. The s e n s i t i v i t y of motor v e h i c l e e m i s s i o n r a t e s and c o m p o s i t i o n s t o such o p e r a t i n g v a r i a b l e s as ambient temperature, a l t i t u d e , and average speed i s discussed. Hydrocarbon and carbon monoxide e m i s s i o n r a t e s a r e g e n e r a l l y m i n i m i z e d a t ambient temperatures o f about 24°C (75"F), and e l e v a t e d a t h i g h e r and l o w e r temperatures. These emissions a r e a l s o e l e v a t e d by h i g h a l t i t u d e and reduced average speed o p e r a t i n g c o n d i t i o n s . N i t r o g e n o x i d e e m i s s i o n r a t e s a r e n o t as s e n s i t i v e t o v e h i c l e operating conditions. The r a t i o o f hydrocarbon t o n i t r o g e n o x i d e emissions, o f importance t o t r o p o s p h e r i c ozone c h e m i s t r y , v a r i e s w i t h o p e r a t i n g c o n d i t i o n s f r o m about 1 t o 5. The c o m p o s i t i o n o f hydrocarbon emissions v a r i e s w i t h v e h i c l e speed and ambient temperature; e l e v a t e d p a r a f f i n i c f r a c t i o n s a r e t y p i c a l o f h i g h speed and h i g h t e m p e r a t u r e o p e r a t i o n , and e l e v a t e d o l e f i n i c f r a c t i o n s a r e t y p i c a l o f l o w speed and l o w temperature o p e r a t i on.
-
INTRODUCTION Since enactment o f t h e 1970 Clean A i r Act, ozone has proven t o be t h e most p e r v a s i v e and d i f f i c u l t t o c o n t r o l o f a l l U.S. t h e o t h e r p o l l u t a n t s addressed by t h i s Act, from
sources;
rather,
it
results
from
a i r pollutants.
Unlike
ozone i s n o t d i r e c t l y e m i t t e d
complex
photochemical
reactions
i n v o l v i n g s u n l i g h t and v a r i o u s p r e c u r s o r e m i s s i o n s t h a t emanate f r o m b o t h man's a c t i v i t i e s and n a t u r a l processes.
Atmospheric t r a n s p o r t has c o m p l i c a t e d
e f f o r t s t o c o n t r o l ozone as a u t h o r i t i e s charged w i t h m a i n t a i n i n g l o c a l a i r q u a l i t y a r e o f t e n f r u s t r a t e d by ozone p r e c u r s o r s r e s u l t i n g f r o m a c t i v i t i e s hundreds o f m i l e s upwind o f t h e i r j u r i s d i c t i o n .
The phenomenon o f p o l l u t a n t t r a n s p o r t has a l s o awakened a growing i n t e r n a t i o n a l concern a b o u t changes i n stratospheric
a i r chemistry
wherein t h e
r a t e o f ozone
d e s t r u c t i o n i s being
86 accelerated
by
compounds
transported
from
the
earth's
surface.
Both
t r o p o s p h e r i c and s t r a t o s p h e r i c t e m p e r a t u r e change can a l s o be a s s o c i a t e d w i t h emissions a t t h e e a r t h ' s s u r f a c e .
The c h e m i s t r y o f t h e e a r t h ' s atmosphere i s
v e r y complex and t h e s u b j e c t o f much h y p o t h e s i z i n g and s t u d y .
It i s apparent
t h a t t h e t r o p o s p h e r i c and s t r a t o s p h e r i c systems a r e c o u p l e d and s h o u l d be c o l l e c t i v e l y c o n s i d e r e d when examining t h e impact o f man's a c t i v i t i e s on t h e atmosphere. One o f t h e most r a p i d l y growing a n t h r o p o g e n i c a c t i v i t i e s o f i m p o r t a n c e t o atmospheric ozone i s t h e use o f highway m o t o r v e h i c l e s . t r a t o r o f t h e U.S.
Lee Thomas, Adminis-
Environmental P r o t e c t i o n Agency (USEPA), r e c e n t l y n o t e d
t h a t s i n c e 1970 t h e U.S. economy grew a b o u t 44 p e r c e n t ,
t h e p o p u l a t i o n 18
p e r c e n t , and t h e k i l o m e t e r s d r i v e n by American m o t o r i s t 58 p e r c e n t ( r e f . 1) There a r e many compounds e m i t t e d f r o m m o t o r v e h i c l e s t h a t p a r t i c i p a t e i n atmospheric chemical and p h y s i c a l processes w h i c h i n f l u e n c e t h e c o n c e n t r a t i o n s o f t r o p o s p h e r i c and s t r a t o s p h e r i c ozone. n i t r o g e n o x i d e s (NOx o r ozone.
Methane
(CH4)
V o l a t i l e o r g a n i c compounds (VOC) and
NO + NO2) a r e t h e p r i m a r y p r e c u r s o r s o f t r o p o s p h e r i c and
carbon
monoxide
reactions
(CO)
control
the
atmospheric c o n c e n t r a t i o n s o f h y d r o x y l r a d i c a l (OH) w h i c h i n t u r n c o n t r o l s t h e atmospheric r e s i d e n c e t i m e o f compounds i m p o r t a n t t o r a d i a t i v e h e a t i n g o f t h e t r o p o s p h e r e (green house e f f e c t ) and compounds i m p o r t a n t t o ozone c h e m i s t r y i n c l u d i n g s t r a t o s p h e r i c ozone d e p l e t i o n .
CO,
although o f lower r e a c t i v i t y
t h a n most VOCs, i s a l s o c o n s i d e r e d a p r e c u r s o r o f t r o p o s p h e r i c ozone.
The
n i t r o u s o x i d e (N20), Freon-12 (CF2C12), and CH4 t r a n s p o r t e d f r o m t h e e a r t h ' s surface t o t h e stratosphere
p a r t i c i p a t e i n ozone d e p l e t i o n c h e m i s t r y .
A
p r o d u c t o f d e p l e t e d s t r a t o s p h e r i c ozone i s more i n t e n s e UV r a d i a t i o n i n t h e t r o p o s p h e r e where i t d r i v e s t h e f o r m a t i o n o f ozone.
Ozone, N20, CH4,
CF2C12,
and carbon d i o x i d e (C02) a l s o a l l i n f l u e n c e t h e r a d i a t i v e b a l a n c e o f t h e e a r t h ' s atmosphere.
I n c r e a s e d a t m o s p h e r i c c o n c e n t r a t i o n s o f t h e s e compounds
w i l l e l e v a t e t h e t e m p e r a t u r e o f t h e t r o p o s p h e r e and decrease t h e t e m p e r a t u r e o f t h e stratosphere. These t e m p e r a t u r e changes can i n f l u e n c e t h e r a t e s o f r e a c t i o n s f o r m i n g and d e s t r o y i n g ozone. MOTOR VEHICLE EMISSIONS The atmospheric c o n c e n t r a t i o n s o f CF2C12,
N20, CO,
C02,
and CH4 a r e
c u r r e n t l y i n c r e a s i n g a t annual r a t e s o f a p p r o x i m a t e l y 5%, 0.2%, 1-2%, 0.5%, and 1%, r e s p e c t i v e l y ( r e f .
2).
There a r e many a n t h r o p o g e n i c and b i o g e n i c
sources o f most o f t h e s e compounds.
The r e l a t i v e s t r e n g t h s o f t h e v a r i e d
sources a r e o f t e n debated and a r e i m p o r t a n t
t o the potential
impact o f
anthropogenic emissions c o n t r o l .
Only highway m o t o r v e h i c l e sources w i l l be
discussed i n
The U.S. government
t h i s presentation.
has t a k e n
measures t o
reduce ambient l e v e l s o f VOC,
NOx,
CO,
and i n d i r e c t l y C02, through motor
v e h i c l e emissions ( t a i l p i p e and evaporative) and f u e l economy regulations. Table 1 summarizes some o f these regulations. Countering the government mandated emission r a t e reductions have been t h e previously mentioned dramatic growth o f vehicle-kilometers-traveled
(VKT) and
a d i s t u r b i n g l y l a r g e amount o f v e h i c l e emission c o n t r o l system tampering. Fig. 1 i l l u s t r a t e s U.S.
light-duty
and heavy-duty v e h i c l e urban and r u r a l VKT
growth during the period 1975 t o 1985, w i t h p r o j e c t i o n s through 2000 ( r e f . 3). During the 1975 t o 1985 decade, l i g h t - d u t y urban and r u r a l VKT increased 26.8% and 29.2%, respectively, and heavy-duty urban and r u r a l VKT increased 53.0% and 61.1%, respectively. The r e s u l t s o f t h e 1986 USEPA Motor Vehicle Tampering Survey (15 c i t i e s ,
7541 vehicles)
suggested t h a t one o u t o f every f i v e
passenger cars and l i g h t - d u t y t r u c k s i n the U.S. the emission c o n t r o l
system tampered
(ref.
had a t l e a s t one component o f 4).
An a d d i t i o n a l 25% were
c l a s s i f i e d as "arguably tampered,''
meaning t h a t a determination could n o t be
made as t o whether t h e v e h i c l e ' s
c o n d i t i o n was due t o tampering o r poor
maintenance.
Tampering and m i s f u e l i n g can cause dramatic increases i n VOC,
CO, and NOx emissions.
For example, disconnected a i r pumps (found on 8% o f
the surveyed vehicles so equipped) can increase VOC emissions 200% and CO emissions 800%, and disconnected exhaust-gas-recirculation systems (found on
7% of
surveyed vehicles
so
equipped)
M i s f u e l i n g c a t a l y s t equipped vehicles vehicles
Fig. 1.
requiring
U.S.
unleaded f u e l )
can
can
increase
NOx
emissions
175%.
w i t h leaded gasoline (found on 9% o f increase
VOC emissions 500% and
motor v e h i c l e kilometers traveled, 1975 t o 2000.
CO
1972 1973 1974 1975 1977 1978 1979 1980 1981 1982 1983 1984 1985 1987
LDV; LDT" LDV, LDT HDGV, tDDV5 LDV, LDT' LDV LDV LDT LDV LDT HDGV, HDDV LDV LDV LDT LDV LDV LDV LDT LDV8 HDGV8 HDDV LDT HDGV HDDV
2.2 ;/mi 3.4 i / m i 3.4 g l m i
-
1.5 g/mi 2.0 g/mi 1.5 g/mi 1.5 g/mi 2.0 g/mi 1.5 g/mi 1.7 g/mi 1.5 glbhp-hr 0.41 g l m i 0.41 g/mi 1.7 g/mi 0.41 g/mi 0.41 glmi 0.41 glmi 0.8 glmi 0.41 glmi 2.5 glbhp-hr 1.3 glbhp-hr 0.8 g/mi 1.3 glbhp-hrg 2.5 glbhp-hr 1.3 glbhp-hr . .
23 ;/mi 39 glmi 39 glmi 40 glbhpyhr 15 glmi 20 glmi 15 gfmi 15 g/mi 20 glmi 15 glmi 18 glmi 25 glbhp-hr 7.0 glmi 3.4 glmi 18 g/mi 3.4 glmi 3.4 glmi 3.4 glmi 10 glmi 3.4 glmi 40 glbhp-hr 15.5 'glbhp-hr 10 g/mi 15.5 g/bhp-hr 40 glbhp-hr 15.5 g/bhp-hr
3.0 g/mi
-
3.1 3.1 2.0 2.0 3.1 2.0 2.3 2.0 1.0 2.3 1.0 1.0 1.0 2.3 1.0
g/mi g/mi glmi glmi g/mi g/mi glmi
-
glmi glmi g/mi glmi glmi g/mi glmi g/mi
16 g/bhp-hr -
10 g/bhp-hr
10.7 g/bhp-hr 10.7 g/bhp-hr
1.2 glmi 6.0 glbhp-hr 6.0 glbhp-hr 6.0 glbhp-hr
-
6 gltest 2 gltest 2 gltest
-
2 2 2 6 6 6 6
g/test gltest g/test7 g/test gltest g/test g/test
-
6 gltest 2 g/test 2 gltest 2 gltest 2 gltest 2 gltest 2 gltest 2 gltest 3 gltest, 4 gltest 2 gltest 3 gltest 4 gltest
--
18 mpg
-
19 mpg
-
20 mpg 22 mpg
-
24 mpg 26 mpg 27 mpg
--
27.5 mpg
-
.........................................................................................................................
1). LDV: l i g h t - d u t y passenger car; LDT: l i g h t - d u t y truck; HDGV: heavy-duty gasoline t r u c k l b u s ; HDDV: heavy-duty d i e s e l truck/bus, g/mi = grams per mile; g/bhp-hr = grams p e r brake horsepower hour, mpg = m i l e s p e r gallon. 2). 7-mode t e s t procedure f o r t a i l p i p e emissions 3). carbon t r a p procedure f o r evaporative emissions 4). CVS-72 t e s t procedure f o r t a i l p i p e emissions 5). 13-mode t e s t procedure f o r t a i l p i p e emissions 6). CVS-75 t e s t procedure f o r t a i l p i p e emissions 7). SHED procedure f o r evaporative emissions 8). t r a n s i e n t t e s t procedure f o r t a i l p i p e emissions 9). v e h i c l e s l a r g e r than 14,000 pounds gross-vehicle-weight
emissions 400%. The survey i n d i c a t e d t h a t l o c a l l y administered Inspection and Maintenance Programs and Antitampering Programs reduced tampering and m i s f u e l i n g by 35% and 50%, respectively. Highway motor vehicles are b u t one category o f anthropogenic source. combined impact o f motor v e h i c l e emissions regulations, VKT growth, tampering,
and
the
relative
importance
of
transportation
anthropogenic sources are i l l u s t r a t e d i n Figs. 2,3, NOx, respectively,
and
The and other
and 4 f o r VOC, CO, and 5). U.S. emissions
f o r t h e period 1940 t o 1985 ( r e f .
peaked during the e a r l y 1970's.
Since then,
NOx emissions have remained
r e l a t i v e l y constant, and VOC and CO emissions have decreased.
Transportation
as an anthropogenic source o f VOC has v a r i e d from 28.3% i n 1940, t o 45.6% i n 1970, t o 33.8% i n 1985.
S i m i l a r observations suggest t h a t t r a n s p o r t a t i o n
accounted f o r 35.9% o f CO i n 1940, 72.7% i n 1970, and 70.4% i n 1985, and accounted f o r 32.4% o f
NOx i n 1940, 42.0% i n 1970, and 44.2% i n 1985. I n 1985,
the estimated national t r a n s p o r t a t i o n VOC, CO, and NOx mass emission r a t e s were 7.2 m i l l i o n metric tons/yr, 47.5 m i l l i o n m e t r i c tons/yr, and 8.9 m i l l i o n m e t r i c tons/yr,
respectively.
This data was taken from t h e National A i r
Q u a l i t y and Emissions Trends Report,
1985, published February,
1987, which
used t h e EPA computer model MOBILE 3 t o estimate t r a n s p o r t a t i o n c o n t r i b u t i o n s . The current developmental version o f t h i s model ( t o be released as MOBILE 4 )
w i l l increase the estimated c o n t r i b u t i o n o f t r a n s p o r t a t i o n sources t o t h e nationwide VOC inventory. For example, using MOBILE 4, USEPA r e c e n t l y estimated t h a t motor vehicles c o n t r i b u t e d 48% o f t h e 1983 t o t a l U.S. non-
30
25 0 l0
H S o l i d Waste IS M i s c S t a t i o n a r y Combustion
27.2
rn
H I n d u s t r i a l Processes MTransportation
20
.r(
5 15 0)
x
u3 < 0
4
1985
e
10 5 0
33.8 % 1940197019801985 Year Source:EPA-450/4-86-018,
Fig. 2.
Jan. 1987
V o l a t i l e organic compound emissions trend, 1940 t o 1985.
The d i f f e r e n c e s between MOBILE 3 and
methane hydrocarbon i n v e n t o r y ( r e f . 6).
MOBILE 4 VOC e s t i m a t e s w i l l be discussed i n d e t a i l l a t e r . c a n t change i n v o l v e s
t h e use of
area-specific
The most s i g n i f i -
gasoline v o l a t i l i t i e s
and
ambient temperatures which s u b s t a n t i a l l y increases t h e magnitude o f evaporat i v e emission estimates d u r i n g
120
the
h i g h temperature
periods o f
7 H S o l i d Waste
the
summer
6 Misc
S t a t i o n a r y Combustion H I n d u s t r i a l Processes ,mTransportation
1985
6 % 70.4 %
Year Source: EPA-450/4-86-0 18, Jan. 1987 F i g . 3.
Carbon monoxide emissions trend, 1940 t o 1985.
2 m
5
1
1
m
S
o
u
i
d Waste 6 M i s c
S t a t i o n a r y Combustion
20
D I n d u s t r i a l Processes
c 0 I.fl
l
mTransportation
15
L
c,
2 10 (D
1985
< 0
e4 4 . 73
-+5
%
n u
1940 1970 1980 1985
Year Source:EPA-450/4-86-018.
Fig. 4.
N i t r o g e n o x i d e emissions t r e n d , 1940 t o 1985.
Jan. 1987
91 months.
CO and NOx emission estimates were n o t s i g n i f i c a n t l y changed.
Data i s n o t as r e a d i l y a v a i l a b l e f o r unregulated emissions such as N20,
C02, and CF2C12.
However, estimates can be made o f t h e r e l a t i v e strengths o f the anthropogenic sources o f these compounds. The t r a n s p o r t a t i o n sector accounted f o r l e s s than 10% o f 1985 anthropogenic N20 emissions ( r e f .
7), about 24% o f 1985 CFC emissions, i.e. nonaerosol CFC-11, CFC-12, and CFC-113 ( r e f . 8 ) , and about 14% o f 1985 anthropogenic COP emissions ( r e f . 9,lO). Fig. 5 depicts t h e r e l a t i v e strengths o f various sources o f C02 and CFC i n t h e U.S. during 1985. The 1985 t r a n s p o r t a t i o n mass emission r a t e s o f N20 and CFC can be estimated a t about 80 thousand m e t r i c tons/yr and 48 thousand m e t r i c tons/yr, respectively. Anthropogenic C02 emissions a r e associated p r i m a r i l y w i t h the combustion o f f o s s i l f u e l s and bio-mass. Globally, f o s s i l f u e l combustion has been estimated t o be responsible f o r about 50-70% o f C02 emissions ( r e f . 9). DeLuchi r e c e n t l y estimated t h a t i n 1985 highway motor v e h i c l e f u e l combustion was responsible f o r about 14% o f f o s s i l f u e l C02 emissions g l o b a l l y and 24% i n t h e U.S. ( r e f . 10). He estimated t h a t U.S.
Carbon Dioxide
Coal--21.6%
8 n 10A9 Metric Tons
Chlorofluorocarbons Solvents--26.
o b i l e A/C--23.5%
F l e x i b l e Foans--;3 g i d Foae--i8.9%
frigeration--6.9%
2 n 10A5 M e t r i c Tons Fig. 5. 1985 carbon d i o x i d e and nonaerosol chlorofluorocarbon emissions by source category.
92 highway motor vehicles emitted about 1.1
b i l l i o n m e t r i c tons o f C02 during
1985. VOC, CO, NOx emissions
Motor v e h i c l e emissions
are sensitive t o
maintenance, s i z e o f the vehicle, things,
the type o f engine,
type o f f u e l being used, and among o t h e r
t h e conditions under which t h e v e h i c l e i s operated,
a1 t i t u d e ,
age,
and ambient temperature.
e.g.
speed,
Depending on these considerations, the
composition and r a t e o f emissions w i l l vary.
The USEPA maintains a model
(MOBILE 3 c u r r e n t release, MOBILE 4 i n development) u s e f u l f o r p r e d i c t i n g f l e e t average VOC, CO, and NOx emission c h a r a c t e r i s t i c s as a f u n c t i o n o f many of these v a r i a b l e s (ref. 11).
Table 2 provides an example o f the i n f o r m a t i o n
t h a t can be obtained from t h i s model. Seven categories o f motor v e h i c l e s are incorporated. For each calendar year and v e h i c l e category, t h e VKT and emissions tailpipe
are d i s t r i b u t e d over emissions,
g/km
20 model years.
equivalents
of
The model
incorporates
evaporative emissions,
and g/km
equivalents o f r e f u e l i n g emissions ( i n t h e developmental v e r s i o n ) i n the THC emission rates.
The algorithms used t o c a l c u l a t e t h e g/km equivalents o f
evaporative and r e f u e l i n g emissions are based on the r e l a t i o n s h i p s : Evap., g/km = (Di t TPD x Hs) / KPD where
Di
d i u r n a l emissions, g/day;
(1) TPD = average t r i p s per day; Hs = hot
soak emissions, g / t r i p ; and KPD = average kilometers d r i v e n per day, and Refuel., g/km = RF / FE where RF = r e f u e l i n g emissions, g / l i t e r ; and
(2)
FE
= f u e l economy, k m / l i t e r .
Mobile 3 used 3.05 and 50.0 f o r f l e e t average TPD and KPD, r e s p e c t i v e l y .
The
developmental v e r s i o n o f t h i s model, MOBILE 4, v a r i e s TPD and KPD according t o the age o f the vehicle. The t a i l p i p e r a t e s can be reported as THC emissions (as regulated), o r as nonmethane hydrocarbon (NMHC) emissions. As i n d i c a t e d i n Table 2, emission c h a r a c t e r i s t i c s vary among v e h i c l e categories, and f l e e t average values, therefore, depend on t h e composition o f t h e f l e e t , VKT mix.
i.e.
the
The mix given i n Table 2 represents t h e model d e f a u l t values f o r
1985 and are used f o r most scenarios discussed i n t h i s paper.
This mix can be
v a r i e d t o correspond t o l o c a l f l e e t compositions. Fig. 6 i l l u s t r a t e s how MOBILE 4 characterizes f l e e t average THC, CO, and NOx emissions f o r the p e r i o d 1975 through 2000, a t 152 m (500 f t ) a l t i t u d e ,
24°C (75"F), 32 km/h (20 mi/h) average speed, w i t h Inspection and Maintenance
93
Veh. Spd, km/h 32.2 VKT Mix 0.652 Exhaust NMHC, g/km 1.06 Exhaust HC, g/km 1.14 Evap. HC, g/km 0.86 Refuel. HC, g/km 0.21 THC, g/km 2.21 11.95 COY g/km NOx, g/km 1.24
32.2 0.218 2.08 2.19 1.33 0.27 3.79 20.96 2.09
32.2 0.040 3.20 3.44 4.51 0.44 8.37 86.74 3.46
32.2 0.023 0.24 0.25
32.2 0.008 0.38 0.39
32.2 0.054 2.80 2.88
32.2 0.007 2.22 2.37 2.11
0.25 0.80 0.86
0.39 0.96 1.02
2.88 7.76 12.84
4.48 12.40 0.52
-
-
-
c
1.45 1.54 1.05 0.21 2.79 16.33 2.13
I------------------------------------------------------------------------------................................................................................ a l t i t u d e 152 m y ambient temperature 23.9OCY w i t h I n s p e c t i o n and Maintenance/Anti tampering Programs LDGV: l i g h t - d u t y g a s o l i n e v e h i c l e ; LDGT: l i g h t - d u t y g a s o l i n e t r u c k ; HDGV: heavy-duty g a s o l i n e v e h i c l e ; LDDV: 1 i g h t - d u t y d i e s e l v e h i c l e ; LDDT: 1 i g h t - d u t y d i e s e l t r u c k ; HDDV: heavy-duty d i e s e l v e h i c l e ; MC: m o t o r c y c l e
(I&M) and Anti-Tampering Programs (ATP).
From 1975 t o 1985 f l e e t average THC
emis s io n r a t e s were reduced 57%, CO e m i s sion r a t e s 62%, and NOx emissions r a t e s 35%.
The i n d i c a t e d e m i s s i o n r a t e s were det ermined u s i n g l a b o r a t o r y
simulations
of
E
urban d r i v i n g
conditions
as
used
in
Federal
Emissions
40
Y
\
m
E 0
10
0
0
75
80
Note: 24OC, 32 km/h, F ig . 6.
.
85 90 Year
95
00
152 m a l t i t u d e
F l e e t average NMHC, C O Y and NOx e m i ssion r a t e s , 1975 t o 2000.
U
C e r t i f i c a t i o n ( r e f . 12). Fig. 7 i l l u s t r a t e s how MOBILE 4 p r e d i c t s f l e e t average emission r a t e s as
NMHC and CO emission r a t e s continuously decrease as average speed i s increased. The 1985 f l e e t average NMHC and CO r a t e s a t 88 km/h (55 mi/h) were 32% and 12%, r e s p e c t i v e l y , o f t h e values a t 8 km/h (5 mi/h). The NOx f l e e t average emission r a t e passed through a minimum i n t h e 32 - 48 km/h (20 - 30 mi/h) range, and was elevated a t both lower and h i g h e r a f u n c t i o n o f v e h i c l e speed.
Fig. 7. speed.
1985 f l e e t average NMHC, CO, and NOx emission r a t e s as a f u n c t i o n o f
speeds. The NMHC/NOx r a t i o v a r i e d from 2.2 a t 8 km/h (5 mi/h) t o 0.7 a t 88 km/h (55 mi/h). Fig. 8 i l l u s t r a t e s how MOBILE 4 p r o j e c t s t h e s e n s i t i v i t y o f emission r a t e s t o ambient temperature.
The 1985 f l e e t average NMHC and CO emission
r a t e s were lowest a t 24OC (75OF), whereas NOx emission r a t e s continuously decreased as the temperature increased. The NMHC/NOx r a t i o i s minimum a t 24°C (75OF) and maximum a t 38°C (lOO°F), 1.3 and 4.6, respectively. The e l e v a t i o n o f t h e NMHC/NOx r a t i o a t 38OC (100°F) occurs p r i m a r i l y because o f increased evaporative HC emissions p r e d i c t e d by MOBILE 4. MOBILE 4 uses algorithms t o a d j u s t both t a i l p i p e and evaporative emission r a t e s f o r changes i n ambient temperature. Tailpipe emission rates are adjusted over t h e e n t i r e
35
Note: 32 km/h, 152 m altitude F i g . 8. 1985 f l e e t average NMHC, CO, and NOx e m i s s i o n r a t e s as a f u n c t i o n o f ambient temperature. s u m e r - w i n t e r temperature range, and e v a p o r a t i v e e m i s s i o n r a t e s o n l y i n t h e summer range.
A v a i l a b l e d a t a i s inadequate t o d e f i n e e v a p o r a t i v e emissions
s e n s i t i v i t y t o temperalures below 20°C (68°F).
Likewise, a v a i l a b l e data i s
c u r r e n t l y inadequate t o d e f i n e r e f u e l i n g emissions s e n s i t i v i t y t o ambient temperature. F i g . 9 i l l u s t r a t e s how MOBILE 4 p r o j e c t s t h e i n f l u e n c e o f a l t i t u d e on t h e c h a r a c t e r i s t i c s o f motor v e h i c l e emissions. increased
when
decreased.
vehicle
altitude
is
NMHC and CO e m i s s i o n r a t e s a r e
increased,
and
NOx
emission
rates
CO e m i s s i o n r a t e s a r e most s e n s i t i v e w i t h 1985 f l e e t average
v a l w s i n c r e a s i n g 55% as t h e v e h i c l e o p e r a t i n g a l t i t u d e i s i n c r e a s e d f r o m 152 m (500 f t ) t o 1676 rri (5500 f t ) .
The c h e m i s t r y o f t r o p o s p h e r i c NMHC/NOx r a t i o ( r e f . 13).
ozone f o r m a t i o n
depends c r i t i c a l l y on
When t h i s r a t i o i s l o w t h e ozone f o r m i n g p o t e n t i a l
i s dependent on HC r e a c t i o n r a t e s ,
v a r y i n g w i t h t h e s t r u c t u r e o f t h e HC
compound; b u t when t h i s r a t i o i s h i g h t h e r e l a t i v e l y l o w c o n c e n t r a t i o n s o f NOx a r e l i m i t i n g and t h e s t r u c t u r e o f t h e HC becomes l e s s i m p o r t a n t .
With motor
v e h i c l e emissions, t h i s r a t i o v a r i e s w i t h speed and t e m p e r a t u r e as i n d i c a t e d i n Fig.
10.
Over t h e s c e n a r i o s
p r e d i c t e d f o r 8 km/h (5 m i / h ) ,
examined,
the
highest
ratio,
38OC (100°F) o p e r a t i n g c o n d i t i o n s ,
5.31,
is
and t h e
96
Note: 24'C,
32 km/h
Fig. 9. 1985 f l e e t average NMHC, CO, and NOx emission rates as a function a1 titude.
-
37.8"C 23.9"C
.........
10.o"c 1111111111111111
-3.9"c -111
Fig. 10. 1985 f l e e t average NMHC/NOx temperature and average speed.
ratios as a function
of
ambient
lowest ratio, 0 . 6 7 , i s predicted for 88 km/h (55 mi/h), 24°C (75OF) operating conditions. There i s l i t t l e sensitivity of t h i s ratio t o ambient temperature from -3.9"C (25°F) t o 24°C ( 7 5 ° F ) a t 88 km/h (55 mi/h). The high values a t 38OC (100°F) result primarily from large increases in evaporative hydrocarbon emission rates predicted by MOBILE 4.
97 F ig . 11 compares t h e d i s t r i b u t i o n o f HC emission r a t e s between t a i l p i p e , ev a pora t iv e , and r e f u e l i n g sources p r o j e c t e d by MOBILE 4 a t 10°C (5OoF), 24°C (75"F), and 38°C (100°F).
A t 32 km/h (20 mi/h),
34% o f NMHC emissions were
from e v a p o r a t i v e sources a t 10°C (50°F), 39% a t 24°C (75"F),
--10.0"C
8
32 89
23.9"C
8
32 89
m R e f ue 1i n g
37.8'C
8
and 73% a t 38°C
BEvaporative Tailpipe
32 89
Speed, km/h Fig. 11. 1985 NMHC m o t o r eva pora t iv e , and r e f u e l i n g .
vehicle
emissions
distribution:
tailpipe,
(100°F). The s u b s t a n t i a l e v a p o r a t i v e e m i ssions i n c r e a s e p r o j e c t e d a t 38°C (100°F) r e s u l t s f r o m c o n t r o l system design. The e v a p o r a t i v e c a n i s t e r was developed t o p e r m i t compliance w i t h Federal Emissions C e r t i f i c a t i o n which i n c l u d e s measurement o f d i u r n a l e m i s s i o n s o v e r a 16"
-
29°C
(60"
-
84°F)
temperature ramp w i t h 60.0 t o 63.4 kPa (8.7 t o 9.2 p s i ) Reid Vapor Pressure (RVP) f u e l . The d a t a used i n MOBILE 4 were developed w i t h s u r v e i l l a n c e f l e e t v e h i c l e s u s i n g commercially marketed f u e l s w i t h an average RVP o f about 79.3 kPa (11.5 p s i ) . A d d i t i o n a l l y , t h e 38°C (100°F) t e s t s measured d i u r n a l emissions ov er a 29" 42°C (84"-108"F) t e m p erat ure ramp. There i s no dat a t o
-
su pport a djus t me n t o f e v a p o r a t i v e o r r e f u e l i n g emissions f o r v e h i c l e average speed. However, s i n c e t h e e v a p o r a t i v e c o n t r o l c a n i s t e r i s regenerat ed w h i l e t h e engine i s operated, and t y p i c a l l y t h e s e devices do n o t purge w h i l e t h e en g ine i s i d l i n g , e v a p o r a t i v e emissions c o u l d be e l e v a t e d when v e h i c l e s a r e op e ra t e d a t lo w average speed c h a r a c t e r i z e d by g r e a t e r engine i d l e o p e r a t i o n . W i t h MOBILE 3 a t 32 km/h ( 2 0 mi/h), 39% o f HC emissions were p r o j e c t e d f r o m e v a p o r a t i v e sources a t 24°C (75"F), and 34% a t 38°C (100°F). MOBILE 3 and MOBILE 4 NMHC e m i s s i o n r a t e s . Tailpipe,
evaporative,
and
refueling
HC
emissions
F ig. 12 compares are
emitted
at
98 different
times
considering
and
the
locations
during
impact o f motor
normal
vehicle
vehicle
emissions
operation.
When
on atmospheric
ozone,
however, t h e aggregate o f these sources must be considered. o f t h e VOC emissions from t a i l p i p e ,
evaporative,
The composition
and r e f u e l i n g sources a r e
d i f f e r e n t and t h e aggregate composition w i l l , t h e r e f o r e , depend on t h e r e l a -
88.5 km/h, 37.8OC
8.0 k d h , 37.8OC
< E
m
10
.$ 81 m U
12
0
I
6.35
10
d
cr8 m
6
u 6
4
.2 4
.II 2
.II 2
u
w o
C 0 .ri
C
v1
E
n
v1
E
Mob 4 Mob 3
Mob 4 Mob 3 Mode 1
Model
0T a i l p i p e
Evaporative
88.5 k d h , 23.9.C
Refueling 8 . 0 km/h.
23.9"C
< E
12 m 10
oi
cle m
c 0
.rl
ul
4
2 2 E w o
Mob 4 Mob 3 Model
F i g . 12.
Model
Mobile 3 versus M o b i l e 4 NMHC emission r a t e s .
t i v e amounts o f each.
Considering v e h i c l e c a t e g o r i c a l emission s t r e n g t h s and
VKT (see Table 2 ) , l i g h t - d u t y g a s o l i n e v e h i c l e s , r e s p o n s i b l e f o r about 802 o f t o t a l VOC, dominate t h e aggregate composition.
The compositions o f l i g h t - d u t y
g a s o l i n e v e h i c l e t a i l p i p e , e v a p o r a t i v e , and r e f u e l i n g VOC emissions have been examined and Table 3 provides data r e f l e c t i v e o f each source ( r e f . 1 4 ) . values
presented
gasolines.
are
considered
reasonable
for
currently
marketed
The U.S.
The Motor V e h i c l e Manufacturers A s s o c i a t i o n p e r i o d i c a l l y p u b l i s h e s
surveys o f n a t i o n a l g a s o l i n e c h a r a c t e r i s t i c s a s i n d i c a t e d i n Table 4 ( r e f .
15).
Emissions composition would be expected t o v a r y as t h e range o f g a s o l i n e
composition.
99 TABLE 3. T a i l p i p e , e v a p o r a t i v e , and r e f u e l i n g hydrocarbon e m i s s i o n s c o m p o s i t i o n
-------_-----___-_______________________------------------------------_--_--_________-_______________________-----------------------------Hydrocarbon C1a s s i f ica t i on
Ta i1p i p e
Evaporative
Refueling
55 5 4 18 25 2
72 23 15 10
85 32 19
paraffinic, % n-butane, % isopentane, % olefinic, % aromatic, % acetylenic, %
11 4
18
-_______________________________________------------------------...................................................................... Source:
Black (1988)
Both e v a p o r a t i v e volatile paraffinic Considering refueling
the
sources
and r e f u e l i n g emissions
components o f g a s o l i n e ,
fractional
contributions
indicated i n Fig.
a r e dominated b y t h e more
e.g. of
n-butane and isopentane.
tailpipe,
evaporative,
and
11, t h e c o m p o s i t i o n o f t h e aggregate
emissions w i l l v a r y w i t h speed and ambient t e m p e r a t u r e as i n d i c a t e d i n F i g . 13.
T h i s p r e s e n t a t i o n assumes, a t t h e r i s k o f o v e r s i m p l i f i c a t i o n , t h a t t a i l -
p i p e , e v a p o r a t i v e , and r e f u e l i n g e m i s s i o n s c o m p o s i t i o n s a r e n o t h i g h l y s e n s i t i v e t o speed and temperature, are, i.e.
b u t t h a t t h e r e l a t i v e c o n t r i b u t i o n s o f each
t h e compositions o f t a i l p i p e , e v a p o r a t i v e , and r e f u e l i n g e m i s s i o n s
i n d i c a t e d i n Table 3 a r e used i n a l l speed-temperature s c e n a r i o s . g a t e compositions ranged f r o m 70.8% p a r a f f i n i c (21.7% n-butane,
TABLE 4 Gasoline c o m p o s i t i o n
-
The aggre-
14.1%
isopen-
summer, 1986, w i n t e r 1986/1987
............................................................................. ............................................................................. Regular Leaded
Regular Unleaded
Premium Unleaded
SUMMER FUELS, JULY 1987 RVP, kPal R+M 2 Paraffinic, % Olefinic, % Aromatic, %
Octane,
71.0 (60.0
-
80.7) 89.8) 62.0 (55.6 - 68.3) 10.8 (6.6 - 15.0) 27.3 (23.9 - 31.3) 88.6 (86.2
71.7 86.9 59.8 10.6 29.5
(57.9 - 80.0) (85.1 88.4) 54.0 - 65.5) 7.3 - 16.1) (25.7 33.3)
-
t
-
73.8 91.8 58.3 7.1 34.6
(57.2 - 80.0) (89.6 - 92.5) 50.4 - 67.7) 3.7 - 13.5) (26.4 - 40.6)
I
W I m U E L S , JANUARY 1987 RVP, kPa
R+M
Octane, Paraffinic, % Olefinic, % Aromatic, %
93.1 (70.3 88.6 (85.1
-
-
110.3) 91.5)
93.1 87.3 62.1 5.9 32.0
-
(72.4 114.5) (84.0 - 90.8) (43.3 78.0) (2.2 - 16.6) (17.1 47.5)
92.4 91.8 59.9 5.1 35.0
(75.8 - 106.9) (85.9 - 94.7) (46.3 - 80.8) (1.0 - 14.0) (15.0 - 45.6)
............................................................................. NA NA NA
RVP - R e i d Vapor Pressure: Source: MVMA (1987)
average ( r a n g e )
100 tane), 10.8% o l e f i n i c , 18.2% aromatic, and 0.2% a c e t y l e n i c hydrocarbon a t 38°C (lOO°F),
88
km/h
(55
mi/h)
to
59.5%
paraffinic
(9.6% n-butane,
6.8%
isopentane), 16.2% o l e f i n i c , 22.9% aromatic, and 1.4% a c e t y l e n i c hydrocarbon a t 24°C (75"F), 8 km/h ( 5 mi/h).
The c o n t r i b u t i o n o f n-butane and isopentane
ranged from 35.8% a t 38°C (lOO°F), 88 km/h (55 mi/h) t o 16.4% a t 24°C (75"F), 8 km/h (5 mi/h). A t lower temperatures, the aggregate would be more dominated by t a i 1p i p e emi ss ions composition.
8 km/h,
88 km/h,
37.8.C
37.8OC
/ ther--35
other--39.8 isopentane--g.8 n-butane--14.5
Olef i n i c
isopentane--l4.1 -butane--21.7
18. 0.
@ Aromatic @ Acetylenic
8 km/h, 23.9OC
88.5 km/h, 23.9OC ther--38.2 18.
isopentane--6.8
Fig. 13. Aggregate hydrocarbon emissions ambient temperature and average speed.
Methane,
n o t being a component
eopentsne--l2.2
composition as
o f gasoline,
a function o f
i s emitted e x c l u s i v e l y
from the t a i l p i p e during engine operation. Over the temperature and speed array o f t h i s presentation, t h e CH4 f r a c t i o n o f t a i l p i p e emissions i s n o t h i g h l y v a r i a b l e f o r any selected calendar year. For example, d u r i n g 1985 c o n s t i t u t e d 5.69 f 0.23% o f t a i l p i p e THC emissions over the e n t i r e temperature-speed array. Because of t h e v a r i e d c o n t r i b u t i o n o f t a i l p i p e
CH4
emissions t o the t o t a l aggregate,
t h e CH4 f r a c t i o n o f the aggregate v a r i e d
from 0.58% a t 88 km/h (55 mi/h), 38°C (100°F) t o 4.92% a t 8 km/h (5 mi/h), -3.9"C (25°F). CH4 i s n o t reduced as e f f e c t i v e l y by c a t a l y s t c o n t r o l systems as other HC's, and therefore, t y p i c a l l y c o n s t i t u t e s a l a r g e r Thus, t h e CH4 f r a c t i o n o f f r a c t i o n o f exhaust from w e l l c o n t r o l l e d cars. t a i l p i p e and aggregate emissions increases w i t h calendar year. During
101 1975 CH4 c o n s t i t u t e d 5.00% o f t a i l p i p e and 2.95% o f aggregate HC emissions a t 32 km/h (20 mi/h), 24°C (75OF); and during the year 2000, i t i s p r o j e c t e d t o c o n s t i t u t e 8.99% o f t a i l p i p e and 4.57% o f aggregate HC emission a t 32 km/h (20 mi/h), 24°C (75°F).
The CH4 f r a c t i o n o f t a i l p i p e HC emissions from w e l l
c o n t r o l l e d cars has a l s o been reported t o be s e n s i t i v e t o speed and ambient temperature ( r e f s . 16, 17).
The CH4 f r a c t i o n decreases w i t h decreased average
speed, and w i t h decreased ambient temperature. With w e l l c o n t r o l l e d cars, operating conditions causing increased t a i l p i p e THC emissions w i l l r e s u l t i n decreased CH4 f r a c t i o n s . With
transportation
being
the
primary
source
of
anthropogenic
CO
emission (70% i n 19851, t h e r e has been i n t e r e s t i n using t h i s compound as a t r a c e r f o r motor v e h i c l e emissions.
Lead has been used f o r t h i s purpose
h i s t o r i c a l l y , b u t i s r a p i d l y being phased o u t o f gasoline, and fewer and fewer roadway vehicles are compatible w i t h leaded f u e l s .
Fig.
14 provides an
i n d i c a t i o n o f the v a r i a t i o n o f NMHC and NOx r a t i o s t o CO as a f u n c t i o n o f v e h i c l e speed and ambient temperature.
Over the scenarios examined NMHC/CO
r a t i o s v a r i e d from 0.098 a t 8 km/h (5 mi/h) and
-3.9"C
(25OF) t o 0.594
a t 88
-
37.8.C
......
23.9-C I
1O.O0C 11111111111
-3.9.c 111
"8:O
16.1
2i.l
3i .2
k.3 M . 4
Speed, km/h
ed.6
&.d
-
37.8.C
......
O 0.5 e6*
0 0
0.4
23.9.C
I
-
10.O'C 11111,11111
.
-3.9.c
0.30
z
111
,
0.2
-
Speed, km/h Fig. 14. 1985 f l e e t average NMHC/CO and NOx/CO r a t i o s as a f u n c t i o n o f ambient temperature and average speed.
102 km/h (55 m i / h ) and 38°C (100°F);
and NOx/CO r a t i o s v a r i e d f r o m 0.023 a t 8 km/h
( 5 m i / h ) and 38°C (100°F) t o 0.438 a t 88 km/h ( 5 5 m i / h ) and 24OC (75°F). C h l o r o f l u o r o c a r b o n emissions The f u l l y halogenated c h l o r o f l u o r o c a r b o n s (CFC) most w i d e l y used i n t h e U.S.
a r e CFC-11
(CC13F),
CFC-12
(CC12F2),
and CFC-113
(C2C13F3).
Motor
v e h i c l e s were t h e s i n g l e l a r g e s t nonaerosol s o u r c e o f CFC i n 1976, and a r e p r o j e c t e d t o be second t o s o l v e n t e m i s s i o n s i n 1990 ( r e f . 8 ) .
D u r i n g 1976
29% o f a combined 119 thousand m e t r i c t o n s e m i t t e d i n t h e U.S. m o t o r v e h i c l e a i r c o n d i t i o n i n g systems;
an a d d i t i o n a l
was f r o m
3.8% was f r o m t h e
p r o d u c t i o n o f f l e x i b l e foam f o r m o t o r v e h i c l e a p p l i c a t i o n s .
Emissions a r e
p r o j e c t e d t o i n c r e a s e t o 250 thousand m e t r i c t o n s d u r i n g 1990 w i t h 22% o f this
total
from
motor
vehicle
air
conditioning
e x c l u s i v e l y used i n m o t o r v e h i c l e a i r c o n d i t i o n i n g ;
systems.
CFC-12
is
CFC-11 i s used i n t h e
p r o d u c t i o n o f f l e x i b l e foam.
T a b l e 5 p r o v i d e s a summary o f m o t o r v e h i c l e
CFC-12 e m i s s i o n sources ( r e f .
18).
most s i g n i f i c a n t sources i n 1976.
R e p a i r s e r v i c i n g and l e a k a g e were t h e V e h i c l e d i s p o s a l i s p r o j e c t e d t o become
an a d d i t i o n a l s i g n i f i c a n t s o u r c e i n 1990 p r o j e c t i o n s .
NO, L
of
emissions It has been e s t i m a t e d t h a t t r a n s p o r t a t i o n c o n t r i b u t e d l e s s t h a n 10% 1985 g l o b a l
a n t h r o p o g e n i c N20 e m i s s i o n s f r o m f o s s i l
fuel
combustion
(ref. 7). S t u d i e s c h a r a c t e r i z i n g m o t o r v e h i c l e N20 e m i s s i o n s a r e sparse when compared t o t h o s e examining r e g u l a t e d THC, C O Y NOx emissions. Table 6 sumnarizes a v a i l a b l e e m i s s i o n s d a t a ( r e f s .
19-25).
Emissions were examined
f r o m v a r i e d v e h i c l e t y p e s under v a r i e d d r i v i n g c o n d i t i o n s . A l t h o u g h t h e d a t a i s l i m i t e d , i t can be concluded t h a t N20 e m i s s i o n s a r e e l e v a t e d a b o u t a n o r d e r of
magnitude
from
gasoline motor
vehicles
using catalysts
compared
to
103
noncatalyst configurations.
Other observations i n t h e a v a i l a b l e data i n c l u d e
an inc re as ed N20 e m i s s i o n r a t e as t h e v e h i c l e average speed i s decreased, i f EGR (exhaust gas r e c i r c u l a t i o n f o r NOx c o n t r o l ) i s d i s a b l e d , and as v e h i c l e i n e r t i a w e i g h t i s increased, passenger c a r emission r a t e s .
i.e. t r u c k emission r a t e s a r e g r e a t e r t han Using t h e v e h i c l e c a t e g o r i c a l average emission
f a c t o r s o f T abl e 6 and t h e 1985 f l e e t VKT d i s t r i b u t i o n , a f l e e t average N20 emis s io n f a c t o r o f about 30 mg/km can be estimated.
T h i s assumes t h a t l i g h t -
d u t y g a s o l i n e VKT i s d i s t r i b u t e d 80-20 c a t a l y s t - n o n c a t a l y s t .
Coupled w i t h
t o t a l f l e e t k i l o m e t e r s t r a v e l e d d u r i n g 1985, highway mot or v e h i c l e s e m i t t e d about 80 thousand m e t r i c t o n s o f N20.
L i ht-duty gasoline ?no c a t a l y s t ) L i ht-duty gasoline ?catalyst) light-duty diesel heavy-duty g a s o l i n e heavy-duty d i e s e l
3.7
1.9
37.9
1.9
NA 45.4 29.2
6.8 29.8 19.3
-
9.9
19,20
145.4
19,20,21,22,23
29.8 60.3 46.6
19 24 24, 25
The dat a base was examined f o r r e l a t i o n s h i p s between N20 emissions and
NOx
(n.38) diesel
emissions.
The
observed
N20/NOx
r a t i o s were
f o r c a t a l y s t equipped g a s o l i n e v e h i c l e s , trucks,
catalysts).
and
0.0055
f
0.0028
(n=2)
0.0018 for
*
0.0437
2
0.0002
(n=5) f o r
gasoline
0.0414
trucks
(no
The " c a t a l y s t equipped" d a t a base i n c l u d e d more t e s t v e h i c l e s
and a l a r g e r a r r a y o f d r i v i n g c o n d i t i o n s , i.e. speed, ambient temperature, m a l f u n c t i o n , and m i l e a g e accumulation, t han t h e t r u c k dat a base. The range o f observed N20/NOx r a t i o s was t h e r e f o r e g r e a t e r t h a n observed w i t h the trucks. There i s no c e r t a i n t y t h a t t h e t r u c k s w i l l e x h i b i t t h e same s e n s i t i v i t y t o these variables. As t h e w o r l d ' s v e h i c l e f l e e t s h i f t s t o c a t a l y s t t e c hnol o g y f o r abatement o f u r b a n ozone, CO and NOx, t h e c o n t r i b u t i o n o f t r a n s p o r t a t i o n sources t o g l o b a l N20 burden w i l l grow. Carbon d i o x i d e emissions As p r e v i o u s l y mentioned,
highway m o t o r v e h i c l e s
were e s t i m a t e d
t o be
r e s p o n s i b l e f o r about 24% o f C02 emissions f r o m 1985 f o s s i l f u e l combustion i n t h e U.S.
( r e f . 10).
The e m i s s i o n r a t e o f C02 f r o m motor v e h i c l e s i s a
104 function
of
fuel
economy and f u e l
consumed per kilometer driven, Significant
fuel
characteristics,
i.e.
and grams o f carbon
l i t e r s o f fuel
per l i t e r o f
fuel.
economy improvements have been r e a l i z e d i n the U.S.
in
recent years as a consequence o f the combined e f f e c t s o f market demand and federal regulations.
Fig.
15 i s i l l u s t r a t i v e o f f u e l economy improvements
i n both l i g h t - d u t y and heavy-duty v e h i c l e categories since 1975 w i t h p r o j e c t i o n s t o t h e year 2000 ( r e f . 3).
\
E
Y
10
>;8 E 0
= 6 0
"
75 80 85 90 95 00 Year
Light-Duty Vehicles Heavy-Duty V e h i c l e s All V e h i c l e s Source: Mobile 3 F u e l Consumption Model EPA-AA-TEP-EF-85-2, Feb. 1985 Fig. 15. Motor v e h i c l e f u e l economy, 1975 t o 2000. The two m a j o r t r a n s p o r t a t i o n typically
have 619 t o
respectively.
654 and
fuel
categories,
gasoline
and d i e s e l ,
706 t o 741 grams of carbon per l i t e r , respec-
Most o f t h i s carbon i s converted t o C02 w i t h l e s s e r amounts
t o CO and HC during combustion i n motor v e h i c l e engines.
C02 emission r a t e s
can be c a l c u l a t e d from f u e l economy data according t o the carbon balance relationship:
105
C02, glkm = ((KlxFD, where:
gla)
1 FE, kmla
- K1xHC,
g/km
- K2xC0,
K1 = carbon weight f r a c t i o n o f f u e l = .866;
f r a c t i o n o f CO = .429;
glkm) 1 K3
(3)
K2 = carbon weight
K3 = carbon weight f r a c t i o n o f C02 = .273;
FD = f u e l
density; and FE = f u e l economy. Combining MOBILE 4 THC and CO emissions data w i t h f u e l economy data,
C02
emission r a t e s can be c a l c u l a t e d as presented i n Table 7.
The trend, w i t h
improved f u e l economy, has been reduced C02 emission rates.
During t h e 1975
t o 1985 decade, the f l e e t average C02 emissions r a t e was reduced about 22%. During t h a t same period o f time VKT increased 30% (as i n d i c a t e d i n Fig. l), thus increasing the atmospheric C02 burden from motor v e h i c l e s on roadways i n the U.S.
Combining the estimated f l e e t average emission r a t e with estimated
nationwide miles traveled, metric tons o f COP i n 1985.
highway motor vehicles emitted about 0.9
billion
This value i s somewhat lower than t h e 1.1 b i l l i o n
metric tons estimated by DeLuchi, e t a l . ( r e f . 10).
1975 1985 1995
352.4 270.0 208.8
395.8 330.8 284.8
614.4 532.5 555.3
283.3 236.1 199.5
204.2 271.0 252.0
1293.7 1076.1 908.1
426.2 334.1 268.2
SUMMARY AND CONCLUSIONS
Stratospheric and tropospheric ozone concentrations are c o n t r o l l e d by complex chemical and physical processes which are influenced by both anthropogenic and biogenic emissions a t the earths surface. One o f t h e most r a p i d l y growing human a c t i v i t i e s important t o atmospheric ozone i s the use o f highway motor vehicles. Miles d r i v e n by American m o t o r i s t have increased 58% since 1970. There are many compounds emitted from highway motor vehicles t h a t p a r t i c i p a t e i n atmospheric processes important t o ozone formation and/or destruction i n c l u d i n g VOC, CO, NOx, C02, N20, and CFC-12. It has been estimated t h a t during 1985 7.2 m i l l i o n m e t r i c tons o f VOC were emitted from U.S. t r a n s p o r t a t i o n sources (about 34% o f the anthropogenic t o t a l ) , 47.5 m i l l i o n m e t r i c tons o f CO (about 70% o f the anthropogenic t o t a l ) ,
and 8.9
106 m i l l i o n m e t r i c t o n s o f NOx (about 45% o f t h e anthropogenic t o t a l ) .
Recent
improvements t o MOBILE 3, t h e model used t o c a l c u l a t e f l e e t average emission
will
factors,
increase the estimated transportation
contribution
to
VOC
emissions t o n e a r l y 50% o f t h e anthropogenic t o t a l .
Sumner month e v a p o r a t i v e
hydrocarbon emission
increased.
estimates
are
significantly
U.S.
motor
v e h i c l e s were a l s o estimated t o have been r e s p o n s i b l e f o r about 48 thousand m e t r i c t o n s of CFC d u r i n g 1985 (25% of U.S. anthropogenic t o t a l ) , and about 1 b i l l i o n m e t r i c tons o f COP (14% o f t h e anthropogenic t o t a l ) . Motor v e h i c l e s c o n t r i b u t e l e s s than 10% o f anthropogenic N20 emissions, b u t t h i s c o n t r i b u t i o n i s expected t o grow as t h e f r a c t i o n o f c a t a l y s t equipped v e h i c l e s increases. Through t h e c o o p e r a t i v e e f f o r t s o f government and i n d u s t r y , s u b s t a n t i a l reduction decade.
o f motor v e h i c l e
emissions
has been achieved d u r i n g
the past
From 1975 t o 1985, motor v e h i c l e VOC emission r a t e s were reduced
about 57%, CO r a t e s about 62%, NOx r a t e s about 35%, and C02 r a t e s about 22%. Much o f t h i s r e d u c t i o n was o f f s e t ,
however,
by a c o n c u r r e n t 30% growth o f
VKT. Motor v e h i c l e emission r a t e s a r e s e n s i t i v e t o d r i v i n g c o n d i t i o n s such as speed,
temperature, and a l t i t u d e .
G e n e r a l l y , VOC and CO emission r a t e s
a r e increased by reduced average speed. NOx emission r a t e s , n o t as s e n s i t i v e t o speed,
a r e g e n e r a l l y minimumized a t about 32 t o 48 km/h and i n c r e a s e
s l i g h t l y a t lower and h i g h e r average speeds.
VOC and CO emission r a t e s a r e
minimumized a t about 24°C (75°F) and i n c r e a s e a t l o w e r and h i g h e r temperatures.
NOx
emission
rates
increase
as
ambient
temperature
is
reduced.
T y p i c a l l y , VOC and CO emissions r a t e s i n c r e a s e as a l t i t u d e i s increased, and NOx emission r a t e s decrease. t h e emissions,
These v a r i a t i o n s i n f l u e n c e t h e NMHC/NOx r a t i o o f
an i m p o r t a n t c o n s i d e r a t i o n t o t r o p o s p h e r i c ozone chemistry.
T h i s r a t i o v a r i e s from about 0.7
t o 5.3 over t h e examined range o f d r i v i n g
conditions.
VOC emissions from motor v e h i c l e s o r i g i n a t e from t a i l p i p e , and r e f u e l i n g sources.
evaporative,
The composition o f each i s d i f f e r e n t , w i t h t h e more
v o l a t i l e C4 and C5 p a r a f f i n s dominating e v a p o r a t i v e emissions and, even more
s o , refueli,ng emissions. The aggregate emissions composition w i l l depend on t h e r e l a t i v e c o n t r i b u t i o n o f each, a f u n c t i o n o f v e h i c l e speed and ambient temperature.
A t 24°C (75"F), 8 km/h (5 mi/h),
1985 motor v e h i c l e VOC emis-
s i o n s were about 77% t a i l p i p e , 19% evaporative, and 4% r e f u e l i n g ; a t 38°C (lOO°F), 88 km/h (55 mi/h) t h e emissions were about 10% t a i l p i p e , 86% evapora t i v e , and 4% r e f u e l i n g .
The aggregate composition was 60% p a r a f f i n i c , 16%
o l e f i n i c , 23% aromatic, and 2% a c e t y l e n i c a t 24°C ( 7 5 " F ) , 8 km/h ( 5 m i / h ) ; and 71% p a r a f f i n i c , 11%o l e f i n i c , 18% aromatic, and 1%a c e t y l e n i c a t 38°C (lOO"F), 88 km/h (55 mi/h).
107 CFC-12,
t h e primary chlorofluorocarbon emitted from. motor vehicles,
r e s u l t s p r i m a r i l y f r o m a i r c o n d i t i o n i n g r e p a i r s e r v i c e and leakage. d i s p o s a l i s p r o j e c t e d t o become a s i g n i f i c a n t source b y t h e 1990's. U.S.
Vehicle motor
v e h i c l e CFC emissions a r e p r o j e c t e d t o be about 55 thousand m e t r i c t o n s p e r y e a r by
1990.
N20 emissions f r o m m o t o r v e h i c l e s have n o t been w i d e l y
s t u d i e d , b u t a v a i l a b l e d a t a suggests t h a t e m i s s i o n r a t e s v a r y o v e r a b o u t an order-of-magnitude
range
f r o m about
3.7
mg/km
from noncatalyst
gasoline
passenger c a r s t o about 37 mg/km f r o m c a t a l y s t s equipped g a s o l i n e passenger cars.
L i m i t e d d a t a suggests t h a t heavy-duty t r u c k e m i s s i o n r a t e s a r e g r e a t e r
t h a n passenger c a r e m i s s i o n r a t e s configurations).
( w i t h s i m i l a r engine emission c o n t r o l
F l e e t average C02 e m i s s i o n r a t e s were reduced f r o m about 426
g/km i n 1975 t o about 334 g/km i n 1985. F u r t h e r emission
rate
reduction
v e h i c l e tampering and m i s f u e l i n g , the
Congress
U.S.
evaporative,
is
i s possible
through c u r t a i l m e n t o f
and improved maintenance.
considering
expanded
Additionally,
regulation
and r e f u e l i n g emissions, and f u e l composition.
of
tailpipe,
U l t i m a t e l y , as
t h e p o t e n t i a l o f emission r a t e r e d u c t i o n becomes r e a l i z e d , o n l y c u r t a i l m e n t o f VKT growth w i l l be a v a i l a b l e t o l i m i t motor v e h i c l e emissions. ACKNOWLEDGEMENTS A l t h o u g h t h i s r e p o r t has been s u p p o r t e d b y t h e U n i t e d S t a t e s E n v i r o n mental P r o t e c t i o n Agency, therefore,
i t has n o t been s u b j e c t e d t o Agency r e v i e w and,
does n o t n e c e s s a r i l y r e f l e c t
t h e views o f t h e Agency and no
o f f i c i a l endorsement s h o u l d be i n f e r r e d .
The a u t h o r wishes t o acknowledge
and express g r a t i t u d e t o Susan Bass f o r a s s i s t a n c e i n m a n u s c r i p t p r e p a r a tion.
REFERENCES 1.
L.M. Thomas, Next Steps i n t h e B a t t l e A g a i n s t Smog, EPA J o u r n a l , 13(8) (1987) 2-4. - .R.T. Watson, M.A. G e l l e r , R.S. S t o l a r s k i , and R.H. Hamoson. Present S t a t e o f Knowledge o f t h e Upper Atmosphere: Processes t h a t C o n t r o l Ozone and O t h e r C1 i m a t i c a l l-y I m.p o r t a n t Trace Gases, NASA Assessment Report, January , 1986. M.A. Wolcott, D.F. Kahlbaum, MOBILE 3 Fuel Consumption Model, EPA-AA-TEB-EF-85-2, U.S. Environmental P r o t e c t i o n Agency, O f f i c e of M o b i l e Source, Ann Arbor, M I , February, 1985. M. Casey, 1986 M o t o r V e h i c l e Tampering Survey R e s u l t s Issued, U.S. EPA Press Release, October 6, 1987. N a t i o n a l A i r P o l l u t i o n Emission Estimates, 1940-1985, EPA-450/4-86-109, U.S. Environmental P r o t e c t i o n Agency, O f f i c e o f A i r Q u a l i t y P l a n n i n g and Standards, Research T r i a n g l e Park, N.C., January, 1987. \ - - - .
2.
3.
4. 5.
I
ino
-
V o l a t i l i t y Regulation f o r 1989 and L a t e r Notice o f Proposed Rulemaking Comnercial Gasoline. Review D r a f t , U.S. Environmental P r o t e c t i o n Agency, O f f i c e o f Mobile Source, Ann Arbor, M I , March, 1987. EPA Workshop on N 0 Emissions from Combustion, EPA-600/8-86-035, U.S. 7. Environmental Pro&ction Agency, A i r and Energy Engineering Research Laboratory, Research T r i a n g l e Park, N.C. September, 1986. Economic I m p l i c a t i o n s o f Regulating Chlorofluorocarbon Emissions from 8. Nonaerosol Applications , EPA-560/12-80-001 , U.S. Environmental P r o t e c t i o n Agency, O f f i c e o f P e s t i c i d e s and Toxic Substances, Washington, D.C. , October, 1980. H.A. Mooney, P.M. Vitousek, and P.A. Matson, Exchange o f M a t e r i a l s 9. Between T e r r e s t r i a l Ecosystems and t h e Atmosphere, Science, November 13, 1987, pp. 926-932. 10. M.A. DeLuchi, R.A. Johnston, and D. Sperling, Transportation Fuels and the Greenhouse E f f e c t , UER-182, Universitywide Energy Research Group, U n i v e r s i t y o f C a l i f o r n i a , Davis, CA, December, 1987. (Mobile Source Emissions Model), Guide to MOBILE 3 11. User's EPA-460/3-84-002 , U.S. Environmental P r o t e c t i o n Agency, Motor Vehicle Emissions Laboratory, Ann Arbor, M I , June, 1984. 12. U.S. Code o f Federal Regulations, T i t l e 40, Part 86 Control o f A i r P o l l u t i o n from New Motor Vehicles and New Motor Vehicle Engines' C e r t i f i c a t i o n and Test Procedures, July, 1983. 13. Dodge, M.C. , Combined E f f e c t s o f Organic R e a c t i v i t y and NMHC/NOx R a t i o on Photochemical Oxidant Formation A Modelling Study, Atmos. Env., 18 (1984) 1657-1665. Hydrocarbon Emissions from Late Model Gasoline Motor 14. F. M. Black, Vehicles, JAPCA, i n review, U.S. Environmental P r o t e c t i o n Agency, Research T r i a n g l e Park, N.C. January, 1988. 1986/1987, Motor 15. MVMA National Gasoline Survey: Sumner -1986, Winter Vehicle Manufacturers Association, D e t r o i t , M I , 1987. 16. J.E. Sigsby, S. Tejada, and W. Ray, V o l a t i l e Organic Compound Emissions from 46 In-use Passenger Cars, Environ. Sci. Technol. 21(5) (1987) 466-475. 17. F. Stump, S. Tejada, W. Ray, D. Dropkin, F, Black, W. Crews, R. Snow, P. Suidak, C.O. Davis, L. Baker, and N. Perry, The I n f l u e n c e o f Ambient Temperature on T a i l p i p e Emissions from Late Model Light-Duty Gasoline Motor Vehicles, Atmos. Env. , i n review, U.S. Environmental P r o t e c t i o n Agency, Research T r i a n g l e Park, N.C. January, 1988. 18. R. E. Burt, Domestic Use and Emissions o f Chlorofluorocarbons i n Mobile A i r Conditioning , I n t e r n a t i o n a l Research and Technology Corporation, F i n a l Report #IRT-20000/1, A p r i l , 1979. 19. BMW AG, Annual Report t o USEPA on Emissions Characterization i n Compliance w i t h Section 202(1)(4) o f t h e Clean A i r Act, U.S. Environmental P r o t e c t i o n Agency, O f f i c e o f Mobile Sources, Ann Arbor, M I , December , 1986. 20. C.M. Urban, and R.J. Garbe, Regulated and Unregulated Exhaust Emissions from Malfunctioning Automobiles, SAE 790696, Society o f Automotive Engineers, Warrendale, PA, June, 1979. 21. J.N. Braddock, Impact o f Low Ambient Temperature on 3-way C a t a l y s t Car Emissions, SAE 810280, Society o f Automotive Engineers, Warrendale, PA, February , 1981. 22. L.R. Smith, and F.M. Black, Characterization o f Exhaust Emissions From Passenger Cars Equipped w i t h 3-way C a t a l y s t Control Systems, SAE 800822, Society o f Automotive Engineers, Warrendale, PA, June, 1980. 23. L.R. Smith and P.M. Carey, Characterization o f Exhaust Emissions from High Mileage Catalyst-equipped Automobiles, SAE 820783, Society o f Automotive Engineers, Warrendale, PA, June, 1982. 24. H.E. Dietzmann, M.A. Parness, and R.L. Bradow, Emissions from Gasoline and Diesel D e l i v e r y Trucks by Chassis Transient Cycles, American Society of Mechanical Engineers, New York, NY, October, 1981. 6.
-
-
-
25. H.E. Dietzmann, M.A. Parness, and R.L. Bradow, Emissions from Trucks by Chassis Version of 1983 Transient Procedure, SAE 801371, Society o f Automotive Engineers, Warrendale, PA, October, 1980.
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T.Schneideret al. (Editors),Atmospheric Ozone Research and its PolicyImplications 0 1989 Elsevier Science PublishersB.V.,Amsterdam - Printed in The Netherlands
111
EMISSION INVENTORIES FOR EUROPE
C. Veldt M.T.-TNO, P.O. Box 3 4 2 , 7300 AH
Apeldoorn (The Netherlands)
ABSTRACT An overview is given of the efforts made in Europe on air pollutant inventories of NOx and VOC, accomplished ones as well as those in progress. Differences and similarities both in data bases and results are indicated. Available data are confronted with what is needed by atmospheric scientists for modeling purposes. An attempt is made to summarize available knowledge about emission estimation techniques. From these two follow incompletions in emission data and gaps in the knowledge to estimate them. Priorities are suggested for the work that should be done for minimizing the difference between data supply and demand. Continuation of international cooperation is advocated.
1. INTRODUCTION
It is well known that nitrogen oxides and organic substances largely control photochemistry during episodes, the mayor substance of concern being ozone. In addition to these, carbon monoxide and methane have been recognised to be also of influence on long-term atmospheric phenomena such as the fate of ozone in the free troposhere. Further, several chemical species that for long were considererd as unimportant in atmospheric chemistry appeared to really cause adverse effects. Examples of these are chloro-fluoro-hydrocarbons and nitrous oxide. Of all these substances the emissions of nitrogen oxides have been estimated for some time, together with sulfur oxides. The latter, hardly important as precursors of ozone, have an even longer history of emission inventorying. Of the other species, having attracted attention only later, less emission data are available. The only exceptions to this are carbon monoxide that usually is inventoried simultaneously with NO,
and SO, and volatile organic substances
that only recently took the same place. The collection of emission data often started with the estimation of national annual totals for some base year and for some main source categories. Next, episodic model studies initiated the acccumulation of experience in making detailed inventories because they need spatially and temporally resolved input data, but this experience in general is restricted to the "classic" pollutants NO, and SOx and, to some lesser extent,
112 to organic compounds as a sum. The addition to data bases of technical and economical data made it possible to update inventories and study abatement scenarios. Since the study of long-term effects does not need such details, emission estimations of CO, CH4 etc. until now have only been made on a global scale. It has been learnt that natural sources of these species are larger contributors to initial concentrations in the air than antropogenic activities (with the exception of CLF-hydrocarbons). And since the understanding of the contribution of natural processes to atmospheric phenomena is very incomplete, the estimation of emissions of these substances still is developing. Therefore, for a discussion about what has been achieved and what is being done in Europe in the field of emission inventorying a restriction is made here to oxides of nitrogen and organic substances. 2. DEFINITIONS
Although consensus exists nowadays about what is meant by NO,,
there is not
yet a similar acceptance about organic compounds. In this paragraph therefore an attempt is made to define a term that is unambiguous with respect to atmospheric scientists' needs. The still used word "hydrocarbons" (HC), that at least linguistically excludes substances like alcohols and ketones, should not be used any more. Instead, all organic compounds should be involved. Users of emission data bases should decide what substances are of interest. Data base developers should present anything that their knowledge allows. In this way total organic emissions-notably from combustion sources consist
of
solid
and
liquid
particulate
as
well
as
-
will
gaseous material.
Particulate fractions could raise a problem in quantifying reactivity. For emission estimations in Europe this problem can be ignored because organic emissions form industrialized countries for a very large part consist of volatile substances. (However, for regions where the combustion of biomass considerably contributes to total organic emissions, attention should be given to this in clearly defining the emission factors involved). Thus, for emission inventorying a useful term for organic matter is "volatile organic compound(s)". The definition of VOC might be: any organic substance that, released into the atmosphere, is present there in the gaseous state. This definition is pragmatic in that volatility is not defined. Meanwhile the term gradually has found its way in the field of atmospheric science. VOC emissions should be reported without exclusions. Distinctions between substances on account of their reactivity should be bases only upon composition profiles. That is, wherever NMVOC is reported, the methane fractions should be given also.
113 3 . OVERVIEW OF EMISSION IVENTORIES
In Europe the first international programme on emission estimation was started by the OECD in the early seventies. A result of this activity was the Geneva ECE Convention on Air Pollution. Since 1983 the OECD has its Major Air Pollutants project (MAP), whereas about the same time the CEC started an inventory of emissions form large combustion sources in member countries and the Federal Republic of Germany and the Netherlands commenced a programme for Photochemical Oxidants and Acid Deposition Model Application (PHOXA). The acidification study of IIASA as well as the newest development, the CEC's programme on information about the state of the environment (CORINE) part of which is the CORINAIR project on information about air pollutants need also be mentioned. Mention could further be made of many national projects for the inventorying of national emissions or for air pollution studies for which transboundary inventories have been or are developed. It will be clear from this very brief survey that a considerable acceleration of emission inventorying activities has taken place in the last few years: obviously, as a result of an acceleration in atmospheric science. Maybe it is characteristic for a development like this that several inventories, serving different objectives, were developed more or less simultaneously although they have much in common. Meanwhile, fortunately, also a - still increasing cooperation has started and maybe it is no demonstration of over-optimism when a joint European air pollutants data base can be foreseen in the near future. Results of these activities are summarized in tables 1 and 2 . The amount of footnotes accompanying these tables might serve as an illustration of an European data base not yet about to be established. Similarities more often can be read from these tables than marked differences. Many of the latter can be explained, but within the scope of this survey this would go too far. Some remarks are appropriate, however: data bases a) A good agreement is to be expected between the OECD - and ECE
-
because both are filled with officially approved data. b) National methodologies for emission estimation, underlying OECD
-
and ECE
data, expectedly have less in common than they could have. c) The data used in the PHOXA-project and in IIASA's RAINS model are the result of work of research teams who basically operated independently of national experts, using chosen emission factors and published statistics. Consequently, emission data show inherent uniformities that can be considered to be too large. For a survey of similarities and differences between these projects reference is made to table 3 .
114 As a final comment it may be said, that in view of the growing awareness of the importance of reliable emission data and the increasing international cooperation in emission inventorying, emission data from European countries will be produced in the near future that are based on a common methodology but also
reflect
deviations
because
of
characteristic
differences
between
countries. In other words, in such a situation there always will be sound, technical reasons for the use of different emission factors. 4 . DEMAND AND SUPPLY
Cleaning the atmosphere obviously is the ultimate objective of air pollution studies. For this, concerted action of scientists, abatement engineers, economists and politicians is required and the emission inventory developer has to present his data in such a form and to such detail that the different diciplines are not at a loss about what to do with some quantification of the effects of human behaviour on the environment. In other words, by comparing the emission data users' needs - or demands
-
with the supplied inventory developers'
knowledge, gaps between the two will appear and attention should be focused on these. The study of atmospheric pollution needs, as far as modeling is concerned, spatially and temporally resolved emission data of selected substances and information about the extent of the penetration of emissions into the atmosphere. The degree of temporal resolution depends on the type of model used. Long-term models, especially when operated with statistical meteorological data, only require seasonal or yearly average emissions. Episodic models, on the other hand, need a temporal resolution down to one or some hours, because they are operated in a real time mode. Concentrations and depositions of pollutants can vary
considerably in time because
of
changing meteorological conditions
(temperature, relative humidity, UV-light intensity, rainfall etc.) and because of varations in emissions (some of which also are influenced by meteorological phenomena). Spatial resolution depends on the sophistication of the model. In practice values of grid cell sizes have a range of one order of magnitude. The organization of pollution abatement requires some technical background data about emissions. The type of activity - in economic terms - and its intensity - in capacity and production units
-,
installations connected to one spe-
cific stack, fuel data and abatement appliances in use are examples that serve this objective. They can also be used by economists to put in their scenarios. With the feedback of results, modelers continue to predict the outcome of proposed changes that, finally, enables policy makers to make a choice.
115 The inventory developers' knowledge can be listed by a description of the emission registration projects that take place in Europe nowadays. It should, however, be
emphasized
that, due
to
the
consequences of
international
cooperation and the independently developed histories of emission inventorying in countries, the present scope of these projects does not fully reflect todays' state-of-the-art. In table 3 ongoing work is presented in a simple scheme. It can e.g. be seen that only PHOXA has highly resolved emission data. But it obviously would be incorrect to conclude from this that the other projects do not have the means for this (insofar they need it). At first sight, then, table 3 presents a fairly complete set of instruments, apart from only PHOXA having information about VOC compositions. Of course this is not surprising since organizers of these projects can be expected to have done a complete as possible job. However, in the background is one European data base (which might be called EURAD). The increasing cooperation between projects already has been mentioned. Proposals for the organization of such a data base already have been submitted [1,21
So one could compare the demand with a supply that provides anything (or, at least, most) that is necessary for any modeling study, abatement strategy development and policy making. It will appear, then, that gaps in the knowledge of emission inventorying are found mainly among emission factors and temporal allocation procedures. 5. GAPS IN EMMISION INVENTORYING It is commency understood that the main contributors to air pollution by NOx and VOC are:
- large combustion sources - road traffic
-
solvent evaporation
- vegetation The first two emit between 80 an 90% of antropogenic NO,.
The second and third
emit about three quarters of antropogenic VOC. Although NO, emission factors for stationary combustion sources have been and still are
-
subject to intensive discussion, it is questionable whether
more measurements will add substantially to the quality of NOx estimation in terms of systematic error (quality in terms of uncertainty certainly can be improved by compiling and analyzing as much as possible reliable measurement data in the right way). To stimulate harmonization the CORINAIR project requested a group of experts on NO,
formation to discuss the present knowledge and propose a set of NO,
116 emission factors to be used in the project. The group recently finished its task. Of course, the proposed factors are not the final answer. Instead, they reflect the present state-of-the-art. Another remark that should be made is that in the CORINAIR project these factors are not meant to arrive at some artificial uniformity. Evidently there are differences between - and also in
-
countries that need be taken into account. Harmonization should be understood as a common basis with which differences in estimation techniques can be accounted for. More or l e s s the same can be said about mobile NOx sources. But contrary to stationary emitters, mobile ones - especially gasoline powered vehicles
-
still
are likely to have a systematic error because of incomplete understanding of the influence of cold starts and subsequent driving with a warming-up engine. (The influence on NOx of cold starting, as a matter-of-fact, is far less pronounced than is the case with VOC and CO. More serious is the still inadequate estimation of transiently driven vehicle kilometers). Another difference with stationary sources is that CORINAIR up to now has no expert group for mobile ones. Work is in progress, however, to establish one soon.
From the above it appears that, with respect to emission factors, the improvement of inventorying is necessary for VOC in the first place. About mobile sources as total exhaust VOC emitters the same remarks that have been made about NO, and valid, but the need of a reliable cold start correction is more evident. Another source of VOC from vehicles is the evaporation of gasoline. In contrast to the US, in Europe not much attention has been paid to this source that is estimated to emit about lo6 tons of gasoline vapour annually in OECD-Europe [ 3 ] . Recent investigations, however, raise the expectation that this gap can be filled [ 4 ] . It is very important to sufficiently investigate the independence on ambient temperature of these evaporative emissions. In modeling studies temporally and spatially resolved ambient temperature data are used to modify them. The second large contributor to anthropogenic VOC emissions is the use of solvents. No well-defined economic
OK
social activity - not even a group of
them - covers these emissions. The collective term demonstrates the lack of knowledge about emission estimation techniques and, simultaneously, the way it is attempted to overcome this lack, i.e. the application of national mass balances. An emission factor based on the products themselves hardly plays a role here. Values generally are unity: what is used, is lost. The reason for the purchase of solvents is their loss and if this is caused by their presence in
117 finished products, losses into the atmosphere occur when products are applied. Some products show a time-delay in this process. Where mass balancing fails, it is tried to relate emissions to products, e.g.
manufactured automobiles,
applied paint. In Europe, interest for solvent emission estimation seems to be only at the beginning. Only in a very few countries attempts have been made up to now to make detailed national mass balances. Among other things, work is hampered by an almost complete lack of relevant statistics which, as a matter-of-fact, shows that societies' very detailed statistical data serve economic and social, but not yet environmental purposes. A cooperative action is needed to fill this important gap and to better understand the effects of the use of solvents, of which annually several megatonnes are released in Europe. First attempts to quantify emissions with total yearly per capita
data [5] should now be considered
as
obsolete
OK,
at most,
sparingly used as a default value. Work to be done already has been indicated in this paragraph: development of emission factors per unit of activity and simultaneously - as a control measure - analyses of mass flows. Next to anthropogenic emissions, nature itself releases matter into the atmosphere that is chemically more or less comparable to what is produced by human activities. There are indications that natural NO, emissions (NO + N02) are much less in Europe than antropogenic emissions. But is has also be shown that natural VOC cannot be ignored and during episodes, even can become important. Little is known about natural VOC. With the exception of methane generating processes, the main source is chlorophyll bearing vegetation. It has been demonstrated that emission rates are influenced by many variables. Ambient temperature, light incidence, humidity and of course, the sort of vegetation are examples of these. Measurements therefore are complicated and comparison of results is difficult. The scarce measurements that have been done in Europe should be followed by a cooperative research programma. To date it is simply assumed that data from investigations done elsewhere
-
predominantly in the U.S.
-
also apply to
European species. 6 . COMPOSITION OF EMISSIONS
An important lack of knowledge will be dealt with separately in this paragraph. It is remarkable that the increasing attention that is given to the inventorying of emissions
so
poorly is parallelled by investigating their
composition. In Europe, speciated VOC has been inventoried by Dement and Hov [ 6 ] and in the PHOXA project [ 7 ] . A distinction between NO and NO2 and between SO2 and
SO4 only has been applied in the PHOXA project.
118 It is worthwile to use the state-of-the-art of the knowledge about composition in a coherent way. For most source groups this knowledge is too incomplete to describe relevant national differences and this situation is likely to remain s o in the near future. Therefore averaged composition data should be used to be modified only whenever deviations can be made acceptable. It should become standard practice to report NO,-
and SOx factors together
with their N02- and SO"4-fractions respectively. In the case of NO,,
N20-frac-
tions should also be considered. Only scarce data exist about antropogenic N20 emissions and their contribution should be studied. In describing VOC compositions, anything that is known about them should be included. Apart from the fact that mass comparisons are facilitated there are no good reasons to exclude compounds because of their slow conversion in the atmosphere. (The term NMVOC derives its meaning from the corresponding TVOC's methane content
so
if this is not known, NMVOC suggests more than it can ful-
fil). Compositions should be stated in mass fractions. Simple conversions can be applied for what other units are needed for specific purposes. An important conversion of this kind is one that provides a quantification of the reactivity of a VOC emission. Several condensed chemistries are in use today for the modelling of photochemical phenomena. VOC profiles, that always should be part of VOC emission factors, easily can be transformed into any required chemistry. An example is given in table 4 . Whereas it is easy to record data about NO,
and SOx because only a few
substances are involved, listing of organic species is more complicated because of their abundance. Although from a technical point of view there is no real problem in handling large numbers of organic species, one can doubt the use of filling e.g. all different alkane isomers from a source (supposing they are known). In practice some compromise will be found, but as knowledge of composition - and reactivity - is limited, it is sensible to record all available information.
7. TEMPORAL DISTRIBUTION OF EMISSIONS For the study of short term air pollution phenomena a disaggregation of emissions with respect to time is needed. Short range studies can allocate emission data by making use of existing statistical data and well known habits in the area involved; it is performable to fill gaps by surveys if the area is not too large (8.91. For long range studies, on the other hand, such an approach generally will be prohibitive. Relevant data are incomplete or non-existent in countries and some time pattterns out of necessity even have to be developed from guess work.
119
Cooperation in European emission inventorying ought to comprise also work on this subject. It can be expected that several time-patterns are not restricted to national habits. Just as there are climatic zones that cross national borders, one can think of zones of comparable social and economic behaviour, such as time patterns of transport and working hours. Of course there are differences between countries, due to e.g. legislation but anything that is expected to be comparable should be jointly investigated as a part of emission inventorying activities.
8. ACCURACY OF EMISSION INVENTORIES In terms of demand and supply users of emission data will take into account uncertainties in model structure, meteorological data etc. when they state desired levels of uncertainty of emission data. They will also take into account the fragmentary knowledge about the relation between uncertainty of emission data and uncertainty of model output. Finally they will consider the lack of any supply in this field up to now. In discussions between modelers and inventory developers tentative values of required uncertainties have been proposed: 90% confidence limits of 20% and 30% are desired for national annual NOx respectively VOC emissions. Additional uncertainties o f temporal and spatial distributions are not known but should be kept at a minimum of course. Analytical and synthetical work on the quantification of accuracy is scarce, which is not surprising in view of the problem involved. In the U.S. it has now a structured position within NAPAP [10,11]. In Europe recently a workshop has been held about the subject [12]. This initiative may be expected to be considered as a first step in a joint action in this field. Noteworthy contributions were an uncertainty analysis of the emission inventory in the U.K. [13] and a proposal for a system to quantify uncertainty in the CORINAIR emission inventory structure [ 1 4 ] . Attention was drawn to the large amounts of measured data, stored in many countries, that should be put to use for this purpose [15]. To optimally continue this relatively new work, cooperation between the U.S.
and Europe is
worthwile.
9. SUMMARY AND CONCLUSIONS Of the known precursors of ozone only NO, and - to
a
lesser extent - VOC
have been inventoried to an extent that makes it possible to take stock of what has been done and is going on in Europe. From a initial stage in which countries more shifted
OK
less independently prepared national inventories activities have
to an international scale in the last few years. Today, there still
120 are differences in inventories between countries that are not compatible with combined knowledge. It can, however, be expected that, stimulated by international organizations, in the near future only those differences will remain that reflect economic and social differences between countries. From a comparison of the needs of atmospheric research with the available supply of emission inventory developers gaps in existing knowledge are deduced. Priorities for further work are suggested. These are:
- Correction of automobile exhaust emissions for cold start and subsequent driving with the engine in thermal inbalance.
-
Emission factors for solvent evaporation per activity. Emission factors for natural VOC.
- Composition data for all NO,
and VOC emission factors (sub-priority: most
important VOC sources, i.e. road transport, solvent evaporation and vegetation).
- For episodic model studies: temporal resolution of emissions. It is important to continue this work on an international scale, exchanging experience to finally arrive at a coherent European data base that reflects similarities as well as differences between national emission estimates. In this paper emission inventorying in Europe has been discussed. Where cooperation is advocated it is not suggested that this should be restricted to this part of the world. Particularly since global effects of pollutants have entered
the scene a broader approach has
become necessary. Exchange of
knowledge between Europe and the USA mutually might stimulate emission inventory developers. REFERENCES B.Liibkert and K.-H.Zierock, A Proposal of International Worksharing in Maintaining a Permanent European Air Pollutant Emission Inventory, Proc. Int. Workshop on Methodologies for Air Pollutant Emission Inventories, Paris, June 29 - July 2, 1987, pp. 39 - 61. P. Grennfelt and T. Levander, Emission Inventories in Europe: the Possibility for a Joint Data Base, ibid, pp. 63-65. A.H. Edwards et al, Volatile Organic Compound Emission: An Inventory for Western Europe, CONCAWE Rep. No. 2 / 8 6 . Den Haag, May 1986. J.S. Mc Arragher, An Investigation into Evaporative Hydrocarbon Emissions from European Vehicles, CONCAWE Rep. No. 8 7 / 6 0 , Den Haag, September 1987. C. Veldt, VOC Composition of Automotive Exhaust and Solvent Use in Europe, Proc. Znd Annual Acid Deposition Inventory Symp., November 1985, EPA Report 6 0 0 / 9 - 8 6 / 0 1 0 (April 1986). R.G. Derwent and A.M. Hough, Ozone Precursor Relationships in the United Kingdom, AERE Report R 12408, December 1986. C. Veldt et al, PHOXA Emission Data Base, PHOXA Report No.1 (in preparation) and Th. Miiller et al, Temporal and Spatial Allocation of S O q - , NO,VOC-Emissions in Baden-Wurttemberg, Proc. Int. Workshop on Methodologies for Air Pollutant Emission Inventories, Paris, June 29 - July 2, 1987, pp. 249 261
121 9 B. Boysen et al, Methods for the Investigation of Emissions from Road Transport, in [ 121. 10 C.M. Benkovitz, Uncertainty Analysis of NAPAP Emission Inventory, Proc. Znd Annual Acid Deposition Emission Inventory Symposium, (November 1985), EPA Report 600/9-86/010 (April 1986). 11 C.M. Benkovitz and N.L. Oden, Uncertainty Analysis of NAPAP Emissions Inventory, Progress Report FY 1986, Brookhaven Nat.1. Lab. Report BNL 52132 (December 1987) (NTLS). 12 IIASAlNILU Task Force Meeting on Accuracy of Emission Inventories, Laxenburg, Austria, March, 8-10, 1988. 13 H.S. Eggleston, Accuracy of National Air Pollutant Emission Inventories, in [121. 14 R. Bouscaren, European Inventory of Emissions of Pollutants into the Atmosphere, in (121. 15 C. Veldt, Examples of data for Estimating the Accuracy of Emission Inventories, in [12]. 16 B. Liibkert and S. de Tilly, the OECD-MAP Emission Inventory for S02, NOx and VOC's in Western Europe, Proc. Int. Workshop on Methodologies for Air Pollutant Emission Inventories, Paris, June 29 - July 2 , 1987, pp. 263 276. 17 National Strategies and Policies for Air Pollutant Abatement, Convention on Long-Range Transboundary Air Pollution, Report ECE/EB.AIR/14, UN, New York 1987. 18 B. Lubkert, A model for Estimating Nitrogen Oxide Emissions in Europe, IIASA Working Paper WP-87-122, December 1987. 19 T. de Ryck and W. van Hove, Raming van de NO, - uitworp in Belgie (Estimation of NO, emissions in Belgium), Leefmilieu 1985/3, pp. 78-81. 20 W. Heck and G. Kayser, Les Bmissions de polluants atmosph6rique.s produits par la combustion en Belgique - Un bilan de dix annees, Trib. Cebedeau 38 (1985) 21-31. 21 A. Semb and E. Amble, Emissions of Nitrogen Oxides from Fossil Fuel Combustion in Europe, Norwegian Institute for Air Research Report TR 13/81 (November 1981).
122 TABLE 1 Estimated NO, emissions in European countries 1980; l o 6 kg
Power plants OECD Austria
20
Belgium
853) 1074)
CSSR Denmark Finland France
121 106
FRG GDR Greece Hungary
PHOXA
IECD
13l)
139
119 253 126
280
2511)
803
792 218
Ireland 287 Italy Luxemburg Netherlands 79 Norway 11) Poland 20 Portugal Spain Sweden 11) 5 Switzerland UK 85 1 Yugoslavia
Road transport
581)
2413) 1504)
PHOXA
OECD
841) (145)2 180
216
132 a3
74 1506) 1021
526 (1015)2 1472 238
1469 916) 816)7)
All sources
::31 3984) 243 284 1950 3094
441)
264 57
247 70 282
75 19 1105
Sources: OECD = [ 1 6 ] , PHO only).
IIASA
216
186
505
442
426
779 253
1204 25 1 280 1867
63 1 270 244 1976
3100 8005) 127 2707)
2.688 520 2 18 220
10721) 3182 1193
67 a4 1410-1550 452 35 23 40 466lO) 535 494 106 2159) 173 1704 8409) 1484 166 149 780 95 1 265 2897) 297 196 161 2642 1916 2454 19012) 339 98
1556
-
ECE
1301)
199l)
18
79
PHOXA
182 1386) 663
: [7],
517 119 166
179 971
ECE: [17
319 194 1924
IIASA: [ l a ] (combustion sources
1 ) Country partly in PHOXA area; 2 ) Calculated for whole country; 3 ) Ref. [ 1 9 ] ; 4 ) Ref. [ 2 0 ] ; 5 ) Ref. [ l a ] ; 6 ) ECE, all mobile sources; 7 ) 1984; 8) 1983; 9 ) 1985; 10) mob. sources: road transport only; 11) OECD and PHOXA 1982; 12) Ref. [ 2 1 ]
123
TABLE 2 Estimated VOC emissions in European countries 1980; lo6 kg
Road transport OECD PHOXA exhaust evap. Austria
98
130
99 209 48
6l) (10)2) 14 10 6
305l) 5802) 593 393
451) (8412) 1106) 12
677
491) (ao)2)
Belgium CSSR Denmark Finland France FRG GDR Greece Hungary
1233) 54 785) 1097 688
Solvents 3ECD PHOXA
96l) (173)2) 33
Ireland Italy 9 Luxemburg 172 Netherlands 217 41 44 Norway 8, Poland 498 Portugal Spain 111 206 Sweden Switzerland 925) UK 5 13 612 Yugoslavia
1664) 32
729
2.5l) (4.5)2 3
1 20 5
481) (75)2 127 76 67 3711) (698)2 40a7) a4
IECD 25 1
119l)
25011)
3514)
289 385 132
350
106 129 2192 1864
17
11
5 9 17) 48 178
1759 630
-2300 1800
158
301)
99 50
All sources PHOXA ECE
63 458 137
16 436 103 948
62 43412) 16013) 37 1
13
93
107
71
630
73 1
Sources: OECD = [16], PHOXA: [7], E only).
:
[17], IIASA
413 307 1541
254 1624
4279) 311 1961
[18] (combustion sources
1) Country partly in PHOXA area; 2 ) Calculated for whole country; 3) Ref. [ZO]; 4) nat.1. estimate for 1985 (CORINAIR); 5) ECE; all mobile sources; 6) calculated with PHOXA emission factor; 7) non-industrial; 8) OECD and PHOXA 1982; 9 ) 1980; 10) 1983; 11) 1984; 12) 1981; 13) 1985
124 TABLE 3
Current European Data Bases
~~
Ct PHOXA
OECD
EMEP
COR I NAI R
Large combustion source i n v e n t o r y
~~
IRIGINAL IBJECTIVE
itudy o f transIoundary f l u x e s i y 1ong-rangelong-term model
\bat ement j t r a tegy ievelopment
Study o f photochemistry and a c i d i f ic a t i on d i t h long-range e p i s o d i c and long-term models
)efinition of rroposed d i r e c t i v e ! )n l a r g e combustior nstallations with i a t ional backgrounc lata
Gathering and organizing o f consistent inf o r m a t i o n on a i r pollutants
WEA
iurooe
Yember c o u n t r i e
P a r t o f W.Europe P a r t o f E.Europe
lember c o u n t r i e s
Member c o u n t r i c
'OLLUTANT!
SO,,
SO,,
SO,, NO,, VOC (incl. detailed composi t i on) CO, NH3
;Ox, NO, CO 1art.matter
SO,
INFORMATI(
.(ember c o u n t r i f
Member c o u n t r ie
Contractants
lember c o u n t r i e s
Member c o u n t r i c
SOURCE RESOLUTIOl
None
Det a i 1 ed
Detailed
Zomb. sources > 300 MWth i n d i v . ; Dther comb. source i n ranges (nat.1. totals)
Detai 1 ed
SPATIAL RESOLUTIOI
150 x 150 km
50 x 50 km EMEP g r i d
30'long x 1 5 ' l a t Geogr . g r i d
None
EMEP g r i d
Smallest t e r r i . torial unit wi information fol gridded data
TEMPORAL RESOLUTIOI
None
None
Hourly
None
None
~~
NO,
NO,
VOC
NO,
VOC
125 TABLE 4 Transformation of VOC profiles in chemistries used for modeling. Example: exhaust emissions of LPG-powered vehicles.
Substance
%
CBM-IV reactive by wt. species mollkg
9
me thane
ethane propane ethylene acetylene propylene xylenes formaldehyde acetaldehyde organic acids l)
3 35 15 22 8
1,5 4 1 1.5 100
1) C
5
3 assumed
OLE PAR FORM ALD ETH UNR
2.4 24.0
1.35 0.10 5.4 25.8
TADAP reactive species wt.fraction ALKA ETHE ALKE AROM HCHO RCHO SLHC
0.015 l) 0.17 0.08 0.015 0.04
0.01
0.67
This Page Intentionally Left Blank
T. Schneider et al. (Editors),Atmospheric Ozone Research and its Policy Implications 0 1989 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands
127
A.P.Altshuller Atmospheric Sciences Research Laboratory, U.S. Rwiromental Protection Agency, Research W i a q l e Park, North Carolina (USA)
A number of s i g n i f i c a n t Scurces of Ozone e x i s t i n t h e planetary boundary
layer, t h e f r e e troposphere and t h e 1-r stratosphere. "he c o n t r i t u t i o n s are estimated f o r each of these Scurces of ozone to g r a n d l e v e l ozone concent r a t i o n s . Both n a t u r a l and anthropogenic Scurces are considered. Horizontal and v e r t i c a l t r a n s p o r t of ozone and its precursors also are important i n determining the a m s p h e r i c d i s t r i t u t i o n of ozone. The measuretlents of the concentration and canposition of non-methane hydrocarbons and nitrogen o x i d e s have been evaluated a t both rural/ranote c o n t i n e n t a l sites and a t tropospheric backgramd locations. The e f f e c t s d i t ; cussed of t h e r e a c t i o n s of precursors with hydroxyl r a d i c a l s , ozone and nitrogen t r i o x i d e r a d i c a l s are discussed along with t h e l i f e t i m e s of o r g a n i c s and on t h e i r a m s p h e r i c canposition. Ratios of nonmethane hydrocarbons to nitrogen o x i d e s are important i n determining the e f f i c i e n c e s of ozone production. Experimental and modeling approaches to e s t h a t i n g t h e s e e f f i c i e n c i e s are reviewed. IrnrnICN
-
T h i s work w i l l f i r s t consider the sources of -one i n the v a r i c u s regions of the a m s p h e r e . Saxces both i n the f r e e troposphere and planetary bounddetail. The c o n t r i t u t i o n s of h o r i z o n t a l and a r y l a y e r are discussed i n vertical t r a n s p o r t of ozone and its precursors also are considered. The ranoval of organic species by r e a c t i o n s with -one,
nitrogen trioxide
The l i f e t i m e s of the
r a d i c a l s and e s p e c i a l l y hydroxyl r a d i c a l s is reviewed. individual species vary g r e a t l y influencing strongly the c a r p o s i t i o n of
organics a s they are transported f r a n sources through the planetary bamdary l a y e r and t h e f r e e trcposphere. The r e l a t i o n s h i p s between hydrocarbon to nitrogen oxide ratios and ozone production are inportant to understanding ozone d i s t r i t u t i o n s i n t h e atmosphere.
128
Organic c o n cen t r at i o n s and c a n p o s i t i o n a l measurements a t c o n t i n e n t a l r u r a l / r m t e sites are t a h l a t e d and discussed.
The corresponding measure-
ments of o r g a n i c species i n t h e background troposphere a t mid l a t i t u d e s i n t h e Northern Hemisphere are considered.
The l i m i t e d measuranents of nitroge n
o x i d e i n rural renote c o n t i n e n t a l and marine l o c a t i o n s a l s o are pre se nte d. The s i g n i f i c a n c e of p r ecu r s o r emissions and atmospheric c onc e ntra tion measurements to v ar i o u s r eg i o n al and t r w s p h e r i c models a l s o a r e emphasized. S(XIRCES OF OZONE I N THE FREE TROPOSPHERE
Se v e r a l types of ozone scurces c o n t r i b u t e to t h e ozone measured i n t h e trcposphere. 1-r
These Ozone scurces include (1) exchange of ozone f r a n t h e
s t r a t o s p h e r e a c r o s s t h e tropcpause i n t o t h e f r e e troposphere ( 2 ) i n s i t u
photochemical ozone production i n the f r e e trcposphere ( 3 ) ozone p r h c t i o n w i t h i n the p l a n e t a r y bcundary l a y e r .
Vertical t r a n s p o r t b e t m e n t h e pla ne ta ry
bcundary l a y e r , up to a h t 2 km, and t h e f r e e trcposphere can be important to t h e mvernent of ozone and its p r ecu r s o r s .
Stratospheric
to troposphere exchange
o f ozone
Se v e r a l processes can c o n t r i h t e to the f l u x of ozone from the 1-r s t r a t o s p h e r e i n t o t h e trcposphere ( r e f . 1 ) . H a e v e r a t m i d l a t i t u d e s i n t h e Northern Hemisphere l a r g e scale eddy t r a n s p o r t i n t h e region of the jet s t r e a n , o f t e n r e f e r r e d to as trcpopause f o l d ing ( r e f . 2 ) , is considered to be t h e daninant p r o ces s ( r e f . 3 ) . Analyses of the f r q u e n c y of such trapopause folding e v e n t s based on t h e Occurrence o f 5OO-mb low-pressure
t r o u g h s i n d i c a t e s t h e presence of a bout 4
t r c u g h s per day o v e r t h e Northern Hemisphere and about 1 t r q h per day sanewhere over North America ( r e f s . 3 , 4 )
?he frequency of such troughs vary
w i t h season, latitude and l o n g i t u d e ( r e f . 4 ) .
Aircraft masurements of t h e ozone p r o f i l e s d e f i n i n g dmnward m v 6 r e n t of ozone i n s t r a t o s p h e r i c air thrcugh t h e f r e e troposphere are available ( r e f . 5 ) . Ihe r e s u l t s i n d i c a t e that the s t r a t o s p h e r i c a i r t e n d s to bend ove r i n t o h o r i z o n t a l l a y e r s i n t h e f r e e troposphere o f t e n f a r above t h e t o p of the Secondary meteorological proc e sse s rm st be u t i l i z e d t o acccunt f o r s t r a t o s p h e r i c ozone mixing dcwn i n t o t h e pla ne ta ry boundary l a y e r . 'ho of t h e p o s s i b l e mechanism have sane theoretical and experimental
p l a n e t a r y bavldary layer.
support ( r e f . 5 ) .
These two m c h a n i s n s involve e i t h e r (1) coupling of the
s t r a t o s p h e r i c layer i n t h e f r e e troposphere to a f r o n t a l zone a s s o c i a t e d w ith
a c o l d f r o n t and t r a n s p o r t to the s u r f a c e by f r o n t a l d a m d r a f t s or ( 2 ) e n t r a i m n t i n organized f r o n t a l or p r e f r o n t a l convection w i t h t r a n s p o r t t o t h e su r f a c e i n d a m d r a f t s a s s o c i a t e d w i t h rainshcwers or thunderstorms ( r e f . 5).
129 These two mechanisns also would account f o r t r a n s p o r t of ozone produced by
s i t u photochemical
&
p r o ces s es i n t h e middle to upper f r e e trcposphere d m t o
t h e surface. Three-dimensional a i r p a r c e l trajectories have been used t o trace t r a n s p o r t of ozone f r a n the t r o p q x ws e down to the 7 0 0 4 level, 3 o b s e r v a t i o n s are a v a i l a b l e ( r e f s . 5 , 6 ) .
The -one
)an,
when meteorological
f l u x c a n be c a l c u l a t e d darn
through the area of the s u r f ace estimated to be involved a t the 7 0 0 4 level. The f r q u e n c y of ground l e v e l impacts of stratospheric ozone and t h e a s s o c i a t e d ozone co n cen t r at i o n s can be ev al u ate d f r a n episbdic reports i n t h e
literature.
A
c c n p i l a t i o n of 10 ep i s o d es h a s been made based on the criteria
used by the o r i g i n a l i n v e s t i g a t o r s f o r epis3des between 1964 and 1978 ( r e f . 6 ) . The o b s e r v a t i o n s were made a t l o c a t i o n s i n t h e United S t a t e s and Western Europe. u s u a l l y t h e e l e v a t ed ozone co n cen t r at i o n s o cc ur f o r periods of a f r a c t i o n of a n hcur t o s e v e r a l hcurs.
S ev er al o b s er v at i o n s of -one
c onc e ntra tion above 100
ppb a t ground l e v e l seem implausible conpared with ozone c onc e ntra tions b e b e e n The f r q u e n c y of 5 0 0 4 1 and 700-mb d u r i n g episodes observed a l o f t ( r e f s . 4-6). high ozone c o n c en t r at i o n s a t g r a d level a s s o c i a t e d w i t h s t r a t o s p h e r i c intrus i o n s reaching t h e s u r f ace were estimated t o occur less than 1%of t h e t h e (ref. 6 ) . A
number of estimates have been r ep o r t ed of seasonal c o n t r i b u t i o n of
s t r a t o s p h e r i c ozone to s u r f ace ozone concentration.
About 10 ppb of the s u r f a c e
ozone concentration h a s been a t t r i h t e d t o ozone of s t r a t o s p h e r i c o r i g i n ( r e f . 7).
me
in-situ photochemical production of ozone i n t h e troposphere A second SaJrce of Ozone is its photochenical prcduction f r a n reactions
involving m t h a n e , carbon mn o x i d e and o t h e r longer-lived volatile o r g a n i c s w i t h nitrogen o x i d es i n t h e f r e e troposphere ( r e f . R,9).
Because of several
shortcanings of earlier m d e l i n g s t u d i e s only t h e mre re c e nt s t u d i e s are p e r t i n e n t (ref. 9).
The results f r a n a number of these re c e nt s t u d i e s have been reviewed
elsehere ( r e f . 7 ) .
I f a n t h r o p g e n i c n i t r o g en oxide scurces a t the surface are
not included i n t h e model scenario, a h t 15 ppb of ozone is ge ne ra te d photochenic a l l y a t 1 km under sumnertime co n d i t i o n s a t mid l a t i t u d e s i n t h e Northern Hemisphere. I f t h e s u r f ace n i t r o g en oxide and non-methane hydrocarbon f l u x e s p r e s e n t i n remote areas a r e included t h e photochemically generated ozone c o n c e n t r a t i o n s in c r e a se to the 30 t o 50 ppb range ( r e f s . 7,lO). Several approaches have been used to es t im a te the h i s t o r i c background of ozone frcm n a t u r a l p r e c u r s o r s a t r u r a l l o c a t i o n s ( r e f . 10).
The approaches in-
c lu d e (1) r e s u l t s from scenarios ap p l i ed to v a rious trc posphe ric photochemical models ( 2 ) statistical an al y s es of t h e h i s t o r i c a l t r e n d s i n ozone c onc e ntra tions and ( 3 ) use of 7% and/or 90Sr tracers of the o r i g i n s of ozone i n t h e stra tosphe i
130 and/or upper trcposphere.
An
average late spring-smmr natural backgrmnd of
ozone i n the range of 10 to 20 p N can be obtained from the r e s u l t s a t midl a t i t u d e s i n the Northern Henisphere (ref. 10). Other sources of ozone The t h i r d major group of Scurces a r e those pmchcirq Ozone photochanically within the planetary boundary layer.
Active cumulus clouds often form under
the sane conditions favorable to ozone formation.
Updrafts in a c t i v e cumulus
can c a r r y ozone i n t o the lover f r e e traposphere ( r e f s . 11,12).
These updrafts
i n these venting clouds a l s o shculd transport o t h e r species including hydrocarbons, carbon mnoxide and nitrogen oxide a l o f t along w i t h the ozone.
SOURCES OF OZONE WITHIN THE PJANETARY BOUNWRY IAYER The r e s u l t s available up to 1984 on the characteristics of ozone formation within plumes a s w e l l as the episodic formation of ozone during passage of warm high pressure systems have been reviewed ( r e f . 7 ) .
Elevated ozone concentra-
t i o n s have been reported to occur within urban plumes, plumes f r m f o s s i l f u e l
m r plants and p l u m s f r m i n a s t r i a l m c e s ( r e f . 7 ) .
All of these w r c e s
can make a contribution to the regional backgroud of ozone. Ozone formation within urban plumes Because of cptimum hydrocarbon to nitrogen oxide ratios and t h e presence of highly reactive hydrocarbons t h e conditions i n urban plumes f r a n both large and -11 cities are favorable t o t h e rapid formation of ozone ( r e f . 7 , 13-17). Excess ozone concentrations 50 to 100 pfi above regional b a c k g r m d of ozone a r e observed during t h e f i r s t day of transport of urban plumes. Such plumes have been tracked by a i r c r a f t measuranent out to several hundred lan dwnwind of a number of large cities i n the united states ( r e f . 7 ) . plumes with less excess ozone have been observed from smller cities. In p r a c t i c e , i n heavily populated a r e a s plumes fran two or mre large and/or snaller c i t i e s can be canbined. Excess ozone over t h a t measured i n t h e a i r advected i n t o St. Louis was detectable i n the S t . mis plum on 189 days i n April through October 1975 and 1976 (ref. 13).
The 1-h maximum i n excess ozone over t h e regional background
during midday hours q u a l l e d or exceeded 40 ppb on abcut half of these 189 days.
The 1-h maximum i n excess Ozone qualled or exceeded 100 ppb on 4% of
These owne concentrations were measured a t nonurban m n i t o r i n g s t a t i o n s located up t o 40 lan outside of these days and exceeded 200 pfi on several days.
St. Lcuis. During those days on which the maxinnnn excess ozone 100 ppb t h e regional background of ozone based on ozone measuranents a t several upwind monitoring s t a t i o n s ranged f r a n 64 to 107
pN and averaged 81 ppb.
131 Aircraft measuranents tracking the St. Louis urban plume were available on four days i n 1975 and 1976 ( r e f . 13).
Excess ozone above regional background
on the edges of the plumes were tracked to 100 to 150 km d m i n d of St. Louis. urban plume widths viere estimated f r a n the a i r c r a f t measuremnts of the edges of plumes a s w e l l a s the ozone d i s t r i b u i t o n s a t monitoring s t a t i o n s ( r e f . 13). Based on plume transport distances and plume widths f r a n St. -is
and
other cities it has been estimated t h a t 5 to 10%of the land area west of the Appalachian Mountains and east of 105OW longitude is hpacted by excess ozone within urban plumes during t h e April t o October periods (ref. 13).
The @act
of urban plumes in this region is most frequent f o r the wind f l w s t h a t prevail f r a n t h e m t h e a s t to southwest sector onto land areas d m i n d . Fran measuremnts mde on four a i r c r a f t f l i g h t days i n A u g u s t 1978 when
t h e urban plume fran Boston traveled c u t over the Atlantic Ocean, t h e lifetime of nitrogen oxides ( l / k ) was calculated t o range frun 4 to 7 hcurs and averaged 5.5 hours under sunny sumrertine conditions ( r e f s . 14,15).
Fran measuremnts
made on two a i r c r a f t f l i g h t days in July and August 1979 the upper limit l i f e -
times ( l / k ) f o r nitrogen oxide i n the Philadelphia plume were estimated a s less than 5 and 8 hours respectively ( r e f . 1 6 ) . Therefore nitrogen oxides a r e r e l a t i v e l y rapidly depleted within urban plumes. The average rate of ranoval of ethylene was nearly the sane as f o r nitrogen oxides based on ethylene to acetylene ratios measured &ring traverses of the Boston plume ( r e f . 15). Several mdeling grcups have used Lagrangian t r a j e c t o r i e s to investigate 03 formation &ring t h e transport of urban plumes over non-urban a r e a s ( r e f . 7 ) . I n i t i a l conditions of the m d e l s have been based upon the urban concentrat i o n s of precursors f r a n s p e c i f i c u.S. cities. 'Ihe predicted ozone concentrations obtained a r e i n reasonable agreenent with observed ozone concentrations in plumes.
The e f f e c t of hydrocarbon to nitrogen oxide ratios on ozone production,
nitrogen oxide ranoval r a t e s and cycling of nitrogen oxide thrcugh proxyacyl n i t r a t e in multiday simulations have a l l been investigated. In scme of these modeling s t u d i e s the e f f e c t of added biogenic hydrocarbon on ozone formation has been simulated f o r emissions i n and around s p e c i f i c
cities and f o r generalized conditions ( r e f s . 7,18-20).
The results indicated
less than a 10%e n h a n c m n t of ozone formation i n urban plumes as a r e s u l t of biogenic hydrocarbons a n i t t e d i n t o the Tanpa-St. Petersburg, FL and Houston, TX plumes ( r e f . 18,19). The e f f e c t on ozone production i n the urban plume of a hypothetical c i t y was insignificant when biogenic hydrocarbons were a n i t t e d i n t o the urban plume during the afterncon hours ( r e f . 20).
However, when
132 biogenic hydrocarbons were e n i t t e d upwind of the hypothe tic a l urban area i n t h e morning t h e y e r e p r e d i c t e d to enhance ozone production i n t h e urban plume i n
late afternoon by 18%f o r a maximum i s cp r en e c onc e ntra tion of 63 ppbc and by 8% f o r a maximum i s cp r en e co n cen t r at i o n o f 11 ppbc ( r e f . 20). Ozone formation i n plumes f r a n f o s s i l f u e l power p l a n t s Excess ozone co n cen t r at i o n s over regional backgraind ranging f r a n 20 to 50 pP, h a s been m e a w e d &r i n g a i r c r a f t traverses of plumes fran f o s s i l f u e l
pwer p l a n t plumes i n the e a s t e r n United S t a t e s ( r e f . 7). Occurrences of total ozone c o n c e n t r a ti o n s above 100 ppb a t several g r a n d l e v e l monitoring s t a t i o n s i n t h e s c u t h e a st er n United S t a t e s have been a s s o c i a t e d w ith plumes f r a n f o s s i l f u e l p#er p l a n t s ( r e f . 21).
T h i s conclusion is based on c o r r e l a t i o n s of Ozone
and s u l f u r dioxide co n cen t r at i o n s and on t r a j e c t o r y a na lyse s.
The inpact on
t h e plumes a t the g r a n d l e v e l l o c a t i o n s occurred 3 to 8 h a r r s and f r a n t h e time of emission f r a n t h e power p l a n t s t a c k s ( r e f . 21). I n c o n t r a s t , e x c e s s ozone co n cen t r at i o n s have not been observed i n s e v e r a l f o s s i l f u e l power p l a n t plumes t r a v e l i n g o v er r u r a l areas of the western United S t a t e s or over areas of Ocean ( r e f . 7). The d i f f e r e n c e s i n Ozone prockction can be a s s o c i a t e d with t h e a v a i l a b i l i t y o f hydrocarbon emissions i n t h e areas t r a v e l e d over by the plumes. o x i d e s, bt lack hydrocarbons.
F o s s i l f u e l p e r p l a n t p l u m s are r i c h i n nitroge n Hydrocarbons are r q u i r e d to mix i n t o t h e
plumes to o b t a i n hydrocarbon to n i t r o g en o x i d e s ratios fa vora ble to ozone production.
S u f f i c i e n t hydrocarbon m i s s i o n s o f t e n are not a v a i l a b l e i n remote c o n t i n e n t a l areas nor are they a v a i l a b l e o v e r water, The hydrocarbon emissions need to g en era te ozone i n t h e f o s s i l f u e l puer p l a n t plumes may b e a n t h r q x q e n i c or bicgenic.
Highly r e a c t i v e hydrocarbon species w i l l g e ner at e ozone more r a p i d l y i n t h e s e p l u m s . -ling results for ozone p r h c t i o n w i t h i n t h e dimensions of p e r p l a n t plumes have not been published. Modelings have been r ep o r t ed of ozone formation a s s o c i a t e d w ith i s o l a t e d n i t r o g en oxide g r a n d l e v e l scurce 1 km on a s i d e assuning s e v e r a l d i f f e r e n t emission rates i n rural t e r r a i n ( r e f . 20).
Substantial increases i n
ozone c o n c e n t r a t i o n s a r e p r e d i c t e d f r a n i s cp re ne and d.-pinene m i s s i o n s associa t e d with q t i m u m hydrocarbon to n i t r o g en o x ide ratios. The incremental ozone a s s o c i a t e d w i t h t h e a d d i t i o n of the b i cg en i c hydrocarbon m i s s i o n s are very s e n s i t i v e to t h e emission rate of t h e n i t r o g e n oxides. Unfortunately it is d i f f i c u l t to kncw h a r u s e f u l such c a l c u l a t i o n s are
me p e r p l a n t plumes a l o f t are i s o l a t e d f r a n any grcund level SOurces of hydrocarbons f r a n late a fte rnoon
with respect t o pmer p l a n t plumes emitted a l o f t .
or e a r l y evening i n t o t h e morning h cu r s a f t e r s u n r i s e a s t h e n o c t u r a l s u r f a c e
133 in v e r si o n forms and disappears.
Mixing i n t o real plumes a l o f t may n o t be a s
hamgeneam a s a s s a d i n such s i mp l i f i ed lnodeling scenarios ( r e f . 2 2 ) . Ozone formation i n i n d u s t r i a l plumes Excess ozone h as been observed w i t h i n s eve ra l ind-lstria l plumes ( r e f . 7 ) . These p l u m s wre a s s o c i a t e d with several petroleum r e f i n e r i e s and w i t h a large autcmotive p a i n t p l an t . These Scurces are r i c h i n hydrocarbons as would
be o t h e r i n d u s t r i a l sources such a s petrochemical canplexes. These plumes tended to be n a r r m and d i f f i m l t to tra&. They also tend to involve less r e a c t i v e hydrocarbons mixed with l i mi t ed amcunts of nitroge n oxides. mperimental results on ozone formation d u r i n g the passage of warm high p r e s s u r e systems The a v a i l a b l e experimental s t u d i e s up to 1985 on ozone f o n r a t i o n a ssoc ia te d with warm high p r es s u r e systems i n t h e e a s t e r n United S t a t e s and M s t e r n Eurcpe have been reviewed elsewhere ( r e f . 7 ) . Aspects of v e r t i c a l s t r u c t u r e , d i u r n a l ozone p r o f i l e s , v a r i a t i o n of ozone with passage of a high pre ssure system, nocturnal j e t s and h o r i z o n t a l p r o f i l e s need to be considered ( r e f s . 7,23-27). The v e r t i c a l s t r u c t u r e of ozone is c o n s i s t e n t with a layer of e l e v a t e d ozone a l o f t d e v e l o p i q a t 1 to 2 km a l o f t during t h e cmrse of the episode ( r e f s . 2 3 , 2 4 ) . 'his layer is t h e r e s u l t of photochemical production of ozone i n t h e planetary boundary l a y e r &r i n g p r e v i m s d a y ( s ) and it is preserved i n t o the
following d a y ( s ) . A t t h e s u r f ace, ozone is d eple te d i n nonurban areas by d r y As the noc tura l inve rsion
d e p o si t i o n and chemical r e a c t i o n overnight ( r e f . 25).
breaks up t h e ozone a l o f t mixes down to i n cr ea se s u r f a c e ozone ( r e f .
26,27).
I n t h e f o l l m i n g hours f u r t h e r i n cr eas es i n m one occur a t t h e s u r f a c e because
of photochemical production ( r e f . 27). A s a r e s u l t by midday t h e r e is a damward g r a d i e n t i n t h e ozone co n cen t r at i o n f r m t h e surfa c e to several k i l a n e t e r s a l o f t ( r e f . 23,24).
ozone co n cen t r at i o n s near the surfa c e cutside of plumes
c a n h i l d up to 100 p@ and above ( r e f . 23,251. A t n i g h t h o r i zo n t al t r a n s p o r t can be increased by the noc tura l jet phenomena ( r e f s . 7,26).
Strong n o ct u r al jets are observed over c e r t a i n areas of t h e United
S t a t e s , e s p e c i a l l y over t h e Great P l ai n s , which can t r a n s p o r t species including ozone and its p r e cu r s o r s hundreds of kilaneters daunwind. A i r c r a f t traverses i n d i c a t e co n s i d er ab l e h o r i z o n t a l s t r u c t u r e i n the o m n e This s t r u c t u r e 1s the result
p r o f i l e s w i t h i n high p r es s u r e systans ( r e f . 23,25).
of t h e presence of i n d i v i d u al plumes co n t ai n i ng e xc e ss ozone a s disc usse d above.
134 mnger-range t r a n s p o r t o f ozone There is experimental evidence of t h e continued presence of e l e v a t e d conc e n t r a t i o n s of ozone during multiday t r a n s p o r t w ithin the p l a n e t a r y bcundary layer (ref. 7).
Tr an s p o r t times ranging f r a n 8 t o 48 h c u r s f o r ozone have been
observed over oceanic areas near c o n t i n e n t s ( r e f . 7 ) . Direct e va lua tion of longer-range ozone t r a n s p o r t over land ismore d i f f i c u l t s i n c e it depends upon p r q e r e s t i m a t i o n of a nunber of parmters r e l a t e d to production and ranoval of Ozone and its p r e c u r s o r s a s w e l l a s h o r i z o n t a l and v e r t i c a l t r a n s p o r t . k x k l i n g e f f o r t s t o simulated multiday t r a n s p o r t of omne began w ith the use of s i m p l i f i e d Lagrangian long-range t r a n s p o r t models ( r e f s . 28,29). i n i t i a l r e s u l t s from such e f f o r t s =re
approaches are u s ef u l i n r eg u l at o r y a p p l i c a t i o n s of modeling. l a r g e n&r
While the
i n t e r e s t i n g it is not clear t h a t such Aside f r u n t h e
of s i mp l i f y i n g as s u n p t i o n s made, t h e Lagrangian approach does n o t
appear p r a c t i c a l f o r g en er at i n g t h e l a r g e f i e l d of ozone c onc e ntra tions over a n e n t i r e region of a co n t i n en t needed i n p r a c t i c a l a p p l i c a t i o n s . More r e c e n t l y a three dimensional Eu l eria n re giona l oxida nt model (RCM) h a s been develcped.
This mDdel is capable of h a x l y p r e d i c t i o n s of t h e concen-
t r a t i o n s of Ozone and other species w i t h i n g r i d areas 18 km on a s i d e ( r e f s . 30-32). 'he second g en er at i o n v er s i o n of t h e mdel i n c l u d e s ( a ) day and n i g h t photcchenistry including subgrid c h e n i s t r y ( b ) anthropogenic and biogenic emissions of hydrocarbon and n i t r o g en o x i d e s d i s a g g r q a t e d by g r i d e l e m n t ( c ) h o r i z o n t a l t r a n s p o r t including t e r r a i n e f f e c t s ( d ) mesoscale v e r t i c a l n o t i o n and eddy e f f e c t s (e) cumulus cloud e f f e c t s ( f ) noc turna l jet p h e n m n a and (4) removal p r o c e ss es ( r e f . 31).
The 18 km g r i d s i z e r e s o l v e s abcut 80% of t h e
me of t h e major problems is t h a t f o r over 10% of t h e 200 h i g h e s t scllrce cells f o r hydrocarbon and nitroge n oxide emissions i n t h e United S t a t e s the tm anthrcpogenic i n v e n t o r i e s a v a i l a b l e , hydrocarbon and n i t r o g en o x i d e emissions ( r e f . 30).
d i f f e r by 300% and mre ( r e f . 3 0 ) . C l h t o l o g i c a l patterns o f ozone i n t h e United S t a t e s The climatological p a t t e r n s o f ozone co nc e ntra tions obta ine d f r a n m n i -
t o r i n g s t a t i o n s east of l O O o W l o n g i t u d e have been develcped.
The approach used
involved c a l c u l a t i n g monthly means of d a i l y maximum ozone c onc e ntra tons and d i sp l a y i n g t h e r e s u l t s a s monthly isopleth maps f o r July and August 1977 to 1981.
The maps i n d i c a t e that monthly means i n a geographical area can vary by
10 to 50 p@ during t h es e tem sumx m n t h s .
W n t h l y mean c o n c e n t r a t i o n s
d e c r e a s e by 20 t o 25 ppb across the midwestern United S t a t e s f r a n east to w e s t f r a n c e n t r a l Ohio and e a s t e r n Misscuri to northwestern Icwa.
I n northwestern
Icwa the ceone c o n cen t r at i o n s range f r a n belcw 40 ppb up to 60 ppb.
The ozone c o n c e n t r a t i o n s also are 1cw i n the extrew northe rn United S t a t e s . In c o n t r a s t i n mre heavily pcpulated areas such a s c e n t r a l Ohio, the Washington, DC area
135 and Connecticut almost identical ozone concentrations are obtained f o r values averaged over July-August 1977-1981.
The variations observed a t any given location
a r e a t t r i h t e d t o differing paths of the migratory high pressure systens ( r e f . 33).
However, differences in emission d e n s i t i e s of hydrocarbon and nitrogen
oxides across the midwestern United S t a t e s and less favorable meteorological conditions for ozone f o r m t i o n i n the northern United S t a t e s a l s o should c o n t r i t u t e t o the observed geographical variations in the m n t h l y mean values of ozone. 'Ihe incremntal omne concentrations observed climatologically i n the sumrer months a t grcund level over the mre pcpulated areas of the United S t a t e s a r e best explained by photochemical generation of ozone within the planetary bcundary
layer fran local or regional hydrocarhn and nitrogen oxide enissions ( r e f . 7 ) . Urban plumes a l s o are detectable ring the spring m n t h s ( r e f . 1 3 ) . Regional photochenical 03 production a l s o occurs during t h i s period of the year.
A
detailed analysis of ozone p r o f i l e s &ring both day and nighttime h m r s a t a r u r a l site a t G i l e s , TN is best explained by the substantial importance of daytime photochenistry during t h e spring m n t h s ( r e f . 21). A'IMDSF'HERIC LIFETIMES OF OFGRZiNIC SPECIES
The ranoval of most types of v o l a t i l e organic carpounds fran t h e atmosphere is predaninantly determined by t h e i r chemical reactions in the atmosphere r a t h e r than by wet or dry deposition. with the exception of alkenes, organic species react more rapidly w i t h hydroxyl r a d i c a l s than with omne or NO3 r a d i c a l s ( r e f s . 34-40).
Although alkenes react a t substantial r a t e s w i t h ozone ( r e f .
34), the daytime lifetimes of ethene, prcpene and other 1-alkenes also are primarily determined by t h e i r r a t e s of reaction with hydroxyl r a d i c a l s ( r e f s . 34,35). Alkenes with internal dcuble bonds react very rapidly with ozone ( r e f . 35). In addition acyclic alkenes such a s 2-methyl-2-tutene and related mlecules, most terpenes and cresols react rapidly w i t h nitrogen trioxide ( r e f s . 36-40). Solar photolysis c o n t r i t u t e s t o the rerPval of aldehydes and ketones f r a n t h e atmosphere.
The r a t e of f o r m t i o n of hydroxyl r a d i c a l s depends on t h e photolysis
of ozone to 0 ( b ) by u l t r a v i o l e t solar radiation and the reaction of O ( 1 D ) with
water vapor ( r e f . 34). Hydroxyl radical concentrations decrease rapidly a t low s o l a r radiation i n t e n s i t i e s ( r e f . 4 1 ) . Therefore hydroxyl radical reactions are only important in calculating daylight lifetimes of organics. Ozone is present in the atmosphere a t varying concentrations a t g r a n d level and a l o f t throughout the day and nighttime h m r s ( r e f . 7). Nitrogen trioxide radical concentrations increase during t h e nighttime hcurs t u t rapidly photolyzes to very l m concentrations a f t e r sunrise ( r e f . 36).
136 The l i f e t i m e s of alkenes w i t h i n t e r n a l double bonds are h c u r s or less both i n the day and n i g h t because ozone, hydroxyl r a d i c a l s or n i t r o g e n t r i o x i d e r a d i c a l s are a v a i l a b l e to r a p i d l y d e p l e t e t h e s e a l k e n e s ( r e f s . 34-36,39). l h e r e f o r e such a l k e n e s would not be expected to be d e t e c t a b l e a t nonurban l o c a t i o n s or r e g i o n s a l o f t u n l e s s r e c e n t l y impacted by source m i s s i o n s c o n t a i n i n g t h e s e canpounds. Based on t h e s e c o n s i d e r a t i o n s an a p p r c p r i a t e s i m p l i f i c a t i o n is to c o n s i d e r
only t h e rates of r e a c t i o n s of o r g a n i c species w i t h hydroxyl r a d i c a l s and the corresponding atmospheric l i f e t i m e s .
The rate c o n s t a n t s f o r the r e a c t i o n of
hydroxyl r a d i c a l s with a nunber or o r g a n i c species i n Table 1 are based e i t h e r on c a n p i l a t i o n of a v a i l a b l e experimental v a l u e s or on a n empirical c q u t a t i o n technique f o r e s t i m a t i n g t h e s e rates ( r e f s . 34,35,42). 'KI e s t i m a t e t h e l i f e t i m e s l i s t e d i n Table 1 a hydroxyl r a d i c a l c o n c e n t r a t i o n h a s to be s e l e c t e d .
A value
of 4 x 105 m l e c u l e s cm-3 as a n average d i u r n a l c o n c e n t r a t i o n v a l u e was used and
i s based on r e c e n t OH m e a s u r e m n t s near grcund l e v e l ( r e f . 41).
Based on
t r e n d s i n 7 y e a r s of m e a s u r a n t s of methyl chloroform a t f i v e backgrcund s t a t i o n s t h e average hydroxyl r a d i c a l c o n c e n t r a t i o n f o r 30" t o 90"N and 500 to 1000 mb is c a l c u l a t e d to be 4.95 0.9 x 105 molecule ( r e f . 43). i n Table 1 *re
The c a l c u l a t i o n s
m d e f o r a s m r t i m e atmosphere i n t h e p l a n e t a r y b a m d a r y
l a y e r assuning a n average t e n p e r a t u r e of 298°K.
For longer-lived species t h a t
s u r v i v e to be d i s t r i h t e d throughout t h e f r e e troposphere such as ethane or a c e t y l e n e this l i f e t i m e d o e s not q u a 1 their average t r o p o s p h e r i c l i f e t i m e .
For
a m l e c u l e such a s ethane its rate c o n s t a n t with hydroxyl r a d i c a l s i n t h e f r e e trcposphere is about 40% o f its rate i n t h e p l a n e t a r y boundary l a y e r . c o n s t a n t of a c e t y l e n e with hydroxyl r a d i c a l s w i l l be i n a f a l l - o f f t h e atmospheric p r e s s u r e s i n t h e upper troposphere.
The rate
region a t
For such molecules t h e
average t r o p o s p h e r i c l i f e t i m e s are somewhat l o n g e r than t h o s e g i v e n i n Table 1. The rate c o n s t a n t s and l i f e t i m e s w i t h i n a class of o r g a n i c species, a l k a n e s , a l k e n e s or a r m t i c s vary by f a c t o r s of 10 to 50.
Even w i t h i n a subclass such
a s t h e Cg t o Cg a l k a n e i m r s , rate c o n s t a n t s and l i f e t i m e s can vary by a f a c t o r of 10.
The c a n p o s i t i o n of o r g a n i c species a t r u r a l l o c a t i o n s o f t e n depends on the e x t e n t a l o c a t i o n is i s o l a t e d f r a n nearby m r c e emissions.
137 Table 1.
Rate C o n s t a n t s f o r s e l e c t e d Nonmethane Organic Canpcunds w i t h
Hydroxyl R a d i c a l s and Estimated L i f e t i m e s o f t h e s e species
e!?!EE!
Rate Constant
E s t i m a t e d L i f e t i m e s of
1012K, 298O~, m 3 m1-1s-1
Organic Species, day&
ethane
0. 274a
prcpane
1.18"
23
n-bu t a n e
2.53a
11
2-me thylprcpane
2.37a
12
100
n-pentane
4.06a
7
2-methyltu t a n e
3.9a
7
hexanes
1.8 t o 5.5b
heptanes
2.9 to 7.7b
3.6 t o 9
octanes
1.1 to 9.2b
3 t o 25
nonanes
2.2 to 11.0b
acetylene
0.7&la
benzene
1.28a
(760 torr)
5 to 15
2.5 t o 1 2 35 21
monoalkylbenzenes
5.7 t o 7.5a
3.6 to 4.8
o r t h o and para-
11 to 15a
1.8 to 2.5
m e t a l d i a l k y l benzenes
17, 24.5a
1.6, 1.1
trialkylbenzenesC
33 to 62.
0.4 to 0.8
e thene
8.54"
3.2
prcpene 1-htene
26.3
1.0
31.9"
0.8
2-
d i a lkylbenzenes
thylpropene
51.4"
.5
cis2-bu tene
56. la
.5
t rans-2-bu t e n e
63.7a
.4
2-methyl-2-bu t e n e
R6.ga
.3
cyc lohexene
fi7.4a
.4
1 3-bu t a d i e n e
66.aa
.3
2-methyl-l13-butadiene
101.a
.3
d -pinene
53.2a
.5
-p inene
78. 2a
.4
,
138 Table 1. (continued)
Rate Constant
Compound
1012K, 298'K,
Estimated L i f e t h e s of Qn3
Kd-151
Organic Species, day&
formaldehyde
9.0a
acetaldehyde
16. 2a
acetone
0.23a
120
methylethylketone
1.0a
27
methanol
0.9a
30
ethanol
2.9a
9
3 1.7
me thy1 c h l o r i d e
0.04a
>365
methylene d i c h l o r i d e
0. 14a
chlorofo m
0.10
>180 >180
trichloroethylene
2.3ha
9
perchloroethylene
0. 17a
->180
a R e c m n d e d value a t 298OK f r a n experimental measurements i n r e f e r e n c e 34 C a l c u l a t e d f r a n enpirical method given i n r e f e r e n c e 42
c Rased on a d i u r n a l l y averaged OH c o n c e n t r a t i o n o f 4 x 105 molecules cm-1
139
A
number of the organic species listed i n Table 1 such as ethane, prcpane,
a c e t y l e n e , acetone, methanol, methyl c h l o r i d e , methylene d i c h l o r i d e , perchloroe th y l e n e and benzene react very slcwly w i t h hydroxyl radicals as w e l l a s w ith Other halocarbons are even longer live d. Such species shculd be w e l l d i s t r i b u t e d th-h t h e f r e e trcposphere a t midlatitudes
ozone and n i t r o g en t r i o x i d e .
i n t h e Northern Hemisphere.
Therefore, t h e s e orga nic s should c e r t a i n l y c o n t r i b u t e
t o t h e carbon loading of t h e background on "clean" trcposphere. REIATIMSHIFS FIE'J3EEN OIGWIC CCf@OSITIM AND NON-I@Ell@NE OKANIC NITWX;EN
CcMpCuM,
TO
CXIDE RATIOS 'Rl OZONEiFORKCffi POTENTIAL
Extensive simulated s u n l i g h t e n v i r o m n t a l c h a r experimental s t u d i e s involving hydrocarbonnitrogen oxide mi x t u r es i n a i r c a r r i e d out during t h e 1950's to the 1970's danonstrated both the e f f e c t s of orga nic c a nposition a s well a s organic substance to n i t r o g en oxide ratios on v a r i o u s r e a c t i v i t y p a r a n e t e r s ( r e f s . 44-52). These r e a c t i v i t y paraneters involved nitroge n oxide conversion rates, ozone formation, peroxyawl n i t r a t e y i e l d s , aldehyde y i e l d s and b i o l o g i c a l e f f e c t s , p l a n t damage and eye i r r i t a t i o n ( r e f s . 45,46). orga nic c a n p o s i t i o n was s h a m t o have a strong e f f e c t on these r e a c t i v i t y paraneters ( r e f s . 44-49,51,52). Ambient a i r measurenents made &r i n g t h e 1960's indic a te d t h a t a lka ne s were the most a h d a n t class of organic ccanpounds i n p o l l u t e d atmospheres ( r e f . 48). Therefore it was recognized t h a t t h e e f f e c t s on ozone formation of a lka ne s and t h e s u b s t i t u t i o n of other classes of o r g a n i c s f o r a lka ne s r q u i r e d addit i o n a l i n v e st i g a t i o n ( r e f s . 47,49,52). Alkanes and other lcwer r e a c t i v i t y o r g a n i c s were shown to becare r e l a t i v e l y more e f f i c i e n t i n producing ozone a t h ig h e r ratios to nitrogen oxide carpared to alke ne s and other highe r r e a c t i v i t y o r g a n i c s ( r e f . 47,49). I n a s u b q u e n t study involving mixtures of several alkanes, a l k e n e s and aranatics with n i t r o g en oxide s s u b s t i t u t i o n of a lka ne s or a r m t i c s f o r al k en es a t lawer hydrocarbon to nitroge n oxide ratios reduced ozone f o n m t i o n ( r e f . 52). These r e s u l t s were c o n s i s t e n t w ith t h e earlier s t u d i e s t h a t used less c m p l e x systems ( r e f s . 47,49). These experimental studies a t t r a c t e d the a t t e n t i o n of p h o t c c h m i c a l mdelers i n t h e 1980's ( r e f s . 53-55). Photochemical models were used to i n v e s t i g a t e the e f f e c t s of o r g a n ic ccmposition a s well as o r g anic canpcunds to nitroge n oxide ratios with p a r t i c u l a r i n t e r e s t i n ozone-forming p o t e n t i a l . The azone-forming p o t e n t i a l of mi x t u r es of r+kutane, prcpene and carbon m n o x i d e (with snall i n i t i a l co n cen t r at i o n s of aldehydes, hydrogen pe rioxide , ozone, peroxylacetyl n i t r i t e and n i t r c u s a c i d ) were inve stiga te d w i t h nitrogen oxide c o n c e n t r a t i o n s s e l e c t e d t o g i v e ratios of 4.3/1, 53).
me
13.9/1 and 43/1 ( r e f .
r e l a t i v e ozone-forming p o t e n t i a l s of n-tutane t o prcgene inc re a se d
140 w i t h increasing hydrocarbon to nitrogen oxide ratio f r a n 0.14 a t a 4.3/1 ratio t o 0.34 a t a 43/1 ratio.
Another approach to estimating ozone-forming p o t e n t i a l
involved a d d i t i o n of prcpane or trans-2-htene
to two d i f f e r e n t n-txltane-pre
pene-~4( c a r p o s i t i o n mixtures a t carbon c o n t e n t s q u a 1 to 10% o f the i n i t i a l carbon content of the mixture ( r e f . 52). The oxidant-forming p o t e n t i a l was
evaluated by determining the m n t of the i n i t i a l mixture which had to be subtracted to restore the ozone concentration to its o r i g i n a l level.
For both
mixtures it was f m d that the ozone-forming p o t e n t i a l of trans-2-txltene t o prcpane decreased d r a s t i c a l l y with increasing ratio. For exanple t h e r e l a t i v e omne-forming p o t e n t i a l of trans-2-htene to prcpane was 20.9 and 12.7 a t a ratio of 4/1 f o r the two base mixtures carpared t o 5.1 and 2.4 a t a ratio of 40/1. Higher hydrocarbon to nitrogen oxide ratios were considered to occur as a i r masses are transported downwind of urban sarces. Therefore, the ozoneforming p o t e n t i a l of t h e lcwer molecular weight alkanes was concluded to beccme much mre important relative to a l k e n e s a s a i r masses are transported d m i n d
(ref. 53). I n a s u b s q u e n t modeling study a n i n i t i a l mixture was developed based on snbient a i r hydrocarbon measurments i n Atlanta GA ( r e f . 54). S i x hydrocarbons were t r e a t e d e x p l i c t l y i n the mechanisn. Sunmer daytime c o n d i t i o n s were used. Isopleths of maximcan ozone concentrations were develcped modeling the i n i t i a l mixture a t ratios f r a n 3/1 t o 30/1. l M l v e individual o r g a n i c s were added one a t a time to this mixture a t a concentration q u i v a l e n t t o 10% of the carbon c o n t e n t of the mixture. The d i f f e r e n c e i n maximum ozone c o n c e n t r a t i o n s a t t a i n e d was used a s the m a s u r e of ozone-forming p o t e n t i a l f o r these organics. Ethane was the least e f f e c t i v e organic i n ozone f o r m t i o n w h i l e a t laver ratios the a d d i t i o n of ethene, prcpene, trans-2-butene, E x y l e n e , formaldehyde and acetaldehyde a l l caused large i n c r a e n t s i n ozone concentrations. prcpane, ?butane, toluene, methanol and ethanol a d d i t i o n caused rnoderate incremental i n c r e a s e s i n ozone. H m v e r , t h e ozone concentration i n c r a n e n t s f o r those o r g a n i c s which were l a r g e a t low ratios decreased r a p i d l y w i t h i n c r e a s e i n ratio. For example, a d d i t i o n of trans-2-butene caused a n increment of 106% i n t h e 03 concentration a t a 3/1 ratio, a n 03 increment of 11%a t a 10/1 ratio and a 03 incranent of 2% a t a 30/1 ratio. Similar behavior was c a l c u l a t e d f o r ethene, propene, E x y l e n e , fonmldehyde and acetaldehyde. The increments i n 03 r e s u l t i n g f r a n a d d i t i o n s of prcpane and n-txltane were mall a t low ratios but decreased more slowly with increasing ratio. A t ratios above 10/1 and 20/1 toluene and m x y l e n e a d d i t i o n s r e s u l t e d i n decreases i n maximum ozone concentrations. overall t h e increments i n maximum ozone concentrations r e s u l t i n g f m n t h e i n c r e a s e s of 10% i n the carbon c o n t e n t s of the mixtures a t ratio above 10/1 f e l l w i t h i n +lo% f o r a l l twelve organics. I t was concluded t h a t the ozone forming p o t e n t i a l of ozone
141 c a n be r e l a t e d t o t h e rates of r e a c t i o n of hydroxyl radicals w i t h o r g a n i c s a t The negative e f f e c t s of t o l u e n e and m x y l e n e on
lw,but not a t high r a t i o s .
ozone formation a t higher ratios was a t t r i i x t e d to sane of their products, t h e
cresols and t h e aromatic aldehydes, serving as s i n k s f o r n i t r o g e n o x i d e s ( r e f . 53). It was concluded t h a t a t t h e higher alkene to n i t r o g e n oxide ratios trans-2-butene becaws less e f f e c t i v e a t forming o m n e than ethene because of t h e r a p i d consunption of t h e ozone a s it is p r a c e d by i n t e r n a l l y d o u b l e b a s e d alkenes ( r e f . 54). Because of t h e importance of removal of n i t r q e n oxides, a r e a c t i v i t y para-
meter based on both ozone formation and n i t r i c oxide consumption h a s been proposed ( r e f . 5 5 ) . A l i m i t i n g i n c r e n e n t a l r e a c t i v i t y a s the incremental o r g a n i c concentration approaches zero also was suggested.
These concepts were a p p l i e d
t o a d d i g or s u b s t r a c t i n g s i x o r g a n i c s to a four-hydrocarbon-NOk
mixture.
The
i n c r e m n t a l r e a c t i v i t i e s decreased w i t h i n c r e a s i n g r e a c t i o n time w i t h those o f toluene beccrnirq negative. always negative.
me
The i n c r e n e n t a l r e a c t i v i t y of benzaldehyde was
increnrental r e a c t i v i t y of trans-2-butene
also becam nega-
T h i s effect was a t t r i t x t e d more to t h e high
t i v e a t lorqer r e a c t i o n tines.
p e r x q a c e t y l n i t r a t e formation serving a s a n NO, sink than to the d i r e c t r a p i d r e a c t i o n of trans-2-butene
with ozone ( r e f . 5 5 ) .
No higher molecular weight alkanes were i n v e s t i g a t e d i n the s t u d i e s discussed above ( r e f s . 53-55).
Higher molecular weight a l k a n e s can form s u b s t a n t i a l
alkyl n i t r a t e yields ( r e f . 41).
Both r a d i c a l sources, t h e a l k y l p r o x y r a d i c a l s ,
and nitrogen dioxide are r e m v e d by the formation of a l k y l n i t r a t e s ( r e f . 42). However, t h e a l k y l n i t r a t e y i e l d s are dependent on the s t r u c t u r e of the alkane
imr.
Larger a l k y l n i t r a t e y i e l d s are a s s o c i a t e d with alkane isaners forming
secondary proxy r a d i c a l s ( r e f . 42).
As
a r e s u l t of high a l k y l n i t r a t e y i e l d s ,
i n t h e r e a c t i o n s of some of t h e h i g h molecular weight a l k a n e s o m n e y i e l d s shcllld decrease rapidly and becaw negative a s alkane t o n i t r o g e n oxide ratios
increase, H Y C R X Y W D N AND NITRCGEN OXIDE MEFSUREMENTS AT GKXJND
LEVEL RJRAL/RlXlTE SITES
Measuranents of hydrocarbons obtained on s a n p l e s c o l l e c t e d a t rural/ranote l o c a t i o n s i n t h e u n i t e d S t a t e s between 1975 and 1982 are t a b u l a t e d i n Table 2 ( r e f s . 4,27,56-63).
The molecular weight range f o r carpcunds r e p o r t e d covered
d i f f e r s among t h e s e s t u d i e s .
For sane s t u d i e s only i d e n t i f i e d canpounds are
r e p o r t e d ( r e f s . 4,55, 57,61). I n o t h e r s t u d i e s i d e n t i f i e d and u n i d e n t i f i e d ccanpounds are included ( r e f . 37, 59-61,63).
I n one study o n l y biogenic hydro-
carbons a r e i d e n t i f i e d , b u t total normethane hydrocarbon c o n c e n t r a t i o n s are given ( r e f . 2 7 ) . I n scme s t u d i e s m e a s u r m n t s of o n l y a few a l k a n e s above the pentanes are included ( r e f s . 56-58).
I n s e v e r a l s t u d i e s only t h e c6 to c8
aromatic hydrocarbons are included ( r e f s . 56-58,62)
but i n tw of t h e s e s t u d i e s
142 Table 2.
Non-mthane Hydrocarbon Concentrations Measured a t G m n d level Rural/Ranote Locations i n the United S t a t e s
m i a n or ( m a n Concentration), pgbc Total Month
Alkanes
Alkenes Armtics Ident. m t a l
m a t ion
Year
(C7-Cg)
(Bigenic) (c6-C~)
Glaqcw, I L
7-8/75
NAa(16)
1.0
0.7
NMHC NMHC Ref. -56
95 51
NA 82 NA 112 <60 -
49
NA
58
116
121
60
136
170
60
NA (8.)
33
NA (3.) NA 14.(5.) 25 (17) 1.6(NA) NA 4. (NA) NA
31
8.(4.) 9.(7.)
57
Elk ton, MD
8-9/75
NA (16)
Belfast,
6-7/75
Central FL
Jetmore, KA
5/76 4-5/76
Robinmn, IL
6-7/77
NA 51 49 NA
a. picnic area
1/78
86(73)
b. forested
1/78
82(66)
2.5
18(3)
34(18)
48
5.
15(3)
20
88
104
61
7-9/78
NA
NA
NA(<.l)
NA
NA
65
27
7-8/80
NA
NA
NA(8.5)
NA
NA
100
27
36
NA
62
27
NA
62
(10) (29) (49) (37.5)
<0.5 4.5
d' 1.
3.(NA)
13
58 59 4
Jones S t a t e pk.
area
S m k y M t . Natl. Pk. 9/78 (Sevier Co,
TN) Central SD
Blue Ridge MT, VI Pawnee Grasslands, CO
6/80 N i w o t Ridgerm 8/9-11/
NA(21) NA(16)
82 Smth. Appalachian
9/81/ t o 10/82 12.1(9.4) b. Grandfather M t . 30.6(24.8) c. L i n v i l l e Gorge 22.6(17.8) MT, NC
a. Roan M t .
d. Rich M t .
22.5(17.3)
e. Deer pk.
24.2(19.4)
a not available
b not meamred
1.0 0.8
26(0.4) 5.6(1.1)
3.4(3.1) 6.5(5.8)
19 44
40 79
1.0
6.6(5.)
4.6(4.01) 35
85
63 63 63
1.0 1.0
2.8(1.1) 3.0(0.5)
4.8(4.1) 5.4(5.0)
73 68
63 63
31 34
143 benzene and 0-xylene are not l i s t e d ( r e f s . 56, 57) w hile i n a nothe r study only benzene and t o l u en e are r ep o r t ed ( r e f . 6 2 ) . The total i d e n t i f i e d non-methane hydrocarbons re porte d range f r a n 13 to 136 p@c. This is a wide range even t ak i n g i n t o c onside ra tion the a n a l y t i c a l limitations d i sc u s s ed above. Indeed, t h e 2nd lcwest va lue f o r total i d e n t i f i e d non-methane hydrocarbons a t Roan Mountain ( r e f . 63) and the two h i g h e s t va lue s
a t Jones S t a t e Park, Texas ( r e f . 60) involved use of very similar a n a l y t i c a l I n part the se d i f f e r e n c e s are reduced i f
c a p a b i l i t i e s by the smne laboratory.
u n i d e n t i f i e d hydrocarbons are included ht even f o r the total non-methane hydrocarbons, i d e n t i f i e d and u n i d en t i f i ed , a four-fold range of c onc e ntra tions f r a n 40 t o 170 p&c h a s been reported. The d i f f e r e n c e s i n hydrocarbon concent r a t i o n s amng these s t u d i e s may r e s u l t f r a n one or more of the follcwing f a c t o r s ( a ) t h e d i f f e r e n c e s i n a n a l y t i c a l technique as a lre a dy disc usse d b r i e f l y above (b) d i f f e r e n c e s i n "remoteness" of sampling sites ( c ) seasonal v a r i a t i o n s i n hydrocarbon c o n cen t r at ions. I t is d i f f i c u l t to assess the "renoteness" of t h e sites where hydrocarbon
m a s u r a n e n t s have been md e.
One example is t h e " five remote sites i n north-
western North Carolina" ( r e f . 6 3 ) .
Although a l l f i v e sites are designed as
renote, t h e m a n Mmntain l o c a t i o n is s t a t e d to be "probably geographically the most m t e sanpled &r i n g t h e stUdy". The average age f o r the anthropogenic hydrocarbons reaching t h es e r m t e sites w a s estimated a s 3 to 4 hours.
At
N i w o t Ridge, CO it h a s been clear that t h e "renoteness" of the s i t e i n terms of
ozone and its p r ecu r s o r s depended o n whether the wind f l m is f r a n the west or f r a n t h e east.
I f the flcw w a s f r a n t h e east much highe r pre c ursor concentrations
were m a s u r e d t r an s p o r t ed from the nearby Boulder-Denver urban areas ( r e f . 64). These examples are g i v en t o enphasize t h e ine xa c titude of the term "rarote" a s used i n the l i t e r a t u r e c i t e d . Differences i n the c onc e ntra tions of the n o m t h a n e hydrocarbons can be t h e r e s u l t of the degree of isolation or "raroteness" of v a r i w s of t h es e r u r a l sites f r m urban emissions, non-urban ve hic ula r
or non-urban s t a t i o n a r y scarce m i s s i o n s o f hydrocarbons. The t h i r d p os s i b l e explanation of the v a r i a b i l i t y of the non-methane hydrocarbon m i s s i o n s a t t h e s e r u r a l sites are seasonal e f f e c t s . Seasonal
e f f e c t s can be a ss o ci at ed w i t h i n cr eas es i n orga nic l i f e t i m e s a s the o x i d i z i n g
species d e c r e a s e s i n co n cen t r at i o n f m n sumner t o winter. Seasonal e f f e c t s also can r e s u l t f r a n d ecr eas es i n emission rates because of l m r te rrpe ra ture s or solar r a d i a t i o n i n t e n s i t i e s . They also can be caused by v a r i a t i o n s i n meteorological e f f e c t s such a s seasonal changes i n wind d i r e c t i o n r e s u l t i n g
144 i n d i f f e r e n t m i s s i o n stxrces impacting a site or changes i n mixing d e p t h i n f l u e n c i n g t h e accumulation of local emissions such a s a l k a n e s f r a n n a t u r a l gas/petrolemn related a c t i v i t i e s ( r e f . 4,60,62). s e a s o n a l r e s u l t s are a v a i l a b l e f r a n t h e study i n northwestern North C a r o l i n a ( r e f . 63).
Concentrations of the follcwing classes of hydrocarbons were p l o t t e d
i n t h i s study ( r e f . 6 2 ) v e r s u s month of t h e y e a r ( a ) sun of a l k a n e s , a l k e n e s and a r w t i c s ( b ) a c e t y l e n e ( c ) NO seasonal v a r i a t i o n s
-pinene ( d ) i s o p r e n e ( e ) u n i d e n t i f i e d species.
are e v i d e n t f o r the classes l i s t e d i n ( a ) or ( b ) but t h e
-pinene and iscprene p l o t s shw t h e expected s e a s o n a l i t y with large d e c r e a s e s i n c o n c e n t r a t i o n during the cooler m n t h s .
The u n i d e n t i f i e d species s h m a
weaker seasonal e f f e c t than does iscprene b u t enough of a seasonal e f f e c t to suggest t h e presence of
~ ~ 1 1 1biogenic 3
component ( r e f . 6 3 ) .
I n t h e s t u d i e s w i t h t h e mre ccmplete hydrocarbon s p e c i a t i o n , a l k a n e s make up 54 to 73% of t h e i d e n t i f i e d hydrocarbon ( r e f s . 59-61,63).
The percentage
a l k a n e s c o n s t i t u t e of total i d e n t i f i e d hydrocarbons by site are as follcws: C e n t r a l F l o r i d a ( r e f . 5 9 ) , 54%; Jones S t a t e Park (ref. 6 0 ) , i n c l u d i n g p i c n i c
area, 74%, and f o r e s t e d area, 60%; Mt.
( r e f . 6 3 ) , 64%; Grandfather M t .
65%; Rich M t .
M t . Natl. Park ( r e f . 6 0 ) , 55%; Roan
( r e f . 6 3 ) , 70%; L i n v i l l e Gorge ( r e f . 6 3 ) ,
( r e f . 6 3 ) , 73%; Deer Park ( r e f . 6 3 ) , 71%. AraMtic hydrocarbons
u s u a l l y were m a s u r e d a t h i g h e r c o n c e n t r a t i o n s t h a n a l k e n e s a t t h e r u r a l / r a n o t e
sites. The total n o m t h a n e hydrocarbons measured a t t h e r u r a l / r a n o t e sites l i s t e d i n Table 2 are a t about 10 to 20% of t h e c o n c e n t r a t i o n s r e p o r t e d w i t h i n U.S.
cities ( r e f . 65-67).
Alkanes c o n s t i t u t e d 50 to 60% of the nonmethane
hydrocarbons r e p o r t e d w i t h U.S. c i t i e s (ref. 6 6 ) . Hydrocarbon and Nitrogen Oxide Concentrations and Ratios a t Ground Level Rural/
Remote S i t e s I n mst of the i n v e s t i g a t i o n s a t r u r a l / r a n o t e sites c o n c u r r e n t hydrocarbon and n i t r o g e n o x i d e c o n c e n t r a t i o n s are not reported.
Total NWC c o n c e n t r a t i o n s
o b t a i n e d by Sumning 20 to 50 peaks c h r a n a t o g r a p h i c a l l y a t two d e t e c t a b l e peaks
a t two sites e r e a s f o l l w s ( a ) c e n t r a l South Dakota (240 km west northwest of P i e r r e ) , 65 ppbc, ( b ) western slopes of Blue Ridge M t s . (ref. 27).
,Virginia,
100 ppbc
The corresponding NO, c o n c e n t r a t i o n s r e p o r t e d we$e 1.2 ppb (ref.44,51)
and 2.3 p@ ( r e f . 51) r e s u l t i n g i n a NMHC t o N 4 ( ratio a t the South Dakota site of 54 and a t the V i r g i n i a site o f 43 (ref. 27).
A t a site i n a f o r e s t preserve
10 km w e s t of S t a t e College, PA t h e C3 to C10 anthropogenic hydrocarbon concent r a t i o n over a 4 day period i n July 1986 v a r i e d f r a n abcut 10 ppbc t o 40 ppbc ( r e f . 6 8 ) . Including t h e biogenic isoprene c o n c e n t r a t i o n s the t o t a l NMHC reported ranged f r a n 20 to 68 ppbc. The average N 4 ( d u r i n g t h e day was reported a t about 1 ppb so t h e NMHC t o NOx ratios v a r i e d f r m about 20 to 68 ( r e f . 6 8 ) .
145
These g r a n d level rural W C t o N4( ratios are nuch higher than urban W C t o NO, ratios in eastern and midwestern cities (ref.67).
W. Gemny the C2 to C5 hydrocarbon concentrations totaled 13 p@c and t h e corresponding N 4 ( concentration was 2.7 p@ so t h e mean total M C t o N% r a t i o would be 2 5 ( r e f . 69). A t t h e five Applachian Mcuntain sites the A t Deuselbach,
ratios of C2 to Cj hydrocarbons to total non-methane hydrocarbons ranged f r a n 0.21 t o .31 and averaged 0.25 ( r e f . 63).
I f this ratio is applied a t Deuselbach the
m a n t o t a l NlrMC t o N 4 ( ratio would be abcut 20. Hydrocarbon and Nitrogen oxide Measuranents i n the Tropospheric Background in the Northern Hemisphere Badcgrcund trcpospheric masurenents of hydrocarbons i n the Northern
me r e s u l t s l i s t e d are limited t o off shore sanples taken f r a n shipboard or f r a n a i r c r a f t a t midlatitudes to higher l a t i t u d e s , 30° to 75O N. Ihe p o s s i b i l i t y of a c o n t r i h t i o n f r a n cont i n e n t a l Scurces a l s o mst be considered f o r sane of t h e sanples taken off shore kut still not d i s t a n t fran continental scxlrces ( r e f . 73,74). Large seasonal variations in the concentration of ethane have been ShaJn to occur with Season in renote tropospheric q l e s collected between 30 and 75O N l a t i t u d e ( r e f . 75). Ethane concentrations in June and septenber are 40% of Hemisphere a r e tabulated i n Table 3 ( r e f . 70-76).
its concentration i n December and March. Substantial decreases between winter values and the spring and suTII113r concentration values f o r prcpane and n-butane have been observed a t the reasonably renote site a t Point Arena, CA (ref.74).
urge decreases in benzene and toluene concentrations f m n winter to suraner a l s o have been observed a t Cape Wares OR and Barrcm, AK ( r e f . 7 7 ) . mese seasonal variations in hydrocarbons contrast with lack of seasonal v a r i a t i o n s reported for anthrqmgenic hydrocarbons a t sites in northwestern North Carolina ( r e f . 63). Late fall/winter hydrocarbon masurenents have been reported over the
Atlantic ( r e f . 7 2 ) and P a c i f i c ( r e f . 7 4 ) .
me values f o r ethane, acetylene and
prcpane a r e i n good agreenent f o r these two studies.
The ethane, acetylene,
p r q a n e , butane and pentane concentration values observed i n April/May over the Atlantic ( r e f . 7 3 ) a t about 2 Km a l t i t u d e are s a n e h a t 1-r fall/winter values fran t h e shimoard sanples ( r e f . 7 2 ) .
than the late
146
Table 3.
Concentration Levels of Hydrocarbons in the Tropospheric Backgrand
at Middle and Higher Latitudes in the Northern Hemisphere Concentration of Hydrocarbon, in ppbc mation
sanpling period
40-64'N
NOV/DeC
2.3 to
Pacific
1975
2.9
N D N D N D
N D N D
ND
70
2.0
ND
0.5
ND
N D N D
ND
71
4 to 5
ND
0.6
2 to ca 0.75
ND
ND
ND
72
5.5
ND
73
3.3
ND
74
37'N
April 1977
30-50'N
Jan/Feb
Atlantic
1979
30-70°N
April/May
Atlantic
1980
30-40"N
Nov/Dec
E.Pacific
1981
30-EON
Sept 1984 i.72+0.42 DeC 1984 4.6220.70
ND
Mar 1985 4.4050.78 June 19R5 1.8620.24 CEt/NOV
Pacific
1983
a i-C4H10
kf.
ND
Pacific
40-50'"
c6 to % C5H13 Aran.
%
to 1.2 3 to 4
0.2 to 2
4.7
ND
0.2
to 0.6
0.24
0.92
to 3 0.9
(0.3
.1 to
.3a
to 1.5 2.4
0.15
2.9
ND ND
N D N D
ND
ND
75
N D N D
ND
ND
75
ND ND
N D N D
ND
ND
75
ND
ND
ND
ND
ND
75
ND
ND
N D N D
ND
0.8
76
ND
ND
ND
ND
147
The total C2 to C5 hydrocarbon measured over the North A t l a n t i c i n April/ May ranged f r a n 5 to 9 ppbc ( r e f . 73) wh i l e the total C2 t o C5 hydrocarbon measured over the P a c i f i c i n Nov/Dec averaged about 15 ppbc ( r e f . 74).
These
measurements ( r e f s . 73,74) d o not incllrde the hexanes and highe r a lka ne s nor any of t h e ammatics.
Total
C, to C, a m t i c hydrocarbons i n t h e P a c i f i c a t
mid-latitudes reported i n another study averaged 0.8 pgbc ( r e f . 76).
Hcuever, i n
the q u a t o r i a l p a c i f i c aromatic hydrocarbon c onc e ntra tions averaging abcut 8
p&c have been reported ( r e f . 62).
These high background a m t i c hydrocarbon
c o n c e n t r a t i o n s were a t t r i h t e d to v o l a t i z a t i o n of a rc m a tic s from seawater contaninated by marine t r a f f i c and o f f shore petrolem production ( r e f . 62). The total i d e n t i f i e d non-methane hydrocarbons a t s e v e r a l of the mre
remte c o n t i n e n t al sites ( r e f s . 58,63) i n t h e United S t a t e s (Table 2 ) were within the sirme range a s the backgrcund c onc e ntra tions disc usse d above ( r e f s . 62,73,74,76).
The acet y l en e co n cen t ra tions a t a nunber of continen-
t a l sites ( r e f s . 56,58,62,63) *re wi t h i n a f a c t o r of two of the a c e t y l e n e c o n c e n t r a t i o n s measured i n the b ack g r an d trcpsphere a i r ( r e f s . 71-74). Therefore, minimal contamination of the a i r measured a t these c o n t i n e n t a l
sites by v e h i a l a r m i s s i o n s appears to occur.
on
the other hand, t h e ethane and prcpane c onc e ntra tions m a s u r e d a t
s e v e r a l c o n t i n e nt al sites including Jehore, KA ( r e f . 4 ) , Jones S t a t e Park,
TX ( r e f . 6 0 ) and the Pawnee Grasslands,
CO ( r e f . 62) were f a c t o r s of f i v e
to t e n h i g h e r than i n b ack g r an d t r c p s p h e r i c a i r ( r e f s . 70-75).
Butane
and pentane c o n cen t r at i o n s also were high a t tw of these c o n t i n e n t a l sites ( r e f s . 4,60).
These sites were i d e n t i f i e d as being under t h e influe nc e of
n a t u r a l g a s / p e t r o l eu mr el at ed a c t i v i t i e s ( r e f s . 4,60,62).
S i m i l a r influe nc e s
were reported f o r ethane co n cen t r at i o n s measured a t a r u r a l site i n Southwestern Louisiana near n a t u r a l g a s wells ( r e f . 27) and on propane concentrat i o n s a t r u r a l sites near n a t u r a l g a s processing f a c i l i t i e s i n t h e Piceance Creek area of R i o Blanco C amt y , CO ( r e f . 61). These n a t u r a l gas/petroleun scurces c o n t r i h t e longer-lived al k an es a v a i l a b l e f o r t r a n s p o r t not only to a d j a c e n t r e g i o n s of c o n t i n e n t s ht over ad j ac e nt areas of ocean.
LOW c o n c e n t r at i o n s of halogenated substances have been measured i n the
b a c k g r a n d trcposphere i n t h e eastern P a c i f i c ( r e f s . 79,80).
The halogenated
substances with l i f e t i m e s of less than a year, (Table 1) and ( r e f . 3 4 ) , total abcut 150 p p t i n t h e t r cp o s p h er i c b ack g r an d of the Northern Hemisphere ( r e f .
80).
148
Acetone h a s a long atmospheric l i f e t i n e w i t h respect to r e a c t i o n w i t h
hydroxyl radicals (Table 1) and ( r e f . 3 4 ) . Its l i f e t i m e w i t h respect t o p h o t o l y s i s i n sane regions of t h e atmosphere is c a r p a r a b l e to that w i t h respect to r e a c t i o n with hflroxyl r a d i c a l s ( r e f . 81). Ihe concentration of acetone a t 35'N over t h e A t l a n t i c h a s been rreasured a t about 500 p p t (ref. 82).
Hydroxyl r a d i c a l r e a c t i o n w i t h prcpane h a s been c a l c u l a t e d to acccunt
f o r abcut half of t h e observed concentration of acetone ( r e f . 81). These r e s u l t s from trcpospheric background measuremnts suggest t h a t considerable v a r i a b i l i t y is p o s s i b l e i n the concentration of o r g a n i c s even over the oceans. me seasonal v a r i a t i o n s have been attrituted to t h e seasonal d i s t r i h t i o n s of hydroxyl radicals ( r e f s . 7 4 , 7 5 ) . Hcmever, v a r i a t i o n i n scurce s t r e n g t h s of emissions f r a n both c o n t i n e n t a l and oceanic mrces of p o l l u t i o n along with s h i f t s i n d i r e c t i o n s of flcm are l i k e l y to be s i g n i f i c a n t c o n t r i b u t o r s to o r g a n i c s over s o l ~ eoceanic regions. Relatively few n i t r o g e n oxide m a s u r e n e n t s are a v a i l a b l e i n t h e lcmer remote trcposphere.
At
maritime sites i n E i r e , Adrigole and -head concentrations between 0.2 and
5
Lighthouse, nitrogen oxide 0.5 ppb have been reported. These marithe
sites can be inpacted by polluted a i r masses transported f r a n t h e United
Kingdm and/or t h e continent ( r e f . 43). ASSUMED HYDROCARBON AND NITROGEN OXIDE OONCENTRATIONS I N TROFOSF'HERIC bDDELS
Non-methane hydrocarbons have been included i n the photochenical nodules of t h e troposphere used to c a l c u l a t e i n a n h r of t h e one-dimnsional -1s average mid-latitude mone concentrations i n t h e Northern hmisphere. R e s u l t s f r a n three of t h e s e modeling s t u d i e s w i l l be discussed h e r e ( r e f s . 83-85). The hydrocarbon and nitrogen oxide concentrations near t h e s u r f a c e based on assumed emission f l u x e s are t a b u l a t e d i n Table 4. Wxklers o f t e n a d j u s t concentrations to include other members of the srme series not included i n t h e simplified surrogate d e l s used.
H a e v e r , these s i m p l i f i c a t i o n s ignore
d i f f e r e n c e s i n m c h a n i s n s including r a d i c a l and/or nitrogen dioxide s i n k s involved i n mre d e t a i l e d chemical rrechanisns.
Arcmatics are excluded f r a n
a l l of t h e s e mechanisns although these are p r e s e n t i n s i g n i f i c a n t a n t s
ccanparable t o t h e a l k e n e s (Tables 2 and 3). The total n o m t h a n e concentrations selected range f r a n 4.1 ppbc i n a marine e n v i r o m n t .04 to 15.85 ppbc a t a c o n t i n e n t a l l o c a t i o n ( r e f . 85). The assuned marine concentration of n o m t h a n e hydrocarbons is lcmer than the observed values a t marine sites i n Table 3.
Zhe assumed c o n t i n e n t a l
L)
z
.d
a C e
t%
a u
El
.d
v
co
m
m
-?
C
v
co
In
d
9
0
‘9
0
?
m
Ln
d
B
v
B 0
‘c.
0
m
C
B
d
9
0
B
N
0
B
9
N d
m
9 v
m 0
In
r;
rl
‘9
9 N
rl
9 r;
9 Fl
rl
‘?
9 d
B 9 v
m
? rl
9
N
m
0
9
co
0
m N
4
rl
143
150
v a l u e s i n two of the s t u d i e s ( r e f s . 83,84) are l a u e r than t h e l a u e s t measured v a l u e s of nowmethane hydrocarbons i n r u r a l / r a n o t e sites (Table 2 ) . A l l t h r e e of these modeling studies appear c o n s i s t e n t i n p r e d i c t i n g a
moderate i n c r e a s e i n ozone f o r m t i o n w i t h a d d i t i o n of n o m t h a n e hydrocarbon
to methane-carbon monoxide-nitrogen o x i d e s systems.
I n two of the studies w ith
i n i t i a l s u r f a c e n i t r o g en oxide co n cen t r at i o n i n the 250 t o 400 p p t range, a 30% i n c r e a se i n sumertirre ozone co n cen t r at ion w ithin t h e pla ne ta ry bcundary l a y e r are p r e d i c t ed w i t h the a d d i t i o n of 8 ppbc of n m t h a n e hydrocarbon ( r e f s . 83,84).
I n the t h i r d study tests of t h e s e n s i t i v i t y of ozone production
t o v a r i a t i o n s i n non-methane hydrocarbon co nc e ntra tion are made ( r e f . 8 5 ) .
A
f a c t o r of tm changes i n NMHC co n cen t r at i o n when ( a ) nitroge n o x i d e s are belcw 4 ppb r e s u l t s i n -what less than a 30% change i n Ozone p r h c t i o n ( b ) nitrogen o x i d e i s 6.5 ppb r e s u l t s i n abcut a 50% change i n ozone production. ozone production w i t h no a d d i t i o n a l o v er n i g ht h i l d u p of hydrocarbons is pred i c t e d to i n c r e a s e f r a n 20 ppb a t 0.25 ppb of nitroge n o x i d e s t o 40 ppb a t 1 ppb of nitrogen oxide ( r e f . 85).
Higher s e n s i t i v i t i e s to i n c r e a s e s i n n i t r -
gen oxide o c c u r when n i t r o g en o x i d e s a r e l i m i t i n g , a t ve ry lcw nitroge n oxide c o n c e n t r a t i o n s, a s would be expected.
None of the s t u d i e s provide tests of
the e f f e c t s of charges i n hydrocarbon can p osition.
These models are n o t
a p p r c p r i a t e f o r u s e i n c o n t i n e n t a l r eg i o n s with varying s t r e n g t h mrces of hydrocarbons and n i t r o g en o x i d e s over r e l a t i v e l y s h o r t t r a n s p o r t dista nc e s. Under t h e se c o n d i t i o n s the three-dimensional re giona l &ls
de sc ribe d earlier
i n t h i s m& are much more a p p l i c a b l e ( r e f s . 28-31).
co~usIoNs 1.
Only a mall c o n t r i h t i o n to g r a n d l e v e l ozone c onc e ntra tions, perhaps a b c u t 10 ppb, o r i g i n a t e s i n the lower s t r a t o s p h e r e and is t r a n s p o r t e d thrcugh the trcposphere to t h e surface.
S h o r t e pisode s of 1cw fre-
quency do o ccu r where larger c o n t r i b u t i o n s of s t r a t o s p h e r i c ozone a t s u r f a c e l o c a t i o n s have been reported. 2.
?he n a t u r a l background c o n s i s t i n g not only of the s t r a t o s p h e r i c c o n t r i -
bution, b u t the i n s i t u ozone f o r m t i o n i n t h e trc posphe re f r a n n a t u r a l m t h a n e , carbon monoxide and n i t r o g e n oxide m i s s i o n s , is estimated to c o n t r i h t e 10 t o 20 ppb of Ozone a t g r a n d l e v e l i n the spring-simmer period. 3.
I f a d d i t i o n s of n i t r o g en oxide f r a n s u r f a c e m i s s i o n s of a n t h r c p g e n i c
or biogenic o r i g i n i n cr eas e n i t r o g en o x i d e s t o the 1 ppb c onc e ntra tion l e v e l , i n c r en en t al ozone p r h c t i o n of 20 ppb over the c onc e ntra tions c i t e d above are p r ed i ct ed .
151 4.
The h i g h e r monthly average p e a k - h a r ozone c onc e ntra tions observed r e g i o n a l l y over t h e e a s t e r n United S t a t e s are a t t r i b u t a b l e to addit i o n a l incremental photochenical ozone prochction w i t h i n t h e pla ne ta ry boundary l a y e r of a t least 20 to 25 ppb.
5.
on an e p i so d i c b a s i s ozone co n cen t r at i o ns during the
SUIoner
months
are on a r e gi o n al scale t o 100 ppb and above. 6.
On t h e geographical scale of urban plumes and other plumes, inc re w n-
t a l ozone production o f 50 to 100 ppb over re giona l background can be observed over r u r a l areas. An estimate f o r the i n t e r i o r region of the United States i n d i c a t e s that urban plumes can c o n t r i b u t e such incremental ozone co n cen t r at i o n s over 5 to 10% of t h e surfa c e areas.
7. Rapid v e r t i c a l t r a n s p o r t of ozone, sl-r r e a c t i n g hydrocarbons, c a h n monoxide and n i t r o g en o x i d es t h r a g h a c t i v e cumulus cloud u p d r a f t s can result i n l o c a l and/or r eg i ona l s u r f a c e c o n t r i h t i o n s of ozone and p r ecu r s o r s to i n s i t u ozone production i n the 1-r f r e e troposphere.
a.
Lower raqe t r a n s p o r t can result i n ozone and p r e c u r s o r s e n i t t e d
mny hundreds of k i l o met er s away c o n t r i b u t i n g on t h e same and subs q u e n t d a y s to Ozone co n cen t r at i o n s i n d i s t a n t re c e ptor areas. 9.
Continental s u r f ace emissions of o r g a n i c s w i t h longer l i f e t i m e s , a month to s e v er al months, c o n t r i h t e to ozone formation i n the Northern Hemisphere mid-latitude tropospheric background.
10. One-dimensional t r cp o s p h er i c models have been used to test o u t t h e
e f f e c t s of a nunber of parameters on ozone formation. Such mdels can be u s e f u l p a r t i c u l a r l y i n renote marine or l i g h t l y populated continen-
t a l areas. 11.
I n more heavily populated c o n t i n e n t a l areas and a d j a c e n t areas of oceans, three-dimensional models with both d e t a i l e d meteorological and c h e n i c a l m c h a n i s t i c modules are necessary to a d q u a t e l y p r e d i c t
ozone concentration d i s t r i b u t i o n s .
These models r q u i r e -11
grid
e l a n e n t s w i t h accurate r ep r es en t at i o n of surfa c e f l u x e s of p r e c u r s o r s t o make a c c e p t ab l e p r e d i c t i o n s of ozone concentrations.
152
1.
E. R. Reiter "Stratospheric-Tropospheric Exchange ProcesSeS, "
Rev. -
Geophys. Space Phys.
2
(1975) 459-473.
2.
R. J. Reed and E. F. Danielsen " F r o n t s i n t h e v i c i n i t y of the Trcpcpause," Arch Meteorol. Geophys. Bioklin. Series A, B11 (1979) 1-7.
3.
E. F. Danielsen and V. A. Mohnen " P r o j e c t Dustorm Report: Ozone Transport i n Measurgllents and Meteorological Analyses of Trcpopause Fomings," J Geophys. 87: (1977) 5867-5877.
situ
e.
4.
W. V i e z e e , W. 0 . Johnson and H. 0 . s i g h " Airborne W a s u r e m n t s of S t r a t o s p h e r i c Ozone I n t r u s i o n i n t o the Troposphere over t h e u n i t e d S t a t e s , " F i n a l R e p o r t SRI P r o j e c t 6690, CRC-APRAC C o n t r a c t No. WA-15-76 (1-80). Coordinating Research Council Inc. 219 Perimeter Center Parkway, A t l a n t a , GA 30364 (1979).
5.
W. B. Johnson and W. Viezee " S t r a t o s p h e r i c Ozone i n t h e Lmer Troposphere I. P r e s e n t a t i o n and I n t e r p r e t a t i o n of A i r c r a f t Measuranents," Atmos. Environ. (1981) 1309-1323.
6.
W. V i e z e e , W. B. Johnson and H. R. S i g h " S t r a t o s p h e r i c Ozone i n the Lmer Trcposphere - 11. Assessnent of Dwnward Flux and Gramd-Level Impact," Atmos. m v i r o n 17 (1983) 1979-1993.
7.
A. P. Altshuller "The R o l e of Nitrogen o x i d e s i n Nonurban Ozone Formation i n t h e P l a n e t a r y Roundary Layer o v e r N. America, W. (1986) Eurcpe and Adjacent Areas of Ocean, "Atmos. m v i r o n .
-
3
245-268. 8.
H. Levy " N o r m a l Atmosphere: Large Radical and Formaldehyde Concentrations P r e d i c t e d , " Science 173 (1971) 141-143.
9.
J. Fishnan "Ozone i n the Troposphere," I n S t r a t o
( e d i t e d by V h i t t e n R. C. and S. P r a s a d ) , e Nostrand Reinhold, New Yo& (1984). 10.
n
h e r i c Ozone -
A. P. A l t s h u l l e r "Estimation of t h e National Backqramd of m n e p r e s e n t a t S u r f a c e Rural Location," 2. A i r P o l l u t . Control Assoc. (1987) 1409-1417.
~-
11. G. K. Greenhut, J. K. S. Ching, R. Pearson Jr. and T. P. Repoff "Transport of Ozone by Turbulence and Clouds i n a n Urban Boundary J GeOphyS. ReS. (1984) 4759-4766. Layer," -
-
12.
as
and D. A. Brewer J.K.S. Chins, S . T. Shiplev, E. V. m-11 armU1u.s Cl&d Venting of Mixing Layer Ozone," proceed Ouadrennial Ozone symposium, H a l k i d i d i , G r e e c e d
Of
13.
A. P. A l t s h u l l e r " S a w Characteristics of Ozone F o r m t i o n i n t h e Urban Plume of S t . Lais, Mo." Atmos. Emiron. 22 (1988) 499-510.
153 14.
G. W. S p i c e r "Nitrogen Oxide Reactions i n the urban p l m of BOston," Science 215: (1982) 1095-1097.
15.
C. W. Spicer, J. R. Koetz, G. W. Keigley, G. M. sverdmp and G. F. W a d "Nitrogen Oxide Feactions Within Urban plumes Transported Over the Ocean, "Battelle-Columtus Report to E n v i r o m n t a l S c i e n c e s Research Laboratory, U. S. E n v i r o m n t a l
P r o t e c t i o n Agency, Research T r i a r q l e Park, N. C. 27711, Contract 68-02-2957 (1982).
NO.
16.
C. W. S p i c e r and G. M. Sverdrup "Tracer Nitrogen Chenistry During t h e Philadelphia o x i d a n t Enhancernent Study, 1979," Battelle-Oolmmbus Report to t h e o f f i c e of A i r Q u a l i t y Planning and Standards, u. S. E n v i r o m n t a l P r o t e c t i o n Agency, Research Triangle Park, N. C. 27711 (1981).
17.
C. W. S p i c e r , D. W. Joseph and P. R. S t i c k s e l "An I n v e s t i g a t i o n of t h e Ozone P h m of a S m a l l City," 2. A i r P o l l u t . Control. As=. 2: (1982) 278-281.
18.
K. Ganesan "Mathmatical Modeling of Oxidant production
in
PhD. D i s s e r t a t i o n , Washington State University, (3311ege of Engineeri q (1981). 19.
F. W. L m n n , B. Nitta, K. Ganesan and A. C. Lloyd "Modeling P o t e n t i a l Ozone Impacts f r a n Natural Sources 111. ozone Modeling i n T a n p d S t . Petersburg, F l o r i d a , " Atmos. mviron. E: (1984) 1133-1143.
20.
F. LULMM, A. C. Lloyd and B. Nitta "Modeling Potential Ozone I n p a c t s f r a n Natural sources 11 Hypothetical Biogenic HC mission Scenerio Modeling, It Atmos. Environ. (1983) 1951-1963.
21.
-
-
17:
J. F. Meagher, N. T. Lee, R. J. Valente and W. J. earlthurst "Rural
Ozone i n t h e S a t h e a s t e r n United states. 60 5-6 15.
Atrnos. Environ.
21:
(1987)
22.
L. H. J. M. Janssen, "Mixing of Ambient A i r i n a Plume and its E f f e c t s on t h e Oxidant of NO, "Atmos. m v i r o n . 20: (1986) 2347-2357.
23.
D. L. Blumenthal, J. A. McDonald, W. J. Keifer, J. B. T a m e r d a h l , M. L. Saeger and J. H. mite "Three-Dimensional P o l l u t a n t D i s t r i h t i o n and Mixing Layer S t r u c t u r e i n t h e Northeast U.S. Sunnary of S u l f a t e Rgional Experiment (SURE) A i r c r a f t Measurements," A ~ S .m v i r o n . (1984) 733-749.
Is:
24.
F. M. Vukovich, J. Fishnan and E. V. B r a e l l I' The Reservoir o f Ozone i n t h e B a n d a q Layer of t h e Eastern United S t a t e s and its P o t e n t i a l Impact on t h e Global ozone Budget," J. Geophys. E. 90: (1985) 5687-5698.
154
25.
C. E. Decker, L. A. Ripperton, J. J. B. Wrth, F. M. Vukovich, W. D. Bach, J. B. " r e r d a h l , F. S m i t h and D. E. Wagoner "Fbrm-
a t i o n and T r a n s p o r t of Oxidant Along Gulf C o a s t and i n N o r t h e a s t e r n (1976).
U. S. EPA Report 450/3-76-033
26.
R. B. Evans ''The ( b n t r i t u t i o n of Ozone A l o f t t o S u r f a c e Omne Maxima," PhD. T h e s i s , U n i v e r s i t y of North C a r o l i n a a t Chapel H i l l , School of P u b l i c Health, Dept. o f Environmental Engineering (1979).
27.
N. A. K e l l y , G. T. Wslff and N. A. F e m n "Saurces and S i n k s of Ozone i n R u r a l Areas," Atms. h v i r o n . g: (1984) 1251-1266.
28.
0. Hov, E. Hesstvedt and I.S.A. I s a k s e n "Long-Range T r a n s p o r t of Tropospheric Ozone," Nature 273: (1978) 341-344.
29.
A. E l l i a s s e n , 0. Hov, I.S.A. Isaksen, J. S a l t b o n e s and F. S t o r d a l "A Lagrangian Lmg-Range T r a n s p o r t Model w i t h A b m s p h e r i c Bcundary
Layer C h e n i s t r y ,
"2.pppl. Met. 21:
(1982) 1645-1661.
30.
R. G. Lanb, "Numerical Simulation of Photochemical Air P o l l u t i o n i n the Northeastern u n i t e d states: A p p l i c a t i o n s , "u. S. EPA R e p o r t 600/3-86/038 ( 1986)
31.
R. G. Lanb "Design and A p p l i c a t i o n of t h e R e g i o n a l o x i d a n t M o d e l (R@l)," Presented a t North Arnerican Oxidant Symposium, mebec, Canada (1987).
32.
J. H. Novak and J. A. Reagan "A Canparison of Natural and Mannade
33.
F. M. vukovich and J. Fishrdn "The C l i m a t o l ~of Sumrertime 0 3 and So2 (1977-1981), A m o s . h v i r o n . 20: (1986) 2423-2433.
34.
R. Atkinson " K i n e t i c s and Mechanisns of the Gas-Phase Reactions of
Eanission Inventory Necessary f o r R e g i o n a l Acid Deposition and Oxidant Modeling," Presented a t 7 9 t h A i r P o l u t i o n Control A s s o c i a t i o n Annual Meeting, Minneapolis, Minn. (1986).
t h e Hydroxyl R a d i c a l w i t h Organic Canpounds Under Atmospheric Rev. E: (1985) 69-201. Conditions,"
e.
35.
R. Atkinson and W. P. L. C a r t e r " K i n e t i c s and Mechanisms of the G a s p h a s e Reaction of Ozone w i t h Organic Caqcunds Under Atmospheric Conditions," Rev. (1984) 437.
-.
z:
A. M. Winer, R. Atkinson and J. N. P i t t s Jr.
36.
" Gaseous Nitrate Radical: W s s i b l e Nightime Atnospheric Sink f o r Biogenic Organic Canpounds," Science 224: (1984) 156-159. --
37.
R. Atkinson, C. N. Plum, W. P. L. Carter, A. M. Winer and J. N. P i t t s , Jr. "Rate Constants f o r the Gas-phase m a c a t i o n s o f Nitrate R a d i c a l s w i t h a Series of Organics i n A i r a t 298+1K, "J. Phys. Chen. (1984)
as:
1210-1215.
155
38.
R. Atkinson, W. P. L. Carter, C. N. Plum, A. M. Winer and Jr. " K i n e t i c s of t h e Gas-phase Reactions o f No3 Radicals with a Series o f Aromatics a t 269+2K," 2. @ i ~ Kinet. 2: (1984) 887-898. J. N. P i t t s ,
39.
x.
R. Atkinson, S. M. A s c b n n , A. M. Wiser and J. N. P i t t s , Jr., "Kinetics and Atnospheric I m p l i c a t i o n s of the Gasphase Reactions of N+ Radicals w i t h a Series of Monoterpenes and Related Organics 21 294+2K," m v i m . mchnol. 2: (1985) 159-163.
g.
40.
R. Atkinson, S.M. Aschmann and M. A. Goodman " K i n e t i c s of t h e G a s p h a s e Reaction of N& Radicals w i t h a series of Alkvnes. Haloalkenes, and a,B U n G t u r a t e d Aldehydes, I n t . 2. C h e n . ' K i n e t . 19: (1987) 299-307.
-
41.
42. 43.
B. Shirinzadeh, C. C. bhy and D. 0. Dew "Diurnal Variation of t h e Oh Concentration i n ZLnbient Air, "Geophys. E. E. (1987) 123-126.
14:
W. P. L. Carter and R. Atkinson "Abmspheric Chanistry of Alkanes" Chm. 3: (1985) 377-405.
-J. -AtmOS. -
R. P r i m D. Cunnold, E. Ramussen, P. Simmons. F. Alyea, A. Crawford, P. Fraser and R. Rosen 'Atnospheric Trends i n Methychloroform and t h e Global Average f o r t h e Hydroxyl Radical," Science 238: (1987) 945-950.
--
44.
A. J. Haagen-Smit, C. E. Bradley and M. M. FDx," Ozone Formation i n Photochenical Oxidation of organic Substances," Ind. mgus. man. (1953) 2086-2089.
45.
A. P. A l t s h u l l e r , "Reactivity of Organic Substances i n Abnospheric Photooxidation Reactions," Air and I n s t . P o l l u t . 2. 2. (1966) 713-733.
46.
A. P. A l t s h u l l e r "An Evaluation of Techniques f o r t h e Determination
45:
g:
-
of t h e Photochemical R e a c t i v i t y of Organic Bnissions", (1966) 257-260.
Control A S S . 16: -
2. -A i r Pollut.
47.
A. P. A l t s h u l l e r , S. L. Kopczynski, D. Wilson, W. L m n a ~ nand F. D. S u t t e r f i e l d , " Photochenical R e a c t i v i t i e s of n butane and O t h e r P a r a f f i n i c Hydrocarbon", 2. A i r Pollut. contFol AS=. 19: (1969) 787-790.
48.
A. P. A l t s h u l l e r , S. L. Kcpczynski, D. Wilson, W. LonneMn and F. D. S u t t e r f i e l d "Photochemical R e a c t i v i t i e s of P a r a f f i n i c HydrocarbonNitrogen Oxide Mixtures Upon Addition of Prcpylene or Toluene," J Air P o l l u t . Control ASS. (1969) 791-194.
-
-- 19:
49.
A. P. Altshuller, S. L. Kapczynski, W. A. LOnnaMn, F. D. S u t t e r f i e l d and D. L. Wilson "Photochemical € & a c t i v i t i e s o f Aromatic HydrocarbonsNitrogen Oxide and Related Systens," ~m v i r o n sci. mhnol. 4: (1970) 44-49.
156
=.
50.
B. Dimitriades, E f f e c t s of Hydrocarbons and N i t ro g e n Oxides on photochemical .Smg F o r m a t i 0 6 "mviron. e l . 5: (1972) 253-260.
51.
S. L. Kopczynski, A. P. A l t s h u l l e r and F. D. S u t t e r f i e l d 'I photchemical & a c t i v i t i e s of Aldehyde- Nitrogen Oxide Systems," Environ. Sci. Technol. (1974) 909-918.
s:
--52.
S. L. KoDczvnSki. R. L. Kuntz and J. J. B u f a l i n i "Reactions o f
Canplex &d-roca&ns
Mixtures," Environ.
g. Technol. 2:
(1975)
648-653.
Dodae "Ozone-Formim P o t e n t i a l of L i a h t s a t u r a t e d Hydrocarbons," m v i r o n . ~ h n & . (1983) 308-3 11.
53.
J. J. B u f a l i n i and M. C.
54.
M. C. Dodge "Canbined E f f e c t s of Organic R e a c t i v i t y and NMHC/Nq( Ratio on Photochemical Oxidant Formation A k d e l i n g Study" ~ t m o s . Environ. g: (1984) 1657-1665. --
55.
W. P. L. Carter and R. Atkinson "An Experimental Study of Increment Hydrocarbon Reactivity", Environ. E.Technol. 2: (1987) 670-679.
56.
R. A. R a m s s e n , R. B. C h a t f i e l d and M. W l d r e n "Hydrocarbons and Oxidant Chenistry Observed a t a S i t e Near St. Louis, "U.S. EPA Report 600/7-77-056 ( 1977).
57.
R. A. Rasnussen, R. A , , R. B. C h a t f i e l d , M. Holdren and E. Robinson "Hydrocarbon Levels i n a Midwest @en-Forested Area," Technical
s.
x:
-
-
Report to Coordinating Research C a n c i l Inc. 219 Perimeter Center Drive, Atlanta, GA, 30346 (1976). 58.
K. Sexton and H. Wstberg "Normethane Hydrccarbon Ccn@osition of Urban and Rural Atmsspheres," Atmos. m v i r o n . g: (1984) 1125-1132.
59.
W. A. L O n m n , R. L. S e i l a and J.
60.
R. L. Seila "Nowurban Hydrocarbon Concentration i n Ambient A i r North of H a s t o n , Texas," U.S. EPA Report 600/3-79-010 (1979).
61.
R. R. Arnts and S. A. Meeks "Bioaenic Hvdrocarbon O o n t r i b t i o n to the Ambient A i r i n S e l e c t e d Areas," itmos. Environ. g: (1981) 1643-1651.
62.
J. P. G r e e n b e r s and P. R. Zimm?nnan "Normethane Hvdrocarbons i n Ranote, Continental and Marine Atmospheres," J. G&phys. E.
J.
=.
B u f a l i n i "Ambient A i r Hydrocarbon O m c e n t r a t i o n s i n Florida," Environ. Technol. 12 (1978) 459-463.
89:
(1984) 4767-4778.
157 63.
R. L. Seila, R. R. A r n t s and J. W. Buchanan " A m s p h e r i c mlatile Hydrocarbon Ccmposition a t Five Remote S i t e s i n
Northwestem North C a r o l i n a , " i n Transaction E m i r o r m e n t a l
ct of Natural Dnissions (Aneja V. P., ed) pp 125-140, Imps-A i r P o l l u t . Control Assoc. S p e c i a l t y Conf. Research T r i a n g l e Park, N. C. (1984) 64.
J. M. Roberts, F. C. Fehsenfeld, S. C. Lin, M. J. B o l l i n g e r , C. Hahn, D. I,. A l b r i t t o n and R. E. Sievers "Measuranents o f Aramtic Hydrocarbon R a t i o s and N9( C o n c e n t r a t i o n s i n the
Rural Trcposphere: Observation of Air Mass Photochemical Q u i p . and N 4 ( Remval", Atmos. Environ. (1984) 2421-2432.
Is:
65.
W. A. Lonntrnan "The Measuranent of Oxidant P r e m r s o r s and their R e l a t i o n s h i p t o Ozone Formation," p r e s e n t e d a t North American Oxidant symposium, Ouebec, Canada, Feb. 25 27, 1988.
-
-
66.
W. A. Lonneman "Conparison of 0600
67.
K. B a y u e s "A Review of NMOC, N4( and M D C m Ratios Measured i n 1984 and 1985, "U.S. EPA Report 450/4-86-015 (1986).
68.
M. T r a i n e r , E. J. W i l l i a m s , D. D. p a r r i s h , M. P.
69.
D. Perner, U. P l a t t , M. T r a i n e r , G. HUber, J. Dnmnond, W. J u n k e m n n , J. Randolph, B. Schubert, A. Volz, D. H. Ehhalt, K. J. Runpel and G. Helas "Measuremnts of 'rrcpospheric OH Concentrations: A Canparison of F i e l d Data w i t h M o d e l Pred i c t i o n s , " 2. Atmos. Chm. 5: (1987) 185-216.
70.
H. B. Singh, L. J. S a l a s , H. S h i g e i s h i and E. S c r i b n e r Atmospheric Halocarbons, Hydrocarbons and S u l f u r H e w f l o r i d e : G l o b a l D i s t r i h t i o n s , S c u r c e s and S i n k s , " Science 203: (1979) 899-903.
71.
D. Cronn and E. Robinson " T n p o s p h e r i c and Laver S t r a t o s p h e r i c Vertical p r o f i l e s of Ethane and Acetylene "Geophys. E. E. 6: (1979) 641-644.
7 2.
J. Rudolph and D. H. Ehhalt "Measuranents of C2-Cg Hydrocarbons
0900 AM Hydrocarbon Canposition Obtained f r a n 20 cities" Proceedings of 1986 EPA/APCA Symposium on Measuranent of Toxic A i r P o l l u t a n t s ( 1986).
Wr, E. J. A l l w i n e , H. H. Wsstberg, F. C. Fehsenfeld and S. C. Liu "Models and Observations of t h e Inpact of N a t u r a l Hydrocarbons on Rural Ozone," Nature 329: 705-707 (1987).
Over the North A t l a n t i c , " 964. 73.
2.
Geophys.
e.86:
(1981) 11, 959-11,
D. H. Enhalt, J. Rudolph, F. Meixner and U. Schnidt " M e a s u m n t s of S e l e c t e d C r C 5 Hydrocarbons i n t h e EEickgrcund "rcposphere: Vertical and L a t i t u d i u a l V a v i a t i u a l , " 2. Atmos. Chen. 2: (1985) 29-52.
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159
T. Schneider et al. (Editors),Atmospheric Ozone Research and its Policy Implications 1989 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands
TRENDS I N ATMOSPHERIC TRACE GASES
S.A.
PENKETT
U n i v e r s i t y o f East Anglia, Norwich, NR4 7TJ, U.K.
ABSTRACT Many measurement programs are now showing t h a t a l a r g e number o f atmospheric trace gases are increasing i n concentration. These i n c l u d e molecules which can increase the atmospheric temperature, molecules which can destroy ozone i n the stratosphere and molecules which can produce o r destroy ozone i n the troposphere. S i m i l a r l y there i s now f i r m evidence t h a t stratospheric ozone i s being depleted, p a r t i c u l a r l y a t high l a t i t u d e s , and suggestions t h a t tropospheric ozone i s increasing i n concentration i n much o f the northern hemisphere. P r e d i c t i n g the e f f e c t s o f these changes i n atmospheric composition i s very d i f f i c u l t , b u t they are u n l i k e l y to be b e n e f i c i a l .
INTRODUCTION It i s now known t h a t t r a c e gases a t l o w concentration have a c o n t r o l l i n g
i n f l u e n c e on many atmospheric properties.
Examples include ozone i n the
stratosphere a t concentrations i n the range 1 t o 10 ppmv ( p a r t s i n
lo6 by
volume), oxides o f nitrogen and c h l o r i n e compounds, which a t the ppbv (parts i n
lo9 by volume) l e v e l c o n t r o l the stratospheric ozone concentration, and oxides o f nitrogen a t the 0.1 ppbv l e v e l which e x e r t a l a r g e i n f l u e n c e on t h e concentration o f hydroxyl r a d i c a l s and ozone i n the troposphere.
I n addition t o
t h e i r chemical properties t r a c e gases can also e f f e c t the temperature o f the atmosphere through i n t e n s i f i c a t i o n o f the greenhouse e f f e c t . This includes carbon dioxide a t the 300 ppmv l e v e l , methane a t the 1.5 ppmv l e v e l , and many other gases i n c l u d i n g tropospheric ozone, a t the 1 t o 100 ppbv l e v e l . Concentrations o f trace gases i n t h e e a r t h ' s atmosphere are such t h a t they are capable o f being influenced s u b s t a n t i a l l y on a l o c a l , regional and even a global scale by anthropogenic emissions. Many examples o f high concentrations o f gases such as sulphur dioxide i n urban l o c a t i o n s are known, s i m i l a r l y ozone has been shown t o be formed on a very l a r g e regional scale during photochemical
More r e c e n t l y global concentrations o f some trace gases have been shown to be increasing r a p i d l y and approaching l e v e l s where e f f e c t s on stratospheric and tropospheric ozone can be episodes i n the s u m r i n Europe and the United States.
160 A review o f global increases f o r many trace gases was published i n
detected.
( r e f . 1) and informationpertinent to ozone i n both the troposphere and the stratosphere was published recently i n Nature ( r e f . 2). TRENDS I N TROPOSPHERIC OZONE AND PRECURSOR CONCENTRATIONS
Tropospheric ozone has two main sources, transfer from the stratosphere, where 90% o f the ozone i n the atmosphere resides, and i n - s i t u production i n the troposphere.
This l a t t e r i s caused by photolysis o f nitrogen dioxide i n
the presence o f other trace gases such as hydrocarbons and carbon monoxide.
NO2
>NO+O
hv
M+O+02NO + 0, CO + OH
>03+M
-> NO2 + 02 -> C02 +
H+02HO,
(1)
A < 400 nm
+ NO
H
> Ho2
-> OH
+
NO2
Ozone i s formed i n step (2) and removed i n step (3). Hydrocarbon and carbon monoxide oxidation by hydroxyl radicals (shown above) produces superoxide radicals (H02) which convert NO to NO, ozone t o accumulate.
i n reaction (61, allowing
Fishman e t a1 and more recently L i u ( r e f . 4 ) have shown
t h a t t h i s process continues to generate
ozone down to NO levels o f 50 pptv and
calculate t h a t the tropospheric source o f ozone i s as large as transfer from the stratosphere on a global scale.
I t i s sensible therefore to examine
whether ozone concentrations i n the lower atmosphere have been perturbed due to increasing emission o f precursor molecules w i t h time. Several reviews of ozone trends have been formulated recently (refs. 5 and 6 ) .
Probably the longest recent record o f data on ozone, which i s s t i l l
a c t i v e l y being collected, i s that from the network o f the Meteorological Service of the German Democratic Republic (GDR). This was comissioned i n 1952 and has been maintained a t 5 stations across the GDR u n t i l the present. A survey of the data collected between 1956 and 1984 was recently published i n the Journal o f Atmospheric Chemistry (ref. 1). A t Cape Arkona, situated on the B a l t i c coast (550N, W E , 42 m a l t i t u d e ) ozone concentrations a t ground level increased substantially throughout a l l months o f the year w i t h an average increase o f 2.6% per year over the period i n question. Trend rates o f +1.84% per year and +1.93% per year respectively were observed a t the Fichtelberg s t a t i o n o f the GDR network and the Hohenpeissenberg s t a t i o n i n the Federal Republic o f Germany (FRG) over the period 1972-1984.
The B a l t i c coast
161
data therefore could w e l l be t y p i c a l of the behaviour o f ozone i n the boundary l a y e r over l a r g e p a r t s o f Europe. This assumption was made by Volz and Kley ( r e f . 8) who have compared the Arkona data s e t w i t h a nuch e a r l i e r one c o l l e c t e d a t the Montourfs Observatory i n Paris between the years o f 1876 and 1905. A f t e r c a r e f u l v e r i f i c a t i o n o f the techniques used t o c o l l e c t the e a r l i e r data they produced the comparison p l o t shown i n Figure 1. T h i s c l e a r l y shows t h a t average ozone concentrations measured a t ground l e v e l f l u c t u a t e considerably from year t o year b u t t h a t no r e a l t r e n d was observed between the years 1876 t o 1905. However from 1956 onwards ozone concentrations increase so t h a t the y e a r l y average concentration measured i n the penultimate decade o f the twentieth century a t Arkona i s approximately twice t h a t recorded a t the beginning o f the century i n Paris. Figure 1 a l s o suggests t h a t much o f t h i s increase has occurred w i t h i n a r e l a t i v e l y s h o r t period o f t i m e (40 years). Data on the composition o f a i r i n former times can be e x t r a c t e d from c a r e f u l analysis o f p r e c i p i t a t i o n stored as g l a c i a l i c e and from a n a l y s i s o f gaseous a i r encapsulated by the ice. Figure 2 shows t h a t the n i t r a t e content o f snow, stored as i c e i n Alpine glaciers, has increased s u b s t a n t i a l l y since the l a s t century, probably by a f a c t o r o f f i v e , and t h a t most o f the increase occurred a f t e r 1940 ( r e f . 4 ) . Since these n i t r a t e concentrations w i l l r e f l e c t changes i n the NO, content o f a i r over Europe, then i t i s n o t unreasonable t o conclude t h a t the increases i n ozone concentration over Europe shown i n Figure 1 i s caused by increased emissions o f precursors, i n t h i s case NO and NO,. It i s also possible t h a t these higher emissions o f precursor molecules a r e a f f e c t i n g ozone i n remote areas since increasing n i t r a t e concentrations have also been observed i n Greenland i c e (ref.10). Analysis o f a i r stored i n Antarctica i c e showed a l a r g e increase i n the methane concentration over the l a s t one hundred years ( r e f . 11). There are no r e l i a b l e data on t h e concentration trends f o r t h e more r e a c t i v e hydrocarbons than methane b u t trends have been published i n 1988 ( r e f . 12) f o r carbon monoxide, which w i l l probably m i r r o r the non-methane hydrocarbon s i t u a t i o n to a l a r g e extent. The carbon monoxide data i n d i c a t e s t h a t concentrations are r i s i n g f a s t e s t a t mid-latitudes i n the Northern Hemisphere and t h a t s t a t i s t i c a l l y s i g n i f i c a n t trends o f approximately 1%per year are observed f o r the Northern Hemisphere as a whole. I n the Southern Hemisphere i t i s p o s s i b l e t h a t there i s no increase i n concentration, although Samoa a t 1205 does s h w a p o s i t i v e trend. These increases i n precursor concentrations are capable o f producing m r e ozone, a t l e a s t throughout much o f the Northern Hemisphere and data from some long running measurements o f ozone a t remote l o c a t i o n s tend to bear t h i s out.
162
30-0
-
'
0.0 1850
I
I
I
I
1
1875
1900
1925
1950
1975
2000
YEAR F i g . 1. Annual mean ozone concentrations a t Montsouris (1876-19101 and a t Arkona (1956-83 1. 0
0 0
k
loo 0 1860
lSe0
1900
1920
1940
I960
1980
YEAR
F i g . 2. Increase i n n i t r a t e i o n concentration i n melted g l a c i a l i c e c o l l e c t e d on the C o l l e G n i f f e t t i , Switzerland.
163 Ozone data has been c o l l e c t e d a t more remote s i t e s than c o n t i n e n t a l Europe i n both the Northern and Southern Hemispheres by the NOAA GMCC program since 1973 ( r e f . 13). 1.37
f
These suggest p o s i t i v e trends o f 0.76
f
0.6% yr''
and
0.61% y r - ' a t P o i n t Barrow i n Alaska and Mauna Loa, Hawaii r e s p e c t i v e l y
f o r the Northern Hemisphere s i t e s over t h e p e r i o d 1973-1984. hemisphere a negative t r e n d (-0.92
I n t h e southern
0.95% y r - l ) was recorded a t American
Samoa and v i r t u a l l y no t r e n d (-0.12 ?: 0.49% y r - l ) was recorded a t t h e South Pole. Trends i n ozone concentration between 0.5% and 3%yr''
have a l s o been
observed i n the free troposphere a t m i d - l a t i t u d e s i n the Northern Hemisphere ( r e f s . 14 and 15). Combined together these data do suggest t h a t the increase i n ozone concentration i s o c c u r r i n g on a very wide scale i n t i e Northern Hemisphere.
I t i s also p o s s i b l e t h a t the ozone concentration i s decreasing i n
the southern hemisphere, a1 though there i s much less evidence t o support t h a t concl us ion. CHANGES I N SEASONAL CONCENTRATION PATTERNS
Many o f the more r e a c t i v e trace gases i n the atmosphere show d i s t i n c t i v e seasonal v a r i a t i o n s .
This i s mostly associated w i t h t h e seasonal v a r i a b i l i t y
o f the f l u x o f photons which i n i t i a t e most o f the chemical changes observed i n t h e atmosphere. I n the case o f ozone, which i s a secondary p o l l u t a n t , seasonal change can be due t o d i f f e r e n c e s i n photochemical a c t i v i t y i n the troposphere o r due t o seasonal d i f f e r e n c e s i n the f l u x o f ozone from the stratosphere t o the troposphere.
The study o f Volz and Kley ( r e f . 8) has revealed major
d i f f e r e n c e s i n the seasonal v a r i a t i o n o f ozone a t ground l e v e l over Europe over the l a s t one hundred years. F i g u r e 3 shows a comparison o f the average seasonal v a r i a t i o n o f ozone observed a t Montsouris between 1876 and 1886 w i t h t h a t observed i n 1983 a t Cape Arkone on the B a l t i c coast o f the German Democratic Republic.
This
modern ozone seasonal p a t t e r n i s t y p i c a l o f many which are now observed a t many l o c a t i o n s i n Europe and elsewhere ( r e f . 16).
I t i s c h a r a c t e r i s e d by a
maximum i n the l a t e s p r i n g (May) w i t h a l a r g e overlap i n elevated concentrations i n t o the summer.
The summer bulge has been a t t r i b u t e d
c o r r e c t l y t o regional photochemical a c t i v i t y , b u t the s p r i n g maximum, which i s also observed a t very remote s i t e s ( r e f . 51, has up t o naw been a s c r i b e d t o increased i n p u t o f ozone from the stratosphere during t h a t season.
The study
by Volz and Kley ( r e f . 8 ) suggests t h a t t h i s may n o t be the complete answer since the unperturbed ozone concentrations shown i n F i g u r e 3 f o r Montsouris show only a small increase i n ozone o c c u r r i n g q u i t e e a r l y i n the y e a r
164
1
a
PI U
2 0
N
10
0
Montsouris 18'76-1886 I
I
I
I
I
I
I
I
I
I
I
J F M A M J J A S O N D F i g . 3. Average seasonal v a r i a t i o n o f ozone a t Montsouris (1876-86, south-west sector only) and a t Arkona. LO1
30C
200 b
L
8 8
z
100
0
1
1
1
1
JanF
1
M
A
1
1
1
I
M J JulA S 0 Time of year '80181
N
1
1
1
I
1
D b n F
I
,
M
A
F i g . 4. V a r i a t i o n o f PAN concentrations i n northern hemisphere background a i r a t 51ON.
I
165 (February to May) a t mid-latitudes i n the Northern Hemisphere.
It i s quite
possible therefore t h a t a substantial p a r t o f the presently observed seasonal change i n ozone concentration i s caused by tropospheric production, which w i l l maximise i n l a t e spring.
Regional photochemical a i r p o l l u t i o n w i l l produce
s i g n i f i c a n t l y higher l e v e l s i n the boundary l a y e r o f the atmosphere during the summer but i s u n l i k e l y t o s i g n f i c a n t l y increase winter concentrations shown i n the observations. Wide scale production o f ozone i n t h e f r e e troposphere away
from the ground surface sink i s almost c e r t a i n l y needed t o produce t h e observed differences i n ozone seasonal behaviour shown i n Figure 3.
Some
evidence to suggest t h a t t h i s may be occurring i s presented i n Figure 4 which shows the seasonal v a r i a t i o n o f peroxyacetyl n i t r a t e (PAN) observed i n 'clean' a i r a t 500N. PAN and ozone are formed simultaneously from the photochemical
degradation o f many carbon compounds containing two o r more carbon atoms. Studies made f o r many years a t H a m e l l i n southern England and i n t h e Netherlands show t h a t PAN concentrations maximise i n August and show minimum values i n December ( r e f . 17 and 18). A t Harwell, however, simultaneous measurements made o f the i n e r t t r a c e r CFC1, and CMeC13 allowed separation o f the t o t a l data set i n t o various categories ( r e f . 19).
For the cleanest a i r ,
i n d i c a t e d by concentrations o f the i n e r t t r a c e r molecules i d e n t i c a l t o those i n the background troposphere o f the northern hemisphere, PAN concentrations showed c l e a r evidence o f a maximum i n the spring months (Figure 5 ) .
The
maximum concentration o f PAN observed i n May would correspond t o the tropospheric production o f a substantial amount o f ozone since the r a t i o o f rates o f formation o f ozone t o PAN observed i n the UK and the Netherlands ranged from 30:l to 75:l ( r e f . 18 and 20). The t i m i n g o f the production suggests t h a t a t l e a s t p a r t o f the p r e s e n t l y observed ozone s p r i n g maximum i s due t o tropospheric chemistry
.
The main u n c e r t a i n t i e s i n t h i s argument concern the r a t i o o f formation rates o f the two molecules a t the end o f winter and t h e i r differences i n l i f e t i m e s i n the atmosphere.
I n t h i s respect PAN has a much longer l i f e t i m e
i n winter than i t has i n summer because the molecule i s thermally unstable. The l i f e t i m e o f ozone i s seasonally dependent however, i n the same sense. Estimating the amount o f ozone formed i n the troposphere throughout the year from PAN data can only be done successfully therefore w i t h the a i d o f a comprehensive model o f the o v e r a l l chemistry. There seems l i t t l e doubt t h a t increasing emissions o f many t r a c e gases, p a r t i c u l a r l y oxides o f n i t r o g e n and hydrocarbons, have perturbed chemical processes responsible f o r producing ozone on a l a r g e scale i n the northern hemisphere and t h a t troposphere ozone and many other trace gases are increasing i n concentration.
166
REFERENCES Atmospheric Ozone, 1985, WMO Global Ozone Research and M o n i t o r i n g Project, Report No. 16, World Meteorological Organisation Geneva, 1986. 2. C. Rogers, Nature, 332, 1988, 201. 3. J. Fishman, S. Solomon, and P.J. Crutzen, Tellus, 31, 1979, 432-446. 4. S.C. Liu, Paper presented a t NATO Advanced Workshop on Regional and Global Ozone I n t e r a c t i o n s and i t s Environmental Consequences, Lillehammer, June 1-5, 1987, Reidel, Amsterdam, 1988. 5. J.A. Logan, J. Geophys. Res. 90, 1985, 10,463-10,482. 6. R.D. Bojkov, J. Climate and Appl. Meteor., 25, 1986, 343-352. 7. U. F e i s t e r and W. Warmbt, J. Atmos. Chem., 5, 1987, 1-21. 8. A. Volz and D. Kley, Nature, 332, 1988, 240-242. 9. D. Wagenbach, K. Munnich, U. Schotterer and H. Oeschger, Annals o f Glaciology, 10, 1988, 182-187. 10. A. N e f t e l , J. Beer, H. Oeschger and F. Zurcher, Nature, 314, 1985,
1.
611-613.
11.
B. S t a u f f e r , G. Fischer, A. N e f t e l and H. Oeschger, Science, 22, 1985,
1386-1389. 12. M.A.K. K h a l i l and R.A. Rasmussen, Nature, 332, 1988, 242-245. 13. S.J. Oltmans and W.D. Komhyr, J. Geophys. Res. 91, 1986, 5229-5236. 14. W. Attmannspacher, Gesellschaft f u r Strahlen- und U m e l tforschung mbH, Munchen, BPT B e r i c h t 5/82, 1982, 12-17. 15. J.K. Angel1 and J. Korshover, J. Climate Appl. and Meteor. 22, 1983, 1611-1627. 16. R.G. Dement (Ed.), Ozone i n the United Kingdom, Department o f the Envi ronment, London, 1987, pp. 29-39. 17. K.A. Brice, S.A. Penkett, D.H.F. Atkins, F.J. Sandalls, D.J. Bamber, A.F. Tuck and G. Vaughan, Atmos. Environ., 18, 1984, 2691-2702. 18. R. G u i c h e r i t (Ed. 1, Atmospheric Precursors and Oxidants Concentrations i n the Netherlands, TNO 's-Gravenhage, Netherlands, 1978, pp.20-59. 19. S.A. Penkett and K.A. Brice, Nature, 319, 1986, 655-657. 20. S.A. Penkett, F.J. Sandalls and B.M.R. Jones, Ozon und Begleitsubstanzen i m photochemischen Smog, VDI-Berichte Nr. 270, 1977, 47-54.
T. Schneider et al. (Editors),Atmospheric Ozone Research and its Policy Zmplicatwm 1989 Elsevier Science Publishers B.V., Amsterdam -Printed in The Netherlands
167
CONCENTRATIONS AND PATTERNS OF OZONE IN WESTERN EUROPE
Robert Guicherit (Ph.D) TNO Division of Technology for Society, P.O. Box 217, 2600 AE Delft (The Netherlands)
ABSTRACT Formation of 0 3 in the Planetary Boundary Layer (PBL) during photochemical pollution episodes has now been observed world-wide as a predominant type of regional air pollution. It may give rise to an 03 concentration ranging from 150 to more than 300 ppb over Europe, with monthly averages showing a maximum in summer. The frequency of such episodes is controlled by meteorology and varies widely with place and time. There is, however, a general tendency for 03 concentrations to be lower in urban areas than in downwind rural areas, because in urban areas some 03 is removed by reactions with other pollutants, mostly NO which is rapidly converted into N02. Some NO2 is removed from the PBL by dry deposition; a substantial amount of NOx in Europe may be converted into PAN, and the remainder into nitrates and peroxynitrates. Dry and wet deposition remove HNO3 and PAN. Some PAN decomposes into NO2 and peroxy radicals. The decomposition rate of PAN depends on temperature. however. At lower temperatures it is slow enough for PAN to be transported over very long distances away from its source. Many stations now in operation in the northern hemisphere show an upward 0 3 trend. Comparison of recent data with much earlier ones collected near Paris at the turn of the century show that the levels were at least a factor two lower at that time. We argue that increased transport of NOx via PAN, and increased anthropogenic CO, CH4 and NMHC are responsible for the 0 3 increase in the northern hemisphere, and for the observed PAN and 0 3 maximum in spring (May) in the background troposphere over Europe. INTRODUCTION Forest decline in Europe, which was first observed about a decade ago in West Germany, has been ascribed to a variety of factors including climatological influences such as drought and frost, pathogens, inbalance of soil nutrients and air pollution. Atmospheric pollutants suspected of playing a role are sulphur dioxide, nitrogen oxides, ammonia and photo-oxidants. It is now believed that photo-oxidants are a critical factor in the alarming decline in Central Europe's coniferous forests [ref. 11. High ozone levels not only play a role in damage to plant species including horticultural- and fruit crops, but also lead to irritation of mucous membranes and therefore affect human health in an adverse way. Ozone is furthermore damaging to materials such as elastomers, fibers, dyes and paints. Moreover, elevated ozone levels are often accompanied by a decline in visibility and ozone also exhibits absorption bands in the infra-red e.g. the 9.6 km band in the atmospheric window. For this reason it absorbs upward directed terrestrial radiation and thus contributes to the greenhouse effect as do C02, CH4, N20 and CFC's. Especially ozone changes in the upper troposphere are very effective in changing the surface temperature of the earth. Finally ozone is a precursor molecule for OH, which plays a dominant role in oxidation processes in the atmo-
168 sphere. For this reasons there is considerable interest in tropospheric ozone climatology and its possible changes due to human activity. HIGH OZONE CONCENTRATIONS IN THE PBL Photochemical oxidants are readily produced during so called photochemical episodes which take place when there is a well defined boundary layer over Europe, where emissions accumulate and react through photochemical processes; i.8. in high pressure systems. These episodes may have a duration of several days and may lead to ozone levels of over 150 ppb over large areas of Europe [ref. 2, 3, 41. Ozone and its precursors have such long lifetimes that polluted airmasses from urban and industrial areas can affect sub-urban and rural areas considerable distances (500 to over 1000 km) downwind. Indeed, elevated ozone concentrations have been measured in many downwind rural areas, where local ozone precursor sources are lacking. In fact there is little evidence for significant geographical variation in the maximum hourly ozone concentrations recorded at widespread locations over Europe during major continentalscale photochemical episodes. Although elevated ozone concentrations appear to be widely distributed, this does not imply that photochemical ozone concentrations are evenly distributed across Europe. For example the location of the high pressure areas and their centers determine which geographical regions will experience high concentrations. From an analysis [ref. 51 it follows that when a high pressure center is located over north-western or north-central Europe high ozone concentrations can simultaneously be observed in the UK, Scandinavia and major parts of the European continent. If the high pressure center is located more to the west, i.e. over the UK and the North Sea, high concentrations can persist in the UK and over parts of the European continent; but in those cases concentrations are much lower in Scandinavia. A first analysis of measured ozone levels over western Europe shows a quite clear gradient with increasing concentrations from the north-west towards the south-east [ref. 61. Finally it should be pointed out that the frequency of photochemical episodes is controlled by meteorology. This is the reason why meteorological variability from year to year and, over Europe mainly accounts for the variability of frequency and intensity of episodes from year to year over different parts of Europe. Year to year variability for the Netherlands is demonstrated in Table 1 OZONE TRENDS IN THE TROPOSPHERE Tropospheric ozone is not only ozone which is transported downward from its stratospheric source region along isentropic surfaces and through tropopause folding, but is also photochemically produced within the free troposphere by CH4, CO and NMHC, provided enough NO is available. This process takes place on a hemispheric or global scale over much longer time periods. If an ozone build up occurs this will be reflected in increasing background ozone concentrations (monthly, seasonal of yearly averages) in remote areas of the PEL. On the contrary rneasurements in urban areas will hardly show an ozone trend or even a slight downward trend due to high and increasing levels of NOX and the high reactivity of NO towards ozone.
169
Year Station
No. of hours with 03 2 0.06 0.08 0.10ppm
1976 Delft
353
145
71
61
29
26
0.20
691
298
149
95
48
29
0.27
742
327
181
100
50
29
0.22
102 106 34
21 31 13
4 2 4
26 19
6 5 4
1 2 2
0.12 0.10 0.1 1
(urban) Vlaardingen (industrial) Vlissingen (remote/ coastal area)
1977 Delft Vlaardingen Vlissingen
No. of days with 03 2 0.06 0.08 0.10ppm
10
Max. 1 hour conc. (ppm)
1976 no. of days with Tmax 2 25°C (46) 1977 no. of days with Tmax 2 25°C (7) Observations have clearly demonstrated an ozone increase of (1-2)% per year during the last two to three decades at middle and high latitudes over Europe [ref. 7,8,91.If we compare these data with much earlier data collected at the Montsouris observatory in Paris between 1876 and 1907 [ ref. lo],which show no distinct trend, levels in the eighties are approximately twice that recorded at the beginning of the century at the same latitude. Ozone data have been collected at more remote sites in both hemispheres by NOAA's GMCC program since the early seventies. Most stations in the northern hemisphere, show positive trends of approximately 1 %/year over the period 1973-1984. In the southern hemisphere a slight negative trend or no trend at all has been recorded on American Samoa and at the South Pole. Less information is available for the lower free troposphere. An indication of the ozone content of the lower free troposphere at the latitude of the Netherlands has, however, been obtained as follows. For high wind velocities accompanied by low pollution levels, when convective mixing is most effective, ozone from the troposphere above the boundary layer is most likely to influence ozone distribution in the boundary layer itself. This is demonstrated in Fig. 1, which is a plot of summer 98% ozone values and ozone values for high wind velocities. High winds tend to distribute ozone evenly, and the distinction between levels in the more and in the less polluted parts of the country is lost. We have plotted the monthly ozone concentration at Delft as a function of windspeed for a period of 8 years. The graphs In Fig. 2 show that the ozone concentration no longer varies at windspeed of more than 12 m.s-1. If we now plot the monthly maxima, which may be regarded as ozone concentrations representative for the troposphere above the boundary layer, a maximum
170 is observed in May (Fig. 3). This is in contrast to the mid-summer maximum in the boundary layer which is influenced by human activity. The same trend emerges when we look at ozone concentrations measured on the island of Terschelling, in the north-west of the country, for trajectories from the sea, where no sources of pollution are to be expected (Fig. 3). The same figure also plots measurements in remote areas of Canada at 53-59"N [ref. 111. From Fig. 3 we have deduced the zonal average ozone concentration at a latitude of 50 to 60"N. Over the year this concentration is given in Fig. 4, which also depicts oxidant (03, + N02) levels measured in western Europe. In areas with low levels of NOx, oxidant levels will be essentially equal to ozone levels. In areas with higher NOx levels, ozone levels will be lower. The figure shows that yearly average oxidant levels are 26 to 55% higher than so-called background ozone levels. When these data are compared with the annual averages of 10 to 15 ppb recorded at the turn of the century at Montsouris Observatory, it follows that there has been an increase of some 200%. It should be stressed that it is most probable that all aforementioned ozone concentrations, even the Paris data, are influenced by human activity and can therefore not be regarded as 'natural background'.
Terschelling
0
0
Fig. 1. 98% large-scale 0 3 pollution levels for the Netherlands (summer 1982) and wind velocities on April 28; 1985 (0100 GMT) when national 0 3 levels were around 70 pg.m-3. Source: Nation wide measuring network operated by the National Institute for Public Health and Environmental Hygiene (RIVM). Ozone trends in the free troposphere over the northern hemisphere are less well established. Trends between 0.5% and 3% per year for the lower free troposphere have been reported [ref. 11, 121, while data given in [ref. 121 indicate an increase of about l%/y at 9 km altitude between 1967 and 1982 from ozone soundings at Hohenpeissenberg in the Federal Republic of Germany. This in contrast to observations of 0 3 in the free troposphere over Lindau showing a non-significant trend of 0.2%/ y at 500 hPa over ten years [ref. 131.
171
5
10
u___ 20
_
-/
-/
0 '0 5
W
15
-
Ins-1
Fig. 2.
Monthly average 0 3 concentrations for Delft as a function of wind speed.
Fig. 3.
Background ozone levels.
Fig. 4. Background 03 levels (derived from Fig. 3) and oxidant levels as measured in west Europe (hatched area).
172 MECHANISM OF TROPOSPHERIC OZONE PRODUCTION Ozone can only be produced In the troposphere from the photolysis of nitrogen dioxide. NO2 + hv ( ~ 4 0 0 nm) 0+02+M
NO + 0 --Q+M
--
jW2)
The ozone formed in this way reacts with NO
--- NO2 + 0 2
NO+@
k(NO + 03)
Thus a photochemical equilibrium exists and the ozone equilibrium concentration can be calculated from the following expression:
This equilibrium is disturbed by the oxidation of NO to NO2 by peroxy radicals formed in the course of oxidation of CO and hydrocarbons by hydroxyl radicals. CO+OH H+02 H@+NO
--- C02+H
-----
HO;! N02+OH
and for hydrocarbons (RH) RH+OH R +02 RO;!+NO RO+@
-------
R+H20
RO+N02 --- RCHO+HOp
The net result of this chemistry is the accumulation of ozone. HO2 may also react with 03 to form 0 2 and OH by which ozone molecules are destroyed. It has been argued [ref. 14, 151 that ozone formation prevails over ozone destruction for NOx concentrations in excess of about 15-30 ppt (ppt = part in 10E12 by volume). As a consequence of industrial development, growing energy consumption, increasing traffic density, an ever increasing stock of cattle, an increasing area of wet agricultural land such as rice paddies and an increasing use of fertilizers, the anthropogenic emissions of CO, NOx, CH4 and NMHC have increased world-wide, especially in the northern hemisphere. Throughout a large part of the troposphere, NOx seems to be the rate limiting precursor for ozone formation. Conversion rates of NOx in the PBL are high; ranging from a few percent per hour in winter to over 15%/hr during photochemical episodes in western Europe [ref. 161. NO is first rapidly oxidized to NO2 with ozone. Apart from some NO2 that is removed from the boundary layer by dry deposition, a considerable amount is converted into PAN. The remainder is converted into NO3, either directly by reaction with OH, or indirectly by reactions initiated by 03. Dry and wet deposition remove NO3 and PAN. Due to the fact that NOXhas such a short lifetime, the effect of man-made NOX emissions should only be seen on a regional scale; namely several
173 hundreds of kilometers. The decay rate of PAN, however, is temperature controlled. Especially in cooler air masses, with a low NOIN02 ratio, its decay rate is long enough for it to be transported over very large distances. Due to turbulent exchange cooler air with considerable PAN concentrations might be raised in temperature, and NOx might be formed again by decomposition of PAN. In its turn N4( may enter the photochemical cycle in the free troposphere. An analysis of ozone measurements shows that in polluted sites In the PBL the maximum values occur in summer. At more remote sites not influenced by man-made pollution and in the lower free troposphere, however, the ozone concentrations show a clear maximum in spring, and concentrations decrease in summer. Plots of monthly average PAN concentrations for wind directions from the sea also show a spring maximum, as is the case for ozone (Fig. 5). The conventional view regarding the ozone spring maximum was that stratosphere-troposphere exchange is most effective during the late winter and early spring [ref. 17, 181. Since the lifetime of ozone in the troposphere is relatively short (one to a few months), one may expect concentrations of tropospheric ozone to be largest in spring. However, tropospheric PAN concentrations also show a peak in spring. Because PAN is only formed by photochemical reactions in the troposphere itself, one might speculate that, at our latitudes, the ozone maximum is also due to photochemical reactions in the troposphere. There are, in fact, indications that, in winter PAN, ozone and their precursors may accumulate in air masses at higher latitudes. As soon as there is enough UV-light available, which is the case from early spring on, precursors will begin to react rapidly and together with the 0 3 and PAN accumulated in winter add to the observed ozone and PAN maxima.
ppb PAN
n
I
0
0 J
Fig. 5.
I
i \
I
F
M
A
M
J
0 J
A
S
O
N
Background ozone and PAN concentrations in west Europe.
D
174 OZONE TRENDS DEDUCED FROM MODEL CALCULATION Jdodellina Because no reliable measuring data are available for ozone concentrations in urban (polluted) parts of the boundary layer prior to 1970, we have deduced the ozone trend in a study by modelling exercises [ref. 191. A receptor oriented trajectory model was developed by TNO and the National Institute for Public Health and Environmental Hygiene, in cooperation with the Royal Netherlands Meteorological Service and the Institute for Meteorology and Oceanography of the State University of Utrecht. The model describes the transport of two air parcels along 74 h back trajectories. The transport of one of these parcels describes advection of air within the mixing layer in the morning of the arrival day. The other parcel is transported along a trajectory which is representative for advection of a polluted layer above the mixing layer. This layer consists of 'aged smog' which is fumigated in the mixing layer during the morning. To study the influence of emission reduction on the level of photochemical pollutants, the model was run for a number of emission scenarios. In the scenario calculations 5 more or less 'representative' trajectories arriving in the central part of the Netherlands were considered. The results of calculated ozone, NOx and PAN are given in Figure 6.Also depicted in the figure are the estimated historical NOx emissions. Although due to uncertainties in natural emissions at times when anthropogenic sources became less Important and about the accuracy of the chernicat scheme used under these conditions, the concentration trends seem not to be unrealistic for summertime conditions at our latitude. Ozone concentrations during episodes were on the increase until the mid sixties, after which a decrease due to chemical 'quenching' by NO occurred. Moreover, ozone concentrations in urban areas during episodes have increased less than long term averages in background areas. This is not surprising, because in remote areas ozone formation depends much more on a NOx increase than is the case in more polluted areas.
Fig. 6. Historical
during episodes.
175 the free -t For increased release rates of CO, NOx, NMHC and CH4 of 0.5% for CH4 and 3% for the other precursors, an increase in tropospheric ozone by about 1%/y has been calculated [ref. 201 with the most susceptible effect exerted by NOx. Such a scenario which is not unrealistic (CH4 increases in fact may even be more than 0.5%) may have serious consequences. First of all there is no trace constituent in the troposphere where the difference between noeffect level and toxic level is so marginal as is the case for ozone. Some phytopathologists hold the opinion that background ozone levels at our latitude are already beyond toxic levels for sensitive plant species. It is also interesting to note that model calculations [ref. 21 and cited in 131 show a temperature increase by 0.7-0.9 K at the earth's surface for a doubling of tropospheric ozone. Using a 1-D radiative convective model [ref. 321 also show a temperature rise of 0.3 K for a tropospheric ozone increase by 3%/y from 67/68 to 80/81, which is a 13 year period corresponding with about 50% ozone increase. We therefore may conclude that a doubling of the tropospheric ozone concentration might very well take place within the coming 50-70 years, at least over the northern hemisphere. In that case ozone might then be one of the major greenhouse gases we will have to deal with. CONCLUSIONS Data are now available from which we may conclude that major changes have taken place in the ozone climatology of at least the lower troposphere of the northern hemisphere since the turn of the century and probably most pronounced after 1950. Ozone concentrations in the background northern hemisphere are on the increase and are associated with increased emissions of precursor molecules; particular NOx from anthropogenlc sources. An ozone increase gives reasons for concern because ozone plays a crucial role In the radiation budget of the atmosphere, ozone may have a direct adverse effect on man; vegetation and materials and ozone determines to a great extend the oxidation capacity of the atmosphere. Because we are dealing with processes which take place on a hemispheric to global scale there is a need for a concerted research effort among countries world wide to study the processes involved in order to give guidance in taking appropriate actions to minimize the adverse effects of these changes. REFERENCES 1. B. Prinz, G.H.M. Krause and H. Stratman (1982), LIS-Berichte 28. 2. R.A. Cox, A.E.J. Eggleton, R.G. Derwent, J.E. Lovelock and D.H. Pack (1975), Long range transport of photochemical ozone in north-western Europe, nature, 372-376. 3. R. Guicherit and H. van Dop (1977), Photochemical production of ozone in western Europe and its relation to meteorology, Atmos. Environ. 11145-155. 4. J. Scholdager, H. Dovland, P. Grennfelt and J. Saltbones (1981), Photochemical oxidants in north-western Europe. A pilot project: Lillestrram Norwegian Institute for Air Research (NILU OR 19/81). 5. J. Scholdager (1984), Observations of photochemical oxidants in connection with long range transport. Proc.: Workshop on evaluation and assessment of the effects of photochemical oxidants on human health, agriculture, forestry, materials and visibility, Gothenburg Sweden. 6. P. Grennfelt, J. Saltbones and J. Scholdager (1 987), Regional ozone concentrations in Europe. In: Air Pollution and Ecosystems. Ed. P. Mathy Reidel Dordrecht. 7. R. Hartmannsgruber, W. Attmanspacher and H. Claude (1985), Opposite behaviour of the ozone amount in the troposphere and lower stratosphere during the last years, based on
176
8. 9.
10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22.
the ozone measurements at the Hohenpeissenberg observatory. In: Zerefos C.S. and A Ghazi (Eds.). 'Atmospheric Ozone' Proc. of the Quadrennial Ozone Symposium in Halkidiki, Greece, Sept. 1984. U. Feister and W. Warmbt (1985). Long term surface ozone increase at Arkona. In: C.S. Zerefor and A Ghazi (Eds.). 'Atmospheric Ozone' Proc. of the Quadrennial Ozone Symposium in Halkidiki, Greece, Sept. 1984. R. Reiter and H.J. Kanter, Time behaviour of C02 and 0 3 in the lower troposphere based on recordings from neighbouring mountain stations between 0.7 and 3.0 km ASL including the effects of meteorological parameters. WMO Techn. Conf. on Observation and Measurement of Atmospheric Contaminants (TECOMAC), Vienna, Oct. 1983. A. Volz and D. Kley, Ozone measurements in the 19th century. An evaluation of Montsouris series (submitted for publication). J.A. Logan, Troposphere ozone: seasonal behaviour. trends and anthropogenic influences. J. Geophys. Res. 90,10463, 1985. W. Attmannspacher (1982), The behaviour of atmospheric ozone during the last 15 years, based on the results of ozone soundings at Hohenpeissenberg FR.G. Gesellschaft fur Stahlen und Urnwelt forschung mbH Munchen BPT-Bericht 5/82, 12-17. U. Feister and W. Warmbt (1987), Long term measurements of surface ozone in the German Democratic Republic. Journ. of Atmosph. Chemistry 5, 1-21. P.J. Crutzen (1974), Photochemical reactions initiated by and influencing ozone in unpolluted tropospheric air. Tellus 25, 47-57. J. Fishman, S.Solomon and P.J. Crutzen (1979), Observational and theoretical evidence in support of a significant in-situ photochemical source of troposphere ozone. Tellus 31, 432446. R. Guicherit, K.D. van den Hout, C. Huygen, H. van Duuren, F.G. Rdmer and J.W. Viljeer, Conversion rate of nitrogen oxides in a polluted atmosphere. Proc. 11th NATO- CCMS Int. Techn. Meeting on Air Pollution Modelling and its Applications, Amsterdam, Nov, 1980. E.F. Danielsen, Stratosphere-troposphere exchange based on radioactivity, ozone and potential vorticity. J. Atmos. Sci. 25, 502, 1968. J.D. Mahlmann and W.J. Moxim, Tracer simulation using a global general circulation model; Results from a mid-latitude instantaneous source experiment. J. Atmos. Sci. 35. 1340, 1978. K.D. van den Hout, R.M. van Aalst, A.C. Besemer, P.J.H. Builtjes and F.A.A.M. de Leeuw (1985), Rekensysteem luchtverontreiniging XLVIII. Rapport CMP 85/03, TNO-Delft. I.S.A. Saksen and 0. Hov (1986), Calculation of trends in the tropospheric concentration of 03, OH, CO. CH4 and N G , Tellus (in print). J. Fishman, V. Ramanathan, P.J. Crutzen, S.C. Liu(l979), Troposphere ozone and climate. Nature 282, 818-820. R.D. Bojkov (1984), Tropospheric ozone its changes and possible radiative effects. WMO special Environmental Report no. 16.
177
T. Schneider et al. (Editors),Atmospheric Ozone Research and its Policy Implicatwna 0 1989 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands
CONCENTRATIONS AND PATTERNS OF PHOTOCHEMICAL OXIDANTS I N THE UNITED STATES B.E.
b T i l t o n a and S.A. Meeks
Envi ronmenbal C r i t e r i a and Assessment Officea, and Atmospheric Sciences Research Laboratory , U. S. Environmental P r o t e c t i o n Agency, Research T r i a n g l e Park, NC 27711, USA
ABSTRACT A broad overview i s f i r s t given o f concentrations o f ozone and PAN a t urban s i t e s i n the U.S. and o f ozone a t selected nonurban s i t e s . Then, sample d i u r n a l curves f o r ozone a t suburban and nonurban s i t e s are presented. Highest concentrations o f both oxidants occur i n C a l i f o r n i a , where t h e second-highest 1-hr concentration o f ozone i n 1983 was 0.37 ppm and t h e highest PAN concentrat i o n reported i n t h i s decade was 0.047 ppm, i n 1980. A t selected nonurban s i t e s , maximum 1-hr ozone l e v e l s f o r 1978-1981 were about h a l f t h e secondhighest 1-hr ozone l e v e l s a t urban s i t e s i n those years. Examples presented o f temporal p a t t e r n s o f ozone show d i s t i n c t seasonality and d i u r n a l i t y , demons t r a t e some general differences i n d i u r n a l i t y and seasonality a t suburban versus nonurban s i t e s , and p o i n t up p o t e n t i a l i m p l i c a t i o n s f o r exposures t o ozone o f populations, vegetation, and o t h e r receptors. Data on to-occurrences o f ozone w i t h n i t r o g e n dioxide o r s u l f u r d i o x i d e i n d i c a t e r e l a t i v e l y few such events a t l e v e l s o f p o t e n t i a l concern f o r vegetation. Data on ozone and n i t r o g e n dioxide a t l e v e l s o f possible concern f o r p u b l i c h e a l t h show even fewer instances o f co-occurrence. INTRODUCTION Aerometric data f o r ozone are essentia
i n t h e United States f o r deter-
mining compliance by i n d i v i d u a l states w i t h the National Ambient A i r Q u a l i t y Standards (NAAQS) purposes,
f o r ozone.
including:
I n a d d i t i o n , such data a r e useful f o r o t h e r
(1) performing comprehensive exposure assessments;
(2) i d e n t i f y i n g those components o f exposure dynamics t h a t e l i c i t observed e f f e c t s , such as mean and peak concentrations, d i u r n a l i t y o f concentrations, and r e s p i t e s between peak concentrations; (3) designing experiments such t h a t t h e protocols,
p o l 1u t a n t measurements, and s t a t i s t i c a l methods used w i 11
produce time-resolved data on exposure-response r e l a t i o n s h i p s ; and (4) formul a t i n g the best exposure s t a t i s t i c ( s )
f o r NAAQS f o r t h e p r o t e c t i o n o f p u b l i c
h e a l t h and welfare. Through examples, d e s c r i p t i v e i n f o r m a t i o n i s given here on some geographic and temporal p a t t e r n s o f ozone and PAN concentrations observed i n the U.S.
that
have p a r t i c u l a r relevance f o r assessing exposures and f o r designing experiment a l protocols. OVERVIEW OF OXIDANT CONCENTRATIONS Nationwide frequency d i s t r i b u t i o n s a r e shown i n Figure 1 f o r 3-yr averages o f the f i r s t - ,
second-, and t h i r d - h i g h e s t 1-hr concentrations, measured by UV
o r chemiluminescence, a t predominantly urban monitoring s t a t i o n s i n t h e U.S.
178 (Ref.
1). This f i g u r e a l s o shows t h e highest 1-hr concentration a t s i t e s o f
the National A i r P o l l u t i o n Background Network (NAPBN)., averaged f o r t h e same
3 yr.
This network, established t o monitor ozone concentrations i n nonurban
areas m i n i m a l l y a f f e c t e d by manmade sources, National Forests i n Oregon (OR), Missouri (MO),
Louisiana (LA),
Arizona (AZ),
consisted o f e i g h t s i t e s i n Montana (MT), Wisconsin ( W I ) ,
N o r t h Carolina (NC),
and Vermont (VT) (Ref. 2).
As these data i n d i c a t e , 50 percent of t h e second-highest 1-hr concentrations f o r 1979 through 1981 a t t h e urban s t a t i o n s were 50.12 ppm, t h e l e v e l o f t h e c u r r e n t U.S.
NAAQS f o r ozone.
Second-highest 1-hr ozone concentrations a t t h e
e i g h t NAPBN s i t e s were about two-thirds t h e urban concentrations a t t h e 50th p e r c e n t i l e b u t o n l y about t w o - f i f t h s t h e urban l e v e l s a t t h e 95th p e r c e n t i l e . The data f o r urban areas, i t should be noted, a r e h e a v i l y i n f l u e n c e d by data from C a l i f o r n i a because o f t h e d i s p r o p o r t i o n a t e l y l a r g e number o f monitoring s t a t i o n s and the greater frequency o f occurrence o f h i g h ozone concentrations i n C a l i f o r n i a (Ref. 1).
88.88 88.8 88 0.40
E,
-
4 0.35 -
a! Oa30 -
8680
70 60 30
10 6 2 1 0.2
0.01
-
HIGHEST -----2nd-HIGHEST -.--.J&HIGHEST
r
:0.20 8 0.16 I
-
Y
STATIONS WITH PEAK 1.hour CONCENTRATIONS <STATED PERCENTAGE
Figure 1. Distributions of the three highest 1 -hour ozone concentrations at valid sites (906 station-years) aggregated for 3 years (1 979, 1980, and 1981 ) and the highest ozone concentrations at NPABN sites aggregated for the same years (24 station-years) (Refs. 1,2).
Figure 2 shows ozone data f o r 1983 f o r respective geographic regions o f the U.S.
(Refs. 1, 3).
Shown here f o r each region are t h e population ( i n thou-
sands), number o f standard m e t r o p o l i t a n s t a t i s t i c a l areas (SMSAs) i n t h e region t h a t have populations 20.5 m i l l i o n , the average o f t h e 1983 second-highest 1-hr ozone concentrations f o r those SMSAs, and the range o f t h e 1983 second-highest value among the SMSAs.
(The second-highest 1 - h r value f o r a given s i t e and
year i s determined from a v a l i d a t e d data s e t c o n s i s t i n g o f a l l 1-hr d a i l y maxima i n t h a t year a t t h a t s i t e .
Here t h e second-highest 1-hr values f o r t h e
179
SOUTH
0 0.14 A 0.12-0.15
0 0.13 A 0.09-0.17
Figure 2. Average and range of second-highest 1-hour daily maximum ozone concentrationsfor 1983 for geographic regions of the U.S., derived from data for SMSAs with populations 20.5 million (Key: population, millions; A no. of SMSAs in regions with population 20.5 million; 0 average of second-highest 1-hour daily maxima; A range of second-highest 1-hour daily maxima.)
year at all sites in the SMSAs have been used to derive SMSA averages and ranges.) As shown, in 1983 the highest 1-hr ozone concentrations (i.e. I the second-highest 1-hr values) occurred on the Pacific coast, especially in California; i n the northeast (New England and Middle Atlantic states); around the Great Lakes (East North Central states); and in the Gulf Coast area (West South Central states). For each of these areas, the causes of elevated pollution levels are unique, complex, and interactive, such that meteorology and population-related factors combine to produce the regional concentrations shown here. No air quality standard for peroxyacetyl nitrate (PAN) exists in the U.S. and PAN is therefore not monitored routinely. Available data all come from special field investigations, and thus are sparse as well as not very comparable, since sampling intervals, time of day, and even seasons have differed among studies. Data from the more comparable studies in urban and suburban areas, however, are briefly summarized in Table 1 (Refs. 1, 4-14).
1130 TABLE 1. Summary o f PAN concentrations i n urban areas o f the United Statesa Sampling period
Urban area ~~
Ref.
~~~~
Riverside, CA Claremont, CA Riverside, CA Riverside, CA Riverside, CA West Covina, CA Riverside, CA Los Angeles, CA Houston, TX Dayton, OH S t . Louis, MO New Erunswick, NJ :Only
4.9 13 1.6 7 3.6 9 4.6 31 0.4 0.7 1.8 0.5
G O b
1980; Sept., OCE.' 1977; Apr., May 1977; Jul., Aug. ,bOct. b 1975-76; May-Oct., 1977; Aug., Sept. 1967-68; Aug. -Ap6. 1965; Septt-Oct. 1976; Jul. 1974; Jul. , Augtc 1973; Jgn. -Aug. 1978-80
41.6 47 5.7 18 32 20 58 214 11.5 10 19 10.6
(4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (13) (14)
studies w i t h a minimum o f 10 days o f sampling.
12 hr/day, daytime. '24 hr/day. d5 hr/day, 0800-1300. Data on PAN i n nonurban areas o f the U . S . ,
l i m i t e d t o studies done i n the
1970s, indicate t h a t nonurban concentrations o f PAN overlap those found a t urban locations outside California.
A t remote nonurban locations, PAN concen-
t r a t i o n s are generally somewhat lower s t i l l , w i t h average concentrations on the order o f about 0.1 t o 0.6 ppb (Ref. 15). TEMPORAL PATTERNS OF OZONE CONCENTRATIONS The common features o f the occurrence o f ozone i n ambient a i r i n the U.S. have been we1 1-documented i n the open 1i t e r a t u r e and have a1so been reviewed a t length i n a r e l a t i v e l y recent p u b l i c a t i o n o f the U.S. Environmental Protect i o n Agency (Ref.
1). Among the more commonly recognized characteristics o f
ozone i n ambient a i r are i t s temporal and s p a t i a l patterns, which are such t h a t higher concentrations o f ozone occur i n the U.S.: mid-fall;
(1) i n mid-spring through
(2) i n mid- t o l a t e afternoon; (3) a t higher elevations, i f mean
concentrations are the indices used; (4) outdoors, rather than indoors; and
(5) i f short-term peak concentrations are the indices used, i n urban versus nonurban areas (Ref. 1). Examples are given subsequently o f some temporal patterns i n ozone concent r a t i o n s t y p i c a l l y observed i n the U.S.
The obvious should be emphasized,,
however; t h a t i s , f o r each generalized example many exceptions can be found, especially i n an area as large and topographically and meteorologically diverse as the U.S. The seasonality o f d i s t r i b u t i o n s o f 1-hr ozone concentrations i s shown i n Figure 3 f o r f i v e urban s i t e s and one suburban s i t e (Morris County, NJ) i n
181 various geographic areas o f t h e U.S.
Although t h e d i s t r i b u t i o n s v a r y somewhat
w i t h l o c a l i t y , as they would w i t h year as w e l l , a seasonal t r e n d i s obvious, e s p e c i a l l y i n t h e maximum 1 - h r values f o r each month.
Note t h a t t h e monthly
means do n o t d i f f e r w i d e l y among s i t e s , i n c o n t r a s t t o t h e 1-hr maxima f o r each month.
I POMONA.CA 0.30
n
I1 1OENVER.CO
0.25 0.20 n
0.15
g 0.10
5 0.05
K
c =w
g
n0.35 0.30
8 0.25 0
0.20 0.15
I
1
i i 7I 1
WASHINGTON, OC
DALLAS, TX
MORRIS CO., NJ
n
i
MONTH OF YEAR
Figure 3. Seasonal distributions of ozone concentrations as indicated by monthly averages w ) and the 1-hour maximum ( ) in each month at selected urban and suburban sites, 1981 (Ref. 1).
(
Seasonal d i s t r i b u t i o n s f o r s i x NAPBN nonurban s i t e s and f o r Whiteface Mountain, NY, are shown i n Figure 4 (Ref. 16).
Note t h a t b o t h peak and mean
concentrations are highest i n s p r i n g a t most o f these s i t e s .
Note a l s o t h e
s i m i l a r i t i e s i n seasonal d i s t r i b u t i o n s o f average 1-hr maxima a t NAPBN s i t e s i n Oregon and Montana. l a t i t u d e s o f 44'13'
These two NAPBN s i t e s are located, r e s p e c t i v e l y , a t and 45O14' and a t e l e v a t i o n s o f 1250 and 1350 m.
These
s i t e s and t h e one i n M i s s o u r i a l s o show a p a t t e r n o f e l e v a t e d ozone i n l a t e summer o r e a r l y f a l l . Average d i u r n a l curves f o r r e s p e c t i v e q u a r t e r s o f t h e year o f f e r a s u c c i n c t demonstration o f both t h e s e a s o n a l i t y and d i u r n a l i t y o f ozone concentrations. F i g u r e 5 (Refs. 2, 17, 18) shows average q u a r t e r l y d i u r n a l curves f o r s i t e s i n d i f f e r e n t p a r t s o f t h e country:
(A)
and (C) NAPBN s i t e s (Ref. 2);
(B) a
suburban s i t e i n a c i t y i n t h e Los Angeles basin, Azusa, CA, which had t h e maximum second-highest d a i l y 1-hr c o n c e n t r a t i o n i n t h e U.S. i n 1985 (Ref. 181, and (D) a suburban s i t e i n a small c i t y , Lancaster, PA, which i s s i t u a t e d i n a
182
JFMAMJJASOND JFMAMJJASOND MONTH OF YEAR
Figure 4. Seasonal distributions of ozone at nonurban sites of the NAPBN and at Whiteface Mountain, NY: (A) means of all daily 1-hour values at sites in Wisconsin (WI), Missouri (MO). Vermont (VT), North Carolina (NC), Oregon (OR), and Montana (MT) and (B) in New York (NY): (C) means of daily 1-hour maxima in each month for sites in MO, NC, WI, and VT; and (D) in M T and OR.
farming r e g i o n i n t h e n o r t h e a s t U.S. i n 1985 (Ref.
and which had no c o n c e n t r a t i o n s 20.12 ppm
18).
D i u r n a l curves f o r t h e NAPBN s i t e s i n F i g u r e 5(A) a r e composite curves d e r i v e d from d i u r n a l data from 1979 f o r a l l s i x s i t e s .
F i g u r e 5(C) presents
q u a r t e r l y d i u r n a l d i s t r i b u t i o n s a t a separate NAPBN s i t e l o c a t e d i n t h e Apache Sitgraves National Forest, AZ, a t 33O45' l a t i t u d e and an e l e v a t i o n o f 2500 m (Ref.
17).
The q u a r t e r l y d i u r n a l d i s t r i b u t i o n s o f d a t a from t h e s i x NAPBN
s i t e s are n o t u n l i k e those from many nonurban s i t e s and some o f t h e suburban s i t e s monitored i n t h e U.S.
(Ref. 1). Peak-to-mean r a t i o s a t t h e Arizona s i t e ,
however, were close t o 1.0 each q u a r t e r .
Peak-to-mean r a t i o s a t t h e o t h e r s i x
NAPBN s i t e s (using composited data and t h e average o f a l l d a i l y 1-hr O3 maxima as t h e peak) were 1.2,
1.2,
1.3,
and 1.3,
r e s p e c t i v e l y , f o r Q1through 44
(see Ref. 2). The NAPBN s i t e s a t which t h e d a t a shown i n F i g u r e 5(A) were o b t a i n e d a r e known t o be a f f e c t e d by ozone generated from manmade emissions o f precursors (Ref. Z ) ,
as determined from t r a j e c t o r y analyses and from forward stepwise
regression analyses o f ozone c o n c e n t r a t i o n s versus m e t e o r o l o g i c a l v a r i a b l e s such as temperature (T) and r e l a t i v e h u m i d i t y (RH);
T and RH a r e i n d i c a t i v e
o f oxidant-forming p o t e n t i a l o f l o c a l versus t r a n s p o r t e d a i r masses.
Note,
however, t h e r e l a t i v e l y h i g h c o n c e n t r a t i o n s i n t h e evening, n i g h t t i m e , and e a r l y morning hours.
These a r e t y p i c a l o f c o n c e n t r a t i o n s i n nonurban areas,
where surface d e p o s i t i o n r a t h e r t h a n NO scavenging appears t o be t h e c h i e f
183
0.16
1
I
lBl MT. WI. MO. U.NC. W 0.06
o,12 0.10 0.08
0
p
-
1
-
I I I I I I 1 I I I I I I I I I I I I I om -
ICI NAPBN SITE: 0 0 8 - APACHENF,AZ 0.07
UUSA.CA ISUB/RESI
0.34
0.07
-
-____________------
-
??a!
ID1 UNCASTER. PA ISUB/INDI
0.00-
0.04
0.04
0.03
0.03 0.02
03 0.01
0.01
04
0
0
OOW
0400
0800
12W
1800
2000
Do00
M O O
0800
1200
1600
2000
MOUR OF DAY. LOCAL TIME
Figure 5. Quarterly diurnal curves for ozone a t nonurban and suburban sites: (A) composite quarterly distributions (1979)for six NAPBN sites in MT, WI, MO, LA, NC, and VT;(C) quarterly distributions (1979)at a remote, high-elevation (2500 m MSL) NAPBN site in Arizona (AZ); (B) and (D) quarterly distributions (1986) at suburban/residental site in Azusa. CA (South Coast Air Basin) and at suburbanAndustria1 site in Lancaster, PA (small city in farming area of northeast) (Refs. 2. 17, 18). removal mechanism.
Note the occurrence i n the second and t h i r d quarters (smog
season) o f rather broad peaks p e r s i s t i n g through much o f the afternoon a t the s i x NAPBN sites.
The second- and third-quarter curves f o r Azusa, CA, on the
other hand (Figure 581, show the more t y p i c a l pattern--sharper peaks occurring closer t o midday--for a source area i n which the ozone measured i s generated l o c a l l y o r transported from nearby, o r both.
The quarterly diurnal curves from
the s i t e a t Lancaster, PA (Figure 501, show f a i r l y broad plateaus from the morning through l a t e evening i n the smog season (Q1 and Q2), but the curves have characteristics t h a t make them intermediate between the NAPBN and the Azusa curves. These are: (I) lower post-midnight concentrations than those a t NAPBN sites; (2) greater i n f l e c t i o n around 6:OO t o 8:OO a.m.
than seen i n data
from NAPBN sites; and (3) lower afternoon but higher evening concentrations than those a t Azusa. I n urban and suburban areas, ozone concentrations during the evening,
nighttime, and early morning hours are usually minimal, o f t e n
approaching zero (Ref. 1). Thus, ozone concentrations i n some o f these areas can fluctuate widely w i t h i n a day, especially i n the second and t h i r d quarters, as exemplified by the Azusa curves i n Figure 5(B).
184 Questions remain i n t h e h e a l t h and vegetation l i t e r a t u r e as t o t h e r e l a t i v e importance o f the respective components of t h e dynamic nature of ozone i n ambient a i r . For example, do short-term peak excursions above given l e v e l s induce more severe e f f e c t s than s t a t i c , low-level ozone concentrations; o r a r e cumulative doses t h e most important aspect of exposure t o ozone? I n Table 2, therefore, examples o f several simple measures o f ozone a i r q u a l i t y are given f o r t h e d i u r n a l curves presented i n Figure 5.
The q u a r t e r l y means
f o r ozone concentrations a t Lancaster and Azusa have been c a l c u l a t e d f o r 24 h r and f o r 14 hr, t h e l a t t e r being t h e peak d a y l i g h t hours from 6:OO a.m. 8:OO p.m.
to
Data were n o t a v a i l a b l e f o r c a l c u l a t i n g d a y l i g h t means f o r t h e
composite NAPBN s i t e s o r t h e NAPBN s i t e i n Arizona.
Data f o r d a y l i g h t hours
are important f o r assessing population exposures, since most people who a r e outdoors f o r any appreciable l e n g t h o f t i m e are t h e r e i n d a y l i g h t ; and since vegetation, though exposed 24 hr/day, i s a f f e c t e d d u r i n g the hours when p l a n t stomates are open and gas exchange and photosynthesis are occurring. For t h e 14-hr d a y l i g h t period, annual cumulative ozone a t Lancaster i n 1985 was 63 percent o f t h a t a t Azusa and second- and t h i r d - q u a r t e r cumulative ozone a t Lancaster was 60 percent o f t h a t a t Azusa.
The second-highest 1-hr
ozone concentration a t Lancaster f o r t h e year, however, was o n l y 32 percent o f the same measure a t Azusa. TABLE 2. Summary ozone s t a t i s t i c s f o r s i t e s i n Figure 5 (ppm) Lancaster, PA 24-hr
14-hrb
0.018 0.033 0.031 0.012 0.024
Second-hi ghest 1-hr O3 i n yr Cumulative OJyr 92 + 93 Annual
24-hr
14-hr
"Backgroind site" 24-hr
Apache NF, A2 24-hr
AVg. 03 concn. /quarter,ppm
Quarter
QIC 42 93 44 Annual
Azusa, CA
0.022 0.041 0.038 0.014 0.029
0.017 0.043 0.044 0.020 0.031
0.114 140 210
101 148
0.023 0.064 0.068 0.027 0.046 0.360
192 272
169 235
0.030 0.040 0.034 0.025 0.032 0.125 162 280
0.039 0.049 0.040 0.037 0.041 N A ~
195 361
aTreats t h e s i x NAPBN s i t e s as one hypothetical s i t e f o r m o n i t o r i n g bcontinental background O3 a t ground l e v e l . D a y l i g h t hours, 6:OO a.m. through 7:OO p.n. 'Q1= January-March; 42 = April-June; 43 = July-September; 44 = OctoberdDecember. Data n o t available.
185
I f one uses t h e q u a r t e r l y mean concentrations found from t h e composite
NAPBN data t o represent one h y p o t h e t i c a l s i t e (nonurban area), t h e t o t a l ozone t o which a r e c e p t o r could t h e o r e t i c a l l y be exposed i n a year a t such a s i t e would be ca. 280 ppm ( i . e .
,
exposed 24 hr/day, 365 days/yr).
As d i f f i c u l t as
i t may be t o grasp, t h e cumulative 1-yr ozone c o n c e n t r a t i o n i s somewhat g r e a t e r
a t t h e h y p o t h e t i c a l "background s i t e " and one and one h a l f times g r e a t e r a t t h e h i g h - e l e v a t i o n NAPBN s i t e i n Arizona--where q u a r t e r l y mean ozone concentrations range from about t h e lower t o t h e upper bounds o f estimated U.S. c o n t i n e n t a l background ozone (Ref. 1)--than a t t h e Azusa, CA, s i t e where t h e second-highest d a i l y 1-hr l e v e l f o r 1985 was 0.360 ppm, t h e h i g h e s t such value measured i n t h e whole n a t i o n i n 1985.
Comparison o f t h e p o s s i b l e cumulative exposures a t these
s i t e s d u r i n g t h e second and t h i r d q u a r t e r s , however, r e v e a l s t h a t about
70 percent o f t h e cumulative ozone f o r t h e year occurs i n those q u a r t e r s a t Azusa b u t o n l y 58 percent a t t h e h y p o t h e t i c a l "background s i t e . "
Thus, t h e
cumulative ozone d i f f e r s l i t t l e between Azusa and t h e h y p o t h e t i c a l s i t e , b u t the "dose r a t e s " o f t h e p o t e n t i a l exposures o f b i o l o g i c a l receptors a t t h e two s i t e s d i f f e r somewhat more s u b s t a n t i a l l y . These very simple s t a t i s t i c s r e i n f o r c e t h e n e c e s s i t y f o r o b t a i n i n g addit i o n a l concentration-response data f o r h e a l t h and v e g e t a t i o n e f f e c t s , e s p e c i a l l y data on concentration times time r e l a t i o n s h i p s ( C x T).
Further i n q u i r i e s are
needed, f o r example, i n t o t h e d i f f e r e n c e s i n observed e f f e c t s t h a t occur w i t h exposures t o low-level
,
sodic concentrations,
as w e l l as i n t o t h e e f f e c t s o f cumulative exposures
steady-state concentrations versus i n t e r m i t t e n t , e p i -
g e n e r a l l y and s p e c i f i c a l l y t h e e f f e c t s from cumulative ozone exposures a c c r u i n g a t v a r y i n g dose r a t e s . The q u a r t e r l y d i u r n a l curves presented here mask t h e day-to-day v a r i a t i o n s t h a t can occur a t t h e same m o n i t o r i n g s i t e .
F i g u r e 6 shows t r u e d i u r n a l
curves (single-day curves) a t t h e Azusa, CA, s i t e and a t a r e s i d e n t i a l / r u r a l s i t e i n San Bernardino, CA, about 35 t o 40 m i l e s southeast o f Azusa b u t a l s o w i t h i n t h e Los Angeles a i r basin.
Note e s p e c i a l l y t h e d i v e r s i t y o f t h e
p a t t e r n s f o r t h e 3 successive days a t Azusa. 1-hr concentrations s h i f t e d from 1:00 p.m. (1500) on August 25.
The t i m e o f t h e r e s p e c t i v e peak
(1300) on August 24 t o 3:OO p.m.
The 1 - h r peak concentrations were 0.36 ppm on August 24,
0.22 ppm on August 25, and 0.09 ppm on August 26.
The 24-hr means f o r those
3 days were 0.089, 0.082, and 0.026 ppm, r e s p e c t i v e l y . those 3 days were, r e s p e c t i v e l y , 4.04,
2.68,
Peak-to-mean r a t i o s f o r
and 3.46.
Comparison o f t h e d i u r n a l curves from t h e two s i t e s i s o f n o t e p a r t l y t o p o i n t o u t t h e elevated O3 concentrations d u r i n g t h e evening, n i g h t , and e a r l y morning hours a t t h e San Bernardino s i t e ( a t midnight, 0.04 ppm on June 18 and 0.08 ppm on June 13), a p a t t e r n s i m i l a r t o t h a t seen i n t h e NAPBN data.
Peak-to-mean r a t i o s f o r these 2 days a t t h e San Bernardino s i t e a r e
1136
0000
0400
0800 1200 1600
2000 0000 0400 0800
1200 1600
JUNE18
-
2000 0000
TIME OF DAY, hr
Figure 6. (A) Diurnal curves for 3 successive days, Azusa. CA. August 24-26, 1985; (B) diurnal curves at San Bernardino, CA, for day with the maximum 1 -hour value for the year (June 18,1985) and day with the maximum 1-day mean for the year (June 13,1986) (Ref. 18).
lower than those a t t h e Azusa s i t e :
1.62 f o r June 13 (0.240/0.148
2.22
Nevertheless,
f o r June 18 (0.300/0.135
ppm).
f o r t h e days d e p i c t e d here and f o r t h e year, San Bernardino s i t e : f o r San Eernardino.
ppm) and
cumulative ozone,
both
i s much g r e a t e r a t t h e
272 ppm ozone per y e a r f o r Azusa versus 464 ppm p e r year I n passing i t should be noted t h a t t h e San Bernardino s i t e
r e f l e c t s p o t e n t i a l exposures o f t h e mixed-conifer f o r e s t i n t h e San Eernardino Mountains, since a i r p a r c e l s monitored a t t h i s s i t e o f t e n pass i n t o t h e mount a i n range (Ref.
1).
The San Eernardino f o r e s t has been documented as showing
ozone-induced damage (Ref. 1 and references t h e r e i n ) . Ozone i s commonly perceived t o be a r e g i o n a l p o l l u t a n t , b u t concentrat i o n s can d i f f e r markedly i n s p a t i a l d i s t r i b u t i o n ,
as t h e d i f f e r e n c e s i n
d i u r n a l d i s t r i b u t i o n s shown f o r these two s i t e s i n t h e same a i r s h e d would suggest.
Such d i f f e r e n c e s i n s p a t i a l d i s t r i b u t i o n s can r e s u l t i n f a i r l y
s u b s t a n t i a l g r a d i e n t s and d i f f e r e n c e s i n p o t e n t i a l exposures t o ozone w i t h i n t h e same a i r s h e d o r even t h e same c i t y .
Downwind o f well-mixed urban plumes,
concentrations i n a c i t y o r area can be r e l a t i v e l y homogeneous; b u t i n a l a r g e m e t r o p o l i s , appreciable g r a d i e n t s i n ozone concentrations can e x i s t from one s i d e o f t h e c i t y t o t h e o t h e r (Ref. 1). Recent data, f o r t h e Los Angeles megalopolis are shown i n F i g u r e 7 f o r f i v e s i t e s i n c l u d i n g t h e Azusa and San Bernardino s i t e s a l r e a d y discussed. episode days ( i . e . ,
As F i g u r e 7 shows, t h e number o f
days when ozone c o n c e n t r a t i o n s were 20.20 ppm) v a r i e d
w i d e l y among s i t e s w i t h i n , east, and southeast o f Los Angeles (LA) i n t h e years shown (Ref. 19).
Some o f these c i t i e s i n t h e Los Angeles area a r e w i t h i n d a i l y
commuting d i s t a n c e o f each other.
Thus, such d i f f e r e n c e s i n p o t e n t i a l expo-
sures t o ozone should be taken i n t o c o n s i d e r a t i o n , where p o s s i b l e , i n exposure assessments.
187
80
70
60 rn
2 so n
p
40
30 20 10 0
1
2
3
4
6
Figure 7. Comparison of ozone episodes (20.2 ppm) at selected monitoring stations in the California South Coast Air Basin (1-Riverside; 2-Sen Bernardino; 3-Azura; 4-Anaheim; 6downtown Los Angeles (Ref. 19). One f i n a l p o i n t may be o f i n t e r e s t w i t h respect t o ozone: t h a t i s , the extent o f i t s co-occurrence w i t h other major gas-phase pol 1utants such as NO2 and SO2,
both o f which have been shown t o be respiratory i r r i t a n t s and
t o be i n j u r i o u s t o vegetation i f present a t t o x i c levels.
The diurnal curves shown e a r l i e r f o r ozone i n urban areas would indicate, if they are t y p i c a l , t h a t the l i k e l i h o o d o f the co-occurrence o f ozone w i t h NO2 i n short-term peaks a t levels o f concern should be minimal, since NO2 concentrations peak twice per day, i n morning and evening (Ref. 1). Where diurnal patterns are f l a t t e r - - a s i n many nonurban o r smaller urban areas--the l i k e l i h o o d o f simultaneous co-occurrence o f ozone and NO2 i s greater but a t lower concentrations o f both. Since about 95 percent o f manmade emissions o f SO2 come from stationary sources, diurnal patterns are less clearcut and thus co-occurrences o f SO2 w i t h ozone, NO2, o r both, may possibly be more frequent. Lefohn and Tingey (Ref. 20) examined data f o r r u r a l o r other agricult u r a l l y important s i t e s f o r May through September 1981, from three aerometric monitoring networks i n the U.S. (SAROAD, EPRI-SURE, TVA; see Ref. 20), t o determine whether O3 co-occurs w i t h SO2 and NO2. They selected a concentrat i o n c u t o f f o f 20.05 ppm (1-hr average) and simultaneous occurrence w i t h i n the same hour as the c r i t e r i a f o r defining co-occurrences. The concentration c u t o f f was based on reports showing e f f e c t s on vegetation o f 2 ppm NO2 plus 0.05 ppm SO2 and 0.05 ppm O3 plus 0.05 ppm SO2 (see Ref. 20). Data from a l l types o f s i t e s (e.g., urban, r u r a l , p o i n t source-related) were examined t o ensure lack o f bias by type o f location. Their analysis showed t h a t cooccurrences i n the U.S. o f SO2-03, N02-03, o r SO2-NO2 p o l l u t a n t p a i r s are short-lived (hours), widely separated i n t i m e (weeks, sometimes months), and t h a t periods o f co-occurrence represent a very small p o r t i o n o f the growing
188
periods of a g r i c u l t u r a l crop species.
Figure 8 (Ref. 20) shows the frequency
d i s t r i b u t i o n o f 03-SO2 and 03-NO2 co-occurrences by number o f s i t e s and number (1-hr each) o f co-occurrences. Data are s i m i l a r f o r the two p o l l u t a n t p a i r s
100 I
1
NUMBER OF CO-OCCURRENCES
Figure 8. Frequency distribution of co-occurrence of ozone with nitrogen dioxide or sulfur dioxide. Co-occurrence is defined as the simultaneous occurrence of 1-hour concentrationsof 20.05 ppm ozone and either 10.05 ppm nitrogen dioxide or 20.05 ppm sulfur dioxide. Data are from 176 site-years of ozone-sulfur dioxide co-monitoring and 194 site-years of ozone-nitrogen dioxide co-monitoring (Ref. 20).
except f o r the upper end o f the d i s t r i b u t i o n f o r O3 plus NO2.
This upper end
o f the range represents high-NO2 r u r a l / a g r i c u l t u r a l s i t e s and may represent high-03 s i t e s as well, since i n lower-03 and lower-NO2 areas the two diurnal curves would most l i k e l y overlap a t l e v e l s lower than the concentration c u t o f f s chosen. I n subsequent work,
Lefohn e t a l .
(Ref. 21) expanded t h e i r d e f i n i t i o n
o f to-occurrences t o include the occurrence w i t h i n the same 24-hr period o f p o l l u t a n t p a i r s (among SO2, NO2, 03) a t concentrations o f 20.03 ppm and >0.05 ppm. They also included data on additional r u r a l / a g r i c u l t u r a l s i t e s
-
(Ref. 21).
Results confirmed the e a r l i e r analysis (Ref. 20), i.e.,
NO2 a t 1-hr concentrations each o f
SOq and
20.03 and O3 a t 20.05 ppm occur
infrequently, e i t h e r singly o r i n combination, a t r u r a l - a g r i c u l t u r a l s i t e s . These findings are consistent w i t h the analysis of Jacobson and McManus (Ref. 22), who found t h a t simultaneous (same-hour) co-occurrences o f SO2 and NO, were infrequent i n the Ohio River Valley, even i n an area t h a t contains four c o a l - f i r e d power plants. Data from population-oriented monitoring s i t e s (mainly c e n t e r - c i t y and suburban) were subsequently examined (Ref. 23) t o determine whether O3 cooccurs w i t h NO2 a t those s i t e s a t concentrations o f p o t e n t i a l concern f o r
p u b l i c health.
Co-occurrences were defined as t h e occurrence o f b o t h p o l l u t -
ants w i t h i n t h e same 24-hr p e r i o d a t 1-hr average concentrations o f 0.12 ppm
O3 and 0.3 ppm NO2.
These concentrations were selected on t h e b a s i s o f sug-
gested o r demonstrated h e a l t h e f f e c t s a t l e v e l s o f 20.12 ppm O3 f o r 2 h r Ref. 24) and a t l e v e l s o f 20.3 t o 20.5 ppm NO2 f o r (1 h r (e.g.,
(e.g.,
Ref. 25).
Analyses were done on 4787 site-years o f
O3 data and 2141 site-years
o f NO2 data f o r A p r i l through October, 1978 through 1984.
M u l t i p l e years of
data from t h e same s i t e were t r e a t e d as independent data sets i n t h e analysis. Episodic l e v e l s o f both p o l l u t a n t s occurred during these years a t urban s i t e s i n a t l e a s t e i g h t states, b u t co-occurrences i n t h e same-hour,
same 24 hr, o r
both were found o n l y i n data from monitoring s t a t i o n s i n southern C a l i f o r n i a . There,
1-hr NO2 concentrations 20.3 ppm preceded, followed, o r accompanied
1-hr O3 concentrations 20.12 ppm a t o t a l o f 23 times i n 3 yr (1979-1981) among 15 separate s i t e s .
NO2 and O3 occurred together i n t h e same hour a t t h e
s p e c i f i e d concentrations o n l y 6 o f the 23 times.
Thus, t h e data i n d i c a t e t h e
infrequent co-occurrence o f 1-hr concentrations o f O3 and NO2 a t l e v e l s o f possible concern f o r health.
Co-occurrences o f O3 and NO2 a t urban s i t e s a t
lower l e v e l s f o r m u l t i p l e hours are a subject f o r f u r t h e r i n v e s t i g a t i o n , as are the possible co-occurrences o f O3 p l u s SO2 a t l e v e l s o f p o t e n t i a l concern. Figure 9 shows an example o f d i u r n a l curves f o r 03, SO2, and NO2 derived from 1-hr measurements made on t h e same day a t a s i t e i n Fontana, CA (Ref. 20), a high-N02, high-03 s i t e . These curves, along w i t h t h e data o f Lefohn e t a l . ( R e f . 23) on co-occurrences o f
O3 p l u s NO2, suggest the relevance o f h e a l t h
Figure 9. Example of diurnal curves of ozone, sulfur dioxide, and nitrogen dioxide on the same day at Fontana, CA.(Ref. 20).
190
e f f e c t s research i n v o l v i n g sequential exposures t o O3 p l u s NO2 o r SO2 and simultaneous exposures t o NO2 p l u s SO2.
The l a t t e r might be e s p e c i a l l y
r e l e v a n t , f o r example, i n t h e study o f responses o f m i l d asthmatics. TEMPORAL PATTERNS I N PAN CONCENTRATIONS The more common features o f peroxyacetyl n i t r a t e (PAN) behavior i n ambient a i r i n the U.S. have been i d e n t i f i e d b u t are l e s s well-documented than f o r ozone because o f t h e p a u c i t y o f data on PAN.
The d i s t r i b u t i o n s o f PAN concen-
t r a t i o n s i n ambient a i r may be concisely summarized by saying t h a t they q u a l i t a t i v e l y resemble those o f ozone (Refs. 1, 15). Two examples are presented here o f the temporal d i s t r i b u t i o n s o f PAN i n ambient a i r i n the U.S.
Figure 10 (derived from Ref. 5) shows t h e seasonal
d i s t r i b u t i o n s o f PAN concentrations from August through A p r i l , 1967-1968 and 1980. D i s t r i b u t i o n s were n o t shown by Temple and T a y l o r (Ref. 4) f o r May through J u l y , which are known t o be high-oxidant months i n Riverside, CA. Other data presented (below and Table 2) i n d i c a t e , however, t h a t higher average concentrations o f PAN are seen i n the l a t e s p r i n g and summer months, w i t h t h e occurrence of the lowest average PAN concentrations b u t some o f t h e higher maxima i n w i n t e r , as i s evident from t h i s graph.
A
S
O N D J F MONTH OF YEAR
M
A
Figure 10. Seasonal distribution of daylight average and maximum PAN concentrations at Riverside, CA, 1967-1968 and 1980 (Ref. 4).
An i n t e n s i v e study o f photochemical a i r q u a l i t y i n t h e South Coast A i r Basin o f C a l i f o r n i a was conducted i n summer 1987.
Among t h e p o l l u t a n t s
measured were ozone, n i t r o g e n d i o x i d e , v o l a t i l e organic compounds, PAN and various o t h e r t r a c e nitrogenous species, s u l f u r dioxide, t o t a l s u l f a t e , and t o t a l n i t r a t e . P r e l i m i n a r y data a r e r e p o r t e d here f o r t h e observed concent r a t i o n s and p a t t e r n s o f PAN and o t h e r t r a c e nitrogenous species.
191
Measurements o f PAN were made each 15 min f o r 24 hr/day a t Claremont, CA, f o r most o f the June 9 through September 3 study. PAN was measured by GC-ECD (Ref. 26) and measurements were calibrated by I R spectrophotometry (PAN syn-
thesis, Ref. 27; PAN q u a n t i f i c a t i o n by I R , Ref. 28).
Results f o r the PAN
measurements from the t o t a l study period are given i n Table 3. TABLE 3. PAN concentrations a t Claremont, CA, June 9 through September 3. 1987
June
Jul.
-
Aug. Sept.
Total period
Concn., ppb Maximum Minimum Average Median (No. samples)
25.49
19.61
23.92
(0.01
(0.01
25.49 (0.01
4.77 2.94
2.97 1.96
3.90 2.94
2.57
(2021)
(2185)
(1638)
3.88 (5844)
When compared with other 24-hr/day data f o r the smog season i n the South Coast A i r Basin, these data show both maxima and means t o be q u i t e s i m i l a r t o values reported from the l a t e 1960s through the 1980s (e.g.,
Refs. 5, 9, 10).
Compared w i t h 11 days o f data from the same Clarernont s i t e i n 1980 (Ref. 5), the PAN concentrations measured i n 1987 were somewhat lower. Meteorological conditions i n C a l i f o r n i a i n summer 1987 are known, however, t o have been atypical, r e s u l t i n g both i n lower PAN and lower ozone concentrations than are usually observed. Ozone data f o r 6 o f the most intensively monitored days o f the study are shown i n Table 4. along w i t h PAN-to-ozone r a t i o s f o r those days.
Ozone
concentrations f o r the 6 days ranged from 51 ppb t o 286 ppb and PAN
A t n i g h t and i n the e a r l y x 1001 ranged as high as 360 percent. I n a l l but one instance o f extremely high r a t i o s , however, reported ozone levels were below the reconmended range f o r the monitoring instrumentation. Thus, PAN-to-ozone r a t i o s were calculated f o r Table 4 only f o r the 1-hr d a i l y maximum concentration o f ozone f o r each day. Though both PAN and ozone concentrations were lower than t y p i c a l because o f the atypical meteorology f o r the s m e r , the PAN-to-ozone r a t i o s are s i m i l a r t o those reported by A l t s h u l l e r f o r urban areas i n C a l i f o r n i a i n the 1970s (Ref. 15). The diurnal curves f o r 03, PAN, HONO, HN03, and NH3 f o r 2 days, including the day having the highest maximum PAN i n the 3-month study period, are shown i n Figure 11. Inorganic species were measured by annular denuder methodology concentrations ranged f o r 0.6 ppb t o 20.8 ppb.
morning,
PAN concentrations exceeded those o f ozone; and [(PAN/03)
192 TABLE 4. Ozone concentrations (ppb) and PAN-to-ozone r a t i o s a t Claremont, CA, J u l y 13-15 and August 27-29, 1988
0 concn.; 2r r a t i o
24- h r average 14- h r average
24-hr cumulative 14-hr cumulative Daily 1-hr maximum
Oate
?/13
7/14
7/15
8/27
8/28
8/29
Average
61 92 1463 1383 215
60 94 1446 1413 235
43 68 1043 1024 147
64 101 1538 1515 239
76 120 1824 1796 286
80 122 1911 1833 244
64 100 1494 1494 228
6
6
5
6
8
9
7
a6:00 a.m. through 8:OO p.m. readings covering 14 hours. (Ref. 29) as modified by Vossler e t al. (Ref. 30). t i e s i n timing and magnitude o f PAN and HN03 peaks.
Note the general s i m i l a r i I n e a r l i e r work reported
by Tuazon e t a l . (Ref. 7), PAN formation was shown t o t r a i l t h a t o f ozone somewhat and i t s disappearance t o p a r a l l e l t h a t o f HN03.
The ozone peaks
occurred a t t h i s p a r t i c u l a r s i t e a t around 3:OO t o 4:OO p.m. (1500 t o 1600). somewhat l a t e r than reported f o r ozone by Tuazon e t a l . f o r 1979 (Ref. 7). 300 280 260 240 220 200 180
3
160 140 120 100 80
2 e
5z
8
60
40 20
OOOO 0400 0800 1200
I600 2000
oo00 0400 0800
0 1200 ls00 2000 2400
nouR OF DAY. POT Figure 11. Diurnal curves for ozone and PAN and other trace nitrogenous compounds, August 27 and 28, 1987, Claremont, CA.
SUMMARY
A broad overview o f concentrations o f ozone and PAN i n the U.S. has been I n addition, aerometric data f o r ozone and PAN from selected s i t e s
presented.
have been examined f o r patterns o f i n t e r e s t
in r e l a t i o n t o p o t e n t i a l exposures
193
o f populations o r vegetation.
Simple s t a t i s t i c s t h a t o f t e n serve as i n d i c e s o f
ozone a i r q u a l i t y have been compared f o r q u a r t e r l y d i u r n a l ozone data from selected nonurban and suburban s i t e s i n t h e U.S.
These show t h a t higher
long-term average concentrations and greater cumulative ozone exposures can occur i n nonurban than i n urbadsuburban areas.
They i n d i c a t e , as w e l l , t h a t
d a i l y f l u c t u a t i o n s i n ozone concentrations and i n dose r a t e s i n the warm-weather months are greater i n urbadsuburban areas than i n nonurban areas. I n a d d i t i o n , t h e co-occurrence o f ozone w i t h NO2 o r SO2 has been examined and determined t o be infrequent a t l e v e l s o f concern f o r vegetation.
The co-occurrence of ozone
w i t h NO2 i n urban areas a t 1-hr l e v e l s o f concern f o r h e a l t h e f f e c t s has been shown t o be even more infrequent. REFERENCES T. McMullen, E. Robinson, and B. T i l t o n , i n A i r Q u a l i t y C r i t e r i a f o r Ozone and Other Photochemical Oxidants, Vol. 11, U.S. Environmental P r o t e c t i o n Agency, Research T r i a n g l e Park, NC 27711, 1986; EPA/600/8-84/020bfI Ch. 5, pp. 5-1--5-127. 2. G. Evans, P. F i n k e l s t e i n , B. Martin, N. Possiel, and M. Graves, JAPCA, 33( 1983)291-296. 3. U.S. Oept. o f Commerce, Bur. o f Census, S t a t i s t i c a l Abstract o f t h e United States, 103rd edn., U.S. Govt. P r i n t i n g O f f i c e , Washington, DC, 1982, p. 221. 4. P. J. Temple and 0. C. Taylor, Atmos. Environ. 17(1983)1583-1587. 5. D. Grosjean, Environ. Sci. Technol. 17(1983)13-19. 6. H.B. Singh, L.J. Salas, H. Shigeishi, A.J. Smith, E. Scribner, and L.A. Cavanagh, Atmospheric D i s t r i b u t i o n , Sources, and Sinks o f Selected Halocarbons, Hydrocarbons, SF6, and N20, U. S. Environmental P r o t e c t i o n Agency, Research T r i a n g l e Park, NC. , 1979, Rept. No. EPA-600/3-79-107. 7. E.C. Tuazon, A.M. Winer, and J.N. P i t t s , Jr., Environ. Sci. Technol., 15( 1981)1232-1237. 8. J.N. P i t t s , Jr., and D. Grosjean, D e t a i l e d Characterization o f Gaseous and Size-Resolved P a r t i c u l a t e P o l l u t a n t s a t a South Coast A i r Basin Smog Receptor Site, C a l i f o r n i a A i r Resources Board, Sacramento, CA, 1979, Rept No. ARB- R- 5- 384- 70- 100. 9. C.W. Spicer, i n J.N. P i t t s , Jr, R.L. Metcalf, and A.C. Lloyd (Eds.), Advances i n Environmental Science and Technology, Vol. 7, John Wiley and Sons, New York, NY, 1977, pp. 163-261. 10. 0. C. Taylor, JAPCA, 19(1969)347-351. 11. H. Mayrsohn and C. Brooks, Presentation a t Western Regional Meeting o f the American Chemical Society, Los Angeles, CA, November 1965. ( C i t e d i n Ref. 1.) 12. H. Westberg, K. Allwine, and E. Robinson, Measurement o f L i g h t Hydrocarbons and Oxidant Transport: Houston Area 1976, U.S. Environmental P r o t e c t i o n Agency, Research T r i a n g l e Park, NC 27711, 1978, Rept. No. EPA-600/3-78-662. 13. C.W. Spicer, The f a t e o f Nitrogen Oxides i n t h e Atmosphere, U.S. Environmental P r o t e c t i o n Agency, Research T r i a n g l e Park, NC 27711, 1976, Rept. No. EPA-600/3-76-030. 14. T.E. Lewis, E. Brennan, and W.A. Lonneman, JAPCA, 33(1983)885-887. 15. A.P. A l t s h u l l e r , Atmos. Environ., 17(1983)2383-2427. 16. J.A. Logan, J. Geophys. Res. , 90(1985)10463-10482. 17. G.F. Evans, The National A i r P o l l u t i o n Background Network, F i n a l P r o j e c t Report, U. S. Environmental P r o t e c t i o n Agency, Research T r i a n g l e Park, NC 27711, 1985, p . 9.
1.
.
134
18. 19.
20. 21. 22. 23. 24. 25. 26. 27. 28.
29. 30.
AIRS, Aerometric Information R e t r i e v a l System data base, Data f i l e f o r 1985, U. S. Environmental P r o t e c t i o n Agency, Research T r i a n g l e Park, NC 27711, 1988; Disc, A S C I I . A i r Q u a l i t y Digest, South Coast A i r Q u a l i t y Management D i s t r i c t , E l Monte, CA 91731, F a l l 1987. A.S. Lefohn and D.T. Tingey, Atmos. Environ., 18(1984) 2521-2526. A.S. Lefohn, C.E. Davis, C.K. Jones, D.T. Tingey, and W.E. Hogsett, Atmos. Environ. , 21(1987)2435-2444. J.S. Jacobson and J.M. McManus, Atmos. Environ., 19(1985)501-506. A.S. Lefohn, L.R. McEvoy, Jr., and B. T i l t o n , I n preparation. W.F. McDonnell, D.H. Horstmann, M.J. Hazucha, E. Seal, Jr., E.D. Haak, S. Salaam, and D.E. House, J. Appl. Physiol.: Respir. Environ. Exercise Physiol , 54(1983)1345-1352. M.A. Bauer, M. J. U t e l l , P.E. Morrow, D.M. Speers, and F.R. Gibb, Am. Rev. Respir. Dis., 129(1984)A151 (Abstr. 1. W.A. Lonneman, J.J. B u f a l i n i , and G.R. Namie, Environ. Sci. Technol., 16( 1982)655-660. B.W. Gay, R.C. Noonan, J.J. B u f a l i n i , and P.L. Hanst, Environ. Sci. Technol. , 10(1976)82-85. E. R. Stephens, Anal. Chem. , 36(1964)928-929 (see a1 so E. R. Stephens, i n J.N. P i t t s , Jr., and R.L. M e t c a l f (Eds.), Advances i n Environmental Sciences, Vol. 1, Wiley-Interscience, New York, NY, pp. 119-146. M. Possanzini, A. Febo, and A. L i b e r t i , Atmos. Environ., 17( 1983)2605-2610. T.L. Vossler, R.K. Stevens, R.J. Paur, R.E. Baumgardner, and J.P. B e l l , I n press.
.
ACKNOWLEDGMENT Ozone data i n Table 4 were c o l l e c t e d by General Motors Research Labs, Warren, M I , USA.
The authors g r a t e f u l l y acknowledge D r . George W o l f f o f
General Motors Research Labs f o r p r o v i d i n g them w i t h the data.
T. Schneider et al. (Editors),Atmospheric Ozone Research and its Policy Implications 1989 Elsevier Science Publishers B.V., Amsterdam -Printed in The Netherlands
TRENDS
IN AMBIENT OZONE AND
PRECURSOR EMISSIONS I N U.S.
135
URBAN AREAS
CURRAN
T.C.
O f f i c e o f A i r Q u a l i t y Planning and Standards, U.S. Environmental P r o t e c t i o n Agency, MD-14, Research T r i a n g l e Park, NC 27711 (USA)
ABSTRACT T h i s paper discusses ambient ozone t r e n d s i n t h e U n i t e d S t a t e s based upon data c o l l e c t e d a t over 200 m o n i t o r i n g s i t e s f o r t h e 1977-86 t i m e period. The ozone m o n i t o r i n g s i t e s used i n t h i s a n a l y s i s were s e l e c t e d t o ensure a c o n s i s t e n t data base over time. The i n t e r p r e t a t i o n o f t h e l o n g t e r m ambient ozone t r e n d i n t h e U.S. i s discussed as w e l l as associated f a c t o r s such as measurement methodology and meteorological c o n d i t i o n s which can a f f e c t these trends. Precursor emission t r e n d s a r e presented based upon n a t i o n a l emission estimates. P r a c t i c a l problems associated w i t h t h e s e types o f t r e n d s a r e b r i e f l y discussed.
INTRODUCTION Ambient ozone c o n c e n t r a t i o n s c o n t i n u e t o be a major environmental concern i n urban areas o f t h e United States. were l i v i n g i n U.S. t o meet t h e U.S. ozone.[ll
I n 1986, 75 m i l l i o n people
c o u n t i e s w i t h measured a i r q u a l i t y l e v e l s t h a t f a i l e d
National Ambient A i r Q u a l i t y Standards (NAAQS) f o r
Because o f t h e p e r v a s i v e n a t u r e o f t h e ozone problem, t h e r e i s
considerable i n t e r e s t i n assessing progress i n t h e c o n t r o l o f t h i s pollutant.
A i r p o l l u t i o n m o n i t o r i n g programs i n t h e U.S.
have produced a
data base t h a t makes i t p o s s i b l e t o study ambient ozone trends.
This paper
uses these d a t a t o examine ambient t r e n d s f o r t h e 1977-86 t i m e period. This 10-year p e r i o d i s p a r t i c u l a r l y i n t e r e s t i n g , n o t o n l y i n terms o f t h e a c t u a l ozone trends, b u t i n s e r v i n g t o i l l u s t r a t e t h e p r a c t i c a l problems t h a t can occur i n terms o f changes i n measurement methodology and v a r i a t i o n s i n meteorological c o n d i t i o n s . METHODOLOGY Data Base The ozone data used i n these analyses were obtained from t h e U.S. Environmental P r o t e c t i o n Agency's (USEPA) Aerometric I n f o r m a t i o n R e t r i e v a l System (AIRS), a comprehensive computerized d a t a base f o r a i r p o l l u t i o n data.
These data were c o l l e c t e d p r i m a r i l y by S t a t e and l o c a l agencies and
136 t h e n submitted t o USEPA and s t o r e d i n AIRS.
The b a s i c d a t a are 1-hour
averages t h a t a r e t h e n summarized as d a i l y maximum values.
I n o t h e r words,
t h e d a i l y maximum ozone v a l u e i s t h e h i g h e s t o f t h e 1-hour averages f o r t h a t day.
Because o f t h e s t r o n g s e a s o n a l i t y o f ozone, many s t a t e s a r e
allowed t o l i m i t t h e i r ozone m o n i t o r i n g t o a c e r t a i n p o r t i o n o f t h e year, termed t h e ozone season. U.S.
During 1983-85,
97 percent o f t h e days i n t h e
w i t h c o n c e n t r a t i o n s exceeding t h e ozone standard were i n t h e months o f
A p r i l through October.
The l e n g t h o f t h e ozone season m o n i t o r i n g
requirements v a r i e s across t h e U.S.
While A p r i l through October i s
t y p i c a l , States i n t h e south and southwest may m o n i t o r t h e e n t i r e year. S t a t e s f u r t h e r n o r t h g e n e r a l l y have s h o r t e r ozone seasons such as May through September f o r North Dakota.
This a n a l y s i s uses t h e s e ozone seasons
on a S t a t e by S t a t e b a s i s t o ensure t h a t t h e d a t a completeness requirements a r e a p p l i e d t o t h e r e l e v a n t p o r t i o n s o f t h e year. Trend S i t e S e l e c t i o n To ensure a c o n s i s t e n t d a t a base f o r ozone t r e n d s , two types o f data completeness requirements were used i n s e l e c t i n g s i t e s .
The f i r s t a p p l i e d
t o annual d a t a completeness w h i l e t h e second r e q u i r e d h i s t o r i c a l c o n t i n u i t y by s p e c i f y i n g a minimum number o f y e a r s o f d a t a over time.
The
annual d a t a completeness requirement s p e c i f i e d t h a t a t l e a s t 50 percent o f t h e d a i l y maximums had t o be present d u r i n g t h e ozone season f o r a y e a r o f d a t a a t a s i t e t o be considered "valid."
The h i s t o r i c a l c o n t i n u i t y
requirement s p e c i f i e d t h a t a t l e a s t 75 percent o f t h e y e a r s d u r i n g t h e t i m e p e r i o d o f i n t e r e s t must be v a l i d f o r t h e s i t e t o be i n c l u d e d i n t h e t r e n d s analysis.
This requirement s t a b i l i z e s t h e t r e n d s d a t a base so t h a t changes
i n measured ozone l e v e l s over t i m e should n o t be simply t h e r e s u l t o f a changing d a t a base.
This t r e n d s i t e s e l e c t i o n process r e s u l t e d i n a d a t a
base o f 242 ozone t r e n d s i t e s f o r t h e 1977-86 t i m e p e r i o d and 539 t r e n d s i t e s f o r t h e 1982-86 t i m e period. These s i t e s a r e l o c a t e d p r i m a r i l y i n t h e more populated areas o f t h e U.S.
For example, every urban area w i t h a
p o p u l a t i o n g r e a t e r t h a n 200,000 i s r e q u i r e d t o have a t l e a s t two ozone monitoring sites.
This paper focusses p r i m a r i l y on t h e 10-year d a t a base
b u t t h e l a r g e r 5-year data base i s used t o i l l u s t r a t e c e r t a i n r e c e n t changes. Trend S t a t i s t i c The primary i n t e r e s t i n ozone t r e n d s i n t h e U.S. i s assessing progress towards meeting EPA's ozone standard.
Therefore, t h i s study focusses on
summary s t a t i s t i c s t h a t a r e c l o s e l y r e l a t e d t o t h i s standard.
The ozone
197
NAAQS i.s d e f i n e d i n terms o f t h e d a i l y maximum, t h a t i s , t h e h i g h e s t h o u r l y
average f o r t h e day, and s p e c i f i e s t h a t t h e expected number o f days p e r y e a r w i t h v a l u e s g r e a t e r t h a n 0.12 p a r t s p e r m i l l i o n (ppm) s h o u l d n o t be For convenience of t e r m i n o l o g y , a d a i l y maximum v a l u e
g r e a t e r t h a n one.
g r e a t e r t h a n 0.12 ppm, a c t u a l l y g r e a t e r t h a n o r equal t o 0.125 ppm a f t e r a l l o w i n g f o r rounding, i s termed an exceedance.
The a c t u a l i m p l e m e n t a t i o n
o f t h i s s t a n d a r d i n v o l v e s a d j u s t i n g f o r m i s s i n g d a t a and a v e r a g i n g t h e number o f exceedances o v e r m u l t i p l e y e a r s , t y p i c a l l y t h r e e years.[2]
To
f a c i l i t a t e t h e i n t e r p r e t a t i o n o f t h e t r e n d i n terms o f i n d i v i d u a l y e a r s , a s i m p l i f i e d s i n g l e y e a r i n t e r p r e t a t i o n i s employed i n t h i s s t u d y and t h e second h i g h e s t d a i l y maximum f o r t h e y e a r i s used i n t h e s e p r e s e n t a t i o n s . However, o t h e r p o s s i b l e t r e n d s t a t i s t i c s a r e a l s o d i s c u s s e d and compared. AMBIENT OZONE TRENDS Ambient ozone t r e n d s i n t h e U.S.
a r e p r e s e n t e d i n F i g u r e 1 f o r t h e 242
l o n g - t e r m t r e n d s i t e s f o r t h e 1977-86 t i m e p e r i o d .
These t r e n d s a r e shown
f o r t h e second h i g h e s t 1-hour d a i l y maximum ozone v a l u e f o r t h e y e a r w h i c h e s s e n t i a l l y corresponds t o a one y e a r i n t e r p r e t a t i o n o f t h e USEPA’s ozone standard.
B o x p l o t s a r e used t o g r a p h i c a l l y d i s p l a y t h e data.
This p l o t t i n g
t e c h n i q u e enables t h e t r e n d t o b e d i s p l a y e d f o r t h e e n t i r e d i s t r i b u t i o n o f s i t e s r a t h e r t h a n s i m p l y t h e composite average. p l o t t i n g c o n v e n t i o n s used i n t h e b o x p l o t s .
The i n s e t d e s c r i b e s t h e
For example, i n 1986 t h e 7 5 t h
p e r c e n t i l e d e p i c t e d i n t h e b o x p l o t i s 0.137 ppm meaning t h a t f o r 75 p e r c e n t o f t h e s e s i t e s t h e second h i g h e s t d a i l y v a l u e i n 1986 was l e s s t h a n o r equal t o 0.137 ppm. these s i t e s
A l t e r n a t i v e l y , i t f o l l o w s t h a t f o r 25 p e r c e n t o f
t h e second h i g h e s t d a i l y v a l u e was g r e a t e r t h a n 0.137 ppm.
F i g u r e 1 shows t h a t r e c e n t y e a r s have g e n e r a l l y had l o w e r ozone l e v e l s t h a n e a r l i e r years.
These d i f f e r e n c e s may be shown t o be s t a t i s t i c a l l y
s i g n i f i c a n t by u s i n g A n a l y s i s o f V a r i a n c e t e c h n i q u e s [ l ]
but there are
c e r t a i n f e a t u r e s o f t h e d a t a t h a t w a r r a n t d i s c u s s i o n t o more f u l l y e x p l a i n t h e patterns.
F o r example, a c a l i b r a t i o n change f o r ozone measurements
o c c u r r e d i n t h e 1978-79 t i m e p e r i o d i n t h e U.S.[3]
which i s why d a t a b e f o r e
1979 appears i n t h e s t i p p l e d p o r t i o n o f t h e graph.
The c o m p l i c a t i o n s
a s s o c i a t e d w i t h i n t e r p r e t i n g t r e n d s across t h i s c a l i b r a t i o n change and t h e d i f f i c u l t i e s i n q u a n t i f y i n g t h i s e f f e c t have been d i s c u s s e d p r e v i o u s l y . [ l ] While t h e general e f f e c t o f t h e c a l i b r a t i o n change would be t o y i e l d l o w e r ozone r e a d i n g s , t h e e x a c t magnitude o f t h i s d i f f e r e n c e was a f f e c t e d by several factors.
Also, n o t a l l agencies made t h e change a t t h e same t i m e
and t h e adjustment i s not”needed f o r some d a t a .
There have been a t t e m p t s
t o develop an e s t i m a t e o f t h e average a f f e c t o f t h i s c a l i b r a t i o n change,
perhaps on t h e o r d e r o t a 10-20 p e r c e n t decrease, b u t i t s i n t e r p r e t a t i o n needs t o b e viewed w i t h c a u t i o n . has been suggested.[4]
The e s t i m a t e o f an 18 p e r c e n t decrease
I f t h i s proposed c o r r e c t i o n were a p p l i e d t o t h e
composite average i n F i g u r e 1, e x c l u d i n g t h e C a l i f o r n i a d a t a which has a l r e a d y been a d j u s t e d , t h e 1977 and 1978 l e v e l s a r e s t i l l h i g h e r t h a n t h o s e f o r 1984-86. C o n s i d e r i n g o n l y d a t d a f t e r t h i s c a l i b r a t i o n change, t h e r e was a 13 p e r c e n t improvement i n ambient ozone l e v e l s between 1979 and 1986. However, t h i s has n o t been a smooth downward t r e n d and a n o t a b l e f e a t u r e o f t h e U.S. years.
ozone d a t a i s t h a t 1983 was much h i g h e r t h a n t h e a d j a c e n t
The widespread c o n s i s t e n c y o f t h i s p a t t e r n can b e seen i n F i g u r e 2
which h i g h l i g h t s t h e 1982-84 p e r i o d f o r t h e t e n USEPA Regions.
This F i g u r e
uses t h e 539 s i t e s t h a t met t h e t r e n d s s e l e c t i o n c r i t e r i a f o r t h e 1982-86 t i w period.
This l a r g e r data s e t should provide b e t t e r geographic
i o v e r d g e f o r t h e more r e c e n t t i m e p e r i o d .
The USEPA Regions a r e
a d m i n i s t r a t i v e g r o u p i n g s b u t can b e used t o r o u g h l y d e l i n e a t e g e o g r a p h i c a l a r e s : New England (Region I ) , New York-New J e r s e y (Region 1 1 ) , M i d - A t l a n t i c (Region I I I ) , Southeast (Region I V ) , Great Lakes (Region V), (Region V I ) ,
Midwest (Region V I I ) ,
Rocky Mountain (Region
(Region I X ) , and t h e P a c i f i c Northwest (Region X).
South C e n t r a l
VIII), West
As shown i n F i g u r e 2,
o n l y t h e P a c i f i c Northwest d e p a r t e d f r o m t h e p a t t e r n o f 1983 b e i n g t h e highest o f t h e t h r e e year period.
T h i s 1982-83 i n c r e a s e and 1983-84
decrease i s l i k e l y a t t r i b u t a b l e t o m e t e o r o l o g i c a l c o n d i t i o n s i n t h e U.S. b e i n g more conducive t o ozone f o r m a t i o n t h a n t h o s e i n a d j a c e n t y e a r s . has been d i s c u s s e d i n n a t i o n a l t r e n d s s t u d i e s [ 5 ]
This
and i n more d e t a i l e d
c i t y - s p e c i f i c analyses.[6] Another p o i n t o f i n t e r e s t i s whether i t i s p o s s i b l e t h a t annual peak ozone v a l u e s a r e s o v a r i a b l e t h a t t h e i r t r e n d s a r e n o t i n d i c a t i v e o f g e n e r a l ozone t r e n d s .
F i g u r e 3 p r e s e n t s t h e 1977-86 10-year ozone t r e n d s
f o r s e v e r a l d i f f e r e n t annual summary s t a t i s t i c s : maximum v a l u e , t h e p r e v i o u s l y d i s c u s s e d second maximum, t h e 9 0 t h p e r c e n t i l e o f t h e d a i l y maximums, and t h e seasonal average of t h e 1-hour d a i l y maximums.
While
t h e 9 0 t h p e r c e n t i l e and seasonal average c o u l d b e viewed as more s t a b l e t r e n d s t a t i s t i c s , t h e y y i e l d t h e same g e n e r a l p a t t e r n s a l r e a d y d i s c u s s e d f o r t h e annual second maximum.
The peak v a l u e summary s t a t i s t i c s g a i n
s t a b i l i t y when aggregated o v e r a l a r g e number o f s i t e s . Another p o s s i b l e t r e n d s t a t i s t i c i s p r e s e n t e d i n F i g u r e 4, which shows t h e 1977-86 t r e n d s i n t h e number o f exceedances o f t h e U.S.
ozone s t a n d a r d .
T h i s s t a t i s t i c shows t h e same g e n e r a l p a t t e r n o f l o n g - t e r m improvement, a g a i n w i t h t h e f l u c t u a t i o n i n 1983.
While t h e general p a t t e r n s a r e
133 c o n s i s t e n t and h i g h l y c o r r e l a t e d , i t s h o u l d be n o t e d t h a t t h e r a t e s o f change can d i f f e r a p p r e c i a b l y .
For example, t h e 1979-86 ozone improvement
i n t h e f o u r t r e n d s t a t i s t i c s p r e s e n t e d i n F i g u r e 3 i s 15 p e r c e n t f o r t h e maximum, 13 p e r c e n t f o r t h e second maximum, 9 p e r c e n t f o r t h e 9 0 t h p e r c e n t i l e , and 4 p e r c e n t f o r t h e seasonal average.
The more s t r i k i n g
c o n t r a s t i s w i t h t h e 38 p e r c e n t improvement between 1979 and 1986 f o r t h e expected number o f exceedances p e r y e a r shown i n F i g u r e 4.
The s t a b i l i t y
o f t h e number o f exceedances as a t r e n d s s t a t i s t i c i s a f f e c t e d by how many exceedances t h e r e are.
F o r s i t e s w i t h few exceedances p e r year, t h e y e a r
t o y e a r v a r i a b i l i t y on a percentage b a s i s i s l i k e l y t o be much g r e a t e r t h a n f o r s i t e s w i t h numerous exceedances. PRECURSOR E M I S S I O N TRENDS
T a b l e 1 p r e s e n t s t h e 1977-86 e m i s s i o n t r e n d s f o r v o l a t i l e o r g a n i c compounds (VOC) which, a l o n g w i t h n i t r o g e n o x i d e s , a r e i n v o l v e d i n t h e atmospheric chemical and p h y s i c a l processes t h a t r e s u l t i n t h e f o r m a t i o n o f ozone.[l,71
D u r i n g t h i s t e n y e a r p e r i o d , t o t a l VOC emissions a r e
e s t i m a t e d t o have decreased by 19 p e r c e n t w h i l e VOC e m i s s i o n s f r o m highway v e h i c l e s , a subset o f t h e t r a n s p o r t a t i o n c a t e g o r y , were e s t i m a t e d t o have decreased 39 p e r c e n t d e s p i t e a 24 p e r c e n t i n c r e a s e i n v e h i c l e m i l e s o f t r a v e l d u r i n g t h i s same p e r i o d .
For t h e 1977-86 t i m e p e r i o d , t o t a l
e s t i m a t e d n i t r o g e n o x i d e (NOx) emissions decreased b y 8 p e r c e n t , w i t h t h e c o n t r i b u t i o n f r o m highway v e h i c l e s d e c r e a s i n g by 13 percent.[7]
Ambient
n i t r o g e n d i o x i d e (N02) l e v e l s were 14 p e r c e n t l o w e r i n 1986 t h a n 1977. These annual mean NO2 l e v e l s i n c r e a s e d f r o m 1977 t o 1979 and t h e n showed a general decrease t h r o u g h 1986 except f o r a s l i g h t r i s e i n 1984. It s h o u l d be noted t h a t t h e p r e c u r s o r VOC t r e n d s a r e based upon e m i s s i o n
e s t i m a t e s r a t h e r t h a n measured ambient data.
I n c o n t r a s t t o ozone, t h e
h i s t o r i c a l d a t a base f o r ambient VOC measurements i s v e r y sparse.
For
example, when t h e same t y p e o f t r e n d s s e l e c t i o n c r i t e r i a t h a t was used f o r ozone was a p p l i e d t o non-methane hydrocarbon d a t a f r o m USEPA's d a t a base only three s i t e s qualified.
With t h e i n t e r e s t i n ozone and t h e added
concern about ambient a i r t o x i c s , a d d i t i o n a l VOC m o n i t o r i n g programs a r e being i n i t i a t e d .
However, i t w i l l t a k e t i m e f o r t h e s e d a t a bases t o be
adequate f o r t r e n d s and t h e r e w i l l be a need t o ensure t h a t t h e measurement methodologies a r e p r o d u c i n g d a t a t h a t can b e compared o v e r time. DISCUSSION
Although t h i s paper has presented ozone t r e n d s and d i s c u s s e d t h e i n t e r p r e t a t i o n o f some o f t h e s e r e s u l t s , i t i s p r o b a b l y u s e f u l t o p r o v i d e
200
an o v e r v i e w o f t h e p r a c t i c a l consequences o f a s s e s s i n g p r o g r e s s i n ambient ozone l e v e l s .
Obviously, once an ozone c o n t r o l program i s i n s t i t u t e d t h e r e
s h o u l d be i n t e r e s t i n d e t e r m i n i n g whether o r n o t p r o g r e s s i s b e i n g
made.
It a l s o f o l l o w s t h a t , i f t h e r e i s an ambient ozone standard, t h e p r o g r e s s s h o u l d b e j u d g e d i n terms t h a t r e l a t e t o t h e standard.
As shown i n F i g u r e s
3 and 4, w h i l e t h e r e may b e g e n e r a l agreement among t r e n d s t a t i s t i c s , t h e r e can be a p p r e c i a b l e d i f f e r e n c e s i n t h e r a t e o f change.
I t seems p r e f e r a b l e
t o have a t r e n d s t a t i s t i c w i t h a r a t e o f change t h a t i s r e l e v a n t and can b e r e l a t e d t o t h e progress t h a t i s o f concern.
A d e f i n i t e problem i n d e t e r m i n i n g p r o g r e s s i n ozone c o n t r o l i s w h e t h e r t h e expected change i s l a r g e enough so data.
t h a t i t can be d e t e c t e d f r o m t h e
Given t h e p o s s i b l e e f f e c t s o f measurement m e t h o d o l o g i c a l changes o r
v a r i a t i o n s i n m e t e o r o l o g i c a l c o n d i t i o n s , i t may b e d i f f i c u l t t o q u i c k l y i d e n t i f y p r o g r e s s f r o m one y e a r t o t h e n e x t .
It may be p o s s i b l e t o
a n t i c i p a t e and c a r e f u l l y e v a l u a t e changes i n measurement methodology t o account f o r t h e i r e f f e c t .
However, t h e i n f l u e n c e s o f v a r y i n g
m e t e o r o l o y i c a l c o n d i t i o n s p r e s e n t s a r e a l problem f o r ozone. F i g u r e 2, annual second maximum ozone l e v e l s i n t h e U.S. 12 p e r c e n t h i g h e r t h a n i n 1982 and 1984.
As shown i n
i n 1983 averaged
T h i s makes i t q u i t e u n l i k e l y
t h a t l e s s pronounced annual improvement c o u l d be i d e n t i f i e d u n l e s s t h e p o s s i b l e e f f e c t o f changing m e t e o r o l o g i c a l c o n d i t i o n s can be accounted f o r . The p r e s e n t s t a t e o f knowledge on m e t e o r o l o g i c a l a d j u s t m e n t o f ozone t r e n d s i s p r o b a b l y n o t s u f f i c i e n t t o unambiguously a d j u s t t h e d a t a .
However, i t
may be p o s s i b l e t o i d e n t i f y c e r t a i n c l a s s e s o f m e t e o r o l o g i c a l c o n d i t i o n s and examine how ozone l e v e l s changed from one y e a r t o t h e n e x t on s i m i l a r t y p e s o f days. The above concerns a p p l y t o ambient ozone d a t a b u t t h e r e a r e o t h e r p r a c t i c a l concerns about d e t e r m i n i n g p r e c u r s o r emi s s i on t r e n d s .
The 1ack
o f a h i s t o r i c a l ambient VOC d a t a base r e s u l t s i n a r e l i a n c e on e m i s s i o n e s t i m a t e s b u t t h e r e a r e r e s e r v a t i o n s about how w e l l e m i s s i o n e s t i m a t e t r e n d s f o r ozone p r e c u r s o r s correspond t o t h e a c t u a l trends.[8,9]
In
f a c t , b o t h q u a n t i t a t i v e and q u a l i t a t i v e d i s c r e p a n c i e s have been found between e s t i m a t e d and a c t u a l p r e c u r s o r emi s s i o n trends.[8]
T h i s suggests
t h a t a d d i t i o n a l ambient m o n i t o r i n g d a t a on p r e c u r s o r emissions would b e u s e f u l i n a s s e s s i n g t h e e f f e c t i v e n e s s o f ozone c o n t r o l programs.
It i s
a l s o a d v i s a b l e t o ensure t h a t t h e p r e c u r s o r e m i s s i o n t r e n d s a r e r e l e v a n t f o r ozone t r e n d s .
F o r example, a l t h o u g h an i n c r e a s i n g c o n t r i b u t i o n t o VOC
emissions f r o m wood s t o v e s may be an e n v i r o n m e n t a l concern, t h e d i f f e r e n t seasonal p a t t e r n may d i s c o u n t t h e impact on ozone l e v e l s .
201 Despite these complications, i t s t i l l seems reasonable t h a t progress, o r l a c k o f progress, i n ozone c o n t r o l w i l l have t o be evaluated.
Therefore,
these p r a c t i c a l problems need t o be recognized and f u t u r e d a t a needs should be evaluated i n l i g h t o f what has been l e a r n e d t o d a t e o f t h e d i f f l c u l t i e s i n assessing ozone trends. REFERENCES
1 National A i r Qual it y and Emissions Trends Report, 1986, EPA-450/4-83Research T r i a n g l e Park, NC, 001, U.S. Environmental P r o t e c t i o n Agency, . . February 1988. 2 T.C. Curran, "Guidelines f o r t h e I n t e r p r e t a t i o n o f Ozone A i r Q u a l i t y Standards," EPA-450/4-79-003, U.S. Environmental P r o t e c t i o n Agency, Research T r i a n g l e Park, NC, January 1979. 3 Measurement of-Ozone i n t h e Atmosphere, 43 Federal R e g i s t e r 26971, June 22. 1978. 4 H.M. Waiker, Journdl o f t h e A i r P o l l u t i o n Control A s s o c i a t i o n , 35 ( 1985) 903-91 2. 5 National A i r Qualit y and Emissions Trends Report, 1984, EPA-450/4-86-001, U.S. Environmental P r o t e c t i o n Agency, Research T r i a n g l e Park, NC, A p r i l 1986. 6 T.A. Sweitzer and D.J. Kolaz, i n Transactions o f t h e APCA/ASQC S p e c i a l t y Conference, " Q u a l i t y Assurance i n Air P o l l u t i o n Measurement", Boulder, Colorado. 1985. 7 National - A i r P o l l u t a n t Emission Estimates 1940-1986, EPA-450/4-87-024, U.S. Environmental P r o t e c t i o n Agency, - . Research T r i a n g l e Park,. NC.. January 1988. 8 G.Kuntasal and T.Y. Chang, Journal o f t h e A i r P o l l u t i o n C o n t r o l Association, 37(1987)1158-1163. 9 O.P. Chock and J.M. Heuss, Environ. Sci. Techno1.,21(1987)1146-1153. Table 1. National V o l a t i l e Organic Compound Emission Estimates, 1977-1986. (mi 1 l i o n m e t r i c t o n s l y e a r ) 1977
1978
1979
1980
1981
1982
1983
1984
1985 1986
Transportation
10.0
9.7
8.9
8.2
7.9
7.4
7.3
7.3
6.7
6.5
Fuel Combustion
1.4
1.6
1.9
2.2
2.3
2.5
2.6
2.6
2.3
2.3
Industri d l Processes
9.3
9.9
9.8
9.2
8.3
7.4
7.8
8.7
8.4
7.9
Non-Indust r i a1 Organic Solvent Use
1.9
1.9
2.0
1.9
1.6
1.5
1.6
1.8
1.5
1.5
S o l i d Waste
0.8
0.8
0.7
0.6
0.6
0.6
0.6
0.6
0.6
0.6
M i scel 1aneous
0.8
0.8
0.9
1.0
0.9
0.7
1.1
0.9
0.7
0.7
24.1
24.7
24.3
23.0
21.6
20.1
20.9
21.9
Source Category
Total NOTE:
20.3 19.5
The sum o f sub-categories may n o t equal t o t a l due t o rounding.
ra
OZONE TREND, 1977-1986
0 N
fun-lNc-RlRm
(ANNUAL 2ND DAILY MAX HOUR)
9 m -
CONCENTRATION, PPM
0.35 . . . . . . . . . . . . . . . . . . .................. .................. .................. 0.30 -.. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. ..
%mmzam.€
242 SITES
oo(0QIE-
B
h
m
mwILB(IIl
0.25
0.20 0.15 NAAQS
.... ..
0.10 .................. ................. ............. ................. ................. ................. ..............- - .
1
0.00
1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 Figure 1 .
Roxplot p r e s e n t a t i o n o f U.S. ozone trends 1977-86.
w 4.
c3 [Y;
I
I
W 0
0
I
$6 w z
x
LL
203
204
CONCENTRATION, PPM 0.20
0.15
1 ---
-,-___-,
90th Percentile
------------
0.05-
Seasonal Average
0.00 1977
Figure 3.
20
---------
-------
0 . lo
1978
1979
1980
1981 1982 1983 1984 1985
1986
Illustration o f different ozone trend s t a t i s t i c s , 1977-86.
CONCENTRATION, PPM ......... ......... .........
I
242 SITES
... ... ... ... ... .........:..
....... .. .. .. .. .. .. .. ... . . . . . .-*.:.-
.. .. .. .. .. .. .. ... . . . . . .'2 . . . . . . . .']...I...;.; .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .........
,
,
,
I
,
I
I
,
0
1977 1978 1979 1980 1981 1982 1983 1984 1985 1986
Figure 4 .
Trend in exceedances o f U.S. ozone standard, 1977-86.
205
T. Schneider et al. (Editors),Atmospheric Ozone Research and its Policy Implications 0 1989 Elsevier Science Publishers B.V., Amsterdam -Printed in The Netherlands
RELATIONSHIPS AMONG OZONE EXPOSURE INDICATORS I N THE UNITED STATES
T
.
McCurdy
Ambient Standards Branch, U.S. Environmental P r o t e c t i o n Agency, Research T r i a n g l e Park, NC 27711
ABSTRACT The paper p r e s e n t s r e s u l t s o f e x t e n s i v e d e s c r i p t i v e s t a t i s t i c a l analyses o f ambient ozone d a t a i n U n i t e d S t a t e s m e t r o p o l i t a n s t a t i s t i c a l areas (MSAs). The analyses u t i l i z e d a t a f r o m t h e 1982 t o 1986 t i m e p e r i o d i n 216 MSAs. F u n c t i o n a l mathematical r e l a t i o n s h i p s were f i t t e d t o c u m u l a t i v e frequency d a t a i n o r d e r t o make i n f e r e n c e s r e g a r d i n g what exposure regime ( w i t h r e s p e c t t o c o n c e n t r a t i o n l e v e l and a v e r a g i n g t i m e ) would r e s u l t f r o m a l t e r n a t i v e n a t i o n a l ambient a i r q u a l i t y s t a n d a r d s (NAAQSs) j u s t b e i n g a t t a i n e d i n t h e MSAs. The mathematical r e l a t i o n s h i p s used i n c l u d e l o g i s t i c and n e g a t i v e e x p o n e n t i a l f u n c t i o n s .
EXPOSURE INDICATORS The U.S.
Environmental P r o t e c t i o n Agency (EPA) c u r r e n t l y i s r e v i e w i n g
i t s NAAYS f o r ozone.
S i x a l t e r n a t i v e exposure i n d i c a t o r s a r e b e i n g
analyzed d u r i n g t h i s r e v i e w : expected number o f exceedances o f t h e c u r r e n t 0.12 ppm 0 3 NAAQS, b o t h (Hereafter often c i t e d one and f i v e expected exceedances p e r year. as t h e 1 and 5 ExEx i n d i c a t o r s . Note: These a r e two s e p a r a t e a i r qua1 it y in d i c a t o r s . ) t h e second-highest 1-hour d a i l y maximum ozone c o n c e n t r a t i o n . ( H e r e a f t e r o f t e n c i t e d as t h e 2nd-high d a i l y max index.) t h e expected number o f days i n an ozone season w i t h a 8-hour d a i l y maximum average >0.08 ppm. ( H e r e a f t e r o f t e n c i t e d as t h e 8-hour ExEx i n d i c a t o r . ) t h e maximum m o n t h l y mean o f 1-hour d a i l y maximum ozone c o n c e n t r a t i o n s . ( H e r e a f t e r o f t e n c i t e d as t h e max m o n t h l y mean index.) O
t h e maximum 3-month mean o f 8-hour d a i l y maximum averages. ( H e r e a f t e r o f t e n c i t e d as t h e 3-month mean i n d i c a t o r . )
The 1 ExEx and 2nd-high d a i l y max i n d i c a t o r s a r e t h o s e n o r m a l l y used by EPA t o a s c e r t a i n an a r e a ' s a t t a i n m e n t s t a t u s f o r t h e c u r r e n t ozone NAAQS
i f o n l y one y e a r o f d a t a a r e a v a i l a b l e .
The 5 ExEx i n d i c a t o r i s a v a r i a n t
of t h e f i r s t i n d i c a t o r , a l l o w i n y more exceedances o f t h e c u r r e n t 0.12 d a i l y maximum ozone NAAQS.
ppm
I t w i l l be r e p r e s e n t e d h e r e by t h e 6 t h h i y h e s t
206
1-hour d a i l y maximum d e s i g n v a l u e r e c o r d e d i n a m e t r o p o l i t a n s t a t i s t i c a l area (MSA).
The r e m a i n i n g t h r e e i n d i c a t o r s a r e p o t e n t i a l l y u s e f u l f o r m u l a t i o n s
f o r a l t e r n a t i v e l o n g e r - t e r m p r i m a r y and secondary ozone NAAQS.
The
8-hour ExEx i n d e x i s u s e f u l f o r d e s c r i b i n g how many days have an 8-hour exposure g r e a t e r t h a n an ozone c o n c e n t r a t i o n l e v e l t h o u g h t by some r e s e a r c h e r s t o cause adverse w e l f a r e e f f e c t s ( r e f . 1 ) o r adverse h e a l t h e f f e c t s ( r e f . 2).
The m o n t h l y i n d i c a t o r i s a p o s s i b l e s u r r o g a t e f o r b o t h s h o r t - and
long-term standard formulations i n t h a t i t i s r e l a t i v e l y c l o s e l y associated w i t h them ( i n a s t a t i s t i c a l sense).
The l a s t i n d i c a t o r - - t h e 3 month
mean--is a s i m p l i f i e d f o r m u l a t i o n o f t h e 7-hour l o n g - t e r m mean used by many r e s e a r c h e r s i n i n v e s t i g a t i n g ozone i m p a c t s on a g r i c u l t u r a l c r o p s ( r e f . 3). Even though t h e i n d i c a t o r i s o r i e n t e d t o w a r d p l a n t e f f e c t s , i t would a p p l y i n urban areas i f a NAAQS were e s t a b l i s h e d t o p r e v e n t s a i d e f f e c t s .
A l l of
t h e s e i n d i c a t o r s have been e x t e n s i v e l y a n a l y z e d i n Ref. 4 and Kef. 5; t h e s e two r e p o r t s form t h e b a s i s f o r a l l r e s u l t s p r e s e n t e d i n t h i s paper u n l e s s o t h e r w i s e noted. AMBIENT OZONE A I R QUALITY I N URBAN AREAS T h e r e a r e 331 MSAs i n t h e 50 s t a t e s .
Ozone a i r q u a l i t y d a t a f o r
e v e r y MSA were reviewed a g a i n s t EPA's 75% d a t a completeness c r i t e r i o n . S i t e s m e e t i n g t h i s c r i t e r i o n were d e t e r m i n e d t o have " v a l i d d a t a ' ' and were used t o d e t e r m i n e which s i t e i n a MSA had t h e h i g h e s t y e a r l y 2nd-high d a i l y max v a l u e f o r t h e 1983-1985 t i m e p e r i o d .
Each MSA i s
r e p r e s e n t e d by o n l y one y e a r o f data. The 1983-1985 d a t a were supplemented i n some areas w i t h v a l i d 19801982 d a t a when r e c e n t v a l i d d a t a were n o t a v a i l a b l e . MSAs.
T h i s was done i n 11
I n c l u d i n g t h e s e areas, v a l i d ozone d a t a a r e a v a i l a b l e f o r 236 MSAs--
about 71% o f a l l U.S.
m e t r o p o l i t a n areas.
Expected Exceedances o f t h e E x i s t i n g Ozone NAAQS The d a t a i n d i c a t e t h a t 112 MSAs (47.5% o f t h o s e w i t h d a t a ) have more t h a n one expected exceedance o f t h e ozone NAAUS. p r o p o r t i o n o f U.S.
Thus, a s i g n i f i c a n t
urban areas exceeded t h e e x i s t i n g 0 3 s t a n d a r d c o n c e n t r a t i o n
l e v e l d u r i n g t h e 1983-1985 t i m e p e r i o d . A p a r t o f t h e c u m u l a t i v e f r e q u e n c y d i s t r i b u t i o n o f 1-hour ExEx d a t a i s shown i n T a b l e 1, a l o n g w i t h s i m i l a r i n f o r m a t i o n f o r t h r e e o t h e r exposure i n d i c a t o r s t h a t a r e d i s c u s s e d l a t e r . 1-hour expected exceedances i s 2.0; i n t h e data.
The median number o f
however, t h e r e i s a l o t o f v a r i a b i l i t y
A l t h o u g h n o t d i r e c t l y o b s e r v a b l e i n T a b l e 1, 35% o f t h e
MSAs i n v e s t i g a t e d have 0 exceedances.
The mean o f t h e sample, a l m o s t 6
exceedances, i s much g r e a t e r t h a n t h e median due t o t h e v e r y h i g h number
207
o f expected exceedances i n t h e worst areas.
The w o r s t MSA i s Los Angeles.
w i t h about 149 exceedances. Second- and Sixth-Highest 1-hour D a i l y Maximum and 8-Hour ExEx Exposure Indicators Cumulative frequency d e s c r i p t i v e d a t a f o r t h e s e t h r e e exposure i n d i c a t o r s a l s o appear i n T a b l e 1.
The T a b l e i n d i c a t e s t h a t t h e median
2nd-high 1-hour design value f o r t h e sample of 216 MSAs i s s l i g h t l y g r e a t e r than t h e c u r r e n t ozone NAAQS l e v e l .
The mean i s even higher,
TABLE 1 Cumulative frequency d e s c r i p t i v e s t a t i s t i c s associated w i t h peak and m u l t i p l e - h o u r ozone a i r q u a l i t y i n d i c a t o r s i n urban areas
Statistic Mean Standard D e v i a t i o n
2nd-Hi gh 1-Hour Dai 1y Maximum (PPm)
Expected Exceedances o f 0.12 ppm 1-Hour D a i l y Maximum
6th-Hi gh 1-Hour Daily Maximum (PPm)
Expected Exceedances o f 0.08 ppm 8-Hour D a i l y Maximum
5.9 14.2
.131 .041
.110 .033
18.3 21.8
Minimum Median 75th P e r c e n t i l e
0.0 2.0 6.6
.039 ,145
.033 .lo5 ,121
0.0 11.8 25.9
90th Percentile 95th Percentile Maximum
14.1 21.7 149.2
.173 .203 .370
.144 .160 .330
39.2 54.2 160.0
.123
Sample S i z e 216 216 213* 216 m i s i n d i c a t o r cannot be computed f o r t h r e e MSAs due t o l a c k o f a d a t a f o r t h e MSA design value monitor. 0.131 ppm, because o f very h i g h design values seen i n a few MSAs. instance, 10% o f t h e MSAs have a 2nd-high d a i l y max >0.17
5% have a design value NI.20 ppm.
ppm.
For
The w o r s t
The h i g h e s t design v a l u e s i t e s a r e
l o c a t e d i n MSAs near o r adjacent t o t h e New York, Los Angeles, and Chicago major m e t r o p o l i t a n areas. The 6th-highest 1-hour d a i l y maximum design value i s a s u r r o g a t e i n d e x f o r t h e 5 ExEx i n d i c a t o r .
The p e r c e n t i l e values a r e 80-8546 l o w e r
t h a n t h e corresponding 1-hour design v a l u e f o r t h e same p e r c e n t i l e rank. As can be seen, o n l y 25% o f MSAs exceed a 5 ExEx 0.12 ppm ozone concentration. T u r n i n g t o t h e l a s t i n d i c a t o r , t h e r e a r e many expected exceedances
o f an 8-hour d a i l y maximum 20.08 ppm.
There a l s o i s wide v a r i a b i l i t y i n
t h e i r number, from 0 f o r 18 MSAs t o 160 f o r t h e worst MSA.
The mean i s
208
about 18, and t h e standard d e v i a t i o n o f t h e sample I s l a r g e r t h a n t h e mean. Longer-term Exposure I n d i c a t o r s The two longer-term I n d i c a t o r s o f i n t e r e s t a r e t h e max monthly and 3month mean indices.
The d a i l y maximum averaging t i m e used f o r t h e s e
i n d i c a t o r s i s 1-hour and 8-hour,
respectively.
Cumulative frequency
d e s c r i p t i v e i n f o r m a t i o n f o r t h e s e two i n d i c a t o r s i s shown i n T a b l e 2.
TABLE 2 Cumulative frequency d e s c r i p t i v e s t a t i s t i c s a s s o c i a t e d w i t h l o n g e r - t e r m ozone a i r q u a l i t y i n d i c a t o r s i n urban areas Maximum Monthly Mean f o r 1-Hour D a i l y Maximums (ppm)
S t a t i s t ic
Maximum 3-Month Mean f o r 8-Hour D a i l y Maximums (ppm)
Mean Standard D e v i a t i o n
.074 .020
.057 .014
Minimum Median 75th Percentile
.025 .072 .084
.016 ,056 .063
90th Percentile 95th Percentile Maximum
.094 .lo2 .219
.072 .078 .140
Sample S i z e
2 1 3*
216
Y h i s i n d i c a t o r cannot be computed f o r t h r e e MSAs due t o l a c k o f a v a l i d 3-month mean f o r t h e MSA design value monitor. There i s moderate sample v a r i a b i l i t y i n t h e two i n d i c a t o r s , as evidenced by t h e small d i f f e r e n c e between t h e mean and median values and t h e small standard d e v i a t i o n s r e l a t i v e t o t h e i r means.
The l a r g e 3-month
means o f t h e t o p 50% MSAs i n t h e sample should be noted. value i s 0.056 ppm.
The median
The worst area has a maximum 3-month mean o f 8-hour
d a i l y maximum averages o f 0.140 ppm--higher t h a n t h e c u r r e n t 1-hour d a i l y maximum NAAQS!
(The area i s Los Angeles.)
RELATIONSHIPS AMONG EXPOSURE INDICATORS I N URBAN AREAS As an i n t r o d u c t i o n t o r e l a t i o n s h i p analyses among exposure i n d i c a t o r s , we consider F i g u r e 1.
Depicted a r e Pearson product-moment l i n e a r c o r r e l a t i o n
c o e f f i c i e n t s among t h e a i r q u a l i t y i n d i c a t o r s o f i n t e r e s t . depict a correlation c o e f f i c i e n t
>I
.751.
Solid lines
Only t h e r e l a t i o n between t h e
209
Exposure Patterns o f I n t e r e s t Mu 1t i p l ePeak, ShortTerm
Peak, ShortTerm
6th-high 1-hour Daily Maximum
4
LongTerm Average
Expected Number o f .90
++
8-hour Days '.08 D a i l y Max.
J. Maximum 3Month Mean o f 8-hour D a i l y Maximums
D a i l y Max.
.70 Expected Number o f Days >.08( Maximum
T Fig. 1.
D a i l y Max. .82
*go$
i
.ir .85
Maximum 3Month Mean o f 8-hour D a i l y Maximums
Maximum Monthly Mean JSg2 o f 1-hour D a i l y Max.
Correlations among short- and long-term a i r q u a l i t y i n d i c a t o r s .
2nd-high d a i l y max and 3-month mean i n d i c a t o r s i s
< I .75).
Note t h a t t h e
max monthly mean index i s h i g h l y c o r r e l a t e d w i t h b o t h s h o r t - t e r m and longterm a i r q u a l i t y indicators. Numerous analyses o f r e l a t i o n s h i p s among t h e s i x exposure i n d i c a t o r s o f i n t e r e s t a r e reported i n Refs. 4 and 5.
The focus o f these analyses was
t o s i m u l a t e attainment o f one exposure i n d i c a t o r i n a l l areas and i n v e s t i g a t e how t h i s a f f e c t e d t h e subsequent frequency d i s t r i b u t i o n o f o t h e r a i r q u a l i t y exposure i n d i c a t o r s .
The s i m u l a t i o n was accomplished by f i t t i n g
a l o g i s t i c o r exponential equation t o t h e frequency d i s t r i b u t i o n o f s t r a t i f i e d data sets.
The r a t i o n a l e and procedure used f o r t h e s t r a t i f i c a t i o n
i s described i n Ref. 4.
As i s t o be expected whenever r e l a t i o n s h i p s a r e f i t t o data, t h e r e i s some " s c a t t e r " around t h e f i t t e d curves.
I n t h i s case, t h e s c a t t e r occurs
f o r t h e s t r a i g h t - l i n e f i t s t o yarameters o f t h e l o g i s t i c o r exponential r e l a t i o n s h i p s t h a t were subsequently used, w i t h o u t u n c e r t a i n t y , t o s i m u l a t e attainment o f an i n d i c a t o r .
Obviously t h e r e i s u n c e r t a i n t y i n h e r e n t i n t h e
use of these curves due t o t h e c u r v e - f i t t i n g procedure.
There i s a d d i t i o n a l
u n c e r t a i n t y associated w i t h t h e concept i t s e l f o f u s i n g s t a t i s t i c a l l y d e r i v e d r e l a t i o n s h i p s f o r c u r r e n t a i r q u a l i t y d a t a s e t s and a p p l y i n g them t o a f u t u r e s i t u a t i o n t h a t may be i n h e r e n t l y d i f f e r e n t than t h e present condition.
I n p a r t i c u l a r , t h e frequency d i s t r i b u t i o n o f f u t u r e a i r q u a l i t y
under a p o s t - c o n t r o l s i t u a t i o n may be d i f f e r e n t than t h e p r e - c o n t r o l d i s t r i b d t i o n c u r r e n t l y observed.
While t h i s i s l i t e r a l l y t r u e , I do n o t
t h i n k t h a t the r e l a t i o n s h i p s among i n d i c a t o r s would be g r e a t l y a f f e c t e d under a p o s t - c o n t r o l scenario f o r t h e reasons e l a b o r a t e d upon i n g r e a t d e t a i l i n Ref. 4. U n c e r t a i n t y o f t h e f i r s t t y p e can be addressed s t a t i s t i c a l l y .
However,
as o f t h e present, a " g o o d n e s s - o f - f i t "
s t a t i s t i c c o u l d n o t be found f o r t h e
l o g i s t i c o r exponential r e l a t i o n s h i p s .
Undoubtedly such a s t a t i s t i c e x i s t s ,
b u t i t i s not i n t h e general s t a t i s t i c a l l i t e r a t u r e . c u r r e n t l y underway t o uncover s a i d s t a t i s t i c ) .
(An e f f o r t i s
The second t y p e o f un-
c e r t a i n t y probably i s best addressed u s i n g a " s e n s i t i v i t y a n a l y s i s " approach, where a l t e r n a t i v e hypotheses regarding p o s t - c o n t r o l a i r q u a l i t y d i s t r i b u t i o n s c o u l d be tested. however.
Resources t o do t h i s a r e n o t a v a i l a b l e a t t h i s time,
The reader must r e a l i z e t h a t t h e i n a b i l i t y t o e x p l i c i t l y address
u n c e r t a i n t y i n t h e r e l a t i o n s h i p s d e p i c t e d below i s an a n a l y t i c shortcoming o f t h i s paper. The r e l a t i o n s h i p s among c e r t a i n . exposure i n d i c a t o r s a r e g r a p h i c a l l y depicted i n Figures 2 through 5.
F i g u r e 2 r e l a t e s t h e number o f 8-hour
d a i l y maximum averages >.08 ppm ( x a x i s ) t o t h r e e a l t e r n a t i v e 1-hour
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F i g . 2. P r o p o r t i o n ( i n p e r c e n t ) o f urban s i t e s exceeding s p e c i f i e d expected number o f 8-hour d a i l y maximum averages 0.08 pprn f o r t h r e e 1-hour d a i l y maximum standards ( a t t a i n e d i n a l l areas i n t h e d a t a s e t ) .
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F i g . 3. Proportion ( i n p e r c e n t ) o f urban s i t e s exceeding s p e c i f i e d maximum monthly 1-hour d a i l y maximum values f o r t h r e e 1-hour d a i l y maximum standards ( a t t a i n e d i n a l l areas i n t h e d a t a s e t ) .
213 standards:
0.08,
0.10,
and 0.12 ppm.
Since t h e x-axis v a r i a b l e i s
an i n t e r v a l - s c a l e expected exceedance v a r i a b l e i n t h i s case, t h e c u r v e s f o l l o w a n e g a t i v e e x p o n e n t i a l shape. An example o r t w o may a i d t h e reader i n r e a d i n g F i g u r e 2 and subsequent f i g u r e s .
F i g u r e 2 i n d i c a t e s t h a t i f a 0.12 ppm 1-hour d a i l y
maximum s t a n d a r d i s met by a l l s i t e s i n t h e d a t a set, 10% o f a l l MSAs m i g h t have 1 7 o r more days w i t h an &hour
d a i l y maximum >.08 ppm.
l e a s t one area m i g h t have as many as 30 days.
At
F i f t y p e r c e n t o f t h e MSAs
m i g h t have 4 o r more days w i t h an 8-hour ExEx i n d i c a t o r >.08 ppm.
If the
1-hour d a i l y maximum a i r s t a n d a r d was lowered t o 0.10 ppm and a t t a i n e d by a l l areas i n t h e d a t a s e t , 10% o f t h e MSAs may have 8 o r more days o v e r a
If a 0.08 ppm d a i l y max 1-hour were
0.08 ppm d a i l y max 8-hour average.
a t t a i n e d , no area would have any day w i t h an 8-hour ExEx v a l u e >.08 ppm. F i g u r e 3 shows t h e l o g i s t i c t y p e of c u r v e common f o r t h e c o n t i n u o u s concentration variables.
The x - a x i s r e p r e s e n t s t h e maximum m o n t h l y mean
a i r q u a l i t y i n d i c a t o r ( f o r 1-hour d a i l y maximum values).
The c u r v e s a r e
I f a 0.12 ppm 1-hour s t a n d a r d
f o r t h e t h r e e 1-hour d a i l y rnax i n d i c a t o r s .
was a t t a i n e d i n a l l areas, 10% o f a l l MSAs m i g h t have a max m o n t h l y mean o f 0.075 ppm o r h i g h e r .
T h i s drops t o 0.063 ppm f o r 50% of t h e areas.
A t i g h t e r s t a n d a r d o f course reduces t h e percentage of s i t e s a t o r
above any s p e c i f i c c u t p o i n t on t h e x-axis.
For example, 30% o f MSAs
would see a max m o n t h l y mean o f 0.062 ppm o r h i g h e r i f a 0.08 ppm 1-hour d a i l y max s t a n d a r d i s a t t a i n e d by a l l areas.
T h i s p r o p o r t i o n drops t o
a p p r o x i m a t e l y 5% f o r a 0.10 1-hour standard. The n e x t r e l a t i o n s h i p t h a t w i l l be d e s c r i b e d i s t h e one between t h e 2nd-high d a i l y max and 3-month mean i n d i c a t o r s . o f t h i s r e l a t i o n s h i p appears as F i y u r e 4.
A yraphic d e p i c t i o n
The F i g u r e shows t h a t t h e 3-
month means i n MSAs a r e n o t a l t e r e d g r e a t l y by a t t a i n i n g a 0.10 ppm 2ndh i g h d a i l y max s t a n d a r d r a t h e r t h a n a 0.12 ppm standard. d r a m a t i c a l l y f o r a 0.08 ppm standard,
however.
The means d r o p
O f course, i t i s q u i t e
d i f f i c u l t t o a t t a i n such a r e l a t i v e l y l o w peak ozone value.
I f a 3-month
mean i n d i c a t o r i s o f i n t e r e s t i n MSAs, such an i n d i c a t o r s h o u l d be addressed d i r e c t l y by e s t a b l i s h i n g a NAAQS w i t h a maximum 3-month 8-hour d a i l y maximum a v e r a g i n g time.
T r y i n g t o l o w e r a l o n g - t e r m mean w i t h a
peak a i r q u a l i t y s t a n d a r d i s d i f f i c u l t t o accomplish. F i g u r e 5 d e p i c t s t h e impact o f a t t a i n i n g a l t e r n a t i v e 5 expected exceedance standards on t h e 2nd-high 1-hour d e s i g n value.
As can be seen,
a 0.12 ppm 5 ExEx s t a n d a r d may a l l o w a 2nd-high d e s i g n v a l u e o f almost 0.14 ppm i n t h e w o r s t 10% o f MSAs.
The 2nd-high d e s i g n v a l u e m i g h t be
o v e r 0.12 ppm i n t h e w o r s t 10% o f MSAs w i t h a 5 ExEx s t a n d a r d o f 0.10 ppm. To j u s t a t t a i n a 2nd-high 1-hour d e s i g n v a l u e o f 0.12
ppm i n t h e w o r s t
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F i g . 4. Proportion ( i n p e r c e n t ) o f urban s i t e s exceeding s p e c i f i e d threemonth 8-hour d a i l y maximum averages f o r t h r e e 1-hour d a i l y maximum standards ( a t t a i n e d i n a l l areas i n t h e d a t a s e t ) .
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F i g . 5. P r o p o r t i o n ( i n p e r c e n t ) of urban s i t e s exceeding s p e c i f i e d secondh i g h 1-hour d a i l y maximum c o n c e n t r a t i o n values f o r t h r e e 5-expected exceedances standards ( a t t a i n e d i n a l l areas i n t h e d a t a s e t ) .
216 10% o f MSAs r e q u i r e s a 5 ExEx standard o f 0.097 ppm; t h i s then, i s a reasonable "equivalency r e l a t i o n " between t h e two expected exceedances standards. SUMMARY
T h i s paper presented d e s c r i p t i v e ozone data f o r s i x exposure i n d i c a t o r s associated w i t h peak, multiple-peak, times.
and longer-term averaging
Analyses were performed on r e l a t i o n s h i p s between s e l e c t e d p a i r s
o f t h e s i x exposure i n d i c a t o r s . I t was suggested t h a t a maximum monthly mean o f one-hour d a i l y maximum
ozone concentrations c o u l d f u n c t i o n as a s u r r o g a t e exposure i n d i c a t o r o f both s h o r t - and long-term exposure averaging times.
Using t h i s , o r
any o t h e r surrogate i s a t b e s t a compromise, however, f o r t h e more d i r e c t and r i g o r o u s approach o f u s i n g a s e t o f d i f f e r e n t averaging t i m e standards t o p r o t e c t a g a i n s t adverse e f f e c t s s p e c i f i c t o those averaging times. REFERENCES E.H. Lee, D.T. Tingey, and W.E. Hogsett. S e l e c t i o n o f t h e Best ExposureResponse Model Using Various 7-Hour Ozone Exposure S t a t i s t i c s , C o r v a l l i s , OR: U.S. Environmental P r o t e c t i o n Agency, 1987. P.J. Lioy, T.A. Vollmuth, and M. Lippmann. "Persistence o f Peak Flow Decrement i n C h i l d r e n f o l l o w i n g Ozone Exposures Exceeding t h e n a t i o n a l J. A i r Pol. Cont. Assoc. 35: 1068ambient a i r q u a l i t y standard," 1071, 1985. W.W. Heck and D.T. Tingey. "Ozone Time-Concentration Model t o P r e d i c t Acute f o l i a r I n j u r y , " pp. 249-255 i n : H.M. Englund and W.T. Berry (eds), Proc. o f t h e Second I n t e r . Clean A i r Cong., New York: Academic Press, 1971. T. McCurdy. " D e s c r i p t i v e S t a t i s t i c a l Analyses o f Ozone A i r Q u a l i t y I n d i c a t o r s i n Rural/Remote and M e t r o p o l i t a n Areas," Durham, N.C.: S t r a t e g i e s and A i r Standards D i v i s i o n , U.S. EPA, May 1987. T. McCurdy. " A d d i t i o n a l Ozone A i r U u a l i t y I n d i c a t o r s i n M e t r o p o l i t a n Areas," Durham, N.C.: S t r a t e g i e s and A i r Standards D i v i s i o n , U.S. EPA, J u l y 1987.
217
SESSION 111
EFFECTS ON VEGETATION AND ECOSYSTEMS
Chairmen
K. Verhoeff W. Heck
This Page Intentionally Left Blank
T. Schneider et al. (Editors),Atmosphenk Ozone Reaearch and its Policy Implications 0 1989 Elsevier Science Publishers B.V.,Amsterdam -Printed in The Netherlands
219
ANALYSIS OF CKOP LOSS FOR ALTERNATIVE OZONE EXPOSURE INDICES
DAVID T. T I N G E Y l , WILLIAM E. HOGSETTl and E. HENRY LEE2 l U . S . Environmental P r o t e c t i o n Agency, 200 SW 3 5 t h S t r e e t , C o r v a l l i s , OR, 97333 (U.S.A.)
2Northrop S e r v i c e s , Inc.,
200 SW 3 5 t h S t r e e t , C o r v a l l i s , OR, 97333
(U.S.A.)
ABSTKACT Determining t h e a p p r o p r i a t e exposure i n d e x that b e s t relates p l a n t response t o 0 3 exposure is r e l i a n t on a c o n s i d e r a t i o n of t h e u n d e r l y i n g b i o l o g i c a l basis f o r t h e response and a method of c h a r a c t e r i z i n g t h e temporal concentrat i o n v a r i a t i o n s in p o l l u t a n t occurrence. Numerous e m p i r i c a l and m e c h a n i s t i c models have been developed t o assess t h e impact of 0 3 on crop l o s s . I n t h i s paper, a series of exposure i n d i c e s (having d i v e r s e characteristics) are e v a l u a t e d using p l a n t growth d a t a from s e v e r a l c r o p s t o determine which i n d i c e s perform t h e "best." Although r e s u l t s i n d i c a t e that no s i n g l e exposure i n d e x is " b e s t " f o r a l l s p e c i e s , t h e d a t a c l e a r l y i n d i c a t e several g e n e r a l t r e n d s and c o n c l u s i o n s : 1) peak c o n c e n t r a t i o n s are more i m p o r t a n t t h a n low c o n c e n t r a t i o n s in determining p l a n t r e s p o n s e , 2) p l a n t s respond t o t h e cumulative impacts of exposure and 3 ) p l a n t s e n s i t i v i t y v a r i e s w i t h t h e p h e n o l o g i c a l s t a g e of p l a n t development.
INTKOUUCTION
The g o a l of a i r p o l l u t a n t r e s e a r c h is to determine t h e r e l a t i o n s h i p between p o l l u t a n t exposure and p l a n t response.
The q u a n t i f y i n g f u n c t i o n f o r t h i s
p r o c e s s is f r e q u e n t l y termed "dose-response;"
however, i n t h i s d i s c u s s i o n of
exposure dynamics i t w i l l be termed "exposure-response," concept.
a more g e n e r i c
An understanding o f exposure r e s p o n s e r e q u i r e s t h r e e t y p e s of
i n t o r m a t i o n : 1 ) a measure of p l a n t response; 2) a n a p p r o p r i a t e i n d e x t o d e s c r i b e t h e p o l l u t a n t exposure; and 3) a mathematical f u n c t i o n that relates p l a n t response t o p o l l u t a n t exposure.
Defining t h e a p p r o p r i a t e exposure i n d e x
t h a t " b e s t " relates p l a n t r e s p o n s e t o exposure n e c e s s i t a t e s a c o n s i d e r a t i o n of t h e underlying b i o l o g i c a l b a s i s f o r t h e response and a method f o r characteri z i n g t h e temporal v a r i a t i o n s in p o l l u t a n t occurrence. P l a n t s react d i f f e r e n t i a l l y t o temporal v a r i a t i o n s i n p o l l u t a n t concentrat i o n s [ r e f s . 1-41; c o n s e q u e n t l y , i t is n e c e s s a r y t o elect exposure i n d i c e s that s p e c i t i c a l l y account f o r t h e temporal v a r i a t i o n in exposure. I f p l a n t
response were not moditied by t h e e p i s o d i c n a t u r e ( t e m p o r a l v a r i a t i o n ) of t h e e x p o s u r e s , t h e n i t would be s u f f i c i e n t t o c h a r a c t e r i z e t h e exposure w i t h a n
index such as a mean t h a t does n o t r e f l e c t t h e c o n c e n t r a t i o n v a r i a t i o n over time. I n e v a l u a t i n g exposure i n d i c e s that c h a r a c t e r i z e p l a n t response, t h e u l t i m a t e g o a l is t o develop exposure i n d i c e s t h a t i n c o r p o r a t e a l l c o n t r i b u t i n g f e a t u r e s and account f o r a l l ( o r most) of t h e v a r i a t i o n i n t h e exposure response.
A second, more p r a c t i c a l l y o r i e n t e d g o a l i s t h e development o f
exposure i n d i c e s u s e f u l i n t h e s t a n d a r d s e t t i n g process.
An i n d e x f o r a
s t a n d a r d should be easy t o develop and a p p l i c a b l e t o a wide range of s p e c i e s and environmental/exposure c o n d i t i o n s . T h i s o b j e c t i v e may r e p r e s e n t a compromise i n t h e f e a t u r e s i n c l u d e d i n t h e f o r m u l a t i o n of t h e " b e s t " exposure index. The magnitude of p l a n t response t o 03 i s a l t e r e d by s e v e r a l components i n c l u d i n g 1) c l i m a t i c and edaphic f a c t o r s ; 2) b i o l o g i c a l f a c t o r s such as phenological s t a g e of development and g e n e t i c p o t e n t i a l ; and 3) t h e temporal Because t h e s e components and t h e i r i n f l u e n c e on
v a r i a t i o n i n 03 exposure.
p l a n t response have been r e c e n t l y reviewed [ r e f s . 3-41,
t h i s presentation w i l l
focus on t h e e v a l u a t i o n and development of exposure i n d i c e s t h a t i n c l u d e t h e temporal components of t h e exposure.
EVALUATION OF EXPOSURE INDICES There i s no consensus about t h e most a p p r o p r i a t e exposure index ( m e t r i c ) f o r d e p i c t i n g p l a n t response t o 03 exposure [ r e f s .
4-51.
Different indices
have been used, but t h e i r adequacy f o r c h a r a c t e r i z i n g long-term exposures (over a season) i s d o u b t f u l , s i n c e t h e y do n o t account f o r exposure dynamics (i.e.,
temporal v a r i a t i o n ) . A d d i t i o n a l l y , t h e i n d i c e s d o n o t account f o r o t h e r
known i n f l u e n c e s , such as e f f e c t s of exposures a t s p e c i f i c and perhaps c r i t i c a l periods i n p l a n t development.
Most i n d i c e s , such as a s e a s o n a l mean,
do n o t cumulate t h e impact of t h e exposure over t h e growing period. An
a p p r o p r i a t e exposure index should u l t i m a t e l y be d e r i v e d from a
c o n s i d e r a t i o n of t h e underlying b i o l o g i c a l basis f o r t h e response and a procedure f o r q u a n t i f y i n g t h e temporal v a r i a t i o n s i n 03 occurrence. An e v a l u a t i o n of v a r i o u s exposure i n d i c e s i s e s s e n t i a l l y a comparison of t h e i n f l u e n c e of d i f f e r e n t s c a l i n g s of t h e exposure v a r i a b l e on t h e exposure response f u n c t i o n (Fig.
1). The comparison i s based on a s i n g l e set of
b i o l o g i c a l responses (e.g.,
p l a n t y i e l d ) but they are r e l a t e d t o d i f f e r e n t
mathematical c h a r a c t e r i z a t i o n s of 0 3 exposure ( s c a l e s ) such as a mean or a cumulation of hourly c o n c e n t r a t i o n s . The d i f f e r e n t i n d i c e s o r s c a l i n g s do not change t h e magnitude of t h e measured p l a n t response, but t h e y do govern how t h e s e responses are p o s i t i o n e d along t h e exposure a x i s (Fig. 1).
221
I
Exposure Index Fig. 1. An example of a h y p o t h e t i c a l exposure-response f u n c t i o n i l l u s t r a t i n g t h e t h r e e key elements i n understanding exposure dynamics. The exposure index connotates a d e s c r i p t i o n of 03 exposure and i s used a s a scaling factor. A pair of examples i l l u s t r a t e s t h e e f f e c t of using d i f f e r e n t i n d i c e s f o r
c h a r a c t e r i z i n g t h e temporal v a r i a t i o n s i n 03 exposure ( F i g . 2).
In the f i r s t
example (Fig. 2A, B), a l f a l f a p l a n t s were exposed t o e p i s o d i c 03 exposures [ r e t . 21 and harvested (when t h e p l a n t s reached one-tenth bloom) t h r e e times during t h e season. A comparison was made between two exposure i n d i c e s : 1) t h e 7-h (0900 t o 1559) s e a s o n a l mean c o n c e n t r a t i o n [ r e f . 61 and 2) t h e g e n e r a l i z e d phenologically weighted cumulative impact (GPWCI) t h a t cumulated t h e exposure and emphasized t h e peak c o n c e n t r a t i o n s [ref.7].
The f i t of t h e same exposure-
response f u n c t i o n t o t h e i d e n t i c a l response d a t a was c l e a r l y b e t t e r when t h e GPWCI (Fig. 2B) was used t o a r r a y t h e observed p l a n t responses a l o n g t h e exposure a x i s than when t h e 7-h s e a s o n a l mean was used (Fig. 2A).
With t h e
GPWCI, t h e t r e n d f o r reduced p l a n t growth w i t h i n c r e a s i n g exposure i s p l a i n l y seen; however, t h i s p a t t e r n is not e v i d e n t when t h e mean is used. A second example (Fig. 2C. D) is provided by a comparison of t h e maximum y i e l d l o s s observed i n a range of crop s p e c i e s . The e v a l u a t i o n of exposure i n d i c e s compared t h e 7-h s e a s o n a l mean and t h e t o t a l exposure (sum of c o n c e n t r a t i o n s throughout t h e study). I n t h i s example, as i n t h e p r e v i o u s one (Pig. 2A, B), t h e r e i s a c l e a r t r e n d showing a n i n c r e a s e i n maximum y i e l d l o s s w i t h i n c r e a s i n g i n c r e a s i n g exposure (Fig. ZD); however, when t h e 7-h s e a s o n a l mean was used t h i s t r e n d was n o t e v i d e n t (Fig. 2C). The p r i n c i p a l d i f f e r e n c e between t h e two
I n d i c e s was t h e i n c l u s i o n of exposure d u r a t i o n (number of days) i n t h e t o t a l exposure index. Several of t h e s t u d i e s had e s s e n t i a l l y t h e same 7-h s e a s o n a l
222 mean, but t h e s t u d y d u r a t i o n s d i f f e r e d by a p p r o x i m a t e l y two-fold,
which caused
t h e l a c k of a clear t r e n d i n t h e d a t a . In both examples, t h e mean was n o t a n a p p r o p r i a t e index ( s c a l i n g f a c t o r ) f o r d e s c r i b i n g t h e r e s p o n s e of p l a n t s t o
long-term (e.g.,
growing s e a s o n ) e x p o s u r e s t o e p i s o d i c a l l y o c c u r r i n g
c o n c e n t r a t i o n s of 03.
100,
e
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’
60- 0 , Q,
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A83
2 8040-
s 20. -
C82 C81
C82
S83 S83
S80
W82
we2
t
0.00
0.02
0.04
0.06
0.08
0.10
1
7-h Seasonal Mean (ppm)
BI
100
D
A83
3 800
A83
A84
’
C82 C81 C82
60-
9
.
Q,
5 40S 20 ’
A84
s%32
S83 583
W82
-#83
GPWCI Pig. 2. Two comparisons o f d i f f e r e n t exposure i n d i c e s u s i n g t h e same b i o l o g i c a l r e s p o n s e d a t a . The d a t a i n F i g u r e 2A and B were d e r i v e d from Hogsett e t a l . [ r e f . 21 and t h e d a t a i n F i g u r e ZC and D a r e from Lee e t a l . [ r e f . 141. I n F i g u r e 2C and D, t h e symbols i n d i c a t e t h e y e a r of t h e s t u d y and t h e s p e c i e s used; A = a l f a l f a , C = c o t t o n , S = soybean, W = wheat. The mathematical mean of t h e h o u r l y 03 c o n c e n t r a t i o n s , o v e r v a r i o u s t i m e p e r i o d s , i s f r e q u e n t l y used t o c h a r a c t e r i z e p o l l u t a n t e x p o s u r e s . The 7-h (M7) and 12-h (M12) s e a s o n a l means have g a i n e d c r e d e n c e f o r r e l a t i n g p l a n t y i e l d t o 03 exposure because of t h e i r u s e i n t h e N a t i o n a l Crop Loss Assessment (NCLAN)
program [ r e f s . 6 , 8 , 9 ] . The s p e c i f i c 7-h p e r i o d (0900-1559)
s e l e c t e d was
thought t o correspond t o t h e p e r i o d o f g r e a t e s t p l a n t s e n s i t i v i t y and t h e h i g h e s t 03 l e v e l s [ r e f . 61. The s e a s o n a l mean c o n c e n t r a t i o n is a summation of a l l hourly c o n c e n t r a t i o n s ( f o r t h e s e l e c t e d t i m e p e r i o d ) d i v i d e d by t h e number
of o b s e r v a t i o n s .
Cure e t a l . [ r e f . 81 r e p o r t e d t h a t s e a s o n a l mean
c h a r a c t e r i z a t i o n s of 03 e x p o s u r e were much l e s s s e n s i t i v e t h a n t h e 1-h maximum to yearly variations i n
03 p a t t e r n s . An i n f i n i t e number of h o u r l y
d i s t r i b u t i o n s (from t h o s e c o n t a i n i n g many peaks t o t h o s e c o n t a i n i n g none) can y i e l d t h e same 7-h s e a s o n a l mean. If a mean is s e l e c t e d a s a n exposure i n d e x i o r c h a r a c t e r i z i n g e x p o s u r e s , c e r t a i n assumptions are implied and must be considered in a s t u d y ' s i n t e r p r e t a t i o n : o A mean t e n d s t o minimize t h e c o n t r i b u t i o n s of peak c o n c e n t r a t i o n s t o t h e response, implying t h a t peak e v e n t s do n o t need t o be g i v e n s p e c i a l cons i d e r a t i o n .
o All c o n c e n t r a t i o n s w i t h i n t h e s e l e c t e d a v e r a g i n g t i m e are e q u a l l y e t t e c t i v e in e l i c i t i n g a response. o Reduced crop y i e l d r e s u l t s from t h e accumulation of d a i l y 03 i m p a c t s o v e r t h e growing season. o Exposure d u r a t i o n is n o t s p e c i f i c a l l y included: i.e.,
t h e mean can not
d i s t i n g u i s h between exposures t o t h e same c o n c e n t r a t i o n but of d i f f e r e n t durations (i.e.,
10 o r 100 days).
o The d i s t r i b u t i o n of hourly 03 c o n c e n t r a t i o n s ( o v e r t h e a v e r a g i n g t i m e ) a r e unimodal and not h i g h l y skewed. However, ambient 03 c o n c e n t r a t i o n d i s t r i b u t i n s a r e f r e q u e n t l y skewed toward t h e h i g h e r c o n c e n t r a t i o n s . I d e a l l y , t h e s e l e c t i o n o f t h e most a p p r o p r i a t e exposure i n d e x would be derived irom s c i e n t i i i c p r i n c i p l e s and be v a l i d a t e d by e x p e r i m e n t a l s t u d i e s
s p e c i t i c a l l y designed f o r that purpose.
However, t h i s approach would d e l a y
r e s o l v i n g t h e s e l e c t i o n of exposure i n d i c e s f o r y e a r s u n t i l t h e n e c e s s a r y experiments were designed and conducted. An a l t e r n a t i v e approach i s t o conduct a r e t r o s p e c t i v e a n a l y s i s ot e x i s t i n g p l a n t - r e s p o n s e d a t a . T h i s approach p e r m i t s t h e r e a n a l y s i s of e x i s t i n g d a t a f o r e v a l u a t i n g o r developing a range o t exposure i n d i c e s and d e r i v i n g p r i n c i p l e s of exposure response.
Nevertheless,
t h e i n d i c e s developed by t h i s method w i l l u l t i m a t e l y need t o be v a l i d a t e d e x p e r i m e n t a l l y . A major l i m i t a t i o n w i t h r e t r o s p e c t i v e a n a l y s i s is that t h e s p e c i t i c s t u d i e s were not designed t o r developing exposure i n d i c e s o r t e s t i n g exposure hypotheses; consequently t h e u s a b i l i t y of t h e d a t a is l i m i t e d . An e v a l u a t i o n of e x i s t i n g and proposed exposure I n d i c e s was conducted [ r e f .
7 1 on c r o p y i e l d d a t a o b t a i n e d from t h e U.S.
Environmental P r o t e c t i o n Agency's
NCLAN Program [ r e t . 91. P l a n t p r o d u c t i o n and hourly 03 m o n i t o r i n g d a t a were
o b t a i n e d from t h e NCLAN Data L i b r a r y in R a l e i g h , North Carolina.
Data from
f i e l d experiments on soybean, wheat, c o r n , sorghum, and c o t t o n were used i n t h e a n a l y s e s . Crops were grown a c c o r d i n g t o s t a n d a r d a g r i c u l t u r a l p r a c t i c e s and exposed t o a range of 03 c o n c e n t r a t i o n s (ambient l e v e l s and above) i n open-top chambers [ r e f . 9 ] . Exposure i n d i c e s were c a l c u l a t e d from c r o p y i e l d data f o r t h e f i v e s p e c i e s ( w i t h m u l t i p l e y e a r s and c u l t i v a r s f o r a t o t a l o f 17 i n d i v i d u a l cases). The d e t a i l s of t h e data s o u r c e s and a n a l y t i c a l procedures used i n t h e r e t r o s p e c t i v e
224 a n a l y s i s are d e s c r i b e d by Lee e t a l . [ r e f . 71. The a u t h o r s e v a l u a t e d s i x d i f f e r e n t t y p e s of exposure i n d i c e s f o r t h e 17 i n d i v i d u a l cases; t h e d i f f e r e n t t y p es of i n d i c e s had d i s p a r a t e c h a r a c t e r i s t i c s . The v a r i o u s t y p e s of exposure i n d i c e s used i n t h e a n a l y s e s are compared i n Tab l e 1 and t h e a b b r e v i a t i o n s used i n Table 1 are d e s c r i b e d : 1. One Event: i n c l u d e s t h e maximum 7-h (P7) and maximum 1-h ( P l ) d a i l y a v e r a g e s [ r e f . 61 and t h e 9 0 t h (PERSO), 9 5 t h (PER95), and 9 9 t h (PER99) p e r c e n t i l e s of hourly d i s t r i b u t i o n . 2. Mean: i n c l u d e s t h e s e a s o n a l means [ r e f . 61 o f 7-h d a i l y means (M7), 1-h d a i l y means ( M l ) and t h e e f f e c t i v e mean [ r e f . 107](EFFMEAN). 3. Cumulative: r e p r e s e n t s t h e s e a s o n a l sum of a l l h o u r l y c o n c e n t r a t i o n s , i.e., t o t a l exposure (TOTDOSE).
4. C o n cen t r at i o n Weighting: Two s e p a r a t e t y p e s of w ei g h t i n g i n d i c e s were used; a. Sum C o n c e n tr a ti o n (Sum Conc) i n d i c e s cumulated t h e exposure and used e i t h e r d i s c o n t i n u o u s or c o n t in u o u s weighting of c o n c e n t r a t i o n [ r e f . 41. The d i s c o n t i n u o u s i n d i c e s i n c lu d e d s e a s o n a l sum of h o u r l y c o n c e n t r a t i o n s a t o r above 0.06 ppm (SUMO6), 0.07 ppm (SUMO7), 0.08 ppm (SVMOS), or 0.10 ppm (SUM10); s e a s o n a l censored sum of h o u r l y c o n c e n t r a t i o n s a t o r above a t h r e s h o l d , i.e., c u m u l a t iv e sum o f t h e area o v er t h r e s h o l d of 0.08 ppm ( A O M B ) or 0.10 ppm (AOT10). The co n t i n u o u s i n d i c e s i n cl u d ed t o t a l impact [ r e f . 111 (TIMPACT); ALLOMETRIC i n which t h e h o u r l y c o n c e n t r a t i o n was r a i s e d t o a power and summed; and SIGMOID i n which t h e h o u r l y c o n c e n t r a t i o n was m u l t i p l i e d by a sigmoid w ei g h t i n g f u n c t i o n (inflection 0.062 ppm) and summed [ r e f . 71.
-
b. Number of Episodes (Num Episodes) i n d i c e s counted t h e e p i s o d e s o v e r a growing season. This t y p e of i n d e x i n c lu d ed t o t a l h o u r s w i t h co n cen t r at i o n s a t or above t h r e s h o l d s of 0.08 ppm (HRSOB) o r 0.10 ppm (HRS10); t h e number of e p i s o d e s above a t h r e s h o l d of 0.08 ppm (NuMEPO8) or 0.10 ppm (NUMEP10); and a v e r a g e e p is o d e l e n g t h u s i n g t h r e s h o l d s of 0.08 ppm (AVGEP08) o r 0.10 ppm (AVGEP10).
5. Multicomponent: t h e s e i n d i c e s i n c o r p o r a t e s e v e r a l c h a r a c t e r i s t i c s o f exposure [ r e f . 41. Lee e t a l . [ r e f . 71 e v a l u a t e d a number o f multicomponent i n d i c e s 0 5 0 0 ) that in c l u d e d d i f f e r e n t w ei g h t i n g 8 f o r concent r a t i o n and p h e n o lo g i c a l stages of development. T h i s e v a l u a t i o n u s e s t h e i r [ r e f . 71 " b e s t" multicomponent i n d ex (GPWCI) which has t h e f o l l o w i n g f e a t u r e s : 1) a sigmoid c o n c e n t r a t i o n w e i g h t i n g f u n c t i o n ( i n f l e c t i o n p o i n t 0.062 pprn), 2 ) e x p o s u r e s o c c u r r i n g 20 t o 40 d ay s b ef o r e harvest were g i v en maximum weight, and 3) t h e weighted h o u r l y c o n c e n t r a t i o n s were cumulated f o r t h e exposure p e r io d .
-
6. R es p i t e Time: t h e a v e r a g e number o f days between e p i s o d e s ( a n e p i s o d e was d e f i n e d as a n e v e n t w i t h h o u r l y 03 c o n c e n t r a t i o n s above a t h r e s h o l d v a l u e ) u s i n g t h r e s h o l d v a l u e s o f 0.08 ppm (DAYBETO8) o r 0.10 ppm (DAYBET10). The exposure i n d i c e s were computed from a c t u a l h o u r l y 03 m o n i t o r i n g d a t a and r e g r e s s e d a g a i n s t i n d i v i d u a l chamber h a r v e s t y i e l d s u si n g t h e Box-Tidwell model [ r e f . 71. The " b e s t" exposure i n d e x f o r each set of r esp o n se data ( c a s e )
was t h e one d i s p l a y i n g t h e minimum r e s i d u a l sum of s q u a r e s (RSS). For a n i n d i v i d u a l case, t h e r e l a t i v e performsnce of a n i n d ex was measured as t h e r a t i o of i t s RSS t o t h e i n d e x w i t h t h e minimum RSS and ranked i n ascen d i n g o r d e r , i.e.,
t h e " b e s t" i n d e x f o r a case has a r e l a t i v e RSS o f 1. For o v e r a l l
comparison, t h e exposure i n d i c e s were e v a l u a t e d a c c o r d i n g t o t h r e e c r i t e r i a :
225 (1) t h e average s c o r e c a l c u l a t e d as t h e mean r e l a t i v e RSS's averaged a c r o s s t h e 17 c a s e s ; (2) t h e range of r e l a t i v e RSS's; and (3) p e r c e n t v a r i a t i o n ,
(i.e.,
[range/mean s c o r e ] x 100). The nonparametric Wilcoxin signed ranks test
was used t o perform p a i w i s e comparisons of r e l a t i v e RSS's among i n d i c e s a c r o s s cases i r e f . 1 2 ) . TABLE 1. Comparison of v a r i o u s exposure I n d i c e s . Exposure Index GPWCI SUMO7
SUM06 SIGMOID SUM08 AOTO8 PER99 TIMPACT
EFFMEAN M7 TOTDOSE ALLOMETKIC
PER90 PER95 AOTlO MI SUM10
P7 P1 NUMEP08 HKSlO AVGEPOB HKSOU
AVGEP 10 NUMEPlO DAYbET 10 DAYBETO8
Mean Score
1.12 1.14 1.15 1.17 1.17 1.18 1.19 1.20 1.20 1.20 1.21 1.22 1.22 1.23 1.24 1.26 1.27 1.31 1.40 1.40 1.43 1.46 1.49 1.74 1.78 4.49 5.35
Minimum Maximum Range Score Score
1.02 1.01 1.04 1.04 1 a05 1.01 1 .oo 1.01 1.02 1.02 1.02 1.01 1.01 1.00 1.02 1.02 1.00 1.00 1.07 1 .oo 1 .00 1.01 1.05 1.00 1.03 1.37 1.49
1.36 1.32 1.38 1.35 1.54 1.80 2.06 1.70 1.65 1.63 1.63 1.74 1.86 1.99 2.84 2.11 2.96 2.32 2.34 2.04 4.67 4.93 5.07 4.08 5.46 15.20 17 .OO
0.34 0.31 0.34 0.31 0.49 0.79 1.06 0.69 0.63 0.61 0.61 0.73 0.85 0.99 1.82 1.09 1.96 1.32 1.27 1.04 3.67 3.92 4.02 3.08 4.43 13.83 15.51
x Variation
Index 5Pe
30 Multicomponent 27 Sum Conc Sum Conc 30 26 Sum Conc 42 Sum Conc Sum Conc 67 One Event 89 58 Sum Conc 52 Mean 51 Mean Cumulative 50 Sum Conc 60 One Event 70 80 One Event Sum Conc 147 Mean 87 Sum Conc 154 One Event 101 91 One Event 74 Num Episode 257 Num Episode 268 Num Episode 270 Num Episode 177 Num Episode 249 N u m Episode 308 R e s p i t e Time 290 R e s p i t e Time
No s i n g l e exposure index performed "best" (based on minimum RSS) f o r a l l p l a n t s p e c i e s / c u l t i v a r s , but t h e r e was p o s i t i v e agreement among t h e top-ranked i n d i c e s f o r t h e 17 c a s e s [ r e f . 71.
A comparison of t h e 27 i n d i c e s used found
that 20 had average s c o r e s of 1.20 o r h i g h e r (Table 1).
The p a i r e d sample
Wilcoxin signed ranks test showed no s i g n i f i c a n t d i f f e r e n c e s ( a t t h e 0.05 l e v e l ) between t h e top-ranked
Index (GPWCI) and o t h e r i n d i c e s which a l s o gave
g r e a t e r weight t o e l e v a t e d c o n c e n t r a t i o n s and cumulated t h e exposures (SUM07, SUM06, SIGMOID, SUMO8, AOTO8, ALLOMETRIC, AOT10, SUM10).
The weighted
cumulative i n d i c e s SUM07, SUMO6, and SIGMOID had s i m i l a r average s c o r e s (1.14,
1.15, and 1.17 r e s p e c t i v e l y ) and d i s p l a y e d s i m i l a r p e r c e n t v a r i a t i o n s t o t h e
226 top-ranked GPWCI i n d e x a c r o s s a l l s p e c i e s / c u l t i v a r s .
Although t h e SUMOB,
AOTOB, and PER99 i n d i c e s were n o t s i g n i f i c a n t l y d i f f e r e n t from t h e top-
performing i n d e x , t h e y d i s p l a y e d g r e a t e r p e r c e n t v a r i a t i o n t h a n t h e toppertorming GPWCI index.
I n p a r t i c u l a r , t h e noncumulative i n d e x , PER99, had
r e l a t i v e f i t s ranging from 1.00 t o 2.06 a c r o s s t h e c a s e s , which r e p r e s e n t s a t h r e e - t o l d i n c r e a s e o v e r t h e top-performing
GPWCI's range of r e l a t i v e RSS's.
Three i n d i c e s , ALLOMETKIC, SUMl0, and AOT10, had a v e r a g e s c o r e s g r e a t e r t h a n 1.20,
but were n o t s i g n i f i c a n t l y d i f f e r e n t from t h e top-ranked GPWCI i n d e x due
t o a n e x t r e m e l y poor f i t i n a s i n g l e c a s e ( t h e 1981 c o t t o n s t u d y w i t h droughtstressed plants).
Based on o u r c r i t e r i a , SUM07, SUM06, and SIGMOID were
n e a r l y e q u a l i n performance t o t h e top-ranked
GPWCI index. Based on a v e r a g e
s c o r e and v a r i a t i o n , t h e M7 performed b e t t e r t h a n PER99 (non-cumulative i n d i c e s ) , but i t s performance was s i g n i f i c a n t l y i n f e r i o r t o t h e f o u r top-ranked i n d i c e s (GPWCI, SUMO7, SUMOC, and SIGMOID). For t h e s e a n a l y s e s , t h e exposure i n d i c e s t h a t emphasize peak c o n c e n t r a t i o n s and cumulate c o n c e n t r a t i o n s o v e r t i m e performed b e t t e r t h a n t h o s e t h a t only a v e r a g e c o n c e n t r a t i o n s .
S i m i l a r c o n c l u s i o n s were reached by Lefohn e t a l . [ r e f . 131 and Lee e t a l . ( r e f . 141 who used NCLAN d a t a and c u m u l a t i v e i n d i c e s w i t h sigmoid [ r e f . 131 and a l l o m e t r i c [ r e f . 141 c o n c e n t r a t i o n weighting f u n c t i o n s .
of Lee e t a l .
[ r e f . 7 1 found t h a t t h e sigmoid-weighting
The r e c e n t work
f u n c t i o n s were
p r e f e r r e d t o a l l o m e t r i c ones. The GPWCI i n d i c e s w i t h sigmoid w e i g h t s (which emphasized c o n c e n t r a t i o n s >0.06 ppm) performed b e t t e r t h a n d i d d i s c o n t i n u o u s l y weighted cumulative exposure i n d i c e s that i g n o r e h o u r l y c o n c e n t r a t i o n s below t h r e s h o l d s of 0.08 ppm and higher.
However, t h e d i s c o n t i n u o u s l y weighted
cumulative i n d i c e s (SUMO7 and SUMO6) t h a t used t h r e s h o l d c o n c e n t r a t i o n s (0.06 o r 0.07 ppm) t o emphasize c o n c e n t r a t i o n and accumulated e x p o s u r e performed s i m i l a r l y t o t h e top-ranked
GPWCI index.
CONCLUSION
Our a n a l y s e s s u p p o r t t h e c o n c l u s i o n s from p r e v i o u s s t u d i e s t h a t demonstrated t h e importance of peak c o n c e n t r a t i o n s i n d e t e r m i n i n g p l a n t r e s p o n s e .
Although
no s i n g l e i n d e x was deemed " b e s t " ( i n a l l cases) f o r r e l a t i n g 03 exposure t o p l a n t r e s p o n s e , t h e top-performing
exposure i n d i c e s were t h o s e that ( 1 )
cumulate t h e h o u r l y 03 c o n c e n t r a t i o n s o v e r t i m e , ( 2 ) emphasize c o n c e n t r a t i o n s o f 0.06 ppm and h i g h e r e i t h e r by c o n t i n u o u s sigmoid w e i g h t s o r by d i s c r e t e (0 o r 1) w e i g h t s of t h e t h r e s h o l d i n d i c e s , and ( 3 ) gave g r e a t e r weight t o exposures o c c u r r i n g 20 t o 40 d a y s b e f o r e h a r v e s t .
When a s s e s s i n g t h e impact of
03 on p l a n t growth, t h e s e f i n d i n g s i l l u s t r a t e t h e importance of exposure
d u r a t i o n , t h e importance o f r e p e a t e d peaks, and t h e t i m e of i n c r e a s e d p l a n t sensitivity.
227 REFERENCES R.C. Musselman, R.J. Oshima and R.E. G a l l a v a n , " S i g n i f i c a n c e of p o l l u t a n t c o n c e n t r a t i o n d i s t r i b u t i o n i n t h e r e s p o n s e of ' r e d kidney' beans t o ozone,'' J. Am. SOC. Hortic. Sci. 108 (1983) 645-648. W.E. H o g s e t t , D.T. Tingey and S.R. Holman, "A programmable exposure c o n t r o l system f o r d e t e r m i n a t i o n of t h e e f f e c t s o f p o l l u t a n t exposure regimes on p l a n t growth," Atmos. Environ. 19 (1985) 1135-1145. U.S. Environmental P r o t e c t i o n Agency, A i r Q u a l i t y Criteria f o r Ozone and o t h e r Photochemical O x i d a n t s , 1986 I , Research T r i a n g l e Park, NC, EPA-LOOI 8-84-020aF. W.E. H o g s e t t , D.T. Tingey and E.H. Lee, Exposure i n d i c e s : Concepts f o r development and e v a l u a t i o n of t h e i r u s e . In: Assessment o f Crop Loss from Air P o l l u t a n t s : Proceedings of t h e i n t e r n a t i o n a l c o n f e r e n c e , R a l e i g h , N.C., USA, (ed.) W.W. Heck, O.C. Taylor and D.T. Tingey, London, Elsevier Applied Science, 1988 (In p r e s s ) . A.S. Heagle, and W.W. Heck, F i e l d methods t o assess crop l o s s e s due t o o x i d a n t a i r p o l l u t a n t s . In Crop Loss Assessment: Proceedings o f E.C. Stakman Commemorative Symposium, ed. by P.S. Teng and S.V. Krupa, Misc. P u b l i c a t i o n # 7 , U n i v e r s i t y of Minnesota, St. P a u l , 1980, pp. 296-305. W.W. Heck, W.W. Cure, J.O. Rawlings, L.J. Zaragoza, A.S. Heagle, H.E. Heggestad, K.J. Kohut, L.W. Kress and P.J. Temple, "Assessing i m p a c t s of ozone on a g r i c u l t u r a l c r o p s : I. Overview," J. A i r P o l l u t . C o n t r o l Assoc.
34: (1984) 729-735. E.H. Lee, D.T. Tingey and W.E.
10
11
12 13 14
H o g s e t t , " E v a l u a t i o n of ozone exposure i n d i c e s i n exposure-response modeling. In Assessment of c r o p l o s s from a i r pollutants," Environ. P o l l u t . (1988) (In p r e s s ) . W.W. Cure, J . S . Sanders and A.S. Heagle, "Crop y i e l d r e s p o n s e p r e d i c t e d w i t h d i f f e r e n t c h a r a c t e r i z a t i o n s of t h e same ozone t r e a t m e n t s , " J. Environ. Qual. 15: (1986) 251-254. W.W. Heck, O.C. T a y l o r , R.M. Adams, G. Bingham, J. Miller, E. P r e s t o n and L. Weinstein, "Assessment of c r o p l o s s from ozone,'' J. A i r P o l l u t . C o n t r o l Assoc. 32: (1982) 353-361. K.I. Larsen and W.W. Heck, "An a i r q u a l i t y d a t a a n a l y s i s system f o r i n t e r r e l a t i n g e f f e c t s , s t a n d a r d s , and needed s o u r c e r e d u c t i o n s : P a r t 8 . An e f f e c t i v e mean 03 c r o p r e d u c t i o n mathematical model," J. A i r P o l l u t . C o n t r o l Assoc. 34: (1984) 1023-1034. R . I . Larsen, A.S. Heagle and W.W. Heck, "An a i r q u a l i t y d a t a a n a l y s i s s y s t e m f o r i n t e r r e l a t i n g e f f e c t s , s t a n d a r d s , and needed s o u r c e r e d u c t i o n s : P a r t 7. An 03-502 l e a f i n j u r y mathematical model," J. A i r P o l l u t . C o n t r o l A S ~ O C . 33: (1983) 198-207. W.J. Conover, P r a c t i c a l Nonparametric S t a t i s t i c s . John Wiley & Sons, New York, 1971, 461 pp. A.S. Lefohn, J.A. Laurence and R.J. Kohut, "A comparison of i n d i c e s that d e s c r i b e t h e r e l a t i o n s h i p between exposure t o ozone and r e d u c t i o n i n t h e y i e l d of a g r i c u l t u r a l c r o p s , " Atmos. Environ. (1988) (In p r e s s ) . E.H. Lee, U.T. Tingey and W.E. H o g s e t t , S e l e c t i o n of t h e b e s t exposureresponse model using v a r i o u s 7-hour ozone exposure statistics, U.S. EPA, Oi-tice of A i r Q u a l i t y Planning and S t a n d a r d s , Research T r i a n g l e P a r k , NC,
1987.
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T. Schneider et aL (Editors), Atmospheric Ozone Research and its Policy Implications 0 1989 Elsevier Science Publishers B.V., Amsterdam -Printed in The Netherlanda
223
EFFECTS OF OZONE ON AGRICULTURAL CROPS
S.V. KRUPAL and M. NOSAL' 1 Department o f Plant Pathology, U n i v e r s i t y o f Minnesota, S t . Paul, Minnesota 55108 (USA) a Department o f Mathematics and S t a t i s t i c s , U n i v e r s i t y o f Calgary, Calgary, A l b e r t a T2N 1N4 (Canada). ABSTRACT Time s e r i e s , s p e c t r a l coherence a n a l y s i s showed t h a t a t low 0s f l u x dens i t y , median h o u r l y Oa concentration provided t h e h i g h e s t coherence w i t h a l f a l f a h e i g h t growth, w h i l e a t h i g h Oa f l u x density, i t was t h e cumulative i n t e g r a l o f exposure. These and a d d i t i o n a l r e s u l t s f o r Oa and o t h e r approp r i a t e exposure terms f o r SO' were j o i n t l y u t i l i z e d i n a non-linear regression t o r e l a t e ambient p o l l u t a n t exposure dynamics t o a l f a l f a harvest biomass. INTRODUCTION
Much o f t h e e a r l y research on t h e e f f e c t s o f ozone ( O a ) on crops was d i r e c t e d t o acute exposures and p r o d u c t i o n o f v i s i b l e i n j u r y under c o n t r o l l e d environment and greenhouse c o n d i t i o n s .
Such e f f o r t s , among o t h e r d i s c o v e r i e s ,
l e d t o t h e i d e n t i f i c a t i o n o f s e n s i t i v e crop genera, species. and c u l t i v a r s . However, over t h e p a s t two decades, t h e emphasis has s h i f t e d toward examining chronic 0s exposures and changes i n crop growth, p r o d u c t i v i t y , and q u a l i t y ( r e f . 1). According t o Krupa and Manning ( r e f . 2), answering t h e key q u e s t i o n o f whether o r n o t 0s s i g n i f i c a n t l y a f f e c t s c r o p growth and y i e l d has proven t o be e x t r a o r d i n a r i l y d i f f i c u l t .
This i s due t o t h e n a t u r e o f t h e p o l l u t a n t and
i t s d i s t r i b u t i o n i n t h e ambient a i r .
During t h e crop growth season, Oa i s
an a l l - p e r v a s i v e p o l l u t a n t , making i t d i f f i c u l t t o exclude i t and s t i l l have c o n d i t i o n s t h a t are r e l e v a n t t o those t h a t occur I n nature.
Side-by-side
com-
parisons o f t h e e f f e c t s o f ambient Or on crops a r e impossible, unless some way can be devised t o exclude 01 from t h e c o n t r o l treatment t o background levels.
Development o f a u n i v e r s a l l y accepted method, under normal c o n d i t i o n s
has n o t been s u c c e s s f u l l y accomplished a t t h i s time.
This means t h a t a l l
experimental determinations o f t h e e f f e c t s o f ambient Oa on crop growth and y i e l d must be q u a l i f i e d by t h e i n h e r e n t l i m i t a t i o n o f whatever method was used t o achieve them (Table 1).
230 Table 1. Comparative advantages and disadvantages o f some f i e l d assessment methods o f O3 exposure and c r o p response.
1)
Oprn-top chambers (up-draft)
2)
Open-top Chambers (downdraft)
a) Most u l d r l y used system l n the w: a) A r t l f l c l a l chambrr e f f e c t on p l a n t growth and p r o d u c t l v l t y present. s c m 15 years o f h l s t o r l c a l records. b) Wlqh c o s t f o r (ncludlng s u f f t c l e n t b) Many crops can be groun t o w t u r l t y undrr condltlons s a w h a t a~ulogws number of t n a t m n t s and labor lntenslr e, t o the amblmt. c) L f f r c t s o l rlr p o l l u t a n t s can be c) Conplea colputer c o n t r o l l e d systrm requlred t o mlnlck amblent p o l l u t a n t evaluated s l n g l y o r as mlxtuns. exposure dynamlcs u l t h l n the chambar. d) CDlnparlsons can be made b e t w e n 4 ) P o l l u t a n t flat u l t h l n the chambrr f l l t e r e d (OMp o l l u t a n t removal) a r t l f l c l a l and not s l m l l a r to the and u n l l l t e r r d a d l m t a l r , ablent. a) I l o d l f l c a t l o n s I n t h r n l c r o c l l n r t e a) Reasonable c o n t r o l on e n v l n n u l t h l n the chimbrr can b a d t o a l t e r e d mrntal variables u l t h l n the chabrr lncldencr of pathogens and pests 1) Raln shadows prasent g l Is subject t o weather hazards, lncludlng lncurslon of a d l e n t a l r i n t o the chambrr.
a t tlnrs. a ) Sam as (a). (b). l c ) . and 1.1
of f ( 1 )
b) 0. r a c l u s l o n (ran the m b l e n t a t r enterlng the c h a d a r varles from 255 t o
1M c ) Anblent r a l n I s excluded. d ) As u l t h ( I ) . I s subject t o w a t h e r hazards, 3)
Oprn-alr. chanberlrss. a r t l f l c l a l f i e l d exposure
a ) Wo chamber a f f e c t
b) Largr n d r r of plants can b r raposrd t o varylng 01 exposure re9 l n r s ,
c ) Oeslrablr approach if(b). I d ) . and (e) under the dlradrantages am rec tl f led.
a) -11 chanqrs l n u l n d t u r b u l r n c r can cause l a r q r chanqrs l n 0. concrntratlons. b) Hlgh p r r c l s l o n i n a frrd-back c o n t r o l of 01 r r l r a s c and l n t r n s l v r and r x t c n s l v r monitorlng o f 01 w l t h l n the study p l o t rrqulrrd.
c) Control, study p l o t d l f f l c u l t t o d r r l w i t h due t o the m l - p r e s r n c a of 01. d ) I n t r n s l v r and r x t c n s l v r monltortnp of other a t r p o l l u t o n t s and a n v l r o m n t a l varlablas r r q u l rrd, e) Powerful. m u l t l v a r l a t r . tlmr s r r l r s modrls r r q u l r r d t o f u l l y #valuate t h r r c s u l t s .
4)
Natural pradlents of ambient 0.
a) Lvaluatlon of the n a l world sltuitlon. b ) lllqh degree of nilkith posslble
5)
Chrmlcal protectants (ant!-oxldmts)
a) Close t o the r e a l world b) Wlgh degree of n p l l c a t l o n poltlblr
6[
C u l t l v a r scnanlng
Modlflad from Krupa ( r e f . 23)
a) S u f f l c l r n t number of treatments (varylng 01 rxposure r e g l w s ) u l t h l n a s n s l l gropraphlc arra requlrrd. b) 0 s and o t h r r p o l l u t a n t s . and envlronmental varlablcs must be i n t r n s l v r l y monltorrd a t each sltc. c ) V a r l a b i l l t y due to t h e i n f l u r n c a of l o l l must be accounted, unlrss standardlied sol1 i s usrd a t a11 study sites. d) saw as ( C ) Of f(3) e ) Year t o y r a r v a r l a b l l l t y I n 0, raposurr and crop responsr must be accountrd I) L f f r c t o f t h r p r o t r c t a n t l t s r l f on p l a n t
grobth and y l c l d posslble: thus p r l o r testlng rrqulrrd b) The amount of p r a t e c t l o n provtdrd by d l f f e r r n t chrnlcal dose on d l f f r r e n t p l a n t speclei not f u l l y undrrstood. c ) Snr as a l l o t h r r s l l s t r d under (4).
a) Closest t o the m a 1 world
a) D l f f r r r n c e s I n t h r t h r o n l c rrrponses
b) No chambers. no chmlcal protectants
of c u l t l v a r c t o 01 exposurrs must be knaun . b) S a i i s (b). (d). and ( e l l l s t e d I n f(4).
231 ESTABLISHING NUMERICAL D E F I N I T I O N S
OF CAUSE (CHRONIC 0 0 EXPOSURE) - EFFECTS
(CROP RESPONSE) RELATIONSHIPS
A necessary step i n a l l exposure s t u d i e s i s t h e q u a n t i t a t i v e d e s c r i p t i o n o f t h e cause-effect r e l a t i o n s h i p s .
While a number o f i n v e s t i g a t o r s have devel-
oped models t o e x p l a i n such r e l a t i o n s h i p s ( r e f . 3), t h e mathematical d e f i n i t i o n o f 03 exposure parameters u t i l i z e d i n such models has been t h e s u b j e c t o f much debate ( r e f s . 3-7).
According t o Krupa and K i c k e r t ( r e f . 3 ) . any
d e f i n i t i o n of t h e 00 exposure q u a n t i f i c a t i o n term(s) must be b i o l o g i c a l l y meaningful and must be b r o a d l y a p p l i c a b l e .
While achieving t h a t goal could
prove t o be mathematically complex, a i r q u a l i t y r e g u l a t o r s and p o l i c y makers wish simple, a d m i n i s t r a t i v e l y a p p l i c a b l e s o l u t i o n s .
I n addressing t h i s objec-
t i v e , t h e use o f o v e r - s i m p l i f i e d 00 exposure terms, such as t h e a p p l i c a t i o n o f crop growth season average 00 concentrations ( r e f . 8) has been subjected t o much c r i t i c i s m ( r e f s . 3 . 5 ) .
Such c r i t i c i s m s a r e based on t h e l a c k o f b i o -
l o g i c a l meaning and u n i v e r s a l a p p l i c a b i l i t y o f such models ( r e f s . 6.7.9). I n t h e i r a n a l y s i s o f t h e numerical models o f a i r p o l l u t a n t exposure and Krupa and K i c k e r t ( r e f s . 3.10) concluded t h a t a
vegetation response (Table 2 ) ,
s a t i s f a c t o r y expression o f t h e p o l l u t a n t exposure term(s) should consider: a)
The a r t i f a c t s of p o l l u t a n t averaging techniques, since t h e frequency d i s t r i b u t i o n s o f ambient 00 concentrations, i n general, a r e n o t normally d i s t r i b u t e d .
They a r e b e s t described by t h e f a m i l y o f Weibull
f u n c t i o n s ( r e f s . 11.12); b)
t h e e p i s o d i c i t y o f t h e occurrence o f ambient Oa o r t h e peak exposures (refs
c)
.
7.1 3.14.1 5.1 6) ;
t h e t i m e i n t e r v a l s between such episodes, t h e r e s p i t e t i m e f o r t h e crop t o e s t a b l i s h some degree o f r e p a i r o r e x h i b i t p r e - d i s p o s i t i o n ( r e f s . 17,18,19);
d)
and
t h e r e l a t i o n s h i p between t h e occurrences o f Oa episodes and t h e d i f f e r i n g p h y s i o l o g i c a l s e n s i t i v i t y o f t h e crop growth stages ( r e f s . 7.20).
I n attempting t o r e c o n c i l e w i t h these and o t h e r requirements. a number o f i n v e s t i g a t o r s i n t h e U.S.
have developed and evaluated t h e a p p l i c a b i l i t y o f
0 s exposure i n d i c e s ( r e f s . 6.7).
The conclusion drawn from a l l these
studies i s t h a t no s i n g l e numerical d e f i n i t i o n o f 00 exposure has y e t been found which i s u n i v e r s a l l y a p p l i c a b l e .
This i s n o t s u r p r i s i n g s i n c e t h e
ambient 0 s exposure-crop response r e l a t i o n s h i p s must be considered t o be inherently stochastic i n nature ( r e f . 21).
Further, such r e l a t i o n s h i p s a r e
obviously i n f l u e n c e d by a number o f v a r i a b l e s ( c r o p species and c u l t i v a r i n question, occurrence o f o t h e r p o l l u t a n t s , pathogens and pests. a g r i c u l t u r a l P r a c t i c e s , o t h e r non-pollutant atmospheric and edaphic v a r i a b l e s , e t c . ) . Given t h i s complexity, one wonders about t h e v a l i d i t y o f r e g i o n a l s c a l e
232
Table 2. Sumnary comments on some numerical models used to relate O3 exposures to crop responses. Reference
Type of Model
0. Ixposure Parameters
1.
Benson e t a l . (24)
Non-linear. polynomial o r multivariate. linear
Sum of h o u r l y average On Concentration p e r day o r sums o f h o u r l y average 01 concentrations. weekly over t h e growth season.
2.
Heagle e t a l . (8)
Various forms o f non-linear Weibull and polynomials
1-hrlday. seasonal mean
3.
Heck e t 11. (25)
Linear, p l a t e a u l i n e a r
1-hrlday. seasonal mean
4.
Kinsman e t a l . ( 2 6 )
Linear. l o g - l i n e a r . exponential second degree p o l ynoni a 1, quadratic , square r o o t and Y e i b u l l
12-hr m a n . 1-hr mean. 12-hr t o t a l , 1-hr t o t a l . 1 5 t h p e r c e n t i l e of 12-hr values. 9 0 t h p e r c e n t l l e of 12-hr values, a l l d u r i n g f l w e r i n g t o m a t u r i t y of soybean.
5.
Lefohn e t a l . ( 6 )
Linear. Weibull
Number of occurrences equal t o o r above s p e c i f i c h o u r l y mean concentration: sun of a l l h o u r l y m a n concentrations equal t o o r above a selected concentratlon; weighted sum o f a l l h o u r l y mean concentrations.
b.
Loehman and Y i l k l n s o n (21)
L i n e a r o r n o n - l i n e a r quadratic
1-hr d a i l y continuous concentration
1.
Nosal (12)
M u l t i v a r i a t e . polynomial. Fourier
Peak concentratlon, frequency of exposure. cumulative i n t e g r a l of exposure
8.
Oshima e t 11. (20)
linear
Sum o f h o u r l y average 0 s concentration >0.10 pprn d u r i n g d a y l i g h t hours over e n t i r e growth season.
9.
Roue and Chestnut (29)
Llnear
Average h o u r l y 0 s concentrations per m n t h surmed over growth season o r number o f d a y l l g h t hours of 0 . >0.10 ppn.
Tingey e t a l . ( 1 )
Box-Tidwcll
Maximum 7-hr and maaimum 1-hr d a l l y averages and the 90th. 95th. and 9 9 t h p e r c e n t i l e s o f h o u r l y d i s t r i b u t i o n ; seasonal means o f 1 - h r d a i l y means; 1-hr d a i l y m a n s and e f f e c t i v e mean; seasonal sum of a l l h o u r l y concentrations: two separate types of concentration welghting. seasonal sum o f h o u r l y concentrations a t o r above 0.06 ppn. 0.01 ppm. 0.00 ppm. o r 0.10 ppn; seasonal censored sum of h o u r l y concentrations a t o r above a threshold, i . e . . cumulatlve sum o f t h e area over t h r e s h o l d of 0.00 ppn o r 0.10 ppm, t o t a l impact i n which t h e h o u r l y concentratlon was r a i s e d t o a power and s u m d ; o r t h e h o u r l y c o n c e n t r a t i o n was m u l t i p l i e d by a s i g m i d weighting f u n c t l o n ( i n f l e c t i o n 0.062 ppm) and sunmed. t o t a l hours w i t h concentrat l o n s a t o r above thresholds o f 0.08 ppn o r 0.10 ppm; average episode l e n g t h using thresholds o f 0.00 ppm o r 0.10 ppm: multi-component which included d i f f e r e n t weightlngs on c o n c e n t r a t i o n and phenologlcal staqes o f development; t h e average n u e e r o f days between c p l sodel using t h r e s h o l d values o f 0.00 ppm o r 0.10 ppm.
10.
-
Modified from Krupa and K i c k e r t ( r e f . 3 )
233 0s-induced crop l o s s assessment ( r e f . 22).
Such assessments, however,
obviously have a c r i t i c a l impact on t h e promulgation and implementation o f a i r q u a l i t y regulatory p o l i c i e s . I n an attempt t o determine t h e Importance o f various Oa exposure parameters i n crop response, Nosal ( r e f . 12) found t h a t t h e frequency o f exposure, peak 01 concentration, and t h e cumulative i n t e g r a l o f Oa exposure over t h e crop growth season were a l l important i n examining soybean y i e l d responses. These conclusions were r e c e n t l y s u b s t a n t i a t e d ( r e f . 7). R e g r e t f u l l y , many o f t h e e f f o r t s t o develop Oa exposure i n d i c e s a r e based upon studies, t h e r e s u l t s o f which a r e d e r i v e d from i n a p p r o p r i a t e experimental design ( r e f s . 3.10).
While Oa may be t h e s i n g l e dominant a i r p o l l u t a n t
v a r i a b l e i n a p a r t i c u l a r p l a c e and time, one should n o t f o r g e t t h a t ambient a i r i s n o t f r e e o f o t h e r p o l l u t a n t s , pathogens and pests.
Any Oa exposure
i n d i c e s developed must consider these f a c t o r s and must be based on r e a l i s t i c ambient parameters. APPLICATION OF TIME SERIES, SPECTRAL COHERENCE ANALYSIS, AND BEST NON-LINEAR REGRESSION TO RELATE AMBIENT Oa AND SO2 EXPOSURES TO ALFALFA RESPONSES
I n a study conducted i n Minnesota, a l f a l f a (De Kalb 120) was grown i n open a i r i n a comnon s o i l type a t 9 s i t e s over two sunmers. were obtained a t each s i t e . scale O a and
SO2
A t o t a l o f 7 harvests
During t h e study t h e p l a n t s were exposed t o area
from a p o i n t source.
During each harvest period, t h e h e i g h t growth o f a l f a l f a was measured once a week a t each s i t e and i n d i v i d u a l growth curves f o r t h e h a r v e s t p e r i o d were developed using an exponential model.
Based on these growth curves, a l f a l f a
growth a t each s i t e d u r i n g each harvest was d i v i d e d i n t o t h r e e phases (1-15 days; 16-30 days and 31-45 days, h a r v e s t ) .
The impacts o f O a and
SO2 on each growth phase were evaluated using t h e f o l l o w i n g exposure para-
meters:
mean; median; p e r c e n t i l e s ; peaks; frequency o f exposure and cumula-
t i v e i n t e g r a l o f exposure. F o u r i e r transformations and time s e r i e s , s p e c t r a l coherence a n a l y s i s were used i n examining t h e r e l a t i o n s h i p s between t h e p o l l u t a n t exposure dynamics and a l f a l f a h e l g h t growth.
The u n d e r l y i n g concept o f these numerical methods
i s t h a t each t i m e s e r i e s or f u n c t i o n o f t i m e can be m e a n i n g f u l l y represented as a l i n e a r combination o f pure s i n e waves sunmed over d i f f e r e n t frequencies, w i t h d i f f e r e n t amplitude and phase a t each frequency ( r e f . 30).
Spectral
a n a l y s i s proceeds by F o u r i e r t r a n s f o r m a t i o n o f t h e t i m e s e r i e s t o o b t a i n t h e c o e f f i c i e n t s o f sinusoids a t a d i s c r e t e s e t o f frequencies. grouping nelghbouring frequencies i n t o frequency bands and e s t i m a t i n g various q u a n t i t i e s i n one frequency band a t a time.
234 The s p e c t r a l d e n s i t y o f a v a r i a b l e i s estimated by computing t h e average squared amplitude o f t h e sinusoids w i t h i n a frequency band.
T h i s estimated
s p e c t r a l d e n s i t y i s p l o t t e d as a f u n c t i o n o f frequency (more p r e c i s e l y as a f u n c t i o n of band frequency c e n t e r and frequency bandwidth).
The s p e c t r a l
d e n s i t y i n d i c a t e s how t h e v a r i a t i o n e x h i b l t e d by t h e data i s d i s t r i b u t e d over t h e d i f f e r e n t frequency bands. Spectal a n a l y s i s o f i n d i v i d u a l v a r i a b l e s can be u s e f u l l y extended t o p a i r s o f t i m e s e r i e s and i n v e s t i g a t i o n s o f t h e i r i n t e r r e l a t i o n s h i p .
One o f t h e most
important frequency domain concepts i s t h e coherence f u n c t i o n ( r e f . 31). Coherence resembles t h e usual a n a l y s i s o f two random v a r i a b l e s .
Only here
adjacent frequencies w i t h i n a frequency band t a k e t h e p l a c e o f t h e independent observations.
Coherence i s a measure o f a s s o c i a t i o n between t h e two t i m e
s e r i e s (expressed i n terms o f t h e i r frequencies) s i m i l a r t o squared c o e f f i cient of correlation.
The phase, o r phase d i f f e r e n c e between t h e two t i m e
s e r i e s i n d i c a t e s t h e d i r e c t i o n o f t h e a s s o c i a t i o n and i s analogous t o t h e s i g n of the correlation coefficient.
Broadly speaking, t h e coherence i s intended
t o measure t h e degree t o which t h e two t i m e s e r i e s vary t o g e t h e r and t h e phase captures t h e e x t e n t t o which they a r e i n step. A sumnary o f t h e r e s u l t s o f t h e t i m e s e r i e s , s p e c t r a l coherence a n a l y s i s
between Oa exposure dynamics and a l f a l f a h e i g h t growth dynamics i s provided i n Table 3 .
O f a l l t h e exposure parameters examined, "median" h o u r l y 00 con-
c e n t r a t i o n provided t h e h i g h e s t coherence value w i t h t h e a l f a l f a h e i g h t growth, when t h e degree o f OS f l u x d e n s i t y (expressed as frequency) was low.
However,
when t h e O a f l u x d e n s i t y was high, t h e "cumulative i n t e g r a l " o f OS exposure provided t h e h i g h e s t coherence value w i t h t h e a l f a l f a h e i g h t growth.
These
f i n d i n g s a r e extremely important i n t h e c o n t e x t o f previous s t u d i e s conducted by others ( r e f e r t o Table 2 ) .
I n those e f f o r t s a s i n g l e o r m u l t i p l e exposure
q u a n t i f i c a t i o n term(s) computed over t h e whole growth season were used i n examining t h e cause-effects r e l a t i o n s h i p s and no s i n g l e d e s c r i p t o r o f t h e exposure parameter was deemed t o be t h e best.
The r e s u l t s o f t h e t i m e s e r i e s ,
coherence a n a l y s i s p r o v i d e an e x p l a n a t i o n f o r t h e conclusion reached.
The
exposure parameter p r o v i d i n g t h e h i g h e s t coherence value w i t h t h e crop growth dynamics, changes w i t h t h e degree o f O a f l u x d e n s i t y .
Ambient 01 exposure
regimes a r e governed by t h e s t o c h a s t i c i t y and t h e v a r i a b i l i t y o f t h e c l i m a t o l o g i c a l processes. time.
Thus, Oa f l u x d e n s i t y i s h i g h l y v a r i a b l e i n space and
The c h a r a c t e r i s t i c s o f t h i s f l u x d e n s i t y appear t o determine t h e t y p e
o f exposure parameter t h a t can b e s t d e s c r i b e t h e crop response a t any given time.
Since t h e crop growth stage o r phenology a l s o changes w i t h time,
a p p r o p r i a t e d e s c r i p t o r s o f exposure must be i d e n t i f i e d f o r each growth stage and u t i l i z e d i n t h e f i n a l equation(s) e x p l a i n i n g t h e c r o p y i e l d responses.
235 Table 3 .
Study S i t e 1
1
2 2 3 3 4 4 5 5 6 6 1
1 9 9 10 10
Time s e r i e s , s p e c t r a l a n a l y s i s o f coherence between 0s exposure parameters and a l f a l f a h e i g h t growth.
01 Exposure Parametera Median Concentration (MC) Cumulative I n t e g r a l ( C I ) MC C I MC CI MC C I MC CI MC CI MC CI MC CI MC C I
Highest Coherence
Frequencyb
0.64b 0.98b 0.44 0.92 0.56 0.96 0.60 0.95 0.58 1 .oo 0.36 0.88 0.40 0.96 0.46 0.96 0.56 0.98
0.004 0.480 0.004 0.480 0.055 0.480 0.380 0.480 0.055 0.480 0.385 0.480 0.155 0.480 0.380 0.480 0.060 0.480
a OS exposure parameters were computed from h o u r l y data, 24 hrs/day. Frequency = l / p e r i o d i c i t y ; a t lower frequencies, median 0s concentrations provided t h e highest coherence; w h i l e a t h i g h e r frequencies, cumulative exposure i n t e g r a l provided t h e h i g h e s t coherence w i t h a l f a l f a h e i g h t growth.
236 Table 4.
R e l a t i o n s h i p s between ambient ozone ( 0 s ) and s u l f u r d i o x i d e exposures and a l f a l f a l e a f d r y weight p e r 100 stems.
(Sol)
A l f a l f a l e a f d r y weight p e r 100 stems = 0.92 x Oa Med. 1 + 0.001 x Oa I n t . 1 + -4.2 x Oa Med. 2 + -0.28 x Oa Peak. 2 + 0.002 x Oa I n t . 2 + 3.6 x Oa Med. 3 + -0.001 x Oa I n t . 3 + 0.19 x Oa Peak. 1 + 0.47 x SO2 Ep'is. 2 t -0.002 x SO2 Peak. 1 P2 + -0.02 x SO2 Epis. 2 P2 + 0.0001 x SO2 I n t . 2 P2 + -0.013 x SOa Epis. 3. P2. Best non-linear regressiona, Ra = 0.90
V a r i a b l eb 1) 2) 3) 4) 5) 6)
Hed. 1 Int. 1 Hed. 2 0 s Peak. 2 0s Int. 2 0 s Med. 3 Oa Oa Oa
Contribution t o RaC 0.02 0.01 0.13 0.09 0.12 0.15
M u l t i p l e c o r r e l a t i o n = 0.95; a Mallows Cp = 9.34;
Variableb 7) 6) 9) 10) 11)
C o n t r ib u t t o n t o R2C
Oa I n t . 3 Oa Peak. 1
S o t Epis. 2 SO2 Peak. 1 P2 SOa Epis. 2 P2 1 2 ) soz I n t . 2 P2 13) SOa Epis. 3 P2
0.01 0.04 0.01 0.03 0.01 0.01 0.01
S i g n i f i c a n c e ( T a i l Prob.) = 0.0000
A t o t a l o f 63 treatments were i n c l u d e d i n t h e regression.
Med. = Median concentration; I n t . = Cumulative i n t e g r a l o f exposure; Peak = peak concentration; Epis = number o f episodes o r frequency o f exposure. Exposure parameter f o l l o w e d by 1, 2 o r 3 i n d i c a t e s f i r s t (1-15 days), second (16-30 days) o r t h i r d (31-45 days) growth phase o f a l f a l f a . Exposure parameter ending as P2 i n d i c a t e s power 2 o f t h e term. F o r Oa. a l l parameters were computed from h o u r l y data; f o r SO,, a l l parameters were computed from continuous data. The value o f t h e f i n a l R 2 i s s e q u e n t i a l l y reduced by t h e f r a c t i o n i n d i c a t e d i n each case.
237 Krupa and Nosal ( r e f . 32) p r e v i o u s l y developed a d u a l t i m e s e r i e s model t o r e l a t e SOz exposures t o a l f a l f a responses.
This model consisted o f a com-
b i n a t i o n o f t i m e s e r i e s a n a l y s i s and response surface methodology.
The
r e s u l t s o f t h e a p p l i c a t i o n o f t h e same model w i t h t h e a d d i t i o n o f t h e approp r i a t e Om exposure parameters i d e n t i f i e d from t h e t i m e s e r i e s coherence a n a l y s i s a r e presented i n Table 4.
The "median" h o u r l y Om c o n c e n t r a t i o n and
t h e "cumulative i n t e g r a l " o f exposure d u r i n g 1-15 days o f growth were t h e best p r e d i c t o r s o f t h e f i n a l harvested a l f a l f a biomass.
The Om peaks were Impor-
t a n t b u t were i d e n t i f i e d by t h e regression as t h e f o u r t h and t h e e i g h t h best p r e d i c t o r s among a l l independent v a r i a b l e s i n c l u d e d i n t h e equation.
The
SOz exposure parameters i n t h i s p a r t i c u l a r study were l e s s i m p o r t a n t than
t h e 01 exposure parameters.
The reader should n o t conclude, however. t h a t
t h i s i s a u n i v e r s a l statement a p p l i c a b l e t o o t h e r cases i n v o l v i n g S O Z . SUMMARY We have discussed i n t h i s paper some considerations r e l e v a n t t o t h e numeric a l a n a l y s i s o f a i r p o l l u t a n t exposure and crop response.
Based on t h i s , we
have described an approach c o n s i s t i n g o f F o u r i e r t r a n s f o r m a t i o n and t i m e s e r i e s , s p e c t r a l coherence a n a l y s i s i n i d e n t i f y i n g numerical d e s c r i p t o r s o f
Om exposure parameters t h a t best describe a l f a l f a growth dynamics.
The
exposure parameter p r o v i d i n g t h e best d e s c r i p t i o n o f t h e crop growth response varied w i t h the 0 s f l u x density.
Since t h e f l u x d e n s i t y o f 01 v a r i e s i n
t i m e and space, one can conclude t h a t a p p r o p r i a t e exposure term(s) should be i d e n t i f i e d f o r each s p e c i f i c crop growth stage and such terms a p p l i e d i n t h e f i n a l equation d e s c r i b i n g t h e crop y i e l d response.
Thls paper provides an
explanation as t o why previous e f f o r t s by others t o i d e n t i f y a s i n g l e , u n i v e r s a l l y a p p l i c a b l e exposure term were unsuccessful. ACKNOWLEDGEMENTS The s e n i o r author i s h i g h l y g r a t e f u l t o t h e United States Department o f A g r i c u l t u r e , Cooperative S t a t e Research Service f o r p r o v i d i n g t h e f i n a n c i a l support f o r t h i s research.
The s e n i o r a u t h o r would a l s o l i k e t o convey h i s
a p p r e c i a t i o n t o D e l l a Patton f o r her very a b l e assistance i n t h e p r e p a r a t i o n o f t h i s manuscript. REFERENCES
1 2
3
United States Environmental P r o t e c t i o n Agency. A i r Q u a l i t y C r i t e r i a f o r Ozone and Other Photochemical Oxidants, Vol. 111, U.S. EPA, Research T r i a n g l e Park, 1986. S.V. Krupa and W.J. Manning, Environ. P o l l u t . , 50 (1988) 101-137. S. Krupa and R.N. K i c k e r t , Environ. P o l l u t . , 44 (1987) 127-158.
238 4 5 6 1
8 9 10 11 12 13 14 15 16 11 18 19 20 21
22 23 24 25 26 27 28 29 30 31 32
W.E. Hogsett, D.T. Tingey and E.H. Lee, i n W.W. Heck, D.T. Tingey and O.C. T a y l o r ( E d i t o r s ) , Proc. I n t . Conf. Assessment o f Crop Loss from A i r P o l l u t a n t s , E l s e v i e r Applied Science, Barking. 1988, i n press. A.S. Lefohn and V.C. Runeckles. Atmos. Environ., 21 (1987) 561-568. A.S. Lefohn, J.A. Laurence and R.J. Kohut, Atmos. Environ., (1988) I n press. D.T. Tingey, W.E. Hogsett and E.H. Lee, Proc. 8 5 t h A i r P o l l u t . C o n t r o l Assoc. Ann. Meetings, Dallas, i n press. A.S. Heagle, V.M. Lesser, J.O. Rawlings, W.W. Heck and R.B. Philbeck, Phytopathology, 76 (1986) 51-56. E. Brennan, I . Leone, B. Greenhalgh and 6. Smith, J. A i r P o l l u t . C o n t r o l ASSOC., 37 (1987) 1429-1433. S.V. Krupa and R.N. K i c k e r t , An Analysis o f Ambient A i r P o l l u t i o n Exposure Regimes i n Vegetation Response Research, A l b e r t a Government-Industry A c i d i c Deposition Research Program, Calgary, 1988, i n press. A.S. Lefohn and H.M. Benedict, Atmos. Environ., 16 (1982) 2529-2532. M. Nosal, Proc. 1 7 t h A i r P o l l u t . C o n t r o l Assoc. Ann. Meetings, San Francisco. 84-104.5 (1984) 1-16. W.E. Hogsett, D.T. Tingey and S.R. Holman, Atmos. Environ., 19 (1985) 1135-1 145. A.S. Lefohn and C.K. Jones, J. A i r P o l l u t . C o n t r o l Assoc., 36 (1986) 1123-1 129. R.C. Musselman. A.J. Huerta, P.M. McCool and R.J. Oshima, J. Am. SOC. H a r t . Sci., 111 (1986) 410-413. G.C. P r a t t , R.C. Hendrickson, 8.1. Chevone, D.A. Christopherson, M.V. O'Brien and S.V. Krupa, Atmos. Envlron., 1 7 (1983) 2013-2023. J.W. Johnston, J r . and A.S. Heagle, Phytopathology. 72 (1982) 381-389. V.C. Runeckles and P.M. Rosen, Can. J. bot., 52 (1974) 2607-2610. E.H. Steinberger and Z. Naveh, A g r i c . Environ., 7 (1982) 255-263. U.T. alum and W.W. Heck, Environ. Expt. Bot., 20 (1980) 13-85. S.V. Krupa and P.S. Teng, Proc. 7 5 t h A i r P o l l u t . C o n t r o l Assoc. Ann. Meetings, New Orleans, 82-6.1 (1982) 1-10. R.M. Adams, S.A. Hamilton and 8.A. McCarl, J. A i r P o l l u t . Control Assoc.. 35 (1985) 938-943. S.V. Krupa, Proc. 1 1 t h A i r P o l l u t . C o n t r o l Assoc. Ann. Meetings, San Francisco, 84-104.2 (1984) 1-13. F.J. Benson, S.V. Krupa, P.S. Teng and D.E. Welsch, F i n a l Rept., Minnesota P o l l u t . Control Agency, R o s e v i l l e , pp.270. W.W. Heck, O.C. Taylor, R. Adams, 6. Bingham, J. M i l l e r , E. Preston and L. Weinstein, J. A i r P o l l u t . Control ASSOC., 32 (1982) 353-361. J.D. Kinsman, W.P. Saunders and R.E. Wyzga, Environ. P o l l u t . (1988) i n press. E. Loehman and T. Wilkinson, Purdue Univ. Agr. Expt. Sta. B u l l . , 426 (1983) pp.38. R.J. Oshima, M.P. Poe, P.K. Braegelmann. D.W. B a l d i n g and V. van Way, J. A i r P o l l u t . Control Assoc., 26 (1916) 861-865. R.D. Roue and L.G. Chestnut, J. A i r P o l l u t . C o n t r o l Assoc. 35 (1985) 128-134. P. Bloomfield, F o u r i e r Analysis o f Time Series, John Wiley & Sons, New York. 1976. W.A. F u l l e r , I n t r o d u c t i o n t o S t a t i s t i c a l Time Series. John Wiley b Sons, New York, 1976. S.V. Krupa and H. Nosal. Environ. P o l l u t . (1988) submitted.
T.Schneideret al. (Editors),Atmospheric Ozone Research and its P o l e Implicatwna 0 1989Elsevier Science PublishersB.V.,Amsterdam -Printed in The Netherlands
239
EFFECTS OF OZONE AND OZONE-ACIDIC PRECIPITATION INTERACTION ON FOREST TREES IN NORTH AMERICA
William J. Manning Department of Plant Pathology, University of Massachusetts, Amherst, MA., 01003, USA
ABSTRACT Ozone is the principal cause of declines of ponderosa and Jeffrey pine in California, 1. hartwegii, p. montezumae and p. patula around Mexico City, and sensitive eastern white pines in the northeast USA and Canada. There is no evidence that ozone, or ozone-acidic precipitation interaction, is involved in sugar maple decline, red spruce decline, or radical growth reductions of yellow pines. Ozone and acidic precipitation can affect ectomycorrhizal associations in roots of tree seedlings. INTRODUCTION Ozone (0,) is the most prevalent and phytotoxic gaseous air pollutant in North America [ l ] . For many years, researchers have focused primarily on the effects of O3 on the productivity of crop plants.
During the last few years,
however, increased attention has been given to the possible direct or interactive role that O3 may play in what appears to be unusual or accelerated declines in several forest trees.
These declines are usually characterized by
visible symptoms and reduced terminal and radial growth which results in tree decline and eventual death.
The several tree decline syndromes have been ex-
tensively described by others [ 2 , 3 , 4. 5, 61 and are summarized in Tables 1 and 2 . My purpose is to review the possible effects of Og, alone and in combination with acidic precipitation, on the growth, productivity and longevity of several North American forest trees.
240
TABLE 1 Examples where ozone or ozone/acidic precipitation may cause tree injury and decline in forests in North America Trees
Locations
References
Caused by ozone Pinus hartwegii Pinus montezumae
Mountains around Mexico City
Pinus jeffreyi Pinus ponderosa
San Bernadino and other mountains in Southern California
[9-181
Pinus strobus -
Northeast USA and Southeast Canada
[ 19-28]
Ozone or ozonelacidic precipitation may be involved Abies religiosa Acer saccharum
Mountains around Mexico City Northeast USA and Southeast Canada
Picea rubens --
Northeast and southern Appalachian mountains
Pinus echinata Pinus rigida
New Jersey Pine Barrens
Pinus echinata Pinus elliottii Pinus taeda --
Southeast USA
[ 7 , 81 [29-351
[36-461 [ 4 , 47-48]
DIRECT EFFECTS There are only a few examples where the direct effects of 0, on trees have been extensively investigated and well-documented.
Long-term exposure to
ambient O3 has resulted in injury, decline, and disappearance of sensitive genotypes within natural populations of several species of pine in southern California, Mexico, and the eastern USA and Canada [ 2 , 4 , 7 , 81 (Table 1 ) . Pines in California and Mexico By the early 1 9 6 0 ' ~the ~ continued effects of O3 transport from Los Angeles to the San Bernadino Mountains began to be noticed on stands of trees [ 9 ] . Ponderosa pine ponderosa) and Jeffrey pine (p. ieffreyi) were the most
(m
seriously affected, white fir
(wconcolor) and California black oak
(Quercus k e l l a ) were moderately affected, while sugar pine (p. lambertiana) and incense cedar (Libocedrus decurrens) were least affected.
Since then,
similar symptoms have been noticed on ponderosa and Jeffrey pine elsewhere in southern California mountains [ l o , 111 and on the western slopes of the Sierra Nevada Range [ 1 2 ] . O3 from the San Joaquin Valley and San Francisco has recently been shown to reduce radial growth for large Jeffrey pines in Sequoia
241 and Kings Canyon National Parks (131. Symptoms of O3 injury on sensitive ponderosa and Jeffrey pine include chlorotic needle mottle and tip necrosis, with reduced needle length, number and retention. 191.
Carbohydrate production in older needles is reduced [14],
leading to reduced terminal and radial growth. Branches die from the base of the crown upward.
Roots decline and may be more readily invaded by the root
pathogen Heterobasidion annosum [l, 15, 161.
03-injured ponderosa pines are
readily invaded by bark beetles, which hasten their decline and death [17, 181. Many 0,-sensitive ponderosa pines have died and disappeared. The effects of O3 on ponderosa pine seedlings, under controlled experimental conditions, have been investigated extensively. Needle symptoms observed in the field have been confirmed as symptoms of 0, injury [9. 11, 181.
As a
result, it is generally accepted that O3 causes needle injury. tree decline and death of sensitive genotypes of ponderosa pine in southern California. Mexico City is located in a basin, surrounded by high mountains.
As in
southern California, winds carry O3 to the forests in the mountains at Ajusco where several species of pine (p. hartwegii, p. montezumae, p. montezumae var. Lindleyi, and p. patula) exhibit needle symptoms identical to those of ponderosa pine in southern California. 1. hartwegii is the most severely affected. Sensitive individuals decline, are invaded by bark beetles, and then die. Infestations of dwarf mistletoe are also more extensive on weakened trees [7.
(w
religiosa) are declining in radial 81. At Desierto de 10s Leones, firs growth. Older needles develop white stipples and turn brown and die. O3 is the suspected cause of this fir decline. Eastern white pine White pine (Pinus strobus) is widely-distributed in eastern USA and Canada. In the 1960'6, there were many reports of foliar injury to individual trees that resembled possible O3 injury [19]. Needles on affected trees had chlorotic mottling or banding, with tip necrosis. Needle length and retention were reduced as were terminal and radial growth [20. 211.
Needle symptoms
have been duplicated under controlled conditions with known
03
concentrations
[22, 231. In the Blue Ridge Mountains of Virginia, Os-weakened trees were more readily invaded by the root pathogen Verticicicladiella procera and by bark beetles [24]. This is similar to ponderosa pine decline in southern California.
Sensitive and tolerant trees in a 25-year-old plantation in Tennessee were evaluated for growth and development. Tolerant trees were 3 times taller and had nearly double the radial growth of sensitive trees with symptoms. Sensitive trees had fewer and shorter needles, which was considered to be responsible for growth reductions [25]. In a labelled carbon study with needles from
242 these trees, 0, was shown to accelerate senescence of older needles, which are the primary source of photosynthate for new developing needles [ 2 6 ] . Annual increments of diameter growth for 50-year-old white pine in the Blue Ridge Mountains were determined for trees with different degrees of foliar symptoms. Average annual increment of diameter growth correlated with predicted degree of sensitivity of different genotypes to O3 [ 2 7 ] . Also in the Blue Ridge Mountains, white pine seedlings were grown in opentop field chambers for three years. Those grown in carbon-filtered ambient air were 45% taller than those in ambient air chambers where O3 was present [281.
SUSPECTED EFFECTS OF OZONE/ACIDIC DEPOSITION Sugar Maple Sugar maple (& saccharum) is a major hardwood tree in eastern North America. Since 1900, tree declines of several kinds have been attributed to various abiotic and biotic causes [ 4 , 291.
In several cases, exact causal
relationships have not been determined. The most recent incidence of sugar maple decline began in Canada in the late 1970's [ 4 ] . Symptoms include small chlorotic leaves, gradual leaf drop, branchlet death from the top of the crown downward, peeling bark on main branches and tree death. Trees tapped for maple syrup are more affected than forest trees. Syrup yields are reduced and tap holes heal very slowly [ 4 ] . Decline seems most severe in southern Quebec in highly humid areas and in thin soils at high elevations. Decline and dieback have also been noted on American
(w
beech (Fagus grandifolia) , balsam fir balsamea) , white ash (Fraxinus americana), white spruce (Picea glauca) and yellow birch (Betula alleghaniensis) 1301.
In Vermont and Ontario, feeding by insects such as the maple webworm and saddled prominent caterpillar, is known to reduce carbohydrate translocation to roots. Weakened trees are more susceptible to drought [ 3 1 ] or invasion by the root rot fungus Armillaria mellea. mortality [321.
This leads to dieback and shoot
Insect infestations have not been a problem in Quebec and
tree recovery is not improving [ 4 ] . Ozone is another stress factor that is known to affect photosynthate translocation in trees [ 3 3 ] .
Incidence of maple decline in North America also
coincides with an area known to be impacted by ambient 0,.
While reductions in
growth and photosynthesis have been reported for sugar maple seedlings [ 3 4 , 351, there is no evidence to relate O3 to sugar maple decline in North America. Red Spruce Red spruce (Picea rubens) is a major component of the spruce-fir forests
243
of the eastern USA and Canada.
It grows on a wide variety of soil types and
at a pH range of 3.6 to 5 . 0 [ 4 ] . In the 1 9 5 0 ' s and 1 9 6 0 ' 6 , tree growth ring studies indicated a decline in red spruce growth rates. This was first noted at high elevations and later at lower elevations in a less drastic form [ 3 . 361. At high elevations in New York and New England, declining red spruce die from the top down and from older branch regions to newer ones.
The newest
needles on the outer tips of branches at the tops of tree crowns become chlorotic and then die and drop [37, 381. In the southern Appalachian mountains, decline proceeds in reverse order. Chlorosis and needle drop progress from oldest to youngest needles and inside outward on branches and from the lower crown upward [ 3 9 ] . This resembles 03caused pine decline in southern California, Norway spruce decline in central Europe [ 4 ] , and 0,-induced
injury to white pine in eastern North America [ 2 ] ,
(Table 2 ) . Red spruce decline has received much attention and has been ascribed to one or more of the following causes: winter damage due to excessive nitrogen from acidic precipitation, dessication from cold injury. drought, frost plus air pollution, long range transport of pollutants, ozone/acidic precipitation, natural stand ageing and decline processes, or acceleration of these due to long-term climatic changes [ 4 ] . Historical records have been examined and trends have been constructed for the last 180-200 years.
One explanation for red spruce decline is that climate
change, particularly a warming trend, since 1800 is the major reason for declines in radial growth [ 4 0 , 411.
Recent increases in tree declines can also
be viewed as due to unique combinations of climatic stresses or interactions with air pollutants [ 4 2 ] .
If, however, changes that occur over a very long
time period are viewed with a short-term perspective, misleading conclusions can be drawn regarding causal relationships [ 4 0 ] . Red spruce growth decline can also be viewed as a normal phenomenon when allowance is made for different growth rates at different tree ages [ 4 3 ] . All growth reductions are not necessarily evidence of tree declines, but may be explained as expected reduced growth for natural stands as they mature [ 4 4 ] . Experiments designed to determine the effects of 03 and other pollutants on red spruce seedlings have not produced results comparable to those achieved for ponderosa and Jeffrey pine and white pine [ 2 ] . 0 3 injury on red spruce seedlings has not been reported. When red spruce seedlings were exposed to acidic mist, acidic precipitation, O3 and two types of collected soils, no interactive effects were observed [ 4 5 ] . Evidence is lacking that 0 3 or other air pollutants adversely affect red spruce growth and physiology [ 2 ] .
244 TABLE 2 Summary of symptoms expressed by trees involved in forest declines in North America. Trees
Symptoms Caused by ozone
Pinus hartwegii Pinus montezumae Pinus jeffreyi Pinus ponderosa
Chlorotic mottle, banding, and tip necrosis of older needles Reduced needle retention Reduced terminal and radial growth Branches die from the base of the crown upward
Pinus strobus --
Chlorotic mottling, flecking or banding of needles Needle tip necrosis Reduced needle retention Thin crowns Reduced terminal and radial growth
Ozone Abies religiosa Acer saccharum
or ozone/acidic precipitation may be involved White stipples, turning brown, on upper needle surfaces Small chlorotic leaves Gradual leaf drop Crown dieback from the top downward Peeling of bark on main branches
Picea rubens --
New York and New England Chlorosis and needle drop, beginning with newest needles and outer tips of branches Branches die from top of crown downward Southern Appalachians Chlorosis and needle drop, beginning with oldest needles, progressing from older to young branch sections Branches die from base of crown upward
Pinus echinata Pinus rigida
Abnormally narrow growth rings, beginning in 1955
Pinus echinata Pinus elliottii Pinus taeda --
Widespread decreases in annual growth rates, without other symptoms
-
Yellow pines Loblolly (Pinus taeda), shortleaf
(p.
echinata), and slash
pines are common lumber trees in the southeastern USA.
(11.
elliottii)
Widespread decreases
in radial growth have been noted, without any other symptoms [ 4 ] . It is not known whether these declines are due to natural processes or are in response to stress. Possible causes include: the combined effects of increased density and ageing of natural stands, which results in tree growth rate decreases,
245 more intense competition from hardwood species, and chronic O3 stress [ 4 6 ] . There is no evidence that O3 reduces radial growth of yellow pines. Abnormally narrow growth rings in shortleaf and pitch pines (P. rigida) in the Pine Barrens area of southeastern New Jersey were reported to begin around 1955 [ 4 7 ] . Soils in this area are sandy, with low pH values and low cationexchange capacity. Acidic precipitation has been suggested as a cause of radial growth declines [ 4 7 1 . The area is also impacted by ambient Os [ 4 ] .
When pitch pine seedlings were grown in soil cores from the Pine Barrens, and treated with synthetic acid rain, at pH 5.6, 4.0 or 3.0, through two cycles of growth, no negative effects were observed [ 4 8 ] . There is no evidence that O3 affects the growth of shortleaf and pitch pines in the New Jersey Pine Barrens. USE OF FIELD CHAMBERS TO DETERMINE EFFECTS OF O3 ON TREES Several types of field chambers have been used to determine the effects of Growth in ambient air or ambient air plus 0, can be compared to that in charcoal-filtered air. Most 0, on crop plants and to a lesser extent trees [ l ] .
studies to date have been short-term in nature, but many long-term studies with open-top chambers and O3 and Os/acidic precipitation interactions are now in progress, especially with yellow-pines. Portable fumigation chambers were placed over representative plants in major plant communities and Os fumigations were conducted at 0.15, 0.25, 0.30 or 0.40 ppm 0, for two hours. Trembling aspen (Populus tremuloides) had the lowest injury threshold at 0.15 ppm 0, [ 4 9 ] . Height growth for native seedlings of tulip poplar (Liriodendron tulipifera), sweetgum (Liquidambar styraciflua), black locust (Robinia pseudoacacia), eastern hemlock (Tsuga canadensis), table mountain pine (Pinus pungens), eastern white pine (Pinus strobus), and Virginia pine
(wvirginiana).
after
two years growth in carbon-filtered air in open-top chambers in Shenandoah National Park, was increased, when compared to trees in ambient air chambers
DO]. Reductions in total above-ground biomass for clonal hybrid poplars (P. masimowiczii x trichocarpa), grown in open-top chambers for 17 days, and exposed to 0.06 or 0.10 ppm 03, were 14 and 30%, respectively [ 5 1 ] . Ambient air reduced productivity and height growth for hybrid poplars, black locust and eastern cottonwoods (Populus deltoides), grown in carbon-filtered or ambient air open-top chambers in Millbrook, N.Y.
A growth reduction of
19% for hybrid poplar was statistically significant and occurred without visi-
ble O3 injury symptoms [ 5 2 ] . Ambient O3 in New Jersey had no effects on symptom expression, growth, or chlorophyll content of potted seedlings of green ash (Fraxinus pennsylvanica)
246 or white ash (Fraxinus americana), in open-top chambers, over a three-year period [53]. OZONE ACIDIC PRECIPITATION INTERACTIONS There has been a great deal of interest in possible interactions between 0, and acidic precipitation. Until recently, most investigations focused on crop plants, rather than trees. Interaction studies with trees have been done for short durations and with seedlings, rather than older trees. Results usually indicate no direct effects of the synthetic acid rain (SAR) solutions used on leaves, unless pH values are lowered to below pH 3.0.
In most cases, signif-
icant, reproducible interactions between SAR and O3 do not occur. O3 reduced photosynthesis in sugar maple and red oak (Quercus rubra) seed-
lings, but SAR at pH 3.0, 4.0, and 5.0 had no effects nor did interactions occur between O3 and SAR [35]. Treatment of paper birch (Betula papyrifera) seedlings with SAR at pH 3.5 for 1 2 weeks caused increased seedling growth, especially in seedlings exposed to 0.06 to 0.08 ppm 0, for the same period [55]. SAR, at pH 3.0 or 5.6. applied just before or after O3 fumigations had no significant effects on yellow poplar or white ash seedlings [56, 571. SAR at pH 2.5, however, decreased all growth parameters for yellow poplar seedlings that were exposed to O3 for eight weeks 1541. Dry matter production for yellow poplar seedlings, wetted with SAR prior to O3 fumigations, was significantly reduced when compared results where SAR was applied after O3 fumigations [56]. Based on limited work with tree seedlings, there is no evidence to support 03/SAR interactions that result in direct foliar effects.
O3 injury may be en-
hanced, however, by increasing leaf wetness or relative humidity [4]. SECONDARY EFFECTS OF OZONE Primary effects of 0, on trees are reflected in changes in growth and physiology. As a result of these changes, other changes, known as secondary effects, can occur. These affect important relationships that trees have with potential plant-pathogenic fungi, insects and ectomycorrhizal fungi [58]. Secondary effects of 0, include previously considered increases in susceptibility of 03injured pines to bark beetle infestations and incidence of root disease fungi [14, 16, 17, 241.
The association of ectomycorrhizal fungi with the fine roots of most trees is essential for their growth and development. The formation of ectomycor-
rhizae, as a result of invasion of fine roots by ectomycorrhizal fungi, affects uptake of water and nutrients and serves as a barrier to invasion by root disease fungi. The effects of O3 and SAR on ectomycorrhizal formation by roots of tree seedlings has recently been reviewed [ 5 9 ] .
247 In open-top and greenhouse chamber studies with red oak, white pine and sugar maple seedlings, SAR was found to decrease naturally-occurring ectomycorrhizae on red oak and white pine, white O3 increased ectomycorrhizae on red oak and white pine.
There were no interactions between SAR and O3 [60]. Treatment of white birch seedlings, grown in soil infested with the mycor-
rhizal fungus Pisolithus tinctorius, caused increases in seedling growth which was more apparent in seedlings also exposed to 03. No interactions between O3 and SAR were found [55]. Cenococcum graniforme also increased growth of yellow birch seedlings exposed to 0, [61]. P. tinctorius infected feeder roots of loblolly pine seedlings were protected from the effects of 0,. p. tinctorius apparently increased the demand for photosynthate translocation to roots and negated the expected negative effects
of O3 on root development [62]. CONCLUSIONS During the last few years, there has been a great increase in funding for research on the effects of O , , SAR and other air pollutants on tree growth and physiology. Many large experiments are currently in progress and a considerable amount of data will be obtained in the next two to three years.
In the
meantime, however, some conclusions, based on current reports in the literature, can be made regarding the effects of 0, and 0, acidic precipitation in interaction on trees in North America: 0, directly affects growth of ponderosa and Jeffrey pines in California,
several Pinus spp. near Mexico City, and sensitive genotypes of eastern white pine in the northeast USA and eastern Canada. There is no evidence that 0, is a factor in sugar maple, red spruce and yellow pine declines and decline of
Abies
religiosa in Mexico.
Direct effects of SAR on tree leaves has not been demonstrated, nor have significant interactions between 0, and SAR been demonstrated in studies with tree seedlings. The secondary effects of O3 or SAR on incidence of diseases, insects and mycorrhizal fungi may be of considerable importance and warrant further investigation. REFERENCES
S. V. Krupa and W. J . Manning, Environ. Pollut., 52 (1988) 101-137. B. I. Chevone and S. N. Linzon, Environ. Pollut., 50 (1988) 87-99. R. M. Klein and T. D. Perkins, Bot. Rev., 54 (1988) 2-24. J. L. Kulp, Chapter Seven, in NAPAP Interim Assessment Document, Vol IV (1987) U. S. Govt.. Washington, D.C. 5 S. B. McLaughlin, J. Air Poll. Contr. Assoc., 35 (1985) 512-534. 6 R. Stottlemyer, Environ. Management, 11 (1987) 91-97.
1 2 3 4
248 7 M. L. deBauer. T. H. Tejeda and W. J. Manning, J. Air Poll. Contr. Assoc. 35 (1985) 838. 8 M. L. de Bauer, T. Hernandez and D. Alvarado, Proc. Int. Bot. Congress, Berlin (1987) p. 404. 9 P. R. Miller, J . R. Parmeter, 0. C. Taylor and E. A. Cardiff, Phytopathology, 53 (1963) 1072-1076. 10 P. R. Miller and A. A. Millecan, Plant D i s . Rep., 55 (1971) 555-559. 11 B. L. Richards, 0. C. Taylor, and G. F. Edmunds, J. Air Poll. Contr. ASSOC., 18 (1968) 73-77. 12 W. T. Williams, M. Brady and S. C. Willeson, J. Air Poll. Contr. Assoc., 27 (1977) 230-234. 13 D. L. Peterson, M. J . Arbough, V. A. Wakefield and P. R. Miller, J . Air Poll. Contr. ASSOC., 37 (1987) 906-912. 14 J. R. Parmeter and P. R. Miller, Plant Dis. Rep., 52 (1968) 707-711. 15 R. L. James, F. W. Cobb, P. R. Miller and J. R. Parmeter, Phytopathology, 70 (1980) 560-563. 16 P. R. Miller, in D. D. Davis. A. A. Miller and L. Dochinger (Eds.) Proc. Air Pollution and the Productivity of Forests, Izaak Walton League, Washington, D. C., (1983) p . 161-197. 17 F. W. Cobb, Jr., D. L. Wood, R. W. Stark and J. R. Parmeter. Jr., Hilgardia, 34 (1968) 141-152. 18 P. R. Miller, J. R. Parmeter, B. H. Flick and C. W. Martinez, J. Air Poll. Contr. Assoc.. 9 (1969) 435-438. 19 C. R. Berry and L . A. Ripperton, Phytopathology, 53 (1963) 552-557. 20 E. M. Hayes and J. M. Skelly, Plant Dis. Rep., 61 (1977) 778-782. 21 R. W. Usher and W. T. Williams, Plant Disease, 66 (1982) 199-204. 22 Y. S . Yang, J. M. Skelly and B. I. Chevone, Can. J. For. Res., 12 (1982) 803-808. 23 D. B. Houston, Can. J. For. Res., 4, (1974) 65-68. 24 J. M. Skelly, Y. S. Yang, B. I. Chevone, S. J. Long, J. E. Nellesen, and W. E. Winner, in D. D. Davis, A. A. Miller, and L. D. Dochinger (Eds.) Proc. Izaak Walton League, Washington, D. C., (1983) p. 143-159. 25 L. K. Mann, S. B. McLaughlin and D. S. Shriner, Environ. Exp. Bot.. 20 (1980) 99-105. 26 S. B. McLaughlin, R. K. Conathy, D. Durick and L. K. Mann, For. Sci., 28 (1982) 60-70. 27 L. F. Benoit, J. M. Skelly, L. D. Moore, and L. S . Dochinger, Can. J . For. Res., 12 (1982) 673-678. 28 S. F. Duchelle, J. M. Skelly, and B. I. Chevone, Water, Air, Soil Pollut., 18 (1982) 363-373. 29 W. D. McIlveen, S. T. Rutherford and S. N . Linzon, Ontario Ministry of the Environment, Report No. ARB-141-86-Phyto and A. P . I. 0. 5.-010/86 (1986). 30 L. Robitaille, in Maple Decline, Maple Producers Information Session, Quebec City, Canada, 1986, AGDEX 300/637. 31 W. M. Banfield, Phytopathology, 57 (1967) 338. 32 R. A. Gregory, M. W. Williams Jr., B. L. Wong and G. J. Hawley, IAWA Bulletin, 7, (1986) 357-369. 33 D. R. Cooley and W. J. Manning, Environ. Pollut., 47 (1987) 95-113. 34 P. B. Reich and R. G. Amundson, Science, 230 (1985) 566-570. 35 P. B. Reich, A. W. Schoettle and R. G . Amundson, Environ. Pollut., 40 (1986) 1-15. 36 S. B. McLaughlin, J. Air Poll. Contr. Assoc.. 35 (1985) 512-534. 37 A. H. Johnson and T. G. Siccama, Environ. Sci. Tech., 17 (1983) 294-306. 38 J. T. Scott, T. J. Siccama, A. H. Johnson and A. Briesch, Bull. Torrey Bot. Club, 111, (1984) 438-444. 39 R. I. Bruck, in H. S . Stubbs (Ed.), Proc. Air Pollutants Effects on Forest Ecosystems, The Acid Rain Foundation, St. Paul, MN., (1985), p . 137-155. 40 S . P. Hamburg and C. V. Cogbill, Nature, 331 (1988) 428-431. 41 A. H. Johnson and S . B. McLaughlin. in Acid Deposition Long-term Trends, National Academy Press, Washington, D. C., (19861, p. 200-230. 42 S. B. McLaughlin, D. J. Downing, T. J. Blasing, E. R. Cook and H. S. Adam.
249 Occologia, 72 (1987) 487-501. 43 D. M. Hyink and S. M. Zedaker, Tree Phys., 3, (1987) 17-26. 44 J. W. Hornbeck, R. B. Smith and C. A. Federer, Water, Air, Soil Poll., 31 (1986) 425-430. 45 G. E. Taylor, Jr., R. J. Norby, S. B. McLaughlin, A. H. Johnson and R. S. Turner, Occologia, 70 (1986) 163-171. 46 R. M. Sheffield and D. N. Cost, J. For., 85 (1987) 29-33. 47 A. H. Johnson, T. G. Siccama, D. Wang, R. S . Turner and T. H. Barringer, J. Environ. Qual., 10 (1981) 427-430. 48 G. A. Schier, Can. J. For. Res., 16 (1986) 136-142. 49 M. Treshow and D. Stewart, Biol. Conservation, 5 (1973) 209-214. 50 S. F. Duchelle, J. M. Skelly and B. I. Chevone, Water, Air, Soil Poll., 18 (1982) 363-373. 51 P. B. Reich, J. P. Lassoie and R. G. Amundson, Can. J. Bot., 62 (1984) 2835-2841. 52 D. Wang, F. H. Bormann and D. G. Carnosky, Env. Sci. Tech., 20 (1986) 11221125. 53 C. L. Elliott, J. C. Eberhardt and Eberhardt and E. G. Brennan, Environ. Pollut., 44 (1987) 61-70. 54 L. S. Dochinger and K. F. Jensen, USDA For. Serv. NE Forest Exp. Sta. Res. Paper, NE-572, 1985. 55 K. D. Keane and W. J. Manning, Environ. Pollut., 52 (1988) (In Press). 56 A. H. Chappelka, B. I. Chevone and T. E. Burke, Environ. Exp. Bot., 25 (1985) 232-244. 57 A. H. Chappelka and B. I. Chevone, Can. J. For. Res., 16 (1986) 786-790. 58 W. J. Manning and K. D. Keane, in W. W. Heck, 0. C. Taylor and D. T. Tingey (Eds.), Proc. Crop Loss Assessment Cong., Raleigh, 1987, Elsevier, London (In Press). 59 K. D. Keane and W. J. Manning, Proc. APCA Meeting, New York, 1987, Program no. 87-36.4. 60 P. B. Reich, A. W. Schoettle, H. F. Stroo, and R. G. AMundson. J. Air Poll. Contr. Assoc., 36 (1986) 724-726. 61 D. L. Krupczak and W. J. Manning, Phytopathology, 77 (1987) 1616. 62 M. J. Mahoney, B. I. Chevone, J . M. Skelly and L. D. Moore, Phytopathology, 75 (1985) 679-682.
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T. Schneider et al. (Editore),Atmospheric Ozone Research and its Policy Implications 0 1989 Elsevier Science Publishers B.V.,Amsterdam - Printed in The Netherlands
251
EVALUATION OF OZONE EFFECTS ON VEtiETATION I N THE NETHERLANDS
A.E.G.
Tonneijck
Research I n s t i t u t e f o r Plant Protect on, P.O. (The Nether1 ands)
Box
9060,
6700
GW
Wageningen
ABSTRACT The current knowledge concerning ozone-induced e f f e c t s on vegetation i n t h e Netherlands i s discussed. Results w i t h i n d i c a t o r p l a n t s show t h a t ozone occurs i n phytotoxic concentrations throughout t h e country each year. F o l i a r i n j u r y i s generally most severe i n t h e western p a r t o f t h e country. The region w i t h t h e highest average e f f e c t i n t e n s i t i e s does not necessarily c o i n c i d e w i t h t h e region w i t h t h e highest average ozone concentrations. Ozone i s considered as t h e most important a i r p o l l u t a n t i n terms o f crop loss. It i s estimated f o r 1983 t h a t ambient a i r p o l l u t i o n reduced crop production w i t h 5%, o f which 70% i s caused by ozone. Especially h o r t i c u l t u r a l crops are affected. From 1i t e r a t u r e data maximum acceptable ojone concentrations3for p r o t e c t i o n o f v g e t a t i o n have been proposed: 150 .yg.m’ f o r 1 h, 65 1.1g.mf o r 8 h and 50 pg.m” f o r the growing season. Ambient ozone concentrations i n t h e Netherlands, measured i n t h e period 1980-1985, s u b s t a n t i a l l y exceeded these values. The frequency o f exceedances appears t o increase w i t h an increase i n t h e d u r a t i o n o f exposure.
I NTRODUCT I ON V i s i b l e i n j u r y o f p l a n t s i s o f t e n t h e e a r l i e s t and most obvious i n d i c a t i o n o f the presence o f a i r p o l l u t a n t s . I n t h e Netherlands t h e f i r s t observations o f ozone-induced
plant
symptoms
were made i n 1965 ( r e f . 1). For t h e purpose t o
monitor t h e e f f e c t s o f a i r p o l l u t i o n i n t h e
Netherlands
the
Dutch
National
Monitoring Network was established i n t h e e a r l y 1970’s. Subsequently, f o l i a r i n j u r y on i n d i c a t o r p l a n t s f o r ozone such as spinach, bean, c l o v e r species and tobacco
has
been
frequently
observed.
Besides, ozone i n j u r y on f i e l d grown
crops has been recorded (ref. 2). This paper evaluates t h e vegetation
in
current
knowledge o f
ozone-induced
effects
on
the Netherlands, Information on exposure-response re1 ationships
i s incorporated t o assess t h e p o t e n t i a l f o r ozone i n j u r y t o t h e vegetation. The foliar
injury
response o f
tobacco
ambient ozone. The impact o f ozone on provide
Be1 crop
W3
i s r e l a t e d t o concentrations o f productivity
ozone concentrations were derived from an evaluation o f t h e values
is
quantified.
To
f u r t h e r information f o r pol i c y abatement s t r a t e g i e s maximum acceptable literature.
These
are subsequently compared w i t h ambient ozone concentrations as measured
i n t h e Netherlands.
252 AMBIENT OZONE AND FOLIAR INJURY ON INDICATOR PLANTS
Since t h e e a r l y 1970's an extended network f o r monitoring t h e e f f e c t s o f a i r pollution
on
i n d i c a t o r p l a n t s has e x i s t e d i n t h e Netherlands. This network i s
managed by t h e Research I n s t i t u t e f o r Plant Protection, Wageningen, and forms a part
t h e National Monitoring Network f o r A i r P o l l u t i o n t h a t i s d i r e c t e d by
of
t h e National I n s t i t u t e o f Public Health and Environmental Cultivars
Hygiene,
Bilthoven.
o f ozone s e n s i t i v e p l a n t species such as bean, spinach, subterranean
c l o v e r and tobacco have been used t o levels.
indicate the
presence
of
toxic
ozone
I n many countries, t h e f i r s t i n d i c a t i o n o f ozone r e s u l t e d from t h e use
o f the s e n s i t i v e tobacco c u l t i v a r Be1 W3 ( r e f . 3). Therefore, t h e response o f t h i s p l a n t species w i l l be described i n more d e t a i l . During t h e growing season tobacco p l a n t s were exposed t o ambient a i r f o r one week and t h e n other
groups.
replaced
by
E f f e c t s were immediately determined a f t e r exposure by assessing
percentage i n j u r y on a l l leaves o f f o u r p l a n t s per l o c a t i o n . High e f f e c t i n t e n s i t i e s on tobacco g e n e r a l l y elevated
occurred
after
periods
with
concentrations o f ozone ( r e f . 4). P l a n t s were s l i g h t l y more s e n s i t i v e
t o ozone i n autumn than i n spring. I n each week a t l e a s t several p l a n t s a t some locations
showed f o l i a r i n j u r i e s . This i n d i c a t e s t h e continuous r i s k f o r ozone
i n j u r y t o t h e vegetation. Analyses o f t h e
results
for
the
period
1976-1983
showed t h a t t h e average i n j u r y l e v e l on tobacco p l a n t s was reasonably constant over years ( r e f . 5). The geographic d i s t r i b u t i o n s o f
ambient
ozone
concentrations
and
effect
i n t e n s i t i e s on tobacco f o r t h e summers of 1984 and 1985 are presented i n Fig. 1. F o l i a r i n j u r y was g e n e r a l l y more severe i n t h e western p a r t o f t h e
whereas
the
highest
injury
intensities
southwest depending on t h e year. always
occurred
in
the
The
norhtwestern
highest part
located f a r from t h e p o l l u t i o n sources and i s practices.
average
ozone
largely
used
for
agricultural
These r e s u l t s show t h a t , a t l e a s t i n geographical terms, a c l e a r - c u t not
exist.
Varying
c o n d i t i o n s and t h e presence o f o t h e r a i r p o l l u t a n t s a r e l i k e l y t o p l a y
an a d d i t i o n a l r o l e i n b r i n g i n g about t h e p a t t e r n o f exposure
concentrations
of t h e Netherlands. This area i s
r e l a t i o n s h i p between ambient ozone and f o l i a r i n j u r y does weather
country,
occurred i n t h e northwest o r i n t h e
regime a l s o may
be
important:
the
plant
frequency
injury. of
The peak
ozone ozone
concentrations i s greater i n t h e southern regions than i n t h e n o r t h ( r e f . 7). Fumigation experiments
have shown t h a t t h e i n j u r y l e v e l o f tobacco changed
more i n response t o a s e r i e s o f ozone concentrations t h a n t o a s e r i e s o f exposure times between 1-7 days ( r e f . 8). However, tobacco p l a n t s already showed some i n j u r y due t o average ozone concentrations o f ca 3 0 ~ g . m - ~a f t e r a 7 days exposure p e r i o d both under l a b o r a t o r y c o n d i t i o n s and i n t h e f i e l d (Fig. 2).
253
Fig. 1. (ieographic d i s t r i u t i o n o f mean values of 24 h average ozone concentrations ( r i g h t , dg.m-’) and o f i n j u r y i n t e n s i t i e s t o tobacco Be1 W3 ( l e f t ) f o r t h e summers o f 1984 and 1985 ( r e f . 9).
Fol i a r ambient
injury ozone
observations
on
tobacco
exceeded recorded
plants
further
increased
60-70 ~ ~ 9 . m ’ ~(Fig.
10-20%
injury
2).
i n weeks
when c o n c e n t r a t i o n s o f
Over
t h e years
with
concentrations below 80 ~19.m’~. These r e s u l t s suggest t h a t
all the
several
hourly
ozone
importance
of
peak concentrations i n terms o f f o l i a r i n j u r y should n o t be over-estimated. Other
indicator
plants
for
ozone
such
as
spinach,
bean,
poplar
subterranean c l o v e r g e n e r a l l y showed l e s s symptoms a t t h e f i e l d l o c a t i o n s
and than
tobacco Be1 W3. This i n d i c a t e s t h e r e l a t i v e l y h i g h s e n s i t i v i t y o f t h e tobacco cultivar. However, i n f u m i g a t i o n experiments bean ( r e f . 8) and p o p l a r (unpublished d a t a ) appeared t o be more s e n s i t i v e than tobacco
and
p l a n t species showed s i m i l a r i n j u r y responses t o ozone ( r e f . 5).
some
other
254
Follar Injury, X
241
'I 6
0 0
120
SO
24h average
180
O3 conc..
Fig. 2. F o l i a r i n j u r y t o tobacco Be1 W3 i n r e l a t i o n t o t h e 24 h average ozone c o n c e n t r a t i o n (1983 f i e l d data).
OZONE
DAMAGE TO CROPS
Negative e f f e c t s o f ozone on frequently
described
for
the
North
growth
America
w i t h o u t signs o f v i s i b l e i n j u r y ( r e f .
and y i e l d (ref.
9).
of
crops
have
been
These e f f e c t s can occur
10). I n r e c e n t years
it
became e v i d e n t
t h a t ambient ozone a l s o reduced crop p r o d u c t i v i t y i n European c o u n t r i e s l i k e UK and Denmark ( r e f s . 11-12).
Since ozone c o n c e n t r a t i o n s i n t h e
Netherlands
are
s i m i l a r t o t h e l e v e l s i n these c o u n t r i e s ( r e f . 13) n e g a t i v e e f f e c t s o f ozone on Dutch crops are v e r y l i k e l y t o occur. A study was undertaken i n order t o determine t h e impact o f a i r p o l l u t i o n
Dutch
crop
production
(ref.
14).
Ozone e f f e c t s
were
on
evaluated u s i n g t h e
exposure-yield r e l a t i o n s h i p s o f Linzon e t a l . ( r e f . 15). The ozone exposure was expressed (10.00-17.00
as
the
seasonal
mean
of
the
7-h
daily
mean
crop l o s s was c a l c u l a t e d f o r each of 14 crops (Table 1) and (Table
2).
concentrations
h r s ) from May through September. Based on 1983 d a t a ozone-induced The
1983 ozone
level
with
for
each
region
a mean o f 8 9 ~ g . m -was ~ considered
r e p r e s e n t a t i v e f o r t h e whole p e r i o d 1980-1985.
255 TABLE 1 Estimated crop l o s s (X) f o r 14 crops caused by ambient ozone i n 1983. Crop l o s s ( X )
Crop Fruit Floriculture Arbor ic u l t ure F1ower bulbs Grass seeds Pasture Cereals
Crop l o s s ( X )
Crop Glassh. vegetables Vegetables Glassh. potted p l a n t s Fodder crops Potatoes Glassh. c u t flowers Legumes
0.0 0.0 0.0 0.0 1.6 1.6 1.7
Estimated crop losses caused by ambient legumes,
potatoes,
cut
flowers
and
ozone were
3.1 4.4 4.6 6.2 6.3 6.3 6.6
relatively
lower f o r vegetables and potted plants. The highest percentage calculated
for
large
for
fodder crops. Crop losses were s l i g h t l y
the province o f Zuid-Holland.
crop
loss
was
The l a r g e amount o f crop l o s s i n
t h i s province mainly r e s u l t e d from t h e extensive c u l t i v a t i o n o f vegetables glasshouse
crops.
The importance o f a i r p o l l u t i o n i n c l u d i n g ozone i n r e l a t i o n
t o t h e extensive glasshouse crop production occurring i n t h e Netherlands principal
matter
of
concern.
Research
has
i n s i d e glasshouses can increase up t o 70% o f when
ventilators
combination
are
with
and
open
sulfur
(ref.
16)
d i o x i d e and
is
a
shown t h a t ozone concentrations ambient
and t h a t
concentrations these
outdoors
concentrations
in
n i t r o g e n d i o x i d e can cause s i g n i f i c a n t
losses t o tomatoes ( r e f . 17). TABLE 2 Estimated crop l o s s ( X ) i n t h e 12 Dutch provinces caused by ambient
ozone
i n 1983. Crop l o s s (X)
Province Fries1 and Noord-Hol 1and Limburg Overi j s s e l Utrecht Noord-Brabant ~~
1.7 1.8 2.2 2.7 2.7 2.9
Gel d e r l and Gronlngen Drenthe Zeel and IJsselmeerpol ders Zuid-Holland
~~
~
I n general,
Crop l o s s (X)
Province
~
3.5 3.5 3.8 3.9 4.2 4.7
~ _ _ _
a i r p o l l u t i o n causes r e l a t i v e l y l i t t l e damage t o t h e producers
due t o p r i c e supports ( r e f . 14). Consumers, thus, are t h e primary b e n e f i c i a r i e s from
a decrease
in
the
levels
Netherlands would be reduced t o
of
air
pollution.
I n case ozone i n t h e
background concentrations,
consumers. would
experience a n e t galn o f D f l 460 m i l l i o n ( r e f . 18). I n the
Dutch
study
(ref.
14) i t i s estimated t h a t i n 1983 a i r p o l l u t i o n
i n c l u d i n g ozone, s u l f u r d i o x i d e and hydrogen f l u o r i d e reduced crop production
256
Exposure time
1OQdays
.
.
.-• :.
10
i 0
\=
12 hours. 1
BOmIn.
1
i
.. . .. .. . ' . : . . .. . . . .. a
':*
0
.
0 . . 0 .
1
**
8 .
1
10
' *'
102
103 2'.103
0, conc. In porn*
Fig. 3. Concentration-time model used t o i nj u r y t o vegetation.
derive
limiting
values
for
ozone
5% and t h a t 70% o f t h e t o t a l r e d u c t i o n i s caused by ozone. Observations i n t h e USA have i n d i c a t e d t h a t o f t h e crop loss due t o a i r p o l l u t i o n , ozone i s by
responsible
9016, which
for
amounts
t o 2 t o 4% o f t h e t o t a l crop production
( r e f . 19). I n view o f these r e s u l t s ozone i s l i k e l y t o be
the
most
important
p o l l u t a n t i n terms o f crop loss. MAXIMUM OZONE CONCENTRATIONS FOR THE PROTECTION
OF THE VEGETATION
The concept o f determining l i m i t i n g values as presented e a r l i e r by Jacobson ( r e f . 20) was used t o provide i n f o r m a t i o n on doses
on t h e vegetation.
the
and y i e l d reduction as reported by Guderian e t a1 concentration-time
effects
of
specific
ozone
Data on ozone-induced f o l i a r i n j u r y as well as growth
. (ref.
3) are presented i n
a
model (Fig. 3 ) . The o b j e c t i v e o f t h i s model i s t o determine
t h e boundary conditions between combinations o f concentration and t i m e t h a t a r e probably
i n j u r i o u s and
those
conditions
t h a t are not. Each p o i n t i n Fig. 3
represents t h e lowest concentration and exposure d u r a t i o n used i n a study resulted
i n a negative e f f e c t . The curve has been drawn under t h e points. For
c x t combinations below and t o t h e l e f t vegetation
that
is
not
to
be
side
of
this
curve,
injury
to
the
expected. Above and t o t h e r i g h t s i d e o f t h e curve
ozone exposures may cause negative e f f e c t s on p l a n t s .
257 From Fig. 3 l i m i t i n g values f o r t h r e e d i f f e r e n t exposure durations have been selected
(Table
3).
The
1 h and
8 h values were chosen a t l e v e l s without
v i s i b l e i n j u r y t o t h e vegetation caused by acute ozone exposures. The 8 h value i s considered t o be extremely relevant since, i n t h e Netherlands, t h e maximal 8 h concentrations o f ambient ozone are concentrations
slightly
less
than
May through
maximal
1 h
4). The average concentration during t h e growth season,
(Table
expressed as t h e average of 7-h d a i l y mean concentrations from
the
(10.00-17.00
hrs)
September, was chosen as an i n d i c a t o r f o r chronic exposures
since: (a) reductions i n growth and y i e l d by chronic ozone exposures can occur without v i s i b l e symptoms ( r e f . 10) (b) no clear-cut r e l a t i o n s h i p e x i s t s between t h e frequency o f h i g h ozone peaks and the average concentrations during t h e summer ( r e f . 7).
I t should be emphasized t h a t
the
datasets
used,
and
hence
the
derived
l i m i t i n g values, r e f l e c t i n a d d i t i o n t h e l i m i t a t i o n s i n experimental techniques and measurements. Furthermore, i t should be pointed out
that
data
are
only
r e l a t e d t o experiments i n which t h e e f f e c t s o f ozone as a s i n g l e component were studied, although t h e r e i s ozone,
sulfur
dioxide
and
increasing
evidence
for
synergistic
effects
of
nitrogen d i o x i d e ( r e f . 21). On t h e o t h e r hand t h e
presented data i n t e g r a t e t h e ozone responses o f a wide v a r i e t y o f p l a n t species under a varying set o f external conditions. TABLE 3 L i m i t i n g values
and
proposed maximum acceptable
ozone
concentrations f o r
p r o t e c t i o n o f vegetation. Duration o f exposure
L i m i t i n g values ( ~ ~ g . m - ~ ) ’ Max. concentrations ( ~ ~ g . m - ~ )
1 hour 8 hours growing seasonb
150 65 50
200 75 60 ~~
L i m i t i n g values derived from Fig. 3 Expressed as t h e seasonal mean o f t h e 7-h d a i l y mean concentrations (10.00-17.00 hrs) from May September.
-
However, recent i n f o r m a t i o n suggests t h a t t h e l i m i t i n g values in
Table
as
presented
3 do not e n t i r e l y prevent t h e vegetation from ozone i n j u r y under a l l
conditions. I n experiments w i t h poplar, c o n t r o l c u t t i n g s l o s t more leaves EDU-treated
cuttings
concentration o f 5 9 ~ g . m - ~f o r 6-7 weeks ( r e f . 22). Wolting (ref. 17) that
60 ~ ~ g . m -ozone ~
of
tomatoes
reported
i n t h e presence o f s l i g h t l y elevated concentrations o f
s u l f u r d i o x i d e and n i t r o g e n d i o x i d e caused leaves
than
when exposed t o ambient a i r w i t h a daytime average ozone
premature
ageing
of
the
oldest
and y i e l d losses o f 12-19 X . Therefore, i t i s considered
258 necessary
to
propose
an
additional
set
of
maximum acceptable
ozone
concentrations t h a t are lower than t h e derived l i m i t i n g values (Table 3). CURRENT STATUS OF AMBIENT OZONE I N RELATION TO VEGETATION INJURY
Some data regarding ambient ozone measured i n t h e
monitoring
concentrations
in
network from 1980-1985,
the
Netherlands,
as
a r e presented i n Table 4
( r e f . 23). During t h e growing season, t h e maximum values o f t h e 1 h and 8 h ozone concentrations are 230-430 and 190-350 jg.m' 3 , respectively. The
maximal
average concentration during t h e growing season v a r i e s but
increased
up
between
70-90
j g .n~-~,
t o almost l 2 O ~ l g . m ' ~ i n a y e a r w i t h increased production o f
photochemical oxidants. TABLE 4 Sumnary o f data o f concentrations o f ambient ozone ( ~ g . m - ~ )i n t h e during t h e growing seasons o f 1980
- 1985.
50 Perc.
95 Perc.
Netherlands
98 Perc.
Maximum
183-263 157-223
227-431 191-350 77-117
~~
Max. 1 h Max. 8 h Growing season
78-104a 64- 90b 70- 91
159-223 134-122
--
--
Ranges i n d i c a t e d i f f e r e n c e s between l o c a t i o n s Data are mean concentrations i n stead o f 50 p e r c e n t i l e values Not determined From Tables
3 and
f r e q u e n t l y exceed
the
4 i t i s concluded t h a t concentrations o f ambient ozone proposed maximum acceptable
concentrations
and t h e
l i m i t i n g values. Calculations showed ( r e f . 18) t h a t t h e 1 h value o f 1 5 0 ~ g . m - ~ and t h e 8 h value of 65$g.me3 respectively,
of
the
days
a r e exceeded on 10-15% and d u r i n g an
average
on
more than
50%
growing season. The proposed
maximum acceptable ozone concentration f o r t h e growing season (50 y9.m' 3)
was always exceeded a t a l l l o c a t i o n s i n every year. These r e s u l t s i n d i c a t e t h a t t h e frequency w i t h which ambient ozone concentrations exceed t h e proposed maximum acceptable
concentrations
for
protection
of
vegetation,
increases w i t h an
increase i n t h e d u r a t i o n o f exposure. CONCLUSIONS Ambient ozone concentrations adversely a f f e c t t h e vegetation throughout
the Netherlands. F o l i a r i n j u r y t o p l a n t s such as t h e ozone s e n s i t i v e tobacco Be1 W 3 has been f r e q u e n t l y observed a f t e r ozone.
periods
with
elevated
concentrations
of
This i n j u r y response i s n o t c l e a r l y r e l a t e d t o average ozone concentra-
t i o n s . The value o f simple exposure-response functions r e l a t i n g a s i n g l e
para-
253 meter
o f p l a n t response t o a s i n g l e exposure parameter, i s s t i l l questionable.
Interactions o f
ozone w i t h environmental
c o n d i t i o n s and w i t h
other
air
p o l l u t a n t s may be important. Because production o f photochemical oxidants, and hence concentrations o f ozone, depend on
s u i t a b l e weather
conditions,
these
i n t e r a c t i o n s are very complex and u r g e n t l y need f u r t h e r i n v e s t i g a t i o n s . Although
ozone
concentrations
d u r i n g t h e growing season are s u f f i c i e n t t o
reduce growth and y i e l d of Dutch crops, s p e c i f i c information i s mostly lacking. Ambient
ozone
concentrations i n the Netherlands s u b s t a n t i a l l y exceed proposed
maximum acceptable frequency
of
concentrations
for
protection o f
the
vegetation.
The
exceedances appears t o increase w i t h an increase i n t h e duration
o f exposure. Therefore, studies need t o be conducted t o determine t h e i n f l u e n c e o f chronic ozone exposures on t h e vegetation. REFERENCES 1 J.G. Ten Houten, Landbouwk. T., 78 (1966) 2-13. 2 A.E.G. Tonneijck, Neth. J. P1. Path., 89 (1983) 99-104. 3 R. Guderian, D.T. Tingey and R. Rabe, i n R. Guderian ( E d i t o r ) , A i r p o l l u t i o n by photochemical oxidants. Formation, transport, c o n t r o l , and effects on plants. Springer-Verlag, B e r l i n , 1985, pp. 129-333. 4 A.E.G. Tonneijck and A.C. Posthumus, VDI-Ber., 609 (1987) 205-216. Tonneijck and H. Floor, Bedrijfsontwikkeling, 15 (1984) 440-443. 5 A.E.G. 6 Anonymous, L u c h t k w a l i t e i t . Jaarverslag 1984 en 1985, R i j k s i n s t i t u u t voor Vol ksgezondheid en Milieuhygiene, Bilthoven, 1986. 7 F.A.A.M. de Leeuw, i n R. Guicherit, J. van Ham and A.C. Posthumus (Editors), Ozon: fysische en chemische veranderingen i n de atmosfeer en de gevolgen, Kluwer, Deventer, 1987, pp. 40-44. 8 A.E.G. Tonneijck, i n P. Grennfelt ( E d i t o r ) , Proc. I n t . Workshop on t h e evaluation and assessment o f t h e e f f e c t s o f photochemical oxidants on human health, a g r i c u l t u r a l crops, f o r e s t r y , m a t e r i a l s and v i s i b i l i t y , Goteborg, Sweden, Febr. 29- March 2, 1984, Swedish Environmental Research I n s t i t u t e , Goteborg, 1984, pp. 118-127. 9 D.T. Tingey, i n P. Grennfelt ( E d i t o r ) , Proc. I n t . Workshop on t h e evaluation and assessment o f t h e e f f e c t s o f photochemical oxidants on human health, a g r i c u l t u r a l crops, f o r e s t r y , m a t e r i a l s and v i s i b i l i t y , Goteborg, Sweden, Febr. 29 March 2, 1984, Swedish Environmental Research I n s t i t u t e , Goteborg, 1984, pp. 60-75. 10 J.S. Jacobson, i n M.H. Unsworth and D.P. Ormrod (Editors), E f f e c t s o f gaseous a i r p o l l u t i o n i n a g r i c u l t u r e and h o r t i c u l t u r e , Butterworths, London, 1982, pp. 293-304. 11 M.R. Ashmore, i n P. Grennfelt ( E d i t o r ) , Proc. I n t . Workshop on t h e evaluation and assessment o f t h e e f f e c t s o f photochemical oxidants on human health, a g r i c u l t u r a l crops, f o r e s t r y , m a t e r i a l s and v i s i b i l i t y , Goteborg, Sweden, Febr. 29 March 2, 1984, Swedish Environmental Research I n s t i t u t e , Goteborg, 1984, pp. 92-104. 12 H. Ro-Poulsen, L. Mortensen and I. Johnsen, i n P. Grennfelt ( E d i t o r ) , Proc. I n t . Workshop on t h e evaluation and assessment o f the e f f e c t s of photochemical oxidants on human health, a g r i c u l t u r a l crops, f o r e s t r y , materials and v i s i b i l i t y , Goteborg, Sweden, Febr. 29 March 2, 1984, Swedish Environmental Research I n s t i t u t e , Goteborg, 1984, pp. 105-112. 13 P. Grennfelt, J. Saltbones and J. Schjoldager, Oxidant data c o l l e c t i o n i n OECD-Europe 1985-87 (Oxidate). A p r i l September 1985, Norwegian I n s t i t u t e f o r A i r Research, L i l l e s t r a m , 1987. Tonneijck and J.H.M. Wijnands, Environ. P o l l u t . 14 L.M. van der Eerden, A.E.G.
-
-
-
-
260
15 16
17 18 19 20 21 22 23
(1988), i n press. S.M. Linzon, R.G. Pearson, J.A. Donnan and F.M. Durham, Ozone e f f e c t s on crops i n Ontario and r e l a t e d monetary values, Ontario M i n i s t r y o f t h e Environment , 1984. H.G. Wolting, E.A.M. van Remortel and N. van Berkel, Acta H o r t i c u l t u r a e , 174 (1985) 351-357. H.G. Wolting, Annual Report 1986, Research I n s t i t u t e f o r Plant Protection, Wageningen, 1986, p.43. W. S l o o f f , R.M. van Aalst, E. Heijna-Merkus and R. Thomas ( E d i t o r s ) , Ontwerp basisdocument ozon, R i j k s i n s t i t u u t voor Volksgezondheid en Milieuhygiene, Bilthoven, 1987. W.W. Heck, O.C. Taylor, R. Adams, G. Bingham, J. M i l l e r , E. Preston and L. Weinstein, J. A i r P o l l u t . Control ASSOC., 26 (1982) 325-333. J.S. Jacobson, VDI-Ber., 270 (1977) 163-173. A.S. Lefohn and D.P. Ormrod, A review and assessment o f t h e e f f e c t s o f p o l l u t a n t mixtures on vegetations. Research recomnendations, EPA, Corvall i s , 1984. H.G. M o l t i n g and J. Mooi , B e d r i j f s o n t w i k k e l i n g , 15 (1984) 449-454. uurgemiddelde ozonJ. Erisman, Enkele aspecten van 1 uur- en 8 concentraties i n Nederland, R i j k s i n s t i t u u t voor Volksgezondheid en Milieuhygiene, Bilthoven, 1987.
T. Schneider et al. (Editore),Atmospheric Ozone Research and it8 Policy Implications 1989 Elsevier Science Publishers B.V., Amsterdam -Printed in The Netherlands
261
CONSEQUENCES OF DECREASED ATMOSPHERIC OZONE: EFFECTS OF UTRAVIOLET RADIATION ON PLANTS
L.O.
BJURN
Department of P l a n t P h y s i o l o g y , U n i v e r s i t y o f Lund, Box 7007, 5-220 07 Lund, Sweden
ABSTRACT A r e v i e w i s g i v e n o f t h e work on e f f e c t s o f u l t r a v i o l e t r a d i a t i o p on p l a n t s (and r e l a t e d work) t h a t has been c a r r i e d o u t by o u r group o v e r t h e p a s t few years.
INTRODUCTION The t o t a l amount o f ozone i n t h e e a r t h ' s atmosphere shows a d e c r e a s i n g t r e n d (1.0% p e r y e a r ) s i n c e many y e a r s ( r e f . 1 ) .
A t t h e same t i m e , t h e b i o l o g i c a l l y ef-
f e c t i v e u l t r a v i o l e t r a d i a t i o n , somewhat s u r p r i s i n g l y , a l s o shows a d e c r e a s i n g t r e n d ( 0 . 5 t o 1% p e r y e a r i n t h e U n i t e d S t a t e s , r e f . 2 ) . S i n c e we do n o t unders t a n d t h e causes o f e i t h e r change, no r e l i a b l e f o r c a s t can be made. I t i s i m p o r t a n t i n t h i s s i t u a t i o n t o a q u i r e some knowledge a b o u t t h e r e a c t i o n s o f o r ganisms, i n c l u d i n g p l a n t s and t h e ecosystems i n which t h e y p a r t i c i p a t e , on poss i b l e f u t u r e increases i n d a y l i g h t u l t r a v i o l e t r a d i a t i o n . Most r e s e a r c h on t h i s s u b j e c t has been c a r r i e d o u t i n t h e U n i t e d S t a t e s , and some i n West Germany. A g r i c u l t u r a l experiments i n d i c a t e t h a t f o r each p e r c e n t decrease i n ozone, one m i g h t expect about one p e r c e n t h a r v e s t r e d u c t i o n i n some c r o p s ( r e f . 3,4), w h i l e t h e e f f e c t s on h a r v e s t s from t h e sea m i g h t b e g r e a t e r ( r e f . 5) A g r i c u l t u r a l experiments o f t h e t y p e performed by Teramura a r e v e r y expens i v e and time-consuming.
D i f f e r e n t p l a n t s r e a c t v e r y d i f f e r e n t l y t o enhanced UV
r a d i a t i o n ( t h i s i s t r u e even for. d i f f e r e n t c u l t i v a r s o r ecotypes w i t h i n t h e same s p e c i e s ) . I t i s t h e r e f o r e n o t f e a s i b l e t o c a r r y o u t such e x p e r i r i c n t s w i t h e v e r y p l a n t v a r i e t y o f i n t e r e s t . We must understand t h e reasons f o r t h e d i f f e r ences i n UV s e n s i t i v i t y , and we must understand j u s t what UV does t o t h e p l a n t . UV work i n o u r group has proceeded a l o n g f i v e d i f f e r e n t l i n e s , w h i c h w i l l be
d e s c r i b e d be1ow:
( 1 ) E f f e c t s o f u l t r a v i o l e t r a d i a t i o n on p h o t o s y n t h e t i c e l e c t r o n t r a n s p o r t . ( 2 ) E f f e c t s o f u l t r a v i o l e t r a d i a t i o n on stomata.
262 ( 3 ) Penetration o f u l t r a v i o l e t r a d i a t i o n i n t o p l a n t s measured by a f i b e r o p -
t i c probe, and e v a l u a t i o n o f f a c t o r s a f f e c t i n g penetration. ( 4 ) Development o f a computer program far e s t i m a t i n g d a y l i g h t UV and i t s b i o l o g i c a l a c t i o n under d i f f e r e n t circumstances. (5) Probing u l t r a v i o l e t r a d i a t i o n e f f e c t s on p l a n t s by measuring p l a n t l u m i nescence. EFFECTS OF UV RADIATION ON PHOTOSYNTHETIC ELECTRON TRANSPORT Bornman e t a l . ( r e f . 6) determined an a c t i o n spectrum f o r i n h i b i t i o n o f phot o s y n t h e t i c e l e c t r o n t r a n s p o r t i n i s o l a t e d spinach choroplasts. Action spectra were determined a l s o by i r r a d i a t i n g i n t a c t leaves o f EZodea and Oxalis ( r e f . 7 ) . I n ha2i.s i r r a d i a t i o n was from e i t h e r t h e upper o r the lower side, and i t was
found t h a t the p l a n t s were much more s e n s i t i v e f a r i r r a d i a t i o n from t h e lower side. The explanation was found i n a d i f f e r e n t amount o f screening compounds i n the epidermis. The a c t i o n spectra determined i n t h i s way a r e i n good agreement w i t h a c t i o n spectra f o r i n h i b i t i o n o f e l e c t r o n t r a n s p o r t measured by o t h e r groups. However, they are much f l a t t e r than a c t i o n spectra f o r complete photosynthesis (carbon dioxide uptake) measured by several groups w i t h simultaneous i r r a d i a t i o n by UV and p h o t o s y n t h e t i c a l l y a c t i v e 1 i g h t . T h i s discrepance,
important f o r computing
r a d i a t i o n a m p l i f i c a t i o n f a c t o r s and e f f e c t s o f ozone depletion, has n o t y e t been explained. For f u r t h e r discussion o f r a d i a t i o n a m p l i f i c a t i o n f a c t o r s , see r e f . 8. The reader i s r e f e r r e d t o Bornman ( r e f . 9) f o r more i n f o r m a t i o n on t h i s aspect o f UV work a t our department. EFFECTS OF UV RADIATION ON STOMATA U l t r a v i o l e t i r r a d i a t i o n o f p l a n t s causes stomata t o close. Action spectra w i t h d i f f e r e n t background 1 i g h t s f o r t h e c l o s i n g a c t i o n have been determined by Negash & B j o r n ( r e f . 10) and Negash ( r e f . 11). Radiation o f 305 nm o r longer wavelength has l i t t l e e f f e c t . I t i s thought t h a t the UV e f f e c t on stomata takes place v i a an e f f e c t on t h e potassium i o n content of t h e guard c e l l s ( r e f . 12, 13). Since the c l o s i n g i s prevented by strong v i s i b l e l i g h t , i t i s doubtful whether stomata1 c l o s i n g by UV r a d i a t i o n i s e c o l o g i c a l l y important. For f u r t h e r discussion o f UV e f f e c t s on stomata, see ref. 14. PENETRATION OF UV RADIATION INTO PLANTS The basic procedure f o r measuring t h e p e n e t r a t i o n o f l i g h t i n t o p l a n t s using f i b e r o p t i c s was described by Vogelmann & Bjorn ( r e f . 15). I t was f u r t h e r d i s cussed by Chwirot & S l e v i n ( r e f . 161, B j o r n (ref.17)
and Vogelmann & B j o r n
263 ( r e f . 181, and has been used w i t h d i f f e r e n t p l a n t o b j e c t s by Vogelmann & Haupt ( r e f . 1 9 ) , Vogelmann e t a l . ( r e f . 20) and Widell E Vogelmann ( r e f . 21). I n short t h e procedure involves heating a glass f i b e r and p u l l i n g i t t o a f i n e t i p (a few POI diameter), properly t r e a t i n g the t i p and the surface o f t h e f i b e r , i n s e r t i n g the f i b e r t o the place o f measurement i n the p l a n t t i s s u e using a micromanipulator, and c o l l e c t i n g t h e l i g h t a t t h e o t h e r end o f the f i ber i n t o a spectroradiometer. Great a t t e n t i o n must be p a i d t o c a l i b r a t i o n , c o l l e c t i n g l i g h t i n proper d i r e c t i o n s , and adding the measurements i n a c o r r e c t way. The procedure has been adapted f o r measurements o f u l t r a v i o l e t r a d i a t i o n by Bornman & Vogelmann ( r e f . 2 2 ) i n Vogelmann's laboratory. The main change necessary f o r measurements o f UV i s the use o f a quartz f i b e r instead o f a glass fiber; t h i s i n t u r n necessitates heating t h e f i b e r ( f o r p u l l i n g i t t o a f i n e t i p ) w i t h an acetylene-oxygen flame instead o f an e l e c t r i c c o i l . Other improvements include covering the f i b e r surface w i t h l a y e r s o f metal t o exclude entrance o f l i g h t except a t the t i p . Borman & Vogelmann ( r e f . 22) found t h a t (a) UV-A r a d i a t i o n (360 nm) i s more r a p i d l y attenuated i n spruce and f i r needles than i s b l u e l i g h t (460 nm); ( b ) l i t t l e blue l i g h t o r UV-A was attenuated by the e p i c u t i c u l a r wax l a y e r ; ( c ) most o f the UV-A was attenuated by the epidermal c e l l s I n spruce (Picea engel-
m n n i i ) about 7% o f the i n c i d e n t 360 nm r a d i a t i o n remained a t 100 Um depth, w h i l e i n fir (Abies lasiocarpa) only 1.5% remained a t t h e same depth. I n spruce t h i s attenuation i s almost completely due t o soluble UV-absorbing substances (presumably flavonoids) i n t h e epidermal l a y e r , w h i l e i n f i r o t h e r substances may contribute. D i f f e r e n t s t r u c t u r e s o f t h e mesophyll f u r t h e r accentuate d i f ferences i n penetration f u r t h e r i n t o needles. DEVELOPMENT AND TESTING OF COMPUTER PROGRAMS FOR ESTIMATING DAYLIGHT UV AND I T S BIOLOGICAL EFFECTS The computer program described by Bjorn & Murphy ( r e f . 23) has undergone
some modifications and extensive comparisons w i t h o t h e r programs. D e t a i l s o f t h i s are discussed by Bjorn ( r e f . 241, and I s h a l l l i m i t myself here t o some aspects. The program c a l c u l a t e s the d i r e c t and scattered spectral components of dayl i g h t seperately, which, i n t h e recent version, allows t h e i r combinations as e i t h e r spectral i r r a d i a n c e on
a h o r i z o n t a l o r t i l t e d surface o r spectral f l u -
ence rate. As fluence r a t e i s the more appropriate magnitude i n most photobiol o g i c a l applications, w h i l e o t h e r programs u s u a l l y g i v e irradiance, t h i s i s a great advantage. The program a l s o has a b u i l t - i n choice o f various a c t i o n spect r a (weighting functions) , so an expression f o r effectiveness f o r various phot o b i o l o g i c a l DroceSses can he obtained e a s i l y . This f l e x i b i l i t y has allowed a
264 comparison w i t h spectroradiometric measurements as we1 1 as various more special i z e d procedures and measurements w i t h s p e c i a l i z e d detectors, such as t h e Robertson-Berger meter. Bjorn ( r e f , 24) shows comparisons between r e s u l t s obtained by t h i s program and several others ( r e f . 25-27) as w e l l as comparison w i t h measured values. EFFECTS OF ULTRAVIOLET RADIATION ON PLANT LUMINESCENCE Two d i f f e r e n t kinds o f luminescence from p l a n t s should be distinguished, exc l u d i n g fluorescence. One i s "photosynthetic luminescence", "afterglow" o r "delayed l i g h t emission", discovered by S t r e h l e r & Arnold ( r e f . 28) and extensivel y used i n many l a b o r a t o r i e s f o r e x p l o r i n g the mechanism o f photosynthesis. T h i s l i g h t i s generated by the recombination o f charges separated by the primary phot o s y n t h e t i c process i n photosystem 2 ; thus, somewhat s i m p l i f i e d , i t can be described as reversal o f photosynthesis. We have constructed a "phytoluminograph" ( r e f . 29,30) w i t h which t h e p l a n t can be imaged i n i t s own luminescence l i g h t . Such an image shows the s p a t i a l d i s t r i b u t i o n o f t h e c a p a c i t y f o r photosynthesis. I t can be used a l s o f o r studying the s p a t i a l d i s t r i b u t i o n o f u l t r a v i o l e t damage
t o the photosynthetic system (Fig. 1).
Fig. 1. Phytoluminogram of an u l t r a v i o l e t i r r a d i a t e d l e a f of oxutis deppei. Dur i n g i r r a d i a t i o n p a r t o f t h e l e a f was shaded by a metal r i n g , t o provide a cont r o l area. The 1 i g h t e m i t t i n g c a p a c i t y (an i n d i c a t o r o f photosynthetic c a p a c i t y )
265 was decreased by u l t r a v i o l e t i r r a d i a t i o n . From r e f . 29. Recently we have modernized the phytoluminograph (Fig.2) and connected i t t o a computerized image processing system, and intend t o resume use o f i t f o r UV e f f e c t studies
.
Fig. 2. View o f the present phytoluminograph. I t c o n s i s t s of a l i g h t - t i g h t samp l e box ( t o the l e f t ) , l i g h t source, f i b e r o p t i c l i g h t guide and s h u t t e r assemb l y , image i n t e n s i f i e r and video system. The other k i n d o f 1uminescence i s " u l traweak luminescence" a r i s i n g through various biochemical reactions unrelated t o photosynthesis. Most p l a n t c e l l s exh i b i t t h i s k i n d o f luminescence, b u t the i n t e n s i t y v a r i e s considerably. P a r t of i t i s due t o peroxidation o f unsaturated l i p i d s . The phenomenon has been reviewed by Abeles ( r e f . 31) and, i n a more popularized way, by Popp r e f . 32).
Ultraweak luminescence, as the name implies, i s exceedingly f a i n t , and a t present cannot be used f o r generating images. To record i t , we have t o use a cooled p h o t o m u l t i p l i e r i n the photon counting mode. I n t e r e s t i n g i n t h i s context i s t h a t ultraweak luminescence i s
g r e a t l y stimu-
l a t e d by exposure o f p l a n t t i s s u e t o u l t r a v i o l e t r a d i a t i o n (Fig. 3)
266
3000
I
0
200
400
600
800
1000
1200
seconds Fig. 3. Ultraweak luminescence from non-photosynthetic p l a n t t i s s u e ( c e l e r y r o o t ) . Sections 1, 3 and 5 o f t h e curve show background photon count ( i n the absence of sample). Section 2 shows the luminescence from the sample before irr a d i a t i o n , section 4 a f t e r a p e r i o d o f u l t r a v i o l e t i r r a d i a t i o n . Possibly the luminescence and i t s decay can g i v e i n f o r m a t i o n on t h e nature and f a t e o f the primary products o f the damaging photochemical reactions. REFERENCES 1. K.P. Bowman, Science 239 (1988) 48-50. 2. J. Scotto, Science 239 (1988) 262-264. 3. R.C. Worrest, t h i s volume. 4. A.H. 5. A.H.
Teramura, Physiol. Plantarum 58 (1983) 414-427. Teramura, J.G. T i t u s ( E d i t o r ) , Effects o f Changes i n Stratospheric
Ozone and Global Climate, Vol. 2, US Environmental P r o t e c t i o n Agency, Washing1986, 255-262. ton, D.C., 6. J.F.
Bornman, L.O.
( 1984) 305-31 3. 7. L.O. Bjorn, J.F.
B j o r n and H.-E.
Akerlund, Photobiochem. Photobiophys. 8
Bornman and E. O l s o n , i n R.C.
Worrest ( E d i t o r ) , Proc. NATO
Adv. Res. Workshop on The Impact o f S o l a r U l t r a v i o l e t (UV-B Radiation) upon Ter-
restrid Ecosystems. I. A g r i c u l t u r a l Systems, Springer, B e r l i n , 1986, pp. 185197. 8. L.O.
Bjorn,
J.F.
Bornman and L. Negash, J.G.
Titus (Editor), Effects o f
267 Changes i n Stratospheric Ozone and Global Climate, Vol 2, US Environmental Prot e c t i o n Agency, Washington, D.C.
, pp.
263-276.
9 J.F. Bornman, E f f e c t s o f U t r a v i o l e t Radiation on Plants, Doctoral Dissertat i o n , Lund 1985. 10. L. Negash and L.O.
Bjorn, Physiol. Plantarum 66 (1986) 360-364.
11 L. Negash, P l a n t Physiol. Biochem. 25 (1987) 753-760. 12 L. Negash, P. Jensen and L.O. Bjorn, Physiol. Plantarum 69 (1987) 200-204. 13 L. Negash and L.O. Bjorn, P l a n t Physiol. Biochem. 26 (1988) 14 L. Negash, Response o f Stomata t o U l t r a v i o l e t Radiation, Doctoral Dissertat i o n , Lund 1988.
15 T.C.
Vogelmann and L.O. Bjorn, Physiol. Platarum 60 (1984) 361-368.
16 S. Chwirot and J. Slevin, Physiol. Plantarum 67 (1986) 493-494 17 L.O.
Bjorn, Physiol. Plantarum 67 (1986) 493-499.
18 T.C.
Vogelmann and L.O. Bjorn, Physiol. Plantarum 68 (1986) 704-708.
19 T.C. 20 T.C.
Vogelmann and W. Haupt, Photochem. Photobiol. 41 (1985) 569-576. Vogelmann, A.K. Knapp, T.M. McClean and W.K. Smith, Physiol. Plantarum
72 (1988) 623-630. 21 K.-0. Widell and T.C Vogelmann, Physiol. Plantarum 72 (1988) 706-712. 22 J.F. Bornman and T.C. Vogelmann, Physiol. Plantarum 72 (1988) 699-705. 23 L.O. Bjorn and T.M Murphy, Physiol. Veg. 23 (1985)555-561 24 L.O.
Bjorn, i n B.L.
D i f f e y ( E d i t o r ) , Radiation Measurement i Photobiology,
Academic Press, London 1986, pp.
25 R.E.
B i r d and C. Riordan, J. o f Climate and Appl. Meteorology, 25 (1986)
87-97. 26 S.A.W.
Gerstl, A Zardecki and H.L. Wiser, UV-B Handbook, vol. I , Los Alamos
National Laboratory, Los AlamOs, N.M.
1983.
27 W. Josefsson, Solar U l t r a v i o l e t Radiation i n Sweden, Swedish Meteorological and Hydrological I n s t i t u t e , Norrkoping 1986.
28 B.L.
S t r e h l e r and W. Arnold, J. Gen. Physiol.
34 (1951) 609-820.
29 E. Sundbom and L.O. Bjorn, Physiol. Plantarum 40 (1978) 39-41. 30 L.O. Bjorn and A.-S. Forsberg, Physiol. Plantarum 47 (1979) 215-222. 31 F.B. Abeles, Annu. Rev. P l a n t Physiology 37 (1986) 49-72. 32 F.-A. Popp, B i o l o g i e des L i c h t s : Grundlagen der ultraswachen Zellstrahlung, Paul Parey, Berlin/Hamburg 1984.
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T. Schneider et al. (Editors),Atmospheric Ozone Research and its Policy Implications 0 1989 Elsevier Science Publishers B.V., Amsterdam -Printed in The Netherlands
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WHAT ARE THE EFFECTS OF UV-B RADIATION ON MARINE ORGANISMS?
R. C. Worrest
U. S.Environmental Protection Agency, Environmental Research Laboratory, Corvallis, Oregon 97333 (U.S.A.)
INTRODUCTION Marine systems, covering a vast area, contribute significantly to global productivity (ref. 1). The coastal kelp forests have productivities said to rival those of tropical rain forests, generally considered the world's most productive plant ecosystems (refs. 2-3). Of the five major marine habitats, the microscopic plants of the open sea are the most productive, contributing 75% of the total marine production through photosynthetic processes, or 24% of the global total. As early as 1925, scientists were aware of damaging effects on aquatic organisms from the ultraviolet component of sunlight (refs. 4-12). It was shown at these early dates that there exists a differential sensitivity among species to UV radiation, and that this differential sensitivity might relate to the depths at which the species were normally found. Several more recent studies on the effects of UV-B radiation (290-320 nm) have examined a variety of marine organisms (ref. 13). Regardless of the species investigated, each study has potential importance through the role of the particular organism in its environmental or food-web context. Some studies, in addition, have considered economically important zooplankton species, such as larval stages of certain shrimp, crab, and fish. Literature reviews (refs. 14-18) have summarized the results of most of these studies. PHYSICAL EFFECTS ON ORGANISMS UV-B radiation is readily absorbed by proteins and nucleic acids, and induces photochemical reactions in plants and animals (refs. 19-21). Even though proteins and nucleic acids are commonly involved in biological responses to UV-B radiation, the action spectra for tissue damage in many organisms may differ because of wavelength-dependent refraction, reflection, or absorption, and hence protection, by outer tissues (ref. 22).
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Based on a model of total incident solar radiation, a 10% ozone reduction at 45ON latitude would result in only a 1% increase in total solar ultraviolet (290-360 nm) daily exposure at the surface of the earth. This would be of minimal consequence if radiation throughout the solar spectrum were of equal biological effectiveness. However, when biological weighting functions based on the action spectra are employed, a very different picture emerges (ref. 23). Based on DNA damage (ref. 24), a 10% ozone reduction would result in a 28% increase in biologically effective radiation (Table 1). The generalized terrestrial plant response (damage) (ref. 25) would increase by 21%. TABLE 1 Relationship between ozone depletion and biological effectiveness of . . UV-R .-r Ozone e 10% 20%
30% 40%
790-370nm 2 8YO 17% 27% 38%
9 1.l% 2.4% 3.7% 5.2%
0 28% 67% 125% 21 3%
-
0 21 Yo 49% 85% 132%
aAction spectra are referencedto 300 nm = 1.OO. Levels of UV-B irradiance vary latitudinally, with the highest exposures in the tropics. The current difference between the extremes of exposures is about 3- to 6fold, but biota probably are adapted to levels that are normally experienced at their current locations. The increased exposure to biologically effective (DNA, Plant) ultraviolet radiation resulting from a 10% decrease in stratospheric ozone would be equivalent to migrating over 30° latitude toward the equator-a substantial ecological change. PHYTOPLANKTON The amount of UV-B radiation reaching the ocean's surface has long been suspected to be a factor influencing primary production. Research convincingly shows that ultraviolet radiation, at levels currently incident at the surface of natural bodies of water, is either at or near levels that inhibit phytoplankton productivity (refs. 26-28). It has been calculated that, near the surface of the ocean at temperate latitudes, enhanced UV-B radiation simulating a 25% reduction in ozone concentration would cause a decrease in primary productivity by about 35% (ref. 29). The estimated reduction in production for the whole euphotic zone would be about 10%. These calculations are based on attenuation lengths, i.e., the product of depth in the water
271
column and the diffuse attenuation coefficient of the water. On this basis, waters of various turbidities and absorption characteristics can be compared. Effects induced by solar UV-B radiation have been measured to depths of more than 20 m in clear waters and more than 5 m in waters with significant productivity (ref. 18). The euphotic zone (i.e., those depths with levels of light sufficient for positive net photosynthesis) is frequently taken as the water column down to the depth at which the surface level of photosyntheticallyactive radiation is reduced 99%. In marine ecosystems, UV-B radiation penetrates about the upper 10% of the euphotic zone before it is reduced 99% from its surface level of irradiance. Penetration of UV-B radiation into natural waters is a key variable in assessing the potential impact of this radiation on any aquatic ecosystem. If one assumes that present phytoplankton populations sense and control their average vertical position in such a way as to limit UV-B exposure to a tolerable level, then a 10% increase in solar UV-B radiation would necessitate a downward movement of the average position, thereby reducing the average UV-B exposure by 10%. There would be a corresponding reduction of light for photosynthesis. The loss of photosynthetically active radiation in many locations might not be significant. However, in some very productive areas, especially high latitude ocean areas, photosynthetically active radiation is the primary limiting factor for marine productivity (ref. 30). The loss of photosyntheticallyactive radiation from optical measurements has been estimated to be in the range of 3 to 5% for a 10% increase in UV-B radiation (ref. 31). If the photosynthetic base of aquatic ecosystems were perturbed, one would expect ramificationsto extend throughout the food web as a result of predator-prey relationships. Experiments with marine diatoms have shown significant reductions in biomass, protein and chlorophyll at UV-B irradiances equivalent to ozone reductions ranging from 5 to 15 percent. In addition, studies on chain-forming diatoms and other phytoplankton in the laboratory show that increased growth occurs when the UV-B radiation is filtered out of the incident solar radiation, indicating that existing levels of UV-8 radiation depress productivity (refs. 15, 32). Furthermore, indirect effects of ambient levels of UV-B radiation have been shown to endanger the survival of some freshwater microorganisms (Euglena, some blue-green algae) by decreasing their motility and by inhibiting phototactic and photophobic responses (refs. 33-34). This reduces the ability of a population to move into favorable environments, which could impair growth and development. Direct measurements of photosynthesisthat span only a single day could underestimate the overall action of solar UV exposure by failing to account for the next day's reduced population level. Due to growth delay or direct mortality, the subsequent population could fall below the numbers that an unexposed population would attain. Prolonged delays (about two days) in growth of the suwivors have been
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observed when two strains of the diatom Thalassiosira were irradiated with simulated solar UV-B radiation at doses below lethal levels (ref. 35). If unicellular organisms are in a rapid growth phase, a growth delay equalling the time of one growth cycle produces the same effect on the subsequent population as would be produced by 50% mortality (without growth delay). In Hawaii (USA) long-term photoinhibition of growth of six algal species under natural sunlight has been measured (ref. 36). Two strains could not grow at all at the levels of irradiance for full natural surface sunlight. Of the species tested, those collected from tropical surface water showed the greatest adaptive power, but it is reasonable to conclude that resistance to solar UV radiation is achieved through expenditure of resources that can be better applied to other needs in less exposed species. In marine microcosms enhanced UV-B radiation levels, simulating decreases in ozone of 15 percent, resulted in shifts of the species diversity and community composition of phytoplankton communities (ref. 37). Thus, in natural communities, a change in species composition rather than a decrease in net production might be a more likely result of an enhanced UV-B exposure. The decreased species diversity observed in simulated field studies is usually not accompanied by deleterious effects on biomass and chlorophyll accumulation, or by deleterious effects on total community primary productivity. However, a change in community composition might result in a more unstable ecosystem and might influence higher trophic levels (ref. 38). One effect of enhanced levels of UV-B radiation would be to alter the size distribution of the component producers in a marine ecosystem. Increasing or decreasing the size of the representative primary producers upon which consumers graze can significantly increase the energy allotment required from consumption, thereby reducing the feeding efficiency of the consumer. In addition, the food quality of the producers is altered by exposure to UV-B radiation. It has been demonstrated that the protein content, dry weight, and pigment concentration are all depressed by enhanced levels of UV-B radiation (refs. 39-42). ZOOPLANKTON Zooplankton are critical components in typical aquatic food webs (nutrient pathways) that lead to larger animals, including those comprising commercial fisheries (finfish and shellfish) and therefore man himself. With respect to potential impacts of enhanced solar UV-B radiation, only the zooplankton living in daylight in the upper several meters would be directly affected. Most zooplankton species are vertical migrators and normally spend a significant portion of their life very close to the surface. The near-surface layer is a very important zone in the interactions of the physical/chemical/biological components of aquatic systems. Zonplankton have apparently evolved mechanisms and behavior by which they have adjusted to current
273
levels of UV radiation (ref. 43), but they may not be able to adjust to relatively rapid increases in solar UV radiation. Ifthere were changes in abundance of zooplankton species, those changes would have an impact far beyond any direct effects because of the critical role of zooplankton in energy transfer within the ecosystem. Karanas et at. (refs. 44-45) presented evidence that acute exposure of a marine invertebrate zooplankton resulted in reduced survival of the organisms. They also showed that exposure of this species to sublethal exposures of UV-B radiation could also reduce the fecundity of the parents. It has been demonstrated that current levels of UV-B radiation significantly reduce the development of several species of shellfish (ref. 46). For some species a 10% decrease in total atmospheric ozone could lead to as much as an 18% increase in the number of abnormal larvae produced. Before feeding by zooplankton can begin, variations in exposure to UV-B radiation may cause stresses at various stages of egg and very early larval development, causing in the absence of behavioral avoidance responses significant numbers of mortalities or an alteration in time of occurrence at the surface. The matching in time of the onset of larval feeding and the spring phytoplankton bloomwhich, in turn, depends on climatic events for its timely occurrence-will, in fact, determine the sizes of year classes of grazers (ref. 47). FISHERIES Fish stocks suffer most from the vagaries of climate through the effects that changes in ambient conditions have on the larvae or their food source. The biological dynamics at the larval stages in the life cycles of fishes and aquatic invertebrates have a short-time horizon and are highly variable. Instant mortality coefficients during the larval stages range between 300 and 400, while they are 0.2 to 1.5 in the juvenile and adult stages (ref. 48). The most catastrophic and not all that rare event that can befall larvae is a mismatch in time between their food needs and the prevalence of their food (ref. 47). Larval stages last on the order of days. Small as the biomass of fishes is during very early life, their future numbers are largely determined then and not later in life, when the biomass is large and when the commercial fishery takes its toll. Hunter el al. (ref. 49) exposed anchovy eggs and larvae and mackerel larvae to high doses of UV-B radiation in small closed containers. Their data indicated that anchovy larvae off southern California are typically centered in moderately productive ocean water having about 0.5 rng Chl a m-3. Baker et al. (ref. 50) calculated surface DNA-effective UV-B irradiance levels expected for this area, and Smith and Baker (ref. 51) calculated the penetration of UV-B radiation into the moderately productive ocean water. Regardless of the cellular-level responses to UV irradiation, it is usually noted that up to some level of UV exposm there is no apparent effect on the target organism (refs. 52-53). At greater doses either the repair systems themselves may have become
274
inactivated by the radiation, or the damage to the general tissues is beyond the capacity of the repair systems (ref. 54). To be effective, these threshold levels probably must be exceeded during several consecutive days. The apparent UV thresholds are near current incident UV levels. The thresholds for all groups in one test appeared to be above the present median solar incident UV levels at the test location, at least until late in the time span of natural occurrence near the surface. This season could be significantly shortened by a 20% ozone reduction. Whether or not the populations could endure with a drastically reduced time of near-surface occurrence is not known. Success of any year-class depends on the timing of a great number of other events in addition to levels of exposure to UV-B radiation (ref. 49). Apparently at all months about 36% of the larval anchovy population is above 10 m (ref. 55). The greatest numbers of anchovy larvae are found in April (20% of annual population), so that, based on one experiment, 7.2% of the annual larval population would be eliminated with a 9% ozone decrease. Based on this experiment, the total predicted loss, due to a 9% decrease in total atmospheric ozone, would be about 8% of the larval anchovy population. Because of complex interactions between mixing-depths, vertical distribution of larval anchovy, seasonal changes in solar irradiance and the penetration of UV radiation into seawater, and seasonal changes in anchovy abundance, there is not a linear relationship between mixing-depth and predicted annual loss of anchovy larvae. In addition to the direct effects upon the fisheries, it is possible that with less primary production of organic biomass there would also be an increased mortality in larval fish due to food limitation. There may also be a synergistic effect on mortality such that some animals die from direct exposure, some die from lack of food, and some die from the combination of a reduction in food and the weakening from exposure (or are weakened and become outcompeted by other fauna for limited food reserves). The impact on marine fisheries as a food supply to humans would be significant if the species of phyto- and zooplankton to enhanced levels of UV-B radiation were of different nutritional value (if UV-B irradiation altered the growth and fecundity of the consumers). If the indirect impact of suppression upon consumers were linear, a 5% reduction of primary production would result in a 5% reduction in fish production. A question still under investigation is whether the trophodynamic relationships might be nonlinear. For example, there may be an amplification factor that results in a relatively greater impact at higher trophic levels than at the primary-producer level. As illustrated would give an annual yield of in Table 2, a 5% reduction in primary production (PI) 115 x 109 kg of fish flesh (a 5% reduction); whereas a 5% reduction in the ecological efficiency of energy transfer (e) would yield 103 x 109 kg of fish flesh (a 14% reduction).
275
TABLE 2 Annual fish production in coastal waters. Baseline data for coastal waters d from R W 56). Baseline Primary production, kJ m-2 y r l , (PI)
4200
-5% P i 4000
-5% e 4200
Ecological efficiency per trophic level, (e)
0.15
0.15
0.14
Number of trophic levels from plant production to fish production, (n)
3
3
3
Fish production, kJ m-2 y r l , (Pien)
14
13
12
Total fish production, lo9 kg y r 1 (using Winberg's transformation, 4.2 kJ = 1 g fish flesh)
121
115
103
(95%)
(86Yo)
Percentage of baseline fish production
(100%)
The recovery of a depleted fishery population may require many years, even if catches are prohibited in the meanwhile. Economic survival of the existing resource industry may, however, depend upon continuing catches, even though these will delay rebuilding of the stock and perhaps increase the probability of the population's collapse. In the language of the mathematical theory of games, common-property resource exploitation has the characteristics of the so-called 'prisoner's dilemma'. SUMMARY AND CONCLUSIONS Various experiments have demonstrated that UV-B radiation causes damage to fish larvae and juveniles, shrimp larvae, crab larvae, copepods, and plants essential to the aquatic food web. These damaging effects include decreases in fecundity, growth, survival and other functions of these organisms. In natural marine plant communities a change in species composition rather than a decrease in net production is the probable result of enhanced UV-B exposure. A change in community composition may result in a more unstable ecosystem and would likely have an influence on higher trophic levels. A decrease in total atmospheric ozone would shorten the season of greatest abundance for near-surface zooplankton. Whether the population could endure a significant shortening of this season is unknown. The direct effect of UV-B radiation on food-fish larvae closely parallels the effect on invertebrate zooplankton. Information is required on seasonal abundances and vertical distributions of fish larvae, vertical mixing, and penetration of UV-B radiation
276
into appropriate water columns before effects of incident or increased levels of exposure to UV-8 radiation can be predicted. However, in one study involving anchovy larvae, a 20% increase in incident biologically damaging UV-8 radiation (a result of about a 9% decrease in the total atmospheric ozone) would result in all of the larvae within a 10-meter mixed layer in April and August being killed after 15 days. It was calculated that about 8% of the annual larval population throughout the entire water column would be directly killed by a 9% decrease in total atmospheric ozone. The usual effects of many environmental stresses are changes in overall productivity and reductions in species diversity. Diversity is often associated with stability in ecosystems, allowing alternate routes and choices within food webs. In field situations under slight stress, one often cannot measure changes in productivity or size of specific populations, but sometimes changes in species diversity can indicate that adverse effects are occurring. With loss of species an ecosystem may lose some of its natural resiliency and flexibility. In aquatic ecosystems we must consider a great number of species, with different life stages and different trophic levels. With increased knowledge of ecosystems and the physicakhemical environment, the effects of enhanced solar UV radiation on single species could be placed in perspective. Many of the changes that occur in marine ecosystems as a result of natural or man-made events occur on time scales of tens of years. The changes may be associated, in some general context, with gradual climatic trends, but ecological changes seem to occur quite rapidly, with relatively persistent communities existing in the intervening periods. In any region rather than having one 'ecosystem', there are two, or possibly several, alternatives-each resilient to some range of variability but capable of being replaced if some factors in the environment pass a threshold. To this natural episodic response, we must now add the effects of anthropogenic perturbations such as enhanced UV-B stress. The evidence suggests that we shall continue to have such changes but shall have added questions of attributing cause to natural stresses or to stresses resulting from human activities. Although we may not be able to predict when, or possibly why, such changes occur, they can be regarded as alternative ecological solutions. Once again, whether we consider these changes deleterious or beneficial is a matter of human values, but we must keep in mind that these problems are occurring on a global scale. This manuscript has been reviewed in accordance with the U.S. Environmental Protection Agency's peer and administrative review policies and approved for presentation and publication.
277
REFERENCES
I 2 3 4 5 6
7 8 9 10 11 12 13 14 15 16 17 18 19 20
21 22 23
24 25 26 27 28 29 30 31
32
R.H. Whittaker and G.E. Likens, in H. Lieth and R. H. Whittaker (Eds.), Primary Productivity of the Biosphere. Ecological Studies 14, Spnnger-Verlag, Berlin, Heidelberg, New York, 1975, pp. 305-328. K.H. Mann, Science, 182 (1973) 975-981. H. Lieth, in H. Lieth and R. H.Whittaker (Eds.), Primary Productivity of the Biosphere. Ecological Studies 14, Springer-Verlag, Berlin, Heidelberg, New York, 1975, pp. 203-215. A.G. Huntsman, Contrib. Can. Biol., 2 (1925) 83-88. A.B. Klugh, Can. J. Res., 1 (1929) 100-109. A.B. Klugh, Can. J. Res., 2 (1930) 312-317. J.M. Harvey, Contnb. Can. Biol., 5 (1930) 85-92. C.E. ZoBell and G.F. McEwen, Biol. Bull., 68 (1935)93-106. A.C. Giese, Biol. Bull., 75 (1938)238-247. G.M. Bell and W.S. Hoar, Can. J. Res., 28 (1950) 35-43. C.E. Dunbar, Progr. Fish Cult., 21 (1959)74. J.Y. Marinaro, and M. Bernard, Pelagos, 6 (1966)49-55. National Research Council, Causes and Effects of Changes in Stratospheric Ozone: Update 1983, National Academy Press, Washington, D.C.,.I 984 J. Calkins, in J. Calkins (Ed.), The Role of Solar Ultraviolet Radiation in Marine Ecosystems, Plenum, New York, 1982, pp. 685-689. R.C. Worrest, in J. Calkins (Ed.), The Role of Solar Ultraviolet Radiation in Marine Ecosystems, Plenum, New York, 1982, pp. 429-457. R.C. Worrest, in V. Covello et al. (Eds.), The Analysis of Actual Versus Perceived Risks, Plenum, New York, 1983, pp. 303-315. R.C. Worrest, Physiol. Plant., 58 (1983) 428-434. R.C. Worrest, in J. G. Titus (Ed.), Effects of Changes in Stratospheric Ozone and Global Climate, Vol. 1 : Overview, United States Environmental Protection Agency and United Nations Environment Programme, 1986, pp. 175-191. M.M. Caldwell, in A.C. Giese (Ed.), Photophysiology, Vol. 6, Academic Press, New York, 1971, pp. 131-177. T. Murphy, in D. S. Nachtwey, M. M. Caldwell, and R. H. Biggs (Eds.), Impacts of Climatic Change on the Biosphere, Part I - Ultraviolet Radiation Effects, U.S. Dept. Transport. Climatic Impact Assessment Program, Monogr 5, NTIS, Springfield, Virginia, 1975, pp. (1)3-(1)30. A.C. Giese, Living with Our Sun's Ultraviolet Rays, Plenum, New York, 1976. L. Cheng, M. Douek and D. Goring, Limnol. Oceanogr., 23 (1978) 554-556. M.M. Caldwell, L.B. Camp, C.W. Warner and S.D. Flint, in R. C. Worrest and M. M. Caldwell (Eds.), Stratospheric Ozone Reduction, Solar Ultraviolet Radiation and Plant Life, Springer-Verlag, Berlin, Heidelberg, New York, Tokyo, 1986, pp. 87111. R.B. Setlow, Proc. Natl. Acad. Sci. (USA), 71 (1974) 3363-3366. M.M. Caldwell, Ecol. Monogr., 38 (1968) 243-268. E. Steemann Nielsen, J. Cons. Cons. Int. Explor. Mer, 20 (1964) 130-135. H.R. Jitts, A. Morel and Y. Saijo, Aust. J. Mar. Freshwater Res., 27 (1976) 441-454. L. Hobson and F. Hartley, J. Plankton Res., 5 (1983) 325-331. R.C. Smith, K.S. Baker, 0. Holm-Hanson and R. Olson, Photochem. Photobiol. 31 (1980) 585-592. W.D. Russell-Hunter, Aquatic Productivity, MacMillan, 1970. J. Calkins and M. Blakefield, in J.G. Titus (Ed.), Effects of Changes in Stratospheric Ozone and Global Climate, Vol. 2: Stratospheric Ozone, United States Environmental Protection Agency and United Nations Environment Programme, 1986, pp. 21 1-235. B.E. Thomson, R.C. Worrest and H. Van Dyke, Estuaries 3 (1980) 69-72.
33 D.-P. Hader, in R. C. Worrest and M. M. Caldwell (Eds.), Stratospheric Ozone Reduction, Solar Ultraviolet Radiation and Plant Life, Springer-Verlag, New York, Heidelberg, Berlin, 1986, pp 223-233. 34 D.-P. Hader, in J.G. Titus (Ed.), Effects of Changes in stratospheric Ozone and Global Climate, Vol. 2: Stratospheric Ozone, United States Environmental Protection Agency and United Nations Environment Programme, 1986, pp. 197201. 35 J. Calkins, in J. Calkins (Ed.), The Role of Solar Ultraviolet Radiation in Marine Ecosystems, Plenum, New York, 1982, pp. 651-661. 36 P.L. Jokiel and R.H. York, Jr., Limnol. Oceanogr., 29 (1984) 192-199. 37 R.C. Worrest, B.E. Thomson and H. Van Dyke, Photochem. Photobiol., 33 (1981) 861-867. 38 J.R. Kelly, in J.G. Titus (Ed.), Effects of Changes in Stratospheric Ozone and Global Climate, Vol. 2: Stratospheric Ozone, United States Environmental Protection Agency and United Nations Environment Programme, 1986, pp. 237251. 39 G. Dohler, Z. Naturf., 39 (1984) 634-638. 40 G. Dohler, J. Plant Physiol., 118 (1985) 391-400. 41 G. Dohler and I. Biermann, J. Plankton Res., 9 (1987) 881-890. 42 G. Dohler, R.C. Worrest, I. Biermann and J. Zink, Physiol. Plantarum., 70 (1987) 51 1-515. 43 D.M. Damkaer, in J. Calkins (Ed.), The Role of Solar Ultraviolet Radiation in Marine Ecosystems, Plenum, New York, 1982, pp. 701-706. 44 J.J. Karanas, H. Van Dyke and R.C. Worrest, Limnol. Oceanogr., 24 (1979) 11041116. 45 J.J. Karanas, R.C. Worrest and H. Van Dyke, Mar. Biol., 65 (1981) 125-133. 46 B.E. Thomson, in J.G. Titus (Ed.), Effects of Changes in Stratospheric Ozone and Global Climate, Vol. 2: Stratospheric Ozone, United States Environmental Protection Agency and United Nations Environment Programme, 1986, pp. 203209. 47 D.H. Cushing, Symp. Zool. SOC.London, 29 (1972) 213-232. 48 B.J. Rothschild, BioScience, 31 (1981) 216-222. 49 J.R. Hunter, S.E. Kaupp and J.H. Taylor, in J. Calkins (Ed.), The Role of Solar Ultraviolet Radiation in Marine Ecosystems, Plenum, New York, 1982, pp. 459497. 50 K.S. Baker, R.C. Smith and A.E.S. Green, Photochem. Photobiol., 32 (1981) 367374. 51 R.C. Smith and K.S. Baker, Photochem. Photobiol., 29 (1979) 311-323. 52 D.M. Damkaer, D.B. Dey, G.A. Heron and E.F. Prentice, Oecologia, 44 (1980) 149158. 53 D.M. Damkaer and D.B. Dey, in J. Calkins (Ed.), The Role of Solar Ultraviolet Radiation in Marine Ecosystems, Plenum, New York, 1982, pp. 417-427. 54 D.M. Damkaer and D.B. Dey, Oecologia, 48 (1983) 178-182. 55 J.R. Hunter, S.E. Kaupp and J.H. Taylor, Photochem. Photobiol., 34 (1981) 477486. 56 J.H. Rylher, Science, 166 (1969) 72-76.
279
SESSION IV
EMERGING HEALTH STUDY METHODOLOGIES AND ISSUES
Chairmen
R. Kroes F.G. Hueter
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T. Schneider et ol. (Editors ), Atmospheric Ozone Research and i t s Policy Implications 1989 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands
28 1
CRITICAL ISSUES I N INTRA- AND INTERSPECIES DOSIMETRY OF OZONE
FREDERICK J. MILLER and JOHN H. OVERTON H e a l t h E f f e c t s Research Laboratory, U.S. Environmental P r o t e c t i o n Agency, MD 66, Research T r i a n g l e Park, N o r t h C a r o l i n a 27711 ( U S A )
ABSTRACT Knowledge o f dose a t t h e t a r g e t s i t e i s a fundamental s t a r t i n g p o i n t i n making i n t e r s p e c i e s d o s i m e t r i c comparisons. To t h e e x t e n t t h a t i n f o r m a t i o n i s a v a i l a b l e on t h e e f f e c t i v e dose o f a compound, o u r c o n f i d e n c e i n r i s k assessments i s increased. To f a c i l i t a t e judgments about e f f e c t s determined i n animals r e l a t i v e t o l i k e l i h o o d o f r i s k a s s o c i a t e d w i t h human exposure t o ozone ( O 3 ) , a mathematical d o s i m e t r y model has been developed f o r i n t e r s p e c i e s comparlsons. The model i n c o r p o r a t e s t h e major f a c t o r s a f f e c t i n g t h e a b s o r p t i o n of 0 3 i n t h e r e s p i r a t o r y t r a c t : t h e morphology o f t h e r e s p i r a t o r y t r a c t , t h e r o u t e , depth and r a t e o f b r e a t h i n g , physicochemical p r o p e r t i e s o f 03, t h e p h y s i c a l and chemical processes which govern gas t r a n s p o r t , and t h e physlcochemical p r o p e r t i e s o f t h e l i n i n g f l u i d s and t i s s u e m a t e r i a l o f t h e airways and gas exchange u n i t s . T h i s model i s used t o i d e n t i f y i s s u e s c r i t i c a l l y i m p o r t a n t t o t h e modeling process i t s e l f , such as model v a l i d a t i o n and modeling uptake o f 03 i n t h e head. A l s o discussed a r e t h e a p p l i c a t i o n o f t h e dosimetry model f o r examining age-dependent s u s c e p t i b i l i t y t o 03 and t h e p o t e n t i a l u s e f u l n e s s o f such models f o r r e l a t i n g m i c r o d o s i m e t r y t o m l c r o t o x l cology. INTRODUCTION
Ozone i s a u b i q u i t o u s a i r p o l l u t a n t .
In t h e United States, m i l l i o n s o f
people a r e exposed t o 03 l e v e l s t h a t exceed t h e c u r r e n t N a t i o n a l Ambient A i r Q u a l i t y Standard (NAAQS) of 0.12 t h a n once per year.
ppm for one hour, n o t t o be exceeded more
Recently, t h e need f o r an e i g h t - h o u r 0 3 s t a n d a r d has
been advocated s i n c e l a r g e segments o f t h e p o p u l a t i o n may b e r o u t i n e l y exposed f o r extended p e r i o d s t o 03 l e v e l s j u s t below t h o s e o f t h e c u r r e n t 1-hour standard ( r e f .
1).
The r a t i o n a l e f o r such a recommendation i s based m a i n l y
upon: 1 ) well-documented biochemical and f u n c t i o n a l e f f e c t s i n l a b o r a t o r y animals and man a s s o c i a t e d w i t h b r i e f exposures t o 03 ( r e f . 2), and 2 ) a concern t h a t long-term exposure t o e l e v a t e d 03 l e v e l s may p o s s i b l y l e a d t o t h e development of c h r o n i c l u n g diseases.
W h i l e v a r i o u s m o r p h o l o g l c and
Disclaimer: T h i s paper has been reviewed by t h e H e a l t h E f f e c t s Research Laboratory, U.S. Environmental P r o t e c t i o n Agency, and approved f o r p u b l i c a tion. Mention o f t r a d e names o r commercial p r o d u c t s does n o t c o n s t i t u t e endorsement or recommendatlon f o r use.
282 h i s t o p a t h o l o g i c changes have been observed i n a n i m a l s exposed s u b c h r o n i c a l l y and c h r o n i c a l l y t o 03 ( r e f .
2,
3, 41, whether such changes l e a d t o i r r e v e r s i -
b l e disease has n o t y e t been e s t a b l ished. logy, human c l i n i c a l s t u d i e s ,
Among t h e f i e l d s o f epidemio-
and animal t o x i c o l o g y ,
animal s t u d i e s can
p r o v i d e t h e most complete d a t a on t h e a r r a y o f e f f e c t s a s s o c i a t e d w i t h c h r o n i c exposure. Mathematical models have been developed ( r e f .
5,
6 ) f o r use i n i n t e r -
s p e c i e s comparisons o f dose when a s s e s s i n g t h e r e l e v a n c e and I m p l i c a t i o n o f r e s u l t s from animal s t u d i e s f o r t h e l i k e l i h o o d o f s i m i l a r e f f e c t s o c c u r r i n g a t 03 l e v e l s t o which humans a r e exposed.
While advances have been made i n
our u n d e r s t a n d i n g o f t h e r e s p i r a t o r y t r a c t d o s i m e t r y o f 03, v a r i o u s t o p i c s r e l a t i v e t o t h e models per se, t o t h e i n p u t d a t a r e q u i r e d by t h e models, and t o model a p p l i c a t i o n must b e addressed i n l i g h t o f t h e i n c r e a s e d u t i l i z a t i o n o f t h e s e models t o make i n t r a - and i n t e r s p e c i e s d o s i m e t r l c comparisons.
A
d i s c u s s i o n of some o f t h e s e t o p i c s i s t h e i n t e n t o f t h i s paper.
DOSIMETRY MODEL:
FORMULATION AND COMPUTER SIMULATION
D e t a i l e d d e s c r i p t i o n s a r e a v a i l a b l e elsewhere ( r e f . d o s i m e t r y model used i n t h i s paper.
Here,
5,
6, 7 ) o f t h e 03
a b r i e f d e s c r i p t i o n o f t h e model
f o r m u l a t i o n s and t h e computer s i m u l a t i o n program i s p r o v i d e d t o i n f o r m t h e r e a d e r o f t h e n a t u r e o f t h e d o s i m e t r y model and a p p l i c a t i o n s o f it. Major f a c t o r s a f f e c t i n g t h e u p t a k e o f 03 a r e t h e morphology o f t h e r e s p i r a t o r y t r a c t , t h e route,
depth,
and r a t e o f b r e a t h i n g ,
physicochemical proper-
t i e s o f 03, t h e p h y s i c a l processes g o v e r n i n g gas t r a n s p o r t , and t h e p h y s i c o chemical p r o p e r t i e s o f t h e r e s p i r a t o r y t r a c t l i n i n g f l u i d s and t i s s u e o f t h e a i r w a y s and gas exchange u n i t s .
The complex i n t e r a c t l o n o f t h e s e f a c t o r s
determines t h e dose d e l i v e r e d t o t a r g e t s i t e s w i t h i n t h e r e s p i r a t o r y t r a c t . Although i t i s d e s i r a b l e t o c o n s i d e r as many as p o s s i b l e o f t h e above f a c t o r s i n d e v e l o p i n g a s i m u l a t i o n model, simp1 i f y l n g assumptions and s t r u c t u r e s a r e o f t e n r e q u i r e d t o make t h e modeling problem t r a c t a b l e . Species lung dimensions a r e t a k e n i n t o a c c o u n t u s i n g anatomical or a i r w a y models such as t h o s e a v a l l a b l e f o r t h e r a t ( r e f . (ref.
9).
In t h e s e models,
8) and for man
lower r e s p i r a t o r y t r a c t (LRT) a i r w a y s a r e charac-
t e r i z e d b y a sequence o f s e t s of r i g h t c i r c u l a r c y l i n d e r s . r e s p i r a t o r y t r a c t (URT) r e g i o n i s i n c l u d e d , r a t i o n s " o r s e q u e n t i a l segments.
I f t h e upper
I t c o n s l s t s o f p r e t r a c h e a l "gene-
Data on t h e number o f a i r w a y s or segments
and t h e i r d i a m e t e r s and l e n g t h s a r e needed f o r each g e n e r a t i o n o r segment i n t h e model r e s p i r a t o r y t r a c t .
Also,
e s t i m a t e s o f a l v e o l a r volumes and
s u r f a c e a r e a s must b e a v a i l a b l e for t h e pulmonary r e g i o n , w h i l e s u r f a c e a r e a and volume e s t i m a t e s a r e needed for URT segments.
283 Given t h e 03 concentration a t t h e f i r s t model segment (e.g.,
nose,
mouth, o r trachea), t h e model simulates t h e t r a n s p o r t and absorption o f 03 i n each airway,and a l v e o l a r space o f t h e a n a t m l c a l model d u r l n g one o r more breaths.
During t h e simulated b r e a t h l n g cycle, changes I n lung volume a r e
accounted f o r by l s o t r o p l c a l l y v a r y l n g t h e l i n e a r dlmenslons o f t h e LRT a l r way generations.
Volume f l o w r a t e s can be simulated d u r l n g b r e a t h l n g based
e i t h e r upon experimental data o r upon an assumed time-dependent f u n c t l o n . Gas t r a n s p o r t I n t h e lumen and a i r spaces, as w e l l as chemical r e a c t l o n s and t r a n s p o r t I n t h e l i q u i d I l n l n g , t i s s u e , and blood compartments,
Is taken
i n t o account i n t h e s l m u l a t l o n model v l a p a r t i a l d l f f e r e n t l a l equations.
The
complex s e r i e s o f r e a c t i o n s o f 03 w l t h v a r i o u s b i o l o g i c a l c o n s t l t u e n t s I s s i m p l l f i e d t o one r e a c t i o n i n v o i v l n g an e f f e c t l v e second-order
r a t e constant
and t h e o v e r a l l constant c o n c e n t r a t i o n o f chemical components ( r e s u l t i n g I n a pseudo f i r s t order r e a c t i o n ) t h a t r e a c t w l t h 03. conditions,
Given l n l t i a l and boundary
I n a d d i t i o n t o values f o r t h e physical, chemical, and b l o l o g l c a l
parameters o f t h e model, t h e s o l u t i o n s o f t h e equatlons p r o v i d e p r e d i c t e d 03 doses f o r each model compartment I n any given a n a t m l c a l generatlon.
Conse-
quently, r e s p i r a t o r y t r a c t p a t t e r n s can be compared among various animal species and man f o r s p e c i f i e d 03 concentrations. CRITICAL ISSUES
Model V a l i d a t i o n The usefulness o f doslmetry models t o r i s k assessment and e x t r a p o l a t l o n modeling depends t o a l a r g e e x t e n t on t h e degree t o whlch model p r e d i c t l o n s agree w i t h t h e r e s u l t s o f experlments.
U n t l l r e c e n t l y t h e r e was v e r y I l t t l e
experlmental data a v a i l a b l e f o r 03; however, technlques have been and a r e being developed t o measure t h e uptake and d l s t r l b u t l o n of 03 I n t h e r e s p l r a t o r y t r a c t o f humans and animals ( r e f . 10, 1 1 ) . ( r e f . 10) f o r r a t s and o f G e r r i t y e t at.
The d a t a of Wlester e t a1
( r e f . 1 1 ) f o r humans c h a r a c t e r l z e
t h e t o t a l uptake and t h e URT and LRT uptakes o f 03, r e s p e c t i v e l y .
However,
these data a r e i n s u f f i c i e n t t o I n f e r t h e d l s t r l b u t l o n of absorbed 03 w l t h l n t h e tracheobronclal (TB) and pulmonary r e g l o n s o f t h e LRT.
P o s l t l o n emlsslon
tomography and isotope r a t l o mass spectroscopy a r e experlmental methodologies t h a t may a l l o w t h e determination o f t h e d i s t r l b u t l o n o f absorbed 0 3 I n speclf l e d regions o f anlmals and humans.
The r e s u l t s of a l l these experlmental
approaches w i l l a l l o w f o r t h e refinement o f t h e values o f t h e p h y s l o l o g l c a l parameters used i n doslmetry models, r e s u l t l n g I n more accurate p r e d i c t i o n s and an Increased confidence I n doslmetry model r e s u l t s .
284 Accounting f o r 03 Loss I n t h e URT Because t h e URT can remove as much as f o r t y percent ( r e f . 1 1 ) and p o s s i b l y more o f 0 3 from i n s p i r e d a l r , t h i s r e g i o n p l a y s a major r o l e I n t h e dose o f 03 d e l l v e r e d t o d i f f e r e n t l o c a t l o n s I n t h e LRT.
The major e f f e c t o f
t h e URT i s t o reduce t h e q u a n t i t y o f 03 t h a t penetrates t o t h e LRT; however, t h e e f f e c t on t h e r e l a t i v e d i s t r i b u t i o n o f absorbed 0 3 I s probably minor (ref.
12).
Modeling uptake I n t h e LRT by o n l y s p e c i f y i n g an e m p i r i c a l l y
derived concentratlon a t t h e t r a c h e a l entrance can lead t o l a r g e e r r o r s I n p r e d l c t e d LRT dose, depending on specles and magnltude o f URT removal ( r e f . 12).
Thus, a complete r e s p l r a t o r y t r a c t model t h a t a c c u r a t e l y p r e d l c t s URT
uptake f o r a wide range o f v e n t i l a t o r y parameters and specles i s necessary. One way t o account f o r URT removal i s t o use a simple chamber t h a t removes t h e a p p r o p r i a t e q u a n t l t y o f 0 3 (determined by experiments) I n t h e animal species belng modeled.
A t t h e o t h e r extreme, v a l l d a t e d mathematical models
t h a t take I n t o account t h e complex URT anatomy and p h y s l o l o g l c a l processes o f 03 removal could be used.
In e l t h e r case, experiments conducted s p e c i f i c a l l y
t o c h a r a c t e r l z e uptake by t h e URT o f l a b o r a t o r y animals and humans a r e c r i t i c a l l y needed.
Age S u s c e p t l b l l l t y t o Ozone I n 1974, B a r t l e t t and coworkers ( r e f . 13) suggested t h a t young anlmals have an increased s e n s i t l v l t y t o 03, although t h e experlrnental design o f t h e l r s t u d i e s d i d n o t r e a l l y p r o v i d e t h e a p p r o p r l a t e framework f o r such an Inference. Biochemical changes I n t h e lung have been more r e a d i l y observed i n neonatal and young animals than i n o l d e r animals ( r e f . 14,151.
On t h e o t h e r hand,
postnatal r a t s a r e r e s i s t a n t t o 0 3 exposure u n t l l weaning ( r e f . 16).
In
s t u d i e s comparlng t h e e f f e c t s o f 0.12 ppm and 0.25 ppm 03 on t h e proximal a l v e o l a r r e g i o n o f j u v e n l l e and a d u l t r a t s , B a r r y e t a l .
( r e f . 3) found no
s t a t i s t l c a l l y s l g n l f i c a n t age-dependent e f f e c t s on a m u l t l t u d e of morphom e t r l c measures o f volume, s u r f a c e area, and d e n s l t l e s o f c e l l s and o t h e r t i s s u e components.
However, e f f e c t s l n d l c a t i v e o f e p i t h e l i a l i n j u r y were
a t t r i b u t a b l e t o 0 3 even a t t h e 0.12 ppm exposure l e v e l I n b o t h j u v e n i l e and adult rats. In humans, t h e r e I s evidence from epidemiological and f i e l d s t u d i e s t h a t e x e r c i s i n g c h i l d r e n and adolescents may experience decrements i n pulmonary f u n c t l o n when exposed t o amblent l e v e l s o f 03 below t h e p r e s e n t NAAQS o f 0.12 ppm d u r i n g normal a c t l v l t l e s ( r e f . 17,18).
However, expo-
sures o f a d u l t s f o r two hours w i t h I n t e r m i t t e n t heavy e x e r c i s e t o 0.1 does n o t a l t e r pulmonary f u n c t i o n ( r e f . 19).
ppm 03
285 While t h e above s t u d i e s would appear t o support an a s s e r t i o n t h a t c h i l d r e n are more s e n s l t l v e t o 03 than adults, t h e s t u d l e s do n o t p r o v l d e a d e f l n i t l v e answer s l n c e b o t h groups were n o t examlned under comparable condltlons.
To date, o n l y McDonnell and coworkers ( r e f . 20) have compared t h e
e f f e c t s o f 03 exposure on t h e pulmonary f u n c t l o n o f c h l l d r e n and non-smoklng adults, normallzlng t h e e x e r c l s e f o r body s i z e t o y l e l d a mlnute v e n t l l a t l o n
( V E ) o f approxlmately 35 l i t e r s per min per square meter o f body s u r f a c e area
.
Demographlc, d e s c r l p t l v e s t a t l s t l c a l , and r e s p l r a t o r y f u n c t l o n data from t h e M c b n n e l l e t a l . ( r e f . 20) study a r e given I n Table 1.
Wlth r e s p e c t
t o t h e t y p i c a l l y r e p o r t e d measurements o f forced v i t a l capacity (FVC) and forced e x p i r a t o r y volume I n one second (FEVI), t h e r e appears t o be a simll a r l t y i n response t o 0.12 ppm 03 between c h l l d r e n and a d u l t s f o r l e v e l s o f exerclse y l e l d l n g comparable VE normalized f o r body s u r f a c e area (BSA). However, w l t h respect t o t h e r e p o r t l n g o f cough as a symptom associated w l t h t h e 0 3 exposure, a d u l t s experlenced a s l g n l f l c a n t Increase (p<0.005) c h i l d r e n d i d n o t (p=0.16).
while
As McDonnelI e t a l . ( r e f . 20) note, c h i l d r e n
appear t o be less responsive t o 0 3 r e g a r d l n g t h e l n d u c t l o n o f cough.
TABLE 1 A comparison o f t h e e f f e c t s o f 0.12 PPm O3 I n c h l l d r e n and a d u l t s a
Ch I I dren 9.9 141
Age ( y r s ) Height (cm)
Alr Heart r a t e (beats/mln) VE (I/mln) VE /BSA (I/min/m2) FVC ( % ) FEVl ( $ ) Cough
158
2
Adu I t s 22.5 180
Ozone
13
38.2 32.4
+
-0.1 -0.5 0.0
+ 0.7 1.1 2 0.1
6.2 3.3
158 39.4 33.3
2
15
+
7.4 3.4
-1.8 t 0.7 -3.4 1.1 0.1 2 0.2
-P
Alr 166
0.08 0.03 0.16
2
p
Ozone
10
163
66.2 t 7.6 34.9 3.1
68.0 34.3
-0.9 t 0.4 -1.1 0.5 0.1 2 0.0
-4.3
2
12
z+
7.4 2.9
-3.1 + 1.1 0.8
2
0.04 1 1 0.02 0 2 (0.005
aThis t a b l e was constructed fran Tables 2 and 3 o f McDonnell e t a l . ( r e f . 20). Slgn 1 f 1Sample s i z e s vary between 17 and 23 f o r t h e e n t r i e s I n t h e t a b l e . cance p r o b a b i l l t l e s (P) f o r c h i l d r e n were determfned usfng p a i r e d - t e s t s and f o r a d u l t s uslng non-parametric WIIIlams' t e s t s . How do doslmetry modellng p r e d l c t l o n s o f 03 dose compare f o r t e ages and exerclse l e v e l s used by McDonnell e t a l . ( r e f . 20)?
Overton and Graham
( r e f . 21) u t l l l z e d several sources o f data on age-dependent LRT volumes, agedependent alrway dlmenslons, an a d u l t tracheobronchlal r e g i o n model,
and a
model o f t h e a d u l t pulmonary aclnus t o c o n s t r u c t t h e o r e t l c a l LRT lung models f o r humans from b l r t h t o adulthood.
They then used an ozone doslmetry
286 model ( r e f . 5, 6 ) t o estlmate dose p a t t e r n s I n t h e v a r l o u s anatomlcal models. Uslng t h e same procedure and doslmetry model, we have slmulated t h e absorption o f 03 I n c h l l d r e n and a d u l t s n o t o n l y w i t h t h e average ages and v e n t l l a t o r y parameters t h a t correspond t o t h e s u b j e c t s I n t h e McDonnelI e t a l ( r e f . 20) l n v e s t l g a t l o n , b u t a l s o for these ages undergoing q u l e t b r e a t h i n g . In F l g u r e l A , t h e LRT dose p a t t e r n s f o r doses from t h e trachea t o t h e most d i s t a l a l v e o l l are shown f o r t h e 9.9
and 22.5 year o l d s d u r l n g q u l e t
breathing and f o r heavy e x e r c l s e w l t h VE equal t o t h a t glven by McDonnelI e t a l . ( r e f . 20) f o r t h e two age groups.
F l g u r e l B , from r e f e r e n c e 21,
I I l u s t r a t e s dose p a t t e r n s f o r two "extreme" ages ( b i r t h and a d u l t ) and
0 2 4 6 8 101214161820222426
GMAATIONS
A
0 2 4 6 8 101214161820222426 GENERATIONS
3
0 2 4 6 8 10121416182022241
0 2 4 6 8 101214181~2022241
eEHRITIoNs
SENERATIOHS
B
Flg. 1. Net and t i s s u e dose versus generatlon. The f l g u r e s I l l u s t r a t e t h e e f f e c t o f several b r e a t h l n g s t a t e s and d l f f e r e n t ages on t h e d l s t r l b u t l o n o f absorbed ozone I n t h e r e s p l r a t o r y t r a c t o f humans, given t h a t t h e t r a c h e a l ozone c o n c e n t r a t l o n s are equal. TB and P l n d l c a t e tracheob r o n c h l a l r e g l o n and pulmonary r e g l o n , r e s p e c t l v e l y . Flg. 1A. Ventllat o r y parameters and ages based on M c b n n e l l e t a t . ( r e f . 20). Flg. 18. tlExtreme" age and vent1 l a t o r y parameters used (based on r e f . 21, w l t h permlsslon).
breathing s t a t e s ( q u i e t and maximal breathing).
Both n e t ( t h e t o t a l 03
removed i n t h e l i q u i d l i n i n g , t i s s u e , and blood) and t i s s u e dose curves are depicted I n t h e figures.
The d e f i n i t i o n o f dose I s t h e q u a n t i t y o f 03
absorbed per minute per u n i t area f o r a given generation and cunpartment(s) d i v i d e d by t h e amblent 03 concentration.
Only t h e t i s s u e dose i s depicted
f o r t h e pulmonary r e g i o n because, here, t i s s u e dose i s e s s e n t i a l l y e q u i v a l e n t t o n e t dose,
d i f f e r i n g by a few percent due t o absorption o f 03 I n t h e blood
and n e g l i g i b l y i n t h e l i q u i d l i n i n g . According t o Fig.
lA.,
t h e LRT dose p a t t e r n s f o r q u i e t b r e a t h i n g and f o r
heavy e x e r c i s e ( V E normalized t o body s u r f a c e area) a r e e s s e n t i a l l y t h e same f o r t h e 10 and 22 y r o l d .
Fig. 18 c o n t r a s t s LRT dose p a t t e r n s f o r t h e I n f a n t
compared t o t h e a d u l t f o r q u i e t b r e a t h i n g and maximal exercise.
The TB doses
are independent o f age; however, major d i f f e r e n c e s i n t i s s u e dose occur i n t h e pulmonary r e g i o n as a f u n c t i o n o f age and l e v e l of a c t i v i t y .
With
q u i e t b r e a t h i n g t h e I n f a n t receives, on t h e average, a s i g n i f i c a n t l y g r e a t e r pulmonary t i s s u e dose o f 03 than does t h e adult.
Although n o t depicted I n
F i g . lB, t h e pulmonary dose curves f o r o t h e r ages between i n f a n t and a d u l t g e n e r a l l y f a l l between t h e two q u i e t b r e a t h i n g curves w i t h dose per generat i o n decreasing w i t h increasing age ( r e f . 21).
In c o n t r a s t t o q u i e t breath-
ing, a t maximal work most pulmonary generations i n t h e a d u l t lung r e c e i v e a greater del ivered dose o f 03 compared t o t h e i n f a n t .
In t h e f i r s t t o t h e
middle p o r t i o n o f t h e pulmonary generations dose Increases w i t h age; between t h e 22nd and 24th generations t h e age-specific curves cross so t h a t dose decreases as age increases. I n view o f t h e above, (FVC,
it i s apparent t h a t i f pulmonary f u n c t l o n changes
F E V l ) a r e mediated through r e c e p t o r s i n t h e TB or I n t h e pulmonary
region, then, based on McDonnelI e t a t . ( r e f . 20) and from a d o s i m e t r i c viewpoint, c h i l d r e n and a d u l t s should be e q u a l l y s e n s i t i v e t o 03 d u r i n g exercise i n which t h e i r V E ' S ,
normalized t o body s u r f a c e area, a r e equal.
However, s i n c e very young (preschool) c h i l d r e n exposed d u r i n g normal r e s p l r a t i o n o r l i g h t a c t i v i t y a r e l i k e l y t o r e c e i v e g r e a t e r pulmonary doses o f
03 than adults, t h e p o t e n t i a l f o r e f f e c t s on t h e pulmonary f u n c t i o n o f these c h i l d r e n may be greater.
I t should be noted t h a t t h e p o s s i b l e v a l i d i t y
o f t h e above inferences a r e l i m i t e d t o assumption o f upper r e s p i r a t o r y t r a c t removal of 03, mucous composition, mucus thickness, e t c . being t h e same i n c h i l d r e n and adults. Microdosimetry o f 03 f o r T o x i c o l o g i c a l Assessments I n t h e c o n t e x t o f t h i s section, microdosimetry r e f e r s t o e s t i m a t i n g t h e
03 dose t o more l o c a l i z e d areas w i t h i n t h e lung such as a s p e c i f i c pulmonary
288 aclnus o r along a glven path from t h e trachea.
The c r l t l c a l Importance of
v a l l d a t l n g mathematlcal doslmetry models was dlscussed e a r l l e r .
Obviously,
t h e more complex t h e model and t h e more l o c a l i z e d one wlshes t o p r e d l c t dose, t h e more d l f f l c u l t It may be t o o b t a l n model v a l l d a t l o n .
However,
t h l s should n o t a c t as a d e t e r r a n t t o v a l l d a t l n g models and t o uslng them t o examlne l o c a l l z e d dose and correspondlng t o x l c o l o g l c a l I n j u r y . The p o t e n t l a l value o f mlcrodoslmetry f o r t o x l c o l o g l c a l assessment
Is enormous, e s p e c i a l l y f o r e v a l u a t l n g t h e development or lack t h e r e o f o f c h r o n l c lung dlsease assoclated w l t h low l e v e l exposures t o environmental pollutants.
Although morphometrlc s t u d l e s a t t h e e l e c t r o n mlcroscoplc l e v e l
a r e c o s t l y and labor Intensive, t h e y a r e r e q u l s l t e f o r e s t a b l l s h l n g s t r u c t u r a l a l t e r a t i o n s and dlsease assoclated w l t h envlronmentally r e l e v a n t c h r o n l c exposure l e v e l s .
An example o f t h e type o f morphometrlc data t h a t
has been obtalned from 0 3 exposure s t u d l e s Is glven I n Flg. 2 , whlch shows t h e volume denslty o f Type I e p l t h e l l u m I n t h e proxlmal a l v e o l a r r e g l o n s o f c o n t r o l and 03-exposed r a t s .
VOLUME OF TYPE
I
EPITHELIUM A 0
a W
V
so
0.30
0.25
I
0
..
0 0 0
Am
.
A
A
0
O
a
Oa
0
".% m
o
015-.
CONTROL
0.12 ppm OZONE 0.25 ppm OZONE
F l g . 2. Volume d e n s l t y o f t y p e 1 e p i t h e l i u m I n t h e proximal a l v e o l a r r e g l o n s o f c o n t r o l and Oyexposed r a t s . Each column o f f o u r l d e n t l f l c a l symbols represents t h e four data values c a l c u l a t e d f o r t h l s parameter f o r each animal. The h o r l z o n t a l bar I t 1 each symbol c l u s t e r represents t h e mean for t h e animals I n t h a t group. (Reproduced w l t h permlsslon from r e f . 3 . )
289 Could knowledge about l o c a l i z e d d l s t r l b u t l o n s o f 03 dose w l t h l n t h e r e s p i r a t o r y t r a c t Impact, from b o t h c o s t and deslgn vlewpolnts, t h e use o f morphometry t o assess e f f e c t s ?
To answer t h l s question,
l e t us f l r s t
examine some aspects o f dose p a t t e r n s t h a t may be r e l e v a n t . three-dimensional
Utlllzlng
r e c o n s t r u c t l o n techniques, Mercer and Crapo ( r e f . 22)
determlned t h e dead space volume t o and t h e gas volume o f 71 v e n t l l a t o r y u n l t s sharing a common branch p o l n t from t h e lobar bronchus o f t h e l e f t lung o f a r a t .
A v e n t l l a t o r y u n i t Is deflned as a s t r u c t u r e whlch Includes
a l l d i s t a l gas-exchange s t r u c t u r e s from a s l n g l e b r o n c h l o l a r - a l v e o l a r junction.
Flg. 3 d e p l c t s a r e c o n s t r u c t l o n w l t h t h e b r o n c h l a l a l v e o l a r
j u n c t l o n s (darkened areasVshown a t t h e end o f t h e alrways, along w l t h t h e r e l a t l v e q u a n t l t y o f f r e s h a l r p r e d l c t e d t o be d e l l v e r e d on l n s p l r a t l o n t o the ventllatory u n i t s d l s t a l t o the junctlons.
Whlle t h e m a j o r l t y o f
ventllatory u n l t s recelve slmllar quantltles o f delivered fresh a l r , 3 - f o l d greater than average q u a n t l t l e s , as w e l l as 3 - f o l d
less a r e posslble.
Analogously, when Overton e t at. ( r e f . 23) modeled 03 absorption I n t h e r a t along fflongestlt and " s h o r t e s t " paths glven by Raabe e t a t . ( r e f . 241, they found s l g n l f l c a n t l y d l f f e r e n t n e t dose p r o f l l e s .
Whlle t h e maxlmum
dose along each path occurs I n t h e f l r s t a l v e o l a t e d duct, t h e r e Is a 3 - f o l d increase I n n e t dose a t t h l s l o c a t l o n for t h e " s h o r t e s t f f path as compared t o t h e "longesttt path.
RELATNE
DOSE
Fig. 3. D l s t r l b u t l o n o f f r e s h l n s p l r e d gas. The l l l u s t r a t l o n Is a repres e n t a t i o n o f a three-dlmenslonal r e c o n s t r u c t l o n o f alrways o f f o f a lobar bronchous. The f i g u r e s on t h e dlagram a r e t h e r e l a t l v e q u a n t l t l e s o f f r e s h a i r d e l i v e r e d t o t h e v e n t l l a t o r y u n l t s on l n s p l r a t l o n . The darked I n areas I n d i c a t e t h e j u n c t l o n between t h e v e n t l l a t o r y u n l t s and t h e alrways. (Reproduced w l t h perrnlsslon from r e f . 22).
230 The above k i n d s o f analyses p r o v i d e a p l a u s i b l e e x p l a n a t i o n as t o why p a t h o l o g i s t s observe a patchy d i s t r i b u t i o n o f i n j u r y when examining s l l d e s c u t randomly through parenchymal t i s s u e .
I f t h e e x t e n t o f 03
v a r i a b i l i t y i n i n j u r y can be demonstrated t o be due i n l a r g e p a r t t o t h e path length from t h e trachea t o t h e v e n t i l a t o r y u n i t , then It may be p o s s i b l e t o t a k e advantage o f t h i s f a c t i n t h e f o l l o w i n g way.
Morphanetric analyses,
such as I l l u s t r a t e d by Fig. 2, c o u l d u t i l i z e r e c o n s t r u c t i o n techniques so t h a t e x a c t l y t h e same v e n t i l a t o r y u n i t l o c a t i o n s c o u l d be examined i n c o n t r o l and 03 exposed animals.
This c o u l d decrease t h e observed experlmental v a r i a t i o n i n
i n j u r y s u b s t a n t i a l l y , thereby r e q u i r i n g fewer animals t o demonstrate s t a t i s t i c a l s i g n i f i c a n c e as w e l l as y i e l d i n g l a r g e c o s t savings. accounting f o r path distance,
Moreover, by
it f o l l o w s t h a t concentration-response data may
be generated by comparing d i f f e r e n t v e n t i l a t o r y u n i t s w i t h i n t h e same animal.
SUMMARY
T h i s paper has
discussed t h e r o l e o f dosimetry models i n r e c o g n i z i n g
and assessing c r i t i c a l issues i n I n t r a - and i n t e r s p e c i e s dosimetry o f ozone. As a background, t h e f o r m u l a t i o n of an ozone dosimetry model was o u t l i n e d . Discussed n e x t was t h e importance o f model v a l i d a t i o n and t h e need f o r URT dosimetry models and experimental data on URT removal.
Following t h i s ,
two examples were given o f t h e use o f dosimetry modeling I n c o n j u n c t i o n w i t h experlmental r e s u l t s t o gain a b e t t e r understanding o f t o x i c i t y and dosimetry.
I n t h e f i r s t example, r e s u l t s o f t h e e f f e c t o f 03 on t h e p u l -
monary f u n c t i o n o f c h i l d r e n and a d u l t s was discussed i n t h e l i g h t of dosimetry model p r e d i c t i o n s o f l o c a l doses i n c h i l d r e n and a d u l t s .
In t h e
second, model p r e d i c t i o n s o f l a r g e v a r i a t i o n s o f dose I n t h e c e n t r i a c l n a r r e g i o n were discussed and compared t o t h e observed l a r g e v a r i a t i o n s i n morphological i n j u r y due t o 03; a method f o r r e d u c i n g t h e v a r i a b i l i t y I n observed e f f e c t s as w e l l as f o r reducing t h e c o s t o f morphological analyses was suggested. ACKNOWLEDGEMENTS The authors thank Carolyn Wheeler for t y p i n g and Sharon Campfield f o r graphic support. REFERENCES
1 2 3
P.J.A. Rombout, P.J. Lioy, and B.D. Goldstein, JAPCA, 36 (1986) 91 3-91 7. U.S. Environmental P r o t e c t i o n Agency, A i r Q u a l i t y C r i t e r i a f o r Ozone and Other Photochemical Oxidants, Vol 4, EPA/600/8-84/020eF, Research T r i a n g l e Park, NC, 1986. B.E. Barry, F.J. M i l l e r , and J.D. Crapo, Lab. Invest., 53 (1985) 692-704.
.
231
8 9 10
11 12
13 14
15 16 17 18
19
20
21 22
23
24
B.E. Barry, R.E. Mercer, F.J. M i l l e r , and J.D. Crapo, Exp. Lung Res., 14 (1988) 225-245. F.J. M I I l e r , J.H. Overton, Jr., R.H. Jaskot, and D.B. Menzel, T o x i c o l . Appl. Pharmacol., 79 (1985) 11-27. J.H. Overton, R.C. Graham, and F.J. M I I l e r , T o x l c o l . Appl. Pharmacol., 88 (1987) 418-432. F.J. M l l l e r , J.H. Overton, Jr., E.D. Smolko, R.C. Graham, and D.B. Menzel, I n Pharmacokinetics I n Risk Assessment/Drlnklng Water and Health, N a t l o n a l Academy Press, Vol. 8, Washlngton, DC, 1987, pp 353-368. H.C. Yeh, G.M. Schum, and M.T. Duggan, Anat. Rec., 195 (1979) 483-492. E.R. Welbel, Morphometry o f t h e Human Lung, Academic Press, New York, 1 963. M.J. Wiester, T.B. WlIIlams, M.E. King, M.G. MBnache, and F.J. M l l l e r , T o x l c o l . Appl. Pharmacol., 89 (1987) 429-437. T.R. G e r r i t y , R.A. Weaver, J. Berntsen, D.E. House, and J.J. O'Neil, J. Appl. Physiol., (1988), I n press. J.H. Overton and R.C. Graham, i n Program and A b s t r a c t s of t h e 1985 Annual Meetlng o f t h e American Assoclates f o r Aerosol Research, November 1985, A b s t r a c t *9P7, pp. 223. D. B a r t l e t t , C.S. Faulkner, I I , and K. Cook, J. Appl. Physiol., 37 (1974) 92-96. N.M. Elsayed, M.G. Mustafa, and E.M. P o s t l e t h w a l t , J. T o x l c o l . Environ. Health, 9 (1982) 835-848. C.A. Tyson, K.D. Lunan, and R.J. Stephens, Arch. Envlron. Health, 37 ( 1982) 167-1 76. R.J. Stephens, M.F. Sloan, D.G. Groth, D.G. Negl, and K.D. Lunan, Am. J. Pathol., 93 (1978) 183-200. J. Kagawa and T. Toyama, Arch. Envlron. Health, 30 (1975) 117-122. M. Llppmann, P.J. Lloy, G. L e l k a u f , K.B. Green, D. Baxter, M. Morandl, B.S. Pasterhack, 0. F l f e , and F.E. Speizer, I n Lee e t a t . ( E d l t o r s ) , The Biochemical E f f e c t s o f Ozone and Related Photochemical Oxldants, P r i n c e t o n S c l e n t l f l c P u b l i s h e r s , P r l n c e t o n , 1983, pp.423-446. L.J. Follnsbee, B.L. Drlnkwater, J.F. Bedi, and S.M. Horvath, i n F o l i n s b e e e t a l . ( E d i t o r s ) , Environmental S t r e s s : I n d i v i d u a l Adaptation, Academic Press, New York, 1978, pp. 111-124. W.F. McDonnel I , R.S. Chapman, D.H. HOrstman, M.W. Lelgh, S. Abdul-Salaam, I n S.D. Lee (Editor), E v a l u a t i o n o f t h e S c i e n t l f l c B a s l s for Ozone/ Oxidants Standards, A i r P o l l u t l o n C o n t r o l A s s o c l a t l o n , P l t t s b u r g h , 1985, 31 7-328. J.H. Overton and R.C. Graham, i n Proceeding of t h e 2 6 t h Hanford L l f e Sclences Symposium, Rlchland, Washington, October 20-23, 1987 ( s u b m i t t e d for p u b l l c a t l o n ) . R.R. Mercer and J.D. Crapo, I n Crapo e t a t . ( E d i t o r s ) , E x t r a p o l a t l o n o f D o s l m e t r l c R e l a t l o n s h l p s f o r I n h a l e d P a r t l c l e s and Gases, Academic Press, New York, 1988 ( s u b m i t t e d for pub1 I c a t l o n ) . J.H. Overton, A.E. B a r n e t t , and R.C. Graham, i n Crapo e t a l . ( E d i t o r s ) , E x t r a p o l a t l o n o f D o s l m e t r l c R e l a t l o n s h l p s for I n h a l e d P a r t i c l e s and Gases, Academlc Press, New York, 1988 ( s u b m i t t e d for pub1 I c a t l o n ) . O.G. Raabe, H.C. Yeh, G.M. Schum, R.F. Phalen, i n Tracheobronchial Geometry: Human, Dog, Rat, Hamster, LF-53, Lovelace Foundation, Albuquerque, New Mexlco, 1976.
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T.Schneider et al. (Editors),Atmospheric Ozone Research and its Policy Implicatwns 0 1989 Elsevier Science PublishersB.V.,Amsterdam - Printed in The Netherlands
293
DO FUNCTIONAL CEANGES IN EulvLNS CORRELATE WITE THE AIRWAY REMOVAL EFFICIENCY OF OZONE?
T.R. Gerrity and W.F. McDonnell Clinical Research Branch, Inhalation Toxicology Division, Health Effects Environmental Protection Agency, Research Triangle Research Laboratory, U.S. Park, North Carolina (U.S.A.)
ABSTRACT One of the more commonly observed responses to acute exposure to ambient levels of ozone during exercise is a decline in tidal volume and UI increase in breathing frequency. It has been hypothesized that thia response helps to limit the dose of ozone to the lower respiratory tract. To test this hypothesis we exposed 20 healthy non-smoking male volunteers to 0.4 ppm ozone whale undergoing continuous exercise with a target minute ventilation of 20 L/min/m -body surface area. At the beginning and at the end of exercise we measured the uptake efficiency of ozone by the upper and lower respiratory tract. Tidal volume and breathing frequency were measured immediately following each ozone uptake measurement. Spirometric and plethysmographic measurements of lung function were made before and after exposure. Tidal volume significantly fell by 25% (p<0.003) during exposure. At the same time the ozone uptake efficiency of the lower respiratory tract significantly fell by 9% (p<0.04). We found that these declines were significantly correlated (p<0.004), suggesting that the tidal volume reduction experienced during ozone exposure with exercise helps to limit the amount of ozone delivered to lower respiratory tract tissue. DISCLAIMER The research described in this article has been reviewed by the Health Effects Research Laboratory, U.S. Environmental Protection Agency and approved for publication. Approval does not signify that the contents necessarily reflect the views and policies of the Agency nor does mention of trade names or commercial products constitute endorsement or recomendation for use.
INTRODUCTION Acute exposure of exercising individuals to ambient levels of ozone in controlled environmental chambers has been shown to induce decrements in pulmonary function (PFT) and alterations in breathing pattern. The breathing pattern alterations include decreased tidal volume (V,) and increased breathing frequency (f) while minute ventilation (tE) remains constant (ref.1). Mathematical model predictions of ozone uptake efficiency in the lower respiratory tract (LRT) predict that ozone uptake efficiency in the lower respiratory tract ),F( should fall with a reduction in Vt (ref.2-3). Ozone dose rate is proportional to the product of the rate at which ozone, enters the respiratory tract and the fractional efficiency by which the LRT takes it up. Thus for the LRT, the dose rate ),,D( in ug/min for 0.4 ppm ambient ozone is given by:
2'34
bLRT
I
2.0 Camb
iE PUT
where Camb is the ambient ozone concentration in ppm, iE is minute ventilation in L/min, PLRT is the ozone uptake efficiency of the lower respiratory tract, and the coefficient 2.0 is a conversion factor. Eqn.1 predicts that if i, remains constant and PUT falls during exposure, DLRT should also decrease. To test whether ozone uptake efficiency and the dose rate of ozone to the lower respiratory tract decline in relation to tidal volume during ozone exposure, twenty healthy subjects were exposed to 0 . 4 ppm ozone while exercising continuously at a moderate level for one hour. We measured the ozone uptake efficiencies of the upper respiratory tract (URT) and the total respiratory tract (T) in each subject. Prom these two quantities, the uptake efficiency of the lower respiratory tract (LRT) was computed. In conjunction with the ozone uptake measurements we measured Vt and f. Pre- and post-exposure PPT's were also measured. METEODS Subjects Twenty healthy non-smoking males between 18 and 35 years of age were recruited. Each subject gave a medical history and underwent a complete physical examination including a nasopharyngeal examination to determine health status prior to acceptance into the study. Upon acceptance into the study each subject signed a consent form. The protocol and consent form were approved by the University of North Carolina Committee on the Protection of the Rights of Euman Subjects. Protocol Each subject was exposed continuously for one hour to 0 . 4 ppm of ozone. During exposure each subject walked on a treadmill at a speed and inclination 2 sufficient to induce a gE of 20 L/min/m body surface area. While walking, each subject had a noseclip in place to limit breathing to the oral pathway. Five minutes after the beginning of exercise (designated as period EX1) and 5 minutes before the end of exercise (designated as period EX2) measurements of ozone uptake efficiency of the URT (PURT) and the total respiratory tract (P,) were made. Immediately following each uptake efficiency measurement Vt and f were measured with a pneumotachograph. Prior to, and immediately following exposure, each subject had measurements of spirometry and plethysmography. These measurements included forced vital capacity (FVC), forced expired volume in one second (PEV1), airways resistance (Raw) and specific airways resistance (sRaw).
295
Ozone Uptake Efficiency Measurements The measurements of FmT and FT were based on techniques reported earlier by Gerrity et a1 (ref.4). At each measurement period (EX1 and EX2) a small French X8 polyethylene infant feeding tube was inserted through a patent nostril until the tip was positioned in the posterior pharynx approximately 0.5 cm below the soft palate. The proximal end of the tube was attached to a solenoid valve. A common port on the valve was connected to a chemiluminescent ozone analyzer (Monitor Labs 8410) that had been modified to increase its frequency response (90% rise time equalled 1.2 sec) (ref.4) thus enabling breath-by-breath measurements of ozone concentration in the posterior pharynx. The ozone analyzer sampled air at a rate of 300 mllmin. The analog output of the ozone analyzer was passed through an analog-to-digital converter and the data stored on and IBH-PC/XT for later analysis. The valving arrangement enabled alternate sampling of chamber ozone concentration and pharyngeal ozone concentration. During periods of chamber ozone sampling, 100 ml/min of clean air were passed distally through the tube to keep i t clear of condensation, saliva, and mucus. Pharyngeal ozone concentration was measured for approximately 30 seconds during each of EX1 and EX2. The concentration measurements were affected by a small amount of ozone lost in the sample tube (approximately 5%) and by the finite response time of the ozone analyzer. To account for loss of ozone in the sample tube, chamber ozone was drawn through the tube into the analyzer both prior to insertion of the tube and after its removal. The mean of the fractional loss of ozone in the sample tube from these two measurements was used to correct the pharyngeal ozone concentration data. The loss of ozone in the sample tube was approximately 5%. The finite response time of the analyzer was compensated for by determining its frequency space transfer function. The output of the analyzer was found to behave in a linear fashion in response to square wave pulses of ozone. In analogy to electrical circuit theory, the transfer function used was that which would transform an analogous input square wave voltage to an output voltage across a capacitor in a series RC circuit with a time constant equal to 1.86. This transfer function was divided into the fourier transform of the data. The result of this division was inverse-fourier transformed to recover a more accurate representation of the pharyngeal concentration-time signal. The corrected data were used to compute ozone uptake efficiencies. FmT is the fractional mass uptake of ozone in the URT and is given by:
where
Hins is
the mass of ozone reaching
the posterior
pharynx
during
296
inspiration and Hamb is the total mass of ozone inhaled. PT is the fractional mass uptake of ozone in the total respiratory tract and is given by:
where H is the mass of ozone reaching the posterior pharynx during exP (Note: expiration. this definition of PT does not include any ozone taken up in the URT during expiration). To obtain the ozone masses consider the following: The mass (H) of a uniformly mixed sample of ozone flowing past any point in an aribitrary tube over a time interval At is given by: H =
(5)
JC(t)i(t)dt
where C(t) is the instantaneous ozone concentration as a function of time, t(t) is the instantaneous flow as a function of time, and the integral is over the time period AT. Since we were unable to measure t(t) concurrently with C(t), we assume constant inspiratory and expiratory flow rates. This assumption leads to the following equations for FmT and PT: FmT = 1
FT = 1
-
-
JC(t)dt/AtinsCamb
JC(t)dt/AtexpCamb
(7)
where Atins and At are the time intervals over inspiration and expiration exP respectively. The onset of inspiration and expiration were defined as occurring coincidentally with sudden increases and decreases, respectively, in C(t). This assumption is based on results from a previous study (ref.4) that demonstrate this association. FT and FmT are the primary ozone uptake efficiency measurements. From FmT and FT the fraction of ambient ozone mass taken up in the lower respiratory tract (PLRT) can be computed:
Furthermore, the fractional mass upake efficiency of the LRT mass of ozone entering the LRT (FbT) can also be calculated:
relative
to
the
297
In analogy with eqn.1, dose rates to the total respiratory tract and upper respiratory tract can be defined:
bT
-
2.0 Camb
ir,
PT
(10)
and
Statistics Total and regional ozone uptake efficiencies, Vt, f, and iE, measured during EX1 and EX2, were compared by paired t-tart#. Pro- and port-expomure PPT'r, were also compared by paired t-tests. The influence of tidal volume changes on uptake efficiencies and dose rater was examined by correlation analysis. The critical level of significance was set equal to 0.05. RESULTS
Between EX1 and EX2 Vt significantly fell from 1650*334(SD) ml to 1239i309 ml iE, (p
290
to those observed by HcDonnell et intermittent heavy exercise for 2 hours.
a1
(ref.1)
when
subjects underwent
DISCUSSION We found that the decrement in tidal volume that is observed when exercising individuals are exposed to ozone correlates with a decrease in the uptake A direct relationship efficiency of ozone in the lower respiratory tract. F b T is predicted by the modeling work of Hiller et a1 between AVt and A (ref.2-3). We observed a 9% fall in PbT. Over a similar range of tidal volumes as in this study, Hiller et a1 (ref.2) predict a fall in F b T of approximately 15%. Considering that the model predictions were made with virtually no experimental data for direct comparison, this difference is not unreasonable. When dose rates were computed from the uptake data we found that whereas FT did not change between EX1 and EX2, DT significantly decreased. Eowever, 'LRT PbT,and bmT each significantly declined while both FmT and bmT remained unchanged. These apparent incongruent findings may be the result of the In dependence of FLRT and P b T upon the primary measurements of PT and FmT. addition, bmT depends upon VE. Consequently we attatch a relatively high level of confidence to the results for FT and FmT since they are the primary measures of uptake efficiency. We assign a secondary level of confidence to the results for FLRT and F h T since these are computed from the FT and PUT. The dose rates are more derivative in nature owing to their dependence on both uptake efficiency and minute ventilation and are therefore likely to be subject to greater errors. In light of the above considerations we speculate that the decline in FUT (and in turn the decline in P b T ) is real and that the small, though non-significant, incresse in PmT, in combination with the decline in FmT, resulted in a non-significant decline in FT. The correlation of both AFmT and AFT with AVt supports this speculation. The fact that AFmT was not correlated with AVt implies that the former correlations were not influenced by the upper respiratory tract, thus adding further support. The observation of a significant drop in DUT, but not a significant correlation of this drop with OV,, is possibly due the accumulation of error in the computation of bmT. This is supported by the observation that AbT was significantly correlated with AVt while bbmT was not. The relationship between bbT and AVt may be a reflection of an underlying relationship between AVt and A'DLRT, but that this relationship is masked. In all of this discussion, i t must be recognized that the analysis of the data of this study is being reported without regard to the impact of multiple
299 comparisons on the level of significance that can be attached to the results. Iiowever, the present examination of the data is important because it permits better definition of the important variables that must be controlled in future investigations. If we accept the above interpretation of the data, then the results of this study have health implications when considering repeated ozone exposures. Studies of the functional responses of rats acutely exposed to ozone demonstrate an ablation of the tidal volume response after repeated daily exposures (ref.5). A similar dimunition of response in humans is likely, though it has not been investigated specifically. Polinsbee et a1 (ref.6), in their study on adaptation to PFT response to ozone, did not see any response of tidal volume. This may have been due to the relatively low work load at which their subjects exercised. If the tidal volume response adapts upon repeated exposures, our results suggest that the potentially beneficial effect of reduced ozone dose with decreased tidal volume disappears. This leads to the conclusion that so-called adaptation to ozone may not be a beneficial response with respect to chronic exposure scenarios. In addition, those individuals who show no tidal volume response at all during single exposures will not reduce the ozone dose to their lower respiratory tract. Furthermore, when tidal volume decreases in response to ozone, the model of Hiller et a1 (ref.3) predicts that the highest regional ozone doses shift proximally from the respiratory bronchioles and alveoli toward the terminal bronchioles. Thus, the lack of a tidal volume response may lead to a persistant high ozone dose to sensitive peripheral lung tissue. In conclusion, we found that during exposure to ambient levels of ozone, exercising individuals decrease the efficiency of ozone uptake in the lower respiratory tract. This decrease is likely to be caused by their reduction in tidal volume. The effect of these reductions may be to reduce the dose rate of ozone to the lower respiratory tract, though cumulative measurement errors may have obscured this in the present study. These observations may be important in evaluating whether ozone adaptation is a beneficial chronic response. ACKNOWLEDGEMENTS The authors appreciate the skilled technical assistance of Hs. Sills, Hs. Paulette DeWitt, Hr. Arthur Strong and Hr. Ralph Cook.
Valerie
REFERENCES 1 W.P. HcDonnell, D.H. Horstman, H.J. Hazucha, E. Seal, E.D. Eaak, S.A. Salaam, and D.E. Bouse, J. Appl. Physiol. 54 (1983) 1345-1352. 2 P.J. Hiller, D.B. Henzel, and D.L. Coffin, Env. Res. 17 (1978) 84-101. 3 F.J. Hiller, J.H. Overton, R.B. Jaskot, and D.B. Henzel, Toxicol. Appl. Pharmacol. 29 (1985) 11-27.
300 4 T.R. Gerrity, W.A. Weaver, J. Berntsen, D.E. House, and J.J. O'Neil, J. Appl. Physiol. In Press. 5 J.S. Tepper, D.L. Costa, H.F. Weber, H.J. Wester, G.E. Hatch, H.J. Selgrade, Am. Rev. Respir. Dis. 135(2) (1987) A283. 6 L.J. Folinsbee, J.P. Bedi, and S.M. Horvath, Am. Rev. Respir. Dis. 121 (1980) 431-439.
T. Schneider et al. (Editors),Atmospheric Ozone Research and its Policy Implkatwns 0 1989 Elsevier Science Publishers B.V., Amsterdam -Printed in The Netherlands
301
EXTRAPULMONARY EFFECTS OF LOW LEVEL OZONE EXPOSURE
E.YOKOYAMA1, I.UCHIYAMA1 and H.ARIT0' 'Department of Industrial Health, 4-6-1 Shirokanedai, Minato-ku, Tokyo 108 (Japan 1 'National Institute of Industrial Health, 6-21-1 Nagao, Tama-ku, Kawasaki 214 (Japan 1 ABSTRACT Effects of acute exposure to ozone(0 ) on the circulatory and vigilance s t a t e s were studied in conscious r a t s . %hr exposure to 1 ppm 0 caused a marked decrease in heart r a t e and mean a r t e r i a l blood pressure, and a Qrequent occurrence o f arrhythmia. These changes tended to recover during the post exposure period,although n o t complete within 5 hrs. When t h i s exposure was repeated consecutively, the changes in heart r a t e and blood pressure became less marked gradually. 6-hr exposure to 0.5 ppm 03 caused similar, t h o u g h a l i t t l e less remarkable, changes. The similar exposure caused a significant decrease in the amount of paradoxical sleep. T h i s change recovered almost completely within 5 hrs of the post exposure period, and became l e s s marked when the exposure repeated.
I NTROOUCT I ON Now available are reports showing extrapulmonary responses t o atmospheric pol 1 utants ( r e f . 1 ) . Because these responses have been reported to occur e a r l i e r i n some cases than do pulmonary responses, i t i s essential t o elucidate the detail of these extrapulmonary responses. The objectives of t h i s study are 1 ) t o measure the dose-effect relationships of extrapulmonary responses in experimental animals exposed t o low level of 03, and 2 ) to f i n a l l y gain an insight into i t s significance as health risk. METHODS 01 exposure The animals were exposed to f i l t e r e d air o r O3 i n a cubic,stainless-steel chamber which was supplied with f i l t e r e d a i r the r a t e of which was adjusted t o ventilate about 18-20 times/hr. O3 was produced by passing pure oxygen through a silent-discharge O3 generator a n d mixed with the a i r stream a t the entrance of the chamber. The concentration of O3 in the chamber was monitored by a Mast O3 analyzer.
Circulatory studies in r a t s One day before the experiment, the r a t s (Wistar, male, 10-11 wk o l d ) were
302 anesthetized by ip pentobarbital sodium (45 mg/kg body weight) and subjected to introduction of an a r t e r i a l catheter and attachment of electrodes f o r recording of electrocardiogram ( E C G ) . The methods f o r preparing equipment and recoding a r t e r i a l blood pressure and ECG were previously reported in detal (ref.2) and are therefore described in b r i e f . The a r t e r i a l catheter was made of a polyethylene PE 50 tube which was connected i n s e r i e s with a polyethylene P E l O tube and a silicon medical tube (No.OO), and inserted into the l e f t femoral a r t e r y so t h a t i t s t i p was placed in the abdominal aorta. Another end of the catheter was guided under tbe skin to the back and out and ligated. A system of the chest bipolar leads was prepared t o record ECG using a commercial connector which had three leads. A white-gold c i r c l e electrode was glued to the ends of a l l leads and attached with s i l k thread t o the connective tiseues over the apex of the heart, the manubrium s t e r n i , and the lumbar vertebrae. The leads were guided under the skin t o the back and out, and the connector was fixed a t the skin. On the day of experimant, the ECG electrodes and the a r t e r i a l catheters were connected to an extended cord and tube, respectively; and then the rats were transferred t o an individual cage inside the exposure chamber. The r a t s were able to move freely inside the cages. ECG and the a r t e r i a l blood pressure were recorded on an ink-writing oscillograph (RM-20. Nihon Koden C. L t d . , Tokyo) with the electrocardiograph (Fukuda Demshi Co. Ltd. , Tokyo) and a pressure tranducer (MP-0.5A, Nihon Coden Co.Ltd. , Tokyo) , respectively. ECG and the blood pressure were recorded every 10-15 m i n before and d u r i n g exposure t o 03. The heart r a t e was calculated from the R wave of ECG, and the mean a r t e r i a l pressure (MAP) was read from the records of a r t e r i a l blood pressnre. El ectroenceDhalo4raDhi c studies in r a t s Rats(Wister s t r a i n , male, 4 wk old) were housed i n comnunity cages ( 5 r a t s / cage) and maintained under a 12-hr light-12-hr dard cycle t u r n i n g fluorescent l i g h t automatically on from 18:OO to 0 6:OO. A t 8 wk old, the r a t s were surgically implanted w i t h 3 kinds of electrodes under pentobarbital anesthesia ( i p , 40 mg/kg): 2 electroencephalographic (EEG) electrodes on the r i g h t frontal cortex and the l e f t parietal cortex, a reference electrode on the cerebellum, 2 electromyographic(EMG) electrodes i n the r i g h t and l e f t neck muscles and an electrocardiographic (EEG) electrode on the heart following the method previously described (ref . 3 ) . Those electrodes were soldered t o a miniature socket and then fixiated on the skull w i t h the dental cement. The animals were allowed 10 days f o r recovery from the surgical damage. The electrode-implanted rats were attached w i t h f l e x i b l e cables on the head sockets and housed in the individual recording cages i n the exposure chamber for 3 days before the exposure to O3 and the polygraphic recording
303 were s t a r t e d .
Exposure t o O3 was performed f o r e i t h e r 3 h r (12:OO-15:OO) EEG, EMG and ECG a c t i v i t i e s o f electrode-implanted
6 h r (12:OO-18:OO).
or rats
were recorded a t a paper speed o f 0.75 cm/sec on 18-channel EEG i n s t r u m e n t (Type IA59, San-Ei Ltd., Tokyo) and simultaneously s t o r e d w i t h a 21-channel data r e c o r d e r (SRF-71
, TEAC,
Inc.
, Japan).
The v i g i l a n c e s t a t e s o f each r a t were c l a s s i f i e d i n t o wakefulness (W), slow-wave sleep (SWS) and paradoxical s l e e p (PS) by v i s u a l i n s p e c t i o n o f t h e polygraphic records f o l l o w i n g the c r i t e r i a o f EEG and EMG a c t i v i t i e s p r e v i o u s l y described
( r e f . 3 ) ,and sleep-wakefulness stage diagrams and h o u r l y
amounts o f W, SWS and PS were constructed w i t h t h e 6 h r p o l y g r a p h i c r e c o r d s which had been separated i n t o t h e t h r e e stages. Statistics Values were u s u a l l y represented as means
2
SD.
S t u d e n t ' s t e s t was used t o
compare t h e values between t e h groups. RESULTS C i r c u l a t o r v responses Fig. 1 shows HR and MAP of r a t s d u r i n g t h e exposures t o f i l t e r e d a i r (N=6) o r 1 ppm O3 (N=6) f o r 3 hr.HR and MAP a r e expressed as values r e l a t i v e t o t h e preexposure l e v e l . Before t h e exposures, HR and MAP were p r a c t i c a l l y t h e same i n the b o t h exposure groups: HR was 425 was 131
2
9 and 133
2
47 and 427
2 5 nun Hg, r e s p e c t i v e l y .
t
58 beats/min, and MAP
Although s l i g h t f l u c t u a t i o n s were
noted, HR and MAP were almost constant d u r i n g t h e exposure t o f i l t e r e d a i r f o r 3 h r and f i n a l l y reached 94 and 92% o f t h e i n i t i a l l e v e l s , r e s p e c t i v e l y .
The
response o f HR and MAP o f r a t s exposed t o 1 ppm O3 was s t r i k i n g l y c o n t r a s t i n g t o those exposed t o f i l t e r e d a i r .
HR decreased s t e a d i l y and reached a p l a t e a u
90 min a f t e r the s t a r t o f the exposure t o 1 ppm 03, and remained n e a r l y unchanged d u r i n g the remaining p e r i o d o f exposure. HR a t t h e end o f exposure t o 1 ppm O3 f o r 3 h r was 197
2
16 beats/min, 47% o f the i n i t i a l l e v e l . S i m i l a r
t o the HR, the decrease i n MAP was observed d u r i n g t h e exposure t o 1 ppm 03. MAP reached t h e l o w e s t l e v e l , 95 2 6 mn Hg, 135 min a f t e r t h e s t a r t o f exposure, and then tended t o recover s l i g h t l y , reaching t o 105 i n i t i a l l e v e l , by the end o f t h e exposure.
2
16 mm Hg, 81% o f t h e
I n a d d i t i o n t o t h e hypotension and
bradycardia, t h e changes i n PR i n t e r v a l and QRS complex, and a r r h y t h m i a were observed i n t h e t r a c i n g o f ECG 90 min a f t e r t h e s t a r t o f exposure t o 1 ppm 03. The measurement demonstrated t h e s i g n i f i c a n t increases i n PR i n t e r v a l (P< 0.005) and QRS complez ( P <
0.05 ) a t t h e end o f exposure
.
Premature a t r i a l
c o n t r a c t i o n was f r e q u e n t l y observed i n t h e a l l r a t s d u r i n g t h e exposure t o 1 ppm O3 except f o r t h e f i r s t 30-40 min. A d d i t i o n a l l y , incomplete A-V b l o c k (Wenchebach type) was observed i n 4 r a t s .
F i g 2 shows a t y p i c a l example o f t h e
304 tracing of arterial blood pressure and ECG obtained from a r a t 90 min a f t e r the s t a r t of exposure: Incomplete AV block was noticed. F i g 3 shows the change in HR of rats during breathing a i r a f t e r the end of exposure t o 1 ppm O3 for 3 hr. Their HR tended t o recover steadily and gradually, b u t the recovery was n o t complete within 5 hr of post-exposure period. HR slightly increased immediately a f t e r the s t a r t of exposure t o 0.5 ppm O3 for 6 hr (N=6), b u t then decreased steadily, reaching a plateau about 3 hr after the s t a r t o f exposure. H R a t the end of exposure was about 68% of the i n i t i a l level. Simi 1 ar response was observed in MAP, and MAP a t the end of
- 70 - 60 I
-
OZONE
i
Fig.1. Changes i n heart rate and mean arterial blood pressure of the rats during exposure t o 1 ppm O3 or filtered a i r for 3 hrs. .
.
.
I
.
-
.
1-1
-r
arterial blood pressure
1
- 7 -
-- .,__
!
(8)
-
50 U c
0.5 scc
1W
ECG
Fig.2. An original tracing of arterial blood pressure and ECG obtained from a rat 90 min after the s t a r t of exposure t o 1 ppm 0 3 .
305
(u
40-
c
-
O
20-
8 a:
-
c c
-
=
I
o
o3 E x p o s u r e
1 ppm
1
1SE
~
l
"
~
l
~
"
exposure was about 82% o f the i n i t i a l l e v e l .
l
l
"
'
l
'
l
I n the t r a c i n g o f ECG, the
s i g n i f i c a n t increase was n o t i c e d i n PR i n t e r v a l , b u t n o t i n QRS complex. Premature a t r i a l c o n t r a c t i o n was commonly observed, b u t incomplete A-V b l o c k was observed i n o n l y 3 i n 6 r a t s . Fig. 4 shows the changes i n HR o f rats(N.6) d a i l y f o r 3 consecutive days.
exposed t o 1 ppm
O3 f o r 3 h r
The extent o f change i n HR was the l a r g e s t a t
the 1 s t day, and became gradually smaller a t the 2nd and 3 r d day. HR a t t h e end of exposure a t each day were 53.9 f 2.1% , 63.4 25.0 %, and 76.1 2 5.1%, respectively: t h e differences between each values were s i g n i f i c a n t . (P o r 0.01 1
0.05,
Electroencaphaloqraphic response The r a t s exposed t o f i l t e r e d a i r , as c o n t r o l ,showed polyphasic p a t t e r n s o f sleep-wakefulness: each o f W, SWS and PS stages rapidly..changing, and the hourly amounts o f W, SWS and PS and the 15-min values of HR were maintained constant during the exposures t o f i l t e r e d a i r (Figs.5). The r a t s exposed t o 1.0 PPm ozone for 3 h r s were c a r a c t e r i z e d by an i n i t i a l increase i n W and a t o n i c suppression o f PS i n a d d i t i o n t o a decrease i n HR.
Hourly amounts o f PS s i g n i f i c a n t l y decreased throughout the 3-hr
exposure period as shown i n Fig. 5 .
PS recovered completely o r exceeded t h e pre-exposure l e v e l i n some cases w i t h i n 3 h r s o f the post-exposure period.
306
C.
-a
I
1 s i DAY 2ND
DAY
*-+I 3RD
DAY
I
I
1
30
60
90
I
120
1I IIE (nI NJ 150 180
Exposure Time (min.) Fig.4. Changes i n h e a r t r a t e o f the r a t s during exposure t o 1 ppm 03 f o r 3 hrs performed d a i l y f o r the consecutive 3 days. On the o t h e r hand, the recovery o f HR was much more slow than t h e PS. The PS suppression and the decrease i n HR were a l s o observed i n the r a t s .exposed t o 0.5 ppm O3 f o r 6 hrs.
It was manifested much l a t e r i n the exposure
t o 0.5 ppm O3 than 1.0 ppm 03, and the h o u r l y amounts o f PS s i g n i f i c a n t l y decreased during the 3rd
-
5 t h h r o f the exposure. (Fig.7)
Exporuro for 6 hra to alr rtroam (Day 1) 16 W
12 00
1 0
:
: (o
:
:
in
:
:
im
10
:
:
:
zu
w
--4
aw
yo
(Rat 0200-1-9)
Fig.5. Three v i g i l a n c e s t a t e diagram and h e a r t r a t e d u r i n g exposure t o f i l t e r e d a i r
307 AS the exposure was consecutively repeated, the changes i n v i g i l a n c e s t a t e became smaller gradually.
Consequently, there were no s i g n i f i c a n t
differences i n the hourly amounts o f W , SWS and PS and the 15-min values of HR between the r a t s exposed t o f i l t e r e d o r 1.0 ppm O3 4 times. Exporuro for 3 hrr to 1.0 PPY
J
:
:
:
M
0
:
;
:
120
:
:
Otono (Day 1)
:
:
:
,
Wl
140
1-
a i r and those exposed t o 0.5 pprn
(Rat 0210-1-6)
Fig.6. Three v i g i l a n c e s t a t e diagram and heart r a t e o f a r a t during and a f t e r exposure t o 1 ppm O3 f o r 3 hrs. Exnoruro tor 6 hrr to 0.1 PPY Ozono (Day 1) I2
w
i 0
16 00
:
: 10
: 120
:
: im
I0
;
: 210
: : sw
w
: am
(Rat o z o s - l - 1 )
Fig.7. Three v i g i l a n c e s t a t e diagram and h e a r t r a t e o f a r a t during exposure t o 0.5 ppm O3 f o r 6 hrs.
:
,
308 DISCUSSI ON Pulmonary e f f e c t s of inhaled O3 have been extensively documented ( r e f . l ) , and we a l s o have studied lung-functional and -biochemical e f f e c t s of O3 ( r e f . 4,5). Recently, extrapulmonary or systemic e f f e c t s of O3 are t a k i n g a growing i n t e r e s t in researches, although only a few reports are practically available yet. I t i s our viewpoints t h a t not only pulmonary b u t extrapulmonary e f f e c t s should be evaluated in order to assess health risk of inhaled 03. The r e s u l t s reported here are the ones we have j u s t observed in electcardiogram ( t h e principal investigator: 1.Uchiyama) and electroencephalogram ( t h e principal investigator:H.Arito) of r a t s exposed t o 03. I t i s very interesting t h a t markedly depressive e f f e c t s on HR and MAP of r a t s were shown by exposure t o 03. The level of HR and MAP reached 47 a n d 81% of the i n i t i a l levels a t the termination o f exposure t o 1 ppm O3 in r a t s . I t meant t h a t the pressure-rate product decreased markedly and reached about 38% of the i n i t i a l level, which was usually judged t o be a s t a t e of cardiac shock. This e f f e c t o f O3 was evidently dose-dependent. We now have no explanation on causes of such a depressive e f f e c t of O3 on heart r a t e and blood pressure, b u t a participation of the change in parasympathetic nervous a c t i v i t i e s was suggested by our preliminary study which measured the response of heart r a t e of r a t s to atropine and propranolol during exposure to 03. Studies on the circulatory responses of emphysematous and hypertensive r a t s a r e now in progress. The e f f e c t s o f O3 on vigilance s t a t e of r a t s were a l s o so striking t h a t paradoxical sleep almost disappeared d u r i n g the whole priod of exposure t o 1 ppm 03. This e f f e c t was also dose-dependent. Arito e t a l . ( r e f . 3 , 6 ) observed disturbed rhythms of vigilance s t a t e in r a t s exposed t o methylmercury and toluene, b u t never found the complete disappearance of paradoxical sleep as demonstrated by the present r a t s exposed to 1 ppm 03. Causes of the e f f e c t of O3 on vigilance s t a t e of r a t s are unknown a t the present, and i t i s d i f f i c u l t t o explain t h i s e f f e c t by only circulatory depression, because the time courses of recovery of the heart rate and blood pressure and the vigilance s t a t e were not necessarily similar. The r a t s appeared t o acquire adaptation t o the above e f f e c t s of O3 a s repeatedly exposed within 3-4 days, and we may need t o know how long t h i s adaptation will persist. Thus, many problems remain t o be solved before f i n a l l y assessing health risk imposed by these extrapulmonary e f f e c t s of inhaled 03, b u t we present the depressive e f f e c t s on heart r a t e and blood pressure and the modifying effects on vigilance s t a t e of 03, when concentration i s a t a level inducing no change in the l u n g weight, because of physiological significance o f such a circulatory depression and a modification of vigilance s t a t e will
309
be great. REFERENCES 1 National Research Council, Ozone and Other Photochemical Oxidants, N a t i o n a l Academy o f Sciences, Washington,D.C., 1977. 2 1.Uchiyama and E.Yokoyama, J.Jap.Soc.Air P o l l . , 20(1985) 46-53. 3 H.Arito, N.Hara and S . T o r i i , Toxicology, 28(1983) 335-345. 4 E.Yokoyama, I.Ichikawa, Z.Nambu, K.Kawai and Y.Kyono, Environ.Res., 33(1984) 271 -283. 5 E.Yokoyama, Z.Nambu, I . l c h i k a w a , 1.Uchiyama and H.Arakawa, Environ.Res., 42( 1987) 114-122. 6 H.Arito, H.Tsuruta and K.Nakazaki, Toxicology, 33(1984) 291-301.
This Page Intentionally Left Blank
T. Schneider et al. (Editors),Atmospheric Ozone Research and its Policy Implications 0 1989 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands
311
RESPCNSES OF SELECTED REACTIVE AND "REACTIVE WXIJNTeEFS ?D OZONE MFOSURE I N HIGH AND LOW POLUlTION SEASCNS
Jack D. Hackney, W i l l i a m S . Linn, Deborah A. S h m , and Elward L. Avo1 Rancho Los Amigos Medical Center/University of Southern California School of Medicine, 7601 Imperial Highway, Dmney, California 90242 U.S. ABSIWCT W e masured r e a c t i v i t y to 0.18 ppm ozone (2-hour exposure including heavy exercise and heat stress) in 59 volunteer Los Angeles residents i n spring 1986, before the ambient oxidant pollution season. We restudied reactive and mreactive subgroups, selected on the basis of lunq function response, in auturm 1986 ( late in high-oxidant season), winter 1987 ( l o w oxidant season), and spring 1987 (1 year a f t e r original study). Nonreactors showed l i t t l e l q function response in any exposure. Reactors shawed seasonal variation, w i t h l i t t l e respcnse i n autum or winter, tut a substantial function loss in spring 1987 s i m i l a r to that in sprinq 1986. Individual responses mre strongly correlated from spring to spring, tut less so in intervening seasons. Reactors shawed mre a l l e r g i e s , greater airway r e a c t i v i t y to mthacholine, and greater self-reported s e n s i t i v i t y to a i r pollution than did mnreactors.
I-CTION The objective of the experimnt described in t h i s paper w s to identify
factors which help explain individual differences in respiratory response to ozcne (0 exposure. Numerous laboratory exposure studies of volunteers 3 have shown t h a t a minority of the population are "reactors" or "responders" to 0
3
( r e f . 1). Such individuals are of special concern to air q u a l i t y
regulators, who are required to set standards to protect the mst s e n s i t i v e groups in the population.
"Reactors" experience c l i n i c a l l y maningful
respiratory i r r i t a t i o n (with svmptonrs and reduced lung function) durinq d e r a t e 0 exposures (e.q. 0.15-0.20 for 1-2 burs with exercise) 3 which pmduce rx3 obvious c l i n i c a l e f f e c t s in mst people. We biological basis of individual differences is 0 r e a c t i v i t y is
largely u n k m .
3 Some evidence indicates that individual r e a c t i v i t y
c h a r a c t e r i s t i c s p e r s i s t for periods of m n t h s to years ( r e f . 2).
On the other hand, short-term changes in r e a c t i v i t y are possible, as evidenced by the phenomenon of "adaptation" or "tolerance" to 0 ( r e f . 1). In successive 3 d a i l y laboratory exposures to high conceptrations (e.g. 0.4 or 0.5 ~ p m ) ,one
312
typically finds the mst severe synptoms and lung function changes on the second day, and l i t t l e or no response by the fourth day. The "adaptation" is lost a f t e r a few days with no exposure. These fimlitqs raise the question 6 Anqeles, can induce whether frequent exposures to ambient 0 , as in k 3 "adaptation". Although sow earlier evidence suqgested t h a t Los Anqeles
residents miqht be "adapted" ( r e f . 31, a recent review of laboratory dose-respcnse studies showed no substantial differences between groups of subjects from Los Anqeles and other qroups from cleaner areas (ref. 4 ) . I t is reasonable to h p o t h e s i z e t h a t respiratorv a l l e r g i e s or asthma,
which cause the airways to be mre s e n s i t i v e to other stresses, miqht contribute inportantly to 0 reactivity. A number of studies have tested 3 t h a t hypothesis indirectlv, but no c l e a r and convincinq excess response to has been d e m s t r a t e d thus f a r in a l l e r q i c or asthmtic volunteers ( r e f . 3 1). A recent investigation by McDonnell e t a l . ( r e f . 5) of subjects with
0
c l i n i c a l l y evident allerqic r h i n i t i s and positive allergy skin tests, but without asthma (i.e. with norm1 airway r e a c t i v i t y to a bronchoconstrictor challenqe), showed l i t t l e difference in response to 0 frcm a normal 3 (non-asthmatic, non-allergic) volunteer group. Also, a i m a y r e a c t i v i t y to histamine aerosol did m t apear to correlate with r e a c t i v i t y to 0
3
.
In the present w r k , we tested both short- and lonq-term respiratory i l l n e s s factors €or associations with 0 r e a c t i v i t y . 3
W e also investigated
the variation in r e a c t i v i t y over tire, to look f o r possible "adaptation" to recent ambient 0 exposures. Our strateqy differed f m past s t u d i e s in 3 t h a t we f i r s t selected very "reactive" and very "nonreactive" subject groups
from a larqer volunteer populaticn, m the basis of their responses to an i n i t i a l 0 exposure. The selected groups then underwent extensive c l i n i c a l 3 characterization and further 0 exposures to identify factors associated 3 with their reactivity. M!ZJXODS A l l 0 exposures t o o k place in a controlled-environment chamber a t
3 31 C and 35% r e l a t i v e humidity, a t a concentration of 0.18 Fpm. They lasted 2 hours, during which subjects exercised heavily (inducing a ventilation 0
r a t e of approxiwtely 35 L/min per square reter of boay surface a r e a ) f o r 15 minutes of every half hour. Control studies with clean a i r were conducted in conjunction with followup 0 exposures. 3
Control data are not reported here
since no maninqful responses were found.
A t f i r s t , 59 volunteer young adult residents of metropolitan Lcs Angeles were recruited and exposed in late spring
1986, a f t e r about 7 m n t h s free of severe ambient 0 exposures. 3
These
313
v o l u n t e e r s were unselected i n terms of their c l i n i c a l s t a t u s , e xc e pt that a special e f f o r t was rmde to r e c r u i t people expected to be "reactors"-those
with
r e s p i r a t o r y a l l e r g i e s , mild a s h , or previous evidence of high r e a c t i v i t y to 0
3
i n a l a b o r a t o r y study.
From the i n i t i a l population of 59, excluding a few who chose to withdraw or who showed erratic test performance, the 16 mt r e a c t i v e and 16 least r e a c t i v e s u b j e c t s , as determined by lunq function t e s t i n g (i.e. change i n forced expired velum i n one second, Fev during exposure) w x e s e l e c t e d 1' f o r followup. To c h a r a c t e r i z e their chronic r e s p i r a t o r y i l l n e s s e s ( i f a ny), they underwent s k i n tests wi t h 13 cormxln local p l a n t a l l e r g e n s , measurements of "nonspecific" airway r e a c t i v i t v by challenge with m t h a c h o l i n e aerosol, and a q u e st i o n n a i r e interview to determine any h i s t o r y of r e s p i r a t o r y illness or self-perceived s e n s i t i v i t y to ambient p o l l u t ion.
To c h a r a c t e r i z e any a c ute
r e s p i r a t o r y i l l n e s s , thev underwent determinations of serum imnunoglotmlin E, white blood cell count, sedimentation rate, and antibody titers f o r 9 c m n r e s p i r a t o r v d i se as e v i r u s e s before each 0 exposure. 3
'he followup
exposures t o o k place i n auturm 1986, a f t e r 3 to 4 m n t h s with fre que nt o p p o r t u n i t i e s f o r ambient 0 e x p a u r e s , and i n w inte r 1987, a f t e r 2 to 3 3 m n t h s with q e n er al l y low ambient 0 l e v e l s . W e expected t h a t , i f 3 adaptation to ambient exposures Occurred, the reactive s u b j e c t s m u l d lose their reactivity t y the time of the auturm exposure and regain it by the time o f the winter exposure.
Twelve reactors and 13 nonreactors completed the two
followup exposures; t h e i r c h a r a c t e r i s t i c s are s u m r i z e d in Table 1. As indicated i n the R es u l t s s e c t i o n , reactors d i d lose r e a c t i v i t y by
auturm tut d i d not regain i t by winter.
To h e l p confirm the seasonal
v a r i a t i o n , an a d d i t i o n a l followup 0 exposure was performed i n s p r i n g 1987, 3 one year a f t e r the i n i t i a l e x m u r e study. Eiqht reactors and 9 nonreactors
were a v a i l a b l e to p a r t i c i p a t e i n t h i s f i n a l followup; their average responses i n the earlier exposures were s i m i l a r to the cmplete qmups'.
314
TABLE 1 (HWTERISTICS OF REACTIVE AND "REACTIVE SUBJECTS ~~
Age, years (man
5 s.d.)
285 7
Height, cm
170 5 10
170 67
Weight, kg
66
5 12
change in screening exposure, % 1 Spptom change in screening exposure ( a r b i t r a r y score)
+1
2 3
*FEV
+7 5 6 5 femle 8 male
Clinical respiratory s t a t u s (by history)?
265 6
13 normal
-12
5
8
5 10
2
5
+23 5 23 7 female 5 male 4 normal 6 allergic 2 asthmtic
*Criterion for selection of reactors and nonreactors. +Objective tests of c l i n i c a l status are described in Results.
RESULTS
Figure 1 shows the chanqe in FEV during 0 expcsure a t each 1 3 season for reactors and nonreactors who completed the auturm and winter followups, and for the subgroups who completed the f i n a l spring followup. Nonreactors remained nonreactive throughout the investigation, showing no s t a t i s t i c a l l y s i g n i f i c a n t variation in response across seasons (P > 0.05 by repeated-masures analysis of variance). Reactors s h d s i g n i f i c a n t (P < 0.01) variation, with considerably s n a l l e r man respcnses in auturm and winter than in the i n i t i a l spring exposure.
In the f i n a l spring followup, m a n
response was similar to t h a t in the i n i t i a l expasure one year earlier.
In the
17 subjects who completed the spring followup, individual FEY respcnses 1 were r e l a t i v e l y consistent between spring 1986 and spring 1987 ( c o r r e l a t i o n c o e f f i c i e n t = 0.79, P < 0.001).
A
similar degree of correlation was found by
McDonnell e t a l . i n duplicate exposures to 0 concentrations between 0.18 3 and 0.40 ppm, spearated by periods of a few weeks to mre than me year, in subjects n o t extensively exposed to ambient 0 ( r e f . 2 ) . 3
315
Tests for acute respiratory i l l n e s s were not helpful in explaining
Nearly a l l subjects showed positive v i r a l individual r e a c t i v i t y to 0 3' titers in one or mre instances. The overall incidence was greater in reactors than in nonreactms, ht the difference was explained by two reactors in than nearly a l l r e s u l t s wre positive. One of these was highly reactive in a l l exposures in tern of FEV loss, bt the other showed seasonal variation 1 similar to t h a t of the reactor group as a whole. Abnormal h w n q l o b u l i n E assays, sedimntation rates, or white ell counts were rare in reactors as tell as mreactors. Table 2 shows the proporticns of reactive and nonreactive subjects with allergy history, "nonspecific" airmay hyperreactivity as determined by a mthacholine challenge, and positive answers to questions concerning s e l f perceived s e n s i t i v i t y to a i r pollution. Both allergy history and airway r e a c t i v i t y to mthacholine were strongly associated with r e a c t i v i t y to 0 3'
A w l +200 ML
-
.............
A W W
SPRING
1988
w m
SPRING 1987-
Figure 1. Seasonal variaticn in response (change in forced expired v o l m in one second a f t e r 2 b u r s of ozone exposure). Points = mans; f l a g s = standard deviations. Solid circles = subjects studied through winter: open circles = subjects studied in spring 1987.
316 TABLE 2 ASSOCIATIONS RFIWEEN INDIVICUAL SCREENING MAMINATION FINDINGS AND REACTIVITY TO OZONE, I N 25 SURJECTS WHO C@lPLEl'ED W'IUMN-WINTER F O W P D<poSURES "REACMRS
FINDING
P*
REF\CTORS
yes no
0 13
8 4
.0005
History of nonrespiratory a l l e r g i e s yes no
2 11
6 6
.Oll
Methacholine PD20 < 1000 breath u n i t s ( "reactive airways" )
Yes no
0 13
8
.0005
Increased upper respiratory swtoms an = m m Y days
Yes no
2 11
9 3
,004
Increased lower resp. symptoms with exercise on smggy days
Yes no
1 12
5 7
.063
Increased lower resp. symptoms a t rest cn srnggy days
Yes
0 13
2
.220
no
10
More s e n s i t i v e to smg than mst
yes no
6 6
.005
13
Yes no
3 10
10 2
.004
History of respiratory allergies'
people of similar age "Positive" €or any of above 4 characteristics
0
4
.
*Probability that associatian is due to chance, determined bq one-tailed Fisher exact test l'Association of ozone r e a c t i v i t y with allergy was confirmed bq skin tests: see text.
F m past experience in t h i s laboratory, the l o w e r l i m i t of normal airway
r e a c t i v i t y , expressed as the provocative dose of mthacholine necessary to
(PD ), was estimted to be 1,000 1 ,20 breath units. (One breath u n i t is defined as one vital-capacity breath of aerosolized solution containing one microgram of mthacholine chloride per milliliter.) Nonreactors' PD values ranged from 1,250 to mre than 6,000 20 breath units. Only 4 reactors had PD above 1,000: the other 8 reactors' 20 values ranged from 4 to 470 breath units. In their answers to intervew questions, reactors were s i g n i f i c a n t l y mre l i k e l y than nonreactors to report excess respiratory symptoms on smggy days, and to r a t e themselves as "mre induce a 20 percent decline in FEV
s e n s i t i v e to s m q " than nost people t h e i r m age.
317
h n g nonreactors, 8 subjects had no c l e a r l y positive skin test r e s u l t s (no wheal-and-flare responses of 2+ or greater i n t e n s i t y ) , 2 subjects had sinqle positive tests, 2 subjects had 2 p i t i v e tests each, and one subject was rot tested. ?rmng reactors, m l y 4 subjects had rn c l e a r l y p s i t i v e tests, and the other 8 subjects had 5 or mre positive tests each. "?E difference in positive respcnses between reactors and nonreactors was s i g n i f i c a n t (P < 0.05, Wilcoxon-Mann-Whitnev rank-sum test). DISCUSSION
These r e s u l t s suggest, mre strocqly than previous information, t h a t some
ms Angeles area residents show seasonal variation in t h e i r r e a c t i v i t y to 0 3
, consistent
with "adaptation" to repeated ambient exposures during the
sumner pollution season.
However, t h i s apparent "adaptation" vas not
consistent with predictions from laboratory wrk: it seemed im p e r s i s t for m n t h s in the absence of frequent ambient exposures, whereas laboratory "adaptation" is lost a f t e r a few days.
These r e s u l t s also suggest, mre
strongly than previous information, that upper-respiratory a l l e r g i e s or as-
mv be r i s k factors for excess r e a c t i v i t y
to 0 3
.
A t the
same time, both
these and previous findings show that high r e a c t i v i t y is by no means a consistent finding in a l l e r g i c or asthmatic persons.
The present questionnaire
answers indicate that self-perceptions of " s q s e n s i t i v i t y " m y be f a i r l y accurate in residents of an 0 -polluted area. 3
Thus amnunity-wide
questionnaire surveys m y be useful in research to identify and characterize reactive subgroups of the wpulation. b t h major findinqs from t h i s experimnt-the a w a r e n t seasonal variation i n response and the apparent association of asm or allergy with reactivitym y have important i w l i c a t i o n s for p l b l i c health, and thus for regulatory policy. H m v e r , the findings cannot be considered d e f i n i t i v e , qiven the limitations of the experimental design and the ccnparatively few subjects. They should be reinvestigated in a laver popllatim followed for a longer period of time. I t m y turn out that individuals who are inherently highly reactive to 0 or cannot "adapt" are nost a t r i s k f r a n ambient exposure, in 3 t h a t t h e i r repeated short-term responses eventually lead to i r r e v e r s i b l e lung damage and d i s a b i l i t y . Conversely, it m y turn out t h a t individuals who are consistently nonreactive or "adapt" readily are mt a t r i s k , i f curmlative pathological responses to 0 occur independent of the observable short3 term response. These possibilities need to be investigated, through basic
318
science to elucidate the mechanisms of response to 0 and through 3 empirical, longitudinal epidemiologic surveys of 0 - e x w e d pnxllatims. 3 REFERENCES
A i r Quality C r i t e r i a f o r Ozone and Other Photochemical Oxidants, 1J.S. Environmental Protection Agency, Fssearch Triangle Park, North Carolina, 1986. W.F. McDonnell, D.H. Horstmn, S.A. Salaam, and D.E. House, Am. Rev. Ilespir. D i s . 131 (1985) 36-40. J.D. Hackney, W.S. Linn, R.D. Buckley, and H.J. Hislop, Environ. Heal. Perspectives 18 (1976) 141-145. S.R. Hayes, A.S. Fasenbarn, T.S. Wallsten, R.G. Whitfield, and R.L. Winkler, Assessment of Lung Function and Synptorn Health R i s k s Associated with Attainnent of Alternative Ozone NAAQS ( f i n a l report, Environmental Protection Pgency c o n t r a c t 68-02-4313) , Systems Applications Inc., San Rafael, California, 1987. W.F. McDwvlell, D.H. Horstman, S.A. Salaam, L.J. Faqgio, and J.A. Green, Toxicol. Indust. Heal. 3 (1987) 507-517.
T.Schneideret al. (Editors),Atmospheric Ozone Researchand its Policy Implications
313
0 1989 Elsevier SciencePublishersB.V., Amsterdam - Printed in The Netherlands
WSIMETRIC MODEL OF ACUTE HEALTH EFFECTS OF OZONE AND ACID AEROSOLS IN CHILDREN
M.E. Raizennel and J.D. SpenglerZ 'Health and Welfare, Canada, Environmental Health Directorate, Room 203, Tunney's Pasture, Ottawa, Ontario, Canada, K1A OL2 2Harvard School of public Health, 655 Huntingdon Avenue, Boston, Massachusetts, 02115
USA,
FblmxFicr
During the summer of 1986, 112 young females, 7 to 14 years of age attended one of three, 2 week sessions, at a residential s m e r camp located on the north shore of Lake Erie, Ontario, Canada. Children performed standardized spirometry each afternoon and on at least one occassion completed a standardized exercise test. Over the course of the 41-day study, 0,, SO,, NO,, and acid aerosols (H2S04) were continuously monitored. Hourly ozone varied between 40 and 143 ppb. The 12 hour acidic particle concentrations expressed as H2S0, equivalent was 28 pgg/m3 during one episode and fine particle sulphate was 100 kg/m3 for the peak hour. During the exercise test minute volume (V,) and heart rate (HR) were measured. Each day different children wore portable heart rate recording devices which recorded heart rates for each minute for up to twelve hours. Using a dosimetric model, a child's estimated dose of ozone and [H+] was calculated for various time periods prior to the time of lung function testing. This paper reports the development of individual exposure estimates, based on time-activity data, and relates these exposures to changes in lung function observed in children.
1mcr10N
In the past decade significant improvements have been made in the design of air pollution studies through the incorporation of improved measurements of both
biologic and aerometric indices of exposure.
However, important
limitations remain in relating ambient concentrations of air pollutants to actual population exposures (ref. 1).
This is a critical issue in the
functional transition of data between clinical and epidemiologic studies. Epidemiologic studies assessing the acute health effects of ozone exposures have provided supporting evidence of relationships reported in human chamber studies (ref. 2).
Human studies have repeatedly demonstrated that ozone at
concentrations currently observed in ambient air, elicit significant transient physiological changes in lung function and increased respiratory symptomatology (refs. 3-11).
However the intercomparison of laboratory and atmospheric
studies for acidic aerosol exposures is less clear.
320
In order to improve our understanding of the relationship between exposures and adverse health responses, the estimate of personal exposure and/or dose delivered to the respiratory system requires greater resolution.
Complex
models have been developed which estimate the delivered dose of gases to the lower respiratory tract (ref. 12,13).
These have provided vaLuable information
in predicting delivered dosages to specific areas of the respiratory tract. The models however are limited by their irrelevance to "free living" exposures where the dynamics of multiple factors (i.e. breathing mode, exercise, anatomical and behavioral variability) increase or reduce the effective dose delivery of pollutants. Mage et al. (ref. 14) demonstrated that an increase in activity, as reflected by heart rate measurements, could modify the estimated airway/lung dose of ozone by 70%. The delivered dose or cumulative dose may be the important determinant of altered lung function responses.
Thus more
accurate estimates of dose would reduce error inherent in the reliance on measurements of concentrations or even exposures in the population. environmental chambers, concentrations during
In
exposure and dose are assumed
correlated since many variables can be controlled and monitored. However, the limitations inherent to chamber studies in general (ref. 15) also limit the development of dose over extended periods of time. In this paper subject specific and day specific dose estimate models for ozone and for acidic aerosols are developed. These estimates will then be used to assess the relationship between dose estimates and observed changes in lung
function in children. IIE!l!EOJlS
An acute respiratory health study was conducted in southern Ontario during the s m e r of 1986. One hundred and twelve (112) healthy young females, 7 to 14 years of age, attended one of three, 2 week residential s m e r camp sessions
in July and August. The camp was located on the north shore of Lake Erie, near Dunnville, Ontario.
Prior to attending the camp, parents completed a self-
administered respiratory questionnaire and signed an informed consent for their child to perform the health tests. 15:OO
and
17:OO
hours,
spirometric maneuvers.
In the afternoon of each camp day, between
children performed
standard
forced
expiratory
On at least one occassion a 12 minute, graded cycle
ergometer exercise test, to a target heart rate of 170 beats/min, was completed by all children.
Heart rate (HR) and minute volume (V,)
throughout the exercise test.
were recorded
In addition, on each of 24 days, 5 randomly
chosen children wore portable heart rate monitors that recorded mean heart rate each minute for up to 12 consecutive hours throughout their daily activities (Sport-tester, PE 5000, Finland). acid aerosols (i.e. H,SO,)
Air pollution monitoring for 0, and strong
was performed at the camp site. Ozone was measured
321 continuously by a Monitor Labs 8410E chemiluminescent monitor and sulphur measurements were derived from the modified Meloy speciation flame photometry analyzer (ref. 16).
particle
285 thermal
With a thermal volatilization
technique this instrument can measure the presence of strong acid particle sulphur.
Details of health and aerometric methodologies have been reported
elsewhere (refs. 9,17). ExposuRE/DosE D O -N
To examine the relationship between exposure-dose and changes in lung function, day specific and child specific dose estimates to 0, and equivalent were calculated.
H,SO,
To demonstrate the development and application of the
dose estimate we will use the aerometric data collected during the second camp period when a significant episode of high ozone and high acid particle levels was observed.
The hourly mean, minimum and maximum values for air pollutants
on a low pollution day (July 16th) and on the episode day (July 25th) are presented in table 1.
The analyses of data for all children and all days will
be reported elsewhere. The following general formula was applied to calculate dose for any time period : Dose (pg) = r * V, * t [pollutant] (eq. 1) The symbol 'r' is the retention factor to the respiratory tract. For ozone, data from Young have suggested that ozone retention/penetration beyond the oropharyngeal region is a complex function of V, and 0, concentration (ref. 18).
A step function for r over a range of V, at .1 ppm was used to calculate
appropriate retention factors since the ambient measurements were distributed around .1 ppm.
For acidic particles the penetration factor was fixed at 0.6
because most of the acidic component is contained in particle sizes between 0.2 and 0.6
pm
(ref. 19) and the depositional characteristics of hygroscopic
acidic aerosols in this size range have deposition characteristics described by Tu et al. (ref. 20).
Adult airway characteristics have commonly been used in
gas and particle penetration studies. factors in estimating ozone and H,SO,
Thus the application of retention
dose in children is recognized to be of
limited accuracy. V,
child.
(minute volume) estimates were derived from empirical data for each Individual functions for minute ventilation were generated by
regressing the logarithm of the exercise minute ventilation against the heart rate obtained for each child separately. These were expressed in the form: V,
= exp (a + 8 HR) where a is the logarithm of V,
relationship between HR and V,.
(eq. 2) at zero heart rate and 13 defines the
322 TABLE 1.
Aerometric Profile (Hourly Data) on Control Day (July 16th) and Episode Day (July 25th) 8:OO to 19:oo Control (July 16th)
Episode (July 25th)
Mean
Min
Max
Mean
Hin
Max
03 (PPb)
44
39
50
121
93
143
SO, (PPb)
0.6
bdl
2
bdl
15
SO, (w/m’)
4.0
1.7
7.2
84
71.5
101.6
HzSG (pg/m’)
0.2
bdl
0.5
23.7
bdl
47.7
1.1
bdl
2
5.1
2.0
10.0
1.2
1.0
2.0
4.5
2.0
7.0
21.7
18.6
24.9
24.5
21.7
25.7
48
17
81
77
91
NO,
(PP~)
NO2 (PPb)
Temp.(“C) Relative Humidity ( % )
59
9.4
bdl : below detection limit Individual mean hourly heart rates were then substituted in the equation 2 to determine the mean minute ventilation for each hour. rates (8:OO
-
Mean hourly heart
18:59 hours, 11 hours total) were calculated for each subject on
the day they wore the heart rate monitor. The symbol ‘t‘ is the duration of exposure and represents an interval of time.
‘[pallutant]’ is
defined as
the mean
concentration over
the
corresponding period of time for the pollutant of interest. The estimate of cumulati-ge dose for the ith child, Di, is given by: OZONE W S E (pg) = 0, Di
J 0, D, =
E t, * 03 r,, j=1
V=I,
[03I3
where, t, = one hour for all j; j = index for time interval; J
=
number of time
intervals; 0, r,, = ozone retention factor in airways for the ith child, in the jth time interval; H,SO,
ri, = 0.6 retention factor; V,
=
ventilation rate
323 for ith child, in the jth time interval (L/hr); [O,], = ozone concentration for jth time interval (pg/L); [H,SO,], = H,SO, concentration for jth time interval (W/L). RESULTS
Since heart rate data for each child were only available on one day it was necessary to extrapolate the heart rate values to all days of lung function testing in order to develop a unique exposure measure per child.
However a
major interest in this paper was to investigate the exposure profile on the day of a large episode in which no heart rate measurements were taken. A mixed effects model was used to investigate the source of variation for heart rate. The response, heart rate, involved up to 11 hourly average measurements on 104 children, with approximately 5 children sampled each day for 24 days. The mean hourly heart rate over the daytime interval is presented in figure 1.
Heart
rate was modelled by the child's age, height and weight, with variance components, day, child within day and time (hour).
Time explained the largest
percentage of variation, 60%. while child explained 36% and day
Since the
4%.
variation in heart rate between days is the smallest we replicated each child's hourly heart rate pattern across days. Thus for the 27 children at the camp on the day of the episode we applied individual heart rate profile from their sample day and from this we derived estimates of minute ventilation (eq. 2). Figure 1
Mean Heart Rates vs Time of Day (Mean
5
1 standard deviation)
130 125
120 115 110 105
100 95
90 85
-- 1
Rll
7
I
I
I
I
I
I
I
I
I
I
I
8
9
10
11
12
13
14
15
16
17
18
Time of Day ( h o u r )
19
324 In order to relate heart rate to minute volume ventilation, each child performed an exercise test in which the logarithm of minute ventilation was regressed on heart rate for each child separately.
This linear function
explained approximately 99% of the variation in each child's response. Colucci (ref. 21) developed a series of equations relating V, equation for children (V,
=
and heart rate.
His
1.635 exp (0.0185 HR)) closely approximates our
results (V, = 2.200 exp (0.016 HR)) when the calibration slopes are averaged across all children.
The coefficient of determination was .72 when a common
slope for all children was derived from the logarithm of V,
to heart rate.
Since we had child specific slope estimates we chose to use individual slopes rather than an average slope for all children. The dose estimate model is derived in part from ventilation rates and it has been necessary to assume that heart rates are correlated with physical activity. Ventilation rate in turn is derived from heart rate therefore it was necessary to assess the independent effect of heart rate on lung function. This was examined by regressing lung function on the average heart rate in the hour previous to the test and adjusting for the child's age, height and weight This analysis indicated little evidence that heart rate was related
(N=107).
to lung function changes. Figures 2 and 3 are plots of the percent change in PEFR versus the cumulative dose estimates to 0, and H,SO,,
respectively, for the 6 hour period
prior to the lung tests. Figure 4 is a plot of the episode day, hourly polluFigure 2
Individual 6 Hour Estimated Cumulative Dose f o r Ozone vs P e r c e n t Change PEFR, Episode Day (July 25, 1986) 8
6 4
2 0 -2 -4 -6 U
-8 -10
-12 -14 -16
L
--
-
0
0 0
0 1
.
1
.
I
I
I
I
*
I
,
325 Figure 3
Individual 6 Hour Estimated Cumulative Dose for H2S04 vs Percent Change PEFR, Episode Day (July 25,1986) 9 7
E W a
0
5 3
0. -- ----_0----_ 0 0 ---__ a0 ----- ---_----_
: A
; d
0
0
0
0
.-
c" 2 0
0
0
-1
-3
m
-5 -7
0
----,
0
0
-9
0
0
-1 1
-13 0 -
-15
-17
'
20
I
I
I
I
I
I
40
60
00
100
120
140
Estimated H,SO,
mean = -1.45
160
Dose (Micrograms)
_--------
slope = -.033
Figure 4
Mean Hourly Pollutant Concentrations Episode Day (July 25, 1986) 300
"
50
h
E
280
\
I
40
v
v
"v, -0
2 60
240 220
h
c
a
200
\
10
3 , v
180
0
326 tant concentrations.
From this figure it can be seen that both 0, and H,SO,
followed a similar pattern.
However the increase in acid was markedly
different in that the concentration increased threefold between 1O:OO and 14:OO for H,SO,.
For the same interval, ozone levels increased by 70 pg/m3 and are
noted to be relatively stable for the
hour period prior to the lung tests.
4
The percent change in lung function is calculated using the mean of the child's lung function value measured daily at camp and subtracting this value from the observed value on the episode day and divided this difference by the mean value.
The mean percent decrement is given by the broken line (N=27) and
the least squares regression liie for percent change on dose is also given in these figures.
Although the slopes of these lines did not differ from zero
(p>.lO) there exists a negative trend in lung function as cumulative dose
increases for both 0, and H,SO,. DISCUSSION
We
have
used
biometric
and
aerometric data
collected during
environmental health study to provide exposure and dose estimates.
an The
dosimetric model examined reflects the observed relationships between exposure and decreases in lung function, specifically PEEX.
Decreases in lung function
have been observed for ozone and acidic aerosols in chamber studies and, for ozone, in acute epidemiologic studies.
Without individualized dose estimates
all children would have been assumed to experience the same exposure as measured by the fixed site monitors. The data presented here indicate that the range of personal exposures to air pollutants varies markedly
between
individuals. All essential variables required in the development of an exposure/dose estimate have been quantitatively addressed.
The retention factors used in
equations 2 and 3 were derived from limited data and estimated for ozone (ref. 18)
and for aerosols (ref. 20).
Retention factors for ozone have not been
included in dose estimates in original studies and in dose assessment reviews (refs. 10,21).
As proposed by Young, 'rl is a complex function of mode of
breathing, minute ventilation and exposure concentration (ref. 1 8 ) .
Evidence
from human clinical studies have indicated that -50% of inspired ozone is removed by the upper airways (Gerrity, this symposium).
It has also been shown
that the lung function response is dependent on ventilation rate and on 0, concentration (refs. 22-24). then the estimates of ,V estimates.
Since r is a function of V,
and concentration
take on greater significance in dose modelling and
Recently, Folinsbee et al. reported calculations of effective dose
for 6.6 hour exposures to ozone at .120 ppm (ref. 10).
The cumulative dose
estimates for adult subjects were approximately 1500 pg of ozone however these calculations did not include a penetration/retention factor. The same authors
32 7
also calculated cumulative exposures for other chamber studies with exercise and varying duration.
The mean exposure ranged from 490 to 1164 pg.
For
children at our camp, on a high pollution day, we estimate the mean ozone dose in children to be approximately 300 pg when a retention/penetration factor is included.
In contrast, without a retention/penetration function applied, a
mean ozone dose of 1100 pg would be estimated.
This latter dose estimate is
remarkably similar to data reported for adults in chamber studies where lung function changes have been associated with ozone exposures (refs. 10.21.22). The
data
described
in
this paper
does
not
indicate
significant
relationships between decreases in lung function and modelled dose.
However,
the direction and magnitude of the lung function changes are consistent with results of acute epidemiologic studies where small changes in lung function have been associated with ozone (refs. 3-11) and other air pollutants (refs. 26,27).
Note that the purpose here is to demonstrate the application of a
child specific dose model to determine if it should be used for the entire data set. Using integrated particulate acid data Spengler et al. (ref. 16) have estimated that children would experience acidic aerosol doses having a mean H+ concentration of 2350 nmoles (230 pg equivalent H,SO,
) over a 12 hour period.
It was also noted that this dose estimate was to reported values in chamber exposures ( - 110 pg equivalent H,SO,
)
to acid aerosols.
We examined the
cumulative dose for the 6 hours preceding the lung tests using the continuous particle sulphur data.
For this paper we make a simplifying assumption that
all the particle sulphur volatilized at 120°C is equivalent to sulphuric acid. This will be
an underestimate if there are additional acidic particle
volatilizated at 300°C.
The mean H,SO,
retention fraction of 60% was
-
91 pg.
equivalent
F,
hour dose estimate with a
The relationship of the 6 hour dose
estimate to lung function was similar to that observed for ozone in that the model predicts that small changes in lung function can be expected to be related to acid exposures (figure 2). The day to day variation in heart rate and the variation in heart rate across children were observed to be less than the hour to hour variations. These results indicate that, at least for this specific camp, the daily program elicited a similar heart rate profile each day.
As
noted previously, the
differences in heart rate between children and across hours of the day are strong sources of variation in heart rate and V,.
Nonetheless, the dose
estimates derived for each child on the episode day indicate that small changes in lung function, could be observed to be related to cumulative dose estimates for both ozone and H,SO,.
328 SUlllvLRY
The application of a child specific dose calculation is an advantage over the alternative methods for exposure estimates. The conventional approach used in previous acute health studies has equated dose to ambient concentrations. Typically, the maximum one hour ozone concentration occurring in the previous 12 or 24 hours is used as the exposure measure. Similarly, particle exposures were time averaged concentrations. Using these conventional approaches, assumes that all children have the same ventilation volume, retention and are exposed to time and spatially averaged pollution. The errors associated with these assumptions are never explicitly stated nor incorporated in the analysis. Hourly pollution data and child specific ventilation volume were used to estimate an ozone and acidic particle dose for children participating in an acute respiratory health study. A single 6-hour episodic event was selected to demonstrate this approach. Calculated dose varied substantially among children. Ozone dose ranged from 150 pg to 750 pg. The equivalent sulfuric acid dose ranged from 50 pg to 150 pg. The conventional approach would implicitly assume a single value for all children. This study is important because it illustrates the
"between subject
variation in dose" not accounted for in previous studies.
We recognize that
this has been a demonstration exercise.
Nevertheless, it suggests that
refining exposure measures may enhance the ability of acute health studies in ascertaining effects. -
A
The authors which to acknowledge the collaboration of Mr. Douglas Haines and Dr. Richard Burnett in the preparation of this manuscript. We also wish to thank Dr. M. Lippmann for his review and comments on the manuscript.
1. M. Lippmann, P.J. Lioy, Environ. Health Perspect., 62 (1985) 243-258. 2. D.W. Dockery and D. Kriebel, in E.J. Calabrese and D. Gilbert (Editors), Proceedings of the Northeast Regional Public Health Environment Center: Ozone Risk Communication Conference, 1987, Lewis Publishers (in press). 3. M. Lippmann, P.J. Lioy, G. Leikauf, K.B. Green, D. Baxter, M. Morandi, B.S. Pasternack, D. Fife and F.E. Speizer, in S.D. Lee, M.G. Mustafa and M.A. Mehlman (Editors), Advances in Modern Environmental Toxicology, Vol. 5, Princeton Scientific, Princeton, 1983, pp. 423-446. 4. N. Bock. M. Lippmann, P. Lioy, A. Munoz, F.E. Speizer, in S.D. Lee (Editor) Scientific Basis for Ozone/Oxidant Standards, APCA International Specialty Conference TR-4; Houston, Texas, 1984, pp. 297-308. 5. P.J. Lioy, T.A. Vollmuth, M. Lippmann, JAF'CA, 35 (1985) 1068-1071. 6. D.M. Spektor, M. Lippmann, P.J. Lioy, G.D. Thurston, K. Citak, D.J. James, N. Bock, F.E. Speizer and C. Hayes, Am. Rev. Respir. Dis., 137 (1988) 313320. 7. M.E. Raizenne, R.T. Burnett, J.D. Spengler, Arch. Environ. HealthSubmitted April, 1988.
329
8. M.E.
Raizenne, R.T. Burnett. B. Stern, C.A. Franklin, J . Spengler, Proceedings from the International Symposium on the Health Effects of Acid Aerosols, Submitted to Environ. Health Perspect., Presented October 19-21,
1987. 9. L.J. Folinsbee, W.F. McDonnell and D.H. Horstman, JAFCA, 38 (1988) 28-35. 10. E.L. Avol, W.S. Linn, D.A. Shamoo, L.M. Valencia, U.T. Anzer, T.G. Venet, J.D. Hackney, Am. Rev. Respir. Dis., 132 (1985) 619-622. 11. W.F. McDonnell 111, R.S. Chapman, M.W. Leigh, G.L. Strope, A.M. Collier, Am. Rev. Respir. Dis. 132 (1985) 875-879. 12. F.J. Miller, J.H. Overton Jr., R.H. Jaskot, D.B. Menzel, Toxicol. Appl. Pharmacol., 79 (1985) 11-27. 13. J.H. Overton Jr., in F.J. Miller and D.B. Menzel (Editors), Fundamentals of
Extrapolation Modeling of Inhaled Toxicants: Ozone and Nitrogen Dioxide, Hemisphere, U.S.A., pp. 273-294. 14. D.T. Mage, M.E. Raizenne, J.D. Spengler, in S.D. Lee (Editor) Scientific Basis for Ozone/Oxidant Standards, APCA International Specialty Conference TR-4; Houston, Texas, 1984, pp. 238-249. 15. M.J. Utell, in R. Frank, J.J. O'Neil, M.J. Utell, J . D . Hackney, J. Van Ryzin and P.E. Brubaker,(Editors) Inhalation Toxicology of Air Pollution: Clinical Research for Regulatory Policy. American Society for Testing and Materials, Philadelphia, 1985, pp. 43-52. 16. G.A. Allen, W.A. Turner, J.M. Wolfson, J.D. Spengler, Description of a Continuous Sulphuric Acid/Sulphate Monitor. Presented at the 4th National Symposium on Recent Advances in Pollutant Monitoring of Ambient Air and Stationary Sources., Raleigh, NC.. 1984. 17. J.D. Spengler, G.J. Keeler, P. Koutrakis, M.E. Raizenne, C.A. Franklin, Proceedings from the International Symposium on the Health Effects of Acid Aerosols, Submitted to Environ. Health Perspect., Presented October 19-21, 1987. 18. J. Young, Johns Hopkins University School of Hygiene and public Health,
Baltimore, (Master's Essay), 1977. 19. P.E. Koutrakis, J.M. Wolfson, J.D. 20. 21. 22. 23.
24.
Spengler, B. Stern, C. Franklin, submitted for publication, Harvard School of Public Health, Boston, Mass. K.W. Tu, and E. 0. Knutson, Aerosol Sci. Technol. 3 (1984) 453-465 A.V. Colucci, in T. Schneider and L.Grant (Editors), Air Pollution by Nitrogen Oxides, Elsevier, Amsterdam, 1982, pp. 427-440. M.J. Hazucha, J. Appl. Physiol., 62 (1987) 1671-1680. M. Hazucha, F. Silverman, C. Parent., S. Field, D. Bates, Arch. Environ. Health, 27 (1973) 183-188. F. Silverman, L. Folinsbee, J. Bernard, R. Shephard, J. Appl. Physiol., 41
(1976) 859-864. 25. W. McDonnell, D. Horstmann, M. Hazucha, E. Seal Jr., E.D. Jaak, S.A. Salaam, D.E. House, J. Appl. Physiol. 54 (1983) 1345-1352. 26. D.W. Dockery, J.H. Ware, B.G. Ferris,Jr., F.E. Speizer, N.R. Cook, JAPCA 32 (1982) 937-942. 27. W. Dassen, B. Brunekreef, G. Hoek, P. Hofschreuder, B. Staatsen, H. de Groot, E. Schouten, K. Biersteker, JAPCA 36 (1986) 1223-1227.
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T. Schneider et al. (Editors), Atmospheric Ozone Research and its Policy Implicatwns 0 1989 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands
331
Is There a Threshold for Human Health Risk from Ozone? Daniel B. Menzel', Robert L. Wolpert2 Department of Pharmacology'2, Departme9 of Medicine', and Institute of Statistics and Decision Sciences Duke University, Durham, NC 27710 (U.S.A.)
ABSTRACT The existence of a "threshold," or concentration below which no adverse health effects are observed, is the basis for current air quality standards in the U.S. After using a regional dosimetry model (Miller-Overton) to adjust for variations in animal species, exposure scenario, breathing patterns, etc., measurements of several different toxicity end-points reported by different laboratories were found to lie on a straight line passing through the origin, suggesting the absence of a threshold or no-effect level in animals. On the other hand, the biochemistry of ozone and its detoxification mechanisms suggests that a threshold should exist. Two mathematical population models are examined to illustrate how repair mechanisms affect such thresholds and how a population-wide threshold might not exist. The probability of injury can, however, be calculated so that an acceptable level of risk can be chosen. The models also illustrate how specific populations at risk can be identified, in this case for vitamin E deficiency as in cystic fibrosis patients. INTRODUCTION Toxic chemicals are currently classified as either "threshold chemicals, having some concentration of exposure below which no observable toxic effect occurs, or as "nonthreshold" chemicals, exhibiting some toxic effect even at vanishingly small exposure concentrations. Carcinogens, mutagens and other genotoxic chemicals are thought to be "nonthreshold" chemicals, while the majority of non-genotoxic or systemic toxic chemicals are thought to be "threshold" toxicants. Two different regulatory approaches have evolved as a consequence. "Non-threshold chemicals are regulated at levels which will produce a socially acceptable level of risk, such as 1 adverse reaction in lo6 members of the exposed population. "Threshold" chemicals are regulated by establishing an "acceptable daily exposure (or intake)" level, judged to provide an "adequate margin of safety." Exposure to the accepted daily exposure level should not result in any adverse reactions, because of the margin of safety incorporated into the selection. Ozone and other air pollutants that are not established carcinogens are regulated in the U.S. under the assumption that an acceptable time-averaged exposure level can be tolerated by most individuals without injury, and that an adequate margin of safety can be provided to prevent adverse reactions even in highly susceptible subpopulations. The advent of mathematical dosimetry models (ref. 1) allows nne to combine evidence from several different human and animal experiments from different laboratories to examine the relation between the delivered dose, called molecular dose here, and toxic response. Observing the same
332
molecular dose-toxic end-point relationship in several animal species enhances our confidence that the same events and molecular dose-response will occur in humans. The Miller-Overton dosimetry model can be used to predict the molecular dose sustained by an animal at any lung site during a specxed period of exposure to a given concentration of an air pollutant; of course the animal species, strain, sex, size, and breathing pattern must be specifled in detail. Since the model’s molecular dose predictions are proportional to the exposure concentration and duration, they may be summarid in the form of a constant p (which we call the Miller modulus). the predicted molecular dose for an exposure to 1.0 ppm for 1.0 day. Upon comparing observed health effects with model predictions of molecular dose from a number of r e p o d ozone exposure experiments, no threshold or no-observable-effect level has been found for ozone in any animal species. From the biochemistry of owne injury, an individual threshold, 8, is hypothesized and two population-based models are presented to examine how biological repair of owne-induced injury affects risk and how a subpopulation’s deficiency in repair may leave that subpopulation at high risk to the effects of ozone toxicity. The models are used to present a way in which an acceptable level of risk from ozone exposure might be calculated, even in the absence of a population-wide threshold. favorine a thmhold for ozone The toxicity of ozone has been reviewed recently by Menzel and Shoaf (refs. 2,3). The theory proposes that ozone’s toxicity stems from its oxidation of essential protein groups, thiols, and polyunsaturated fatty acids (PUFAs). The toxic symptoms are thought to arise from the cytotoxic effects of oxidation of the PUFAs in the cellular membrane. This hypothesis is supported by the evidence that vitamin E, the principal intracellular antioxidant, has a profound effect on ozone toxicity. The reaction of owne with PUFAs is one of the few reactions with high enough reaction rates to account for the removal of inhaled ozone from the airways (nf. 1). Ozone exposure causes major increases in the metabolic pathways leading to detoxification of lipid peroxides (ref. 2). Pulmonary edema, a common symptom of ozone toxicity in several animal species (including humans), arises from cell membrane destruction caused by lipid peroxidation. Lipid peroxidation is initiated by the combination of owne with ethylene groups of membrane PUFAs leading to the production of ownides (ref. 4). Ozonides can decompose directly to peroxides capable of further free-radical reactions in the presence of oxygen. As reported elsewhere in this symposium by Rietjens and Alink (ref. S), glutathione can react with and detoxify ownides by inhibiting the further promotion of lipid peroxidation. Similarly, vitamin E reacts with both ozone and lipid peroxides to terminate lipid peroxidation (ref. 4). The induction of glutathione peroxidase by owne could also facilitate the elimination of lipid peroxides. These molecular defenses all suggest that major lipid peroxidation is unlikely to occur until the cell defenses (primarily vitamin E) are overwhelmed, and hence that there should exist a threshold below which no cytotoxicity will occur. If cytotoxic effects are primarily responsible for the observed toxic effects of ozone, this suggests the existence of a threshold
333
for omne toxicity.
..
m b i m l e-al The animal exposure experiments reviewed in (refs. 2.3) study different effects of ozone in differing species at varying concentrations, exposure regimens, and breathing patterns. We have sought to render the experiments more nearly comparable by correlating reported exposure-related injury, not to ambienr concentration, but to the estimated time-integrated regional dose at the site of tissue injury in each study of ozone toxicity. We have used the Miller-Overton ozone dosimetry model (ref. 1) to estimate regional doses for each animal species, ambient concentration, exposure regimen, body size, and breathing pattern employed in experiments reported in the literature. Under the assumptions inherent in the Miller-Overton model the ozone burden at each site in the lung of each species, under each exposure regimen and breathing pattern, is proportional to the product of the exposure concentration and the exposure duration; the proportionality constant is the Miller modulus, p. It is convenient to use units of (pgozone)/(g wet tissue weight).ppm .d for p. so that an exposure to c ppm ozone for t days will lead to a tissue burden at the site of injury of p c .t pg 03/gtissue.ppm .d. We assume that molecular ozone is the toxicant. With tabulated values of the Miller modulus p for various sites, animal species, body weights, breathing patterns, etc. it is possible to measure exposure doses on the same scale for all experiments (pg 0 3 / gtissue.ppm .d at the site of injury) to assist in comparing or combining the results of different studies and in making health effect predictions for one species on the basis of evidence gathered about another. Examples of p calculated for mice and adult humans are ~ ~ 7 0and . 4~ ~ ~ 1 pg 7 03/g . 8 tissue.ppm d ,respectively. 1000
0
900
.
0
.
I
.
.
I
~
~
~
~
"
~
"
"
~
"
.
'
"
'
I
10 20 30 40 50 60 70 Total Lung Dose of Ozone (pg)
Figure 1. Increase in lung lavage fluid protein in rats following omne exposure. Each point represents a separate study reported in the literature. Total lung molecular dose was estimated using the Miller-Overton dosimetry model.
334
We have reported such inter-species extrapolations and comparisons of ozone toxicity evidence elsewhere (ref. 6). Figure 1 illustrates the results of such a research synthesis studying pulmonary edema in rats. This evidence does not support the existence of a threshold for ozone toxicity in rats. A variety of other end-points follow the same type of relationship as shown in Figure 1.
A FAMILY OF MATHEMATICAL MODELS FOR OZONE TOXICITY If each individual in the population has a threshold tissue burden 0>0 (measured in pg03/gtissue.ppm.d) below which that individual will sustain no injury, and if for each OQ<- the function F ( x ) gives the fraction of the population with a threshold 0 lower than x , then an ozone exposure leading to a tissue concentration of x pg 03/gtissue.ppm .d (causing injury in all the individuals with thresholds k x ) will lead to injury in F(x)x100% of the population. For randomized experiments F ( x ) would give the probability that an individual drawn from the population at random would sustain injury at a tissue burden of x pg 0 3 / g tissueppm .d. We can study a family of ozone toxicity models by considering different possible population distributions F ( x ) for individuals' thresholds, and different possible relations between the time-dependent ozone exposure concentration of c (t) (in ppm) and the tissue burden (in pg 03/gtissueppm .d). We will study and compare the model predictions for two simple distributions F ( x ) for individual thresholds within the population: the log-normal distribution, where the quantities log(0) have a normal probability distribution with some mean m and variance os2,and the log-logistic distribution, where log(0) has a logistic distribution with some mean m and dispersion parameter oS. In each case e m = Z D # is the molecular burden at which half the population would die. We will later consider a truncated normal distribution where every individual's threshold lies within a fixed interval [LDg*e-3a8, LD#'e+3u8 I. If no repair mechanism existed then upon continued exposure to a constant concentration of c ppm ozone, the tissue concentration b ( t ) at a possible site of injury would simply increase linearly at a rate given by the Miller modulus, b(t)=p.c.t. Under a linear repair mechanism, the molecular burden b = b ( t ) at the site would instead satisfy a differential equation of the form
Here p is the Miller modulus and p20 (with units d-') is the (daily) linear repair m e . The same methods can be applied to the study of more complex repair mechanisms, e.g. saturable ones in which the repair rate may depend on vitamin E membrane concentration or on the reinsertion of molecules in the cell membrane. The simplest case to consider is that in which the repair rate is negligible, i.e. p=O, in which case the solution to (1) with no initial burden is simply
335
or, for constant exposure concentrations, b (t ) = P.C
.t.
(2)
With threshold-distribution F ( x ) , the proportion of individuals in the population who would sustain injury following exposure at constant concentration c for duration t (starting with no ozone burden) would be M ( t ) = p[e s p c . t ] = F ( p C . t ) .
For the log-normal distribution this is simply M ( t ) = o(og-l ln(pc.t/LD?fP')),
(3a)
where @ ( z ) denotes the probability that a standard normal random variable would not exceed z . It follows that the mortality curve at fixed concentration c should follow a probit evolu-
tion, i.e.
@ ( M ( r ) ) = og-' In(t) + [og-l ~ n ( p . c / ~ ~ ? f P ' ) ] .
(3b)
In our study of the effect of vitamin E and polyunsaturated fat diets on ozone mortality in Swiss Webster 0 - 1 mice (ref. 7) we observed and reported just such a relationship. Under linear repair at rate p>o the solution to (1) with initial condition b=O is I
b ( t )= p j c ( J ) e * ( t - s ) b 0
or, for constant exposure concentrations, b ( t ) = p.c.p-'(l
- e?').
In the absence of a repair mechanism the lung burden b ( t ) = pc .t would increase without bound during exposure at a constant concentration c ; with linear repair b is always bounded by its asymptotic value, b ( t ) < b , Ipclp. Again we can calculate the mortality curve, this time finding M ( t ) = p[e s b(t)l = F(p.c.p-l(i - e-"))
For short exposures or low concentrations this will be indistinguishable from the no-repair case (3a), but now the asymptotic (or lifetime) mortality rate is bounded by
M, = F ( p ~ / p <) 1,
(5)
while M, = 1 in the absence of repair. Either with or without repair, the question of whether or there is a threshold concentra-
336 tion below which ozone exposure is nonfatal has an ambiguous answer: For each individual, there is a threshold molecular burden 0 and a corresponding threshold dose c .r = 8/c( below which that individual is not at risk, with or without a repair mechanism; For any positive dose c .t there will be some individuals in the population whose threshold 0 is sufficiently low as to cause injury. if the threshold distribution F ( x ) S for each x>o (i.e. if arbitrarily low thresholds B T ~possible). Both the log-normal distribution and the log-logistic distribution satisfy that criterion, and hence no population-wide threshold exists under either distribution. Of course, the log-normal and log-logistic distributions are only intended to serve as approxi-
mations to the true distribution of individual thresholds, and cannot describe that distribution exucrly; in particular, there are only finitely many individuals in the population and so there must be a strictly positive lower bound to the finite set of individuals' thresholds. The interesting possibility arises that the true population distribution of thresholds differs in important but almost undetectable ways from the log-normal distribution: in particular, that for some strictly positive number 00,
P[~<E]=F(E)=O. Such a number E would constitute a population-wide threshold for the molecular burden, and p . ~ a population-wide threshold for ambient dose. It is quite possible for the true 8distribution to exhibit such threshold behavior and yet for the log-normal distribution to provide an entirely satisfactory fit to our data. For example, only one time in 740 will a lognormal random variable be smaller than LB#e-3u'; many hundreds of observations would be required before an investigator would have a good chance of observing a subject with such a small threshold. It would be difficult to detect by experiment whether or not the population contains any individuals with thresholds below LD!#e-3a1, and no conceivable experiment could detect a threshold lower than LDge-kl since the probability (under the log-normal model) of seeing an individual with such an abnormally low threshold would be less than one in three million. In our data set (described below) e-50r = 4.6%. Thus we cannot rule out the possibility that a population-wide threshold does exist, possibly as large as 5%-10% of
mg. Risk estinlgfes from lop-Dmbit and l o d o & models Under the no-repair assumption and the log-probit model we found the mortality rate for an exposure of duration t at constant concentration c to be
leading to an estimate of cq
=[m@/p]
,'I*-'(')
for the dose leading to a population mortality of lOOR % for each O I R $1. With the estimates
337
[LD#/p] = 30pprn.d and as = 0.617. arising from our exposure experiments with SwissWebster CD-1mice (ref. 7), this leads to numerical estimates in Table 1. Table 1. Probit Model Ozone Risk Estimates for CD-1 Mice
0.50
# 4.1
= 30.0 -2.326~~
= 7.14
10-2
[Wf@l e
lo4
[ ~ ~ ' ; t p ' /e-3.719a1 pl = 3.02
10-~
[LD';tp'/p]e4.265a1 = 2.16
lo4
[ ~ ' ; t p ' 4 1e -4.753a1 = 1.60
Many investigators have noted that a logit model often fits data as well as does a probit model. If the population distribution of thresholds 8 follows, not the log-normal distribution, but the "log-logistic'' distribution with median LD # and scale parameter os, then the resulting evolution would be log-logit:
M
(t = p[e
s p.c -11= F (p.c . t )
or 1-M(t)
= (p.c-t/LD#).
The normal and logistic distributions are quite similar over most of their ranges (they are both "bell-shaped"), and differ most significantly in their tail behavior. The normal has sharp tails, making outliers rare, while the logistic has flatter tails. In consequence the two models may fit small data sets equally well, though their differing tail behaviors will lead to differing low-do9 extrapolation predictions. Taking logarithms of (6a), we find the log-logit analogue of (3b):
Again LD# is the median, but now as-' is the slope of the log-logit plot (rather than the log-probir as before). The corresponding risk estimates become M ( t ) = (1
+ (pc*r/LD?;P')+I-l)-l
for the risk of d days' exposure to concentration c and c 't
= [LDg'/p] (-pR
1-R
330
for the dose lcading to a risk of lOOR%. Under log-logit regression our estimate of [LD?fp'/p]remains 30 ppm.d but the scale estimate changes to as = 0.374, leading to Table 2.
Table 2. h g i t Model Ozone Risk Estimates for CD-1 Mice
Dose (in pprn d ) 0.50 10-2 lo4 lod
[LD@ /p](0.5/0.5)"1 [D @ /p](10-'/0.99)"~ [D @ /p](10-90.9999)"' [D 'itp'/p](10-5/0.99999)a1
= 0.95 = 0.40
[ D @ / p ] (lod/0.999999)a1
= 0.17
= 30.0 = 5.37
Some of the consequences of these calculations give cause for concern. For example, eighteen months' (548 days') continuous exposure to a concentration of 0.01 pprn ozone leads to a cumulative dose of c*r = 5.48 ppmed. leading to the prediction that from 1% (for the log-logit model) to 15% (for the log-probit model) of mice would die from the effects of lifetime exposure to ozone at an average concentration of 0.01 ppm, a level commonly found in urban areas. Below when we extrapolate human health risk from the animal data we will find that humans would enjoy a median injury-free time of only about 15 years due to the effects of ozone at the common ambient level of 0.005 pprn under either model. Since this appears to be inconsistent with epidemiological data, we must reject the simple no-repair log-logit and log-probit models and explore the consequences of a repair mechanism. POSITIVE REPAIR RATES While we can calculate exact risk estimates on the basis of the log-probit and log-logit models with any positive repair rate p > 0, it is simpler (and conservative) to consider only the asymptotic or steady-state risk at a given concentration c . For the probit model, this has already been calculated in equation (5):
M, = ~ ( p . c . p - ' )= @(og8'ln(p.c/p.Dgl)), leading to the calculated value c = p F-'(M,)
I p = ~LL@ e
oI O-'(R )
Ice.
(7a)
for the concentration leading to a life-time risk of l00R %. The asymptotic calculation (7a) is the (constant) concentration which would lead to a risk of R for an infinitely-long exposure; exposed only for its lifetime, an animal would experience a somewhat smaller risk. In that sense the use of asymptotic value is "conservative." The calculation under the log-logit model is similar, and is also conservative:
339 c = p F-'(MJ I p = pm#
(-)"I
R
1-R
For (assumed) repair rates of 0.1%. 1%. and are given in Table 3.
I p.
(7b)
lo%, the concentration limits for the two models
Table 3. Daily Repair Rate: Lifetime Risk
0.1%
0.50
0.030 0.007 0.003 0.002 0.002
10-2 10-4 10-5 10-6
1.0%
10% log-probit c @pm) 0.300 0.071 0.030 0.022 0.016
3.000 0.714 0.302 0.216 0.160
0.1%
1.0%
10%
log-logit c (ppm)
0.0300 0.0054 0.0010 O.OOO4 0.0002
0.300 0.054 0.010 0.004 0.002
3.000 0.538 0.096 0.040 0.017
If a linear repair mechanism proceeds at a daily rate of at least 1%. then under either model a constant concentration of 0.005 ppm would be expected to lead to a risk of no more than lK5or so, while the risk at 0.2 ppm would only be under if the repair rate is at least p=50% for the log-logit model or ~ ~ 1 1for% the log-pmbit model. Note that the flatter tails of the logistic distribution lead to predictions of wider variability among individuals' thresholds for the log-logit model than for the log-probit model, and consequently lead to higher risk estimates at a given (low) concentration or, conversely, to lower concentration bounds for guaranteeing a specified bound on the risk.
..
W m a t ing the rate of repair of ozone inilary In the absence of an assumed repair mechanism the dose and consequent molecular burden were both exactly proportional to c'r for exposure at a fixed concentration, or more generally to jc(r)dr, so an arbitrary exposure regimen would be expected to have the same health effect as a constant exposure with the same average concentration. Under linear repair the exposure regimen i s no longer unrelated to the expected health effects: a short exposure to a very high concentration, followed by a long period Without exposure, leads to higher molecular burdens and consequently to more harmful health effects than does a long exposure to the same average concentration. An exposure with peaks and valleys will be more harmful than a constant exposure to the same average concentration. Instead of interpreting the log-probit model without repair (3a) as a regression equation relating the survival log-probit to time, we can interpret it as a regression equation relating survival for a fixed time to concentration or, more generally, to a multiple log-probit regression equation:
340
The striking feature of this equation is that the coefficients expressing the dependence of the survival probit upon log-time and upon log-concentration are both equal to the same quantity, namely as-'. Under the competing hypothesis of linear repair a log-probit regression of mortality on concentration will still yield an estimate of ag-', but when plotted against log-time the mortality probit will eventually level off at the bound
This suggests that we first estimate the asymptotic mortality M , and then estimate the repair rate by:
Under the log-logit model the estimate is even simpler:
It is more problematic to estimate p if an estimate of the asymptotic mortality rate M, is not available, but any leveling of the log-logit or log-probit plots of mortality against time is evidence in favor of a repair mechanism; routine statistical methods permit one to test the hypothesis of no-repair or to estimate the rate by numerical optimization. Under the ( l o g - n o d ) probit model with estimated parameters LD#=30.0 and at an og=0.617, the daily repair rate would have to be ~25.6%to attain a risk as low as average environmental concentration of 0.12 ppm ozone, and would have to be ~ 2 7 . 5 %for a risk as low as la-6 (see Equation 7a). The log-logistic (or logit) model's broader tails suggest that a higher repair rate would be necessary to attain such low risks. With our previously estimates of LD#=30.0 and ag=0.374 for this model, the repair rates would have to be at and would have to be ~270.2%to attain a lo4 risk (see least ~229.7%for a risk of Equation 7b). for ozone .
.
Each of the possible mechanisms for ozone toxicity suggested above is amenable to biological repair. For example, regions of lipid peroxidation might be removed from cell membranes, or damaged mature cells might be replaced by immature progenitor cells. Vitamin E oxidized by ozone could easily be replaced, leading to a membrane free of ozone damage. Reacylation of phospholipids with polyunsaturated or saturated fatty acids to replace oxidized PUFAs could also lead to such repair. The remodeling observed in rodent and primate lungs exposed to ozone for prolonged periods suggests that some ozone damage may be repaired by replacing Type 1 cells with Type 2 cells. Several of these mechanisms might proceed at rates as high as those suggested in the paragraph above.
34 1
HIGH-RISK HUMAN SUBPOPULATIONS It is possible that some segments of the population can tolerate significantly less ozone than would be expected by l o g - n o d or log-logistic models. Cystic fibrosis patients seem to represent just such a subpopulation. In (ref. 7) we observed that mi= fed diets low in (or enrhly lacking) vitamin E suffered far greater ozone damage than did mice fed diets containing higher mounts of vitamin E. The low-vitamin E diets comspond to about the same value as the current Recommended Daily Allowance of vitamin E (ref. 8). In our studies of vitamin E in cystic fibrosis patients at the Duke University Medical Center we have found 41.2% of the patients to have unusually low levels (c 5.0 pgImL) of serum vitamin E. If the mouse data of (ref. 7) is representative of the relative risk of humans consuming low vitamin E diets, then cystic fibrosis patients have a higher relative risk than the n o d population. The risk calculations based on lognormal or logistic models do not account for such high-risk subpopulations.
CONCLUSIONS The division of hazardous compounds into "non-threshold and "threshold" chemicals is arbitrary and misleading. An individual might have the ability to withstand a certain dose of chemical, as in our population models above, but neither epidemiological evidence nor laboratory experiments will enable the detection or identification of a population-wide threshold. Even for non-carcinogenic compounds, there may be no dose at which the entire human population is safe. The presence of subpopulations of individuals unusually susceptible to the toxic effects of a chemical (due to an inherited defect or to a preexisting disease) casts doubt on extrapolated low-dose risk estimates which do not account for those subpopulations, and complicates the use of extrapolated data from animal exposure experiments for the prediction of human health effects. Estimates of lifetime human cancer risk from various compounds have played an important role in the deliberations of regulatory agencies. These estimates are usually made by extrapolating data from lifetime bioassays of healthy animals exposed to high concentrations, in an effort to predict the health effects for humans exposed to much lower environmental concentrations. Multistage mathematical models are often used in the extrapolation. Concenare often trations leading to conservatively predicted human mortality risks of lo4 or regarded as acceptable to society, providing the "adequate margin of safety" required by the U.S.Clean Air Act. It is now apparent that these methods must be supplemented by a study of the molecular mechanisms of toxicity and by estimates of the rates of repair of tissue damage, both in the general population and in unusually susceptible subpopulations, in order to reach defensible standards. The mice experiments with varying levels of dietary vitamin E suggest that individuals with unusually low serum levels of vitamin E may be at high risk for cell damage from exposure to environmental ozone. Cystic fibrosis patients appear to represent a subpopulation of such individuals. The high rate of incidence of this disease (about 1 in 1600 live births) and
342
of its genetic marker (about 1 in 20 individuals carries the gene for cystic fibrosis) suggest that this group should be examined for health risk from ozone exposure. The existence of a biological repair mechanism would invalidate the common assumption that toxic effects depend linearly on the time-integrated dose, or on the product c.2 for an exposure of duration t to a concentration c . This assumption, which underlies many commonly used dose-effect and low-dose extrapolation models, leads to a systematic overestimation of the long-term effects of low-dose exposure as exnapolated from short-term high-dose experiments. The effect is magnified if the repair mechanism is saturable. Ozone exposures in urban areas show a marked diurnal pattern, with peaks during and just following the morning and evening rush-hours and generally higher levels during the summer than during the winter. Meteorological events and seasonal patterns contribute to the unevenness of urban ozone exposure. Under linear repair (and even more so under saturable repair) this exposure pattern will pose a somewhat higher risk than would a constant exposure to the same average concentration. The magnitude of this effect would depend on the rate of repair. The identification of the molecular processes involved in both causing and repairing ozone damage, and the measurement of the rates of the relevant chemical and biological processes, would improve greatly our ability to estimate the human health risks associated with the observed patterns of environmental exposure to ozone. The study of those processes in high-risk subpopulations is especially important in enabling reliable low-dose extrapolations.
ACKNOWLEDGEMENTS Drs. F.J. Miller and J.H. Overton, Jr. generously supplied the ozone dosimetry model used in this work. Dr. C.R. Shod supplied the data on vitamin E, and Mr. J.R. Boger III assisted with computer programming. Although the research described in this article has been funded in part by the U. S. EPA through the Center for Extrapolation Modeling agreement number CR813113 to Duke University, it has not been subjected to the agency’s peer and policy review and, therefore, does not necessarily reflect the views of the agency and no official endorsement should be inferred.
REFERENCES 1
FJ. Miller, J.H. Overton, Jr.. R.H. M o t , and D.B. Menzel. Toxicol.Appl. Phurtnacol. 79 (1985) 11-27.
2
D.B. Menzel, J. Toxicol. Environ. Health 13 (1984) 183-204. C.R. Shoaf and D.B. Menzel, in C.K. Chow (Mmr). Cellular Anti-Oxidant Defense Mechanisms, C.R.C. Ress (1988). J.N. Roehm, J.G. Hadley, and D.B. Menzel. Arch. Environ. Health 23 (1971) 142-148. I.M.C. Rietjens and G.M. Mink. These proceedings, 1988. E.D. Smolko, DJ. McKee, and D.B. Menzel, J. Amer. Col. Toxicol. 5 (1986) 589-598. D.H. Donovan, SJ. Williams, J.M. Charles. and D.B. Menzel, Toxicol.Left. 1 (1977) 125-139. U.g National Academy of Sciences, Food and Nutrition Board Recommended Daily Allowunces (9 edn.), National Academy of Sciences. Washington D.C., 1979.
3 4 5 6 7 8
343
T. Schneider et al. (Editors), Atmospheric Ozone Research and its Policy Implications 0 1989 Elsevier Science Publishers B.V., Amsterdam -Printed in The Netherlands
OZONE-INDUCED CBANGBS IN TEE PULUONARY CLBARANCB OF 99?'c-DTPA E.R. KEERL',
L.n. VINCENT',
D.E. EORSTMN',
R . J . KOVALSKY~,
IN HAN J.J. ~"EIL1,
V.E. HcCARTNd, and P.A. BROMBERG3
'Clinical Research Branch, USEPA:Eealth Effects Research Laboratory, Research Triangle Park, 27711 2Department of Radiology, School of Hedicine, University of North Carolina, Chapel Bill 27514 3Center for Environmental Hedicine and Lung Biology, School of Hedicine, University of North Carolina, Chapel Bill 27514
ABSTRACT
Ozone is a respiratory irritant that has been shown in aniMlS to increase the permeability of the respiratory epithelium. We have recently reported that respiratory epithelial permeability was similarly affected in eight healthy non-smoking young men exposed to ozone (ARRD, 135 (1987) 1124-8). Permeability was evaluated by determining the pulmonary clearance of inhaled aerosolized 99mTc-DTPA with sequential posterior lung imaging by a computer-assisted gaua camera. Ve now report our findings for an additional 16 subjects. In a randomized crossover design, the 16 young men were exposed for 2 h to purified air and 0.4 ppm ozone while performing intermittent high intensity treadmill exercise; forced vital capacity (WC) was measured before and at the end of exposures. The pulmonary clearance of 99mTc-DTPA vaa measured 75 minutes after the exposures. Ozone exposure was associated vith a man endexposure W C decrement of 0.50 liters (10% of baseline; p 0.007). The mean (* SIN) 99mTc-DTPA pulmonary clearance rate of 1.16 + 0.08 W m i n observed after ozone exposure was over 60% greater than the rate of 0.71 0.08 %/.in following air exposure (p < 0.001). The results demonstrate that ozone exposure increased respiratory epithelial permeability. Such an increase may be a manifestation of direct ozone-induced epithelial cell injury, lung inflammation or both.
-
*
DISCLAIMER:
This paper has been reviewed by the Eealth Effects Research Laboratory, U.S. Environmental Protection Agency and approved for publication. Approval does not signify that the contents necessarily reflect the views and policies of the Agency nor does mention of trade names or commercial products does not constitute endorsement or recommendation for use.
344
INTRODUCTION Hembrame permeability coefficients membranes can be derived when the membrane area is known and the transmembrane driving forces with the resultant fluxes of tracer molecules are measured. Recently, nuclear medicine techniques for evaluating respiratory epithelial permeability have been developed that are both non-invasive and suitable for human study. This approach involves inhalation of an aerosol of a radiolabelled probe molecule and then monitoring its clearance from the lung with sequential gamma camera imaging. Although this methodology does not provide the information required for the computation of permeability coefficients, the measurement obtained is considered to reflect the permeability of the respiratory epithelium. It is a method that has been sucessfully utilized by numerous laboratories in a variety of investigative settings (refs. l-S)! most laboratories have used as the probe molecule, the chelating agent diethylenetriamine pentaacetate labelled with technetium ( 99?c-DTPA). Increased 99%-DTPA clearance has been observed in persons with interstitial lung disease (refs. 1,2), cigarette smokers (ref. 3) and patients with diffuse pulmonary injury who manifest lung edema (ref. 4). We have used the pulmonary clearance of inhaled aerosolized "%-DTPA to evaluate changes in respiratory epithelial permeability due to ozone exposure in human subjects. An ozone-induced increase in permeability seemed likely since the respiratory epithelial membrane is the first cellular barrier encountered by inhaled pollutant gases and ozone is very reactive gas with the potential for disrupting cellular membranes, tight junctions and enzyme systems necessary for maintaining epithelial integrity and function. Furthermore, studies in animals have shown that exposure to ozone causes both measureable increases in permeability (refs. 6,7) and histologic changes (refs. 8, 9) consistent with a damaged, more permeable membrane. Such changes could have potential health consequences as the permeability properties of the respiratory epithelium play an important role in regulating the composition of membrane surface liquid and maintaining normal lung homeostasis. In a previous report, we described our findings of increased 99?c-DTPA pulmonary clearance in eight subjects following exposure to sufficient ozone to cause respiratory symptoms and an obvious decrement in the spirometric performance in most of the subjects (ref. 10). We have now repeated the study with an additional 16 subjects. These results form the basis for this report.
34 5 METH0D S The subjects were 16, healthy, nonsmoking, 20 to 30 year old, white men. The subjects were informed of the purpose, risks, and procedures of the experiment and signed informed consent forms. This study was approved by both the Committee on the Protection of the Rights of Human Subjects and the Radiation Safety Committee of the University of North Carolina School of Medicine. Prior to the exposures, the subjects were trained in the performance of spirometry, body plethysmography, and treadmill walking; for each subject, the treadmill speed and elevation required to elicit a target ventilation (3,) of 35 l/min per m2 body surface area was determined. The subjects were then exposed in a randomized, cross-over double-blinded fashion for 2.25 hours to both 0.4 ppm ozone and clean air with an initial five minute 0.1 ppm ozone sham. The exposures were separated by a minimum of two weeks. During their exposures in the chamber the subjects alternately rested for 15 minutes and performed 15 minutes of treadmill exercise at the predetermined speed and elevation; measurements of iE were obtained during each exercise interval. Pulmonary function was measured prior to exposure in clean air and at endexposure while still in the chamber atmosphere. Endexposure measurements were obtained within 10 minutes of the last exercise interval. Before and after the exposures, the subjects also answered a symptom questionnaire. The exposures were conducted in a 4 X 6 X 3.2 meter stainless steel chamber maintained at 22O C and 40% relative humidity. The control systems, ozone generating system, monitoring systems, and operating characteristics of this chamber have been previously described (refs. 11). Specific airways resistance (SRaw), the product of airways resistance and its concomitant thoracic gas volume, was measured at a panting frequency of 1.5 Hz in a body plethysmograph (CPI Model 2000). The middle value of three SRaw measurements obtained during the testing sessions was selected for data analysis. At least three preexposure and endexposure measurements of forced vital capacity (FVC) were obtained on a 12 liter dryseal spirometer (Ohio Instruments Model 220) with volumes corrected to BTPS. The single largest FVC maneuver of each testing session was selected for data analysis. Due to either technical reasons or subject performance, complete plethysmography and spirometry data sets were obtained for only 12 and 14 subjects respectively. 8,, obtained during the 11th and 12 minutes of each exercise, was determined from the integration of the digitized flow signal of a heated pneumotachometer (Pleisch no. 3) and corrected to BTPS. Seventy-five minutes following the exposure (90 minutes after the last exercise), respiratory epithelial permeability was evaluated by determining the clearance rate of inhaled aerosolized 99?c-DTPA. The radiopharmaceutical was prepared with Nag9%04 and an AN-DTPA kit (Syncor International Corp.); binding of the 99%2 to the DTPA was routinely greater than 98%. The aerosol
346
was generated with the Syntevent aerosol delivery system (Synaco, Inc.), a system which has been characterized as producing a particle with a dry mass median aerodynamic diameter of 0.50 to 0.65 um and a geometric standard deviation of 2.0. The subjects inhaled the aerosol through a mouthpiece for two minutes of tidal breathing8 the amount of radioactivity calculated to be delivered to the mouthpiece was 0.50 - 1.0 mCi. During aerosol inhalation and for the subsequent 20 minutes, sequential 15 second frame scintillation images of the posterior upright chest were acquired with a computer assisted gamma camera (Elscint Apex 415) equipped with a low-energy collimator (Elscint APC-1). A "region of interest" (ROI) was selected to include the entire right lung and the natural logarithm of lung radioactivity (corrected for radioactive decay) within the ROI was plotted as a function of time. The negative slope (clearance constant, K value) of this relationship for the first seven minutes after peak lung radioactivity was determined by the least squares method and expressed as per cent decrease in radioactivity per minute. This approach does not correct for background activity but minimizes the effects of increasing blood and tissue radioactivity upon both total lung counts and back diffusion by fitting the line to the initial portion of the curve. The methods used were similar to those first described by Chopra et al. (ref. 12) and subsequently expanded upon by Rinderknecht and co-workers (ref. 1). The hypothesis of no difference in the postair and postozone K values was tested with multivariate analysis of variance. We also tested the hypotheses of no differences in FVC and SRaw between the changes observed from preexposure to endexposure during the air and ozone exposures with multivariate analysis of variance.
RESULTS After air exposures, the individual "9c-DTPA clearance rates ( K values) showed considerable variability with a range from 0.25 to 1.33 %/min and a mean (f SEH) value of 0.71 f 0.08 X/min. However, compared with the air K value, 15 of the 16 subjects showed an increase in "9c-DTPA clearance after ozone exposure; the mean of 1.16 f 0.10 %/inin was more than 60% larger than the clearance rate observed after air exposure. An ozone-induced increase of 1.08 W m i n in "9c-DTPA clearance, the largest change observed, was incurred by two subjects (No. 3 and 13). The K values observed 75 minutes after air and ozone exposures and the preexposure and endexposure measurements of FVC on the two exposure days are presented in Table 1.
347
TABLE I Postexposure permeability constants and pre and postexposure FVC measurements.
K valuesa AIR SUBJECT NUUBBR
FVC (liters)
OZONE
75 min postexp
01
0.46
0.68
02
0.73
AIR preexp
OZONE postexp
5.12
5.15
03
0.35
1.56 1.43
04
1.10
1.05
05 06
0.61
0.89
5.50 4.90 4.95
0.67 0.25
0.83
5.11
preexp
postexp
5.24
5.26
5.45
5.64
5.22
4.96
4.91
4.41
4.79
4.96
4.83
5.26 5.19
4.99 5.02
07 08
5.08
0.52
0.85 1.11
5.19 5.12
5.29
5.35
5.17
5.25
09
1.33
1.58
5.46
10
0.43
1.28
5.46 4.72
4.68
5.09 4.72
3.35 3.50
11 12
1.01 0.69
1.11
6.17
6.17
6.25
4.86
0.82
13
1.23
2.31
5.70
5.78
0.74
1.06
3.84
6.00 3.84
5.91
14 15
3.84
3.68
0.69 0.62
1.06 0.99
4.92 4.98
4.76
4.73
4.77
4.82
4.59 4.19
0.71
1.16
5.13
5.13
4.64
0.08
0.10
0.14
5.12 0.16
0.15
0.19
16
Hean f SEH
a~ values expressed as per cent decrease in activity per minute
The baseline pulmonary function of the 16 subjects was very similar with all but one subject (No. 9 ; 7%) showing less than 4X individual variance in preexposure FVC performance between the two exposure days. The ventilatory responses to exercise were also nearly identical with a mean (f SEH) tE over the final three exercise intervals of 58.6 f 2.5 and 60.3 f 2.1 l h i n on the air and ozone exposure days respectively. Following ozone exposure, most subjects reported respiratory symptoms of cough and chest tightness. There was a significantly greater increase in SRaw from the baseline of 3.8 f 0.3 to
348 5.1 f 0.4 cmH20*sec following ozone exposure than the change from 3.9 f 0.4 to 4.1 f 0.3 cmH20.sec observed during air exposure (p = 0 . 0 0 2 ) . In comparing the air and ozone responses, most subjects (8 of 14) shoved more than a 0.3 1 decrement in PVC attributable to ozone exposure and three subjects incurred decrements in excess of 1.3 liters. The mean decrement observed during ozone exposure vas 0.49 1 (10% of baseline value; p 0.007).
-
DISCUSSION The most important aspect of our study is the convincing demonstration that healthy volunteer6 acutely develop accelerated pulmonary clearance of 99?c-DTPA when exposed to ozone under these conditions These results confirm the findings of our previous study (ref. 10). The observation that 15 of 16 subjects showed increased 99%-DTPA clearance after ozone exposure suggests that this measurement is a sensitive indicator of ozone's effects. Indeed, when comparing the air and ozone exposure performances, only 10 of 14 subjects experienced a decline in FVC of greater than 100 ml attributable to ozone exposure. Thus it appears that the determination of ''%-DTPA pulmonary clearance may rival the sensitivity of forced expiratory spirometry in detecting the effects of ozone exposure. The mean ozone-induced decrement in NC of 10% observed in this study was less than the 14% demonstrated in our previous report (ref. 10) or than was expected from past work in our laboratory (ref. 13). Also, given the exposure conditions, there were a relatively large number of non-responders. This is likely due to the inherent unpredictable variability of the ozone response (ref. 14) as other conditions including exercise intensity, ozone concentration, duration of exposure and subject selection criteria were similar to those described in the previous reports. We attribute the accelerated 99%-DTPA clearance observed in our study, at least in part, to an ozone-induced increase in the permeability of the respiratory epithelium. This contention is supported by animal studies that used more direct measures of respiratory epithelial permeability and found that increases occur in both guinea pigs (ref. 6) and rats (ref. 7) exposed to ozone. There are, hovever, several other mechanisms that could possibly account for an increase in 99@Tc-DTPA clearance after ozone exposure. Ozone exposure might simply enlarge the effective lung surface area available for "%c-DTPA transfer by altering the aerosol deposition pattern' or increasing lung volume. The latter is unlikely, for even in the setting of large ozone-induced decrements in spirometric volumes, functional residual capacity remains unchanged (ref. 13). As for a change in deposition, the radioaerosol
was inhaled during resting tidal breathing and ozone exposure should not appreciably affect inspiratory flow rates or volumes. Additionally, examination of the gamma camera images showed no discernible differences between the air and ozone exposure days. Of note, Euchon and co-workers clearance observed in smokers (ref. 5) have shown that the increased "?c-DTPA with overt obstructive lung disease is mainly attributable to their smoking status and not the presence of airways disease. Consequently, small unrecognized differences in aerosol deposition due to changes in respiratory timing or small airways dysfunction, would likely not affect the clearance rate. Thus, the accelerated pulmonary clearance of "%c-DTPA observed in our subjects is probably not due to an ozone-induced augmentation of effective lung epithelial surface area. Another means of accounting for increased 99?c-DTPA clearance is the has a dissociation of the gamma-emitting technetium from the DTPA. "%04much faster clearance than the ''?c-DTPA complex and dissociation of even small of amounts "%c (rapidly oxidizes to 99%04-) would greatly influence is well the overall clearance rate (ref. 15). Radiolabel instability recognized as a problem with ultrasonic aerosol generation (ref. 16), but not with the compressed gas jet nebulization system used in our studies. Additionally, multiple tests of our 99yc-DTPA solution always showed greater to the DTPA both before and after than 98% binding of the 99%04nebulization. Along similar lines, Nolop and co-workers (ref. 15) have demonstrated that in vitro oxidative stress of "Yc-DTPA solutions causes rapid dissociation of "%04from the DTPA. These same investigators have shown that in vivo oxidative stripping of the 99%04- from the DTPA may be partially responsible for the rapid clearance observed in smokers (ref. 15). Since inflammation entails leukocyte infiltration with the creation of an oxidative milieu as well as increased permeability, lung inflammation could potentially lead to accelerated clearance of the isotope by both mechanisms. It is certainly possible that the accelerated 99%-DTPA clearance after ozone exposure manifested by our subjects was partly due to the increased permeability and oxidative environment brought on by lung inflammation. Indeed, inflammation is an integral component of the response of the lung to ozone exposure. In dogs, inflammation has been implicated in the enhanced bronchoconstriction to inhaled histamine observed after ozone exposure (ref. 17). Similarly, Seltzer and co-workers (ref. 18) found an increased number of neutrophils in the bronchoalveolar lavage fluid of human volunieers obtained three hours after exposure to 0.4 or 0.6 ppm ozone; the presence of neutrophilia was associated with an ozone-induced increase in bronchial reactivity to inhaled methacholine. More recently, Devlin and co-investigators (ref. 19) demonstrated both an increase in neutrophils as well as the total
350 protein and albumin in lavage fluid of volunteers obtained 18 hours after exposure to 0.4 ppm ozone in a protocol identical to the conditions employed in our study. It is not known, however, whether neutrophil infiltation of the respiratory surfaces is present as early as 75 minutes after a two hour exposure to ozone. Thus, inflammation of the lung in response to ozone exposure and the mediators of inflammation may contribute to the accelerated pulmonary clearance of "Yc-DTPA observed in our study both by increasing respiratory epithelial permeability and promoting an oxidant environment favoring dissociation of the It also is likely that direct ozone chelated "Yc in the form of 99%04-. toxicity upon the epithelium with the resultant cellular injury and disruption of integrity is partially responsible for the increase in lung 99?c-DTPA clearance. Histologic studies in animals have shown that injury occurs to the ciliated airways epithelium and type I alveolar cells in both rats (ref. 8) and monkeys (ref. 9) after short-term exposures to less than 1.0 ppm ozone. Such an injury pattern would provide a likely morphologic correlate for an increase in permeability, especially since the submicronic size of the radioaerosol inhaled by our subjects favors deposition in the gas exchange regions and small airways of the lung. Although the exact mechanisms for the flux of "Yc-DTPA across the respiratory epithelium and into the blood remain unclear, it appears that the is a useful and sensitive technique for pulmonary clearance of "?'c-DTPA evaluating the effects of ozone and other inhaled pollutants upon human respiratory function. Other than bronchoalveolar lavage, the measurement of "%c-DTPA pulmonary clearance is the only available method that has successfully detected the effects of ozone in the gas exchange regions of human subjects. It is a relatively easily performed technique that can be applied to the unsettled concerns regarding the response of human subjects to ozone exposure as well as provide a means of correlating human and animal ozone toxicology.
REFERENCES 1 J. Rinderknecht, L. Shapiro, H. Krauthammer, G. Taplin, K. Yasserman, J.H. Uszler, and R.H. Effros, Am Rev Respir Dis, 121 (1980) 105-17. 2 H.P. Jacobs, R.P. Baughman, J. Eughes, and M . Pernandez-Ulloa, Am Rev Respir Dis, 131 (1985) 687-9. 3 J.G. Jones, P. Lawler, J.C. Crawley, B.D. Minty, G. Eulands, and N. Veall, Lancet, 1 (1980) 66-8. 4 G.R. Mason, R.H. Effros, J.H. Uszler, and I. Hena, Chest, 88 (1985) 327-34.
351
5 G.J. Huchon, J.A. Russell, L.G. Barritault, A. Lipavsky, and J.F. Murray, Am Rev Respir Dis, 130 (1984) 457-60. 6 P.C. Hu, F.J. Miller, M.J. Daniels, G.E. Hatch, J.A. Graham, D.E. Gardner, and M.K. Selgrade, Environ Res, 29 (1982) 377-88. 7 D.L. Costa, S.N. Schafrank, R.W. Wehner, and E. Jellett, J Appl Toxicol, 5 (1985) 182-6. 8 R.J. Stephen, M.F. Sloan, M.J. Evans, and G. Freeman, Am J Pathol, 74 (1974) 31-58. 9 W.L. Castleman, D.L. Dungworth, L.W. Schwartz,and W.S. Tyler, Am J Pathol, 98 (1980) 811-40. 10 H.R.. Kehrl, L.M. Vincent, R.J. Kowalsky, D.H. Horstman, J.J. O’Neil, W.H. McCartney, and P.A. Bromberg, Am Rev Respir Dis, 135 (1987) 1124-8. 11 D.E. Glover, J.H. Bernsten, W.L. Crider, and A.A. Strong, J Environ Sci Health, 16 (1981) 501-22. 12 S.K. Chopra, G.V. Taplin, D.P. Tashkin, and D. Elam, Thorax, 34 (1979) 63-7. 13 W.F. McDonnell, D.H. Horstman, M.J. Aazucha, E. Seal Jr., E.D. Aaak, S.A. Salaam, and D.E. House, J Appl Physiol, 54 (1983) 1345-52. 14 W.F. McDonnell, D.H. Horstman, S.A. Salaam, and D.E. House, Am Rev Respir DiS, 131 (1985) 36-40. 15 K.B. Nolop, D.L. Maxwell, J.S. Fleming, S. Braude, J.M.B. Hughes, and D. Royston, Am Rev Respir Dis, 136 (1987) 1112-6. 16 D.L. Waldman, D.A. Weber, G. Oberdsrster, S.R. Drago, M.J. Utell, R.W. Hyde, and P.E. Horrow, J Nucl Mcd, 28 (1987) 378-82. 17 M.J. Holtzman, L.M. Fabbri, P.M. O’Byrne, B. Gold, 8. Aizawa, E. Walters, S.E. Alpert, and J.A. Nadel, Am Rev Respir Dis, 127 (1983) 686-90. 18 J. Seltzer, B.G. Bigby, M. Stulbarg, M.J. Holtzman, J.A. Nadel, I. Ueki, G. Leikauf, E. Goetz1,and H.A. Boushey, J Appl Physiol, 60 (1986) 1321-6. 19 R. Devlin, D. Graham, W. Kozumbo, R. Mann, and H.S. Koran, J Leuk Biol, 42 (1987) 394.
ACKNOWLEDGEMENT: The writers thank Susan McCallister of UNC and the staff of Environmental Monitoring and Services for technical assistance. Statistical analyses were performed by Dennis House of the Biostatistics Branch of tha Biometry Division, USEPA:Health Effects Research Laboratory.
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353
SESSION V
GLOBAL ATMOSPHERIC CIRCULATION AND MODELING
Chairmen
C.J.E. Schuurmans W. Johnson
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T. Scbneider et al. (Editors),Atmospheric Ozone Research and its Policy Implications 1989 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands
CHEMISTRY OF STRATOSPHERIC OZONE DEPLETION UNDERLYING THE ANTARCTIC OZONE HOLE
355
INCLUDING P O S S I B L E MECHANISMS
G .D. H a y m a n E n v i r o n m e n t a l and M e d i c a l S c i e n c e D i v i s i o n , H a r w e l l Laboratory, D i d c o t , O x o n O X 1 1 ORA, UK
Our understanding of the distribution of ozone in the stratosphere has
improved substantially since Chapman (ref. 1) first proposed that the ozone concentration was controlled by a series of reactions in which 'odd-oxygen' is produced, lost or interconverted.
0 +02+M
= 03tM
interconversion
....(1) ....( 2 )
+ hv
= 0 t o 2
interconversion
....( 3 )
= 202
loss
....( 4 )
loss
....( 5 )
02
03
+ hv
= 0
0 t O3 0 t o
t o
( X<243
nm
production
)
0 2 t M
t M
Reactions ( 4 ) and (5) were found to be too slow to account for the observed abundance and height distribution of ozone in the stratosphere. It was recognised that other species could catalytically destroy ozone (refs. 2 and 3 ) ,
X
to3
=
xo +
0
txo
=
x
net
02
to2
0 t O3 = 202
where X = H I OH, NO, CI or Br.
or
t o 3
=
xo
t 02
XO t 03
=
x
t 202
X
203
= 302
where X =' OH
the net effect of these cycles being a faster loss of odd oxygen than the direct
reactions, the cycles being commonly known as the HO,, NO,, CIO, and BrO, cycles. The efficiency of these catalytic cycles for ozone depletion are given in Table 1, taken from ref. 4 .
TABLE 1 Relative contributione of the major rate-limiting chemical reactions to the removal of ozone Re action Altitude (km)
0 t O3
0
+
NO2
+
0 t c10
0
4 10 16 13 8 5 1
52 31 10 4 2 1 1
H02
H02 t O3
(percentage contribution) 25 29 18 11 10 2 1
50 45 40 35 30 25 20
7 24 53
68 69 18 70
-
1 3 8 26
The overall efficiency of the individual cycles in causing ozone depletion has been moderated by the reactions which couple the different families, e.g. CIO t NO2 t M H02
+
NO
CIONO2 t M
= OH
+
NO2
....(6 ) ....(7 )
and by the reactions which lead to the removal of the active radical species, e.g. , CI
t
cH4
=
HCI
OH
+
H02
=
H20
cH3
+
02
... ....(9) .(0)
O u r present understanding of the middle stratosphere is one in which the major loss of ozone is through the NO, cycle with minor roles for the CPO, and HO, cycles. At higher altitudes, the HO, cycle plays a more important role. With increased emissions of Chlorofluorocarbons (CFC's) and Halons, the CtOX and BrO, cycles are expected to become more significant.
The observation of major depletions in the total ozone column over
357
Antarctica each spring by Farman et al. (ref, 5), subsequently confirmed by satellite (ref. 6) and other ground based measurements (ref. 7) has led to a reassessment of our understanding of and the impact of man's activity on the atmosphere. The initial field measurements indicated that the major ozone loss occurred at altitudes between 12 and 20 km (ref. 8) and that the stratospheric temperatures were very low, approaching 190 K (ref. 9). Various theories have been proposed to account for these observations and measurements. These can be classified'as follows: (I) A Dynamical theory (ref, 10) in which upwelling of ozone-poor tropospheric air into the stratosphere as a result of solar heating reduces the total ozone column abundance.
,
( 2 ) Solar activity (ref. 11) leading to an increased production of nitrogen
oxides in the upper atmosphere. Transport of these oxides into the lower stratosphere causes the observed depletions. (3) An enhanced role for chlorine chemistry. Although the burden of chlorine in the atmosphere has increased (ref. 12), the role of chlorine chemistry was not expected to significantly increase ozone depletions due to the coupling reaction (6) of CIO with NO2 to produce C10N02 which removes active chlorine. It was suggested that chlorine chemistry could account for the ozone depletions if C1ONO2 reacts at the surface of aerosols and particulates (ref. 13 ) to form more photochemically-active chlorine-containing molecules such as Ct2 or HOCI One of the features of the Antarctic stratosphere is the presence of Polar Stratospheric Clouds (PSCIs) (ref. 14). Thus, reactions such as (10) and (ll), which are known to be slow in the gas phase (ref. 15) could occur on the surface of these clouds.
.
CION02 t HCI = C12 t HN03
....(10)
CdON02 t H20 = HOCI t HN03
....(11)
Reaction (11) was favoured over the reaction with HC1 (10) as the PSC's were initially thought to be mainly water condensed on to H2SO4 aerosols. It was suggested that PSCIs could be hydrates of HN03 (ref. 1 6 ) , thereby removing HNO3 and NOx from the gas phase and ensuring that any HNO3 produced by reactions (10) and (11) remained in the condensed phase,
3 58 A number of catalytic cycles involving chlorine which lead to ozone loss were proposed. All the theories require the new heterogeneous chemistry outlined above to release the active chlorine and to reduce the NO, concentration.
CYCLE 1 (ref. 13) HOCf t hv = OH t C1 CI
t
03 = CIO t 02
OH
t
O3 = H02 t O2
CIO
+ H02 =
02
+ .HOCI
....(12) ....(13) ....(14) ....( 1 5 )
CYCLE 2 (ref, 17)
Br
t
03 = BrO t O2
CI
t
O3 = CIO t O2
BrO
t
CIO = Br t CI
+ o2
....(16) ....(13) ....(17a)
Note reaction (17) also has a product channel forming OCPO, symmetric BrO
t
CIO = Br t OCIO
....(17b)
chlorine dioxide. OCIO acts as a temporary reservoir at night, storing CnO. When the sun rises, OCIO is rapidly photolysed to regenerate CIO.
OCIO t hv = C10 + 0
....(18)
The production of an 0 atom will ameliorate the effect of the O3 depletion since
0 t
O2
t
H
03 t H
...
.(2)
CYCLE 3 A cycle proposed by Holina and Holina (ref, 18) involves the formation and photolysis of a symmetric CIO dimer, CIOOCI.
359
C10
t
C1202
+ hv
+ M
CIO
Cl202 t M = ClOO
C100 + M 2(Ct
= c10
O3
t
+
c1
....(19) ....(20)
t 0 2 t M
....( 21)
+ 02)
....(13)
Note that the formation of an asymmetric dimer would reduce the effect of the above cycle due to
C10
t
= OC10
t
c1
....(22) ....(23)
hv
= c10
t
0
....( 18)
03
= CIO
t
02
.... ( 1 3 )
+
M
....(2)
C10
C1OCtO
+ hv
OC10
t
C1 0
+ 0 2
net
-
t
M = CfOCIO t M
+ M = 0 3
a null cycle
The overall effect of cycles 1-3 is to convert ozone into oxygen, 203 = 302. Each of these cycles requires (1) low concentrations of NO,,
removed from the gaseous phase into the
condensed phase as HN03. (2) elevated levels of C10 and BrO. and ( 3 ) for cycles 1 and 3, the presence of a species which can be photolysed in the near ultraviolet (x>300 nm). The large solar zenith angles and hence long atmospheric absorption paths present when the sun first rises restricts photolytic processes to those occurring at wavelengths greater than 300 run. As a result of the large depletions and the need to test the different chemical depletion mechanisms, field campaigns to Antarctica were arranged for the austral springs of 1986 and 1987 (National Ozone Expeditions). In these campaigns, a number of key species thought to be active in the O3 depletions such as C10 and NO2 as well as O3 itself and conservative tracers such as N20 and CHI were measured by infrared, microwave and ultraviolet spectroscopic techniques. In 1987 as well, a series of flights from Punta Arenas, Chile into the south polar vortex region were undertaken to monitor these key constituents.
360
The results of the campaigns clearly indicate that (1) the ozone depletion is confined principally to the lower stratosphere (ref. 8). The depletion is highly structured with almost total removal of ozone at certain altitudes. The depletions are highly correlated with the presence of PSC' s.
(2) low concentrations of NOx (ref. 19 and 20) and elevated concentrations of CPO (ref, 21) were observed. The concentration of CPO reached a peak of 1 ppbv which is almost a factor of 100 larger than normal stratospheric concentrations. (3) the ratios of HC1 to HF and to CmONO2 were highly perturbed (ref. 20)
(4) low concentrations of tracers such as N20 were observed (ref.22)
and (5) the first atmospheric observation of OCPO (ref, 23) These observations provide strong support for the photochemical mechanisms requiring elevated concentrations of CPO and reduced levels of nitrogen oxides. They would seem to rule out those theories requiring upwelling as the concentration of trace gases such as N20 is much reduced. The measurements of low levels of nitrogen oxides is at variance with the requirements of the solar cycle mechanism. Recent results from the laboratory (see below) and model studies (ref. 24) further support the thesis that the depletions arise from heterogeneous reactions converting CPON02 into active chlorine and removing nitrogen oxides from the gaseous phase. There is now a consensus that the CPO dimer mechanism (cycle 3) can account for the O3 loss with a significant component from the BrO/CmO cycle (2). (1) Heteroseneous chemistry. Both the nature of the PSC's as well as the reactions occurring on them have been the subject of laboratory studies (refs, 25-27). It is clear that at temperatures prevalent in the Antarctic stratosphere, condensation of nitric acid hydrates and hydrogen chloride hydrates can occur, Further, HC1 incorporated into the condensed phase is very labile. Sticking and accommodation coefficients for reaction (10) have been obtained. These show that this reaction can proceed rapidly enough to remove nitrogen oxides and release C I ~ ,which is readily photolysed.
361
(2) Chlorine chemistry. Our group at Harwell and others elsewhere have investigated aspects of the gas phase chemistry which cause the ozone loss, in particular, the properties of the C10 dimer. We have obtained a W absorption spectrum for the dimer, peaking at 245 ML, but which has a long tail into the critical near W region (ref. 28). It can be shown that the dimer is stable at stratospheric temperatures and pressures and that photolysis is the major loss process. We have demonstrated the existence of a CI atom forming channel when the dimer is photolysed which proceeds with unit quantum efficiency.
C12O2 t hv =
CIOO
+
....
(20)
CI
We find no evidence for an asymmetric dimer. (3) Bromine chemistry. Study of the BrO t C10 reaction has also been made by several groups. It now appears, contrary to the published work of Hills et al. (ref, 29) that the reaction has a negative temperature dependence (ref. 30).
BrO t CIO = Br t CI t o2 = Br t
-
BrCI
OCIO 02
....(17a)
....(17b) ....(17c)
There is evidence for the existence of three product channels (refs. 30 and 31). The abundance and diurnal variation of OC1 0 in the Antarctic stratosphere can be well reproduced using reaction (17b) as the sole source of OCfO (ref, 32). The calculation utilises the NASA rate expression (ref. 15) rather than the higher value determined by Sander et al. (ref, 30) with BrO and CfO concentrations of 7 pptv and 0.6 ppbv respectively. The existence of a BrCn-forming channel acts as a reservoir for BrO during the polar night. It is however rapidly photolysed by near W radiation to release Br and C1 a t o m which rapidly reform BrO and 00. This channel may explain the asymmetry in the twilight behaviour of OCfO although BrON02 has also been postulated as a reservoir (ref. 32 )
.
The laboratory and modelling studies together with the field measurements thus provide strong support for the CIO dimer and BrO/CfO catalytic cycles as causing the ozone hole over Antarctica once heterogeneous chemistry has 'denitrified' the stratosphere and released the chlorine.
At a scientific level, further laboratory study is needed to characterise the reactions and species involved in the catalytic cycles. There is still considerable uncertainty associated with a number of the key kinetic and photolytic parameters (1) the formation rate of the C10 dimer at stratospheric temperatures and
pressures, (2) the long wavelength tail of the absorption spectrum of the C80 dimer, (3) the photolytic channels and products of the dimer, (4) the temperature dependence and products of the BrO
+
C10 reaction,
and (5) the reactions and properties of BrON02. Also a more detailed understanding of the heterogeneous processes is needed. At a policy level, the question arises "Are these depletions ltxalised to Antarctica because of its unique climatology, meteorology and chemistry or do these depletions have global implications?" A campaign to find evidence for the formation of a similar 'ozone-hole' in the Arctic took place this winter. The depletions are expected to be less pronounced due to the fact that arctic stratospheric temperatures are typically 20-30 K warmer than those observed in Antarctica which leads to less frequent occurrence of PSC's and a weaker polar vortex.
We await the results of modelling studies in which the heterogeneous and new chlorine chemistry are treated fully to see if these depletions herald significant global reductions in ozone concentrations. The support of the UK Department of the Environment is gratefully acknowledged. The article reflects the personal views of the author and does not necessarily represent the policy of the funding agency. REFERENCES (1) S. Chapman, Mem. Roy. Meteorol. Soc., 3 (1930) 103.
(2) H. Johnston, Science, 173 (1971) 517-522.
363
(3) M. J. Molina and F. S. Rowland, Nature, 249 (1974) 810-812. (4) R. P. Wayne, 'Chemistry of Atmospheres', Clarendon Press, Oxford, (1985). (5) J. C. Farman, B. G. Gardiner and J. D. Shanklin, Nature, 315 (1985) 207-210. (6) R. S. Stolarski, A. J. Krueger, M. R. Schoeberl, R. D. McPeters, P. A. Newman and J. C. Alpert, Nature, 322 (1986) 808-811, (7) S. Chubachi, Mem. Natl. Inst. Polar Res. Spec. Issue Jpn., 34 (1984) 13. (8) D. J. Hofmann, J. W. Harder, S. R. Rolf and J. M. Rosen, Nature, 326 (1987) 59-62. (9) K. Labitzke, Phil. Trans. Royal SW. London A, 297 (1980) 7-18. See also papers in the November Supplement of Geophys. Res. Lett., 13 (1986) on 'Antarctic Ozone Depletions', (10) K.-K. Tung, M. K. W. KO, J. M. Rodriguez and N. D. Sze, Nature, 322 (1986) 811-814. (11) L. B. Callis and M. Natarajan, J. Geophys. Res., 91 (1986) 10771-10795. (12) 'Atmospheric Ozone 1985 Assessment of our understanding of the processes controlling its present distribution and change', NASA/WMO global ozone research and monitoring project report number 16. D. R. Cronn, W. L. Bamesberger, F. A. Menzia, S. F. Waylett, A. S. Waylett, T. W. Ferrara, H. M. Howard and E. Robinson, Geophys. Res. Lett., 13 (1986) 1272-1275. (13) S. Solomon, R. R. Garcia, F. S. Rowland and D. J. Wuebbles, Nature, 321 (1986) 755-758. M. P. McCormick, H. M. steele, P. Hamill, W. P. chu and T. J. Swissler, J. Atmos. Science, 39 (1982) 1387-1397. W. B. DeMore, J. J. Margitan, M. J. Molina, R. T. Watson, D. M. Golden, R. F. Hampson, M. J. Kurylo, C. J. Howard and A. R. Ravishankara, 'Chemical Kinetics and Photochemical Data for use in Stratospheric Modelling', Evaluation number 7, JPL publication 85-37, Jet Propulsion Laboratory, Pasadena, California, USA. 0. B. Toon, P. Hamill, R. P. Turco and J. Pinto, Oeophys. Res. Lett., 13 (1986) 1284-1287. P. J. Crutzen and F. Arnold, Nature, 324 (1986) 651-655. (17) M. 8. McElroy, R. J. Salawitch, S. C. Wofsy and J. A. Logan, Nature, 321 (1986) 759-762. (18) L. T. Molina and M. J. Molina, J. Phys. Chem., 91 (1986) 433-436. (19) G. H. Mount, R. W. Sanders, A. L. Schmeltekopf and S. Solomon, J. Geophys. Res., 92 (1987) 8320-8328. (20) C. B. Farmer, G. C. Toon, P. W. Schaper, J.-F. Blavier and L. L. Lowes, Nature, 329 (1987) 126-130. (21) R. L. de Zafra, M. Jaramillo, A. Parrish, P. Solomon, B. Connor and J. Barrett, Nature, 328 (1987) 408-411. P. M. Solomon, B. Connor, R. L. de Zafra, A. Parrish, J. Barrett and M. Jaramillo, Nature, 328 (1987) 411-413. (22) A. Parrish, R. L. de Zafra, M. Jaramillo, B. Connor, P. M. Solomon and J. W. Barrett, Nature, 332 (1988) 53-55. (23) S. Solomon, G. H. Mount, R. W. Sanders and A. L. Schmeltekopf, J. Geophys. Res., 92 (1987) 8329-8338. (24) M. B. McElroy, R. J. Salawitch and S. C. Wofsy, Planetary and Space Science, 36 (1988) 73-87. (25) M. J. Molina, T.-L. TSO, L. T. Molina and F. C.-Y. wang, science, 238 (1987) 1253-1257. (26) M. A. Tolbert, M. J. Rossi, R. Malhorta and D. M. Golden, Science, 238 (1987) 1258-1260. (27) S. C. Wofsy, M. J. Molina, R. J. Salawitch, L. E. Fox and M. B. McElroy, J. Geophys. Res., (in press, 1988). (28) R. A. Cox and G. D. Hayman, Nature, (in press, 1988). (29) A. J. Hills, R. J. Cicerone, J. 0. Calvert and J. W. Birks, Nature, 328 (1987) 405-408. (30) S. P. Sander and R. R. Friedl, personal Communication. ,(31)P. J. Bennett, G. D. Hayman and R. A. Cox, unpublished work. (32) S. Solomon, R. W. Sanders, M. A. Carroll and A. L. schmeltakopf, J. Geophys. Res., (in press, 1988).
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T. Schneider et al. (Editors), Atmospheric Ozone Research and itrr Policy Implicatwne 0 1989 Elsevier Science Publishers B.V., Amsterdam -Printed in The Netherlands
365
POTENTIAL EFFECTS O F STRATOSPHERIC OZONE DEPLETION AND GLOBAL TEMPERATURE RISE ON URBAN PHOTOCHEMISTRY
M.W. G E R Y ~ R.D. , EDMOND, AND C.Z.
WHIT TEN^
'Systems Applications, Inc., 927 Boylston St., Boston, MA 021 16 (United States) *Systems Applications, Inc., 101 Lucas Valley Rd., San Rafael, CA 94903 (United States)
ABSTRACT Potential increases in Greenhouse gas concentrations and decreases in stratospheric ozone could result in increased temperature and ultraviolet radiation near the earth's surface. In urban areas, this could augment both t h e speed and magnitude of photochemical ozone formation. An investigation of the effects of these changes indicates t h a t t h e reactivity of urban atmospheres, as measured by t h e amounts and rates of ozone and hydrogen peroxide production, can be highly sensitive to these changes. This paper describes the chemical dynamics associated with these global changes, and investigates the possible consequences with respect to ozone production in a number of large cities in t h e United States. INTRODUCTION The detection of significant and continued ozone column decreases during Antarctic spring, and possible decreases at mid-latitudes and in the Arctic, indicate t h a t important dynamical alterations may be occurring in all parts of the upper atmosphere. Chemical simulations indicate that this ozone depletion could be due to increased penetration of anthropogenic substances (halocarbons, methane, and nitrous oxide) into t h e stratosphere. Such decreases in stratospheric ozone concentration would allow increased transmission of middle ultraviolet (UVB) radiation to t h e troposphere, since ozone is the principal stratospheric attenuator of UVB radiation. Besides depleting stratospheric ozone, these and other substances (especially carbon dioxide) could be altering t h e thermal structure of the atmosphere, possibly resulting in increased surface temperatures through realization of the "Greenhouse Effect." New health and economic impacts could result directly from these atmospheric changes. However, it is also probable that existing conditions t h a t a r e now recognized to pose hazards to human health, and where costly measures are already being implemented, could be significantly exacerbated. Areas of particular concern in the United States a r e urban airsheds, where expensive emission reduction schemes a r e currently being implemented to minimize photochemical ozone production. It has been known for decades that ultraviolet and thermal radiation provide the energy which drives the urban photochemical smog system. The projected changes in upper atmosphere gas concentrations could result in future enhancement of
366 radiative and thermal energy at the surface. Currently, the economic and health decisions related to these urban airsheds are based on the assumption of continued, present-day energy distributions. The objective of this study was to identify whether the projected global changes could have a detectable impact on chemical dynamics in urban airsheds. W e simulated possible future conditions for representative cities to analyze the dynamics of important chemical processes, and the ranges of these effects. APPROACH
Tools The atmospheric simulation model we chose was a two-level trajectory model (ref. 1) designed to simulate urban photochemistry with very complex chemical mechanisms. In this study the Carbon-Bond Mechanism-X (ref. 2) and the Carter, Atkinson, Lurmann and Lloyd Mechanism (ref. 3) were used. Selection of this model allowed us to focus on chemical dynamics, while still retaining important physical variables such as the changes of temperature, inversion depth, and other atmospheric parameters available for each evaluation day. In addition, because the model is relatively simple compared to gridded models, a larger number of atmospheric measurement periods from more cities could be simulated. Potentially diminished ozone column densities will manifest as increased UVB irradiation; and therefore, more rapid photolysis rates for certain UVB-absorbing species (ozone, formaldehyde and larger aldehydes). To calculate variable photolysis rates for these species, we coupled the trajectory model with an algorithm that determines near-surface,
UVB actinic flux (ref. 4). This algorithm provided a means of calculating present, and potential future, spectral actinic flux throughout each evaluation day depending on changing zenith angle, atmospheric and optical thickness, altitude, albedo, and ozone column density. For each ozone episode and scenario simulated, the actinic flux was calculated for local conditions, and from this the photolysis rates could be determined throughout the day. Fig. I shows the calculated rate for photolysis of ozone to O(ID) for Seattle and Los Angeles on I August as a function of time and ozone column density. I t is evident that an approximate doubling of the ozone photolysis rate occurs with t h e decrease in ozone column from 0.300 to 0.200 cm-atm. For formaldehyde photolysis rates, the change is only about 20 percent, because the enhanced surface light is less efficiently absorbed by formaldehyde. We also show in Figure I, that the latitudinal differences between Seattle and Los Angeles leads to about a 14 degree variation in solar elevation (at solar noon), causing about a 20 percent difference in ozone photolysis rates around that time. Methodology
We attempted to provide the widest range of evaluation data by utilizing atmospheric measurements from as many cities as possible. Air quality measurement data was available
367
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Fig 1. Calculated ozone photolysis rates f o r Seattle, Washington, and Los Angeles, California f o r 1 August a t 0.300 and 0.200 an-atm overhead ozone column.
368 from a total of 45 cases for ten major cities in t h e United S t a t e s (Boston, Chicago, Los Angeles, Nashville, New York, Philadelphia, Phoenix, Seattle, Tulsa, and Washington). Initially, w e simulated the conditions of these days with our trajectory and actinic flux models to identify t h e days for which t h e measured ozone concentration profiles were accurately predicted, Thirteen days from seven different cities were selected. These evaluation episodes were then used to assess t h e range of future effects due to decreases in stratospheric ozone and increases in surface temperature. The protocol for this assessment required creation of future scenarios based on the evaluation episodes. Because the potential global changes a r e expected to occur within a few decades, many cities would ideally have attained t h e National Ambient Air Quality Standard (NAAQS) of 0.12 ppm ozone, as mandated by law. Therefore, we c r e a t e d future scenarios by utilizing t h e method recommended by the United S t a t e s Environmental Protection Agency to determine the amount of non-methane organic carbon reductions expected to achieve the present ozone standard for each case (ref. 5). To do this we combined t h e trajectory model with t h e Empirical Kinetics Modeling Approach. This facilitated calculation of a possible set of future conditions with which t h e NAAQS for ozone (the future base case) might be achieved. These sets of episode conditions, each producing a maximum ozone concentration of 0.12 ppm, were t h e future base case d a t a
sets. Once t h e future base case scenarios were established, the effects of changes to the temperature and UVB (photolysis rate) parameters were assessed. The measured (or calculated) temperature profile specific to each test day was used for t h e base case simulations. Also, since ozone column density d a t a were not available for these cities, w e used a value of 0.300 cm-atm (300 Dobson Units) as t h e base case overhead ozone column density when calculating diurnally varying photolysis rates. Projected future perturbations to these two parameters were made by simply adding 2 and 5 Kelvin to t h e base case temperatures, and by calculating photolysis r a t e s for overhead ozone column densities of 0.250 and 0.200 cm-atm. We chose t h e t 2 Kelvin and 0.250 cm-atm conditions as possible in a few decades, while t 5 Kelvin and 0.200 cm-atm a r e considered extreme, but useful in analysis of chemical dynamics. By testing all combinations of t h e base case and two altered values, 9 future scenarios were simulated for each evaluation day. RESULTS The results of this investigation c a n be subdivided into: (1) the potential changes to urban airshed chemical dynamics associated with potential future surface temperatures and ozone column densities, and (2) the range of possible effects from these potential changes in t h e cities studied. Chemical Dynamics Results from this study indicate t h a t changes to urban photochemistry could b e caused by decreased stratospheric ozone or increased surface temperature. The impacts of these
369 global variations will differ because of the d i f f e r e n t periods over which increased energy occurs. Enhanced UVB irradiation caused by diminished stratospheric ozone absorption can only occur in t h e daytime. Conversely, energy input t o the earth's surface through Greenhouse warming takes a less direct route and should have a less diurnal pattern. Photochemical systems also respond in different ways depending on the type of energy (thermal and radiant). Increased UVB leads to enhanced photolysis rates for a few important photoreceptor species. This generally provides a larger rate of radical production, and a higher capacity for oxidation. However, temperature changes induce certain chemical reactions to occur more rapidly while other r e a c t at a slower rate. Hence, t h e effect of temperature change can be different depending upon the extent to which a chemical system has reacted, and on what specific types of chemical reactions a r e dominant at the time of temperature change. In the urban episodes simulated, two distinct types of possible future impacts could be identified. First, surface temperature increases tended to increase reactivity and provide a greater r a t e of formation for ozone and oxidized products throughout an entire simulation period. This is shown in Fig. 2, the results for a Philadelphia scenario from 24 June 1980. The figure shows the predictions from four simulations, the base case (measured temperature and 0.300 cm-atrn ozone column), 5 Kelvin warmer than the base cases, and 0 and +5 Kelvin for 0.200 cm-atm ozone column case. I t is evident that a slightly higher reactivity occurs in the +5 Kelvin simulations for either ozone column. This causes a relatively constant increase in the r a t e of ozone production throughout the day. This reactivity difference also translates into slightly higher yields of oxidized products, including nitric acid and hydrogen peroxide, for t h e higher temperature simulations. Conversely, peroxyacetyl'nitrate (PAN) yields are shown to be lower at higher temperatures. This is because t h e unimolecular decomposition of PAN is one of the most temperature sensitive reactions in photochemical smog, with much higher r a t e s of decomposition occurring at higher temperatures. The second type of possible future impact results from enhanced UVB irradiation due to diminished absorption by stratospheric ozone. As noted, this increase in UVB translates into faster photolysis rates for radical-producing species. Hence, because radicals r e a c t rapidly in the atmosphere, and, because a maximum occurs for direct solar irradiation at solar noon, the effects are short-term and centered around midday. This also is evident in the simulation results shown in Fig. 2. In the simulations with the diminished ozone column density (0.200 cm-atm), the rates of ozone, nitric acid, hydrogen peroxide, PAN, and radicals (OH and HOZ) a r e all largest near solar noon (1308 hours). Nitrogen dioxide is also consumed most rapidly at that time. Increased temperatures always produced somewhat higher ozone concentrations and increased UVB always produced higher midday ozone production rates. However, the maximum ozone concentration was not always higher for the higher UVB days. This difference, related to the different modes of energy input discussed above, is clearly shown in Fig. 3. In these Tulsa, OK simulation results for 1 July 1981, there is greater
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373 photochemical reactivity and more rapid ozone production for the case of diminished ozone column. However, the maximum (final) ozone concentration is lower for the cases of enhanced UVB. This effect is a result of the chemical characteristics of urban airsheds. The NO2 plot in Fig. 3 indicates that the NOx precursors necessary to continue ozone formation were consumed in both sets of simulations, but more rapidly in the set with greater UVB. Hence, the more reactive systems can become "NO, starved" (and very inefficient at producing ozone) earlier in the day, while the less reactive scenarios remain in a more optimum ozone production mode for a longer period of the day. Such results indicates that urban areas with relatively low precursor emissions may actually produce lower maximum ozone concentrations a t lower ozone column densities, because the enhanced reactivity may consume a large fraction of t h e precursor species earlier in the day under conditions that are less favorable for oxidant formation. However, Fig. 2 has already shown that conditions of sufficient precursor loading will result in high levels of ozone much earlier, sometimes hours earlier, than for base case conditions. Thus, for either situation, the production of high levels occurs earlier for lower ozone column densities. This is important if one is interested in measures of human exposure, as opposed to maximum ozone concentration because earlier peaks generally occur closer to the emission sources and the population centers. Simulation Results To consolidate these episodes into groups with similar chemical dvnamics characteristics, we identified three types of days based on their ozone production, and indirectly related to their emissions and the meteorology on t h e evaluation day. These classifications are: Group I: Days when the NAAQS of 0.12 ppm ozone was exceeded by a large amount. Here we include all days with maximum hourly ozone values greater that 0.17 ppm. There were 10 such days in the 45 days simulated. These data sets are from Los Angeles, Chicago, New York, Boston, Philadelphia, and Washington; representing regions where severe ozone episodes are common. Group 2: Less extreme nonattainment days, often representing cities thought to require moderate emission controls. Hourly maximum ozone concentrations are between 0.17 and 0.14 ppm in this group. Local meteorological conditions can influence the magnitude of the ozone production in many of these cities. Group 3: Days that are nearly in compliance with the NAAQS for ozone. These data sets provide future sensitivity tests with current ozone production at 0.13 pprn or less. The data are scattered between a few test cities, including Boston, Nashville, and Tulsa. For these general groups of scenarios, our simulations predict an average increase in
maximum hourly ozone (over the 0.12 ppm of each future base case) of about 1.4 2 0.5 percent per degree Kelvin increase (2.5 t 0.9 percent per degree Fahrenheit). Table 1 shows the average rate of increase for each group at each ozone column density. The largest
374 effect (1.8 percent/K) was observed for the Group 1 cities, with less impact through Group 2 to t h e least in t h e Group 3 cities. Even for t h e worst case Group I predictions, a 2 Kelvin increase would result in 4ppb e x t r a production, a 5 Kelvin increase in 1 I ppb. Recall, however, t h a t t h e future base case was derived through control of a large fraction of known emissions, If the I 1 ppb increase was deemed important, it could be extremely expensive to control, or even find, the additional emissions. As displayed in the figures, the results for changes t o ozone column are somewhat more pronounced. Our simulations predict a n average increase in maximum hourly ozone of about 0.4 2 0.1 percent per percent decrease in ozone column density ( I percent equals 0.003 cmatm). Table 2 shows, however, that t h e differences between city groups is more pronounced. In the Group 1 city, a change of over 1 percent was found for a 1 percent change in ozone column density. Conversely, negative changes were observed for Group 3. Such effects have been shown for Philadelphia and Tulsa in Figs. 2 and 3. For the Group I cities, these effects are important, since a 1.1 percent change translates into a n ozone concentration of 0.132 ppm if t h e ozone column is 0.270 cm-atm. Such changes already occur on a seasonal basis in mid-latitudes. We also analyzed our results to identify indications of synergistic interaction between the two perturbations. We found that, for all cases available, t h e combined effects of coincident increases in both parameters were sometimes additive, but not synergistic. Such a finding is consistent with our description of t h e urban photochemical processes, assuming that there is a limit to the oxidant-forming potential of a n air mass based on a limited amount of ozone precursor species. CONCLUSIONS Possible increases in surface temperatures and decreases in ozone column densities a r e expected to lead t o enhanced reactivity in urban photochemical systems. In most cases, t h e enhanced reactivity is expected to yield higher levels of ozone and other oxidized products. In all cases the r a t e of ozone formation was increased. This may result in greater human exposure since t h e peak concentrations could occur closer to population centers. In addition, although the expected changes in t h e global parameters a r e not expected to result in dramatic increases in urban ozone concentrations, t h e additional ozone production may be significant enough to warrant additional emission controls. If this is the
case, those controls will probably be very expensive. Hence, it is recommended t h a t t h e conditions considered here be considered when calculating present day emission controls. Acknowledgement. This work was funded by the United S t a t e s Environmental Protection Agency. We thank Mr. Bruce Gay, Dr. Joseph Bufalini, Mr. John Hoffman, and Mr. Dennis Tirpak for their support. The project was conducted under Interagency Agreement No, DW 14931805 with the United S t a t e s Department of Interior. We are grateful to Mr. Don Henderson, who supervised t h e agreement for the National Park Service.
375 TABLE 1. Average Rate of s u r f a c e ozone i n c r e a s e ( p e r c e n t ) per kelvin increase in s u r f a c e temperature. ~~
Ozone Column Density (cm-atm) C i t y Class
0.300
0.250
0.200
1 2
1.8 1.3
1.2
3
1.1
1.9 1.2 0.9
0.9
All
1.4
1.4
1.2
1.4
Average r a t e of s u r f a c e ozone increase ( p e r c e n t ) per percentage decrease i n ozone column density.
TABLE 2.
Temperature ( k e l v i n ) C i t y Class
0.300
0.250
0.200
1
3
1.1 0.1 -0.1
1.1 0.1 -0.1
1 .o 0.1 -0.1
All
0.4
0.4
0.4
2
REFERENCES 1 H. Hogo, and C.Z. Whitten, Guidelines for Using OZIPM-3 with CBM-X or Optional Mechanisms, Volume I, Description of the Ozone Isopleth Plotting Package, Version 3, US. Environmental Protection Agency, Research Triangle Park, NC, 1985. 2 G.Z. Whitten, J.P. Killus, and R.C. Johnson, Modeling of Auto Exhaust Smog Chamber Data for EKMA Development, EPA-600/3-85-025, U.S. Environmental Protection Agency, Research Triangle Park, NC, 1985. 3 F.W. Lurmann, W.P.L. Carter, and L.A. Coyner, A Surrogate Species Chemical Reaction Mechanism €or Urban-Scale Air Quality Simulation Models. Volume 11. Guidelines for Using the Mechanism, U S . Environmental Protection Agency, Research Triangle Park, NC, 1987. 4 P.F. Schippnick, and A.E.S. Green, Analytical Characterization of Spectral Actinic Flux and Spectral Irradiance in the Middle Ultraviolet, Photochemistry and Photobiology, 35 1982 89-101. 5 United States Environmental Protection Agency, Guidelines for Using the Carbon-Bond Mechanism in City-Specif ic EKMA, EPA-450/4-84-005, US. Environmental Protection Agency, Research Triangle Park, NC, 1984.
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T.Schneideret al. (Editors),Atmospheric Ozone Research and its Policy Implications 0 1989Elsevier Science PublishersB.V., Amsterdam - Printed in The Netherlands
377
A SCENARIO STUDY OF THE GREENHOUSE EFFECT
J .ROTMANS Centre for Mathematical Methods, National Institute of Public Health and Environmental Protection, P.O.Box 1, 3720 BA Bilthoven (The Netherlands) ABSTRACT A simulation model of the greenhouse effect, IMAGE, has been developed and used on an operational level at the RIVM. The philosophy which underlies IMAGE is explained and the role of long-term scenario models is discussed. IMAGE is a modular built-up scenario model; the characteristics of the separate modules are outlined as well as the interrelationship between the modules. Finally the crucial role of sensitivity analysis in this class of models is stressed. INTRODUCTION Twenty years after the foundation of the "Club of Rome" it is now widely accepted that empirical scenario studies are a powerful tool for analysing long-term decision problems. In this context a scenario study has to be interpreted as a matter of forecasting rather than predicting. The greenhouse problem belongs to the class of long-term decision problems society nowadays is faced with. The greenhouse problem is primarily related to the release into the atmosphere of GO2 from combustion of fossil fuel. However, the Villach Conference in 1985, "l", mentioned that the role.of other trace gases like CHq, N20, CFC-11 and CFC-12 might be as important. The warming effects of these gases are due to a radiative absorption of the infra-red part of the spectrum. The consequences of such a world wide temperature rise are thoroughly described in "2" and quantified for the Netherlands in "3". For the Netherlands the most threatening effects comprise (i) the sea level rise (safety, watermanagement, environment) (ii) climatic changes (agriculture, shipping, energy supply) (iii) effects for society as a consequence of governments reacting policies (curtailment of car driving, pollution taxes, etc.). In this paper a scenario study of the greenhouse problem is dealt with. The study has resulted in the building of a computer simulation model, called IMAGE, which stands for Integrated Model for the Assessment of the Greenhouse Effect ( " 4 " ) .
IMAGE-PHILOSOPHY Commissioned by the Dutch Government, the National Institute of Public Health and Environmental Protection (RIVM) has developed a simulation model of the greenhouse problem, IMAGE. The prime objectives of this model are threefold: first to offer policy agencies a concise overview of the quantitative aspects of the greenhouse problem (from this perspective it is worth mentioning that IMAGE has been demonstrated in the Dutch Lower House), second to identify uncertainties or crucial gaps in current knowledge, and third to get insight into the effects of several possible policy options concerning the greenhouse problem. In the long run it will grow into a decision support system, meant to be an interactive tool for policy-makers. IMAGE is based on an integrated approach, covering the whole divergent scientific field of disciplines concerning the greenhouse problem. Clearly, this interdisciplinary research is dependent on the effective interaction of scientists from several fields, which is in general difficult to realize. In the case of IMAGE both an extensive study of literature and knowledge transfer after having had consultations with Dutch experts on their specialty uaw). were the basis of the interdisciplinary method ( " 5 " , " 6 "
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The integrated information in the model yields insights that scattered information cannot offer. Furthermore, such an integrated model continually reveals weaknesses in discipline-oriented models. Although the integrated approach is conceptually attractive, it is an assailable one, because of the failures and uncertainties in modelling the individual disciplines. Consequently, the main goal of this integrated way of modelling is to better understand the interrelations between the various scientific skills. MODEL DESCRIPTION The greenhouse problem has been modelled as a dynamic system which evolves in discrete time as a non-stationary Markov chain. The components discerned in the model are represented in figure 1. where an arrow from a component to another one means a driving influence (process) of the first component to the second one. The associated computer simulation program, IMAGE, consists of independent modules. Each module (component) is a separate entity. These modules are linked in a natural way with output of one module serving as input for another. The modular structure allows improvements to be implemented gradually without affecting the basis structure. Although the aim is to get one level of aggregation this is not yet the case. Most modules however are highly aggregated with an elaborate dynamic structure. Our program works with a time step of one year, with a simulation time of
200 years, from 1900 to 2100. In each iteration the next state is computed as
379 a function of the present state, the functional interrelationships between the modules and the scenarios. In view of the time scale of our simulation model, the system has a gobal character, entailing absence of spatial dimensions. As mentioned before the simulation concerns the period 1900-2100.For the period 1900-1985 the emissions are based on the current estimates of historical emissions, population growth and economic development. For the
period 1985 to 2100 four social tendencies are regarded, leading to four sets of emission scenarios. An emission scenario is defined as an integrated perception on a possible development of future emissions, without pretending to be a prediction. Then, a set of scenarios is a mutually consistent development of the trace gases, economic/social tendencies and political interventions. The four examined scenarios can be characterized by the following interpretation: Scenario A: continued trends, assuming a continuation of economic growth not limited by environmental constraints Scenario B: reduced trends are based on the presently considered environmental measures Scenario C: changing trends assume implementation of international movement towards stricter policies Scenario D: forced changes assess the possibilities of maximum efforts towards global sustainable development. Without going into detail, the structure of the different modules and characteristics of the interconnected relationships are described. At present the model deals with five greenhouse gases: Cog, CH4, N20, CFC-11 and CFC-12, and two other trace gases: CO and OH. The emission lodule serves as a transformer of a chosen scenario into global annual emission rates of these trace gases. The underlying energy scenarios in the module are based on the present state of the art on this subject ("9","10") The emission module provides the input for the copcentration rodule. Concerning COP the concentration module is interrelated with the ocean and terrestrial biota module, together reflecting the C-cycle. This C-cycle is modelled according to Goudriaan and Ketner, "5". The other trace gases are treated differently, due to the decay by atmospheric chemistry ("11"). Methane (CH4) for instance is investigated by simulating the CH4-CO-OH cycle. The CH4-concentration is computed as a function of current annual emission, CO-concentration, OH-concentration and the state dependent atmospheric lifetime of CH4 ("12". "13"). The underlying input is formed by tropospheric
380 ozone and NOx-concentrations. Figure 2 shows the structure of the methane module; the figure shows the cyclic character of the system. As opposed to other models ("14"and "15"), the CH4-simulation model includes an extensive investigation of the sources of methane and carbon monoxide and leads to enhanced insight in the driving forces of the CH4-CO-OH cycle ("16"). Similarly, remaining trace gases are modelled where each one has its
own
"chemical" characteristics. The temperature lodule receives its input from the concentration module. In this module the radiative absorption factors of the greenhouse gases control the relative influences. CO -induced warming depends logarithmically 2
upon increases in CO -concentration,while the other trace gases are scaled 2 linearly according to "17". Feedback mechanisms are modelled by means of a discount-rate representing these still insufficiently known diminishing processes ("18"). In the sea level lodule the effect of global warming on potential sea level rise is determined by four independent processes: thermal expansion of ocean water, alphine glaciers melting, and ablation or accumulation of the Greenland and Antartic ice caps. The information necessary for describing these various complicated aspects of the phenomenon sea level rise has been integrated and aggregated to a high level of abstraction ("19"). Analogous to the procedures used in the temperature model the internal dynamic has been conditioned by differential equations in which factors, reflecting the input-output relation of a dynamic subsystem, have been incorporated as parameters. For thermal expansion a time lag of 25 years after equilibrium temperature rise is assumed ("18"). Experiments with IMAGE are discussed in detail in "4" and " 1 3 " . SENSITIVITY ANALYSIS The role of sensitivity analysis in large scale scenario models such as IMAGE in documenting the relative importance of factors and interrelationships is critical. Although sensitivity analysis can lead to an overwhelming quantity of numbers, a careful interpretation can be the key to improved understanding of complex models. Moreover, sensitivity analysis in modelling will be more useful and insightful in the future because of advances in computational capacity. On different places in IMAGE parameters are characterized by uncertainties with respect to their precise level and role. Upper and lower bounds for these parameters were found in international literature "18". In the model these parameters are treated as factors influencing the independent variables. In order to differentiate between the relative
381
importance of these factors, sensivity analysis has been applied on IMAGE, using the technique of metamodelling. The re.sults are given in " 2 0 " . FUTURE DEVELOPMENT IMAGE is yet far from complete. Figure 1 shows which modules (represented by dotted lines) will be added to the existing model in the near future. In the first place more trace gases will be built in (such as other CFC). Secondly the Edmonds & Reilly global energy C02-model will be coupled to IMAGE. Thirdly the C-cycle model will be improved and extended with a deforestation module. Additionally, modules of regional changes and impacts on society are planned. And last but not least an interactive version of IMAGE will be implemented, the first ste? towards the realization of a decision support system. SUMMARY IMAGE is a computer simulation model of the greenhouse effect, which falls
within the scope of long-term scenario decision models. Such models, IMAGE included, have not the intention of making predictions, but should be used only to conduct policy experiments, to answer "what if" questions. IMAGE consists of independent modules, with each module acting as a separate entity, and linked together in a natural way; usually output of one module serves as input for another one. The modular structure allows improvements to be implemented step by step without affecting the basic structure. The model gives a highly aggregated overview of the interrelations between social and economical developments, emissions, concentrations, temperature increase and sea level rise. In the future the model will become an interactive decision support system. In view of the many uncertainties and deficiencies of the model, and in general of long-term integrated models, the role of sensitivity analysis is of crucial importance. Sensitivity analysis can play a decisive part in analysing these models and in differentiating between the relative relevance of sensitivities and uncertainties. REFERENCES
1. B.Bolin (Editor), How much Cog will remain in the atmosphere, Scope 29, 1985. 2. Health Council of the Netherlands, 2e Deeladvies inzake C02-problematiek, Staatsuitgeverij, 's-Gravenhage,1987. 3 . J.Rotmans and M.J.P.den Elzen, Consequences of the Greenhouse Problem for the Netherlands, in preparation, 1988. 4 . J.Rotmans, H.de Boois and R.J.Swart,An Integrated Model for the Assessment of the Greenhouse Effect: The Dutch Approach, submitted for __ publication, 1988. 5. J.Goudriaan and P.Ketner, A simulation study for the global carbon cycle including man's impact on the biosphere, Climatic Change 6 (1984) 16j192.
382 6. J.Oerlemans, in W.Bach (Editor), Carbon Dioxide, Reidel, Dordrecht, 1983, pp. 235-238. 7. H.G.Wind (Editor), Impact of Sea Level Rise on Society, Balkema, Rotterdam, The Netherlands, 1987. 8. P.A.Ocken, Energy and the greenhouse issue, Stichting Energie-onderzoek Centrum Nederland, ESC-40, The Netherlands, 1987. 9. J.A.Edmonds and J.M.Reilly,Uncertainty in future global energy use and fossil fuel C02-emissions 1975 to 2075, US Department of Energy, report TRO 36, Washington DC, 1986. 10. J.A.Edmondsand J.M.Reilly,Future global energy and carbon dioxide emissions, in Atmospheric Carbon Dioxide and the global carbon cycle, USDOE, 1985. 11. P.J.Crutzenand T.Y.Graede1,in W.C.Clark and R.E.Mann (Editors), Sustainable Development of the Biosphere, 1986, pp. ? ? 12. J.Rotmans and E.Eggink, Methane as a greenhousegas: a simulation model of the atmospheric chemistry of the CH -CO-OH-cycle,report nr. 758471002, RIVM, Bilthoven, The Netherlands, 1488. 13. J.Rotmans, R.J.Swart,O.J.Vrieze, Simulation of the CH4-CO-OH-cycle, submitted for publication, 1988. 14. Ch.Briih1 and P.J.Crutzen, Scenarios of possible changes in atmospheric temperatures and ozone concentrations due to man's activities, estimated with a one-dimensionalcoupled photochemical model, Climate Dynamics 2 (1988) 173-203. 15. A.M.Thompson and R.J.Cicerone, Possible perturbations to atmospheric CO, CH and OH, Journal of Geophysical Research 92 (1986) 10853-19864 16. R.j.Swart, Global anthropogenic emissions of carbon monoxide and nonmethane volatile organic compounds as input for the CH4-CO-OH-cycle module; A contribution to IMAGE, report nr. 758471004, RIVM, Bilthoven, The Netherlands, 1988. 17. V.Ramanathan et al.. Trace gases and their potential role in climate change, Journal of Geophysical Research 90 (1985) 5547-5566. 18. J.Rotmans, De ontwikkeling van een simulatiemodel voor de mondiale CO2problematiek, report nr. 840751001, RIVM, Bilthoven, The Netherlands, 1986. 19. J.Oerlemans, Greenhouse warming and changes in sea level, invited paper presented at the symposium on C02 and other greenhouse gases, Brussels, 3-5 November 1986. 20. J.Rotmans,O.J.Vrieze,G.H.J.C.Peek and W.N.G.M.Veraart, Experimenteel ontwerp ten behoeve van metamodellering van een CO2-sirnulatiemodel, report nr. 758471003, RIVM. Bilthoven, The Netherlands, 1988.
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385
SESSION VI
MOBILE SOURCE CONTROL TECHNOLOGIES
Chairmen
L.C. van Beckhoven M. Walsh
This Page Intentionally Left Blank
T.Schneider et al. (Editors),Atmospheric Ozone Research and its Policy Implications 0 1989 Elsevier Science Publishers B.V., Amsterdam -Printed in The Netherlands
307
MOTOR VEHICLE CONTRIBUTION TO GLOBAL AND TRANSPORTED AIR POLLUTION Michael P.Walsh') and Curtis A.Moore 2) 1 ) Consultant, 2800 North Dinwiddie Street, Arlington, Virginia 22207, USA 2) Minority Counsel, Committee on Environment and Public Works, U.S.Senate, Washington D.C. 20510, USA
Motor vehicles generate more air pollution than any other single human activity. They are the dominant source of carbon monoxide, oxides of nitrogen, and hydrocarbons, as well as a significant source of carbon dioxide and, particularly in the U.S., chloroflurocarbons. All of these cause or contribute to the formation of ground level ozone. Some also destroy stratospheric ozone or contribute to its destruction.1,Z Concentrations of ground level ozone are increasing, and stratospheric ozone is being destroyed globally. During the Antarctic spring a "hole" the size of North America is depleted of ozone and, at certain altitudes, is destroyed almost completely because of manmade chemicals.3 Researchers who recently reanalyzed a European data set on tropospheric ozone concentrations from the turn of the century concluded that ozone concentrations had doubled over the past 100 years.4 One commentator described the finding "as remarkable as the observation of a hole in the stratospheric ozone layer over Antarctica and potentially is just as consequential."' Pollutants emitted by motor vehicles are a major cause of each of these environmental threats. Means of abating these pollutants are both economically and technically feasible, but they are being implemented at a rate far short of what technology would allow and prudence would dictate. MOTOR VEHICLE SHARE OF OECD POLLUTANT EMISSIONS* (1000 tonnes, 1980) POLLUTANT
TOTAL EMISSIONS
M/V SHARE
NOx
36,019
17,012 (47.2%)
HC
3 3 ,869
13,239 (39.1%)
co
119,148
78,227
(65.7%)
their precursors are Ozone, acidic compounds, and transported over great distances. There is recent evidence that even carbon monoxide is transported over great distances.l,a
388
Some of these compounds react with each other in ways only recently understood. For example, hydroxyl radicals (OH) which scavenge many anthropogenic and natural trace gases from the atmosphere, are themselves removed by carbon monoxide. CO increase, tropospheric Therefore, as concentrations of concentrations of OH decrease, thus allowing other trace gases (e.g. methane and reactive hydrocarbons) to accumu1ate.B , l o EFFECTS
Human health: Controlled human exposures and field studies at frequently encountered ambient levels of ozone have demonstrated that it causes healthy, exercising children, adolescents, and young adults to lose lung function;11 and, children in day camp to experience a linear increase in lung decrement with increased exposure time, with decreased lung function for up to one week;1*,1a When levels of ozone increase, so do hospital admissions for pulmonary distress.l',ls In animal studies, chronic exposure to ozone causes serious morphological change, including cell damage to ciliated and non-ciliated cells, increases in inflammatory cells, distal airway narrowing and lesions similar to those observed in smokers.14,lT Some researchers have concluded that air pollution in the United States, especially fine particles, may cause 2 to 4 percent of the nation's excess mortality.18 Ozone's precursors and associated pollutants also damage human health. Oxides of nitrogen, for example, caused significant decrements in pulmonary function in subjects with chronic emphysema who were exposed while performing bronchitis or moderate exercise.19 Benzene, a demonstrated human carcinogen, causes anemia, bone-marrow hypoplasia and other diseases in laboratory animals.'@ Lead destroys intelligence in children, increases susceptibility to infectious agents, and causes 50,000 deaths per year of heart attack and stroke in United States among white males over the age of 40.21,2* Forest Damages: Forest declines ("Waldsterben") throughout Europe and Eastern North America have focused considerable press attention on "acid rain" from sulphur dioxide and oxides of nitrogen.23 A more likely explanation for these declines may be ozone or ozone in combination with acid deposition and other air pollutants, or in combination with natural stresses (e.g. insects) . a 4 Visible symptoms of Waldsterben first appeared in Europe in 1979-80 and within four years the disease had spread over large areas of the continent. As of late 1985, the disease was still increasing in intensity and geographic area. It is associated with an alarming frequency of damage from secondary stress factors such as insects, needle and root fungi, and climatic stress such as frost, wind and emow damage. It now
389
affects virtually every tree species in Europe including the four most important conifers (spruce, fir, pine, larch) and six angiosperms (beech, birch, oak, ash, maple and alder). According to one analysis, European damage is worst in West Germany, where 55 percent of the trees are injured, followed by Switzerland, where 33 percent of the stands are suffering from "Waldsterben" . a 5 , * a The government of the United States views the nature, extent and possible causes of forest damage in North America more conservatively.2' This view is not shared by non-governmental observers.Za Although not assembled in a single government document, there are nonetheless reliable reports of extensive damage to yellow pine, white pine, red spruce, fraser fir, sugar and yellow maple, beech, birch, red maple and a wide variety of other tree species throughout eastern North America.2n , 3 0 , 3 1 , 3 2 , 3 3 Field and other experiments have confirmed that levels of ozone commonly encountered throughout the eastern United States can cause significant reductions in growth and net photosynthesis.S4,3Sl One scientist has concluded that-(1)n areas where known anthropogenic air pollution takes place, trees are in fact statistically more symptomatic than trees from non-polluted areas, trees from polluted areas are in fact significantly more suppressed in terms of their growth rates over the past 25-30 years as compared to non-pollutant sites and surface soils have in fact accumulated lead, often an order of magnitude above that of non-polluted region soils. 3 8 Aquatic and soils effects. Ozone is not reported to directly impact either soils or aquatic ecosystems, but oxides of nitrogen may. Sulfuric acid and nitric acid increase the levels and toxicity of some metals, including mercury and aluminum." They also acidify soils, accounting for the extensive acidification of deep soil horizons'in many sensitive areas.08 Crop damages. The U.S. National Acid Precipitation Assessment Program has estimated that ozone damage to agricultural crops is about $1 billion per year in the United States.a* Buildings and materials. More than two decades o f research have established that ozone reacts with both natural and man-made materials to destroy their integrity or otherwise cause damage. The most susceptible materials are textiles, elastomers, and paints . 4 0 EMISSIONS Europe: As source of air
noted earlier, motor vehicles are the major pollution, including ozone, throughout Europe.
330
Virtually all of the lead and carbon monoxide in cities and an increasing proportion of the fine particles originates with vehicles. OECD recently noted that "The primary source category responsible for most NOx emissions is road transportation roughly between 5 0 and I0 per cent...Mobile sources, mainly road traffic, produce around 50 per cent of anthropogenic VOC emissions, therefore constituting the largest man-made VOC source category in all European OECD countries."41 U.S.: During 1985, transportation sources were responsible for 73 percent of nationwide lead emissions, 70 percent of the CO, 34 percent of the volatile organic compounds (HC), 4 5 percent of the NOx, and 18 percent of the particulate. In some cities, the mobile source contribution is even higher. Growth in vehicle miles travelled and less stringent controls on other mobile sources are reducing the overall gains from the automobile standards. According to EPA estimates,'2 the overall reductions in emissions from all transportation sources across the U.S. during the last decade were 88 percent for lead, 2 5 percent for CO, and 30 percent for HC. These reductions occurred despite a 26 percent increase in vehicle miles travelled during this same time period. However, because standards for these pollutants have been more lenient or implemented later, overall reductions have been only 1 percent for NOx and there has been no reduction in particulate. GLOBAL IMPACTS OF MOTOR VEHICLE POLLUTANTS
To put the global problems with motor vehicle pollut on in perspective, it is important to realize that motor vehicle usage has increased tremendously in a relatively brief period of time. In 1950, less than 50 million cars were on the world's roa s , 85 percent of them in North America. Only one generation later, the car popu1,ation is approaching 350 million, almost a seven fold increase.43 Outside North America, the growth has been especially high, from slightly under 7 million in 1950 to 125 million by 1980. While the rate of growth has slowed in the highly industrialized countries, population pressures, increased urbanization and industrialization are accelerating motor vehicle growth in other areas. Whereas the number of people in Europe and the U.S. is increasing moderately, the global population is expected to double (compared to 1960 levels) by the year 2000, driven by more than a doubling in Asia and an almost 150 percent increase in Latin America. Beyond the overall growth in population, an increasing portion of Asia's and South America's people are moving to cities, driving up the global urban population." One result is that global automobile production and use are projected to continue to grow substantially over the next decade. By the year 2000, the global vehicle population will likely exceed 500 million, with annual car production rising from about 3 3 million today to about 38 million.45
391
Ozone destruction and production. Motor vehicles produce ground level ozone both directly and indirectly. Vehicular emissions of NOx and HC directly cause ground level ozone by reacting to form it. Other pollutants emitted by motor vehicles produce ground level ozone indirectly by destroying stratospheric ozone. Ozone in the stratosphere blocks ultraviolet radiation from the sun. But ozone is also created by this same solar radiation, which fractures oxygen (02) molecules, allowing them to recombine as ozone (03). As stratospheric ozone is destroyed by chemicals, the amount of ultraviolet radiation penetrating to ground level-and the ozone which it produces--increases. The chemicals which destroy stratospheric ozone, and thus indirectly increase ground level ozone, are chloroflurocarbons (CFCs) (more commonly known in the United States by the DuPont Corporation’s tradename of Freons).46 CFCs are used in vehiclular air conditioners. About 40 percent of the United States production of CFCs and 30 percent of European production is devoted to refrigeration. Mobile air conditioning accounted for 56,500 metric tons of CFCs--28 percent of the CFCs used for refrigeration in the United States, or about 13 percent of total production. In contrast, home refrigerators accounted for only 3,800 metric tons.47 Thus, approximately one of every eight pounds of CFCs manufactured in the U.S.is used, and emitted, by motor vehicles. (CFCs also are used as a blowing agent in the production of seating and other foamed products but this is a considerably smaller vehicular use. Global climate destruction. Motor vehicles also emit substantial quantities of trace gases which increase global temperatures, destroying prevailing climates. Hothouse gases emitted by (or attributable to) motor vehicles include carbon dioxide (COZ), CFCs, nitrous oxide (N20), methane (CH4), water and, ground level ozone.48 CFCs are the most potent hothouse gases, now contributing about over a third of the total global warming effect.49 Carbon dioxide is the other major hothouse gas. A single tank of gasoline produces between 300 and 400 pounds of C02 when burned.50 Motor vehicles emit about 2.77 gigatons of C02 per year, which is 13.5 percent of the world’s production. In the U.S., motor vehicles are responsible for 23.5 percent of the total C02 emissions.51 Doubled C02 concentrations (or the trace gas equivalent thereof) are projected to increase the global average temperature between 1.5 and 4.5 degrees Centigrade.32 Changes likely to accompany this temperature increase include the following: large stratospheric cooling (with the potential to accelerate stratospheric ozone depletion); global mean precipitation increase; reduction of sea ice; polar winter surface warming; summer continental dryness; high latitude precipitation increase; and, rise in global mean sea level.53
392
Other consequences which investigators have suggested include failure of the Asian monsoons and sudden onset of a European ice age.3 4 ,5 3 Partially because of recent unexplained extreme events (e.g. drought, proliferation of icebergs, etc.) some commentators have begun to speculate whether the global climate destruction has already begun to occur.66 The years 1 9 8 1 , 1 9 8 3 and 1 9 8 7 are reported to be the hottest on rec0rd.s'
CONTROL OPTIONS
Mobile Sources: Before emission reductions were mandated, gasoline vehicles emitted pollutants at the rates listed in Table A , which also displays the current U . S . requirements. TABLE A Vehicle Emissionst Pol1u tant
Uncontrolled
Hydrocarbons Exhaust Crankcase Evaporative Carbon Monoxide Oxides of Nitrogen
8.2 4.1 2.9 90 3.5
Current .41 3.4 1.0
1: Exhaust emissions as determined by the 1 9 7 5 U . S . Federal Test Procedure, expressed in grams per mile.
Initial Controls: To meet the relatively lenient HC and CO standards that applied in the early 1 9 7 0 ~ 1 ,auto manufacturers generally relied on enleanment of the air/fuel mixture and modification of spark timing. Newer combustion chamber designs were introduced to reduce hydrocarbon emissions, with faster flames to limit increased nitrogen oxides. When HC and CO standards were tightened, the engine modification approach continued to predominate, with the addition of certain new wrinkles such as transmission controlled spark timing and antidieseling throttle control. Attainment of initial HC and CO standards with limitations on NOx increases was generally possible without significant fuel consumption penalties. However, as emissions standards were tightened (especially in 1 9 7 3 and 1 9 7 4 ) it became more and more difficult for domestic cars employing conventional engine designs to achieve low levels of CO, HC and NOx without unacceptable compromises in performance or fuel economy. As a result there was a fundamental shift in the technology to the catalytic converter. Catalysts: Two
basic types of catalysts have been developed
- oxidation and three way.
333
An oxidation catalyst converts HC and CO to carbon dioxide and water. Three-way catalysts are so called because they lower three pollutant levels--HC, CO and NOx--simultaneously. First introduced in the U.S. in 1977, they are now almost universally used on cars and light trucks there and in Japan. Because they require .that air-fuel ratios be precisely controlled, three-way catalysts have fostered improved air-fuel management systems including advanced carburetors, throttle body injection, and electronic controls (ironically, leading General Motors to become the world largest producer of computers). Diesel Fueled Vehicles: To solve the air pollution threats in many areas would require improvement in the currently inadequate controls on diesel fueled vehicles, which not only emit NOx, HC, and particulate, but pose a significant cancer risk.58 In the U.S. attention has focused particularly on diesel trucks and buses, leading to the adoption of standards intended to spur technological developments similar to those which occurred for cars. Basic approaches to diesel engine emission control fall into three major categories: 5 9 1 6 0 1 6 1 1: engine modifications, including combustion chamber configuration and design, fuel injection timing and pattern, turbocharging and EGR; 1: exhaust aftertreatment, catalysts; and
including
trap
1: fuel modifications, including control of fuel additives, alternative fuels.
oxidizers
and
fuel properties,
NOx controls being phased into the diesel population now include variable injection timing and pressure, charge cooling, and exhaust gas recirculation. Retarding injection timing, while a well established method of reducing NOx formation, can lead to increases in fuel consumption, particulate and hydrocarbon emissions. These problems can be mitigated by varying the injection timing with engine load or speed. Also, high pressure injection can reduce these problems. Coupled with electronic controls, these and other techniques could simultaneously reduce NOx and improve fuel economy.
THE WORLD The evolution of vehicle controls since crankcase regulations in 1963, has made dramatically lower vehicle emissions through one of the following: ( 1 ) engine modifications (2) controls and ( 3 ) in-use controls. Increasingly,
REGULATIONS AND STANDARDS AROUND
the first U . S . it possible to or a combination add-on catalytic countries around
334
the world have been taking advantage of them, although with different degrees of stringency. Japan and the United States currently impose the most stringent emissions controls, but as knowledge of these technological developments has spread and the damage caused by vehicular pollutants has become evident, more and more nations have imposed controls. For example-t The Netherlands and the Federal Republic of Germany have adopted innovative economic incentive approaches to encourage purchase of low pollution vehicles; and,
+ Canada, Austria and Switzerland have decided to implement U.S. standards for the 1988 Model Year, while Norway and Sweden will do so by 1989; + Australia has adopted standards similar to those used in the U.S. in the mid to late 1 9 7 0 ' s when catalyst technology was first introduced. A Divided Europe: In many ways, Europe is a microcosm of global motor vehicle issues--confronted by rapid environmental deterioration and an ensuing public outcry and its manufacturers able to build either clean or dirty vehicles, Europe's governments are moving toward tighter and tighter controls, but at a pace which is much slower than technology would allow. This is largely because the nations of Europe are sharply divided.
Members of the so-called Stockholm Group, including Austria, Norway, Sweden and Switzerland, have adopted state-of-the-art emissions requirements. Perhaps more importantly, the group has retained the U.S. 1975 Federal Test Procedure ( ' 7 5 FTP) to judge whether manufacturers are complying with the law. Because these nations are not members of the EEC, they were free to act on their own. The EEC nations have adopted more lenient tailpipe standards and test procedures embodied in the "Luxembourg compromise", which is a non-binding guideline. While member states are free to adopt the provisions of the Luxembourg compromise, they are equally free to reject them and continue to rely on the older, Because EEC members are barred binding standards of R 15-04. from requiring more stringent controls, a schism has developed that threatens the Community's unity. Nations like West Germany and the Netherlands are encouraging motorists to buy clean cars by offering tax breaks, while Denmark has threatened to unilaterally align itself with the Stockholm Group. To accurately measure the
leniency of
the standards of the
335
Luxembourg compromise, it is necessary to compare their outcomes with those of the test procedures adopted by the Stockholm Group procedure (the ' 7 5 FTP), as follows: Stockholm Group levels ( 0 . 4 1 grams per mile HC, 3 . 4 CO, 1.0 would be in the range of 1.5 to 2.5 grams per teat for HC, 1 5 to 2 0 CO, and 1 . 5 to 2 . 5 for NOx. The best single point estimate of the standards is estimated at 2 . 2 grams per test HC, 2.4 NOx and 16 CO. The Luxembourg compromise standards as summarized below are much more lenient than these levels, up to three times higher depending upon vehicle size.
NOx)
Engine Size
co
HC+ NOx
under 1.4 liters
45
156
1.4 to 2 . 0
30
8
above 2.0
25
6.5
NOx
3.5
A key ingredient of all programs directed toward state of the art emissions standards is the widespread availability of unleaded gasoline. At this time, most major automotive markets in the world have introduced unleaded fuel and when it is mandated across the Common Market by the end of the decade, it appears that the era of leaded fuel will be finally drawing to an end.
CONTROL O P T I O N S
Mobile sources: Although emissions from cars have been substantially reduced from uncontrolled states, further reductions could be achieved by tightening tailpipe standards (especially on trucks, buses, heavy duty engines, and dieselpowered vehicles); imposing in-use controls (e.g. inspection and maintenance programs); switching fuels (e.g. natural gas or, in limited cases, methanol); or changing vehicle use patterns (e.g. lowering speed limits). Proposals to adopt changes in many of these areas are being seriously considered throughout the world. United States: Legislation awaiting Senate consideration in the U . S . Congress would lower emissions from both gasoline and diesel powered vehicles in an effort to reduce air pollution in the roughly 7 0 cities where air quality levels are unhealthy. These are summarized below.
336
Automobiles (Light Duty Vehicles) Carbon Monoxide ICOI Hydrocarbons (HC) Oxides of Nitrogen INOX) Particulate Light Duty Trucks (Above 6000 lbs. CVW) Carbon Monoxide (CO) Hydrocarbons (HC) Oxides of Nitrogen (NOx) Particulate Heavy Duty Trucks grams/brake horsepower hour Oxides of Nitrogen (NOx) Particulate
Current
Revi sed
grams/mile
erams/miln
2.4
2.4
0.41 1.0 0.2
0.25 (1992) 0.4 (1990) 0 . 0 8 (1990)
grams/mile 10.0
grams/mile 5.0 (1990)
0.8 2.3 0.26
0.50 (1990) 1.7 (1990) 0.5 (1992)
10.6 5.0 (1991) 0.25 (1991)
6.0 (1990) 4.0 (1991) 1.7 (1995) 0.25 (1991)
0.10 (1994)
0.10 (1994)
0.08 (1990)
Cold starts: Because U . S . data show that emissions of carbon monoxide from motor vehicles are higher when the ambient temperature is low and the engine is cold (so-called “cold starts“), the bill addresses this specific problem. It requires that at temperatures between 2 0 and 6 8 degrees Fahrenheit CO emissions be reduced by 90 percent from 1970 levels. At 20 degrees, this new level is calculated to be 6.2 grams per mile. Similar legislation has been introduced in the House of Representatives, but delayed by the opposition of the Committee Chairman, Rep. John Dingell of Detroit, Michigan, home of the Both bills would also make impose major U . S . automakers. additional requirements on use of motor vehicles, including more stringent inspection and maintenance programs and controls on refueling emissions. Europe: Small cars represent almost 6 0 percent of the car population in Europe and their Standards are scheduled to be tightened during the 1990’s. Should they be lowered to levels in the range of 15 grams per test CO, and 2 grams per test each for HC and NOx, the overall environmental impact of the package could improve considerably. If relatively weak levels (for example, equal to or more lenient than the medium car standards of 30 CO and 8 for HC plus NOx, as proposed earlier this year by the
397
European Commission) are adopted, the Community will be condemned to serious air pollution problems well into the next century. Global: Mobile source C02: Mobile source emissions of carbon dioxide could be substantially reduced through the use of more fuel efficient vehicles. For example, in late 1 9 8 5 , the Toyota Corporation tested a prototype model AXV which utilizes presently available technologies (e.g. low weight, low aerodynamic drag, direct injection diesel engine, and continuously variable transmission). The car received an EPA fuel economy rating of 9 8 miles per gallon on the combined urban/highway test. , By comparison, U . S . automobiles average 19 mpg and non-U.S. cars about 2 4 mpg. 6 1 Global: Mobile source CFCs: Significant reductions in CFC releases could be achieved through improvements in air conditioner seals and, especially, through changes in repair shop work practices because CFCs are intentionally vented to the air when air conditioners are repaired. CFC consumption in the U.S. has been estimated as follows: ESTIMATED U . S . CONSUMPTION OF CFC-12 FOR MOBILE A/C (1000 TONNES)O' Use
CFC Consumption
X of Total
14.7
1.0
27.2 5.2 1.8
13.5 18.2 3.9
25.0 33.6 7.2
Initial charge of units U.S.
Imported Aftermarket Recharge of Units After leakage After service venting After accident
2.8
Compliance Programs For In Use Vehicles: To comply with emission standards in-use, cars must be maintained properly. Inspection and Maintenance (I/M) programs are essential to assure this and therefore a key element in the control programs of many countries.64 While I/M programs in the U . S . have focused on HC and CO control, countries such as Germany have taken the lead in exploring the feasibility of I/M for NOx and diesel particulate control. Stationary sources: NOx controls: Technologies are currently available and in use for the control of oxides of nitrogen from stationary including low NOx burners (up to 7 0 percent reduction from uncontrolled states); and selective catalytic reduction
(SCR) (90 percent or greater reduction). To date SCR has been installed on more than 100 units in Japan and more than 50 in Germany. NOx can also be reduced through the use of combustion systems such as fluidized bed and integrated gasificationcombined cycle, but a detailed discussion of these is beyond the scope of this paper.65 Due in part to the availability of these control options, major revisions of air quality regulations have been adopted by a number of European nations, including Belgium, West Germany, Hungary, and Switzerland.66 CONCLUSIONS
Motor vehicles account for more of the world’s air pollution than any other human activity. They are responsible for virtually all of the carbon monoxide and lead in the air of cities, and a major portion of the NOx, VOC’s, fine particles and toxic chemicals. In addition, as the major consumer of oil in the world, vehicles also emit substantial amounts of carbon dioxide and other gases which contribute to giobal warming. Due to expanded CFC use in vehicle air conditioners, vehicles also play a significant role in the stratospheric ozone depletion. The d a m g e caused by vehicular pollutants is becoming inescapably apparent. Increases in the number of vehicles and the number of vehicle mile travelled is overwhelming the reductions which have been achieved to date, although almost fifty percent of all new cars produced this year are equipped with state of the art emissions controls. The Common Market countries of Europe stand out as the slowest industrialized area to implement state of the art requirements. It is likely that unless the Community moves closer to the standards of the Stockholm Group Europe will see further deterioration of its environment. More stringent small car standards, on the order of 16 grams per test CO and 2 grams per test each for HC and NOx, would represent a large step in the right direction. While NOx and particulate control technologies for diesel cars are not as advanced as for gasoline cars, progress is accelerating and very low levels have been demonstrated. Emission control of trucks and buses is of particular importance because of past neglect, but fortunately, it appears that technologies developed for cars can be transferred. Eliminating the use of CFCs in automotive air conditioners or, in the short term prohibiting unnecessary venting to the air, would not only protect the stratosphere, but the troposphere as
399
well. Mandatory fuel efficiency standards throughout the world would slow the growth in C02 emissions which are increasing global temperature and destroying prevailing climates. However, continued growth in the number of vehicles and their use is undercutting the overall benefits of these technological gains. The global vehicle population has climbed from under 50 million just one generation ago to more than 350 million. By the year 2000, it is projected to exceed 500 million. Unless this growth is constrained, global pollution will continue to increase, many areas which currently have relatively clean environments will deteriorate, and the few areas which have made progress will see some of these gains erode. With the increasing likelihood that the global changes will be irreversible and of unknowable proportions, it is imperative that the nations of the world confront and surmount these obstacles. Otherwise, as 250 of the world's scientists warned in Villach, Austria in December, 1985 "Mankind is conducting a gigantic experiment with the Earth's future without knowing the outcome.' ' 6 7
1. OECD Environmental Data, Organization operation and Development, Paris, 1987.
for
Economic
Co-
2. Regulatory Impact Analysis: Protection of Stratospheric Ozone, Environmental Protection Agency, Washington, D.C. (December, 1 9 8 7 ) 3. Testimony of F.S. Rowland and R. Watson, Committee on Environment and Public Works, U . S . Senate, Washington, D.C. (March 30, 1 9 8 8 ) . ' 4 . A. Volz & D. Klev. "Evaluation of the Ozone Measurements Made in the Nineteenth ( 1 9 8 8 ) 240-43.
5. S.A. Penkett, "Atmospheric Chemistry: Ozone," Nature 332 ( 1 9 8 8 ) 204.
Montsouris Series of Century," Nature 332
Increased Tropospheric
6. OECD, n. 1.
7. Khalil, M.A.K. & Rasmussen, R.A., "Carbon Monoxide in the Earth's Atmosphere: Indications of a Global Increase", 332 Nature 245 (March, 1 9 8 8 ) . 8 . Acid Rain and Transported Air Pollutants: Implications for U.S. Congress, Office of Public Policy (Washington, D.C.: Technology Assessment, OTA-0-204, June, 1 9 8 4 ) .
9 . Testimony of D.R. Blake before the Committee on Energy and Natural Resources, U.S. Senate, Washington, D.C. (Nov. 9 , 1 9 8 7 ) .
lO.Thompson, A.M. b Cicerone, R.J., "Atmospheric CH4, CO from 1 8 6 0 to 1 9 8 5 , 3 2 1 Nature 1 4 8 - 5 0 ( 1 9 8 6 ) .
and OH
11. W.F. McDonnell, D.H. Horstman, et. al., Pulmonary Effects of Ozone Exposure During Exercise:Dose-Response Characteristics, JAppl. Physiol.:Respir. Envir. Exercise Physiol. 54 ( 1 9 8 3 ) 1 3 4 5 - 5 2 . 1 2 . M. Lippman, J.H. Cunningham, et.al., "Effect of Ozone on the Pulmonary Function of Children," Advance in Modern Environmental Toxicology. Ed: S . D . Lee, et.al. Princeton Scientific Publishers, 1983. 1 3 . P.J. Lioy, T.A. Vollmuth & M. Lippman, Persistence of Peak Flow Decrement in Children Following Ozone Exposures Exceeding the National Ambient Air Quality Standard. J. Air Poll. Control Assn. 3 5 ( 1 9 8 5 ) 1 0 6 8 - 7 1 . 1 4 . D.V. Bates & R. Sizto, Relationship between air pollution levels and hospital admissions in Southern Ontario, Can. J . Public Health 7 4 ( 1 9 8 3 ) 1 1 7 - 2 2 . 1 5 . D.V. Bates 8 Sizto, A Study of Hospital Admissions and Air Pollutants in Southern Ontario, Aerosols, Eds. S.D. Lee, et. al. Lewis Publishers, Chelsea, Michigan ( 1 9 8 6 ) . 1 6 . D.V. Bates, "The Effects of Ozone on Individual and Human Populations," North American Oxidant Symposium, Ministere de 1'Environment du Quebec, Quebec (Feb. 1 9 8 7 ) . 1 7 . Ibid. 18. H. Ozkaynak, J . Spengler, et. al. Health Effects of Airborne Particles, Energy and Environmental Policy Center, John F. Kennedy School of Government, Harvard University, Boston (Feb.
1986). 1 9 . Bauer, 1 9 8 6 ,
1987.
2 0 . M.I. Luster & J.A, Blank, "Molecular and Cellular Basis of Chemically Induced Immunotoxicity," Ann. Rev. Pharmacol. Toxicol. 27 ( 1 9 8 7 ) 3 7 . 2 1 , Ibid. at 3 2 . 2 2 . The Nature and Extent of Lead Poisoning in Children in the United States: A Report to ConRress (Draft), Agency for Toxic Substances and Disease Registry, U.S. Department of Health and
401
Human Services, Atlanta, Ga. (1988). 23. M. Keating, "Withering Death of Forests Spreading Across the East," The Globe and Mail, Toronto, Canada, August 6, 1987. 24. G.H. Weyerhauser, "Ozone, Not Acid Rain, Main Forest Growth," Financier IX (December 1985) 34-36.
Threat to
25. World Resources 1986, World Resources Institute, Washington, D.C. (1986)v p. 204-5. 26. P. Schutt & E. Cowling, "Waldsterben--a General Decline of Forests in Central Europe: Symptoms, Development and Possible Causes," Plant Disease 69 (1985) 448-58. 27. Review, n. 16, at X-24. 28. American Forestry Association, "The Forest Effects Pollution," Am. Forests, Nov./Dec., 1987, pp. 37-44.
of Air
29. R.I. Bruck,. "Decline of Boreal Montane Forest Ecosystems in Central Europe and Eastern North America-Links to Air Pollution and the Deposition of Nitrogen Compounds," EPA-EPRI Joint Symposium #18, New Orleans, La. (1987). 30. H.A. Knight, "The Pine Decline," J. of Forestry, pp. 25-28.
Jan. 1987
,
31. S.M. Zedaker, et. al., "Growth Declines in Red Spruce," J. of Forestry, 85 (1987) 34-6. 32. Review, n. 16, pp. X-26-28. 33. 33. Joint Report to Bilateral Advisory and Consultative Group: Status of Canadian/U.S. Research in Acidic Deposition, U.S. National Acid Precipitation Assessment Program (NAPAP), Washington, D.C., Feb. 1987. 34. D. Wang & F.H. Borman, "Regional Tree Growth Reductions Due to Ambient Ozone: Evidence From Field Experiments," Environ. Sci. Technol., v. 20, no. 11 (1986) pp. 1122-25. 35. P.B. Reich & R.G. Amundson, "Ambient Levels of Ozone Reduce Net Photosynthesis in Tree Species," Science, 230 (Nov. 1985) 566-70, 36. Bruck, n.29.
402
37. P. Campbell, P. Stokes, & J. Galloway, "Acid Deposition: Effects on Geochemical Cycling and Biological Availability of Trace Elements," Tri-Academy Committee on Acid Deposition, National Acad. Press, Washington, D.C. (1985). 38. C.O. Tamm & L. Hallbacken, "Changes in Soil Acidity in Two Forest Areas with Different Acid Deposition: 1920s to 19809," Ambio 17 (1988) 56-61. 39. Interim Report of the National Acid PreciDitation Assessment Program (NAPAP): Executive Summary, NAPAP, Washington, D.C. (19871, p. 1-9. 40. Review, n. 16, pp. X-36-40. 41. "An Emission Inventory For S02, NOx and VOC's in N o r t h Western Europe", Lubkert, de Tilly, Organization for Economic Cooperation and Development, 1987. 4 2 . National Air Quality and
Emissions Trends Report 1985, U . S . Environmental Protection Agency, Washington, D.C. (1987). 43.
MVMA Motor Vehicle Facts and Figures, MVMA, 1986
44."World Resources 1986 - An Assessment of the Resource Base that Supports the Global Economy". World Resources Institute and the International Institute for Environment and Development. New York: Basic Books, Inc., 1986. 45. OECD (1982), "The Future of the World Automobile Industry", OECD Directorate for Science, Technology and Industry, Paris. 46. Stratospheric Ozone: The State of the Science and NOAA's Current and Future Research, National Oceanic and Atmospheric Administration, Washington, D.C. (1987) pp. 11-15. 47. Regulatory Impact Analysis, note 2 . 48. DeLuchi, M.A. Greenhouse Effect,", Record.
et.al., "Transportation Fuels and the submitted to the Transportation Research
49. Ramanathan, R.J., et.al. "Trace Gas Trends and Their Potential Role in Climate Change," J. of Geophysical Research, 9 0 (1985) 5547-66.
403
5 0 . Private communication, Office of Technology Assessment, U.S. Congress ( 1 9 8 8 ) . 5 1 . DeLuchi, n. 5 0 . 5 2 . Current Issues in Atmospheric Change, Board on Atmospheric Sciences and Climate, National Academy of Sciences, National Academy Press, Washington, D.C. 1 9 8 7 , p. 9 . 5 3 . Ibid at 9 - 1 0 . 5 4 . T.P. Barnett, et. al., "The Effect of the Eurasian Snow Cover on Global Climate," Science, 2 3 9 ( 1 9 8 8 ) 5 0 4 - 7 .
5 5 . W.S. Broecker, ( 1 9 8 7 ) 74-82.
"The
Biggest
Chill,"
Natural
History, 9 6
5 6 . R.A. Kerr, "Is the Greenhouse Here?" Science, 2 3 9 ( 1 9 8 8 ) 5 5 9 61. 5 7 . J. Hansen & S . Lebedeff, "Global Surface Air Temperatures: Update Through 1 9 8 7 , " (accepted, but not yet published), J. of Geophys. Research ( 1 9 8 8 ) . 5 8 . E.T. Wei & H.P. Shu, "Nitroaromatic Carcinogens in Diesel Soot," Amer. J. of Public Health 7 3 ( 1 9 8 3 ) 1 0 8 5 - 8 8 . 5 9 . Diesel Technology, Report of the Technology Panel of the Diesel Impacts Study Committee, National Academy of Sciences, 1982, 6 0 . "Environmental Guidelines On The Diesel Vehicle", Clavel and Walsh, United Nations Environment Program, March 1 9 8 4 . 61. "Trap Oxidizer Technology For Light-Duty Diesel Vehicles: Feasibility, Costs and Present Status", A Report To The US Environmental Protection Agency by Energy and Resource Consultants, Inc., March 1 9 8 3 . 6 2 . Energy for a Sustainable World, Washington, D.C. ( 1 9 8 7 ) , p. 8 .
World
Resources Institute,
6 3 . Analysis, n. 2 . 6 4 . M.P. Walsh, "The I/M Success Story: Where do We Go From Here?" SAE Paper No. 8 7 0 6 2 3 , SOC. of Automotive Engineers, Feb. 23-27,
1987.
404
65. Report of the Committee on Environment and Public Works to accompany S. 1894, the Clean Air Standards Attainment Act, Report No. 100-231, U . S . Congress, 100th Congress, 2d Session (1987), pp. 73-4.
66. P.H. Sand, "Air pollution in Europe: responses," Environment 29 (1987) 16-29. 67. Concluding Statement, UNEP-WMO Villach, Austria, December, 1985.
International policy
International
Assessment,
T.Schneideret al. (Editors),Atmospheric Ozone Research and its Policy Implicatwna 0 1989 Elsevier Science PublishersB.V., Amsterdam - Printed in The Netherlands
405
EVAPORATIVE AND REFUELING EMISSIONS: OPTIONS FOR CONTROL IN THE U.S.A. Richard A. Rykowski and John F. Anderson Standards Development and Support Branch, Office of Mobile Sources, U.S. Environmental Protection Agency, 2565 Plymouth Road, Ann Arbor, MI 48105, (U.S.A.)
ABSTRACT To date, U.S. EPA has taken two major steps to reduce evaporative emissions from gasoline-fueled motor vehicles. Beginning with the 1971 model-year, manufacturers were required to equip passenger cars with charcoal canisters to absorb evaporative emissions. These systems were about 30 percent effective in reducing evaporative emissions at a cost of $ 7 . 0 0 per vehicle (all costs in 1986 $US). In 1978, U.S. EPA adopted the SHED test procedure which greatly improved the efficiency of the resultant emission controls by measuring emissions coming from anywhere on the vehicle. By 1981, new vehicle emissions were to be reduced 90 percent from uncontrolled levels at a total cost of less than $22-32 per vehicle, ignoring fuel savings. Two additional control programs were recently proposed. The first would reduce the volatility of commercial fuels to levels existing in the early 1970s at a cost of 1.56 per gallon of gasoline. Gradual commercial fuel volatility increases have reduced the in-use efficiency of the 1981 evaporative controls to roughly 60 percent. The second proposal would control roughly 95 percent of refueling losses by modifying the current Fuel evaporative emission control system at a cost of $19 per vehicle. savings would reduce both these costs by roughly 35-65 percent. INTRODUCTION The U.S. Environmental Protection Agency (EPA) has taken a number of actions
over
the
past
20
years
to
reduce the
amount of
hydrocarbon (HC) emissions from gasoline-fueled motor
evaporative
vehicles.
Current
actions are also underway to further reduce evaporative HC emissions and to control HC emissions during vehicle refueling. and current EPA actions.
This paper reviews these past
Future actions to address evaporative HC emissions
from the fuel tank while the vehicle is operating are also discussed. The
paper
is
organized
into
six
sections, the
first being
this
introduction. The second section describes the types of emissions mentioned above, the situations in which they normally occur, and the vehicle test procedures EPA has developed to measure these emissions.
The third and
fourth sections describe the various techniques available to control these emissions via the vehicle and the fuel, respectively.
The fifth section
presents the costs, emission reductions and cost effectiveness of past and current EPA
regulatory actions and discusses the
possibility of
actions. Finally, the sixth section summarizes the paper.
future
406 DESCRIPTION OF FUEL-RELATED EMISSIONS AND PROCEDURES FOR THEIR MEASUREMENT Before plunging into a discussion of the techniques available to control fuel-related emissions, their cost and effectiveness, it is important to have a thorough understanding of the precise emissions being addressed.
It is
also critically important to understand the test procedures involved as the specifics of these procedures often have a controlling influence on the level of emissions measured (i.e., temperatures, driving patterns, etc.). Below, fuel-related emissions are evaporative
emissions,
emissions.
The
2)
remainder
refueling of
this
categorized
into three types:
emissions, paper
will
and
running
3)
follow
this
1) loss
three-fold
categorization.
Evaporative emissions In motor vehicles, fuel-related evaporative emissions originate in two parts of the fuel system--the fuel tank and the fuel metering system [that is, the carburetor or fuel injectors]. episodes of
increased temperature
Evaporative
losses occurring during
Significant evaporation occurs during
in
these
parts
of
the
fuel
system.
these higher-temperature periods
are
called "hot-soak'' and "diurnal" emissions. Hot-soak emissions are generated by the continued heating of the fuel by the engine and exhaust system after the engine is turned off.
During this
period, fuel in the fuel line, the carburetor or fuel injection system, and the fuel tank rises in temperature. evaporation
are lost from
The vapors created through the resulting
the fuel metering system
(much more
so with
carburetors than with most fuel injectors) as well as from the fuel tank. Diurnal emissions are caused by the daily heating of the fuel tank by outside air. Hot soak emission testing is performed by first operating a vehicle for a specified period of time and then turning off the engine and measuring the emissions that occur thereafter.
The diurnal test is performed entirely
while the vehicle is sitting with its engine off.
A heat blanket is used to
raise the temperature of the fuel tank a specified number of degrees and the emissions are again measured. The earliest official EPA testing of vehicular evaporative HC emissions employed what is known as the carbon trap technique.[ref.
11
Vapor carrying
lines from both the carburetor and fuel tank were connected to a canister filled with carbon (charcoal) just prior to a vehicle hot soak or diurnal test.
The increased weight of the trap after the test was assumed to be the
amount of emissions occurring. and accurately measured lines.
This technique was simple and inexpensive,
the emissions passing through the vapor carrying
However, it inherently assumed that no vapors were leaving the system
407 through other openings in the carburetor and fuel tank. Section
VI,
these
unmeasured
emissions
were
discussed in
As
eventually
found
to
substantial and EPA standards based on this test procedure were not
be
fully
effective. The second generation of evaporative HC measurement techniques markedly improved upon the carbon trap procedure and remain satisfactory to this day. This technique is known as the SHED, where SHED stands for Sealed Housing for Evaporative Determination.[ref.
The SHED techniques utilize a plexiglass
21
garage in which the vehicle is parked.
The garage is designed to have no
leaks and a large fan mixes the air inside once the garage doors are closed. The HC
concentration is measured
both
before
and
after
the
test.
The
difference in the concentration multiplied by the garage volume is the amount of emission occurring.
The primary advantage of this technique is that it
measures emissions occurring anywhere on the vehicle and encourages vehicle manufacturers to address all emission sources. EPA's current test procedure begins with the vehicle being driven over a 7.45 mile, Urban Dynamometer Driving Schedule (UDDS) on the dynamometer.[ref. 31
No emissions are measured.
This driving simply ensures some degree of
consistency for vehicles entering the test sequence and that some purge of the charcoal canister has occurred. The next step is the diurnal test.
The vehicle is refueled with fresh 9
RVP fuel up to the 400 full level and pushed into the SHED and the fuel tank temperature is raised from 15.6OC (60°F) to 28.9'C
(84°F) over one hour.
The
resulting emissions are measured. Following an overnight soak of the vehicle, the exhaust emissions test occurs.
The vehicle is driven over one UDDS begun from a cold start.
The
vehicle is left to sit for 10 minutes and then restarted and driven over half of a UDDS.
(The second half of this second UDDS is assumed to produce the
same emissions as the second half of the first UDDS.) Immediately after the exhaust emissions test, the vehicle is pushed into the SHED and left for one hour, when emissions are measured.
This is the
hot-soak test. Even with the SHED technique, there exist a number of test parameters which can reduce or enhance its effectiveness. probably the primary
factor, as
a more
The volatility of the fuel is
volatile
fuel will
produce
more
emissions under any fixed set of conditions. EPA has found the most relevant fuel parameter to be the Reid vapor pressure (RVP), which is defined as the vapor pressure of the fuel in pounds per
square
vapor/liquid
inch
absolute
(psia)
ratio of 4:l.[ref.
41
at
37.8'C
(100'F)
An indicator
such as the percent of fuel evaporated at 71.1°C
with
an
initial
of mid-range volatility, (using ASTM distillation
408 procedures
(Method D86),
can also be useful in more precisely estimating
emissions from the carburetor, as carburetor temperatures often reach this level during hot soaks.
However, the recent predominance of fuel injection
over carburetion in the U.S. control
makes
the
and the high degree of U . S . carburetor emission
close
monitoring
of
mid-range
volatility
unnecessary.[ref. 5 1 Temperature also plays an important role in evaporative emissions. the
initial
emissions.
and
final
fuel
tank
temperatures
strongly
affect
Both
diurnal
The temperature at which a vehicle is operated also affects the
ensuing hot-soak emissions. Finally, for diurnal emissions, the amount of fuel in the tank also is an important parameter.
Generally, the more empty the tank, the greater the
amount of emissions. Tables 1 and 2 contain the results of evaporative emission testing of post-1980 gram,
model year,
SHED
in-use vehicles
standard).[ref.
61
These
(i.e., data
vehicles certified to the 2 simply
serve to show how the
various test parameters can effect emissions from well-controlled vehicles. Table 1 shows the effect of fuel RVP on the emissions of hundreds of in-use vehicles tested at EPA's Ann Arbor, Michigan laboratory.
As will become more
relevant later, these vehicles were all certified to meet a hot-soak plus diurnal standard with 9 RVP fuel.
TABLE 1 Evaporative emissions from post-1980 in-use, U . S . light-duty vehicles vs. RVP (s/test)[ref. 61 Vehicle Type and No.
Fuel RVP (psia)
Hot-Soak
Diurnal
155 Carbureted Vehicles
9 11.5
2.57 4.26
2.60 10.33
163 Fuel-Injected Vehicles
9 11.5
0.88 2.70
1.67 8.51
Table 2 shows the results of more varied testing on more limited number of
vehicles
at
an EPA
contractor
laboratory.
Due
to excessive
cooling
occurring during vehicle operations, these latter results cannot be directly compared to EPA's own testing.
However, the data serve well in showing the
relative changes in emissions which occur when temperatures and RVP both vary.
409 TABLE 2 Diurnal emissions from post-1980 in-use, U.S.
light-duty vehicles
RVP and
VS.
temperature (g/test)[ref. 61 RVP Starting (psia) Temp (OF)
Vehicle Type and No. 3 Carbureted Vehicles
9.0
10.4
11..8
3 Fuel-Injected Vehicles
9.0
10.4
Diurnal Temperature Rise +15"F +20"F +24'F
60 68 75 60 68 75 60 68 75
0.71 0.96 1.82 1.23 1.72 2.79 2.12 4.17 9.99
1.05 1.57 3.54 2.10 4.29 9.08 4.24 10.85 24.14
1.45 2.70 6.54 3.80 9.05 16.72 8.14 19.31 42.38
60 68 75 60 68
0.45 0.41 0.53 0.61 1.02 1.70 0.97 2.03 7.68
0.68 0.80
1.01 1.61 3.69 2.65 7.59 16.35 6.21 17.99 41.26
15
11.8
60 68 I5
1.45
1.33 3.32 7.00 2.74 8.09 21.79
Refueling emissions As a general category, refueling emissions refer to those emissions of gasoline vapor associated with fuel tank refueling operations.
They consist
of vapors displaced from the fuel tank during the refueling event plus any fuel
spillage
which
occurs.
The
dominant
emissions
are
from
vapor
displacement, which represents about 95 percent of total refueling emissions, The amount of vapor generated during a refueling event is not a matter of simple displacement of the vapors in the tank by liquid fuel. time
that
the
volumetric
displacement
is
occurring,
there
At the same are
dynamic
processes such as the entrainment of liquid droplets in the vapor stream and
evaporation/condensation
due
to
temperature
and
volatility
differences
between the residual fuel in the fuel tank and the new fuel being added. number
of
studies of
refueling emissions
have
identified
the
A
following
parameters as the dominant variables affecting refueling emissions: fuel RVP, temperature of the dispensed fuel (T ) , temperature difference between the D tank fuel and the dispensed fuel (AT), and the fuel tank configuration. For
any given vehicle,
the
fuel
tank
configuration
is
fixed.
In .this
situation, an EPA test program developed the following relationship between refueling emissions and the other factors:[ref.
71
410 Refueling loss (g1U.S. gal of dispensed fuel) = -5.909 - O.O949[AT("F)]
+ 0.0884[T~(OF)] + 0.485[RVP(psi)]
Using this relationship, for U.S.
conditions.
(1)
average emission factors have been calculated
Weighted average temperature and RVP values along with
the resulting refueling emission rate are shown in Table 3.
To get total
refueling emissions, a spillage factor of 0.3 g/gal should be added to these figures
.
TABLE 3 Refueling vapor emissions for U.S. national average conditions[ref. 7 1
Season
RVP (psi)
TD (OF)
Annual Average Summer (Apr-Sept) Winter (Oct-Mar) Peak Ozone (May-Sept)
12.6 11.5 13.9 11.3
68.9 76.2 60.3 78.8
AT
Emission Factor (q/U.S. qal)
(OF)
+4.4 +8.8
5.9 5.6 6.2 5.6
-0.8
+9.4
Since there is no current standard for refueling emissions, there is no official test procedure for their measurement. new standard with an associated draft basically
test
However, EPA has proposed a procedure.
The
procedure
is
a SHED based procedure where the vehicle is refueled while within
the SHED and total refueling emissions measured
(including any
spillage).
The only modifications required to conduct such measurements with a standard evaporative emissions SHED consist of the addition of an access port for the dispensing nozzle with a boot and seal around the nozzle spout to retain all emissions within the SHED. The
proposed
refueling
test
consists
of
conditioning and the refueling measurement itself.
two
main
parts,
vehicle
The vehicle conditioning
sequence is designed to provide a means of placing the vehicle control system (which is assumed to be an activated carbon adsorption based technology) in a condition approximating that at the time of a normal refueling event with a minimum of testing resources. to
control
both
For a control system using the same canister
evaporative and
refueling emissions
(the most
economical
approach), the conditioning involves first loading the vehicle canister with refueling vapors to an approximation of canister saturation and then driving a sequence simulating three days of typical operation ( a typical day here meaning three UDDS driving sequences, each separated by a one hour hot soak, followed by one diurnal). that
this
sequence of
Test programs conducted by EPA have determined
operations
is capable of
"stabilizing" the carbon
canister at essentially the same loading level it will have when the fuel tank is fully empty.[ref.
81
41 1 Following vehicle conditioning, the vehicle is then placed inside the SHED and the refueling is conducted.
the
controlling
parameters
Based upon in-use data collected for
described
above,
has
EPA
proposed
test
requirements for the dispensed fuel temperature, the initial temperature of the residual fuel in the tank and the RVP of the fuel so as to insure control capability over essentially all expected refueling events.[ref.
Under
81
these conditions, tests of prototype control systems have shown that near total control of refueling emissions is possible (down to levels in the 0.01 to 0.05 g/gal range).
Running loss emissions The measurement of running loss emissions is quite complex, because it essentially involves building a SHED around a vehicle dynamometer. very difficult to eliminate.
Also,
Leaks are
the engine must consume air during its
operation, so either air must be provided from outside the S H E D without affecting engine performance or the amount of air consumed from within the
Also, since the cause of the running loss is
S H E D must be accounted for.
fuel tank heat-up, the tank temperature increase during dynamometer driving must closely simulate that occurring on the road.
No official EPA test method exists. preliminary
test program
at
a
However, EPA has conducted one
contractor
laboratory.[ref.
91
In
this
program, air within the S H E D which was consumed by the engine was estimated and
used
to
calculate
the
amount of
replacement air entering the S H E D .
dilution occurring
Also,
due
to
fresh
auxiliary fuel tank heating was
needed to reach in-use levels. A s part of this test program, ten 1983-86 cars and one 1987 light-duty
truck were tested with 10.5 and 11.7 RVP fuels. averaged 0.53 and 5 . 4 g/mi, respectively.
Running loss emissions
Compared to EPA's current exhaust
emission standard of 0.41 g/mi for light-duty vehicles, neither figure can be ignored, particularly the result with 11.7 RVP gasoline.
The results were
even more shocking when the gas cap from one vehicle was removed.
Running
losses increased to 6 . 4 and 35.8 g/mi. respectively, on the t;so fuels. These results must be viewed with caution since the test procedure is still under development.
However, the marked difference between
running
losses on 10.5 and 11.5 RVP fuels indicates how important this parameter can be.
Also, the size of these emissions relative to the highly controlled U.S.
exhaust
and
investigation.
evaporative
emissions
indicates
the
need
for
further
412 VEHICLE CONTROL TECHNOLOGY Evaporative emissions Controlling evaporative emissions on the vehicle is conceptually quite simple.
The first step is to seal off those portions of the vehicle from
which Euel could evaporate.
Since those areas where Euel is handled under
pressure are inherently sealed, the primary locations needing to be addressed are the carburetor (when present) and the fuel tank. The second step is to provide a single escape route for these trapped vapors
which
leads to
a
charcoal
containing
canister.
This
is
usually
accomplished with steel and polymer tubing. The third and final step is to provide for purging the charcoal canister This involves a line leading from a purge vent on the
of the trapped vapors.
canister to the throttle body just above or below the throttle plate or to the intake manifold.
Purging to
a
location
above
the
throttle has
the
advantage of naturally providing a vacuum that is generally proportional to engine fuel demand.
This minimizes the potential effect of the purge vapors
on engine airlfuel ratio for a given overall purge flow rate. is the relatively low degree of vacuum provided. below the throttle is the high amount of vacuum.
The drawback
The advantage of purging However, this vacuum is
highest at idle and lowest at full throttle and greater care must be taken to avoid large swings in the engine's airlfuel ratio when purging. All purge systems also have some type of control valve present..
The
simplest is an on-off valve which prevents purge at certain conditions (e.g., when the engine is off, idle, wide-open throttle, etc.).
More sophisticated
valves would
include:
1) damping
ratio
opening
closing,
2)
and
to
smooth
multiposition
or
airlfuel infinitely
swings upon
variable
valves
controlled by the engine's computer to maintain proportionality between purge flow and engine air flow, and 3 ) a very recent development reported by Ford [ref. 101 to include HC vapor sensing in the valve itself.[ref. 61 All
three aspects
of
evaporative
controls
standards have become more stringent over time.
have
progressed
as
EPA's
Table 4 shows the sequence
of EPA standards since 1970, the test procedure used to measure emissions and the resulting emissions.
As can be seen in-use control effectiveness has
steadily increased over time.
Also, note the effect of the SHED procedure.
In-use effectiveness increased markedly even though the allowable level of emissions went up from 2 to 6 grams per hot-soak plus diurnal. The most glaring problem with the canister procedure was that it did not test the system's seals. a
lesser
Thus, seal effectiveness increased dramatically in extent,
to
standard.
Because of better seals, more HC vapor reached the canister and
had to be purged during the 1.5
again
in
1981 due
to
the
lower
2 gram
1978 and,
UDDSs occurring between the diurnal and
413 hot-soak tests.
This required enhanced purge systems to not only purge the
canister, but to do so without affecting HC and CO exhaust emissions which came under more stringent standards in 1980 and 1981.
TABLE 4 EPA evaporative standards, procedures and control effectiveness[ref. 6 1
Standard (Diurnal + Hot-Soak) and Test Procedure
Model
Y
x
Pre-1971 1971 1972-77 1978-80 1981+ Carbureted
No Standards 6 g-carbon trap
2 g-carbon trap 6-9-SHED 2 g-SHED 9 RVP 11.5 RVP Fuel-injected 9 RVP 11.5 RVP
Uncontrolled Emissions (9) Hot-Soak Diurnal
Control Effectiveness Hot Soak Diurnal
22.45 22.45 22.45 18.50
47.99 47.99 35.45 28.36
--
--
2 80 4 5% 7 60
200 340 440
10.36 17.47 5.20 9.00
15.40 28.36 15.40 28.36
7 80 770 a40 7 10
820 600 890 68%
The recently proposed regulations (bottom of Table 4) seek to eliminate two additional problems with the procedures.
The first is fuel volatility,
with controls on commercial fuels aimed at ensuring vehicles' controls are designed for the fuels with which they will be driven.
The second is the
loading of the charcoal canister to breakthrough prior to the preparatory UDDS cycle which precedes the diurnal test.
This latter action will increase
EPA's assurance that purge rates are sufficient for in-use performance. All in all, while the original 6 and 2-gram evaporative HC standards of 1971 and 1972 promised 90+0 effectiveness. by
the
early
199O's,
all
post-1981
far less was achieved.
vehicles
should
achieve
However, an
in-use
effectiveness of 85-950.
Ref ue 1 inq Refueling controls have been used on experimental vehicles in the United States for well over a decade.
The earliest approaches were based upon the
perceived need for modifications to standard vehicles to accomplish three primary functions:
sealing of the fillneck to prevent the escape of vapors
during refueling, the addition of valving and hoses to direct the vapors and use of a canister of activated carbon to collect vapors.
Since American cars
were already using canister based systems for the collection of evaporative emissions,
provisions
for
canister purge
already
existed
(although
some
enhancement may be needed to purge the larger quantities of vapors associated with refueling).
The new functions were accomplished by the addition of some
form of a sealing ring which would seal snuggly around the nozzle when it was inserted into the fillneck,
a normally
closed vapor vent valve which was
opened by
a mechanical
linkage actuated by
the dispensing nozzle when
inserted through the fillneck seal, and an enlargement of the carbon canister and the vapor hoses connecting the canister to the fuel tank.
Fairly large
diameter hoses were required because the vapors weie being routed to remote canister locations at the Cront of the vehicle. Subsequent development work has been able
to
required hardware to collect refueling emissions. fillneck seal is no longer needed.
greatly
simplify
the
First, the mechanical
Modern vehicles use fillpipes of much
smaller diameter than in the past, and the liquid flow down the fillpipe itself forms a seal which prevents the escape of vapors out the fillpipe.
In
addition, these vehicles already incorporate a separate refueling vapor line to handle the escaping vapors.
Thus, the basic requirement is simply to
redirect this vapor line away from an escape to the ambient air and into the canister.
It is still important to have a control valve for this line to
provide protection from the possible release of fuel in the event of a vehicle rollover in an accident. are no longer needed.
However, mechanically actuated vent valves
Sophisticated rollover valves have already come into
widespread use for the safe routing of fuel tank evaporative emissions and have shown themselves capable of handling refueling vapor flow with little modification.
Finally,
although
the
enlargement, the vapor lines may not.
canister
will
still
need
some
This is because the canister can
readily be relocated to the rear of the vehicle near the fuel tank, greatly shortening the required length of vapor hose. much
shorter, they
can
also
be
made
Since the lines are then made
proportionately
smaller
without
increasing the overall flow resistance from the line.
Running losses
No standards for the control of running losses have yet been proposed or promulgated.
Thus, any discussion of control technology must be conceptual
in nature.
As the primary, if not sole, source of running losses is the combination of high fuel tank temperatures and high fuel volatility. control techniques must focus on either controlling these parameters or on handling the vapors generated.
The latter would appear to be the most difficult task based on
EPA's preliminary testing which shows uncontrolled vapor generation rates as high as 4 5 grams per mile (g/mi).
These vapors, along with those generated
during hot-soaks, diurnals and refueling, would have to be handled without affecting exhaust emissions. Fortunately, EPA's proposed commercial fuel volatility control program will
eliminate
one
half
of
the
problematic
combination,
high
fuel
415
volat lity.
Even using the results
at 10.5 RVP (no data yet exist at 9
RVP), running losses would be reduced by nearly 90%.
level
However, even at this
running losses could be as high as 0 . 5 3 g/mi and vehicular controls
may still be necessary. These
controls
temperature.
would
probably
focus
This could be achieved by
first on
lowering
fuel
tank
reducing heat transfer from the
exhaust system, by reducing heat input from recirculated fuel (via reduced circulation
or
recirculated
fuel
cooling),
or
by
enhancing
fuel
tank
cooling.
Much of this may be achievable for only the cost of redesign and
tooling.
However, the addition of cooling fins and baffles could raise
vehicle prices a small amount even in the long run.
Like evaporative control
systems, fuel that is now being lost would be retained and balance these costs to at least some degree. FUEL TECHNOLOGY Gasoline volatility affects all three types of emissions being addressed in
this
paper:
evaporative,
refueling
and
running
loss.
Controlling
commercial gasoline volatility can be very important in ensuring that vehicle controls are effective.
All vehicle controls have some limit to the amount
of vapor they can store and purge and any additional vapors simply pass through the charcoal canister and are emitted.
However, controlling gasoline
volatility alone cannot eliminate even 500 of uncontrolled emissions before fuel would become so involatile that cars would have difficulty starting. Thus, commercial fuel controls become most relevant once vehicle controls are implemented. For all three types of emissions, the predominant fuel parameter is the front-end volatility and, more specifically, RVP. dominated by its butane content. while
pentanes have
The RVP of gasoline is
(Butanes have blending RVPs of 60-65 psia,
blending RVPs
of
15-21 psia.)
Thus, lowering RVP
essentially means reducing butane content. Butane can be lowered primarily in two ways. butane is added to gasoline.
First, in the U.S., much
One reason for this is octane: butane's R+M/2
octane is 92 while that of regular unleaded gasoline is 8 7 .
However, the
primary reason is economic; butane costs only 80% as much per gallon as gasoline and displaces gasoline in a 1:l proportion. costs
associated with
octane.
removing this
Thus, there are two
"discretionary" butane:
volume
and
The former dominates the overall cost.
After all the discretionary butane has been removed (i.e., never added), butane must be distilled from the various gasoline blendstocks which contain butane.
This is more costly since a new operation, debutanization, must be
added to the refinery.
416 Based on refinery modeling studies conducted by Bonner and Moore, Inc., under
contract
to EPA,
we
have
found
that
the
cost of each succeeding
reduction of 1.0 RVP is generally 30% more expensive than the last.[ref.
61
Using a crude oil price of $20 per barrel, EPA has estimated the incremental costs for RVP control shown in Table 5 (1986 $U.S.).
TABLE 5 Refinery costs for RVP control [ref. 61 Initial RVP (psi)
Final RVP (psi)
11.25 10.25 9.25 8.25 7.25
Cost per 1.0 RVP (F! per qallon)
10.25 9.25 8.25 7.25 6.25
0.43 0.63 0.81 1.05 1.37
Once butane is removed from gasoline, an alternative use must be found for it.
In the U.S.,
EPA expects butane's price to drop modestly (roughly
15%) during the summertime control period.[ref. 61
market reactions.
One,
This will drive a number
significant amounts of butane are expected to be
stored until after the end of the control period.
Two, butane is expected to
displace some ethane, propane and other ethylene plant feedstocks. imports of butane are expected to lessen.
Third,
And fourth, low priced butane may
be transformed into iso-butane and isobutylene for alkylation or conversion into methyl tertiary-butyl ether (MTBE). A unique U.S.
problem is how to regulate the RVP of gasohol, a 1:9
mixture (by volume) of ethanol and gasoline. currently well
above
that
of
gasoline.
Ethanol's production cost is
However,
Federal
credits make ethanol blending economical in many areas.
and
state
tax
Adding ethanol to
gasoline in these proportions raises the RVP of the base gasoline roughly 0.76 psi RVP.[ref.
111
Reducing the RVP of gasohol can only be accomplished by reducing the RVP of the base gasoline, which would follow the same economics as shown above.
Reducing gasohol's RVP to that of gasoline would require an additional 0.76 psi RVP reduction beyond that of alcohol-free gasoline because gasohol is starting out with a higher RVP.
This would be EPA's desired approach to
ensure emissions from gasohol-fueled vehicles were no more than those from gasoline-fueled vehicles.[ref.
121
While this added step would increase the
price of gasohol-bound gasoline, the octane of this base gasoline could be lower
than normal
due
to ethanol's
relatively high
benefit appears to outweigh the RVP cost.[ref. base
gasoline
would
have
to
be
distributed
131
octane. However,
separately
The
octane
this special from
directly
417 marketable gasoline, adding to its cost.
To date, EPA has been unable to
determine whether such a base gasoline could be produced and distributed at a sufficiently low cost to allow continued ethanol blending. likely that the U.S.
Thus, it appears
ethanol industry would not survive a requirement that
gasohol meet the same RVP standard as gasoline.[ref.
121
The alternative is
to allow gasohol's RVP to be 1.0 psia higher than that of gasoline to allow continued splash-blending.
COST-EFFECTIVENESS OF EPA ACTIONS Past actions concerning evaporative emissions As described in the section entitled "Vehicle Control Technology," EPA's evaporative emission controls have progressed through four steps since 1970. Table 6 shows the cost (1986 $ U . S . ) ,
emission reduction and cost per metric
ton of HC reduced for each step.
TABLE 6 Cost effectiveness of past EPA evaporative emission standards
Total Hardware Cost Per Vehicle1
Standard 6 g-Carbon Trap 2 g-Carbon Trap 6 g-SHED 2 g-SHED 1
Approx. $ 7.48 $20.65 $23.1833.32
Total Emission Reduction (g/mi)2
$ 5.00 [ref. 141 [ref. 141
Potential Value of Controlled HC
Overall cost Effectiveness ($/Mg)
0.93 1.38 1.78 1.87
$18.25 $22.08 $34.93 $36.70
87 88 189 202-290
[ref. 151
1987 U.S. dollars Assumes 3.05 hot-soaks, 1.0 diurnal, and 31.1 miles per day. The emission reductions were derived from the information in Table 4
using a simplified model for evaporative emissions. The model was contained in the MOBILE2 emissions model and assumes that vehicles experience 3.05 trips (hot-soak) and a single diurnal per day and are driven 31.1 miles per day.
Both MOBILE3 and MOBILE4 are somewhat sophisticated, wherein the number
of trips and miles per day vary with vehicle age.
However, on average the
MOBILE2 assumptions are still quite good and are much easier to follow. The costs per megagram of HC controlled were derived by assuming that all
costs
occurred
in
the
year
of vehicle purchase
reductions occurred evenly over a vehicle miles.
life
of
and
that
10 years
and
emission lPO.000
Cost and emission reductions were discounted to the year of vehicle
purchase using 108 discount rate. The potential engine was
value of the HC emissions captured and routed to the
calculated in
a
similar
manner.
The
present
value
of
the
418 discounted lifetime emissions determined above (in Mg) was multiplied by a value
of
$319.35/Mg.
This
value
was
derived
by:
1) assuming
that all
emissions were butane, 2) that butane was as valuable per unit of chemical energy as gasoline, and 3) that gasoline cost $0.82
per gallon.
Of course,
it is unlikely that the older vehicles could burn these vapors as efficiently as
liquid
fuel.
However, the 1981 and later,
computer-equipped vehicles
should be able to consume these vapors quite efficiently.
As can be
seen
from Table 6, the value of these vapors can actually be more than the cost of the control hardware, resulting in essentially free emission control.
Current EPA actions EPA recently proposed two regulations.
The first addressed evaporative
emissions from current vehicles and gasoline volatility.[ref. addressed emissions from vehicle refueling.
141
The second
The costs, emission reductions
and cost effectiveness of these proposals are presented below. (i)
Evaporative emissions.
vehicles certified to comply with poorly on 11.5 RVP fuel. matching that of
As presented
in Table
the 2 gram,
SHED standard perform very
As the average RVP of U.S.
the EPA test procedure
is nearly
1 above, current
gasoline in climates 11.5
RVP,
these high
emission test results are occurring in-use. The fundamental problem is that the RVP of EPA's match the RVP of commercial fuel.
test fuel does not
The problem can be solved by raising the
RVP of the test fuel to that of commercial fuel or vice versa.
The RVPs of
the two fuels can also be matched anywhere in between. Table 7 presents the cost of this match-up at various RVP levels. weight
penalty
shown is a fuel cost due to the increased weight of
vehicle due to a larger canister.
The
refinery-level
costs
include
The the the
TABLE 7 Lifetime consumer costs of vehicle and fuel controls ($/vehicle)[ref. 121 Certification/ In-use Matched RVP Level (psia)
Total Vehicle cost
11.5 11.0 10.5 10.0
3.41 2.71 2.05 1.43 0.81 0.22 -0.39 -0.80
9.5
9.0 8.5 8.0
1
Vehicle Weight Penalty 0.32 0.24 0.18 0.12 0.05 0.00
-0.04 -0.09
Totall Refinery cost -5.09 -3.66 -1.70 0.80 4.19 8.17 12.99 17.87
Includes 5 months per year of savings from content and recovered evaporative emissions.
Net Cost To Consumer -1.36 0.71 0.53 2.35 5.05 8.39 12.56 16.98 increased
fuel
energy
419 savings from the increased energy content of the fuel as well as the savings from using fuel that would have otherwise been lost through evaporation. As
can be
seen, vehicle-oriented
control is the cheapest, with fuel
savings actually being larger than hardware costs.
However, vehicle-based
control would produce significant emission reductions primarily in the long term, only after a number of model years of vehicles could be equipped with improved emission control systems. hand, would produce implemented.
In-use fuel RVP control, on the other
significant emission reductions
soon
as
as
it
were
Moreover, even after vehicle controls were fully implemented,
more commercial
fuel-oriented controls
reductions
other
gasoline-related
comment
is quantified
from
would
produce
emission
additional
sources
emission
not affected by
vehicle controls. This
last
effectiveness levels.
of
matching
commercial
in Table
8,
and
fuel
test
which
shows the cost
RVPs
at
different
The analysis presented in Table 8 depicts the costs and benefits of
controls on the entire issue fleet in the year 2010, when essentially all vehicles in the fleet have been certified to the appropriate in-use control level.
The refinery costs included are those occurring during a
5-month
summertime control period (4-month legal control period plus an average of two weeks on either end for distribution lead and lag time).
The emission
reductions occurring during this 5-month period were multiplied by 2.4 represent that occurring if RVP was controlled year-round.
to
This was done to
allow the costs per Mg in Table 8 to be comparable to those in Table 6 and other cost effectiveness actuality,
the
reductions)
occur during
great
analyses, which majority
of
the summer.
In
assume year-round benefits.
HC-related That
benefits
is why
EPA
(i.e.,
proposed
ozone only
a
4-month control period for commercial fuels.
TABLE 8 Long-term (year 2010) cost effectiveness of matching commercial gasoline and test fuel RVP1[6]
Fuel RVP (psia) 11.5 11.0 10.5 10.0 9.5 9.0 8.5
8.0
Emission Reduction (glmi) 0.53 0.56 0.59 0.61 0.63 0.65 0.67 0.68
Cost-Effectiveness ($/Mg) Overall Incremental -18-(-20) -lo-( -11) 1-6 20-29 49-61 82-96 122-139 161-181
-18-(-20) 76-128 197-257 400-470 721-808 868-955 1273-1375 1345-1456
Test fuel RVP equals that of commercial gasoline in ASTM Class C areas. Commercial fuel RVP in Class A and B areas would be 21.7% and 13% lower, respectively.
As can be seen, matching commercial and test fuels at 11.5 RVP is the least expensive alternative.
While the overall cost effectiveness remains
below $200/Mg, the incremental cost effectiveness (that applying to just the last step of 0.5 RVP) increases much more quickly.
However, due to the
cities. EPA believes costs as
high ozone levels occurring in most large, U . S .
high as those of the 9 RVP scenario and possibly beyond will be necessary to bring all areas into compliance with Standard for ozone.
the National
Ambient
Air
Quality
Thus, EPA formally proposed the 9 RVP control scenario
on August 19, 1987. (ii)
Refueling emissions
EPA has proposed the control of refueling
emissions to less than 0.10 g/US gal of dispensed fuel when tested under the proposed test procedure conditions (current emissions for those rather severe conditions are approximately 7.2 g/gal).[ref.
161
Development, certification
and installation of the control hardware needed to meet this standard is expected to initially increase the cost of a typical light-duty vehicle by approximately $17.[ref.
17, for all figures in this section]
of the vehicle, approximately $4 of this cost will be
Over the life
recovered by
the
consumer in the form of a small fuel consumption benefit associated with capturing
and
burning
the
refueling vapors
in the
engine.
Costs
for
controlling light duty trucks are somewhat higher. at approximately a $23 increase in first price and $6 of fuel recovery credit.
For heavy-duty
gasoline-fueled engines EPA's cost estimates are for a $31 increase in first price and an offsetting $15 in fuel savings. the
U.S.
The weighted average cost for
fleet is approximately $19 per vehicle, with a $5 fuel savings.
Given this relatively low cost and the high degree of control possible, the overall cost effectiveness of onboard refueling controls is quite good. To evaluate cost effectiveness, EPA conducted an analysis of both costs and benefits over a 3 3 year time period.
Using a standard 10 percent discount
rate for all costs and benefits, the weighted cost effectiveness for applying onboard
controls
to
all
gasoline
fueled vehicles
(light-duty vehicles,
light-duty trucks and heavy-duty engines) is approximately $850/Mg.
Future EPA actions The most
immediate future actions EPA will
take will likely be to
promulgate its two proposals described in the previous section.
These two
final actions will hopefully complete EPA's efforts to control evaporative and refueling emissions.
The last area to be addressed is that of running
loss emissions. EPA is not yet to the point of estimating the costs and benefits of the control of running losses.
As mentioned in Section 1V.C.
lowering commercial
fuel volatility will eliminate the majority of running losses.
How much
421 running losses remain thereafter is not yet known.
EPA is actively planning
new test programs to determine if future controls are necessary.
SUMMARY EPA
activity
emissions has emissions
to
been
should
control
a gradual
be
largely
evaporative, process
refueling
since
eliminated.
1971.
By
some
By
and
running
1992,
slightly
loss
evaporative later
date,
refueling, emissions from new vehicles should also be virtually eliminated. Running losses, a recent product of advanced fuel systems and high commercial fuel volatility, should be largely eliminated by the promulgation of EPA's proposed
volatility
controls.
Future
actions
to
further
limit
these
emissions must await the development of more data. While the last steps of EPA's proposed commercial fuel volatility and onboard
refueling
controls
evaporative emission
control
cost are
nearly quite
$1,00O/Mg, cost
the
effective.
initial In
steps
fact,
of
given
today's advanced engine controls, such control may actually save consumers more through lower fuel consumption
than
they
cost
in
terms
of
vehicle
hardware.
REFERENCES 1 2 3
4 5 6
7
8
9
10
11
12 13
Federal Register, Vol. 33, p. 8304, 1968. Federal Register, Vol. 42, p. 32954, June 28, 1977. Title 40 of the U. S. Code of Federal Regulations, Section 86.130-78. ASTM Method D323. Federal Register, Vol. 52, p. 31303, August 19, 1987. Draft Regulatory Impact Analysis, Control of Gasoline Volatility and Evaporative Hydrocarbon Emissions from New Motor Vehicles, Office of Mobile Sources, Office of Air and Radiation, U.S. EPA, July 1987, EPA Docket A-85-21, Document No. 111-B-1. D. Rothman and R. Johnson, Refueling Emissions From Uncontrolled Vehicles, Technical Report, Standards Development and Support Branch, Emission Control Technology Division, Office of Mobile Sources, Office of Air and Radiation, U.S. EPA, EPA-AA-SDSB-85-6. Summary and Analysis of Comments o n the Recommended Practice for the Measurement of Refueling Emissions, Standards Development and Support Branch, Emission Control Technology Division, Office of Mobile Sources, Office of Air and Radiation, U.S. EPA, March 1987. R. E. Simkins, Evaporative Running Loss Emissions, Final Report, National Institute for Petroleum and Energy Research, for U . S . EPA and U.S. DOE, Contract No. DE-FC22-83FE60149, July 1987, NIPER-266. Ford Motor Company Response to the EPA on Proposed Refueling Regulations and Fuel Volatility and Evaporative Emission Regulations, February 1988, EPA Docket No. A-85-21, Document No. IV-D-160. Guidance on Estimating Motor Vehicle Emission Reductions From the Use of Alternative Fuels and Fuel Blends, Technical Report, Emission Control Technology Division, Office of Mobile Sources, Office of Air and Radiation, U . S . EPA, January 29, 1988, EPA-AA-TSS-PA-87-4. Federal Register, Vol. 52, p. 31292, August 19, 1987. Alcohol Fuel Blending and Commingling, Sobotka and Co. for U.S. EPA. July 10, 1986, EPA Docket No. A-85-21, Document No. 11-A-15.
422 14
15
16
17
Environmental and Economic Impact Statement, Revised Evaporative Emission Regulation for the 1978 Model Year, Mobile Source Air Pollution Control, Office of Air and Waste Management, U.S. EPA. June 1977. Environmental and Economic Impact Statement, Revised Evaporative Emission Regulation for the 1981 and later Model Year Gasoline-Fueled Light-Duty Vehicles and Trucks, Mobile Source Air Pollution Control, Office of Air and Waste Management, U.S. EPA, August 7. 1978. Federal Register, Vol. 52, p. 31162, August 19, 1987. Draft Regulatory Impact Analysis: Proposed Refueling Emission Regulations f o r Gasoline-Fueled Motor Vehicles, Office of Air and Radiation, U . S . EPA, July 1987, EPA-450/3-87-001, 2 Volumes.
T. Schneider et al. (Editors), Atmospheric Ozone Research and its Policy Implications 0 1989 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands
423
EVAPORATION AN0 REFUELING LOSSES: OPTIONS FOR CONTROL I N EUROPE AXEL FRIEDRICH Umweltbundesamt ( F e d e r a l E n v i r o n m e n t a l Agency) B i s m a r c k p l a t z 1, D-1000 B e r l i n 33
ABSTRACT I n t h e European Community, a compromise was found, w h i c h w i l l lower t h e exhaust hydrocarbon emissions i n t h e future. F o r t h e e v a p o r a t i v e e m i s s i o n s i t was n o t p o s s i b l e t o r e a c h an agreement on t h e measurement method. Two d i f f e r e n t p r o p o s e d t e s t methods (Shed t e s t and T r a p t e s t ) w i l l be compared. The v a l u e s o b t a i n e d i n t h e T r a p - t e s t a r e l o w e r t h a n t h o s e o b t a i n e d i n t h e Shed t e s t . The r e s u l t s show t h a t t h e t r a p s do n o t c o l l e c t t h e t o t a l e v a p o r a t i v e e m i s s i o n s . S p e c i a l meas u r e m e n t s o f t h e h y d r o c a r b o n e m i s s i o n s t h r o u g h t h e w a l l of p l a s t i c t a n k s produced very h i g h e m i s s i o n values. A d d i t i o n a l l y 40 r e p r e s e n t a t i v e r a n d o m l y s e l e c t e d s p a r k i g n i t i o n e d e n g i n e v e h i c l e s were t e s t e d i n o r d e r t o d e t e r m i n e e m i s s i o n f a c t o r s for t h e e v a p o r a t i v e emissions. V e h i c l e s with a carbon can i s t e r t r a p have emissions 1 0 t i m e s l o w e r t h a n v e h i c l e s w i t h o u t a c o n t r o l system. A p r e d i c t i o n o f t h e e v a p o r a t i v e e m i s s i o n s from v e h i c l e s w i t h s p a r k i g n i t i o n e d e n g i n e s was made f o r t h e F e d e r a l R e p u b l i c o f Germany based o n a model w h i c h i n c l u d e s t h e t e m p e r a t u r e d i s t r i b u t i o n i n t h e F e d e r a l R e p u b l i c o f Germany and f u e l comp o s i t i o n . The e v a p o r a t i v e e m i s s i o n s ( w i t h o u t r e f u e l i n g e m i s s i o n s ) were c a l c u l a t e d t o be a b o u t 220,000 t p e r year. T h i s i s a b o u t 26 % o f t h e t o t a l hydrocarbon emissions from passenger v e h i c l e s . F o r t h e r e f u e l i n g e m i s s i o n s t h e s i t u a t i o n i n Europe w i l l be described. INTRODUCTION I n 1986, t h e h y d r o c a r b o n e m i s s i o n s f r o m i n - t r a f f i c m o t o r ve6 1.10 1 0 t , c o r r e s p o n d i n g t o 47.5 % o f
h i c l e s amounted t o a p p r o x .
t h e t o t a l h y d r o c a r b o n e m i s s i o n s . O t t o e n g i n e p a s s e n g e r c a r s had a 3 s h a r e o f approx. 840 10 t i n t h e s e e m i s s i o n s . T h i s f i g u r e i n t u r n i n c l u d e s a p p r o x . 220,000 t o f e v a p o r a t i v e e m i s s i o n s .
The
emissions r e s u l t i n g from t h e r e f u e l i n g of O t t o engine v e h i c l e s amounted t o a p p r o x . 40,000 t i n 1985. EVAPORATIVE LOSSES E v a p o r a t i v e e m i s s i o n s are t h e h y d r o c a r b o n e m i s s i o n s o r i g i n a t i n g f r o m f u e l l i n e s and f u e l c o n t a i n e r s . I n a p r o j e c t commissioned by t h e F e d e r a l E n v i r o n m e n t a l Agency, t h e Technical I n s p e c t i o n Service o f Rhineland-Westphalia
i n Essen
has d e t e r m i n e d t h e e v a p o r a t i v e e m i s s i o n s o f 5 0 r e p r e s e n t a t i v e ,
424
randomly s e l e c t e d O t t o e n g i n e v e h i c l e s .
I n addition, 7 vehicles
equipped w i t h e m i s s i o n r e d u c t i o n systems were i n v e s t i g a t e d .
The
e v a p o r a t i v e em i s s i o n s g i v e n o f f d u r i n g t a n k h e a t i n g were measured analogous t o t h e US p r o c e d u r e , b u t w i t h a t e m p e r a t u r e i n t h e shed
o f 15-12. T h i s r e f l e c t s r e a l c o n d i t i o n s more a c c u r a t e l y . I t was n o t p o s s i b l e t o a c h i e v e l o w e r t e m p e r a t u r e s w i t h t h e t e s t appar a t u r s . The e m i s s i o n f a c t o r s f o r h o t soak were d e t e r m i n e d on t h e b a s i s o f t h e t e s t c a r s r u n n i n g t h r o u g h t h e US highway d r i v i n g c y c l e t w i c e . F u rth e rm o re , t h e e m i s s i o n f a c t o r s f o r warm soak were c a l c u l a t e d a f t e r one r u n t h r o u g h t h e ECE d r i v i n g c y c l e . With t h e a i d o f d a t a on d r i v i n g p a t t e r n s (1 ,2 ),
t h e t o t a l number o f d r i v e s
and o f h o t and warm soak p ro c e s s e s can be e s t i m a t e d f o r t h e Fed e r a l R e p u b l i c o f Germany. The d a t a t h u s o b t a i n e d , t o g e t h e r w i t h t h e e m i s s i o n f a c t o r s d e te rmi n e d , a r e t h e n used t o c a l c u l a t e t h e o v e r a l l e m i s s i o n s r e s u l t i n g fro m the h o t and warm soak. I n o r d e r t o d e t e r m i n e t h e t a n k e m issi ons,
d a t a on average tempe-
r a t u r e d i f f e r e n c e s were o b t a i n e d , f o r each month and f o r t h e d i f f e r e n t regions o f t h e Federal Republic, from m e t e o r o l o g i c a l r e c o r d s o f s e v e r a l years.
W i t h t h e a i d o f d a t a on t h e R e i d vapour
p r e s s u r e s o f t h e t y p e s o f p e t r o l a v a i l a b l e on t h e German market, t h e o v e r a l l t a n k e mi s s i o n s can be e s t i m a t e d . F u e l t a n k s made o f p l a s t i c a r e a f u r t h e r i m p o r t a n t component which can be t h e cause o f e v a p o r a t i v e emi ssi ons. I n o r d e r t o d e t e r m i n e hy dr o c a rb o n e m i s s i o n s t h r o u g h t h e p l a s t i c s i d e s o f such t a n k s two v e h i c l e s were f i l l e d h a l f - f u l l and t h e e n g i n e s s w i t c h e d o f f i n t h e g a s - t i g h t chamber a t 19'C
1K. F i g u r e 5 shows t h e
temporal progression o f the evaporative emissions a t constant tem per at ur e. However, as t h e e n t i r e v e h i c l e s were p l a c e d i n t h e g a s - t i g h t chamber t h e r e s u l t s do not. e n a b l e any d e c i s i v e c o n c l u s i o n s t o be drawn as t o t h e p e r m e a b i l i t y f o r f u e l o f t h e p l a s t i c s i d e s o f t h e t a n k . A p l a s t i c f u e l t a n k was t h e r e f o r e f i l l e d h a l f - f u l l and s e a l e d g a s - t i g h t .
F i g u r e 6 shows t h e
t e m p o r a l p r o g r e s s i o n o f t h e e v a p o r a t i v e emi ssi ons a t c o n s t a n t t e m p e r a t u r e (19'C 2 1 K ) o v e r a p e r i o d o f 18 hours. D u r i n g t h i s t e s t p e r i o d o f 18 hours the emissions through t h e s i d e s o f t h e t a n k were found t o be around 125 g. I n mid 1985, approx. 1.25 m i l l i o n v e h i c l e s were equi pped w i t h p l a s t i c t a n k s . Assuming an e m i s s i o n f a c t o r o f 100 g/day,
the
t o t a l e m i s s i o n s t h r o u g h t h e w a l l s o f t h e t a n k s i s e s t i m a t e d t o be approx.
45,000
t/a.
425
There i s no s u f f i c i e n t evidence s u p p o r t i n g t h e v a l i d i t y o f t h e e m i s s i o n f a c t o r o f 100 g/day, s i n c e i n v e s t i g a t i o n s s t u d y i n g the e x t e n t t o which t h e e m i s s i o n r a t e i s dependent on f u e l composit i o n s , t e m p e r a t u r e and wind c o n d i t i o n s and on t h e v e h i c l e t y p e have n o t been conducted. However, a s i m p l e e s t i m a t e shows t h e importance o f t h i s p o i n t . I f a l l Otto engine vehicles i n t r a f f i c i n t h e Federal Republic had been equipped w i t h such t a n k s i n 1985, t h e n t h e t o t a l emiss i o n s t h r o u g h t h e w a l l s o f t h e t a n k s would have exceeded 850,000 t / a T h i s i s more t h a n t h e p r e s e n t exhaust p i p e emissions. Comparison o f t h e SHE0 t e s t w i t h t h e Traps method I n Europe, two procedures f o r t h e d e t e r m i n a t i o n o f e v a p o r a t i v e emissions have been proposed: t h e SHED t e s t and t h e Traps method. W i t h t h e SHED t e s t (Sealed Housing f o r E v a p o r a t i v e Determinat i o n ) , t h e v e h i c l e i s p l a c e d i n a g a s - t i g h t chamber and t h e evap o r a t i v e e m i s s i o n s determined by measuring t h e hydrocarbon conc e n t r a t i o n i n t h e chamber. T h i s ensures t h a t a l l sources o f evap o r a t i v e emissions from t h e v e h i c l e a r e i n c l u d e d . W i t h t h e t r a p s method t h e openings o f t h e v e h i c l e which can g i v e o f f e v a p o r a t i v e emissions i n t o t h e atmosphere a r e s e a l e d w i t h a c t i v a t e d carbon t r a p s and t h e e v a p o r a t i v e emissions d e t e r mined by w e i g h i n g t h e t r a p s b e f o r e and a f t e r t h e t e s t .
The t r a p s
method has t h e advantage t h a t t h e c o s t s o f t h e measuring e q u i p ment a r e l o w e r because no g a s - t i g h t chamber i s r e q u i r e d . Comparative measurements u s i n g b o t h methods and conducted on d i f f e r e n t t y p e s o f v e h i c l e s e s t a b l i s h e d t h a t t h e e v a p o r a t i v e emiss i o n s measured u s i n g t h e t r a p s method o n l y amounted t o between 7 and 50 % o f t h e v a l u e s determined u s i n g t h e SHED t e s t . I n o r d e r t o determine how many hydrocarbon e m i s s i o n s a r e n o t r e c o r d e d by t h e t r a p s , t h e t e s t s w i t h t h e t r a p s were a l s o c a r r i e d o u t i n t h e g a s - t i g h t chamber. F i g u r e s 1-3 show t h e p a t t e r n o f emissions f o r 3 d i f f e r e n t t y p e s o f v e h i c l e s u s i n g b o t h methods o f measurement t o determine e v a p o r a t i v e emissions a f t e r t h e h o t eng i n e had been s w i t c h e d o f f i n t h e g a s - t i g h t chamber. I f t h e t r a p s method r e c o r d e d a l l hydrocarbon e v a p o r a t i v e e m i s s i o n s t h e n no e v a p o r a t i v e emissions s h o u l d have been determined i n t h e g a s - t i g h t chamber when t h e t r a p s method was used. However, t h i s was n o t t h e case.
I f t h e e r r o r was t h e same w i t h a l l v e h i c l e s t h e use o f t h e
t r a p s method would have produced comparable values.
However, t h e
426
I
without t rc
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time t (min)
Fig. 1: Evaporative emissions gradient with and without activated charcoal trap
without trap A
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Renault R5
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Fig. 2: Evaporative emissions gradient with and without activated charcoal trap
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Renault R25
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Fig. 3:
Evaporative emissions gradient with and without activated charcoal trap
--
20.0-
-
A
0 v
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a/
without trap /
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8.0:
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0 ’
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0
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.4with
trap (mass of traps 1.9 g)
-
-
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time t (min)
Fig. 4:
Evaporative emissions gradient with and without activated charcoal trap
428
10.
-
Parking of vehicles with plastic tanks
**-
ZT
W
E v)
cn
Ambient temperature:
-
n
19 degree centigrade
6.-
(+/-1K)
-
4. -
2. v
vehicle 2 vehicle 1
IM
0.-I 0
I
80
40
120
200
160
2
time t (min)
Fig. 5 : Emission gradient of plastic fuel tank
'20'ISwitching off a plastic fuel tank 80.-
100. n
IT
W
E ul
Ambient temperature: 19 degree centigrade (+/- 1 K)
60.-
cn
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20.-
0.
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0
120
240
360
480
600
720
840
time t (min)
Fig. 6: Diffusion through the wall of a plastic fuel tank
960
1
429
f i g u r e s c l e a r l y show t h a t t h i s was n o t t h e case. I n a d d i t i o n , t h e t o t a l e m i s s i o n s r e c o r d e d i n t h i s way (sum o f t h e hydrocarbon emiss i o n s from t h e t r a p and i n t h e g a s - t i g h t chamber) a r e s i g n i f i c a n t l y l o w e r t h a n t h e v a l u e s measured u s i n g t h e o r i g i n a l SHED t e s t . Here, t oo,
t h e d i f f e r e n c e v a r i e s f o r d i f f e r e n t types o f vehicles,
w i t h d i f f e r e n c e s o f between 20 and 45 %.
The d i f f e r e n c e between
t h e t w o methods d u r i n g t a n k h e a t i n g ( f i g u r e 4 ) (1 v e h i c l e ) i s p a r t i c u l a r l y s t r i k i n g . The o r i g i n a l SHED t e s t produced a measurement o f 20.46 g HC. When u s i n g t h e t r a p s method i n t h e g a s - t i g h t chamber o n l y 5.76 g HC were r e c o r d e d (1.9 g f r o m t h e t r a p , 3.86
g HC i n t h e chamber), p r o d u c i n g a d i f f e r e n c e o f 14.7 g
o r approx. 72
% vis-&-vis
t h e SHED t e s t r e s u l t . T h i s shows t h a t
d i f f u s i o n i s s i g n i f i c a n t l y impeded when t h e t r a p s a r e a p p l i e d . These r e s u l t s show f i r s t l y t h a t t h e a p p l i c a t i o n o f t h e t r a p s s i g n i f i c a n t l y impedes d i f f u s i o n . The hydrocarbon e m i s s i o n s which a r e r e c o r d e d i n t h e g a s - t i g h t chamber a r e caused by t h e f o l l o w i n g :
-
W i t h v e h i c l e s where t h e t a n k v e n t i l a t i o n i s v i a t h e f i l l e r cap a gas- and H C - t i g h t h o u s i n g which l e a d s i n t o an a c t i v a t e d c h a r c o a l t r a p must be f i t t e d o v e r t h e f i l l e r cap. The p o s s i b i l i t i e s f o r a p p l y i n g t h e h o u s i n g depend on t h e d e s i g n and shape o f t h e t a n k
f i l l e r openi n g and cannot a l w a y s be achi eved w i t h o u t a j u s t i f i a b l e dead volume.
-
Leakages t h e r e f o r e cannot be r u l e d o u t .
Applying t h e traps t o the a i r i n t a k e pipe i s d i f f i c u l t .
The
f a c t t h a t t h e p a r t s o f t h e a i r f i l t e r h o u s i n g a r e i n some cases o n l y f i t t e d t o g e t h e r means t h a t l eakages can occur t h r o u g h which t h e e v a p o r a t i v e e m i s s i o n s can escape,
thus avoiding the
traps.
-
E v a p o r a t i v e e mi s s i o n s can a l s o escape from t h e f u e l l i n e s t h r o u g h s l i g h t l e a k s which c a n n o t even be d e t e c t e d by means o f pressure t e s t s .
Conc lus ions D e t e r m i n i n g e v a p o r a t i v e e mi s s i o n s u s i n g t h e t r a p s method i s u n r e l i a b l e and l e a d s t o i n c o r r e c t r e s u l t s because d i f f u s i o n i s i n h i b i t e d by t h e t r a p and because d i f f u s e e m i s s i o n sources cannot be det er m ined. I n view o f t h e s i g n i f i c a n t e m i s s i o n s from p l a s t i c f u e l t a n k s a s e p a r a t e f u e l t a n k t e s t would be n e c e s sary i f t h e t r a p t e s t was i n t r o d u c e d . T h i s would n o t be r e q u i r e d i f t h e SHED t e s t was i n tro duc ed. P l a s t i c f u e l t a n k s i n v e h i c l e s r e g i s t e r e d under t h e
430
p r o v i s i o n s o f t h e USA, Japan o r a c c o r d i n g t o Annex X X I I I StVZO (Road L i c e n s i n g R e g u l a t i o n s o f t h e F e d e r a l R e p u b l i c o f Germany) and w h i c h a r e t h e r e f o r e t e s t e d u s i n g t h e SHED t e s t a r e made i m permeable b y s u l p h o n a t i o n o r t h e i n s e r t i o n o f a g a s - t i g h t m e t a l foil. REFUELING EMISSIONS There a r e a l s o two p o s s i b i l i t i e s f o r l o w e r i n g r e f u e l i n g e m i s sions: t h e f i l l i n g s t a t i o n approach (vapour balance procedure) and t h e v e h i c l e a p p r o a c h ( " l a r g e c a n i s t e r " ) . S e v e r a l d e m o n s t r a t i o n s t a t i o n s u s i n g t h e vapour balance p r o c e d u r e a r e b e i n g o p e r a t e d i n t h e F e d e r a l R e p u b l i c o f Germany.
I t i s i n t e n d e d t o use t h e s e s t a t i o n s f o r i n v e s t i g a t i n g t h e e f f i c i e n c y of t h i s procedure.
P a r a l l e l t o t h i s , on-board
s o l u t i o n s a r e p l a n n e d t o b e i n s t a l l e d i n European v e h i c l e s f o r t h e p u r p o s e o f s t u d y i n g t h e e f f i c i e n c y o f t h i s p r o c e d u r e . Upon completion o f these investigations,
t h e t w o p r o c e d u r e s w i l l be
compared. REFERENCES 1 P e t e r H e i n e and Arno B a r e t t i , F o r s c h u n g s b e r i c h t 1 0 4 05 149 U m w e l t f o r s c h u n g s p l a n ; Umweltbundesamt, i n p r e p a r a t i o n 2
J u t t a K l o a s and H a r t m u t K u h f e l d , V e r k e h r s v e r h a l t e n i m Verg l e i c h , D I W B e i t r a g e zur S t r u k t u r f o r s c h u n g H e f t 9 6 , 1987; Dunker i Humblot, B e r l i n
T.Schneideret al. (Editors),Atmospheric Ozone Research and its Policy Implications 0 1989 Elsevier Science PublishersB.V., Amsterdam - Printed in The Netherlands
431
HEAVY DUTY DIESEL EMISSIONS CONTROL: IMPLICATIONS FOR FUEL CONSUMPTION H.D.Freeman,
Ricardo Consulting Engineers plc., Shoreham by Sea (England)
ABSTRACT During recent years, the pressures on emissions control has come predominantly from the United States with the introduction of the transient test and proposals for severe legislation for the future. Europe is currently considering its future policy on emissions control and is concerned not only with the emissions levels but also on the implications on operating costs from higher fuel consumption. This paper considers diesel combustion and emissions formation and reviews the emissions legislation and test procedures with respect to European driving conditions. Based on experiences at the author's company. the possibilities of reducing emissions are discussed with respect to the main technologies available and the likely emissions levels that might be achieved.
D I E S E L COMBUSTION & E M I S S I O N S FORMATION
When discussing emissions it is perhaps pertinent to first consider which emissions are the subject of legislation. then to set the scene by considering the main sources of emissions within a typical direct injection diesel engine. Legislation, either current or proposed, exists for emissions in three market areas, Europe, USA and Japan, and covers hydrocarbons (HC), Oxides of Nitrogen ( N O x ) . carbon monoxide (CO), smoke and particulates.
Q
Piston
Fig.1 Scheruatic Diagram to Show Hydrocarbon Sources in the Combustion Chamber
432 SMOKE AND HYDROCARBONS Essentially t h e products of slow or incomplete combustion of f u e l and engine
oil,
smoke and
hydrocarbons
may be
related
t o insufficient
air.
inadequate f u e l air mixing or l o c a l a i r f u e l r a t i o s outside t h e range f o r combustion. Factors which may e f f e c t hydrocarbons are depicted i n Fig. 1. Smoke and 'hydrocarbons are inversely dependent upon charge temperature and mixing time hence they are reduced by advancing the timing of events.
Unburned
hydrocarbons emitted i n t o the atmosphere are not i n an inherently s t a b l e form and may r e a c t with constituents of the atmosphere t o form other compounds. O X I D E S OF NITROGEN NOx is derived from t h e reaction of nitrogen and oxygen i n the combustion
air.
The process is d i r e c t l y dependent upon temperature ( e s s e n t a i l l y above
2000K). oxygen atom concentration and residence time.
The majority of NOx is
produced during t h e e a r l y high temperature a c t i v i t y and once t h e temperature drops the NOx l e v e l is "frozen".
The later p a r t of t h e combustion does not
reach the c r i t i c a l temperature and thus contributes n e g l i g i b l e NOx.
Pressure
is a l s o a major f a c t o r influencing the reaction and is also highest a t the e a r l i e r stages of combustion.
NOx is reduced by r e t a r d i n g t h e timing of
events, usually penalising output and f u e l economy. Carbon Monoxide The production of carbon monoxide is t h e r e s u l t of incomplete combustion of f u e l , which would otherwise be f u l l y oxidised t o carbon dioxide.
As d i e s e l
engines operate with excess air. even a t f u l l load, carbon monoxide l e v e l s are very low and l i t t l e d i f f i c u l t y is encountered i n meeting l e g i s l a t e d l e v e l s . Particulates Diesel p a r t i c u l a t e
is defined as any s o l i d
(except water)
which
is
collected on a f i l t e r fed from an a ir d i l u t e d exhaust stream a t a temperature below 52OC (as set by US l e g i s l a t i o n ) .
The material is e s s e n t i a l l y carbon
i n t o which v o l a t i l e material such a s hydrocarbon compounds and sulphates a r e absorbed.
Trace amounts of materials from engine wear, f u e l and o i l additives
may a l s o be present.
By v i r t u e of the current measurement technique, some of
the more v o l a t i l e material is lost t o atmosphere. EMISSIONS LEGISLATION Whilst l e g i s l a t i o n e x i s t s f o r USA, Europe and Japan, t h e prime i n t e r e s t f o r
433 t h i s paper lies i n the USA and Europe and f o r simplicity t h e latter is not covered.
I n the USA, emission l e v e l s f o r heavy d i e s e l engines are i n force with increased s e v e r i t y l e v e l s planned f o r t h e future.
Measurements are made on the
Up t o 1984 model year, a steady state
test bed and expressed i n s p e c i f i c form.
13-mode test w a s used but a t t h i s point t r a n s i e n t cycle t e s t i n g became optional and indeed mandatory f o r 1985 model year onwards.
The reasons f o r moving t o a
t r a n s i e n t cycle were t o make the test more representative of conditions, p a r t i c u l a r l y as l i m i t s were lowered.
in-service
The test is run twice, f i r s t
with a cold engine s t a r t , the second with a hot engine start and the two r e s u l t s weighted t o give t h e f i n a l emissions values.
P a r t i c u l a t e measurements
a r e required f o r model year 1988 and t h e l e g i s l a t e d l e v e l s f o r t h i s and the following years are as shown i n Table 1.
Deterioration f a c t o r s have t o be
taken i n t o account when assessing the c a p a b i l i t y of an engine t o meet the legislation. It is of note t h a t proposals f o r off-highway vehicle l e g i s l a t i o n a t similar
levels
are being considered
in
California.
The
test
method
will
not
necessarily be the transient test. TABLE 1
PROPOSED US EMISSIONS LEGISLATION FOR HEAVY DUTY ENGINES Year
Hydrocarbons (HC)
Oxides of Nitrogen "0x1
Carbon Monoxide (CO)
1985 1988 1990 1991 1994
1.3 1.3
10.7 10.7
1.3 1.3
6.0
15.5 15.5 15.5 15.5 15.5
5.0 5.0
1.3
Particulates
0.6 0.6 0.25* 0.1
0.1 f o r buses
( a l l l e v e l s are expressed i n g/bhp.h measured according t o t h e U S transient
m) wear
Deterioration f a c t o r s are operational l i f e .
applied
The transient
is based upon freeway and non-freeway
test
itself
to
account
for
engine
over
its
driving
conditions around New York and Los Angeles which when combined provides the complicated speed load cycle as shown i n Fig. 2.
This i s broken down i n Fig. 3
and shows t h a t t h e transient test is predominately high speed. The r a p i d i t y of change within the cycle necesnitfltee the use of a complex computer controlled
434 test bed with logging facilities and a constant volume sampling system for emissions and particualte measurement (as typified by the Ricardo system shown in Fig. 4) which together require significant investment. Breakdown
Fig.2 Speed/Load Trace over the US FTP Transient Test Cycle
Fig.3 Number of Points in Each Regime of the US FTP Transient Test Cycle
Europe At present there is no emissions legislation in force for heavy duty engines within the EEC. Discussions are continuing within the EEC on the adoption of the ECE Regulation 49 procedure, a 13-mode steady-state test, as defined by Table 2. It was proposed that legislation relating to new models would come into force in January 1988 and for existing models in October 1990. There are currently no proposals regarding particulate emissions from heavy
duty diesel engines. It has been agreed that the emission levels will be lower than specified in the draft document. The current understanding of ECE R49 based emissions legislation is shown in Table
3.
Certain countries have formed
the so called 'Stockholm Group" consisting of Sweden, Austria, Switzerland, Finland and Denmark, plus Canada.
This group is interested in more severe
legislation. Austria and Switzerland have already introduced
R49 based
legislation whilst Sweden favours tax incentives to meet more stringent levels. Exhaust smoke levels are currently regulated by
ECE Regulation 24
(equivalent to EEC Directive 72/306) which covers both full load smoke across the operating speed range of the engine and free acceleration smoke from idle
to governor run-out speed. Measurements are taken using light absorption type apparatus. It is expected that ultimately, the exhaust emission legislation may become more severe in Europe and that levels could be equivalent to the severest US proposals. Neither levels nor a suitable test method have been agreed to date, especially in respect of particulate emissions.
TABLE 2 EUROPEAN 13-MODE TEST CYCLE This test was developed as a test for medium and heavy duty diesel engines based upon European operating conditions. The test comprises 13 steady state test conditions, the emissions from which are weighted as shows below:
Mode
5 6 7 8 9 10 11
12 13
Speed
Idle Intermediate Intermediate Intermediate Intermediate Intermediate Idle Rated Rated Rated Rated Rated Idle
x 10 25 50
75 100
-
100
75 50 25 10
Weighting Factor
0.083 0.080 0.080 0.080 0.080 0.250
0.083 0.100 0.020 0.020 0.020 0.020
0.083
The results are then processed to give overall specific emissions levels, expressed as g/kW.h averaged over the cycle..
TABLE 3 ECE R49 BASED EMISSIONS LEGISLATION IMPLEMENTATION (model year)
co
ECE49
-
14.0
3.5
18.0
EEC Proposal
Not in force
11.2
2.45
14.4
Switzerland ECE R49 13 Mode
1.10.1987
8.4
2.1
14.4
Austria 13 Mode
1.1.1988
11.2
2.8
14.4
Sweden ECE R49 13 Mode
1995 (tentative)
4.9
1.2
9.0
COUNTRY
HC (Elkwh1
NOx
436
Fig. 4
Schematic D i a g r a m o f t h e T r a n s i e n t T e s t i n g F a c i l i t y a t Ricardo
TEST PROCEDURES
The
problem
facing
the regulating
bodies
in
the
world
today
is i n
test method t h a t is r e p r e s e n t a t i v e of t h e c o n d i t i o n s i n s e r v i c e . On t h e one hand t h e US have adopted a t r a n s i e n t s t r a t e g y which, based on a c t u a l road measurements, is closer t o o p e r a t i v e c o n d i t i o n s b u t is
establishing a
u n r e p r e s e n t a t i v e of operation.
European d r i v i n g due t o i t s b i a s
On t h e o t h e r hand i n Europe.
towards high
speed
t h e R49 13 Mode s t e a d y state test
cannot be s a i d to be properly r e p r e s e n t a t i v e o f i n - s e r v i c e c o n d i t i o n s i n view of
t h e 6 minutes s p e n t at each o f
s i g n i f i c a n t time t o settle. measurement method.
t h e 13 modes,
allowing the engine a
This test does n o t c u r r e n t l y e n t a i l a p a r t i c u l a t e
Work is, however, under way w i t h i n t h e EEC t o c o n s i d e r t h e
means by which r e p r e s e n t a t i v e p a r t i c u l a t e samples might be o b t a i n e d from t h e c u r r e n t test,
e i t h e r by t h e use of
a separate paperlpoint
or one paper
throughout with d i f f e r e n t sampling times/point t o p r o v i d e a s u i t a b l e weighting over t h e test. While t h e 13 Mode test can be s a i d t o be closer t o European
conditions,
(Figs.
driving
5 and 6.) with its weighting f a c t o r s b i a s e d towards peak
torque speed, t h e test a t p r e s e n t does n o t c o n t a i n any t r a n s i e n t element as would be encountered i n a c t u a l road use.
A f e a t u r e e s t a b l i s h e d from t r a n s i e n t
t e s t i n g of heavy d u t y engines is t h a t t h e o i l consumption can be up to 20 times g r e a t e r under t r a n s i e n t c o n d i t i o n s . contribution
to
both
hydrocarbons
This h a s been shown t o r e f l e c t i n t h e o i l and
particulates.
Up
to
40% o f
the
p a r t i c u l a t e may be d e r i v e d from o i l . The formation of some emissions such as p a r t i c u l a t e s are exacerbated by t r a n s i e n t o p e r a t i o n ,
e s p e c i a l l y when r a p i d
437 changes in load are encountered.
A
transient cycle will highlight any
inadequacy in the fuel injection equipment or turbocharger specification during transient operation. In general, the transient effects of diesel engine operation are significant in terms of public consciousness of exhaust emissions, particularly in urban conditions.
If in the future a decision is
made to adopt transient based legislation in Europe then the form of transient cycle would require development to ensure that it is representative of operational conditions and that repeatable results can be obtained. Measurement of transient particulate levels would not be possible using the current conventional techniques and the use of real time analysis may be required. Researchers in many areas have established good correlation between 13 Mode and transient test with regard to HC. CO and NOx but as lower particulate levels are achieved there would appear to be an offset on the transient axis. This is thought to be related to the increasing oil consumption under transient conditions. Consideration of the correlation of transient test results to 13 Mode steady state tests and 13 Mode results extracted from a transient test suggests that NOx values for a 13 Mode "transient" test would be lower (24%) while HC and particulates would be close (7%) to the steady state results (Table 4). This brief study suggests that NOx levels need carful consideration in any evaluation of different types of test cycle.
Fig. 5
Typical European Driving Characteristics
Fig. 6
W E R49 13 Mode Weighting Factors
438 TABLE 4
NOx HC Particulates
Ratio A/C
R a t i o BfC
0.82
0.76
1.67
0-93 1.05
1.20
C o r r e l a t i o n obtained from Ricardo test d a t a . COMPARISON OF TRANSIENT AND STEADY STATE EMISSIONS TEST RESULTS A = US T r a n s i e n t FTP B = 13-mode r e s u l t e x t r a c t e d from t r a n s i e n t test d a t a ( A ) C = European 13-mode ( s t e a d y state) r e s u l t
POSSIBILITIES FOR LOWERING EMISSIONS The approach t o t h e reduction o f emissions f a l l s i n t o two c a t e g o r i e s : 1.
Improvement of combustion e f f i c i e n c y t o reduce smoke and hydrocarbons, by
increasing
cylinder
and
t h e amount of a i r t h a t can be introduced successfully
burned.
This
requires
i n t o the
improved
fuel
i n j e c t i o n equipment t o atomise and mix t h e f u e l with t h e a i r and the optimum combustion chamber/cylinder h e a d / i n l e t p o r t arrangement.
2.
Providing a combustion system t o l e r a n t t o r e t a r d t h u s e n a b l i n g lower
rates o f p r e s s u r e r i s e , lower charge temperature and reduced charge r e s i d e n c e time i n o r d e r t o reduce NOx. The technologies a v a i l a b l e may be summarised as follows:-
-
provides lower f r i c t i o n , n o i s e and t h e o p p o r t u n i t y Reduced engine speed for b e t t e r matching o f combustion r e l a t e d parameters over t h e speed range
-
s w i r l , f u e l spray p e n e t r a t i o n , volumetric e f f i c i e n c y and turbocharger match. Increased Rating
-
Provides a b e t t e r t r a d e o f f from
increased
power/litre
i n terms o f s p e c i f i c emissions. Fuel
Injection
c a p a b i l i t y allows
Equipment
(FIE) and Timinp;
-
Increased i n j e c t i o n pressure
t h e u s e o f smaller holed nozzles
thus providing b e t t e r
a t o m i s a t i o n for t h e r e q u i r e d p e n e t r a t i o n w h i l s t maintaining s h o r t i n j e c t i o n periods.
This allows a greater degree of r e t a r d thereby reducing NOx, without
s i g n i f i c a n t i n c r e a s e i n smoke and hydrocarbons.
P r e s s u r e i t s e l f is n o t t h e
only answer and some degree of i n i t i a l rate shaping is considered necessary t o
433 c o n t r o l t h e e a r l y "pre-mix burning" which has a significant effect on NOx. Optimum timing across t h e speed and l o a d range and under t r a n s i e n t c o n d i t i o n s may be achieved by t h e use of e l e c t r o n i c c o n t r o l with f u t u r e h i g h p r e s s u r e f u e l PUPS. Turbocharging and Charne Cooling
- Higher s p e c i f i c o u t p u t n e c e s s i t a t e s
the
u s e of turbocharging t o provide s u f f i c i e n t air t o burn with t h e i n c r e a s e d fuelling levels.
Excess a i r is b e n e f i c i a l for e f f i c i e n t combustion (assuming Whilst warm
good mixing) under high load c o n d i t i o n s t o reduce smoke and HC.
air assists with t h e HC a t l i g h t load by avoiding misfire, cool air a t f u l l load reduces NOx generation, hence t h e need f o r a h i g h degree o f f u l l load charge c o o l i n g but with l i g h t load modulation.
The u s e of v a r i a b l e geometry
turbocharging enables a more e f f e c t i v e match to be achieved a c r o s s t h e speed and load range, with b e t t e r w a r m up c h a r a c t e r i s t i c s f o r smoke and hydrocarbons, and t h e p o s s i b i l i t y of a t r a n s i e n t s t r a t e g y with e l e c t r o n i c c o n t r o l .
Engine
Design Features
- S t a r t i n g with
t h e premise o f a good b a s e engine
-
f u l l y optimised b r e a t h i n g , manifolds v a l v e timing and s w i r l l e v e l , c e r t a i n o t h e r design f e a t u r e s used such as r e - e n t r a n t or l i p p e d combustion bowls may provide a more r e t a r d e d optimum timing t h u s h e l p i n g to reduce NOx. Compression r a t i o s can be increased to h e l p reduce HC s i n c e w i t h i n limits any i n c r e a s e i n c y l i n d e r p r e s s u r e is o f f s e t by t h e requirement of r e t a r d e d timing for low NOx. Good o i l c o n t r o l becomes a n e c e s s i t y
f o r low emissions engines r e q u i r i n g
p a r t i c u l a r a t t e n t i o n a t t h e design stage t o minimise l i n e r d i s t o r t i o n , and optimise
the
piston,
ring
and
liner
combination,
whilst
not
penalising
performance and economy through higher f r i c t i o n . External Engine Features
-
Whilst exhaust gas r e c i r c u l a t i o n
(EGR)
reduces
NOx a t l i g h t load on l i g h t duty engines and NOx is also reduced by water i n j e c t i o n , n e i t h e r approach is considered a c c e p t a b l e for d u r a b i l i t y on heavy duty engines. A t p r e s e n t i t would appear t h a t t h e low p a r t i c u l a t e l e v e l s o f 0.1 g/bhph
w i l l only be achievable by use of some form of r e g e n e r a t i n g filter system.
T h i s is l i k e l y t o i n c r e a s e t h e average back p r e s s u r e on t h e engine thus producing some f u e l economy penalty. The i n t r o d u c t i o n of e l e c t r o n i c c o n t r o l f o r t h e f u e l i n j e c t i o n equipment and
turbocharger provides t h e opportunity t o i n c l u d e power t r a i n management which would
run
t h e engine a t optimum c o n d i t i o n s a t
improvements i n f u e l economy.
all
times with
possible
440
POSSIBLE FUTURE EMISSIONS LEVELS & FUEL CONSUMPTION What of the emissions levels achievable for the future? basis for current engines, Fig.
7
On a HC vs NOx
suggests that while naturally aspirated
engines should be able to achieve the proposed introductory levels of the ECR
49 test, they will have difficulty in achieving the levels proposed for Sweden
L'oool-rT-r Fig.
7
Hydrocarbon NOx Trade-off over the European R49 13 Mode Test
Direc !ctior
Dcnal %iki
-
-1 for 1995, whilst turbocharged and intercooled turbocharged direct in 3Ct on (DI) engines plus indirect injection (IDI) engines would achieve these levels based on the current test incorporating HC, NOx and CO only. These results must not be viewed in isolation since the strategies required to produce low NOx have a significant bearing on smoke and particulates and it is possible that the smoke limits may be exceeded with certain current technology engines. The introduction of a particulate standard in Europe would likely put future legislation at a level similar to the US, thus it is better to compare the more critical particulate/NOx trade off to establish future capabilities. Fig. 8 shows that in order to achieve 1991 levels, it will be necessary to utilise a turbocharged and aftercooled engine with the latest technology in high pressure fuel injection equipment, possibly with electronic timing and modulated aftercooling. Even with low oil consumption. with current technology it will be necessary to fit some form of trap to achieve the 0.1 g/BW particulate level. Against this scene, the likelihood of a lowering in fuel quality must also
44 1
be considered, usually with fuel consumption penalties.
Such feators may
themselves force the introduction of high technology equipment and control systems which at the present emission level requirements could be advantageous to fuel economy.
When the fuel consumption/NOx trade off is considered,
Fig. 9. it is seen that there is a very severe penalty in fuel economy as low NOx levels are approached. Recent work at Ricardo suggests this can be as up to 25% increase, against the optimum fuel consumption build. 300 280
260
- 240 L
. p.
L
n
E 220 u
LL
s 2w 02
' - B e s t I D 1 Engine
1996
/ >L A s-,\
n 2
Fig.
Best DI High Pressure F I E Electronic Timing TC tAC Above + Low 11 Cons -As ,Above t Trap
4
6 NOx Iglbhphl
8
180
160
I
I
I
I
I
I
I
I
I
10 10'1
8 Particulate NOx Trade-off over the US FIT Transient Test Cycle
Fig. 9
Brake Specific Fuel Consumption - NOx Trade-off over the US FI'P Transient Test Cycle (Hot start data only1
CONCLUSIONS Of the current legislation, no one test exactly replicates the style of European driving. The US Federated transient test is unrepresentative of European practice of driving around peak torque speed whilst the European 13 Mode although based towards peak torque speed contains no transient element. Transient conditions of operation generally can influence emissions formation significantly through combustion effects, resulting in significantly increased particulate levels. Future heavy duty engines are likely to be turbocharged and aftercooled with high pressure fuel injection equipment, possibly with electronic control for the FIE aftercooler, any variable geometry turbocharger and power train management
.
442
To achieve the ultimate 0.1 g/BHE'h particulate level specified by the 1994 US regulations, some form of after treatment will be necessary, whilst the requirement for low NOx levels will impose severe fuel consumption penalties despite improvements in combustion by other means, such as wide-spread use of high pressure injection systems. REFERENCES J.M. Hales and M.P. M a y , Transient Cycle Emissions Reduction at Ricardo 1988 & Beyond. SAE 860456. C.C.J. French, Internal Combustion Engines for the Nineties and Beyond Challenges and Opportunities. 1985 Calvin Rice Lecture for ASME. R.D. Cuthbertson;P.R. Shore, L. Sundstrom and P-0. Heden. Direct Analysis of Diesel Particulate-bound hydrocarbons by Gas Chromatography with Solid Sample Injection. SAE 870626. R.E. Winsor, A.J. Vander Bok. W.G. Hammer, The New DEDEC Series 60 Diesel Engine. SAE 870616. W.P. Cartillieri and W.F. Wachter. Status Report on the Preliminary Survey of Strategies to meet US 1991 HD Diesel Emission Standards without Exhaust Gas Aftertreatment. SAE 870342. G.M. Cornetti. K. Klein, G.J. FrClnkl and H.J. Stein, US Transient Cycle Versus ECE R49 13 Mode. SAE 880715. J.R. Needham and M.H. Sandford, A Truck Engine for the 1990's. ASME 87-ICI-50.
T. Schneider et al. (Editors), Atmospheric Ozone Research and its Policy Implications
443
0 1989 Elsevier Science Publishers B.V.,Amsterdam -Printed in The Netherlands
EFFECTIVENESS OF CONTROL TECHNOLOGY IN USE AND IMPLICATIONS FOR A POLICY ON TRAFFIC EMISSIONS
L.C.
VAN BECKHOVEN and W. J. ZWALVE
Directorate-General of Environmental P r o t e c t i o n , D i r e c t o r a t e A i r , P.O.
Box 450, 2260 MB Leidschendam (The Netherlands)
ABSTRACT As p a r t of t h e Netherlands p o l i c y f o r t h e abatement of environmental damage by a c i d r a i n and ozone t h e emission r e d u c t i o n g o a l s f o r t h e main sources of p o l l u t i o n among which road t r a f f i c have been updated. For a number of y e a r s a l r e a d y s c e n a r i o ' s have been developed t o see whether e s t a b l i s h e d and a n t i c i p a t e d p o l i c y would a l l o w f o r t h e g o a l s t o be reached i n t h e not t o o d i s t a n t f u t u r e . In t h e work r e p o r t e d t h e two major f a c t o r s i n t h e s e c a l c u l a t i o n s , i . e . f u t u r e growth and a c t u a l f i e l d performance of m i s s i o n s c o n t r o l equipment, have been reviewed and updated on t h e b a s i s of t h e most r e c e n t i n s i g h t s and d a t a . The r e s u l t s provide f o r i n d i c a t i o n s o f t a r g e t emission l e v e l s , of f u t u r e EEC-legislation and a l s o whether t h e t e c h n i c a l approach will i n a l l s i t u a t i o n s and f o r a l l v e h i c l e c a t e g o r i e s p r o v i d e a s a t i s f a c t o r y s o l u t i o n .
INTRODUCTION
In t h e
Netherlands damage
to
forests
is one of
t h e most
pregnant
examples of t h e e f f e c t s o f a i r p o l l u t i o n . In t h i s c o n t e x t t h e terms a c i d i f i c a t i o n and a c i d r a i n a r e g e n e r a l l y used b u t i t i s well recognised t h a t photochemical
o x i d a n t s p l a y a perhaps
e q u a l l y important r o l e .
abatement p o i n t of view o x i d e s of n i t r o g e n
(Nh)
From t h e
form a common p r e c u r s o r
p o l l u t a n t , hydrocarbons (HC) on t h e o t h e r hand p l a y i n g an i m p o r t a n t r o l e s p e c i f i c a l l y i n ozone formation. Both N4, and HC t o a l a r g e extend d e r i v e from road t r a f f i c ( r e € . l ) .
."
In t h e I n d i c a t i v e Multiyear Programae on A i r , P o l l u t i o n 1985-1989 ( r e f . .
2 ) a f i r s t attempt was made t o d e f i n e t h e problem and t o set t a r g e t s for
r e d u c t i o n of t h e p o l l u t a n t s involved.
For N 4 , t h e t a r g e t w a s set at 33%,
f o r HC a t 50% r e d u c t i o n r e l a t e d t o t h e 1980 s i t u a t i o n . '
444
An
important s t e p i n t h e development of p o l i c y t o c o n t r o l automotive
emissions was t h e agreement reached by t h e EEC-ministers of envirorment , t h e sc-called
Luxemburg 1985 agreement. A t t h a t t h e t h e philosophy l a i d
down i n t h i s agreement g i v e n t h e e x i s t i n g views on t r a f f i c growth could b e expected t o l e a d t o t h e a t t a i n m e n t of t h e t a r g e t s around t h e y e a r 2000.
In t h e I n d i c a t i v e P r o g r a m e i t was f u r t h e r announced t h a t a n e x t e n s i v e progrmme t o i n t e n s i f y r e s e a r c h on e f f e c t s and c a u s e s of f o r e s t d i e b a c k was t o be c a r r i e d o u t . Although t h e r e s u l t s of t h i s p r o g r a m e were announced t o b e e v a l u a t e d towards t h e end of 1988 an i n t e r i m e v a l u a t i o n h a s a l r e a d y been made ( r e f . 3 ) . No new t a r g e t s f o r r e d u c t i o n of e m i s s i o n s have been set y e t , b u t i t i s concluded t h a t t h e s e w i l l have t o b e c o n s i d e r a b l y more s t r i n g e n t t h a n t h e ones p r e l i m i n a r y set in 1985. T a r g e t s of 60 t o 90% r e d u c t i o n s a r e expected t o be needed. At
t h e same t i m e a new p r o g n o s i s o f
economic growth by t h e C e n t r a l
Planning Bureau is a v a i l a b l e t h a t p r e d i c t s c o n s i d e r a b l y h i g h e r i n c r e a s e s i n m i l e a g e b o t h f o r passenger and comnercial v e h i c l e s . In
a l s o g i v e n slow p r o g r e s s
t h e s e c i r c u m s t a n c e s and
d e v e l o p e n t of t h e Luxemburg 1985 Agreement,
in
the
further
i t was decided t o r e e v a l u a t e
t h e p o t e n t i a l of t e c h n o l o g i c a l means t o reduce a i r p o l l u t i o n by road t r a f fic.
This w i l l
then a l s o i n d i c a t e whether
such means w i l l
sufffice
or
whether measures t o c o n t a i n t h e growth of t r a f f i c a r e needed. A t t h e same
t h e t h e need
f o r EEC-policy
beyond
t h e Luxemburg
1985 Agreement w i l l
become a p p a r e n t . The p r e s e n t
paper
describes
a broad
brush
assessment
of
abatement
p o t e n t i a l i n r e l a t i o n t o more s t r i n g e n t r e d u c t i o n g o a l s . S p e c i a l a t t e n t i o n h a s been paid t o t h e long term performance i n service of e m i s s i o n s c o n t r o l equipment.
PROGNOSES OF TRAFFIC DEVELOPMENT The prognoses of t r a f f i c development i n 2000 and 2010 have been deve loped o n t h e b a s i s of s c e n a r i o s of t h e C e n t r a l P l a n n i n g Bureau by means of a model developed by t h e Netherlands Economic I n s t i t u t e . The model c a l c u -
lates f u t u r e k i l a m e t r a g e s by a u t o m o b i l e s and t r u c k s . Table 1 shows t h e res u l t s f o r t h e s c e n a r i o ' s of l o w , medium and h i g h economic growth.
445
TABLE 1
Prognoses o f kilometrages
,
109 km/yr
1980 cars trucks
62.8 9
Economic growth
1ow
medium
high
2000
cars trucks
74.9 9.4
93.2 12.6
102 15
2010
cars trucks
91.5 11.7
105.5 16.5
119 21.3
As r eg ar d s t h e r o l e of p e t r o l , LPG and d i e s e l v e h i c l e s no d r a s t i c changes a r e expected over t h e p e r i o d provided t h e r e are no changes i n f i s c a l p o l i cy . The l a t t e r i n t h e Netherlands s t r o n g l y i n f l u e n c e s t h e c h o i c e f o r e i t h e r of t h e s e f u e l s i n t h e automobile s e c t o r .
PERFORMANCE OF EMISSIONS CONTROL EQUIPMENT I N SERVICE In t h e r e g u l a t i o n s on t h e c o n t r o l of automotive emiss ons around t h e world type approval requirements have been t h e primary measure. s e r v i c e emissions however are of parirmount
The in-
importance i n d et er m i n i n g t h e
s u cces of emissions c o n t r o l programnes. Private cars D e t e r i o r a t i o n of e m i s s io n s performance i n service and t h e improvements o b t ai n ed by proper maintenance have been t h e s u b j e c t of e x t e n s i v e s t u d i e s i n t h e Federal Republic of Germany. On a semple r e p r e s e n t a t i v e f o r t h e 1985 car f l e e t (ref.4)
i t was found t h a t proper maintenance c l e a r l y reduced
emissions of carbonmonoxide by 20 t o 25 p er cen t f o r low t o medium speed d r i v i n g . For hydrocarbons t h e e f f e c t v a r i e d from -5 t o +5 p e r c e n t whereas f o r o x i d es of n i t r o g e n g e n e r a l l y an i n c r e a s e of about 5 p er cen t over t h e speed range was found. When a d j u s t e d c o r r e c t l y t h e m i s s i o n s on average
were below t h e l i m i t s f o r conformity of production, i n t h e case o f hydrocarbons and o x id e s of n i t r o g e n with c o n s i d e r a b l e margin, e.g.
30 t o 60%.
The former a p p l i e s t o t h e s i t u a t i o n i n which em i ssi o n s t a n d a r d s could be m e t by engine d e s i g n measures. F u tu r e s t a n d a r d s a s d i s c u s s e d i n t h i s paper w i l l r e q u i r e t h e use of
external control
i n a d d i t i o n t o en g i n e d esi g n
measures, e.g. exhaust g a s r e c i r c u l a t i o n , c a t a l y t i c a f t e r t r e a t m e n t .
The d u r a b i l i t y of such systems h a s been t h e s u b j e c t o f i n t e n s i v e d i s c u s -
sions.
In
a
1986 paper
(ref.5)
t h e US Environmental P r o t e c t i o n Agency
r e p o r t e d f o r v e h i c l e s a t 35.000 t o 60.000 miles t h e f o l l o w i n g a v e r a g e conv e r s i o n e f f i c i e n c i e s : 77, 16 and 31 p e r c e n t f o r CO, HC and NOx r e s p e c t i v e l y . The r e d u c t i o n e f f i c i e n c y f o r NOx may seem low, b u t h e r e EGR i s t h e main factor in controlling
NG.
Good l o n g term perfomance i n European d r i v i n g h a s been r e p o r t e d by TW f o r 135 c a r s f i t t e d w i t h h - c o n t r o l l e d threeway c a t a l y s t s ( r e f . 6 ) .
The anis-
sions on a v e r a g e were found t o b e w i t h i n t h e s t r i n g e n t US 1983 r e q u i r e m e n t s a t k i l o m e t r a g e s r a n g i n g from 12.000 t o 145.000. Another long term assessment of c a t a l y s t performance h a s been made by UTAC ( r e f . 7 ) .
Although o n l y one c a r w i t h lambda c o n t r o l and threeway c a t a -
l y s t was i n v o l v e d t h e t e s t programme c a r r i e d o u t must b e c o n s i d e r e d t o b e s e v e r e . Emissions performance o v e r 80.000 km was r e p o r t e d f o r a v a r i e t y o f t e s t c o n d i t i o n s well r e p r e s e n t a t i v e of European d r i v i n g .
From t h e d a t a so f a r t h e c o n c l u s i o n seems j u s t i f i e d t h a t c a t a l y s t s can perform well a l s o under more s e v e r e European d r i v i n g c o n d i t i o n s . A remaining q u e s t i o n
then
is how c a t a l y s t s perform i n u n c o n t r o l l e d
s e r v i c e . In a r e c e n t s t u d y by US-EPA
( r e f . 8 ) on t h e problem of tampering
w i t h e m i s s i o n s c o n t r o l equipment a r a t e of c a t a l y s t removal or p o t e n t i a l p o i s o n i n g by m i s f u e l i n g o f 9% i n r e p o r t e d . It i s well known t h a t t h e u s e of leaded g a s o l i n e is d i s a s t r o u s t o c a t a l y s t o p e r a t i o n . To avoid t h i s s i t u a t i o n a r i s i n g i n Europe d i r e c t i v e 85/211/ EEC reconmends t h e s t i m u l a t i o n o f sales of unleaded g a s o l i n e by s u i t a b l e means.
A number of c o u n t r i e s i n Europe have t h e r e f o r e m o d i f i e d g a s o l i n e
t a x a t i o n t o h e l p keep t h e r e t a i l p r i c e of unleaded g a s o l i n e below t h a t of leaded gasoline.
It
i s believed t h a t t h i s policy together with general
a v a i l a b i l i t y w i l l t o a l a r g e e x t e n d p r e v e n t t h e p u b l i c from m i s f u e l i n g . The l a t t e r of c o u r s e b e i n g a n i m p o r t a n t c a u s e of t h e problems i n t h e USA. Other e n g i n e - e x t e r n a l e m i s s i o n s c o n t r o l e q u i p e n t are e x h a u s t g a s r e c i r c u l a t i o n (EGR) and a i r i n j e c t i o n (PA)
systems.
c o n t r o l b y EGR i n f i v e 1975 US-vehicles
I n one s t u d y ( r e f . 9 ) N 4 -
i n s e r v i c e up t o 200.000 Ian was
shown t o a c t u a l l y improve. Ref.8 i n d i c a t e s a tampering r a t e f o r EGR-systems which through t h e y e a r s 1982 t o 1986 d i m i n i s h e s t o a l o w v a l u e of 3%. On t h e whole however i n f o r m a t i o n on d u r a b i l i t y of EGR-
and PA-systems i s
447 limited.
It i s c l e a r t h a t i n s p e c t i o n and maintenance are becoming more
important t o a s s u r e good m i s s i o n s performance w i t h e x t e r n a l s y s t e m s , t h e more so t h e h i g h e r t h e i r c o n v e r s i o n e f f i c i e n c y . hission
f a c t o r s f o r threeway c a t a l y s t p l u s lambda-control
have been
d e r i v e d from t h e aforementioned s o u r c e s , see Annex I. F a c t o r s f o r v e h i c l e s meeting t h e Luxemburg 1985 l i m i t v a l u e s have been based on t h e l i m i t v a l u e s f o r urban o p e r a t i o n . For extra-urban
o p e r a t i o n d a t a on t h e performance o f
Lux'85 v e h i c l e s and an assesment of t h e p o t e n t i a l of l e a n or d i l u t e b u m e n g i n e s p l u s o x i d a t i o n c a t a l y s t s based on ongoing r e s e a r c h programmes could be used ( r e f . 10, 1 1 ) . The emission f a c t o r s t h u s d e r i v e d a p p l y t o t h e t h r e e c a r s i z e c a t e g o r i e s and t h e f u e l t y p e s , see Annexes 11 and 111. Composite e m i s s i o n f a c t o r s f o r p r i v a t e c a r s were t h e n c a l c u l a t e d t a k i n g i n t o a c c o u n t t h e d i s t r i b u t i o n of k i l o m e t r a g e s over t h e s i z e , f u e l and road t y p e c a t e g o r i e s , see Table 2. In t h e c a s e s of c a t a l y s t technology a 10% f a i l u r e r a t e f o r 2000 and a 5% f a i l u r e r a t e f o r 2010 has been taken i n t o account.
Using t h e c o n v e r s i o n
e f f i c i e n c i e s of Annex I V t h e e n g i n e o u t e m i s s i o n s c o u l d b e determined. The l a t t e r were t h e n t a k e n t o r e p r e s e n t t h e e m i s s i o n s f o r t h e 5 and 10% f a i l u r e c a s e s , i.e. complete f a i l u r e was assumed f o r such c a t a l y s t s .
No d e t e r i o r a t i o n has been assumed f o r EGR- and PA-systens. For t h e 1980 v e h i c l e f l e e t t h e e m i s s i o n f a c t o r s used by t h e C e n t r a l Bureau of S t a t i s t i c s i n i t s e s t i m a t e s o f e m i s s i o n s i n t h e N e t h e r l a n d s have been used ( r e f . 1 2 ) .
TABLE 2 Composite emission f a c t o r s , a l l c a r s , g / b . No t a p e r i n g HC
co
N4, ~
1983 f l e e t Lux'85, < 1.4a Lux'85, < 1.4b Lux'85 + EU s t d s US'83
~
~~~~
2.1
11.6
0.80 0.55 0.55
4.5
1.44
3.6 2.9 2.7
1.17 1.00
0.34
2.50
0.32
L i g h t commercial v e h i c l e s For t h i s c a t e g o r y l i t t l e i n f o r m a t i o n i s a v a i l a b l e on t h e performance of advanced e m i s s i o n s c o n t r o l equipment. There i s no r e a s o n however t o b e l i e v e
448
t h a t t h e emissions performance will be any d i f f e r e n t from t h a t i n p r i v a t e c a r s . P a r t i c u l a r l y so s i n c e t h e g a s o l i n e fueled v e h i c l e s a r e used predomin a n t l y i n urban and suburban d e l i v e r y work, t h e d i e s e l fueled ones more o f t e n on longer d i s t a n c e s i n higher speed operation.
For t h e s e v e h i c l e s t h e CBS emission f a c t o r s f o r urban and e x t r a urban d r i v i n g were again taken a s a b a s i s . For t h e g a s o l i n e and LPG-versions t h e assumption of a reduction potential. for both HC and N4, of 38% for 2000 and of
75% €or 2010 was made.
The already
low emissions of
the ID1 diesel
engine were accepted throughout t h e e x e r c i s e although some small gains may
s t i l l be a v a i l a b l e here. The
resulting
composite emission
factors
again t a k i n g
i n t o account
c a t a l y s t f a i l u r e r a t e s of 10 and 5% f o r 2000 and 2010 resp. a r e shown i n Table 3. TABLE 3 Composite emission f a c t o r s f o r t h e l i g h t commercial v e h i c l e , g/km
HC
co
N4,
1983 f l e e t
2.90
15.3
2.40
Gasoline + LPG 38% reduced, d i e s e l unchanged
1.97
9.9
1.64
Gasoline + LPG 75% reduced, d i e s e l unchanged
1.06
4.5
0.94
Heavy commercial v e h i c l e In t h e case of t h e HD-diesel v e h i c l e t h e CBS-values were a l s o taken t h e b a s i s f o r t h e 1980 emission f a c t o r s ( r e f . 1 2 ) . reductions of HC and NO, concluded
that
as
The s u b j e c t of a t t a i n a b l e
has been reviewed e a r l i e r ( r e € . l ) .
It was then
50% reduction although s e v e r e i s a t e c h n i c a l l y f e a s i b l e
goal. More recent l i t t e r a t u r e ( r e f . 13, 14) i s f e l t t o confirm t h i s view, be it t h a t considerable f u r t h e r development t o minimise negative e f f e c t s on f u e l e f f i c i e n c y or o t h e r p o l l u t a n t s needs t o be done. In t h e case of t h e heavy duty d i e s e l v e h i c l e no d e t e r i o r a t i o n has been accounted f o r . For HC t h i s might be a debatable choice. The emission f a c t o r s f o r HD d i e s e l trucks a r e shown i n Table 4.
449
TABLE 4 h i s s i o n f a c t o r s f o r HD v e h i c l e s , d i s t a n c e weighted a v e r a g e s , g/km
co
HC
N4, ~
4.2 2.1
4.8 2.4
CBS 1983 f l e e t 50% r e d u c t i o n
16.9 8.5
SCENARIOS OF EMISSIONS OF HC AND NOx BY ROAD TRAFFIC The combination of
t o t a l v e h i c l e k i l m e t e r s d r i v e n and t h e composite
emission f a c t o r s l e a d s t o t o t a l e m i s s i o n s f o r e a c h c a t e g o r y o f v e h i c l e s . This has been l i m i t e d t o t h e medium growth s c e n a r i o only. T o t a l emissions have been c a l c u l a t e d f o r t h e v a r i o u s l e v e l s o f e m i s s i o n s c o n t r o l . For g a s o l i n e and LPG powered p r i v a t e c a r s :
-
Luxemburg 1985, f o r small c a r s f i r s t s t e p o n l y (marked "a") Same f o r small c a r s second s t e p (marked "b")
-
Same p l u s extra-urban-cycle
-
US'83 requirements
requirements based on l e a n or d i l u t e burn +
c a t a l y s t technology
For l i g h t comnercial v e h i c l e s :
-
38% r e d u c t i o n f o r g a s o l i n e and LPG c a r s
-
sme b u t 75% r e d u c t i o n .
For heavy commercial v e h i c l e s
-
-
25% r e d u c t i o n of HC and N%
50%
'I
I1
I1
I1
I1
Table 5 shows a compilation o f 1 e r e s u l t s f o r two emissions c o n t r o l , i.e. mild
- p r i v a t e c a r s Lux
- light - heavy severe
-
' 8 5 p l u s e x t r a urban c o n t r o l
commercial 38% r e d u c t i o n comnercial 25% r e d u c t i o n
p r i v a t e cars US'83
- l i g h t commercial 75% r e d u c t i o n - heavy commercial 50% r e d u c t i o n
fferent levels o
450 TABLE 5 A t t a i n a b l e emission l e v e l s , mln kg. 1980 Legislation HC Private
car l i g h t cwmercial " heavy total traffic total traffic %
NO -
Private car light c m e r c i a l heavy comnercial total t r a f f i c total traffic, %
2010
2000 mild
severe
146 11,s 24 181,s 100
59 11 16,5 86,s 48
43 6 16,s 65,s 36
154 9, 5 84,s 248 100
93 9,s 88 190,s 77
56 5D
58 119,5 48
mild
severe
44
62 15 43 120 66
8
21,5 73,s 40
48
105 13 114 232 94
7 76 131 53
It i s c l e a r t h a t t h e Luxemburg agreement g i v e n t h e p r o j e c t e d growth o f
t r a f f i c cannot l e a d t o any s i z e a b l e r e d u c t i o n o f o v e r a l l e m i s s i o n s , p a r t i c u l a r l y i n t h e c a s e of N&.
Requirements t h a t a r e based on b e s t a v a i l a b l e
t e c h n o l o g i c a l means l i k e US-requirements t i o n s o f HC
-
and NOx-emissions
f o r c a r s and t r u c k s e n a b l e reduc-
t o be achieved of a b o u t 60 and 50% respec-
tively. An a s p e c t t h a t has n o t been c o n s i d e r e d y e t
have been s e t f o r US control
equipment
-
-
is t h a t US'83
requirements
v e h i c l e s under US-driving c o n d i t i o n s . The e m i s s i o n s threeway
catalyst
+
c l o s e d -loop
control
-
when
o p t i m i s e d f o r European v e h i c l e s and European d r i v i n g c o n d i t i o n s could l e a d t o b e t t e r emission f a c t o r s y e t , Luxemburg 1990l In such a c a s e r e d u c t i o n s OE 64% f o r HC and 53% f o r NOx could b e achieved i n 2010. T h i s i s a c l e a r
c a s e of d i m i n i s h i n g r e t u r n s on investment. The reason b e i n g t h a t t h e l a r g e r p a r t of emissions i n t h i s s i t u a t i o n d e r i v e s from heavy commercial t r a f f i c where
only
modest
reductions
are
available.
A
continued
search
for
improving technology f o r emission r e d u c t i o n of t h e HD-diesel e n g i n e o r even
i t s replacement t h e r e f o r e seans e s s e n t i a l i n c a s e o v e r a l l r e d u c t i o n s o f t h e o r d e r of 60 t o 90% are t o be achieved. Another means t o lower t r a f f i c e m i s s i o n s i s of c o u r s e t o l i m i t ( t h e growth o f ) t r a f f i c . A f i r s t a n a l y s e s o f t h e magnitudes involved h a s been made f o r t h e f o l l o w i n g c a s e s : A. p r i v a t e c a r use c u r t a i l e d ,
t h e i r projected course.
l i g h t and heavy commercial v e h i c l e s
follow
451
B. A l l v e h i c l e s reduce pro r a t o C. Comnercial v e h i c l e u s e c u r t a i l e d ,
privat e c a r s follow t h e i r projected
course, Table 6 shows t h e r e s u l t s i n terms o f a f f o r d a b l e t r a f f i c volumes f o r p r i v a t e c a r s and o r commercial v e h i c l e s r e s p e c t i v e l y as a p e r c e n t a g e of t h e pro jec ted k i lomet r ages, TABLE 6 A f f o r d a b l e t r a f f i c volumes f o r t h r e e c a s e s A, B and C, % of prognosis
Emission reduction, X
Year
Mild l e g i s l a t i o n 50
HC
2010
10011001100 501 161 50 501 631 0 01 451 0
281 6 5 1 32 01 531 15 O/ 3 9 1 0 01 321 0
Stringent legislation 50 2000 2010 70 2000 2010
1001100 I100 10011001100 7 5 1 831 51 511 741 36
1001100 I 1 00 851 951 92 191 621 28 01 561 31
70
2000 2010 2000
I t w i l l be seen t h a t i n t h e c a s e s where t h e r e d u c t i o n i s sought i n one s p e c i f i c v e h i c l e c a t e g o r y (A or C) a requirement f o r 50% N&-reduction
in
t h e c a s e of mild l e g i s l a t i o n would l e a d t o v i r t u a l e l i m i n a t i o n of e i t h e r category. In t h e c a s e of s t r i n g e n t l e g i s l a t i o n t h i s requirement would have
l i t t l e e f f e c t on t r a f f i c volume. I n t h i s c a s e however a requirement f o r 70% N&-reduction
would a l s o l e a d t o near e l i m i n a t i o n of e i t h e r c a t e g o r y .
I n c a s e t h e burden i s spread over a l l v e h i c l e c a t e g o r i e s 50% NOx-reduct i o n would e n t a i l l i t t l e o r no t r a f f i c r e d u c t i o n whereas 70% N&-reduction would l e a d t o h a l v i n g t o t a l t r a f f i c volume.
In a l l c a s e s t h e consequences f o r r e d u c t i o n of t o t a l HC-emissions
are
scnnewhat less t h a n f o r a similar r e d u c t i o n o f NO,-ePissions.
CONCLUSIONS
-
S t u d i e s of e n v i r o m e n t a l e f f e c t s o f t h e m i s s i o n s o f HC and NO by t o t a l road t r a f f i c i n d i c a t e r e d u c t i o n s o f t h e o r d e r o f 60 t o 90% t o b e neces-
452
s ar y . To r ea c h such g o a l s maximum u t i l i z a t i o n of a v a i l a b l e t e c h n o l o g i c a l
-
means i s n ec e s s a r y a s well as c o n t r o l o f t r a f f i c volune. Abatement t e c h n o l o g ie s a v a i l a b l e or under development a l l o w f o r reduct i o n s of 60% f o r HC and 50% f o r NOx w i th o u t a need f o r t r a f f i c volume control
-
C o n t r o l of m i s s i o n s of t h e p r i v a t e c a r t o t h e Luxemburg 1985 l e v e l inc l u d i n g extra-urban
requirements w i l l a l r e a d y i n t h e y ear 2000 r e q u i r e
d r a s t i c c o n t r o l of t r a f f i c volume t o meet environmental g o a l s .
In het
extreme it would mean t o t a l e l i m i n a t i o n o f p r i v a t e or commercial t r a f f i c
-
Fmissions c o n t r o l a t t h e US'83
l e v e l w i l l depending on t h e n ecessar y
r ed u ct i o n a l s o r e q u i r e i n or a f t e r t h e y ear 2000 c o n t r o l of t r a f f i c volume, b e i t a t a c l e a r l y h ig h e r l e v e l .
-
The cau s e of t h e moderate e f f e c t of even more d r a s t i c c o n t r o l of p r i v a t e c a r m i s s i o n s , a p a r t from s t r o n g growth o f t r a f f i c , i s t h e l i m i t e d means t o a b a t e diesel v e h i c l e e m is s i o n s , i n p a r t i c u l a r t h o s e of HD-vehicles.
REFERENCES 1. L.C. van Beckhoven and C . J . S l i g g e r s , Proceedings o f t h e I n s t i t u t i o n o f Mechanical Engineers, London, November 1987. 1989, S t a a t s d r u k 2. I n d i c a t i v e MuLtiyear Programma on A i r P o l l u t i o n 1985 k e r i j The Hague. 3. I n t e r i m Eva l u a ti o n o f t h e P o l i c y on A c i d i f i c a t i o n , M i n i s t r y of Housing, Physical Planning and Environment, The Hague t h e N et h er l an d s, 1987. 4. D. Haesel e t a1, TUV Rheinland, K6Ln FRG, 1987. 5. A. Sabourin, S o c i e t y o f Automotive E n g i n eer s p u b l i c a t i o n no. 860568, D e t r o i t USA, 1986. 6. TUV Rheinland, Forschungsbilanz 1986, K i l n FRG, 1987. 7. J.M. B i r en et a l , Collogue s u r l a P o l l u t i o n d e L ' A i r p ar Les T r a n s p o r t s , P a r i s France 1987. 8. US Environmental R o t e c t i o n Agency, Motor v e h i c l e tampering su r v ey 1987, Ann Arbor USA, 1987. S o c i e t y of Automotive Engineers p u b l i c a t i o n n r . 9. D.A. Drake e t a l , 830984, Detroit USA, 1983. 10. B. Hollemans and R.C. R i jk e b o e r , VROM/RDW s t e e k p r o e f c o n t r o l e van v o e r t u i g e n i n h e t v e r k e e r IW-TNO, D e l f t t h e N et h er l an d s, 1988. 11. Ricardo C o n s u l ti n g E n g i n e e r s , Research Report DP 8710889, Shoreham by Sea UK. 1987. 12. Q u a r t e r l y Environmental S t a t i s t i c s , C e n t r a l Bureau of S t a t i s t i c s , 1985 n r . 2, Voorburg t h e N e t h e r la n d s , 1985. 13. W.P. C a r t e l l i e r i and W.F. Wachter, S o c i e t y o f Automotive Engineers p u b l i c a t i o n nr. 870342, D e t r o i t USA, 1987. 14. Ricardo C o n s u l ti n g E n g i n e e r s , Research Report DP 87/1520, Shoreham by Sea UK, 1987.
-
-
453
Annex I Emission f a c t o r s €or threeway c a t a l y s t s with A - c o n t r o l , g / h . Average f o r 80.000 km, no tampering. Condition
HC
co
NQX
ECE 15 cold ECE 15 warm FTP ‘75
0.9 0.27 0.25 0.15 0.12 0.18
7.5 1.25 3.0 1.2 1.2 3.0
0.20 0.10 0.60 0.17 0.13 0.60
Extra urban* ECC e x t r a urban Mot or way*
*
( r e f . 7)
Annex I1 Emission f a c t o r s f o r g a s o l i n e c a r s i n s e r v i c e , g / h . No tampering. Leg i s l a t i o n
Eng ine size
1983 f l e e t
Urban HC
CO
Extra urban
NOx
HC
CO
NOx
4.0
24
2.1
0.82
3.4
2.7
Lux ‘85
> 2 1.4-2 <1.4a
0.59 0.95 1.75
4.4 6.2 11.0
0.15 0.95 1.75
0.17 0.32 0.90
2.1 2.5 6.1
0.38 1.50 2.20
Lux ‘85
> 2 1.4-2 <1.4b
0.59 0.95 0.95
4.4 6.2 6.2
0.15 0.95 0.95
0.17 0.32 0.32
2.1 2.5 2.5
0.38 1.50 1.50
0.59 0.95 0.95
4.4 6.2 6.2
0.15 0.95 0.95
0.17 0.32 0.32
2.1 1.15 1.15
0.38 1.25 1.05
0.59
4.4
0.15
0.17
2.1
0.38
Lux ‘85 + EU s t d s US ‘83
> 2
1.4-2 <1.4b
454
Annex 111 Emission f a c t o r s f o r c a r s , a v e r a g e i n s e r v i c e , g / b . No tmnpering. Legislation
Fuel
1983 f l e e t
G
D LPG Lux '85,
1.4a
G
D LPG
Lux '85,
1.4b
G
D LPG
Lux '85 + EU c o n t r o l
G
D LPG US '83
G
D LPG
co
NOx
2.53 0.62 1.13
15.4 2.8 1.5
2.91 1.11 1.65
0.81 0.60 0.81
5.5 2.8 1.5
1.48 1.11 1.48
0.55 0.55 0.55
4.2 2.8 1.5
1.18 1.11 1.18
0.55 0.55 0.55
3.2 2.8 1.5
1.0 1.0 1.0
0.34 0.34 0.34
3.0 2.8 1.5
0.29 0.60 0.29
HC
Annex IV Conversion o f f i c i e n c i e s of threeway c a t a l y s t s w i t h A - c o n t r o l .
ECE 15 c o l d ECE 15 warm FTP '15 Steady state 90 km/h E x t r a urban* EEC e x t r a urban Steady state 120 km/h
*
(ref. 7)
HC
co
NO,
12 81 88
71 79 89
69 85 92
83 90 11
74 11 13
95 91 88
82
12
91
T. Schneider et al. (Editors), Atmospheric Ozone Research and its Policy Implicatiom 0 1989 Elsevier Science Publishers B.V., Amsterdam -Printed in The Netherlands
455
OVERALL PROGRAMME FOR MONITORING THE EMISSION BEHAVIOUR OF NEW AND IN-TRAFFIC MOTOR VEHICLES
K. BECKER
Umweltbundesamt,
B i s m a r c k p l a t z 1, D-1000 B e r l i n 33
ABSTRACT An o v e r a l l programme f o r m o n i t o r i n g t h e e m i s s i o n b e h a v i o u r o f customer-owned c a r s and f o r m a i n t a i n i n g t h e l o w e s t p o s s i b l e e m i s s i o n l e v e l a t a l l operating conditions and throughout the c a r ' s l i f e i s proposed, w h i c h i n c l u d e s t h e f o l l o w i n g components:
-
T y p e - a p p r o v a l o f p r o t o t y p e c a r s , t o be c a r r i e d o u t by t h e c a r manufacturer; T e s t i n g f o r c o n f o r m i t y o f p r o d u c t i o n by t h e m a n u f a c t u r e r a n d by t h e a p p r o v a l a u t h o r i t y ; E x t e n s i o n o f t h e p r o c e d u r e s f o r t y p e a p p r o v a l and c o n f o r m i t y o f - p r o d u c t i o n t e s t i n g with t h e o b j e c t i v e o f e n s u r i n g t h a t the lowest possible emission l e v e l i s maintained a t a l l operat i n g c o n d i t i o n s and throughout t h e c a r ' s l i f e t i m e ; R e g u l a r s p o t checks o f c a r s i n t r a f f i c t h r o u g h o u t t h e i r l i f e t o c o n t r o l c o m p l i a n c e with t h e l i m i t v a l u e s e s t a b l i s h e d ; R e q u i r i n g p r o o f o f t h e e f f i c i e n c y o f e m i s s i o n - r e l e v a n t comp o n e n t s t o b e f u r n i s h e d f o r a l l c a r s i n t r a f f i c on a r e g u l a r basis.
INTRODUCTION I n t h e F e d e r a l R e p u b l i c o f Germany, t h e e x i s t i n g e m i s s i o n r e g u l a t i o n s f o r motor v e h i c l e s s t i p u l a t e t h a t a p r o t o t y p e o f c a r s w h i c h a r e p r o d u c e d i n s e r i e s a n d u n i f o r m i n c o n s t r u c t i o n be type-approved e x e m p l a r i l y . I f t h e p r o t o t y p e c a r has s u c c e s s f u l l y passed t h i s exhaust e m i s s i o n t e s t , t h e K r a f t f a h r t b u n d e s a r n t (KBA
-
F e d e r a l O f f i c e o f Road T r a n s p o r t a t i o n ) g r a n t s t h e g e n e r a l
a p p r o v a l ( A l l g e m e i n e B e t r i e b s e r l a u b n i s - ABE) f o r t h e o p e r a t i o n o f c a r s o f t h i s t y p e . The p r e r e q u i s i t e f o r g r a n t i n g such a p p r o v a l i s t h a t t h e c a r s t o be p r o d u c e d i n s e r i e s a t a l a t e r d a t e be i d e n t i c a l w i t h the type-approved v e h i c l e i n terms o f the design o f t h e i r e m i s s i o n - r e l e v a n t components a n d o f p e r t i n e n t a d j u s t ment p a r a m e t e r s .
Control o f t h i s required conformity o f the cars
p r o d u c e d i n s e r i e s with t h e t y p e - t e s t e d c a r i s p o s s i b l e on t h e
456
b a s i s o f t h e same e m i s s i o n r e g u l a t i o n s . These p r o v i s i o n s merely co v er new c a r s . D u r a b i l i t y r e q u i r e m e n t s t o b e met by c a r s t h a t a r e i n use have as y e t o n l y been i n c o r p o r a t e d i n t o Annex XXIII t o
-
A r t i c l e 47 o f t h e StraOenverkehrszulassungs-Ordnung (StVZO Road T r a f f i c C e r t i f i c a t i o n A c t ) , which, analogous t o t h e U.S. emiss i o n s t a n d a r d s , s t i p u l a t e s t h a t t h e exhaust e m i s s i o n s t a n d a r d s be adhered t o ov e r an 80,000
km d r i v i n g d i s t a n c e .
The d e c i s i v e f a c t o r . i n f l u e n c i n g a i r q u a l i t y a r e t h e a c t u a l p o l l u t a n t e m i s s i o n s from i n - t r a f f i c v e h i c l e s t h r o u g h o u t t h e i r e n t i r e lifetimes.
P o l l u t a n t e m i s s i o n s from new c a r s t h e r e f o r e have a
l i m i t e d i n f l u e n c e , w h i l e t h e emission behaviour o f a p r o t o t y p e c a r has no i n f l u e n c e whatsoever on a i r q u a l i t y .
The e x i s t i n g
r e g u l a t i o n s g o v e r n i n g a p p r o v a l and, more i m p o r t a n t l y , t h e c u r r e n t p r a c t i c e o f t h e i r i m p l e m e n t a t i o n do n o t do j u s t i c e t o t h i s d i f f e r e n c e i n im p o rta n c e .
While t y p e - t e s t i n g ,
i.e.
t h e measurement
is i n f a c t b e i n g p e r formed f o r a l l c a r t y p e s approved f o r t h e German market, t e s t i n g
o f p o l l u t a n t emissions o f a prototype car,
f o r c o n f o r m i t y o f p r o d u c t i o n - which a c t u a l l y i s more i m p o r t a n t i s done v e r y r a r e l y as compared t o t h e l a r g e number o f t y p e t e s t s conducted; o f f i c i a l c o n t r o l o f i n - t r a f f i c v e h i c l e s i s , as des c r i b e d above, n o t p o s s i b l e due t o a l a c k o f c o r r e s p o n d i n g r e gulatory provisions. Thus, c o n t r o l l i n g t h e e m i s s i o n s from customer-owned c a r s and maintaining the lowest possible emission l e v e l s a t a l l operating c o n d i t i o n s and t h r o u g h o u t t h e c a r ' s l i f e i s o f c r u c i a l i mportance f o r c o n t r o l l i n g a i r q u a l i t y . An o v e r a l l programme which t a k e s t h e m ent ioned p r i o r i t i e s i n t o a c c o u n t and which i s desi gned t o i m p l e ment t h e r e q u i r e m e n t s d e s c r i b e d above i s p r e s e n t e d i n t h e f o l l o w ing: OVERALL PROGRAMME FOR THE APPROVAL AND M O N I T O R I N G OF MOTOR VEHICLES T y pe- appr ov al The a d m i n i s t r a t i v e p r o c e d u r e f o r award o f a g e n e r a l a p p r o v a l (ABE) by t h e KBA on t h e b a s i s o f measurements o f t h e p o l l u t a n t e m i s s i o n s o f p r o t o t y p e c a r s s h o u l d be r e t a i n e d . However, t h e exhaus t e m i s s i o n measurements s h o u l d no l o n g e r be c o n s i d e r e d t h e r e s p o n s i b i l i t y o f an o f f i c i a l i n s p e c t i o n s e r v i c e , b u t s h o u l d be made t h e r e s p o n s i b i l i t y o f t h e m a n u f a c t u r e r s themselves. When
457
a p p l y i n g f o r award o f a g e n e r a l a p p r o v a l , t h e manufacturer s h o u l d submit some t y p e o f e mi s s i o n s s t a t e m e n t which w oul d have t o be s u b s t a n t i a t e d by r e c o r d s on e x h a u s t e m i s s i o n measurements conduc t ed by t h e m a n u fa c tu re r on company t e s t s t a n d s . The KBA t h e n would m e r e l y have t o check t h e p l a u s i b i l i t y o f t h e documents and o f t h e measuring d a ta s u b m i t t e d .
T h i s pr oc e d u re would have t h e advantage o f i t s s i m p l i f y i n g and a c c e l e r a t i n g t h e a p p r o v a l p ro c e s s which has,
i n the past,
been
hampered r e p e a t e d l y by b o t t l e n e c k s , as was t h e case r e c e n t l y when l o w - p o l l u t a n t v e h i c l e s were i n t r o d u c e d . Testing f o r conformity o f production For improving the c o n t r o l o f s e r i e s production, a t w o - t i e r e d
pr oc edur e i s proposed. Car m a n u f a c t u r e r s shou I d be o b l i g e d t o per
-
form a s s e m b l y - l i n e t e s t i n g r e g u l a r l y on a l l approved car t y p e s . t h e s i z e o f which would depend on t h e number o f c a r s p ro d u c e d , would have t o be t a k e n a t
F o r t h i s purpose, a sample o f cars,
r e g u l a r i n t e r v a l s and s u b j e c t e d t o t h e compl ete a p p r o v a l t e s t . The measuring r e s u l t s would have t o be s u b m i t t e d t o t h e KBA as supplementary s u b s t a n t i a t i o n f o r t h e award or t h e c o n t i n u e d v a l i d i t y o f the approval. T h i s s e l f - t e s t i n g by t h e m a n u f a c t u r e r s would have t o be complemented by s p o t checks t o be o r d e r e d by t h e KBA and p e r f o r m e d by t h e i n s p e c t i o n s e r v i c e on i t s t e s t stands. T h i s t y p e o f c o n t r o l o f t h e c o n f o r m i t y o f p r o d u c t i o n would, on t h e one hand, have t h e advantage o f a l l o w i n g t h e a p p r o v a l a u t h o r i t y t o g e t a complete p i c t u r e o f t h e e m i s s i o n behavi our o f new c a r s ; on t h e o t h e r hand, t h e number o f sample i n s p e c t i o n s o r d e r e d by t h e a u t h o r i t i e s c o u l d be k e p t r e l a t i v e l y s m a l l . E x t e n s i o n o f t h e a p p r o v a l p ro c e d u re The pr oc ed u re u n d e r l y i n g t y p e a p p r o v a l and c o n f o r m i t y - o f - p r o d u c t i o n t e s t i n g must be complemented by d u r a b i l i t y r e q u i r e m e n t s , i.e., t h e r e q u i r e m e n t o f adherence t o t h e e m i s s i o n s t a n d a r d s thr oughout t h e c a r I s l i f e t i m e or w i t h i n a d e f i n e d d r i v i n g d i s t a n ce. As t h e d e f i n i t i o n o f
t h e c a r ' s l i f e t i m e , a d a p t i o n o f t h e "use-
f u l l i f e t i m e " , as d e f i n e d i n t h e U.S.
exhaust e m i s s i o n l e g i s l a -
t i o n , which has a l r e a d y been i n c o r p o r a t e d i n t o Annex XXIII, i s proposed. A c c o rd i n g t o t h i s d e f i n i t i o n ,
the emission standards
458
must be c o m p l i e d w i t h o v e r an 80,000 a p e r i o d o f 5 years.
km d r i v i n g d i s t a n c e o r o v e r
I n t e s t i n g d u r a b i l i t y w i t h i n t h e framework
o f t h e p r o c e d u r e s f o r t y p e a p p r o v a l and con f o r m i t y - o f - p r o d u c t i o n
testing,
i t w i l l r e m a i n i n d i s p e n s i b l e t o r u n the t e s t c a r s o v e r
t h e f u l l 80,000 km d i s t a n c e as l o n g as c o n c l u s i v e and r e c o n s t r u c t i b l e i n f o r m a t i o n on d e t e r i o r a t i o n f a c t o r s i s n o t a v a i l a b l e . Such i n f o r m a t i o n c o u l d be o b t a i n e d , f o r example,
from t h e s p o t checks
c a r r i e d o u t on i n - t r a f f i c v e h i c l e s , w hi ch a r e d e a l t w i t h i n t h e next chapter. The second main o b j e c t i v e i n e x t e n d i n g t h e t e s t p r o c e d u r e i s t o make i t more r e p r e s e n t a t i v e o f t h e a c t u a l d r i v i n g p a t t e r n s . As t h e European c y c l e merely d e s c r i b e s s t o p - a n d - g o - t r a f f i c
i n the
i n n e r c i t y , i t w i l l have t o be supplemented t o a l s o r e f l e c t r o a d and motorway d r i v i n g . Even i f a r e p r e s e n t a t i v e motorway d r i v i n g c y c l e i s implemented, i t c o u l d s t i l l n o t cover t h e t e c h n i c a l m a x i -
mum speed o f a l a r g e number o f c a r s ,
due t o t e s t - s t a n d s p e c i f i c
t e c h n i c a l l i m i t a t i o n s and due t o t h e expedi ency o f a d a p t i n g a u n i for m t e s t p r o c e d u r e f o r a l l t y p e s o f v e h i c l e s .
T h e r e f o r e , a 100 %
coverage o f a l l o p e r a t i n g c o n d i t i o n s i s n o t l i k e l y e v e r t o be
i t w i l l a l w a y s be d i f f i c u l t t o d e f i n e , r e c o g n i z e and p r e v e n t t h e s o - c a l l e d c y c l e - b e a t i n g or d e f e a t d e v i c e s . Re-
a t t a i n e d . Thus,
f e r e n c e i s made i n t h i s c o n t e x t t o t h e s o - c a l l e d f u l l - t h r o t t l e enr ic hm ent s w i t c h , which u n d e r f u l l l o a d o p e r a t i o n s w i t c h e s o f f t h e lambda c o n t r o l i n c l o s e d - l o o p three-way
c a t a l y s t sytems. Even
t h e p r o v i s i o n s o f Annex XXIII, s t i p u l a t i n g t h a t t h e e m i s s i o n - r e d u c i n g e f f e c t be a t t a i n a b l e a t a l l speeds, c o u l d n o t p r e v e n t t h e
use o f such s w i t c h e s . F u t u r e e x h a u s t e m i s s i o n r e g u l a t i o n s s h o u l d t h e r e f o r e i n c l u d e d e t a i l e d and u n e q u i v o c a l p r o v i s i o n s on t h e b a s i s o f which d e f e a t d e v i c e s c a n be c l e a r l y d e f i n e d and r e c o g n i z e d and
which a l l o w l e g a l a c t i o n t o be t a k e n i n cases where such d e v i c e s a r e used. Spot checks o f v e h i c l e s i n t r a f f i c The p e r t i n e n t p r o v i s i o n s o f t h e S t V Z O which empower t h e KBA t o order conformity-of-production
t e s t i n g on samples o f c a r s s h o u l d
be ex t ended t o i n c l u d e s p o t checks o f c a r s i n t r a f f i c . On t h e
or-
d e r o f t h e KBA, t h e i n s p e c t i o n s e r v i c e would have t o t a k e o u t o f t r a f f i c a s t a t i s t i c a l l y s u f f i c i e n t number o f c a r s o f each o f t h e c a r t y p e s s e l e c t e d and s u b j e c t them t o t h e compl ete a p p r o v a l t e s t .
453
The p r e r e q u i s i t e f o r i n c l u d i n g i n d i v i d u a l c a r s i n t h e t e s t i s t h e i r p r o p e r use - i.e., f o r example, t h e use o f l e a d - f r e e p e t r o l i n t h e case o f c a t a l y t i c - c o n v e r t e r equipped v e h i c l e s - and t h a t p r o o f be f u r n i s h e d t h a t maintenance work was done r e g u l a r l y and c o r r e c t l y . T h i s is i m p o r t a n t because w h i l e , on t h e one hand, t h e c a r m a n u f a c t u r e r s s h o u l d be h e l d r e s p o n s i b l e f o r t h e i r c a r s ' comp l i a n c e with the emission standards throughout t h e i r s e r v i c e l i f e , they cannot be blamed, however, f o r any shortcomings caused by improper use on t h e p a r t o f t h e c a r owner. Should such a s p o t check r e v e a l t h a t a p a r t i c u l a r c a r t y p e does not comply w i t h t h e e m i s s i o n s t a n d a r d s , t h e m a n u f a c t u r e r would then, a t f i r s t , have t o be g i v e n t h e o p p o r t u n i t y t o e x p l a i n t h e t e c h n i c a l causes o f non-compliance and t o s u b m i t p r o p o s a l s r e g a r d i n g improvement work t o be c a r r i e d o u t on t h e c a r s o f t h i s t y p e which a l r e a d y a r e i n use. I f t h e e x p l a n a t i o n p r o v i d e d i s uns a t i s f a c t o r y or i f t h e a c t i o n t a k e n t o remove t h e causes o f noncompliance w i t h t h e e m i s s i o n s t a n d a r d s i s i n s u f f i c i e n t , t h e KBA should be empowered t o o r d e r t h e r e c a l l o f t h e c a r s concerned. There s h o u l d be a s u f f i c i e n t number o f v e h i c l e t y p e s i n s p e c t e d a n n u a l l y so as t o o b t a i n , i n t h e c o u r s e o f a few years, a n e a r l y complete p i c t u r e o f t h e e m i s s i o n b e h a v i o u r o f t h e v e h i c l e t y p e s on t h e market. P r o o f o f t h e e f f i c i e n c y o f e m i s s i o n - r e l e v a n t components
The s p o t checks d e s c r i b e d i n t h e p r e c e d i n g s e c t i o n do n o t p r e c l u d e t h e p o s s i b i l i t y o f e m i s s i o n - r e l e v a n t components b e i n g def e c t i v e or e m i s s i o n - r e l e v a n t a d j u s t m e n t parameters n o t c o n f o r m i n g w i t h m a n u f a c t u r e r s p e c i f i c a t i o n s i n i n d i v i d u a l c a r s , even ift h e s p o t check has a s c e r t a i n e d compliance w i t h t h e e m i s s i o n s t a n d a r d s f o r t h e v e h i c l e t y p e concerned. The causes f o r t h i s may, f o r i n stance, be t h a t no o r o n l y poor maintenance work was done o r t h a t t h e c a r was handled i m p r o p e r l y - r e f e r e n c e i s a g a i n made t o t h e use o f l e a d - f r e e p e t r o l i n c a t a l y t i c - c o n v e r t e r equipped v e h i c l e s -, b u t d e f e c t s may a l s o occur i n s p i t e o f proper maintenance and h a n d l i n g . When i n s p e c t i n g c a r s f o r d e f e c t i v e components or f a u l t y adjustment parameters, t h e s o l e o b j e c t i v e i s t o i d e n t i f y such d e f e c t s ; i n so doing, i t i s i r r e l e v a n t whether t h e p o l l u t a n t emissions a f f e c t e d by t h e m l i e above or below t h e e m i s s i o n s t a n d a r d s i n t h e complete e m i s s i o n t e s t conducted on t h e p a r t i c u l a r c a r
460
concerned. I n any case, t h e purpose o f t h e i n s p e c t i o n and o f any c o r r e c t i v e work t h a t may subsequently become necessary i s t o countermand t h e i n c r e a s e i n emissions caused by d e f e c t i v e components o r f a u l t y a d j u s t m e n t parameters. The'refore, such a t e s t need n o t show any c o r r e l a t i o n t o t h e r e s u l t s o f t h e complete e m i s s i o n t e s t . As d e f e c t s caused by poor maintenance o r improper h a n d l i n g a f f e c t c a r s on an i n d i v i d u a l b a s i s ,
i t i s necessary t o i n s p e c t
each i n d i v i d u a l c a r a t r e g u l a r i n t e r v a l s .
Thus,
t h e t e s t t o be
conducted must, above a l l , be short: i n o r d e r t o be a b l e t o i n s p e c t a l a r g e number o f c a r s r e g u l a r L y and t o keep i n s p e c t i o n f e e s r e l a t i v e l y low. I n t h e F e d e r a l R e p u b l i c o f Germany, such a s h o r t t e s t - t h e " i d l e CO" t e s t - was conducted i n t h e p a s t by t h e t e c h n i c a l i n s p e c t i o n s e r v i c e s o r by a u t h o r i s e d r e p a i r shops w i t h i n t h e framework o f t h e i n s p e c t i o n c a l l e d f o r under a r t i c l e 29 S t V Z O . F o r c o n v e n t i o n a l O t t o e n g i n e v e h i c l e s , t h i s t e s t has r e c e n t l y been superseded by t h e s o - c a l l e d ASU ( p e r i o d i c i n s p e c -
t i o n o f exhaust emissions from i n - u s e v e h i c l e s ) , which i s n o t coupled w i t h t h e a r t i c l e 29 i n s p e c t i o n b u t may be c a r r i e d o u t i n dependently by t h e t e c h n i c a l i n s p e c t i o n s e r v i c e s and t h e a u t h o r i s e d r e p a i r shops. I n p r a c t i c e , ASU i s m o s t l y p e r f o r m e d by r e p a i r shops. T h i s has r e v e r s e d t h e b a s i c p r i n c i p l e u n d e r l y i n g t h e a r t i c l e 29 i n s p e c t i o n , which p r o v i d e s f o r a s e p a r a t i o n o f i n s p e c t i o n and r e p a i r : Now, i n n e a r l y a l l cases,
i n s p e c t i o n and r e p a i r
a r e i n t h e hands o f one and t h e same s e r v i c e c e n t e r . Designed f o r t h e i n s p e c t i o n o f c o n v e n t i o n a l O t t o e n g i n e v e h i c l e s ( w i t h o u t exhaust t r e a t m e n t ) , ASU i s s t r i c t l y a components-ins p e c t i o n t e s t , c h e c k i n g t h e most i m p o r t a n t o f t h e b a s i c a d j u s t ment parameters: i d l e speed, i d l e CO, i g n i t i o n t i m i n g , and d w e l l a n g l e (where necessary). S i n c e t h i s t e s t i s n o t s u i t a b l e f o r O t t o e n g i n e v e h i c l e s equipped w i t h exhaust t r e a t m e n t measures, n o t a b l y w i t h c a t a l y s t s , and f o r D i e s e l v e h i c l e s , s u i t a b l e s h o r t t e s t p r o cedures must be developed f o r t h e s e types' o f c a r s and i n c o r p o r a t e d i n t o the StVZO.
Given t h e i n c r e a s e i n t h e number o f D i e s e l
and l o w - p o l l u t a n t O t t o e n g i n e v e h i c l e s ,
as w e l l as t h e s t r o n g i n -
crease i n t h e t r a n s p o r t and t r a f f i c volume p r o j e c t e d f o r heavyd u t y t r u c k s , t h e i n t r o d u c t i o n o f an ASU t e s t f o r t h e s e t y p e s o f v e h i c l e s has a h i g h p o l i t i c a l p r i o r i t y as w e l l .
Therefore,
the
F e d e r a l E n v i r o n m e n t a l Agency has commissioned. two T e c h n i c a l I n s p e c t i o n S e r v i c e s (Rheinisch-West f a l i s c h e r TGV and TUV-Rheinland)
461
t o develop and t e s t ASU t e s t p r o c e d u r e s f o r D i e s e l and c a t a l y t i c c o n v e r t e r equ i p p e d v e h i c l e s ( r e f . 1). The f i e l d - t r i a l phase, conduc t ed by s e v e r a l T e c h n i c a l I n s p e c t i o n S e r v i c e s and i n c l u d i n g sev e r a l t hous an d c a r s ( r e f . 2-31, and t h e development o f compl ete t e s t f a c i l i t i e s ( r e f . 4 ) have p ro g re s sed t o a s t a g e a l l o w i n g b o t h s h o r t t e s t s t o be used w i t h i n t h e framework o f mass p e r i o d i c i n s p e c t i o n s . B o t h p ro c e d u re s are based on t h e measurement o f exhaust em is s ions und e r l o a d o p e r a t i o n a t s t e a d y s t a t e ;
these measure-
ments a r e conducted on a r e l a t i v e l y s i m p l e c h a s s i s dynamometer. They are des ig n e d so as t o a l l o w b o t h D i e s e l and O t t o e n g i n e v e h i c l e s , as w e l l as l i g h t - d u t y t r u c k s , t o be i n s p e c t e d on one and t h e same c h a s s i s dynamometer.
Heavy-duty t r u c k s may be t e s t e d
on a f r e e r u n n i n g s e t o f r o l l e r s o r on t h e r o a d , e n g i n e o u t p u t s uppr es s ion b e i n g a c h i e v e d by a c t u a t i n g t h e v e h i c l e b r a k e s . B oth pr oc edur es s h o u l d be c l o s e l y l i n k e d t o t h e main i n s p e c t i o n p r e s c r i b e d by l a w ( a r t i c l e 29 StVZO) and c a r r i e d o u t by i n s p e c t i o n s e r v i c e s and r e p a i r shops a u t h o r i z e d f o r t h i s purpose; t h i s would r e e s t a b l i s h t h e s e p a r a t i o n o f i n s p e c t i o n and r e p a i r , a concept which i s t o be advocated i n p r i n c i p l e . The mai n purpose o f t h e l e g a l l y p r e s c r i b e d i n s p e c t i o n o f components s h o u l d be t o i d e n t i f y and r e c t i f y any d e f e c t s and f a u l t s caused by maintenance e r r o r s and improper h a n d l i n g t o be a s c r i b e d t o t h e c a r owner. principle,
Thus, i n i t i s t h e owner who has t o see t o t h e n e c e s s a r y c o r -
r e c t i v e or r e p a i r work t o be p e rfo rmed, u n l e s s the d e f e c t s occur i n s p i t e o f pro p e r maintenance and h a n d l i n g . If t h e owner i s a b l e t o f u r n i s h proof t o t h a t e f f e c t , i t i s not his/her r e s p o n s i b i l i t y t o r e e s t a b l i s h t h e c a r ' s p ro p e r c o n d i t i o n , b u t t h a t o f t h e c a r m anuf ac t ur er .
Corresponding w a rra n ty p r o v i s i o n s would t h e r e f o r e
have t o be i n c o r p o r a t e d i n t o t h e l e g a l r e g u l a t i o n s .
(1) T es t pro c e d u re s f o r c a t a l y t i c - c o n v e r t e r equipped v e h i c l e s . F o r c a r s equip p e d w i t h c l o s e d - l o o p three-way
t r a t i o n s o f carbon monoxide ( C O ) ,
c a t a l y s t s , concenh y d rocarbons (HC) and n i t r o g e n
monoxide (NO) c o n t a i n e d i n t h e e x h a u s t gas a r e t o be measured on a c h a s s i s dynamometer a t 7 kW and 50 km/h; i n a d d i t i o n , CO and HC c o n c e n t r a t i o n s a re t o be measured w i t h t h e e n g i n e i d l i n g .
Figure 1
shows a scheme o f t h e t e s t , c o m p r i s i n g t h e f o l l o w i n g stages: c o n d i t i o n i n g o f t h e v e h i c l e on t h e c h a s s i s dynamometer a t
-
7 kW and 50 km/h;
-
once t h e o p e r a t i n g t e m p e r a t u r e i s reached, t h e CO,
HC and NO
c o n c e n t r a t i o n s a t 7 kW and 50 km/h are measured w i t h t h e veh i c l e o p e r a t i n g i n t h e t h i r d gear o r t h e a u t o m a t i c t r a n s m i s s i o n i n p o s i t i o n 0;
-
CO and HC c o n c e n t r a t i o n measurement w i t h t h e e n g i n e i d l i n g ;
compar i s o n between measured c o n c e n t r a t i o n s a n d r e f e r e n c e val u e s , s p e c i f i c t o t h e s i n g l e makes,
for the operating condi-
t i o n s under c o n s i d e r a t i o n . The t e s t d u r a t i o n is a p p ro x . 5 t o 7 mi nutes.
conditioning
rnml
ph8.0 Of
8tabllioatlon
nl08UIIO-
ml
vehicl. delivering b
F i g u r e 1: S i n g l e s t a g e s o f t h e t e s t f o r c a t a l y t i c - c o n v e r t e r equipped v e h i c l e s The t e s t d e s c r i b e d above has been c a r r i e d o u t on approx. 4 000 i n - t r a f f i c cars equipped w i t h c a t a l y t i c c o n v e r t e r s so f a r ;
this
dat a, t o g e t h e r w i t h t h e d a ta o b t a i n e d f r o m t h e p r e c e d i n g b a s i c s t u d y ( r e f . 1 ) and t h e p r e l i m i n a r y r e s u l t s o f s t i l l o n g o i n g work on l o n g - t e r m e m i s s i o n b e h a v i o u r ( r e f . 5 1 , w i l l a l l o w an e m i s s i o n s a n a l y s i s t o be made on a b r o a d base o f data. The d i s t r i b u t i o n o f t h e NO c o n c e n t r a t i o n s under l o a d i s exemp l i f i e d i n F i g u r e 2 f o r a t y p e f a m i l y as approved a c c o r d i n g t o Annex XXIII S t V Z O (US s t a n d a r d ) , c o n s i s t i n g o f about 600 v e h i c l e s w i t h an e n g i n e c a p a c i t y o f 1.8 l i t r e s and an e n g i n e power o f 66 kW, and equip p e d w i t h c l o s e d - l o o p three-way c a t a l y s t s and manual t r a n s m i s s i o n s ( r e f . 6 ) . Such fre q u e n cy d i s t r i b u t i o n s a l l o w r e f e r ence r anges t o be e s t i m a t e d f o r a v e h i c l e t y p e f a m i l y .
E xact r e fer enc e v a l u e s presuppose c o n c e n t r a t i o n d i s t r i b u t i o n s f o r which
any i n c o r r e c t a d j u s t m e n t s ponents can be r u l e d o u t.
or d e f e c t s o f e m i s s i o n s - r e l e v a n t com-
463
NO (ppm) load point F i g u r e 2 : R e l a t i v e f r e q u e n c y d i s t r i b u t i o n o f NO c o n c e n t r a t i o n s u n d e r l o a d ( r e f . 6) The q u e s t i o n as t o what e x t e n t t h e m a r g i n a l d i s t r i b u t i o n r a n ges a r e d e t e r m i n e d by d e f e c t i v e c a r s was i n v e s t i g a t e d on s e v e r a l c a r s w h i c h had a t t r a c t e d a t t e n t i o n i n t h e s h o r t t e s t due t o t h e i r e x h i b i t i n g h i g h l e v e l s o f one
o r s e v e r a l o f t h e p o l l u t a n t com-
p o n e n t s i n one or b o t h o f t h e t e s t modes.
I n s p e c t i o n o f these
vehicles revealed i n c o r r e c t engine s e t t i n g s s i o n - r e l e v a n t components.
or d e f e c t s i n emis-
E l i m i n a t i o n o f these d e f e c t s r e s u l t e d
i n lower emission l e v e l s b e i n g reached i n the s t a t u t o r y d r i v i n g cycle for a l l vehicles.
A f t e r r e p a i r and a d j u s t m e n t ,
t h e concen-
t r a t i o n s o f t h e c o n s p i c u o u s p o l l u t a n t components were f o u n d t o be much lower i n t h e s h o r t t e s t as w e l l . These f i n d i n g s a p p l y e q u a l l y t o v e h i c l e s which comply w i t h t h e e m i s s i o n s t a n d a r d s e s t a b l i s h e d f o r t h e s t a t u t o r y d r i v i n g c y c l e as w e l l as t o t h o s e whose e m i s s i o n s exceed t h e s e s t a n d a r d s f o r one
o r s e v e r a l p o l l u t a n t components. F i g u r e 3 g i v e s an example o f t h e e m i s s i o n r e d u c t i o n p o t e n t i a l a c h i e v e d f o r a v e h i c l e for which c o n s p i c u o u s d e v i a t i o n s h a d been o b t a i n e d i n t h e s h o r t t e s t and w h i c h was s u b s e q u e n t l y e x a m i n e d i n greater d e t a i l . A f t e r e l i m i n a t i o n o f the defects:
"jammed s e n s o r
p l a t e i n t h e a i r f l o w s e n s o r " and " l e a k a g e i n t h e i n j e c t i o n n o z z l e
464
o f t he 2nd c y l i n d e r " , t h e e x h a u s t e m i s s i o n b e h a v i o u r i n t h e FTP d r i v i n g c y c l e was fo u n d t o have i mp roved by 35 % t o 51 %.
HC, NOx
'
$/km
110
co 4
glkm 3 2
1
0 maintenance and repair F i g u r e 3: Improvement o f t h e e x h a u s t e m i s s i o n b e h a v i o u r as a r e s u l t o f r e p a i r work ( r e f . 6)
(ii) T e s t p r o c e d u r e s f o r D i e s e l e n g i n e v e h i c l e s . As a s h o r t t e s t f o r measuring smoke e m i s s i o n s from D i e s e l e n g i n e v e h i c l e s , s e v e r a l c o u n t r i e s have u s e d t h e p r o c e d u r e o f measuri ng t h e smoke d e n s i t y d u r i n g f r e e a c c e l e r a t i o n o r o t h e r p r o c e d u r e s deduced therefrom.
I n t h e F e d e r a l R e p u b l i c o f Germany,
t h i s procedure
which i s based on ECE r e g u l a t i o n N o 24 has n o t as y e t been i m plemented. T h i s i s due t o t h e f a c t t h a t e x t e n s i v e i n v e s t i g a t i o n s p e r f o r m e d under c o n t r a c t t o t h e F e d e r a l E n v i r o n m e n t a l Agency ( r e f s . 3, 7-61 have f u r n i s h e d e v i d e n c e t h a t t h e r e i s no c o r r e l a t i o n between smoke d e n s i t y u n d e r f r e e a c c e l e r a t i o n and smoke d e n s i t y under f u l l l o a d o p e r a t i o n and t h a t use o f t h e f r e e - a c c e l e r a t i o n me'thod may even r e s u l t i n g r a v e m i s i n t e r p r e t a t i o n s . The p r o c e d u r e proposed t h e r e f o r e d i r e c t l y c o n s i d e r s t h e oper a t i n g c o n d i t i o n with t h e h i g h e s t smoke emi ssi ons, w hi ch is a l s o t h e c o n d i t i o n p r e s c r i b e d i n the s t a t u t o r y approval procedure. The s h o r t t e s t as i l l u s t r a t e d i n F i g u r e 4 p r o v i d e s f o r tw o smoke
d e n s i t y measurements, each i n accordance w i t h t h e Bosch F i l t e r method, t o be ta k e n u n d e r s t e a d y s t a t e f u l l l o a d o p e r a t i o n and r a t e d speed, as w e l l as a t 45 % o f r a t e d speed. The smoke v a l u e s t h u s measured must l i e below e m i s s i o n s t a n d a r d s t h a t have y e t
465
t o be e s t a b l i s h e d . L i g h t - d u t y t r u c k s and passenger c a r s have t o be t e s t e d on a c h a s s i s dynamometer,
w h i l e heavy-duty t r u c k s may
o r on t h e r o a d . I n t h i s i n s t a n c e , e n g i n e o u t p u t s u p p r e s s i o n is a c h i e v e d by a c t u a t i n g
be t e s t e d on a f r e e r u n n i n g s e t o f r o l l e r s t h e v e h i c l e brakes.
F i q u r e 4:
S i n g l e s ta g e s o f th e s h o r t t e s t f o r D i e s e l e n g i n e vehicles
The r e s u l t s o b t a i n e d f r o m t h e a p p l i c a t i o n o f 4,000
c a r s and 1,000
the s h o r t t e s t t o
t r u c k s showed a v e r y good c o r r e l a t i o n t o t h e
measurement o f exhaust gas o p a c i t y t a k e n d u r i n g t y p e a p p r o v a l t e s t i n g pur s ua n t t o Annex X V t o a r t i c l e 47 S t V Z O (ECE R e g u l a t i o n
No 241, s i n c e t h e o p e r a t i n g c o n d i t i o n s ( f u l l l o a d ) u n d e r l y i n g b o t h t e s t pr oc e d u re s a r e i d e n t i c a l . T h e r e f o r e , i t i s p o s s i b l e t o d e r i v e emission standards f o r the i n s p e c t i o n o f Diesel engine v e h i c l e s i n use on t h e b a s i s o f t h e e m i s s i o n s t a n d a r d s as s t i p u l a t e d i n Annex XV. I n c o n t r a s t t o O t t o e n g i n e v e h i c l e s , any f e a t u r e s s p e c i f i c t o t h e e n g i n e t y p e need n o t be t a k e n i n t o account. F i g u r e 5 i l l u s t r a t e s t h e frequency d i s t r i b u t i o n o f t h e smoke r e a d i n g s i n accordance w i t h t h e Bosch method a t f u l l l o a d and r a t e d speed. What is s t r i k i n g i s t h a t more t h a n 20 % o f the D i e s e l e n g i n e passenger c a r s examined e x h i b i t e d a Bosch number above 5.0; t h i s a l s o a p p l i e s t o t h e l o w e r speed t e s t e d . I n accordance w i t h t h e e x i s t i n g c o r r e l a t i o n t o t h e t y p e - a p p r o V a l t e s t , a l l D i e s e l e n g i n e passenger c a r s e x h i b i t i n g a Bosch number above 5.0 were c l a s s i f i e d as conspicuous, and some o f 'them were examined e x e m p l a r i l y i n g r e a t e r d e t a i l . For n e a r l y a l l o f
466
t h e h i g h - e m i s s i o n D i e s e l e n g i n e v e h i c l e s t h u s examined, t h e Bosch number was f ou n d t o h a v e d ro p p e d b e l o w 5.0 r e p a i r and maintenance work had been done.
a f t e r appropriate
F i g u r e 5: R e l a t i v e fre q u e n c y d i s t r i b u t i o n o f smoke r e a d i n g s a t f u l l l o a d a n d r a t e d speed ( r e f . 6 ) REFERENCES 1 D. Has s el, F.-J. Weber, A . R i c h t e r , E rprobung e i n e s V e r f a h r e n s f u r d i e AbgasprUfung i m Rahmen der p e r i o d i s c h e n Uberwachung f u r Fahrzeuge, d i e r n i t K a t a l y s a t o r ausger D s t e t s i n d . S c h l u Q b e r i c h t UBA-FE-Vorhaben 1 0 4 05 345, August 1985. 2 H.J. Voss, e t a l . , P r a x i s e r p r o b u n g e i n e s P r i i f v e r f a h r e n s z u r p e r i o d i s c h e n Uberwachung d e r Abgasemission von s c h a d s t o f f armen Otto-Pkw und D i e s e l fahrzeugen. S c h l u Q b e ri c h t d e r V e r e i n i g u n g der Technischen Uberwachungs-Vereine e.V., May 1987. G. Krebs, D. Hassel, M . Herrmann, H. H o l t e i , P r a x i s e r p r o b u n g e i n e s RuQmeljverf a h r e n s i r n Rahmen der 5 29-VorfUhrung. SchluQb e r i c h t UBA-FE-Vorhaben 1 0 4 05 344, J u l y 1984. L a s t e n h e f t z u r S p e z i f i k a t i o n der P r i i f a n l a g e fiir d i e E m i s s i o n s unt er s uc hun g von O t t o - bzw. D i e s e l motoren. V e r e i n i g u n g der Technischen Uberwachungs-Vereine e.V., December 1986. 0. Has s el, H. Waldeyer, G . Weyrauther, L a n g z e i t v e r h a l t e n von Fahrzeugen m i t g e r e g e l t e m D r e i w e g k a t a l y s a t o r u n t e r e u r o p a i s c h e n B e t r i e b s bedingungen. Zwischenber i c h t UBA-FE-Vorhaben 104 05 147, F e b r u a r y 1987 ( u n p u b l i s h e d ) . C. W o l f f , H. Waldeyer, WirkungsprOfung z u r p e r i o d i s c h e n Uberwachung von s c h a d s t o f f armen Fahrzeugen. V D I - B e r i c h t e N r . 639, D i i s s e l d o r f , 1987, pp. 407 - 423. Untersuchung der Abgastrubung b e i D i e s e l m o t o r e n h i n s i c h t l i c h d e r K o r r e l a t i o n zwischen Messungen b e i g l e i c h b l e i benden D rehz a h l e n und b e i f r e i e r Be s c h l e u n i g u ng. S c h l u Q b e r i c h t UBA-FE-Vorhaben 104 05 541, December 1978. 8 H. H o l t e i , Neuere MeQverfahren z u r E r m i t t l u n g d i e s e l m o t o r i s c h e r Emissionen, V D I - B e r i c h t e N r . 559, D u s s e l d o r f , 1985.
T. Schneider et al. (Editors), Atmospheric Ozone Research and its Policy Implications 0 1989 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands
467
MOBILE SOURCE CONTROL STRATEGIES I N THE NETHERLANDS
MARTIN KROON,
M i n i s t r y of Housing, P h y s i c a l P l a n n i n g and Environment of
The N e t h e r l a n d s , A i r P o l l u t i o n D i r e c t o r a t e .
ABSTRACT Road t r a f f i c i s a major s o u r c e of a i r p o l l u t i o n i n t h e N e t h e r l a n d s , produi n 1987 780,000 t o n s of CO ( = 7 0 % ) , 190,000 t o n s o f HC (145%) and cing 285,000 t o n of NOx (= 5 5 % ) . The Dutch environmental p o l i c y towards road t r a f f i c i s s e t up i n a 3-step approach ( r e g a r d i n g a i r p o l l u t i o n and n o i s e ) : 1 ) Source c o n t r o l through v e h i c l e emission s t a n d a r d s ; 2 ) Reducing motor v e h i c l e use ( " a u t o m o b i l i t y " ) ; 3 ) T r a f f i c measures t o c o n t r o l a i r q u a l i t y i n urban a r e a s .
-
-
The paper d e s c r i b e s t h e d i f f e r e n t measures under t h e s e 3 t r a c k s and t h e Dutch p o s i t i o n w i t h i n t h e EC n e g o t i a t i o n s , aimed a t e s t a b l i s h i n g s t r i c t e r emission s t a n d a r d s . S p e c i a l a t t e n t i o n i s g i v e n t o t h e d e v e l o p e n t of a coo r d i n a t e d approach f o r t h e r e d u c t i o n of c a r use and t h e promotion of p u b l i c t r a n s p o r t and b i c y c l e use. P r i o r i t y i s given t o t h e f o l l o w i n g s t r a t e g i e s : 1. The N e t h e r l a n d s w i l l do e v e r y t h i n g i n i t s power t o e n s u r e t h a t t h e EC a d o p t s t h e s t r i c t e s t p o s s i b l e m i s s i o n s t a n d a r d s f o r t r u c k s and passenger c a r s based on t h e maximum e x p l o i t a t i o n of c u r r e n t technology. 2. A t t h e end of 1988 an e v a l u a t i o n of p r o g r e s s t o d a t e w i l l b e c a r r i e d o u t , and i f n e c e s s a r y t h e p o s i t i o n w i t h r e g a r d t o t h e EC w i l l be recons i d e r e d i n c o n s u l t a t i o n w i t h like-minded Member S t a t e s .
3. I f t h e r e d u c t i o n t a r g e t s f o r NOx (33%) and f o r HC (50%) are t o be t i g h t e n e d up and t h e p r o p o r t i o n of m i s s i o n s accounted f o r by t r a f f i c reduced, t h e u s e of motor v e h i c l e s or a t l e a s t t h e i n c r e a s e in it w i l l have t o be reduced s i g n i f i c a n t l y .
4. A r o a d - p r i c i n g system w i l l be adopted, t h i s may become e f f e c t i v e o n l y a f t e r 1995. Subsequent t o c o n s u l t a t i o n s w i t h P a r l i a m e n t , f u r t h e r measures designed t o l i m i t t h e use of passenger c a r s w i l l b e drawn up i n c l o s e c o o p e r a t i o n between t h e T r a f f i c and Environment d e p a r t m e n t s . 5. I n o r d e r t o meet ambient a i r q u a l i t y s t a n d a r d s urban t r a f f i c w i l l be s u b j e c t t o s t r u c t u r a l change, i n c l u d i n g a r e d u c t i o n i n c a r u s e . T h i s may l i k e w i s e reduce a c i d i f i c a t i o n and ozone f o r m a t i o n .
468
INTRODUCTION
Road t r a f f i c is a major s o u r c e
f a i r pollution.
In t h e Netherlands more
t h a n 5 . 5 m i l l i o n motor v e h i c l e s t r a v e l a t o t a l o f about 85 b i l l i o n k i l o meters a y e a r ,
carbon monoxide (W), 190,000
producing 780,000 t o n s of
t o n s of hydrocarbons (HC), and 285,000 t o n s of n i t r o g e n o x i d e s (NO,).
Road
t r a f f i c a l s o s c o r e s high i n s h a r e s of t o t a l emissions i n t o t h e a i r : 70% o f COD 55% of N 4 , and 45% o f HC (1987). Through i t s N4,-
and HC-output,
t r a f f i c c o n t r i b u t e s s u b s t a n t i a l l y t o t h e l a r g e s c a l e long term
road
problems o f
a c i d i f i c a t i o n and photochemical a i r p o l l u t i o n . Furthermore road t r a f f i c is f a r and away t h e l a r g e s t s o u r c e of environment a l p o l l u t i o n i n urban a r e a s , n o t o n l y f o r t h e compounds mentioned above b u t a l s o f o r p a r t i c u l a t e s , a s b e s t o s and Sop. Environmental p o l l u t i o n by road t r a f f i c i s produced i n a 3-step way, inv o l v i n g ( 1 ) t h e v e h i c l e emission
factor,
(2)
t h e "automobility"
volume
f a c t o r , and ( 3 ) t h e t r a f f i c / d r i v e r f a c t o r . The Dutch e n v i r o w e n t a l p o l i c y towards road t r a f f i c is set up a l o n g p a r a l -
l e l l i n e s : l S t , v e h i c l e emission s t a n d a r d s f o r n o i s e and a i r p o l l u t i o n , 2nd, reducing motor v e h i c l e u s e ("automobility")
,
3rd, ( u r b a n ) t r a f f i c measures.
1 . Emission s t a n d a r d s ( t h e f i r s t t r a c k ) The lst t r a c k approach i s d i r e c t e d towards e s t a b l i s h i n g and improving emission s t a n d a r d s for a l l vehicles
and
trucks,
categories
especially
of
through
(new)
private cars,
EC-directives.
delivery
Together
with
( n a t i o n a l ) t a x i n c e n t i v e s f o r "clean" c a r s , t h i s should l e a d t o an i n t r i n s i c a l l y "clean" c a r p o p u l a t i o n from t h e y e a r 2000. It should be r e a l i z e d t h a t t h e European Cornunity
n a l body w i t h 11 member states garding ( t e c h n i cal) market.
-
-
being a supranatio-
h a s almost e x c l u s i v e r e g u l a t o r y power re-
s t a n d a r d s f o r p r o d u c t s t o be marketed w i t h i n t h e EC-
Consequently
EC-directives
mark
the
L i m i t s w i t h i n which member
s t a t e s may set v e h i c l e s t a n d a r d s f o r a i r p o l l u t i o n , n o i s e e t c . As a member s t a t e , t h e Netherlands p a r t i c i p a t e s
i n negotiations regarding pollution
s t a n d a r d s and t r i e s t o r e a c h agreements on t h e h i g h e s t p o s s i b l e Levels of abatement and c o n t r o l . C o n s i d e r a b l e p r o g r e s s has t o be made on a wide v a r i e t y of
i s s u e s t o be
covered by EC-standards b e f o r e t h e s e r e g u l a t i o n s can b e s a i d t o be equival e n t t o t h e more s t r i n g e n t US-standards.
469
T h i s y e a r new EC-standards
have t o b e e s t a b l i s h e d f o r t h e f o l l o w i n g items:
"small" passenger c a r s (
1400 c c ) f o r t h e p e r i o d a f t e r 1992/1993;
a h i g h speed t e s t
commercial v e h i c l e s ; diesel-emissions
of p a r t i c l e s and gaseous compounds;
from gasoline-engined
light
c y c l e and h i g h speed emssions; evaporation losses
c a r s ; enforcement and d u r a b i l i t y s t a n d a r d s f o r c a t a -
l y s t s and o t h e r r e d u c t i o n equipment.
1.1. The s t r a t e g y adopted by t h e N e t h e r l a n d s The Dutch G o v e r w e n t sees t h e "Luxembourg Agreement" as a f i r s t s t e p on t h e way t o e s t a b l i s h i n g s t r i c t e r s t a n d a r d s f o r a l l c a t e g o r i e s of v e h i c l e . The s t r a t e g y of t h e Netherlands is t o win wide s u p p o r t and i n t e r n a t i o n a l l y
-
-
both n a t i o n a l l y
f o r s t r i c t e r s t a n d a r d s on t h e b a s i s of t h e r e s u l t s
of s c i e n t i f i c s t u d i e s . These s t a n d a r d s must b e based p r i m a r i l y on what i s technically feasible.
The aim i s t o f i x and implement t h e new emission
s t a n d a r d s i n t h e f o l l o w i n g manner: 1. D i r e c t i n g our e f f o r t s towards e s t a b l i s h i n g e m i s s i o n s t a n d a r d s compara b l e t o t h o s e i n f o r c e i n t h e USA. T h i s means, among o t h e r t h i n g s , t h a t s t a n d a r d s f o r "small" c a r s ( l e s s than 1400 c c ) must a l s o b e based on c a t a l y t i c c o n v e r t e r technology.
Without t h e u s e of c a t a l y t i c conver-
ters, it w i l l not be p o s s i b l e even t o approach t h e e m i s s i o n s s t a n d a r d s i n f o r c e i n t h e USA. The N e t h e r l a n d s h a s s u b m i t t e d p r o p o s a l s ( 4 , 5 grams NO,
2. F i s c a l i n c e n t i v e s f o r "clean" t h e i n t r o d u c t i o n of date,
-
5,5
+ HC per t e s t ) . cleaner
c a r s must be c o n t i n u e d . passenger
In a d d i t i o n t o
c a r s a t t h e earliest
possible
t h e r a p i d i n t r o d u c t i o n of c l e a n e r t r u c k s is a l s o d e s i r a b l e .
A
gentlemens'agreement signed with t h e m a n u f a c t u r e r s and importers on 29 September 1987 r e p r e s e n t s t h e f i r s t s t e p i n t h i s d i r e c t i o n ,
establi-
s h i n g a 10-15% NOx-reduction p e r t r u c k f o r 80% o f a l l newly s o l d heavy t r u c k s . T h i s approach
-
u s i n g economic i n c e n t i v e s t o compensate f o r t h e
a d d i t i o n a l c o s t s of c a t a l y t i c and o t h e r e m i s s i o n r e d u c t i o n equipment proves t o b e an e f f e c t i v e way t o "clean-up"
t h e passenger
-
car f l e e t
l o n g b e f o r e such c o u l d be reached by compulsory (EX) measures a l o n e . On April
1,
1986,
several
f i s c a l measures
entered
into
force
N e t h e r l a n d s i n o r d e r t o promote t h e i n t r o d u c t i o n of "clean"
in
the
c a r s . From
t h a t d a t e r e g u l a r leaded g a s o l i n e was r e p l a c e d b y unleaded r e g u l a r , and f i s c a l p r o f i t s were a t t r i b u t e d t o t h e p u r c h a s e of "clean" m e e t t h e new EC-standards.
cars that
As a r e s u l t today about 25% of a l l newly
sold gasoline-fueled c a r s i s catalyst-equiped,
w h i l e more t h a n 65% i n
470
t o t a l meets t h e s e s p e c i a l t a x r e q u i r e m e n t s . 1.2. O t h e r EC-standards t o b e f i x e d i n 1988 and 1989
*
A supplement t o t h e c u r r e n t measuring p r o c e d u r e (which i s d e s i g n e d f o r urban
traffic)
cycle").
to
take
account
of
extra-urban
driving
("high-speed
The c o r r e s p o n d i n g e m i s s i o n s t a n d a r d s w i l l a l s o have t o b e l a i d
down i n 1988. I t is e s t i m a t e d t h a t NOx-emissions
from a l l c a t e g o r i e s of
g a s o l i n e - d r i v e n c a r s can be reduced by s e v e r a l t e n t h s ( % ) .
*
An e x t e n s i o n of c u r r e n t t y p e a p p r o v a l s t a n d a r d s t o i n c l u d e a s p e c i f i c d u r a b i l i t y r e q u i r e m e n t . The N e t h e r l a n d s i s p r e p a r i n g a r e g u l a t i o n based
on t h e D i r e c t i v e of 3 December 1987, which s e t s o u t a q u a l i t a t i v e durab i l i t y requirement.
The r e g u l a t i o n w i l l
result
i n lower e m i s s i o n s of
n i t r o g e n o x i d e , hydrocarbons and c a r b o n monoxide.
*
"Second-phase"
s t a n d a r d s f o r gaseous m i s s i o n s
and s t a n d a r d s for par-
t i c l e e m i s s i o n s from t r u c k s . A d e c i s i o n i s d u e t o be t a k e n by t h e end of 1988. The N e t h e r l a n d s i s a d v o c a t i n g r e d u c t i o n s i n c u r r e n t NOx e m i s s i o n s of 40-50% p e r v e h i c l e .
*
S t a n d a r d s f o r t h e e m i s s i o n of hydrocarbons r e s u l t i n g from gasoline-evaporation
(passenger c a r s ) .
reduction
A
of
80% compared w i t h c u r r e n t
emission l e v e l s i s b e i n g sought.
*
Emission s t a n d a r d s f o r d e l i v e r y v e h i c l e s analogous w i t h t h o s e a p p l y i n g f o r p r i v a t e c a r s . A r e d u c t i o n o f approx. 70% from c u r r e n t l e v e l s should be f e a s i b l e .
1.3. N a t i o n a l r e g u l a t i o n s and measures
*
I n a d d i t i o n t o t h e c o n t i n u a t i o n of f i s c a l i n c e n t i v e s f o r c l e a n c a r s , i s important
t h a t "Euro super"
it
unleaded g a s o l i n e s h o u l d become w i d e l y
a v a i l a b l e soon. T h i s w i l l s t i m u l a t e t h e s a l e of c a r s f i t t e d w i t h c a t a l y -
tic
converters.
Through d i f f e r e n t i a l
t a r i f f s enacted April
Eurosuper can b e marketed 5 c t c h e a p e r t h a n leaded Super. f u t u r e Eurc-unleaded
1,
1988,
I n the near
w i l l r e p l a c e unleaded R e g u l a r , r e s u l t i n g i n a r e a l
two-grade system.
*
The r e s e a r c h and d e m o n s t r a t i o n program on c l e a n and f u e l - e f f i c i e n t w i l l b e pursued w i t h v i g o u r
p r o p o s a l s i n EC-
i n order
cars
t o formulate solidly-researched
and o t h e r r e g u l a t o r y frameworks.
The sum of HF1. 3.2
m i l l i o n has been earmarked f o r t h i s program i n 1988.
*
A t t h e end of 1988 assessment will be performed t o e s t a b l i s h whether t h e
Luxembourg Agreement and t h e supplumentary d e c i s i o n s which were i m p l ~
47 1
mented i n c o n n e c t i o n w i t h i t have s u f f i c i e n t l y f u l f i l l e d t h e i r objectives.
I f n o t , t h e N e t h e r l a n d s w i l l see i t s e l f f o r c e d t o r e c o n s i d e r i t s
position
in
the
EC-consultations,
Germany and Dewark.
together
with
countries
such
as
Given t h e s e r i o u s n e s s of t h e e n v i r o m e n t a l e f f e c t s
and t h e a v a i l a b i l i t y of e f f e c t i v e technology, t h e N e t h e r l a n d s h a s no int e n t i o n o f s u p p o r t i n g emission s t a n d a r d s which l a g f a r behind t h e c u r r e n t s t a t e of the art.
*
In o r d e r t o g u a r a n t e e t h a t c a r s do n o t c a u s e more a i r p o l l u t i o n t h a n s t r i c t l y necessary during t h e i r l i f e , general periodic c a r inspections
w i l l be extended t o c o v e r e n v i r o m e n t a l a s p e c t s . In a d d i t i o n , a n extens i v e random-sample
i n s p e c t i o n program will b e u n d e r t a k e n o v e r t h e n e x t
5 y e a r s t o check t h e conformity o f p r o d u c t i o n and t h e d u r a b i l i t y of t h e
a n t i - e m i s s i o n s d e v i c e s i n use.
*
L a s t month a p u b l i c i t y campaign on "clean"
cars,
catalytic converters
and unleaded g a s o l i n e was o r g a n i s e d . The campaign s e e k s b o t h t o remove
sane of t h e m i s u n d e r s t a n d i n g s s u r r o u n d i n g t h e s e t o p i c s and t o promote t h e sale of c a r s f i t t e d with c a t a l y t i c c o n v e r t e r s . T h i s campaign was set up i n c l o s e c o o p e r a t i o n with t h e Dutch petroleum i n d u s t r y and c a r manuf a c t u r i n g and i m p o r t i n g b u s i n e s s .
1.4. R e s u l t s from t h e f i r s t t r a c k approach I f t h e decision-making p r o c e s s i n t h e EC i s based on m a x h u n e x p l o i t a t i o n of a v a i l a b l e technology, t h i s s t r a t e g y could r e s u l t ( a t most) i n aver a g e r e d u c t i o n s i n m i s s i o n s from g a s o l i n e (NO,)
and LPG-driven
c a r s of
f
80%
and f 90% (HC) p e r v e h i c l e b y t h e y e a r 2000 ccmpared w i t h c u r r e n t
average v a l u e s .
It should c e r t a i n l y be p o s s i b l e t o reduce p a r t i c l e mis-
s i o n s from d i e s e l - d r i v e n
p r i v a t e c a r s by a t l e a s t h a l f (which would s t i l l
l e a v e them a t h i g h l e v e l s ) , whereas gaseous e m i s s i o n s from d i e s e l - d r i v e n p r i v a t e c a r s a r e expected t o d e c r e a s e o n l y s l i g h t l y from t o d a y ' s a l r e a d y r e l a t i v e l y low l e v e l s . It should b e p o s s i b l e t o r e d u c e e m i s s i o n s of n i t r c gen oxide and hydrocarbons from t r u c k s by between 40 and 50% p e r v e h i c l e ; u n f o r t u n a t e l y , t h e r e i s a s y e t no p r o s p e c t of t e c h n i c a l developments which would p e r m i t f u r t h e r r e d u c t i o n s . Obviously f u r t h e r r e d u c t i o n s i n emission v a l u e s p e r v e h i c l e and an i n t e n sified trucks.
r e s e a r c h e f f o r t are
still
The t e c h n i c a l p o s s i b i l i t i e s
essential,
e s p e c i a l l y with
regard
to
f o r f u r t h e r reductions w i l l continue
t o be i n v e s t i g a t e d i n c o l l a b o r a t i o n w i t h t h e motor v e h i c l e i n d u s t r y .
472
r.1
2. Reducing c a r u s e ( a u t o m o b i l i t y .
t h e second t r a c k )
F u t u r e l e v e l s of NOx and HC e m i t t e d b y t r a f f i c w i l l be determined by
i""l
t h e a v e r a g e v e h i c l e emission
factor
Fl
( m i s s i o n p e r v e h i c l e p e r km) and
t o t a l m i l e a g e by a l l v e h i c l e s ( f i g . 1 ) .
EMISSION
EM ISSIONS
YEAR
FACTOR (fig.1)
D i f f e r e n t emission r e d u c t i o n s c e n a r i o ' s are i n d i c a t e d i n t h e c o n t r i b u t i o n o f Van Beckhoven and Zwalve. The 2nd track-approach
i s r e l a t i v e l y new and w i l l b e developed and impleThe r a t i o n a l e behind i t i s t h a t t h e expected
mented i n t h e coming y e a r s .
h i g h growth of automobile u s e of 3 t o 5 p e r c e n t a y e a r w i l l i n e v i t a b l y consume a l a r g e p a r t of t h e emission r e d u c t i o n s r e s u l t i n g from t h e "clean" c a r program, t h u s f r u s t r a t i n g e n v i r o m e n t a l o b j e c t i v e s f o r N4,
and HC-emission
r e d u c t i o n s on both an ( i n t e r l n a t i o n a l and an urban s c a l e . Based upon a medium rate of economic growth and f u l l the this
(stricter) year
and
EC-standards next
mentioned
it
years),
t h e present acid-reduction
implementation of
(which s t i l l must be e s t a b l i s h e d
appears
now
that
in
the
year
2000
p o l i c y g o a l (33% r e d u c t i o n ) can be e a s i l y met.
I f t h i s g o a l i s t o be f i x e d at 50%- o r 75% o n l y t h e most s e v e r e damage
-
-
reduction l e v e l s t h a t prevent
t h e n a n o t h e r 50.000 or 125.000 t o n s of NO,-
r e d u c t i o n should be reached by road t r a f f i c . A f t e r t h e year 2000 t h e l a r g e r p a r t of N%-output
will be e m i t t e d by t r u c k s ,
due t o a h i g h e r growth of
road t r a n s p o r t and l i m i t e d t e c h n i c a l r e d u c t i o n p o t e n t i a l s . Continued high r a t e s of economic growth c r e a t e more t r a f f i c and may even worsen t h e outcome. The same may b e t r u e f o r HC,
a l t h o u g h a r e d u c t i o n of
50% i n 2000 i s expected t o be f e a s i b l e . It may b e deduced from t h e above t h a t t h e growth i n t h e volume of t r a f f i c i s an independant f a c t o r whose e f f e c t on t o t a l e m i s s i o n l e v e l s i n c r e a s e s in relation t o the failure
t o i n t r o d u c e s t r i c t e r emission s t a n d a r d s , or
t h e d e l a y involved i n i n t r o d u c i n g them. o f t h e growth i n
In t h e long term, t h e p r o p o r t i o n
Dutch t r a f f i c volume accounted f o r by f r e i g h t t r a f f i c
assumes an even more i m p o r t a n t r o l e . Thus, t h e growth f a c t o r r e i n f o r c e s t h e n e c e s s i t y t h a t t h e EC should do a l l i t can t o minimise t h e v e h i c l e
473
emission f a c t o r ,
t h e more because a l l EC manbers c o u n t r i e s expect high
growth rates u n t i l a t l e a s t 2010. The grid t r a c k b r i n g s about a fundamentally d i f f e r e n t approach from t h e "classical" even
for
However ,
approach i n both t r a f f i c and e n v i r o m e n t a l p o l i c y . reducing
traffic
a
jams
substantial
reduction
of
c a r use
is
thought t o be j u s t i f i e d and e f f e c t i v e . Thus both environmental and t r a f f i c p o l i c y g o a l s may be reached simultaneously by t h e sane i n s t r u m e n t ,
r e d u c t i o n o f car use.
Meanwhile,
it may
t u r n o u t v e r y soon t h a t t h e p r e s e n t a c i d r e d u c t i o n g o a l s w i l l be updated and t h a t
-
inter alia
- NO,-emissions
must be reduced by 75% or more. T h i s
will l e a d t o t h e need t o e x p l o i t t h e f i r s t t r a c k as r i g o u r o u s l y a s poss i b l e and, moreover, it may lead t o t h e need f o r not only r e d u c t i o n of t h e growth of motorized t r a f f i c b u t even a f r e e z e o f t r a f f i c volume as such (depending on t h e r e d u c t i o n l e v e l chosen). T h i s may b r i n g about t h e r e t u r n t o a t r a n s p o r t modal s p l i t as it was two or t h r e e decades ago, when p u b l i c t r a n s p o r t and t h e b i c y c l e had a c o n s i d e r a b l e s h a r e i n a l l forms o f personal mobility ( f i g . 2) Current t r e n d s i n c a r use a l l f a c e i n t o t h e wrong d i r e c t i o n . ownership and c a r u s e a r e growing, w i t h c a r ownership f a c t o r f o r t h e growth o f c a r use today t o about 7 use,
-
- which
Both c a r
is a strong
c o n t i n u i n g t o grow from about 5 m i l l i o n
m i l l i o n around 2010. Without any measures t o reduce c a r
t o t a l ( p a s s e n g e r c a r ) mileage may r i s e from 75 b i l l i o n km today t o
105 b i l l i o n km i n 2010.
Truck mileage shows even more growth from t o d a y ' s
11.5 b i l l i o n km t o 12.6 i n 2000 and 16.5 i n 20101 2.1. L i m i t s t o t h e r e d u c t i o n of c a r u s e
-
To what e x t e n t may c a r u s e be l i m i t e d mileage
- without
o r a t l e a s t t h e growth o f t o t a l
d i s t u r b i n g t h e economy o r s o c i e t y as a whole?
S e v e r a l s t u d i e s show t h a t a g r e a t d e a l of c a r u s e i s n o t " e s s e n t i a l " .
An
e s t i m a t e d 30% t o 40% o f a l l c a r mileage may be judged as having a reasona b l e s u b s t i t u t e i n p u b l i c t r a n s p o r t o r t h e b i c y c l e . Nearly h a l f of a l l c a r movements are performed w i t h i n r e a s o n a b l e c y c l i n g d i s t a n c e ( 5 km) o r even walking d i s t a n c e ( 2 km) ( t a b e l 1 and 2 ) .
From an NOx/HC-reduction
p o i n t of view both long d i s t a n c e d a i l y t r a v e l l i n g
and f r e q u e n t s h o r t c o l d s t a r t ting,
-
and
-
s t o p t r i p s by c a r (shopping, conmu-
s o c i a l and e d u c a t i o n a l v i s i t s ) should be s u b s t i t u t e d w i t h p r i o r i t y .
(tabel 3)
474
Although c a r u s e i n Holland
i s d e v e l o p i n g towards t h e same d i s a s t r o u s
l e v e l as it i s today i n t h e United S t a t e s or most European c a p i t a l s , t h e N e t h e r l a n d s i s provided w i t h t h e most e f f e c t i v e and e c o l o g i c a l answer t o t h e needs f o r e v e r y d a y ' s m o b i l i t y :
12 m i l l i o n b i c y c l e s . Moreover p u b l i c
t r a n s p o r t i s r e l a t i v e l y well developed and t h e Dutch r a i l w a y s a r e t h e b e s t run i n Europe i n t e r n s of p r o d u c t i v i t y . On t h e o t h e r hand,
a g r e a t many
f a c t o r s s t r u c t u r a l l y favour c a r u s e : t h e autonomous growth i n c a r owning/ d r i v i n g age-groups,
t h e psycho-social b e n e f i t s of c a r o w n e r s h i p , t h e physi-
c a l s t r u c t u r i n g of housing and employment l o c a t i o n s , growing j o b m o b i l i t y , r i s i n g j o b p a r t i c i p a t i o n f o r m a r r i e d women, and
-
last but not
least
-
f i s c a l and o t h e r i n c e n t i v e s ,
t h e i n h e r e n t a d v a n t a g e of c a r s i n terms of
s p e e d , p r i v a c y and freedom. Moreover t h e Dutch and t h e i r p o l i t i c a l repres e n t a t i v e s show a s t r o n g a v e r s i o n t o governmental i n t e r f e r e n c e i n behaviour
,
private
e s p e c i a l l y when such measures are u n c o n v e n t i o n a l or burdensome
or b o t h .
2 . 2 . Which measures could l i m i t c a r use?
Given t h e importance of t h e c a r i n modern s o c i e t y , s u b s t a n t i a l l i m i t a t i o n s on i t s i n c r e a s e d u s e w i l l r e q u i r e fundamental measures. The key t o a c h i e v i n g such an aim l i e s i n t h e f a c t t h a t t h e r e i s c o n s i d e r a b l e scope f o r g r e a t e r u s e o f p u b l i c t r a n s p o r t and of b i c y c l e s i n c o w u t e r t r a f f i c and i n o t h e r non-business
t r a f f i c . E x p l o i t i n g t h i s scope w i l l r e q u i r e measures
d e s i g n e d t o i n f l u e n c e p e o p l e ' s c h o i c e of mode of t r a n s p o r t . L i m i t a t i o n of t h e growth i n c a r t r a f f i c a l s o f e a t u r e s i n t h e p o l i c y d e s i g ned t o s o l v e t h e problem of t h e poor a c c e s s i b i l i t y t o towns i n t h e Rands t a d . T h i s p o l i c y i s c o n t a i n e d i n t h e Randstad A c c e s s i b i l i t y P l a n , which c o n t a i n s a wide r a n g i n g package of measures aimed a t o p t i m i s i n g and extend i n g t h e i n f r a s t r u c t u r e and p u b l i c t r a n s p o r t s e r v i c e s and l i m i t i n g t h e u s e of c a r s .
S t u d i e s performed under
p o l i t i c a l circumstances d i r e c t and major
-
t h i s Plan reveal t h a t
-
under c u r r e n t
t h e r e are no s i m p l e measures which would have
e f f e c t s on t h e growth
of
traffic.
Only a
package of
measures which complement each o t h e r can have any s i g n i f i c a n t e f f e c t . An a n a l y s i s of p r a c t i c a l l y a l l " c o n v e n t i o n a l " o p t i o n s has r e v e a l e d t h a t t h e most e f f e c t i v e package w i l l have t o i n c l u d e t h e f o l l o w i n g e l e m e n t s :
*
an i n c r e a s e i n v a r i a b l e d r i v i n g c o s t s ,
p o s s i b l y i n combination w i t h a
reduction i n fixed costs;
*
reduced p a r k i n g f a c i l i t i e s f o r comnuter t r a f f i c ;
475
* * *
i n c r e a s e d a t t r a c t i v e n e s s of p u b l i c t r a n s p o r t ; optimum u s e of t h e o p p o r t u n i t i e s o f f e r e d by p h y s i c a l p l a n n i n g ; measures with regard t o t h e e x i s t i n g system o f t a x a l l o w a n c e s and o t h e r f i n a n c i a 1 , a d v a n t a g e s f o r c o w u t e r s and f o r t h e u s e of c a r s f o r b u s i n e s s
None of t h e s e o p t i o n s can b e r e a l i s e d o v e r n i g h t ; some o f them w i l l r e q u i r e amendments t o l e g i s l a t i o n , w h i l e t h e p r e c i s e advantages and d i s a d v a n t a g e s of o t h e r s s t i l l need t o be s t u d i e d c a r e f u l l y , which means t h a t t h e y cannot be i n t r o d u c e d f o r some t i m e y e t . A s i s a l r e a d y known, any a t t e m p t t o s h i f t t h e burden of t h e c o s t of r u n n i n g
a c a r from f i x e d t o v a r i a b l e c o s t s ( f o r example, b y imposing h i g h e r d u t i e s of l e v i e s o n . f u e 1 while r e d u c i n g road t a x e s ) , meets w i t h c o n s i d e r a b l e opp o s i t i o n p a r t l y on account of t h e e f f e c t which such measures would have i n border a r e a s . Another, more e f f e c t i v e i n s t r u m e n t i s 'road p r i c i n g " ,
possi-
b l y i n combination with a r e d u c t i o n i n f i x e d c o s t s . I f t h i s i n s t r u m e n t were used more widely and i n t e n s i v e l y than d e c i d e d i n t h e Randstad A c c e s s i b i l i t y
Plan, a f u r t h e r r e d u c t i o n of t h e growth i n t r a f f i c volume i s t o b e expecte d . More r e c e n t l y t h e Gorvernment d e c i d e d t h a t a r o a d - p r i c i n g system i s t o be made o p e r a t i o n a l a s soon a s p o s s i b l e . I t i s expected t h a t a s y s t e m w i l l be ready €or u s e w i t h i n 4 y e a r s ,
t o be implemented on a l a r g e s c a l e by
1996. R e s t r i c t i o n s on f r e e parking i n c o n u r b a t i o n s would have a m a j o r imp a c t on l e v e l s of commuter t r a f f i c . In a d d i t i o n t o improved enforcement of t h i s i n s t r u m e n t , a c o h e s i v e p a r k i n g p o l i c y a t c o n u r b a t i o n l e v e l i s necessary. Wherever p u b l i c t r a n s p o r t p r o v i d e s a r e a s o n a b l e a l t e r n a t i v e t o c a r s ( e s p e c i a l l y i n and around urban a r e a s ) i t should be o f s u f f i c i e n t c a p a c i t y t o a t t r a c t t t a v e l l e r s who a t p r e s e n t u s e t h e i r c a r and t h u s have a c h o i c e . P u b l i c t r a n s p o r t a l s o h a s t o b e made s u f f i c i e n t l y a t t r a c t i v e t o win new customers and t o r e t a i n i t s e x i s t i n g ones. The key t o making p u b l i c t r a n s p o r t more a t t r a c t i v e t o t r a v e l l e r s l i e s i n improvements t o t h e i n f r a s t r u c t u r e and t h e q u a l i t y of t h e s e r v i c e s provided r a t h e r t h a n i n p r i c i n g p o l i c y . The e x t e n t of t h e p u b l i c t r a n s p o r t network, t h e speed o f t r a n s p o r t ,
and t h e p o s s i b i l i t i e s
for u s i n g o t h e r forms of
t r a n s p o r t t o connect w i t h t h e p u b l i c s e r v i c e s ( t h e b i c y c l e ) are o f c r u c i a l importance. P h y s i c a l p l a n n i n g h a s a r o l e t o p l a y through t h e concept o f t h e "compact c i t y " , whereby more i n t e n s i v e u s e i s made of u r b a n s p a c e through concentrat i o n and urban renewal. T h i s p o l i c y i s designed t o b r i n g t h e p l a c e s where
476 people l i v e and work c l o s e r t o g e t h e r i n t h e l o n g term, a t l e a s t i n urban areas.
Building near public t r a n s p o r t
f a c i l i t i e s a l s o h a s an
important
c o n t r i b u t i o n t o make i n l i m i t i n g t h e growth of c a r t r a f f i c and s t i m u l a t i n g t h e u s e of p u b l i c t r a n s p o r t . Very r e c e n t l y and f o r b u d g e t a r y r e a s o n s , a f i r s t s t e p was set t o r e d u c e f i s c a l i n c e n t i v e s f o r c a r u s e i n comnuting and f o r b u s i n e s s purposes. F u r t h e r measures a r e b e i n g worked o u t . A package of measures such as t h e one d e s c r i b e d above c o u l d r e d u c e t h e u s e
o f c a r s by approximately 25% compared w i t h t h e l e v e l s f o r e c a s t i f p o l i c y remains unchanged. The s i z e of t h e e m i s s i o n r e d u c t i o n t a r g e t s , t h e e x t e n t t o which e m i s s i o n s can b e reduced by t h e t e c h n i c a l measures r e f e r r e d t o above, and t h e volume of e m i s s i o n s from t r u c k s w i l l d e t e r m i n e t h e t a r g e t l e v e l f o r t h e r e d u c t i o n of t h e u s e of p r i v a t e c a r s . These measures
will
be
further
e l a b o r a t e d ( S e p t . / O c t .1988)
within
the
framework o f t h e S t r u c t u r e Scheme f o r T r a f f i c and T r a n s p o r t and t h e Naticn a l Environmental P o l i c y P l a n . However, it s t i l l remains u n c e r t a i n :
1) i f t h e r e w i l l b e enough p o l i c i t a l s u p p o r t for t h e unpopular measures t h a t e f f e c t i v e l y r a i s e t h e c o s t s of c a r u s e and r e d u c e a u t o m o b i l i t y ; 2) i f
such measures r e a l l y
provoke
t h e mass b e h a v i o u r r e s p o n s e amongst
motorists a s necessary;
3 ) i f we can s t a y away i n t h e long run from more d i c t a t o r i a l ways of inf l u e n c i n g p e o p l e ' s c h o i c e of t r a n s p o r t mode;
4 ) i f we can g e t g r i p s on t h e growth r a t e of t r u c k - m i l e a g e t h r o u g h i n f l u e n c i n g t h e f r e i g h t t r a n s p o r t modal s p l i t
-
w i t h o u t e m b a r r a s s i n g t h e Dutch
p o s i t i o n i n i n t e r n a t i o n a l t r a n s p o r t and d i s t r i b u t i o n .
3. Urban t r a f f i c measures ( t h i r d t r a c k ) A i r q u a l i t y s t a n d a r d s a r e most f r e q u e n t l y exceeded i n town c e n t e r s and n e i g h b o u r i n g areas, and a l o n g busy r o a d s with c o n t i n u o u s h i g h - r i s e
buil-
d i n g s . Recent r e s e a r c h i n t o t h i s s u b j e c t h a s r e v e a l e d about 1,000 highemission l o c a t i o n s , s e v e r a l dozen of which r e q u i r e i m n e d i a t e a c t i o n , i n c l u d i n g c o n s i d e r a b l e r e d u c t i o n s i n c o n c e n t r a t i o n s o f CO, NO2 and C,Hy.
477 For COY Pb and NO2 ambient a i r q u a l i t y s t a n d a r d s are set i n 1987. Excessive l e v e l s of a i r p o l l u t i o n and n o i s e n u i s a n c e cannot e n t i r e l y be e l i m i n a t e d by tougher m i s s i o n s t a n d a r d s a l o n e . I n a d d i t i o n t o t h e abovementioned g e n e r a l measures designed t o reduce t h e u s e of c a r s t h e followi n g measures would h e l p t o a l l e v i a t e t h e problems:
*
a p h y s i c a l planning p o l i c y a t t h e l o c a l l e v e l designed t o promote t h e " c e n t e r function" of c i t i e s and t o i n c r e a s e t h e a t t r a c t i v e n e s s of p u b l i c transport
* *
s t r i c t e r enforcement of parking p o l i c y ; t r a f f i c e n g i n e e r i n g , e s p e c i a l l y e x e r t i n g i n f l u e n c e on d r i v e r s ' c h o i c e of routes;
* *
route signs for freight through-traffic; t r a f f i c dosaging on approach roads t o c i t y c e n t e r s ;
*
p u b l i c i t y designed t o i n f l u e n c e p e o p l e ' s d r i v i n g h a b i t s ;
*
i n t r o d u c t i o n of low speed zones.
This approach combines environmental p r o t e c t i o n w i t h road s a f e t y . The implementation of t h e p o l i c y o u t l i n e d above w i l l i n t h e f i r s t i n s t a n c e be t h e r e s p o n s a b i l i t y of
the municipalities,
a l t h o u g h sane elements of
the
p o l i c y a r e more w i t h i n t h e realm of c e n t r a l government. The f o l l o w i n g asp e c t s are important:
-
The newly amended Road T r a f f i c Act w i l l make it l e g a l l y p o s s i b l e t o implement t r a f f i c measures s o l e l y o r p a r t l y on environmental grounds.
- Central
government g r a n t s f o r municipal i n f r a s t r u c t u r e w i t h i n t h e frame-
work of t h e v a r i o u s schemes w i l l be c o o r d i n a t e d as f a r as p o s s i b l e ; red u c t i o n s i n t h e environmental e f f e c t s of
traffic,
f o r example on t h e
b a s i s on environmental t r a f f i c maps, w i l l b e g i v e n a h i g h p r i o r i t y .
- Where
improvements t o road i n f r a s t r u c t u r e a r e made p r i m a r i l y as a means
of combating n o i s e nuisance and a i r p o l l u t i o n ,
t h e M i n i s t r y o f Housing,
P h y s i c a l Planning and Environment may make a g r a n t t o t h e m u n i c i p a l i t i e s under t h e T r a f f i c Noise Scheme ( b u d g e t s f o r t h e s e g r a n t s have been inc r e a s e d from HF1. 10 m i l l i o n t o HF1. 15 m i l l i o n per annum f o r t h e y e a r s 1987-1992).
-A
scheme i s i n s t i t u t e d t o promote t h e drawing o f "environmental
traffic
maps" which enable t h e m u n i c i p a l i t i e s t o p l a n measures t o improve t h e l i v i n g and working environment. every y e a r .
HFl. 4 m i l l i o n i s s p e n t on t h e scheme
478 tabel 1 MODAL S P L I T THE HAGUE I N % ( 1 9 8 4 )
DESTINATION
0 = PARKING VOLUME L I M I T S tabel 2 CAR USING EMPLOYEES (THE HAGUE 1 9 8 4 ) IN % ESSENTIAL FREE CHOICE
~ C F I N G
FREE CHOICE
CITY
OUTER CITY
PERIPHERY
17
20
23
8
25
32
1 PUBLIC CAR
T
51
TRANSP.
19
II
tabel 3 AVERAGE DAILY EMISSIONS 1 9 8 3 CAR < 1400 CC I N COMMUTING / SHOPPING DISTANCE
FUEL CONS.
(2x1 3 KM
(2X) 6 KM
180 gram
250 gram
40 gram
60 gram
14 gram
25 gram
0,7 L
l,o L
I 23-1
BICYCLE
I'
I
1 13A
IllOdSNWI nrlgnd
UW3
'
,
I I
I
001
wn
N-IQ
- 021
This Page Intentionally Left Blank
SESSION VII Chairmen
MECHANISMS OF HEALTH EFFECTS L. van Bree
D.Horstman
This Page Intentionally Left Blank
T.Schneideret al. (Editors),Atmospheric Ozone Research and its Policy Implications 0 1989 Elsevier Science Publishers B.V.,Amsterdam -Printed in The Netherlands
PERSISTENCE OF OZONE-INDUCED RESPONSIVENESS
CHANGES
IN
LUNG
FUNCTION
483
AND
AIRWAY
.
L. J FOLINSBEE~and M.J. HAZUCHA2 'Environmental Monitoring Services, Inc., Dr. 1200, Chapel Hill, NC, 27514 (USA)
C-E
Environmental,
'Center for Environmental Medicine and Lung Biology, Carolina, Chapel Hill, NC, 27599-7310 (USA)
800 Eastowne
University
of
North
ABSTRACT Functional recovery from acute ozone exposures in man proceeds rapidly but is not complete within 24 hours. Previous studies have shown that the mean deficit in FVC may be as large as 4-5% after 12 H but only of the order of 1-3% after 24 H . In the studies where spirometry changes persisted, the immediate post-exposure decreases in PVC or FEVl were of the order of 15% or greater. Furthermore, repeated ozone exposure studies indicate that a second ozone exposure within 24-48 hours produces a (30-50%) larger functional decrement than the initial exposure. It has also been shown that ozone exposure causes causes a short-lasting increase in airway responsiveness and an airway inflammatory response which persists for at least 16 H. To examine whether the persistent pulmonary function effects could be related to increase airway responsiveness we exposed 18 healthy young women to 0.35 ppm ozone and followed the time course of the change in pulmonary function and airway responsiveness over the next 42 hours. During the 70 min exposures, the subjects exercised for two 30 min periods with ventilation of approximately 40 Llmin. We determined the dose of methacholine aerosol which produced a 100% increase in the baseline SRaw (PD100) within 2 H, and at 18 H and 42 H post-exposure. Immediately post-exposure, forced expiratory tests showed a marked decrease in function (FVC, -14%; FEV1, -22%; PEF25-75%, -32%; and MW, -17%) At 18 H post-exposure, FVC and FEVl were still 3% and 4% below pre-exposure baseline. Airway responsiveness was increased after ozone exposure in 14 of 18 subjects; the mean PDlOO decreased from 59 cumulative inhalation units (CIU) after air exposure to 41 CIU after ozone (P<0.05). 18 H after ozone exposure, the mean PDlOO continued to be lower than after air exposures (45 CIU) but there was considerable intersubject variability. Airway responsiveness to methacholine is increased immediately after ozone exposure, but i t is unclear whether this effect persists for 18 H.
INTRODUCTION Ozone inhalation causes a variety of functional and morphologic alterations in both the airways and gas exchange regions including decrements in spirometry , increased airway resistance, hyperresponsiveness to certain pharmacologic stimuli, altered mucus secretion and transport, increased airway permeability, as well as damage to cells throughout the respiratory tract. The time course of change in spirometry following ozone exposure, although not extensively documented, is better known than the time course of other
484
ozone-induced effects, such as changes in airway responsiveness or clearance. Recovery of spirometric functional decrements begins shortly after exposure and, although i t proceeds rapidly, some functional deficit may persist for up to 24 hours. Folinsbee et a1 (ref 1) studied three groups of subjects exposed to 0.50 ppm (KI), while performing either mild, moderate, or heavy exercise. They noted that, during the post-exposure recovery period, a substantial of the decrement in lung function was recovered within 2 H portion post-exposure (Table 1). The percentage of recovery of the spirometric changes varied considerably between subject groups but ranged from approximately 40% to 65% of the acute decrement. Bates and Bazucha (ref 2) had previously reported data on the recovery of decrements in spirometry following exposure to 0.75 ppm ozone in 10 nonsmokers. They observed an approximate 20% acute decline in both FVC and FEVl which had decreased to approximately 8-9% after 2 H of recovery. A similar rapid initial recovery was observed by Avo1 et a1 (ref 3). These investigators reported that the decrement in FEVl after one hour of recovery was only about 50% of the FEVl decrement seen immediately after exposure. Figure 1 illustrates the recovery time course for subjects exposed to 0.75 ppm ozone (KI) for two hours with intermittent exercise (Silverman and Folinsbee, unpublished observations). These data are illustrative of the longer duration of recovery in subjects with pronounced decrements in lung function. Even after five hours, one of the more reactive subjects was still experiencing an obviously reduced FVC. The recovery began immediately after exposure and was complete within 30 minutes in the least reactive subject. The magnitude of functional effects which persist for 24 hours is generally quite small, i f any effects are indeed present. It has been observed, in two studies, (ref 4,5) that a small residual deficit in lung function was present
TABLE 1 Percentage changes in FVC and FEVl immediately and two hours exposure to 0.50 ppm ozone in 3 groups of exercising subjects. Time of Heasurement FVC Post FVC Post+LH FEVl Post FEVl Post+2H
Exercise ventilation during ozone exposure 30 L h i n 49 L/min 67 L/min -7.9 -6.0
-9.9 -2.7
-17.0 -7.5
-12.7 -8.2
-14.2 -6.6
-23.8 -9.2
From Folinsbee et a1 (ref. 1)
following
435 at both 12 and 24 hours after ozone exposure. Twelve hours after a 1 R exposure to 0.25 ppm ozone while performing continuous heavy exercise, the FVC and FEV1.O were still 4.3% and 4.0%, respectively, below the initial pre-exposure baseline. corresponding differences 24 hours after exposure, in another subject group, were 2.4% and 1.6%. The latter differences did not attain statistical significance. Although the initial functional recovery is rapid, the recovery was not complete within 24 hours. In some studies of repeated ozone exposure, there was a trend for a decline in baseline performance on forced expired spirometry (50 to 200 ml) (ref 6,7). A similar small decline in baseline FVC, seen by Farrel et a1 (ref 8) in subjects exposed to air for five consecutive days, suggests that there may be some small decrement in spirometry which may be associated with repeated testing, possibly due to inadequate effort. The extent to which this factor contributes to the decline in baseline FVC in some repeated exposure studies is unclear. The observations from these several studies suggest, collectively, that, within the first two hours after ozone exposure, approximately 50% of the decrement in function is recovered, but the total recovery of spirometric function may require as much as 24 hours and possibly longer. In studies of repeated ozone exposure, a particularly consistent finding is that the pulmonary function (FVC, FEV1) response to ozone is much greater This after the second ozone exposure than after the first (ref 5,7,9,10,11). observation suggests that the effects of ozone on spirometry are potentiated for at least 24 hours and possibly as long as 48 hours after an initial exposure. The time course of the potentiation of spirometric response has been the subject of two studies. Folinsbee and Horvath (ref 5) found that the increased pulmonary function response was similar at both 12 H and 24 H following exposure; the FEVl response increased by 50% and 72%, relative to the first exposure, respectively. Corresponding changes in FVC are shown in Figure 2. Bedi and coworkers (ref 12) observed a marked accentuation (the AFEV1 was 71% larger) of the acute response to moderate exercise in 0.45 ppm ozone at 48 hours following the initial exposure. The initial ozone-induced changes in FEVl were of the same order observed in the Folinsbee and Horvath (ref 5) study although the latter investigators found a much smaller (19%) increase in response at 48 H. Not only was the ultimate response increased, but Folinsbee and Horvath (ref 5) also reported that the changes in symptoms began earlier with the second exposure. Similarly, Polinsbee et al's (ref 9) and Bedi et al's (ref 12) data suggest a more rapid decrease in function on the second exposure. Changes in airway responsiveness consequent to ozone exposure have also been followed for in excess of 24 hours. There are several difficulties in following temporal changes in airway responsiveness which include the rather large variability in the measurement of pharmacologically induced changes in
406
u
> LL
5
10
0
w -10 m
g -20 0
X -30 % W
-40
0
8 -50 a
-60
TIME (MINI Fig. 1. Percentage decrease in Forced Vital Capacity for four subjects exposed to 0.75 ppm ozone for 2 H with mild intermittent exercise (shaded area). Measurements continued during recovery for 2 H and for 5 H in one subject. (Silverman and Folinsbee, unpublished results)
EXP C 1 EXP #2 INTERVAL BETWEEN EXPOSURES Fig. 2. Mean percentage decrease in Forced Vital Capacity for 4 groups of subjects exposed twice to either 0.25 ppm ozone for 1 H with continuous heavy exercise or to 0.45 ppm ozone(*) for 2 H with moderate intermittent exercise. The interval between the two exposures is indicated on the abscissa. Data from Folinsbee and Horvath (ref 5) and Bedi et a1 (ref 12)*.
487
specific airway resistance (ref 13) and the possibility of interaction between tests repeated at short intervals. Holtzman et a1 (ref 14) showed that airway responsiveness to both histamine and methacholine was increased after exposure to ozone (2 H with light intermittent exercise to 0.60 ppm-KI). One day following the exposures, airway responsiveness to both substances had returned to baseline levels. Kulle et a1 (ref 15) measured airway responsiveness with repeated exposure to ozone. They found an increase in responsiveness after the initial exposure but, with subsequent daily exposures, the acute increase in airway responsiveness gradually lessened. More recent evidence (ref 16) indicates that airway responsiveness may be increased at much lower ozone concentrations with exposures of longer duration. The time course of changes in mucociliary clearance and airway permeability, consequent to ozone exposure, have not been studied sufficiently in man. However, i t is evident that the time course of the recovery from various ozone-induced alterations in lung function is likely to be different for each mechanism and that the time course will vary according to the extent of acute lung injury. We have recently investigated the time course of the response to ozone in a group of 19 young adult females exposed once to 0.35 ppm ozone for 65 minutes. We then followed their responses for up to 42 hours. METHODS Subjects A total of 28 young adult females were recruited for this study, of whom 19 completed the series of exposures and followup tests. A summary of their anthropomorphic characteristics is presented in Table 2. Four of the subjects had mild positive responses to epicutaneous allergy tests. All subjects participated in a training procedure to thoroughly familiarize them with all the required test procedures. Subsequent to training, the subjects were screened to determine whether they were sensitive to ozone. For screening, subjects were exposed to 0.35 ppm ozone for a total of 45 min during which
TABLE 2 Physical Data and Lung Function Characteristics of Female Subjects (N-19) Age Yrs
Height cm
Weight kg
FVC ml
FEVl ml
FEVlX
MEAN
22+2.7
167+6
60.3i7.0
3991+511
3310+458
83+7
RANGE
19-28
152-179
46-71
2850-4812
2538-4261
70-94
488
they walked on a treadmill for two 20 minute periods. Changes in forced expired spirometry were used to determine whether the subjects responded to ozone. For the studies of the time course of the response, we used only those subjects who were "sensitive," since there was no reason to follow subjects who showed minimal or no response to ozone. Subjects were included if they demonstrated at least a 5% decrement in one or more measures of spirometry or else demonstrated marked symptoms such as cough and pain on deep inspiration. Experimental Design and Protocol Each subject was exposed twice, in random order, once each to filtered air and 0.35 ppm ozone. Follow-up tests were performed after each exposure at 18 and 42 hours. Prior to each exposure, a series of lung function tests including forced expiratory tests and plethysmographic measures of specific airway resistance were performed. The subject then entered the chamber and began walking on a treadmill for 30 min at a speed and grade sufficient to evoke a ventilation of approximately 10 U m i n per liter of vital capacity with a maximum of 45 l/min and a minimum of 35 l/min. Two forced expiratory maneuvers were performed in the 5 min period following the first exercise period. The subject then walked for another 30 min after which the series of lung function tests were repeated. After leaving the exposure chamber the subject was administered a methacholine inhalation challenge. At least one hour elapsed between the completion of the exercise in ozone and the methacholine challenge. The subject subsequently returned to the laboratory in the morning of the next two days (i.e., 18 H and 42 H postexposure) for lung function tests and a methacholine challenge. We had initially planned to study airway responsiveness more frequently but were not satisfied that this could be done at short intervals without some interference between tests. Measurements Spirometry was performed on a 12 L dry rolling seal spirometer interfaced to a minicomputer. Ventilation was determined with a pneumotachograph using software integration of flow signals. Airway resistance was measured in a constant volume body plethysmograph using standard methods (see ref 16). The methacholine challenge procedures are similar to those reported previously from this laboratory (ref 13,16). A custom-designed apparatus (ref 17) was used to administer a methacholine aerosol generated by an ultrasonic nebulizer. Volume of inspired methacholine aerosol and breathhold time were interactively controlled and measured. From a graph of cumulative methacholine dose versus specific airway resistance, we estimated the dose which would have caused a doubling of the baseline specific airway resistance. We used linear extrapolation between the doses immediately above and below the SRaw doubling point to estimate the doubling dose (PD100).
483
RESULTS AND DISCUSSION Screening Exposures The effects of the screening.exposure on forced expiratory spirometry are shown in Table 3. There was an average 10% decrease in FVC and 16% decline in FEV1. Other forced expiratory parameters also indicated marked decreases in function: -19.7%, peak flow; -24.51, FEF25-75%; -20.6%, FEP75.
TABLE 3.
Pulmonary function responses before and after exposure to
0.35 ppm ozone for 45 min with heavv exercise.
FVC
FEVl
PEAK FLOW
FEF25-75
PEP75
PRE-MEAN *S.D.
4.00 iO.52
3.30 iO.42
7.47 i1.11
2.12 iO.59
1.79 k0.69
POST-MEAN iS.D.
3.60 iO.56
2.76 iO.53
6.00 i1.37
1.60 i0.58
1.42 i0.58
The ozone sensitive subjects who participated in the main study experienced marked decreases in expired spirometry. The mean percentage decreases in forced expiratory parameters (relative to pre-exposure baseline levels) ranged from a 14% decline in FVC to a 32% drop in FEF25-75%. Gibbons and Adams (ref 18) and Lauritzen and Adams (ref 19) have studied the responses of female subjects under similar conditions. Gibbons and Adams reported that, for female subjects who were exposed to 0.30 ppm for 60 min while breathing approximately 50 l/min, FVC decreased 14% and FEVl decreased 16.5%. Lauritzen and Adams (ref 19) also studied female subjects exposed to 0.3 and 0.4 ppm ozone for 60 min while breathing 35 l/min. They reported FVC and FEVl declines of 8.3% and 12.6% at 0.3 ppm and 13.9% respectively. Thus, the present results are in accord female subjects studied under similar conditions. At the first followup measurement, 18 hours after the expiratory measurements remained below baseline by an
and 17.1% at 0.4 ppm with other studies of exposure, the forced average of about 4-5%
with the largest residual deficit in function being an 7% decrease in FEF25-75%. In contrast, 42 hours after the clean air exposure, all forced inspiratory parameters were within *3% of the preexposure baseline. There were no significant differences from baseline function by 42 hours after the exposure. These data are presented in Table 4.
430
TABLE 4. Percentage changes in expired spirometry immediately following 65 min exposure to 0.35 ppm ozone. FEVC
FEVl
FEF25-75%
-14
-21
-31
-24
Post-18
-2
-4
-7
-5
Post-42
-1
-2
-3
-3
Post
*
and
18 and
42 hours
FEFmax
*Percentage changes relative to the pre-exposure baseline.
Ventilation during exposure was determined near the end of each exercise period. The subjects' ventilation averaged 40.3k6.9 L/min which translates to a lung-volume specific ventilation of 10 L/min/L-FVC. This ventilation is comparable to about 50 L/min for male subjects. The subject's heart rates during exposure averaged 142 beatshin which is estimated to be approximately 58% of maximum aerobic power. Differences in breathing pattern between the ozone and air exposures are shown in Table 5. Of 18 subjects, 11 had increased respiratory frequency and decreased tidal volume, 4 had no change, and in 3 the ventilations were too dissimilar for a meaningful comparison. Airway responsiveness was measured approximately 1 hr postexposure and again at 18 H and 42 H postexposure. There was a significant reduction, after the ozone exposure, in the methacholine dose required to double SRaw. Ten of the 18 subjects showed an obvious decrease in PDlOO 1-2 H after ozone exposure
TABLE 5. Ventilation, breathing frequency, tidal volume, and heart rate during exercise in subjects exposed to 0.35 ppm ozone for 65 min. (n-15) AIR EXPOSURE 1ST EXER 2ND EXER Ven ilation (L/min)
OZONE EXPOSURE 1ST EXER 2ND EXER
39.8
38.3
40.7
40.7
. Freq.
29.3
29.4
31.7
34.0
Tidal Volume (L)
1.4
1.4
1.3
1.2
141.0
147.6
143.8
141.7
Res
Heart Rate
431
100
80
c
4A I R
-+-OZONE
T
-
I
I
60 40
I
I
I
I
2oL 0 10 20 30 40 TIME AFTER OZONE EXPOSURE (H) Fig. 3. Dose of methacholine aerosol required to cause a 100% increase (PD100) in SRaw. The time after the completion of exposure to either clean air or 0.35 ppm ozone with heavy, nearly-continuous exercise is indicated on the abscissa. Values are means*S.E. (n-18)
but only 5 subjects clearly had increased methacholine responsiveness 18 H after the exposure. The mean trends are indicated in figure 3. There was a trend, both in spirometry and airway responsiveness, for the effect of ozone to persist beyond the immediate post-exposure period. It has been observed (Koren et al, this volume) that an airway inflammatory response persists for as long as 16 hours after exposure. The persistence of very small decrements in expired spirometry is consistent with previous Baseline bronchial reactivity is not predictive of observations (ref 5-7). the magnitude of ozone-induced increase in responsiveness to methacholine or histamine (ref 14,16) or spirometry. Furthermore, previous studies have not reported concordance, within subjects, of spirornetric changes and increased responsiveness to methacholine (ref 16). Although the evidence is not reported here, there was no suggestion of such an association in the present study, either acutely or in the followup studies.
ACKNOWLEDGMENTS The writers appreciate the technical assistance of B. Faucette and P. Ives, the staff of the Clinical Research Branch of the U.S.E.P.A., and the staff of Environmental Monitoring and Services, Inc. The research was performed in the Clinical Environmental Laboratory, Clinical Research Branch, Inhalation
492
Toxicology Division, Health Effects Research Laboratory of the U. S. Environmental Protection Agency. The work was supported in part by Cooperative Agreement 807392-03 to the University of North Carolina.at Chapel Hill. This paper has not been subjected to the Agency’s peer and policy review and therefore does not necessarily reflect the views of the Agency and no official endorsement should be inferred.
REFERENCES 1 2
3 4 5 6
7 8 9 10 11
12 13 14 15 16 17 18 19
L.J. Folinsbee, B.L. Drinkwater, J.F. Bedi and S.M. Horvath, in L.J. Folinsbee et a1 (eds), Environmental Stress: Individual Human Adaptations, Academic Press, New York, 1978. D.V. Bates and M.J. Hazucha, Proc. Conf. on Health Effects of Air Pollutants, NAS/NRC, U . S . Government Printing Office X5270-02105, (1973) pp. 507-540. E.L. Avol, W.S. Linn, T.G. Venet, D.A. Shamoo and J.D. Hackney, JAPCA, 34 (1984) 804-809. S.M. Horvath, J.A. Gliner and L . J . Folinsbee, Am. Rev. Respir. Dis., 123 (1981) 496-499. L.J. Folinsbee and S.M. Horvath, Aviat. Space Environ. Med., 57 (1986) 1136-1143. L.J. Folinsbee, J.F. Bedi, J.A. Gliner and S.M. Horvath, in, S.D. Lee, M.G. Mustafa and M.A. Mehlman, (eds), The Biomedical Effects of Ozone and Related Photochemical Oxidants, Princeton Scientific, Princeton Junction NJ, 1983, pp. 175-187. E.D. Haak, M.J. Hazucha, R.W. Stacy, B.T. Ketcham, E. Seal, L.J. Roger and J.R. Knelson, U.S.E.P.A. Report # EPA-600/X-84-033, 1984. B.P. Farrel, H.D. Kerr, T.J. Kulle, L.R. Sauder and J.L. Young, Am. Rev. Respir. Dis., 119 (1979) 725-730. L.J. Folinsbee, S.M. Horvath and J.F. Bedi, Am. Rev. Respir. Dis., 121 (1980) 431-439. J.D. Hackney, W.S. Linn, J.G. Mohler and C.R. Collier, J. Appl. Physiol., 43 (1977) 82-85. W.S: Linn, D.A. Medway, U.T. Anzar, L.M. Valencia, C.E. Spier, F.S. Tsao, D.A. Fischer and J.D. Hackney, Am. Rev. Respir. Dis., 125 (1982) 491-495. J.F. Bedi, D.M. Drechsler-Parks and S.M. Horvath, Am. Ind. Hyg. Assoc. J., 46 (1985) 731-734. M.J. Hazucha, J.F. Ginsberg, W. F. McDonnell, E. D. Haak, R.L. Pimmel, S.A. Salaam, D.E. House, and P.A. Bromberg. J. Appl. Physiol. 54 (1983) 730-739. M.J. Holtzman, J.H. Cunningham, J.R. Sheller, G.B. Irsigler, J.A. Nadel and H.A. Boushey, Am. Rev. Respir. Dis. 120 (1979) 1059-1067. T.J. Kulle, H.D. Kerr, B.P. Farrell, L.R. Sauder and M.S. Bermel, Am. Rev. Respir. Dis., 126 (1982) 996-1000. L.J. Folinsbee, W.F. McDonnell and D.H. Horstman, JAPCA, 38 (1988) 28-35. A.A. Strong, M.J. Hazucha, D.A. Lundgren, and E.R. Cerini, Med. Instrument., 21 (1987) 189-194. S . I . Gibbons and W.C. Adams, J. Appl. Physiol., 57 (1984) 450-456. S.K. Lauritzen and W.C. Adams, J. Appl. Physiol., 59 (1985) 1601-1606.
T. Schneider et al. (Editors),Atmospheric Ozone Research and its Policy Implications 0 1989 Elsevier Science Publishers B.V.. Amsterdam-Printed in The Netherlands
493
OZONE-INDUCED LUNG FUNCTION CHAWGES IN NORMAL AND ASTHMATIC SUBJECTS AND THE EFFECT OF INDOMETHACIN
W.L. ESCHENBACHER~,R.L. Y I N G ~ ,J.W. KREIT~, K.B.
GROSS^
'pulmonary and Critical Care Medicine , University of Michigan Medical School, Ann Arbor, MI, 48109-0026, USA 'Biomedical Science Department, General Motors Research Laboratories, Warren, MI, 48090, USA ABSTRACT We performed a two-part study to determine 1) the effect of 0.4 ppm of ozone on subjects with already increased airways responsiveness (asthmatics), and 2) whether indomethacin could alter the pulmonary effects of ozone in normal subjects. After 2 hours of ozone exposure, both the normal and asthmatic subjects had significant, reversible falls in lung function (FEV1, FVC, FEV %, IC) with greater decreases in FEVl and FEV1% for the asthmatics. Both groups also had increases in airways responsiveness to methacholine after the ozone exposure but the asthmatics had increases in responsiveness after exercise in air alone. The results of the second part of the study showed that pretreatment with indomethacin partially prevented the ozoneinduced changes in lung function for normal subjects. Indomethacin did not prevent the ozone-induced increase in airways responsiveness. INTRODUCTION Inhalation of ozone by normal subjects can cause reversible decrements in lung function (primarily restrictive changes) and increases in non-specific airways responsiveness. Although the mechanisms for these ozone-induced changes are unknown, results from animal studies would suggest that products of the cyclooxygenase pathway of arachidonate metabolism may play a critical role. Possible mediators such as PGFZar PGD2, and TxA2 have potent bronchoconstricting properties (refs. 1-3). Administration of exogenous prostaglandins can stimulate lung irritant receptors causing cough and pain (ref. 4). TxA2 and PGD2 have been shown to increase airway smooth muscle responsiveness (refs. 5,6) which could contribute to increased non-specific airways responsiveness. Since ozone can cause increased airways responsiveness to such non-specific stimuli as methacholine, we
494 wondered how individuals with already increased methacholine responsiveness (asthmatics) would respond to inhalation of ozone. This was evaluated in the first part of our study. Also, since cyclooxygenase products may play an integral role in ozone-induced pulmonary changes, and since indomethacin has been shown to prevent ozone-induced increases in airways responsiveness in a canine model (ref. 7 ) , we hypothesized that pretreatment of normal subjects with indomethacin might have an inhibitory effect on the changes in lung function and increases in airways responsiveness after ozone exposure. This was the purpose of the second part of our study. METHODS Sub?ects Non-smoking volunteers between the ages of 18 and 35 were used in these studies. Subjects were classified as asthmatic if they had a history of reversible chest tightness and wheezing, had previously had a diagnosis of asthma made by a physician, and had a PCIOOMeth (the concentration of methacholine required to double baseline specific airways resistance (SRaw)) less than 1.5 mg/mL (methacholine challenge test described in Protocol). Normal subjects had no history suggestive of reversible airways disease and had normal baseline pulmonary function tests. In addition, all normal subjects had a PCIOOMeth greater than 5.0 mg/mL. Nine normal and nine asthmatic subjects participated in the first part of the study and ten normal subjects participated in the second part of the study. Protocol (i) Phase I: Asthmatics vs. Normals. Each subject underwent two randomly assigned exposures to either 0.4 ppm ozone or air alone for 2 hours. To minimize persistent changes in airways responsiveness after ozone exposure, the exposure to air alone occurred at least three weeks after ozone exposure. Subjects with asthma withheld oral bronchodilators for 3 6 hours and inhalable bronchodilators for 12 hours before any exposure. At the beginning of each study day, the subject underwent complete pulmonary function testing including measurements of SRaw, lung volumes and forced expiratory flow rates. At this time, airways responsiveness to methacholine was also determined. Progressively
495
increasing concentrations of methacholine were administered to the subject by aerosolization using a dosimeter and a hand-held nebulizer (DeVilbiss Model 1 6 4 6 ) . The initial concentration of methacholine administered to the asthmatics and normals was usually 0.0625 and 1.0 mg/mL respectively. The test was stopped when the SRaw had more than doubled from the baseline value or when the maximum concentration of methacholine had been given (128 mg/mL). The PCIOOMeth was determined by interpolation of the log transformed data. A period of ninety minutes followed to allow for the SRaw to return to baseline. Another set of pulmonary function tests was then performed. The subject then entered the exposure chamber for a two-hour period. The exposure period was divided into alternating fifteen-minute intervals of rest and exercise (a rest period was first). Workload on a cycle ergometer was adjusted so that a target minute ventilation of 30 L/min/m2 of body surface area based upon ideal body weight was achieved. Midway through each of the four rest periods, pulmonary function testing again was performed. After the final exercise period, the subject left the chamber and performed the final pulmonary function test. Ninety minutes after leaving the chamber (again to allow for the SRaw to return to baseline) the subject had a repeat methacholine challenge. This completed the protocol for the first part of the study. (ii) : h se I 't Zgdomethacin, Each normal subject underwent the exposure protocol to ozone as described above on three separate occasions. Each subject received in a random fashion pretreatment for 4 days prior to the exposure day with either indomethacin (150 mg/day), placebo, or no medication. The exposures were separated by at least 2 weeks. The investigators were kept blind as to the specific treatment administered to each subject. RESULTS Phase I: Asthmatics vs. -N (i) ' s There were no significant changes in lung function or airways responsiveness to methacholine for the normal subjects after exposure to air alone (TABLE 1). As expected, after ozone exposure, the normal subjects had decreases in lung function. The changes for the normal subjects after ozone were more restrictive than obstructive in quality (decreases in FVC and
496
IC with a decrease in FEVl that was proportional to the decrease in FVC). Also as expected, there was an increase in airways responsiveness for the normal subjects after ozone exposure as reflected by a fall in the PCIOOMeth from 33 mg/mL methacholine to 8.5 mg/mL methacholine (-74.2%)
.
TABLE 1 Percent changes in lung function and airways responsiveness for normal and asthmatic subjects after exposure to air alone and after ozone exposure. FVC FEVl FEV1% IC RV TLC SRaw Pcloo Air Alone Normal 0.8% 2.5% 2.0% 0.9% 16.3% 5.0% 14.1% 14.9% Asthmatic 0.2% 0.6% -0.5% -0.7% 8.6% 4.0% 42.7% -43.8% Ozone Exposure Normal -9.4% -13.2% -4.3% -15.2% 15.6% -1.9% 29.3% -74.2% Asthmatic-14.8% -24.0% -12.5% -17.6% 26.6% -0.8% 92.9% -63.5% (ii) Asthma tic Sub4ects. In contrast to the normal subjects, there was some change in lung function and airways responsiveness for the subjects with asthma after exercise in the air alone (TABLE 1). Specifically, the SRaw increased by 42.7% and the PCIOOMeth for methacholine fell by 43.8% (0.48 mg/mL methacholine to 0.27 mg/mL methacholine). After the ozone exposure, the asthmatic subjects had both decreases in lung function and increases in airways responsiveness. The changes for the asthmatic subjects after ozone were both obstructive and restrictive in quality. In fact, in comparison to the normal subjects, there were significantly greater decreases in the parameters of obstruction (FEV1, FEV1%, and the FEF25,75) for the asthmatic subjects. As with exercise in air alone, there were increases in airways responsiveness for the asthmatic subjects after ozone exposure: decrease in the mean PCIOOMeth from 0.52 mg/mL methacholine to 0.19 mg/mL methacholine (-63.5%). Subjects with Indomethac in Phase 11: Pretreatment of NoAs in the initial phase of the study (see Results: Phase I above), after receiving no premedication, the normal subjects had decrements in lung function and increases in airways responsiveness after ozone exposure (TABLE 2). Pretreatment with
497
indomethacin partially protected these subjects from the ozoneinduced decreases in lung function (TABLE 2) but there was no statistical difference in the increase in airways responsiveness after ozone when indomethacin was given: decrease in mean PCIOOMeth with no premedication of -44.9% vs. decrease in mean PCIOOMeth with indomethacin premedication of -31.7%.
TABLE 2 Percent changes in lung function and airways responsiveness for normal subjects after ozone exposure with different pretreatments Pretreatment FVC* FEV, * PC, ,,Meth+ Control (No medication) -19.1% -21.5% -44.9% Placebo -12.6% -14.4% -58.4% Indomethacin -10.6% -31.7% -6.8%
* change after no medication is significantly different from change after indomethacin (p < 0.05). no significant differences among the three pretreatments
+
DISCUSSION We have found that exposing normal and asthmatic subjects for 2 hours to 0.4 ppm ozone results in restrictive-type lung function changes in both groups (decreases in FVC and IC) but obstructivetype changes (decreases in FEVl out of proportion to the decreases in FVC, and decreases in FEV1%, and FEF25,75) in the asthmatic subjects. Also, as with the normal subjects, the subjects with asthma had increases in airways responsiveness to methacholine after ozone exposure. It is difficult to compare the ozoneinduced increases in airways responsiveness between these two groups because of the differences in baseline responsiveness (PClO0Meth for normals: 33 mg/mL methacholine; PCIOOMeth for asthmatics: 0.52 mg/mL). However, both groups had decreases in PCIOOMeth of similar magnitude: -74.2% for the normal subjects and -63.5% for the asthmatic subjects. It is of interest that exercise in air alone resulted in an increase in airways responsiveness for the asthmatic subjects (decrease in PCIOOMeth of -43.8%). We have also found that pretreatment of normal subjects with indomethacin partially inhibited the ozone-induced restrictive changes in lung function but that indomethacin was not effective
498
in preventing the ozone-induced increase in airways responsiveness for these normal subjects. The mechanisms for ozone-induced changes in lung function and airways responsiveness for human subjects are unknown. From animal studies, it is thought that products of the cyclooxygenase pathway of arachidonic acid metabolism may play an important role. Leikauf et a1 (ref. 8) have found that ozone can augment the production of eicosanoids from tracheal epithelial cells including PGD2 and PGFZo. Seltzer et a1 (ref. 9) found an increase in PGFZa in the bronchoalveolar lavage fluid of normal human subjects who had been exposed to ozone. Since it is known that cyclooxygenase products such as PGD2 and PGFZo are potent bronchoconstricting agents in subjects with asthma (ref. 2 ) , it would be expected that increased amounts of these mediators after ozone exposure could result in greater obstructive changes in the asthmatic subjects compared with the normal subjects. We did find this result in our study. It is also possible that ozone exposure could result in the release of other bronchoconstrictor agents as yet to be identified. It is also known that prostaglandins can stimulate lung irritant receptors leading to cough and pain (ref. 4). It may be that prostaglandins released into the airways as a result of ozone exposure cause the restrictive lung changes through this irritant effect. Blocking the airway afferent neural pathways with lidocaine has been shown to prevent these ozone-induced restrictive changes (ref. 10). In our study, indomethacin partially protected the normal subjects from the ozone-induced restrictive-type lung function changes. It is assumed that this occurred by the inhibition of the formation of cyclooxygenase products by indomethacin. Exposure to ozone did result in increases in airways responsiveness in subjects with asthma. We are uncertain as to the mechanism for this increase either in the normal subjects or in the subjects with asthma. In the canine model it is suggested that TxA2 production is responsible for the increase in airways responsiveness (ref. 5). Other mediators have been shown to modulate neuromuscular transmission resulting in increases in nonspecific airways responsiveness; e.g., PAF, leukotrienes, substance P. It is uncertain if any of these other mediators may be involved in ozone-induced increases in airways responsiveness.
499
We are also uncertain as to the clinical significance of the increase in airways responsiveness that occurred with the asthmatic subjects after ozone exposure; especially when finding that exercise alone resulted in some increase in airways responsiveness for these subjects. We were not able to show that indomethacin could prevent the ozone-induced increase in airways responsiveness. In the canine model, indomethacin was effective in preventing the increase in airways responsiveness (ref. 7). It is possible that species differences may account for the lack of protective effect of indomethacin in humans. Other mediators that could be released into the lung after ozone exposure may be responsible for the increases in airway responsiveness in humans. Future lavage studies will be needed to determine if other mediators are present in the lung of human subjects after ozone exposure.
REFERENCES A.P. Smith, M.F. Cuthbert, and L.S. Dunlop, clin. sci. Mol. Med., 48 (1975) 421-430. C.C. Hardy, C. Robinson, A.E. Tattersfield, and S.T. Holgate, N. Engl. J. Med., 311 (1984) 209-213. J. Svensson, K. Strandberg, T. Tuvemo, and M. Hamberg, Prostaglandins, 14 (1977) 425-436. P.J. Gardiner, J.L. Copas, R.D. Elliott, and H.O.J. Collier, Prostaglandins, 15 (1978) 303-315. H. Aizawa, K.F. Chung, G.D. Leikauf, I. Ueki, R.A. Bethel, P.M. O'Byrne, T. Hirose, and J.A. Nadel, J. Appl. Physiol., 59 (1985) 1918-1923.
R.W. Fuller, C.M.S.Dixon, C.T. Dollery, and P.J. Barnes, Am. Rev. Respir. Dis., 133 (1986) 252-254. P.M. O'Byrne, E.H. Walters, H. Aizawa, L.M. Fabbri, M.J. Holtzman, and J.A. Nadel, Am. Rev. Respir. Dis., 130 (1984) 220-224.
G.D. Leikauf, K.E.
Driscoll, H.E. way, Am. Rev. Respir. Dis.,
137 (1988) 435-442.
J. Seltzer, B.G. Bigby, M. Stulbarg, M.J. Holtzman, J.A. Nadel, I . F . Ueki, G.D. Leikauf, E.J. Goetzl, H.A. Boushey, J. Appl. Phvsiol., 60 (19861 1321-1326. 10 M.S. Hazucha, 'D.V..Bates, P.A. Bromberg, Am. Rev. Respir. Dis., 133 (1986) A214.
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T.Schneider et al. (Editors),Atmospheric Ozone Research and its Policy Implications 0 1989 Elaevier Science Publishers B.V.,Amsterdam - Printed in The Netherlands
501
EFFECTS OF OZONE ON THE PRODUCTION OF ACTIVE BACTERICIDAL SPECIES BY ALVEOLAR MACROPHAGES M.A. Amorusol, J.E. Ryer-Powder2, J . Warren3, G. W i t d and B.D. Goldsteinl lUMDNJ-Robert Wood Johnson Medical School, Dept. of Environmental and Cornunity Medicine, 675 Hoes Lane, Piscataway, NJ 08873 'Children's Hospital of LA, Division of Neonatology, 4650 Sunset Blvd., Los Angeles, CA 90027 3Brunel University, Dept. of Biochemistry, Uxbridge, Middlesex, England ABSTRACT The potentiation by ozone of bacterial infections in laboratory animals has been well documented. The mechanism appears to be related to a pollutantinduced defect in lung bactericidal capability. Recent studies in our laboratory have shown that relatively low level ozone exposure (0.11 ppm x 3 hr) produces a decrement in the ability of murine alveolar macrophages to produce superoxide anion radical ( 0 2 : ) and related bactericidal species. This defect is not accompanied by any change in phagocytic ability and thus resembles the finding observed in human chronic granulomatous disease. Preliminary results suggest that the basis for this ozone-induced defect in alveolar macrophage 02' production may be due to changes in macrophage membrane dynamic properties and/or oxidative decomposition of membrane cytochrome b55a. INTRODUCTION It has been well established that laboratory animals exposed to ozone exhibit an enhanced susceptibility to pulmonary bacterial infections (1-4). This effect has been observed in different laboratories following inhalation of ozone concentrations as low as 0.08 ppm for 2 and 3 hours (5,6). The mechanism of this potentiation of bacterial infection appears to be related to a pollutant-induced defect in lung bactericidal capability as no inhibition of mucociliary clearance has been observed at these ozone concentrations (7). In the lung, resident alveolar macrophages play a major role in host defense against inhaled bacteria (8).
The ability of these mononuclear
phagocytic cells to ingest and kill inhaled bacteria on the lung surface has been clearly demonstrated (9).
Central to the antimicrobial function of these
phagocytes is their ability to reduce molecular oxygen to toxic oxygen metabolites such as superoxide anion radical ( 0 2 ' ) via an NADPH dependent membrane bound oxidase (10,ll). Elucidation of this pathway has, to a large extent, resulted from the observation that individuals with the rare inherited disorder chronic granulomatous disease (CGD), who have recurrent infections leading to death at an early age, are unable to produce a burst of oxygen
502 consumption or the resulting 02' and other reactive species that play a role in the bactericidal process (12). In this laboratory we have been evaluating whether the mechanism by which exposure to ozone leads to a heightened susceptibility to pulmonary bacterial infection might be related to a CGD-like impairment in the alveolar macrophages of exposed animals. Previous studies in rats exposed to ozone showed that inhalation of concentrations of 1.6 ppm or greater for 3 hours was necessary to decrease the ability of alveolar macrophages to produce 02: (13). However, compared with the mouse, the rat is relatively resistant to the potentiation of bacterial infection by oxidant air pollutants (14,15).
In recent studies, utilizing a microassay technique, the production of 02: by mouse alveolar macrophages was found to decrease markedly following
exposure to as little as 0.11 ppm ozone for three hours.
Furthermore, the
observed decrement in mouse 02' production was not associated with any change in phagocytic ability as measured by both latex bead ingestion and 51Crlabeled sheep red blood cell ingestion. At an exposure concentration of 0.2 ppm the effect is apparently linearly related to duration of exposure between
1 and 6 hours. In order to explore the basis for the decrease in 02' production we have evaluated both changes in macrophage membrane dynamic properties as well as alterations in levels of macrophage membrane cytochrome b558* METHODS pollutant ExDosure Me thoda Swiss Webster male mice or Sprague-Dawley female rats were exposed to ozone in a 5.5 cu ft plexiglass exposure chamber.
The ozone was formed from
pure oxygen (Jersey Welding) passing through an ozone generator (OREC Model 03V1-0 Ozonator, Ozone Research and Equipment Corporation, Phoenix, Arizona). Ozone levels inside the chamber were monitored continuously by W absorption with a PCI Model LC-1 Ozone Analyzer (Pollution Control Industries, West Caldwell, NJ). Alveolar Macr-
m.
PreDarat-
Following either air or ozone exposure, the mice were anesthetized
with a lethal intraperitoneal injection of sodium pentobarbital.
A tracheal
cannula was inserted through an incision in the neck and 1.0 ml of sterile, 37'C
phosphate-buffered saline (PBS) pH 7.4 was carefully instilled into the Each lung was lavaged with a
lungs via a syringe attached to the cannula. total of 4 ml of PBS.
The lavage fluid containing the alveolar macrophages
from the control or ozone exposed animals was collected from each animal and centrifuged at 400 x g for 6 minutes.
The respective pellets were suspended
in complete media (RPXI 1640 media, Gibco, Grand Island, NY, 10% fetal calf
503 serum, 1mM Hepes buffer) to a cell concentration of 2 x lo5 cells/ml. For each cell suspension, i.e., each animal, 2 coverslips were placed into separate 35 mm tissue culture dishes. 0.5 ml of either the control or experimental cell suspension was added to each tissue culture dish. Alveolar macrophages were allowed to adhere to the coverslips in a 37"C, 5% COP incubator for 2 hours. The tissue culture dishes containing the coverslips with the adhered macrophages were washed twice with sterile PBS to remove the non-adherent cells. More than 98% of the cells were macrophages as detected by Wright-Giemsa staining, and there was more than 97% viability as measured by trypan blue dye exclusion. Alveolar && ,fimacrophages .
were isolated from female Sprague-Dawley rats
(250-300 grams) as previously described (13) and purified on a Ficoll-Paque gradient (Pharmacia Fine Chemicals, Piscataway, NJ).
The purified
macrophages were suspended in a balanced salt solution at 1 x lo7 cells/ml. on R a d a ProdPitroblue t e t r a z u reduction. The production of superoxide anion radical by mouse PAM was determined qualitatively by the reduction of nitroblue tetrazolium using a technique adapted from a peritoneal macrophage system (16).
The nitroblue tetrazolium (NBT) test depends on the ability of
the dye to be reduced to a dark blue, water insoluble diformazan by 02' (17). Nitroblue tetrazolium (0.2% NBT) (Sigma, St. Louis, MO) was added to all of the plates containing the adhered alveolar macrophages. Phorbol myristate acetate (0.2 ug/ml PMA; Chemicals for Cancer Research, Inc., Eden Prairie,
MN), mezerein (0.2 ug/ml MEZ; Chemicals for Cancer Research, Inc., Eden Prairie, MN), or opsonized zymosan (1.4 m u m 1 ZYM; Sigma, St. Louis, MO) and BSS were added to both plates from each sample. Plates were incubated for 1 hour at 37'C,
5% Cog.
Plates were then removed and washed 2 times with PBS.
Coverslips were then mounted on slides and 02' production was detected in activated cells by counting the number of formazan positive cells (blue) in a field of 250 cells. A baseline value was obtained from the samples containing 0.5 mg/ml superoxide dismutase (SOD) (Sigma, St. Louis, MO). 02' production was measured in stimulated ec m. alveolar macrophages by the superoxide dismutase inhibitable reduction of ferricytochrome C as previously described (13).
Typical reaction mixtures
containing 1.25 x lo6 cells/nl were incubated in the presence of 44 Un cytochrome c (type 111, horse heart, Sigma, St. Louis, MO) at 37'C
for 30
minutes with the soluble respiratory burst initiator, phorbol myristate acetate (1.72 ug/ml assay mixture).
Following the incubation, cells were
pelleted and the absorbance of the supernatant was recorded from 600-500 nm on a Perkin Elmer 552 spectrophotometer. 02. production was calculated (E
- 21.1
m - l c m - l at 550 nm) using a baseline value obtained from a sample containing
504 PMA and superoxide dismutase (34 ug/ml). ocvtos~ Following adherence of macrophages to coverslips, macrophage monolayers were washed with PBS and incubated with a suspension of Fluoresbrite fluorescent monodisperse carboxylated microspheres (1.51 f 0.06 um, Polysciences, Inc., Wattington, PA) in PBS (1 drop from dispenser into 2.5 ml of PBS).
The macrophages were allowed to phagocytize the particles for 1 hour
at 37°C.
The monolayer was then washed and the number of cells which ingested
the beads as well as the number of beads per cell were counted using light microscopy.
-58 Alveolar macrophages isolated from either air or ozone-exposed rats were suspended in BSS to at least 5 x lo6 cells/ml.
For each group 2 ml of the
cell suspension were placed in both sample and reference cuvettes and scanned from 600
-
400 nm on a Perkin Elmer Lambda 4B spectrophotometer to obtain a
baseline. An oxidized vs reduced spectrum was then recorded from 600
-
400 nm
following the addition of a small amount of dithionite to the sample cuvette. The reduction of intact rather than disrupted cells was used because dithionite penetrates membranes slowly (18) and thus it reduces the cytochrome b which is in the plasma membranes (19) more readily than components within the cytoplasmic granules.
It has also been suggested that the reduction of
intact cells overcomes the problems of distortion of the spectrum by intracellular peroxidases and cytochromes (20).
The extent of reduction of
the cytochrome b was calculated by measuring the height of the absorption band at 559 nm above a line joining the two troughs on each side of the band (21) using an extinction coefficient of 21.6 cm-lmM-l (22).
RESULTS
* V
2'
Production As shown in Table 1, there was an inhibition in the ability of mouse alveolar macrophages to produce superoxide anion radical following exposure to ozone levels as low as .11 ppm.
Superoxide anion radical production in PAM
from rats exposed to ozone was not inhibited until the rats were exposed to at least 1.6 ppm for 3 hours.
In the mouse, the inhibition in superoxide anion
radical production following ozone exposure ranged from 6% at 0.03 ppm to 96% at 1.08 ppm.
In the rat, the inhibition in superoxide anion radical
production following ozone exposure ranged from 0 at 0.9 ppm to 93% at 3.5 ppm. The IC50 for mice was 0.41 ppm whereas that for rats was 3.0 ppm. The correlation coefficients for the relationship between ozone concentration and inhibition of superoxide anion radical were .97 and .96 for the mouse and
505
rats, respectively. Measurement of superoxide anion radical production using the ferricytochrome c assay and the NBT assay were found to be comparable. TABLE 1 Inhibition of phorbol myrfstate acetate stimulated 02' production in mouse and rat alveolar macrophages following
in
Mouseb 03 Concentrationa 02' Production (PP4 ( % Inhibition)
.03 .ll .42 .70 .95 1.08
6.0
25.0 45.0 72.0 03.0 96.0
exposure to ozone. RatC 03 Concentrationa 02' Production (PPd (% Inhibition)
0.9 1.6 3.0 3.2 3.3 3.5
0.0 28.0 57.0 75.0 79.0 93.0
aAll exposures were for three hours. bThe data plotted for mice is the mean percent decrease in formazan positive alveolar macrophages for ozone-exposed mice compared with the mean number of formazan positive cells from the control mice where the mean f SD of formazan positive cells from control mice was 160 f 15 per 250 cells counted. CThe data for rats is the mean percent inhibition in cytochrome c reduction from a pooled population of alveolar macrophages from ozone-exposed rats compared with the mean cytochrome c reduction of a pooled population of alveolar macrophages from control rats. The mean +- SD 02? produced by control macrophages was 23 f 6 nanomoles per 1.25 x lo6 cells. w e c t of In Vivo Ozone ExDosure on Mouse Alveolar -cvtosb
As shown in Table 2 , alveolar macrophages isolated from mice exposed to ozone concentrations ranging from 0.42 ppm to 1.2 ppm for 3 hours experienced no suppression in phagocytosis as measured by latex bead ingestion. However, at the same ozone concentrations there was a dose dependent decrease (45%.
04%, 97% and 100%. respectively) in mouse alveolar macrophage superoxide anion radical production.
506 TABLE 2 Effect of
in YiYp
ozone exposure on mouse alveolar macrophage superoxide anion
radical production and phagocytoais.a*bs C Letex Bead Ingestion
%
Cells Ingesting
> 4 Beads f SD
02: Production ( % of Control)
Experiment 1 Control 0.42 ppm 03
84 f 11 81 f 6
55.5
Experiment 2 Control 0.95 ppm 03
86 f 2 92 f 2
16.7
Experiment 3 Control 1.0 ppm 03
95 f 1 93 f 4
13.0
-+ 6 98 f 3
0.0
Experiment 4 Contro1 1.2 ppm 03
87
‘All exposures were for 3 hours. bSuperoxide anion radical production was measured by NBT reduction. cPhagocytosis was also measured by the ingestion of 51Cr-labeled sheep red blood cells. There was no statistically significant difference in the counts per minute f SD from macrophages obtained from 03-exposed animals (1 ppm 03 x 3 hrs) vs. control macrophages. EEfect of In Viva Ozone Exnosure on Rat A1veolar M a c r e Cvtochrome h558 As the measurement of cytochrome b558 requires a large number of cells,
these studies were performed in rats rather than mice.
For each data point,
PAM were pooled from 25 animals. The mean level of cytochrome b558 in rat PAM was 32 f 8 pmoles / lo6 cells compared with the reported level for cytochrome b558 in human PAM or 9.9 k 2.6 pmoles
/ lo6 cells (23).
The spectra obtained with PAM from ozone-
exposed rats showed a decrease in absorbance at 427 run and 558 nm.
In 3
experiments in which rats were exposed to 3 ppm ozone for 3 hours, there was 50%, 43% and 86% decrease in cytochrome b558 compared with controls. These results are indicative of an alteration in the cytochrome b558 component of the electron transport chain. Alveolar macrophages from air or ozone-exposed rats from the three experimental groups showed a 7%, 28% and 36% inhibition in superoxide anion radical production compared with controls, as measured by the superoxide dismutase inhibitable reduction of ferricytochrome c.
TABLE 3
Effect of
in
-
507
ozone exposed on rat alveolar macrophage cytochrome b558 and
superoxide anion radical produc tiona Experiment
1
* c.
02: Production (% Inhibition)
Cytochrome b558 (% Inhibition)
7
1 2 3
50 43 86
28 36
aAll exposures were for 3 hours at 3 ppm ozone. bSuperoxide anion radical production was measured using the superoxide inhibitable reduction of cytochrome c. CCytochrome b558 was measured using a dithionite reduced minus oxidized spectrum. DISCUSSION A number of studies have shown that the most consistently observed adverse effect of low level ozone exposure is a potentiation of bacterial infections in animals (2,3,4,5,6). It has been suggested that this potentiation of pulmonary bacterial infections by ozone might be due to an interference in the ability of alveolar macrophages to either undergo phagocytosis and/or produce active bactericidal species such as superoxide anion radical. Neutrophils from children with fatal chronic granulomatous disease ingest bacteria normally but have a diminished capacity to kill certain organisms (24); they also fail to reduce nitroblue tetrazolium dye at a normal rate during
i0
phagocytosis of latex particles (25).
In order to test the hypothesis that
in YIYp
ozone exposure can damage
alveolar macrophages causing them to behave like chronic granulomatous disease neutrophils we examined the effects of
in
ozone exposure on mouse
alveolar macrophage phagocytosis and superoxide anion radical production. The rationale for the use of mice was related to observations in other laboratories which showed that the mouse was the most susceptible of the laboratory animals tested with respect to the potentiation of bacterial infection by ozone (6,7). The lowest ozone level at which this potentiation was observed in mice following an acute ozone exposure (2-3 hours) was 0.08
-
0.35 ppm, depending upon the investigator. This was below the lowest ozone level at which a decrease in alveolar macrophage superoxide anion radical production in rats (1.6 ppm) had been observed (13).
Accordingly,
phagocytosis and superoxide anion radical production in mouse alveolar macrophages were examined following 3 hour exposures to lower levels of ozone. Using the NBT test, it was shown that
ylyn exposure of mice to ozone
results in a dose-dependent decrease in superoxide anion radical production by
alveolar macrophages isolated from the exposed animals. Furthermore, this effect occurred in mice at a much lower level of ozone than in rats. In order to preclude the possibility that the decrease in superoxide anion radical production following exposure to ozone was specific to the use of phorbol myristate acetate as an initiator of the respiratory burst, other initiators which stimulate the respiratory burst via different pathways were tested in the NBT system (data not shown).
Phorbol myristate acetate and mezerein are both soluble Initiators of the respiratory burst whose mechanisms of action are believed to be dependent upon their entering the cell whereas zymosan is a particulate initiator which is believed to act at the level of the cell membrane (26).
In each experiment, regardless of the initiator,
macrophages isolated from ozone-exposed animals were less able to produce superoxide anion radical than controls. The inhibition in superoxide anion radical production was dose-dependent (r-.97).
The ozone-induced decrease in
superoxide anion radical production therefore does not appear to be specific for a particular initiator of the oxygen burst. Using both the latex bead and 51Cr-labeled sheep red blood cell phagocytosie assays, there was no statistically significant effect of ozone exposure on mouse alveolar macrophage phagocytosis.
vivo
This finding
supports the conclusion that ozone exposure can lead to alveolar macrophages which exhibit chronic granulomatous disease-like characteristics. Comparison of the effect of ozone inhalation in Swiss-Webster mice with that in Sprague-Dawley rats revealed the latter as much less susceptible to inhibition of alveolar macrophage superoxide anion radical production. The IC50 for rats was 3.0 ppm whereas that for mice was 0.41 ppm ozone.
In the
mouse, the 25% decrease in alveolar macrophage superoxide anion radical production observed at 0.11 ppm ozone, a level below the current US ambient standard, is statistically significant at p < .05. Furthermore, in recent studies we have demonstrated that this ozone-induced decrease in macrophage 025 production increases in a linear fashion during a 6 hour ozone exposure (Amoruso at al, unpublished data).
Such findings suggest that the current
practice of limiting the averaging time of ozone to a one hour period may be inappropriate and not fully protective of public health. In order to further explore the mechanism by which 02: production was inhibited following ozone exposure, we decided to examine the effect of ozone on cytochrome b558.
This membrane-bound cytochrome is believed to function as
the terminal electron acceptor in the reduction of oxygen to 02i
(22).
The
importance of cytochrome b558 is suggested by its absence in the neutrophils of certain patients with X-linked chronic granulomatous disease (27). A decrease in this electron carrier component of the respiratory chain might
509 explain the ozone-induced decrease in the ability of the alveolar macrophage to reduce oxygen to superoxide anion radical.
In addition, since it has been suggested that ozone exerts its adverse pulmonary effects through the production of free radicals in cellular membranes (28,29), a heme-containing membrane component, such as cytochrome b558 could be a likely target for free radical attack induced by ozone.
In fact, exposure of rabbits to 1 ppm ozone
for 90 minutes results in decreased levels of lung microsomal cytochrome P-450 (30).
The measurement of cytochrome b558 in rat alveolar macrophages
presented a number of technical problems.
It is present in human neutrophils
and human alveolar macrophages at very low levels (20.23). sufficiently low that there was some degree of controversy as to its existence after the initial report. It had not previously been reported to be present in rodent alveolar macrophages. However, using intact cells rat alveolar macrophage cytochrome b558 could be detected when alveolar macrophages were pooled from a least 25 animals for each data point. Reduced-oxidized spectra of intact cells from air-exposed rats clearly demonstrated the alpha, beta, and gamma (or Soret) absorption bands of a cytochrome b.
The mean level of cytochrome b558 in rat alveolar macrophages
was 32 k 8 pmoles / lo6 cells, compared with the reported level for cytochrome b558 in human alveolar macrophages which was 9.9 f 2.6 pmoles / lo6 cells (23). The spectra obtained with alveolar macrophages from ozone-exposed rats showed a 43-86% decrease in absorbance at 427 nm and 558 nm. These results are indicative of an alteration in the cytochrome b558 component of the electron transport chain in the NADPH-dependent respiratory burst oxidase. However, there was a much lesser extent of decrease in rat PAM 02’ production in the three studies for which this data was also available. It has been suggested that under aerobic conditions not all electrons which flow from NADPH to oxygen (to form superoxide anion radical) necessarily pass through the cytochrome b.
Several possibilities for such a branched
chain flow of electrons could be constructed in which cytochrome b would nonetheless be an essential component for catalytic activity. It should be emphasized however that this study has not proven cytochrome b558 to be an integral participant in the 03 induced inhibition of the respiratory burst. Another mechanism of ozone toxicity which we are investigating is the effect of oxidative damage on cell-membrane fluidity (31-36). In previous studies from our laboratory ozonization of erythrocyte ghosts was shown to result in an increase in both DPH and protein polarization (37). With respect to DPH polarization, increases in this parameter have been interpreted to reflect decreases in membrane lipid fluidity or in lipid rotational mobility. Since the dynamic properties of cell membranes are thought to have an important role in normal cell function and regulation, changes in membrane
510 fluidity may result in abnormal cell function. Studies by Rimon et a1 have shown that changes in membrane fluidity can alter the activity of membrane bound enzymes (38).
More recently, Pate1 and Block (39) have shown that exposure of pulmonary endothelial cells to NO2 causes significant decreases in fluidity in the hydrophobic interior of the plasma membrane lipid bilayer accompanied by subsequent depressions in plasma membrane dependent transport of 5-hydroxytryptamine. In our studies (data not shown), alveolar macrophages
isolated from rats exposed to ozone exhibited a dose-dependent increase in fluorescence polarization indicative of decreases in membrane lipid fluidity. Such decreases in membrane fluidity might be responsible for the decreased activity of the membrane bound NADPH oxidase in these cells. It remains to be determined whether such changes in the dynamic properties of these cells results directly from ozone-induced oxidative membrane damage or from the interaction of the alveolar macrophages with products formed as a result of ozone-induced lipid peroxidation. However, such changes in the dynamic properties of cell membranes may constitute yet another mechanism by which the toxic effects of ozone are manifested. REFERENCES 1
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21
D.L. Coffin, E.J. Blommer, D.E. Gardner, and R.S. Holtzman, Proceedings of the Third Annual Conference in Atmospheric-Contaminants in Confined Space: Wright-Patterson Air Force Base, Aerospace Medical Research Laboratories, (1986) 75-80. D.L. Coffin and D.J. Blommer, in I.H. Silver (Editor), Aerobiology, Academic Press, New York, 1970, pp. 54-61. D.L. Coffin, AEC Symp. Ser. 18 (1970) 257-264. D.L. Coffin and D.E. Gardner, Ann. Occup. Hyg. 15 (1972) 218-234. D.L. Coffin and E.J. Blommer, J. Air Pollution Control Assoc 15 (1965) 523-524. R. Ehrlich, Arch. Environ. Health, 6 (1963) 638-642. E. Goldstein, W.S. Tyler, P.D. Hoeprick and C. Eagle, Nature 229 (1971) 262-263. G.H. Green and E.H. Kass, J. Exp. Had, 119 (1964) 167-175. E.H. Kass, G.H. Green and E. Goldstein, Bacteriol. Rev., 30 1966) 488497. B. Babior, New Engl. J. Hed. 298 (1978) 659-668. R.G. Johnston, Fed. Proc. 37 (1978) 2759-2764. B. Babior, New Engl. J. Hed. 298 (1978) 721-734. H.A. Amoruso, G. Witz and B.D. Goldstein, Life Sci., 28 (1981) 2215-2221. A. Kimura and E. Coldstein, J. Infect. Dis., 143 (1981) 247-251. E. Goldstein, H.C. Bartlema, M. van der Ploeg, P. van Duijn, J.G.H.H. van der Stag and W. Lippert, J. Infect. Die., 138 (1978) 299-311. B. Czerniecki, S.C. Gad, C. Reilly, A.C. Smith and G. Witz, Carcinogenesis, 7 (1986) 1637-1641. B.H. Park, S.H. Jikring and E.U. Smithwich, Lancet, 2 (1968) 532-534. R. Lamburg and H.E. Cutler, Biochin. Biophys. Acta, 197 (1970) 1-10. A.W. Segal and O.T.G. Jones, Biochim. Biophys. Acta, 88 (1979) 130-134. A.W. Segal, R. Garcia, H. Goldstone, A. Cross and O.T.G. Jones, Biochem. J., 196 (1981) 363-367. A.R. Cross, O.T.G. Jones, A.M. Harper and A.W. Segal, Biochem. J., 194 (1981) 599-606.
511 22 A.W. Segal, in J.F. Gallin and A.S. Fauci (Editors), Advances in Host Defense Mechanisms: Vol. 3, Chronic Granulomatous Disease, Raven Press, New York (1983) 121-143. 23 S. Cholet-Martin, C. Pasquier, C. Marquetty, P. Soler, A. Hance, F. Basset and J. Hakim, Am. Rev. Resp. Dis., 132 (1985) 836-838. 24 B. Holmes, P.G. Quie, D.B. Windhorst and R.A. Good, Lancet, 1 (1966) 12551258. 25 R.B. Johnston and S.L. New-man, Ped. Clin. North Am., 24 (1977) 365-376. 26 L.C. McPhail, P.M. Henson and R.B. Johnson, J. Clin. Invest., 67 (1981) 710-724. 27 A.W. Segal, A.R. Cross and R.C. Garcia, N. Engl. J. Med., 308 (1983) 558561. 28 B.D. Goldstein and O.J. Balchum, Proc. SOC. Exp. Biol. Med., 126 (1967) 356-358. 29 J.N. Roehm, J.G. Hadley and D.B. Menzel, Arch. Environ. Health, 24 (1972) 237 - 242. 30 B.D. Goldstein, S. Solomon, B.S. Pasternack and D.R. Bickers, Res. Commun, Chem. Pathol. Pharmacol., 10 (1975) 759-762. 31 B.D. Goldstein, S.J. Hamburger, G.W. Falk and M.A. Amoruso, Life Sci., 21 (1977) 1637-1644. 32 S.J. Hamburger and B.D. Goldstein, Env. Res., 19 (1979) 292-298. 33 B.D. Goldstein, Env. Health Persp., 30 (1979) 87-89. 34 B.D. Goldstein, G.W. Falk, L.J. Benjamin and E.M. McDonagh. Blood Cells, 2 (1977) 535-540. 35 B.D. Goldstein and E.M. McDonagh, J. Clin. Invest., 57 (1976) 1302-1307. 36 B.D. Goldstein, M.G. Rosen and M.A. Amoruso, J. Lab. Clin. Med., 93 (1979) 687-694. 37 G. Witz, M.A. Amoruso and B.D. Goldstein, In: S.D. Lee, M.G. Mustafa, M.A. Mehlman (Editors), Advances in Modern Environmental Toxicology: Vol. V. International Symposium on the Biomedical Effects of Ozone and Related Photochemical Oxidants, Princeton Scientific Publishers, New Jersey (1983) 263-272. 38 G. Rimon, E. Hanski, S. Braun and A. Levitsky, Nature, 276 (1978) 394-399. 39 J.M. Pate1 and E.R. Block, Free Radical Bio. and Med., 4 (1988) 121-134.
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T.Schneider et al. (Editors),Atmospheric Ozone Research and its Policy Implications 0 1989 Elsevier Science Publishers B.V.,Amsterdam - Printed in The Netherlands
513
IMPACT MECHANISMS OF OZONE AT CELL LEVEL
I . R1ETJENS1v4, L. VAN BREE2. A. KONINGS3, P. ROMBOUT2 AND G. ALINKl lDepartment of Toxicology, Agricultural University, Bomenweg 2, 6703 HD Wageningen (The Netherlands) 2National Institute of Public Health and Environmental Hygiene, Department of Inhalation Toxicology, P.0.Box 1 , 3720 BA Bilthoven (The Netherlands) 3Department of Radiopathology, University of Groningen, Bloemsingel 1 , 9713 BZ Groningen (The Netherlands) 4Present address: Department of Biochemistry, Agricultural University, Dreijenlaan 3. 6703 HA Wageningen (The Netherlands)
ABSTRACT Mechanisms of toxic action and cellular defense against ozone were studied using an in vitro model in which cell cultures can be exposed to gaseous compounds. Formation of fatty acid ozonides seems to be involved in the mechanism of toxic action. Cellular defense against ozone can be provided by atocopherol, ascorbic acid and glutathione. The protective role of glutathione cannot be ascribed to the glutathione peroxidase-catalyzed detoxification of lipid hydroperoxides. Glutathione rather functions in the detoxification of lipid ozonides, a reaction that may be catalyzed by glutathione S-transferases. INTRODUCTION The impact of ozone at cell level may be twofold. Ozone may have direct injurious effects on exposed lung cells. On the other hand, ozone ray have effects that result in modulation of the toxicity of other xenobiotic compounds, such as for example changes in pulmonary cytochrome P-450 activities (refs. 1,2). The direct toxic effects of ozone may result from the oxidation of unsaturated fatty acyl moieties in membrane phospholipids or from the oxidation of cellular proteins. Theories pointing at these mechanisms of toxic action of ozone are primarily based on in vitro studies under abiotic conditions (refs. 3-10).
Amino acid residues in proteins may be damaged by direct oxidation or by a radical mechanism initiated by hydrogen abstraction followed by oxygenation. These reactions may eventually result in crosslinking of membrane proteins by dlsulfide or dityrosine bridges (refs. 9-10). Studies using pure fatty acids or aqueous emulsions of fatty acids have demonstrated the ability of ozone to react with unsaturated lipids i) either by a radical mediated lipid peroxidative pathway initiated by'hydrogen abstraction
514 and resulting in formation of lipid hydroperoxides or ii) by a mechanism initiated by the addition of ozone to the double carbon-carbon bond of the unsaturated lipid molecules resulting in formation of lipid ozonides (refs. 3-5, 7-8). The dominant reaction pathway in ozone initiated oxidation of pure fatty acids seems to involve a direct attack of ozone on the fatty acid double bond, followed by ozonide formation (refs. 3.5). However, when the fatty acids are exposed to ozone in aqueous emulsions, the oxidation proceeds in part by a radical mediated peroxidative reaction pattern as well (refs. 3.4). This indicates that the mechanism(s) occuring in ozone induced oxidation depend on the node of fatty acid exposure. From these observations it clearly follows that the mechanism by which ozone actually initiates its oxidative damage can only be studied adequately using intact cell models. This consideration formed part of the basis for the work presented here: control and polyunsaturated fatty acid (PUPA) enriched cells were exposed to ozone in vitro. The most convincing evidence f o r the involvement of radical mediated lipid peroxidaton in intact cell models and animal lung can be found in the protection provided by the phenolic antioxidant vitamin E (a-tocopherol) (refs. 11-13) and in the increased amount of ethane or pentane detected in the breath of ozone exposed animals (refs. 14.15). However, it is not known whether the initial reaction leading to the oxidative breakdown of cellular membrane lipids is an allylic hydrogen abstraction, or that ozone mediated lipid oxidation is initiated by the ionair Criegee mechanism leading to ozonide intermediates which may possibly only in second instance give rise to radical mediated lipid peroxidation (refs. 4,7). Therefore another part of the work presented here, was based on a comparison between the mechanisms for cellular protection against ozone and nitrogen dioxide toxicity. Nitrogen dioxide reacts with unsaturated membrane phospholipids by a radical aediated peroxidative reaction pathway initiated by hydrogen abstraction (refs. 16,17). If ozone induced cell damage is caused by the same mechanism, similar protection by cellular antioxidant systems against ozone and nitrogen dioxide should be observed. In addition, the protective role of glutathione against ozone induced cell damage was studied in more detail. If ozone induced cell damage does not proceed by formation of lipid hydroperoxides but rather by formation of lipid ozonides, protection by glutathione may not be mediated by its role in glutathione peroxidase catalyzed detoxification of lipid hydroperoxides as suggested in the literature (ref. 18). In the present study the mechanisms of toxic action of ozone and of cellular defense against the oxidative gaseous compound were investigated using an system in which cell cultures can be exposed to gaseous compounds by means of gas diffusion through a teflon film (rep. 19).
51 5 METHODS Cell culture and exposure Cells of the alveolar type I 1 cell-line A549 were cultured as described (ref. 20). Alveolar macrophages and type I 1 cells were isolated from the lungs of Wistar rats
(%
200 g) and cultured as described previously (refs. 21-23).
Cells were cultured for 3 days in order to attach and stretch on the teflon f i l m of the petriperm dish (Petriperm. Heraeus. Hanau, P.R.G.) before they were exposed to the gaseous compound. During these days cellular antioxidant levels or the cellular fatty acid composition could be modified as previously described (refs. 22-23). Before exposure, cells were washed and fresh medium without serum was added to the cells. Cells were exposed to ozone or nitrogen dioxide by means of gas diffusion through the teflon film of the petriperm dish (refs. 20-23). The amount of gaseous compound that diffused through the teflon film into the dish was determined as described (ref. 22).
Animal exposure Seven-week-old, male Wistar rats (145
f
20 g) were exposed to 0 or 1.5
t
0.1
mg ozone/mJ (0.75 ppm) f o r 4 days as described (ref. 21).
Biochemical and cellular assays Glutathione (reduced form) was measured by the method of Hissin and Hilf (ref. 25). Glutathione peroxidase activity was measured according to Lawrence and Burk (ref. 26) in 50 SM iDidaZOle buffer pB 7.0 with hydrogen peroxide as a substrate. Protein was determined by the method of Lowry et al. (ref. 27). Cellular levels of a-tocopherol were measured as described (ref. 22). The PUPA (polyunsaturated fatty acid) content of alveolar macrophages was determined as previously described (ref. 23). Methyl linoleate ozonide was synthesized as previously described (ref. 24) Phagocytosis was determined after incubation of alveolar macrophages for 1.5 h at 37'C
in the presence of approximately lo7 dead yeast cells, coloured by
boiling them for 30 minutes in a congo red (Pluka, Buchs, Switzerland) PBS solution. Viability was assessed by counting the percentage of trypan blue excluding cells 5-10 minutes after addition of 0.5% trypan blue (BDH, chemicals, Poole,
U.K.). Survival of A549 cells was calculated as the product of viability and cell number. Data are presented as mean
f
standard error of the mean. and statistical ana-
lysis was carried out using the paired Student's t-test.
516 RE S0L TS Increased ozone sensitivity of PUFA enriched cells From the results presented in Table 1 it can be concluded that PUPA enriched rat alveolar macrophages demonstrated an increased sensitivity towards ozone.
TABLE 1 Effect of preincubation of rat alveolar macrophages with BSA (37.5 pM) or with BSA/20:4 (37.5 @4/150
m)
towards ozone (n=5). ***
=
on their PUPA content (n-2) and their sensitivity p < 0.001
parameter
BSA control
BSA/2Q :4
I PUFA
48
t 3
56
?:
5
ozone dose in nmol/dish
29
2
1
27
f
1
phagocytosis t of unexposed cells
67
f
2
48
?:
3
***
Comparison of antioxidant protection against ozone and nitrogen dioxide Table 2 summarizes the results obtained when the protection of alveolar macrophages against ozone by cellular antioxidant systems was compared to the protection provided against an equally toxic dose of nitrogen dioxide, known to react by a radical mediated peroxidative pathway. From these data it can be seen that depletion of the cellular level of glutathione resulted in a significant increase in the sensitivity of the cells towards ozone, but in a less pronounced increase in their nitrogen dioxide sensitivity. Furthermore, preincubation of the cells with vitamin C protected the cells against both oxidative compounds, but provided a significantly better protection against nitrogen dioxide than against an equally toxic dose of ozone. Similar protection against both oxidative gaseous compounds was provided by atocopherol, although the results in Pig. 1 Indicate that equally toxic doses of both gasses did not affect the cellular level of a-tocopherol to the same extent. Cells exposed to nitrogen dioxide. demonstrated a significantly (p < 0.01) greater decrease in their a-tocopherol level, although their phagocytotic capacity was affected to the same extent as observed for the ozone exposed cells.
517 TABLE 2 Sensitivity of glutathione depleted, vitamin C enriched and a-tocopherol enriched rat alveolar aacrophages towards ozone and an equally toxic amount of nitrogen dioxide. Phagocytosis is expressed as percentage of the phagocytotic capacity of non-exposed cells.
**
= p
< 0.01.
***
= p < 0.001. n.s. = not significant
paraaeter
ozone exposed
- dose in naol 03 or N02/dish - phagocytosis -control -glutathione depleted
-
dose in nmol 03 or N O ~ / d i s h phagocytosis -control -vitamin C enriched
-
dose in nmol 03 or N02/dish - phagocytosis -control -a-tocopherol enriched
nitrogen dioxide exposed 54
7 t 1
*** t
4
86 3 X n.s. 75 t 10 x
8 7 2 1 % 4524%
17
t
n.8. 177
I
t
22 7 3 n.s.
2722%
21 t
8824%
93 t 4
***
***
14
5
172
2
t
x **
8
2223%
20
8324%
80 t 10 X n.8.
***
**+
03 phagocytosis aT /1$ cells
5 X n.s.
NO1
phagocytosis ,aT/10 6 cells
Pig. 1. Effect of ozone (21 t 1 naol/dish) and nitrogen dioxide (271 11 ,nmol/ dish) on phagocytosis and a-tocopherol content of alveolar aacrophages, preincubated for 2 days in the presence of 2 3 pM a-tocopherol. * = p < 0.05, ** = p < 0.01, *** p < 0.001
518 The role of glutathione in the nlutathione Deroxidase catalyzed detoxification Of fatty acid hydroperoxides in ozone exposed Cells In addition to alveolar nacrophages (Table 2), cells of the alveolar type I 1 cell-line A549 also demonstrated an increased ozone sensitivity upon depletion of their glutathione content (Fig. 2). However, no activity of glutathione peroxidase could be detected in these cells.
GSH content
- *
cell survival after 0, exposure
-
MSO/DEM
treated
Fig. 2. Level of reduced glutathione (GSH) and the ozone sensitivity of glutathione depleted (MSO/DEM treated) and control A549 cells. The ozone dose amounted to 25 2 2 nnol/dish ( ~ 4 ) .** = p < 0.01, *** = p < 0.001. In another series of experiments it was deaonstrated that alveolar macrophages and type I 1 cells, isolated froa the lungs of ozone exposed rats, did not show an increased resistance against ozone in spite of a aarked increase in their cellular glutathione peroxidase activity (Table 3).
Cellular antioxidant Drotection against an ozonide model compound Methyl linoleate ozonide caused a dose-dependent Inhibition of the phagocytosis of rat alveolar macrophages exposed in vitro to concentrations varying from 10-5 to 10-4 M (Fig. 3). From the data depicted in Pig. 3 it can also be seen that glutathione depleted cells demonstrate an increased sensitivity towards the ozonide, whereas atocopherol enriched alveolar macrophages were significantly less sensitive. Preincubation of the cells with vitamin C resulted in very little protection against methyl linoleate ozonide.
519 TABLE 3 Glutathione peroxidase (GSHPx) activity and in vitro ozone sensitivity of alveolar macrophages ( A M ) and type I 1 cells (tII) isolated from control and ozone exposed rats (1.5 r 0.1 mg ozone/m3 : 4 days).
*
= p < 0.05
cell type
AM
=
p < 0.01, n.s. = not significant
parameter
-
derived from control rats ozone exposed rats
GSHPX u/io8 cellsa) U/g proteina)
8.2 t
1.1 213
818
f
62
t
5
62
f
5
n.s.
- phagocytosis after in vitro exposure to 0.47 pg ozone/dishb)
41
t
11
46
f
11
n.s.
- GSHPX u/io8 cellsa) u/g proteina)
38
t
10
84
f f
0.5 14
- viability after & exposure to 0.19 pg ozone/dishb)
49
t
5
52
f
5.2 411
viability after vitro exposure to 0.41 G o n e / d i shb )
t
0.9 t
0.2
2.1
2.0 142
n.s.
f
-
tII
**
5
88 88
n.8.
5
aU = pmol NADPH/min bz of unexposed control
I
-5 5
I
-5 0
I
-4.5
4 s
log
plLciJ
Fig. 3. Toxicity of methyl linoleate ozonide (MLO) towards rat alveolar macrophages ( - o - ) , and the effect of cellular glutathione depletion ( 4 - 1 Utocopherol supplementation ( - r n - ) and vitamin C supplementation (-0-1 on the sensitivity of rat alveolar macrophages towards HLO. The concentration of MLO is in M. Cells were exposed for 2.5 h at 37-12 in medium without serum. = p < 0.05, ** = p < 0.01, *** = p < 0.001 (n-5)
520 The role of nlutathione in fatty acid ozonide detoxification
From the results presented in Pig. 4 it can be seen that preincubation of methyl linoleate ozonide with reduced glutathione caused a significant detoxiPication of the ozonide. In addition, the reaction could be catalyzed by rat liver glutathione S-transferases, since the additional presence of rat liver glutathione S-transferases completely abolished the toxicity of the ozonide model compound. Control incubations using BSA demonstrated that this result is not caused by an aspecific protein effect.
l
o
o
~
,
l
o
o
Y v1 0
c
I
GSH 1mM GSHTr O.Olmg/ml BSA O.lOmg/ml
-
-
-
-
+
-
+
-
-
-
+
+
Fig. 4. Detoxification of methyl linoleate ozonide (86 pM) by preincubation of the ozonide for 2.5 h at 37OC with glutathione (GSH) (1 mH), glutathione Stransferases (a mixture of rat liver isoenzymes 0.01 g/ml) or both. Control incubations were carried out using BSA at 0.10 mg/ml. Toxicity towards alveolar macrophages was determined as described in Pig. 3. ** = p < 0.01, *** p < 0.001 (n=5)
-
DISCUSSION The present paper focusses on the impact mechanisms of ozone at cell level: its node of toxic action and the mechanisms providing cellular protection against this gaseous coapound. Cells enriched in their polyunsaturated fatty acid (PUPA) content by preincubation with arachidonic acid ( 2 0 : 4 ) complexed to bovine serru albumin demonstrated an increased in vitro sensitivity versus ozone. suggesting the involvement of lipid oxidation in the mechanism by which ozone damage is induced in an intact cell system. These results correspond to earlier findings reported by Konings (ref. 28) who
found an increased ozone sensitivity of PUPA enriched
mouse lung fibroblast LM cells. Comparison of cellular antioxidant protection against ozone and nitrogen dioxide clearly indicate that the kind of reactive intermediates and thus the
521 reaction mechanism involved is different in ozone and nitrogen dioxide induced cell damage. This was concluded from the observations which showed that i) vitamin C provided significantly less protection against ozone than against nitrogen dioxide ii) glutathione depletion affected the cellular sensitivity towards ozone to a greater extent than the sensitivity towards nitrogen dioxide, and iii) equally toxic doses of ozone or nitrogen dioxide resulted in a dissimilar breakdown of cellular a-tocopherol. A hypothesis compatible with all above mentioned data would be that ozone induced damage proceeds by the formation of toxic fatty acid ozonides and not by a peroxidative pathway initiated by hydrogen abstractjon. This hypothesis was mentioned earlier in the literature
(refs.
7 , 29-31).
Additional support for the intermediate role of fatty acid ozonides in the process of ozone induced cell damage arises from the observation that the antioxidant protection of cells against methyl linoleate ozonide shows characteristics similar to those of antioxidant protection against ozone itself: an increased sensitivity of glutathione depleted cells, protection by a-tocopherol and a less efficient protection provided by vitamin C. The protection by glutathione was studied in more detail and was shown not to be mediated by the glutathione peroxidase catalyzed detoxification of lipid hydroperoxides as has been suggested in the literature (ref. 18). This could be concluded from several lines of evidence. i) In spite of a significantly increased glutathione peroxidase activity, alveolar nacrophages and type I1 cells isolated from the lungs of ozone exposed rats did not show an increased resistance towards a subsequent in vitro ozone exposure as comphred to cells isolated from non-exposed animals. ii) In addition, A549 cells which do not contain a detectable glutathione peroxidase activity still demonstrated a significantly increased ozone sensitivity upon depletion of their cellular glutathione content. Additional results presented, clearly point t o a role for glutathione as a direct scavenger of toxic fatty acid ozonide intermediates. This detoxification of lipid ozonides by glutathione may be catalyzed by glutathione Stransferases. In summary, results obtained with an intact cell system suggested that oxidation of unsaturated membrane phospholipids by a mechanism that results in the formation of fatty acid ozonides is involved in the mechanism of ozone induced cell damage. The role of glutathione in the cellular defense against ozone induced cell damage can no longer be ascribed to its function in the glutathione peroxidase catalyzed detoxification of lipid hydroperoxides. Glutathione rather functions as a direct scavenger of the toxic lipid ozonide intermediates.
522 REFERENCES 1 Y. Takahashi and T. Miura. 2 I.M.C.M. Rietjens, J.A.M.A.
Environ.Res. 42 (1987) 425-434. Dormans. P.J.A. Rombout and L. van Bree. J.Toxicol.Environ.Health, "in press". 3 J.N. Roehm. J.G. Hadley and D.B. Menzel, Arch.Environ.Health, 23 (1971) 142-148. 4
W.A. Pryor, J.P. Stanley, E. Blair and G.B. Cullen, Arch.Environ.Health. 36 (1976) 201-210.
5 E.V. Srisankar and L.K. Patterson, Arch.Environ.Health. 6
34 (1979) 346-349.
J.B. Mudd, R. Leavitt. A. Ongun and T.T. McManus, Atmosph.Environ., 3 (1969) 669-682.
D.B. Menzel, J.Toxicol.Environ.Health, 13 (1984) 183-204. 8 W.A. Pryor, D.G. Prier and D.F. Church, Environ.Res., 24 (1981) 42-52. 9 A.J. DeLucia. M.G. Mustafa. M.Z. Hussain and C.E. Cross, J.Clin.Invest., 55 7
(1975) 794-802.
10 H. Verwey. K. Christianse and J. van Steveninck. Biochim.Biophys.Acta.
701
(1982) 180-184.
11 12 13
B.L. Fletcher and A.L. Tappel, Environ.Res., 6 (1973) 165-175. C.K. Chow, C.G. Plopper and D.L. Dungworth, Environ.Res., 20 (1979) 309-317. C.K. Chow, C.G. Plopper. M. Chiu and D.L. Dungworth, Environ.Res., 24 (1981)
14
E.E. Dumelin. C.J. Dillard and A.L. Tappel. Arch.Environ.Hea1th. 33 ( 1 9 7 8 )
15 16 17
E.E. Dumelin. C.J. Dillard and A.L. Tappel, Environ.Res., 15 (1978) 38-43. W.A. Pryor and J.W. Lightsey, Science 214 (1981) 435-437. W.A. Pryor, J.W. Lightsey, and D.P. Church, J.A..Chem.Soc., 104 (1962)
315-324. 129-135.
6685-6692. 18 19 20 21 22 23 24 25 26 27
C.K. Chow and A.L. Tappel, Arch.Environ.Health, 26 ( 1 9 7 3 ) 205-208. G.M. Alink, J.C.M. van der Hoeven, F.M.H. Debets, W.S.M. van de Ven, J.S.M. Boleij and J.H. Koeaan, Chemosphere, 2 (1979) 63-73. I.M.C.M. Rietjens, G . M . Alink and R.M.E. Vos. Toxicology, 35 (1985) 207-217. I.M.C.M. Rietjens, L. van Bree. M. Marra, M.C.M. Poelen, P.J.A. Rombout and G.M. Alink, Toxicology, 37 (1985) 205-214. I.M.C.M. Rietjens. M.C.M. Poelen, R.A. Hempenius, M.J.J. Gijbels and G.M. Alink, J.Toxicol.Environ.Health, 19 (1986) 555-568. I.M.C.M. Rietjens, C.A.M. van Tilburg, T.R.R. Coenen. G.M. Alink and A.W.T. Konings, II.Toxlcol.Envlron.Health, 2 1 (1987) 45-56. I.M.C.M. Rietjens, H.H. Lemnink, G.M. Alink and P.J. van Bladeren, Chen.Biol.Interactions, 62 (1987) 3-14. P.J. Hissin and R. Hilt, Anal.Biochen., 74 (1976) 214-226. R.A. Lawrence and R.P. Burk, Biochen.Biophys.Res.Commun., 71 (1976) 952-958. O.H. Lowry, N.J. Rosebrough. A.L. Farr and R.J. Randall, J.Biol.Chen., 193
(1951) 265-275. 28 A.W.T. Konings, J.Toxicol.Environ.Hea1th. 18 (1986) 491-497. 29 D . B . Menzel. R.J. Slaughter, A.M. Bryant and H.O. Jauregui, Health, 30 (1975) 298-301. 30 D.B. Menzel, R.J. Slaughter, A.M. Bryant and H.O. Jauregui, Arch.Environ.Health. 30 (1975) 234-236. 3 1 R. Cortesi and O.S. Privett, Lipids. 7 (1972) 715-721.
Arch.Environ.
T. Schneider et aL (Editors),Atmaspheric Ozone Research and its Policy Implications 0 1989 Elsevier Science Publishern B.V.,Amsterdam -Printed in The Netherlands
523
OZONE-INDUCED STRUCTURAL CHANGES IN MONKEY RESPIRATORY SYSTEM D. M. HYDE', C. G. PLOPPER'. J. R. HARKEMA', J. A. St. GEORGE'. W. S. TYLER' AND D. L. DUNGWORTH' 'Departments of Anatomy and Pathology. School of Veterinary Medicine, University of California, Davis, CA 95616 (USA) 'Lovelace Biomedical Research Institute, P. 0. Box 5890, Albuquerque, NM 87112 (USA) ABSTRACT The principal sites of ozone-induced damage in the respiratory tracts of monkeys are the anterior nasal cavity and respiratory bronchioles. Intermittent exposures (8 h/day) for 6 or 90 days to 0.15 or 0.30 ppm ozone resulted in ciliated cell necrosis, shortened cilia, and secretory cell hyperplasia with less stored glycoconjugates in the nasal region. Respiratory bronchiolitis was also observed in these monkeys at 6 days and persisted to 90 days of exposure. Even at the lower concentration of 0.15 ppm O, nonciliated bronchiolar cells appeared hypertrophied and increased in abundance in respiratory bronchioles. The response of respiratory bronchioles to intermittent (8 h/day), long-term ozone exposure of 0.4 or 0.64 ppm included the following morphometric changes: I) a thicker wall and narrower lumen. 2) thicker epithelial compartment and a much thicker interstitial compartment, 3) shifts in epithelial cell populations with many more nonciliated bronchiolar epithelial cells and fewer squamous type I epithelial cells, 4) larger nonciliated bronchiolar epithelial cells with a larger compliment of cellular organelles associated with protein synthesis, 5) greater volumes of interstitial fibers and amorphous ground substance and 6) greater numbers of interstitial smooth muscle cells, neutrophils, macrophages and mast cells per surface area of epithelial basal lamina. Following cessation of exposure there was persistence of some degree of the hyperplastic and metaplastic epithelial changes. but worsening of interstitial fibrosis. The principal lesion in response to intermittent (8 h/day) 0, exposure of 0.25 ppm daily or to cyclical exposures (9 cycles of 1 month of 0, followed by 1 month of filtered air) for 18 months was respiratory bronchiolitis. Cyclically exposed monkeys, but not those exposed daily, had significantly increased total lung collagen content, chest wall compliance and inspiratory capacity. The conclusions of this study are: 1) there is persistent epithelial injury in the anterior nasal cavity and respiratory bronchiole by as low as 0.15 ppm O,, 2) there is worsening of the respiratory bronchiole lesion in monkeys in the post-exposure period and 3) cyclical exposures cause more severe injury than continued daily exposures. INTRODUCTION The principal lesions resulting from the inhalation of ambient concentrations of the oxidant air pollutant ozone (0,) are located in the nasal cavity and at the junction between conducting airways and alveolar gas exchange regions (1-6).
These affected
regions appear to be species independent, while the damage within the regions appears to
be
species dependent.
Some differences
in
response are
observed in
the
centriacinar region of different species according to the anatomical features of the region.
In species whose centriacinar region is composed of terminal bronchioles
opening directly into alveolar ducts, such as the rat and mouse. the acute response to 0, exposure is damage to the epithelial components of
both the distal terminal
524
bronchiole
and
proximal
alveolar
ducts
and
infiltration
into
the
peribronchiolar
connective tissue and alveolar air spaces of large numbers of mononuclear leukocytes (7).
Longer exposures (3 months or longer) to ambient 0, concentrations produces
epithelial
cell
peribronchiolar
hyperplasia spaces and
along
pulmonary alveolar macrophages (8.9). the
formation of
with
accumulation
respiratory
thickening
and
in
spaces
alveolar
increased of
cellularity
large
of
numbers of
Rats exposed to 1 ppm 0, for 3 months show
bronchiole
segments that
are formed from proximal
alveolar ducts where epithelial necrosis is most conspicuous (10).
In those species whose centriacinar regions include extensive respiratory bronchioles (RB), such as nonhuman primates and carnivores, bronchiolar
region.
similar to rodents (4,ll). nonciliated
the acute lesion is focused in the respiratory
However, epithelial injury and the inflammatory infiltrate is
bronchiolar
Longer term exposures (3 months and over) produce
cell hyperplasia.
increased peribronchiolar fibrosis, and large
accumulations of alveolar macrophages (5,6.12).
Little information is available about
the persistence of these lesions if exposure is terminated.
Acute lesions apparently
resolve to the control state within 7 days after termination of exposure in rats (13), but this resolution appears to be less complete in the rhesus monkeys during the same time period (4).
Recovery from longer exposures (3 months) is only partially resolved
by 60-90 days in rats (8) and mice (9). The purpose of this paper is to summarize briefly our findings in 0,-exposed monkeys, particularly with reference to the emphasis on the nature of the nasal and
RB lesions at ambient levels and the extent to which they are reversible in postexposure periods. METHODS Exoerirnental
a
Male macaque monkeys, colony born and ranging in age from 5 to 11 years or young monkeys 7 months old, were used.
They were free of disease on the basis of clinical
examination, chest radiographs, hemograms and blood chemistry. Eaposure Techniaues Adult monkeys were randomly divided into groups of four animals each and matched by age and weight.
They were housed individually in open mesh stainless steel cages
inside 4.2 cubic meter animal exposure chambers similar to those described by Hinners All monkeys were housed in chambers for one month prior to starting 0,
et al. (14). exposure.
Monkeys were exposed to various concentrations of 0, for variable periods
of time as described in the results section.
Ozone was produced from medical-grade
oxygen by silent arc discharge ozonizers (Erwin Sander Co., Model IV).
The Ozone
concentration in each chamber was monitored at least once every eight minutes with an ultraviolet ozone monitor (Dasibi Environmental Corp., Model 1003-AH). Necroosv and Monkeys were anesthetized with 100 mg ketamine intramuscularly and 60 mg sodium
525
pentobarbital intravenously then killed by exsanguination.
Nasal cavity, trachea and
lung tissue were fixed, lung volumes measure and tissue blocks selected as previously described (I -6).
MorDhometrv Paraffin sections (6 um) or araldite sections (1 urn) were used for light microscopy, while araldite sections (60 nm) were used for transmission electron microscopy. generation respiratory bronchioles were selected by microdissection (5).
First
Multi-level
cascade sampling schemes using stratified random sampling were used for all tissues
(5.6).
Morphometric calculations used standard stereolgical formulas as previously
described (5.6).
Statistical evaluation of morphometric data using animal means by
exposure group was performed by analysis of variance and the 2-tailed t-test (P7D of BMDP program) with p 5 0.05 being the level of significance (15). RESULTS Nasal Ga& Intermittent exposures (8 hours/day) for 6 or 90 days to 0.15 or 0.30 ppm ozone resulted in quantitative changes in the nasal transitional and respiratory epithelium overlying the anterior preturbinate portions of the lateral and septal walls. consisted of
Lesions
ciliated cell necrosis. shortened cilia. and secretory cell hyperplasia.
Inflammatory cell influx was only present at 6 days of exposure.
At 90 days there
were also ultrastructural changes in goblet cells and increased numbers of cells with intracytoplasmic lumena which were not observed after 6 days of exposure.
After
exposure for 6 days there were significant increases in both acidic and neutral glycoconjugates stored in transitional and respiratory epithelium. was significantly less mucosubstance than
at 6 days.
After 90 days there
Only in the
transitional
epithelium did the total and sulfated mucosubstance remain greater than that of controls.
Changes in nasal cavities of monkeys exposed to higher concentrations of
0,were not evaluated. Intermittent exposures (8 hours/day) of monkeys for 6 or 90 days to 0.15 or 0.30 ppm ozone resulted in a respiratory bronchiolitis that persisted at 90 days.
There was
a greater inflammatory infiltrate in RBs at 6 than at 90 days at both concentrations of O*
Even at the lower concentration of 0.15 ppm 0, nonciliated bronchiolar cells
appeared hypertrophied and increased in abundance in RBs and alveolar macrophages were observed throughout the RB lumena. Intermittent exposures (8 hours/day) of monkeys for 1 year to 0.64 ppm 0, did not result in fixed lung volumes or specific lung volumes that were different from monkeys exposed to filtered air for 1 year.
Respiratory bronchioles had a simple
cuboidal epithelium dispersed among squamous epithelial cells.
Alveoli in their walls
were lined by type 1 and type 2 pneumonocytes increased in frequency distally (Fig 1A. 2A).
Lesions within first generation RBs did not differ appreciably among lobes
526
or between cranial and caudal locations within a lobe.
However. within acini there
was a gradient of epithelial changes that decreased in severity from the proximal regions to the more distal regions.
There were no detectable abnormalities in the
proximal alveolar duct.
In the lungs of animals exposed to 0, for I year, a comparison of cross-sectional diameters of RBs between groups showed a significantly smaller diameter (27%) in exposed monkeys as compared to controls.
RBs of these monkeys showed nonciliated
bronchiolar epithelial cells that appeared larger, were more numerous and extended in some cases down into alveoli (Fig
1B. 2B).
In some areas,
small nodules of
nonciliated bronchiolar epithelial cells projected into the airway lumen. alveolar
outpocketings
contained
large
numbers
of
type
2
Many of the
pneumonocytes.
The
epithelial population of the RB showed 81% more nonciliated bronchiolar cells and 87% fewer type 1 pneumonocytes.
Further, nonciliated bronchiolar cells and type I1 cells
had 79% and 67% larger cell volumes, respectively, whereas type 1 pneumonocytes had
a 76% smaller cell volume and a much smaller cell surface area exposed to airspace. Peribronchiolar spaces were enlarged cells
(Fig
2B).
There
lymphocytes/plasma
were
and contained significantly more inflammatory
more
cells (307%) and
neutrophils
(1523%),
interstitial macrophages
mast
cells
(266%).
(274%),
There were
increases in the numbers of fibroblasts and the volume of extracellular fibers when compared to control values by 44% and 31%, respectively. but these changes were not statistically significant. When compared to lungs of controls, monkeys exposed to 1 year 0, followed by 3 months
of
filtered
peribronchiolar
air had
space
RBs
remained
that
enlarged
were
significantly narrower
with
numerous
smooth
(10%).
The
muscle
cells,
fibroblasts, mast cells and extracellular fibers, but there were fewer neutrophils and mononuclear
inflammatory
cells and less amorphous material compared to monkeys
necropsied at the end of the 1 year Os exposure (Fig 2C). of these post-exposure
Epithelial changes in RBs
monkeys included fewer type I1 and nonciliated
bronchiolar
epithelial cells than those necropsied at the end of the 1 year 0, exposure, but the nonciliated bronchiolar
cells appear hypertrophied (Fig I C, 2C).
There also were
fewer alveolar macrophages in RBs of the post-exposure monkeys. Monkeys exposed to 0.4 or 0.64 ppm 0, (8 h/day) for 3 months showed similar changes to monkeys exposed for 1 year.
The epithelial population of the RB showed
80% and 112% more nonciliated bronchiolar cells and 86% and 83% fewer type 1 pneumonocytes at 0.4 and 0.64 ppm 0,. respectively.
Cell volumes of nonciliated
bronchiolar cells were increased in a dose dependent fashion by 31% and 55% at 0.4 and 0.64 ppm 0, as compared to controls.
Further, more of the organelles associated
with protein synthesis in the nonciliated bronchiolar cell were significantly larger in volume in a dose-dependent fashion.
These increases in organellar volumes at 0.64
ppm 0, were: nucleus 42%, mitochondria 82%, rough E R 103% and polyribosomes 73%.
527
Smooth muscle cells showed a dose dependent increase of 2-fold and 3-fold at 0.4 and 0.64 ppm 0,.respectively.
Monkeys exposed to 0.25 ppm 0, daily (8 h/day) or cyclically (9 cycles of 1 month of 0, followed by I month of filtered air) for 18 months showed a persistent respiratory bronchiolitis.
Both groups had significantly more respiratory bronchiolar
volume but no change in diameter.
However, fixed lung volumes or specific lung
volumes were not increased over filtered air controls.
Cyclically-exposed monkeys,
but not those exposed daily for the entire 18 months, had significantly increased total lung
collagen
content,
chest
wall
compliance
and
inspiratory
capacity.
Other
biological differences between the two exposed groups were minor even though the cyclically-exposed monkeys were exposed only half as many days as the daily group.
bronchioles
from monkeys
exposed for I year to 0.00 ppm 0, (A), 1 year to 0.64 ppm Os (3)and
1 year to 0.64
Fig.
1.
Scanning electron
micrographs
of
pprn 0, plus 3 months to 0.00 pprn Os (C). epithelium on septa1 bars.
respiratory A
-
alveolar outpocketing and E =
Fig. 2.
Montages of transmission electron micrographs of respiratory bronchioles from
monkeys exposed for 1 year to 0.00 ppm 0, (A), to 0.64 ppm Os (B) and to 0.64 pprn 0, plus 3 months to 0.00 ppm O,.(C). L = RB lumen, E = epithelium, SM = smooth muscle and = extracellular fibers.
529
DISCUSSION The principal lesions observed in the lungs of monkeys resulting from exposure to ambient concentrations of 0, (0.15 to 0.64 ppm) were found in the anterior nasal region and the central acinus.
Although the epithelial changes in the anterior nasal
region persisted, the chronic damage to the respiratory bronchioles during exposure and the worsening of the peribronchiolar fibrosis after exposure have much greater significance for an understanding of the linkage between oxidant injury and pulmonary disease.
No attempt has been made to find the no effect level below 0.15 ppm 0, in
monkeys, but it certainly will be lower than that concentration. Our investigations in the anterior nasal region showed secretory cell metaplasia, ongoing loss of ciliated cells, deciliation, and ciliogenesis occurred at 90 days of exposure to ambient levels (0.15 ppm) of 0,.
While monkeys exposed for 6 days
showed an increase in epithelial mucosubstance, monkeys exposed for a longer term showed less stored mucosubstance and a significant shift in acidic glycoconjugates from sialomucins to sulfomucins.
0,-induced
changes in the amount of stored
secretory product in the anterior nasal cavity may also reflect alterations in the overlying mucous layer.
Together with ciliated cell injury in the anterior nasal region
these changes may represent a compromise of mucociliary clearance (16).
If there is
significant functional impairment to nasal clearance. this may allow more potentially harmful agents to reach the distal airways. Narrowing of respiratory bronchioles was one of the most significant lesions of the 1 year exposure to 0, that persisted after 3 months in filtered air.
The narrowing
was accompanied by thickening of the peribronchiolar wall that became more fibrous in the post-exposure
period.
Although the connective tissue fibers were increased
over controls in all of the long-term 0, exposed monkeys, there was no significant increase in the fibroblast population. synthesis.
the cell type usually associated with collagen
It seems unlikely that fibroblast number increased early in the 0,-induced
lesion only to decrease by the time of necropsy at 3 months or latter. Increased collagen Increased
crosslinking collagen
and/or
decrease
collagen
breakdown
without
increase
in
crosslinking
are
fibroblast
more
number
plausible. has
been
demonstrated in cats chronically exposed to diesel exhaust and allowed to recover for 6 months in filtered air (17).
Similar observations have been made on the collagen
from monkeys exposed to 0.61 ppm 0, (8h/day) for 1 year (18).
Smooth muscle
hyperplasia and hypertrophy in RB walls was observed after 3 months exposure to 0, and in the 1 year post-exposure monkeys and may represent a more common response of the monkey RB to long-term 0, inhalation.
Cosio et al. (19) identified smooth
muscle hypertrophy in the bronchiolar walls of long-term cigarette smokers. The toxic effects of 0, on cells is thought in part to be due to oxidation and peroxidation of membrane lipids.
It is possible that the large membrane surface of
type I pneumonocytes enhances the susceptibility of these cells to injury.
Their
530
sensitivity
may
be
further
heightened
by
their
low enzymatic activity and
concentrations of protective antioxidant enzyme systems.
low
Such preferential damage to
the type I pneumonocyte would explain the halving of the number and a 10 fold reduction in the surface area of type 1 pneumonocytes observed in monkeys exposed for 3 months or longer to 0 3 .
These epithelial cells with reduced surfake area and
volume may represent type I1 epithelial cell progeny
that do not attain the full
phenotypic differentiation characteristic of type I cells in controls. exposure,
adaptation of metabolic
pathways
augments
With short-term
production of
ozone-sensitive
It is reasonable
to
assume that this adaptive process would be maintained with continued 0, exposure.
It
cellular substrates
and enhances antioxidant production (20).
is possible that in RBs with about a doubling of nonciliated
bronchiolar cells in
monkeys exposed to 0, for I month or longer is a morphological expression of this biochemical adaptation. month-long exposures to 0, were
Monkeys from the cyclical exposure group where
interrupted by a month in filtered air may have lost this cellular and biochemical adaptation during each of the post-exposure periods.
This would imply a naive lung
was present at the beginning of each of the 9 exposure months, whereas the lungs of the monkeys exposed daily remained adapted.
Another explanation for the more
severe RB injury and collagen accumulation in the multiple post-exposure
monkeys
would be multiple acute inflammatory infiltrates composed primarily of neutrophils and monocytes as compared to a more constant alveolar macrophage population in the daily exposed monkeys.
Further, the total number of cells in inflammatory infiltrates The role of the
was much greater in acute than long-term exposures to 0, (4).
neutrophil as a contributor to oxygen-induced injury is well documented (21) as is the experimental neutrophils
lung
injury
resulting
from
intrabronchial
instillation
of
stimulated
that generate oxidants and release proteolytic enzymes into surrounding
tissue (22).
Also, experimental evidence suggests that monocyte-derived macrophages
are the most injurious alveolar macrophages (23).
If both a lack of adaptation and a
greater load of injurious inflammatory cells were present in RBs of monkeys, then epithelial necrosis and connective tissue reaction would continue to progress rather than stabilize. Chronic respiratory bronchiolitis in young human smokers (19), diesel-exposed cats (17),
and
0,-exposed
monkeys
have
interstitial inflammatory cells and fibrosis.
similar
increases
in
alveolar
macrophages,
The respiratory bronchiolitis seen in lungs
exposed to 0.25 or 0.4 ppm 0, was similar, but less severe than that reported in the lung of smokers (24).
The relative length of the smoking history compared to the
exposure periods and the concentrations of pollutants may be factors in the relative severity.
It appears that following long-term exposures to oxidant air pollutants or
cigarette smoke, alterations indicator of lung injury.
in the morphometry of small airways are a sensitive It is notable that 3 months in filtered air after a 1 year
531
exposure Os exposure in monkeys, or 6 months in filtered air after a 27-month diesel exhaust
exposure
inflammation
but
in
cats,
persistence
the of
lungs RB
progression of peribronchiolar fibrosis. of
show
substantial
narrowing and
resolution
of
epithelial metaplasia
cellular and
a
These observations imply a common response
the proximal acinar region to chronic inflammation in species with extensive
respiratory bronchioles and are particularly relevant to susceptible individuals of the urban human population who are exposed to photochemical smog. REFERENCES I
2 3 4
5 6
7
8 9 10 11
12 13 14 15
16
J.R. Harkema, C.G. Plopper, D.M. Hyde, J.A. St. George. D.W. Wilson and D. L. Dungworth, Response of the Macaque Nasal Epithelium to Ambient Levels of Ozone. A Morphologic and Morphometric Study of the Transitional and Respiratory Epithelium, Am. J. Pathol. 128 (1987) 29-44. J.R. Harkema, C.G. Plopper, D.M. Hyde, J.A. St. George and D. L. Dungworth, Effects of an Ambient Level of Ozone on Primate Nasal Epithelial Mucosubstances. Quantitative Histochemistry, Am. J. Pathol. 127 (1987) 90-96. D.W. Wilson, C.G. Plopper and D.L. Dungworth, The Response of the Macaque Tracheobronchial Epithelium to Acute Ozone Injury. A Quantitative Ultrastructural and Autoradiographic Study, Am. J. Pathol. 116 (1984) 193-206. W.L. Castleman, D.L. Dungworth, L.W. Schwartz and W.S. Tyler, Acute Respiratory Bronchiolitis. An Ultrastructural and Autoradiographic Study of Epithelial Cell Injury and Renewal in Rhesus Monkeys Exposed to Ozone, Am. J. Pathol. 98 (1980) 811-840. R.K. Moffatt, D.M. Hyde, C.G. Plopper, W.S. Tyler and L.F. Putney, OzoneInduced Adaptive and Reactive Cellular Changes in Respiratory Bronchioles of Bonnet Monkeys, Exp. Lung Res. 12 (1987) 57-74. L.E. Fujinaka, D.M. Hyde, C.G. Plopper, W.S. Tyler, D.L. Dungworth and L.O. Lollini, Respiratory Bronchiolitis Following Long-Term Ozone Exposure in Bonnet Monkeys: A Morphometric Study, Exp. Lung Res. 8 (1985) 167-190. D.L. Dungworth, C.E. Cross, J.R. Gillespie and C.G. Plopper, The Effects of Ozone On Animals. in J.S. Murphy and J.R. Orr (Editors). Ozone Chemistry and Technology: A Review of the Literature 1961-1974, Franklin Institute Press, Philadelphia, 1975, pp. 29-51. P.F. Moore and L.W. Schwartz, Morphological Effects of Prolonged Exposure to a Mixture of Ozone and Sulfuric Acid on the Rat Lung. Exp. Molec. Pathol. 35 (1981) 108-13. P. Penha and S. Werthamer, Pulmonary Lesions Induced by Long-Term Exposure to Ozone, Arch. Environ. Health 29 (1974) 282-289. B.B. Barr, D.M. Hyde, C.G. Plopper and D.L. Dungworth, Distal Airway Remodeling in Rats Chronically Exposed to Ozone, Amer. Rev. Respir. Dis. 137 (1988) 924-938. P.M. Mellick, D. Dungworth, L. Schwartz and W. Tyler, Short Term Morphological Effects of High Ambient Levels of Ozone on Lungs of Rhesus Monkeys, Lab. Invest. 35 (1977) 82-90. G. Freeman, R. Stephens, D. Coffin and J. Stara, Changes in Dog’s Lungs After Long-Term Exposure to Ozone, Arch. Environ. Health 26 (1973) 209-216. C.G. Plopper, C.K. Chow, D.L. Dungworth, M. Brummer and T.J. Nemeth, Effect of Low Level of Ozone in Rat Lungs. 11. Morphological Responses During Recovery and Re-Exposure, Exp. Mol. Pathol. 29 (1978) 400-41 1. R.G. Hinners, J.K. Burkart and C.L. Punte. Animal Inhalation Exposure Chambers, Arch. Environ. Health 16 (1968) 194-206. W.J. Dixon, BMDP Statistical Software, University of California Press, Berkeley, 1983, pp. 105-115. J.L. Kenoyer, R.F. Phalen and J.R. Davis, Particle Clearance from the Respiratory Tract as a Test of Toxicity: Effect of Ozone on Short and Long Term Clearance, Exp. Lung Res. 2 (1981) 111-120.
532
17 18 19 20 21 22 23 24
D.M. Hyde, C.G. Plopper, A.J. Weir, R.D. Murnane, D.L. Warren, J.A. Last and W.E. Pepelko, Peribronchiolar Fibrosis in Lungs of Cats Chronically Exposed to Diesel Exhaust. Lab. Invest. 52 (1985) 195-206. K.M. Reiser. W.S. Tyler, S.M. Hennessy, J.J. Dominguez and J.A. Last, Long-Term Consequences of Exposure to Ozone. 11. Structural Alterations in Lung Collagen of Monkeys, Tox. Appl. Pharm. 89 (1987) 314-322. M.G. Cosio, K.A. Hale and D.E. Niewoehner, Morphologic and Morphometric Effects of Prolonged Cigarette Smoking on the Small Airways, Am. Rev. Respir. Dis. 122 (1980) 265-271. C.K. Chow and A.L. Tappel, An Enzymatic Protective Mechanism Against Lipid Peroxidation Damage to Lungs of Ozone-Exposed Rats, Lipids 7 (1972) 518-524. D.M. Shasby, R.B. Fox, R.N. Harada and J.E. Repine, Reduction of the Edema of Acute Hyperoxic Lung Injury by Granulocyte Depletion, J. Appl. Physiol. 5 (1982) 12237- 1244. I.U. Schraufstatter, S.D. Revak and C.G. Cochrane, Proteases and Oxidants in Experimental Pulmonary Inflammatory Injury, J. Clin. Invest. 73 (1984) 1175-1 184. P.M. Henson, G.L. Larsen, J.E. Henson. S.L. Newman, R.A. Mussonand C.C. Leslie, Resolution of Pulmonary Inflammation, Fed. Proc. 43 (1984) 2799-2806. D.E. Niewoehner, J. Kleinerman and D.B. Rice, Pathologic Changes in the Peripheral Airways of Young Cigarette Smokers, N. Engl. J. Med. 291 (1974) 755758.
533
SESSION Vlll
CHRONIC OZONE EXPOSURE HEALTH EFFECTS
Chairmen
R. van der Lende J. Graham
This Page Intentionally Left Blank
535
T.Schneider et al. (Editors), Atmospheric Ozone Researchand its Policy Implications 1989 Elsevier Science Publishers B.V.,Amsterdam - Printed in The Netherlands
THE IMPACT OF A 12-MONTH EXPOSURE TO A DIURNAL PATTERN OF OZONE ON PULMONARY FUNCTION, ANTIOXIDANT BIOCHEMISTRY AND IMMUNOLOGY
E.C. A.G.
GROSE’, STEAD’,
STEVENSP, G.E. HATCH’, R.H. COSTA,’ and J.A. GRAHAM’
M.A. D.L.
JASKOTP, M.J.K.
SELGRADE’,
1U.S. Environmental P r o t e c t i o n Agency, Health E f f e c t s Research Laboratory, Research T r i a n g l e Park, NC, 27711
PNorthrop Services, I n c . PO Box 12313, Research T r i a n g l e Park, NC, 27709
ABSTRACT Rats were exposed f o r 1 2 months, 13 hr/day, 7 days/week t o 0.06 ppm 03; Monday through Friday, t h e animals received a 9 h r spike reaching a maximum concentration o f 0.25 ppm. An increase i n t h e r a t e o f lung n i t r o g e n washout was observed i n the 03-exposed r a t s . Residual volume and t o t a l lung c a p a c i t y were reduced. Glutathione peroxidase and reductase a c t i v i t i e s were increased but pulmonary superoxide dismutase was unchanged. Alpha tocopherol l e v e l s were decreased i n lung lavage supernatant and unchanged i n lavaged c e l l s , however, ascorbic a c i d and lavage f l u i d p r o t e i n was increased. Immunological changes were not observed. Thus, chronic exposure t o 03 caused ( 1 ) f u n c t i o n a l lung changes i n d i c a t i v e o f a s t i f f e r lung; ( 2 ) biochemical changes suggestive o f increased a n t i o x i d a n t metabolism; and ( 3 ) no observable immunological changes. INTRODUCTION
Due t o t h e adverse h e a l t h e f f e c t s o f ozone (03) EPA has s e t a National Ambient A i r Q u a l i t y Standard (NAAQS) f o r t h i s p o l l u t a n t a t 0.12 ppm 03 ( h o u r l y average).
A
wide
array of
e f f e c t s a r e reported as a r e s u l t o f
acute o r
subchronic exposure t o 03, b u t very few s t u d i e s documenting c h r o n i c e f f e c t s have been published (1).
General conclusions drawn from t h e e n t i r e data base
were t h a t 03 causes chronic lung disease and o t h e r e f f e c t s on lung morphology, biochemistry, and host defense systems a f t e r long-term exposures. Although a m u l t i t u d e o f
chronic s t u d i e s were possible,
designed t o address two s p e c i f i c o b j e c t i v e s :
t h i s study was
1) t o determine t h e progressive
e f f e c t s o f chronic exposure t o 03 on t h e development o f chronic lung disease as
i n d i c a t e d by p h y s i o l o g i c a l ,
biochemical,
morphometric and immunological
endpoints; and 2 ) t o determine t h e r e v e r s i b i l i t y o r progression o f t h e e f f e c t s a f t e r a clean a i r post-exposure
period.
chosen t o enhance i n t e r p r e t a t i o n o f 5 time p o i n t s .
A r e a l - w o r l d exposure regimen was
t h e study.
Animals were evaluated a t
This r e p o r t describes t h e e f f e c t s o f a 12-mo exposure on phy-
s i o l o g i c a l , biochemical, and immunological endpoints. i s reported separately ( 2 ) .
The morphometric study
536 METHODS Animals Male
Fischer
Laboratories,
344
rats
Kingston, NY.
were
obtained
from
Charles
River
Breeding
This s t r a i n was chosen because (1) body weights
i n adulthood are l e s s than o t h e r s t r a i n s , enabling increased chamber populations;
( 2 ) t h i s s t r a i n has been used f o r previous subchronic r a n g e - f i n d i n g
s t u d i e s o f pulmonary physiology and morphometry;
and ( 3 ) t h e r e i s a l a r g e ,
h i s t o r i c a l c o n t r o l data base a v a i l a b l e f o r q u a l i t y c o n t r o l .
During exposure,
r a t s were housed i n i n d i v i d u a l cages; food and water were a v a i l a b l e ad l i b i tum. Animals were randomly a l l o c a t e d t o treatment combinations and assigned unique i d e n t i f i e r s .
Individual
i n v e s t i g a t o r s were b l i n d as t o t h e treatment
regimen u n t i l the end o f t h e study. Exposure Reqjmmn Data from the National Aerometric Data Bank (NADB) o f t h e O f f i c e o f A i r Q u a l i t y Planning and Standards
(OAQPS),
EPA and Southern C a l i f o r n i a Edison
were used t o assess d i u r n a l p a t t e r n s f o r 03. The i n t e n t o f these analyses was t o focus on days when p o l l u t i o n l e v e l s were e l e v a t e d and d i s c e r n t h e n a t u r e o f the d i u r n a l p a t t e r n .
The 03 exposure p a t t e r n chosen f o r t h i s study represents
f r e q u e n t l y o c c u r r i n g worst cases f o r urban summer environments.
The 03 expo-
sure f o r 12 months consisted o f a background l e v e l o f 0.06 ppm f o r a p e r i o d o f 13 hours, a broad exposure s p i k e r i s i n g t o a 1 h r maximum o f 0.25 ppm over 9
hours from 12:30 pm t o 9:30 pm, and a downtime o f 2 hours (8:30 am t o 10:30 am) f o r s e r v i c i n g t h e f a c i l i t y .
I n t e g r a t i o n o f t h e s p i k e p o r t i o n o f t h e curve
shows t h a t t h e exposure was equivalent t o a square wave t h a t averaged 0.19 ppm.
The background exposure l e v e l was maintained on weekends.
Some animals
were h e l d i n clean a i r f o r 6 months a f t e r t h e cessation o f exposure. Exposure F a c i l i t y The exposure chambers were i d e n t i c a l , w a l k - i n environmental rooms, and are described i n d e t a i l by Davies e t a l .
(3).
The chambers p r o v i d e approximately
1 4 . 2 cubic meters (500 cubic f e e t ) o f exposure volume each.
ments were monitored and c o n t r o l l e d by mechanical
systems
Chamber environproviding
tem-
peratures o f 74f3'F and r e l a t i v e h u m i d i t i e s o f 60f10&. The chambers were operated a t a v e n t i l a t i o n r a t e o f 9-10 a i r changes per hour.
The d e l i v e r y o f 03 t o t h e chambers was r e g u l a t e d by mass f l o w con-
t r o l l e r s , which could be c o n t r o l l e d e i t h e r a u t o m a t i c a l l y o r manually. was generated by passing c y l i n d e r - s u p p l i e d
Ozone
oxygen through a s i l e n t a r c 03
generator (Ozone Research and Equipment Corporation Mode O3V-0) and d i l u t e d
537 with filtered air.
Redundant components provided back-up for all critical
chamber systems. Ozone i n the chamber was monitored using continuous chemiluminescent analyzers [Bendix Model 8002 for 031 according to EPA reference method RFOA-0176-007. The analyzers were calibrated bi-weekly to a UV-based standard following EPA procedures ( 4 , 5 ) . Prior to the study, the spatial distribution of the pollutant in the exposure chamber (with and without animals) was tested to determine gas homogeneity.
Spatial testing was performed to cover the range of gas con-
centrations to be used during the study. The study requirements were that the range of concentrations within a chamber would not exceed f 8% of the target concentration. Pulmonary Physiology A resting breathing analysis was performed, which included measures of tidal volume, frequency, airway flow and breath timing parameters. Functional changes indicative of structural abnormalities were assessed by measuring various lung volumes, ventilation/perfusion, lung elasticity, and alveolar gas diffusing capacity. Small airway integrity was evaluated by analysis of the maximal expiratory flow-volume (MEFV) curve (6).
Vital capacity, residual
volume (RV), total lung capacity (TLC) and single-breath diffusing capacity were determined using gas dilution techniques ( 7 ) , while functional residual capacity was calculated using a plethysmographic application of Boyle's Law ( 8 ) . Ventilation/perfusion was tested using the multiple breath nitrogen (Np) washout technique, and elasticity of the lung was evaluated by analysis of the
deflation component of the quasi-static pressure volume curve (9).
Wet and
dry lung weights were recorded to detect changes in tissue growth or edema. The total number of animals required for statistical evaluation exceeded the number of animals that could be processed on any given day, therefore, there was a 3 day difference in the total number o f days of exposure for these parameters. Lung Biochemistry Lungs were lavaged 5 times with 0.85% saline containing 10 in?! EDTA after cessation of exposure. Each lavage consisted of 35 ml/kg body weight. An aliquot from the first wash was assayed for protein (10). The cell-free supernatant was evaporated to dryness in a rotary vacuum evaporator at 5OoC, reconstituted with deionized water, and extracted for lipid (11). One lavage cell pellet was extracted for lipid using 0.3 ml of 80% ethanol and another was vortexed in 3% perchloric acid (PCA). All extracts were stored at -80.C until assay. Lipid phosphorous was measured in lipid fractions of the lavage
f l u i d or c e l l s by the method o f Morrison e t a1
12).
assayed i n 20,000 g supernatants of PCA e x t r a c t s by
i q u i d chromatography w i t h
electrochemical
was determined i n l i p i d
detection
(13).
Alpha-tocopherol
Ascorbic
a c i d was
f r a c t i o n s by the method o f Vanderwoude e t a1 (14). Whole lung homogenate t o t a l GSH peroxidase (GSH Px), selenium-dependent peroxidase
(GSH Se-Px),
non-selenium
peroxidase
(GSH non-Se-Px)
reductase (GSH Rd) were assayed as previously described (15,16).
and
GSH
Nonprotein
s u l f h y d r y l s (NPSH) were assayed by a m o d i f i c a t i o n o f the method o f Sedlak and Lindsay (17). Superoxide dismutase (SOD) was measured by the method o f Minami and Yoshikawa (18). Immunoloqy C e l l s from spleen as w e l l as c e l l s from the white blood c e l l f r a c t i o n of the peripheral blood were assessed f o r responses t o T c e l l mitogens phytohemagglutinin (PHA) (Burroughs Wellcome, Greenville, (ConA) (Sigma, S t .
Louis,
Mo.),
and concanavalin A
N.C.)
and t o the B c e l l mitogen Salmonella t y p h i -
murium (STM) (RIB1 Immunogen Research, Inc, Hamilton, MT) using methods previously described (19). Spleen c e l l s were a l s o tested f o r spontaneous natural k i l l e r (NK) c e l l a c t i v i t y using a standard 4 hr s ' C r release assay (19) and 4 e f f e c t o r : t a r g e t c e l l r a t i o s ranging from 25:l t o 200:l.
C e l l s were c o l l e c t e d
from lung lavage f l u i d and assessed f o r t o t a l number and percent v i a b i l i t y (using trypan blue exclusion),
and d i f f e r e n t i a l c e l l counts were performed as
previously described (20). Statistics A m u l t i v a r i a t e ANOVA was f i r s t run f o r endpoints i n v o l v i n g m u l t i p l e p r i -
mary responses.
I f the m u l t i v a r i a t e t e s t was s i g n i f i c a n t , i n d i v i d u a l one-way
ANOVA's were run on each of the primary response variables f o r t h a t endpoint. For each o f these variables,
the appropriate contrasts were tested only i f the
main e f f e c t t e s t was s i g n i f i c a n t (p < 0.05). tested subject t o a Bonferroni correction.
The contrasts themselves were
P r o b a b i l i t i e s o f Type 1 and Type 2
e r r o r s were f i x e d a t 0.05 and 0.20, respectively.
RESULTS
General After
12 months of aging,
the animals body weights
had s i g n i f i c a n t l y
increased by approximately 200%. but there was no d i f f e r e n c e between exposed and c o n t r o l animals.
Lung wet and dry weights were b a s i c a l l y the same, as
were the lung-to-body weight r a t i o s .
533 Pulmonary Physiology Pulmonary f u n c t i o n measurements performed on t h e animals exposed t o 03 f o r 12 months i n d i c a t e d a s l i g h t (3.5%), b u t s i g n i f i c a n t depression i n TLC, and an 8.6% depression i n RV (Table 1).
The slope o f t h e m u l t i b r e a t h Np washout was
a l s o s i g n i f i c a n t l y steeper (12%) i n these animals,
however,
when these data
were normalized f o r d i f f e r e n c e s i n volume, t h e washout slopes (CEV-N2-slope) were unchanged from t h e c o n t r o l r a t s . the Np
Following a 6 month recovery period,
washout slopes and RV were e s s e n t i a l l y unchanged from c o n t r o l s ,
however, there continued t o be a s l i g h t depression i n TLC. A l l o t h e r pulmonary f u n c t i o n measures were unremarkable. TABLE 1.
Pulmonary f u n c t i o n f o l l o w i n g 1 2 months o f ozone exposure and a subsequent 6 month recovery p e r i o d i n c l e a n a i r .
12-month exposure 03
Air
N2-Slopea CEV-N2-Slopeb RV (ml) TLC ( m l )
f .Ole f .01 f -06
-0.31 -0.65 1.56 14.13
f .17
-0.35 -0.65 1.43 13.64
P Value
f .01 f .01 f .04 f .15
0.014 0.912 0.089 0.049
6-month recovery p e r i o d 03
Air
N2-Slopea CEV-N2-Slopeb RV (ml) TLC (ml)
-0.36 -0.63 1.76 14.81
f f f f
.01 .01 .08
.02
-0.36 -0.61 1.71 14.26
f f f f
P Value
.02 .02 .08
.22
0.621 0.502 0.703 0.058
slog %nitrogen/breath ( l o g % n itrogen/breath ) / (cumulative e x p i r a t o r y v o l urne/FRC) CData are expressed as t h e mean f standard e r r o r
Lunq Biochemistry 03 exposure had no e f f e c t on t h e volume o f lavage f l u i d recovered (data not shown).
T o t a l p r o t e i n concentration i n t h e bronchoalveolar lavage (BAL)
supernatants
was s i g n i f i c a n t l y ' increased by 55% over
L i p i d phosphorous concentration was a l s o s i g n i f i c a n t l y smaller degree (26%).
Alpha-tocopherol
controls increased,
(Table 2 ) . but t o a
concentration i n BAL supernatant was
s i g n i f i c a n t l y decreased whether i t was expressed per c(g o f l i p i d phosphorous o r per m l o f BAL f l u i d .
u l
TABLE 2
P
0
E f f e c t o f 12 Month 93 Exposure on S r m c h o a l v e o l a r Lavage A n t i o x i d a n t s ____.
Aira Response
_-
1 I
1
T-Testb
03
NonparametricC Test
---- --
BAL SUPERNATANT P r o t e i n , ug/ml L i p i d Phosphorous, pg/rnl A-Tocopherol, ng/ml
1.10 30.81
A-Tocopherol/L-Phosphorous, ng/pg
f f
7-50
107.00
f
0.11
c
18.50 0.18
f
14.80
1.38 12.38
f
-2.11
O.OlO*
28.60 f
14.79
4-02 2
1.28
0.007*
69.20
0.001* 0.003"
0.001* 0.007*
0.010* O.OOl*
BAL CELLS
A-Tocopherol/L-Phosphorous. ng/pg Ascorbate/Protein,
ng/pg
448.00 5.10
?
?
220.00 1.26
472.00 9.45
a Data expressed as mean ? standard d e v i a t i o n (n=8). S i g n i f i c a n c e p r o b a b i l i t y associated w i t h a 2-sided s t u d e n t ' s , t - t e s t assuming unequal variances. Approximate s i g n i f i c a n c e associated w i t h Wilcoxon two-sample rank sum t e s t .
t .227.00 f 1.91
0.837 0. O O l f
0.637 0.002*
541 Neither c e l l u l a r protein, l i p i d phosphorous nor or-tocopherol
were a l t e r e d
by 03 exposure, however, c e l l u l a r ascorbic acid was s i g n i f i c a n t l y increased by 99%.
Total GSH Px a c t i v i t y i n lung homogenate was s i g n i f i c a n t l y increased above controls,
which
was
reflective of
the
increase i n GSH Se-Px
S i m i l a r l y GSH Rd a c t i v i t y was increased i n 03-exposed tissue.
(Table 3 ) . Superoxide
dismutase a c t i v i t y and NPSH content were not remarkably changed. TABLE 3.
Antioxidant enzyme response i n whole lung homogenate f o l l o w i n g 12 months exposure t o 03.
Endpoin t a GSH GSH GSH GSH
Air
Px Se-Px non-Se-Px Rd
12.93 11.44 1.49 2.37 102.30 2.49
SOD NPSH
f f f f f f
P Value
03
0.56 0.38 0.21 0.06 9.30 0.13
16.15 14.07 2.08 2.85 114.63 2.73
f f f f f f
0.56 0.41 0.28 0.05 7.70 0.18
0.002 0 * 001 0.13 0.0001 0.33 0.31
a A l l values are expressed on a per lung basis, as the mean f standard e r r o r (n=8).
Immunotoxicoloay There was no e f f e c t on the response t o e i t h e r B o r T c e l l mitogens i n r a t s exposed t o ozone nor was there any e f f e c t on NK a c t i v i t y .
Ozone had no e f f e c t
on the t o t a l number o f c e l l s recovered from lung lavage f l u i d .
The v i a b i l i t y
o f these c e l l s as w e l l as the percent macrophages, polymorphonuclear leukocytes, and lymphocytes were unchanged.
DISCUSSION
Animals exposed t o 03 f o r 12 months exhibited lower RV and TLC's and steeper multibreath N2 washout slopes, suggesting a s l i g h t ' s t i f f e n i n g ' o f the lung.
Accelerated N2 washouts have been previously a t t r i b u t e d t o a s t i f f e n i n g
of the small airways and/or ever,
parenchyma i n acrolein-exposed r a t s ( 2 1 ) .
w i t h no corresponding reduction o f lung compliance,
How-
and the apparent
acceleration i n lung washout being l a r g e l y a t t r i b u t a b l e t o the s l i g h t reduct i o n i n lung volume, i n t e r p r e t a t i o n of these r e s u l t s i n the context o f i n t e r s t i t i a l f i b r o t i c changes reported by Chang and coworkers ( 2 ) remains somewhat speculative.
I t may be t h a t the s t r u c t u r a l a l t e r a t i o n s l i e as r e s t r i c t i o n s a t
the extremes o f lung volume and, hence, are not r e a d i l y detectable a t
intermediate volumes where e l a s t i c
properties
(as measured by compliance)
t h e o r e t i c a l l y dominate. The increased BAL supernatant p r o t e i n f o l l o w i n g 12 months o f exposure t o low concentrations o f 03 could be due t o p r o t e i n leakage from the plasma o r t o alterations
in
protein
turnover
in
the
alveoli.
The
fact
that
lipid
phosphorous concentrations were a l s o increased may i n d i c a t e t h a t s y n t h e t i c mechanisms are altered.
03 exposure
ppm,
(0.8
Unpublished data from our laboratory shows t h a t acute
2 h r ) caused increased BAL p r o t e i n i n guinea p i g s
without a l t e r i n g BAL phospholipids. Alpha-tocopherol concentrations have been shown t o be lowered i n the whole lung o f guinea p i g s by acute
( 1 6 hr,
ppm) exposure t o NO2 (22), and
5.0
increased i n the r a t lung f o l l o w i n g repeated ( 7 day, 3 . 0 ppm) exposures ( 2 3 ) . Ozone induced changes i n alpha-tocopherol measurements i n BAL f l u i d s and c e l l s . supernatant alpha-tocopherol
have not been reported,
nor have
The present study showed t h a t BAL
was decreased,
suggesting
t h a t the chronic 03
exposure reduced t h i s p o t e n t i a l s u r f a c t a n t - r e l a t e d defense mechanism. c e l l alpha-tocopherol,
BAL
on the other hand, was unchanged.
Accumulation of ascorbic a c i d i n BAL c e l l s was observed which supports the work o f Dubick and coworkers (24) who found increased whole lung ascorbic acid i n r a t s and mice exposed t o 0.64 t o 1 . 5 ppm 03 continuously f o r 5 t o 7 days. Active transport o f ascorbic acid from plasma i n t o lung t i s s u e i s known t o occur ( 2 5 ) , and i t appears t h a t t h i s mechanism can be induced under conditions o f oxidant stress. Acute exposure t o 03 l e v e l s less than 1 ppm t y p i c a l l y r e s u l t s i n increased a c t i v i t y o f most enzymes o f antioxidant metabolism ( 2 6 , 2 7 ) . increase i n a c t i v i t y i s r e f l e c t i v e o f p r o t e i n synthesis,
Whether t h i s
increased population
o f Type I1 e p i t h e l i a l c e l l s o r a combination o f both has been an issue of debate. reason,
The increase i n Type I 1 c e l l s has been most commonly c i t e d as the however,
the question o f
remains unanswered.
a p r o t e c t i v e mechanism or t o x i c response
The observed increase i n GSH Se-Px and GSH Rd a c t i v i t i e s ,
without a concurrent change i n NPSH or SOD, suggest an a c t i v a t i o n ( i . e . t e i n synthesis)
of
pro-
the redox c y c l e of g l u t a t h i o n e which i s i n d i c a t i v e o f
peroxidation o f polyunsaturated f a t t y acids.
Chang e t a l .
(2) reported an
increased volume and number of Type I1 c e l l s and an increased percentage o f alveolar surface area covered by Type I1 c e l l s , a f t e r 18 mo 03 exposure using the same exposure regimen.
I n l i e u o f these concurrent events,
i t i s our
opinion t h a t the increase i n GSH Se-Px and GSH Rd enzyme a c t i v i t y i s a c e l l specific epithelial
mechanism which cells
peroxidation.
against
reflects
protection
recurrent o x i d a t i v e
of
the
newly
transformed
damage and subsequent
lipid
543 Several s t u d i e s have reported suppression o f mitogen responses i n human p e r i p h e r a l blood c e l l s f o l l o w i n g a s i n g l e exposure t o 03 (28,29,30).
In vitro
exposure o f human lymphocytes t o 03 a l s o depressed t h e response t o mitogens (31),
however,
i n t h e present study,
mitogen responses. studies
chronic 03 exposure had no e f f e c t on
I t should be noted t h a t t h e p r o t o c o l f o r human i n v i v o
included exercise
of
subjects during
enhances t h e response t o mitogens).
t h e exposure p e r i o d
(which
The ozone exposure a f f e c t e d n o t o n l y t h e
mitogen response b u t a l s o t h e p r o d u c t i o n o f s t r e s s hormones as a r e s u l t o f exercise.
This study d i d not i n c l u d e exercise as p a r t o f t h e p r o t o c o l .
It
should a l s o be noted t h a t t h e responses o f c o n t r o l r a t s t o mitogens f o l l o w i n g 1 2 months o f exposure t o a i r were considerably lower than t h a t observed i n
younger
r a t s (15 and 24 wks o l d )
suggesting t h a t a t t h i s time p o i n t t h e
response was already markedly depressed by aging.
However,
no such aging
e f f e c t s were observed w i t h t h e NK response which was a l s o u n a f f e c t e d by ozone exposure. I n summary, chronic exposure t o ambient concentrations o f 03 causes functional disease.
lung
changes
indicative
but
affirmative
of
progressive
lung
However, removal o f t h e 03 challenge confirms r e v e r s i b i l i t y o f t h e
f u n c t i o n a l decrement.
Supplementary changes i n a n t i o x i d a n t mechanisms suggest
a c e l l specific biochemically-initiated cells
not
against
oxidative
challenge
p r o t e c t i o n o f transformed e p i t h e l i a l and
subsequent
lipid
peroxidation.
A l t e r a t i o n s i n systemic immune f u n c t i o n and pulmonary f r e e c e l l populations were not detected a f t e r 12 months o f chronic exposure.
REFERENCES
€PA, A i r Q u a l i t y C r i t e r i a f o r Ozone and Other photochemical Oxidants, Ch. 10-13, EPA-600/8-84-020A ( F i n a l D r a f t ) , ECAO, Research T r i a n g l e Park, NC, 1986. 2 L.Y. Chang, Y. Huang, R.L. S t o c k s t i l l and J.D. Crapo, Proc. I n t . Symposium on Atmospheric Ozone Research and i t s P o l i c y I m p l i c a t i o n s , 1988, pp. 3 D.W. Davies, L.C. Walsh 111, M.E. Hiteshew, M.G. MBnache, F.J. M i l l e r and E.C. Grose, J. Toxicol. Environ. Health, 21 (1987) 89-97. 4 €PA, Technical Assistance Document f o r t h e Chemiluminescence Measurement o f Nitrogen Dioxide, €PA-600/4-75-003, 1975. 5 €PA, Transfer Standards f o r C a l i b r a t i o n o f A i r M o n i t o r i n g Analyzers f o r Ozone, EPA-600/4-79-056, 1979. 6 J.S. Tepper, M.J. Wiester, D.L. Costa, W.P. Watkinson and M.F. Weber, Environ. Health Persp., 72 (1987) 95-103. 7 J. Takezawa, F.J. M i l l e r and J. O'Neil. J. Appl. Physiol., 48(6) (1980) 1052-1059. 8 A.B. DuBois, S.Y. Bothelo, G.N. Bedell, R. Marshall and J.H. Comroe, J r . , J. C l i n . Invest., 35 (1956) 322-326. 9 J.A. Raub, G.E. Hatch, R.R. Mercer, M. Grady and P-C. Hu, Environ. Res., 37 (1985) 72-83. 10 O.H. Lowry, J.J. Rosebrough, A.L. F a r r and R.J. Randall, J. B i o l . Chem., 193 (1951) 2665-2675. 11 E.G. B l i g h and W.J. Dyer, Can. J. Biochem., 37 (1959) 911-917.
1
544 Morrison, Anal. Biochem., I (1964) 218-224. Kutnink, J.H. Skala, H.E. Sauberlich and S.T. Omaye, J. L i q u i d . Chromatog. 8 (1985) 31-46. M. Vandewoude, M. Claeys and I. DeLeeuw, J. Chromatography, 311 (1984)
12 W.R. 13 M.A. 14
116-182. 15 16 11 18 19 20
Jaskot, E.G. Charlet, E.C. Grose, M.A. Grady and J.H. Roycroft, J. Anal. Tox., 7 (1983) 86-88. E.C. Grose, J.H. Richards, R.H. Jaskot, M.G. Mdnache and J.A. Graham, J. Toxicol. Environ. Health, 21 (1987) 219-232. J. Sedlack and R.H. Lindsay, Anal. Biochem., 25 (1968) 192-205. M. Minami and H. Yoshikawa, C l i n i c a Chirnica Acta, 92 (1919) 331-342. M.K. Selgrade, M.J. Daniels, P.C. Hu, F.J. M i l l e r and J.A. Graham, I n f e c t . Immun., 38 (1982) 1046-1054. M.K. Selgrade, G.E. Hatch, E.C. Grose, J.W. I l l i n g , A.G. Stead, F.J. M i l l e r and J.A. Graham, J. Toxicol. Environ. Health, 21 (1981) R.H.
173-185. 21
D.L.
Dis.,
Costa,
R.S.
Kutzman, J.R
Lehmann and R.T.
Drew,
Am.
Rev. Respir.
133 (1986) 286-291.
23
Hatch, R. Slade, M.J.K. Selgrade and A.G. Stead, T o x i c o l . Appl. Pharm. 82 (1986) 351-359. A. Sevanian, N. Elsayed and A.O. Hacker, J. Toxicol. Environ. Health, 10
24
M.A.
22
G.E.
(1982) 743-156. 25 26 21
28
Dubick, J.W. C r i t c h f i e l d , J.A. Last, C.E. Cross and R.B. Rucker, Toxicology, 21 (1983) 301-313. R.J. W i l l i s and C.C. Kratzing, Plugers Arch., 356 (1975) 93-98. C.K. Chow, C.J. D i l l a r d and A.L. Tappel, Environ. Res., I (1914) 311-319. M.G. Mustafa, N.M. Elsayed, J.A. Graham and D.E. Gardner, Biomedical E f f e c t s o f 03 and Photochemical Oxidation, P r i n c e t o n S c i e n t i f i c Pub. I n c . , Princeton, NJ, 1983, pp. 51-73. M.L. Peterson, N. Rummo, D. House, and S. Harder, Arch. Environ. Health,
33 (1918) 59-63. 29 30 31
M.L. Peterson, R. Smialowicz, S. Harder, B Ketcham and D. House, Environ. Res., 24 (1981) 299-308. G.S. Orlando, D. House, H.S. Koren and S. Becker, I n h a l a t i o n Toxicol., 1988; i n press. S. Becker, R.L. Jordan, G.S. Orlando and H.S. Koren. J. T o x i c o l . Environ. Health, 1988 (submitted).
ACKNOWLEDGEMENTS The authors would l i k e t o g r a t e f u l l y acknowledge t h e e x c e l l e n t t e c h n i c a l assistance o f Kay Crissman, Mary Daniels, David W. Hassel H i l l i a r d ,
Michael
Norwood,
Richards,
Judy H.
E.
Hiteshew,
Joseph W.
Valerie S i l l s ,
Davies, Shelley F i t z g e r a l d , Illing,
Ralph Slade,
John McKee,
Diane Starnes,
Joel James
Tannery, Dock T e r r e l l , Mike Thompson, Leon Walsh, 111, and Mary Weber. The authors would a l s o l i k e t o thank D r . Fred J. M i l l e r f o r h i s guidance and support and D r . P h i l i p Johnson f o r h i s c o n s u l t a t i o n on animal care. DISCLAIMER: The research described i n t h i s a r t i c l e has been reviewed by t h e H e a l t h E f f e c t s Research Laboratory, U.S. Environmental P r o t e c t i o n Agency, and approved f o r p u b l i c a t i o n . Approval does n o t s i g n i f y t h a t t h e contents n e c e s s a r i l y r e f l e c t t h e views and p o l i c i e s o f t h e Agency nor does mention o f t r a d e names o r commercial products c o n s t i t u t e endorsement o r recommendation f o r use.
T.Schneider et al. (Editors), Atmospheric Ozone Research and its Policy Implications 0 1989 Elsevier Science Publishers B.V.,Amsterdam -Printed in The Netherlands
Effects of Repeated Exposure t o 0.15 ppm R e a c t i v i t y i n Guinea Pigs (4 hrs/day;
O3
545
f o r Four Months on B r o n c h i a l
5 days/wk)
J. KAGAWA. M. HAGA, and M. M I Y A Z A K I Department o f Hygiene and P u b l i c Health, Tokyo Women's Medical C o l l e g e 8-1 Kawada-cho, Shinjuku-ku, Tokyo 162, Japan
ABSTRACT I n o r d e r t o i n v e s t i g a t e t h e e f f e c t o f repeated d a i l y exposure (4 hrs/day, 5 days/week) t o 0.15 ppm 03 f o r f o u r months on b r o n c h i a l response t o h i s t a m i n e challenge, 12 male H a r t l e y guinea p i g s approximately 4 t o 5-week o f age (mean body weight, 252 g) were used f o r t h e 0 exposure studies, and 11 guinea p i g s were used f o r t h e c o n t r o l ( f i l t e r e d a i r j exposure studies. T o t a l r e s p i r a t o r y f l o w r e s i s t a n c e d u r i n g e x p i r a t i o n ( R t ) and t h e histamine-induced i n c r e a s e i n R t were measured every 3 weeks. 10 t i d a l breaths o f h i s t a m i n e aerosol were administered u n t i l a t l e a s t a 100% increase o f t h e i n i t i a l b a s e l i n e R t occured. Baseline R t before t h e h i s t a m i n e challenge decreased w i t h age, e s p e c i a l l y before body weight was 400 t o 500 g. No s i g n i f i c a n t d i f f e r e n c e s were observed between 03 and f i l t e r e d a i r exposure groups. The e f f e c t i v e c o n c e n t r a t i o n o f h i s t a m i n e t h a t produced a 100% increase o f b a s e l i n e R t i n 03 group was h i g h e r than t h a t o f f i l t e r e d a i r group, and s i g n i f i c a n t d i f f e r e n c e s were observed between b o t h groups, suggesting a d a p t a t i o n d u r i n g repeated exposures t o 03 i n b r o n c h i a l s e n s i t i v i t y t o histamine. INTRODUCTION Bronchial h y p e r r e a c t i v i t y may be i m p o r t a n t i n t h e pathogenesis o f a s t h m a t i c bronchospasm. I t i s w e l l known t h a t a s i n g l e exposure t o ozone (03)p o t e n t i a t e s b r o n c h i a l response t o b r o n c h o c o n s t r i c t o r challenge.
Lee and co-workers (ref. 1)
employing dogs and Golden e t al. (ref. 2 ) s t u d y i n g humans found t h a t a 2-hr
O3 r e s u l t e d i n a i r w a y h y p e r r e a c t i v i t y t o i n h a l a t i o n o f
exposure t o 0.6-1.2
ppm
h i s t a m i n e aerosol.
Dimeo e t al. (ref. 3) i n d i c a t e d t h a t t h e t h r e s h o l d
c o n c e n t r a t i o n o f 03 causing an increase i n b r o n c h i a l r e a c t i v i t y i n h e a l t h y human s u b j e c t s was between 0.2 and 0.4 ppm, and t h a t a d a p t a t i o n t o t h i s e f f e c t o f O3 developed w i t h repeated exposures f o r 3 consecutive days. The purposes o f t h i s s t u d y were t o determine t h e e f f e c t o f repeated exposures t o 0.15 ppm 03, t h a t m i g h t be encountered i n t h e urban atmosphere. on b r o n c h i a l r e a c t i v i t y i n growing guinea pigs, because i t m i g h t be an i m p o r t a n t problem t o i n v e s t i g a t e t h e p o s s i b i l i t y o f b r o n c h i a l h y p e r s e n s i t i v i t y o r h y p e r r e a c t i v i t y t o b r o n c h o c o n s t r i c t i ve agents produced by prolonged repeated exposure t o
O3 i n t h e g r o w t h process o f human.
546
METHODS
23
male H a r t l e y guinea p i g s a p p r o x i m a t e l y 4 t o 5-week o f age were used f o r
t h i s study. Animals weighed 230-300 g a t t h e t i m e o f exposure and were d i v i d e d i n t o t w o groups as t h e mean body w e i g h t was a p p r o x i m a t e t l y same i n b o t h groups. 12 were used f o r t h e
O3
exposure s t u d i e s and 11 were used f o r t h e c o n t r o l
( f i l t e r e d a i r ) exposure studies. Exposures were conducted i n t w o 1.5 m3 s t a i n l e s s - s t e e l c o n t r o l l e d environment chambers m a i n t a i n e d a t 24’C and 65% r e l a t i v e h u m i d i t y (one chamber f o r t h e c o n t r o l s t u d i e s and t h e o t h e r one f o r t h e
O3
exposure studies).
Temperature and r e l a t i v e h u m i d i t y i n t h e a n i m a l housing room were m a i n t a i n e d a t t h e same l e v e l s . F o r t h e c o n t r o l s t u d i e s ,
o n l y a i r f i l t e r e d by h i g h - e f f i c i e n c y
p a r t i c u l a t e m a t t e r f i l t e r s was present. F o r t h e
03
03
exposure s t u d i e s ,
generated b y passing a metered f l o w o f 100% oxygen t h r o u g h a s i l e n t - a r c
03
generator. The c o n c e n t r a t i o n o f chemiluminescent
O3
a n a l y z e r ( D a s i b i Co.,
was c o n t i n u o u s l y m o n i t o r e d ’ u s i n g
a n a l y z e r (Kimoto Co., Model
1003 AH),
was
O3
a
Model 807) and an u l t r a v i o l e t
03
w h i c h were c a l i b r a t e d b y a potassi’um
i o d i d e method ( r e f . 4). N i t r o g e n o x i d e s c o n c e n t r a t i o n s were c o n t i n u o u s l y m o n i t o r e d u s i n g a chemiluminescent NOx a n a l y z e r (Kimoto Co., was c a l i b r a t e d by t h e gas phase t i t r a t i o n method (Kimoto Co.,
NO and NO?
A light-scattering,
single-particle
Model 158). w h i c h Model
c o u n t e r (Rion Co.,
DS-30)
for
Model KC-01)
m o n i t o r e d p a r t i c u l a t e s i n f i v e subranges between 0.5 and 10 pm i n diameter. Animals were exposed t o (Monday t h r o u g h Friday),
0.15
ppm
03
o r f i l t e r e d a i r f o r 4 hr/day,
5 days/week
f o r 18 weeks. Body w e i g h t was measured e v e r y week.
T o t a l r e s p i r a t o r y f l o w r e s i s t a n c e ( R t ) and t h e h i s t a m i n e - i n d u c e d i n c r e a s e i n R t were measured on F r i d a y of e v e r y were n o t exposed t o
O3
3
weeks. On t h e R t measurement day, a n i m a l s
o r f i l t e r e d air.
R t d u r i n g e x p i r a t i o n was measured i n unanesthetized, spontaneously b r e a t h i n g guinea p i g s by an apparatus prepared as o r i g i n a l l y d e s c r i b e d b y Mead ( r e f . 5) and m o d i f i e d by Kagawa (ref.
6).
A diagram o f t h e apparatus i s demonstrated i n
Fig. 1. Each animal was p l a c e d i n s i d e a body plethysmograph w i t h a neck p l a t e w h i c h had a h o l e i n t h e c e n t e r and was covered w i t h s o f t rubber. The mask used f o r measuring a i r f l o w o f a guinea p i g was made f r o m a m e t a l cone t h a t f i t t e d an animal’s face. The opening o f t h e mask was covered w i t h s o f t r u b b e r t h a t f i t t e d c l o s e l y t o t h e f a c e of t h e guinea p i g and made a s e a l w i t h t h e face. The mask has a s m a l l h o l e i n f r o n t t o h o l d a pneumotachograph (Nihon Koden Kogyou
Co.,
Model TV-241T) and a n o t h e r on i t s t o p l e t t i n g a i r o r a e r o s o l in.
The
pneumotachograph was c a l i b r a t e d w i t h a c o n s t a n t f l o w o f a i r a t 2 L/min. plethysmograph has t w o t u b i n g connections:
The
a t r a n s d u c e r p r e s s u r e 1i n e f o r
p r e s s u r e changes i n s i d e t h e plethysmograph and a c o n d u c t i n g t u b e l e a d i n g t o sine-wave pump (5-6 c y c l e s p e r second).
The p r e s s u r e i n s i d e t h e plethysmograph
and t h e f l o w from t h e pneumotachograph were p i c k e d up b y d i f f e r e n t i a l p r e s s u r e
547
F i g . 1. Apparatus used t o measure t o t a l respiratory flow resistance and b r o n c h i a l r e a c t i v i t y t o inhaled s a l i n e o r histamine aerosol.
Osci 1 l o s c o p e
cycles/sec
I -+
Aerosol(Sa1ine o r Histamine)
transducers (Nihon Koden Kogyou Co.,
Model TP-602T and 603T).
R t was o b t a i n e d
f r o m o s c i l l o s c o p e v e c t o r s o f f l o w and p r e s s u r e d u r i n g t h e e x p i r a t o r y phase ( r e f . 6). Measurements o f R t were made a t about 10 seconds i n t e r v a l s f o r 2 minutes. B r o n c h i a l r e a c t i v i t y t o h i s t a m i n e a e r o s o l was assessed by measuring t h e histamine-induced i n c r e a s e i n s t a r t i n g R t . H i s t a m i n e d i h y d r o c h l o r i d e s o l u t i o n s f o r i n h a l a t i o n were prepared d a i l y by d i l u t i n g i n normal s a l i n e s o l u t i o n . The aerosol was generated u s i n g a n e b u l i z e r ( B i r d Co.. compressed-air source ( n e b u l i z e r o u t p u t : 2 L/min).
Model 5041) d r i v e n b y a
To c h a l l e n g e nose-breathing
animals, t h e n e b u l i z e r was connected t o one s i d e h o l e o f t h e mask and a i r f l o w was d i v e r t e d t h r o u g h a second s i d e hole. A f t e r t h e i n i t i a l b a s e l i n e R t was determined,
t h e mask f o r a e r o s o l i n h a l a t i o n was a t t a c h e d t o t h e f a c e (Fig.
1).
R e s p i r a t o r y frequency was m o n i t o r e d as t h e p r e s s u r e changes i n s i d e t h e plethysmograph. 10 b r e a t h s o f normal s a l i n e a e r o s o l were a d m i n i s t e r e d ,
and
i m m e d i a t e l y a f t e r s a l i n e c h a l l e n g e R t was measured a t about 10 seconds i n t e r v a l s f o r 2 minutes. The s a l i n e c h a l l e n g e s were f o l l o w e d by s i m i l a r i n h a l a t i o n o f p r o g r e s s i v e l y i n c r e a s i n g c o n c e n t r a t i o n s o f a e r o s o l i z e d histamine. The h i s t a m i n e a e r o s o l used t o c h a l l e n g e a n i m a l s was generated f r o m 0.0625.
0.125, 0.25,
0.5.
1.0,
1.5,
2.0,
2.5,
and 3.0 % s o l u t i o n s . T h i s p r o c e s s was
repeated u n t i l a t l e a s t a 100% i n c r e a s e of t h e i n i t i a l b a s e l i n e R t occurred.
A two-way a n a l y s i s of v a r i a n c e (ANOVA) w i t h repeated measures across f i l t e r e d a i r and O3 exposures was performed on t h e body weight, hyperresponsiveness data. I n a l l cases, f o r p v a l u e s o f l e s s t h a n 0.05.
pulmonary f u n c t i o n and
d i f f e r e n c e s were c o n s i d e r e d s i g n i f i c a n t
548 RESULTS Environmental data i n t h e exposure chamber O3 c o n c e n t r a t i o n i n t h e 03 exposure chamber was m a i n t a i n e d a t t h e average o f 0.15 ppm (range 0.14-0.16
I n t h e O3 and f i l t e r e d a i r exposure chambers,
ppm).
NO2 c o n c e n t r a t i o n v a r i e d between 0.01 and 0.03 ppm, and NO c o n c e n t r a t i o n v a r i e d between 0.01 and 0.06 ppm. The c o n c e n t r a t i o n o f s u l f u r d i o x i d e was n e g l i g i b l e . The number o f p a r t i c l e s i n t h e 0.5-um
d i a m e t e r v a r i e d between 200 and 400
p a r t i c l e s p e r c u b i c foot. Body growth The animals a t beginning o f t h e exposure weighed t h e f o l l o w i n g : 252.2 16.7 gm (mean
+ S.E.)
i n t h e f i l t e r e d a i r e x p o s u r e group: 253.2
+
+
11.3 gm i n
t h e O3 exposure group. Fig. 2 p r e s e n t s t h e means o f t h e body weights o f these groups d u r i n g t h e exposure t o 03 o r f i l t e r e d a i r . The animals exposed t o f i l t e r e d a i r have a body w e i g h t l e s s than those exposed t o 0 3 T h i s d i f f e r e n c e was s l i g h t , b u t s t a t i s i t i c a l l y s i g n i f i c a n t .
No s i g n i f i c a n t i n t e r a c t i o n was
observed ( T a b l e 1).
Fig. 2. Mean body weight o f guinea p i g s exposed t o filtered air and 0.15 ppm 03. o ' . * . 0
1
2
.
I
.
.
5
4
. 6
. 1
.
8
.
9
.
10
.
11
.
12
:
11
tI 14
15
16
17
18
19
Urek
Table 1. Results o f ANOVA. Bod weigL
Rt
PCloo
%Increase of R t
Exposure (FA, 03)
F ratio P value
29.95 0.0001
0.67 0.4158
6 85 010098
1.11 0.2928
Week
F ratio P value
267 30 0.0601
59.61 0.0001
3.71 0.0018
4.19 0.0006
Exposure x Week
F ratio P value
0.86 0.6281
0.80 0.5693
1.61 0.1470
6:$:0
Pulmonary f u n c t i o n
and
hyperresponsiveness s t u d i e s
Baseline R t b e f o r e t h e s a l i n e and h i s t a m i n e challenges decreased s i g n i f i c a n t l y w i t h age, e s p e c i a l l y b e f o r e body w e i g h t was 400 t o 500 g (Fig.
549
3). Differences between O3 and f i l t e r e d a i r exposure groups i n any week were n o t s i g n i f i c a n t , and no s i g n i f i c a n t i n t e r a c t i o n was oberved (Table 1).
i
I
0.2'
1
0.1
start of I.p0wr.
''
.
&
.
.
.
,
.
.
.
.
.
.
.
Fig. 4 shows an example o f t h e t i m e course o f t h e increase i n R t a f t e r
If
i n h a l a t i o n o f h i s t a m i n e aerosol.
1.0% histamine
D U
. $
2.5
b r o n c h o c o n s t r i c t i o n occurred,
U
it
u s u a l l y d i d so i m m e d i a t e l y a f t e r 10
0, E
breaths o f h i s t a m i n e aerosol. R t
v
4
2.0
reached a maximum value w i t h i n 1 min,
4 + 0
and decreased r a p i d l y t h e r e a f t e r .
The
yl (L D
e f f e c t i v e concentration o f histamine
3
2
LL
1.5
t h a t produced a lOOX i n c r e a s e o f mean
2,
L
b a s e l i n e R t (PC1oo) was presented i n
0
+J
L 4
Fig. 5. Mean o f PC100 i n
n
5
OL
1.0
O3 g r o u p was
h i g h e r than t h a t o f f i l t e r e d a i r
e 4
group except t h e 9-week exposure.
e
D i f f e r e n c e s o f PC100 between
0.5
O3
and
f i l t e r e d a i r groups were s i g n i f i c a n t , b u t no s i g n i f i c a n t i n t e r a c t i o n was 0
I
1
2
3 (min)
o b s e r v e d ( T a b l e 1). I n Fig. 6, t h e mean o f t h e maximal p e r c e n t increase o f R t o f t h e i n i t i a l b a s e l i n e value
Fig. 4. An example o f t i m e course o f increase i n R t a f t e r i n h a l a t i o n o f s a l i n e o r histamine aerosol
aFter PC100 decreased s i g n i f i c a n t l y w i t h age. However, no s i g n i f i c a n t d i f f e r e n c e between b o t h groups and no s i g n i f i c a n t i n t e r a c t i o n were observed ( T a b l e 1).
550 1
2.2
Fig. 5. Mean c o n c e n t r a t i o n o f h i s t a m i n e which produced a 100% increase o f i n i t i a l base1 ine R t (PC), i n guinea p i g s
o
exposed t o f i 1t e r e d
of
%.rt
0.2
i.po,ur.
:
0
t
.
1
.
.
2
.
3
-
4
.
5
.
6
-
1
-
a i r and 0.15 ppm 8
9
10
11
12 11
14
15
16
17
Yeek
I8
O3
19
(Mean f S. E. ).
Fig. 6. Mean o f t h e maximal p e r c e n t increase o f R t o f the i n i t i a l baseline v a l u e a f t e r PClo0 i n guinea p i g s exposed t o f i l t e r e d a i r and 0.15 ppm 03 (Mean
s,ar,
+
C!
S.E.)
a1
i.Po."r.
0
1
2
3
4
5
6
1
8 9 1 0 1 1 1 2 1 1 1 ~ 1 5 1 6 1 1 1 8 1 Ucak
DISCUSSION To c l a r i f y some t e r m s t o d e s c r i b e b r o n c h i a l r e a c t i o n s ,
hypersensitivity
imp1 i e s t h a t a i r w a y responds t o l o w e r t h a n normal c o n c e n t r a t i o n s o f h i s t a m i n e , and h y p e r r e a c t i v i t y i m p l i e s t h a t t h e i n c r e a s e i n t h e response o b t a i n e d b y d o u b l i n g t h e c o n c e t r a t i o n o f h i s t a m i n e i s l a r g e r t h a n normal. I n t h i s study, we have shown t h a t repeated exposure t o 0.15 ppm i n c r e a s e o f body weight,
O3
produced a tendency o f
a s i g n i f i c a n t decrease o f b r o n c h i a l s e n s i t i v i t y ,
but
no s i g n i f i c a n t decrease o f r e a c t i v i t y t o h i s t a m i n e i n t h e guinea p i g s tested.
I t c o u l d n o t be e x p l a i n e d why a tendency o f i n c r e a s e o f body w e i g h t was obseved i n t h e 03-exposed group. A c o n s i s t e n t tendency o f i n c r e a s e o f body w e i g h t i n any week m i g h t be a t t r i b u t e d t o O3 exposure. r e p o r t e d d r i n k i n g a c t i v i t y i n r a t s exposed t o 0.2 ppm a t t h e f i r s t day a f t e r t h e b e g i n i n g o f
O3
exposure,
Umezu e t a l .
O3
( r e f . 7)
f o r 7 days decreased
recovered t o t h e c o n t r o l
l e v e l on t h e second day, and m a i n t a i n e d t h e c o n t r o l l e v e l . One r a t p e r s i s t e n t l y d i s p l a y e d a somewhat h i g h e r d r i n k i n g a c t i v i t y a f t e r t h e second day o f exposure. T h i s s t u d y suggest a p o s s i b i l i t y t o i n c r e a s e somewhat d r i n k i n g a c t i v i t y ,
551 probably a l s o food t a k i n g a c t i v i t y , and t o r e s u l t i n a tendency o f increase o f body weight i n some animals. The mean R t o f t h e guinea p i g s exposed t o O3 f o r 18 weeks d i d n o t d i f f e r from those exposed t o f i l t e r e d a i r . There i s no long-term exposure study of 03 on pulmonary f u n c t i o n i n guinea pigs, although several papers have been published on t h e e f f e c t o f long-term exposure t o ambient l e v e l s o f 03 on pulmonary f u n c t i o n i n r a t and monkey. Raub e t al. ( r e f . 8) r e p o r t e d t h a t peak i n s p i r a t o r y f l o w was reduced 14% and 12% i n neonatal r a t s exposed t o 0.12 and
0.25 ppm 03, 12 h r / d a y . 7 days/week f o r 6 weeks. B a r t l e t t e t a l . ( r e f . 9) r e p o r t e d t h a t a f t e r 30 days o f continuous exposure t o 0.2 ppm 03. r a t s e x h i b i t e d a f u n c t i o n a l l e s i o n resembling t h a t o f e a r l y emphysema, marked by increased l u n g compliance and volume w i t h no apparent morphological damage. Costa e t al. ( r e f .
10) found increased pulmonary r e s i s t a n c e i n r a t s exposed t o
0.2 o r 0.8 ppm of 03, 6 hrlday,
5 days/week f o r 62 exposure days. They a l s o
observed decreased maximum e x p i r a t o r y f l o w s a t low l u n g volumes (25 and 10 percent o f VC) i n these rats. Changes i n maximum f l o w a t l o w l u n g volumes i n d i c a t e p e r i p h e r a l a i r w a y d y s f u n c t i o n and may be r e l a t e d t o decreased a i r w a y s t i f f n e s s o r narrowing o f t h e a i r w a y lumen. E u s t i s e t al. (ref.
11) r e p o r t e d
increased q u a s i s t a t i c compliance o f t h e lung and low-grade c h r o n i c r e s p i r a t o r y b r o n c h i o l i t i s i n monkeys exposed t o 0.5 ppm 03, 8 hr/day f o r 90 consecutive days. Our f a i l u r e t o f i n d impairment o f pulmonary f u n c t i o n may be due t o a c t u a l l a c k o f e f f e c t o f t h e exposure o r i n a b i l i t y o f our methods t o p i c k up s u b t l e abnormal it i e s .
O3 p o t e n t i a t e s t h e e f f e c t s o f drugs t h a t c o n s t r i c t a i r w a y smooth muscle i n m i c e ( r e f . 12), g u i n e a p i g s ( r e f . 13). dogs ( r e f . l),sheep ( r e f . 14), and humans (ref. 2). These i n v e s t i g a t o r s showed t h e increased a i r w a y r e a c t i v i t y t o bronchoconstricing agents i n these animals and humans exposed t o 0.1 t o 1.0 ppm of
O3 f o r 1 t o 2 hrs. Holtzman e t al. (ref.15) r e p o r t e d t h e t i m e course o f 03O3 f o r 2
induced a i r w a y h y p e r r e a c t i v i t y i n dogs exposed t o 1.0 and 2.2 ppm o f
hrs. Airway responsiveness t o a c e t y l c h o l i n e i n 7 dogs increased markedly 1 hr, t o a l e s s e r extent,
24 h r s a f t e r exposure t o 2.2 ppm o f 03, r e t u r n i n g t o
c o n t r o l l e v e l s by 1 week a f t e r exposure. Although i n f o r m a t i o n concerning t h e
O3 on a i r w a y responsiveness i s accumulating, O3 on a i r w a y responsiveness. Although a d a p t a t i o n d u r i n g repeated exposures t o O3 f o r
e f f e c t s o f b r i e f exposures t o
t h e r e i s l i t t l e i n f o r m a t i o n about t h e e f f e c t s o f long-term exposure t o
5 days a l s o occurred i n b r o n c h i a l r e a c t i v i t y t o h i s t a m i n e o r methacholine i n humans (refs.
3.16).
no exposure study was made whether prolonged a d a p t a t i o n i n
b r o n c h i a l r e a c t i v i t y occurred, o r b r o n c h i a l h y p e r s e n s i t i v i t y o r h y p e r r e a c t i v i t y t o b r o n c h o c o n s t r i c t o r challenge developed d u r i n g prolonged esposures t o 03. T h i s study demonstrates considerable wide v a r i a t i o n i n responsiveness t o
h i s t a m i n e among guinea pigs. However, t h e f i l t e r e d a i r exposure group showed three-phase i n t h e p a t t e r n o f b r o n c h i a l s e n s i t i v i t y t o h i s t a m i n e i n r e l a t i o n t o g r o w t h as shown i n Fig. 5, suggesting a decrease i n b r o n c h i a l s e n s i t i v i t y before body weight was around 600 g, then an increase, and again a decrease i n b r o n c h i a l s e n s i t i v i t y a f t e r about 800 g o f body weight. Although PC100 showed a tendency o f an increase i n O3 exposure group i n comparison w i t h f i l t e r e d a i r exposure group except 9-week exposure,
s i g n i f i c a n t d i f f e r e n c e s o f PC100 were
observed between b o t h groups. T h i s suggests t h e decrease o f a i r w a y s e n s i t i v i t y t o h i s t a m i n e i n t h e O3 exposure group and prolonged adaptaton w i t h repeated exposures. However, t h e r e was no s i g n i f i c a n t d i f f e r e n c e between t h e percentage o f increase i n R t o f t h e i n i t i a l b a s e l i n e value a f t e r PC100 i n 03 and f i l t e r e d a i r groups. T h i s suggests prolonged exposure t o 03 may produce a decrease o f b r o n c h i a l s e n s i t i v i t y , b u t no s i g n i f i c a n t change i n b r o n c h i a l r e a c t i v i t y t o h i s t a m i n e chal lenge.
REFERENCES 1
2 3 4 5 6 7 8
9 10
11 12 13 14 15 16
L.-Y. Lee, E.R. B l e e c k e r and J.A. Nadel, J. Appl. P h y s i o l . R e s p i r . E n v i r o n . Exercise Physiol.. 43 (1977) 626-631 J.A. Golden, J.A. Nadel and H.A. Boushey, Am. Rev. R e s p i r . Dis., 118 (1978) 287-294 M.J. Dimeo, M.G. Glenn, M.J. Holtzman, J.R. S c h e l l e r , J.A. Nadel and H.A. Boushey, Am. Rev. R e s p i r . Dis., 124 (1981) 245-248 B. Saltzman, U.S. Government P r i n t i n g O f f i c e , USPHS p u b l i c a t i o n no. 999-AP11, 1965 J. Mead, J. Appl. Physiol., 15 (1960) 325-336 J. Kagawa, Jap. J. Hyg., 21 (1967) 424-436 T. Umezu. N. Shimojo. H. Tsubone, A.K. Suzuki. K. K u b o t a and A. S h i m i z u , Arch. Environ. Health, 42 (1987) 58-62 J.A. Raub, F.J. M i l l e r and J.A. Graham, i n S.D. Lee. M.G. M u s t a f a and M.A. Mehlman (Editor), I n t . Symposium on t h e Biomedical E f f e c t s o f Ozone and March 1982, Related Photochemical Oxidants, Pinehurst, NC, U.S.A. P r i n c e t o n S c i e n t i f i c Publishers, Inc.. 1983, pp. 363-367 (Advances i n Modern Environmental Toxicology, Vo1.5) 0. B a r t l e t t . C.S. F a u l k n e r and K. Cook, J. Appl. P h y s i o l . , 37 (1974) 92-96 D.L. Costa, R.S. Kutzman, J.R. Lehmann, E.A. Popenoe and R.T. Drew, i n S.D. Lee, M.G. Mustafa and M.A. Mehlman (Editor), I n t . Symposium on t h e Biomedical E f f e c t s o f Ozone and Related Photochemical Oxidants, Pinehurst, March 1982, P r i n c e t o n S c i e n t i f i c Publishers, Inc., 1983, pp. NC, U.S.A., 363-367 (Advances i n Modern Environmental Toxicology, Vo1.5) S.L. E u s t i s . L.W. S c h w a r t z , P.C. Kosch and D.L. Dungworth, Am. J. Pathol.. 105 (1981) 121-737 J.W. Osebold, L.J. G e r s h w i n and Y.C. Zee, J. E n v i r o n . P a t h o l . T o x i c o l . , 3 (1980) 221-234 R.E. Easton and S.D. Murphy, Arch. Environ. H e a l t h 15 (1967) 160-166 W.M. Abraham, A.J. Januszkiewicz. M. Mingle, M. Welker, A. Wanner and M.4 Sackner, J. Appl. Physiol. Respir. Environ. E x e r c i s e Physiol., 48 (1980) 789-793 M.J. Holtzman, L.M. F a b b r i , B.E. Skoogh, P.M. O'Byrne, E.H. W a l t e r s , H. Aizawa and J.A. Nadel, J. Appl. Physiol. Respir. Environ. E x e r c i s e Physiol., 55 (1983) 1232-1236 T.J. K u l l e , L.R. Sauder. H.D. K e r r , B.P. F a r r e l l , M.S. B e r m e l and D.M. S m i t h , Am. Ind. Hyg. Assoc. J., 43 (1982) 832-837
T. Schneider et al. (Editors), Atmospheric Ozone Researchand its Policy Implications 1989 Elsevier Science Publishers B.V., Amsterdam -Printed in The Netherlands
RESPIRATORY TRACT DOSIMETRY OF [18]0-LABELED OZONE I N RATS:
553
IMPLICATIONS FOR
A RAT-HUMAN EXTRAPOLATION OF OZONE DOSE
G.E.
HATCH,'
M.J. WIESTER,'
J.H.
OVERTON, JR.,'
'U.S. Environmental P r o t e c t i o n Agency, Research T r i a n g l e Park, NC 27711
and M. AISSA'
Health E f f e c t s Research Laboratory,
2Northrop Services Inc., Research T r i a n g l e Park, NC 27709
ABSTRACT E f f o r t s t o o b t a i n a comparison between r a t s and humans o f t h e dose o f inhaled ozone (03) d e l i v e r e d t o t h e lungs during 03 exposure has been impeded because o f t h e lack o f data on the nasopharyngeal removal o f 03 i n r a t s . The present study sought t o address t h i s need through use o f a newly developed t r a c i n g technique t h a t involved oxygen-18 labeled 0 3 ([l8]O3). Awake r a t s which breathed 1.0 ppm [I8103 f o r 2 hours removed a t o t a l o f 688 nmoles o f [l8]O3 from t h e respired a i r and had 9 9 . 4 nmoles o f [18]0 enrichment i n t h e i r respiratory tract. The [18]0 enrichment was d i s t r i b u t e d as f o l l o w s : 49.3%, nasopharynx; 6 . 5 % , trachea; and 44.0%, lungs. The nmoles o f 03 removed by each r a t and t h e percentage d i s t r i b u t i o n o f [ l 8 ] 0 i n t h e nasopharynx, trachea, and lung were incorporated i n t o a three compartment model from which t h e percentage removal o f 03 by t h e nasopharynx d u r i n g i n s p i r a t i o n was c a l c u l a t e d t o be 1 7 . 4 f 1.5% (S.E.). Comparison o f t h i s r e s u l t t o a published value o f about 40% nasopharyngeal removal i n t h e r e s t i n g human, y i e l d s t h e conclusion t h a t the 03 concentration i n t h e r a t trachea i s about 30% higher than i n t h e t h e human trachea under s i m i l a r exposure conditions. INTRODUCTION
An animal/human e x t r a p o l a t i o n scheme f o r 03 i s being i n v e s t i g a t e d a t t h e U.S.
E.P.A.
f o r the purpose o f making more d i r e c t use o f animal d a t a i n t h e
assessment o f human r i s k s from 03 exposure.
I n i t i a l e f f o r t s have focused on
e m p i r i c a l l y determining t h e removal o f 03 i n t h e nasopharynx and mathematic a l l y modeling 0 3 d e p o s i t i o n i n t h e lower r e s p i r a t o r y t r a c t .
Nasopharyngeal
removal o f 03 i n humans has been determined ( 6 ) by sampling 0 3 concentrations i n the p o s t e r i o r pharynx d u r i n g 0 3 exposure. About 40% o f t h e 0 3 was removed by the nasopharynx, and approximately 95% o f the inhaled 0 3 the r e s p i r a t o r y t r a c t .
was removed by
Wiester e t a1 ( 1 3 ) reported t h a t t h e awake r a t r e t a i n s
about 47% of t h e 03 inhaled.
554 Nasopharyngeal removal o f 03 i n dogs,
r a b b i t s and guinea p i g s has been
determined using an 03 exposure system t h a t draws a i r i n t o t h e nasopharynx and larynx
via
a
tracheal
catheter
(14,15).
nasopharyngeal 03 removal i n r a t s , inhaled 03 i s most p l e n t i f u l .
However,
there
is
no data
on
t h e species f o r which t o x i c o l o g y data on
One reason f o r t h i s l a c k o f data i s t h a t t h e
r a t produces a very l a r g e amount o f mucus, presumably from i r r i t a n t e f f e c t s and trauma,
which tends t o o b s t r u c t t h e t r a c h e a l c a t h e t e r s ( M i l l e r , F.,
per-
sonal communication). Advances i n t h e use o f t h e s t a b l e isotope, oxygen-18 ([l8]0), as a t r a c e r f o r oxygen i n t i s s u e s (9) have made i t p o s s i b l e t o l a b e l t h e 03 molecule and measure r e s i d u a l products o f 03 r e a c t i o n i n t i s s u e s f o l l o w i n g i n h a l a t i o n ( 7 ) . I n t h e present study, we a p p l i e d t h e [18]0 techniques t o determine t h e percent nasopharyngeal removal of 03 i n r a t s .
The exposure o f t h e r a t s was performed
w h i l e measuring b r e a t h i n g parameters and t h e f r a c t i o n a l uptake o f i n s p i r e d 03 ( 1 0 ) i n order t o determine r e l a t i o n s h i p s between these measurements and t h e
t i s s u e concentrations o f [18]0.
METHODS
Animals Male Fischer 344 r a t s were d e r i v e d from a c h r o n i c study t h a t exposed r a t s f o r 1 year t o 03 (0.06 ppm b a s e l i n e and d a i l y graded spikes o f 0.25 pprn f o r D e t a i l s o f t h e chronic exposure are presented i n Gross e t a l , t h i s sym-
1).
posium.
The present paper r e p o r t s on pooled d a t a from 4 r a t s c h r o n i c a l l y
exposed t o 03 and 4 a i r c o n t r o l s which were a c u t e l y exposed t o 1.0 pprn [l8]O3 f o r 2 hours. The r a t s were 14 months o l d when examined and weighed 459 k 8 g (S.E.,
8 r a t s ) . Since no c l e a r d i f f e r e n c e s i n uptake were observed between t h e
chronic 03 and c o n t r o l groups, we pooled t h e data f o r an a n a l y s i s o f r e s p i r a t o r y t r a c t uptake and d i s t r i b u t i o n o f 03
dose.
Acute Exposure t o 1.0 ppm [18]03 f o r 2Hr: Each
rat
was
plethysmograph w i t h
placed
in
a
restrainer
and
sealed
inside
i t s head extending i n t o a g l a s s cone-shaped
exposure chamber as described by Wiester e t a1 (13).
a
body
nose-only
[la103 was generated
from [18]02 (Monsanto Research Corp, Miamisburg, OH) by passing a m i x t u r e o f
5% [l8]02 i n n i t r o g e n through a UV ozone generator and d i l u t i n g t h e 03 m i x t u r e with a i r .
555 Tissue Preparation Immediately upon removal from t h e plethysmograph, t h e lungs and trachea were excised and homogenized and t h e head was skinned. lyophilized.
All
t i s s u e s were
The d r i e d head was trimmed o f s k i n o r mouth t i s s u e s which could
c o n t a i n non-respiratory
[ l a 1 0 and homogenized i n water.
Bone fragments were
removed by 1 G sedimentation, and t h e supernatant was l y o p h i l i z e d again.
I1810 Analysis: The presence of 03 r e a c t i o n products i n d r i e d t i s s u e homogenates was i n d i cated by increased [18]0
above n a t u r a l background l e v e l s .
Procedures f o r
analyzing [18]0 content o f t i s s u e s are described by Santrock and Hayes ( 9 ) . Briefly,
dried
equilibrated
tissues
over
were
elemental
pyrolyzed
at
1O6O0C and t h e p y r o l y s a t e was
carbon t o y i e l d carbon monoxide.
The carbon
monoxide peak detected chromatographically was t h e b a s i s f o r q u a n t i t a t i o n o f t o t a l oxygen content o f t h e tissues. elemental analyzer (Carlo Erba Inc., l y z e r was d i r e c t e d
The above steps were performed using an Peabody, MA).
The e f f l u e n t from t h e ana-
through a heated column c o n t a i n i n g i o d i n e pentoxide i n
order t o convert a l l CO t o C02.
The Cop was f r e e d o f i m p u r i t i e s and trapped
c r y o g e n i c a l l y . Isotope r a t i o mass spectrometry was performed on t h e r e s u l t i n g C02 t o determine t h e abundance o f
[18]0 r e l a t i v e t o t h e t o t a l oxygen pool
([1610 + [1710 + [1810). Model f o r C a l c u l a t i n g t h e Percent Nasopharvngeal Removal Upon I n s p i r a t i o n I n order t o estimate t h e f r a c t i o n of 03 removed by t h e nasopharynx d u r i n g i n s p i r a t i o n , we developed a three compartment model, i n which each compartment (nasopharynx,
l a r n y x + trachea,
lung) removed t h e same percentage o f 03 from
t h e a i r presented t o i t on i n s p i r a t i o n as i t d i d on e x p i r a t i o n . tion,
t h e head compartment removed x percent o f t h e 03
On inhala-
i n the inhaled a i r ;
the tracho-laryngeal compartment removed y percent o f t h e 03
i n a i r entering
i t from t h e head, and t h e deep lung compartment removed z percent o f t h e 03
i t received from t h e trachea.
On exhalation,
t h e 03
remaining i n t h e pulmo-
nary compartment was passed back through t h e t r a c h e a l and nasopharyngeal compartments,
removing t h e same percentages of 03
from t h e a i r presented t o
them. Three non-linear equations were developed t h a t r e l a t e d t h e percentage o f inhaled 03
removed by t h e compartments t o estimates o f t h e percentage o f 03
accumulated i n each compartment.
These estimates were defined as 100 times
the product o f the f r a c t i o n o f t h e i n h a l e d 03 the f r a c t i o n o f [18]0 i n t h e compartment. solved f o r x, y, and z.
r e t a i n e d by t h e animal times
For each animal, t h e equations were
556 RESULTS Table 1 shows t h e average values f o r measurements o f b r e a t h i n g and 03 uptake made on r a t s d u r i n g t h e 2 hours of exposure t o [l8lO3. Measurement of minute v e n t i l a t i o n and 03 concentrations i n t h e a i r s t r e a m past t h e nose o f t h e r a t allowed c a l c u l a t i o n o f t h e amount of
03 i n h a l e d (1276 nmolcs) and t h e
amount o f 03 r e t a i n e d (688 nmoles) (13).
Not e v i d e n t from t h e data i n t h e
t a b l e i s t h e f a c t t h a t a l l o f t h e 8 r a t s showed a pulmonary i r r i t a n t response t o t h e acute [l8]O3 exposure which began between 40 and 80 minutes i n t o t h e exposure.
T i d a l volume was decreased by 50% and b r e a t h i n g frequency was
increased t o 2 x c o n t r o l , however, minute v e n t i l a t i o n d i d not change over t h i s period. TABLE 1. Measurements made on awake r a t s exposed t o 1.0 ppm
[MI03 i n a plethysmograph.
Mean + S.E.
Measurement, u n i t s
T i d a l volume, m l Frequency, breaths/min Minute V e n t i l a t i o n , ml/min (BTPS) 02 consumption, ml/min (STPD) C02 production, ml/min (STPD) Inhaled 03, nmoles/ 2 hour Retained 03, nmoler/ 2 h r Percent r e t a i n e d (whole body),%
2.05 f 0.08 150.0 f 11.1 290.4 f 10.4 8.18 f 0.44 8.49 f 0.57 1276.0 f 47.0 688.0 f 56.0 54.3 f 4.15 ..............................................................
...................................
----
Values represent the mean and standard e r r o r f o r measurements i n 8 r a t s exposed f o r 2 hours. Retained 03 was d e r i v e d from 7 rats.
Table 2 shows t h e t i s s u e d r y weights, oxygen percentages, and [la10 abundance i n t h e r e s p i r a t o r y t r a c t t i s s u e s , which were t h e primary measurements from which other values were c a l c u l a t e d .
The [18]0 abundance i n t h e
lung
t i s s u e from a separate group o f r a t s exposed t o a i r (Table 2C) was s u b t r a c t e d from t h e [18]0 abundance i n t h e t i s s u e s o f r a t s exposed t o [l8]O3 t o o b t a i n the enrichment o f [l8]0 t h a t c o u l d be ascribed s o l e l y t o t h e [l8]O3 exposure (Table 2D).
The enrichment o f
[la10 was approximately t h e same i n t h e
nasopharynx,
trachea and l u n g of
contents o f
t h e three t i s s u e s were a l s o s i m i l a r ,
[l8lO3 exposed animals.
Since t o t a l oxygen
t h e [18]0 per t i s s u e d r y
weight was a l s o s i m i l a r among t h e t h r e e t i s s u e s (Table 2E).
557 TABLE 2. Respiratory t i s s u e measurements o f excess [18]0 f o l l o w i n g
exposure o f r a t s t o [18]O3a
A. Tissue Dry Weight, g
Lung Trachea Head
0.273 f 0.008 0.050 f 0.002 1.263 f 0.024
8. Tissue Oxygen Content, % o f d r y weight
Lung Trachea Head C.
20.51 f 0.10 18.29 f 0.22 17.49 f 0.18
Tissue [l8]0 Abundance, mmoles/mole t o t a l oxygen Lung, A I R EXPOSE0 Lung Trachea Head
D.
2.0053 2.0177 2.0167 2.0175
f f f f
0.0001b 0.0009 0.0010 0.0020
[l8]0 Enrichment, umoles [la10 /mole t o t a l oxygen Lung Trachea Head
12.4 f 0.9 11.4 f 1.0 13.4 f 1.8
E. Excess [18]0 concentration, nmoles [18]0 /g d r y t i s s u e Lung Trachea Head
158.8 f 11.8 129.9 f 10.3 146.3 f 18.6
F. Excess [l8]0 content, nmoles [lB]O
Lung Trachea Head Total Respiratory Tract G.
f f f f
3.5 0.6 5.7 5.3
Percent of [l8]0 I n The Total Respiratory Tract Lung Trachea Head
a
43.3 6.5 49.3 99.4
/ whole t i s s u e
44.0 f 3.3 6.7 f 0.6 49.3 f 3.7
Results represent the mean f S.E. N = 4 r a t s i n t h i s group
f o r 8 rats.
558
Dry t i s s u e of t h e t o t a l r e s p i r a t o r y t r a c t contained about 99.4 nmoles o f excess [18]0 (Table 2F) compared t o the computed 688 nmoles o f 03 the whole animal
(Table 1).
retained by
When the q u a n t i t y o f t o t a l r e s p i r a t o r y t r a c t
[l8]0 was p l o t t e d against the q u a n t i t y o f 03
retained during the 2 hours by
the whole animal, the c o r r e l a t i o n c o e f f i c i e n t ( r ) was
0.54 (N = I, p - 0.2).
The d i s t r i b u t i o n of [18]0 i n the r e s p i r a t o r y tissues i n d i c a t e d the l a r g e s t p o r t i o n (49%) t o be present i n the head, w i t h 44% i n the lungs and 1% i n the trachea/larynx
(Table 20). The percentage o f 03 removed from i n s p i r e d a i r by
the whole animal (54% the r e s p i r a t o r y t r a c t
,
Table 1) and the percentage d i s t r i b u t i o n o f [18]0 i n
(Table 26) served as inputs t o a model described i n
Methods from which the f r a c t i o n o f 03
DURING INSPIRATION was computed. removed 17.4 f 1.5% S.E.
removed by the nasophyarynx and trachea
According t o the model,
t h e nasopharynx
(8.2 t o 24.2%) of the 03 from the i n s p i r e d a i r and
the larnyx/trachea removed 2.7 f 0.4% o f the remaining 03.
DISCUSSION
The present study measured the d i s t r i b u t i o n o f 03 v i v o following i n h a l a t i o n of
[l8]O3 i n r a t s .
r e a c t i o n products i n
Results i n d i c a t e t h a t enrich-
ments i n [la10 were detectable i n the d r i e d homogenates o f the nasopharynx, trachea and lung f o l l o w i n g exposure t o 1.0
ppm [lalo3 f o r 2 hr.
Similar
enrichments were seen i n previous studies i n the lungs o f [l8]03 exposed mice, r a t s and r a b b i t s (4,l).
Although we d i d not examine blood i n the present
study, our previous r e s u l t s showed undetectable enrichments o f [la10 i n blood f o l l o w i n g exposure t o s i m i l a r o r even higher concentrations o f [MI03 (7, and unpublished observations).
A c o r r e c t i o n t h a t should be made t o the [la10 data
i s f o r mucociliary clearance. hr [l8lO3
Clearance o f [la10 from the nose during the 2
exposure could have l e d t o an underestimation o f the f r a c t i o n o f
removed by the nasopharynx.
[l8]O3
We are attempting t o address t h i s issue
by analyzing nasal and lung lavage f l u i d s o f r a t s and humans exposed t o [l8]O3 (5).
The sum of the [18]0 detected i n the nasopharynx, trachea and lungs o f the r a t averaged about 100 nmoles, w h i l e estimates o f the o f 03 during exposure averaged 688 nmoles.
removed by t h e r a t
The f a c t t h a t the [18]0 measured i n the
r e s p i r a t o r y t r a c t amounted t o o n l y 14.4% of the [l8]03 retained by the whole animal might be explained by entrance o f some o f the [l8]0 i n t o the blood, o r degradation of [la103 t o H2[l8]O o r [18]02.
Since d e t e c t i o n o f (1810 i n blood
does not appear t o be possible due t o d i l u t i o n o f the l a b e l i n the t o t a l blood volume
C
unknown.
30 ml), the c o n t r i b u t i o n o f [l8]0 i n blood t o the inhaled [la10 i s Ozone degradation t o H2[18]0 or [l8]02 might be expected t o occur
559 v i a r e a c t i o n s o f 03 etc.),
with antioxidant
substances
(ascorbate,
glutathione,
o r enzymatic degradation o f peroxides generated by t h e 03.
Water was
removed p r i o r t o a n a l y s i s o f t i s s u e [18]0 because t h e h i g h percentage o f [16]0 i n water
C
89% w t / w t )
translocation label.
of
limits
the
s e n s i t i v i t y of
water w i t h i n t h e body i s rapid,
detection,
and because
causing d i l u t i o n o f t h e
I n s p i t e o f the f a c t t h a t o n l y a f r a c t i o n o f t h e [18]0 i s detected i n
the dry tissue,
evidence t o date suggests t h a t t h e [18]0 concentrations i n
t i s s u e s are p r o p o r t i o n a l t o the [18]03 exposure: t h e [18]0 content i n t h e lung increases l i n e a r l y w i t h time o f exposure t o [ l 8 ] 0 3
(4).
Comparison o f t h e i n t e g r a t e d average compartmental dose o f
[18]0 w i t h i n
t h e upper r e s p i r a t o r y t r a c t i n terms o f surface area i s p o s s i b l e through use o f published surface area measurements.
Using values o f 11.6 cm2 f o r t h e r a t
naspharynx (based on Schreider and Raabe, 1 2 ) , and 2.4 cm2 f o r t h e l a r y n x p l u s trachea trachea,
(11) y i e l d s 4.3 respectively,
and 2 . 1
nmoles [18]O/cmr
suggesting t h a t
in
t h e nasopharynx and
t h e 03 dose decreases w i t h d i s t a n c e
from t h e nares. A major purpose o f t h i s study was t o provide data from which t o compare
tracheal concentrations o f 03 i n r a t s and humans so t h a t mathematical models could be used t o compute t h e 03 dose t o the deep lung. measured the tracheal 03
G e r r i t y e t a1 (16)
concentration i n humans by sampling pharyngeal a i r
during i n s p i r a t i o n and reported a mean o f 39.6% removal by t h e nasopharynx. We derived t h e percent nasopharyngeal removal of 03 i n r a t s d u r i n g i n s p i r a t i o n from t h e [18]0 data using a model which segregated o u t t h e [ l 8 ] 0 accumulated during e x p i r a t i o n , and r e p o r t here a mean 06 17.4% of t h e i n s p i r e d 03 removed by the r a t nasopharynx.
Thus,
i t appears t h a t
t h e concentration o f 03 i n
tracheal a i r would be about 30% higher i n r a t s than i n humans.
Mathematical
models p r e d i c t t h a t
i n r a t s and
given equivalent
tracheal
concentrations
humans, 03 d e p o s i t i o n i n t h e c e n t r i a c i n a r r e g i o n (where 03 damage appears t o be most severe) would a l s o be s i m i l a r i n t h e two species (8). I n summary, following
the measurement o f r e l a t i v e t i s s u e concentrations o f
[l8]O3
exposure,
coupled w i t h mathematical modeling,
[18]0
yielded
a
conclusion t h a t r a t tracheal concentrations o f 03 a r e about 30% higher than s i m i l a r l y exposed humans.
Adjustments f o r a t l e a s t r e l a t i v e t o t a l uptake o f
03 and m u c o c i l i a r y clearance o f 03 r e a c t i o n products from t h e nose should be made before t h e comparison of 03 concentrations i n t h e trachea can be considered f i n a l .
Comparison o f [18]0 content i n the nasal and pulmonary lavage
f l u i d s of animals and humans exposed t o [18]03 could a l s o provide an i n t e r s p e c i e s e x t r a p o l a t i o n o f 03
dose t o t i s s u e s .
560 ACKNOWLEDGEMENTS The authors thank Joel
Norwood f o r technical assistance,
Showers, Department o f Marine, University,
for
Earth,
and Atmospheric
isotope r a t i o mass spectrometry,
Dr.
Sciences,
and D r .
William N.C.
State
Daniel Costa f o r
h e l p f u l suggestions i n the preparation o f the manuscript.
REFERENCES F.J. M i l l e r , J.H. Overton Jr., R.J. Jaskot and 0.6. Menzel, Toxicol. Appl. Pharm., 79 (1985) 11-27. Graham and F.J. M i l l e r , Toxicol. Appl. Pharm., 88 2 J.H. Overton, R.C. (1987) 418-432. 4 J. Santrock, G.E. Hatch, R. Slade and J.M. Hayes, Toxicol. Appl. Pharm., (1988) (Submitted). 5 G.E. Hatch, H. Koren and M. Aissa, Health Physics, (1988) ( i n press). 6 T.R. G e r r i t y , J.J. O'Neil, R.A. Weaver, J. Bernsten and 0. House, J. Appl. Physiol., (1988) ( I n Press). 7 G.E. Hatch and M. Aissa, Annual Meeting, American A i r P o l l u t i o n Control Association, Paper No. 87-99.2 (1987). 8 J.H. Overton and F.J. M i l l e r , Annual Meeting, American A i r P o l l u t i o n No. 87-99.2 (1987). Control Association, Paper 9 J. Santrock and J.M. Hayes, Anal. Chem, 59 (1987) 119-127. 10 M.J. Wiester, T.B. Williams, M.E. King, M.G. Menache and F.J. M i l l e r , Toxicol. Appl. Pharmacol. 89 (1987) 429-437. 11 H.C. Yeh, G.M. Schum and M.T. Duggan, Anat. Rec., 195 (1979) 483-492. 12 J.P. Schreider and 0 . 0 . Raabe, Am. J. Anat., 162 (1981) 221-232. Tepper, M.E. King, M.G. Menache and D.L. Costa, 13 M.J. Wiester, J.S. Toxicol. Appl. Pharm., (1988) ( i n press). 14 F.J. M i l l e r , C.A. McNeal, J.M. K i r t z , D.E. Gardner, 0.6. C o f f i n and 0.6. Menzel, Toxicol., 14: (1979) 273-281. 15 E. Yokoyama and R. Frank. Arch. Environ. Health., 25 (1972) 132-138. 1
Correspondence t o : D r . Gary E. Hatch, MD-82, U.S.E.P.A., Research Triangle Park, NC 27711 Disclaimer: This document has been reviewed i n accordance w i t h U.S. Environmental Protection Agency p o l i c y and approved f o r publication. Mention o f trade names o r commercial products does not c o n s t i t u t e endorsement o r recommendation f o r use.
56 1
SESSION IX
ATMOSPHERIC CHEMISTRY AND MODELING
Chairmen
E.H. Aderna J.F. van de Vate B. Dirnitriades
This Page Intentionally Left Blank
T. Schneider et al. (Editors),Atmospheric Ozone Research and its Policy Implications 0 1989 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands
563
THE USE OF OZONE MODELING I N THE DESIGN OF CONTROL STRATEGIES
Edwin L. Meyer, Jr. O f f i c e o f A i r Q u a l i t y P1 anning and Standards, U. S. Environmental P r o t e c t i o n Agency, MD-14, Research 1' r i a n g l e Park, NC 27711, USA
ABSTRACT Two urban s c a l e photochemical models have been approved f o r use i n r e g u l a t o r y a p p l i c a t i o n s i n t h e United S t a t e s (US). These models a r e t h e Urban Airshed Model (UAM) and t h e E m p i r i c a l K i n e t i c s Modeling Approach (EKMA). E s s e n t i a l f e a t u r e s o f each a r e o u t l i n e d . Use o f t h e models t o e s t i m a t e reduct i o n s i n precursors needed t o reach t h e US ambient a i r q u a l i t y standard f o r ozone i s i l l u s t r a t e d . I n a d d i t i o n , use o f t h e models t o s e l e c t most e f f e c t i v e ways t o reduce ozone f o r a given l e v e l o f resources i s i l l u s t r a t e d . INTRODUCTION Highest concentrations o f ozone (03) i n t h e US a r e o f t e n observed w i t h i n about 50 m i l e s (80 km) downwind o f m a j o r c i t i e s .
The US n a t i o n a l ambient a i r
q u a l i t y standard (NAAQS) r e q u i r e s t h a t t h e d a i l y maximum h o u r l y c o n c e n t r a t i o n o f 03 n o t exceed 0.12 ppm more than once per year, on average.
Hence c o n t r o l
s t r a t e g i e s g e n e r a l l y aim a t reducing h i g h e s t c o n c e n t r a t i o n s o f 03.
Urban
s c a l e models a r e t h e p r i n c i p a l means used f o r assessing whether p r o s p e c t i v e c o n t r o l s t r a t e g i e s may be e f f e c t i v e i n reducing 03 and whether contemplated c o n t r o l s w i l l be s u f f i c i e n t t o meet t h e 03 NAAQS.
An urban s c a l e model i s one
i n which t h e modeling domain i s l a r g e enough t o e s t i m a t e impact o f an urban plume w i t h i n about 10 hours t r a v e l t i m e d u r i n g d a y l i g h t hours (e.g.,
8AM-6PM).
Under meteorological c o n d i t i o n s most f r e q u e n t l y corresponding w i t h h i g h 03 i n t h e US, t h i s u s u a l l y i m p l i e s distances about 160 km o r l e s s from t h e c i t y under review.
Ozone/precursors r e s u l t i n g from more remote sources a r e t r e a t e d as
boundary c o n d i t i o n s t o urban s c a l e models. Two urban s c a l e models have been approved f o r r e g u l a t o r y use i n t h e US:
UAM and EKMA.
These models must be capable o f e s t i m a t i n g peak 03.
In the
case o f UAM, t h i s need i s addressed by l i m i t i n g h o r i z o n t a l s i z e o f t h e model's g r i d squares t o l e s s than 10 km on a side.
With EKMA, i t i s assumed observed
d a i l y maximum 03 i s t h e r e s u l t o f a t r a j e c t o r y which maximizes ambient p r e c u r s o r concentrations.
P r i o r t o a p p l y i n g EKMA, wind d a t a a r e checked t o ensure
such an assumption i s p l a u s i b l e .
564 T h i s paper describes key f e a t u r e s o f EKMA and UAM.
Use o f each model t o
demonstrate a t t a i n m e n t o f t h e US NAAQS and t o address a s t r a t e g i c q u e s t i o n l i k e , "what i s t h e most e f f e c t i v e way t o reduce 03 f o r a g i v e n l e v e l of resources" i s i l l u s t r a t e d .
EKMA Because i t i s r e l a t i v e l y inexpensive and easy t o apply, EKMA i s t h e most w i d e l y used model f o r d e s i g n i n g c o n t r o l s t r a t e g i e s .
The model u n d e r l y i n g EKMA
(OZIPM4) i s d e s c r i b e d i n d e t a i l elsewhere ( r e f . 1, r e t . 2).
Briefly, a well mixed column o f a i r i s assumed t o m i g r a t e from c e n t e r c i t y t o t h e s i t e o f t h e observed d a i l y maximum 03.
As i t moves, h e i g h t o f t h e column increases due t o
d i u r n a l r i s e i n t h e m i x i n g h e i g h t , and f r e s h emissions a r e i n j e c t e d i n t o t h e column.
Increase i n column h e i g h t d i l u t e s i t s contents, b u t a l s o r e s u l t s i n
entrainment o f 03/precursors r e s u l t i n g from l o n g range t r a n s p o r t (boundary conditions).
As t h e column moves, i t s c o n t e n t s a r e acted upon by photochemistry
o f r e a c t i v e o r g a n i c s (RHC) and n i t r o g e n o x i d e s (NO,).
The preceding s c e n a r i o
i s repeated numerous times, v a r y i n g o n l y i n i t i a l RHC and NOx c o n c e n t r a t i o n s and emissions.
The r e s u l t i s an "ozone i s o p l e t h diagram" w i t h which one can
e v a l u a t e a v a r i e t y o f s t r a t e g i e s r e f l e c t i n g r e d u c t i o n s i n RHC, NOx o r both. F i g u r e 1 p i c t u r e s t h e model's conceptual b a s i s as w e l l as a r e s u l t i n g i s o p l e t h diagram.
EKMA now i n c l u d e s carbon bond 4 chemistry, t r a n s p o r t e d p r e c u r s o r
l e v e l s and species, t r e a t m e n t o f carbon monoxide and a d i s t i n c t i o n between p o i n t and area sources ( r e f . 2). 0.2 0.4 0.6 0 . 0 1.0 1.2 1.4 1.6 1.0 2.0 .24
.20
.20
.16
.16
.12
.12
.04
.M
.w 0 Fig. l a .
Conceptudl view o f model underlying E M
. lb.
"2 CONCENTRATION. PPMC Example EKMA diagram w i t h various RHC/NO,
ratios
UAM UAM i s a m u l t i l a y e r e d g r i d model p r e d i c t i n g O j / p r e c u r s o r c o n c e n t r a t i o n s f o r
each hour i n each g r i d c e l l . r e f . 4).
T y p i c a l h o r i z o n t a l c e l l s i z e i s 2-4 km ( r e f . 3,
However c e l l s i z e s as l a r g e as 8 km have been used f o r modeling
domains as l a r g e as 250-350 km ( r e f . 5).
Use o f such l a r g e domains may w e l l be
necessary t o adequately c o n s i d e r s t r a t e g i e s i n c o r p o r a t i n g r e d u c t i o n s i n b o t h
565 RHC and NO.,
V e r t i c a l dimension o f t h e model's c e l l s varies d i u r n a l l y .
In the
e a r l y morning, c e l l sizes o f a few tens o f meters provide p o t e n t i a l t o consider effects o f wind shear on emissions a t several elevations.
By midmorning,
v e r t i c a l c e l l s i z e increases t o simulate growth o f surface mixing h e i g h t and decreased wind shear. Emissions w i t h i n each c e l l a r e acted upon by a p h y s i c a l l y consistent wind f i e l d , by t u r b u l e n t d i f f u s i o n between adjacent c e l l s , and by d r y deposition.
Hourly emission r a t e s are needed f o r each c e l l .
Concurrently w i t h these physical phenomena, contents o f each c e l l undergo chemi c a l conversion. quently used.
Carbon bond 4 i s the c u r r e n t chemical mechanism most f r e -
D a i l y 03 p a t t e r n s p r e d i c t e d w i t h UAM may a l s o depend on i n i t i a l Since monitoring data are u s u a l l y i n s u f -
concentrations o f ozone/precursors.
f i c i e n t t o adequately characterize i n i t i a l concentration f i e l d s , simulations are sometimes begun several hours before t h e period o f i n t e r e s t t o reduce i n f l u e n c e o f poorly known i n i t i a l conditions.
EVALUATING CONTROL STRATEGIES Meeting an A i r Q u a l i t y Standard
E.
EKMA i s used as follows t o demonstrate whether a proposed (i) strategy i s s u f f i c i e n t t o meet the U.S. NAAQS.
Oetermi ne whether the model I
s
assumed t r a j e c t o r y i s consistent w i t h
t i m i n g o f observed high 03, surface wind v e l o c i t y and o r i e n t a t i o n o f the monitor. Evaluate performance p r e d i c t i n g base case 03. d a i l y maxima should agree w i t h i n f30X.
Predicted and observed
Table 1 o u t l i n e s p o s s i b l e
remedies f o r improving model performance. Estimate percent RHC reduction needed t o reduce d a i l y maximum 03 t o 0.12 ppm on t h e 5 days having highest observations a t a monitor d u r i n g t h e base period ( g e n e r a l l y 3 years). Note t h a t t h e f o u r t h highest c o n t r o l estimate i s s u f f i c i e n t t o meet t h e NAAQS a t a p a r t i c u l a r monitoring s i t e , assuming complete sampling over a 3-year base period. Repeat steps ( 3 ) and ( 4 ) f o r each monitoring s i t e .
The c o n t r o l t a r g e t
s u f f i c i e n t f o r a c i t y t o meet t h e NAAQS i s t h e highest s i t e - s p e c i f i c c o n t r o l estimate. t a r g e t s obtained w i t h EKMA may be reached i n a v a r i e t y o f ways. The model i s not s p e c i f i c about target
.
which sources
should be c o n t r o l l e d t o reach t h e
566 Tahle 1.
Uncertainties A f f e c t i n g Control Stratsu, E v a l u a t i o n Using EKMA
Source
Remedy
Resul t Could l e a d t o poor e s t i m a t e of r e l a t i v e importance of emission r e d u c t i o n s from known sources
l n p r o v e emission f a c t o r guidance. Make i n v e n t o r y more conprehens ive i n c l u d i n g previously i g n o r e d source c a t e g o r i e s .
Unrep res ent a t ive II)IOC/NOx r a t i o s
Could r e s u l t i n e n t e r i n g i s o p l e t n diagram i n wrong place, l e a d i n g t o inappropriate target
Deploy nmre m o n i t o r s . Review t o ensure consistency w i t h proper s i t i n g guiaance.
Iryroper daily maainum 03 concent r a t ions
Could e n t e r diagram i n wrong p l a c e
Review winds t o ensure s i t e i s downwind. Deploy more m n itors.
Use of d e f a u l t r e a c t iv i t y assumptions
Could a f f e c t shape of i s o p l e t h diagram and estimated c o n t r o l s
Use l o c a l l y measured. s p e c i a t e d NMOC measurements t o derive city-specific reactivity characterizations
Imp r o p e r es t 1mate of d i l u t i o n
Could a f f e c t shape of diagram and r e s u l t i n g c o n t r o l estimates
Measure v e r t i c a l p o l l u t a n t p r o f i l e s . note meteorological c h a r a c t e r i s t i c s a l l o w i n g one t o most c l o s e l y r e p l i c a t e this profile
Inaccurate estimate of "present" t r a n s PoR
Could a f f e c t shape Of diagram and r e s u l t i n g cont r o 1 e s t i m a t e s
Measure morning 03 and NnOC upwind a t r e p r e s e n t a t i v e sites. Accurately estimate winds.
lnrccuate estimate of " f u t u r e " t r a n s -
Could a f f e c t p o s i t i o n of t a r g e t i s p l e t h (e.9..
DOR
0.12 ppm). thereby a f f e c t i n g
Review l i k e l y upwind c o n t r o l programs. Continue development of r e g i o n a l s c a l e mdels and c a r e f u l l y c o n s i d e r appropriate strategies f o r s i n u l a t ion
Poor
inventory
control target
Inaccurate charactcri z a t i o n of c o n t r o l effectlveness
F a l s e i n d i c a t i o n o f AVOC and/OrAN& l e a d i n g t o an apparent c o n t r a d i c t i o n between model p r e d i c t i o n s and observed 03 t r e n d s
More e f f e c t i v e enforcement. B e t t e r c h a r a c t e r i z a t i o n of c o n t r o l measure i n a c t u d l p r a c t i c e . Reduce prcva I ence of extended c o n p l i a n c e B e t t e r characterschedules i z a t ion of i n v e n t o r 1 es. More e f f e c t i v e program t o m n i t o r "reasonable f u r t h e r progress."
.
( i i ) E. There has been l i m i t e d experience u s i n g UAM t o demonstrate t h a t a c o n t r o l s t r a t e g y i s s u f f i c i e n t t o meet t h e US NAAQS. One problem r e s u l t s from t h e model's e x t e n s i v e d a t a needs. degrees o f freedom i n u s i n g UAM.
Lack o f complete d a t a i n t r o d u c e s many
That i s , g i v e n a t y p i c a l data base, one can
e n t e r many "reasonable" s e t s o f i n p u t s c o n s i s t e n t w i t h a v a i l a b l e data.
It i s
recommended t h a t a d e t a i l e d d a t a base be used t o e v a l u a t e model performance i n p r e d i c t i n g observed 03.
Such a procedure reduces s u b j e c t i v i t y i n s e l e c t i n g
p o o r l y known i n p u t parameters.
U n l i k e w i t h EKMA, t h e r e i s no w e l l d e f i n e d pro-
cedure f o r i d e n t i f y i n g s t r a t e g i e s s u f f i c i e n t t o meet t h e U.S.
NAAQS.
However,
t h e f o l l o w i n g procedure has been proposed ( r e f . 6).
(1)
Using an i n t e n s i v e d a t a base, s e l e c t p r o t o t y p i c a l m e t e o r o l o g i c a l
scenarios f o r modeling. c u r r e n t period.
(2)
These scenarios need n o t have occurred d u r i n g t h e
S e l e c t i o n o f 3-6 scenarios i s recommended.
S e l e c t model i n p u t s f o r each scenario, c o n s i s t e n t w i t h observations,
which r e s u l t i n p r e d i c t e d and observed 0 3 L 0.12 ppm agreeing w i t h i n t30%.
567
(3)
Update i n v e n t o r i e s t o r e f l e c t c u r r e n t (base case) emissions.
(4)
S e l e c t a c a n d i d a t e c o n t r o l s t r a t e g y and a p p l y t h e model t o e s t i m a t e 03.
(5)
Demonstrate a t t a i n m e n t o f t h e NAAQS by showing t h a t p r e s c r i b e d c o n t r o l s
f o r each source c a t e g o r y a r e a t l e a s t as g r e a t as t h e maximum r e q u i r e d f o r t h a t source c a t e g o r y t o reduce 03 t o 5 0.12 ppm f o r each m e t e o r o l o g i c a l s c e n a r i o . The f i n a l s t e p needs some e l a b o r a t i o n .
Suppose t h e r e a r e ' t w o s o u r c e c a t e -
g o r i e s (A and B ) and two m e t e o r o l o g i c a l s c e n a r i o s (Iand 11).
If controls f o r
A I > A I I b u t c o n t r o l s f o r BII>BI, t h e strategy demonstrating attainment requires c o n t r o l s on c a t e g o r y A 2 t h o s e needed i n Scenario I w h i l e t h o s e on Category must be 2 t h o s e necessary i n S c e n a r i o 11.
B
The r a t i o n a l e f o r t h i s i s t h a t a
l i m i t e d number o f s c e n a r i o s a r e considered, and t h e p a r t i c u l a r i n c i d e n t r e p r e s e n t i n g a m e t e o r o l o g i c a l s c e n a r i o may n o t be t h e w o r s t such i n c i d e n t . MOST EFFECTIVE WAY TO REDUCE OZONE Models have been used t o assess e f f e c t i v e n e s s o f s t r a t e g i e s i n (1) r e d u c i n g peak 03 and ( 2 ) r e d u c i n g p o p u l a t i o n exposure t o h i g h 03.
To i l l u s t r a t e such
a p p l i c a t i o n s , t h e remainder o f t h i s paper o u t l i n e s how EKMA and UAM can be u s e d t o assess whether s t r a t e g i e s , f e a t u r i n g b o t h RHC and N 4 , c o n t r o l s a r e more e f f e c t i v e t h a n t h o s e i n which o n l y RHC i s reduced. EKMA The CALC r o u t i n e i n OZIPM4 p l o t s p r e d i c t e d 03 vs. t i m e ( r e f . 2 ) .
CALC can
be used t o see whether r e d u c t i o n i n peak 03 accompanying a g i v e n r e d u c t i o n i n RHC i s d i m i n i s h e d f u r t h e r by an accompanying NOx r e d u c t i o n .
The f o l l o w i n g
procedure has been suggested ( r e f . 7).
( 1 ) E s t i m a t e ~ 0 3accompanying a s p e c i f i e d r e d u c t i o n i n RHC o v e r a f i n i t e t i m e (e.g.,
5 years).
U t i l i z e t h e most l i k e l y NO,
projection
f o r t h i s time. (2)
Repeat ( l ) , b u t a l s o e s t i m a t e ANO,
f r o m a d d i t i o n a l NOx c o n t r o l s .
(3)
Compare ~ 0 3 o b t a i n e d i n (1) and ( 2 ) t o see w h i c h r e d u c t i o n i n 03 i s larger.
EKMA i s n o t w e l l s u i t e d f o r e s t i m a t i n g e f f e c t s o f a l t e r n a t i v e s t r a t e g i e s on p o p u l a t i o n exposure t o h i g h 03. i n d i c a t o r ( r e f . 7).
However, t h e f o l l o w i n g can be used as a r o u g h
F i g u r e 2 was o b t a i n e d u s i n g CALC, and i l l u s t r a t e s how t h e
e f f e c t o f r e d u c i n g NOx a l o n e by 50% m i g h t be assessed f o r a p a r t i c u l a r set' o f conditions.
By choosing a r e s u l t a n t w i n d v e l o c i t y (e.g.,
can c o n v e r t t h e x - a x i s t o d i s t a n c e . i n F i g u r e 2.
f r o m 10 AM-4 PM), one
T h i s i s shown f o r a 5 mph r e s u l t a n t wind
Assuming t h e t r a j e c t o r y b e g i n s a t C e n t e r City, F i g u r e 2 suggests
a p o t e n t i a l f o r p o p u l a t i o n exposure t o 03 t o i n c r e a s e w i t h i n about 20 m i l e s o f
568
-28. ,
#
0
.08
w IV, --BASECASE - - W %Nox
H c m x
-
10: 1
1 T I E
Fig. 2.
400
MINUTES
1
800
E f f e c t o f a c o n t r o l s t r a t e g y on p o p u l a t i o n exposure estimated w i t h EKMA.
UAM Use o f UAM t o e v a l u a t e e f f e c t s o f a l t e r n a t e s t r a t e g i e s on peak 03 i s s i m i l a r t o t h e procedure w i t h EKMA. can be considered.
With UAM however, a wider v a r i e t y o f s t r a t e g i e s
UAM a l l o w s e x p l i c i t c o n s i d e r a t i o n o f such f a c t o r s as source
l o c a t i o n and r e a c t i v i t y o f a source c a t e g o r y ' s RHC emissions.
A f o u r step p r o -
cedure f o r u s i n g UAM t o decide whether NOx c o n t r o l i s advisable i s enumerated below. (1)
Simulate base case d a i l y maximum 03 f o r each m e t e o r o l o g i c a l scenario.
(2) Repeat (1) w i t h ARHC a n t i c i p a t e d over a f i n i t e t i m e (e.g.,
5 years).
Do n o t consider changes i n NOx beyond those l i k e l y t o r e s u l t from growth o r programs already i n place.
(3)
Repeat ( 2 ) , b u t a l s o s i m u l a t e NO,
r e d u c t i o n due t o a d d i t i o n a l c o n t r o l s .
(4) Compare p r e d i c t e d changes i n peak d a i l y maximum 03 obtained i n s t e p s ( 2 ) and ( 3 ) t o determine which s t r a t e g y i s most e f f e c t i v e .
569
U n l i k e EKMA, UAM i s w e l l s u i t e d f o r a s s e s s i n g e f f e c t s o f a l t e r n a t e c o n t r o l s t r a t e g i e s on p o p u l a t i o n exposure t o h i g h 03.
This f o l l o w s from t h e model's
c a p a b i l i t y t o display s p a t i a l d i s t r i b u t i o n o f predicted concentrations. E f f o r t s o f c o n t r o l s on p o p u l a t i o n expsure t o ozone may be d e t e r m i n e d as follows. (1)
S i m u l a t e base case c o n d i t i o n s f o r each m e t e o r o l o g i c a l s c e n a r i o .
(2)
Determine ARHC f o r a c o n t r o l s t r a t e g y w i t h i n f i n i t e t i m e (e.g., 5 y e a r s ) and most l i k e l y ANO,
only. (3)
based on growth and p r e s e n t c o n t r o l s
Apply model t o e s t i m a t e r e s u l t i n g 03 c o n c e n t r a t i o n f i e l d .
Repeat (2) i n c l u d i n g a d d i t i o n a l r e d u c t i o n s i n NOx c o r r e s p o n d i n g t o a d d i t i o n a l contemplated c o n t r o l s .
Steps ( 1 ) - ( 3 ) y i e l d g r i d d e d o u t p u t r e f l e c t i n g s p a t i a l / t e m p o r a l d i s t r i b u t i o n o f 03 f o r t h e base case and two c o n t r o l s t r a t e g i e s .
The c a p a b i l i t y now e x i s t s
t o compare p o p u l a t i o n exposed t o 03 between each s t r a t e g y and t h e base case and between t h e two s t r a t e g i e s . (a)
P l o t hO3 i s o p l e t h s (i.e..
T h i s can be done i n s e v e r a l ways. l o c a t i o n s o f constant d i f f e r e n c e i n
p r e d i c t e d 03 f o r t h e model domain f o r hours o f i n t e r e s t (e.g., t o l a t e afternoon).
F i g u r e 3 i l l u s t r a t e s such o u t p u t ( r e t . 8).
midday
By knowing s p a t i a l d i s t r i b u t i o n o f p o p u l a t i o n , n e t g a i n o r r e d u c t i o n i n
p o p u l a t i o n exposed t o 03 can be estimated.
Fig. 3.
Oelta 03 i s o p l e t h p l n t for 50% RHC r e d u c t i o n , SY wind.
570
(b)
U t i l i z e " d e f i c i t diagrams" l i k e those i n F i g u r e 4 ( r e f .
9, r e f . 10).
I n t h e example shown i n F i g u r e 4. a s t r a t e g y f e a t u r i n g g r e a t e r NOx c o n t r o l increases p o p u l a t i o n exposed t o moderate 03 l e v e l s
( < 0.15 ppm), b u t p o p u l a t i o n exposed t o c o n c e n t r a t i o n s >0.15 i s decreased.
-.-10
II
iz
ia
14
is
16
I?
ozowc concctmnr;on
F i g . 4.
is
19
10
ti
za
za
IPPMMI
Changes i n ozone exposure from implementing strategy 2 (RHC =-4S%, NO, vs. strategy 1 (RHC =-36%, NO,=-23%).
=-37%)
SUMMARY
Two ways f o r u s i n g EKMA and UAM t o e v a l u a t e c o n t r o l s t r a t e g i e s have been illustrated:
(1)
i s a s t r a t e g y adequate t o a t t a i n an a i r q u a l i t y standard?
( 2 ) what i s t h e r e l a t i v e e f f e c t i v e n e s s o f s t r a t e g i e s t o reduce 031 The l a t t e r q u e s t i o n can be evaluated b o t h i n terms o f p r e d i c t e d changes i n peak
03 and r e d u c t i o n i n p o p u l a t i o n exposed t o h i g h 03.
RE[:ERENCES 1 U.S. EPA, OAR, OAQPS, G u i d e l i n e f o r Use o f C i t y - s p e c i f i c EKMA i n P r e p a r i n g Post-1987 Ozone SIPS, ( D r a f t ) , (Sept. 1987). Manual f o r OZIPM4 Ozone I s o p l e t h P l o t t i n g w i t h 2s O p t i o n a l Mechanisms/Version 4, ( D r a f t ) , (Sept. 1987). 3 J . Ames, T. C. Meyers, L. E. Reid, 0. Whitney, S. H. Golding, S. R. Hayes and S. 0. Reynolds, S A I Airshed Model Operation Manuals, NTIS Nos. PB85191567 and PB85-191568, (1984). 4 U.S. EPA, OAR, OAQPS, G u i d e l i n e on Air Q u a l i t y Models (Revised), EPA450/2-78-027R, ( J u l y 1986).
571
5
6
7 8 9
S. T. Rao, A p p l i c a t i o n o f t h e Urban Airshed Model t o t h e New York M e t r o p o l i t a n Area, EPA-450/4-87-011, (May 1987). E. L. Meyer, "Urban Scale Modeling Requirements," Paper presented a t t h e Air P o l l u t i o n Control Association S o e c i a l t v Conference on S c i e n t i f i c and Technical Issues Facing Post-1987 Okone Control Strategies," H a r t f o r d , CT, USA, (Nov. 1987) E. L. Meyer, "Consideration o f NOx Control i n S I P S f o r Ozone," ( D r a f t ) , Paper i n c l u d e d i n docket f o r US EPA proposed post-1987 Ozone P o l i c y , (Oct. 1987). J. L. Haney and T. Braverman, E v a l u a t i o n and A p p l i c a t i o n o f t h e Urban Airshed Model i n t h e P h i l a d e l p h i a A i r Q u a l i t y Control Region, EPA 450/4-85-003. (June 1985). Systems A p p l i c a t i o n s , In;. , Analysis o f Population Exposure and Dosaqe
Association. (Nov. 1982). 10 E. L. Meyer; Review o f Control S t r a t e g i e s f o r Ozone and T h e i r E f f e c t s on Other Environmental Issues, N T I S No. PB87-171195/AS, (Nov. 1986).
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T.Schneider et al. (Editore),Atmospheric Ozone Research and its Policy I ~ l i t ~ t i ~ n ~ 0 1989 Elaevier Science Publishera B.V.,Amsterdam -Printed in The Netherlands
573
OZONE AND OXIDANTS IN THE PLANETARY BOUNDARY LAYER
R.M.van Aalst National Institute of Public Health and Environmental Protection, P.O.Box 1, 3720 BA Bilthoven (The Netherlands)
ABSTRACT Some measuring and modelling results for ozone and oxidants (0 + N02)in the boundary layer in the Netherlands are discussed. Backgrouid average ozone levels are estimated, and their relation with tropospheric ozone levels is indicated. A short overview is presented of the chemical and physical processes contributing to buildup and degradation of ozone and oxidant in the boundary layer. An analysis of oxidant measuring data from a meteorological mast provides information about dry deposition of oxidant on grassland. INTRODUCTION: Some results from the basis document In 1987, a basis document for ozone has been finalised (ref. 1). Basis documents are produced in the Netherlands for so-called priority pollutants. They cover aspects of emission, use and origin of the pollutant, its occurrence in air, water and soil compartments, the exposure of humans, vegetation, ecosystems and materials to the pollutant, and an evaluation of the risks with respect to health and damage, as well as technical and economical consequences of reduction of these risks. Information in the basis document on concentrations of ozone in air were mainly obtained from the Netherlands Air Quality Monitoring Network. This network, which is in operation since the mid-seventies, has.30 stations for continuous, hourly meausurement of ozone, and 40 stations for hourly NO and NO2 concentrations. In the Netherlands, the spatial variations of ozone levels is determined to a large extent by the reaction of ozone with
30. As a consequence, ozone and NO2, which is produced in
this reaction, show complementary spatial patterns, while the concentration levels of oxidant (03 + NO2, in ppbv), show little variation (see fig. 1). The Netherlands interim limit value for ozone of 240 ug/m3, hourly aversgo, is exceeded on several thys in an average year, while in years with meteorological conditions favburable for ozone formation, like 1982, exceedance on more than five days has breii rroted on About half of the stations. The 8-hours maximum values, considered to be relevant to expoeure of humans and of vegetation, are not much lower, as is shown in table 1.
574
...................... ..........
0x Fig.
CEnIOoELOE
1. Average concentration of oxidant in the Netherlands in 1987.
TABLE 1 Daily maximum concentrations (ug/m3) of ozone in the Netherlands. The ranges indicate variation over the stations. maximum 98-percentile SO-percentile
1-hour average 227-431 164-227 62- 79
8-hours average 191-350 138-194 48- 71
Modelling studies ( r e f . 2 ) indicate that emissions of volatile organic compounds (VOC) and nitrogen oxides (NOx) in the Netherlands contribute only ca. 10% to these ozone peak levels. The calculations suggest that if exceedance of the interim limit value is to be avoided, European emissions of VOC should be reduced by 20% for an average year, or even by 60% for a year with high ozone peak levels. Emission reduction of NOx in Europe was found to result in relatively small changes in peak levels, with both increases and decreases (ref. 3) Growing season averaged concentration of ozone are of interest to vegetation damage (ref. 4). The averages over the growing season (May to 3 September) at daylight hours (10-17 h) varied from 80 to 95 ug/m over the Netherlands, as an average over the period 1980-1985. In years with
575 enhanced photochemical activity, values of average
levels
are
close
to what
85-115 ug/m3
is believed
are
found, The
to be the tropospheric
background of ozone, for which the growing season daylight hours was estimated at 78 ug/m3 for this five year period (see below).
average
Model calculations of growing season averaged ozone concentrations in the Netherlands have also been carried out: results are reported in ref. 5. Reduction of
is
European emissions of NOx
increased average ozone
expected
to
cause
concentrations in the Netherlands. Reductions of
European VOC emissions will decrease ozone levels but the effects are relatively small. Concurrent reduction of NOx and VOC emissions in Europe can still result in increased ozone levels in the Netherlands. The of
these model
results
concentrations. On Netherlands
is evidenced by
Sundays, the
networks
the weekend
average ozone
reality
effect on ozone
concentration on
the
rural stations are increased by 7% with respect to
weekdays. At Delft, a semi urban location, average ozone concentrations are increased by 11% on Sundays, while VOC and NO
concentrations are 25% lower
than on weekdays (ref. 6). In the industrialised Rijnmond urban area, the average
ozone
levels
on
Sunday are
20-40% increased, while VOC
concentrations are 20% lower, and NOx concentrations 25-35% lower. BACKGROUND CONCENTRATIONS OF OZONE IN THE NETHERLANDS Background concentrations of ozone were derived from data of the National Air Quality Monitoring Network in the period 1980-1986. Hourly were used for the calculation of ozone and 2 NO2) monthly averages for daylight hours (10-17 h). Oxidant
concentrations of ozone and NO oxidant
(03
+
concentrations were considered rather than ozone concentrations in order to avoid effects of local NO-emisisons. The results for Den Helder, a station in the relatively clean North-Western part of the country, and semi-rural location
Cabauw, a
in the centr8, are given in fig. 2 for different wind
directions. The oxidant concentration at Den Helder shows a spring maximum, and
a
secondary maximum
in July/August, which
is more pronounced at
Easterly winds. The spring maximum is also discernible for Cabauw, but summer
maximum
is
more
pronounced
here.
The
spring maximum
the is
characteristic for ozone concentrations at remote locations at Northern midlatitudes (ref. 7) and reflects the seasonal variation of ozone in the lower free troposphere. The summer maximum is likely to orginate from precursor
emissions in Western Europe. This hypothesis is supported by the
dependence of the concentrations of ozone and oxidant on wind speed (see fig. 3). In the first three months of the year, ozone concentrations increase with wind speed, indicating influence of enhanced vertical mixing. During
the
tropospheric ozone by
summer months, oxidant and ozone
concentrations decrease with increasing wind speed, suggesting dilution of oxidant formed in the mixing layer. The behaviour of ozone can be explained
576 from oxidant behaviour and decreasing influence of NOX upon dilution.
Fig. 2. Monthly average concentration of oxidant (ppb) during daylight hours (10-17h) at the stations Den Helder (left) and Cabauw (right) for different wind directions, period 1980-1986. Fiyre 4 shows the concentration of ozone and oxidant at Den Helder at North-Westerly wind with speed in excess of 5 Js. These concentrations are believed to be close to free tropospheric background ozone levels. At four Northerly rural stations, we found quite similar levels, with daylight hours growing season averages for oxidant of 42-44 ppb, and for ozone 38.5-
577 3 39.3 ppb (77-79 ug/m ) . The concentration of ozone during daylight hours on a more landinward station (Cabauw) is compared to these background levels in figure 5.
At
Cabauw,
the ozone
concentration is depleted by
NO-
emissions, especially during the winter months. In summer, the ozone than the background because of concentration is slightly higer photochemical production. Growing season daylight averages for ozone at 3 Cabauw are 85 ug/m ( 4 2 . 5 ppb), and for oxidant 53 ppb.
"I
'1 Fig. 3. Three monthly averaged concentrations (ppb) of oxidant (thick line) and ozone (thin line) as a function of wind speed, for months January to March (left) and July to September (right) at the station Cabauw.
Fig. 4. Monthly average concentration (ppb) of oxidant (thick line) and ozone (thin line) during daylight hours (10-17h) at station Den Helder, for NorthWesterly wind with speed more than 5 m/s. Period 1980-1986.
Both historical evidence (ref. 8) and model calculations (ref. 9 ) indicate that the lower tropospheric background concentration of ozone at our latitudes is to an important extent of antropogenic origin. There is evidence that ozone concentrations have increased by a factor two or more, and the model calculation indicate that emissions of NOx. VOC, methane and CQ have contributed to this increase.
Fig. 5. Monthly average concentration (ppb) of ozone during daylight hours (thick line) and background concentration from fig. 4 (thin line).
BUILDUP AND DEGRADATION OF OZONE IN THE BOUNDARY LAYER Drocessez The main processes contributing to the formation and removal of ozone in the boundary layer are: - vertical transport: stratospheric intrusions and exchange with the troposphere - (photo-)chemical formation - (photo-)chemical degradation - wet and dry deposition Direct emissions of ozone are of minor importance. Vertical transuort Stratospheric intrusions, although relatively frequently occurring, seldom lead to marked increases of boundary layer ozone concentrations (ref. 10). The vertical flux corrected with this transport is estimated for 2 the Northern Hermisphere to 0.02-0.07 ug/m /s (ref. 11). The contribution of this flux to average ground concentration is not well known; the flux could be balanced by dry deposition of an average concentration of 10-35 ug/m 2 , assuming a deposition velocity of 0 . 2 cm/s on a global scale.
573 However, it is estimated that chemical formation and degradation also play an important role in the tropospheric ozone budget (ref. 12). Exchange of boundary layer air with tropospheric air can be brought about by several processes, among which: - mixing layer depth variation vertical transport in high/low pressure systems - vertical transport in clouds These processes are discussed by Builtjes (ref. 13). Mixing layer depth variation is a major cause of diurnal variation of boundary layer ozone and oxidant concentrations. The diurnal variation of oxidant (see fig. 6 ) can be largely explained by dry deposition of ozone during the night, downward transport of ozone aloft due to mixing layer rise in the morning, and photochemical production during the day (ref. 14).
-
"
i
!
I
il*
I
I
Fig. 6 . Diurnal variation of hourly average concentrations (ppb) of oxidant.
photochemical formation Photochemical formation of ozone is a complex process. Rather than reviewing the vast literature on the subject, we would like to touch on a few aspects only. An important aspect of ozone chemistry is its production by photolysis of NO2 and its reaction with NO 1. NO2 + hv --> NO + 0 2. 0 + O2 + M --> O3 + M 3. 03 + NO --> NO2 + O3 leading to the well-known photostationary state relationship.
500 Here, K and kl are proportional to the W-light intensity. The quantities oxidant (Ox O3 + NO2) and NOx (- NO + NO2), expressed in molar units, e.g. ppbv, are consenred in these rapid reactions.
-
In
the Netherlands, where
NOx concentration levels are high, these
reactions are an important factor determining the variations time
and
space. The concentration of
oxidant
of
ozone
in
shows much less spatial
variation than the ozone concentrations. Equations of the form of (1) have been used successfully to calculated hourly average or even monthly averaged N02-concentrations from concentrations of NOx, a species that can be
more easily (ref. 15). However, close to sources of NOx, like
modelled
in urban surroundings or close to roadways, K may deviate from kl/k3. Photochemical formation of oxidant and ozone is mainly the result of oxidation of organic species by hydroxyl radicals (OH).
In this process,
organic peroxy radicals and hydrogen peroxyradicals (H02) are formed, which oxidise NO
to NO2.
regenerates
NO.
Photolysis of
During
the
the oxidation
NO2
formed produces
step, hydroxyl
03, and
radicals are
regenerated: in this way the oxidation process continues as long as sufficient NO and organic compounds are available. Similar reactions occur during the oxidation of unsaturated organic compounds by the
photolysis of
ozone,
and upon
carbonyl species. Many other reactions complicate this
simplified picture (ref. 16). For a quantitative description of oxidant formation. chemical kinetic mechanisms, as a part of photochemical dispersion models, are 17).
The main
function of
oxidant production from the concentrations of various organic NOx
used
(ref.
these mechanisms is to provide the ozone or species
and
in air, resulting from emissions. The enormeous variety of organic
compounds and the many reactions involved precludes complete treatment of
the
relevant
reactions, Either
and
explicit
"surrogate" or
"lumped"
mechanisms are used. In a "surrogate" mechanism, the chemistry of a limited number of species is described, for which ozone formation is assumed to be similar to that from the ambient air organic mix. In groups
of
compounds with
"lumped" mechanisms,
similar properties are represented by a single
species, for which representative chemical reactions are formulated. In the so-called "lumped structure" mechanisms such as the Carbon Bond Mechanisms (ref. 18) functional groups of organic molecules, e.g. methyl groups, double bonded carbon pairs or carbonyl groups are considered rather than complete molecules. Table 1 shows as an example the chemistry of
oxidant
formation from paraffinic carbon units (PAR) in the CBM-I1 chemical kinetic mechanism. The scheme illustrates several characteristic features, such as peroxide radical formation (Me02, HO ) , peroxide radical oxidation of NO t o 2 NO2, and OH radical regeneration, and termination by hydrogen peroxy radical recombination. Note the negative coefficient of PAR in the second reaction. This is necessary in order to maintain carbon balance; the single
58 1 carbon species Me02 cannot produce both the carbonyl unit CARB and another peroxy radical Me02 without consumption of another methyl unit PAR. The reaction is formulated to simulate the reactions of multi-carbon organic peroxy-radicals.
TABLE 2 Chemical reactions describing the photochemical oxidation of PAR by the Carbon Bond Mechanism I1 (ref. 20).
OH
in
k (ppm-' rn1n-l) 1. PAR + OH --> Me0 2. Me02 + NO --> NO; + CARB 3. Me02 + NO --> NO + CARB 4. Me02 + NO --> nierate 5. H02 6. H02
PAR
+
+ +
+ Me02 + H02
-PAR
NO --> NO2 + OH H02 --> H202 + O2
OH --> (1.41 + 0.94 p) OX + 1.41 CARB + 0.94 p OH - 0.47 PAR - 0.04 NOx
1500 4000 8000 500 12000 15000
1500
Although the CBM-I1 mechanism gives a reasonable description of oxidant formation in polluted atmospheres, it is difficult to understand from the mechanism the characteristics of oxidant formation, such as the stoechiometry: the number of oxidant molecules produced per unit of
-
organic species consumed the reaction rate
-
the effect of conditions and of other pollutants, such as NOx, on stoechiometry and rate of oxidant formation
More insight can be gained from an equivalent formulation, which summarizes the
chemistry
in table 1 in one single reaction, also shown in the table.
Here, it has been assumed that the reaction of OH with PAR is the ratelimiting step, and that the concentrations of radical species are in a quasi-steady state. The coefficients in the reaction are derived from the reaction
rate constants. The factor p represents the fraction of hydrogen peroxy radicals reacting with NO to NO2 and OH, and is calculated from the steady state condition. It is a function of the total hydrogen peroxy
radical production rate divided by the square of the NO concentration. From the equivalent reaction it is seen that oxidation of PAR by OH.in the CBM-I1 mechanism produces at most 2.35 molecules of oxidant per "molecule" PAR consumed (less under conditions of low NO concentrations) and is seen to constitute a small sink for OH (more so if NO is low). By this technique, the mechanism CBM-11, consisting of 65 reactions, can be reduced to 12 reactions of 12 species, including the CBM organic species, OH, PAN, HN03, and NOx. This reduces computing time considerably,
582 without affecting model performance, as model calculations for realistic ambient air conditions indicate (ref. 19). Model calculations for the Netherlands (ref. 2 , 3) indicate that the rate of oxidant production in the polluted boundary layer is probably of the order of 10-20 ppb/h during a sunny day in summer. Assuming a mixing height of 1000 m, this is equivalent to 5-10 ug/m 2 /s. From the annual average emission density of VOC in the Netherlands and surroundings (ref. 21), expressed in CBM organic units, and assuming a stoechiometry factor of 2 oxidant molecules per organic unit, an average production density of ca. 2 2 ug/m /s is found. From an analysis of measured oxidant concentrations in the Netherlands (ref. 22), net oxidant production rates of several ppb/h were found on sunny summer days at rural stations. In winter, net production was found to be close to zero during the day. Photochemical deeradatioq The main chemical sinks for oxidant and ozone in the polluted boundary layer are reaction with NO and subsequent nitric acid formation, and reaction with olefines. Reaction with NO produces NO2: O3 + NO --> NO2 NO2 can be converted to nitric acid by OH radicals: OH + NO2 --> HN03 which constitutes loss of one oxidant molecule per molecule nitric acid formed. NO2 can also be converted by O3 to NO3, and directly or via N205 to HN03, in which case three molecules of oxidant are removed to produce two molecules of nitric acid: NO2 + O3 - - > NO3 + O2 NO3 + NO2 - - > N205 N 0 + H 2 0 - - > 2HN03 2 5 Also, photolysis of NO3 into NO and O2 constitutes a loss of two oxidant molecules: NO3 + hv - - > NO + O2 The average loss rate of oxidant by nitrate formation in the Netherlands is estimated of the order of 2 % per hour (ref. 1). Reaction of ozone with olefines does not always contribute to oxidant loss, as ozone may be regenerated in the reaction sequence. In the shortened version of the CMB-I1 mechanism discussed above, reaction of the double bonded carbon pair unit OLE produces net (0.76 p - 0.46) q.Ox, where p and q are factors less than 1, dependent on the NOX -concentration. Under conditions of low NOX concentration, the olefines are a sink for ozone. The ethylenic double bonded species ETH produces, upon reaction with ozone, (0.2 p-1) q Ox, thus constituting a net sink under all circumstances.
583 Wet and drv deDosition Wet deposition is not an efficient removal process for ozone. The time constant for non-reactive scavenging by rain and cloud water may be estimated by H.I./h, where I is the precipitation rate, h the depth of the layer in which precipitation takes place, and H the Henry constant for ozone, equal to about 3 (ref. 23). Assuming h 1000 m and I 800 mm/y, we
-
-
find a removal time constant of the order of negligible with respect to dry deposition removal.
10-'Os-l,
Reaction of ozone with other pollutants in cloud possibly
more
and
completely
rain water
is
efficient. An upper estimate of aqueous phase oxidation of
SO2 by ozone of l%/h (annual average) and concentrations of SO2 and O3 of 10 and 80 ug/m3 gives an estimated effective removal time constant of 2. Dry deposition of ozone is a more efficient removal process. In table 3, the deposition velocity for various surfaces is given. The deposition velocity over water and snow is very low. Over land, an average deposition leads, with a mixing layer height of 1000 m, velocity vd of ca. 0.5 to removal with an effective time constant vd/h of ca. 5.10m6s-l.
ems-'
TABLE 3 Dry deposition velocities (in cm.s-l) for ozone (from ref. 24) summer day niiht
short grass grassland crop (mayze, soybean)
day night day night
forest summer
soil soil (wet) snow sea (water)
0.6 0.3 0.0-1 0.4-1.3 0.1-0.3 0.2-1 0.05-0.1 0.25-0.6 0.1 0.06 0.01-0.05
Recently, new information about dry deposition of oxidant has been obtained from continuous measurements of NO2 and O3 at 4, 100 and 200 m height at the meteorological mast at Cabauw, The Netherlands, 1986.
The
surroundings of
in
the period
1980-
this mast are mainly grassland with some tree
rows and few orchards. From the measurements of oxidant, wind and global 4m and z2 radiation the deposition velocity vd related to the heights z1 100 m was calculated according to
-
-
here, F is the flux, c the oxidant concentration, and resistance:
ra
the
aerodynamic
584
fa (zl,z2)
- i:
l/Kz(z)
&
The coefficient of turbulent diffusion KZ was calculated from the friction velocity u* and Monin Obuhkow lenght L, which, in turn, were calculated from the measured wind speed and global radiation (ref. 2 5 ) . Situations with an estimated mixing layer height below 110 m were excluded from the analysis; this included an important fraction of the nocturnal hours. In order to check for flux divergence, the deposition velocity was also calculated for z1 4m and z2 200m. Only if flux divergence is neglibile, the flux can be equated to the deposition flux.
-
-
. . I
6 1111 u n s s t m
I2
II
__ I I J O_ i u,u m i
1
14
Fig. 7. Deposition velocity (cms
-1
) at Cabauw, as a function of time of the day
average for the period 1980-1986. 0 : as derived from concentration measurement at 4 m and 100 m. +: idem, for 4 m and 100 m.
Fig. 8. Deposition velocity (cms-1 ) at Cabauw, for summer (left) and winter (right) half year periods. Symbols as in fig. 6 .
585 The
average
diurnal
profile
of the deposition velocity is shown in
fig. 7. The deposition velocity, and also the f l w , is higher day
during
the
night, During the morning hours, there is considerable f l w
than at
divergence, as a result of mixing height increase. Fig. 8 shows results for the
summer- and winter
half year periods. During winter, the deposition
velocity is rather low, both because of shorter day value
during
the
day.
lenght,
and
a
lower
In the summer, flux divergence during the morning
hours is large, especially in instable conditions (Pasquill classes A, and C) and for neutral stability (D) in conditions of low mixing height. The flux divergence can be
estimated
from
the
mass
balance
B
equation.
Neglecting smaller terms we have dF/dZ
*
-dc/dt
-
u dc/&
+Q
where u is the horizontal wind, and Q represents chemical reaction. In case of concentration changes due to mixing height increase, we have dc/dt
- l/h
.
.
dh/dt
(c~-c)
and the error in vd can be approximated by
.
I/h. dh/dt
AVd
(C,-C)/C
.A Z
where h is the mixing height, c the concentration and ct the
concentration
above the mixing layer. With l/h.dh/dt of the order of 5O%/h. (ct-c)/@l and A z 100 m, we have vd 1.4 cm/s, which is of the order of the
-
divergence
-
effect
found. The influence of advection (second term) on the
deposition velocity was estimated to be less than 0.05
cm.s-l. A l s o ,
for
oxidant, chemical reaction is not causing important flux divergence. However, the flux of ozone may be strongly affected by chemical reaction
-
with NO. Writing Q k.c. where k is some effective first order rate constant, the estimated effect of chemical reaction on vd is: Avd
F/c
-
kAz
-
-
For reaction of O3 with 5 ppb NO at night, k z and even forb z 4 m. vd 0.8 cm.s-'. Therefore, a deposition velocity for ozone cannot be derived from these measurements. The estimated yearly average deposition flux for oxidant is ca. ug/m 2/s, corresponding to a yearly averaged deposition velocity of ca. -1 cm.s . In summer during daylight hours the flux is ca. 0.9 pg/m 2/s, the deposition velocity 0.8 cm.s-l. In part, this flux is caused by deposition
of
NOp,
which
0.4 0.5 and dry
gives an important contribution to the oxidant
concentration at ground level in Cabauw. It is interesting to compare this flux to the flux from the 2 stratosphere to the troposphere (0.01-0.07 pg/m /s). Even taking into account that dry deposition over sea is an order of magnitude lower than that over land, it still follows that oxidant dry deposition may be larger than this stratospheric flux. In view of tropospheric degradation processes, this points to a considerable chemical production of ozone in the troposphere (ref. 12). Part of this production is taking place in the mixing layer, and in the Netherlands there is an upward flux of oxidant from the mixing layer.to the troposphere. This is indicated by the fact that the average concentration of oxidant, measured at Cabauw at 200 m height, is larger than the background tropospheric concentration, estimated from fig. 4. Averaged for the summer half year, the difference is about 13 ppb. This indicates that the photochemical production in the mixing layer 'is larger than the removal by dry deposition. Acknowledeement The analysis of the CBM-I1 mechanism was carried out in cooperation with J.H.Duyzer (TNO, Delft). The analysis of oxidant data at the Cabauw mast was carried out in cooperation with J.A.van Jaarsveld (RIVM, Bilthoven). REFERENCES 1. W.Slooff, R.M.van Aalst, E.Heijna-Merkus and R.Thomas (eds.), Basis document ozone (in Dutch), National Institute of Public Health and Environmental Protection, Bilthoven, The Netherlands (1987). 2 . K.D.van den Hout and F.A.A.M.de Leeuw, Modelberekeningen met het MPA trajectoritinmodel van episoden met fotochemische luchtverontreiniging, in: Ozon: fysische en chemische veranderingen in de atmosfeer en de gevolgen, Kluwer, Deventer 1987, pp 92-96. 3 . P.J.H.Builtjes and S.D.Reijnolds, Evaluatie en toepassing van een grootschalig verspreidingsmodel voor fotochemie - hat RTM-111-PHOXA model, in: Ozon: fysische en chemische veranderingen in de atmosfeer'en de gevolgen, Kluwer, Deventer 1987, pp 97-105. 4. A.E.G.Tonneijk, Effects on agricultural crops, this symposium. 5. F.A.A.M.de Leeuw, Long-term averaged ozone calculations, this symposium 6. R.Guicherit, TNO, Delft, personal communication, 1987. 7. J.A.Logan, Tropospheric ozone; seasonal behaviour, trends and (1985), p. 10463. anthropogenic influence, J.Geophys. Res. 8. R.D.Bojkov, Monitoring ozone layer and background ozone in the troposphere, this symposium. 9. O.Hov, K.H.Becker, P.Builtjes, R.A.Cox and D.Kley, Evaluation of the photo-oxidants-precursorrelationship in Europe, CEC Air Pollution Research Report-1, 1986. 10. United Kingdom Photochemical Oxidants Review Group, Ozone in the United Kingdom, UK Department of the Environment, 1987. 11. W.Johnson, Global modelling of ozone and trace gases, this symposium. 12. D.Kley, A.Volz and H.G.J.Smit, Tropospheric ozone-natural budget and anthropogenic perturbation, Chemistry related to tropospheric ozone,
.
a
587 proc. workshop COST 611 WP2, Cologne 1985, CEC, 1985. 13. P.J.H.Builtjes, Interaction of planetary boundary layer and free troposphere, this symposium. 14. 1.Colbeck and R.M.Harrison, Dry deposition of ozone: some measurements of deposition velocity and of vertical profiles to 100 meters, Atmos. Environ. (1985), p. 1807. 15. N.D.van Egmond and H.Kesseboom, A numerical mesoscale model for (1985), longterm average NOi and N02-concentrations, Atmos. Environ. p. 587. 16. R.Atkinson and A.C.Llovd. Evaluation of kinetic and mechanistic data for modelling of photkhemical smog. J.Phys. Chem. Ref. Data U (1984) D. 315. 17. R.G.Derwent, Comparison of chemical mechanisms in models, this symposium. 18. G.Z.Whitten, J.P.Killus and R.G.Johnson, Modelling of auto exhaust smog chamber data for EKMA develoriment.. reuort under contract number 68-02. 3735, EPA, 1983. 19. R.M.van Aalst and J.H.Duvzer. unDublished results. TNO, Delft, 1984. 20. G.Z.Whitten et al., M h e l i i n g of Simulated Photochemical smog with kinetic mechanisms Vol 1; interim report EPA-600/3-79-0010, 1979. Huidige emissies van koolwaterstoffen, Basisdocumenten 21. C.Veldt, koolwaterstoffen I (in Dutch), report CMF' 85/01, TNO, Delft, 1985. 22. N.D.van Egmond, H.Kesseboom and R.M.van Aalst, Relaties tussen NO2- NO en 0 -niveaus in de buitenlucht; afleiding van een NO -grenswaarde, RIVM3 report 227905050, National Institute of Publi'd Health and Environmental Protection, Bilthoven, 1982. 23. T.V.Larson, N.R.Horike and H.Harrison, Oxidation of sulfur dioxide by oxygen and ozone in aqueous solution; a kinetic study with significance to atmospheric rate processes, Atmos. Environ. 12 (1978), p. 1597. 24. J.A.Garland, Principles of dry depositon: application to acidic specles and ozone, VDI-berichte 500 (1983) p. 83. 25. D.Onderdelinden, J.A.van Jaarsveld and N.D.van Egmond, Bepaling van de depositie van zwavelverbindingen in Nederland, RIVM report 842017001, National Institute of Public Health and Environmental Protection, 1984.
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T. Schneider et al (Editors), Atnwupheric Ozone Research and its Policy Implications 1989 Elaevier Science Publishers B.V., Amsterdam -Printed in The Netherlanda
589
COMPARISON OF CHEMICAL MECHANISMS IN PHOTOCHEMICAL.MODELS
R.G. DERWENT and A.M. HOUGH Modelling and Assessments Group, Environmental and Medical Sciences Division, Harwell Laboratory, Oxfordshire, England
ABSTRACT The production of photochemical ozone in the atmospheric boundary layer is now a well established occurrence during most summers in Europe. Ozone concentrations during these episodes may approach and exceed air quality criteria values set to protect human health and prevent crop damage. Photochemical models are an accepted tool in the development and assessment of control policies designed to reduce exposure levels to ozone and other secondary pollutants. These models clearly show that abatement of hydrocarbon and nitrogen oxide emissions should bring some improvement in secondary pollutant air quality. To describe the complexity of the atmospheric photochemistry, many hundreds of chemical reactions are required in photochemical models.
In most models, computer limitations require that
drastic simplifications are made to the chemical schemes, in others the realism with which the chemistry is represented is limited only by present understanding and the completeness of emission inventories. The chemical schemes used in 20 photochemical models from the literature have been analysed carefully and implemented in the Harwell trajectory model using common input assumptions and evaluated chemical kinetic data. The implications of the 20 different chemical schemes on model calculated ozone, PAN, nitric acid, hydrogen peroxide and sulphate aerosol concentrations are described. Attention is then directed to the evaluation of two particular ozone control strategies
using the 20 different chemical schemes. INTRODUCTION Photochemical ozone formation over Europe is now a widely recognised regional scale pollution problem of some significance. During summertime anticyclonic conditions, sunlight-driven chemical reactions involving hydrocarbon and nitrogen oxide emissions may lead to t h e build-up of elevated ozone concentrations close to the surface in the atmospheric boundary layer. The hydrocarbons and nitrogen oxides act as photochemically-generated secondary pollutant precursors and are emitted largely from man's activities. The ozone
590 concentrations during these pollution episodes may approach or exceed environmental criteria levels which have been promulgated to protect human health and crops.
Most countries in Europe have the potential to cause some
photochemical secondary pollutant formation; furthermore, long range transboundary transport has been an important feature of this regional scale pollution phenomenon in North West Europe and Scandinavia. The discussion of control policies to combat photochemical air pollution formation is currently underway in several international fora. A coherent policy will require a full understanding of the chemical and physical mechanisms of the formation, transport and removal of photochemical ozone, together with the costs and performance of the available abatement technologies and an understanding of the damage mechanisms in the environment and their dose-response relationships.
This understanding is not complete in detail for
Europe, though much progress can be made if uncertainties and gaps in present understanding are taken adequately into account.
This paper addresses the
chemical mechanisms currently thought to account for photochemical ozone formation and the importance to be attached to the remaining uncertainties in their representation in the large photochemical models used for control policy assessment. MECHANISMS OF PHOTOCHEMICAL OZONE FORMATION AND THEIR REPRESENTATION IN MODELS Over the last three decades, a significant amount of research effort has been devoted to the understanding of photochemical smog chemistry.
This has
involved extensive programmes of ambient air quality monitoring, field studies of ozone transport and deposition and laboratory chemical kinetic studies involving smog chambers. This large body of understanding has been extensively reviewed by a number of sources and the following elements are considered to account for all the essential features of photochemical ozone formation in the atmospheric boundary layer:
-
nitrogen dioxide photolysis, the actual ozone source,
+
NO2
radiation (280 nm CXC 400 nm)
NO
+
0
the photochemical reaction system coupling together nitric oxide (NO), nitrogen dioxide (N02) and ozone ( O 3 ) ,
+
NO2
radiation
+
NO
+
NO
+
0
- o ~ + H
O + 0 2 + M
03
+
NO2
+
02
peroxy radicals (H02 and organic R02) which oxidise NO to NO2, R02
+
NO * RO
+ NO2
hydroxyl radicals which react with hydrocarbons to form peroxy radicals,
+ RH + 02 + M
OH R
-
+
R
+ H20
R02
+M
591 photochemical sources of hydroxyl radicals, O3
+
O(lD) HCHO
H
+
HCO
HOq
-
radiation (280 nm
+ H20 +
02
OH
radiation (280 nm
+M
+ 02 + NO
+HOq H02 +
319 nm)
+ 02
O('D)
+ OH 400 nm)
+
H
+ HCO
+M + CO
OH + NO2
--
radical removal processes,
Hog + H02 + M OH + NO2 + M
H202
+M
HNO3 + M removal processes, largely dry deposition for ozone, PA
HNO3 and hydrogen
peroxide. These points dictate the complex interplay between hydrocarbon and nitrogen oxide emissions. photochemistry, transport and deposition which characterises photochemical air pollution formation. The complete representation of all these processes with adequate spatial and temporal resolution is beyond our current capabilities. We cannot say that all these processes are fully understood and that the computer capacity would be made available to solve all the mathematical equations. Simplifications must be made if progress is to be made on a realistic timescale.
Some of these
simplifications can be identified and evaluated at present.
However, others
necessarily cannot be so evaluated and include such elements as missing or incorrectly evaluated chemical kinetics data and poorly-understood meteorological processes. The simplifcations typically made in the large photochemical models can be divided into two areas: o
those made in the representation of atmospheric dispersion and transport and in the meteorological processes
o
those made in the representation of the atmospheric chemistry.
That is, the problem has meteorological and chemical dimensions and both may require simplification depending on the objectives of the research and the computer resources available. The principle meteorological simplifications may involve replacing the equations of state of the atmospheric system with actual or long-term average observations, together with spatial and temporal averaging. These particular simplifications are not discussed any further here and attention is directed in the remainder of the paper to the principle simplifications made in the treatment of the atmospheric chemistry. PRINCIPLE SIMPLIFICATIONS MADE IN COMPUTER MODELS OF ATMOSPHERIC CHEMISTRY At the outset it is important to differentiate between those parts of this question that can be addressed and those which cannot be taken further. In the latter category is the problem of missing chemistry. Although many of the
592 details of the processeo by which photochemically-generated secondary pollutants are formed have been adequately researched, there is the possibility that some important facet of the complex chemical system has remained explored and Is, as yet, uncharacterised.
It is a matter of
speculation whether any missing chemistry could seriously undermine the evaluation of ozone control strategies which has been performed. No further attention is given to this question in this study and in the paragraphs below the known but uncertain chemistry is addressed. It is straightforward to look at a complex chemical mechanism and to consider that it behaves as a structureless system of processes in which all known chemical reactions between all possible combinations of precursor
molecules, reactive intermediates and secondary pollutants are taken into account. o
In reality this is not the case for several reasons:
atmospheric chemistry occurs on the molecular scale and encounters involving only one, two or three molecules need to be considered,
o
chemical reactivity is highly species-specific and it is relatively unusual for a particular species to undergo atmospheric chemical reactions with more than 10 other species,
o
chemical reactions which contribute negligibly to overall chemical reaction rates under atmospheric conditions have often been noticed and deleted from reaction schemes. Data evaluation procedures have been applied over the years to the chemical
kinetic data of relevance to atmospheric chemistry.
These reviews have
largely addressed simple chemical reactions which are amenable to laboratory investigation. There is scope for extending the coverage of the chemical kinetic data evaluations to include the chemistry of the light (C1
-
c8)
hydrocarbons including their reactive intermediates and degradation products. Generally speaking, most simplifications are made in the formulation of hydrocarbon chemistry and in its range and species coverage.
This is
understandable since ambient hydrocarbon measurements which are adequately split into a range of species are expensive to make and are available for only a few locations. Emission inventories for hydrocarbons are considered to be more uncertain than for other atmospheric pollutants, particularly the oxides of nitrogen and carbon monoxide.
Furthermore, although emission estimates are
made for total hydrocarbons in many countries, few have reliable speciation data available.
In the face of ignorance and without adequate data against
which to compare it, it is often simplest to use only a few hydrocarbon species to represent the hydrocarbon oxidation contribution to the photochemicallygenerated secondary pollutant formation. There has been much debate cowerning the role of methane, the simplest hydrocarbon which contributes to photochemical ozone formation. It is usually
593 the most abundant hydrocarbon in the ambient atmosphere because it has man-made regional scale, man-made global scale and biospheric global scale sources. Ambient measurement techniques to separate methane from the remaining hydrocarbons have been developed and have lead to the formulation of the concept of non-methane hydrocarbons.
Furthermore, early reactivity scales
pointed to a negligible contribution to ozone formation from man-made sources of methane. As a result methane is often omitted from chemical schemes. Nevertheless, methane reacts with hydroxyl radicals and lead. to a significant net ozone formation on the global spatial scale.
Its role is also
not neglible on the urban scale because of the large baseline methane concentration and hence the significant contribution to the OH removal rate. Methane should therefore be included in models of photochemical air pollution formation. Omittine individual hvdrocarbons is an imortant modet
.-
--
The oxidation of methane involves the reaction sequence
OH + CH4 CH3 + 02
+M
H20 + CH3 CH3O2 + M
and these consecutive reactions describe the sole involvement of the methyl
(CH3) radical in air pollution systems. Since the methyl radical is exceedingly short-lived and reacts predominantly by the one route above, it is usual to put the methyl radical into steady state obviating the need for a separate differential equation. Qrnittinn fast reactions in a set of Fonsecutive reactions is an w t a n t model s w i c a t h These considerations do not apply to the methylperoxy (CH3O2) radical which is long lived and takes part in competitive reactions with nitric oxide (NO) and other peroxy radicals
CH3O2 CH3O2
+ NO + R02
-
4
CH3O
+ NO2
products.
The oxidation of NO to NO2 leads to net source of ozone and this is one of the reactions whereby methane oxidation stimulates ozone formation.
The methoxy
radical undergoes rapid consecutive reactions with oxygen and can be omitted
-
from the reaction scheme without loss of valuable detail,
CH3O + 02 HOP + HCHO. Although treatment of the methoxy radical may be omitted, the consequences of the above reaction are important in that formaldehyde (HCHO) is produced together with an H02 radical.
Formaldehyde is an important reactive
intermediate being photochemically-labile. The HOP radical goes onto react' with nitric oxide to reform the hydroxyl radical lost by attack on methane,
H02
+ NO
+
NO2
+ OH
and the accompanying NO to NO2 oxidation acts as a net source of ozone. Overall, after omitting the rapid consecutive steps and the competitive reaction of CH3O2 with HO2 or R02, the methane oxidation looks as follows:
594 02 * CH3O2
OH + CHq NO
+
CH3O2
02 +
NO2
+ H20
+ HOP + HCHO
This would be typical of the representation of a hydrocarbon oxidation in an exulicit chemical scheme. There is an alternative representation which combines both competitive and consecutive reactions in the same overall chemical equation.
-
If in general
terms the competitive reaction fluxes are split a
CH3O2
1-a
CH3O2
+ NO + HOp
+
+ NO2 CH302H + 02
CH3O
then the methane oxidation scheme can be written
OH
+
CH4 * aNO2
-
aN0
+
dim0
+ (2a-1) HOp + (1-a) CH302H
This would be typical of the representation of a hydrocarbon oxidation in a peneralised chemical scheme. These comments are illustrated in the above paragraphs using methane as an example but they apply with equal force to any of the ambient hydrocarbons that take part in photochemical air pollution formation. The general problem with the generalised chemical schemes is how to calculate the a terms and whether these remain constant with time and between model runs.
Such schemes are not
generally suitable for ozone control policy evaluacion. REDUCING THE NUMBER OF HYDROCARBONS REPRESENTED IN CHEMICAL SCHEMES In producing tractible photochemical air pollution models, inevitably one of three constraints has controlled progress:
o
life cycle data for individual hydrocarbons,
o
computer storage,
o
computer time.
If we consider just the c 2 - C ~hydrocarbons then there are over 100 species including their oxygenated derivatives. The above constraints will come into play in different ways depending on model formulation.
In a large Eulerian
grid model, computer storage is often limiting and highly compact chemical sub-models are all that can be fitted into a model with a thousand or more grid points.
In a routine Lagrangian trajectory model, computer storage is not
often a problem since the numerical integration routines do not need to access the entire fields of input data continuously.
In these cases, computer time is
often limiting if results are required for a large number of trajectory arrival times and receptor points.
In a research trajectory or box model with an
efficient numerical integrator, neither computer time nor computer storage are the operational constraint and our current basic undestanding of the atmospheric behaviour of individual hydrocarbons restricts further progress. The life cycles of each hydrocarbon have a number of common features,
595 involving atmospheric emissions, OH radical attack and their subsequent degradation pathways.
Significant progress has been made in the field of
laboratory chemical kinetics, so that much of the data which are required in the construction of degradation pathways and in the prescription of the rates of OH radical attack, are now available in the literature.
Current Droeress is
restricted bv the availabilitv of hiah aualitv hydrocarbon emissions data in many countries. The C2-Ca hydrocarbons can be divided up according to several different characteristics but it is useful to consider the classification into families of organic compounds:
straight or branched chain saturated hydrocarbons. methane ethane propane butanes
(2 isomers)
pentanes
(3 isomers)
hexanes
(4 isomers)
heptanes
(6 isomers)
octanes
(10 isomers)
straight or branched chain olefinic hydrocarbons. ethylene propylene butenes
(4 isomers)
pentenes
(5 isomers)
hexenes
(>lo isomers)
heptenes
(>lo isomers)
octenes
(>lo isomers)
aromatic hydrocarbons. benzene toluene o-xylene m-xylene p-xylene ethyl benzene alicyclic hydrocarbons. cyclobutanes cyclopentanes cyclohexanes oxygenated hydrocarbons. alcohols aldehydes ketones
596 carboxylic acids esters ethers o
chlorinated hydrocarbons. chloroalkanes chloroethers
.
3 chemical schemes and this is an imnortant model simplification At this level of detail, three principal model approaches can now be discerned and these are: o
complete schemes.
o
direct approaches.
o
parameterised approaches. In the, -
the identity of all the hydrocarbons within
any of the above classes is retained and an explicit degradation scheme would be provided for each.
In the absence of emissions data for a particular
hydrocarbon then that hydrocarbon would be omitted from the model.
Clearly,
the explicit scheme approach generates the largest chemical scheme and this level of detail can only be handled with a box or trajectory model. In the direct amroach then the separate identities of all the hydrocarbons within each class are lost and that complete class is replaced by one or two members, which may be real species or ideal members of the class.
These
members act as surrogates for the class and their emission rates are adjusted to reflect the emission rates for the class.
Much of the detailed description
of organic degradation products particularly aldehydes, ketones and peroxyacylnitrates are lost but often these have little significance and there are unlikely to be any observational data against which to compare them against.
Care is required in the selection of surrogates to preserve the
overall reactivity of the class, to maintain the correct balance in degradation product formation and to ensure the same non-methane hydrocarbon concentration in ppbC. These three constraints are not satisfied uniquely for any of the classes given above and errors are introduced in this approach. However the chemistry scheme adopted is the explicit scheme of the hydrocarbons chosen to act as surrogates so these can be evaluated against the chemical kinetic literature. In the parameterised scheme amroach then the separate identities of all the hydrocarbons within each class (or part of a class) are lost and that complete class is replaced by one member. This member acts not only as a surrogate for the class but its degradation scheme is also set up to act for the class. The one parameterised scheme for a particular class would then represent that classes contribution to OH reaction rates, degradation product formation and
597 non-methane hydrocarbon concentrations in ppbC.
These three criteria cannot be
satisfied by a unique lumped scheme. Furthermore, considerable experimentation is required to draw up the imaginary scheme which which often requires non-stoichiometric reaction products to represent a range of degradation pathways from a range of real species. These schemes are often problem specific, of unknown accuracy and cannot be realistically evaluated against the chemical kinetic literature. They can only be evaluated by comparison with the results from a more complete chemical scheme using either test or real emissions data. There is no unique way of lumping the hydrocarbons in one class together to reproduce accurately the contribution to OH reaction rates, degradation product formation and non-methane hydrocarbons concentration in ppbC and two general approaches have been adopted: o o
parameterisation by mass. parameterisation by chemical structure. The Carbon-Bond approach provides important examples of the techniques of
parameterisation by chemical structure.
In this approach hydrocarbons are
split up into structural units such as C-C double bonds, aromatic rings and C-C frameworks as a means of representing the different members of each hydrocarbon class. Several versions of the carbon bond approach have been formulated to generate chemical schemes of varying complexity for incorporation into large Eulerian grid models. CLASSIFICATION OF CHEMICAL SCHEMES USED TO MODEL PHOTOCHEMICAL AIR POLLUTION FORMATION In Table 1, 20 chemical schemes employed in models of photochemical air pollution formation and used to evaluate ozone control strategies have been listed and some of their principal features drawn out for comparison. No attempt has been made to be exhaustive but many of the schemes from the major research models have been included. Each of the mechanisms is different and any classification scheme can only give a general indication of the simplifications which have been used.
Moreover, the definitions of the terms
used to describe such simplifications vary widely. In implementing these schemes for the United Kingdom, a simple trajectory model approach has been formulated to provide an account of the potential for ozone and other secondary pollutant formation downwind of London. The different chemical mechanisms have been applied using the United Kingdom hydrocarbon emission inventory, making use of as much detail as possible in terms of the range of hydrocarbons. The table shows how many emitted hydrocarbons could be used, the number of chemical reactions involved and a comparative measure of the CPU time required for a two day's calculation. The range in computer time requirements covers an order of magnitude showing the gain in speed that can be
achieved using the simplification techniques described above.
The CPU time
required for a two day's calculation. The range in computer time requirements covers an order of magnitude showing the gain in speed that can be achieved using the simplification techniques described above. COMPARISON OF A LARGE NUMBER OF CHEMICAL SCHEMES IN A SIMPLE TRAJECTORY MODEL The model used in this evaluation employed a two-layer trajectory model approach and has been reported in detail elsewhere (ref. 1).
Differences in
model results can arise from a range of factors and the methodology adopted here has the main aim of focussing on the differences introduced by the representation of the hydrocarbon chemistry, and its contribution to ozone formation. This hydrocarbon chemistry is a subset of the entire chemistry used in the model.
The remainder describes the chemistry of the small molecules
containing 0 , H, N ,
S
and C, but excluding any hydrocarbon degradation
reactions. The first steps were therefore to: o
take the published sources for each chemical scheme and remove the small molecule chemistry and replace it by the 54 reaction scheme from ref. 1, using rate coefficients reviewed in refs. 2 and 3.
o
set up life cycles for all secondary pollutants including dry deposition and aerosol scavenging.
o
add the methane chemistry to each scheme if not already included and adjust rate coefficients where necessary.
o
take the hydrocarbon chemical scheme used in the original reference and update all recognisable rate coefficients to the standard set.
o
set up the emissions for each scheme and relate them to the UK hydrocarbons emissions inventory.
o
take out all photochemical processes from the schemes and replace them by a standard set of time-dependent photochemical rate coefficients. In general, the above protocol worked well and for many of the more modern
chemical schemes the changes introduced were minimal and of little consequence. However, for some of the Carbon-Bond schemes with highly parameterised reactions, the chemical rate Coefficients could not be updated and this may present difficulties in interpreting our results. Table 2 presents the peak model concentrations calculated downwind of London for a number of species of interest in the twenty mechanisms and in the nine most recent mechanisms.
There is good agreement in the peak ozone
concentrations found with the different schemes, though with considerably poorer agreement concerning the timing of that peak in each model.
The more
recent schemes show excellent agreement between themselves with a peak ozone concentration of (95.5 t 3.1) ppb. In the case of the peroxyacylnitrates (PANS), the pattern is markedly
599 different with the time of the maxinun defined more accurately than the peak concentration. In fact, the calculated peak concentrations cover a wide range of (4.2
f
1.6) ppb which is not reduced much if attention is restricted only to
the nine more recent mechanisms. This behaviour for PANS is also repeated for hydrogen peroxide with the models showing better agreement on the timing of the maximum rather than on its magnitude. For both hydrogen peroxide and PANs this range of results is large enough to make calculations almost worthless. They show that the formulation of chemical mechanisms is far from perfect and that the good performance found for ozone reflects the careful adjustment and design inherent in the original mechanisms rather than the adequacy of present understanding of the basic atmospheric chemistry. It is nevertheless important to consider how relevant these chemical mechanisms are for ozone control strategy evaluation. EVALUATION OF OZONE CONTROL STRATEGIES It is often stated that although a given model has a limited ability to reproduce a particular behaviour exhibited in the real world, it has the ability to register reliably the consequences of changes in its input data.
In
photochemical air pollution modelling this would mean that a model which had difficulties in reproducing all facets of some observational ozone database for an episode would still have some value in evaluating ozone control strategies. In this paper this topic is investigated using the twenty chemical schemes from Table 1 and a simple scenario formulation which entails a 1984 base case and year 2000 scenarios in which all motor vehicles meet two different sets of emission controls, the Luxembourg Agreement and stringent emission standards (see ref. 4). Table 3 shows the peak concentrations of ozone, PAN and hydrogen peroxide calculated downwind of London in the 1984 base case and in the year 2000 cases in which motor vehicle emissions have been controlled. Despite the scatter in the absolute results, the relative results are encouraging. For ozone, every mechanism predicts a decrease in peak concentration between the 1984 base case and the year 2000 scenario with the Luxembourg Agreement and a further decrease following the implementation of the stringent vehicle emissions scenario. For ozone, the percentage reductions calculated using the nine recent mechanisms are all similar, as indeed are the results from some of the older mechanisms. The percentage decreases in the peak ozone concentration which occur between the 1984 base case and the two year 2000 scenarios appear to be robust with respect to changes in the chemical mechanism employed. For the PANs the pattern is similar to that for ozone although it should be noted that the results for three mechanisms have been excluded since they produced either zero PAN since the mechanism did not include the species or produced unacceptably low concentrations, less than 0.5 ppb.
One important
difference is however apparent looking at the results from the more recent mechanisms. Whereas for ozone the results from the more recent mechanisms were all grouped in the centre of the distribution of results, in the case of the PANs they are spread evenly throughout the entire range of values.
Again the
decrease in going to the year 2000 Luxembourg Agreement from the 1984 base case was smaller than the decrease in going on to the implementation of stringent emission controls. Hydrogen peroxide exhibits model decreases on implementation of the Luxembourg Agreement and further generally small decreases on moving to stringent emission controls.
The recent mechanisms give results which are in
rather better agreement than those obtained for the whole set of chemical mechanisms.
However, although the results of the earlier mechanisms when taken
together as a set are not inconsistent with the results from the more recent schemes, they exhibit little agreement between themselves. CONCLUSIONS In this study we have discussed some of the principle model simplifcations used in the formulation of photochemical air pollution models.
A
classification has been adopted and twenty chemical schemes covering the elements of the classification have been selected for more detailed evaluation from the literature. A simple trajectory model has been assembled and each of the twenty chemical schemes used to evaluate photochemical air pollution formation downwind of London. The results for 1984 base case emissions show that significant ozone, PAN and hydrogen peroxide concentrations develop downwind of London and that model
,
estimates of the peak concentrations depend on the chemical scheme chosen. For ozone. the scatter in the peak concentrations between the twenty chemical schemes amounted to 8.8 ppb or 9.3%. The scatter for PANs and hydrogen peroxide were somewhat higher at 38% and 54%, respectively. In evaluating control scenarios, these differences in absolute concentration seemed less relevant and despite the distinctions between the chemical mechanisms employed, all indicated that substantial decreases in peak ozone concentrations below the base case would result from the implementation of motor vehicle exhaust emission controls. Few mechanisms indicated changes in peak concentration that were demonstrably different from the mean of the results, including some of the earliest mechanisms.
The uncertainties in
photochemical air pollution models have therefore decreased with time for ozone but not necessarily for PAN and hydrogen peroxide. ACKNOWLEDGEMENTS This work was funded by the United Kingdom Department of the Environment as part of an air pollution research programme. The assistance with the
601 calculations of Miss C Reeves of the School of Environmental Sciences, University of East Anglia, Nowich, Norfolk is gratefully acknowledged. REFERENCES 1 A.M. Hough, The significance of physical and chemical processes in a photochemical oxidant model, AERE Report-R12294, H.M. Stationery Office, London, (1987), 79pp. 2 D.L. Baulch, R.A. Cox, R.F. Hampson, J.A. Kerr, J. Troe and R.J. Watson, Evaluated kinetic and photochemical data for atmospheric chemistry, J. Phys. Chem. Ref. Data, 1259-1375, (1984).
u,
3 R. Atkinson and A.C. Lloyd,. Evaluation of kinetic and mechanistic data for modelling of photochemical smog, J. Phys. Chem. Ref. Data,
u, 315-444,
(1984). 4 A.M. Hough and R.G. Dement, Environmental Pollution, &, 109-118, (1987). 5 R.G. Dement and 0. Hov. Computer modelling studies of photochemical air pollution in north-west Europe, AERE Report-R9434, H.M. Stationery Office, London, (1979), 147pp.
a,
1073-1095, (1987). 6 A.M. Hough, Atmospheric Environment 7 W.R. Stockwell, Atmospheric Environment 20, 1615-1632, (1986)
u,437-464, (1985). Geophysical Research a,
8 J.A. Leone and J.H. Sainfeld, Atmospheric Environment 9 F.W. Lurmann, A.C. Lloyd and R. Atkinson, J. 10905-10936, (1986).
10 G.E. Whitten, J.P. Killus and R.G. Johnson, Modelling of auto exhaust smog chamber data for EKHA development, SAX, 101 Lucas Valley Road, Sen Rafael, California, USA, (1985). 11 G. E. Whitten and M.W. Gery, Development of CBM-X mechanisms for urban and regional AQSMs, SAI, 101 Lucas Valley Road, San Rafael, California, USA, (1985), 160pp. 12 A.T. Cocks and I.S. Fletcher, personal communication. 13 A.Eliassen, 0. Hov, I.S.A. Isaksen, J. Saltbones and F. Stordal, A Lagrangian long-range transport model with atmospheric boundary layer chemistry, J. Applied Meteorology 2,1645-1661, (1982). 14 R. Atkinson, A.C. Lloyd and L. Winges, Atmospheric Environment
u,
1341-1355, (1982). 15 W.R. Stockwell and J.G. Calvert, J. Geophysical Research
a,6673-6682,
(1983). 16 A.H. Falls and J.H. Seinfeld, Environmental Science and Technology 1398-1406, (1978).
u,
17 K. Selby, Computer calculation of ozone formation during anticyclonic weather episodes in Europe. Report TNER-85-044. Thornton Research Centre, Shell Research Ltd, PO Box 1, Chester, United Kingdom, (1985).
602 18 J.P. Killus and G.E. Whitten, A new carbon bond mechanism for air quality simulation modelling.
Report EPA 600/3-82-041, U . S . Environmental
Protection Agency, Research Triangle Park, North Carolina, USA, (1982). 19 J.W. Bottenheim and O.P. Strausz, Atmospheric Environment
u,85-97, (1982).
20 H. Rodhe, P. Crutzen and A. Vanderpol, Tellus 33, 132-141, (1981). 21 A.Q. Eschenroeder and J.R. Martinez, Advances in Chemistry
u, 101-167,
(1972). TABLE 1 Twenty chemical mechanisms from the literature used in modelling photochemical air pollution formation.
No
Mechanisms
1 Harwell 2 H-SIMPLE 3 NCAR
Ref.
4,5 6 7 4Ls 8 9 5 UA-Full 6 LLA-Condensed 9 7 CBM-X 10 8 CBM-IV 11 9 CEGB 12 10 EMEP 13 11 ALW 14 12 sc 15 13 FS 16 14 SHELL 17 15 CBM-I 18 16 CBM-I1 18 17 CBM-111 18 18 BS 19 19 RCV 20 20 EM 21
Number of Number of emitted organic hydrocarbons reactions* 36 8 9 15 20 9 10 7 5 8 14 15 6 8 4 5 5 5 2 2
272 38 48 188 246 82 108 34 50 43 60 88 32 71 19 51 58 24 4 9
CF'U time required 345 67 73 300 367 112 121 69 71 78 96 89 57 88 46 69 81 52 36 41
Simplifications used Complete Direct Direct Complete Parameterised Parameterised Parameterised Parameterised Direct Direct Direct Direct Direct Direct Parameterised Parameterised Parameterised Parameterised Direct Direct
Notes Complete: Direct :
all hydrocarbons included with detailed degradation chemistry. each hydrocarbon class represented by one or two members with degradation chemistry represented explicitly. Lumped : each hydrocarbon class represented by one or two members with degradation chemistry approximated by non-stoichiometric coefficients. *: the tabulated number does not include 54 reactions involving small molecules containing 0, H, N, S and C atoms.
603 TABLE 2
The peak concentrations of a number of photochemically-generated secondary pollutants calculated downwind of London in the base case 1984 scenario. Peak Concentrations, ppb Twenty Mechanisms Nine Mechanismsa
Species Ozone
94.95
f
8.79
95.52
f
3.07
PAN8
4.21
f
1.62
4.60
f
1.19
10.18 f 1.03
9.98
f
0.49
HNo3 HCHO~
6.30 f 1.95
5.98 f 0.90
H202
2.25
f
1.21
2.43 f 0.57
Sulphate aerosol
5.17
f
0.55
5.08 f 0.32
OHd
9.77
f
2.68
9.72
f
1.41
Notes: 1 standard deviation or 67% confidence limits quoted. these are the nine most recent mechanisms studied and all have been published since 1984. b: only 19 mechanisms were included. c: only 16 mechanis s were included. d: lo6 molecule cm' f
a:
J.
TABLE 3
The peak concentrations of a number of photochemically-generated secondary pollutants calculated downwind of London in two different scenarios for the year 2000.
(Concentrations in parts per billion by volume).
Species Ozone
Year 2000 Luxembourg Agreement 20 Mechanisms 9 Mechanismsa
Year 2000 Stringent Emission Limits 20 Mechanisms 9 Mechanisms'
83.65
3.05
67.87 f 4.92
f
10.47 86.07
f
69.28 f 2.27
PAN&
3.55 f
1.45
3.98 f 1.01
2.12 f 0.82
2.30
f
0.60
HNo3
9.88 f
1.00
9.88
0.49
7.86 f 0.47
7.79
f
0.25
HCHO~
4.16
f
2.47
4.94 f 0.73
2.75 I 1.55
3.28 i 0.44
H202
1.58 f
0.93
1.68 i 0.52
1.31 i 0.62
1.40
f
0.35
Sulphate aerosol
5.27 f
0.67
5.33 f 0.37
5.60 t 0.46
5.58
f
0.38
10.19 f
3.34
11.88 f 2.48
11.76
f
1.50
0Hd
10.42
f
f
1.71
Notes 1 standard deviation or 67% confidence limits quoted. these are the nine most recent mechanisms studied and all have been published since 1984. b: only 19 mechanisms were included. c: only 16 mechanis s were included. d: lo6 molecule cmf
a:
J.
This Page Intentionally Left Blank
T.Schneideret aL (Editors),Atmospheric Ozone Research and its Policylmplications 0 1989 Elsevier SciencePublishersB.V., Amsterdam
-Printed in The Netherlande
605
INTERACTION OF PLANETARY BOUNDARY LAYER AND FREE TROPOSPHERE
P.J.H. Builtjes, MT-TNO, .Department of Fluid Dynamics, P.O. Box 342, 7300 AH Apeldoorn, the Netherlands
ABSTRACT Results from photochemical episodic dispersion model calculations and historical trends observed in the Los Angelos Air Basin, show that the relation between the precursor VOC- and NOx-emissions leading to hourly 03-concentrations in the atmospheric boundary layer is strongly non-proportional and that substantial emission reductions only lead to relatively small decreases in peak 03- concentrations. However, 03-concentrations during episodes are added upon a background 03-level of about 40-50 ppb which is, at least partly, also from antropogenic origin. Models capable of calculating this 03-background level, and the influence of precursor emissions on these levels, do need a description of the exchange between the free troposphere and the boundary layer, of which only some limited information is available uptill now.
1. INTRODUCTION
Much attention has been devoted in Europe as well as in the United States to the study of photochemical oxidant formation during episodes. These studies are motivated by the adverse effects that high hourly ozone concentrations have on human health. Levels of hourly ozone concentrations of 120 ppb (240 pg/m3), which serve often as an air quality guideline are regularly exceeded in the United States as well as in Europe. Uptill now only limited attention has been paid to more long term average ozone levels. However, there are at least two good reasons to adress long term average ozone levels: long term average ozone levels in the atmospheric boundary layer. for
-
-
example growing season daylight averages, have shown to have adverse effects on vegetation, including forests; episodic photochemical ozone levels are build upon an existing background level, which is closely linked to the long term average ozone level.
Considering the last point, several remarks can be made. Model studies carried out concerning photochemical oxidant formation during episodes clearly
show the non-proportional relationship between VOC- and NO,-precursor
emis-
sions and hourly maximum 03-levels. Recent applications of trajectory models and Eulerian grid models, both for one-day urban type situations as well as for multi-day long range transport situations all reveal similar trends: VOC-emission reduction brings down maximum 03-levels, but less than proportional (quite often calculations indicate for a XX VOC-emission reduction about an 0.5
x 9: reduction of 03-peak levels). NO,-emission
reductions also brings down
maximum 03-levels at locations where NO,-concentrations are low, which means in rural areas relatively far from large NO,-emission sources. However, in situations where NOx-concentrations are high, in and around industrial areas, NO,emission reductions result in an increase of maximum 03-levels (see for recent European calculations for example references 1, 2 , 3, 4 ) . Apart from this rather specific description of calculated effects of NO,and VOC-emission reductions a more general result is that calculations show a remarkable stiff behaviour of episodic 03-concentrations to considerable changes in NO,-and
VOC-emissions. In view of all the discussions devoted to an
evaluation of the historical trends in 03-concentrations in relation to emission trends for VOC and NO, as observed in the Los Angelos Air Basin (ref. 5 ) it can be stated that also reality shows a quite stiff behaviour, which is not in contradiction with model results. Next to this, it should be kept in mind that all these model studies assume a background ozone concentration of about 40-50
ppb which is kept unchanged
when NOx- and VOC-emissions are reduced in the calculations. A recent evaluation by Altshuller (ref. 6 ) pointed out that natural background 03-levels will be in the order of 10-20 ppb. This in in line with the observed increase in 03-concentrations in the (background) free troposphere of about 1% per year (ref. 7) over the last 15 years. Consequently, it is very likely that a substantial part of the background 03-leve1, either at groundlevel at remote places or in the free troposphere is of antropogenic origin. Two-dimensional global model calculations performed by Isaksen (ref. 8 ) do indicate the role of NO,-,
VOC- and CH4- and CO-emissions on the ozone forma-
tion in the free troposphere. Consequently, emission reductions of NO, and VOC will also have an effect on the background ozone level upon which the episodic ozone levels are 'added'. In this way, abatement of background ozone levels will also assist in bringing peak ozone levels down, and will obviously serve in decreasing long term average ozone levels. It is clear that the background ozone levels will be influenced by precursor-emissions over a very large area. However, apart from a first attempt by De Leeuw e.a. (ref. 9 ) , no models have been developed and applied to calculate more long term average background ozone levels in the boundary layer and the influence of precursor emissions.
607 To be able to do this global 2-dimensional models as developed by Isaksen (ref. 8) have to be coupled with boundary layer models. Critical in this is the description of the exchange between the boundary layer and the free troposphere. Some remarks on these exchange processes will be made. First in chapter 2 some observations will be presented. Chapter 3 contains a overview of exchange processes and some descriptions. The paper ends with chapter 4, conclusions and recommandations. 2. OBSERVATIONS OF BACKGROUND 03-LEVELS The atmosphere can be devided in the atmospheric, planetary boundary layer or mixed layer with a height of upto about 2 km, the free troposphere with a height from above the mixed layer upto the tropopause at about 10-15 km and above that the stratosphere. In all three layers ozone is present and photochemical activity occurs. On a yearly averaged basis the 03-concentration increases from groundlevel to reach a maximum at about 1-2 km; further upward a steady decrease is found to about 10 km, after which an 03 increase into the stratosphere is found to levels
reaching 10 ppm
(see
for example ref. 7).
Our interest here are the ozone levels in the background free troposphere and at remote sites far from antropogenic emission sources. The ozone budget in the troposphere (free troposphere + atmospheric boundary layer) consists of four components: transport from the stratosphere, photochemical production, deposition at the ground and photochemical destruction. It is now generally accepted that the photochemical production term is significant and often even dominant (ref. 10, 11).
Some of the background ozone observations will be
described here. At moderate latitudes the seasonal pattern of observed 03-concentrations at remote sites shows a maximum in spring (aprillmay). This maximum has a value of about 40 ppb; the winter minimum is 20 ppb (ref. 11).
As has been stated
earlier, the observations show an increase in this value of about 1-2% per year at the moment. In areas with more industry and traffic the ozone pattern shows a maximum in the summer, a direct consequence of emissions of NOx and VOC from antropogenic origin. Analysis of Dutch ozone-stations for situations where the mean wind velocity was high also showed a seasonal pattern with a maximum in spring of 40-50 ppb (ref. 13, 14). In the situation with high windspeed the mixing is vigorous and the groundlevel 03 values can be considered to be the level of the free troposphere.
608 The question about the origin of the ozone in the free troposphere, where it
has a life time of several weeks is still open. Stratopheric intrusions can play a role, the observed spring 03-maximum is an indication. Tropopause folding at the occurance of a surface cold front associated with a so-called jet-streak can produce strong stratospheric intrusions, see for example Reiter, ref. 15. However, in general these intrusions do not reach ground level but spread out in horizontal direction at a height of 1-2 km. High ozone concentrations observed at ground level are an order of magnitude more often due to photochemical production in the atmospheric boundary layer than to stratospheric intrusions, ref. 16. Obviously the long term average 03 concentration at ground-level will have a stratospheric contribution. It is tempting to compare the rather uncertain estimate of this contribution of 12-15 ppb made by Reiter, ref. 15, with the estimate of the natural ozone level of 10-20 ppb made by Altshuller, ref. 6. However, the contribution of stratospheric intrusions to the ozone in the free troposphere could be larger than this 12-15 ppb and in this way could be of comparable magnitude to the contribution by transport of antropogenic ozone and precursors from the atmospheric boundary layer into the free troposphere. The exact antropogenic part of the ozone levels in the free troposphere is still unknown. 3 . EXCHANGE PROCESSES BETWEEN THE FREE TROPOSPHERE AND THE BOUNDARY LAYER
Most models, Eulerian grid as well as trajectory models which are used to calculate ground level 03-concentrations during episodic conditions have a maximum vertical extent to upto about 2 km, which means that at the upper boundzry the free troposphere starts. Only the 'super'-models which are Eulerian grid models used for the calculation of acidifying pollutants and photochemistry during episodes reach upto about 10 km, see for example ref. 17. These models need this vertical extent to incorporate the convective clouds which play an important role in the formation and transport of acidifying pollutants. Photochemical models in principle do not need this vertical extent explicitly. However, to calculate long term average ozone levels boundary layer models need to be 'coupled' with a model for the free troposphere. Before discussing the exchange processes which have to be described between the boundary layer and free troposphere model some remarks should be made concerning the 'free tropospheric' 2-dimensional model developed by
Isaksen, ref. 8 .
This
zonal
averaged global model has several vertical layers from the ground level upto a height of 17 km. The fluxes at the upper boundary layer were determined by the stratospheric transport into the troposphere as a function of season and latitude. This exchange process as well as the vertical distribution in the model domain itself are determined by using a modification of the mean velocity
609 and diffussion field derived by Plumb and Mahlman (ref. 18) which are a function of the season and month. So in this approach the exchange processes between the boundary layer and the free troposphere are given by the vertical mean velocity and the vertical turbulent diffusivity as prescribed in an averaged way by Plumb and Mahlman, ref. 18. However, to calculate the ground level ozone concentrations for longer time periods using a specific boundary layer model coupled with the for example by the Isaksen-model calculated values at a height of 2 km (the free tropospheric values) the calculations should be performed for the actual meteorological conditions in a brute-force approach (see ref. 9 ) . This requires an explicit description of the exchange processes. The following exchange processes occur between the free troposphere and the atmospheric boundary layer:
-
cumulus convective clouds stratus clouds high and low pressure systems diurnal growth of the mixed layer rain scavenging and wet chemistry frontal systems landlsea breeze and heat island phenomena topographic effects. First, some general remarks should be made. These eight exchange processes
-
can - in a parametrized way most convenient be described by a mean vertical velocity which is either upwind or downwind. Although also real turbulent transport takes place which can be described by gradient type transport the use of a mean vertical velocity is more convenient to avoid 'counter-gradient'-
transport and arbitrary splits between the two descriptions, which are to a large extent splits based on averaging time. In principle, complex weather forecast models as used for example at the European Centre in Reading, United Kingdom. have implicitly incorporated all these exchange processes. However, a calculation with such a forecast model with build-in complex non-lineair chemistry can not be foreseen for the near future, and in addition the grid resolution of those models is quite large which will average out local effects. In recent literature concerning exchange processes most attention is given to cumulus convective clouds, see ref. 19, 20. 21, 22. A cumulus nimbus cloud can reach upto 10 km, with a cloud base at about 0.5-2 km. Vertical upward velocities inside and close to the cloud reach from 1-10 m/s, or even upto 40
m l s . Downward velocities occur in the cloud itself, and also further away,
610 covering a total area around the cloud of about 20 x 20 km. So the cloud causes mixing over a box of about 20 x 20 km upto a height of 10 km, although the effectivity of the mixing process is only about 70% (ref. 2 2 ) . How large the exchange process over an area is depends on the cloud cover. On a long term average basis the exchange depends on the occurence of cumulus clouds. In Europe on a yearly basis this is only 4-8%. In addition cumulus clouds will hardly play a role during photochemical episodes. Stratus clouds are associated with much smaller upward velocities of about 0.05-0.10 m/s. Although these mean vertical velocities are small, stratus
clouds occur frequently in Europe and
so
will play a role in the long term
average exchange process. High and low pressure systems which have a scale of about 1000 x 1000 km are
-
apart from a frontal zone
-
always present. Although the associated vertical
velocity is only about 0.01 m/s, it occurs very frequently. These vertical velocities can easily follow from the divergence and convergence of the horizontal windfield, or simply from the anomaly of the yearly average pressure (which is 1013 Mbar at sea level). The diurnal growth of the mixed layer is of course an important entrainment/ detrainment process which has to be taken into account, but is often already incorporated in the boundary layer models. Rain scavenging and wet chemistry are of less importance for ozone but are essential for a number of other pollutants. Frontal systemslstructures and conveor belts occur in line shaped compact areas and are also associated with vertical upward and downward velocities. Finally, land-sea breeze, heat island phenomena and orography are local effects which can produce vertical velocities. An assessment which of the processes is of more importance can not be given.
This depends heavily on whether episodes or only long term averages are considered, and on the finest horizontal grid resolution desired. It should also be noted that often more than one process will be in operation, for example frontal structures with clouds. Simple parametrizations
of
the
different exchange
processes
are
not
available, but are required in any calculation of ozone in the atmospheric boundary layer where the influence of the free troposphere has to be taken into account. 4 . CONCLUSIONS AND RECOHMANDATIONS
-
Long term average ozone levels should be evaluated because of their adverse
effects on vegetation and their role as background ozone level upon which high episodic ozone levels are 'added'. In view of model results and historic NOxand VOC-emission and ozone trends the effect of emission reductions on peak
611 ozone levels is less than proportional. Abating long term average ozone levels would be an additional way to bring peak ozone levels down.
-
The observed increase of 1-2'6 per year in the background ozone levels in the free troposphere and at remote sites show the influence of antropogenic emissions on these levels. At the moment an accurate quantative value for this contribution to the background ozone levels and the contribution due to stratospheric intrusions can not yet be given.
-
To determine long term average ozone levels in the atmospheric boundary
layer the common type boundary layer models should be coupled with free tropospheric models, for example 2-dimensional global models. A description of the exchange processes between the free troposphere and the boundary layer is required for an adequate coupling, but parametrized descriptions are to a large extent still lacking.
REFERENCES Hov, 0. e.a., Evaluation of the photo-oxidants precursor relationship in Europe, CEC Air Poll. Res. Rep. 1, 1986. Dement, R.G. and Hough, A.M., The impact of emission reduction scenarios on photochemical ozone and other pollutants formed downwind of London, Bamberg Workshop, FRG, October 1987. Builtjes, P.J.H. e.a., PHOXA, the use of a photochemical dispersion model for several episodes in north-western Europe, 16th Int. Tech. Meeting on Air Poll. Modell. and its Appl., Lindau, FRG, April 1987. Selby, K., A modelling study of atmospheric transport and photochemistry in the mixed layer during anticyclonic episodes in Europe, Part 11: Calculations of photo-oxidant levels along air trajectories, J. of Climate and Appl. Met. 26, 1317-1338, October 1987. Kuntasal, G. and Chung, T.Y., Trends and relationships of 03, NOx and HC in the south coast air basin of California, JAPCA 37, 1158-1163, 1987. Altshuller, A.P., Estimation of the natural background of ozone present at surface rural locations, JAPCA 37, 1409-1417, December 1987. Hartmannsgruber, R. e.a., Opposite behaviour of ozone measurements at Hohenpeissenberg 1967-1983. In: Atmospheric Ozone Symp. Halkidiki 1984. Isaksen, I. and Hov, O., Calculation of trends in the tropospheric concentration of 03, OH, CO, CH4 and NO,, Tellus, 1986. Leeuw, F.A.A.M. de, e.a., Long term averaged ozone calculations, Symp. Atm. Ozone Research and its policy implications, Nijmegen, the Netherlands, May 1988. 10 Verkovich, F.M. e.a., The reservoir of ozone in the boundary layer of the
Eastern United States and its potential impact on the global tropospheric ozone budget, J. of Geoph. Res. 90, no. D 3 , pg. 5687-5698, June 1985. 1 1 Logan, J.A., Tropospheric ozone: seasonal behaviour, trends and antropogenic influence, J. of Geoph. Res. 90, pg. 10463, 1985. 12 Bojkov, R.D., Surface ozone during the second half of the nineteenth century, J. of Climate, Appl. Met. 25, 343, 1986. 13 Aalst, R.M. van, Emissions, chemical processes and deposition. In: Dutch Ozone-Symposium, Ede, November 1986 (in Dutch).
612 14 Guicherit, R., Ozone on an urban and regional scale with special reference to the situation in the Netherlands, MT-TNO Rep. no. P 871030, May 1987. 15 Reiter, E.R., Stratospheric-Tropospheric Exchange Processes, Rev. Geoph. and Space Physics 13, 4, 459-474, 1975. 16 Derwent. R.G. editor, Ozone in the United Kingdom, Dep. of Environment Rep., February 1987. 17 Stern, R.M. e.a., Application of a regional model for the transport and
18 19 20
21 22
deposition of acidifying pollutants to Central Europe, 16th Int. Tech. Meeting on Air. Poll. Modell. and its Appl. Lindau, FRG, April 1987. Plumb, R.A. and I.D. Mahlman, The zonally-averaged transport characteristics of the GFDL general circulationltransport model, J. Atm. Scien.. 1986. Ching, J.K.S., Evidence for cloud venting of mixed layer ozone and aerosols, Atm. Env. 22, 2, 225-242, 1988. Isaac, G.A. e.a., The role of cloud dynamics in redistributing pollutants and the implications for scavenging studies, p. 1-13, In: Precipitation Scavenging, Dry Deposition and Resuspension, Pruppacher e.a. editors, Elsevier Science Publish, Co. Inc. 1985. Dickerson, R.R., Thunderstorms: An important mechanism in the transport of air pollutants, Science, vol. 235, 460-464, January 1987. Ching, J.K.S., Modelling non-precipitating cumulus clouds as flow-throughreactor transformer and venting transporter of mixed layer pollutants, Int. Conf. on Energy Transf. and Interactions with small and meso-scale atm. processes, Lausanne, Switzerland, March 1987.
T. Schneider et al. (Editors),Atmospheric Ozone Research and its Policy Implieations 0 1989 Elaevier Science Publishers B.V., Ameterdam - Printed in The Netherlanth
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DEVELOPMENT AND EVALUATION OF THE REGIONAL OXIDANT MODEL FOR THE NOHTHEASTERN UNITED STATES
K.L.
Scherel and R.A.
Wayland2
1National Oceanic and Atmospheric Administration, on assignment t o t h e U.S. Environmental Protection Agency, Research T r i a n g l e Park, NC 2Computer Sciences Corporation, Research Triangle Park, NC
27711 (U.S.A.) 27709 (U.S.A.)
ABSTRACT The second generation U.S. EPA Regional Oxidant Model (ROM2) has been developed over t h e l a s t 10 years and i s now operational. The 3-0 g r i d model has been applied t o t h e Northeast U.S. f o r a 50-day p e r i o d i n 19110. Model evaluation r e s u l t s show t h e ROM2 i s performing w e l l w i t h respect t o p r e d i c t i n g t h e frequency d i s t r i b u t i o n s and s p a t i a l p a t t e r n o f observed D3 concentrations.
INTRODUCTION
The need f o r a comprehensive simulation model o f photochemical smog on regional (1000 km) scales became apparent w i t h t h e r e a l i z a t i o n t h a t t h e 03 and oxidant p o l l u t i o n problem, f i r s t studied i n t h e context of s i n g l e urban areas, o f t e n extended over l a r g e geographical regions o f t h e U.S.,
encompassing many
urban areas. I n response t o t h i s need EPA began a development e f f o r t toward a Regional Oxidant Model (ROM) nearly t e n years ago.
Today we have a second
generation operational model (ROM2) t h a t continues t o be developed, tested, and r e f i n e d ( r e f s . 1-3). The model i s p r i m a r i l y designed f o r use i n e v a l u a t i n g t h e effectiveness o f various emission c o n t r o l s t r a t e g i e s on t h e regional scale. The purpose o f t h i s paper i s t o provide a b r i e f overview o f t h e ROM2 and t o describe the f i r s t phase o f a model evaluation study using data from t h e
.
Northeast U S. MODEL OVERVIEW The ROM has been designed t o simulate most o f t h e important chemical and physical processes responsible f o r t h e production o f photochemically produced 03 on scales o f 1000 km, o r several days o f t r a n s p o r t time. These processes include horizontal transport, atmospheric chemistry (using t h e Carbon Bond I V chemical mechanism, r e f . 4), nighttime wind shear and turbulence episodes associated w i t h t h e nocturnal j e t , cumulus cloud e f f e c t s on v e r t i c a l mass t r a n s p o r t and photochemical r e a c t i o n rates, mesoscale v e r t i c a l motions induced by t e r r a i n and t h e l a r g e scale flow, t e r r a i n e f f e c t s on advection, d i f f u s i o n
614
and deposition, sub-grid s c a l e chemistry processes, emissions o f n a t u r a l and anthropogenic precursors, and d r y d e p o s i t i o n . They a r e mathematically simulated i n t h e 3-D g r i d model w i t h v e r t i c a l r e s o l u t i o n o f 3 1/2 v e r t i c a l l a y e r s i n c l u d i n g t h e boundary l a y e r and t h e capping i n v e r s i o n o r c l o u d l a y e r . H o r i z o n t a l r e s o l u t i o n i s approximately 18.5 km; however, t h e exact g r i d c e l l s i z e v a r i e s somewhat over t h e model domain because t h e c o o r d i n a t e system used i s based on l a t i t u d e - l o n g i t u d e . D e t a i l e d d e s c r i p t i o n s o f t h e t h e o r e t i c a l b a s i s and design o f t h e ROM modeling system a r e a v a i l a b l e elsewhere ( r e f s . 1-3). The t o p t h r e e ROM l a y e r s are p r o g n o s t i c ( p r e d i c t i v e ) and a r e f r e e t o l o c a l l y expand and c o n t r a c t i n response t o changes i n t h e p h y s i c a l processes o c c u r r i n g t h e r e i n . The bottom l a y e r i s a shallow d i a g n o s t i c surface l a y e r designed t o approximate t h e sub-grid s c a l e e f f e c t s on chemical r e a c t i o n r a t e s from a s p a t i a l l y heterogeneous emissions d i s t r i b u t i o n . Layers 1 and 2 model t h e depth o f t h e well-mixed l a y e r d u r i n g t h e day. I n l o c a l areas where s t r o n g winds e x i s t o r t h e surface heat f l u x i s weak, s u b s t a n t i a l wind shear can e x i s t i n t h e f i r s t few hundred meters above ground. This phenomenon can be t r e a t e d s e p a r a t e l y i n l a y e r 1. Layer 3 represents t h e s y n o p t i c s c a l e subsidence i n v e r s i o n , t h e base o f which i s t y p i c a l l y 1-2 km above ground. Clouds, where they e x i s t , are a l s o t r e a t e d i n l a y e r 3. A t n i g h t , t h e r e i s some readjustment i n l a y e r depths as t h e upper l a y e r s become decoupled from t h e lower s u r f a c e i n v e r s i o n l a y e r . MODEL APPLICATION I n t h e c u r r e n t study t h e model has been a p p l i e d t o t h e Northeastern U n i t e d States f o r t h e p e r i o d J u l y 12-August 31, 1980. Several r e g i o n a l photochemical smog episodes occurred d u r i n g t h i s p e r i o d w i t h measured 03 c o n c e n t r a t i o n s as h i g h as 300 ppb i n t h e Northeast U.S.
Emissions, a i r q u a l i t y , and
meteorologlcal data bases were prepared f o r use by t h e ROM modeling system, which includes n e a r l y 30 separate d a t a preprocessing programs. I n a d d i t i o n t o t h e r e g u l a r network o f m e t e o r o l o g i c a l and a i r q u a l i t y m o n i t o r i n g s t a t i o n s already i n place d u r i n g t h e p e r i o d o f i n t e r e s t , s p e c i a l a i r c r a f t and s u r f a c e measurements were taken as p a r t o f an EPA-sponsored f i e l d study, t h e Northeast Regional Oxidant Study ( r e f . 5). A comprehensive anthropogenic source emissions i n v e n t o r y f o r hydrocarbons, NO,
and CO was developed w i t h a s p a t i a l and
temporal r e s o l u t i o n on t h e same s c a l e as t h e ROM ( r e f . 6).
I n a d d i t i o n , an
i n v e n t o r y o f b i o g e n i c a l ly-produced hydrocarbon species was a1 so developed ( r e f . 7 ) and i n c l u d e d as p a r t o f t h e t o t a l emissions i n v e n t o r y .
The model s i m u l a t i o n was s t a r t e d on a day w i t h r e l a t i v e l y c l e a n t r o p o s p h e r i c conditions.
I n i t i a l model concentrations were s e t t o values r e p r e s e n t a t i v e o f
these c o n d i t i o n s , i n c l u d i n g N 4 = 2 ppb, NMHC.15
ppbC, and 03=35 ppb, w i t h no
s p a t i a l v a r i a t i o n considered. Model s i m u l a t i o n proceeded c o n t i n u o u s l y through
615 t h e 50 day p e r i o d , and t h e assumed i n i t i a l c o n c e n t r a t i o n f i e l d was e f f e c t i v e l y swept out o f t h e model domain by t h e f o u r t h s i m u l a t i o n day. I n f l o w boundary concentrations were updated d u r i n g t h e s i m u l a t i o n every 12 hours. Several remotely-located 03 monitors were used t o determine t h e temporal v a r i a t i o n s o f i n f l o w concentrations. MODEL EVALUATION D e t e r m i n i s t i c vs. n o n - d e t e r m i n i s t i c modes The 03 surface m o n i t o r i n g networks o f t h e p o r t i o n s o f t h e U.S.
and Canada
i n c l u d e d i n t h e ROM s i m u l a t i o n domain used here i n c l u d e d 214 s i t e s d i s t r i b u t e d throughout t h e model domain. The vast m a j o r i t y o f t h e m o n i t o r i n g s i t e s a r e l o c a t e d w i t h i n o r near urban and m e t r o p o l i t a n areas. As a r e s u l t t h e r e i s good m o n i t o r i n g coverage i n s e l e c t e d p o r t i o n s of t h e domain and poor s p a t i a l coverage i n much of t h e remainder o f t h e domain. Also, some of t h e urbano r i e n t e d monitors o f t e n show t h e e f f e c t s o f l o c a l N3,
scavenging o f 03.
Nevertheless t h e l a r g e number o f monitors and t h e extended s i m u l a t i o n p e r i o d p r o v i d e u s e f u l data f o r performing an e v a l u a t i o n of t h e a b i l i t y o f t h e ROM t o s i m u l a t e 03 c o n c e n t r a t i o n s over r e g i o n a l scales. We l i m i t our d i s c u s s i o n here t o t h e performance o f t h e model f o r p r e d i c t i n g 03 o n l y near ground l e v e l . H i s t o r i c a l l y , model e v a l u a t i o n e x e r c i s e s have used t h e p r e d i c t i o n s o f s i m u l a t i o n models i n a " d e t e r m i n i s t i c " sense. That i s , t h e model p r e d i c t i o n f o r a given time and a given p l a c e i s determined e x a c t l y by t h e data a s s i m i l a t e d by t h e model and t h e model's component algorithms. T h i s mode o f o p e r a t i o n does n o t e x p l i c i t l y consider model o r data u n c e r t a i n t i e s . For t h e t i m e and space scales used i n urban-scale modeling, t h e d e t e r m i n i s t i c mode may be a p p r o p r i a t e . For t h e 1000 km r e g i o n a l scale, however, where m u l t i - d a y t r a n s p o r t i s simulated, t h e d e t e r m i n i s t i c mode becomes i n a p p r o p r i a t e . This i s b a s i c a l l y because t h e s p a t i a l scales o f many key d a t a elements a r e c o n s i d e r a b l y coarser t h a n t h e scales o f t h e model. For instance, t h e u p p e r - a i r m e t e o r o l o g l c a l network i n North America t h a t provides e s s e n t i a l i n f o r m a t i o n f o r d e t e r m i n i n g t h e t r a n s p o r t component o f t h e ROM has s i t e l o c a t i o n s separated by s e v e r a l hundred k i l o m e t e r s and soundings taken o n l y every 12 hours. I n t h e process o f i n t e r p o l a t i n g t o t h e r e q u i r e d s p a t i a l and temporal scales o f t h e ROM, some of t h e determinism o f t h e d a t a s e t i s l o s t t o t h e v a r i o u s assumptions i n h e r e n t i n t h e i n t e r p o l a t i o n method chosen; numerous i n t e r p o l a t i o n methods e x i s t each w i t h i t s own s e t o f assumptions. Lamb ( r e f s . 8-9) maintains t h a t more a p p r o p r i a t e ways o f i n t e r p r e t i n g t h e r e s u l t s o f r e g i o n a l s c a l e s i m u l a t i o n models a r e i n a " p r o b a b i l i s t i c " o r "quasi - d e t e r m i n i s t i c " sense. I n t h i s study we use t h e " q u a s i - d e t e r m i n i s t i c "
mode, where model p r e d i c t i o n s
and observations a r e n o t compared f o r a s p e c i f i c l o c a t i o n and time, b u t r a t h e r
616 t h e comparisons are made f o r aggregate groups o f r e c e p t o r l o c a t i o n s such t h a t t h e r e e x i s t s a comnon c h a r a c t e r i s t i c u n i t i n g t h e members o f each r e c e p t o r group.
For our a n a l y s i s t h e groups were formed by a n a l y z i n g t h e frequency
d i s t r i b u t i o n s o f d a y l i g h t h o u r l y 03 c o n c e n t r a t i o n s d u r i n g t h e sumner o f 1980 a t t h e m o n i t o r i n g s i t e s i n our s u r f a c e d a t a base. Normalized frequencies o f occurrence o f 03 concentrations between 5 and 20 ppb, 20 and 40 ppb, 40 and 80 ppb, and g r e a t e r than 80 ppb were c a l c u l a t e d f o r each m o n i t o r i n g s i t e . A c l u s t e r a n a l y s i s was performed u s i n g t h i s d a t a and 6 groups o f r e c e p t o r m o n i t o r i n g s i t e s were selected based on t h e i r c h a r a c t e r i s t i c frequencies o f observed 03 concentrations.
The groups i n c l u d e those with r e l a t i v e l y h i g h
frequencies o f >80 ppb 03 (groups 1 and 2), those w i t h more moderate l e v e l s (groups 3 and 4), one w i t h unusually h i g h frequencies o f 03 values <40 ppb (group 5 ) , and one w i t h r e l a t i v e l y few low o r h i g h values (group 6). Data p r e p a r a t i o n Hourly averages o f ROM 03 p r e d i c t i o n s were i n t e r p o l a t e d from g r i d c e l l centers t o t h e coordinates o f each m o n i t o r i n g s i t e l o c a t i o n f o r t h e d u r a t i o n of t h e s i m u l a t i o n p e r i o d by a b i q u i n t i c polynomial scheme. The observed 03 m o n i t o r i n g data was passed through a 15-point h i g h frequency f i l t e r designed t o smooth data associated w i t h those wavelengths s h o r t e r than t h e ROM c o u l d r e s o l v e based on i t s c u r r e n t g r i d r e s o l u t i o n o f 18.5 km. The net e f f e c t o f t h i s f i l t e r i s t o dampen very sharp peaks i n a continuous time s e r i e s o f data. For
03, a non-emitted species formed by atmospheric chemical r e a c t i o n s , sharp peaks i n a temporal record a r e uncommon. Thus t h e f i l t e r ' s e f f e c t on t h e raw d a t a i s minimal. We expect t o see a more pronounced e f f e c t o f t h e f i l t e r on a primary species, such as NO,,
when we prepare t h a t d a t a s e t f o r comparison w i t h ROM
p r e d i c t i o n s l a t e r . Analyses f o r 03 t h e r e f o r e were based on comparisons o f t h e f i l t e r e d observed and s p a t i a l l y i n t e r p o l a t e d p r e d i c t e d d a t a f o r t h e aggregated m o n i t o r i n g s i t e s w i t h i n each o f t h e groups discussed above. I n a d d i t i o n t o t h e group analyses, e v a l u a t i o n o f t h e ROM's a b i l i t y t o r e p l i c a t e "plumes" o f 03 on t h e regional scale was t e s t e d by analyzing s p a t i a l p a t t e r n s i n t h e observed and p r e d i c t e d data. Here, t h e f i l t e r e d observed and t h e h o u r l y averaged g r i d p r e d i c t i o n s were used. A l l ROM p r e d i c t e d data were taken from t h e f i r s t p r o g n o s t i c model l a y e r
above ground, t y p i c a l l y extending from a base o f 30-50 m above ground t o a h e i g h t o f 100-300 m above ground d u r i n y daytime c o n d i t i o n s . The f o r m u l a t i o n o f t h e shallow d i a g n o s t i c surface l a y e r i n t h e model i s n o t y e t complete; t h e r e f o r e p r e d i c t i o n s f o r t h e surface, per se, were n o t a v a i l a b l e . By l i m i t i n g our analyses t o daytime c o n d i t i o n s (0800
-
1900, Local Standard Time) when t h e
lowest p r o g n o s t i c model l a y e r w e l l - r e p r e s e n t s t h e t h e r m a l l y mixed c o n d i t i o n s near t h e surface, we minimize problems t h a t sharp v e r t i c a l g r a d i e n t s might cause
617 i n t h e comparisons. Analyses f o r n i g h t t i m e conditions o r o f sub-grid scale e f f e c t s trust await t h e f i n a l development o f t h e ROM's l a y e r 0 (surface 1ayer)
.
Resu 1t s Table 1 presents a summary of t h e frequency d i s t r i b u t i o n o f 03 concentrations f o r each group of receptors over t h e model s i m u l a t i o n period. Both observed and predicted concentrations are summarized here. The number o f monitoring s i t e s w i t h i n each group i s a l s o indicated. TABLE 1
-
Frequency d i s t r i b u t i o n o f day1 i g h t observed and p r e d i c t e d 03 concentrations w i t h i n receptor groups f o r t h e p e r i o d 14 J u l y
Group
1 2 3 4 5
Number o f sites
35
39 64 54 20
- 31 August
1980.
Percent o f d a y l i g h t (08-19, LST) 03 concentrations between: 5 20 ppb 21 40 P p b T Obs Pred % Obs Pred' Obs Pred
- Preb' - -
-- 8 15 16 22 42
1 1
1 1 2
19 23 28 37 38
7 9 9 12 16
39 41 46 36 19
66 69 79 80 73
-34 21 10 5 1
26 21 11 7 9
These r e s u l t s seem t o i n d i c a t e t h a t t h e ROM performs b e t t e r a t p r e d i c t i n g
03 concentrations greater than 40 ppb than i t does a t lower concentrations. Concentrations o f 40 ppb and l e s s were observed a t t h e 6 groups o f receptors from a high o f 80% of t h e t i m e (group 5) t o a low o f 26% o f t h e t i m e (group 6). The corresponding f i g u r e s f o r predicted concentrations are 18% o f t h e t i m e (group 5) and 4% o f t h e time (group 6). The model's performance f o r p r e d i c t i n g concentrations >80 ppb appears q u i t e good from t h e data i n Table 1, w i t h t h e possible exceptions o f groups 5 and 6. The members o f group 5 were chosen based on an unusually high frequency o f 03 concentrations l e s s than 20 ppb. This i n d i c a t e s t h a t these monitors were most l i k e l y influenced by near-source NOx scavenging o r other l o c a l processes t h a t would cause ambient l e v e l s t o drop considerably below background. Hence t h i s i s a pre-selected group o f s i t e s t h a t are biased low i n comparison t o t h e m d e l ' s expected p r e d i c t i o n s ; t h e data i n Table 1 appear t o confirm t h e expectation. Group 6 contains o n l y 2 s i t e s , those whose observed concentration d i s t r i b u t i o n conforms t o a p a t t e r n c h a r a c t e r i s t i c o f remotely-located s i t e s
(i.e., r e l a t i v e l y few values below tropospheric background l e v e l s ) . I n f a c t , these s i t e s are considerably d i s t a n t from l o c a l source influences. One i s located a t Whiteface Mountain i n northern New York and t h e other i s a t Long
610 Point Park i n southern Ontario. The r e s u l t s f o r t h i s group o f monitors show t h e
ROM t o underpredict t h e occurrence o f >80 ppb 03. Small e r r o r s i n t h e f l o w f i e l d can cause s i g n i f i c a n t e r r o r s i n t h e p r e d i c t e d t r a j e c t o r i e s o f a i r p a r c e l s from p a r t i c u l a r source areas. These e r r o r s tend t o worsen w i t h i n c r e a s i n g distance from t h e source. Since t h e remote s i t e s are located a t l a r g e r distances from source areas, one p o s s i b l e reason f o r t h e R O M l s underprediction o f higher concentrations a t these s i t e s i s e r r o r s i n t h e t r a j e c t o r i e s o f a i r parcels a f f e c t i n g t h e s i t e s from major source areas (see discussion o f determinism i n regional a i r qua1 it y model s above)
.
The data i n Table 1 also show t h a t t h e ROM p r e d i c t s t h e occurrence o f moderate 03 l e v e l s (40-80 ppb) considerably more f r e q u e n t l y (66-93% o f t h e t i m e ) than do t h e observations (19-63% o f t h e time). This r e s u l t f o l l o w s from t h e model's underestimation o f t h e frequency o f low 03 l e v e l s and i s probably r e l a t e d t o t h e l o c a l source i n f l u e n c e a t many o f t h e urban-oriented m o n i t o r i n g sites. Fig. 1 ( a - f ) presents p l o t s o f t h e observed cumulative frequency d i s t r i b u t i o n o f daytime 03 concentrations versus t h e p r e d i c t e d d i s t r i b u t i o n f o r each o f t h e 6 receptor groups. The s o l i d l i n e i n each f i g u r e represents t h e l i n e o f p e r f e c t agreement between t h e d i s t r i b u t i o n s and t h e d o t t e d l i n e s show t h e 210% e r r o r bound about t h e s o l i d l i n e . Each
' + I
symbol represents a
p e r c e n t i l e l e v e l i n t h e frequency d i s t r i b u t i o n , and t h e d e c i l e l e v e l s from 10% t o 100% are marked by t h e i n t e g e r s 1,2,. ..,9,0.
For example, i n receptor group
1. approximately 80% o f t h e observed 03 concentrations and 90% o f t h e p r e d i c t e d
concentrations are l e s s than 100 ppb. The p l o t s c o n f i r m t h e model Is tendency t o overpredict a t lower concentration values over a l l receptor groups. Group 1 contains t h e s i t e s w i t h t h e highest observed concentration values and t h e ROM shows a tendency o f increasing underprediction w i t h concentration l e v e l . The agreement between p r e d i c t i o n s and observations i s best f o r groups 2-4 f o r moderate t o h i g h 03 values, up through t h e 99.5% l e v e l o f t h e frequency d i s t r i b u t i o n s . The maximum value o f t h e d i s t r i b u t i o n i s c o n s i s t e n t l y underpredicted by t h e model. Group 5, as discussed above, i s an anomalous group. Fig. l ( e ) confirms t h i s anomaly by showing systematic overpredictions. Most groups show a more h o r i z o n t a l tendency i n t h e d i s t r i b u t i o n below about t h e 70-80% l e v e l , i n d i c a t i n g t h a t t h e range o f t h e model p r e d i c t i o n s a t lower concentrations i s narrower than t h a t o f t h e observations. Another key aspect o f e v a l u a t i n g t h e ROM i s i t s a b i l i t y t o r e p l i c a t e s p a t i a l patterns o f observed p o l l u t a n t concentrations. Fig. 2(a) shows t h e modeling domain used i n t h i s study. The maximum observed 03 concentrations a t t h e monitoring s i t e s i n t h e eastern p o r t i o n o f t h e domain f o r t h e episode t h a t occurred d u r i n g 20 July 22 July are shown i n Fig. 2(b), and t h e corresponding model p r e d i c t i o n s are contoured i n Fig. 2(c). For t h i s episode t h e model r e p l i -
-
613
zw , , , , (I)
, ,, ,,,, , ,,
, , ,
,,,
I
,
I
,
, , ,
,’
, , , , , ,0
2w -
-
MAX
,
,
(b)
I
I I
I’ 0 8 1 6 PERCENTILE .((PERCENTILE
1w-
160
1w
GROUP 1 14,lW OM. D N A 18.41 PRED. UATA
GROUP 2
33.112 PRED. UATA
24.W Dm DATA 20.612 PRED. UATA
io,mo PRED. DATA
EM U r n DATA iws PREU. UATA
OBSERVED OZONE CUNCENTPaTIDN. onb
F i g . 1. Observed versus ROM-predicted cumulative frequency d i s t r i b u t i o n s o f daytime (08-19 h, LST) h o u r l y ozone concentrations a t each o f s i x groups o f receptor l o c a t i o n s over t h e period 14 J u l y 31 August 1980. Each p e r c e n t i l e l e v e l i n t h e d i s t r i b u t i o n i s shown and every t e n t h l e v e l i s i n d i c a t e d by an integer.
-
F l g . 2 ( a ) . Northeast U.S. ROM domain (dotted lines show F i g s . 2(b) and 2 ( c ) ).
area analyzed i n
621
Fig. 2(b,c). Maximum observed hourly ozone concentrations (ppb) f o r the period 20-22 July 1980 ( b ) , and contours of maximum predicted hourly ozone concentrations (ppb) for each ROM g r i d during t h e same period ( c ) .
622 cated t h e s p a t i a l p a t t e r n o f maximum 03 q u i t e w e l l i n t h e New England area. Portions o f c e n t r a l Connecticut show >200 ppb 03 b o t h i n t h e observations and t h e p r e d i c t i o n s . The ROM p r e d i c t e d another area o f >ZOO ppb 03 over e a s t e r n Long Island, although no m o n i t o r i n g s i t e s e x i s t e d t h e r e . Washington, D.C.
I n t h e c o r r i d o r from
t o Philadelphia, t h e model underestimated maximum 03 concen-
trations.
I n summary, t h e ROM has been a p p l i e d t o t h e n o r t h e a s t e r n U.S.
f o r a 50-day
p e r i o d d u r i n g t h e summer o f 1980. P r e l i m i n a r y model e v a l u a t i o n r e s u l t s show t h a t t h e model reproduces t h e observed frequency d i s t r i b u t i o n s o f 03 concentrat i o n s best f o r moderate t o h i g h values. There appears t o he a systematic tendency t o o v e r p r e d i c t t h e lowest observed values and t o u n d e r p r e d i c t t h e h i g h e s t values. The model r e p l i c a t e d t h e s p a t i a l p a t t e r n o f maximum 03 c o n c e n t r a t i o n s i n t h e New England area q u i t e w e l l f o r t h e 3-day episode c o n t a i n i n g some o f t h e h i g h e s t observed concentrations of t h e summer o f 1980. REFERENCES R.G. Lamb, A Regional Scale (1000 kin) Model o f Photochemical Air P o l l u t i o n . P a r t 1. Th eoret ica 1 Fo rmu1a t ion, E PA-600/ 3 -83-035, U S E PA, Research T r i a n g l e Park, NC 27711, 1983, 239 pp. R.G. Lamb, A Regional Scale (1000 km) Model of Photochemical A i r P o l l u t i o n . P a r t 2. I n p u t Processor Network Design, EPA-600/3-84-085, U.S. EPA, Research T r i a n g l e Park, NC 27711, 1984, 298 pp. R.G. Lamb and G.F. Laniak, A Regional Scale (1000 km) Model o f Photochemical A i r P o l l u t i o n . P a r t 3. Tests o f t h e Numerical Algorithms, EPA/600/3-85/037, 1J.S. EPA, Research T r i a n g l e Park, NC 27711, 1985, 265 pp. G.Z. Whitten and M.W. Gery, Development o f CBM-X Mechanisms f o r Urban and Regional AQSMs, EPA/600/3-86/012, U.S. EPA, Research T r i a n g l e Park, NC 27711, 1986, 160 pp. W.M. Vaughan, Transport o f P o l l u t a n t s i n Plumes and PEPES, EPA/600/3-85/033, U.S. EPA, Research T r i a n g l e Park, NC 27711, 1985, 60 pp. D.A. Taothman, J.C. Yates and E.J. Sabo, Status Report on t h e Development o f t h e NAPAP Emission Inventory f o r t h e 1980 Base Year and Summary o f P r e l i m i n a r y Data, EPA-600/7-84-091, U.S. EPA, Research T r i a n g l e Park, NC 27711, 1984, 91 pp. J.H. Novak and J.A. Reagan, A Comparison o f N a t u r a l and Man-Made Hydrocarbon Emission I n v e n t o r i e s Necessary f o r Regional Acid Deposition and Oxidant Modeling, 79th Annual Meeting o f t h e APCA, A i r P o l l u t i o n Control Association, Pittsburgh, PA, 1986. R.G. Lamb, Atmos. Environ., 18 (1984) 591-606. R.G. Lamb and S.J. H a t i , J. C l i . Appl. Met., 26 (1987) 837-846.
..
T. Schneider et al. (Editors), Atmospheric Ozone Research and its Policy Implicatwna 0 1989 Elsevier Science Publishers B.V., Amsterdam -Printed in The Netherlands
EVALUATION OF OZONE CONTROL STRATEtiIES I N THE NORTHEASTERN REGION
623
OF THE
UNITED STATES N. C. P o s s i e l , *
J. A. T i k v a r t , l J. H. Novak,2 K. L. Schere,2and E. L. M e y e r l
l E n v i ronmental P r o t e c t i o n Agency, Research T r i a n g l e Park, NC
27711 (USA)
ZNational Oceanic and Atmospheric A d m i n i s t r a t i o n on Assignment t o EPA, Research T r i a n g l e Park, NC
27711 (USA)
ABSTRACT
The t r a n s p o r t o f ozone and p r e c u r s o r p o l l u t a n t s o v e r hundreds o f k i l o meters has an i m p o r t a n t impact on a i r q u a l i t y i n t h e N o r t h e a s t e r n U. s. O f p a r t i c u l a r concern i s t h e r e l a t i v e l y c l o s e p r o x i m i t y o f s e v e r a l m a j o r urban areas, j o i n e d w i t h t h e i n f l u e n c e o f l a r g e r u r a l f u e l combustion sources. T h i s paper reviews i n i t i a l a p p l i c a t i o n s o f a r e g i o n a l s c a l e model t o assess t h e e f f e c t o f s e l e c t e d c o n t r o l s t r a t e g i e s f o r r e d u c i n g ozone c o n c e n t r a t i o n s i n t h e N o r t h e a s t r e g i o n , and e s p e c i a l l y i n t h e urban c o r r i d o r . G e n e r a l l y i t i s found t h a t r e d u c i n g emissions o f v o l a t i l e o r g a n i c compounds i s an e f f e c t i v e c o n t r o l measure. The need f o r f u r t h e r j o i n t c o n t r o l s o f v o l a t i l e o r g a n i c compounds and n i t r o g e n o x i d e s i s addressed. INTRODUCTION Ozone and ozone p r e c u r s o r s a r e known t o be t r a n s p o r t e d beyond s o u r c e a r e a s and t o subsequently impact a i r q u a l i t y hundreds o f k i l o m e t e r s downwind.
Such
t r a n s p o r t i s o f p a r t i c u l a r i m p o r t a n c e i n t h e N o r t h e a s t r e g i o n o f t h e U. S. due t o several factors.
The r e g i o n c o n t a i n s f i v e major u r b a n areas i n c l o s e p r o x -
imity: Washington, DC; B a l t i m o r e , MD; P h i l a d e l p h i a , PA; New York, NY and Bost o n , MA.
I n a d d i t i o n , s e v e r a l medium-size c i t i e s and t h e suburban a r e a s s u r -
r o u n d i n g t h e m e t r o p o l i t a n c e n t e r s n e a r l y o v e r l a p t o p r o v i d e an a l m o s t c o n t i n -
uous C o r r i d o r o f sources e m i t t i n g ozone p r e c u r s o r s .
Included a r e s t a t i o n a r y
and m o b i l e sources o f v o l a t i l e o r g a n i c compounds (VOC) and n i t r o g e n o x i d e s (NO,).
Thus, i n t e r u r b a n t r a n s p o r t , t o g e t h e r w i t h c o n t r i b u t i o n s f r o m m a j o r
r u r a l f u e l combustion sources, i s o f concern.
A compounding f a c t o r i s t h e
m e t e o r o l o g i c a l c o n d i t i o n s t h a t e x i s t f r e q u e n t l y i n t h e N o r t h e a s t e r n U. S. d u r i n g t h e summer.
I n p a r t i c u l a r . t h e wind f l o w o f t e n f a v o r s ozone and p r e c u r s o r
t r a n s p o r t between urban areas i n t h e C o r r i d o r and an exchange o f p o l l u t a n t s w i t h other p a r t s o f t h e Northeast.
The r e s u l t may be m u l t i - d a y episodes o f
h i g h ozone c o n c e n t r a t i o n s a l o n g t h e C o r r i d o r and a c r o s s b r o a d areas o f t h e Northeast region ( r e f .
1).
Because o f t h e s p a t i a l s c a l e s i n v o l v e d , c a n d i d a t e p o l l u t i o n c o n t r o l s t r a t e g i e s must be evaluated on a r e g i o n a l s c a l e i n o r d e r t o assess t h e i r o v e r a l l effectiveness.
T h i s r e q u i r e s t h e use o f a complex r e g i o n a l s c a l e photochem-
i c a l model such as t h e EPA Regional Oxidant Model (ROM) which i s now a v a i l a b l e f o r o p e r a t i o n a l use ( r e f s . 2-3).
The purpose o f t h i s paper t h e n i s t o review
some i n i t i a l a p p l i c a t i o n s o f ROM t o assess t h e e f f e c t i v e n e s s o f s e l e c t e d cont r o l s t r a t e g i e s f o r reducing ozone i n t h e C o r r i d o r and i n o t h e r p a r t s o f t h e Northeast.
Thus f a r , a base case w i t h 1980 emissions and t h r e e c o n t r o l s t r a -
t e g i e s have been examined.
NO,
The c o n t r o l s t r a t e g i e s i n c l u d e :
(1) reduction o f
emissions from major f u e l combustion sources i n t h e Northeast r e g i o n ; ( 2 )
r e d u c t i o n o f NOx emissions i n t h e C o r r i d o r from Washington, OC t o Boston, and ( 3 ) r e d u c t i o n of VOC emissions across t h e region.
MA
The need f o r a d d i t i o n a l
j o i n t VOC/NOx c o n t r o l s t r a t e g y assessments i s a l s o discussed.
MODELING APPROACH The Model The ROM i s an episodic, m u l t i l a y e r , E u l e r i a n g r i d model which t r e a t s t h e photochemical f o r m a t i o n o f ozone from VOC and NOx species through t h e Carbon Bond chemical mechanism ( r e f . 4 ) .
It p r o v i d e s a b a s i s t o s i m u l a t e a i r p o l -
l u t a n t c o n c e n t r a t i o n s over a several day/1000 km s c a l e domain and a l s o t o p r o vide county-level spatial resolution.
As shown i n F i g u r e 1, t h i s domain i n -
cludes t h e n o r t h e a s t e r n auadrant o f t h e U.
s.
e x t e n d i n g from Ohio e a s t t o t h e
A t l a n t i c Ocean and from V i r g i n i a n o r t h t o Canada.
The ROM thereby p r o v i d e s
a means f o r understanding t h e r e g i o n a l t r a n s p o r t phenomenon and a i d s i n plann i n g f o r e f f e c t i v e c o n t r o l s t r a t e g i e s t o m i t i g a t e t h e ozone p o l l u t a n t burden. The model i n c l u d e s a 3-D E u l e r i a n framework w i t h 3 1/2 v e r t i c a l l a y e r s ext e n d i n g through t h e boundary l a y e r and t h e capping i n v e r s i o n o r c l o u d l a y e r . Among t h e processes t r e a t e d a r e a d v e c t i v e t r a n s p o r t , photochemistry,
nighttime
wind shear and t u r b u l e n c e episodes, cumulus c l o u d e f f e c t s on v e r t i c a l mass t r a n s p o r t and photochemical r e a c t i o n r a t e s , t e r r a i n i n f l u e n c e s , b i o g e n i c and anthropogenic emissions, and removal by d e p o s i t i o n .
A shallow diagnostic sur-
face l a y e r i s designed t o account f o r t h e s u b - g r i d s c a l e chemical e f f e c t s o f a heterogeneous emissions d i s t r i b u t i o n .
H o r i z o n t a l r e s o l u t i o n o f emissions, met-
e o r o l o g i c a l phenomena and p r e d i c t e d p o l l u t a n t species i s a g r i d t h a t i s 1/6" l a t i t u d e x 1/4" l o n g i t u d e (
,.. 18.5
x 18.5 km g r i d s i z e ) .
Data Bases The emissions i n v e n t o r y used i n t h e present a p p l i c a t i o n s i s based on 1980 emissions f o r VOC, NO,,
and carbon monoxide ( C O ) as compiled under t h e N a t i o n a l
625
F i g . 1. Northeast domain o f the Regional Oxidant Model.
Acid P r e c i p i t a t i o n Assessment Program ( r e f . 5).
Emissions are based on county-
wide estimates which are then a l l o c a t e d t o t h e g r i d s used i n ROM. emissions f o r hydrocarbons are a l s o included ( r e f . 6).
Biogenic
The i n v e n t o r y encom-
passes t h e e n t i r e Northeastern U. S. ROM domain, i n c l u d i n g p o r t i o n s o f Canada. The most e f f i c i e n t use o f ROM i s t o operate i t w i t h multi-day meteorologi c a l scenarios representative o f those events t h a t l e a d t o high p o l l u t a n t concentrations.
Based on previous studies o f meteorological conditions f o r t h e
Corridor, two scenarios are considered from 1980: and a 10-day period i n August.
a 14-day p e r i o d i n J u l y
During t h e J u l y scenario t h e predominant met-
eorological regimes favor t r a n s p o r t from t h e southwest and west t o t h e n o r t h east and east.
On many o f t h e days southwest f l o w occurs along t h e C o r r i d o r
w i t h i n the lower p a r t o f t h e daytime mixed l a y e r and i n t h e nocturnal boundary layer.
A l o f t , a more westerly component p r e v a i l s capable o f t r a n s p o r t i n g p o l -
l u t a n t s from source areas i n t h e western p a r t o f t h e domain i n t o t h e Corridor. I n contrast t h e August scenario i s characterized by more stagnant conditions w i t h a northeast t o e a s t e r l y wind f l o w on several days.
Both scenarios c o n t a i n
multi-day episodes favorable f o r ozone formation w i t h measured maximum daytime 1-hour concentrations exceeding C.15 ppm i n areas along t h e Corridor, as w e l l as near major c i t i e s i n other p a r t s o f t h e region.
626 Limitations I n t e r p r e t a t i o n o f model r e s u l t s should be l i m i t e d t o a q u a l i t a t i v e assessment d e s p i t e t h e appearance o f q u a n t i t a t i v e r e s u l t s . u s i n g t h i s model q u a n t i t a t i v e l y are:
Among t h e l i m i t a t i o n s i n
t h e u n c e r t a i n t i e s and known d e f i c i e n c i e s
i n t h e 1980 i n v e n t o r y used i n t h e model; t h e l a c k o f a complete v a l i d a t i o n o f t h e model; t h e unknown biases i n t r o d u c e d i n assessing p o i n t source dominated s t r a t e g i e s w i t h a r e g i o n a l s c a l e model; t h e adequacy o f a l a r g e g r i d s i z e t o c h a r a c t e r i z e g r a d i e n t s i n p o l l u t a n t concentrations t y p i c a l o f ozone plumes; t h e representativeness o f meteorological scenarios o f t y p i c a l worst-case cond i t i o n s ; and t h e i n h e r e n t u n c e r t a i n t y i n i n i t i a l a p p l i c a t i o n s o f a model. These l i m i t a t i o n s must be k e p t i n mind i n d e s c r i b i n g and u s i n g t h e ROM r e s u l t s .
DESCRIPTION OF STRATEGIES F o r t h i s a n a l y s i s t h e e f f e c t o f several c o n t r o l s t r a t e g i e s have been tested.
The s t r a t e g i e s i n c l u d e independent c o n t r o l s f o r VOC and NO,
within
t h e Northeast region, as w e l l as t h e c o n t r o l o f major i s o l a t e d sources versus c o n t r o l i n t h e urban C o r r i d o r .
The s t r a t e g i e s , which a r e discussed below,
a r e evaluated t o assess (1) t h e r e l a t i v e decrease/increase o f ozone concent r a t i o n s when compared t o t h e 1980 base case and ( 2 ) t h e magnitude and s p a t i a l d i s t r i b u t i o n o f concentrations as they r e l a t e t o t h e N a t i o n a l Ambient Air Q u a l i t y Standard (NAAQS) f o r ozone ( t h e l e v e l o f t h e NAAQS i s a 0.12 ppm, 1-hour value). NOy S t r a t e g y 1
--
Power P l a n t Control A major c o n t r i b u t i o n t o NO, emissions i n t h e Northeast region i s from
c o a l - f i r e d power p l a n t s .
These emission sources a r e d i s t r i b u t e d across t h e
region, b u t about 80 percent o f t h e power p l a n t NO, western p o r t i o n .
emissions emanate from t h e
A s t r a t e g y which c o n t r o l s these sources may p r o v i d e u s e f u l
i n f o r m a t i o n on t h e e x t e n t t o which u t i l i t y NO,
c o n t r o l can be expected t o i n -
fluence areas above t h e ozone NAAQS.
Thus a s t r a t e g y i s considered t h a t i m -
poses s t r i n g e n t , b u t reasonable, NO,
c o n t r o l s on a1 1 power p l a n t s throughout
t h e region. 0.4
T h i s s t r a t e g y v a r i e s c o n t r o l by b o i l e r t y p e and s i z e as f o l l o w s :
lb/MM BTU NO,
emissions l i m i t on t a n g e n t i a l b o i l e r s , 0.5 lb/MM BTU l i m i t
on w a l l - f i r e d b o i l e r s , and 1.0 lb/MM BTU l i m i t on cyclone b o i l e r s . t h i s r e s u l t s i n a 39 percent r e d u c t i o n i n NO, region.
Overall
emissions f r o m u t i l i t i e s i n t h e
This amounts t o an 11 percent r e d u c t i o n i n region-wide t o t a l NOx emis-
sions considering a l l source categories. NOy S t r a t e g y 2
--
Northeast C o r r i d o r / D e t r o i t Control
Since i t i s expected t h a t a major cause o f h i g h ozone concentrations
i s due t o emissions from t h e C o r r i d o r , a second NO,
c o n t r o l s t r a t e g y i s con-
627 s i d e r e d t o examine a more i n t e n s i v e r e d u c t i o n i n NOx emissions c o n f i n e d t o t h e C o r r i d o r i t s e l f ; a g a i n t h e r e d u c t i o n i s t o be s t r i n g e n t , b u t reasonable. I n addition,
s i m i l a r c o n t r o l s are applied t o t h e D e t r o i t area t o determine
t h e e f f e c t s o f such c o n t r o l s i n a more i s o l a t e d u r b a n area, i n c o n t r a s t t o t h e Corridor.
The s t r a t e g y c o n s i s t s o f c o n t r o l on j u s t t h o s e u t i l i t i e s i n
t h e C o r r i d o r and i n D e t r o i t .
Also included are reductions i n mobile source
emissions and reasonable c o n t r o l s on i n d u s t r i a l b o i l e r s i n t h e s e t w o areas. The u t i l i t y emissions a r e c o n t r o l l e d b y l i m i t s i d e n t i c a l t o t h o s e i n S t r a t e g y 1.
F o r m o b i l e sources, a NOx emissions r e d u c t i o n o f 32 p e r c e n t i s e s t i -
mated u s i n g t h e MOBILE3 model t o r e f l e c t t h e n a t i o n - w i d e change i n m o b i l e source emissions between 1980 and 1995 r e s u l t i n g f r o m t h e c u r r e n t F e d e r a l Motor V e h i c l e C o n t r o l Program (FMVCP) standards.
Industrial boilers of at
l e a s t 100 t o n s p e r y e a r were c o n t r o l l e d by b o i l e r t y p e depending on a v a i l a b l e technologies.
Most b o i l e r s were c o n t r o l l e d by 50 p e r c e n t .
The t o t a l e f f e c t
o f c o n t r o l l i n g t h e s e t h r e e source c a t e g o r i e s i s a 22 p e r c e n t r e d u c t i o n o f NOx emissions i n t h e C o r r i d o r and a p p r o x i m a t e l y a 10 p e r c e n t r e d u c t i o n o f t o t a l NOx emissions i n t h e region.
VOC S t r a t e g y
--
Region-wide C o n t r o l
I t i s w i d e l y e s t a b l i s h e d t h a t VOC e m i s s i o n s have a m a j o r impact on ozone
concentrations ( r e f . 7).
Thus t o assess t h e impact o f e x i s t i n g VOC c o n t r o l
r e g u l a t i o n s on ozone c o n c e n t r a t i o n s i n areas above t h e NAAQS, p a r t i c u l a r l y those i n t h e Northeast Corridor, a s t r a t e g y f o r s p e c i f i c c o n t r o l s w i t h i n t h e C o r r i d o r and more general c o n t r o l s t h r o u g h o u t t h e N o r t h e a s t r e g i o n i s considered.
The VOC c o n t r o l s t r a t e g y reduces base case VOC emissions t o r e -
f l e c t a p p r o x i m a t e l y t h e e f f e c t s o f b o t h emissions growth t o 1987 and cont r o l s mandated p r i o r t o t h e r e q u i r e m e n t s o f t h e c u r r e n t c o n t r o l programs. I n a d d i t i o n , t h i s s t r a t e g y i n c l u d e s VOC e m i s s i o n r e d u c t i o n s due t o FMVCP f r o m 1980 t o 1995.
F o r areas c u r r e n t l y exceeding t h e ozone NAAQS, c o u n t y -
wide c o n t r o l s range f r o m 27 t o 7U percent.
F o r a r e a s c u r r e n t l y below t h e
NAAQS a 30 p e r c e n t VOC emissions r e d u c t i o n i s a p p l i e d .
This strategy
t r a n s l a t e s t o a 5 0 p e r c e n t r e d u c t i o n o f VOC e m i s s i o n s i n t h e C o r r i d o r and a
4 2 p e r c e n t r e d u c t i o n i n r e g i o n - w i d e VOC emissions.
No change i n NOx emis-
s i o n s i s considered. RESULTS Using t h e model and d a t a bases d i s c u s s e d above, r e g i o n - w i d e ozone concent r a t i o n s a s s o c i a t e d w i t h t h e base case 1980 emissions and t h e t h r e e c o n t r o l s t r a t e g i e s have been s i m u l a t e d by ROM.
The r e s u l t s a r e d i s c u s s e d below.
628 Base Case ROM p r e d i c t i o n s o f ozone c o n c e n t r a t i o n s f o r base case emissions i n d i c a t e
l a r g e areas above t h e ozone NAAQS, p r i m a r i l y near and downwind o f major urban areas f o r b o t h scenarios.
F o r example, as shown i n F i g u r e 2 a s i g n i f i c a n t area
o f h i g h ozone c o n c e n t r a t i o n s i s p r e d i c t e d a l o n g t h e C o r r i d o r i n t h e J u l y scenario, e s p e c i a l l y from New York t o Boston.
Fig. 2. i4aximurn 1-hour ozone c o n c e n t r a t i o n s (ppm) p r e d i c t e d d u r i n g t h e J u l y 1980 episode.
NOr C o n t r o l o f Power P l a n t s F o r t h e f i r s t NOx s t r a t e g y , c o n t r o l o f power p l a n t s , t h e r e a r e b o t h small r e d u c t i o n s o f ozone peaks i n i s o l a t e d r u r a l areas and moderate increases i n peaks i n o t h e r areas.
The changes i n 1-hour maximum ozone c o n c e n t r a t i o n s
range from approximately a 20 percent i n c r e a s e t o a 10 percent decrease. For example, F i g u r e 3 shows t h e percent change i n maximum 1-hour concentrat i o n s d u r i n g t h e J u l y scenario.
The f i g u r e i n d i c a t e s t h a t t h i s s t r a t e g y
had l i t t l e e f f e c t on peak c o n c e n t r a t i o n s i n most p a r t s o f t h e region, i n cluding the Corridor.
However, ozone i s reduced i n several r u r a l areas i n
Ohio and West V i r g i n i a where l e v e l s i n t h e base case a r e low.
I n contrast,
r a t h e r l a r g e increases a r e p r e d i c t e d i n p o r t i o n s o f c e n t r a l Pennsylvania and i n t h e v i c i n i t y o f P i t t s b u r g h .
I n t h e l a t t e r area, base case p r e d i c -
t i o n s a r e a l r e a d y above 0.12 ppm.
S i m i l a r mixed r e s u l t s a r e found f o r t h e
August scenari 0.
629
Fig. 3. The percent change i n maximum 1-hour ozone c o n c e n t r a t i o n s between t h e base case and NOx power p l a n t s t r a t e g y f o r t h e J u l y 1980 episode.
NO, Control i n t h e Northeast C o r r i d o r / D e t r o i t For t h e second NOx s t r a t e g y , c o n t r o l i n t h e C o r r i d o r and D e t r o i t , t h e r e a r e (1) small reductions o f ozone peaks downwind o f urban areas and ( 2 ) modera t e increases i n peaks near several urban areas.
Large p o r t i o n s o f t h e region, p a r t i c u l a r l y i n t h e C o r r i d o r , remain above t h e NAAQS. The e f f e c t s range from
approximately a 35 percent increase i n I - h o u r maximum ozone c o n c e n t r a t i o n s t o about a 15 percent decrease.
I n t h e J u l y scenario, as shown i n F i g u r e 4, maxi-
mum 1-hour concentrations decrease i n suburban/rural areas between t h e major C o r r i d o r c i t i e s and t o t h e n o r t h e a s t (downwind) o f D e t r o i t as w e l l as over t h e A t l a n t i c Ocean.
Ozone increases, however, i n h i g h l y populated areas, c l o s e - i n
t o New York City, P h i l a d e l p h i a , and D e t r o i t .
S i m i l a r mixed r e s u l t s a r e found
f o r t h e August scenario, although t h e changes a r e i n o t h e r l o c a t i o n s due t o d i f f e r e n c e s i n f l o w p a t t e r n s between t h e two scenarios. VOC Control Regi on-wi de
F o r t h e region-wide VOC s t r a t e g y t h e r e i s widespread r e d u c t i o n i n ozone concentrations w i t h (1) l a r g e d e c l i n e s i n peak values near and downwind of c i t i e s and ( 2 ) no estimated increase i n peak ozone anywhere i n t h e region. Although t h e s i z e o f t h e areas above t h e NAAQS has decreased, t h e r e a r e s t i l l l a r g e areas w i t h I - h o u r maximum c o n c e n t r a t i o n s g r e a t e r t h a n 0.12 ppm.
The
630
Fig. 4. The percent change i n maximum 1-hour ozone concentrations between the base case and NOx C o r r i d o r / D e t r o i t s t r a t e g y f o r the J u l y 1980 episode. e f f e c t s range from a n e g l i g i b l e change t o about a 40 percent decrease i n 1-hour maximum ozone concentrations. As shown i n Figure 5, t h e area o f subs t a n t i v e decrease (greater than 10 percent) i s spread throughout and covers much o f the Corridor, e s p e c i a l l y downwind o f l a r g e urban areas. This i n cludes much o f t h e ocean area considered i n t h e regional g r i d .
Rural areas
f a r beyond major urban/point sources and those p o r t i o n s o f t h e C o r r i d o r immediately adjacent t o upwind r u r a l areas tend t o show n e g l i g i b l e impact. Also, i t i s apparent t h a t f o r many areas p r e v i o u s l y above t h e NAAQS, ozone l e v e l s have improved t o become lower than t h e standard, p r i m a r i l y i n areas on t h e periphery o f t h e Corridor. A s i m i l a r r e s u l t i s obtained f o r t h e August scenario. VOC/NOx STRATEGIES
The above a n a l y s i s i n d i c a t e s t h a t c o n t r o l o f VOC alone may be r e l a t i v e l y e f f e c t i v e i n reducing ozone concentrations across t h e Northeast region. However, t h e r e s u l t s suggest t h a t NOx c o n t r o l alone could produce mixed e f f e c t s , w i t h increases i n ozone concentrations apparently g r e a t e r i n magnitude t h a n any decreases. I n f a c t , t h e r e i s some evidence t h a t i s o l a t e d exceedances could be created w i t h t h e NOx s t r a t e g i e s where none p r e v i o u s l y existed. However, one should n o t i n f e r from t h i s t h e r e l a t i v e m e r i t s o f j o i n t l y c o n t r o l l i n g these two precursor p o l l u t a n t s . There i s evidence t h a t j o i n t c o n t r o l o f both
63 1
Fig. 5. The percent change i n maximum I - h o u r ozone c o n c e n t r a t i o n s between the base case and VOC s t r a t e g y f o r t h e J u l y 1980 episode. p o l l u t a n t s c o u l d o p t i m i z e t h e r e d u c t i o n o f ozone concentrations w h i l e m i n i m i z i n g t h e r e q u i r e d c o n t r o l o f e i t h e r VOC o r NO.,
The need f o r a v a r i e t y o f
c o n t r o l l e v e l s f o r b o t h p o l l u t a n t s and t h e s p a t i a l d i s t r i b u t i o n o f such cont r o l s i s evident.
It i s expected t h a t a range o f j o i n t VOC/NOx c o n t r o l s t r a -
t e g i e s w i l l be considered as p a r t o f f u t u r e EPA model a p p l i c a t i o n s . SUMMARY
This study used a r e g i o n a l s c a l e model t o e v a l u a t e t h e s e n s i t i v i t y o f p r e d i c t e d ozone concentrations t o components o f p o t e n t i a l c o n t r o l a l t e r n a t i v e s i n t h e Northeast U.
S.
The area o f ozone NAAQS exceedance was s i m u l a t e d w i t h
a 1980 emissions base case and then t h e e f f e c t i v e n e s s o f s e l e c t e d c o n t r o l s t r a t e g i e s f o r p r e c u r s o r p o l l u t a n t s was evaluated.
I n general, i t was found t h a t
region-wide c o n t r o l o f VOC was e f f e c t i v e i n reducing ozone c o n c e n t r a t i o n s by up t o 40 percent, w h i l e a l s o reducing t h e area o f c o n c e n t r a t i o n s g r e a t e r t h a n t h e
NAAQS.
However, c o n t r o l o f NOx from major r u r a l p o i n t sources o r from m u l t i p l e
sources i n t h e C o r r i d o r produced a range o f r e s u l t s i n c l u d i n g increases up t o 35 percent and decreases t o 15 percent i n 1-hour ozone concentrations.
I n some
cases exceedances were p r e d i c t e d f o l l o w i n g NOx c o n t r o l where none were p r e d i c t e d i n t h e base case.
The need f o r j o i n t VOC/NOx c o n t r o l s t r a t e g y assessments
t o more r e a l i s t i c a l l y examine t h e l e v e l o f c o n t r o l f o r a i r q u a l i t y improvement was made c l e a r .
632 REFERENCES
N. C. Possiel, et. al., Northeast C o r r i d o r Regional Modeling P r o j e c t : Ozone and Precursor Transport i n New York City and Boston During t h e 1980 F i e l d Program, EPA-450/4-84-011, Research T r i a n g l e Park, NC, 1984. R. 6. Lamb, A Regional Scale (1000 KM) Model o f Photochemcial A i r PolResearch l u t i o n : P a r t l. T h e o r e t i c a l Formulation, EPA-600/3-83-025, T r i a n g l e Park, NC, 1983. R. 6. Lamb, A Regional Scale (1000 KM) Model o f Photochemical A i r Poll u t i o n : P a r t 2. I n p u t Processor Network Design, EPA-600/3-84-085, Research T r i a n g l e Park, NC, 1984. M. W. Gery. et. al., Development and T e s t i n g o f t h e CBM-IV For Urban and Regional Modeling, EPA P r o j e c t Report, Research T r i a n g l e Park, NC 1988. J. K. Wagner, et. al., Development o f t h e 1980 NAPAP Emissions Invent o r y , EPA-600/7-86-057a. Research T r i a n g l e Park, NC, 1986. J. H. Novak and J. A. Reagan, A Comparison o f Natural and Man-made Hydrocarbon Emission I n v e n t o r i e s Necessary f o r Regional A c i d Deposit i o n and Oxidant Modeling, Paper Presented a t t h e 79th APCA Annual Meeting, Minneapolis, MN, 1986. Envi ronmental P r o t e c t i o n Agency, A i r Q u a l i t y C r i t e r i a , EPA-600/8-84020aF, Research T r i a n g l e Park, NC, 1986.
T. Schneider et aL (Editors), Atmospheric Ozone Research and its Policy Implications 0 1989 Elsevier Science Publishera B.V., Amsterdam - Printed in The Netherlands
633
PHOTOCHEMICAL O X I D A N T MODEL APPLICATION WITHIN THE FRAMEWORK OF CONTROL S T R A T E G Y DEVELOPMENT I N THE DUTCH/GERMAN PROGRAMME PHOXA
J. P a n k r a t h Umweltbundesamt,
B i s m a r c k p l a t z 1, D-1000 B e r l i n 3 3
ABSTRACT The D u t c h - G e r m a n Programme PHOXA ( P h o t o c h e m i c a l O x i d a n t a n d A c i d D e p o s i t i o n Model A p p l i c a t i o n i n t h e Framework o f C o n t r o l S t r a t e g y Development) i s concerned w i t h p h o t o c h e m i c a l o x i d a n t s and t h e d e p o s i t i o n o f a c i d i f y i n g species. E f f e c t i v e measures t o reduce e l e v a t e d ozone c o n c e n t r a t i o n s i n Europe need t r a n s b o u n dary s t r a t e g i e s ; i t s impact can o n l y be e v a l u a t e d by a p p l y i n g r e g i o n a l d i s p e r s i o n models which p r o v i d e s u b s t a n t i a l s u p p o r t t o the transboundary c o n t r o l strategies. The o b j e c t i v e o f PHOXA c o n s i s t s i n t h e p r e p a r a t i o n o f a n i n s t r u m e n t a t i o n i n o r d e r t o e v a l u a t e abatement s t r a t e g i e s f o r photoc h e m i c a l o x i d a n t s and a c i d i f y i n g p o l l u t a n t s w i t h r e g a r d t o t h e i r European-wide e f f e c t on a i r q u a l i t y and d e p o s i t i o n . F o r t h e t r e a t ment o f p h o t o c h e m i c a l o x i d a n t s t h e R T M - I 1 1 m o d e l was u s e d t o i n v e s t i g a t e e p i s o d e s o f h i g h ozone c o n c e n t r a t i o n s . The e v a l u a t i o n o f t h e f i n d i n g s shows t h a t t h e l o n g r a n g e d i s p e r s i o n model R I M - I 1 1 p r e d i c t s t e m p o r a l and s p a t i a l p a t t e r n s o f ozone r e a s o n a b l y w e l l i n r u r a l a r e a s b u t u n d e r p r e d i c t s t h e h i g h e s t o b s e r v e d h o u r l y o z o n e v a l u e s i n m o r e i n d u s t r i a l i z e d a r e a s . The e v a l u a t i o n o f some b r o a d e m i s s i o n s c e n a r i o s f o r s e l e c t e d p h o t o chemical episodes supports t h e f a c t t h a t t h e RTM-I11 model responds i n a n e x p l a i n a b l e way t o c h a n g e s i n t h e e m i s s i o n i n p u t .
INTRODUCTION The D u t c h - G e r m a n Programme PHOXA ( P h o t o c h e m i c a l O x i d a n t a n d A c i d D e p o s i t i o n Model A p p l i c a t i o n w i t h i n t h e Framework o f C o n t r o l S t r a t e g y D e v e l o p m e n t ) w h i c h s t a r t e d i n 1984,
i s designed t o apply
s i m p l e a n d c o m p l e x d i s p e r s i o n m o d e l s o n t h e l a r g e s c a l e ( r e f 1). The s t a r t i n g - p o i n t
f o r c a r r y i n g o u t t h e p r o g r a m m e P H D X A was
t h e nowadays g e n e r a l l y acknowledged f a c t t h a t a i r p o l l u t a n t s c o u l d be t r a n s p o r t e d over l a r g e distances;
therefore the region o f im-
pact can be hundreds o f k i l o m e t e r s remote from t h e r e g i o n o f corresponding emissions. A l s o g e n e r a l l y acknowledged i s t h e f a c t t h a t d u r i n g atmospheric t r a n s p o r t p h y s i c a l and c h e s i c a l r e a c t i o n s o c c u r p r o d u c i n g s p e c i e s
634
and a c i d s w h i c h a r e d i s c u s s e d i n c o n t r i b u t i n g t o t h e l a r g e s c a l e d e t e r i o r a t i o n e f f e c t s i n e c o s y s t e m s o f E u r o p e and N o r t h A m e r i c a . I n s o f a r as b o t h groups o f s p e c i e s a r e p a r t i c i p a t i n g i n t h e l o n g r a n g e t r a n s p o r t and a r e p r o d u c e d f r o m t h e i r p r e c u r s o r s t h e r e i s t h e n e c e s s a r y consequence:
A reduction o f t h e i r concentration
and d e p o s i t i o n c a n be a c h i e v e d o n l y b y a E u r o p e a n w i d e r e d u c t i o n o f t h e i r precursors. W i t h r e g a r d t o t h e p h o t o o x i d a n t problem t h e l a r g e s c a l e emiss i o n r e d u c t i o n o f t h e main p r e c u r s o r s , v o l a t i l e o r g a n i c compounds ( V O C ) ,
n i t r o g e n o x i d e s (NOx) and
i s needed.
The o n l y p o s s i b i l i t y
t o p u t s u c h a b a t e m e n t d e c i s i o n s on a q u a n t i t a t i v e and c o n t r o l l e d b a s i s i s t h e a p p l i c a t i o n o f d i s p e r s i o n models ( r e f 2 ) . I n t h i s context short-term necessary.
as w e l l as l o n g - t e r m models a r e
I n t h e f o l l o w i n g t h e f o c u s i s on e p i s o d i c s i t u a t i o n s
i n t h e atmospheric boundary l a y e r ;
corresponding long-range d i s -
p e r s i o n m o d e l s f o r t h e a p p l i c a t i o n i n P H O X A a r e summarised i n fig.
1.
1
[EPISODIC MODELS
LpiGGG-1
j
EULERIAN
II
i n co-oDeration w i t h
receptor-oriented simple meteorology complex chemistry
i
/ THD Model
RTM-I11 Model
3 dim., m u l t i l a y e r simple meteorology l i n e a r chemistry SOx’ NOx
3 dim.,
3 1/2 l a y e r simple meteorology complex gas-phase chemistry
I
ADOM/TADAP Model
3 dim.,
multilayer complex meteorology complex gas- and aqueous-phase
F i g . 1 E p i s o d i c 1o n g - r a n g e t r a n s p o r t m o d e l s f o r a p p l i c a t i o n i n PHOXA. The R T M - I 1 I m o d e l i s e s p e c i a l l y d e s i g n e d f o r t h e s i m u l a t i o n o f p h o t o o x i d a n t s episodes i n t h e atmospheric boundary l a y e r . One o b j e c t i v e o f t h e PHOXA programme i s t o p r o v i d e a t o o l s u i t a b l e f o r e v a l u a t i n g abatement s t r a t e g i e s f o r p h o t o c h e m i c a l o x i d a n t s . T ak i n g i n t o a ccount t h e European-wide
aspect o f t h e formation
o f photooxidants a close co-operating
w i t h t h e ECE programme EMEP
has b e e n e s t a b l i s h e d .
A c l o s e c o - o p e r a t i o n w i t h EEC and OECD h a s
been i n i t i a t e d a l r e a d y i n 1985,
635
P H O T O O X I O A N T E P I S O D E S I N THE BOUNDARY LAYER M o d e l c a l c u l a t i o n s i n t h e PHOXA f r a m e w o r k were a c c o m p l i s h e d f o r s e l e c t e d episodes.
The s e l e c t i o n f o r t h e a d e q u a t e m o d e l t o
b e a p p l i e d i n E u r o p e was made f o r t h e R e g i o n a l T r a n s p o r t M o d e l
I11 (RTM-111) corporation.
w h i c h h a d been d e v e l o p e d by System A p p l i c a t i o n I n -
PHOXA came t o t h i s d e c i s i o n b y c o n s i d e r i n g t h e f i n d i n g s
o f t h e US-EPA/OECD
I n t e r n a t i o n a l C o n f e r e n c e on Long Range T r a n s -
p o r t M o d e l s f o r P h o t o c h e m i c a l O x i d a n t s and t h e i r P r e c u r s o r s ( r e f 3 ) . According t o c e r t a i n c r i t e r i a d e f i n e d a t t h a t conference t h e
R T M - I 1 1 m o d e l was a t t h a t t i m e t h e o n l y E u l e r i a n - t y p e m o d e l b o t h f u l l y o p e r a t i o n a l and a p t f o r c o n t r o l s t r a t e g y d e v e l o p m e n t . The R T M - I 1 1
model was t h e n i n s t a l l e d i n P H O X A a s a s u b s t i t u t e
o f r e g i o n a l t r a n s p o r t models s p e c i f i c a l l y d e v e l o p e d as a t o o l f o r i n v e s t i g a t i n g t h e p e r f o r m a n c e o f d i s p e r s i o n models i n c a r r y i n g o u t s c e n a r i o c a l c u l a t i o n s t o be u s e d i n e m i s s i o n a b a t e m e n t s t r a tegies. To-day able,
f u r t h e r d e v e l o p e d and y e t o p e r a t i o n a l m o d e l s a r e a v a i l -
f o r i n s t a n c e t h e ADOM/TADAP
m o d e l o f t h e German-Canadian
c o - o p e r a t i o n and t h e R A D M model o f t h e U S .
PHOXA t h e ADOM/TADAP
I n t h e framework o f
model i s a t p r e s e n t i n s t a l l e d f o r t h e eva-
luation o f acid deposition;
i n t h e long term i t i s planned t o
u s e i t f o r t h e p h o t o o x i d a n t p r o b l e m as w e l l . I n t h e framework o f PHOXA, p e r s i o n model R T M - I 1 1
t h e long-range
photochemical d i s -
was used t o s i m u l a t e t h e f o l l o w i n g p h o t o -
chemical o x i d a n t episodes: episode
I:J u l y 22
episode
11: May 29
episode
111: June 3
-
-
26,
1980
June 2, 6,
1982
1982
The most i m p o r t a n t c r i t e r i a f o r t h e e p i s o d e s e l e c t i o n h a v e been : ( i ) t h e h o u r l y ozone c o n c e n t r a t i o n s must b e s u f f i c i e n t l y h i g h (more t h a n 80 ppb 03) on l a r g e g e o g r a p h i c a l a r e a s ,
at least i n
t h e r e c e p t o r a r e a s ( t h e F e d e r a l R e p u b l i c o f Germany and t h e N e t h e r lands), ( i i ) t h e h o u r l y ozone c o n c e n t r a t i o n s s h o u l d s t a y h i g h f o r some c o n s e c u t i v e days.
636 The t h r e e e p i s o d e s h a v e b e e n s e l e c t e d o u t o f a l a r g e n u m b e r o f p o s s i b l e c a n d i d a t e s i n s u c h a manner a s t o c o v e r r e a s o n a b l y w e l l s i t u a t i o n s r e p r e s e n t a t i v e f o r photoxidant episodes. I was d e f i n e d b y P H O X A ,
Episode
e p i s o d e I 1 a n d I11 were s e l e c t e d b y PHOXA
i n c o o p e r a t i o n w i t h t h e EEC a n d t h e OECD,
D E S C R I P T I O N OF THE R T M - I 1 1
respectively'.
MODEL
W i t h i n t h e PHOXA programme a model a r e a w i t h t h e f o l l o w i n g
l o o w e s t t o 24O e s t a n d The e n c l o s e d a r e a h a s a n e x t e n s i o n o f 3.13.10 6
b o r d e r l i n e s has been t a k e n a s a b a s i s : 47,5O
t o 60° n o r t h .
km2 a n d c o v e r s m o s t o f t h e i n d u s t r i a l i z e d r e g i o n s i n E u r o p e . The g r i d u s e d i n t h e m o d e l l i n g s t u d i e s h a s s i z e s o f 6 0 ' t u d e and 3 0 '
latitude,
longi-
corresponding t o g r i d c e l l s o f approxima-
t e l y 5 0 km x 5 0 km. The R T M - I 1 1 m o d e l ,
adapted f o r t h e a p p l i c a t i o n i n PHOXA ( r e f
4 ) i s a E u l e r i a n g r i d model based o n t h e n u m e r i c a l s o l u t i o n o f a 3 1/2
l a y e r multispecies d i f f u s i o n equation.
The v e r t i c a l l a y e r s
are :
-
a s u r f a c e l a y e r i m m e d i a t e l y above t h e ground;
-
a mixed l a y e r up t o t h e base o f t h e t e m p e r a t u r e i n v e r s i o n , varies temporally
-
which
and s p a t i a l l y ;
a l o w e r i n v e r s i o n l a y e r i m m e d i a t e l y above t h e b a s e o f t h e temperature inversion;
-
an u p p e r i n v e r s i o n l a y e r above up t o t h e t o p o f t h e m o d e l l i n g region, The m o d e l c o n t a i n s a m o s t r e c e n t v e r s i o n o f t h e C a r b o n - B o n d
Mechanism
-
t h e CMB-IV
-, w h i c h
c o n s i s t s o f 70 r e a c t i o n s d e s c r i -
b i n g t h e chemical k i n e t i c s o f 17 t r a n s p o r t e d species, 7 d i f f e r e n t c l a s s e s o f VOC. CBM-IV
hereby u s i n g
The p h o t o l y s i s r a t e c o n s t a n t s o f t h e
v a r y d i u r n a l l y and s p a t i a l l y a s a f u n c t i o n o f s o l a r z e n i t h
a n g l e and c l o u d c o v e r .
I N P U T DATA BASE P r e r e q u i s i t e t o t h e a p p l i c a t i o n o f d i s p e r s i o n models i s t h e a v a i l a b i l i t y o f s u i t a b l e d a t a bases.
For t h e RTM-I11
model t h e
f o l l o w i n g i n p u t data p r e p a r a t i o n i s necessary: (i) E m i s s i o n i n p u t d a t a a r e p o i n t and a r e a s o u r c e s i n 3 h o u r l y
t i m e r e s o l u t i o n f o r t h e s p e c i e s NO, classes (ethene,
olefins,
paraffins,
NO2,
SO2, SO4, C O a n d 7 V O C -
aldehydes,
formaldehyde,
xy-
637 lenes, toluenes),
which a r e adapted t o t h e CBM-IV
mechanism,
in
each h o r i z o n t a l g r i d ; ( i i ) meteorological i n p u t data are layer-averaged data i n 3 h o u r l y time r e s o l u t i o n f o r h o r i z o n t a l wind v e l o c i t y , mixing height,
temperature
r a i n f a l l and c l o u d c o v e r i n each h o r i z o n t a l g r i d ;
(iii) l a n d use d a t a a r e c a t e g o r i s e d i n 1 0 c l a s s e s ( w a t e r ,
land,
grassland,
permanent c r o p ,
coniferous forests,
b u i l t - u p areas,
mixed f o r e s t s ,
bare s o i l ,
crop-
deciduous f o r e s t s ,
wetland) f o r t h e
c a l c u l a t i o n o f d r y d e p o s i t i o n r a t e s i n each h o r i z o n t a l g r i d ; ( i v ) a i r q u a l i t y d a t a a r e n e c e s s a r y t o d e r i v e i n i t i a l and boundary c o n d i t i o n s . Tab,
1 shows t h e t o t a l y e a r l y e m i s s i o n s o f SO
X,
NOx,
VOC a n d
C O i n 1980 and t h e c o n t r i b u t i o n o f d i f f e r e n t s o u r c e c a t e g o r i e s
t o t h e s e t o t a l e m i s s i o n s i n t h e PHOXA r e g i o n . TABLE 1 P H O X A e m i s s i o n d a t a b a s e 1980. C o n t r i b u t i o n o f d i f f e r e n t s o u r c e c a t e g o r i e s t o t o t a l e m i s s i o n s i n t h e PHOXA r e g i o n .
Source ~
AnthroDoaenic
30.0
12.5
7.6
47.4
T h e p r e p a r a t i o n o f t h e s p e c i f i e d d a t a b a s e s was a m a i n t a s k
f o r t h e PHOXA programme. d a t a base,
The s e t t i n g - u p o f t h e PHOXA e m i s s i o n
i n c l u d i n g programmes t o d e r i v e e p i s o d i c e m i s s i o n f i l e s ,
a l l o w e d f o r t h e f i r s t t i m e t h e u s e o f complex d i s p e r s i o n m o d e l s f o r p l a n n i n g p u r p o s e s i n Europe.
The P H O X A e m i s s i o n d a t a b a s e
i s t h e o n l y d a t a base i n E u r o p e w h i c h h a s a r e l a t i v e l y f i n e r e s o l u t i o n o f s o u r c e s and s o u r c e c a t e g o r i e s f o r a v a r i e t y o f s p e c i e s
630
b e i n g p r e r e q u i s i t e t o t h e development o f e m i s s i o n abatement scenarios.
T h i s p o i n t i s o f u t m o s t i m p o r t a n c e i n so f a r a s no model
is a b l e t o p r o d u c e r e l i a b l e r e s u l t s when t h e n e c e s s a r y i n p u t d a t a a r e n o t a v a i l a b l e or a r e a v a i l a b l e o n l y w i t h i n s u f f i c i e n t q u a l i t y . The m o d e l l i n g o f p h o t o o x i d a n t s i s i n t h i s r e s p e c t p a r t i c u l a r l y s u s c e p t i b l e t o t h e q u a l i t y o f t h e used p r e c u r s o r emissions and t h e s p l i t t i n g o f VOC i n r e a c t i v i t y c l a s s e s . MODEL VALIDATION The t h r e e s e l e c t e d PHOXA e p i s o d e s h a v e b e e n s i m u l a t e d w i t h the RTM-111
5).
model f o c u s s i n g m a i n l y o n ozone c o n c e n t r a t i o n s ( r e f
As a n e x a m p l e f o r a n h o u r l y a v e r a g e d p r e d i c t e d m i x e d l a y e r
ozone f i e l d o v e r Europe t h e c a l c u l a t e d ozone c o n c e n t r a t i o n s a t 03:DO
pm UTC f o r
J u l y 26,
1980 a r e g i v e n i n f i g .
i n boxes a r e measured h o u r l y ozone c o n c e n t r a t i o n s .
2.
The n u m b e r s From a r e v i e w
F i g . 2 C a l c u l a t e d h o u r l y a v e r a g e d ozone c o n c e n t r a t i o n s i n t h e m i x e d - l a y e r o f t h e R T M - I 1 1 m o d e l f o r J u l y 26, 1 9 8 0 , 03:OO p.m. U T C . Numbers i n b o x e s p r e s e n t o b s e r v a t i o n s .
639
o f the results,
i t becomes a p p a r e n t t h a t t h e m o d e l e x h i b i t s some
s k i l l i n p r e d i c t i n g ozone c o n c e n t r a t i o n s ; observed s p a t i a l p a t t e r n are reproduced.
many f e a t u r e s o f t h e Fig.
3 shows e x a m p l e s
f o r p r e d i c t e d and measured ozone c o n c e n t r a t i o n s i n t w o a r e a s o f t h e m o d e l i n g r e g i o n d u r i n g t h e PHOXA e p i s o d e
7/23/80
7/24/80
(bl 4
I
12
16
20
The Netherlands 24
1
0
I2
I6
7/24/80
(d)
I. The m e a s u r e d o z o n e
7/25/80
-
7/26/00
Rhinemond A r e a 20
24
I
8
12
16
20
24
I
7/2weo
I
12
I6
20
24
7/26/80
Langenbrigge, West Germany
F i g . 3 C a l c u l a t e d and measured ozone c o n c e n t r a t i o n s i n two a r e a s o f t h e PHOXA-modelling r e g i o n : ( a ) t h e Rhinemond-area o f t h e N e t h e r l a n d s ( b ) L a n g e n b r u g g e o f West-Germany. c a l c u l a t e d lower i n v e r s i o n l a y e r c a l c u l a t e d mixed l a y e r c a l c u l a t e d ground l e v e l
----
....
p e a k s were i n m o s t c a s e s u n d e r e s i m a t e d b y t h e m o d e l c a l c u l a t o n s . Some s t a t i s t i c a l i n f o r m a t i o n c a n b e i n f e r e d f r o m t a b .
2 which
c o n t a i n s t h e r e s u l t o f t h e t h r e e PHOXA e p i s o d e s ( r e f 6 ) .
640 TABLE 2 Some s t a t i s t i c a l i n f o r m a t i o n f o r t h e t h r e e PHOXA-episodes b y comp a r i n g measured g r o u n d l e v e l ozone c o n c e n t r a t i o n s f r o m 30 t o 40 s i t e s w i t h c a l c u l a t e d m i x e d - l a y e r ozone c o n c e n t r a t i o n s .
episode I
ozone average p r e d i c t e d (ppb) a v e r a g e measured ( p p b ) average c o r r e l a t i o n coefficient percentage o f p r e d i c t i o n s within a factor o f 2
episode I 1
42.4 45.9
47.8 55.4
0.62
56.6 60.7
0.54
76
e p i s o d e I11
0.51
80
78 ~
F a i l i n g i n t h e m o d e l i n g o f t h e o b s e r v e d maximum h o u r l y o z o n e c o n c e n t r a t i o n s may be p a r t l y due t o t h e r e l a t i v e l y l a r g e g r i d r e s o l u t i o n o f a p p r o x i m a t e l y 50 km x 50 km.
A l s o an u n d e r e s t i m a -
t i o n o f t h e a n t h r o p o g e n i c VOC-emissions a n d / o r o f t h e V O C e m i s s i o n s seem p o s s i b l e . with the RTM-I11
the r e a c t i v i t y
Nevertheless,
tests applied
model have d e m o n s t r a t e d ( r e f 7 ) t h e l e v e l o f
performance t o be ( i ) good f o r t h e r e p r o d u c t i o n o f t h e t e m p o r a l and s p a t i a l ozone p a t t e r n i n r u r a l areas, ( i i ) l e s s good f o r t h e r e p r o d u c t i o n o f NOx and o z o n e f i e l d s i n h i g h l y i n d u s t r i a l i z e d areas. S E N S I T I V I T Y ANALYSES S e n s i t i v i t y analyses are very important i n order t o determine t h e response o f t h e model t o e r r o r s i n i n p u t d a t a ;
t h i s procedure
i s u s u a l l y done by a s y s t e m a t i c v a r i a t i o n o f t h e i n p u t . v i t y r u n s have been i n v e s t i g a t e d w i t h t h e R T M - I 1 1
Sensiti-
model i n o r d e r
t o a s c e r t a i n t h e i n f l u e n c e o f c e r t a i n p a r a m e t e r s on t h e m o d e l results. The g e n e r a l c o n c l u s i o n w h i c h c o u l d be drawn f r o m t h e s e s e n s i t i v i t y c a l c u l a t i o n s c a n be s u m m a r i z e d a s f o l l o w s : ( i ) C l o u d a v e r a g e and m i x i n g h e i g h t h a v e a s t r o n g l o c a l e f f e c t on t h e m o d e l r e s u l t s . ( i i ) The i n f l u e n c e o f t h e u p p e r and l a t e r a l b o u n d a r i e s on t h e model r e s u l t s i s s m a l l . ( i i i ) The q u a l i t y o f t h e m o d e l r e s u l t s depends f i r s t o f a l l on t h e q u a l i t y o f t h e d a t a b a s e f o r N O x and n a t u r a l ) - e m i s s i o n s .
and V O C ( a n t h r o p o g e n i c
641
S E N S I T I V I T Y OF THE R T M - I 1 1
AND VOC-EMISSIONS
MODEL T O OVERALL REDUCTIONS OF NOx-
I N THE PHOXA-AREA
To g e t some i n d i c a t i o n o f t h e c h a n g e o f d i r e c t i o n o f o x i d a n t c o n c e n t r a t i o n s when e m i s s i o n s o f NO
X
o r / a n d VOC a r e a l t e r e d ,
the
f o l l o w i n g o v e r a l l e m i s s i o n r e d u c t i o n s have been i n v e s t i g a t e d : ( a ) N O x e m i s s i o n s r e d u c e d b y 50 # , V O C e m i s e i o n s u n c h a n g e d ( b ) NOx e m i s s i o n s u n c h a n g e d , ( c ) NOx- a n d V O C - e m i s s i o n s
VOC-emissions
r e d u c e d b y 50 %
r e d u c e d b y 50 %,
A l l r e d u c t i o n s have been c a r r i e d o u t u n i f o r m l y o v e r t h e w h o l e modeling region,
i n c l u d i n g anthropogenic and n a t u r a l emissions;
a l l o t h e r i n p u t data remained u i s l t e r e d . As an e x a m p l e o f t h e e f f e c t o f t h e s e o v e r a l l h y p o t h e t i c a l e m i s s i o n r e d u c t i o n s t h e c h a n g e i n t h e maximum h o u r l y o z o n e c o n c e n t r a t i o n s compared t o t h e base c s s e o f t h e 1980 e p i s o d e i s d e p i c t e d in fig. episodes
4
.
-
6.
S i m i l a r f i n d i n g s have been o b t a i n e d f o r t h e 1982
F i g . 4 C o n t o u r l i n e s o f c a l c u l a t e d b a s e c a s e maximum h o u r l y o z o n e c o n c e n t r a t i o n s p p b Oj on J u l y 26, 1980. The p e r c e n t a g e c h a n g e o f t h e p r e d i c t e d maximum h o u r l y o z o n e c o n c e n t r a t i o n s d u e t o a 50 X NO - e m i s s i o n r e d u c t i o n i s m a r k e d .
642
F i g . 5 Same a s f i g .
4 b u t f o r a 50 % V O C - e m i s s i o n
F i g . 6 Same a s f i g .
4 b u t f o r a 5 0 X NOx-
reduction
and VOC-emission
reduction
643
The p r e l i m i n a r y c o n c l u s i o n s w h i c h c a n b e d r a w n f r o m t h i s b r o a d s e n s i t i v i t y a n a l y s i s on a p e r c e n t a g e e m i s s i o n r e d u c t i o n f o r t h e t h r e e e p i s o d e s u n d e r c o n s i d e r a t i o n i n t h e PHOXA m o d e l i n g a r e a , a r e summarized q u a l i t a t i v e l y i n t a b .
3
TABLE 3
,
Q u a l i t a t i v e b e h a v i o u r o f a n o v e r a l l 5 0 L r e d u c t i o n f o r NO VOC a n d c o m b i n e d N O x , V O C i n c o m p a r i s o n w i t h t h e b a s e c a s e mo'6el run.
-
-
5 0 X NO.,
03 i n c r e a s e i n l o c a l r e g i o n s w i t h h i g h NOx emi s s i o n s ( u r b a n / i n d u s t r ia 1 i z e d areas)
50
-
x voc
0 decrease i n t h e wffole r e g i o n
0 decrease i n regions 3 w i t h low NOx emissions ( r u r a l areas)
50
X
NO..,
VOC
Diminished O3 increase i n l o c a l regions with high NOx e m i s s i o n s ( u r b a n / i n dus t r i a l i z e d areas) E n h a n c e d O 3 decrease i n regions w i t h l o w NOx e m i s sions ( r u r a l areas)
A d e c r e a s e i n NOx e m i s s i o n s l e a d s t o a n i n c r e a s e i n 0 t r a t i o n s c l o s e t o l a r g e NO
X
3 concensources i n u r b a n / i n d u s t r i a l i z e d areas
a n d a d e c r e a s e i n O 3 c o n c e n t r a t i o n s i n r u r a l a r e a s w i t h l o w NOx emissions there.
T h i s c a n b e u n d e r s t o o d i n q u a l i t a t i v e way b y
k e e p i n g i n m i n d t h a t ozone i s produced p r i m a r i l y as a r e s u l t o f t h e p h o t o l y s i s o f NO2 m o d i f i e d b y p r o d u c t s o f V O C - p h o t o l y s i s , and t h a t ozone i s removed p r i m a r i l y by d r y d e p o s i t i o n a n d r e a c t i o n
w i t h V O C a n d N O x . I n a r e a s w i t h h i g h NOx e m i s s i o n s a NO results i n less O3 o f O3
compared t o t h e b a s e c a s e run.
s i o n s a NO
X
X
reduction
d e s t r u c t i o n which appears as a r e l a t i v e increase I n a r e a s w i t h l o w NOx e m i s -
reduction r e s u l t s i n lesser O3
t o t h e base case run.
p r o d u c t i o n compared
V O C r e d u c t i o n s d i m i n i s h t h e amount o f p e r o x y
r a d i c a l s produced by t h e photochemical degradation o f hydrocarbons w h i c h u s u a l l y c o n v e r t s NO t o N O 2 i n f a v o u r o f O 3 p r o d u c t i o n . Tab.
4 c o n t a i n s c a l c u l a t e d mean o z o n e v a l u e s ( 9 6 h o u r a v e r a g e
f o r t h e w h o l e PHOXA r e g i o n a s w e l l a s f o r t h e r e c e p t o r r e g i o n s (West-Germany
a n d The N e t h e r l a n d s ) w h i c h r e s u l t e d f r o m t h e o v e r a 1
percentage emission r e d u c t i o n scenarios f o r t h e t h r e e s e l e c t e d episodes.
644
TABLE 4 C a l c u l a t e d mean o z o n e c o n c e n t r a t i o n ( 9 6 h o u r a v e r a g e ) f o r d i f f e r e n t p a r t s o f t h e P H O X A r e g i o n a n d i t s mean maximum v a l u e . The p e r c e n t a g e n u m b e r s g i v e t h e c h a n g e s i n t h e s e mean o z o n e c o n c e n t r a t i o n s f o r t h e three hypothetical o v e r a l l emission reduction scenarios. Episode mean ozone concent r a t i o n (ppb) o f t h e base case run Episode I: PHOXA r e g i o n West-Germany The Netherlands Mean peak value i n PHOXA
Percentage o f mean 0) c o n c e n t r a t i o n change by t h e o v e r a l l emission r e d u c t i o n scenarios 50 % NOx 50 X UOC 50 E NOx, VOC
-
-
+ 1.1
36.4 53.0 44.5
+ +
3.8 28.9
56.0
-
1.3
-
-
-
4.2 10.0 15.7 8.0 ~~
Episode 11: PHOXA r e g i o n West-Germany The Netherlands Mean Peak value i n PHOXA
+ 0.3
42.9 49.0 52.9 65.0 ~
Episode I11 PHOXA r e g i o n West-Germany The Netherlands Mean Peak value i n PHOXA
+
8.2 10.6
-
7.7
-k
~
-
50.8 57.4 78.1 97.0
-
4.6 12.2 9.1
-
5.0
-
-
8.0
-
4.4 ~~
-
~
-
+
1.4 1.4 15.9
~
~~
3.5 5.2 3.9
-
__
+
3.2 1.1 1.6
-
8.0
-
6.5 12.0 18.7 10.0
7.3 12.0 12.0 14.0
The d i f f e r e n t b e h a v i o u r o f t h e t h r e e e p i s o d e s d e p e n d s o n t h e l o c a t i o n o f t h e a r e a o f c a l c u l a t e d maximum o z o n e c o n c e n t r a t i o n s . I n e p i s o d e I a n d I 1 o z o n e maxima w e r e c a l c u l a t e d p a r t l y o v e r u r -
b a n / i n d u s t r i a l i z e d areas,
i n e p i s o d e I 1 1 t h e o z o n e maxima o c c u r e d
g e n e r a l l y over r u r a l areas. SUMMARY AND CONCLUSIONS I t i s f o r t h e f i r s t t i m e t h a t i n t h e framework o f t h e PHOXA programme a E u r o p e a n d a t a base, complex l o n g - r a n g e
suitable for the application of
d i s p e r s i o n models,
has been set-up.
means i t became p o s s i b l e t o u s e a n E u l e r i a n m o d e l , model,
t o s i m u l a t e p h o t o c h e m i c a l smog e p i s o d e s .
By t h i s
the RTM-I11
The m o d e l r e s u l t s
f o r t h r e e s e l e c t e d photochemical episodes and t h e comparison of model r e s u l t s w i t h measurements d e m o n s t r a t e d t h a t t h e R T M - I 1 1 model s i m u l a t e d q u i t e w e l l t h e observed long-range
increase o f
ozone c o n c e n t r a t i o n s d u r i n g e p i s o d e s as w e l l a s i t s a v e r a g e t r e n d
645 and l e v e l .
Peak ozone c o n c e n t r a t i o n s ,
The a p p l i c a t i o n o f t h e R T M - I 1 1
however,
were u n d e r e s t i m a t e d .
m o d e l on h y p o t h e t i c a l e m i s s i o n
s c e n a r i o s p r o v e d t h e r e a s o n a b l e r e s p o n s e o f t h e model t o a l t e r a t i o n s i n emission data.
I n a l l e m i s s i o n r e d u c t i o n s c e n a r i o s ozone
maximum c o n c e n t r a t i o n s e x p e r i e n c e d a s t r o n g e r d e c r e a s e t h a n averaged concentrations. The i n v e s t i g a t i o n o f t h e r e d u c t i o n o f h o u r l y ozone maxima w i t h the RIM-I11
model i s s u f f i c i e n t f o r p h o t o c h e m i c a l e p i s o d e s .
i n v e s t i g a t i o n o f l o n g - t e r m a v e r a g e d ozone c o n c e n t r a t i o n s ,
The
however,
demands t h e i n c o r p o r a t i o n o f t h e p h o t o c h e m i c a l r e a c t i o n s o f t h e f r e e atmosphere.
The R T M - I 1 1 model i s n o t y e t d e s i g n e d f o r l o n g
term c a l c u a l t i o n s . W i t h r e g a r d t o t h e e v a l u a t i o n o f t h e e f f e c t o f e m i s s i o n red u c t i o n measures on t h e s h o r t - t e r m
formation o f oxidants,
i t can
be confirmed:
-
q u a l i t a t i v e s t a t e m e n t s can be met w i t h r e a s o n a b l e c o n f i d e n c e , q u a n t i t a t i v e statements a r e merely p o s s i b l e w i t h r e s e r v a t i o n s m a i n l y due t o t h e u n c e r t a i n t i e s i n t h e i n p u t d a t a bases.
I t s h o u l d be emphasized t h a t t h e P H O X A m o d e l l i n g a p p r o a c h i s w e l l e l a b o r a t e d f o r t h e t r e a t m e n t o f r e g u l a t i v e measures.
I f the
e v a l u a t i o n scheme f o r p h o t o o x i d a n t s was f o r m u l a t e d i n t h e E C E c r i t i c a l l e v e l c o n c e p t i t s h o u l d be p o s s i b l e t o i d e n t i f y a n d o p t i m i z e e f f e c t i v e a b a t e m e n t measures. The a p p l i c a t i o n o f t h e PHOXA m o d e l i n g i n s t r u m e n t s i m u l t a n e o u s l y p o i n t s t o f u r t h e r necessary improvements i n o r d e r t o s e c u r e t h e r e l i a b i l i t y o f the findings.
Objectives o f t h i s k i n d are f i r s t
of all: ( i ) t o e x a m i n a t e t h e e m i s s i o n d a t a bases,
VOC and t h e i r s p l i t t i n g i n t o CBM-IV
e s p e c i a l l y of
the
r e a c t i v i t y classes;
( i i ) t o a c c o m p l i s h more s e n s i t i v i t y s t u d i e s u s i n g t h e R T M - I 1 1 model w i t h i m p r o v e d d a t a b a s e s and f i n e r s p a t i a l r e s o l u t i o n a n d t o i n v e s t i g a t e t h e r e a s o n f o r e p i s o d i c peak u n d e r e s t i m a t i o n s ; ( i i i ) t o d e v e l o p and r e a l i z e i n t e r r e g i o n a l measurement camp a i n g n s f o r p r e c u r s o r s and o x i d a n t s i n o r d e r t o v e r i f y t h e complex model c a l c u l a t i o n s . ( i v ) t o f u r t h e r develop d i s p e r s i o n models i n o r d e r t o s i m u l a t e l o n g t e r m o x i d a n t c o n c e n t r a t i o n s i n t h e b o u n d a r y l a y e r and i n t h e f r e e atmosphere.
646
On t o p o f t h i s i t h a s t o b e k e p t i n m i n d t h a t a c o m p r e h e n s i v e abatement s t r a t e g y f o r a i r p o l l u t i o n c o n t r o l s h o u l d t a k e i n t o a c c o u n t p h o t o o x i d a n t s as w e l l as a c i d i c s p e c i e s i n s h o r t - t e r m and l o n g - t e r m s i t u a t i o n s .
Appropriate state-of-the-art
modeling
t o o l s f o r t h e a p p l i c a t i o n i n t h e framework o f c o n t r o l s t r a t e g i e s a r e a l r e a d y u n d e r p r e p a r a t i o n a n d t e s t i n g i n t h e PHOXA programme. REFERENCES
1 C. L u d w i g , H . M e i n l , i n P r e p r i n t s o f t h e 1 6 t h I T M on A i r P o l l u t i o n M o d e l i n g a n d i t s A p p l i c a t i o n , L i n d a u , FRG, A p r i l 6 - 1 0 , 1987. P.J.H. B u i l t j e s , i n P r o c . EPA-OECD I n t . C o n f . o n 2 S . Zwerver April Long-Range T r a n s p o r t R e s e a r c h , EPA T r i a n g l e P a r k , U.S.A., 1985. 3 US-EPA ( E d i t o r ) , P r o c . EPA-OECD I n t . C o n f . o n Long-Range T r a n s p o r t Models f o r P h o t o c h e m i c a l O x i d a n t s and T h e i r P r e c u r s o r s , EPA-600/9-84-006, R e s e a r c h T r i a n g l e P a r k , U.S.A., 1984. 4 D.A. S t e w a r t , R.E. M o r r i s , S.D. R e y n o l d s , F i n a l R e p o r t SYSAPP-87/ 030, S y s t e m s A p p l i c a t i o n I n c . , San R a f a e l , U S A , 1 6 0 p., F e b r u a r y 24, 1 9 8 7 . 5 J. P a n k r a t h , R . S t e r n , P. B u i l t j e s , i n G r e f e n , L o b e 1 ( E d i t o r s ) , E n v i r o n m e n t a l M e t e o r o l o g y , R e i d e l P u b l . Comp., D o r d r e c h t , 1 9 8 7 . 6 R . M . S t e r n , P.J.H. B u i l t j e s , i n ECE/WMO-EMEP W o r k s h o p on Mod e l l i n g T r a n s f o r m a t i o n Processes and T r a n s p o r t o f A i r P o l l u t i o n w i t h S p e c i a l R e f e r e n c e t o N i t r o g e n O x i d e s , Potsdam, GDR, M a r c h 21-24, 1988. 7 P. B u i l t j e s , R . S t e r n , 5. R e y n o l d s , i n P r e p r i n t s o f t h e 1 6 t h I T M on A i r P o l l u t i o n M o d e l l i n g and i t s A p p l i c a t i o n , Lindau, FAG, A p r i l 6-10, 1 9 8 7 .
647
T.Schneider et al. (Editors), Atmospheric Ozone Research and its Policy Implications 1989 Elsevier Science Publishera B.V.,Amsterdam -Printed in The Netherlands
CALCULATION OF LONG TERM AVERAGED OZONE CONCENTRATIONS
1 Frank A.A.M. DE LEEUWl, H.Jetske VAN RHEINECK LEYSSIUS and Peter J.H. BUILTJES2 'National Institute for Public Health and Environmental Protection, P.0.Box 1, 3720 BA, Bilthoven (The Netherlands) 'MT-TNO, Department of Netherlands)
Fluid Dynamics, P.0.Box 342, 7300 AH Apeldoorn
(The
ABSTRACT Seasonal averaged ground level concentrations for ozone have been calculated for the Netherlands by means of a lagrangian long-range transport model. The calculations indicate that the influence of European anthropogenic emissions of nitrogen oxides (NO ) and volatile organic compounds (VOC) on the growing season, day-time averzged (may to September, 10-17h) ozone concentrations in the Netherlands is small. A European VOC emission reduction will lead to a reduction in growing season averaged ozone and oxidant (sum of O3 and NO ) concentrations. A reduction of European NO emissions leads to a reduction 8f oxidant concentrations, but in areas xwith a high NOx concentration such as the Netherlands, an increase in ground level ozone concentrations is predicted due to a shift in the photostationary equilibrium. When VOC emission reductions are combined with NO emission reductions a slightly decreased groundlevel ozone concentration is eftpected.
INTRODUCTION Much attention is given to the calculation of peak-concentrations of ozone during episodes with photochemical air pollution, see for example the number of papers presented at this symposium. Although it is known that short-term exposures to high ozone levels causes adverse effect both on human health as on vegetation, there is a growing evidence that damage is also
caused by
a
long-term exposure to moderate levels. Growth and yield reduction agricultural crops is induced by ambient ozone concentrations above 60 pg during
the
growing season
(ref. 1).
for -3 m For natural vegetation strong visual
effects can be avoided when growing season averaged levels do not exceed 100 pg m-3; the no-effect level is estimated to be ca. 50 pg m-3 (ref. 2). In contrast to the peak values of ozone, which are predominantly determined by processes within the planetary boundary layer, the long-term averaged concentrations at groundlevel strongly depend on the concentrations in the free troposphere (ref. 3). Hodel studies to the influence of anthropogenic emissions of volatile organic compounds (VOC) and nitrogen oxides (NOx) on the ozone production and loss processes therefore requires the application of
648 global tropospheric models (see e.g. ref. 4). From modelcalculations the influence of precursor emissions
this type of on the trend of
tropospheric ozone is deduced. For increased release rates of 3% year-' for C O , NOxl and VOC and 0.5% year-' for CH4 an increase in tropospheric ozone of 1% year- has been estimated (ref. 4). The spatial resolution in the global 2-D models is generally too low to provide information on a continental scale. As zonally averaged concentrations are calculated the influence of European emissions on the concentrations in Europe, and more particularly in the Netherlands, can not be estimated. In order to improve the information on an European scale in this paper a model for the calculation of long-term averaged concentrations in the planetary boundary layer is presented. By means of this model the influence of European anthropogenic emissions on the growing season, day-time averaged (may to September, 10-17h) concentrations in the Netherlands is examined. MODELDESCRIPTION Groundlevel concentrations are calculated by means of a lagrangian longrange transport model. In this receptor oriented trajectory model two air parcels - one representative for the mixed layer, the other representative for the polluted layer above the mixed layer (aged smog layer) - are followed along 96h back trajectories. Long-term averaged concentrations are estimated in a brute-force method, i.e. by averaging the concentrations
calculated
for
four arrivaltimes per day for all days in the considered period. Essentially the long-term model (called MPA-LT model) presented in this paper is a repeated
application of the earlier developed episodic model (HPA-model, ref.
5). The model includes emissions, non-linear atmospheric chemistry, deposition, exchange between boundary layer and free troposphere and fumigation between mixed layer and aged-smog layer. The boundary conditions (initial concentrations at the start of the trajectory and the concentrations in the free troposphere) are obtained from a two-dimensional tropospheric model (ref. 4).
The pressure
long-range transport level which
were
is
described by
obtained
from
trajectories on the 850 mbar the
Western
Meteorological
Synthesizing Centre of ECE/WEP in Oslo. For 1980 information is available for four arrivaltimes per day (00, 06, 12 and 18 GMT) for four the the
receptorpoints
in
Netherlands (see figure 1). Additional meteorological information along trajectory was partly obtained from routine measurements in the
Netherlands
assuming persistence along the trajectory. Other parameters, such
as global radiation, mixing height and stability, were calculated by procedures.
standard
649
Fig. 1. Location of receptorpoints. The emissions of NOx, VOC and SOp are based on the inventories of ECE/EMEP (ref. 6-7); for countries within the PHOXA-area total numbers were adjusted in accordance to the PHOXA-inventory (ref. 6). For the Netherlands and direct surroundings emissions are based on the more detailed TNO-inventory (ref. 9 10).
Dry deposition in the mixed layer is modelled by a deposition velocity v g according to: l/vg The
-
ra + rb + rc (1) aerodynamic resistance ra and the quasi-laminar boundary resistance rb
depend on atmospheric stability (ref. 11). The surface resistance rc is different for every component and depends on the nature and conditions of the surface. There is no deposition of O3 and NO2 on water surfaces. In the present modelversion, where emphasis is laid on the calculation of ozone- and oxidant-concentrations, wet deposition is neglected. In earlier calculations by means of the episodic version of the model. it was found that the influence of wet deposition and concentration is small.
in-cloud oxidation on the oxidant
A vertical exchange of pollutant mass between mixed layer and aged-smog layer is induced by variations in the mixing height (fumigation). Processes
which account for the exchange between the plnnetary boundary layer and the free troposphere are summarized by Builtjes (ref. 12). Among these processes cloud venting (especially cumulus-nimbus) and vertical transport in high and low pressure
areas are
the most
important ones.
For long-term averaged
exchange not only the effectiviness of the process but also the frequency of occurance must be considered. As in the Netherlands cumulus-nimbus is observed
650 only ca. 4% of the time
-
for Europe as a whole this is ca. 8%
-
cloud venting
is initially neglected. However, further research is needed to prove the (in)correctness of this assumption. The downward flux in a high-pressure area is
modelled by a vertical windvelocity which is assumed to be proportional to
the pressure and range from 0 cm s-'
for pressures below 1015 mbar up to 1
cm
9-l for pressures of 1045 mbar or more. The chemical
reactions which
take
place
in both
air
parcels
during
transport are described by a slightly modified version of the CBM-IV mechanism (ref. 13). As mentioned above in-cloud oxidation is in the present version not yet included.
RESULTS A summary of the observed and calculated groundlevel growing season daytime averaged (may to September, 10-17h) concentrations for 1980 is given in table 1 for the reference situation. As NO is to a large extend emitted at groundlevel (emissions from traffic, space heating) the NOx concentration decrease with increasing height. The modelled mixed layer averaged concentration systematically underpredictes the groundlevel concentration. Although a correction, depending on the emission density in the receptor area modelled groundlevel and atmospheric stability, is applied, the NoX concentrations strongly underpredict thp measurements. The effects of a too low NO concentration on the production of ozone on an European scale is X probably small, the local influence is much larger. This is shown by the overestimation of the O3 concentration depicted in table 1. Due to a shift in the photostationary equilibrium an underestimation in NOx concentrations will The result in an overestimation of ozone concentrations. concentrations (Ox, sum of 0 and NO2) are slightly overpredicted. 3
oxidant
TABLE 1 Observed
and
calculated groundlevel growing season day-time averaged (may to
September, 10-17h) concentrations for 1980 (in ppb) for four receptorpoints in the Netherlands.
1 obs
NO NO NO: ox O3
2.0 7.5 9.6 38.8 45.6
2 calc 0.3 1.8 2.2 51.8 53.7
obs 4.9 9.1 14.3 39.8 47.3
receptorpoint 3 calc obs calc 1.0 3.9 4.9 52.2 56.1
3.4 1.2 11.4 4.7 14.9 6.0 40.6 49.6 51.6 54.3
4
obs 5.0 12.2 17.3 41.6 53.6
calc 1.4 5.2 6.6 52.5 57.7
651 The temporal behaviour of calculated NO, and Ox concentrations is in fair agreement with the measurements, see figure 2. Episodes with enhanced Oxconcentrations
are
well
concentrations. For NO
predicted by
the
model,
both
in
concentrations a reasonable correlation
time in
as
in
time
is
found but the underprediction by the model is clearly seen. A least-squares analysis of observed and measured
concentrations
arrival ttmes (about 600 datapoints) showed for ozone correlation coefficient of 0.6-0.7; for oxidant 90-97% of concentrations
are
and the
for
all
oxidant a calculated
within a factor of two of the measurements, for ozone 60-
73% is calculated within this range. Validation
of
other
components involved in the chemical scheme is hardly
possible due to the paucity of measured data, It can only be stated obtained
results
are
not
in disagreemenc with
that
the
measured or modelled data
presented in the literature. In several sensitivity runs the influence of European anthropogenic VOC and NOx emissions on the growing season averaged concentrations in the Netherlands is investigated. An overview of the emission scenarios is presented in table
2. The relative changes in Ox, NOx and O3 concentrations compared to the reference run are given in figure 3. In all calculations a constant CH 4 background concentration is assumed. The natural emissions and the CO emissions, both natural as anthropogenic, are kept constant. TABLE 2 Reductions ( % ) on calculations
European anthropogenic emissions
run number
NoX
7
30 50 70 0 0 30 50
8
50
on
scenario
voc 0 0 0 40 70 40 40 70
As on a local scale the underestimation of NO effect
in
emission reduction
1 2 3 4 5 6
pronounced
applied
the
O3
concentrations
may
have
a
concentrations due to the NO/03 titration, a
correction is applied on the modelled ozone concentrations. In this procedure the relative changes in Ox and NOx concentrations as predicted by the model are applied on the measured concentrations. The O3 concentration is now
652
mcetnet-data:
5
3 1 1
1980
iuli
t-model :
10
juli ippbi
550
I(=
15
i
~
=4 4 5 0
20
25 30 t.ijd (dagen)
1980
; tr a380
grondconcanti-stir;
15
5
10
refel entierun
50
1s
20
30 t i j d rdagen)
25
Thu flar 24 1 0 : 4 9 : 8 5
(ppb)
; tra300
19
gr ondconc e n t r a t I e s
t i j d fdagcn) r e f e r e n t 1erun
Thu M a r 2 4 1 0 : 4 9 : 0 5
Fig. 2. Observed (top) and calculated (bottom) groundlevel Ox and NOx(ppb); july 1980, receptorpoint 3.
15
concentrations
of
653
change in Ox concentration
0
-5 - 10
I
d
1
2
3
4
5
6
7
8
change in NOx concentration
40
I
0
-40
I -80
'
1
2
3
4
5
6
7
8
change in ozone concentratlon
0
- 10
-20
'
1
2
3
4
5
6
7
8
run number Fig. 3. Calculated changes in Ox, NO
X
run: run numbers correspond shaded bar receptorpoint 3. reference
and O3 concentrations to
relative
to
the
table 2; closed bar receptorpoint 1,
654 recalculated
using
an
effective
value for the photostationairy equilibrium
constant which was obtained from the measurements. From figure 3 it is seen that the relative changes in Ox and NO concentrations differ only slightly for the two receptor areas. Larger differences are found in the changes in O3 concentrations due to differences in local NOx emission density.
A
reduction
in NO
Ox concentrations, increase. The
emissions in Europe (scenario 1-3) leads to decreasing
but
reduction
in
the
Netherlands
the
ozone
concentration
will
in Ox concentrations is too small to compensate the
ozone increase resulting from a shift in the photostationary equilibrium. However, in more remote areas with a low NO, emission density i t is expected that the decrease in Ox concentrations will lead to decreasing ozone levels. In global tropospheric models a reduction in yearly averaged, zonally averaged ozone concentrations is calculated in case a NOx emission reduction is assumed (ref. 4). For a 70% reduction in NOx emissions an ozone reduction is found in the less polluted part of the Netherlands but in the more polluted Rijnmond area (receptorpoint 3) the ozone concentrations still increase. Reduction in European VOC emissions (scenario 4-5) results in a lowering of both
Ox
and
O3
concentrations
in
the Netherlands. The NO
concentrations
increase in this situation. For reductions in the order of ten of VOC
emission
reduction
is more
effective than a NO,
percents
lowering the Ox concentrations. For strong -reductions (about 70%) VOC and emission reductions are equally effective. For a concurrent reduction in NOx and VOC
emissions
a
emission reduction in
(scenario
NOx
6-8) the
ozone increase due to NOx emission reduction is compensated by the VOC emission reduction. The net result is a reduction in ozone levels of a few percent. In all scenario calculations the emissions outside Europe were not changed. In a
last
scenario run it was assumed that anthropogenic emission in Europe
were reduced by 40% for VOC and 30% for NOx (comparable with scenario 6 ) but this reduction is counterbalanced by increasing emissions outside Europe in such a way that the total global emissions remain the same. For this scenario the Ox concentrations in the Netherlands decrease by ca. 5% but the ozone concentrations are nearly invariant ( -0.5% for receptorpoint 1. +1.7% for receptorpoint 3 ) . Global emissions have to be stabilize to avoid a further increase in ozone concentrations. CONCLUSIONS The influence of European anthropogenic emissions of VOC growing
season day-time averaged
and
NO,
on
the
ozone concentration in the Netherlands is
small. In all calculations a reduction on an European scale in VOC and/or NOx emissions results in a decrease of Ox levels (sum of O3 and NO2). However, in
655 the NOx-scenarios increasing groundlevel ozone concentrations are found in the Netherlands but in more remote areas with low NOx concentrations a reduction in ozone concentrations is expected. For moderate reductions (about 50% or less) a VOC emission reduction is more effective than a NOx emission reduction in lowering the Ox concentrations. For strong reductions (about 70%) VOC NO emission reductions are equally effective.
and
X
Strong visual effects on vegetation is expected for growing season averaged ozone concentrations of 100 pg The measured values in the Netherlands are ca. 85 pg
Global emissions have to be
stabilized
to
avoid
a
further
increase in groundlevel ozone concentrations. REFERENCES 1 A.E.G. Tonneijck, Evaluation of ozone effects on vegetation in the Netherlands. Third US-Dutch International Symposium, Atmospheric Ozone Research and its Policy Implications, Nijmegen. the Netherlands, May 9-13, 1988. 2 T. Schneider and A.H.M. Bresser (Editors) Dutch priority programme on acidification; interim evaluation. Report 00-04, RIVM, Bilthoven, the Netherlands, 1987. 3 R.M. van Aalst, Emissions, chemical processes and deposition. In: R.Guicherit, J. van Ham and A.C. Posthumus (Editors) Ozone, physical and chemical changes in the atmosphere and its effects. Kluwer, Deventer, pp8491, 1987. 4 I.S.A. Isaksen and 0. Hov, Calculation of trends in the tropospheric concentrations of 0 CO, CH4 and NOx. Tellus, 39B, 271-285, 1987. 5 F.A.A.M. de Leeuw, &e Dutch Aerosol Study: modeling aspects. In: S.D. Lee, T. Schneider, L.D. Grant and P.J. Verkerk (Editors) Aerosols, research, risk assessment and control strategies, Lewis Publishers, Chelsea, pp301315, 1986. 6 A. Eliassen, 0. Hov, I.S.A. Isaksen, J. Saltbones and F. Stordal. A lagrangian long-range transport model with atmospheric boundary layer chemistry. J. Appl. Meteorology, 21, 1645-1661, 1982. 7 A. Eliassen and J. Saltbones, Modelling of long-range transport of sulphur over Europe: a two-year run and some model experiments. Atmospheric Environment 17, 1457-1473, 1983. 8 J. Pankrath, Photochemical oxidant model application within the framework of control strategy development in the Dutch/German joint project PHOXA. Third US-Dutch International Symposium, Atmospheric Ozone Research and its Policy Implications, Nijmegen, the Netherlands, May 9-13, 1988. 9 H.J. Huldy and C. Veldt, Air Quality Management System VI: emissions. CMPreport 80/8, TNO, Delft, 1981. 10 C. Veldt, Air Quality Management System XLVI: current emissions of volatile organic compounds, CMP-report 85/01, TNO, Delft, 1985. 11 M.L. Wesely and D.D. Hicks, Some factors that affect the deposition rate of sulphur dioxide and similar gasses on vegetation. J. Air Pollut. Control ASSOC. 27, 1110-1116, 1977. 12 P.J.H. Builtjes, Interaction of planetary boundary layer and free troposphere. Third US-Dutch International Symposium, Atmospheric Ozone Research and its Policy Implications, Nijmegen, the Netherlands, May 9-13, 1988. 13 G.E Whitten and M.W. Gery, Development of CBM-X mechanisms for urban and regional AQSMs. System Application Inc., 101 Lucas Velly Road, San Rafael, CA94903, USA, 1986.
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T. Schneider et al. (Editors),Atmospheric Ozone Research and its Policy Znrplicatio~ 0 1989 Elsevier Science Publishers B.V.,Amsterdam -Printed in The Netherlande
MODEL CAL(XILATI0NS
657
OF OZONE IN THE ATUXPHWIC BWNDARY LAYER OVER EUROPE
0. HOV Norwegian Institute for Air Research, P.0.Box 64, N-2001 LillestrQm (Nomay1 ABSTRACT Ozone episodes in the atmospheric baundary layer over Europe in the sunner are superimposed on a background level which has an early aumner maximum and which increases 1-3% annually. The Norwegian long-range transport model based on trajectory calculations with chemistry, is used to calculate the concentrations of ozone at 14 rural sites in Europe during the ozone episode 28 May-3 June 1982. The effects of changing physical parameters and emissions of nitrogen oxides and volatile organic canpounds, are discussed.
INTRODUCTION There are canprehensive networks of rural ozone measuring instnnnents in many European Countries and in North America. It is well established that the ozone concentrations can be elevated in episodes during the sumner half year in anticyclonic weather situations. On a different time scale, ozone near the ground Over Europe has an annual cycle with a late spring to early sumner maximum and a mid winter minimum. The monthly mean concentration in the spring maximum was about 45 ppb at R6rvi.k south of Gothenburg in Sweden for the 1980-1983 period and about 25 ppb in the winter minimum (ref. l), while the maximum hourly ozone concentration at t h i s site in 1985 was 107 ppb (ref. 2). The annual variation of ozone at Relxvik for clean air oompared to polluted air situations, judged fran the particle counts, showed that in polluted air the spring maxirmrm is higher and is delayed by more than one month, while in clean air the spring maximum canes earlier and is laver than the average for all measurements (ref. 1). This indicates that there is an anthropogenic influence on the ozone concentrations measured at t h i s rural site throughout the year. Historical records of ozone measurements in Europe and North America indicate that in the last part of the nineteenth century the values were anly about half of the mean of surface ozone measurements taken in the same geographical regions during the last 10-15 years (refs. 3, 4 ) , while measurements Over the last decsdes in Europe support a linear increase in ozone by 1-3%/a (refs. 5-7). Ozone episodes in the atmospheric boundary layer are therefore superimposed on a background level which is slowly
658 increasing. Tne change i n the backgraud concentration is probably con( r e f . 8). t r o l l e d by changes i n the emissions of nitrogen oxides (-) Both changes i n the emissions of volatile organic canpounds (Voc) and Nox are important for changes i n episodic ozone, as w i l l be further discussed i n t h i s paper. MODEL DESCRIPTION Model calculations using the Norwegian lagrangian long-range transport model with CM6-X chemistry (ref. 9) for the time period 28 May 1982, 1200 W , to 3 June 1982, 1200 W, were carried out to 14 receptor points within the grid area, see Figure 1. Calculations were carried o u t every 6 h M, i . e . at arrival times oo00, 0600, 1200 and 1800 @TF a t each site.
Fig. 1. Map of PlIEP grid and 96 h back trajectories for 28 May, 1 and 3 June 1982, 1200 W,t0 (1) Illmitz, A u s t r i a , (2) Langenbrlgge, (3) Schauinsland and (4)Deuselbach, a l l FRG, ( 5 ) Ri&, Denmark, ( 6 ) Rl)rvik, Sweden, (7) Langesund and (8) Jelm, Norway, (9) Sappe-r and (10) Waarde, The N e t h e r l a n d s , (11)Colders, France, (12) Bottesford, (13) Sibton and (14) Stoddey, UK.
659 The model has been described in sane detail previously (refs. 10, 11). The pollutants are assumed to be cunpletely vertically mixed throughout the boundary layer which has a variable depth along the 96 h long 850 mb trajectories. No mass transport takes place through the top of the wellmixed layer. Lateral diffusion is not treated explicitly, but the emission data are given in a 150 km grid where finer details than 150 km in the concentration fields are smoothed out. During transport, pollutants are emitted into the air parcel according to the emission maps for NOx and VOC. Instantaneous concentrations are predicted upon arrival of a trajectory. The horizontal resolution of the concentration fields is determined by the choice of emission grid and density of trajectory arrival points. The canbined effects of vertical wind shear and diffusion due to heat exchange is difficult to handle in lagrangian models. Radiosonde observations are used to estimate the mixing height field over Europe at 1200 C X F every day. Objective analysis of temperature, relative humidity and absolute humidity are carried out at OOOO and 1200 in the 150 )an grid, as vertical averages between the surface and the 850 mb level. The temperature is used to evaluate temperature-dependent reaction rate coefficients. The relative humidity is used as a rough indication of cloud cover, which influences the photodissociation rates. Dry deposition velocites for 1 m above the ground were taken for ozone as 0.5 m / s for daytime over land, 0.05 m / s for nighttime over land and 0 over sea, for NO2 0.5 m / s over land, 0 over sea, for HN03 1.0 cm/s, PAN 0 . 2 m/s. To arrive at a model where average boundary layer concentrations are calculated rather than the concentration at 1 m, the deposition velocities at 1 m for 03,NOz and PAN were simply reduced by 50%. Detailed calculations for June 1985 using meteorological data fran the Numerical Weather Prediction Model at The Norwegian Meteorological Institute for surface pressure, surface stress, sensible heat flux density and temperature at 2 m height together with data for the surface roughness length
and Businger’s equations which relate the deposition velocity at the top of the surface layer (50 m height) to the deposition velocity at 1 m above the ground, show that the deposition velocity for SO2 at 50 m typically was 50-75% of the value at 1 m (ref. 12). The initial concentrations assigned at the starting point of the 96 h long trajectories can be important for the developnent along the trajectory. The integration was started with a set of wncentrations corresponding to a slightly polluted atmosphere, with the removal processes in equilibrium with Nihc and VOC emissions at 10% of the average emissions for Western Europe.
660 The
emissions of
Nox
estimated by the PHOXA-project f o r the ozone
episode in late May 1982 for the part of the g r i d RTM-I11
model
area
covered by
the
13) were found to be about the double of the emis-
(ref.
sions estimated in PlIEP f o r the PHOxA-arsa and for that time of t h e year ( r e f . 12), while the VUC-emissions estimated by PHOXA w e r e canparable with the emissions estimated in connection with model work i n (ref. 10). The doubling of Nox emissions estimated by the PHOXA-project f o r t h e l a t e May 1982 episode wmpared to the emissions estimate f o r t h a t time of the year, w a s applied throughout the PZEp grid, whlle t h e voc emissions were kept approximately as in r e f . 10. RESULTS AND DISCUSSION I n the t i m e period
28 May-3
June 1982, there w a s a high pressure
system located Over north Europe w i t h its center Over Denmark on 30 May 1982, moving eastward and w i t h its center Over E a s t Europe on 2 June. The wind speeds were law, and the maximum hourly ozone concentration recorded w a s about 160 ppb, i n the N e t h e r l a n d s on 1 June. I n Figure 1 is shown 4 day back t r a j e c t o r i e s to the 14 receptor sites for 1200 GWT on 28 May, 1 and 3 June 1982, while i n Figure 2 is shown the 1200 GWT mixing height f i e l d f o r 31 May 1982.
MIXING HEIGHT
24 6 8101214161~0eTzli2~~~~~~8 height f i e l d i n metres f o r 1200 m, 31 May (Contours f r a n 204 to 2492 m i n i n t e r v a l s of 458 m. )
Fig. 2.
Mixing
1982.
661
The measurements of ozone are made near the ground surface, usually only one or a few metres above the pund. This means that the measured concentrations usually are significantly reduced at night through ground removal below the noctural inversion and by local emissions of NOx becoming trapped in the shallow ncctural mixed layer. On the other hand, in the model a concentration representative of a layer with height canparable to the M o n mixing height the day before, is calculated at night. This concentration is only weakly influenced by ground removal at
night, and therefore the calculated diurnal variation of O3 is usually smaller than the measured. It should be kept in m i n d that for measured and calculated ozone concentrations, only the day time values when the atmospheric boundary layer is well mixed, are really canparable. In Figure 3 is shown the caparison of calculation and measurement for 4 sites where the agreement was satisfactory. Sane sites (in particular Colaniers and Illmitz) showed a poor agreemant between measured and calculated ozone concentrations. The calculations with the choice of physical and chemical parameters giving the results shcun in F i g . 3, were canpared with the results of calculations where sane of the most important parameters were altered. In Table 1 is given an indication about the changes calculated in the ozone concentrations when the temperature, mixing height, cloud cover, ground deposition velocities or initial conditions were changed. It can be seen that the parameter changes all influenced the ozone ooncentrations significantly. The degree of change canpared to the reference case can be evaluated fran the b o t h 3 lines of Table 1; increasing T by 2% increases the 03-levels in general less than 10 ppb, 50% reduction in mixing height reduces O3 by typically 10 ppb, a clear sky assumption causes O3 to go up nearly 10 ppb, deposition reduced a factor of 2 increases O3 le8S than 10 ppb, reducing the initial concentfations significantly reduces O3 between 10 and 20 ppb (canpared to an initial concentration of 32 ppb in the reference case). Calculations were carried out to see haw the concentrations of O3 at the 14 receptor sites changed during the 28 May-3 Jue 1982 perid with changes in the emissions of NOx and Mc. Uniform emission changes were carried out throughout the grid.
662
LANGESUNO m
I
1
J
I
SAPPERMEER
1
I
I
y
g I30
<
I
1
I
I
g I!O
83
0
y 100
rh 70
c
90
6C
80
50
70 60
40
50
30
40 30
20
20
10
10
0 1
2
3
4
5
6
7
DAY NUMBER [START ING U ITH 28 W.Y 1982I
BOTTESFORD
1
2 3 4 5 6 7 DAY NUMBER ISTARTING UlTH 28 HAY 1982)
1
2 3 4 5 . 6 1 DAY NUKBER ISTARTlFtG U l T A 28 I?!Y I98?)
DEUSELBACH
DAY NUHBER ISTART!NG UlTH 28 MAY (982)
Fig. 3. Measured (full line) hourly ozone concentrations and calculated values every 6 h (stars) for 28 May-3 June 1982 for Langesund (south w a s t of Norway), S a(The Netherlands), Bottesford (UK) and Deuselbach (FRG).
G63
TABLE 1 Number of cases (out of 25) with ozone costcentrations calculated to exceed 60 ppb for each of the 14 sites and as a total for the trajectories arriving at the 14 sites e v e q 6 h fnm 28 May 1200 m to 3 June 1982, 1200 C3W (350 altogether), for the refcase, 2% increase i n absolute temperature, 50% reduction in mWng height, clear sky, deposition reduced by 50% and initial precursor axcentrations reduced by 90% (Et,o/lO). See Fig. 1 for explanation of site nmbex-8. Site m
1
Parameter change reference T*l .02 ynix/2 clear sky vg/2 Et=O/lO reference, 0 >50 ppb ference, 0 >70 ppb Aference, O3 >80 ppb
A
8 11 8 14 14 4 17 1 2 4
-0
TABLE 2 Percentage of trajectories with more than 60 ppb 0 at the arrival point for the sites in each of 4 geographical areas and fbr the sum of those sites. Time period 28 May 1200 M - 3 June 1982 1200 m (25 trajectories per site). See Fig. 1 for explanation of site nurnbers. Description A N O x ( % ) A=(%)
0 -25 -50 -62.5 -75 0 -50
-25
0 0 0 0 0 -25 -25 -25
FRG
sites vian sites sites ( 2+3+4) ( 5+6+7+8) 29.3 46.7 49.3 41.3 24.0 9.3 33.3 21.3
22.0 24.0 17.0
34.0 22.0
9.3 16.0 28.0 25.3 17.3 4.0 13.3 8.0
19.0 31.7 36.7 33.0 23.0 4.3 25.3 16.7
reduction in NOx emissions by 25% was calculated to increase O3 in all 4 geographical areas where receptor points were located. Reduction in NOx by 50% led to a further increase in O3 over the -25% case, but the increase w a s slight everywhere except in the UK. A further reduction in NOx emissions to -62.5% and then to -75% is 88en to decrease O3 mwhere. The CaSe w i t h ANDX = 50% end A W C = 0 o c Using the PlEP estimate of NDx and VOC emissions for May/June 1982, and starting A
664 f m m t h i s level of Nox emissions a further reduction in NOx
emissions
reduces O3 everywhere. The Nox emissions used in the reference case are so high that the O3 formation is suppressed (ref. 14). A reduction in VOC emissions by 25% is calculated to reduce O3 efficiently both relative to the reference case and to the case where A N O x = -50%. The decrease is dramatic in the A N o x = 0, A V O C = -25% case, which underlines the effect that very high NOx emissions has on episodic boundary layer ozone by prolonging its formation time. This leads to an increase in the probability that the boundary layer air is mixed into the free troposphere before the precursors are depleted. In the free troposphere the precursors are further diluted and take part in an efficient production of free tropospheric ozone. ACKNOWL-
This work is sponsored by the Cannission of the European Carmunities through two subcontracts with TNO, the Netherlands and by the Royal Norwegian Research Council for Science and Technology ("I?). The work has been carried out in co-operation with EMEP MSC-W at the Norwegian Meteorological Institute. REFERENCES
7 8 9 10 11 12 13 14
P. Grennfelt and J . Schjoldager, Ambio, 13 (1984) 61-67. P. Grennfelt and J . Schjoldager. Oxidant data collection in O E O Europe 1985-87 (OXIDATE). LillestrQm (NILU OR 22/87), 1987. R.D. Bojkw, J . Climate Appl. Meteor., 25 (1986) 343-352. A. Volz and D. Kley. Nature, 332 (1988) 240-242. U. Feister and W. Wannbt, J . A b s . chem, 5 (1987) 1-21. W. AttmaMspacher, R. Hartrnannsgruber and P. Lang, Meteomlo. Rdsch., 37 ( 1984) 193-199. 0. Hov, K.H. Becker, P. Builtjes, R.A. Cox and D. Kley, Air Pollution Research Report 1, CEC, Brussels, 1986. I.S.A. I~aksenand 0. H W , Tell-, 39B (1987) 271-285. G.Z. Whitten, J.P. Killus and R.G. Johnson, Modeling of auto exhaust snmg chamber data for EKMA developnent. SAI, California, 1984. A. Eliassen, 0. Hov, I.S.A. Isaksen, J . Saltbones and F. Stordal. J . Appl. Meteor., 21 (1982) 1645-1661. 0. Hov, F. Stordal and A. Eliassen. Photochemical oxidant control strategies in Europe: A 19 days case study using a Lagrangian model with chemistry. Lilles(NILU TR 5/85), 1985. 0 . Hov, A. Eliassen and D. Simpson, in I.S.A. Isaksen (Editor), -eric Ozone, Reidel, Dordrecht, 1988. P.J.H. Builtjes and E. Luken, Developnent of a strategy against photochemical oxidants, Phase VI Long-range transport. mE0, The Netherlands, 1987. S.C. Liu. M. Trainer. F.C. Fehsenfeld. D.D. Parrish. E.J. Williams. D.W. F&y, G. Htlbler and P.C. Murphy; J . Geophys R e s . , 92D (1987). 4191-4207.
SESSION X
STATIONARY SOURCE CONTROL TECHNOLOGIES
Chairmen
J.H. Blorn G.B. Martin
This Page Intentionally Left Blank
T. Schneider et al. (Editors),Atmospheric Ozone Research and its Policy Implications 0 1989 Elsevier Science Publishers B.V., Amsterdam Printed in The Netherlands
-
667
HYDROCARBONS 2000 N. Stenstra Task Force VOC 2000
Much has been said in the last few days about the effects of ozone in the troposphere on animals and plants. Although in many ways, effects cannot be separated from those resulting from mineral acid concentration, effects are nevertheless considered unacceptable. Therefore it is important that ways and means are found to reduce that ozone concentration. As far as Europe is concerned this is a continental problem. As you know the ozone forming in principle can be opposed in two different ways, one by reducing NO, emissions and two by reducing the emissions of volatile organic substances. Dutch Environmental Policy attacks the latter. Scientists among you have told us many times which VOS reductions will be necessary to achieve a negligible effect of ozone on the environment. They say 80 percent would be necessary. Apart from the fact that at this moment it is impossible to produce a quantitative justification for such a reduction it is also a fact that in practice such a very large reduction is unattainable for the time being. For practical purposes, for an intermediate period, up to the year 2000, the Ministry of the Environment in the Netherlands considers that the reduction of 50 percent compared with the base year 1981 would be necessary. In order to see whether such a reduction is possible and to Indicate how it could be achieved in 1986 a project was started named Hydrocarbon 2000. For the record it must be stated that in the context of this presentation volatile organic substances and hydrocarbons must be considered identical. Sources of volatile organic substances in the Netherlands and probably everywhere can be distinguished in a number of categories as specified in the table below together with the accompanying emissions in 1981 and 1985.
668
emissions in millions kg.
traffic industry small business domestic agriculture combustion installations TOTAL
I 1981
I 1985
200 130 83 31 24 10
190 118 80 32 24 10
478
454
I
For traffic emissions in the EEC a policy is being developed that should lead to reduction of the hydrocarbon emissions in that sector of 50 percent. Also with regard to agriculture such a procedure is being followed. Further it must be considered that in combustion installations only a very limited possibility exists to reduce the VOS emissions. As a result, the categories industry, small business and domestic emissions will have to achieve a halving of the emissions in order to achieve the overall desirable reduction of 50 percent. Project Hydrocarbon 2000 is aimed at the last three sectors. Most of the emissions result from some twenty different categories. To name a few: chemical industry, painters, metal industry, households and the oil industry. About 65 percent of those emissions were caused by the use of solvents and about 30 percent by applying paints. Consequently a large part of the reduction must be found by reducing the use of solvents generally and in the application of paints in particular. The approach of Hydrocarbon 2000 is the desire to achieve approximately a 50 percent reduction. The purpose of Hydrocarbon 2000 was to indicate the road which would achieve that reduction; developing a reduction strategy. In that respect the starting points for the Ministry of the Environment were the following: - Hydrocarbon 2000 would have to adress itself to all source categories within society. The problem of hydrocarbons is indeed one of many small contributors which together cause a large emission and that meant that many sectors of enterprises had to be considered. - Hydrocarbon 2000 would have to adress all volatile organic substances. It is true that some substances are more reactive
669 than others but in view of the international character of the ozone problem is wasn't useful to distinguish between them. - Fluorinated hydrocarbons which cause problems because of their non-reactivity in other areas and methane which is very much less reactive than heavier substances have not been considered. A combatment strategy which has as its objective that all sources are reduced by 50 percent did not appear very opportune. The possibility to reduce emissions differ from sector to sector and consequently that had to be taken into account. Another aspect of the approach of the project Hydrocarbon 2000 was the desire that the combatment strategy would have to be developed in very close co-operation with all parties concerned. In other words the purpose was to develop a strategy with the greatest percentage of consensus and which therefore could count on general support. This has been proven possible. The cooperation and concurrence has been obtained from provinces and municipalities (within the framework of the law they are responsible for applying environmental policy), the inspectorate, the Ministry of Economic Affairs and -last but not leastindustry. It will be seen that the method chosen was one, where all concerned, contributed to finding the solutions to problems within their sphere of interest from the beginning rather than reacting to solutions invented behind a desk in the Ministry. The open and interactive structure of the discussion ensured that all areas of concern could be fully ventilated and given its due weight. In this context it must be pointed out that the effectiveness of the Hydrocarbon 2000 strategy is related to the assumption that the ozone problem will be attacked at the European level. Other countries will have to achieve comparable reductions and other categories of emitters such as traffic will have to achieve comparable hydrocarbon emission reductions. Of course in formulating the measures and the goals it had to be assumed that the present knowledge of the mechanisms of photochemical reactions both concerning the part of volatile organic substances as well as the role of nitrogen oxides was essentially correct. The objective to obtain a workable strategy meant that a number of parts would have to be developed: - a Reduction plan which describes how each source of emission will have to be reduced and by what time,
670
- an Implementation plan, which indicates how various reductions will be introduced, and who will be responsible for what,
- a plan for international co-ordination which indicates how the Netherlands in an international environment will try to stimulate the reduction of the emission of volatile organic substances. During the project a need became apparent to create a so-called after care organization which, in the coming years would control and direct the introduction of the strategy and manage necessary or desirable changes. The methodology The first problem the project group KWS 2000 had to tackle was the preparation of an inventory of hydrocarbon emitting sources and the size thereof, hardly a simple task. With the help of several individual companies and trade associations nevertheless, reliable emission data could be accumulated. The next step was preparing an inventory of possible reduction measures where the aspect of cost activity was emphasized. An important aspect was that the policy should be directed as much as possible to realize preventive measures, like replacing solvents by alternative products and replacing and adapting certain processes. On top of that application of additional combatment measures like adsorption, condensation and biofiltration were seen in some cases as a solution to specific problems. From these data per association a choice was made for the measures to be taken and an assessment was made of the reduction in hydrocarbon emission that could be achieved as a result. The primary considerations in this choice were the environmental benefits to be achieved, the cost effectivity and the economic viability. These considerations were based on a number of criteria which had been formulated as an assessment basis for possible measures. The criteria included the absolute percentage-wise emission reduction, the possible infringement on the competitive position of trade associations, societal acceptability (for instance, when the composition of products was changed) sideeffects and micro economic costs. Completing the draft reduction marked the beginning of a very important phase in the project namely that of consultations. With
671
various trade associations extensive discussions were held concerning the viability of the measures and possible alternatives. Constructive discussions were held which led to adjustments in the Reduction plan. This revised plan was again submitted for comments and after including these later comments and suggestions the Reduction plan could be formulated in its definite form. It will be clear that the procedure was carefully followed and as many desires as possible were taken into account. The original plan envisaged that during this procedure at some time a choice would be made on the basis of criteria which measures should be persued and which ones should be dropped. A n objective method to guide the choice was difficult to find and therefore in consultation within the group a choice based on insight and experience was made. As it happened the result in reduction was slightly above 50 percent which removed a significant difficulty. In the meantime, discussions were held with regional government and environmental inspections about an Implementation plan and an after care organization. It will be noted that where the measures had to be paid for by industry the primary lead function in this respect was with industry. In the implementation, the significance of co-ordination with regional authorities was envisaged and thus the lead was laid with the regional governments. After substantial discussions the Reduction plan was also found acceptable to the regional government and the implemention plan and after care organization are still under discussion with the trade associations but expectations are that they can be finalized shortly. After that, in principle the strategy for Hydrocarbon 2000 will be finished. Reduction plan Although the combatment strategy consists of all plans the basis is formed by the Reduction plan in which the measures and the reductions to be achieved per trade association are indicated. The measures and reductions to be achieved are subdivided in four categories, ie; Autonomous reductions: reductions which will occur without formulating separate requirements: Examples are reduction of emissions by replacement of outdated apparatus and/ or inotallationo or reduotiono by
672 changes in the raw material composition. Certain measures : measures which can be applied without any restrictions and therefore are considered mandatory. Conditional measures : measures that can only be applied if certain conditions are met. These conditions can be that a certain combatment method is sufficiently developed or that a product formulation has to be developed.It could be the necessity of international co-ordination with regard to the measures or presence of a sufficiantly large societal acceptability. Uncertain measures : these are measures which in principle are considered achievable but some uncertainties remain, such as the economic position of the trade association at time of introduction measure (which could be some years away) or the uncertainty whether an alternative process or product can be developed at all. Clarity must exist about solving these uncertainties before the viability of the measure can be decided upon definitely. These various kinds of measures - particularly the conditional and uncertain ones for which preliminary actions have to be taken, necessitate a phasing of the introduction. Therefore the measures have been allocated over three periods of four years. For each trade association it has been indicated when the desired measures will have to be achieved. Another reason for this phase approach is that as we look further into the future, uncertainties accumulate. In 1988 it is difficult to predict what the possibilities will be in say eight years, and that implies that the Hydrocarbon 2000 strategy may have to be reviewed and adjusted with some regularity. That review will be made once every four years starting in 1992. These variations will lead to smaller or larger changes in Reduction plan. For the coming four years, the plan is just about fixed however.
673 For the coming 12 years that will result, if all conditions and uncertainties are resolved, in the following reductions for the various categories.
emissions in kton/annum 1981
2000 (KWS 2000)
chemical industry painting metal industry private households oil industry printing industry storage companies gasoline stations carspray paint installations wood conservation foodstuff rubber- synthetic materials dry cleaning metal conservation furniture- wood construction textile industry leather industry automobile trade other industry In total the reduction will follow the cause as outlined below as far as industry, small enterprises and domestic consumption is concerned. KWS
2000
-
Eniissies tot he: jaa: 2000 0res:
Oza mz
voaw
mwoor
Fig. 1. Reduction of VOS (1981-2000)
674
Implementation The various reduction objectives which have been laid down in the reduction plan will have to be realized by the various enterprises and other emitters. Many sources exist and consequently much will be required of the executive bodies for the environmental policy. It has been indicated how each measure will be implemented, that is to say: who will initiate that, what instrument will be used and when can that implementation be expected. In that way it is clear for everybody when certain actions may be expected. For the implementation preferably the choice has been for "soft" instruments: information, guidelines and adapting permits to include certain requirements. Secondly, if necessary, legislation will be introduced. Such an implemention which will have to be realized during the coming 12 years requires a good organization. For that reason a so-called after care organisation will be created, in which again close co-operation will be realized between the Ministry, industry and lower government. If that implementation goes as expected very substantial emission reduction of volatile organic substances will be realized by the year 2000 in the Netherlands. If the countries surrounding us will achieve similar reductions a considerable step will have been set in the direction of an acceptable ozone level.
T. Schneider et al. (Editors),Atmospheric Ozone Research and its Policy Implications 1989Elsevier Science Publishers B.V., Amsterdam Printed in The Netherlands
675
-
VOC CONI'ROL IN STORAGE AND PROCFSS INWSTRY
J.J. Verhoog Environmental Coordinator - ESSO Netherlands, Rotterdam Refinery
ABSTRACI-
VOC emissions from refineries, petrochemical industry and storage companies in the Netherlands were about 52.000 tons in the year 1985, Administrative loss control is not the adequate tool for an emission reduction program. A special environmental loss control is needed on the basis of the following three steps 1) Identification of all potential emission source. 2) A proper design of equipment with respect to emission control. 3) A preventive maintenance program.
INlRODUCTION The contribution to the VOC emissions in the Netherlands from storage and process industry is about 50.000 tons/year or roughly 20% of the total VOC emission level (excluding autanotive exhaust emission). A substantial part of these emissions takes place in the Rotterdam harbour area where the handling, storage and processing of hydrocarbon products (oil products and petrochemicals) is concentrated. You will find there 5 referencies, sane of them with integrated petrochemicals production, several large oil and petrochemical storage and shipping companies and a nunber of petrochemical plants. The VOC emission picture for the Netherlands as a whole has been summarized in the table below.
year 1985 (Ktons/year) Ex refineries Ex petrochem. plant Ex storage companies
14.5* 28.0 19.5 52.0
*
Process 20-40 30-50 5-15
Storage 20-40 10-30 50-70 1
Shipment 20-40 20-40 20-40 1
1985 refinery thruput 60.000 Kton/year (VOC loss = 0.026%)
1
676
ADMINISTRATIVE LOSS CONTROL VOC emission means product loss. The question arises if it is possible to control these losses as part of a general administrative loss control system. The famous gospel song learns us to count our blessings every day. In the oil and petrochemical business it certainly pays to account for your product losses, if not on a daily basis at least on a monthly basis. Occasionally this leads to a surprise. Instead of calculating a loss figure, you will sanetimes calculate a product gain. Sanetimes this f'gainll will compensate partly for a high loss in the previous month and if not you know in advance that you will have to face a high loss figure the next month. It is obvious that reducing of the measurement inaccuracy is the main challenge in the field of administrative loss control. The administrative loss figure will vary from 0.2 up to about 1 weight percent of total thruput. The estimated losses into the air were less than 0.03% for the refinery branch in 1985. In addition to air losses there are losses via effluent water or via waste disposal. Together these environmental losses are called the 'accounted for' losses, The other part, called the 'non-accounted for' losses results from measurement inaccuracies and even at a very low administrative loss figures of 0.2% of total thruput the 'non-accounted for' part of the losses is in general higher than the 'accounted for' part of the environmental product losses. The overall conclusion is: Over and above the administrative loss control there is a need for extra registration and measurement to arrive at a reliable and accurate (at least not too inaccurate) emission figure in other words a separate environmental loss control system.
ENVIROMWTAL. LOSS COMROL As mentioned before there are three VOC emission categories a) Loss from storage tanks. b) Loss fran product loading and unloading. c) Loss from process equipment and activities.
As far as the categories a and b is concerned the VOC emissions are primarily determined by the design of the equipment.
677 It is obvious that product losses €ran a cone roof tank with an open vent into the atmosphere are much higher than a well designed (and properly maintained) tank with a floating roof or an innerfloater. This also implies that emissions in the category a and b can be calculated rather accurately if all relevant parameters like product vapor pressure, storage temperature, meteo conditions, type of seal, loading velocity etc. etc. are taken into account. By several test programs these calculations have been verified by measurements so that accurate registration is possible without frequent measurements in the field. And above mentioned product losses are normally a part of the administrative loss control system as well. When we consider the category c emissions, those are the emissions related to the process activities, it becomes much more difficult. How can this category of emissions be reduced in an effective way and in what way can we follow up whether or not we are really improving the situation. This requires a systematic approach in which the following three steps can be distinguished: Step 1: Identification of all (potential) emission sources. In the first place a systematic inventory has to be made of all the losses which will or can take place. In the following list I have summarized the most important ones: 1. Vent systems into atmosphere. 2. Safety valves leaking in the atmosphere. 3 . Seals of rotating systems (pumps, compressors). 4. Valves, packing glands etc. 5. Draining of product or water with product contamination 6 . Evaporation from sewer systems. 7 . Waste water treatment. 8. Cleaning, turnaround and maintenance activities. 9. Flare systems (incomplete combustion). The above mentioned emissions are also mentioned fugitive emissions and control of something called fugitive is not easy. So one have to set priorities. For each specified situation it has to be established firstly what the main contributors are. The TNO emission registration system in the Netherlands provides general emission factors for all above mentioned types of losses.
678
Step 2 : A proper design of equipment with respect to emission control. We have done certain things in the past which we will not do anymore, In new plant designs we will not have open vent systems, most of the safety valves will be connected to a closed system (safety valve discharge header) and vessel or drum content will be drained via a closed drain header into a low point drain system. In those situations where improvements of older systems will have to be made it will be done preferably in combination with modernisation and replacement investments. A modern and well designed plant will have a low emission figure on paper (represented by a fixed amount in the administrative loss system). However a next step is needed to guarantee that the paper figures (emission factors) are and remain representative for the actual emissions. So
we now have to consider the next step.
Step 3: A preventive maintenance program. New technology will only yield good results when it goes together with a preventive maintenance program to ensure that the equipment is properly maintained and will meet its design conditions. Preventive maintenance will have a direct and an indirect impact. The direct impact is obtained by for instance replacing a packing or seal before it is worn out or at least to replace it as soon as the first leakage will occur. The indirect impact is via an increased reliability of the operations. For instance frequent repairs of pumps requires cleaning and draining activities causing extra emissions, Unit upsets will result in extra flaring and a variation in flaring load means lower combustion efficiency. The final question arises: What can we gain with all these measures? Pollution prevention pays. That is certainly true but as explained earlier, this profit is not measurable due to the inaccuracy of the administrative loss system. But although it is difficult to quantify the money figure what we gain is more than profit. Environmental awareness together with safety and industrial hygiene awareness helps to make business more healthy, more pleasant and more challenging. Or to say it in other words: It is the human factor that counts.
679
Let me finish with a final remark. I have already mentioned the word Industrial Hygiene. Especially in the chemical industry exposure monitoring programs have been developed to protect the workers from exposure by toxic vapors. High exposure will alert the organization and will start an investigation to find the source of the emission. For instance: Is there a leak into the sewer system resulting in high air concentrations in the waste water treatment unit. And when we are able to stop high exposures, we automatically stop VOC emissions. In this respect a well balanced hydrocarbon monitoring and leaking detections system can be of great help to increase awareness to stimulate preventive maintenance and to decrease fugitive emissions.
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T. Schneider et al. (Editors),Atmospheric Ozone Research and its Policy Zmplicatwna 0 1989 Elsevier Science Publishers B.V., Ameterdam - Printed in The Netherlands
NO,
681
CONTROL TECHNOLOGY FOR LARGE COMBUSTION INSTALLATIONS
J. VAN DER KOOIJ Environmental Research Department, N.V. KEMA. P.O. Box 9035, 6800 E T Arnhem (The Netherlands)
ABSTRACT Advances to the state of the art of low NO, combustion technology f o r gas and coal fired boilers offer the possibility for considerable NO, emission reduction. In the Netherlands the utilities have developed on a voluntary basis a concerted NO, Abatement Programme in order to reduce the NOx emissions of both existing and new installations. The programme also comprises a number of demonstration projects in order to assess the applicability of new techniques and to prepare for decisions on cost-effective NO, controls. INTRODUCTION Most of the anthropogenic nitrogen oxides are produced during combustion processes. These processes may occur in stationary or mobile sources. An inventory of the NO, emissions in the Netherlands is presented in Table 1 for the years 1980 and 1985.
TABLE 1 NO, emissions in The Netherlands in 10’ t/a (ref. 1). I980
1985
80 20 44 26 45
83 17 43 20 46
road tcaff ic
264
261
other t canspor tat ion
57 536
57 527
power stations re€ineries industry, combustion industty, processes Other stationary S O U C C B S
Powerstations, refineries and part of the industrial combustion belong to the category of the large combustion installations. Under the idea that 5 0 % of the industrial combustion
602
processes occur in installations w i t h a capacity larger than 50 MWth, approximately 110 ton/a NO, is produced in large combustion installations, equalling 20% of the national emissions. As t h e power stations produce 75% of these emissons, there is a good reason to confine t h e discussion to power station emissions. Another reason is that the emission standards for combustion installations are thus far not applicable to process furnaces whereas government and industry a r e cooperatively investigating the N O x emissions of these installations and the technology to reduce it (ref. 2). Reduction of t h e N O x emissions of the power stations in t h e Netherlands w i l l have a small effect o n ground level concentrations, acid deposition and ozone formation. If however these measures a r e taken in collaboration with neighbouring countries the environmental relevance increases considerably. T h i s can be seen from Table 2 in w h i c h the power plant NO, emissions in a number of countries are given. T h e N O x emissions vary between 12 and 44% of the national emi6sions. w i t h 25% as a n average value. If w e furthermore consider a NO, emission reduction by 408 in agreement vith t h e Proposal for a Council Directive on the limitation of emission of pollutants into the air from large combustion plants w e c a n expect a reduction in t h e average ambient concentrations of NOx typically i n the order of 10% (ref. 3).
TABLE 2 N O X emissions in neighbouring countries. nat iona 1
power: stations
103 t/a
103 t/a
%
Belgium
415
85
20
Denmark
265
115
43
France
2567
297
12
Germany
3 100
850
27
Italy
1595
530
44
00
15
Netherlands
536
683 NOX A B A T E m N T STRATEGY In the United States the New Source Performance Standards came into effect in 1971. This led to the construction of larger furnaces in new power stations and the incorporation of combustion modification. In this respect it is important to note that NOx formation depends strongly on furnace conditions. Even small modifications in the combustion process can greatly influence emission levels. Combustion modifications to reduce NOx are generally based on promoting a more gradual mixing of fuel and air to reduce flame temperature and the use of a richer fuel-air mixture to reduce oxidation of nitrogen in the fuel. In Japan the regulation of NO, emission started in 1973 and was tightened in a number of stages. In early the eighties the standards became so stringent that flue gas treatment was needed in addition to combustion modification. In the Federal Republic of Germany in 1984 a council of environmental ministers promulgated targets for NOx emission standards for both new and existing installations, that were so stringent that flue gas treatment was needed. Moreover the time schedule for the incorporation of the controls was so short that most efforts were directed towards flue gas treatment. In the Netherlands the first applications of combustion modifications occurred in the early seventies. For many power stations the NOx emissions were limited by the provincial authorities in licenses according to the Air Pollution Act. Only in 1987 a General Administrative Order on the emissions of large COmbUStiOn installations came into force (ref. 2). The standards are strict especially for new installations (coal 400 mg/m 3 , oil 300 mg/m3 and gas 200 mg/m 3 ) . However it is expected that the development of low NO, combustion technology has developed so far that with advanced combustion modifications these standards can be met. The differences between these national approaches are so large that it is considered useful to evaluate the state of the art of NOx control technology for large combustion installation in some detail and to describe the efforts of the 1
electric power companies in the Netherlands in their concerted NOx Abatement Programme (ref. 4). This programme is implemented on a volumentary basis. It consists primarily of the application of low N O technology in new and existing inX
684
stallations. In the second part of the programme new technologies are demonstrated to assess their applicability and to prepare for decisions on cost-effective NO, controls.
COMBUSTION MODIFICATIONS FOR GAS/OIL FIRED INSTALLATIONS Since 1980 the amount of fuel oil fired in Dutch power stations has decreased considerably and in the present situation fuel oil is mainly used as a substitute for natural gas. on days when the gas supply is interrupted. Therefore w e have no recent experience with oil fired installations in the Netherlands. However, it is our view that the extremely low N O concentrations that have been reported in the literature, X especially from Japan do not hold for the Dutch situation, because of the differences in fuel oil composition (e.9. sulfur content, residual oil v s . crude oil). Natural gas is a very important fuel for the Dutch power stations. An ambitious programme consists of the repowering of a steam turbine in existing installations with a gas turbine. In these installations the new gas turbine replaces the existing air blowers and the regenerative air heater. The exhaust gases of the gas turbine with an oxygen content of approximately 15% are used instead of fresh air for the combustion of gas or oil in the existing boiler. Increasing the thermal efficiency from a typical value of 40% to 45% and reducing the NOx emission are the main goals of the programme that is applied t o 10 power stations with an equivalent capacity of 3650 MWe (Table 3.1). T h e NO, emission is reduced primarily because of the low combustion temperature in the boiler; as a matter of fact the adiabatic flame temperature is lowered by the inert material in the gas turbine exhaust and the boiler load is reduced to approximately 70% as the other part of the combustion takes place in the gas turbine. A very important point is the selection of the proper gas turbine as there is a close relation between rating of the existing steam turbine and the gas turbine. Therefore there is not a free choice for a gas turbine with a high efficiency an a low NOx emission. The NOx emission of the gas turbine and control measures in the boiler are also important for the NOx emission of the combined cycle. It was expected that the N O X
emission of the power stations could be reduced by 30% and would amount to 100 g/GJ as an average, although some of the installations had high NO, emissions because of the.high thermal load in the furnace. At present it is already known that reductions higher than 5 0 % have been achieved at full load in a number of installations. The usual combustion modifications are applied in a demonstration project of low NO, combustion technology for gas and oil firing in Flevo Station 1. Flevo station 1 has been retrofitted with advanced low NO, burners, after air ports and gas recirculation into the combustion air. The expected emission 3 values are 200 mg/m3 for gas firing and 300 mg/m for oil firing. However the main objective of the project is the application of reburning technology, also known as In Furnace NO, Reduction (Table 3.2). Reburning is a distributed combustionsystem in which part of the fuel is injected into the furnace through burners placed above the top row of main burners. By correct adjustment of the fuel and air distribution. the reburn zone is operated fuel rich, thereby converting NO from primary zone combustion into N2. The aim of the project is to demonstrate the technology for gas and oil firing with rapid load fluctuations and to investigate the optimum NO, emission level, the quality of the combustion process (CO, and unburned carbon) and the mixing processes of upper fuel and over fire air the combustion gases. The NOx goal is 100 mg/m3 for natural gas and 200 mq/m3 for fuel oil.
686
TABLE 3 Concerted NO,
Abatement Programme.
Gas/oil firing Conversion of existing steam boilers to combined cycles power station
capacity (MWe)
commissioning
336 336 328 273 159 645 622
1986 1987 1987 1987 1988 1988 1988 1988 1989 1989
~~
Bergum station 1 Bergum station 2 Harculo station 5 r,age Weide station 5 Merwedehaven station 6 Eems station 2 Hemweg station 7 Waalhaven station 5 Flevo station 3 Waalhavsn station 4
313
451 3 13
Demonstration project o € €or gas and oil firing Flevo station 1
low NO,
combustion technology
capacity 185 MW
commissioninq 1988
- advanced low NO, bucnecs - gas mixing into the combustion air - two stage combustion - infurnace NO, reduction COMBUSTION MODIFICATIONS FOR COAL FIRED INSTALLATIONS I t is known that in a number of coal fired power stations in Japan NOx concentrations have been obtained in the range between 500 and 600 mg/m3 have been obtained. In order to obtain N O concentrations below the desired value of 400 ~ n g / m ~ ~is i tnecessary to equip the boiler with advanced low-NO, burners and two stage combustion. The results obtained in Japan with the PM burner developed by Mitsubishi Heavy Industries for tangentially fired boilers and HT-NR burner developed by Babcock Hitachi for frontwall and horizontally opposed fired boilers prove that the technology has advanced and conforms to the requirements (ref. 5). In the Netherlands the Power Stations Maasvlakte and Borssele have been converted from gas/oil to coal firing. These boilers have tangential firing systems. As the decision about conversion was taken at a time that the P M burner was not yet available for
687 coal firing, the SGR burner was used. Because of enlarged furnace volume, increased over fire air and the application of the Low NOx concentric firing system the boiler manufacturer "de Schelde" considered that NOx Concentrations below 600 mg/m3 can be reached. In the framework of the concerted NOx Abatement Programme a measurement programme is executed (Table 4.1). The preliminary results of Borssele and Maasvlakte are encouraging. For horizontally opposed and frontwall fired installation the experience in the Netherlands with modern combustion modifications is considered to be insufficient. Therefore the decision has been taken to perform a demonstration project in the Maas Station 5 (Table 4.3). The unit will be retrofitted with HTNR burners and after air ports by the boiler manufacturer "Stork Boilers" with a license of Babcock Hitachi. The aim of the project is to show that a NO, concentration of 400 m g / m 3 in new power stations can be obtained by the combination of advanced low NOX burners and two stage combustion in frontwall and horizontally opposed fired boilers. In addition to the primary measures mentioned before, the National Government of the Netherlands is of the opinion that flue gas denitrification has to be applied in future when the results with low NO, combustion technology are insufficient. A demonstration project, fully paid by the government, is in progress in Power Station Gelderland 12. This project is based on MHI high dust SCR technology. Originally the discussion of flue gas treatment technology was dominated by Japanese suppliers and users of SCR systems. However in recent years in Western Europe, with emphasis on Germany, a stormy development has taken place resulting in a large number of installations (ref. 6): 70 pilot SNCR/SCR plants with a total flue gas volume of about 250.000 m3/h 50 demonstration and commercial plants of 12.000 MWel.
688 TABLE 4 Concerted NO,
Abatement Programme.
Coal firing 1 Conversion of gas/oil fired power station to coal firing
Maas station 6 Maasvlakte station 2 Borssele station 12 Maasvlakte station 1
capacity 223 MW 517 MW
commi ss i o n i np 1986 1987
405 MW 517 MW
1987 1988
2 Study in existing power stations Gelderland station 13 AmeK station 8 3 Demonstration project combustion technology Maas station 5
603 MW 645 MW
of
low
180 MW
NO,
pulverized
coal
1988
- advanced low NO, burners - two stage combustion 4 Flue gas denitcification
Gelderland station 12
- SCR is
123 MW
1987
50% of flue gas stream
CONCLUDING REMARKS NO, abatement for stationary sources can be realized primarily by combustion modifications. The low-NOx technology that is applied depends on a number of aspects e.g. retrofit or new installations, fuel and boiler type. On the basis of information obtained thus far estimated NO, emission levels for new installations are presented in Table 5. The use of combustion modifications can be limited by side-effects such as - increased fouling - corrosion by reducing atmospheres - increased CO emission - incomplete burn out. In the Netherlands the quality of the fly ash is considered to be of great importance. There are Bome indications that the physical properties of the ash may change because of the lower
688
furnace temperatures, and that this may have consequences for the applicability of fly ash in construction materials. The potential of combustion modifications is even greater if reburning technology is taken into account, with potential emission reduction in the order of 5 0 % . The technology has been proven for natural gas and fuel oil. There are indications that a highly volatile and low nitrogen containing fuel should be used as a reburn fuel. There is a difference of opinion about the feasibility of the technique with coal as upper fuel. If however combustion modifications are insufficient or are considered to form a great risk. the NO, emissions can be reduced by flue gas denitrification. Selective catalytic reduction is the most promising technology. But other techniques like SNCR or the injection of urea can be cost-effective alternatives especially when the necessary emission reduction is limited. From the first results in Western Germany it seems that SCR can be applied without problems. However it is necessary to point out that there is no long term experience. This is especially important in determining catalyst life, when these materials are subjected to frequent temperature excursions, due to changes in boiler load. Major other problems are the use of different coals and different types of coal fired boilers whose ash may contain constituents that prematurely erode or deactivate the catalyst. Also ammonia slip is considered t o be a potential problem, because of the deposition of ammonium bisulphate in the air preheater and possible contamination of fly ash by these ammonium components.
630 TABLE 5 Estimated NOx emission on levels for new installations in mg/mi (ref. 5 ) .
coa 1
oil
gas
(6% 02)
(3%0 2 )
( 3 % 02)
1000-1400
500-700
300- 600
combustion modifications
600-900
200-300
150-270
advanced low NO, burners) combustion modifications)
300- 600
130-250
5 0 - 110
advanced low NO, burners) combustion modifications) SCR 1
65-130
without control
advanced low NO, burners) combustion modifications) r e bu r ni ng 1
(120-300)
50
65-130
25
25-50
REFERENCES Milieuprogramma 1 9 8 8 - 1 9 9 1 , Tweede Kamer, vergaderjaar 1 9 8 7 - 1 9 8 8 , 2 0 2 0 2 nrs. 1 - 2 . General Administrative Order "Emission standards for combustion installationsaa,Staatsblad 1987. nr. 1 6 4 , 2 8 april 1987.
E C COM ( 8 3 ) 7 0 4 final. Proposal for a Council Directive on the limitation of emissions of pollutants into the air from large combustion plants. W E N . Voorstel Totaal Programma NOx-uitworpbeperkende Maatregelen (maart 1 9 8 6 ) . J.G. Witkamp, J . van der Kooij, M.E.A. Hermans. status of low NO, combustion technology in Japan; a report of a technical visit in KEMA report 02562-MOL 8 6 - 3 0 4 0 . UNIPEDE Sorrento Congress. Actual status of nitrogen oxide reduction technologies in the THERNOX member countries (1988).
T.Schneideret aL (Editors),Atmoepheric Ozone Research and its Policy ZrnpricOtiona 0 1989Elsevier SciencePublishere B.V.,Ameterdam -Printed in The Netherlands
691
PERSPECTIVES FOR LOW-SOLVENT PAINTS
J.C. den Hartog, Sigma Coatings B.V., P.O. Box 42, 1420 AA Uithoorn, The Netherlands.
ABSTRACT Paint is a product with very complicated properties. Before drying it is a fluid which easily can be applied by spraying or with a brush. After drying it forms a durable coating. The functions of the coating are colour and protection. The protective function means conservation of our raw materials. In this respect all paint is ecologically sound. Paint technology was for a great part based on the use of solvents. The solvent was used as the carrier medium for application. It is now generally understood that the use of solvents in paint forms an environmental problem. Per definition, all solvents used in paint are emitted into the atmosphere where they contribute to the production of ozone. The total solvent vapour emission from pain application is in The Netherlands 95 K.Tons a year. This is around 35 % of the total industrial and not industrial emissions. This situation will not significant differ from other industrialized countries. The objective of the project Hydrocarbons 2000 is a 50 % reduction of those VOC emissions in the year 2000. The best way to achieve is to reformulate paint products away from solvents. The new paints developped by the paint industry are: waterborne paints - powder coatings - high solid paints W curing paints The composition of these products and the fields of application will be discussed.
-
PAINT Paint is the name commonly used for surface coatings. It is applied on a variety of materials like metal, wood, concrete, stone and synthetic materials. The main two functions of paint are colour and protection. Because
of these two functiones, we cannot give up the use of paint. Colour makes our world more attractive. Without colour, the world would be much more sad; no paintings, no colour on the furniture in our homes, on our cars, on buildings, etc. But, it is not only the aesthetically function of colour that is important. In some cases the safety function is even more important. Just think of road-marking and road-signs as an example. Without colour road-safety woiild he a much bigger problem than it even is now.
692 The protective function of paint is also obvious. The surface coating forms a protective layer between the substrate and the environment. It prevents metal substrates from corrosion and it prevents wood from attack by moulding or degradation by W radiation. This protective function of paints gives an important cohtribution to the conservation of our raw materials. Paint is indispensable to save our raw materials, and this is why all paint is ecologically sound. COMPOSITION Paint has a number of typical properties (table 1).
It is amazing that all
these properties are combined in a thin layer of maybe 100 um thickness, and that this thin layer retains those properties for many years.
TABLE 1: TYPICAL PAINT PROPERTIES Easy to apply Strong adhesion to substrate Mechanical strong Resistant to weathering Elastic Chemical resistant Colour Gloss Strippable Special properties (anti-corrosive, anti fouling, etc
The technology developed by paint industry in the past decades was based on the use of solvents. Based on this technology, very specialized products were developed and there is a lot of experience in the application and use of these products. TABLE 2: PAINT COMPONENTS
1) Binders 2) Solvents 3) Extenders 4) Pigments 5) Additives
(alkyds, epoxies, polyurethanes, acrylics, etc. ) (hydrocarbon, water) (clay, silica, talc, bariumsulfate, etc.) (organic and inorganic) (defoamers, flow 8gBntS, driers, thickeners, etc.)
Conventional paint consists of 5 different types of raw materials (table 2). First there is the binder. After drying the binder forms a strong layer with
693 the other paint components. Adhesive properties are also determined by the binder. The function of the solvents is to dissolve the binder and it plays a role in the film forming proces on drying
.
The extenders are mostly inorganic materials used as a filler. The pigments can be of organic or inorganic nature. They are used to give the paint colour and special properties like anti-corrosion. The additives are used in small amounts to improve the performance of the paint.
SOLVENTS Of the components used in the formulation of paint, it are the solvents which are highlighted from an environmental point of view. Although all paint is environmentally friendly, the solvents from paint have a negative impact on the environment. Because solvent is used as carrier medium in the paint application, all solvent evaporates into the atmosphere. In the atmosphere the organic solvents are ozone precursors.
TABLE 3: Emission of hydrocarbons in The Netherlands (k tons)
Total process
+ not
industrial
1981
1985
264
248
Paint : Metal products Professional painters Car refinish Wood industry Do-it-yourself
33 38 8 2 15
33 32 11 1,5 16
Total paint
96 (36%)
93,5 (38%)
--
----
The total amount of organic solvents from paint is in The Netherlands approximately 36% (1981) of the total amount of hydrocarbons emitted from process and not industrial sources (table 3). In 1985 it was even 2% more. From these figures it is clear that paint must give a substantial contribution to the reduction of ozone levels, by lower solvent emissions. In co-operation with the authorities, paint industry and paint users a strategy was developed to achieve a considerable reduction in the year 2000 (table 4). For paint there will be an overall reduction of solvent emissions by 45% i n comparison to the emissions in the year 1981.
694
TABLE 4: Percentage of reduction of solvent emissions from paint K tons 1981 Metal products Professional painters Car refinish Wood industry Do-it-yourself
K tons 2000
33
38 8
2 15
----____--_
TOTAL
96
% reduction
15 22 8
54
42 0 60
0,s 7
53
__-______--
_ _ _ _ _ _ _ _ r _ -
45
52,8
EMISSION REDUCTION There are two ways to achieve solvent emission reduction: gas cleaning installations to prevent solvent vapours from escaping the operations and to reformulate paint away from solvents. Gas cleaning equipment like incinerators, carbon absorbers or biofilters are only applicable in stationary sources, and can only give a solution for a part of the problem. Moreover, this equipment is very expensive. Also in some cases another environmental problem is created instead of the air problem. Because of environmental and economical reasons in The Netherlands we choose to formulate away from solvents. It is apparent that this is an enormous challenge for the paint industry.
LOW SOLVENT PAINT PRODUCTS At the moment there are four alternatives to conventional solvent borne paint; the high solids, the waterborne paints, the radiation curing paints and the powder coatings (table 5 ) . TABLE 5 : Solvent content of coating systems % organic solvent
High solids/solvent free Waterborne Radiation curing Powder coating Solvent borne (conventional)
0 5 0
-
25 10 10
0
40
-
60
Powder coatings are a very attractive alternative because they are really solvent free. It is a powdery mixture of resin, pigments and extenders.
695 It is applied by electrostatical spraying onto the substrate, followed by stoving. Because of the electrostatical application there are very little losses from overspray. The radiation cured paints are solvent free or are containing only a few percentages of organic solvent. Those paints are cured by an electron beam or W-radiation. W is mostly used. The technology is based on the use of acrylic prepolymers mixed with low molecular weight acrylates. Those low molecular weight acrylates are used as a reactive diluent. Under influence of W-radiation a polymerisation reaction is started. The reactive diluent is incorporated into the polymer, so there is hardly any emission of organic compounds. To give the paint special properties, sometimes a few percent of organic solvent is added. The waterborne paints are very often dispersions of acrylates in water. The normal water content is 40% by weight. It is a general misunderstanding that waterborne products are completely solvent free. They contain in general 5
-
10 % of a low boiling solvent, as a film forming agent and as co-solvent. Very
often propylglycols are used for this purpose. High solid paints are based on the use of low molecular weight binders with a low viscosity. Because of this low viscosity of the binder less solvent is needed to get the right viscosity of the paint. The normal solvent content of a two-component High Solid paint i s about 20% (w). By still using lower molecular weight binders and reactive diluents, it is even possible to produce so-called solvent free products, for example solvent free epoxies. CURRENT USE AND SUITABILITY
TABLE 6 : Suitability of low solvent coatings Powder W-curing water-borne high solids On site application Temperature sensitive substrates Small series substrates Industrial roller application Dipping Curtain coating Spraying High gloss Metal substrates Wooden substrates
+=
suitable
- = not suitable
+ +
+ + + -I+ + -I+ +
+ + + + + t + +I+ +
+ + + +
+It
+ + +
-
+I
696 The low solvent products are not a panacea to all solvent problems. They all have their specific application and use (table 6). But although there are limitations there are many coating operations where low solvent products can be used. Often the results are even better then with the conventional coatings: Some typical applications are given in table 7.
TABLE 7: Some applications of low solvent paints Powder
W-curing
Do-it-yourself Metal: furniture construction cans cars machines
water-borne
high solids
t
+ + +
Wood : furniture architectural Paper Plastics House painting
+
+ +
+ + + +I+ + + + +
+ = suitable CURRENT USE AND PERSPECTIVES There are no exact figures available on the used amounts of the different coating sytems. An estimation of the current use in Western Europe is given in table 8. TABLe 8: Use of coating systems in Western Europe Usage Conventional solvent borne High solids Waterborne Powder coating Radiation curing
(%I
75 10 10
4 1
Total paint usage : 4,800 I( ton (1986) The conventional solvent borne paints still form the majority; The low solvent paints together form only roughly estimated 25% of the total usage.
697 The reason is that technic81 and economical limitations are still preventing really large scale introduction. Not for every application are low solvent products available with equal performance and quality with respect to conventional systems. Also industry must invest to install new production and application equipment: Because the paint market is an international market, it is also absolutely necessary to take similar measures in the different
countries. However, one of the most important conditions to reduce the amount of solvents emitted from paints, is
8
public understanding that because of
environmental reasons it is absolutely necessary to use low solvent paints whenever it is technical and economical possible. In some cases we also must accept a somewhat different appearance or a higher price of the paint in exchange for a better environment. We need paint for colour and protection, we also need protection of our
environment. This even goes better with low-solvent paints. The perspectives for low-solvent paints can only be good.
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699
SESSION XI
RECENT STUDIES ASSESSING THE NEED FOR AN ADDITIONAL LONG-TERM OZONE STANDARD
Chairmen
P.J.A. Rombout B. Goldstein
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T.Schneider et al. (Editors), Atmospheric Ozone Research and it8 Policy Implications 0 1989 Elsevier Science Publishers B.V.,Amsterdam - Printed in The Netherlands
701
THE NEED FOR AN EIGHT HOUR OZONE STANDARD
P.J.A. ROMBOUT', L. VAN BREEl, S.H. HEISTERKAMP* AND M. HARRA' lhboratory for Toxicology and =Centre for Mathematical Methods, National Institute of Public Health and Environmental Protection, P.O. Box 1, NL.-3720 BA Bilthoven (The Netherlands)
ABSTRACT Analysis of ozone aerometrics demonstrates that exposure of the population may extend over 8 to 12 h per day to levels slightly below the 1 h maximum concentration. Current ozone standards may not be protective for extended exposures since they incorporate averaging times of 1 h and are mainly based on clinical exposure of humans for 1 to 2 h. Information on the impact of exposure time on ozone induced effects is scarce. For that reason animal studies were performed to establish a data base for ozone exposure-response relationships. Concentrations (C) ranged from 0.25 to 4.0 m u m s and exposure times (T) were varied from 1 to 12 h. The time course of protein and albumin concentration in bronchoalveolar lavage fluid was used as the endpoint. A response model described by a quadratic polynomial function indicates a strong influence of T to the response which increases with increasing C. The impact of T is still significant at the 0.25 mg/ms level. The study contributes to the growing data base that supports the introduction of an ozone standard with an 8 h averaging time and a substantially lower concentration than current 1 h mean standards. Furthermore, the health risk of exposure to ambient ozone appears to be more serious than was expected previously. INTRODUCTION In former days photochemical air pollution caused a typical diurnal ozone profile with a rather sharp peak in the early afternoon (ref. 1). Nowadays the emission of ozone precursors is spread out over large areas. This causes the mesoscale character of this type of air pollution and results in rather broad ozone peaks during the late afternoon (ref. 2). Analysis of data gathered by the Dutch National Air Quality Monitoring Network revealed that maximum 4 , 8, and 12 h mean ozone concentrations amount to 95, 85, and 75% of the maximum 1 h mean concentration respectively (ref. 3). The 1 h maximum concentrations reach values of 0.40 mg/ms (0.20 ppm) and higher. Episodes with increased photochemical activity may last from several days to 2 weeks and occur several times during the summer season (ref. 4). Similar diurnal profiles and episodes are encountered in the U.S.A. (ref. 1). Air quality guidelines and standards for ozone are primarily based on controlled human studies in which young healthy exercising volunteers are acutely exposed to ozone for short exposures of 1 to 2 hours and with physiological changes as endpoints (ref. 1). However the actual exposure of
702 the population, including more sensitive subgroups, to submaximal ozone concentrations may last up to 12 hours for several consecutive days. This exposure may exert apart from physiological alterations more serious biochemical, irmaunological or even structural effects (refs. 5
-
7). Therefore concern has risen regarding the health risk involved with these exposure conditions as well as the protection offered by current ozone standards since they restrict the averaging time to 1 h for a single exposure. The classic concept of Haber's rule referring effects to inhaled dose, taken as the product of concentration and exposure tine, is generally accepted in inhalation toxicological studies with systemic acting gases. However the application of this rule to the toxicity of the deep lung irritant ozone has mainly been restricted to acute short term exposures of humans (ref. 8). The recently recognized extended exposure of the population to ozone and the virtual lack of toxicological data on the contribution of exposure duration to acute ozone induced effects prompted us to perform 8 comprehensive, systematic study on concentration (C) and exposure time (T) relationships. A broad range of concentrations (0.25 to 4.0 mg/na) and exposure times (1 to 12 h) were investigated in sedentary and active animals, with influx of protein and 81bUin in bronchoalveolar lavage fluid (BALF) as indicators of lung injury. Results on the contribution of the number of exposure days to the effect are reported by Van Bree et al. (ref. 9). The experiments reported here are part of an ongoing research program on the relationship of ozone exposure patterns and effects. Part of this program is carried out in collaboration with the Toxicology Branch of the Health Effects Research Laboratory of the US Environmental Protection Agency and the Department of Inhalation Toxicology of the Laboratory for Toxicology of the Dutch National Institute of Public Health and Environmental Protection.
KdTHODS Animals Seven week old male, specific pathogen free Wistar rats were obtained from our Institutes breeding colony. They were maintained under barrier conditions during a one week acclimatization period and during exposure. The animals were kept on a normal 12 h light cycle. Food and water were provided ad libituql.
l%zuK== Animals exposures were performed in a facility, consisting of twelve 0.2 m' stainless steel and glass ~nhalationchambers. Haximally 15 rats were housed in one chamber. Air was purified by an activated charcoal, a permanganate and a highly efficient particle filter, and was conditioned at a temperature of 22 5 1'C and 55 f 5% relative humidity. Through each chamber an air flow of 6 ma/h was maintained. An ozone-oxygen mixture, generated by irradiation of oxygen with W-light. was metered into the inlet air stream with a stainless
703 steel mass flow controller. The exposures were performed automatically using an exposure control program running on an Altos 1086 microcomputer interfaced to the exposure equipment. Concentrations in the chambers were measured at
two
minute intervals with Monitor Labs 8810 ozone analyzers, and adjustments of the flow controllers were made to maintain the desired concentrations. The analyzers were checked several times per day against a reference ozone-air mixture and zero-air generated by a Monitor Labs 8550 calibrator, which was calibrated weekly by means of gasphase titration with an NBS-traceable nitric oxide-nitrogen gas mixture. h v a e e f u d urenaration and Bronchoalveolar lavage (BAL) was performed by the method of Hatch et a1
-
(ref. 10) using 40 instead of 35 ml/kg bodyweight of warmed (37'C)
saline.
Cell free lavage fluid supernatant (400 g; 10 min.) was analysed for protein (ref. 11) and albumin (ref. 12).
Protein and albumin concentrations in BALF were transformed to their
natural logarithms. Quadratic polynomial functions were tested with ozone concentration (C), exposure time (T) and autopsy moment (A) as variables. ntal d e s i a Two experiments were performed in which CxT relationships were investigated
in sedentary (experiment 1) or active rats (experiment 2). (i) ExDeriment 1. CXT studv. dav-. To study the time course of protein influx in BALF as a function of C and T, 4 sub-experiments were carried out in which rats were exposed to either 0.75, 1.5, 2.5, or 4.0 mg/d ozone. For each sub-experiment 102 rats were divided at random into 5 groups, and were exposed during day-time for either 0, 1, 2, 4, or 8 h. Exposures started at 08:00, light was on from 08:OO until 20:OO h. BAL was performed in
3 rats at autopsy moments as indicated (x) in the following scheme:
Exposure time (h) 0 1 2 4 8
Autopsy moment (h from start of exposure) 4 8 14 22 34 54 1 2 x x
x x x
x x x x
x x x x X
(ii) ExDeriment 2. CXT study.
X X X X X
X X X X X
X X X X X
ninht-time exuosure .
X X X X X
Number of rats 24 24 21 18 15
To study the time course
of albumin influx in BALF as a function of C and T, 3 sub-experiments were carried out, in which rats were exposed to either 0.25, 0.50, or 0.75 mg/ms ozone. For each sub-experiment 75 rats were divided at random into 4 groups, and were exposed during night-time for either 0, 4, 8 , or 12 h. Exposures
704 started at 18:00, light was on from 06:OO until 18:OO h. BfG was performed in 3 rats at autopsy moments as indicated (x) in the following scheme:
Exposure time (h)
Autopsy moment (h from start of exposure) 4 8 12 24 36 48 72 x x
0 4
a
x x x
12
X X
X X
x x
x x
X X X X
X X X X
X X X
X
Number of rats 21 21 18 15
RESULTS nt 1. C x T . dav-This experiment consisted of 4 sub-experiments that were separated in time by one week. Statistically they were treated as being performed at the same time since the variance in the concentration of protein in BALF of all control
-
animals (n 9 6 ) did not differ from the variance of the protein concentration within any subexperiment. The same considerations were valid for experiment 2. The time course of the protein influx in BALF after acute exposure of sedentary rats displayed a fast increase followed by a gradual decrease of the protein concentration with a maximum response at 22 h from the start of the exposure. Figure 1 shows the data for 1.5 mg/m3 ozone. The protein concentrations were still significantly elevated at 54 h from the start of the exposure for exposure times of 4 and 8 hours. Exposure time exerted a profound, more than proportional concentration dependent influence on the
hars frcm start
Fig. 1. Time course of the protein concentration (mg/l) in bronchoalveolar lavage fluid after day-time exposure of rats to 1.5 mg/m3 ozone for
0 (+), 1 (A), 2
(O),
4 (+), or
8 (A) hours.
705 influx of protein in BALF as can be seen in Table 1. Multivariate regression analysis of the data resulted in the following function, that accounted for 88.6% of the variance of the data: log protein
-+
4.68 - 0.17 C + 0.049 Ca + 0.13 CxT 0.028 A 0.0005 As + 0.0013 TXA
-
0.11 T
-
This function enables the calculation of the influence of T on the influx of protein in BALF for every possible combination of C, T and A within the tested ranges. Figure 2 displays the calculated cuwes for 1.5 mg/m3 and exposure times of 0 , 1, 2, 4 , and 8 h.
TABLE 1 Influence of exposure time on the protein concentration in bronchoalveolar lavage fluid of day-time exposed rats at 22 h from the start of the ozone exposure. Values are given as percentage of control (n
Concentration (mg/ms ozone)
3).
Exposure time (hours) 2 4
1 94 138 120 277
0.75 1.50 2.50 4.00
-
100 180 209 497
119 267 499 1336
8
137 543 2003 8468
7m
600
600-
m-
+
+..."""
,,,,,,,,,....
"'
+............+...,.,_,,,,
'.t......,,
"".+
xa&---4--Q---
en
Fig. 2. Calculated time course of the protein concentration (mg/l) in bronchoalveolar lavage fluid (ng/l) after day-time exposure of rate to ozone for 0 (A), 1 (+), 2 (A), 4 ( O ) , OK 8 (+) hours. 1.5 &ma
706 Fxueriment 2. CxT. The time course of albumin influx in BALF after a single exposure of active rats to ozone differed from that of the protein influx in sedentary rats, since the increase and decrease of the albumin concentration was much more gradual and the maximum response shifted towards a later moment viz. 36 in stead of 22 h for exposure times of 8 and 12 h.(Fig. 3). The absolute changes were large with respect to the relatively low ozone concentrations. Ozone induced effects were detectable for the smallest investigated CxT product of
-
0.25 x 4 1.0 mg.h/d. 72 h after the start of an 8 or 12 h exposure to 0.50 and 0.75 mg/ms, albumin concentrations in BALF were still elevated. The maximum albumin concentration in BALF in ozone exposed rats was proportional to the length of T. The impact of T increases with increasing C (Fig. 4). Furthermore it appeared that e.g. an 80% increase in albumin in BALF was caused by CxT products of 3.0, 2.0, and 1.5 mg h/ma for concentrations of 0.25, 0.50, and 0.75 ng/d and exposure times of 12, 4. and 2 h respectively. Multivariate regression analyaia of the data resulted in the following function, that accounted for 73.2% of the variance of the data: log albumin
-
-
3.89 0.81 C + 1.31 Cz + 0.018 A 0.00024 A'
-
+
0.21 CxT
-
0.044 T
DISCUSSION Ozone can cause permeability changes in the epithelium and endothelium of the respiratory tract in man and animals (refs. 10, 13). It has been demonstrated that these changes are paralleled by inflamnatory processes in the lung (refs. 7, 13). Protein and albumin in BALF are indicators of the degree of pulmonary permeability. Consequently increases in protein and albumin concentration in BALF after ozone exposure are of great significance for the evaluation of health riska aosociated with public ozone exposure. The moment at which the maximum increase in protein and albumin in BALF occurs has not been properly investigated. C as well as T may have influence on this moment. Therefore we chose to study the time course of protein and albumin influx in BALF caused by various CxT products. This enabled the statistical analysis of all data of the c u n w instead of relying on the supposed moment of maximum response. Protein concentrations were increased at 54 h especially for T's of 4 and 8 h of all CxT products. Thia indicates that the lung ia still in a state of repair and that T s e e m to govern the extent of this proces. Experiment 1 demonstrates that the degree of the more than proportional contribution of T progressively on C. Thus the in provoking ozone induced lung injury, &pen& simple product of C and T c u m o t be applied to predict the reaponse for all possible combinations of a given product. A polynomial function demonstrates
707
Fig. 3. Time course of albumin concentration (percentage of control) in bronchoalveolar lavage fluid (BALF) after a single night-time exposure of rats to 0.25 (top), 0.50 (middle), or 0.75 (bottom) mg/ma ozone for 4 (+), 8 (A), or 12 ( 0 ) hours.
708 quantitatively the progressive influence of T with higher C's. This response model can be used to calculate the effect in terms of protein influx in BALF for a single ozone exposure to an arbitrary combination of CxT. For example an 1 h exposure to 2.0 mg/ms causes the same effect as an 8 h exposure to 0.425 mg/ms ozone. These findings are almost in complete accordance with the findings of Costa and coworkers (ref. 14). The model is based in part on experimental data with relatively high CxT products resulting in extreme lung injury. This renders a model that is suitable for generalizations on ozone CXT relationships but is of less value for the evaluation of risk involved with ambient ozone exposure. For this reason similar information for lower ozone concentrations was warranted. It has been shown in h w a n and animal experiments that minute volume exerts a strong positive influence on ozone induced effects (refs. 8, 15). We have observed a twofold increase in effect when rats were exposed to ozone during the night-time compared to day-time exposure (ref. 16). Preliminary data from our laboratory show two periods during the night in which animals displayed an increased breathing frequency. We therefore performed a second CxT experiment in which active animals were exposed during the dark period to ambient concentrations, to compare the results from our animal experiments with data from exposure of exercising humans. The observations of experiment 1 were largely confirmed for lower ozone concentrations by the results of experiment 2. The difference in the shape of the time-reponse curves in both experiments may be caused by the difference in the permeation velocity of protein and albumin and/or by qualitative changes in the ozone dosimetry of sedentary and active rats in terms of the localisation and the extent of the tissue affected by ozone. A seemingly proportional influence of T on the ozone response was observed for these low concentrations. The influence of T again being greater for higher C, but a strong impact of T still exists at 0.25 mg/mr. Koren et al. (ref. 6) measured a significant 120% increase in the albumin concentration of BALF from humans exposed to 0.4 ppm ozone for 2 h during intermittent exercise. Almost identical exposure conditions, 0.75 mg/ms for 2 h, caused an 80% increase in the albumin concentration in active rats. Remarkably the same response wan induced by a 4 h exposure to 0.50 m g / d or a 12 h exposure to 0.25 &ma
(Fig. 4.). So ozone exposure conditions that
normally occur on a large number of day8 during the summer season, will cause injury in rat lungs. Preliminary results from Koren et al. (ref. 6) and HOrStYMM et PI. (ref. 17) point to similar exposure-reponse dynamics for humans. In conclusion ozone exposure-response relationships for single exposures cannot simply be described by the product of C and T. A quadratic polynomial function suitably models the response and demonstrates a significant
709
-,..yo
E w l effect foc
600-
a-
-
o ...-are npmu
.’--O , ,
,/0 . -
,..~*b /./ -.----
.&--,: 0
/.----
-0.-
200-
/-Ll
*--
<---
c
0.-
,.-’
,/’
,.-’ ./-
* *
025 d d 12 h 0.50 m d d t 4 h 0.75 RIo/d 2 h
Joo-
,.-’
.............................
~
................................... a 2 S mL
.................
..............!.......
D
2
D
6
0
10
0
14
Fig. 4. Correlation between exposure time and albumin concentration in bronchoalveolar lavage fluid (BALF) after a single night-time exposure of rats to 0.25 (+), 0.50 (A), or 0.75 ( 0 ) mg/ma ozone. Given CXT products result in a 80% increase in albumin concentration.
contribution of T to the overall effect. The T impact increases with increasing C and is still significant at a concentration of 0.25 mg/ma. Calculations based on quantitative exposure-response relationships and prevailing ozone aerometrics in The Netherlands show that e.g. a 4, 8, or 12 h exposure during a day with a maximum 1 h Concentration of 0.24 mg/ma results in an 8, 27, or 40% increase in effect compared to exposure for one single hour to that maximum. These values will increase progressively with increasing concentration and/or level of exercise. Attainment of an ozone standard with a longer averaging time e.g. 8 h and a concentration substantially lower than predicted by ozone aerometrics is therefore needed to protect the population from the potential serious adverse effects that may be caused by actual exposures. Furthermore it is evident that for these exposure conditions the current ozone standard is neither appropriate nor protective. ACKNOWLEDGEMENTS The authors wish to acknowledge the fruitful discussions with the participants of the US-Dutch research program on health effects of airpollution. Dr. Fred Killer and Dr. Dan Costa from the Health Effects Research Laboratory of the US Environmental Protection Agency. Dr. Bernard Goldstein from the Department of Envrionmental and Community Medicine, University of Medicine and Dentistry of New Jersey, is acknowledged for hie ongoing support on the issue of an 8 h ozone standard.
710 REFERENCES Air Quality for Ozone and other Photochemical Oxidants. US Environmental Protection Agency, Environmental Criteria and Assessment Office, Washington D.C. (1986). R.M. van Aalst, ibid. P.J.A. Rombout, P.J. Lioy and B.D. Goldstein, J. Air Pollut. Control ASSOC., 36 (1986) 913-917. J.W. Erisman. National Institute of Public Health and Environmental Protection, report 758474001, Bilthoven, The Netherlands (1987). L.J. Folinsbee, W.F. McDonnell and D.H. Horstman. J. Air Pollut. Control ASSOC., 38 (1988) 28-35. H.S. Koren, R.B. Devlin, D.E. Graham, R . Mann and W.F. McDonnell, ibid. H. van Loveren, P.J.A. Rombout, S j . Sc. Wagenaar, H.C. Walfoort and J.G. Vos, Toxicol. Appl. Pharnacol. 94 (1988) 374-393. M.J. Hazucha, J . Appl. Physiol., 62 (1987) 1671-1680. L. van Bree, P.J.A. Rombout, I.M.C.M. Rietjens, J.A.M.A. Dormans and M. Marra. ibid. 10 G.E. Hatch, R . Slade, A.G. Stead and J.A. Graham, J. Toxicol. Environ. Health, 19 (1986) 43-53. 11 O.H. Lowry, N . J . Rosebrough, A.L. Farr and R.J. Randall, J . Biol. Chem., 193 (1951) 265-276. 12 L. van Bree. H.P. Haagsman, L.H.G. van Golde and P.J.A. Rombout, Arch. Toxicol., 61 (1988) 224-228. 13 H.R. Kehrl, L.M. Vincent, R.J. Kowalsky, D.H. Horstman, J.J. O'Neil. W.H. McCartney and P.A. Bromberg, Am. Rev. Respir. Dis., 135 (1987) 1124-1128. 14 D.L. Costa, G.E. Hatch, J . Highfill, M.A. Stevens and J.S. Tepper, ibid. 15 W.J. Mautz, T.R. McClure, P. Reischl, R.F. Phalen and T.T. Crocker, J. Toxicol. Environ. Health, 16 (1985) 841-854. 16 L. van Bree, H. Marra and P.J.A. Rombout, The Toxicologist, 7 (1987) 11. 17 D.H. Horstman, W.F. McDonnell, S . A . Salaam, L.J. Folinsbee and P. Ives, ibid.
T.Schneider et al. (Editors), Atmospheric Ozone Research and its Policy Zmplicatwns 0 1989 Elsevier Science Publishers B.V..Amsterdam -Printad in The Netherlands
711
THE DYNAMICS OF HUMAN EXPOSURE TO TROPOSPHERIC OZONE Paul J. Lioy, Ph.D.l and Raymond V. Dyba, Ph.D.2 'Exposure Measurement and Assessment Division, Department of Environmental and Community Medicine, UMDNJ-Robert Wood Johnson Medical School, Piscataway, N . J . ,$USA) Division of Environmental Quality, New Jersey Department of Environmental Protection, Trenton, N.J. (USA) ABSTRACT The ambient conditions conducive to ozone exposure into a context of the time and locations where people affected by high ozone. This is done for both 1 h and Exposures that occurred during a 1982 episode, and an effects study are described in detail.
are examined, and placed would be expected to be 8 h averaging times. associated health
INTRODUCTION The toxicological effects of ozone exposures have been demonstrated in animals at concentrations that approach levels observed in the atmospheric environment.(l) In addition, and consistent with these findings, are results from clinical studies and field health studies which have found effects on pulmonary function and in symptom expression for exercising adults and children at ozone levels near the present United States standard of 120 ppb for 1 h:(1-5)
The purpose of this manuscript is to evaluate the potential for
exposure to atmospheric ozone with an emphasis on the concentrations, and their frequency and duration occurrence (exposure
-
concentration x time).
CONCENTRATION PATTERNS Original mechanistic studies on the diurnal formation and decay of ozone suggested that the highest concentrations would occur for a short time period around midday or in the early afternoon, e.g. in downtown Los Angeles, C A . ( 6 ) From research conducted in the early 1970's, however, it has become apparent that in addition to midday peaks ozone will accumulate to high levels at various times depending upon: the meteorological conditions, the geography, and the precursor emissions density for volatile organic compounds and nitrogen oxides.(7) It has been demonstrated that ozone will start accumulating during the daylight hours, can be transported, and precursors can continue to form over distances greater than hundreds of kilometers for one or more days. During a 1977 episode Wolff and Lioy(8) found that high ozone can extend over a large portion of the Eastern United States creating a virtual "ozone river." Analyses by Vukovich(9) for 1977 through 1981 showed similar results,
712 although, the location of ..xima varied from year to year.
Other analyses by
Lioy and Samson(l0) for 1976-77 showed that in this region of the U.S. episodes will persist for 3 to >10 days, and reach levels in excess of the standard. The U.S. EPA criteria document (7) designated three transport zones for ozone 1: Urban scale, 2: Hesoscale and 3: Synoptic scale. In each case the ozone levels found at a receptor site downwind of a precursor source area depend upon many interrelated factors, including: 1) concentrations of ozone precursors leaving the source area; 2) induction time; 3) turbulent mixing; 4 ) wind speed and wind direction; 5) depletion during transport; 6) injection of new emissions along the trajectory of an air mass; and 7) local and synoptic weather conditions. For urban-scale transport, maximum concentrations of 03 are produced about 20 miles (and about 2 to 3 hours) downwind from the precursor source areas.
For mesoscale transport, 03 has been observed up to
200 miles downwind from the sources of precursors.
Synoptic-scale transport
is associated with large-scale, high-pressure air masses that may extend over and persist for hundreds of miles.(7)
TIME AND DURATION OF EXPOSURE The above indicates that ozone accumulation processes are very dynamic in both time and space. A good example of the regional time-space motion of ozone can be found from the work of Cleveland et al.(ll)
They showed the time
lapsed movement of ozone through the northeast U.S. corridor from the New York Metropolitan area to Boston during one day of an episode in 1974, Figure 1. It is apparent that for this particular day the maximum concentration was not observed at the same time downwind, and the actual concentrations were different along the path of this mesoscale event.
The atmospheric conditions described above indicate that there can be dngle or multiple periods outdoors during which an individual will be exposed to ozone near or above the standard.
The work of Rombout et al.(l2) for New
Jersey, USA, and the Netherlands illustrated episode conditions where the number of hours of ozone concentrations > 100 ppb can be greater than eight on a single day.
Subsequent work by Berglund
et a1.(13) examined this
phenomenon for the entire United States and found 8 h averages above 100 ppb in four large regions. These observations are of concern because this duration of ozone exposure can be related to a health reference: the OSHA standard, and current Threshold Limit Value (TLV) of 100 ppb averaged for eight hours. Thus, ozone is the only known outdoor ambient air pollutant which exceeds a workplace TLV, and does so on a regular basis during the summer.
713
:.*
,.m.
-
100 miles
Key:
9
0
1
,.I.
100 QQb 03
Eigure 1: Yesoscale Ozone Transport Throughout the Day on July 2 , 1974 and the Time-Space Relationship of the Maximum. Adapted from Cleveland et al. (11)
Since the 1 h peak ozone can occur at various times during the day (e.g. 12 noon through midnight) individuals participating in all types of recreational activities, and outdoor employment, such as construction and public works, will have the potential for exposures to high ozone.
This situation can occur
for any of the defined transport regimes and in many sections of a country.(7) The EPA guidance document on USA ozone exposures has a more limited view of what constitutes the time interval of importance during the day and the geographic areas of concern.(14)
This was based in part on 1) the traditional
concept of examining urban areas, and 2) not identifying adults or children exercising during the day or early evening in rural areas as part of the population at risk.
In spite of these weaknesses, their exposure estimates
addressed current ozone concentrations, and a number of human exercise categories, and the results gave basic estimates of the magnitude of the problem.
By extrapolating the results for 10 urban areas to all USA urban
centers, the population potentially exposed to 03 >120 ppb for at least one hour a week and while participating in moderate exercise is approximately 13,000,000. For the same population-exercise regime, 21,000,000 would be exposed to at least one hour of 03 above 100 ppb. Research in other countries has also documented 03 concentration patterns that produce significant one hour and multiple hours of high ozone exposures to individuals in both urban and non-urban settings. (12,15,16) A study conducted in Greater Johannesburg South Africa found 1 h 03 values above 120 ppb during the day through past midnight.(15)
Figure 2a: Frequency of Ozone P & for the end of an Eight Hour Averaging Tir at ' h e l v e S i t e s in New Jersey for k y through September 1986-1987. and only Days When the Peak M above 100 ppb
1
2 3 4 5 End of Peak 8 - h o u r
6
7
8
9
10
11
Ozone Period (P.M., E.S.T)
Figure 2a: Frequency of Ozone Peaks f o r the end of a n Eight Hour Averaging Time at Twelve Sites i n New Jersey for May through September 1986-87, and.only Days When the Peak was above 100 ppb
1
2
4
5
6
7
a
0
Time of Peak Hour Ozone Concentration (P.M.,
10
11
E.S.T)
Figure 2b: Frequency o f Ozone Peaks f o r One Hour Averaging T i m e a t Twelve S i t e s i n New Jersey f o r May through September 1986-87, and o n l y on Days When t h e Peak was above 120 ppb
7 16 The time of the daily 1 h 03 peak, and the end hour of the 8 h average 03 can clearly illustrate the potential for high exposures. To examine this point, the 03 data for May through September, 1986-1987 were analyzed for twelve sites in New Jersey. Figures 2a and 2b.
The results for each averaging time are shown in
The peak for the end hour of the maximum 0 h average
occurred in the evening hours, while the peak for the 1 h ozone maximum above 120 ppb occurred over a broad range of hours that centered at 3 PM. The results are significant because they define the interval of concern for exposures above the ambient and/or occupational standards to be from about noon to at least 8 PM. The Ratio of TLV/NAAQS Violation was 1.20. ACTIVITY PATTERNS The assessments of exposure for most criteria pollutants and other compounds, such as volatile organics, rely heavily on individuals being located very near the source. The sources of these primary pollutants can be located either indoors or outdoors, and the total population affected will depend upon the patterns of source emissions.
In contrast, ozone is a
transportable secondary pollutant, and will affect populations differently. Paul et al.,(l4) and Mage et a1.(17) have identified various activities associated with atmospheric ozone exposures. Mage et al. developed an objective approach to estimating the dose delivered to the lung from the pulmonary ventilation rate associated with a specified activity. An example of the inhaled ozone dose for a 12 year old camper, shown in Table I, provides a perspective on ventilation rates that can result from different exercise regimes and the quantity of ozone presented to the lung.
They considered the
mid-day to be the primary period for experiencing significant activity-related outdoor ozone exposures; although, acknowledging the need to address site specific information on activities and concentrations in any analysis. This type of analysis is important to identify situations conducive to high exposure.
It must be recognized, however, that even limited hours of exposure
to ozone during exercise can produce decrements in pulmonary function and the longer one is exposed to ozone the greater the probability for observing a significant effect.(2,5)
Thus, assessments should focus on the periods when
people in rural, suburban or urban areas are likely to be outside and participating in exercise activities, and have limited concern for other periods. Since there are few indoor sources of ozone, minimal impact would be expected from indoor exposures. Enhancement of any effect would probably be due to 1) the presence of other respiratory irritants, and 2) the penetration of outdoor ozone indoors.
Periods spent indoors could also be associated with
717 TABU I A Sumnary of Parameters used in Dose Calculation by Nage at a1 (17) for a Hypothetical 12 year old Camper Activity
Time
Sleep 0-7:30 Breakfast 7 :30-9:30 Play period 9:30-10:20 Swim 10:20-11:lO Sports 11:lO-12:oo Lunch 12:oo-2:oo Canoeing 2:OO-2:50 Obstacle course 2:50-3:40 Arts/Crafts 3 :40-4:30 Free Time 4:30-5:20 Dinner 5 :20-7 :00 Evening Program 7:OO-1O:OO Sleep 1o:oo-12:oo
03 ppb 26 36 39 40 54 78 98 105 110 100 95 71 60
Vea L/min
Effb Deposit.
Dose ug
5.0
0.015 0.065 0.17 0.23 0.28 0.16 0.31 0.37 0.26 0.25 0.19 0.17 0.06
0.5
7.3 10.0 15.8 16.0 7.3 11.4 16.0 8.6 8.6 7.3 8.6 5.0
1.9 6.5 14.2 23.7 15.1 33.9 60.9 24.1 21.1 19.3 25.8 2.0
Note: calculation requires heart rate, and an indoor infiltration factor found in the paper by Mage et al. (17) a ventilation rate, based on heart rate
efficiency of deposition in the lung.
an individual's rate of recovery from ozone effects. Recovery would be dependent upon the percent of ozone penetrating indoors, and an individual's indoor exercise regime. In air conditioned environments ozone is reduced by greater than 90%. (18,19)
EXPOSURES DURING FIELD HEALTH STUDIES The field health studies conducted by Lippmann,(20) Lioy, ( 5 ) and Spektor(21) were all based at summer camps where children spent a significant portion of their day outdoors. In each instance, there were
decrements in pulmonary function for the ozone concentrations encountered. An interesting example of the potential magnitude of ozone exposure during an episode can be obtained from Lioy et a1.(5) It occurred in the Mendham, NJ ozone health study, where a lag in recovery of the childrens' lung function was found to be related to the peak concentration of ozone present on the five days comprising the episode. After completion of the Rombout et a1.(12) analyses it became apparent that the total dose of ozone might be a more significant parameter in explaining the longer period of recovery. Figure 3 shows the daily variation of ozone in the Mendham area during the four worst days of the episode period. The results are referenced to both the NAAQS 1 h
710 stand8rd 8nd 100 ppb (TLV).
In oithor caso, it can bo soon that the duration
of high ozone concentrations was substantial on each day. In fact, if one uses 100 ppb as a guideline, the number of hours with 03 > 100 ppb were:
7, 9 , 13
and 8 for July 14, 15, 16, 8nd 17, rospctiwly.
Th. paramtors w d by h & o ot a1.(17) to prodict tho d.1ivor.d ozone dose were applied to the four episodr days. Ih. schedule of a hypothetical camper was matched to the actual 03 concentrations, and the predicted doses are found in Table 11.
From 1:00 PM on July 14th through midnight on July 17th, the
predicted outdoor ozone dose was 1740 ug. total (indoor and outdoor) ozone dose.
This was 77.5% of the estimated
The maximum 8 h dose for each day was
411.2, 556.6. 463.9, 358.8 ug, for July 14-17, respectively. The same estimate was made on the clinical data of Folinsbee et a1.(2) using an average ventilation rate of 40 L/min.
The effective dose for their 50 min of exercise
per hour for 6.6 h was 1062 ug.
Therefore, on each day of the episode, Figure
3, the hypothetical Mendham camper would inhale about half the ozone dose of that received by adult clinical volunteers who experienced significant decrements in lung function and displayed symptoms of discomfort after 6.6 h of ozone exposure.
However, the camper would have experienced their dose
level on four consecutive days.
From this comparison it is possible to
hypothesize that the residual ozone effect on pulmonary function was probably due the accruulated dose of ozono rathor than tho poak concontration.
TABLE I1 Estimated Dose delivered to a hypothetical camper and activity schedule from the ozone measured during the July 14 through July 17 Summer of 1982 Episode in Mendham, NJ Using the Approach of Mage et a1 (17). Act ivity Sleep Breakfast Play period Sports Lunch Arts/Crafts Swim Sports Free Time Dinner Play period Indoor Program Sleep
Time
0 00-7:00 7 :00-8:00 8:OO-1o:oo 1o:oo-12:oo 12:oo-l:oo 1 :00-2:00 2 :00-3:00 3 :00-4:00 4 :00-5:00 5 :00-7 :00 7 :00-8:00 8:OO-lO:OO 1o:oo-12:oo
Estimated Ozone Dosage (ug) 7/14 7/15 7/16 7/17 m a 2.1 0.2 15.0 m a 3.7 0.7 3.8 ma 40.7 52.7 37.7 NDa 152.8 162.8 113.9 14.3 21.8 17.9 12.7 28.2 38.4 31.3 19.3 113.3 139.6 92.5 77.5 123.2 136.3 92.2 85.0 50.0 44.6 34.4 31.1 41.4 37.9 29.7 33.9 30.7 37.9 59.1 32.9 19.3 19.4 75.8 21.4 3.4 1.1 4.5 2.0
713
Jh NAAQS
B h TLV
Figure 3: The Diurnal Variation in Ozone Concentration During the Sumer of 1982 Ozone Episode at Mendham, NJ Associated with the Health Effect Study Conducted By Lioy et al. (17)
lka tho precediry it can ba stated that the ozona exposures of people
living and participating in outdoor activities in the western section of New Jersey could be substantial. Obviously, there will be variability in individual exposures with some receiving higher and others lower exposure; although, the persistence of an episode can have a substantial effect on the total ozone dose presented to an individual. Analyses conducted by the California Air Resources board,(6) have shown that the one hour ozone maximum is correlated with the peak eight hour average. This would indicate that in the analyses of Lioy et a1.(5), the one hour peak was probably a surrogate of the parameter associated with the effect. The correlation of the 1 h peak with a longer exposure leads to the hypothesis that the present form of the standard for ambient ozone, 1 h peak adequately addresses situations where a persistent episode may yield concentrations that are of concern to public health. This must be viewed with caution since the results of Berglund et a1.(13), and Rombout et a1.(12) suggest that there will be situations where the present standard does not protect against approximately 25% of the actual exposures to ozone above 100 ppb for ei&t
hours.
SUlQIARY
The dynamics of human exposure to ozone are related to a number of factors that encompass outdoor human activity through formation and transport mechanisms.
Because ozone is a pervasive secondary air pollutant it affects
large segments of a population in both urban and rural locales. A primary feature of ozone exposure in relation to potential health effects is that short term effects can be associated with ozone exposures above 100 ppb that occur between one and eight hours in a particular day.
This indicates that assessments should focus primarily on the periods associated with outdoor activities coupled with periods which can potentially have high ozone levels. It appears that the high concentrations can occur for single or multiple
periods from about noon to late evening.
Further, a health-based standard
should be considered for an interval greater than 1 h.
It should be the
maximum running average 03 concentration for the averaging interval selected, for example 8 h.
Not the average between two arbitrary times, such as 8 AM
-
5 PM. Episodes appear to result in signifcant ozone exposures since these are multiday periods when individuals are likely to be participating in outdoor exercise.
The consequences of repeated episode related exposures must be
examined since the dose delivered to the lung can be significant in a given day and for multiple days.
REFERENCES 1 U.S. EPA, Air Quality Criteria for Ozone and Other Photochemical Oxidants, Vol.IV, EPA-600/8-84-020B, ECAO, Research Triangle Park, NC, 1985. 2 L.J. Folinsbee, W.F. McDonnell, and D.H. Horstman, JAPCA, 38 (1988) 28-35. 3 U.S. EPA, Staff Paper, Review of the National Ambient Air Quality Standard for Ozone, OAQPS, Research Triangle Park, NC, November, 1987. 4 W.F. McDonnell, D.H. Horstman, M.J. Hazucha, E. Seal, E.D. Haak, S.A. Salaan and D.C. House, J. Appl. Physiol., 54 (1983) 1345-1352. 5 P.J. Lioy, T.A. Vollmuth and M. Lippmann, JAPCA, 35 (1985) 1068-1071. 6 California Air Resources Board, Effects of Ozone on Health: Technical Support Document, Research Division, CARB, Sacramento, CA, September, 1987 7 U.S. EPA, Air Quality Criteria for Ozone and Other Photochemical Oxidants, Vol. 11, EPA-600/8-84-020B, ECAO, Research Triangle Park, NC, November, 1985. 8 G.T. Wolff and P.J. Lioy, Environ. Sci. 6 Tech., 14 (1980) 1257-1260. 9 F.U. Vukovich and J. Fishman, Atmos. Environ., 20 (1986) 2423-2433. 10 P.J. Lioy and P.J. Samson, Environ. Internat., 2 (1979) 77-83. 11 W.E. Cleveland, B. Kleiner, J.E. McRae, and J.L. Warner, Science, 191 (1976) 179-181. 12 P.J. Rombout, P.J. Lioy, and B.D. Goldstein, JAPCA, 36 (1986) 913-917. 13 R.L. Berglund, A.C. Dittenhoefer, H.M. Ellis, B.J. Watts, and J.L. Hansen, 1987 Proc. APCA Conf. on The Scientific and Technical Issues Facing Post Ozone Control Strategies, Pittsburgh, PA, 1988. 14 R.A. Paul, W.F. Biller and T. UcCurdy, Proc. Intern. APCA 80th Annual Ueeting, 87-42.7, Pittsburgh, PA, 1987.
-
721 15 C.S. Stevens, Atmos. Environ., 21 (1987) 523-530. 16 2. Vukmirovic, D. Spasova, D. Markovic, D. Veselinovic, D. Vukmirovic, C. Stanojevic, M. Popovic and A. Hadzpavlovic, Atmos. Environ., 21 (1987) 1637-1641. 17 D.T. Mage, M. Raizenne and J. Spengler, Transactions of APCA, S.D. Lee,ed., TR-4 (1985) 238-249. 18 R.J. Allen and R.A. Wadden, Environ. Research, 27 (1982) 136-149. 19 C.F. Contant, B.M. Gehan, T.H. Stock, A.H. Holguin, and P.A. Buffler, Transactions of APCA, S.D. Lee ed., TR-4 (1985) 250-261. 20 M. Lippmann, P.J. Lioy, G. Leifauf, K.B. Green, D, Baxter, M. Morandi, and B.S. Pasternack, Adv. in Med. Environ. Toxicol., M.A. Melman and S.D. Lee, ed., 5 (1983) 423-446. 21 D.M. Spektor, M. Lippmann, P.J. Lioy, G.D. Thurston, K. Citak, D.J. James, N. Bock, F. Speizer and C. Hayes. Am. Rev. of Resp. Dis., In Press (1988).
ACKNOWLEDGEMENT: The authors wish to thank Drs. B. Goldstein and L. Berrafato for discussions on the analyses. Mrs. Arlene Bicknell for diligently typing the manuscript.
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T.Schneider et al. (Editors),Atmospheric Ozone Research and its Policy Implications 0 1989 Elsevier Science Publishers B.V.,Amsterdam -Printed in The Netherlands
723
PATHOBIOCHEMICAL EFFECTS IN RAT LUNG RELATED TO EPISODIC OZONE EXPOSURE
L. VAN BREE.'
P.J.A ROMBOUT,' I.M.C.M. RIETJENS,l'a J.A.H.A.
DORMANS,2 and
M. MARRA' 'Laboratory of Toxicology and %aboratory of Pathology, National Institute of Public Health and Environmental Protection, P.O. Box 1, NL-3720 BA Bilthoven (The Netherlands) SPresent address: Department of Biochemistry, Agricultural University, Dreijenlaan 3, NL-6703 HA Wageningen (The Netherlands)
ABSTRACT Correlation of ozone aerometrics with data from health effect studies on ozone suggests that the present ozone standard is inadequate to protect public health. To develop ozone exposure-effect relationships, the present study was performed to determine the effects of ozone in rats following prolonged, episodic exposure. Acute pulmonary injury and inflammation, as assessed by lung lavage protein increase and neutrophil influx, following 3 consecutive, 12 h nocturnal exposures to 0.4 ppm appeared to be primarily induced by the first exposure and showed full reversibility in spite of continuance of exposure. Biochemical indices for cell proliferation and lung tissue repair, however, showed continual increases during consecutive exposures. Assessment of characteristic cell functions in isolated Clara cells and in alveolar macrophages and type I1 cells following continuous ozone exposure to 0.8 ppm (7 days) or 0.75 ppm (4 days), respectively, revealed that lung cell proliferation coincides with cellular biochemical changes which might be looked upon as potentially adverse. Collectively, these data call upon health risk evaluations of episodic ozone effects and reinforce the need for extension of the data base in this respect. INTRODUCTION Ozone aerometrics in The Netherlands as well as the United States of America reveal that episodes of increased photochemical activity may last up to twelve consecutive days and that several of such episodes may occur during a summer season (refs. 1-2). Moreover, actual diurnal ozone concentration profiles show broad peaks with mean ozone concentrations of 90% of the maximal 1 h mean during 8 h and 80% of the maximal 1 h mean during 12 h (ref. 3). Concern has risen that the present Dutch ozone standard of 0.12 ppm (0.24 mg/ms) as the maximal 1 hour mean concentration not to be exceeded more than three times a year, will not adequately protect the public from the adverse health effects of a single exposure, let alone of (repeated) episodic and extended diurnal exposures. At present there is no literature providing a data base which might be used for risk assessment based on the ozone concentration, exposure time per day,
724 number of consecutive exposure days and sequence of episodes. Therefore, quantitative exposure-response models for ozone exposure need to be developed to create a firm basis for setting rational ozone standards. Rombout et al. (ref. 4) reported on various ozone exposure regimens in rats and showed that both exposure time per day and number of exposure days have a profound influence on acute lung injury and repair, although exposure time per day exerted twice as much effect compared to number of exposure days. There is, however, a scarcity of data on the separate contribution of consecutive exposure days to ozone-induced pulmonary effects and only preliminary results have been mentioned (ref. 5). This paper reports data from animal toxicity studies on the effects of ozone during episodic exposure simulations. The first part will focus on the additional contribution of three consecutive exposure days on ozone-induced acute pulmonary lesions and subsequent tissue repair and is part of a joint research program between the Health Effects Research Laboratory of the US-EPA and the National Institute of Public Health and Environmental Protection of The Netherlands. The second part of this report will light on studies with prolonged ozone exposures which were initiated to determine whether shifts in lung cell populations during pulmonary tissue repair will be accompanied by biochemical and functional changes in type I1 cells and Clara cells. These cell types act as stem cells in the proximal alveolar and terminal bronchiolar regions, respectively, and have characteristic €unctions with respect to lung physiology and metabolism of xenobiotic compounds (refs. 6-11). METHODS Animal exposure Eight-week-old male Wistar rats (180-200 g) were obtained from the Institute's, specific-pathogen-free,breeding colony and were randomized allocated to equal-sized groups. The rats were permanently housed in 0.2-ma stainless steel and glass inhalation chambers with a 12 h light schedule from 06.0018.00 h. The air flow through the chambers was maintained at 6 ma/h. The air was filtered with Purafil-, activated charcoal- and high-efficiency particle filters and was conditioned at a temperature of 22 f 1'C and a relative humidity of 55 f 5%. Ozone was generated from oxygen by irradiation with ultraviolet light (W)and was mixed with the inlet air of the exposure chamber. Ozone concentrations were monitored continously with W-photometric Monitor Labs analyzers, which were calibrated daily. An Altos Corporation microcomputer was used to control the exposures.
725 Lung tissue fractions and cell populations Preparation of lung cytosolic and microsomal fractions from homogenized, perfused lungs were performed as described recently (ref. 12). Bronchiolar Clara cells were isolated using the centrifugal elutriation method (ref. 13), with some modifications to improve the yield of Clara cells and to enhance the cytochrome P-450-linked enzyme activities (refs. 12,14). Alveolar macrophages and type I1 cells were isolated as originally described by Mason et al. (ref. 15), using Percoll density gradient centrifugation (for type I1 cells) and primary cell culturing as reported (ref. 16). Electron microscopy was used to check the reliability and purity of these cell preparations. Preparation of cell-free bronchoalveolar lavage fluid (BAL) was performed as described by Hatch et al. (ref. 17). Differential cell counting in lavage fluid was performed using cytospin preparations, fixation with 96% ethanol and May Grilnwald-Ciemsa staining. Morphometry was performed to quantify the numbers of Clara cells and type I1 cells in rat lung as described recently (ref. 12). Biochemical assays The level of total protein in BAL, lung cytosol and microsomes was quantified by the Lowry method (ref. 18) with bovine serum albumin as the standard. The activity of lactate dehydrogenase (LDH) in lung cytosol was assayed at 37'C in 50 mM Tris-buffer, pH 7.4, with 5 mM EDTA, 0.15 mM NADH and 1.22 mM pyruvate by measuring the decrease in absorbance at 340 nm and was calculated using an extinction coefficient of 6220 M-l .cm-l. Glucose 6-phosphate dehydrogenase (C6PDH) and glutathione peroxidase (CSHPx) activities in lung cytosol and isolated lung cells were measured as described recently (ref. 16). Ethoxyresorufin 0-deethylase (EROD) and pentoxyresorufin 0-dealkylase (PROD) activities in lung microsomes and isolated Clara cells were determined by the direct dynamic fluorometric assay as described by Pohl and Fouts (ref. 19) in the presence of 0.4 mM NADPH and using 1.5 pI4 ethoxyresorufin and 10 f l pentoxyresorufin, respectively. Ethoxycoumarin 0-deethylase (ECOD) was measured according to the fluorometric assay of Ullrich and Weber (ref. 20) using 0.4 mM of the substrate 7-ethoxycoumarin and an NADPH-generating system. Microsomal incubations were run with 0.1-0.2 mg microsomal protein/ml assay. Cellular activities were assayed at maximally 10' cells/ml assay (EROD and ECOD) or at maximally 10' cells/ml assay (PROD) using at least three different cell concentrations.
RESULTS 1. Acute pulmonary effects during episodical ozone exposure
To assess the distinct contribution of consecutive exposure days to the ozone-induced acute effects, rats were exposed to 400 ppb ozone for 1, 2 or 3 days during 12 h/night (i.e. their nocturnal period). BAL protein, as lung permeability parameter, revealed a maximal response 24 h after the start of a single nighttime exposure and reached control level 3 days later (see Fig. la). The same figure depicts that, plotted at the proper time axis, the second and the third nighttime exposure periods contributed only marginally to the effect provoked by the first exposure period and no additional increase or plateau was observed. Similar data were obtained for BAL albumin accumulation (data not shown). Figure lb visualizes BAL. data on the increase in percentage of polymorphonucleated cells (PMN), taken as a marker for lung inflammation. The results indicate that the second and third nocturnal exposure periods did not contribute at all to the increase of PMN following the initial exposure. It appears that PMN levels normalized in spite of the continuance of exposure. When this episodic exposure protocol was applied to study pulmonary tissue repair following ozone-induced injury, the effects are different. Taking lung LDH activity as an indicator of tissue repair, it appears that single, nocturnal ozone exposure induced a significant increase in activity with a maximal effect between 2 and 3 days following the start of exposure (see Fig. lc). In addition, this figure illustrates the increasing effect resulting from a second and third exposure period. These data, however, also show that the additional effect of the third successive nocturnal exposure period became smaller and that the LDH activity remained at a plateau value for several days. Similar results were obtained for antioxidant enzyme activities in lungs of control and ozone-exposed rats (results not shown). 2 . Clara cell characteristics following prolonged ozone exposure
To investigate whether lung cell and tissue repair processes following prolonged ozone exposure will coincide with specific changes in lung cell biochemical function, the Clara cell was studied as the non-ciliated cell type replacing bronchiolar ciliated cells. The prominent cytochrome P-450-linked xenobiotic metabolism feature of this cell type was taken as functional parameter. Rats were exposed to 800 ppb ozone for 24 h/day during 7 days and metabolic capability was characterized in whole lung microsomes as well as in isolated Clara cells using substrates indicative for different cytochrome P450 isoenzymes (EROD, ECOD and PROD). In whole lung microsomes from ozone-
exposed rats EROD and ECOD activities were unchanged or even significantly
727
01 0
1
2
3
4
6
6
7
0
9
2
3
4
1
a
7
a
9
--I
120
-
Im
no
0
1
DAYS AFTER START OF O Z O N
Fig. labc. Postexposure increases of bronchoalveolar lavage fluid (BAL) protein and polymorphonucleated cell (PMN) level and of total lung lactate dehydrogenase (LDH) activity in rats following 0.4 ppn ozone exposure during 3 consecutive, 12 h nocturnal periods. BAL protein and lung LDH data for 1 (+), 2 (A) or 3 (0) periods were plotted as percentage of control, compared with controls at every time point of sacrifice. BAL PMN level was plotted as percentage of total cells after 1(A), 2 (0) or 3 (+) exposure periods and for control rats (+). Data are the means of 4 anioals per group.
dU t
WHaE LING
lKRac4Es
CLARA C a L S
I
Fig. 2. Effects of 0.8 ppm ozone exposure of rats for 24 h/day during 7 days on cytochrome P-450-linked 0-dealkylation of ethoxyresorufin (EROD), ethoxycoumarin (ECOD) and pentoxyresorufin (PROD) in whole lung microsomes and isolated Clara cells. Activity was calculated per milligram microsomal protein ( O ) , picomole cytochrome P-450 ( e ) or loo cells ( 0 ) and expressed as percentage change of control. Values are the means of at least six experiments (for details see ref. 12). Data are statistically significant at p<0.05, unless indicated otherwise, and n.8.- not significant (Student's t-test).
TABLE 1 Effect of ozone exposurea of rats on Clara cell morphometrics and on cellular features of isolated Clara cell preparations.
Parameter Number of Clara cells per mm basal membrane length of terminal bronchiole Number of isolated Clara cells in 10' cells/lung Trypan blue exclusion (a) Percentage of Clara cells Percentage of type I1 cells
Control
Ozone-exposed
47.1 f 2.0
53.7 f 3.5 (n.s.)
1.31 f 0.13 96 f 1 43 2 3 + 1
2.65 f 0.47 97 f 1 (n.s.) 39 f 1 (n.s.) 17f3
+
aExposure is 1.6 f 0.1 mg/na, 7 days, 24 h/day. Morphometric data are the mean f SEM of three animals. Cell isolation data are the mean f SEPI of seven p < 0.01, n.8.- not significant experiments. Significance is indicated as (Student's t-test).
*
729 reduced when expressed per milligram (mg) microsonal protein or per picomole cytochrome P-450, respectively (see Fig. 2). Mfcrosomal PROD activity, however, appeared to be unchanged or significantly induced following ozone exposure when expressed per mg of microsomal protein or per picomole cytochrome P-450, respectively (see Fig. 2). Ozone exposure caused a similar dual effect on substrate metabolism in isolated Clara cell preparations i.e. reduction of EROD and ECOD activity and no change in PROD activity, when calculated on a cell number basis (see Fig. 2). Data from lung morphometric analysis did not show an ozone-induced increase in the number of Clara cells in the terminal bronchiole, although cell isolation data demonstrated that twice as much Clara cells were isolated from ozone-exposed rats compared to control rats (see Table 1).
3. Macrophage/type I1 cell characteristics following prolonged ozone exposure ~
~~~~~~
The effect of prolonged ozone exposure on lung cell proliferation was also studied with alveolar macrophages and type I1 cells. Rats were exposed to 750 ppb ozone for 24 h/day during four days and pulmonary antioxidant enzyme characteristics were determined in both whole lung cytosol and in isolated alveolar macrophages and type I1 cells. Figure 3 depicts the ozone-induced increases in cytosolic protein per lung and in specific activities of G6PDH
Fig. 3. Effects of 0.75 ppm ozone exposure of rats for 24 h/day during 4 days on protein level and glucose 6-phosphate dehydrogenase (G6PDH) and glutathione peroxidase (GSHPx) activity in whole lung cytosol and isolated macrophages and type I1 cells. Values are expressed as percentage change of control and are the means of at least five experiments (for details see ref. 16). Data are statistically significant at p
730
and GSHPx in whole lung cytosol. The ozone-induced increase in specific activity of GSHPx was even larger in alveolar macrophages and type I1 cells, but specific activity of G6PDH was not induced in these cells (see Fig. 3).
DISCUSSION Exposure to near-ambient levels of ozone (below 1 ppm) results in biochemical and morphological changes in lung tissue related to injury and repair. Increases in total protein and PMN level in bronchoalveolar washings have proved to be parameters for acute lung injury indicative for alveolar-capillary damage and inflammation. In this study BAL. protein and PMN data following repeated nocturnal ozone exposure clearly show that the acute injurious and imflammatory effect and its recovery is primarily governed by the first nocturnal period. The lack of significant effect of additional exposure periods and the full recovery even during continuance of ozone exposure suggest the development of a tolerance mechanism. This attenuated response, even developing following single exposure, might also include cross-tolerance to other oxidants like oxygen or nitrogen dioxide (refs. 21-22). The normalizing neutrophil level during continuance of ozone exposure, however, raises serious questions with respect to a compromised host defence system for inflammatory response and urgently requires additional studies. Biochemical data of total lung tissue demonstrate the ongoing and longlasting process of cell proliferation and differentiation during exposure and postexposure periods. This increasing response following three exposure days initially functions as a tissue repair mechanism and might also serve as a better defense against the oxidant environment. The lung’s metabolic response following injury by oxidants is, however, complicated to interpret because changes could be the result of intracellular biochemical changes superimposed on shifts in pneumocyte populations during reepithelialization. Therefore, in the present study cell populations isolated from rats exposed to ozone for several days were biochemically evaluated for some characteristic features. The hypertrophic Clara cell population appeared to have differentially altered cytochrome P-450 isoenzyme activity and studies in our laboratory are underway to evaluate the toxicological consequences of this phenomenon. The increased macrophage and type I1 cell GSHPx activity may be regarded as an adaptive response to oxidant stress, although in-vitro studies have shown that these cells do not exhibit a decreased sensitivity for ozone damage (ref. 16). Studies are warranted to evaluate whether such a preferential induction of the antioxidant enzyme system takes place at the cost of other essential cell functions. Remarkably, it has been demonstrated that a toxic insult which compromizes a reepithelialization process of type I1 cells may favor the development of pulmonary fibrosis (refs. 23-24). In addition to this, it
731 appears that complete maturation and differentiation of type I1 cells and ciliated cells to type I cells and non-ciliated cells, respectively, do not occur during ozone exposure, irrespective of the exposure duration (refs. 2, 25). In conclusion, episodic ozone exposure for several consecutive, nocturnal periods in rats causes acute pulmonary injury and inflammation, which is primarily induced by the first exposure period and which seems to be reversible in spite of continuance of exposure. Whether this effect should be considered as a general tolerance phenomenon remains to be established. A possibly compromized host defense capability merits further attention to assess an increased risk for respiratory infection. The results of prolonged ozone exposure indicate, however, that lung cell proliferation processes in order to repair the damaged tissue proceed during exposure and, in addition, accompany intracellular biochemical changes with the potential of having adverse implications. Further studies are needed to evaluate the adverse health effects of episodic oxidant exposure including the number of exposure days within an episode and the number of intermittent episode exposures with varying postexposure periods of recovery. Recently published animal toxicity data on the larger effects caused by intermittent chronic ozone exposure compared to continuous chronic exposure support this need (ref. 26). Therefore, in addition to the discussion for a multihour ozone standard, rational health risk evaluations of ozone should also address the (adverse) effects of (repeated) episodic exposure. ACKNOWLEDGEME" The authors gratefully acknowledge the Drs. Miller and Costa (HERL-EPA) for their stimulating discussions at the onset of the joint research program with the RIVH (The Netherlands). We would also like to thank Martin Poelen, John Boere, Jan Bos, Paul Fokkens, Ynze Baumfalk and Marian Verhoef for their expert technical assistance. REFERENCES 1 J.-W. Erisman, Enkele aspecten van 1 uur- en 8 uurgeniddelde ozonconcentraties in Nederland [Some aspects of 1 hour and 8 hour mean ozone concentrations in The Netherlands), National Institute of Public Health and Environmental Protection, report no. 758474001, Bilthoven, 1987. 2 U.S. Environmental Protection Agency. Air Quality for Ozone and Other Photochemical Oxidants. Washington, D.C.: Environmental Criteria and Assessment Office, 1986. 3 P.J.A. Rombout, P.J. Lioy and B.D. Goldstein, JAPCA, 36 (1986) 913-917. 4 P.J.A. Rombout, L. van Bree, S.H. Heisterkamp urd N. Marra. in H.F. Hartman (Editor), Proc. 7th World Clean Air Congress, H o h s Ltd., Melbourne, 1986, pp. 203-211. 5 P.A. Bromberg, personal comnmication. 6 L.W. Schwartz, D.L. Dungworth, M . G . Mustafa, B.K. Tarkington and W.S. Tyler, Lab. Invest., 34 (1976) 565-578.
732 7 M.R. Boyd, Nature (London), 269 (1977) 713-715. 8 J.D. Crapo, J. Marsh-Salin, P. Ingram and P.C. Pratt, J. Appl. Physiol.: Respir. Environ. Exercise Physiol. 3 (1978) 370-379. 9 H. Lum, L.W. Schwartz, D.L. Dungworth and W.S. Tyler, Am. Rev. Respir. Die., 118 (1978) 335-345. 10 T.R. Deverew, Environ. Health Perspec., 56 (1984) 95-101. 11 R.M. Philpot and B.R. Smith, Environ. Health Perspect., 55 (1984) 359-367. 12 I.M.C.M. Rietjens, J.A.H.A. Dormans, P.J.A. Rombout and L. van Bree, J. Toxicol. Environ. Health, 24 (1988) 515-531. 13 K.G. Jones, J.F. Holland and J.R. Fouts, Cancer Res., 42 (1982) 4658-4663. 14 T.R. Devereux, J.J. Diliberto and J.R. Fouts, Cell Biol. Toxicol., 1 (1985) 57-65. 15 R.J. Mason, M.C. Williams, R.D. Greenleaf and J.A. Clements, Am. Rev. Respir. Dis., 115 (1977) 1015-1026. 16 I.M.C.M. Rietjens, L. van Bree, H. Marra, M.C.H. Poelen, P.J.A. Rombout and G.M. Alink, Toxicology, 37 (1985) 205-214. 17 G.E. Hatch, R. Slade, A.G. Stead and J.A. Graham, J. Toxicol. Environ. Health, 19 (1986) 43-53. 18 O.H. Lowry, N.J. Rosebrough, A.L. Farr and R.J. Randall, J. Biol. Chem., 193 (1951) 265-275. 19 R.J. Pohl and J.R. Fouts, Anal. Biochem., 107 (1980) 150-155. 20 V. Ullrich and P. Weber, Hoppe-Seylers 2. Physiol. Chem., 353 (1972) 11711177. 21 R.M. Jackson and L. Frank, Am. Rev. Respir. Dis., 129 (1984) 425-429. 22 2. Nambu and E. Yokoyama, Environ. Res., 32 (1983) 111-117. 23 W.M. Haschek and H. Witschi. Toxicol. Appl. Pharmacol., 51 (1979) 475-487. 24 J. Rinaldo, R.H. Goldstein and G.L. Snider, Am. Rev. Respir. Dis., 126 (1982) 1030-1033. 25 M.J. Evans, L.V. Johnson, R.J. Stephens and G. Freeman, Exp. Mol. Pathol., 24 (1976) 70-83. 26 W.S. Tyler, N.K. Tyler, J.A. Last, M.J. Gillespie and T.J. Barstow, Toxicology, 50 (1988) 131-144.
733
T. Schneider et al. (Editors),Atmospheric Ozone Research and its Policy Implications 0 1989 Elsevier Science Publishers B.V.. Amsterdam -Printed in The Netherlands
PULMONARY FUNCTION STUDIES I N THE RAT ADDRESSING CONCENTRATION VERSUS T I M E
RELATIONSHIPS OF OZONE
D.L.
Costa,'
G.E.
Hatch,'
J. H i g h f i l l , 2 M.A.
Stevens,3 J . S . TepperJ
Environmental P r o t e c t i o n Agency, Health E f f e c t s Research Laboratory, Research T r i a n g l e Park, NC, 27711
'U.S.
'Toxicology Branch, MD 82, Health E f f e c t s Research Laboratory, U.S.E..P.A., Research T r i a n g l e Park, NC (USA). 'Biometry D i v i s i o n , MD 55, Health E f f e c t s Research Laboratory, U.S.E..P.A., Research T r i a n g l e Park, NC (USA). 3Northrop Services,
Inc. PO Box 12313, Research T r i a n g l e Park, NC, 27709
ABSTRACT Recent data from human studies suggest t h a t t h e c u r r e n t 1 h r National Ambient A i r Q u a l i t y Standard (NAAQS) f o r 03 may not be appropriate f o r exposures o f several hours. Animal s t u d i e s are being used t o f u r t h e r i n v e s t i g a t e t h i s issue: (1) A polynomial model has been developed t o d e p i c t lung i n j u r y from the i n t e r a c t i o n of 03 concentration (C) and exposure d u r a t i o n ( T ) . The model was derived from lung f l u i d p r o t e i n values i n r a t s exposed i n a m a t r i x design t o 0.1 t o 0.8 ppm 03 f o r 2, 4, o r 8 hrs. Airway dysfunction was correl a t e d only a t the highest CxT products. ( 2 ) Rats, exposed t o 0.5 o r 0 . 8 ppm 03 f o r 2 o r 7 hours w i t h i n t e r m i t t e n t 8% C02 t o augment v e n t i l a t i o n , were e v a l uated w i t h s t a t i c and dynamic lung f u n c t i o n t e s t s . P r o t e i n leakage i n t o the airspace was a l s o assessed. Although, t h e impact o f T on 03 t o x i c i t y appeared t o be C-dependent, loss o f f u n c t i o n was not necessarily l i n e a r . C o l l e c t i v e l y , these studies provide a p r e l i m i n a r y b a s i s f o r the e v a l u a t i o n o f d u r a t i o n o f exposure on the pulmonary response t o 03. INTRODUCTION Controlled human studies c l e a r l y i n d i c a t e acute, pulmonary f u n c t i o n when healthy subjects pheres o f near-ambient
l e v e l s o f 03 (1).
r e v e r s i b l e decrements i n
i n t e r m i t t e n t l y exercise Recently,
i n atmos-
however, a i r monitoring
data from both urban and non-urban l o c a l e s suggest t h a t t h e sharp p r o f i l e o f
03 build-up California
and decay
typical
of
t h e South Coast
i s not broadly applicable
(2).
Rather,
Air
Basin o f
Southern
t h e more common d i u r n a l
p r o f i l e o f 03 i s one characterized by an extended period, 6 hours o r more, o f
03
l e v e l s o f t e n j u s t below t h e 1 hour 03 NAAQS o f 0.12 ppm.
Hence, concern
i s growing t h a t a standard based on h e a l t h data derived from s h o r t ,
peak-
exposure challenges may not represent t h e p o t e n t i a l r i s k o f an extended exposure t o 03
concentrations, o s t e n s i b l y w i t h i n "compliance."
New evidence suggests t h a t the t o x i c i t y o f 03 may, i n f a c t , be cumulative over the course o f several hours. Using data sets compiled from several human
734 studies of 03-induced
lung dysfunction,
Folinsbee and coworkers (3) hypothe-
sized that the f a l l i n F E V l and FVC might f o l l o w a " e f f e c t i v e dose" estimate based on the product of C and T when adjusted f o r v e n t i l a t i o n . This " e f f e c t i v e dose"
-response
relationship
challenged w i t h 0.12
held f o r
ppm 03 f o r
6.6
their
own study
i n human subjects
hours (under conditions o f simulated
"workday" exercise), and most recently, appeared applicable t o as low as 0 . 0 8 ppm under s i m i l a r exposure conditions (4). A t present,
few published animal studies appear t o have any relevance t o
the "effective-dose''
issue,
sometimes r e f e r r e d t o as the CxT issue ( 5 - 7 ) .
These studies suggest a l i n e a r i t i e s i n response due e i t h e r t o predominance o f C over T or t o unknown host o r other stress factors. Thus, as p a r t o f a j o i n t e f f o r t on the p a r t o f investigators o f t h e Health E f f e c t s Research Laboratory of
the USEPA and the Netherlands National I n s t i t u t e o f
Public Health and
Environmental Hygiene (RIVM), animal studies have been i n i t i a t e d t o elaborate on the CxT hypothesis f o r 03. This r e p o r t summarizes two p o r t i o n s o f t h a t e f f o r t being undertaken by the USEPA: [ l ] A lung i n j u r y model based on p r o t e i n permeability i n t o the lung has been developed from a CxT 03 exposure matrix. [ 2 ] Animal studies, patterned a f t e r those i n humans (3,4),
have been conducted
t o evaluate the concept o f time-based cumulative lung t o x i c i t y .
METHODS
General Animal and Exposure Information A l l r a t s used i n these studies were approximately 90 day-old Fischer 344,
males obtained from Charles River Breeding Labs, Raleigh, NC. They were maintained under b a r r i e r (SPF) conditions u n t i l the day o f study (1-2 weeks). The r a t s were randomized by weight groups t o provide s i m i l a r mean f s.e.
body
weights f o r the respective study group comparisons. Ozone exposures were conducted
i n individual
stainless-steel
wire-mesh
modules w i t h i n 0.3 m3 Rochester-type chambers. Control groups were caged ident i c a l l y and exposed t o f i l t e r e d room a i r concurrent w i t h t h e i r respective comp a r i s i o n group(s). Ozone was generated from 02 using a silent-arc-discharge generator (OREC, tion.
03
Phoenix, AZ) and was mixed w i t h f i l t e r e d room a i r f o r d i l u -
The chamber 03 concentration was monitored continuously w i t h e i t h e r a
referenced Bendix chemiluminescent o r Dasibi UV analyzer.
735 111 CxT Matrix Study T h i r t y exposure groups were randomly assigned 6 r a t s each.
Two r e p l i c a t e
experiments were conducted during the same week according the matrix:
[03] ppm I 2 hrs M 4 hrs E 8 hrs
0
0.1
0.2
0.4
0.8
0 0 0
0.2 0.4
0.4 0.8 1.6
0.8 1.6
1.6 3.2 6.4
0.8
3.2
Each c e l l o f the matrix represents the C - T product which could be tested f o r i d e n t i t y o f response (see below).
Bronchoalveolar lavage (BAL) was performed
24-25 hours from the beginning of exposure using 35 m1 s a l i n e per kg body weight and the a c e l l u l a r supernatant was assayed f o r proteir! according t o the method o f Hatch e t a l . ( 8 ) . Selective
lung function t e s t s were performed on cohort groups o f r a t s
immediately a f t e r exposure t o 0.8 o r 1.2 ppm f o r 2, lung properties
were assessed using parameters
expiratory flow-volume elsewhere ( 9 ) . tests.
4. o r 8 hours.
Dynamic
derived from the maximum
and the multi-breath Np washout curves as described
Halothane was used as the anesthesia f o r performance o f these
Immediately thereafter, each r a t was exsanguinated and lavaged f o r BAL
p r o t e i n determination. Two-way ANOVA were conducted f o r C,
T,
and CxT interaction.
Analyses of
the response based on e q u a l i t y o f CxT products was also performed.
Surface
f i t t i n g o f the p r o t e i n data t o develop the response model was based on polynomial f i t t i n g o f i t s log transformation. 121 Acute versus Extended-Duration Exposure Studies Groups ( 6 each) o f r a t s were exposed one time t o 2 o r I hours o f 0.5 o r 0.8 PPm 03. I n t e r m i t t e n t C02 was superimposed upon the 03 exposure t o stimu-
l a t e breathing and induce periodic hyperventilation (10).
This procedure (as
an analogue t o exercise i n human subject t e s t i n g ) was used t o enhance dosime t r y and/or t e s t s e n s i t i v i t y . The 2-hour exposure protocol consisted o f a l t e r nating 15 min Periods of
8% CO2+O3 o r 03 alone while the I
hour protocol
consisted o f seven 45 min periods of 8% CO2+O3 with intervening 15 min r e s t periods w i t h 03
alone.
These protocols were based on human study protocols
previously reported (1,3,4).
Within 1 hour post exposure, each r a t underwent
t e s t s t o assess both s t a t i c and dynamic lung function.
I n a d d i t i o n t o the
dynamic t e s t s represented by the flow-volume and the N2 washout curves, determinations o f lung volume, volume-pressure curve, and d i f f u s i n g capacity f o r CO were conducted ( 9 ) . t e i n was determined.
Thereafrer, as above, the r a t s were lavaged and BAL pro-
736 Data were also analyzed w i t h using 2-way ANOVA assessing both 03 e f f e c t and time e f f e c t ,
as w e l l as,
interaction.
The alpa l e v e l was adjusted t o
p < 0.01 f o r selection o f subgroup comparisons f o r subtesting.
RESULTS 111 CxT Matrix Study The r e p l i c a t e d studies o f the CxT matrix demonstrated v i r t u a l l y i d e n t i c a l values f o r BAL p r o t e i n and hence t h e data m r e combined f o r a l l analyses. Twoway ANOVA f o r the f a c t o r s C and T showed s i g n i f i c a n t i n t e r a c t i o n and therefore complicated the t e s t i n g o f the hypotheses about the i n d i v i d u a l e f f e c t s o f these factors. Limited subtesting indicated s i g n i f i c a n t increases i n BAL prot e i n a t 0.8 ppm a t a l l times and 0.4
ppm a t 8 hours. Tests f o r e q u a l i t y o f
response t o C x T products o f equal value ( o f which there were 4 sets, 0.4. 0.8,
1.6,
and 3.2 ppm-hr) indicated t h a t the respective responses were not
distinguishable.
more
A
refined
descriptive
analysis
was,
therefore,
attempted using response-surface f i t t i n g which could incorporate a l l f a c t o r s and define a continuum o f response across a l l possible C and T values across the range examined. the data,
Although a number o f models could reasonably be f i t t o
a polynomial function o f the l o g transformed p r o t e i n values was
selected. The least squares f i t o f the p a r a m t e r s o f the polynomial was: l o g p r o t e i n = 5.13
-
0.99C
-
0.088T t 0.95Ca + 0.17CT
Figure 1A depicts the response surface incorporating both C and T as determinants. The surface p a t t e r n c l e a r l y shows the greater impact o f T on p r o t e i n permeability as concentration increases. I n j u r y isobars extracted from the surface contour and p l o t t e d as a function o f C and T (Fig. l B ) i l l u s t r a t e the progressive c u r v i l i n e a r shape o f the lowest concentrations. Since o n l y minor a l t e r a t i o n s i n dynamic lung function were observed i n r a t s exposed under quiescent conditions t o 0.8 or 1.2 ppm. only these concentration groups were studied. Figure 2 i l l u s t r a t e s the loss o f f l o w a t FEF25 r e l a t i v e t o ppm-hours o f exposure f o r the 0.8 and 1.2
ppm groups.
The
e a r l i e s t e f f e c t s were observed a t 1.2 ppm f o r 2 hours and 0.8 ppm f o r 4 hours. N2 washout (data not shown) exhibited a varied response p a t t e r n w i t h no ppm-hr
relationship.
The changes i n FEF25 correlated w e l l (r-0.71)
w i t h the BAL
p r o t e i n values obtained from these animals when lavaged immediately post testing
.
737
Ozone Ccncurootion @pm)
A
0
u
M
01
I
Carccnmtion
B Figure 1 Plots of lung permeability response to 0 3 exposures with varying C - T . ( A ) 3-D representation o f log protein in lavage fluid as a surface contour relationship. ( B ) Isobar representation o f specific response contours for C - T relationships.
730
Forced Expiratory Flow at 25% FVC 120 110
1
+
c
-0- 0 exposed 3
Airconimls
&! ?0760 50
0
2
4
6
8
10
ppm-hours ozone
Forced exoiratory flow a t 25% FVC i n r a t s as a f u n c t i o n o f ppm-hours o f exposure ( C v T ) t o 03 a t 0.8 and 1.2 ppm f o r 2 t o 8 hour duration.
121 Acute versus Extended-Duration Exposure Studies Although data analyses are incomplete,
selected parameters derived from
the lung function t e s t s are presented w i t h a t t e n t i o n focused on how duration o f exposure a f f e c t s the concentration-response
r e l a t i o n s h i p . For the purpose
o f comparison, response w i l l be presented as percent o f i t s respective c o n t r o l and "dose" w i l l be represented i n terms o f a r e l a t i v e " e f f e c t i v e " "dose". "relative"
This
dose derives from the ppm-hr products o f 0 3 accumulated over eup-
neic and COP augmented v e n t i l a t i o n
(assumed as 3X eupnea based on previous
work) w i t h the 2 hour exposures a t 0.5
o r 0.8
pprn set a t u n i t y f o r t h e i r
respective 7 hour exposures. The r e s u l t a n t computation o f " r e l a t i v e dose" i s a form o f " e f f e c t i v e dose" as computed by Folinsbee and coworkers ( 3 ) . I n i t i a l l y
739 the e f f e c t i v e dose (ED) was computed as follows: ED = c - T - ~ ~ E
where
PE was the integrated minute v e n t i l a t i o n f o r the respective exposure
period. equal
The ED f o r the 2 hour exposures t o 0.5 and 0.8 ppm were taken as t o unity,
RD=l f o r comparison w i t h t h e i r respective 7 hour
i.e.,
exposure group.
Hence,
both exposure groups a t 7 hours are represented
graphically as 4.38 x the dose o f i t s 2 hour cohort. the Folinsbee e t a l .
A similar translation of
( 3 ) data t o a s s i s t i n comparison o f the human and r a t
data on the basis o f cumulative dose (time dependent i n j u r y a t s p e c i f i c concentrations o f 0 3 ) . Significant
effects
on
lung function were observed f o r
a l l exposure
groups. However, the nature o f the e f f e c t was not necessarily consistent w i t h the concept o f l i n e a r i t y f o r cumulative t o x i c i t y (Figure 3 ) . reported i n human studies ( 3 , 4 ) ,
As has been
however, the FVC f e l l w i t h cumulative dose
(Figure 3 A ) , but while duration o f exposure l e d t o progressive impairment i n each case (0.5 and 0.8 ppm f o r the rats, as w e l l as 0.12 ppln f o r the humans), the impact o f T on the response increased w i t h increasing concentration (as judged by the slope o f the l i n e s ) .
BAL p r o t e i n (Figure 30) shcmed a generally
l i n e a r response w i t h T f o r each C,
but u n l i k e the data from [1] d i d not
correlate p a r t i c u l a r l y w e l l w i t h loss o f function i f compared on ppm-hr basis as was done i n study [l]. DISCUSSION
Human studies have demonstrated t h a t 03 exposures extending over several hours a t or below the current 1 hour NAAQS o f 0.12 ppn cause progressive lung impairment ( 3 , 4 ) .
Moreover, the degree o f impairment appears t o be a product-
function o f C, T, and $,
known as "effective-dose."
From these observations
has emerged the hypothesis t h a t i f v e n t i l a t i o n i s known o r fixed, the product of
CxT can be used t o p r e d i c t adverse e f f e c t s over the range o f
likely
environmental encounters w i t h 03. The concept o f CxT=K f o r the p r e d i c t i o n o f t o x i c i t y i s not new, and has proven h i s t o r i c a l l y t o be q u i t e useful i n characterizing the t o x i c "dose" o f a number o f inhalants (111, including 0 3 ( 5 ) .
However, i t s u t i l i t y was long
ago concluded t o be l i m i t e d t o gross endpoints, e.g., acute,
high-level exposures.
m o r t a l i t y , a r i s i n g from
The r e b i r t h o f t h i s concept f o r a p p l i c a t i o n t o
a i r q u a l i t y standards and p r e d i c t i n g and/or
quantifying adverse e f f e c t s a t
ambient l e v e l s of 0 3 w i l l have, i f shown t o be reasonably v a l i d ,
important
implications i n the assessment o f r i s k and i n the evaluation o f t h e adequacy o f the current NAAQS.
740
Figure 3 Lung function alterations due t o 2 or 7 hours of exposure t o 0.5 o r 0.8 ppm 0 3 with intermittent C o p . Data are plotted as a function of C - T - V E integrating normal and hyperventilation with the 2 hour exposure groups normalized t o 1. Hence the e f f e c t o f time dependent increments i n dose could be cumpared for each concentration group.
741 The studies reported herein demonstrate t h a t there i s indeed i n t e r a c t i o n between C and T i n the expression of non-lethal 03 t o x i c i t y .
However, rather
than a straightforward CxT product (assuming v e n t i l a t i o n t o be f i x e d ) determining the magnitude of effect,
the matrix study c l e a r l y demonstrated t h a t the
dose-determinant r e l a t i o n s h i p o f C and T, over a broad ambient range, was best depicted by response-surface polynomial. This polynomial model of lung i n j u r y predicts t h a t response i s more T-dependent a t higher C's, i.e., the impact of T on response i s C-dependent. I n t e r e s t i n g l y , a t the highest C and T c o o r dinates of the matrix, CxT-product dependence was, i n f a c t , reasonably predictive.
The apparent CxT r e l a t e d reductions o f FCF25 (Figure 2) i n r a t s a t 0.8
and 1 . 2 ppm were consistent w i t h t h i s relationship.
(t0.2 ppm),
however,
A t the lowest C values
the response model depicts hyperbolic contours which
suggested a potentiated i n t e r a c t i o n o f C and T.
I f one uses the isohalogram
concept o f i n t e r a c t i o n between factors which would apply a l i n e a r CxT model across the C response l i n e f o r the curve f a r t h e s t t o the l e f t i n Figure 16, one would see that the response a t any given CxT would be underestimated by the l i n e a r form.
Thus, the model would suggest loss o f the C dependence o f T
a t the lowest C,
but would predict the emergence o f a synergism between the
variables.
I t should be noted,
however, t h a t t h i s p o r t i o n o f the polynomial
i s weakest i n terms o f data due t o the minimal changes observed.
Further low
concentration versus extended time studies should be conducted t o r e f i n e t h i s p o r t i o n o f the model and strengthen o r r e f u t e t h i s i n t e r p r e t a t i o n . The C-dependence o f T i n determining response i s affirmed by the r e s u l t s of the acute/extended exposure studies a t 0.5 and 0.8 ppm. I n t e r e s t i n g l y , r a t s exposed t o 03 experience much the same type o f lung dysfunction as humans, p a r t i c u l a r l y the reduction i n FVC. parallel
those
in
humans
which
Moreover, the r a t studies, indicate
cumulative
03
designed t o
toxicity,
also
demonstrated a T-dependent progression o f dysfunction. Although o n l y two timepoints were examined f o r each concentration o f 03, the reduction o f FVC which was l a r g e l y l i n e a r a t 0 . 5 ppm was markedly i n f l e c t e d a t 2 hours f o r the 0.8 ppm group. This C-dependent s h i f t i n the T o r cumulative aspect o f 03 t o x i c i t y was also seen w i t h lavage f l u i d p r o t e i n from these animals but these variables were not s i g n i f i c a n t l y correlated. The CxT dependence f o r lung function was completely consistent w i t h the matrix r e s u l t s discussed above.
However, the hyperbolic r e l a t i o n s h i p o f low
CxT could not be assessed i n these l a t t e r experiments since 0 . 5 ppm was the lowest concentration studied.
Nevertheless, when combined w i t h the FVC data
742 from humans exposed t o 0.12 ppm f o r 6.6 hours (Figure 3A), there was a cons i s t e n t C-dependence o f T r e l a t i o n s h i p on FVC across the two species.
It
should a l s o be noted t h a t although the FVC reduction seemed t o be l i n e a r l y r e l a t e d w i t h dose, t h i s r e l a t i o n s h i p d i d not not hold f o r a l l f u n c t i o n paramet e r s (Figure 3B,C)
-
a f i n d i n g not s u r p r i s i n g i n view o f the interdependent
mechanical f u n c t i o n o f the lung. I n conclusion, 03 appears t o a l t e r lung f u n c t i o n i n the r a t i n much the same manner t h a t f u n c t i o n i s a l t e r e d i n human subjects. The impact o f 03 on function i n r a t s appears a l s o t o be cumulative w i t h d u r a t i o n o f exposure. However, the i n t e r a c t i o n o f C and T i s not a simple algebraic one. While both lung dysfunction and a l t e r e d lung permeability seem t o be more dependent on concentration of 03 than duration o f exposure i n determining the degree o f injury,
the influence o f T on response increases markedly w i t h increasing
concentration. dose-rate
Hence, the determinant o f t o x i c i t y may be more a f u n c t i o n o f
than e i t h e r C o r T and may invoke other host-related f a c t o r s i n
u l t i m a t e l y d e f i n i n g the f i n a l t o x i c outcome.
ACKNOWLEDGEMENT
The authors wish t o acknowedge the i n t e g r a l c o n t r i b u t i o n s of members o f the Toxicology Branch f o r t h e i r c o n t r i b u t i o n s i n the completion o f these studies. Specific mention i s made o f D r . Fred M i l l e r and D r . Peter Rombout (RIVM, Netherlands) f o r t h e i r e a r l y discussions o f objectives and designs f o r t h i s initiative.
743 REFERENCES
McDonnell, D.H. Horstman, M.J. Hazucha, E. Seal, E.D. Haak, S.A. Salaam, D.E. House, J. Appl. Physiol.: Respirat. Environ. Exercise Physiol., 54(5) (1983) 1345-1352. P. Rombout, P. Lioy, B. Goldstein, JAPCA, 36:8 (1986) 913-911. L.J. Folinsbee, W.F. McDonne11, D.H. Horstman, JAPCA, 38 (1988) 28-35. D.H. Horstman, W.F. McDonnell, S.A. Salaam, L.J. Folinsbee, P. Ives, Proc. APCA Annual Meeting, (1988) i n press. H.E. Stockinger, AHA Archives o f I n d u s t r i a l Health, 15 (1957) 181-190. L. van Bree, P.J.A. Rombout, M. Marra, S.H. Heisterkamp, The Toxicologist,
1 W.F.
2 3 4 5 6
l(1) (1987) 41a.
I W.J. 8 9
Mautz, T.R. McClure, P. Reischl, R.F. Phalen, T.T. Crocker, J. Toxicol. Environ. Health, 16 (1985) 841-854. G.E. Hatch, R. Slade, A.G. Stead, J.A. Graham, J. Toxicol. Environ. Health, 19 (1986) 43-53. D.L. Costa, J.R. Lehmann, R.S. Kutzman, R.T. Drew, Am. Rev. Respir. Dis.,
133(2) (1986) 286-291. 10 J.S. Tepper, M.J. Wiester, M.E. King, M.F. Weber, D.L. Costa, I n h a l a t i o n Toxicology, (1988) i n press. ed. J. Dorell, C.D. 11 M.O. Amdur, Casarett and Doule's Toxicology: Klaassen, M.O. Amdur (1975) p. 622. DISCLAIMER: This document has been reviewed i n accordance w i t h U.S. Environmental Protection Agency p o l i c y and approved f o r publication. Mention o f trade names or commercial products does not c o n s t i t u t e endorsement o r recommendation f o r use.
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T. Schneider et al. (Editors), Atmospheric Ozone Research and its Policy Zmplicatwna 1989 Elsevier Science Publishers B.V., Amsterdam -Printed in The Netherlands
745
THE INFLAMMATORY RESPONSE I N HUMAN LUNG EXPOSED TO AMBIENT LEVELS OF OZONE
HILLEL
s. K O R E N ~ , ROBERT B. D E V L I N ~ ,DELORES E. G R A H A M ~ , RICHARD
MANN~
AND WILLIAM F. MCDONNELL~
l C l i n i c a 1 Research Branch, I n h a l a t i o n Toxicology D i v i s i o n , Health E f f e c t s Research Laboratory, U.S. Environmental P r o t e c t i o n Agency, Research T r i a n g l e Park, NC 2Center f o r Environmental Medicine and Lung Biology, School of Medicine, University of North C a r o l i n a , Chapel H i l l , NC
ABSTRACT Although ozone (03) has been shown t o induce inflammation i n t h e lungs of animals, very l i t t l e is known about its inflammatory e f f e c t s on humans. I n t h i s study, e l e v e n h e a l t h y non-smoking males, a g e s 18-35 were exposed once t o 0.4 ppm 03 and once t o f i l t e r e d a i r f o r two hours w i t h i n t e r m i t t e n t e x e r c i s e . Eighteen hours later, bronchoalveolar lavage (BAL) was performed and t h e c e l l s and f l u i d were analyzed f o r v a r i o u s i n d i c a t o r s of inflammation. There was a n 8.2-fold i n c r e a s e i n t h e percent of polymorphonuclear leukocytes (PMNs) in t h e t o t a l c e l l population, and a small but s i g n i f i c a n t d e c r e a s e i n t h e p e r c e n t of macrophages following exposure t o 03. Immunoreactive n e u t r o p h i l e l a s t a s e o f t e n a s s o c i a t e d w i t h inflammation and lung damage i n c r e a s e d by 3.8-fold i n t h e f l u i d . Markers of v a s c u l a r p e r m e a b i l i t y showed a two-fold i n c r e a s e . S e v e r a l biochemical markers which could a c t as chemotactic o r r e g u l a t o r y f a c t o r s i n a n inflammatory response were examined i n t h e BAL f l u i d (BALF). The l e v e l of complement fragment C3a was i n c r e a s e d by 1.7-fold. The chemot a c t i c l e u k o t r i e n e B4 was unchanged w h i l e PGE2 i n c r e a s e d 2-fold. In a d d i t i o n , f i b r o n e c t i n , t h e f i b r o g e n i c - r e l a t e d molecule was e l e v a t e d 6.4f o l d i n BALF. Urokinase plasminogen a c t i v a t o r (U-PA), a n e u t r a l p r o t e a s e w i t h f i b r i n o l y t i c a c t i v i t y , i n c r e a s e d by 3.6-fold. Preliminary r e s u l t s from a study addressing t h e e f f e c t of extended 0 3 exposure (7 hours, 0.1 ppm) i n d i c a t e d an i n f l a m a t o r y response i n t h e lower airway evidenced by a 4.8-fold i n c r e a s e i n t h e p e r c e n t of PMN i n t h e BAL. Taken t o g e t h e r , t h e f i n d i n g s show t h a t a n a c u t e exposure t o 0.4 ppm 0 3 as w e l l a s a n extended exposure r e s u l t i n i n c r e a s e d l e v e l s of inflammatory c e l l s pot e n t i a l l y capable of producing damage i n t h e lower airways of humans. DISCLAIMER The r e s e a r c h described i n t h i s a r t i c l e has been reviewed by t h e H e a l t h E f f e c t s Research Laboratory, U.S. Environmental P r o t e c t i o n Agency and approved f o r p u b l i c a t i o n . Approval does n o t s i g n i f y t h a t t h e c o n t e n t s n e c e s s a r i l y r e f l e c t t h e views and p o l i c i e s of t h e Agency nor does mention of t r a d e names o r commercial products c o n s t i t u t e endorsement o r recommendat i o n f o r use.
INTRODUCTION Based on e p i d e m i o l o g i c a l s t u d i e s , o c c u p a t i o n a l h e a l t h i n f o r m a t i o n and f i e l d and l a b o r a t o r y exposure s t u d i e s i n an i m al s and humans, ozone i n ambient a i r i s recognized as a p u b l i c h e a l t h h azar d (ref. 1).
Humans
e x p e r i e n c e a c u t e , r e v e r s i b l e changes i n lu n g f u n c t i o n d u r i n g exposure ( r e f . 2).
Ozone exposure a l s o c a u s e s inflammation ( r e f s . 3 , 4 ) , and i n d u ces a
temporary s t a t e of airway h y p e r r e s p o n s iv e n e s s t o b r o n c h o c o n s t r i c t o r d r u g s
in s e v e r a l mammalian s p e c i e s , i n c l u d i n g man ( r e f s . 5,6). Recently, a n e p i d e m i o l o i g a l s t u d y on h e a l t h y c h i l d r e n i n d i c a t e d t h a t a n ep i s o d e r e l a t e d e f f e c t on pulmonary f u n c t i o n can produce decrements in f u n c t i o n that ex te n d f o r p e r i o d s of about a week beyond the e p i s o d e ( r e f . 7 ) . Furthermore, c e r t a i n p o p u l a t i o n s e x i s t , i n c l u d i n g c h i l d r e n and a c t i v e a d u l t s , who on a g i v en day w it h h i g h ozone c o n c e n t r a t i o n s d u r i n g t h e photochemical smog s eas o n w i l l p a r t i c i p a t e i n o u t d o o r a c t i v i t i e s f o r between 4 and 8 hours.
These f i n d i n g s raise t h e p o s s i b i l i t y t h a t ozone ex p o su r e o v er l o n g
p e r i o d s of t i m e might l e a d t o r e c u r r e n t l u n g damage and c h r o n i c l u n g d i s e a s e , a c o n s i d e r a t i o n t h a t h a s o n l y r e c e n t l y begun t o be t e s t e d i n man ( r e f . 8 )
The mechanism of 03 t o x i c i t y a p p e a r s r e l a t e d t o t h e p r o d u ct i o n of f r e e r a d i c a l s , perhaps through l i p i d p e r o x i d a t i o n of c e l l u l a r membranes. T h i s s u g g e s t s t h e p o s s i b i l i t y t h a t long-term ex p o su r e t o ozone w i l l r e s u l t i n pathophysiological processes l e a i n g t o chronic lung dlsease. Our o b j e c t i v e was t o measure a wide range of c e l l u l a r and b i o ch em i cal changes r e s u l t i n g from exposure of human s u b j e c t s t o ozone.
w e ad d r es s ed t h e f o ll o w in g q u e s t io n : ho u r s post-exposure
Specifically,
c a n inflammation be d e t e c t e d 18
t o 0.4 ppm 03 as evidenced by c h a r a c t e r i s t i c markers
of inflammation found i n t h e f l u i d and c e l l s o b t ai n ed by BAL?
W e have
r e c e n t l y a l s o begun t o a d d r e s s t h e same q u e s t i o n r e l a t i v e t o a n extended ( 7 h o u r ) exposure t o 0.1 ppm 03.
We have chosen t o f o cu s on c e l l u l a r and
biochemical changes d e t e c t e d i n BAL w i t h r e l e v a n c e t o inflammation, c h r o n i c l u n g d i s e a s e and t o h o s t d e f e n s e ( r e f s . 9,lO). have chosen t o examine c a n be grouped i n t o :
The materials w e
1) m o l ecu l es a s s o c i a t e d w i t h
chemotaxis, 2 ) enzymes a s s o c i a t e d w i t h damage t o t i s s u e s , and 3) p r o t e i n s t h a t p l ay a n i m p o r t a n t r o l e i n f i b r o t i c and f i b r i n o l y t i c p r o c e s s e s i n t h e lung. The r e s u l t s of t h e p r e s e n t s t u d i e s i n d i c a t e t h a t : 1) a s i n g l e 03 exposure (0.4 ppm f o r 2 h o u r s ) does in d e e d i n d u c e a n a c u t e l u n g inflammatory
response i n humans as evidenced by v a r i o u s measurable c e l l u l a r and biochemical changes a s s o c i a t e d w i t h inflammation, and 2 ) t h a t t h e ex t en d ed ex p o su r e
747 t o 0 3 a t a low c o n c e n t r a t i o n (0.1 ppm f o r 7 ho u r s) a l s o cau ses inflammation though t o a lesser degree.
METHODS Study P o p u l at i o n Healthy, non-smoking male v o l u n t e e r s , 18-35 y e a r s of age (25.4 se r v ed as s u b j e c t s f o r t h i s study.
* 3.5).
The number of s u b j e c t s t h a t p a r t i c i p a t e d
i n t h e a c u t e and extended e x p o s u r e s were 11 and 10 r e s p e c t i v e l y .
The
c r i t e r i a € o r t h e s e l e c t i o n of human s u b j e c t s has been d e s c r i b e d el sew h er e ( r e f . 2).
This s t u d y was approved by t h e Committee on t h e P r o t e c t i o n
of t h e R i g h t s of Human S u b j e c t s of t h e U n i v e r s i t y of North C a r o l i n a School of Medicine. Study Design For each of t h e two s t u d i e s ( a c u t e and extended ex p o su r e) each s u b j e c t was exposed on two s e p a r a t e o c c a s i o n s , once t o f i l t e r e d a i r and once t o 03,
wi t h a t least f i v e weeks between exposures.
A l l ex p o su r es took p l a c e i n
t h e af t er n o o n with th e RAL procedure conducted t h e f o l l o w i n g morning. The o r d e r of exposure was randomized and double b l i n d . T h e exposure and t r a i n i n g p r o t o c o l s f o r t h e a c u t e 03 exposure s t u d y
were similar t o th o s e p r e v i o u s ly employed i n o u r f a c i l i t y which have been B r i e f l y , e x p o s u r es were of 2 hour d u r a t i o n
de s cr i b ed i n d e t a i l ( r e f . 2).
and c o n s i s t e d of a l t e r n a t i n g 1 5 minute p e r i o d s of rest and heavy t r e a d m i l l e x e r c i s e which was performed a t a l e v e l t o produce a minute v e n t i l a t i o n (V,)
of 35 L min
-'
m2 BSA.
FEVl d e c l i n e d by 960 t 180 ( n = l l ) m l
immediately f o l l o w i n g 03 exposure compared t o a i r exposure.
Other lung
f u n c t i o n and symptom changes were s i m i l a r t o t h o s e p r e v i o u s l y r e p o r t e d f o r s i m i l a r exposures ( r e f . 2).
The exposure and t r a i n i n g p r o t o c o l s f o r
t h e extended 03 exposure s t u d y were i d e n t i c a l t o t h o s e d e c r i b e d by Horstman
e t a l . i n t h i s volume. Bronchoalveolar Lavage (BAL) Procedures Bronchoscopy and BAL were performed as p r e v i o u s l y d e s c r i b e d (ref.11) w i t h some m o d i f i cat i o n s .
The bronchoscope was wedged i n a segmental or subseg-
mental bronchus of t h e l i n g u l a .
F i f t y m i l l i l i t e r s of sterile (0.9%)
s a l i n e a t room temperature were slowly i n j e c t e d t h r o u g h the bronchoscope channel.
A s soon as t h e s a l i n e was i n s t i l l e d , i t was g e n t l y a s p i r a t e d
back i n t o t h e same s y r in g e .
T h i s procedure was r e p e a t e d f i v e more times
so t h a t a t o t a l of 300 m l of normal saline w a s i n s t i l l e d .
Recovery of
t h e i n j e c t e d f l u i d was approximately 75% (range 50 t o 80%). The BAL was r ep eat ed i n t h e r i g h t middle lobe, a g a i n u s i n g 300 m l of normal s a l i n e .
748 The v i a b i l i t y of recovered c e l l s exceeded 85% a s judged by t h e t r y p a n blue dye e x c l u s i o n te s t, and was n o t d i f f e r e n t i n a i r v e r s u s 0 3 exposures. C e l l d i f f e r e n t i a l s were done on c y t o c e n t r i f u g e d s l i d e s and s t a i n e d w i t h a modified Wright s t a i n (Leukostat S o l u t i o n , F i s h e r S c i e n t i f i c ) . Measurements of Cell Products and P r o t e i n s i n BAL F l u i d (BALF) T o t a l p r o t e i n was determined w i t h a BioRad P r o t e i n Assay K i t (BioRad, Richmond, CA), f o l l o w i n g t h e manufacturer's i n s t r u c t i o n s . The l e v e l s of albumin, IgG, and elastase i n t h e lavage f l u i d were q u a n t i f i e d with a competitive ELISA assay e s s e n t i a l l y as d e s c r i b e d by Rennard e t a l . ( r e f . 12). R I A k i t s were used t o d e t e c t t h e f o l l o w i n g materials: f i b r o n e c t i n
Stoughton, MA); C3a (Amersham, A r l i n g t o n
(Biomedical Technologies, Inc.,
Heights, IL); and e i c o s a n o i d s (Advanced Magnetics, Boston, and Amersham). Urokinase-type plasminogen a c t i v a t o r (U-PA) a c t i v i t y w a s determined as p r e v i o u s l y d e s c r i b e d ( r e f . 13). S t a t i s t i c a l Analysis C e l l u l a r and biochemical d i f f e r e n c e s between a i r and 03 exposure v a l u e s
were a s s e s s e d by p a i r e d t-tests.
Each s u b j e c t s e r v e d as h i s own c o n t r o l .
The primary hypothesis t o be t e s t e d i n e a c h of t h e s e s t u d i e s was t h a t 03 exposure r e s u l t s i n a n i n c r e a s e of PMNs i n BAL. surements are presented as secondary a n a l y s e s . considered s i g n i f i c a n t .
Other biochemical measure-
A p v a l u e of 0.05 was
A l l v a l u e s are r e p o r t e d as t h e mean f S.E.
RESULTS Ozone I n c r e a s e s t h e Number of PMN i n BAL C e l l c o u n t s and d i f f e r e n t i a l s performed on t h e BAL o b t a i n e d from s u b j e c t s exposed f o r two hours t o a i r o r 0.4 ppm ozone (18 h p o s t exposure) revealed t h e following:
a ) t h e mean number.of c e l l s recovered from
6 s u b j e c t s exposed t o O3 was unchanged compared t o a i r exposure (65.7 x 10 f
5.1 post a i r vs. 68.7 x
lo6
f
7.0 ozone, p = .575); b) t h e rela-
t i v e number of PMN, however, was e l e v a t e d i n t h e BAL of t h e 03 exposed subjects.
The mean r a t i o of t h e p e r c e n t of PMN i n t h e t o t a l c e l l popula-
t i o n ( o z o n e / a i r ) f o r t h e 11 e u b j e c t s was 8.2 f 2.2 (p=.OO9);
c) the
p e r c e n t of macrophages, was s l i g h t l y but s i g n i f i c a n t l y decreased in t h e BAL of 03 exposed s u b j e c t s (87.3% f 1.6
VS.
79.2% f 2.3,
p
d ) no
s i g n i f i c a n t changes i n t h e r e l a t i v e p r o p o r t i o n of lymphocytes were observed a f t e r 03 exposure.
In t h e extended 03 exposure s t u d y t h e mean r a t i o of t h e p e r c e n t of PMN i n t h e t o t a l c e l l p o p u l a t i o n f o r t h e 10 s u b j e c t s was 4.8 f 1.8 (p = .034).
The changes i n t h e o t h e r c e l l p o p u l a t i o n s were minor.
When t h e
mean r a t i o s of PM"s i n b o t h s t u d i e s ( a c u t e and extended) were compared
743 t o each o t h e r , they were found t o be s t a t i s t i c a l l y d i f f e r e n t (p-0.006). It, t h e r e f o r e , appears t h a t a seven hour exposure t o 0.1 ppm 0 3 d o e s
i n c r e a s e t h e percent of PM"s i n t h e BAL, but not as much as a two hour exposure t o 0.4 ppm. The E f f e c t of Ozone on t h e Volume of Recovered Lavage F l u i d and on t h e Levels of Urea i n BAL There was no s i g n i f i c a n t d i f f e r e n c e between t h e a i r and 03-exposed v o l u n t e e r s w i t h r e s p e c t t o t h e recovered volumes of l a v a g e f l u i d o r of Therefore,
e p i t h e l i a l lung s u r f a c e f l u i d based on t h e u r e a c o n t e n t .
t h e volume of recovered f l u i d could be u t i l i z e d as a normalizing f a c t o r when c a l c u l a t i n g and comparing c o n c e n t r a t i o n s of molecules c o n t a i n e d i n BALF. Changes i n P e r m e a b i l i t y Following 03 Exposure Since changes i n v a s c u l a r p e r m e a b i l i t y have p r e v i o u s l y been shown t o be c l o s e l y a s s o c i a t e d w i t h inflammation ( r e f s .
14,151, s e v e r a l i n d i c a t o r s of
W e were a b l e t o demonstrate
p e r m e a b i l i t y i n t h e BALF were measured.
s i g n i f i c a n t i n c r e a s e s i n t o t a l p r o t e i n (mean i n c r e a s e of 2.16 p
albumin (mean i n c r e a s e of 2.19
(mean i n c r e a s e of 2.25 f 0.29-fold,
f
0.35-fold,
p-0.002)
p=0.007),
f
0.2-fold,
and IgG l e v e l s
i n t h e BALF obtained from
s u b j e c t s f o l l o w i n g a two hour exposure of 0.4 ppm 03 compared t o t h a t o b t a i n e d following a i r exposure.
These changes i n d i c a t e i n c r e a s e d
v a s c u l a r p e r m e a b i l i t y i n t h e lower airways of s u b j e c t s exposed t o 03. Levels of N e u t r a l P r o t e a s e s i n BALP of S u b j e c t s Exposed t o 01 and Air. The l e v e l s of U-PA were 3.6
_+
0.6-fold
(p=0.002) h i g h e r i n t h e
BALF o b t a i n e d from s u b j e c t s exposed t o 0.4 ppm 03 r e l a t i v e t o a i r c o n t r o l s . Inmunoreactive n e u t r o p h i l e l a s t a s e w a s assayed i n BALF, and a 3.8 f 0.8-fold
(p=O.OOS) i n c r e a s e i n t h e BALF of t h e 03 exposed group was
detected. Changes i n t h e Levels of Inflammatory P r o t e i n s and L i p i d s i n BAL of S u b j e c t s Exposed t o 07 and Air. To f u r t h e r understand t h e mechanism by which 0 3 induces lung inflammation i n humans, we have assayed t h e BALF of v o l u n t e e r s exposed t o 0.4 ppm 0 3 f o r t h e presence of s e v e r a l s e l e c t e d markers of inflammation. l e v e l s were 6.44
f
1.54-fold
r e l a t i v e t o control.
(p-0.006)
Fibronectin
h i g h e r i n t h e 03 exposed group
Although C5a was not d e t e c t e d t h e l e v e l of C3a was
e l e v a t e d i n t h e 03-exposed s u b j e c t s (1.7f
0.1-fold,
t h a t t h e complement cascade had been a c t i v a t e d .
p4.001),
suggesting
The c o n c e n t r a t i o n of
imuunoreactive PGE2 w a s a l s o i n c r e a s e d (1.9 f 0.2-fold,
p<.OO2) i n
7 50 t h e 03-exposed s u b j e c t s , whereas t h e c o n c e n t r a t i o n s of LTB4 was n o t d i f f e r e n t between groups. DISCUSSION The a b i l i t y of 0 3 i n h a l a t i o n t o cause inflammation in t h e upper and lower ai r way s h a s been p r e v io u s l y shown i n a ni m al s t u d i e s ( r e f s . 16-19) and more r e c e n t l y i n humans ( r e f s . 4.20).
I n t e r e s t in an inflammatory
response induced by ozone s t e m from t h e f a c t t h a t inflammatory ex u d at es c o n t a i n c e l l s and s o l u b l e f a c t o r s which can i n i t i a t e p a t h o l o g i c changes i n l u n g parenchyma.
Our o b j e c t i v e i n t h e p r e s e n t s t u d i e s was t o measure
a range of i n f l am m a t io n - r e la te d b i o l o g i c a l and b i o ch em i cal changes r e s u l t i n g
from exposure of human s u b j e c t s t o ozone.
The f a c t t h a t t h e p e r c e n t of
PMN in t h e BAL i n c r e a s e d t o 8.2 tines c o n t r o l l e v e l s 18 h o u r s a f t e r two hour a c u t e exposure t o 03 (0.4 ppm) is c l e a r l y i n d i c a t i v e of a n inflammatory process.
S e l t z e r e t a l . ( r e f . 4 ) exposed s u b j e c t s t o 0.4 o r 0.6 ppm 03 f o r
2 h r wi t h exercise, and r e p o r t e d a n i n c r e a s e d number of PMNs i n BAL 3 hours a f t e r exposure.
This s u g g e s t s t h a t t h e inflammatory r esp o n se is
i n i t i a t e d promptly and is prolonged i n 03-exposed humans.
In r e g a r d s t o
t h e extended (7 h o u r ) exposure t o l o w 0 3 c o n c e n t r a t i o n s (0.1 ppm), t h e observed i n c r e a s e i n t h e p e r c e n t a g e o f PMN was 4.8-fold
aEter 0 3 ex p o su r e,
which is c l e a r l y i n d i c a t i v e of an a c u t e inflammtory r esp o n se though t o a
lesser d eg r ee t h a n t h e 2 hour exposure t o 0.4 ppm.
It remains t o be s e e n
whether o t h e r i n d i c a t o r s of inflammation were a l s o e l e v a t e d i n t h e ex t en d ed exposure and t o what e x t e n t .
Moreover, i t w i l l be i m p o r t an t t o test t h e
e f f e c t s of even lower c o n c e n t r a t i o n s of 0 3 (e.g.,
0.08 ppm) which were
shown t o cause changes i n lu n g f u n c t i o n tests i n a n ex t en d ed ex p o su r e p r o t o c o l ( s e e Horstrnan e t a l . i n t h i s volume). I n o u r s t u d y , s i g n i f i c a n t 2.2-fold
i n c r e a s e s i n t h e c o n c e n t r a t i o n s of
t o t a l p r o t e i n , albumin, and IgG were observed.
These r e s u l t s i n d i c a t e
t h a t under c o n d i t i o n s used I n t h i s s t u d y 0 3 exposure i n d u ced changes i n p e r m e a b i l i t y r e s u l t i n g i n t r a n s u d a t i o n of serum p r o t e i n s .
0 3 ex p o su r e
has been shown t o alter t h e p e r m e a b i l i t y p r o p e r t i e s of t h e r e s p i r a t o r y e p i t h e l i u m of r o d e n t s (e.g.,
refs.
18,19) and humans ( r e f .
21).
In o u r s t u d y , we were a b l e t o d e t e c t i n c r e a s e d l e v e l s of C3,
(1.7-fold)
i n t h e BALF of the 03 exposed s u b j e c t s . T h i s molecule is cap ab l e of i n d u c i n g pulmonary i n j u r y i n g u i n e a p i g s ( r e f . 22).
Moreover, t h e mere p r esen ce o f
i n c r e a s e d levels of Cga s t r o n g l y s u g g e s t s t h a t t h e complement cascad e h as been a c t i v a t e d , s u g g e s t i n g a l t e r a t i o n s i n t h e l u n g immune system.
751 Products of t h e a r c h i d o n i c a c i d pathway and, i n p a r t i c u l a r , the p r o s t a g l a n d i n s have been shown t o be p o t e n t m ed i at o r s of i n f l a m a t i o n ( r e f s . 9,lO).
Our r e s u l t s show a 2-fold i n c r e a s e of PGE2 i n t h e FJALF of
0 3 exposed s u b j e c t s but n o s i g n i f i c a n t i n c r e a s e i n LTB4.
Seltzer et al.
( r e f . 4 ) were a l s o unable t o d e t e c t a n i n c r e a s e d c o n c e n t r a t i o n of LTB4 i n BALP
3 h o u r s f o l l o win g 03 exposure. Neu t r o p h i l elastase, a p r o t e o l y t i c enzyme cap ab l e of d eg r ad i n g s e v e r a l d i f f e r e n t s t r u c t u r a l components of l u n g t i s s u e i n c l u d i n g e l a s t i n , c o l l a g e n , p r o t eo g l y can s and basement membrane ( r e f . 23) h as teen shown t o be e l e v a t e d i n v a r i o u s l u n g inflammatory states s u c h as i n cigarette smokers ( r e f . 24) or i n a n a c u t e inflammation s e e n i n a d u l t r e s p i r a t o r y d i s t r e s s syndrome ( r e f . 25).
We were a b l e t o demonstrate i n c r e a s e d n e u t r o p h i l elaetase
l e v e l s i n t h e BALP of 03-exposed s u b j e c t s compared t o c o n t r o l s by u s i n g an a n t i - n e u t r o p h i l elastase antibody.
These f i n d i n g s may be s i g n i f i c a n t i n
terms of h e a l t h e f f e c t s s i n c e s e v e r a l s t u d i e s have i n d i c a t e d a c a u s a t i v e r o l e f o r n e u t r o p h i l elastase i n t h e development of emphysema and e l a s t i n d eg r ad at i o n i n PMN-dependent lung i n j u r y ( r e f . 23,26). S i n ce o t h e r s have r e p o r t e d t h a t long-term ex p o su r e t o 03 may induce f i b r o t i c changes in animals ( r e f . 27) i t w a s of i n t e r e s t t o d et er m i n e whether
an a c u t e exposure t o 03 would induce biochemical changes t h a t have been a s s o c i a t e d w i t h E i b r o s is .
F i b r o n e c t i n h a s been shown t o p l a y a key r o l e i n
f i b r o g e n e s i s by p r o v i d i n g a s i g n a l f o r f i b r o b l a s t r e p l i c a t i o n by r e c r u i t m e n t of f i b r o b l a s t s t o sites of inflammation.
i n c r e a s e in t h e c o n c e n t r a t i o n (6.4-fold) t h e BALF of 03-exposed s u b j e c t s .
I n t h e p r e s e n t st u d y , a d r am at i c of f i b r o n e c t i n was observed i n
The i n c r e a s e d f i b r o n e c t i n l e v e l s i n t h e
BALF of t h e 03-exposed s u b j e c t s may r e s u l t p a r t l y from i n c r e a s e d v a s c u l a r p er m eab i l i t y , a s w e l l as from i n c r e a s e d f i b r o n e c t i n s y n t h e s i s by pulmonary
cells.
In t h i s s t u d y we have shown a 3.6-fold
i n c r e a s e i n t h e levels of
U-PA i n t h e BALF of t h e ozone group (two h o ur s a t 0.4 ppm), compared t o c o n t r o l BALF. Taken t o g e t h e r , t h e r e s u l t s c l e a r l y i n d i c a t e t h a t a n a c u t e ( 2 h r ) exposure t o 0.4 ppm 0 3 w i th moderate e x e r c i s e can induce a r e l a t i v e l y prolonged inflammatory response as evidenced by a PMN i n f l u x i n t o t h e lumen i n t h e lower airways in humans.
T h is is uniformly t r u e f o r a l l 11 s u b j e c t s s t u d i e d
under t h e s e exposure c o n d i ti o n s .
The lu n g inflammatory response has been
d es cr i b ed h e r e based on s e v e r a l i n d i c a t o r s of inflammation i n c l u d i n g PMNs, a v a r i e t y of p o t e n t d e g r a d a t i v e enzymes, a n a r c h i d o n i c a c i d meta-
b o l i t e , complement component, and markers of v a s c u l a r p er m eab i l i t y . The inflammatory response i s obviously complex and i n v o l v e s a sequence of ev en t s , each of which can have d e l e t e r i o u s e f f e c t s o n t h e l u n g and i t s
752 h o s t defense f u n c t i o n s .
The a b i l i t y t o d e t e c t t h e changes i n t h e l e v e l s
of inflammatory i n d i c a t o r s by performing BAG p r o v i d e s a n i n s i g h t i n t o t h e p o t e n t i a l r i s k t h a t may r e s u l t from an a c u t e i n h a l a t i o n of 03 and may provide information on p o s s i b l e h e a l t h e f f e c t s induced by c h r o n i c 03 exposure. ACKNOWLEDGEMENTS The a u t h o r s thank Drs. G a r y Hatch and Michael Madden f o r t h e i r c r i t i c a l review of t h i s manuscript.
W e would a l s o l i k e t o thank Louise
Cole, S h i r l e y Harder, Ruth Jordan, and Beth D a n i e l s f o r t h e i r e x p e r t t e c h n i c a l a s s i s t a n c e , and V i c k i e W o r r e l l f o r h e r s k i l l e d a s s i s t a n c e i n t h e p r e p a r a t i o n of t h i s manuscript. REFERENCES Air Q u a l i t y f o r Ozone and O t h e r 1 U.S. Environmental P r o t e c t i o n Agency. Environmental Criteria Photochemical Oxidants. Washington, D.C.: and Assessment O f f i c e , 1986. 2 W.F. McDonnell, D.H. Horstman, M.J. Hazucha, E. S e a l , E.D. Haak, S.A. Salaam, and D.E. House, J. Appl. Physiol., 54(5) (1983) 1345-1352. 3 D.B. Menzel, J. Toxicol. Environ. Health 13 (1984) 183-204. Holtzman, J.A. Nadel, I.F. Ueki, 4 J. S e l t z e r , B.G. Bigby, M. S t u l b o r g , M.J. G.D. Leikauf, E.J. Goetzl and H.A. Boushey, J. Appl. Physiol. 60(4) (1986) 1321-1326. 5 J.A. Golden, J.A. Nadel and H.A. Boushey, Am. R e s . Respir. D i s . 118 (1978) 287-294. 6 M.J. Holtzman, H. Aizawa, J.A. Nadel and E.J. Goetzl, Biochem. Biophys. R e s . Commun. 114 (1983) 1071-1076. 7 P.J. Lioy, T. Vollmuth and M. Lippmann, JAPCA, 35 (1985) 1068-71. 8 L.J. Folinsbee, W.F. McDonne11 and D.H. Horstman, JAPCA, 38 (1988) 28-35. 9 D.O. Slauson, i n C.E. C o r n e l i u s and C.F. Simpson ( E d i t o r s ) , Advances i n V e t e r i n a r y Science and Comparative Medicine, N e w York Academic P r e s s , 26, 1982, pp. 99-154. 10 J.C. Fantone and P.A. Ward 111, Am. Rev. Respir. Die. 130 (1984) 484-491. 11 H.Y. Reynolds, Am. Rev. Respir. D i s . 135 (1987) 250-263. 12 S.I. Rennard and R.G. C r y s t a l , J. Clin. I n v e s t . 69 (1982) 113-122. 13 G. Claeson, P. F r i e b e r g e r , M. Knos and E. Erikson, Haemostasis 7 (1976) 76-78. 14 T.J. Williams and P.J. J o s e , J. Exp. Med. 153 (1981) 136-153. 15 A.C. I s s e k u t z , Lab. I n v e s t . 45 (1981) 435. 16 L.M. Fabbri, H. Aizawa, S.E. A l p e r t , E.H. W a l t e r s , P.M. O'Byrne, B.D. Gold, J.A. Nadel and M.J. Holtzman, Am. Rev. Respir. D i s . 129 (1984) 288-291. 17 S.M. A l p e r t , D.E. Gardner, D.J. Hurst, T.R. Lewis and D.L. C o f f i n , J. Appl. Physiol. 31(2) (1971) 247-252. Graham, J. Tox. Env. Health. 18 G.E. Hatch, R. Slade, A.G. S t e a d and J.A. 19 (1986) 43-53. Graham, D.E. Gardner 19 P.C. Hu, F.J. Miller, M.J. Daniels, G.E. Hatch, J.A. and M.J. Selgrade, Env. Res. 29 (1982) 377-388. 20 D. Graham, F. Henderson and D. House, Arch. Envir. Hlth. i n p r e s s (1988). 21 H.R. Kehrl, L.M. Vincent, R.J. Kowalsky,, D.H. Horstman, J.J. O ' N e i l , W.H. McCartney and P.A. Bromberg, Am. Rev. Respir. D i s . 135 (1987) 11241128. 22 N.P. S t i m l e r , T.E. Hugli and C.E. Bloor, Am. J . Pathol. 100 (1980) 327-348. 23 A. J a n o f f , B. Sloan, G. Weinbaum. V. Damiano, R.A. Sandhaus, J. Elias and P. Umbel, Am. Rev. Respir. D i s . 115 (1977) 461-478. 24 T. Fera, R.T. Abbond, A. R i c h t e r and S.S. Johal, Am. Rev. Respir. D i s . 133 (1986) 568-573.
753 25 26 27
C.T. Lee, A.M. Fein, M. Lippmann, 8. Holtzman, P . K i m b e l and G . Weinbaum, N . Engl. J. Med. 304 (1981) 192-196. R.M. Senior, H . Tegner, C . Kuhn, K. Ohlsson, B.C. Storcher, and J.A. Pierce, Am. Rev. Respir. Dis. 116 (1977) 469-475. J.A. Last and D.B. Greenberg, Toxicol. Appl. Pharmacol. 55 (1980) 108-114.
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T.Schneider et al. (Editors),Atmospheric Ozone Research and its Policy Implicotiona 1989 Elsevier Science Publishers B.V.,Amsterdam -Printed in The Netherlands
755
CBIUSGBS IN P W O N A R Y FUNCTION AND AIRVAY RBACTIVITY WB TO P R O W EXPOSURE TO TYPICAL AHBIBNT O u m B (03)LEVELS
D. EORSI"',
V. HcDONNELL',
L. FOLINSBBB2, S. ABDlJLsLLLMIIl and P. IVBS2
'Clinical Research Branch (HD-58), USBPA:Eealth Research Triangle Park, NC 27711 (USA) 'Environmental
Effects Research Laboratory,
Honitoring and Services, Inc., Chapel Hill, NC 27514 (USA)
ABSTRACX
Previously observed (JAPCA 38:28-35, 1988) pulmonary responses of MBV (-13%), moderate to severe pain upon inspiration, and a doubling of PD fos methacholine folloving prolonged moderate exercise at 0.12 ppm 0 &? of sufficient magnitude to varrant our assessing responses at a lo& range of concentrations, i.e:, 0.08, 0.10 and 0.12 ppm 03. Exposures consisted of six 50-min exercises (V 4 0 Lhin), each followed by 10-rin rest; a 35-.in lunch break vas included. % h e n compared with exposures to 0.00 ppm, substantial pulmonary function decrements, respiratory symptoms and increases in nonspecific airvay reactivity vere observed at all three! 0 concentrations. For example, decreases in PEV (P < 0.01) of 7%, 7% and 1 4 vere observed at 0.08, 0.10 and 0.12 ppm 0 resdctively. The ratios (P < 0.005) of PD observed in 0.00 ppm to t&t in O3 were 1.56 at 0.08 ppm, 1.89 at 0.10 ppm, 2.21 at 0.12 ppm 0 Ve conclude that exercise representative of a day of moderate to h e a d work or play performed during exposures to 0 at levels and pattern often found in aabient air induced clinically .eanidful pulmonary responses.
.
DISCLAIMER The research described in this article has been reviewed by the Health Effects Research Laboratory, U.S. Environmental Protection Agency and approved for publication. Approval does not signify that the contents necessarily reflect the views and policies of the Agency nor does mention of trade names or commercial products constitute endorsement or recommendation for use.
INTRODUCTION Daily ambient O3 levels between 0.08 and 0.12 ppm for periods in excess of 6-hr often occur in many urban, suburban and even rural areas of both the U . S . and Europe (ref. 1). We recently observed substantial decrements in pulmonary functions (eg. AFEV 1 -- -13%,) moderate to severe respiratory symptoms, and a 2-fold increase in nonspecific airway reactivity when young men performed exercise equivalent to a day of moderate to heavy work or play while exposed to 0.12 as compared to 0.00 ppm O3 (ref. 2). Specifically, 6.6-hr exposures
756 consisted of six 50-min periods of moderate exercise (average VE = 42.5 L/min), each followed by a 10-min rest; a 35-min lunch period followed the third exercise. The magnitudes of the 0.12 ppm 03-induced responses clearly indicated that, with similar conditions of exercise-exposure duration and VE, pulmonary responses would also occur at lower O3 concentrations. The purpose of this study was to evaluate pulmonary responses resulting from such exposures to 0.08, 0.10 and 0.12 p p m 03. METHODS Healthy nonsmoking male volunteers (n = 22) were subjects in this study. They were recruited from the Chapel Hill, Durham, and Raleigh North Carolina area, which has relatively clean air. Potential subjects were excluded from participation if they had a history of cardiac disease, allergic rhinitis, asthma, or other chronic respiratory disease; if they were routinely exposed to dusty, caustic or pollutant environments; or if they had participated in our previous prolonged 0 exposure study (ref. 2). Subjects accepted for study 3 were also required to be at least moderately active (i.e. they participated in some form of regular exercise) so that they could sustain a prolonged period of moderate exercise. Health status of potential subjects was assessed by medical history, physical examination, and routine hematologic and biochemical tests. The average subjects' age, height and weight were 24.5 yr, 180.2 cm and 77.0 kg, respectively. The average baseline FVC (5.6 L, range = 3.6-7.9 L) and FEVl (4.4 L, range = 2.9-5.3 L) for these subjects were consistent with values predicted from two reference standards (refs. 3,4). However, their FEV1/FVC averaged 79% as compared to a predicted ratio of 84%. Prior to participation in the study, subjects were informed of the purpose, design, risks and benefits of the study and signed a statement of informed consent. The study protocol and consent form were examined and approved by the University of North Carolina School of Medicine Committee on the Protection of the Rights of Human Subjects. Each subject participated in training session during which he was instructed as to the performance of pulmonary function tests. At this time, the exercise intensity required to elicit a i, of 8 L/min per liter of FVC, but not less than 35 L/min nor greater than 45 L/min, was also determined for both treadmill and cycle ergometers. Each subject was exposed to 0.00 (filtered air), 0.08, 0.10 and 0.12 ppm O3 on separate days. Exposures were separated by a minimum of one week and the exposure sequence was randomized. Neither subjects nor staff directly involved in conduct of exposures and pulmonary testing were informed as to the presence or concentration of O3 in the chamber although the odor of O3 was detectable even at these low concentrations. Although it was not possible to have either single or double blind conditions regarding the presence or absence of 03, the subjects were probably unable to distinguish among the three O3 concentrations.
757 Subjects were exposed in pairs when possible. Upon arrival at the laboratory, each subject was given a brief physical examination. They were not studied if they presented with any condition which contraindicated exposure or exercise, or if they reported an acute respiratory infection within the previous four weeks. Forced expiratory spirometry was measured and pain upon deep inspiration (PDI) was evaluated before (baseline) and after all exposures. Following baseline measurements, the subject entered the chamber, which was already set at the appropriate exposure conditions, and began exercise on either a treadmill or a cycle ergometer at the previously determined exercise intefisity. During each exposure, the subject performed six 50-min periods of exercise, alternating between the treadmill and cycle ergometer; five of the 50-min exercises were followed by a 10-min rest, while a 35-min lunch period followed the third exercise. During each exercise period we measured i,, oxygen consumption (to2) and heart rate (HR) for 3-min after 40-min of exercise. To assess nonspecific airway reactivity, a methacholine inhalation challenge was performed 15- to 20-rain after the 6.6-hr exposure. Exercise iE (BTPS), $Oz (STPD) and AR were derived as described previously HR and electrocardiogram were continually monitored throughout (ref. 5); exposure. Forced expired vital capacity (FVC) was measured in triplicate on a 12-liter dry-seal spirometer; volumes were corrected to BTPS. From the FVC maneuver, expired volume during the first second (FEV1) was determined and the largest FEVl (of the three) was used in the data analysis. PDI was evaluated on the 5-point scale: 0 (none), 1 (just noticeable), 2 (mild discomfort), 3 (moderate discomfort), and 4 (severe discomfort or pain). Hethacholine bronchial challenge procedures conformed to previously published American Thoracic Society guidelines (ref. 6) and were essentially Briefly, the same as that previously reported for this laboratory (ref. 7). methacholine aerosols (HMAD = 1.8 micron, geometric S.D. = 1.4) were generated from solutions of methacholine chloride dissolved in normal saline using an ultrasonic nebulizer; methacholine concentrations were 0.0, 0.63, 1.25, 2.5, 5.0, 10.0, and 20.0 mg/ml. The aerosol was inhaled through a heated Fleisch A microprocessor controlled device was used which both measured pneumotach. and regulated the tidal volume (V,) such that V t was approximately 25% of FVC; end-inspiratory breath-hold time was 4-sec and inspiratory flow was between 300 and 500 ml/S. Beginning with normal saline alone and followed by progressively increasing methacholine concentrations, a series of aerosol inhalations was performed. Each consisted of five breaths of aerosol followed by two measurements of airway resistance, beginning 2-min after the start of aerosol inhalation. This sequence of aerosol inhalation and measurement was repeated at 6 minute intervals until the SRaw was at least double that following inhalation of saline alone. Airway reactivity to methacholine (prococative dose, PDloo), as an indicator of nonspecific airway reactivity, was detetmined
7 58 as the interpolated cumulative dose of methacholine which provoked a 100% increase in SRaw over that observed after inhaling normal saline. Cumulative methacholine dose was expressed as the sum of all doses of inhaled aerosol in An inhalation unit was defined as the cumulative inhalation units (CIU). product of methacholine concentration (mg/ml) and the number of breaths taken at that concentration. Inhalation of one CIU was equivalent to inhalation of 0.035 pg methacholine chloride. Exposures were conducted in a 4 x 6 x 3.2 m stainless steel chamber with continuous reconditioning and recirculation of the chamber air through high-efficiency particle filters. A detailed description of the chambers and Ozone was their operating characteristics has been published (ref. 8). continuously monitored using chemiluminescent ozone analyzers which were calibrated daily by a Dasibi ultraviolet ozone photometer traceable to an NBS standard photometer. For the four exposure conditions, O3 concentrations averaged 0.00, 0.08, 0.10 and 0.12 ppm. NO, NO2, and SOx were also monitored; their concentrations were routinely less than 0.02 ppm, 0.005 ppm, and 0.005 ppm, respectively. The total particle mass with 3 persons in the chamber was The temperature and routinely less than 3 u g h 3 with lo5 particlesh3 relative humidity of the chamber were maintained at 22OC and 40%, respectively. The null hypotheses tested were that (1) there was no difference in the average pre- to postexposure changes in FEVl in 03 as compared to average change in air, and (2) there were no differences in postexposure PDI or PDIOO in O3 as compared to those in air. Responses for all three O3 exposures vere compared to air response using a nonparametric version of the Williams' test Williams' test is appropriate for for randomized block design (ref. 9). comparisons of multiple treatments to a control when treatment is either an increasing or decreasing monotonic function. The nonparametric version of the test was used because the assumptions of equal variances of errors and normal distribution of errors (required for application of parametric tests) were not valid for these data.
.
RESULTS All but one subject completed all four 6.6-hr chamber exposures. This subject was not exposed to 0.12 ppm because he experienced severe respiratory symptoms at 0.10 ppm 03, although the magnitudes of his pulmonary function responses only slightly exceeded the mean responses at 0.08 and 0.10 ppm 03. None of his data were used in the statistical analyses, nor was i t included for calculation of the mean data reported later in this section. The treadmill exercise was a brisk walk = 3.27 mph) up a slight incline (X = 5.7%), while the bicycle exercise was light to moderate = 72 watts). There were no differences among the four exposures for the means of HR, i, and i 0 2 obtained during any of the six exercise periods. Hean BR (beatshin), iE
(x
(x
759 (Llmin) i 0 , (Llmin) averaged over the six exercises were, respectively; 115, 38.5 and 1.53 Llmin at 0.00; 116, 39.4 and 1.60 L/min at 0.08; 115, 38.7 and 1.56 Llmin at 0.10; and 113, 38.7 and 1.64 Llmin at 0.12 ppm 03. The preexposure mean values of all of the pulmonary functions measured were quite similar at the four O3 concentrations and the range of individual subject's coefficients of variation for any of the preexposure measurements of function was quite narrow. For example, FEVl averaged 4.40, 4.39, 4.38 and 4.38 L/min prior to exposures to 0.00, 0.08, 0.10 and 0.12 ppm 03, respectively, while the mean and median individuals' coefficients of variation Significant 03-induced for FEVl were 2.30 + 0.34% and 2.09%, respectively. responses were observed at all three O3 concentrations for the three variables tested in the statistical analyses. While essentially no change (+0.6%) was observed for FEVl at 0.00 ppm, it was significantly (p < 0.005) decreased by 7.0%, 7.0% and 12.3% following exposures to 0.08, 0.10 and 0.12 ppm 03, respectively. Average ratings of PDI were low, but significantly increased (P < 0.05) following exposure to all three O3 concentrations, i.e., 0.62 at 0.08, 0.90 at 0.10 and 1.00 at 0.12 as compared to 0.24 at 0.00 ppm 03. 03-induced increases (P < 0.005) in nonspecific airway reactivity were observed at all three 0 concentrations. The average ratios of PDIOO observed in 0.00 ppm (57.5 CIU) to those observed in O3 were 1.56, 1.89 and 2.21 at 0.08, 0.10 and 0.12 ppm 03, respectively. A wide range of individual responsiveness was exhibited for all variables measured. For example, individual PEVl responses ranged from +6.4 to -4.6% at 0.00, from +7.9 to -25.9% at 0.08, from +2.0 to -22.0% at 0.10 and from +2.8 to -38.9% at 0.12 ppm 03.
DISCUSSION Our results clearly demonstrate that substantial pulmonary responses occur when 5-hr of moderate exercise is performed during 6.6-hr exposures to 0.08, 0.10 and 0.12 ppm 03. The consistency of individual preexposure measurements of pulmonary functions indicates that the status of the subjects' airways and the accuracy of measurement was similar prior to exposure at all O3 concentrations. The large intersubject variability in magnitude of responses which we observed is consistent with results from almost all previous studies of O3 exposure (eg. refs. 2,5). Individual 03-responsiveness has been shown to be quite reproducible indicating that intersubject variability is related to differences in individuals' intrinsic responsiveness to O3 (ref. 10). Thus, our results imply that some individuals will experience substantial pulmonary distress if they exercise (work or play) for prolonged periods at very low O3 concentrations, while others will not experience any effect from such exposures.
760 While not intended as an exact simulation, the overall duration, intensity and metabolic requirements of the exercise performed was equivalent to a day of moderate to heavy work or play. The range of HR and 60, we observed was representative of relative exercise intensities between 30% and 45% maximal to2. Moreover, since both HR and 60, drift upward during prolonged exercise, and since measurements were not obtained until after 40-min of exercise, the actual exercise intensities probably more nearly represented an even lower range of relative effort. There is general agreement that most individuals can comfortably perform prolonged exercise (a-hr) at relative exercise intensities 40% maximal 602, and with low incidence of fatigue at relative exercise intensities between 40 and 50% maximal 602. It should be noted that, like HR and 602, 6, also tends to increase slightly during prolonged exercise and i t may be that measured i, also overestimated the actual average exercise i, (ref. 11). We were not surprised by our earlier findings (ref. 2) of pulmonary responses with the performance of prolonged moderate exercise at 0.12 ppm 03. Pulmonary function changes and respiratory symptoms had been observed when at least 1-hr of heavy exercise (6, > 60 L/min) was performed during 1-hr and 2-hr exposures to 0.12 ppm O3 (refs. 5,12,13). Since pulmonary responses at any O3 concentration are a function of exercise i, and duration (ref. 14), the magnitudes of these variables for our more prolonged exposures to 0.12 ppm O3 were certainly sufficient to induce responses. Similarly, because the pulmonary responses we observed earlier at 0.12 ppm O3 were so large, we expected that, with similar conditions of exercise 6, and duration, measurable responses would also be induced at 0.10 ppm; we were not sure of what to Thus, we were not surprised by the magnitudes of expect at 0.08 ppm. decrements in pulmonary functions and increases in nonspecific airway reactivity observed at 0.10 ppm, while the magnitudes at 0.08 ppm O3 were perhaps somewhat greater than we expected. Consistent with our observations, pulmonary function decrements at 0.08 ppm O3 had been suggested for active children attending summer camps in areas which attained a range of daily ambient O3 with levels as high as 0.15 ppm throughout the camping session (refs. 15,16,17). The FEVl decrement with exposure to 0.12 ppm O3 in our current study and those in our earlier study, (AFEV1 = -13%) were remarkably similar. Likewise, an approximately 2-fold increase in nonspecific airway reactivity was observed in both studies, PDI was rated much lower at 0.12 ppm O3 in the current than in the earlier study; i t was also rated low at 0.10 and 0.08 ppm. We observed essentially no differences in pulmonary function decrements and respiratory symptoms between exposures at 0.08 and 0.10 ppm 03. We have no explanation for the low overall symptom ratings, nor for the lack of concentration/response relationships at 0.08 and 0.10 ppm 03.
<
761 PDIOO did exhibit a concentration/response relationship for all three levels of 03. This 03-induced increase in nonspecific airway reactivity is especially interesting since a strong relationship has been reported between increased airway reactivity to cholinergic agonist and increased numbers of neutrophils in bronchoalveolar lavage fluid following O3 exposure (refs. 18-20). Since an increase of neutrophils is a strong indicator of airway inflammation, 03-induced airway hyperresponsiveness to methacholine may also be a good marker of injury to airway epithelium (ref. 21). We conclude that substantial pulmonary responses occur following 5-hr of moderate exercise performed during 6.6-hr exposures to 0.08, 0.10 and 0.12 ppm 03. These findings are particularly relevant to everyday experiences since the intensity, duration and metabolic requirement of the exercise was representative of a day of moderate to heavy work or play, and the O3 levels and pattern were similar to ambient levels and pattern often recurring in many areas of both the U.S. and Europe.
ACKNOWLEDGEMENTS The writers appreciate the technical assistance of the staff of both the Clinical research Branch and Environmental Monitoring and Services, Inc. Statistical analyses were performed in consultation with Dennis House of the Biostatistics Branch of the Biometry Division, USEPA:Health Effects Research Laboratory.
REFERENCES 1. P.J.A. Rombout, P.J. Lioy and B.D. Goldstein, JAPCA, 36 (1986) 913-917. 2 . L.J. Folinsbee, W.P. HcDonnell and D.H. Horstman, JAPCA, 38 (1988) 28-35.
3. H.W. Higgins and J.B. Keller, Am. Rev. Respir. Dis., 108 (1973) 258-272. 4. D.W. Dockery, J.H. Ware, B.G. Ferris, D.S. Glicksberg, H.E. Fay, A. Spiro and F.E. Speizer, Am. Rev. Respir. Dis., 131 (1985) 511-520. 5. W.F. HcDonnell, D.H. Horstman, M.J. Hazucha, E. Seal, E.D. Haak, S.A. Salaam and D.E. House, J. Appl. Physiol., 54 (1983) 1345-1352. 6. G.J.A. Cropp, I.L. Bernstein, H.A. Boushey, R.W. Hyde, R.R. Rosenthal, S.L. Spector and R.G. Townley, ATS News, 6 (1980) 11-19. 7. H.J. Hazucha, J.F. Ginsberg, W.F. HcDonnell, E.D. Ha&, R.L. Pimmel, S.A. Salaam, D.E. House and P.A. Bromberg, J. Appl. Physiol., 54 (1983) 730-739. 8. D.E. Glover, J.H. Berntsen, W.L. Crider and A.A. Strong, J. Environ. Sci. Health, 16 (1981) 501-522. 9. D.E. House, Biometrics, 42 (1986) 187-190. 10. W.F. HcDonnell, D.H. Horstman, S. Abdul-Salaam and D.E. House, Am. Rev. Respir. Dis., 131 (1985) 36-40. 11. P-0. Astrand and K. Rodahl, Textbook of Work Physiology, HcGraw-Hill, New York, 1977, Chapters 9,10,13. 12. E.S. Schelegle and W.C. Adams, Hed. Sci. Sports Exerc., 18 (1986) 408-414. 13. H. Gong, P.W. Bradley, H.S. Simmons and D.P. Tashkin, Am. Rev. Respir. Dis.9 134 (1986) 726-733. 14. U.S. Environmental Protection Agency, Air Quality Criteria for Ozone and Other Photochemical Oxidants EPA/600/8-84/020aF-eF, Envirinmental Criteria and Assessment Office, Research Triangle Park, NC, Chapters 10,12.
762 H. Horandi, D. Baxter, 15. H. Lippman, P.J. Lioy, G. Leikauf, K.B. Green, B.S. Pasternack. D. Fife and P.E. Soeizer. Adv. Hod. Environ. Toxicol.. 5 (1983) 423-426. 16. P.J. Liov. T.A. Vollmuth and H. Lioomann. JAPCA. 35 (1985) 1068-1071. 17. D.H. Spekior, H. Lippmann, Lioy i:J., -Thurston G.D., K. Citak, N. Bock, F.E. Speizer and C. Hayes, Am. Rev. Respir. Dis., 137 (1988) 313-320. 18. J. Seltzer, B.G. Bigby, H. Stulbarg, H.J. Aoltzman, J.A. Nadel, I.P. Ueki, G.D. Leikauf, E.J. Goetzl and H.A. Boushey, J. Appl. Physiol., 60 (1986) 1321-1326. 19. P.H. O'Byrne, E.H. Walters, B.D. Gold, A. Aizawa, L.H. Fabbri, S.E. Alpert, J.A. Nadel and H.J. Holtzman, Am. Rev. Respir. Dis., 130 (1984) 214-219. 20. P.H. O'Byme, E.H. Walters, H. Aizawa, L.H. Pabbri, H.J. Holtzman, J.A. Nadel, Am. Rev. Respir. Dis., 130 (1984) 220-224. 21. C.G. Hurlas and J.A. Roum, Am. Rev. Respir. Dis., 131 (1985) 314-320.
763
SESSION XI1
SOURCE CONTROL FOR STRATOSPHERIC OZONE PROTECTION
Chairmen
N.C. van Lookeren Campagne D.DuII
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T. Schneider et al. (Editors), Atmospheric Ozone Research and its Policy Zmplicatwm 1989 Elsevier Science Publishers B.V., Amsterdam -Printed in The Netherlands
765
OVERVIEW OF CONTROLS FOR CHLOROFLUOROCARBONS
Dale L.Harmon and Williams J.Rhodes presented by G.Blair Martin U.S.Environmenta1 P r o t e c t i o n Agency, A i r and Energy Engineering Research Laboratory, Research Triangle Park, North Carolina 277 1 1 (United S t a t e s )
ABSTRACT In response t o concerns regarding t h e p o t e n t i a l f o r s t r a t o s p h e r i c ozone d e p l e t i o n , t h e U . S. has joined o t h e r n a t i o n s i n pursuing an i n t e r n a t i o n a l agreement t o l i m i t t h e emf s s i o n s of f u l l y halogenated chlorof luorocarbons (CFCs) and c e r t a i n halons. I n o r d e r t o implement t h e Montreal P r o t o c o l in t h e U. S . , t h e Environmental P r o t e c t i o n Agency (EPA) h a s proposed a n a t i o n a l r e g u l a t i o n t o l i m i t t h e production of t h e s e substances by t h e a l l o c a t i o n of production quotas t o t h e firms engaged i n t h i s a c t i v i t y i n 1986. Many ways e x i s t t o achieve the needed reductions. In t h i s paper t h e various c o n t r o l options with some advantages and disadvantages are discussed f o r t h e major i n d u s t r i e s t h a t use CFCs and halons. INTRODUCTION
On December 1, 1987, new domestic r e g u l a t i o n s r e s t r i c t i n g production and consumption of ozone-depleting CFCs were proposed by t h e EPA Administrator. (Ref. 1) The proposed r u l e s would f u l l y implement t h e Montreal P r o t o c o l , (Ref. 2 ) LP i t e n t e r s i n t o force.
EPA's assessment of the r i s k s of ozone
depletion i n d i c a t e s t h a t t h e P r o t o c o l ' s c o n t r o l requirements are an approp r i a t e response. The P r o t o c o l leaves i t up t o each p a r t y how t o achieve t h e required reductions in production and consumption. EPA's g o a l in implementing t h e Protocol is t o provide t h e marketplace wfth f l e x i b i l i t y t o achieve t h e required reductions i n t h e most economically e f f i c i e n t manner p o s s i b l e .
Two g e n e r a l
approaches For achieving t h e P r o t o c o l ' s required reductions of c o n t r o l l e d substances were evaluated. One approach r e l i e s on market i n c e n t i v e s t o achieve low c o s t reductions i n t h e use of CFCs and halone.
Under t h i s approach EPA
could e i t h e r d i r e c t l y r e s t r i c t t h e supply of CFCs and halons o r assess a regulatory f e e on t h e i r use. E i t h e r would i n c r e a s e t h e c o s t of u s i n g CFCs which would give those f i r m s with r e l a t i v e l y low-cost
reduction o p t i o n s an
economic i n c e n t i v e t o reduce t h e i r use of t h e s e chemicals.
Those f i r m s where
no such reduction o p p o r t u n i t i e s e x i s t would continue t o use CFCs, although they would have t o pay a h i g h e r p r i c e . approaches were evaluated:
Three a l t e r n a t i v e economic i n c e n t i v e
marketable r i g h t s based on auctions, marketable
r i g h t s a l l o c a t e d by quota t o past producers and importers, and regulatory fees.
766 The second g e n e r a l approach is t o use t h e t r a d i t i o n a l engineering c o n t r o l s and product o r chemical bans.
It i n v o l v e s EPA's d e c i d i n g which s p e c i f i c indus-
t r i e s o r u s e s of CFCs and halons should be regulated. u s u a l way EPA r e g u l a t e s p o l l u t i o n .
T h i s approach is t h e
It was considered alone, and as a supple-
ment t o a l l o c a t e d q u o t a s based on t h e e x t e n t t o which CFC u s e r s may be postponing t h e adoption of low c o s t o r easy t o implement reductions. EPA evaluated each of t h e s e o p t i o n s in l i g h t of t h e following criteria:
c e r t a i n t y of achieving t h e d e s i r e d environmental g o a l , economic c o s t s and e f f i c i e n c y in meeting t h a t goal, a d m i n i s t r a t i v e c o s t s and e n f o r c e a b i l i t y , l e g a l EPA decided to implement t h e
c e r t a i n t y , and impacts on small business.
Montreal P r o t o c o l using a system of a l l o c a t e d quotas.
Quotas r e f l e c t i n g t h e
allowable l e v e l of production and consumption w i l l be a l l o c a t e d t o each of t h e firms who engaged i n t h e s e a c t i v i t i e s i n 1986. w i l l be permitted.
Trading of a l l o c a t e d q u o t a s
Exports and imports of t h e r e s t r i c t e d chemicals w i l l be
allowed c o n s i s t e n t with r e s t r i c t i o n s contained in t h e Montreal Protocol.
EPA
b e l i e v e s t h a t t h i s approach w i l l provide a low-cost means of achieving i t s regulatory goal, s p u r t e c h n o l o g i c a l innovation, minimize a d m i n i s t r a t i v e requirements, and f a c i l i t a t e enforcement.
EPA is a l s o c o n s i d e r i n g t h e develop-
ment of s p e c i f i c r e g u l a t i o n s l i m i t i n g CFC and halon use f o r p a r t i c u l a r indust r i e s t o supplement a l l o c a t e d quotas. A Regulatory Impact Analysis (RIA) t o e v a l u a t e t h e c o s t s and b e n e f i t s of
"major r u l e s " is required by Executive Order.
The R I A f o r P r o t e c t i o n of
S t r a t o s p h e r i c Ozone which was completed in December 1987 (Ref. 3) e v a l u a t e s various c o n t r o l options f o r CFCs.
The c o n t r o l o p t i o n s evaluated in t h e R I A
were divided i n t o chemical s u b s t i t u t e s , product s u b s t i t u t e s , and add-on engineering c o n t r o l s / p r o c e s s s u b s t i t u t i o n s .
S e v e r a l f a c t o r s were considered
in a s s e s s i n g t h e p o t e n t i a l emission reduction, c a p i t a l expenditure, and operating c o s t s f o r each c o n t r o l .
F a c t o r s considered w i t h r e s p e c t t o t e c h n i c a l
f e a s i b i l i t y included c o m p a t i b i l i t y with e x i s t i n g equipment, t h e a b i l i t y t o maintain system e f f i c i e n c y and r e l i a b i l i t y , and a v a i l a b i l i t y of s u f f i c i e n t experience f o r commercial a p p l i c a t i o n .
Economic f a c t o r s of i n t e r e s t included
d i r e c t c a p i t a l and o p e r a t i n g c o s t s , o u t l a y s f o r system a p p l i c a t i o n t e s t i n g , p l a n t r e t o o l i n g , and secondary c o s t s such as d i s p o s a l of waste product and increased warranty claims. In a d d i t i o n , s o c i a l f a c t o r s such as s a f e t y , worker h e a l t h , and r e t r a i n i n g of s e r v i c e personnel were considered although many of t h e s e a r e a s a r e d i f f i c u l t t o quantify.
CONTROL OPTIONS I n d u s t r y w i l l u s e a combination of c o n t r o l o p t i o n s in meeting p o t e n t i a l CFC r e g u l a t i o n s .
In t h e RIA, t h e a e c o n t r o l s were evaluated and t h e more favor-
767 (Ref. 4) The c o n t r o l s t h a t appear most l i k e l y t o be
ab le options id entified.
adopted by each a p p l i c a t i o n a r e a were i d e n t i f i e d i n t h e R I A and are l i s t e d i n These c o n t r o l o p t i o n s are d e s c r i b e d b r i e f l y in t h e following sec-
Table I. tions.
Chemical S u b s t i t u t e s
New Chemical S u b s t i t u t e s . s u b s t i t u t e f o r CFC-12.
HFC-134a appears t o be t h e most promising
S i n c e t h e p h y s i c a l p r o p e r t i e s a r e very similar t o
CFC-12, a major equipment change f o r r e f r i g e r a t i o n and a i r c o n d i t i o n i n g a p p l i c a t i o n s may n o t be required. It is c l o s e t o CPC-12 in o p e r a t i n g e f f i c i e n c y . Some drawbacks include a l a c k of a compatible l u b r i c a t i n g o i l and h i g h e r c o s t . T o x i c i t y tests t o d a t e have shown low t o x i c i t y , but f i n a l t o x i c i t y test r e s u l t s w i l l not be a v a i l a b l e f o r about 5 years.
HCFC-123 appears t o be t h e most promising s u b s t i t u t e f o r CFC-11.
Limited
t e s t i n g as a blowing agent f o r r i g i d polyurethane foam h a s r e v e a l e d both posit i v e and n e g a t i v e r e s u l t s .
It h a s performed w e l l i n some f o r m u l a t i o n s and h a s
a slow d i f f u s i o n r a t e through t h e polymer material.
Drawbacks i n c l u d e s l i g h t y
h i g h e r s o l v e n t a c t i o n , h i g h e r thermal c o n d u c t i v i t y , and h i g h e r c o s t .
HCFC-123
is a l s o a p o t e n t i a l s u b s t i t u t e f o r CFC-113 in s o l v e n t metal and e l e c t r o n i c HCFC-123 is a very a g r e s s i v e s o l v e n t and h a s a much lower b o i l i n g
cleaning.
point t h a n CFC-113 which may l i m i t i t s use.
HCFC-123 is a l s o a p o t e n t i a l
s u b s t i t u t e f o r CFC-11 used as a r e f r i g e r a n t i n c e n t r i f u g a l c h i l l e r s . HCFC-124 may be a s u i t a b l e s u b s t i t u t e f o r CFC-12 as a blowing agent i n r i g i d extruded p o l y s t y r e n e foam s h e e t , e x t r u d e d low d e n s i t y p o l y e t h y l e n e foam, low d e n s i t y polypropylene foam, and p o l y v i n y l c h l o r i d e foam. Since i t s d i f f u s i v i t y through t h e foam is high, i t could cause foam c o l l a p s e . C u r r e n t l y Available CFCs and CFC Blends.
One c o n t r o l o p t i o n t o reduce t h e
u s e of CFC-11 blowing agent i n r i g i d polyurethane pour-in-place more water i n t h e formulation.
foam is t o u s e
It may be p o s s i b l e t o achieve LOO p e r c e n t
replacement of CFC-11 w i t h w a t e r i n r i g i d polyurethane packaging. HCFC-22 is used a s a r e f r i g e r a n t i n r e t a i l food r e f r i g e r a t i o n and i n commercial a i r c o n d i t i o n i n g . c e n t t h a t of CPC-12. changes because it:
It h a s an ozone d e p l e t i n g f a c t o r o n l y 5 per-
S u b s t i t u t i o n f o r CFC-12 w i l l r e q u i r e s i g n i f i c a n t d e s i g n r e q u i r e s a 50 p e r c e n t h i g h e r o p e r a t i n g p r e s s u r e , h a s
reduced o i l s o l u b i l i t y which a f f e c t s compressor l u b r i c a t i o n , and h a s a h i g h permeation rate through e l a s t o m e r hoses. S e v e r a l blends c o n t a i n i n g HCFC-22 hold promise f o r u s e a s s u b s t i t u t e s including : CPC-502, a n a z e o t r o p i c mixture of 48.8 p e r c e n t HCPC-22 and 51.2 p e r c e n t CFC-115,
i s used in a l l of t h e l o r t e m p e r a t u r e and 40 p e r c e n t of t h e medium-
temperature r e f r i g e r a t i o n systems i n r e t a i l food s t o r e s .
CPC-502 is a
768
Table I.
C o n t r o l o p t i o n s c o n s i d e r e d most l i k e l y t o be adopted
+ I
Option
. I
I .cations
6 415 -
CHEMICAL SUBSTITUTES HFC-134a IL T ~ I HCFC- 123 LT ILT I HCFC-124 I LT I CFC-1 11Water I HCFC-22 ST I CFC-502 I I RCPC-2 2/HCFC-142 b IT I I CFC- 11/HCFC-2 2 IST I RCFD22/Hydrocarbons I DMEIHCFC-22 ST ST I Petroleum S o l v e n t s ST I I Methyl Chloroform ST I I Methylene C h l o r i d e ST I I Perchloroethylene rn I I 10190 EO/CO2 I I ST N2 Purge/Pure EO I IST HFC-134aIEO I Hydrocarbons Ammonia ST I iT I I co2 PRODUCT SUBSTITUTES I I A l t e r n a t e I n s u l a t i n g Materials I ST I S u b s t i t u t e Food C o n t a i n e r s 1 ST I A l t e r n a t e Packaging M a t e r i a l s 1 ST I Gasket/Flotation A l t e r n a t i v e s I A l t e r n a t e Cushioning M a t e r i a l s ST I Switch t o Disposables ST I I Modified S t i r l i n n C y c l e I I ADD-ON CONTROLSlPR6CESS I4lDIFICATI:ON I I Recove r y l l e c y c l e ST ST I I A l t e r n a t e Leak Test Gas ST I I Market Mix I I Q u a l i t y Engineering I I Water Blown ER Systems I I Minimum Foam D e n s i t y I I Add-on C o n t r o l s ST I I Carbon Adsorption I Food F r e e z i n g A l t e r n a t i v e s iT I ST Aqueous Cleaning ST I I No Clean Option LT I I Hot Vapor Recycle LT I I Improve C o n t r o l s / T r a i n i n g 1 - I I - ST a Application: 1 R i g i d Foam, 2 F l e x i b l e Foam, Refr w t i o n , Miscellaneous, 5 S t e r i l a n t s , 6 - Solvents, 7 Halone 4 b A v a i l a b i l i t y : ST Short Term, MT Medium Term, LT Long Term
I I
ILT
I I
I
-
-
-
-
-
-
-
-
769 p o t e n t i a l s u b s t i t u t e f o r CFC-12 systems e v e n though one of i t s components is c o n t r o l l e d under t h e P r o t o c o l . Overall, CFC-502 h a s a lower ozone d e p l e t i o n p o t e n t i a l t h a n CFC-115 a l o n e o r CFC-12 alone.
The P r o t o c o l r e q u i r e s o n l y a
r e d u c t i o n i n t o t a l weighted production/consumption, not i n e a c h c o n t r o l l e d substance i n d i v i d u al ly .
A HCFC-22/-142b non-azeotropic m i x t u r e of 40 p e r c e n t BCFC-22 and 60 p e r c e n t HCFC-142b is t a i l o r e d t o c l o s e l y match CFC-12.
This mixture has a
good p o t e n t i a l f o r u s e i n small h e r m e t i c a l l y s e a l e d u n i t s such as home r e f r i g e r a t o r s and as an a e r o s o l p r o p e l l a n t . A CFC-ll/RCFC-22
m i x t u r e can be used i n p l a c e of CFC-12 i n p o l y u r e t h a n e
poured and sprayed foam.
However, t h e s u b s t i t u t i o n would r e s u l t i n o n l y a
minor r e d u c t i o n i n ozone d e p l e t i o n p o t e n t i a l . (e.g.,
T h i s and o t h e r drawbacks
poor HCFC-22 solvency and p o t e n t i a l l y h i g h e r d i f f u s i o n rate) w i l l
l i m i t t h e u s e of t h i s s u b s t i t u t e .
A HCPC-22/hydrocarbon m i x t u r e h a s been found t o b e a n a c c e p t a b l e subs t i t u t e f o r CFC-12 as a blowing agent f o r e x t r u d e d p o l y s t y r e n e s h e e t . Dimethyl ether/HCFC-22 m i x t u r e s have been used t o r e p l a c e CFC-11 and -12 i n some e s s e n t i a l a e r o s o l a p p l i c a t i o n s .
A wide v a r i e t y of o r g a n i c s o l v e n t s are used i n
Solvent S u b s t i t u t e s .
e l e c t r o n i c and m e t a l c l e a n i n g i n c l u d i n g petroleum s o l v e n t s , c h l o r i n a t e d hydrocarbons, and CFCs.
I t is p o s t u l a t e d t h a t petroleum s o l v e n t s o r methyl
chloroform w i l l be s e l e c t e d where p o s s i b l e as t h e s h o r t term replacement f o r CFC-113 i n s o l v e n t c o l d - c l e a n i n g a p p l i c a t i o n s .
Methyl chloroform and meth-
ylene c h l o r i d e are expected t o be t h e s o l v e n t replacements of c h o i c e f o r vapor d e g r e a s i n g .
Dry c l e a n i n g a p p l i c a t i o n s are e x p e c t e d t o s w i t c h t o p e r
c h l o r o e t h y l e n e o r methyl chloroform. hydrocarbon-based
A new product which c o n t a i n s a t e r p e n e
c l e a n e r h a s r e c e n t l y been announced which c a n be used t o
r e p l a c e CFC-113 f o r some s o l v e n t c l e a n i n g and degreaeing. Methylene c h l o r i d e a l s o competes w i t h CFC-11 as a blowing a g e n t f o r f l e x i b l e polyurethane foam.
Wider u s e of methylene c h l o r i d e is expected f o r
t h i s application. A major b a r r i e r t o expanded u s e of methylene c h l o r i d e as a blowing a g e n t
or s o l v e n t replacement is t h e p o t e n t i a l f o r f u t u r e r e g u l a t i o n of i n - p l a n t exposure and s t a c k emissions. Sterilant Substitutes.
C o n t r o l o p t i o n "10/90 (EO/C02)" r e f e r s t o replac-
i n g 12/88 ( a 1 2 p e r c e n t e t h y l e n e oxide and 88 p e r c e n t CFC-12 m i x t u r e ) w i t h a 10 p e r c e n t e t h y l e n e oxide and 90 p e r c e n t C02 mixture.
C o n t r o l o p t i o n "N2
purge, t h e n p u r e EO" r e f e r s t o a p r o c e s s where t h e s t e r i l i z a t i o n chamber i s purged w i t h n i t r o g e n b e f o r e s t e r i l i z l n g w i t h p u r e e t h y l e n e oxide.
Control
o p t i o n "HFC-l34a/EO mixture" r e f e r s t o t h e replacement of CFC-12 i n t h e 12/88
770 mixture w i t h EFC-134a.
A l l three of t h e s e o p t i o n e are expected t o be used t o
r e p l a c e t h e 12/88 s t e r i l a n t . The 10/90 (EO/CO2) h a s a disadvantage of r e q u i r i n g
a much h i g h e r o p e r a t i n g p r e s s u r e t h a n 12/88.
The N2 purge, t h e n pure EO o p t i o n
r e q u i r e s t h e use of pure e t h y l e n e oxide which is explosive; t h e r e f o r e , equipment changes a r e needed t o handle t h e explosive gas.
The EFC-l34a/EO mixture
is s t i l l in the development s t a g e and may n o t be a v a i l a b l e f o r 5 t o 7 years. Currently o r Previously Used S u b s t i t u t e s . f i r e t introduced i n t h e mid-l960s, pentane.
When polystyrene foams were
they were blown almost e x c l u s i v e l y w i t h
I n d u s t r y has s h i f t e d away from pentane because of t h e f i r e hazards.
It is p o s s i b l e t o make v i r t u a l l y a l l thennoformable polystyrene foam s h e e t
using hydrocarbons such as pentane f o r t h e blowing agent.
Eydrocarbone such
as ethylene, ethane, propane, propylene, and methane are used as r e f r i g e r a n t s
in l a r g e i n d u s t r i a l r e f r i g e r a t i o n systems in petrochemical p l a n t s .
The u s e
of hydrocarbons i s r e s t r i c t e d by codes and r e g u l a t i o n s s i n c e they a r e h i g h l y flammable. Ammonia is c u r r e n t l y used as a r e f r i g e r a n t in most food p r o c e s s i n g p l a n t s , c o l d s t o r a g e warehouees, ice houses, s k a t i n g rinks, and a percentage
of t h e chemical/petrochemical p l a n t s .
The use of enmonia is r e s t r i c t e d s i n c e
it i s both t o x i c and flammable.
C02 h a s been used as a n a e r o s o l p r o p e l l a n t but s u f f e r s from poor atomizat i o n , varying p r e s s u r e over t h e l i f e of t h e can, and o c c a s i o n a l i n a b i l i t y t o expel t h e e n t i r e c o n t e n t s of t h e can. Some improvements in technology have reduced problems w i t h C02, but they have not been completely eliminated. Product S u b s t i t u t e s A l t e r n a t e I n s u l a t i n g Materials.
Rigid foam luminated
boardstock is
used r o u t i n e l y in t h e c o n s t r u c t i o n of a v a r i e t y of new b u i l d i n g s and a e r e t r o f i t s in e x i s t i n g buildings.
The most l i k e l y short-term c a n d i d a t e c o n t r o l
o p t i o n f o r reducing use of CFCe in t h e s e a p p l i c a t i o n s is t o simply use o t h e r i n s u l a t i o n materials coupled w i t h modified c o n s t r u c t i o n design and/or t h i c k e r m a t e r i a l s to achieve equivalent energy e f f i c i e n c y (e.g.,
thick fibrous glass
b a t t s with t h i c k walls and wide stud spacing). S u b s t i t u t e Food Containers.
Since t h e 19608, polystyrene foam products
have gradually replaced competing products f a b r i c a t e d from t r a d i t i o n a l materials.
The b e n e f i t s of polystyrene foams (e.g.,
l i g h t weight, s t r e n g t h ,
ease of forming, moisture r e s i s t a n c e , low c o s t , and thermal i n s u l a t i o n prope r t i e s ) have spurred t h i s growth.
With few exceptions, t h e polystyrene foam
s e r v e s e s s e n t i a l l y t h e same purpose as t h e material i t h a s replaced.
Materials
t h a t can be used in place of t h e CFC blown polystyrene foam s h e e t f o r food packaging i n c l u d e hydrocarbon blown polystyrene, s o l i d p l a s t i c , p l a s t i c f i l m wrap and bags, and paper and f o i l wraps.
771 A l t e r n a t e Packaging Materials.
Low d e n s i t y p o l y e t h y l e n e and polypro-
pylene a r e used i n a wide v a r i e t y of a p p l i c a t i o n s , f r o a packaging material t o a t h l e t i c equipment.
They have unique p r o p e r t i e s including: cushion e f f e c t i v e -
ness a t a given t h i c k n e s s , unique v i b r a t i o n dampening response, m u l t i p l e drop p r o t e c t i o n , s t r e n g t h , c r e e p r e s i s t a n c e , minimum package weight and s i z e , low shipping c o s t , and s t a t i c d i s c h a r g e p r o t e c t i o n .
Because of t h e s e p r o p e r t i e s ,
t h e s e foams a r e o f t e n used in s p e c i a l l y designed package systems such as f o r a d e l i c a t e computer product o r m i l i t a r y weapon. In t h e s e a p p l i c a t i o n s , replacements may n o t be r e a d i l y a v a i l a b l e . For o t h e r a p p l i c a t i o n s , a l t e r n a t i v e products such as expanded p o l y s t y r e n e (EPS) bead, water-blown
polyurethane
foam, p l a s t i c f i l m bubble wrap, and o t h e r paper and p l a s t i c packaging p r o d u c t s can be used.
Alternate G a s k e t / F l o t a t i o n Device Materials.
Low d e n s i t y p o l y e t h y l e n e and polyvinyl c h l o r i d e foam are used in g a s k e t and s e a l i n g materials and in f l o t a t i o n devices. Gaskets can be made from rubber, p l a s t i c , o r p a p e r prodF l o t a t i o n devices are s t i l l made from a i r - f i l l e d
ucts. fabric.
p l a s t i c or sealed
EPS bead is a l s o used f o r f l o t a t i o n .
A l t e r n a t e Cushioning M a t e r i a l s .
F l e x i b l e polyurethane foam i s t h e
predominant cushioning m a t e r i a l , due t o i t s combined advantages of low p r i c e , d u r a b i l i t y , and v e r s a t i l e p h y s i c a l p r o p e r t i e s . A degree of conversion t o technologies t h a t were replaced by f l e x i b l e polyurethane (e.g.,
l a t e x foam,
b u i l t - u p cushioning, and n a t u r a l and s y n t h e t i c f i b e r f i l l ) are t e c h n i c a l l y feasible. Switch t o Disposables.
To e l i m i n a t e t h e need f o r h o s p i t a l s t o s t e r i l i z e
on s i t e w i t h t h e s t e r i l a n t g a s mixture 12/88, one c o n t r o l o p t i o n is t o switch t o disposables.
A l l items needed f o r a s i n g l e s u r g i c a l procedure would be
packaged and s t e r i l i z e d by t h e manufacturer of t h e d i s p o s a b l e products. Modified S t i r l i n g Cycle.
Modified S t i r l i n g c y c l e r e f r i g e r a t o r s have
been used h i s t o r i c a l l y f o r e x o t i c a p p l i c a t i o n s such a s aerospace and cryogenic Cooling.
One company i s marketing a r e f r i g e r a t e d t r u c k t r a i l e r u s i n g a
modified S t i r l i n g cycle. Add-on Engineering C o n t r o l d P r o c e s s S u b s t i t u t i o n Recovery/Recycle.
The r e f r i g e r a n t s from r e f r i g e r a t i o n and mobile a i r
c o n d i t i o n i n g equipment can be recovered and recycled at rework, s e r v i c e , and d i s p o s a l w i t h t h e use of p o r t a b l e d e v i c e s which c a p t u r e t h e r e f r i g e r a n t from a system r a t h e r t h a n vent i t t o t h e atmosphere.
More s e r i o u s l y cont&nated
r e f r i g e r a n t s can be c o l l e c t e d and t h e n cleaned in a c e n t r a l f a c i l i t y , remanufactured, or destroyed.
Much of t h e waste s o l v e n t from s o l v e n t c l e a n i n g
o p e r a t i o n s can be reclaimed by t h e u s e of on- o r o f f - s i t e d i s t i l l a t i o n .
772 A l t e r n a t e Leak Test Gas.
Mobile a i r c o n d i t i o n i n g and r e f r i g e r a t i o n
equipment must be leak t e s t e d a t manufacture, i n s t a l l a t i o n , and s e r v i c e . The high ozone d e p l e t i n g CFC-11 and -12 r e f r i g e r a n t s which are used t o charge t h e systems a r e u s u a l l y s e l e c t e d f o r l e a k t e s t i n g t o reduce chances of t h e r e f r i g e r a n t s ' being mixed.
CFC emissions can be reduced by switching t o a l e s s
ozone d e p l e t i n g CFC such a s HCFC-22 or t o a d i f f e r e n t g a s such a s helium. Market Mix.
T h i s concept addresses demand f o r new c e n t r i f u g a l c h i l l e r s .
It i s suspected t h a t a p o r t i o n of f u t u r e demand f o r c h i l l e r s whtch use high ozone d e p l e t i o n r e f r i g e r a n t s can be s h i f t e d t o u n i t s using a lower ozone d e p l e t i n g r e f r i g e r a n t such as HCFC-22.
For example, CFC-11 c e n t r i f u g a l
c h i l l e r s a r e known t o be widely used in t h e range of 300 t o 1000 t o n s (270 t o 900 metric t o n s ) of c a p a c i t y .
The market mix o p t i o n assumes t h a t a f r a c t i o n
of f u t u r e i n s t a l l a t i o n s which would u s e CFC-11 c e n t r i f u g a l c h i l l e r s could i n s t e a d use HCFC-22 h e l i c a l screw c h i l l e r s ( e i t h e r s i n g l y or as m u l t i p l e part-capacity u n i t s ) . Quality Engineering.
Leaks from mobile a i r c o n d i t i o n e r s can be reduced
by improvements i n design of system components such a s t h e use of s h o r t e r and l e s s permeable hoses o r t h e a d d i t i o n of f e a t u r e s such a s a r e f r i g e r a n t l e v e l seneor t o shut off the system and a l e r t t h e d r i v e r t h a t t h e charge h a s dropped below a c e r t a i n l e v e l .
These " q u a l i t y engineering'' improvements could be
i n s t a l l e d a t t h e f a c t o r y a s o r i g i n a l equipment o r used a s replacement p a r t s
on mobile a i r c o n d i t i o n e r s a f t e r manufacture. Water Blown HR Systems.
Additional use of water-blown h i g h - r e s i l i a n c e
(HR) chemical systems f o r molded f l e x i b l e foams is a r e a l i s t l c p o s s i b i l i t y f o r s u b s t a n t i a l emission reduction.
There may be a p e n a l t y i n foam versa-
t i l i t y , cushioning p r o p e r t i e s , and p a r t r e j e c t rates. Minimum Foam Density.
Most of t h e a u x i l i a r y blowing agent, CFC-11,
used in f l e x i b l e polyurethane Coam is used f o r low d e n s i t y foam.
CFC-11
emissions can be reduced by e s t a b l i s h i n g a minimum foam d e n s i t y s p e c i f i c a tion. Add-on Controls.
Add-on engineering c o n t r o l s can be u s e d t o reduce
CFC-113 emissions from s o l v e n t c l e a n i n g o p e r a t i o n s .
These c o n t r o l s i n c l u d e
covers, optimum freeboard h e i g h t , and adequate drainage of p a r t s being cleaned v i a drainage racks, hooks, automatic h o i s t s , o r e q u i v a l e n t techntquen. Carbon Adsorption.
Carbon a d s o r p t i o n is c u r r e n t l y used t o c o l l e c t CFCs
from a v a r i e t y of a p p l i c a t i o n s f o r recovery o r d i s p o s a l .
A broader use of
t h i s technology i s t e c h n i c a l l y f e a s i b l e . Food Freezing A l t e r n a t i v e s . quick-freeze foods. l i q u i d food f r e e z i n g .
Liquid food f r e e z i n g u s e s l i q u i d CFC-12 t o
A i r b l a s t f r e e z i n g and cryogenic f r e e z i n g can r e p l a c e A i r b l a s t f r e e z i n g blows c o l d a i r upward through mesh
773 Cryogenic f r e e z i n g u s e s l i q u i d n i t r o g e n o r
b e l t s c a r r y i n g t h e food product.
l i q u i d carbon d i o x i d e sprayed o n t o t h e food. Aqueous Cleaning.
Aqueous c l e a n i n g i s a n a l t e r n a t i v e t o metal and
No s o l v e n t em i ssi o n s o ccu r from t h i s type of
e l e c t r o n i c s c l e a n i n g w i t h CFCs.
c l e a n i n g because t h e c l e a n i n g f l u i d i s w a t e r b a s e d .
No Clean Option.
A lo n g term o p t i o n f o r c l e a n i n g of e l e c t r o n i c c i r c u i t
boards is t h e "no c l e a n approach."
T h i s approach would u s e d i f f e r e n t f l u x e s
which would n o t need t o be removed from t h e c i r c u i t board. Hot Vapor Recycle.
T h i s i s a t e c h n iq u e f o r t h e c o n t r o l of carry-out
s o l v e n t l o s s from conveyortzed s o l v e n t vapor d e g r e a s e r s .
Hot su p er h eat ed
vapor, s u p p l i ed t o a d r y e r i n t h e d e g r e a s e r , h e a t s t h e p a r t b ei n g cl ean ed T h i s method can remove t r ap p ed s o l v e n t i n
above t h e s o l v e n t vapor p r e s s u r e . sp aces as small as 0.05 t o 0.08 mm. Improve C o n t r o l s /T r a in in g .
The most d i r e c t way t o reduce unwanted
d i s c h a r g e s from h a lo n t o t a l - f l o o d e d f i r e p r o t e c t i o n systems which release t h e e n t i r e q u a n t i t y of h a lo n s i n t o an e n c l o s e d s p ace i s to u s e improved d e t e c t i o n and c o n t r o l equipment. I n c r e a s i n g t r a i n i n g of p e r s o n n e l working i n h a l o n system p r o t e c t e d areas c a n a l s o s t g n i f i c a n t l y reduce releases due t o unwanted d i s c h a r g e s and f i r e emissions.
Using halon-121 (HCFC-22) as a s u b s t i t u t e g a s
f o r t e s t i n g t o t a l - f l o o d e d f i r e p r o t e c t i o n systems can reduce em i ssi o n s of t h e high ozone d e p l e t i n g h a lo n s . SUMMARY
On December 1, 1987,
EPA proposed domestic r e g u l a t i o n s t h a t w i l l f u l l y
implement t h e Montreal P r o t o c o l t o p r o t e c t t h e s t r a t o s p h e r i c ozone l a y e r . It was decided t h a t a l l o c a t e d q u o t a s o f f e r t h e most a t t r a c t i v e approach t o l i m i t i n g t h e u s e of CFCs and halons. T h i s approach should p r o v i d e f o r economi cal l y e f f i c i e n t r e d u c t io n s . It i n v o l v e s a minimum of a d d n i s t r a t l v e costs,
i s t h e most e a s i l y e n f o r c e d o p t i o n , and does not raise any p o t e n t i a l legal i s s u e s t h a t might r e s u l t from o t h e r o p t i o n s . C o n t r o l o p t i o n s t h a t might be used by i n d u s t r y t o ach i ev e t h e n e c e s s a r y CPC r e d u c t i o n s are e v a l u a t e d i n t h e RIA. The most l i k e l y long-term c o n t r o l o p t i o n which may be adopted by most a p p l i c a t i o n areas i s a ch em i cal s u b e t i tute.
With t h i s o p t io n , i t may b e p o s s i b l e t o e l i m i n a t e 90 p e r c e n t o r more
of t h e ozone-depleting CFC emissions. A v a r i e t y of c o n t r o l o p t i o n s h o l d
promise f o r short-term a p p l i c a b i l i t y . Some of the e n g i n e e r i n g c o n t r o l s may s t i l l be a p p l i e d even a f t e r new chemical s u b s t i t u t e s (e.g.,
HFC-134a and
RCPC-123) are i n u s e , s i n c e t h e h i g h e r c o s t of t h e r e s u b s t i t u t e s may j u s t i f y recovery.
EPA i s a l s o c o n s i d e r i n g t h e development of s p e c i f i c r e g u l a t i o n s
l i m i t i n g CPC and h a l o n u s e f o r p a r t i c u l a r i n d u s t r i e s t o supplement a l l o c a t e d qu o t as .
774 REFERENCES
-
Federal R e g i s t e r , pp. 57,489 57,523, Vol. 52, No. 239, December 14, 1987. Montreal Protocol on Substances t h a t Deplete t h e Ozone Layer, F i n a l Act, United Nations Environment Programme, September 1987. Regulatory Impact Analysis: P r o t e c t i o n of S t r a t o s p h e r i c Ozone, Volume I: Regulatory Impact Analysis,Document, Prepared by O f f i c e of A i r and Radiation, U. S. Environmental P r o t e c t i o n Agency, Washington, DC, December 1987. Regulatory Impact Analysis: P r o t e c t i o n of S t r a t o s p h e r i c Ozone, Volume 111: Addenda t o t h e Regulatory Impact Analysis Document, Prepared by O f f i c e of A i r and Radiation, U. S. Environmental P r o t e c t i o n Agency, Washington, DC, December 1987.
T. Schneider el al. (Editors),Atmospheric Ozone Research and its Policy lmplicatwns 0 1989 Elsevier Science Publishere B.V., Amsterdam - Printed in The Netherlands
775
MOVING FORWARD: KEY IMPLICATIONS OF THE DAVID DULL1, STEPHEN SEIDELl, and JOHN WELLS2 'Office of Air and Radiation, U.S. Environmental Protection Agency, ANR-445, 401 M Street, SW, Washington, D.C. 20460 2The Bruce Company, Suite 410, 3701 Massachusetts Avenue, NW, Washington, D.C. 20016 ABSTRACT The Montreal Protocol on Substances that DeDlete the ozone Laver represents a landmark environmental agreement. It provides a global response to protecting a global resource -- the earth's protective ozone layer. This paper summarizes some of the key findings of the U . S . Environmental Protection Agency's efforts to implement the Protocol in the United States. The paper addresses three specific areas: 1) sources of atmospheric chlorine; 2) timing of reductions in CFC use; and 3) technological developments. DEALING WITH SCIENTIFIC UNCERTAINTY While the Protocol has now been signed by 31 nations, this widespread participation reflects the degree of consensus on the need for action, not only the large uncertainties that still exist. In fact, one key aspect of the Protocol relevant to this issue of uncertainty is Article 6, ggAssessmentand Review of control Measuresgg, which provides for periodic reassessments of environmental, scientific, economic and technology factors. Based on these reassessments, the parties are to meet periodically to review the need for altering the timing, scope, or stringency of the Protocol's control requirements. The underlying basis for this provision was the recognition that substantial uncertainties in each of these areas remained and that more and better information would be available in future years. For example, -_ Researchers have progressed rapidly in their understanding of the Antarctic ozone hole; _ _ Industrial efforts are progressing rapidly on developing new chemicals to replace chlorofluorocarbons (CFCs) and to recycle those currently being used; -- Research is just beginning on the ecological impacts of the Antarctic ozone hole.
776
Significant advances in our understanding of the link between CFCs and the Antarctic ozone hole and in our estimates of recent trends in global ozone levels were published on March 15, 1988 with the Report of the Ozone Trends Panell. This report suggested that ozone may be depleting at a faster rate than current models suggest. This report further underscores the need for the Protocol and the importance of the assessments called for in Article 6 . MOVING TOWARD IMPLEMENTATION Recognizing that this issue is still evolving rapidly, the U.S. Environmental Protection Agency (EPA) has initiated a number of studies as part of its rulemaking process seeking to address key aspects of moving forward to implement the Montreal Protocol. This paper attempts to summarize some of the key findings in our efforts to understand fully the implications of the Protocol and to minimize the impacts of its implementation. Specifically, this paper addresses three questions: -Sources of Atmospheric Chlorine. Given that our confidence in atmospheric models has been reduced by the findings of the recent ozone trends report, what can be learned by simply looking at the magnitude and sources of future chlorine levels? -- Timing of Reductions in CFC Use. Our analyses show that near-term reductions in CFC use are critical to reducing the overall costs of meeting the Protocol's reduction requirements. -Technological Developments. New technologies are rapidly being developed across a wide range of CFC user industries. while progress is being made, the U.S. is finding that institutional barriers and competing environmental and energy issues must be addressed in shifting away from ozone-depleting chemicals.
Two groups of chemicals are controlled by the Protocol. IIGroup 1" chemicals are the fully-halogenated CFCs: CFC-11, CFC12, CFC-113, CFC-114, and CFC-115. IgGroup2" chemicals are Halon1211, Halon-1301, and Halon-2402, which are brominated compounds use in fire-fighting applications.
777
in Table 1, these chemicals have long lifetimes, which allow them to accumulate in the lower atmosphere and eventually be transported to the stratosphere, where they are dissociated by high-energy solar radiation. They also contain chlorine and/or bromine, which is then released in the As shown
stratosphere and which catalytically destroys ozone2. Their destructiveness to ozone is commonly measured by their @'ozone depletion potentiall', whereby the modelled depletion caused by a mass of each chemical is compared to the modelled depletion caused by an equal mass of CFC-11. Note in Table 1 that the "Group 1" chemicals have ozone depletion potentials greater than 0.6.
ComDounCJ
Li fet ime
Chlorine and/or Bromine atoms per
0
Molecule
Ozone Depletion Potential lDer kilosram)
CFC-11
75
3 c1
1.0
CFC-12
111
2 c1
1.0
CFC-113
90
3 c1
0.8
CFC-114
185
2 c1
1.0
CFC-115
380
1 c1
0.6
1 C1 and 1 Br
3.0
Halon-1211
25
Halon-1301
110
1 Br
10.0
Halon-2402
NA
2 Br
6.0
HCFC-22
20
1 c1
0.05
CH3CC13 6.5 (methyl chloroform)
3 c1
0.1
CCl4 50 (carbon tetrachloride)
4 c1
1.06
Table 1. Relative Depletion Potentials of CFCs and Halons. Sources: Lifetime estimates are based on the WM02. Ozone depletion potentials are those stated in mntreal Protoco1 and approximate those estimated by the LLNL National Laboratory 1-D model. Ozone depletion potential for Halon-2402 was reported at negotiations for m t r e a l Protoco1 and is likely to change.
778
The Protocol requires signatories to freeze their consumption of Group 1 chemicals at 1986 levels by July 1, 1989, or 90 days after entry into force. Consumption must then be reduced to 5 0 percent of 1986 levels by July 1, 1992. Other chlorinated compounds, particularly methyl chloroform (CH3CC13), carbon tetrachloride (CCl4), and HCFC-22 (CHClFZ) are not controlled by the Protocol. These compounds have shorter lifetimes and thus a smaller percentage of their emissions reaches the stratosphere. They have significantly lower ozone depletion potentials than the fully-halogenated CFCs that are controlled by the Montreal Protocol. EPA is currently completing an analysis of the potential sources of atmospheric chlorine and bromine3. The usefulness of this analysis is underscored by the recent Ozone Trends Panel Report, which suggests that current atmospheric models may be underpredicting the amount of depletion for a given increase in atmospheric chlorine. EPAts complementary approach focuses on how the atmospheric levels of chlorine (Cl,) and bromine will change over time under the Montreal Protocol. The merit of examining the potential for future ozone depletion in this manner stems from the fact that chlorine and bromine abundances ultimately determine the risk of ozone depletion. Consequently, information about their abundances can be of use to the decisionmaking process without making final and certain conclusions about the quantitative relationship between their abundances and ozone depletion. The relative contribution of each chlorinated compound to the current C1, concentration of 2.7 parts per billion (ppb) is shown in Figure 1. Note that the controlled Group I compounds account for roughly one-half of the current C1, concentration3. Figure 1 also shows the projected C1, concentration in the year 2100. The concentration has risen to 9.8 ppb despite Protocol reductions. 45 percent of the increase in C1, is attributable to allowable use of Group 1 compounds by signatories. Use of these compounds by non-signatories accounts for 15 percent of the increase in Cl,. The residual increase in C1, levels is due to emissions of chlorinated compounds not covered by the Montreal Protocol 32 percent of the increase in C1, levels is due to emissions of methyl chloroform; and 8 percent from HCFC-22 and carbon tetrachloride3.
.
779
L
CFC- 1 1
w WFC-12 c-113
CFC- 1 1
Fig. 1. Potential future sources of atmospheric chlorine3. This analysis also indicates the benefits of global participation in the a e a l Protocoa. The standard assumption about global participation rates (100 percent for the U.S., 94 percent for other developed nations, and 65 percent for developing nations) leads to a C1, concentration in the year 2100 of 9.8 ppb. If 100% global compliance were achieved, Cl, concentrations would increase only to 7.6 ppb3. The analysis of future sources of chlorine and bromine indicates that even under the Montreal Protocol, concentrations of atmospheric chlorine will increase significantly. Compounds which are not controlled by the Protocol are one major source of chlorine. The degree of global participation that is achieved is another important determinant of future chlorine levels3. Q of Rernctions in CFC Use The Montreal P r o w requires signatories to freeze their CFC consumption at 1986 levels by July 1, 1989 or 90 days after
780
entry into force; reduce it 2 0 % from 1986 levels by July 1, 1992; and reduce it 5 0 % from 1986 levels by July 1, 1998. In the U . S . we have recently become concerned that the stringency of the Protocol may be indirectly tightened due to the increased consumption of CFCs since 1986, the baseline year. Figure 2 shows the historical and projected increases in CFC consumption from 1986 to July 1, 1989, the date of the CFC freeze. Due to increased CFC consumption, this llfreezell may actually entail a cutback of approximately 18 percent. Because of the recent surge in demand, the economic effects of the Protocol would consequently be higher than anticipated in our earlier studies.
I-..................... --,, '21 Q)
200-
1 I
--
I----------
0
. I
85
Fig. 2.
1990
1995
2000
CFC growth is greater than had been projected.
Sources: Historical CFC use is based on estimates developed for Regulatory Impact Analysis4and was updated based on data reported by U . S . International Trade Commission5 and on confidential data reported to the U . S . EPA. Projected use is based on growth rates in EPA4. EPA's
781
The economic effects of the Protocol will be most directly affected by the speed at which firms in the U . S . begin to implement available CFC reduction measures and to introduce chemical substitutes. To implement the Montreal Protocol, the EPA has proposed regulations6 which allocate production and consumption quotas to CFC producers and importers based on their 1986 market shares. As the supply of CFCs is directly reduced by regulation, rising CFC prices will serve as the mechanism which allocates CFCs to the highest value-added end-uses. In this economic-incentives system, the interaction of supply and demand will establish price. Suppose that end-use demand is constant. The reduced supply of CFCs will lead to an increase in their price. If end-use demand is reduced, the CFC prices increase will be less4. Figure 3 shows that the rate at which controls are initiated (and demand is thus reduced) makes a significant difference in the projected CFC price increases.
-tlon
of Current Trend8 Production Scenarios
$7.00
$0.00
$6 DO
h hInormaam
om)
t4.00
$3.00
$2 00
$1.00
10.00 1000
1000
toe1
1002
100s
1094
I6
Fig. 3 . The rate at which controls are initiated makes a significant difference in the CFC price increase*.
782
As alternatives to CFCS are adopted in any application, the aggregate demand for CFCs will be reduced, and thus the CFC price increase will be moderated. In this manner, the interests of disparate industry sectors are thus linked through the price mechanism. Technoloqical DeveloDments As it now stands, the Protocol allows 10 years to achieve its 5 0 percent reduction. This time was provided in part because economic modelling showed that phasing in reductions could significantly reduce control costs. The ten year phase-in period will only reduce costs, however, if industries and governments use the allotted time to develop alternatives and remove barriers to their introduction. As discussed in the previous section, early introduction of alternatives in any one industry, by reducing aggregate CFC demand, will lessen price rises and thus benefit other industries. Several industries in the U . S . have already begun to introduce alternatives. In March, 1988, for example, the food packaging industry announced that it would shift to HCFC-22 and eliminate its use of CFC-12 within one year. The prospect of future profits has led other companies to develop CFC substitutes. A terpene-based solvent, for example, was recently introduced as a cost-effective substitute for CFC-113 in electronics cleaning. Industry has also acted to resolve concerns about alternatives. The level of toxicity of potential chemical substitutes must be well-established before they can be marketed. To accelerate this process, major CFC producing companies from six nations have formed an international consortium, the IIProgram for Alternate Fluorocarbon Testing" to share information three substitutes: FC-134aI HCFC-123, and HCFC-14lb. Another important task to be accomplished during the ten-year phase-in period is the identification and elimination of institutional barriers to CFC alternatives. Issues such as the absence of industry-wide recycling Standards, the existence of military procurement specifications that require CFC use, and concerns about energy efficiency have been identified as potential barriers which industry and government are working to overcome prior to the introduction of reduction technologies.
783
An example of this government-industry cooperation is EPA's work with the automotive air conditioning servicing industry to develop voluntary standards for the purity of recycled refrigerants. In some cases, governmental policies themselves may form barriers that limit alternatives. The U.S. EPA is working with the electronics industry and the military to ensure that procurement specifications do not inadvertently bar the use of CFC substitutes. Alternative insulating materials such as fiberglass and fiberboard can reduce the demand for CFCs, but do not achieve the same insulating capacity as a similar thickness of CFC blown rigid polyurethane foam. In some cases, wall and roofing insulation could be made thicker to achieve the same insulating capacity, but such changes would require changes in building design and practices, which are tightly regulated at the local, state and federal level. Significant coordination would be required in order for these alternatives to be adopted.
CONCLUSIONS
The united States firmly supports the -real Protocol. We signed it in September 1987 and ratified it in April 1988. Several issues related to stratospheric ozone protection have arisen since the Protocol was negotiated in September 1987. In March 1988, the Ozone Trends Panel concluded that significant global depletion has already occurred. This finding underscores the importance of rapidly invoking the provisions for periodic assessment and review. In addition, it suggests that current atmospheric models may be underpredicting future depletion, and supports a complementary analytical approach of evaluating future sources of chlorine concentrations. As it has developed regulations to domestically implement the Protocol provisions, EPA has realized the importance of achieving early CFC reductions, which lower the overall regulatory burden, and has recognized the importance of identifying and eliminating institutional barriers that block the movement to CFC alternatives.
784
REFERFNCES National Aeronautics and Space Administration (NASA), 4 E P 1 R , NASA, Washington, D.C., 1988. world Meteorological Organization (WMO), qfmosDher ic Ozone 1985: Assessment of Our Understan&ins of the Processes controllina its Present Dision and Chanae, WMO Global Ozone Research and Monitoring Project Report No. 16, WMO, Geneva Switzerland, 1986.. Hoffman, J.S., and M.J. Gibbs, "Potential Future Chlorine and Bromine Levels*!, draft report, U.S. Environmental Protection Agency, Washington, D.C., 1988. United States Environmental Protection Agency, Recrulatory ImDact Analvsis: Protection o f StratOSDheric Ozone. U.S. EPA, Washington, D.C., 1987. United States International Trade Commission (ITC), IIPreliminary Report on U.S. Production of Selected Synthetic Organic Chemicals (Including synthetic Plastics and Resin Materials), Preliminary Totals, 1987**,ITC, Washington, D.C., 1988. United States Environmental Protection Agency, "40 CFR Part 82. Protection of Stratospheric Ozone; Final and Proposed Rulev8 , Federal Resister, 52(239): 47486-47523, 1987.
T. Schneider et al. (Editors),Atmospheric Owne Re8emh and ita Policy Zmplicationa 0 1989 Elsevier Science Publishers B.V., Amsterdam Printed in The Netherlande
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785
PREVENTION OF STRATOSPHERIC MODIFICATION L. Reijnders Stichting Natuur en Milieu/Interfacultaire Vakgroep Milieukunde, Universiteit van Amsterdam, p/a Donkerstraat 17, 3511 KB Utrecht, The Netherlands
ABSTRACT Implementation of the 1987 Montreal Protocol will not prevent further deterioration of the ozone layer. Under this Protocol springtime losses of ozone over the Antarctic will probably increase from their present level of about 50% to 80%. To prevent a further deterioration use and/or emission cuts for a number of chlorofluorocarbons in the order of 80-90% are necessary. Substitution and recycling options, currently available in a technical sense, allow for a cut in the use of these chlorofluorocarbons of 84.5-948 in the European Community and for a 79.5-93% cut in all non-communist countries.
INTRODUCTION The protection of the ozone layer is the object of two international agreements, the Vienna Treaty of March 22, 1985 and the Montreal Protocol of September 16, 1987. Current knowledge suggests that these agreements do not and will not prevent a deterioration of the ozone layer. According to the best available current estimates implementation of these agreements will lead to a further increase of springtime loss of total ozone over the Antarctic. This loss will probably increase from its present level of about 50% to 80% (ref. 1). To prevent a further deterioration of the ozone layer use and/or emission cuts for chlorofluorocarbon stratospheric modifiers in the order of 80-905 are necessary (ref. 2,3). In my paper I will deal with the question whether such a reduction is technically feasible in the near future. The Montreal Protocol covers five chlorofluorocarbons (11, 12, 113, 114 and 115) and two halons (1211, 1302). Estimates of the US EPA give the following volumes for use of these substances in 1985 (ref. 4).
706 TABLE 1 Estimated use of chlorofluorocarbons and halons per region in 1985 in 10" kg/year. region USA
halocarbon
chlorofluorocarbon chlorofluorocarbon chlorofluorocarbon chlorofluorocarbon chlorofluorocarbon halon 1211 halon 1301
11 12 113 114 115
79.7 136.9 68.5 4.0 4.5 2.8 3.5
other induetrialized countries 200.7 221.3 75.5 6.6 2.8 3.0 2.4
third world
total
87.8 96.8 33.0 2.9 1.2 1.3 1.1
368.2 455.0 177.0 13.5 8.5 7.1 7.0
In my paper I will confine myself to the chlorofluorocarbons that currently dominate destruction of the ozone layer. These have four mayor applications: aerosols, foamed plastics, cooling and cleaning (ref. 3). I will deal with these types of use in turn. AEROSOLS World-wide about 30% of the chlorofluorocarbons (CFC) 11, 12, 113, 114 and 115 is used in aerosols. In the EC aerosol spray cans in 1985 accounted for 50% of the within EC sales (ref. 3,5). For most applications substitutes for chlorofluorocarbons in spray cans are COmmerCially available (ref. 3). The main substitutes are mixtures of propane and butane, dimethylether, N,O and compressed air (both pumped compression and a two compartment can are commercially available). Of these, the pumped/pressurized air system is, environmentally speaking, the most acceptable. Application of CFC-substitutes, that as a rule do not add to cost, is common in countries like the United States of America, Sweden and Denmark that have banned all or most non-essential uses of chlorofluorocarbons in spray cans. Replacing chlorofluorocarbons in all, but essential, applications will cut world-wide and EC chlorofluorocarbon consumption in aerosols with roughly 95%. Technically speaking this will be feasible in the near future. Recent experience in Denmark, the Federal Republic of Germany and the Netherlands suggests that 2-3 years will suffice for a cutback of 90-95%.
737
FOAMED PLASTICS Foamed plastics accounted for about 30% of the 1985 EC and western world use of chlorofluorocarbons 11, 12, 113, 114 and 115 (ref. 3 , 5 ) . The main applications are: - extruded polystyrene for packaging purposee; - polystyrene and polyurethane closed cell insulation materials: polyurethane open cell foams, used for mattresses, car seats, furniture etc.
-
For packaging purposes a nuarber of alternatives are currently commercially available. If one wants to stick to extruded polystyrene, pentane may be used as a blowing material. For massproduced products the use of pentane is actually cheaper than the use of chlorofluorocarbons. For many packaging purposes one may also switch to expanded polystyrene, that is blown by steam or pentane. Usually this material is available as small spheres that can be moulded into shapes suitable for packaging. This material tends to be cheaper than chlorofluorocarbon extruded polystyrene. There are also other alternatives competitive with foamed polystyrene. These include cardboard, and plastic foils with inserted air bubbles. For insulation purposes there are several materials available that do compete with chlorofluorocarbon blown polystyrene and polyurethane. These include CO,/water blown polystyrene, mineral wool and fibreglass. Although less effective for a given volume these substitutes tend to be cheaper for a similar overall performance, in cases where space is not a significant problem, for instance for application in residential construction. In cases where space is a problem in practice losses in insulation can be kept small (less than 10%) if one uses foams with smaller closed cells. Another possibility that is promising for the near future is the switch to a vacuum technique. This technique has been developed for insulating refrigerators and other appliances. The panels produced with this technique are said to outperform rigid foams made with chlorofluorocarbons and several companies are actively developing this technology (ref. 2). A s to open cell polyurethane foams there are essentially two possibilities. The first is restricting production to relatively
788
high density foams. Relatively high density foams that are used for instance in mattresses and seats can be blown without chlorofluorocarbons. With current technology relatively low density foams cannot be blown without chlorofluorocarbons. However, such low density foams can be replaced by the relatively high density foams accepting an increase of 10-20% in production costs (ref. 6). Another possibility is to recover chlorofluorocarbons from the exhaust of production. Using carbofiltration 40-50% reductions of operating losses may be achieved with pay-back times between 2 and 5 years, as suggested by pilot plants in Denmark and the Netherlands (ref. 3,6). Reviewing these data it would seem likely that a cutback of between 70 and 95% of chlorofluorocarbon u8e related to the production of foamed plastics is currently technically feasable. The costs involved are low to moderate. Judging from experience in the Netherlands and Denmark implementing such a cutback should be technically possible within five years. The cut in emissions from foamed plastics may be lower than the cut in use because of banking of CFCs in insulation materials. The Electrolux Company of Sweden is currently investigating the possibility to reclaim CFCa from discarded insulation foams.
COOLING In non-communist countries cooling, including freezing, refrigerating and air-conditioning, accounted in 1984 for nearly 30% of the use of chlorofluorocarbons 11, 12, 113, 114 en 115 (ref. 5). In the EC cooling accounted for about 10% of total use in 1985 (ref. 3). A s to refrigeration and air-conditioning several technical possibilities have emerged for cutting emissions (ref. 2,6). Firstly, the amount of chlorofluorocarbons necessary in refrigerators may be curbed. This can be done by switching from rotary compressors to reciprocating compressors, that use only one third to one half the refrigerant necessary for rotary compressors. Further advances in equipment design may lead to even lower chlorofluorocarbon requirements. Secondly, leakage from air-conditioners may be decreased. Leakage is especially a problem in mobile air-conditioners. It is estimated that in the United States about 30% of chlorofluorocarbon 12, that is the main chlorofluorocarbon in automobile air-
789 conditioning, is lost due to routine leakage. Redesigning equipment may decrease such routine losses considerably. Thirdly, emissions during servicing and testing may be lowered. This applies especially to air-conditionera and commercial cooling and freezing installations. Good housekeeping while testing and servicing may considerably diminish emissions from such installations. Another possibility is to change cooling substances. Here three approaches are available. First one may substitute relatively damaging chlorofluorocarbons by less damaging ones. Especially the substitution of chlorofluorocarbons 11 and 12 by chlorofluorocarbons 22, 123 and chlorofluorocarbon 134a comes to mind as a serious possibility. Chlorofluorocarbon 22 is currently available and applied in residential air-conditioning, whereas a mixture of chlorofluorocarbons 22 and 115 is widely used for refrigeration purposes by food retailers. Especially for stationary cooling and air-conditioning, where extra weight is not a serious obstacle, the possibility to switch to chlorofluorocarbon 22 may be seriously considered. However, in view of the (probably underestimated) effects of chlorofluorocarbon 22 on the stratosphere a system for recycling of CFC 22 should be developed. Other probably more convenient subsitutes may become available within five years. These include CFC 134a and CFC 123. A further possibility is to substitute chlorofluorocarbons in part by other cooling substances. An eutectic mixture of chlorofluorocarbon 12 and dimethyl ether is currently under research by the AKZO Company. A complete substitution of chlorofluorocarbon has been developed by a Florida company. In this case low vapor pressure hydrocarbons were used in air-conditioning compressor technology. The company involved claims that its system is more energy-efficient than comparable systems using chlorofluorocarbons (ref. 2). A final option to decrease chlorofluorocarbons emissions from air-conditioners and refrigerators is recycling of chlorofluorocarbons at the disposal stage. In the United States recycling systems are cummercially available: they are used especially for the recycling of chlorofluorocarbons from mobile air-conditioners (ref. 2). This is economical when large numbers of cars having those systems are available.
730 A prototype system to recover chlorofluorocarbons 11 and 12 from disposed refrigerators has been developed (ref. 7). This system has a chlorofluorocarbon recovery of 90%. Chlorofluorocarbons can be purified from the recovered material by standard techniques like distillation. The overall success of this recycling option is of course heavily dependent on the system for collecting disposed appliances containing chlorofluorocarbons. All in all cut-backs in emissions between 70 and 90% seem technically feasible within a period of about five years, with a moderate cost for the consumer.
CLEANING Cleaning accounts for about 10% of world-wide and EC use of chlorofluorocarbons 11, 12, 113, 114 and 115 (ref. 2 , 5 ) . The most important chlorofluorocarbon used for cleaning is chlorofluorocarbon 113. This chlorofluorocarbon has found many cleaning applications, especially in the electrotechnical/electronics industry. However, for many cleaning purposes, alternatives are currently available. A Rand study has estimated that at an extra cost of at a maximum 8 5 per pound of chlorofluorocarbon, emissions from use of chlorofluorocarbon 113 as a cleaner may be reduced in the short term by 80%, mainly by substitution and recycling (ref. 8). For many cleaning purposes especially in the electronics industry aliphatic hydrocarbons with a flashpoint exceeding 55°C are an acceptable substitute of chlorofluorocarbon 113 at no cost penalty. For several purposes detergent solutions are an acceptable alternative again at no cost penalty (ref. 3). Moreover, several other subsitutes and other emission reducing possibilities are under investigation as substitutes for chlorofluorocarbon 113. A number of these are summarized in table 2.
-
-
791
TABLE 2 Possible substitutes for chlorofluorocarbon 113 currently under investigation. cleaning operation videohead assembly metal parts (cold) soldering jigs washing thick film developing/resist stripping
possible more acceptable substitutes 2-propanol plus light petroleum 60/80 ethylmethylketone alkaline aqueous solutions 2-propanol aqueous ethanolic solution
In view of these technical options it would seem likely that within a period of five years a cut in emissions of about 90% will be feasible at a moderate cost. CONCLUSION From the foregoing one may conclude that extensive technical possibilities exist to cut chlorofluorocarbon emissions and/or use in the next five years, and that these cuts amount to at worst moderate costs. These possibilities may be summarized as follows: TABLE 3 Summary of technical possibilities for reduction of use within five years in the EC and in all non-communist countries. application
current share of total use EC
aerosol spray cans foamed plastics cooling cleaning total
feasible cut
non-communist countries
50% 30% 10% 10%
30% 30% 30% 10%
100%
100%
overall cut EC
95% 70-95% 70-90% 90%
non-communist countries
47.5 21-28.5 7-9 9
28.5 21-28.5 21-27 9
84.5-94 79.5-93
All in all it seems likely that cuts in use stopping further deterioration are technically feasible in the near future.
792 REFERENCES 1. P. Crutzen, personal communication. 2. A.S. Miller and I.M. Mintzer, The sky is the Limlt, World Resources Institute, Washington DC, November 1986. 3. European Environmental Bureau, The Sky is the Limit, report on the seminar on ozone depletion and climate warming due to CFCs, Brussels 22nd June 1987. 4. Ministerie van Volkshuisvesting, Ruimtelijke Ordening en Milieubeheer, Notitie over het CF'K Beleid, 's-Gravenhage, maart 1988. 5. W.E. Mooz, K.A. Wolf and F. C a m , Potential Constraints on Cumulative Global Production of Chlorofluorocarbons, Rand Corporation, Santa Monica (Ca), May 1986. 6. J. Swager, personal communication. 7. A.G. Vlasman, Het terugwinnen van freon 12 en smeerolie uit afgedankte koelkasten en diepvriezers, Technical University Twente, Enschede, april 1983. 8. F. Camm, T.H. Quinn, A. Bamezai, J.K. Hammitt, M. Meltzer, W.E. Mooz and K.A. Wolf, Social Cost of Technical Control Options to Reduce the Use of Potential Ozone Depleters in the United States, An Update, Rand Corporation, Santa Monica, May 1986.
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SESSION Xlll
HEALTH EFFECTS OF STRATOSPHERIC MODIFICATION
Chairmen
J.C. van der Leun M. Kripke
This Page Intentionally Left Blank
T. Schneider et al. (Editors),Atmospheric Owne Research and ita Policy Zrnplications 0 1989 Eleevier Science Publishers B.V., Ameterdam -Printed in The Netherlands
795
HEALTH EFFECTS OF STRATOSPHERIC OZONE DEPLETION: AN OVERVIEW
Margaret L. Kripke, Ph.D. Department o f Imnunology, The U n i v e r s i t y o f Texas M. D. Anderson Cancer Center, 1515 Holcombe Boulevard, Houston, Texas 77030 (USA)
ABSTRACT Recent growth i n the production and uses o f c e r t a i n chlorofluorocarbon compounds has r a i s e d concerns t h a t t h e concentration o f s t r a t o s p h e r i c ozone may decrease i n t h e future. The major consequence o f a decrease i n stratospheric ozone w i l l be t o increase t h e amount o f u l t r a v i o l e t r a d i a t i o n , p a r t i c u l a r l y r a d i a t i o n i n the UV-B (280-320 nm) wavelength range, i n sunlight. Even a small increase i n ambient UV-8 r a d i a t i o n i s l i k e l y t o have serious consequences f o r p l a n t and animal l i f e on e a r t h and w i l l almost c e r t a i n l y have an adverse e f f e c t on human health. The e f f e c t o f UV-B r a d i a t i o n t h a t has been characterized most thoroughly i s t h e i n d u c t i o n o f basal and squamous c e l l carcinomas o f t h e skin. Other possible e f f e c t s i n c l u d e c o n t r i b u t i o n t o t h e development of cutaneous melanoma, ocular changes leading t o t h e formation of cataracts, and imnunological perturbations o f as y e t unknown significance. Studies on l a b o r a t o r y animals have shown t h a t exposure t o UV-B r a d i a t i o n can i n t e r f e r e w i t h several imnune response, i n c l u d i n g those d i r e c t e d against s k i n cancers. Exposing animals t o low doses o f UV r a d i a t i o n can suppress imnune response l o c a l l y i n t h e i r r a d i a t e d skin, and exposure t o higher doses can suppress imnune r e a c t i o n s occurring a t d i s t a n t s i t e s as well. Evidence f o r s i m i l a r imnunologic a l t e r a t i o n s i n humans i s growing. These f i n d i n g s r a i s e t h e p o s s i b i l i t y t h a t s u n l i g h t exposure might i n t e r f e r e w i t h t h e body's defenses against c e r t a i n i n f e c t i o u s diseases. Because o f recent worldwide growth i n t h e uses and production o f c e r t a i n chlorofluorocarbon (CFC) compounds, t h e ozone l a y e r i n t h e stratosphere i s a t r i s k o f diminishing.
There i s now considerable evidence supporting the theory
t h a t CFCs can r e a c t chemically w i t h ozone i n t h e upper atmosphere, breaking i t down t o d i f f e r e n t molecular species and e l i m i n a t i n g i t s a b i l i t y t o absorb u l t r a v i o l e t rays from the sun (1). Measurements taken i n t h e upper atmosphere confirm p r e d i c t i o n s from atmospheric models t h a t CFCs and t h e i r chemical products are increasing.
I n addition, a recent study by t h e Ozone Trends
Panel concluded t h a t t h e ozone concentration has already decreased an average o f around 2.0% over t h e past 20 years (2).
796
The major effect of this decrease in ozone will be to increase the amount of UV radiation present in natural sunlight. The thin layer o f ozone in the stratosphere is very efficient in absorbing UV rays from the sun. Although the sun emits large amounts of UV-C (200-280 nm), UV-B (280-320 nm), and UV-A (320-400 nm) radiation, only the UV-A radiation and a very small amount of UV-
B radiation actually penetrate through the ozone layer to reach the surface of the earth. The amount of UV radiation present in natural sunlight is therefore dependent on the concentration of ozone molecules in the atmosphere. Wavelengths in the UV-B region are particularly sensitive to small changes in ozone concentration. Although UV-A radiation would also be expected to increase if the ozone concentration decreases, the increase would be very small in relation to the amount of UV-A already present in sunlight. Even a small increase in the amount of UV-B radiation present in sunlight is likely to have important consequences for plant and animal life on earth and will almost certainly affect human health adversely. The most well defined deleterious effect of UVB radiation on health is the production o f basal and squamous cell carcinomas of the skin. Other possible effects include a contribution to the development of cutaneous melanoma, ocular changes leading to the formation of cataracts, and imnunological perturbations of as yet unknown significance (2).
Effect Of UV-B Radiation on the Comnon Skin Cancers Most cutaneous basal and squamous cell carcinomas occur on the most heavily sun-exposed body sites of light-skinned Caucasians, and the incidence rates of these cancers increase with age. These observations suggest that cumulative lifetime exposure to sunlight is responsible for or at least plays an essential role in the induction of these cancers (3).
Surveys of the
incidence of skin cancers in the United States indicate that they have been increasing dramatically over the past few decades (4), and it was estimated that over 400,000 new cases of skin cancer would be diagnosed each year in the United States (4). The upward trend in the incidence of skin cancers is
797 probably due i n p a r t t o t h e increasing exposure o f our population t o both n a t u r a l and a r t i f i c i a l sources o f UV r a d i a t i o n .
For example, the increased
l o n g e v i t y o f the population and changes i n c l o t h i n g s t y l e s and r e c r e a t i o n a l h a b i t s have undoubtedly r e s u l t e d i n increased exposure t o UV rays.
However,
i t i s possible t h a t other as y e t u n i d e n t i f i e d factors, such as chemicals
present i n t h e environment, might also be c o n t r i b u t i n g t o t h e increasing incidence o f s k i n cancer. The increasing incidence o f s k i n cancers observed i n recent decades i s not l i k e l y t o be due t o t h e r e c e n t l y reported decrease i n s t r a t o s p h e r i c ozone
(2).
It i s o n l y w i t h i n t h e past two decades t h a t a measurable decrease i n
ozone concentration has been reported.
T h i s i s probably not long enough o r a
l a r g e enough e f f e c t t o have had a s i g n i f i c a n t impact on the incidence o f s k i n cancers, which are induced over a p e r i o d o f several decades ( 3 ) .
However, i f
s i g n i f i c a n t ozone d e p l e t i o n continues t o occur i n the future, increases I n t h e incidence o f s k i n cancer w i l l be experienced over and above the increases already reported i n recent decades.
Estimates of t h e impact o f ozone
depletion on basal and squamous c e l l carcinomas p r e d i c t t h a t f o r a 1% reduction i n ozone concentration, UV-B r a d i a t i o n w i l l increase by approximately 2%, leading t o an increase o f between 3% and 6% i n t h e incidence o f these s k i n cancers (1).
E f f e c t o f UV-B Radiation on Cutaneous Melanoma U n l i k e t h e comnon s k i n cancers, primary melanomas are n o t r e s t r i c t e d t o t h e most h e a v i l y sun exposed body sites, nor are they associated with occupational exposure t o sunlight.
Nonetheless, t h e r e i s c i r c u m s t a n t i a l
evidence suggesting t h a t a t l e a s t some cutaneous melanomas are associatd w i t h exposure t o UV-B r a d i a t i o n (2).
F i r s t , i n t h e United States, t h e incidence of
melanoma increases w i t h p r o x i m i t y t o t h e equator.
Because UV-B r a d i a t i o n i s
the main environmental f a c t o r known t o e x h i b i t such a l a t t i t u d e gradient, i t i s presumed t o be responsible f o r t h e geographic d i f f e r e n c e s i n t h e incidence
of cutaneous melanoma.
Second, persons w i t h t h e genetic disease xeroderma
pigmentosum have a h i g h r i s k of developing cutaneous melanoma, as w e l l as t h e comnon s k i n cancers (5).
C e l l s from these i n d i v i d u a l s lack t h e a b i l i t y t o
r e p a i r DNA damaged b y UV r a d i a t i o n , suggesting t h a t melanoma may r e s u l t from UV-induced c e l l u l a r damage.
Third, recent studies from our l a b o r a t o r y u s i n g a
mouse model f o r the i n d u c t i o n o f melanomas suggest t h a t UV-B r a d i a t i o n can c o n t r i b u t e t o both t h e i n d u c t i o n and subsequent growth o f cutaneous melanomas
(6). C o l l e c t i v e l y , these f i n d i n g s imply t h a t UV-B r a d i a t i o n i s involved somehow i n t h e development o f melanoma, b u t i t s r o l e i s q u i t e d i f f e r e n t from the one i t plays i n the i n d u c t i o n o f basal and squamous c e l l carcinomas, i n which there i s a d i r e c t r e l a t i o n s h i p between cumulative s u n l i g h t exposure and cancer incidence.
How UV r a d i a t i o n might c o n t r i b u t e t o t h e incidence o f
melanoma i s not a t a l l clear, b u t intense exposure t o s u n l i g h t e a r l y i n l i f e has been proposed as a causative f a c t o r i n the development o f these cancers
(7). Since t h e e a r l y p a r t o f t h i s century, both t h e incidence o f and m o r t a l i t y from cutaneous melanoma have been increasing s t e a d i l y .
Because t h e
r e l a t i o n s h i p between melanoma and s u n l i g h t exposure i s s t i l l tenuous and does n o t seem t o depend on chronic exposure t o UV r a d i a t i o n , i t i s n o t c l e a r whether changes i n t h e incidence o f melanoma are r e l a t e d t o t h e increasing exposure o f t h e population t o s u n l i g h t o r t o other environmental f a c t o r s . Whatever t h e cause o f t h e increase i n the incidence of melanoma i n t h i s century, however, i t i s probably n o t ozone depletion.
As i s t h e case f o r
other s k i n cancers, t h e decrease i n ozone concentration over t h e p a s t two decades would have occurred too r e c e n t l y t o account f o r a t r e n d t h a t began a t t h e t u r n o f the century.
If s i g n i f i c a n t ozone d e p l e t i o n continues t o occur,
however, t h e incidence o f cutaneous melanoma would probably increase beyond the c u r r e n t trend.
Using t h e incidence o f melanoma a t several l o c a t i o n s i n
t h e United States t h a t d i f f e r w i t h respect t o t h e amount o f UV-B r a d i a t i o n present i n ambient s u n l i g h t , i t i s p o s s i b l e t o estimate t h e e f f e c t of an
739
increase i n UVB r a d i a t i o n on melanoma incidence.
Such c a l c u l a t i o n s p r e d i c t
t h a t f o r a 1%reduction i n ozone concentration, t h e incidence o f cutaneous melanoma w i l l increase between 1 and 1.5% (1).
Effects of UV-B Radiation on t h e Imnune System The most r e c e n t l y discovered p h y s i o l o g i c a l e f f e c t o f UV-B r a d i a t i o n i s i t s a b i l i t y t o modify immune function.
Such changes can occur l o c a l l y , w i t h i n
the i r r a d i a t e d skin, o r systemically a t s i t e s d i s t a n t from t h e exposed area. These conclusions are based mainly on studies o f experimental animals; however, there i s increasing evidence t h a t s i m i l a r e f f e c t s o f UV-B i r r a d i a t i o n occur i n humans exposed t o UV r a d i a t i o n from t h e sun o r a r t i f i c i a l l i g h t sources.
Studies on both human and rodent s k i n demonstrated t h a t t h e r e are
populations o f immune c e l l s i n the s k i n t h a t i n i t i a t e imnune responses.
One
such c e l l i s the epidermal Langerhans c e l l , which takes up f o r e i g n substances and processes them i n t o antigens recognizable by T lymphocytes.
Langerhans
c e l l s are thought t o be t h e main antigen-presenting c e l l s f o r t h e i n d u c t i o n o f contact allergy, and they may also be important i n t h e i n i t i a t i o n o f imnune responses t o s k i n cancers and i n f e c t i o u s organisms i n t h e s k i n (8). Experimental studies i n animals showed t h a t a f t e r exposure t o UV r a d i a t i o n , Langerhans c e l l s are no longer capable o f presenting antigen t o helper T lymphocytes.
When a contact a l l e r g e n i s a p p l i e d t o UV-irradiated
skin, i t f a i l s t o induce contact a l l e r g y and, instead, induces suppressor lymphocytes t h a t prevent a subsequent a l l e r g i c response t o t h e same antigen (9.10).
Because suppressor lymphocytes c i r c u l a t e throughout t h e body, what
begins as a l o c a l i z e d e f f e c t o f UV r a d i a t i o n on s k i n i s t r a n s l a t e d i n t o a long-lived,
systemic, imnune suppression.
I n addition t o i t s direct effects
on imnune c e l l s i n t h e skin, exposure o f experimental animals t o UV r a d i a t i o n can also suppress c e r t a i n imnune responses a t d i s t a n t s i t e s (11). Much higher doses o f UV r a d i a t i o n are required t o produce imnune suppression a t u n i r r a diated s i t e s . I n t h i s instance also, imnune suppression i s associated w i t h suppressor lymphocytes.
aoo UV-B radiation-induced a l t e r a t i o n s i n imnune f u n c t i o n seem t o p l a y a fundamental r o l e i n t h e development and growth o f UVB-induced s k i n cancers i n mice (12).
These s k i n cancers are h i g h l y a n t i g e n i c and are imnunologically
r e j e c t e d when transplanted i n t o g e n e t i c a l l y i d e n t i c a l , normal mice.
However,
the s k i n cancers grow p r o g r e s s i v e l y i n mice given repeated exposures t o UV-B radiation.
The UV-B radiation-induced s k i n cancers are a b l e t o grow i n UV-B
i r r a d i a t e d mice because these animals have suppressor lymphocytes t h a t s p e c i f i c a l l y prevent t h e r e j e c t i o n o f these tumors (13).
Whether t h e
suppressor c e l l s are induced by t h e l o c a l o r t h e d i s t a n t imnunologic e f f e c t s o f UV i r r a d i a t i o n o r both i s n o t known. Although t h e r e i s s t i l l l i t t l e information on t h e e f f e c t s o f UV-B r a d i a t i o n on the imnune system i n humans, several studies i n d i c a t e t h a t imnunologic changes occur i n people exposed t o n a t u r a l and a r t i f i c i a l sources o f UV.
Exposure o f human s k i n t o UV rays reduces t h e number and a l t e r s t h e
morphology o f Langerhans c e l l s i n a manner s i m i l a r t o t h a t described i n experimental animals (14).
There i s also evidence t h a t exposure t o UV
r a d i a t i o n decreases contact a l l e r g y t o chemicals a p p l i e d onto i r r a d i a t e d s k i n (15).
Changes i n t h e p r o p o r t i o n o f c i r c u l a t i n g lymphocytes have been reported
t o occur f o l l o w i n g exposure t o UV r a d i a t i o n , and some decreases i n lymphocyte f u n c t i o n have also been observed (16).
Whether suppressor lymphocytes are
a c t i v a t e d i n these i n d i v i d u a l s i s n o t y e t c l e a r because these c e l l s cannot be i d e n t i f i e d e a s i l y i n humans. These f i n d i n g s r a i s e t h e p o s s i b i l i t y t h a t UV-B r a d i a t i o n may c o n t r i b u t e t o t h e i n d u c t i o n o f human s k i n cancers by means o f i t s imnunologic e f f e c t s , i n a d d i t i o n t o i t s carcinogenic e f f e c t s .
T h i s hypothesis i s p a r t i c u l a r l y
a t t r a c t i v e i n the case o f cutaneous melanoma, because i t might h e l p t o e x p l a i n how UV-B r a d i a t i o n c o n t r i b u t e s t o t h e development o f melanomas on unexposed body s i t e s .
I n addition, l o c a l e f f e c t s o f UV r a d i a t i o n on imnune c e l l s i n t h e
s k i n might a l s o p l a y a r o l e i n the growth and spread o f melanomas t h a t do occur on sun-exposed body s i t e s .
The most urgent question r a i s e d by these
studies, however, i s whether an increase in UV-B r a d i a t i o n would increase t h e
801
incidence of severity of infectious diseases by means of its effects on the imnune system.
No information on this question is available in humans and
investigation of the effects of UV-B radiation on infectious diseases in animal models is just beginning.
Conclusions Because of the likelihood that some ozone has already been lost from the stratosphere and more losses are predicted over the next century, it is important to understand the consequences of ozone depletion. Ultraviolet radiation in the UV-B (280-320) nm region increases when the ozone concentration is diminished. This will certainly lead to an increase in the incidence o f the comnon skin cancers and will probably affect the incidence o f cutaneous melanoma as well.
Thus, regions of the world that already have a
substantial problem with skin cancer can expect to see this disease increase even further.
Imnunologic changes may also occur as a result of increased UV-
B radiation, but how such changes might affect the pathogenesis of skin cancers or the incidence of infectious diseases is not yet known.
REFERENCES
.
1 An Assessment of the Risks of Stratospheric Modification John S. Hoffman, ed., U.S. Environmental Protection Agency, March, 1987. 2 Report of the Ozone Trends Panel, NASA, March, 1988. 3 Fears TR, Scotto J, and Schneiderman MA. Mathematical models of age and ultraviolet effects on the incidence of skin cancer among Whites in the United States. Amer J of Epidemiol 105:420-427, 1977. 4 Scotto J, Fears TR, and Fraumeni JF, Jr. Incidence of Nonmelanoma Skin Cancer in the United States. NIH Publication No 83-2433, 1983. 5 Kraemer KH, Lee MM, and Scotto J. DNA repair protects against cutaneous and internal neoplasia: Evidence from xeroderma pigmentosum. Carcinogenesis 5: 511-514, 1984. 6 Romerdahl CA, Donawho C, Fidler IJ, and Kripke ML. Effect of UV irradiation on the development of a transplanted murine melanoma. Cancer Res in press, 1988. 7 Lew RA, Sober AJ, Cook N, Marvel1 R, and Fitzpatrick TB. Sun exposure habits in patients with cutaneous melanoma: a case control study. J Dermatol Surg Oncol 9:981-988, 1983. 8 Sting1 6, Katz SI, Clement L, Green I, and Shevach EM. Imnunologic functions of Ia-bearing epidermal Langerhans cells. J Imnunol 121:20052013, 1978. 9 Toews GB, Bergstresser PR, and Streilein JW. Epidermal Langerhans cell density determines whether contact hypersensitivity or unresponsiveness follows skin painting with DNFB. J Imnunol 124:445-453, 1980.
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10 Elmets CA, Bergstresser PR, Tigelaar RE, Wood PJ, and Streilein JW. Analysis of the mechanism of unresponsiveness produced by haptens painted on skin exposed to low dose ultraviolet radiation. J Exp Med 158:781-794, 1983. 11 Kripke ML. Imnunologic unresponsiveness induced by ultraviolet radiation. Imnunol Rev 80:87-102, 1984. 12 Kripke ML. Imnunologic mechanisms in UV radiation carcinogenesis. Adv Cancer Res 34:69-106, 1981. 13 Fisher MS, and Kripke ML. Suppressor T lymphocytes control the development of primary skin cancers in ultraviolet-irradiated mice. Science 216:1133-1134, 1982. 14 Aberer W, Schuler 6, Sting1 G, Honigsmann H. and Wolff K. Ultraviolet 1 ight depletes surface markers of Langerhans cells. J Invest Dermatol 76:202-210, 1981. 15 Hersey P. Hasic E, Edwards A, Bradley M, Haran 6, and McCarthy WH. Imnunological effects of solarium exposure. The Lancet, March 12, 1983, pp 545-548. 16 Hersey P, Haran G, Hasic E, and Edwards A. Alteration of T cell subsets and induction of suppressor T cell activity in normal subjects after exposure to sun1 ight. J Imnunol 131:171-174. 1983.
T. Schneider et al. (Editors),Atmospheric Ozone Research and its Policy ImpliCatiO~ 0 1989 Elsevier Science Publishers B.V., Ameterdam -Printed in The Netherlands
a03
EFFECTS OF INCREASED W-B ON HUBIAJt HBALTR
J. C. VAN DER LEUN Institute of Dermatology, University of Utrecht, Catharijnesingel 101, NL-3511 GV Utrecht (The Netherlands) ABSTRACT An increased irradiance of solar W-B will not necessarily increase all effects of W-B radiation on man. In some instances the consequences will not be noticeable, especially because of adaptation. The human eye has no adaptation to W radiation. Adverse effects of W-B on the eye, such as keratoconjunctivitis and cataracts, may therefore be expected to increase. The human skin has a powerful adaptation, which is effective against acute W damage such as sunburn. It is not sufficient, however, to cope with long-term damage such as photo-aging and the induction of skin carcinomas. The increase of (non-melanoma) skin cancer to be expected in case of ozone decrease has been studied thoroughly. One conclusion is that the number of patients with skin carcinomas will increase more sharply than the amount of ozone will decrease. The knowledge accumulated even allows quantitative projectiona. Other health effects, such as a possible influence of increased W-B on the incidence of melanomas, have been studied less conclusively, but may be at least as important. INTRODUCTION The prospect of receiving more ultraviolet radiation on the skin does not appear unattractive at first sight, especially for people living in Northern countries. Is not that precisely what we are longing for during a dark winter? When spring finally comes with more sunlight, we feel stimulated and invigorated. The same holds for a holiday in a sunny country; many vacationers return relaxed and tanned, and friends tell them that they look healthier. This is also what many people expect from exposures to ultraviolet lamps in solaria and sunbeds. So, if more ultraviolet radiation is to come with our sunlight, will we develop some more tan in our white skins: will it feel like having a bit more holiday at home? Will this not, for a change, be a pleasant consequence of air pollution? On the other hand, the ultraviolet radiation in sunlight, even as it is now, causes us a painful sunburn now and then. Will that occur more frequently if the ultraviolet radiation increaaea,
004 and to a more severe degree? Solar ultraviolet radiation also occasionally causes snowblindness, especially in snowy mountains: it is a painful affection of the eyes which usually disappears in one or two days. Long-term exposure to solar ultraviolet radiation contributes to the development of cataract, a permanent clouding of the eyelens frequently occurring in elderly people. Will these eye damages increase? There are people with hypersensitivities to sunlight; the sunlight causes various adverse reactions in their skins, such as papules, eczema or swelling, and frequently severe itching. These diseases, known together under the name of photodermatoses, may be so s'evere that the patients can hardly stand even short exposures to sunlight. Will their fate become even worse? There are good indications that most of the changes generally perceived as "aging" of the skin are in fact caused by chronic exposure to sunlight; and that the ultraviolet radiation in sunlight is the cause of most skin cancers, especially in white people. If atmospheric ozone decreases, and the ultraviolet radiation in sunlight consequently increases, will these adverse effects of sunlight increase, too? ONLY A NARROW RANGE OF WAVELENGTHS The consequences of a decrease of atmospheric ozone for human health cannot be examined satisfactorily by listing all known effects of sunlight on man. The assumption that we will have more of all these effects, the beneficial as well as the adverse, would be too simple. One reason is, that a decrease of ozone will change the sunlight in only a narrow range of wavelengths, called the W-8 (280-315 nm). The rest of the sunlight, even the rest of the ultraviolet radiation in sunlight, the W - A (315-400 nm), will be practically unchanged. A better approximation would be achieved, therefore, by making an inventory of effects of W-B radiation on man. This does not make our list much shorter; although the W-B accounts for less than 1 percent of the total energy in sunlight, it is the main cause of many effects of sunlight on the human body. This applies to sunburn, tanning. the formation of vitamin D3 in the skin, snowblindness, immunological changes, skin aging and skin cancer. The effects of sunlight on general well-being have been investigated less conclusively than most of the other effects: as far as these invigorating influences are real, these may well be due to other wavelengths, perhaps even visible light. Eye
805
cataracts have long been ascribed to W - A , but recent research suggests that W - B contributes significantly to the effect. In some of the photodermatoses, the skin reacts mainly to W - A or visible light: there are, however, also photodermatoses characterized by an extreme sensitivity to W - B . The restriction to W - B effects eliminates a few influences of sunlight on man from our considerations, but most influences remain as candidates for being increased in case of ozone depletion: sunburn, certain photodermatoses, tanning, formation of vitamin D3, snowblindness, cataract, immunological changes, skin aging and skin cancer. ADAPTATION TAKES CARE OF SOME EFFECTS The skin has a remarkable power of "adaptation" to its ultraviolet environment. Most white people have to be careful in spring in order to avoid sunburn, but when summer progresses, the problem diminishes, although the ultraviolet irradiance is even higher. The skin has increased its tolerance to ultraviolet radiation, and has become less sensitive to sunburn: this results mainly from thickening of the most superficial skin layers, and to some degree also from tanning. This adaptation of the skin is not a solution for all problems caused by sunlight. People who have their work outdoors, and receive a lot of sunlight everyday, are the people with the highest risk of skin cancer. So, adaptation of the skin appears to be effective against sunburn, not against skin cancer. This difference will also play a role in case of a gradual increase of UV-B irradiance by ozone decrease: some effects of UV-B on the body will be taken care of by adaptation, and some effects will not. It is highly desirable to know beforehand which problems will increase, and which problems will not. An indication may be found by comparing people in different W - B environments as they exist today. That have to be people with comparable genetic background, say, white people. White people have spread all over the globe, and live also in areas much sunnier than their- countries of origin, in N.W. Europe. One intriguing observation is, that in sunny areas the fraction of the white people suffering from photodermatoses is not greater, but smaller than in N.W. Europe. Presumably this has to do with adaptation, or rather, loss of adaptation. The more sunlight the skin receives in winter, the smaller the loss of adap-
tation, and the smaller the difficulty of regaining adaptation in spring. This latter difficulty plays an important role in photodermatoses: many patients with photodermatoses may be helped by a mild UV-B treatment in winter. It is to be expected that these patients will also benefit from an increased irradiance of solar UV-8 in winter. Adaptation is also effective against sunburn, at least on the skin areas which are regularly exposed to sunlight. White people living in sunny countries do not have red faces all the time: they rather tend to have a yellowish complexion. In contrast to these observations stands the fact that the incidence of skin carcinomas among white people is higher in the more sunny countries. This confirms the impression that adaptation of the skin is not sufficient to cope with the induction of skin carcinomas by ultraviolet radiation. The same applies to aging of the skin: that, too, appears to proceed faster in more sunny climates. There is a regularity in these observations. Adaptation of the skin appears to be effective against short-term reactions of the skin to ultraviolet radiation, and not against the long-term reactions of the skin. In case of ozone depletion, the adaptation of the skin is likely to make the same selection: it will take care of most of the short-term reactions of the skin and leave as the main problem the long-term reactions, such as skin cancer. There may be exceptions to this general outline. For instance, during cold winters adaptation cannot operate in skin areas which are kept covered by clothing. Such skin areas are hardly reached by any ultraviolet radiation during that stage. In spring, when temperatures become pleasant, these skin areas are uncovered and exposed to high W-B irradiances, and run the risk of being sunburned. If the W-B irradiances in spring become even greater by ozone depletion, will not this problem increase? In practice, this will not make a great difference. This skin has to bridge quite a gap anyway, and that is managed by increasing the exposures in spring only gradually. The gap will become somewhat greater, but the solution remains the same. It is like climbing a hill: there is a risk of falling down, but that risk depends more on the care with which the single steps are taken than on the height of the hill. A real exception is the eye. The human eye does not have the adaptation to the ultraviolet environment as is found in the skin Any problems caused by W-8 radiation to the eyes, such as snow-
807
blindness and cataracts, will just increase in case of ozone depletion. SOME EFFECTS ARE AMPLIFIED The biological changes brought about will in general not be directly proportional to the decrease of atmospheric ozone. In many cases, "amplification factors" will operate. The "optical amplification" originates in the absorption spectrum of ozone. The gas absorbs much more strongly at 295 nm, at the short-wavelength end of the solar spectrum, than, for instance, at 315 nm. That is the very reason why the solar spectrum ends near 295 nm. In turn, this also means that a decrease of ozone causes a stronger increase of the shorter wavelengths in this range. Therefore, the quantitative effect of ozone depletion on a particular biological reaction to W radiation will be more pronounced if the shorter wavelengths are involved: it will depend on the "action spectrum" of the photobiological reaction. For most of the effects of ultraviolet radiation on man, the action spectrum has a peak near 300 nm, in the W-B. The optical amplification factor calculated for such action spectra is about 2; this means that for a 1% decrease of ozone, the quantity of effective radiation increases by about 2%. For some biological effects there is .also a second amplification. It originates in the relationship between dose and effect and is expressed as the "biological amplification factor". That operates, for instance, in the induction of skin carcinomas by ultraviolet radiation. Comparison of populations at different geographical latitudes has shown that the incidence of skin carcinomas in a population is not directly proportional to the effective W-B irradiance. For one type, the basal cell carcinoma, the incidence is approximately proportional to the square of the effective irradiance. And the incidence of squamous cell carcinomas is even proportional to the third power of the effective irradiance. This has as a consequence that an increase of the effective irradiance by 1% will, in the long run, lead to an increase of the incidence of basal cell Carcinomas by 2% and of squamous cell carcinomas by 3%. The biological amplification factors are 2 and 3, respectively. If the optical and biological amplification factors are taken together, the result is that a 1% decrease of atmospheric ozone leads to a 2% increase of effective irradiance and that, in turn,
808 will lead to an increase of the incidence of basal cell carcinomas by 2 x 2 = 4% and of squamous cell carcinomas by 2 x 3 = 6%. In some of the scenarios which are presently considered realistic, ozone decreases by 5 percent and more are expected after several decades. With the two amplification factors taken into account a depletion by 5 percent would, after again several decades, lead to an increase of basal cell carcinomas by about 22 percent and of squamous cell carcinomas by about 34 percent. It was estimated that for the white populations worldwide this would eventually lead to 360,000 new patients per year with skin carcinomas (ref. 1). It is not easy to weigh the meaning of such numbers. It has been remarked in this connection that skin carcinomas can usually be cured, and that the death rate is less than 1%; and that similar effects result from the habit of taking sunny holidays. This is all true. Yet, the skin carcinomas even as they occur now are considered a real public health problem, especially as they tend to increase. For the same reason there is concern about the widespread use of solaria and sunbeds for tanning. The Health Council of the Netherlands estimated that, if the present active use of ultraviolet equipment in the Netherlands would continue for a long time, that would lead to an increase of the incidence of skin carcinomas by 2 to 5% (ref. 2). Such an increase would also result from an ozone depletion by about 1 percent. This indicates that ozone depletions which at face value appear small, are not necessarily insignificant in terms of the consequences. The comparison also indicates that ozone depletions such as predicted from certain scenarios would have a much stronger impact on the incidence of skin carcinomas than a long-term use of tanning equipment at the present rate. Let us return to the amplification factors. The optical amplification factor is known to a good approximation for many biological effects of sunlight. Calculation of the biological amplification factor requires a more penetrating knowledge of the biological effect under consideration. The induction of skin carcinomas by ultraviolet radiation has been investigated extensively, from long before the ozone issue arose. This gave scientists the possibility of making fairly developed quantitative predictions on skin carcinomas, more so than on most other biological effects of ozone depletion. It may be good to realize that this reflects a difference in knowledge about the various biolog-
809 ical effects, rather than a difference in importance of these effects.
mLANo!ms The melanomas are a type of skin cancer not discussed so far. Melanomas are cancers of the pigment cell system. They are less frequent than the skin carcinomas, but far more dangerous. It is, therefore, important to find out whether or not the incidence of melanomas will be increased by ozone depletion. De Gruijl will discuss especially this problem in his contribution to this book. Therefore I give only a few remarks. There are indications that sunlight plays some role in the development of melanomas, but little is known on how sunlight acts. There is no experimental animal in which melanomas have been reproducibly induced by ultraviolet radiation. It is, therefore, not possible to find out by direct experimentation what waveThe real question in relation to the lengths are responsible ozone issue is, whether or not W-B plays a role. If it does, ozone depletion might increase the incidence of melanomas in man. In order to calculate how much, we would have to know the relationship between dose and effect and that, again, is not known. Various observations on man suggest that any dose-effect relationship for melanoma is rather different from those for the skin carcinomas; it appears even to be different for the various types of melanomas. A possible influence on the incidence of melanomas is one of the most important questions with respect to the effects of ozone depletion on human health. Due to lack of knowledge, the answer is still highly uncertain.
.
IMMUNOLOGICAL CHANGES UV-B radiation coming on the human body influences the immune system. Rapidly expanding, but still fragmentary knowledge exists on particular changes, such as a decreased ability of the immune system to remove cancers induced in the skin by W-B radiation. UV-B radiation also suppresses the development of contact hypersensitivity. A fuller account of these immunological changes is given by M.L. Kripke in her contribution to this book. With respect to the development of skin carcinomas, the effect of W - B on the immune response has been taken into account implicitly in the quantitative estimations given in the present
810 paper. The influence on other aspects of human health is less clear. There are indications that some skin infections, such as herpes, may have more chance under increased W-B irradiance. Several skin diseases aggravate by exposure to ultraviolet radiation: the reasons are usually unknown, but may well have to d o with the immune system. There are, however, also skin diseases which are influenced beneficially by W-8; this is applied In phototherapy. An overall view on what the influences of W-B on the immune system mean to human health has not yet emerged. It is too early, therefore, for a balanced conclusion on the consequences of ozone depletion in this respect. VITAMIN Dj Exposure of the skin to W-B radiation leads to the formation of vitamin D3. The vitamins D are needed for the development and maintenance of bone tissue; they may also be supplied by the food intake. Problems with the bones may develop if the two supplies together are insufficient. That does occur in population segments such as dark skinned children in Northern cities, children in families with strict macrobiotic diets and elderly people who live mainly or completely indoors. The groups of children mentioned may be expected to have some benefit from increased UV-B irradiance. There is no danger that increased W - B irradiance would lead to an oversupply of vitamin D3 in other groups; the formation is selflimiting. CONCLUSIONS Although many of us enjoy the experience of a sunny holiday, there is little reason to think that on balance man will be better off in case of an overall and long-term increase of UV-B irradiance, such as will be ccused by ozone depletion. There will be some beneficial influences, such as on patients with hypersensitivities to sunlight, and on children with vitamin D deficiencies. Many effects of W - B on man will not change appreciably. We will not all have red faces: even on usually covered skin areas, sunburn will hardly be more of a problem that it is now. We will not be more tanned than we are now. For some effects of W-B radiation, the consequences of increased W-B irradiance cannot be predicted as yet. These
811 include the effects on the immune system. It appears likely that there will be favourable as well as unfavourable influences in this respect. There are also problems caused by W-B radiation that will increase. This applies to the risk of occasional snowblindness and to the risk of developing cataract at old age. The skin will develop wrinkles at an earlier age. The incidence of skin carcinomas will increase markedly. The effect of ozone depletion in this respect will be much greater than that of the use of artificial sources of ultraviolet radiation for tanning. It is possible, but less certain, that the incidence of melanomas will also increase. The reader will have noticed that the certainty with which the various predictions are made, is rather different. For some of the effects, such as the increased incidence of skin carcinomas, scientists are sufficiently confident to give quantitative estimations. For other influences they prefer verbal and qualified statements. It may be good to repeat that this reflects differences in knowledge rather than differences in importance of the possible consequences. An influence on melanomas may be less certain than that on skin carcinomas, it might be more important. The predictions on the influence of ozone depletion on the world food supply may be comparatively uncertain; such influences are potentially at least as important to man as the direct influences of increased W - B on his own body. An ominous aspect of the ozone problem is that, when the results become fully certain because they manifest themselves, the process cannot be stopped at short notice. Even if the pollution causing ozone depletion would be suddenly discontinued, the effects will be there for generations to come. ACKNOWLEDGEMENTS Most of this paper also appeared, in Swedish, as a chapter in L . Johansson, P. Crutzen, L.O. Bjbrn and J.C. van der Leun, "Ozonfaran O v h t a t Stor", Kllla/28, Forokningsrhdsngmnden, Stockholm, 1987. The publishers kindly agreed to the use of basically the same material for the present symposium proceedings. The author wishes to thank Dr. Janet F. Bornman for her help in improving the manuscript and Dr. Farrington Daniels, Jr., for stimulating discussions on this issue since 1972.
812
REFERENCES 1 Effects of stratospheric modification and climate change. Report of the Coordinating Committee on the Ozone Layer, Session November, 1986. United Nations Environment Programme, Nairobi,* 1988. 2 W Radiation: human exposure to ultraviolet radiation. Report 1986/9E. Health Council of the Netherlands, P.O. Box 90517, 2509 LM The Hague, 1986.
T. Schneider et al. (Editors),Atmospheric Ozone Research and its Policy Implicotion~ 0 1989 Elsevier Science Publishers B.V.,Amsterdam -Printed in The Netherlands
813
OZONE CHANGE AND MELANOMA
F.R. DE GRUIJL Institute of Dermatology, State University Hospital, Catharijnesingel 101, NL-3511 GV Utrecht (The Netherlands) ABSTRACT The concept that cutaneous melanoma. (CM) in man is caused by ultraviolet ( W ) radiation (the carcinogenic component of sunlight) is supported by latitudinal gradients in the incidence and the correlation to W-related risk factors. As stratospheric ozone filters solar W radiation, a reduction could lead to an increase in the incidence of CM. From the latitude-related W gradient one finds that a 10% reduction in ozone would lead to approximately 520% more CMs in the white population in the USA. The epidemiologic data are, however, not entirely consistent with respect to the involvement of W radiation. And epidemiological correlations by themselves can never establish a causal relationship. An experimental model to prove the possibility of such a causal relationship between CM and W radiation is currently lacking. Differences in histogenetic types and/or locations on the body are often disregarded. There are indications that these kinds of distinctions may be important for a proper understanding of the etiology of CM. It has to be concluded that it is still conjectural to use a UVrelated gradient in CM to assess the effect of an ozone reduction on the incidence of CM. A better understanding of the etiology of CM is mandatory. INTRODUCTION There appears to be a clear relationship between exposure to solar radiation and skin cancer. This relationship holds true particularly for squamous and basal cell carcinomas (see the contribution of J.C. van der Leun to this symposium). The ultraviolet ( W ) component of the solar radiation is carcinogenic, and W radiation has induced squamous cell carcinomas in animal models. There is also a long-standing suspicion that W radiation plays a role in the etiology of cutaneous melanoma (CM), a skin cancer with a much higher mortality rate than non-melanoma skin cancers. The relationship is, however, not as clear as with nonmelanoma skin cancers. For instance, CMs also occur on body sites not regularly exposed to sunlight, and CMs do not dominantly occur in outdoor workers. Nevertheless, the latitudinal gradient in CM over the USA has been used to quantify the relationships between CM and UV radiation (ozone layer thickness) (Ref. 1, 2 ) .
1114
Risk factors A multitude of epidemiological relevant factors is available from a vast body of literature on melanoma. Factors like skin color, hair color, freckles, nevi, may all indicate a llnk with sensitivity to UV radiation. As an example of confounding factors, it can be found that the risk of CM is increased by a history of severe sunburns. However, if this relative risk is corrected for the confounding effect of skin color, the risk goes down and looses its significance (Ref. 3 ) . Thus, the sensitivity to UV radiation appears more important than the actual sunburning. Furthermore, epidemiologic investigations based on questions on a person's past, especially in interviews, have always the risk of a biased or induced remembrance (see for example Ref. 4 on fluorescent lighting as a risk factor). Another problem with epidemiologic studies is that they may produce significant risk factors like social status (Ref. 5 ) , urbanisation, possession of a passport (Ref. 6 ) which leave ample space for all sorts of causative mechanisms related to such risk factors. Instead of providing substantial information this kind of interrelated data may be obscuring essential data. Epidemiologic studies on melanoma should now be directly aimed at possible mechanisms, instead of continuously accumulating 'noise' from available information on combinations of interrelated factors. Xeroderma pigmentosum patients have a deficiency in the repair of UV-induced damage of DNA. The fact that these patients run an increased risk for all types of skin cancers, CM included, also indicates that W radiation may be an important factor in the etiology of melanoma. It has to be stressed, however, that none of these arguments prove that UV radiation is causing CM. In contrast with squamous cell carcinoma, there is no (animal) model in which the relationship between W radiation and CM has been established. It may well be that a person's sensitivity to W radiation makes him also more sensitive to damaging effects of other agents. T y p e s of melanoma and DOE sible differences
in etioloov
Within CMs one can distinguish histogenetic types. There are four main types of CM in Caucasians: the superficial spreading melanoma (SSM), the nodular melanoma (NM), the melanoma originating from a Hutchinson melanocytic freckle (HMFM) (also called lentigo maligna melanoma (LMM)), and the unclassifiable cutaneous
815
melanoma (UCM). Holman et el. (Ref. 7) presented an interesting study for these different types. They found that the risk of SSM in immigrants was strongly related to an early age of arrival in Australia, to a lesser extent the same was true for UCM. They suggested that this indicated the importance of W exposure at an early age (
816 of mortality rates in Australia, New Zealand, United States, Canada and England-Wales showed similar cohort effects and a direct proportionality of the mortality rate to the age to the power 3.2. In this analysis it was found that the cohort effects level off for years of birth after 1920. Apparently, there has been some general environmental, dietary or behavioral change which has strongly increased the occurrence of melanomas on the trunk and legs in birth-cohorts born between 1860 and 1920. An increase in W exposure of not regularly exposed skin areas has been suggested as a possible explanation. However, it is the author's impression that scarcity of clothing and recreational exposures have continued to increase in cohorts born after 1920, perhaps less dramatically than before that time. The HMFM appears mainly on the face, neck, and back of hands and appears to be strongly related to actinically damaged skin (Ref. 11); its etiology appears to be very similar to that of squamous cell carcinomas. It is a small fraction of the CMs occurring in Caucasians, usually
817
induced a melanoma in a mouse in the 92nd week of an experiment in which 40 mice received 2 weeks of heavy W exposure after which croton oil was delivered twice a week. By the time the melanoma occurred, most of the mice had died from other tumors or natural causes. This could indicate that W acted as an initiator €or this melanoma. The occurrence of such a melanoma could be a rare event censored by other causes of death. Experiments that indicate that UV radiation can be a complete carcinogen for the induction of CM are completely lacking. In our laboratory Van Weelden has tried to induce melanomas in pigmented hairless mice by exposure to high doses of UV radiation every fortnight; thus simulating intermittent W exposure. Heavy actinic skin damage was observed, and squamous cell carcinomas but no CMs were found. An early experiment by Epstein et al. (Ref. 15) indicated that UV radiation can act at later stages (as a promotor?). After inducing nevi with 7.12 dimethylbenz[a]anthracene (DMBA), they induced melanomas by subsequent UV irradiation. This experiment has never been reproduced. Indications that W radiation can act in a late stage also come from epidemiologic data: there appears to be an eleven year cycle superimposed on the increasing incidence of CM. This cycle shows a significant correlation with the cycle in the number of sunspots with a 1 to 2 years delay €or Connecticut and 0 to 1 year delay for Finland (Ref. 16). Sunspot activity is known to reduce the incoming cosmic radiation to the earth's atmosphere. This reduction in turn thickens the stratospheric ozone layer due to a reduction in reactive products which destroy ozone. This effect is strongest at the poles and starts there. By redistribution of the ozone the effect occurs later at lower latitudes. This would modulate the W radiation at the earth's surface, such a relatively fast reaction of CM occurrence on sunspot activity would indicate an effect in a late stage of tumor development (most likely tumor growth). Another indication for an environmental short term effect (sunshine?) comes from the similarity in the fluctuations in the annual incidences in men and women (Ref. 17). The fact that UV irradiation can change the immune system and thus induce a systemic effect has been well established (Ref. 18). It is also very plausible that photo-products come in to circulation and thus induce a systemic effect. The relevancy of such a W-induced systemic effect for CM has not been proven in any way.
818
It would provide an explanation for a latitudinal gradient in CMS in non-exposed skin areas. Magnus (Ref. 8 1 , however, points out that the hypothesis of a systemic effect is contradicted by the absence of a latitudinal gradient in CM on feet and by the absence of an increase of non-skin melanoma. The first argument seems not very decisive because of small numberrr of CMs on the feet. Alternative c a w 8 8 of CM Although CMs have not been reproducibly induced with W radiation in animals, chemical agents like urethan have been shown to cause CMs consistenly (e.g. Ref. 19). Genetically determined C M s occur in some animals like the platyfish and in mini-swine8 (Ref. 2 0 ) . In human epidemiology, chemists of the Lawrence Livermore National Laboratory have been shown to run an increased risk of CM (Ref. 21). Also people working in some refineries may run an increased risk (Refs. 22, 231, perhaps due to PCBs. Although the possibility of inducing CMs with chemical agents does not preclude that W radiation is the major causative agent in humans, it is good to keep in mind that chemical induction of CM is experimentally well established! Quantification of the relationshiD between W radiation and CM Baker-Blocker (Ref. 24) showed that there was a significant trend in the mortality rate of CM with latitude in the white female population of the United States. But the trend in the mortality rate of CM with annual UV dose (given in counts of a Robertson-Berger meter) turned out not to be significant. Scotto et al. (Ref. 2 ) presented data that did show a significant trend in the incidence of CM with annual UV dose both for white males and white females. CMs in the regularly exposed areas of face-neck and arm-hand showed a steeper trend with UV dose than C M s in other skin areas. They found for the white population: incidence in regularly exposed areas D (males) 1.0 (females) D o . 6 (males) incidence in irregularly exposed areas 0.5 ea ( females 1 where D stands for the ambient annual UV dose. If we assume the HMFM to be similar to squamous cell carcinomas, it would give (Ref. 2 5 ) : incidence HMFM D 2.9 If the dose-dependence of HMFM would be that strong, the latitudi-
.-
-
-
.
819
nal gradient of CM in exposed skin areas would be fully attributable to HMFM. There are, however no indications of a dramatic shift in the percentage of HMFM with latitude. As 6tated earlier, it is at present not possible to make a separate analysis of the incidence of HMFM versus those of SSM and other CMs in the face and other skin areas. Describing the overall W-dependence of the age-specific incidence of CM by a formula of the type bDC ad (where 'a' stands for age and 'b,c,d' are constants) (Ref. 2 ) may be too crude. One should take into account possible differences in W-dependencies of types of CMs and possible cohort effects on the age specific incidence for different skin areas. However, if we assume a relatively homogeneous population of the United States, and neglect cohort effects, the gradient in CM with latitude and annual W dose, may give a first approximation for W doses in the range measured over the United States. After correcting for differences in the populations (skin colors, etc.) Scotto et al. (Ref. 2 ) found for the white population: CM incidence in regularly exposed areas D O S 5 (males) 0.6 (females D (males) CM incidence in irregularly exposed areas - D O. (females1
-
N
W - cy If we assume that the latitudinal gradient in CM and the related gradient in annual W dose is due to a causal relationship between W radiation and CM, we can try to assess the effect of a reduction in stratospheric ozone on CM. First of all, we assume that the action spectrum for the induction of CM (i.e., the effectivity by which radiation of different wavelengths induce CM) is similar to that of W-carcinogenesis in general and, therefore, similar to the erythema1 action spectrum (Ref. 26, 2 7 ) . A 10% reduction in ozone would then lead to a 15-20% increase in carcinogenic W radiation (Ref. 28). If the CM incidence is directly proportional to D to the power 0.3 to 1.0 we find that a 10% reduction in ozone would result in a 5-20% increase in the incidence of CM in the white population in the United States. Ozone
-
CONCLUSIONS Although there are many indications that W radiation is somehow related to the formation of CMs in man, it is not Yet
820
possible to prove that this relation is due to a causal effect of W radiation. Some chemical agents (e.g. urethan) have been shown t o cause CMs in animal models, but this is not the case for W radiation. If we assume that the association of CM with factors related to W radiation points to a causal relation, then the next step is to establish the role of W radiation: there are indications that it acts in an early stage, in a late stage, and both. There are indications that it may play these various roles depending on the histogenetic type of CM. In sum, dealing with CM as one class of skin tumors may be a crude oversimplification which hampers a proper understanding of the etiology of CMs and the role of UV radiation. Using the latitudinal gradient in CM, and the related gradient in annual W dose, to quantify the possible effect of a etratoapheric ozone reduction on the occurrence of CM is, therefore, still a conjectural exercise. The outcome of such an exercise would be that a 10% ozone reduction would result in an increase in CM with about the same percentage (n 5-204 €or the white population in the United States). REFERENCES 1
2
T.R. Fears, J. Scotto and M.H. Schneiderman, Am. J. Epidemiol., 105 ( 1 9 7 7 ) 420-427. J. Scotto and T.R. Fears, Cancer Invest., 5 ( 4 ) ( 1 9 8 7 ) 275283.
3
C.D'A.J.
Holman, B.K. Armstrong and P.J. Heenan, JNCI,
76 ( 3 ) ( 1 9 8 6 ) 403-414. 4
5 6
B. Muel, J.P. Cesarini and J.M. Elwood, in W.F. Passchier and B.F.M. Bosnjakovic (Editors), Human exposure to ultraviolet radiation: risks and regulations, Elsevier, Amsterdam, 1 9 8 7 , pp. 89-96. J.A.H. Lee, Progr. Clin. Cancer, 8 ( 1 9 7 5 ) 151-161. G.
Eklund and E. Malec, Scand. J. Plast. Reconstr. Surg., 1 2
( 1 9 7 8 ) 231-241. 7
C.D'A.J.
Holman and B.K. Armstrong, JNCI, 7 3 (1) ( 1 9 8 4 )
75-82. 8 9
K. Magnus, Cancer, 32 ( 1 9 7 3 ) 1275-1286. R.G. Stevens and S.H. Moolgavkar, Am. J. Epidemiol., 1 1 9 ( 1 9 8 4 ) 890-895.
10
D.J. Venzon and S.H. Moolgavkar, Am. J. Epidemiol., 1 1 9
11
W.H.
( 1 9 8 4 ) 62-70.
Clark Jr, M.C. Mihan Jr, Am. J. Pathol., 55 ( 1 9 6 9 ) 39-
67. 12 13
14 15
M.S. Blois, R.W. Saghebiel, R.M. Abarbanel, T.M. Caldwell and M.S. Tuttle, Cancer, 52 ( 1 9 8 3 ) 1330-1341. A.W. Kopf. M.L. Kripke and R.S. Stern, J. Am. Aced. Dermatol., 11 ( 1 9 8 4 ) 674-684. M.L. Kripke, JNCI 6 3 ( 3 ) ( 1 9 7 9 ) 541-545. J.H. BpEtein, W.L. Epstein and T. Nakai, JNCI, 38 ( 1 9 6 7 ) 19-
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16 17 18 19 20 21 22 23 24 25 26 27 28
30. A. Houghton, E.W. Munster and M.V. Viola, The Lancet, 1 (19781 759-760. A.J. Swerdlow , Brit. Med. J., 2 (1979) 1324-1327. M.L. Kripke, in H. Hbnigsman and G. Sting1 (Editors), Therapeutic Photomedicine, S. Karger AG, Basel, 1986, pp. 164-175. S.D. Vesselinovitch, N. Mikailovich and W.R. Richter, C ncer Res.. 30 (19701 2543-2547. J.J.'Nordiund and A.B. Lerner, Am. J. Pathol., 89 (1977 443448. D.F. Austin, P.J. Reynolds, M.A. Snyder, M.W. Biggs and H.A. Stubbs, Lancet, 2 (1981) 712-716. L. Rushton and M.R. Anderson, Brit. J. Indust. Mad., 38 (1981 225-234. A.K. Bahn, I. Rosewaike, N. Hermann;P. Grover, J. Stellman and K. O'Leary, New Eng. J. Med., 295 (8) (1976) 450. A. Baker-Blocker, Environ. Res., 23 (1980) 24-28. H. Slaper, A.A. Schothorst and J.C. van der Leun, Photodermatol., 3 (1986) 271-283. C.A. Cole, P.D. Forbes and R.E. Davies, Photochem. Photobiol., 43 (1986) 275-284. H.J.C.M. Sterenborg, Investigations on the action spectrum of tumorigenesis by ultraviolet radiation, Thesis, State University of Utrecht, 1987. A.E.S. Green and T. Mo, In D.S. Nachtwey (Editor), CIAP monograph 5, part 1, Dept. of Transportation, Washington D.C., 1975, chapter 7, p. 127.
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S ESSI0N XIV Chairmen
RISK EVALUATION, CONTROL COSTS AND ASSESSMENT S.Zwerver T. McCurdy
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T.Schneider et al. (Editors),Atmospheric Ozone Research and its Policy Zmplkatwna 0 1989 Elsevier Science Publishers B.V., Amsterdam -Printed in The Netherlanda
APPLICATION OF THE NAAQS EXPOSURE MODEL TO OZONE
T. McCURDYl and R.A.
PAUL2
lAmbient Standards Branch, U.S. T r i a n g l e Park, NC 27711 2PEI Associates, Inc.,
Environmental P r o t e c t i o n Agency, Research
505 S. Duke S t r e e t ; Durham, NC 27707
ABSTRACT An important aspect of h e a l t h r i s k assessment i s t h e estimation o f populat i o n exposure. EPA's Ambient Standards Branch has developed an exposure model s u i t a b l e f o r evaluating a l t e r n a t i v e n a t i o n a l ambient a i r q u a l i t y standards (NAAQS). T h i s model i s known as NEM, an acronym f o r I$IQS Exposure Model.
NEM simulates t h e movement o f selected segments o f t h e human p o p u l a t i o n through d i f f e r e n t geographic areas characterized by d i f f e r i n g ambient a i r p o l l u t a n t levels. T h i s simulation locates population groups w i t h i n various microenvironments t h a t a r e undergoing d i f f e r e n t a c t i v i t i e s on a 10-minute basis. Separate exposure estimates are developed f o r d i f f e r e n t e x e r c i s i n g groups, such as people who undertake heavy o r very heavy exerclse.
With properly constructed i n p u t data, NEM i s capable o f e s t i m a t i n g exposures over a l a r g e urbanized area, such as a c i t y and i t s suburbs. Results from applying NEM t o t e n major urban areas i n t h e United States are presented and discussed. OVERVIEW
One o f t h e cornerstones o f t h e United States approach t o reducing ambient a i r p o l l u t i o n i s t h e s e t t i n g and subsequent implementation o f s t a t e government c o n t r o l programs t o a t t a i n national ambient a i r q u a l i t y standards (ref.
1).
A NAAQS i s an ambient standard t h a t i s designed t o p r o t e c t t h e h e a l t h of s e n s i t i v e persons from adverse e f f e c t s w i t h an adequate margin o f s a f e t y (ref. 2). As an a i d t o determining what c o n s t i t u t e s an adequate margin o f safety from a l t e r n a t i v e NAAQS under review, EPA has developed an exposure methodology t h a t i s p a r t o f a broader r i s k assessment program. Analysis o f population exposure under a l t e r n a t i v e ozone (03) NAAQSs requires t h a t s i g n i f i c a n t f a c t o r s c o n t r i b u t i n g t o t o t a l human exposure be taken i n t o account. These f a c t o r s i n c l u d e t h e temporal and s p a t i a l d i s t r i b u t i o n o f people and ozone concentrations throughout an urban area as people go about t h e i r d a i l y p a t t e r n o f l i f e .
To t h e extent p o s s i b l e w i t h e x i s t i n g
data, t h i s has been done i n t h e NAAQS Exposure Model (NEM), a s i m u l a t i o n
026 model designed t o estimate human exposure t o a i r p o l l u t a n t s i n selected urbanized areas under user-specified r e g u l a t o r y scenarios ( r e f . 3 ) . The 03-NEM model p a r t i t i o n s a l l l a n d w i t h i n a selected urban area i n t o l a r g e "exposure d i s t r i c t s " ( r e f . 4).
There are between t h r e e and f i f t e e n
exposure d i s t r i c t s i d e n t i f i e d i n t h e t e n urban areas used i n t h e ozone NEM analysis.
The number o f d i s t r i c t s i d e n t i f i e d i s d i r e c t l y r e l a t e d t o t h e
number o f monitors having v a l i d a i r q u a l i t y data i n a study area. People l i v i n g w i t h i n each exposure d i s t r i c t , as estimated by t h e U.S. Bureau o f Census i n 1980, are assigned t o a s i n g l e d i s c r e t e point, t h e popul a t i o n centroid. The a i r q u a l i t y l e v e l w i t h i n each exposure d i s t r i c t i s represented by a i r q u a l i t y a t t h e p o p u l a t i o n c e n t r o i d , which I s estimated f o r each hour o f t h e "ozone season" by data from nearby m o n i t o r i n g s i t e s . Because p o l l u t a n t s i n t h e ambient a i r are g e n e r a l l y modlfied considerably when e n t e r i n g a b u i l d i n g o r vehicle, outdoor a i r q u a l i t y estimates a r e adjusted t o account f o r f i v e d i f f e r e n t microenvironments, as noted below. Because degree o f exposure and/or s u s c e p t i b i l i t y t o e f f e c t s o f p o l l u t i o n may vary with age, occupation, and i n t e n s i t y o f exercise, t h e t o t a l p o p u l a t i o n o f each study area i s d i v i d e d i n t o demographic groups. subdivided i n t o t h r e e o r more a c t i v i t y subgroups.
Each group i s f u r t h e r
A typical pattern o f
a c t i v i t y through t h e f i v e microenvironments i s established f o r each subgroup. Units o f population analyzed by NEM are c a l l e d cohorts. Each cohort i s i d e n t i f i e d by exposure d i s t r i c t o f residence, by exposure d i s t r i c t o f employment o r school attendance, by demographic group, and by a c t i v i t y - p a t t e r n subgroup.
During each t e n minute p e r i o d o f a day, each cohort i s assigned t o
a p a r t i c u l a r exposure d i s t r i c t and a p a r t i c u l a r microenvironment.
The assign-
ment i s based upon (1) data regarding human a c t i v i t y p a t t e r n s gathered by EPA and u n i v e r s i t y "time budget'' researchers, and (2) home-to-work t r a n s p o r t a t i o n data gathered by t h e U.S.
Census Bureau.
Using these sources o f information,
NEM simulates t e n minute movements o f cohorts through d i f f e r e n t d i s t r i c t s o f
t h e urban area and through d i f f e r e n t microenvironments; combines these movements w i t h h o u r l y averaged a i r q u a l i t y data; and accumulates t h e r e s u l t i n g exposures over an ozone season. A I R QUALITY CONCENTRATIONS I N MICROENVIRONMENTS NEM r e q u i r e s t h a t hourly a i r q u a l i t y estimates be a v a i l a b l e f o r each
microenvi ronment t h a t every cohort passes through. These estimates a r e obtained by using a simple l i n e a r f u n c t i o n r e l a t i n g outdoor a i r q u a l i t y concentrations t o microenvironment l e v e l s v i a a "transformation" r e l a t i n g outdoor-to-indoor l e v e l s and then adding t o t h i s a p o l l u t a n t concentration due t o sources l o c a t e d i n t h e microenvironment i t s e l f . For ozone, t h e
827 transformation i s e s s e n t i a l l y a m u l t i p l i c a t i v e r a t i o derived from a review o f the ozone exposure l i t e r a t u r e ( r e f . 5). The r e l a t i o n s h i p i s : Xm,t
am,t + (h* x t ) where Xm,t = a i r q u a l i t y i n microenvironment m d u r i n g hour t
(1)
am,t = hourly-averaged p o l l u t a n t concentration due t o sources 1ocated i n t h e m i croenvi ronment bm
= m u l t i p l i c a t i v e r a t i o o f t h e microenvironment concentration value t o t h e monitored a i r q u a l i t y value
xt
= monitor-derived a i r q u a l i t y value f o r t i m e t
Because no s i g n i f i c a n t sources of ozone were i d e n t i f i e d f o r any o f t h e Estimated bm values
microenvironments, am,t = 0 f o r a l l environments.
obtained from t h e l i t e r a t u r e are described i n Table 1.
TABLE 1 Estimates o f m u l t i p l i c a t i v e microenvironmental f a c t o r s (b,) Low Estimate
Code Microenvi ronment 1 2 3 4 5
Indoors-residential Indoors-other Motor v e h i c l e Outdoors-near roadway Outdoors-other
0.36 0.40 0.00 0.13 1.00
Estimated Value ( U n i t l e s s ) Best High Estimate Estimate 0.58 0.52 0.11 0.18 1.00
The x t values are actual monitored values f o r t h e c u r r e n t situation.
0.70 0.62 0.30 0.28 1.00
(or "as i s " )
These monitored values are adjusted mathematically t o represent
a f u t u r e s i t u a t i o n when a i r q u a l i t y i n each study area j u s t meets t h e ozone NAAQS being analyzed.
By d e f i n i t i o n , a NAAQS i s a t t a i n e d when a l l monitors i n
an area have l e s s than one expected exceedance o f t h e standard concentration value ( c u r r e n t l y i t i s 0.12 ppm) i n a year. The exposure analysis i s based
on a ''just a t t a i n s " scenario, where a i r q u a l i t y l e v e l s a t t h e monitor c u r r e n t l y having t h e highest number o f expected exceedances a r e reduced mathematically t o where t h a t monitor j u s t a t t a i ns t h e standard being analyzed. Hourly a i r q u a l i t y data a t tims o t h e r than t h e " j u s t a t t a i n i n y "
hour a r e
adjusted using a non-linear approach described i n Ref. 6. SIMULATION OF POPULATION MOVEMENT Population movement i n NEM i s based upon i n f o r m a t i o n gathered by t h e U.S. Census Bureau regarding householders' home-to-work conmuting patterns.
The
028
data base c o n s i s t s o f m e t r o p o l i t a n a r e a - s p e c i f i c commenting data on t h e census t r a c t l e v e l .
T h i s census t r a c t information i s aggregated f o r exposure
d i s t r i c t s used i n t h e NEM a n a l y s i s t o o b t a i n d i s t r i c t - t o - d i s t r i c t t r i p i n f o r m a t i o n f o r those cohorts t h a t work.
(Otherwise, cohorts are assumed
Because of l a c k o f t r a v e l data f o r non-
t o s t a y i n t h e i r home d i s t r i c t s . )
work a c t i v i t i e s , we assume t h a t a l l shopping i s done i n each c o h o r t ' s r e s i dential d i s t r i c t .
The same assumption a l s o i s made regarding school-related
acti v ities. Three one-way commuting times a r e used t o represent non-household worker commute times:
20, 30, and 40 minutes.
Most workers f a l l i n t o t h e 20 minute
commute t i m e (representing t h e r a t h e r l a r g e i n t e r v a l of 0 t o 24 minutes), since t h e average commuting time i n t h e United S t a t e s i s about 20 minutes. Housewi ves/househusbands are assumed t o have no commuting time. The number o f d i f f e r e n t cohorts e x p l i c i t l y modeled i n an area i s equal t o t h e product o f 54 cohort groups times t h e square o f t h e number o f d i s t r i c t s i d e n t i f i e d i n each study area.
Thus, t h e number o f cohort groups e x p l i c i t l y
modeled varies between 486 and 12,150 i n t h e t e n urban area sample. (See Table 2.) There i s no t r i p i n f o r m a t i o n a v a i l a b l e from t h e U S . Census Bureau regarding weekend i n t e r - d i s t r i c t t r a v e l i n SMSAs.
(There i s information
a v a i l a b l e regarding weekend r e c r e a t i o n a l t r a v e l , b u t i t i s n o t l o c a t i o n a l l y s p e c i f i c n o r i s i t systematic.)
Consequently, a l l cohorts are assigned t o
t h e i r home d i s t r i c t s on weekends i n NEM analysis. EXERCISE MODELING I N 03-NEM
Because dose received by a person exposed t o an a i r p o l l u t a n t i s h i g h l y dependent upon her o r h i s v e n t i l a t i o n r a t e , e x e r c i s e l e v e l i s an important consideration i n exposure modeling.
I n OyNEM, f o u r e x e r c i s e l e v e l s a r e used.
Along w i t h t h e i r associated v e n t i l a t i o n r a t e s ( i n u n i t s o f l i t e r s p e r minute,
or L/min), they are: 1.
low exercise, 25 L/min o r l e s s
2.
medium exercise, 26-43 L/min
3.
heavy exercise, 44-63 L/min
4.
very heavy exercise, 64 L/min or h i g h e r
The amount o f t i m e spent e x e r c i s i n g by any cohort i s q u i t e small. The l a r g e s t p o r t i o n o f any cohort group undertaking heavy e x e r c i s e i s 5.7% f o r cohort #3, which c o n s i s t s o f c h i l d r e n 1 t o 2 year old. cohort c o n s t i t u t e s o n l y about 1.0-1.5%
See Table 3.
o f an area's t o t a l population.
This The
p r o p o r t i o n o f time spent i n heavy exercise by people i n cohorts t h a t undertake such exercise generally i s l e s s than 2%.
TABLE 2
Study areas modeled i n 03-NEM Study Area Population Modeled (10 )
Total Populations o f Included MSAs (10 )
2nd Highest D a i l y Naximum 03 Concentration
Number of Exposure O i s t r ic t s
Number of
E PA Region Numher (s )
Study Area Name
6 A s Included ( i n whole o r i n part)
Chic ago
Aurora-Elgin, IL Chicago, I L Gary, I N Joliet. I L Lake County, I L
7.48
7.82
0.17
9
4.374
5
Denver
Boulder. CO Denver, CO
1.54
1.62
0.14
6
1,944
8
Houston
Houston, TX
2.54
2.74
0.19
7
2,646
6
Los Angeles
Anaheim, CA Los Angeles. CA Riverside. CA San Bernardino, CA
10.22
10.97
0.37
15
12.150
9
M i ami
Fort Lauderdale. FL Riami. FL
1.55
2.65
0.12
4
New Vork
Hiddlesex. NJ Nassau-Sulfolk, Newardk. MI New Vork. NY Stamford. CT
13.62
13.85
0.25
10
5,400
1.2
( PPm 1
Cohorts Modeled
864
NY
4
Phi 1adel p h i a
Philadelphia. PA
4.36
4.72
0.20
7
2,646
3
S t . Louis
S t . Louis, Mo
2.20
2.38
0.18
8
3,456
5,7
Tacoma
Tacoma. MA
0.58
0.46
0.14
3
Uashington, Dc
Yashington. Dc
2.88
3.25
0.14
8
486 3.456
10 3
830 The l a r g e s t p o r t i o n o f any cohort group undertaking very heavy exercise i s 100%,-for male outdoor workers, a group d e f i n e d e x p l i c i t l y t o capture heavily exercising individuals.
Less t h a n 2% o f any study area's population
i s included i n t h i s occupational grouping. TABLE 3 Number o f minutes per week i n each microenvironment by exercise l e v e l f o r c h i l d r e n ages 1-1.9 years M i croenvi ronments
Exercise Level 1 2 3 4 Note:
1
2
3
4
5
6130 280 340
340 0 0
120 0 0
140 230 330
0
0
170 0 0 0
0
0
(1) Non-commuting group (2) Exercise l e v e l s are defined i n t h e t e x t ; microenvironments a r e defined i n Table 1.
The usual p r o p o r t i o n o f e x e r c i s i n g cohort population p a r t i c i p a t i n g i n very heavy exercise i s l e s s than 1%. The combination o f small e x e r c i s i n g f r a c t i o n s and small amounts o f time spent i n heavy or very heavy e x e r c i s e r e s u l t s i n a very small f r a c t i o n o f t o t a l population-time devoted t o exercise, F o r one modeled study area, New York, t h e amount o f t o t a l population-time spent i n exercise i s : 1.
0.9% f o r heavy exercise (Undertaking exercise a t a l e v e l o f 44-63 L/mi n).
2.
0.002% f o r very heavy exercise (undertaking e x e r c i s e a t a l e v e l o f 64 or higher L/min).
The other modeled areas have s i m i l a r , b u t not i d e n t i c a l , f r a c t i o n s o f t o t a l population-time spent i n exercise. NATIONAL ESTIMATES OF POPULATION EXPOSURE TO ALTERNATIVE OZONE STANDARDS I n any NEM analysis, t h r e e d i f f e r e n t i n d i c a t o r s are used t o estimate exposure o f people t o various l e v e l s o f a i r p o l l u t i o n . rences o f exposure":
One u n i t i s "occur-
t h e number o f times a given l e v e l o f p o l l u t i o n i s
experienced by an i n d i v i d u a l .
(If30 people experience a p o l l u t a n t l e v e l o f
1 ppm which remains steady over a 3-hour period, population exposure can be expressed as 30 occurrences of exposure f o r a 3-hour averaging t i m e or 90 A second i n d i c a t o r o f population occurrences f o r a 1-hour averaging time.) exposure i s "people-exposed."
T h i s i s simply t h e number o f people who ex-
perience a given l e v e l o f a i r p o l l u t i o n , o r higher, a t l e a s t one t i m e d u r i n g t h e time p e r i o d o f analysis.
The t h i r d i n d i c a t o r of exposure used i n NEM i s
831 "people a t peak exposure." T h i s i s t h e number o f people who experience t h e i r highest p o l l u t a n t l e v e l w i t h i n a given concentration i n t e r v a l . Examples o f t h e f i r s t two output measures are provided i n t h i s paper. Two d i f f e r e n t exposure averaging t i m e periods a r e used i n 03-NEM: 10 minutes and 1 hour.
Only t h e 1-hour r e s u l t s w i l l be discussed; f o r informa-
t i o n regarding 10 minute exposures see Ref. 4. The n a t i o n a l e x t r a p o l a t i o n o f ozone exposures from t h e modeled t e n urban areas t o t h e n a t i o n ' s urban population as a whole i s achieved by assigning each o f t h e 331 metropolitan s t a t i s t i c a l areas (MSA) i n t h e United States t o one o f t h e t e n study areas.
Each non-modeled area i s assigned on t h e b a s i s
of geographic proximity, c l i m a t o l o g i c a l s i m i l a r i t y , and, when available, peak ozone levels.
National ozone exposure estimates shown i n subsequent t a b l e s
are calculated from study area exposure estimates according t o t h e f o l l o w i n g expression : n E(C) = C Piei(C) i=l
where:
E(C) = The t o t a l number o f exposures t o a concentration i n ozone concentration i n t e r v a l C f o r a l l m e t r o p o l i t a n areas ei(C) = The number o f exposures f o r t h e i t h area o f n m e t r o p o l i t a n areas i n a concentration i n t e r v a T C
Pi = The t o t a l population o f metropolitan areas assigned t o each study area d i v i d e d by t h e population o f t h e r e s p e c t i v e i t h study area.
The t o t a l population included i n t h e e x t r a p o l a t i o n i s 172.3 m i l l i o n people, and t h e t o t a l number o f one-hour occurrences f o r t h i s population i s 1,038,000 m i l l i o n person-hours. f o r each person.
T h i s represents t o approximately 6,024 exposure hours
The reason t h i s f i g u r e i s n o t 8,760 hours per person--the
number o f hours i n the year--is t h a t only t h e "ozone season" i s modeled. Four a l t e r n a t i v e a i r q u a l i t y scenarios are modeled.
The f i r s t i s t h e
"as i s " s i t u a t i o n , which uses recent monitored a i r q u a l i t y data t o represent ozone concentrations i n t h e outdoor-other mlcroenvi ronment.
(Which o f course
i s then modified by t h e bm f a c t o r s shown i n Table 1 t o estimate ozone l e v e l s i n the other microenvironments.)
A i r q u a l i t y f o r t h e "as i s " case comes from
t h e 1983-1985 t i m e period, using whichever year has t h e most complete data base. The remaining a i r q u a l i t y scenarios represent t h e h y p o t h e t i c a l s i t u a t i o n when a national ambient a i r q u a l i t y standard f o r ozone i s j u s t a t t a i n e d i n an urban area (as simulated by t h e non-linear adjustment procedure ment i o n e d e a r l i e r and described i n Ref. 6).
032
Three a l t e r n a t i v e ozone NAAQSs are simulated:
0.08,
0.10,
and 0.12 ppm. ozone
The l a t t e r value, o f course, i s t h e c u r r e n t standard l e v e l o f t h e U.S. NAAQS
.
Estimates o f t h e cumulative number o f 1-hour exposure occurrences seen by t h e U.S.
urban population undertaking any exercise appear i n Table 4.
TABLE 4 Estimate o f cumulative number o f occurrences o f exposure t o 1-hour average ozone i n t h e U.S. urban population d u r i n g t h e ozone season f o r a l l exercise regimes under a l t e r n a t i v e a i r q u a l i t y scenarios ( m i l l i o n s of people occurrences)
A i r Qua1 i t v Scenarios 0 3 Conc. Equaled o r Exceeded
(wm)
The Current Situation
A l t e r n a t i v e NAAQS ( i n ppm) 0.12
0.10
0.08
0.401 0.381
0
*
0 0
0 0
0 0
0.361 0.341 0.321 0.301 0.281
0.1 0.2 0.3 0.8 1.9
0 0 0 0 0
0 0 0 0 0
0
0.261 0.241 0.221 0.201 0.181
3.6 8.2 16.7 26.6 54.0
0 0 0 0 0
0 0 0 0 0
0 0 0 0 0
0.161 0.141 0.121 0.101 0.081
135.6 299.0 656.1 1,224.0 3,778.0
0 0 1.5 68.5 213.6
0 0 0 0.1 43.3
0 0 0 0 .Y
955.0 16,160.0 163,900.0 883,700.0 1,038,000.0
177.3 7,113.0 121,700.0 884,400.0 1,038.000.0
0.061 0.041 0.021 0.001 0.000
11,730.0 56,570.0 224,600.0 890,800.0 1,038,000.0
2,315.0 26,710.0 193,500.0 890,700.0 1,038,000.0
0 0 0 0
S e w e r than 50,000 people-occurrences. The >0.381 category i s estimated t o have almost 9,000 people occurrences, f o r example. These estimates a r e based upon u s i n g "best estimate'' microenvironment f a c t o r s and are i n terms o f m i l l i o n s o f people occurrences o f ozone exposure. The f i r s t column shows t h e ozone concentration t h a t i s equaled or exceeded, and t h e o t h e r f o u r columns show cumulative exposure d i s t r i b u t i o n s f o r t h e f o u r a i r q u a l i t y scenarios p r e v i o u s l y discussed. Because a l l people
83 3 experience t h e same number o f exposures a t o r above 0.0 ppm, t h e e n t i r e universe of people occurrences--1,038,000
x 106--is shown f o r a l l scenarios.
The o v e r a l l p a t t e r n o f data shown i n Table 4 i s : 1.
t h e r e i s a long " t a i l " t o t h e c u r r e n t - s i t u a t i o n scenario, i n t h a t t h e r e are t a b u l a r e n t r i e s f o r t h e higher ozone concentration "cutpoints," even up t o 0.40 ppm.
2.
There i s a short t a i l t o t h e remaining scenario d i s t r i b u t i o n s , w i t h very small t a b u l a r e n t r i e s a t o r above t h e ozone concentration used f o r t h e scenario standard.
What t h i s p a t t e r n i m p l i e s i s t h a t attainment of an a l t e r n a t i v e NAAQS r e s u l t s i n a dramatic reduction i n peak ozone exposures. For instance, t h e number of people-occurrences o f exposure t o ozone l e v e l s 2 0.12 drops t o 1.5 m i l l i o n w i t h attainment o f a 0.12 ppm NAAQS, as compared t o 656.1 m i l l i o n people occurrences under c u r r e n t ozone a i r q u a l i t y conditions.
Attaining
a t i g h t e r ozone NAAYS, e i t h e r 0.10 o r 0.08 ppm, reduces t h e number of people occurrences
2
0.12 ppm t o zero.
The next two tables focus on t h e h e a v i l y e x e r c i s i n g population cohorts. Table 5 d e p i c t s t h e number o f heavy exercisers t h a t a r e exposed t o ozone during heavy exercise (44-63 L/min) regimes.
The population universe f o r
t h i s group of people i s 62.2 million--about 36% o f t h e t o t a l U.S. lation.
MSA popu-
The Table i n d i c a t e s t h a t about 16 m i l l i o n people experience a 1-hour
ozone concentration > 0.12 ppm a t l e a s t once per ozone season as they engage i n heavy exercise. population.
These exercisers c o n s t i t u t e 9.3% o f t h e t o t a l U.S.
MSA
I f the c u r r e n t NAAQS o f 0.12 ppm i s attained, o n l y 600,000
people (0.3% o f t h e t o t a l urban population) would experience t h a t l e v e l o f ozone as they h e a v i l y exercise. The f i n a l Table presented t o i l l u s t r a t e 03-NEM outputs i s concerned w i t h very h e a v i l y e x e r c i s i n g cohorts. These people are e x e r c i s i n g a t 64 L/min o r higher a t some time d u r i n g a t y p i c a l week. urban U.S.
Only 441,800 people i n t h e
are estimated t o undertake such an exercise r a t e f o r an hour o r
longer d u r i n g t h e ozone season.
O f these people, we estimate t h a t about
100,000 people experience an ozone l e v e l > 0.12 ppm d u r i n g a t l e a s t one o f t h e i r heavy exercise regimes.
While o n l y 0.06% o f t h e U.S.
population, t h e
combination o f high ozone exposure and very high exercise l e v e l (and v e n t i l a t i o n r a t e ) makes them a p a r t i c u l a r l y s e n s i t i v e group from a p u b l i c h e a l t h perspective.
I f any o f t h e a l t e r n a t i v e NAAQS analyzed i n Table 6 a r e a t -
tained, we estimate t h a t no one would experience an ozone exposure > 0.12 ppm during very heavy exercise.
834 TABLE 5 Estimate o f t h e cumulative number o f heavy e x e r c i s e r s i n t h e U.S. urban population exposed t o one-hour average ozone d u r i n g t h e ozone season a t heavy exercise under a l t e r n a t i v e a i r q u a l i t y scenarios ( m i l l i o n s o f people)
A i r Q u a l i t y Scenario 03 Conc. Equaled o r Exceeded (ppm)
The Current Situation
A l t e r n a t i v e NAAQS ( i n ppm) 0.12
0.10
0.08
0.361 0.341 0.321 0.301 0.281
0
0 0 0
0 0 0
0 0 0
0.1 0.2
0
0 0
0 0
0.261 0.241 0.221 0.201 0.181
0.4 0.7 1.2 2.1 3.0
0 0 0 0 0
0 0 0
0 0 0 0 0
0.161 0.141 0.121 0.101 0.081
6.2 10.4 16.2 24.4 39.9
0 0 0.6 3.0 16.7
0 0 0 0.2 8.2
0.2
0.061 0.041 0.021 0.001 0.000
49.1 59.4 61.2 62.2 62.2
41.0 56.7 62.1 62.2 62.2
32.3 49.3 62.0 62.2 62.2
14.5 43.2 61.3 61.6 62.2
* *
0
0 0
0 0 0
*
*Fewer than 50,000 people. Note: These are "best estimate" projections.
CAVEATS AN0 LIMITAT IONS The 03-NEM model described above i s undergoing review by t h e public. Undoubtedly, t h i s review w i l l uncover several shortcomings t h a t w i l l r e s u l t i n m o d i f i c a t i o n s t o t h e model.
Two such shortcomings already noted by one
reviewer i s t h a t heavy and very heavy exercise seems t o be o v e r l y concent r a t e d i n o n l y a few hours per day, which seems u n r e a l i s t i c ; i n addition, t h e r e a r e inconsistencies among exercise groups w i t h respect t o sequence o f exercise ( r e f 7).
Another shortcoming i s a l a c k o f u n c e r t a i n t y analyses
regarding both model i n p u t s and p r e d i c t i o n s ( r e f 8). These shortcomings are c u r r e n t l y being addressed.
I n t h e meantime, EPA
i s i n v e s t i g a t i n g another ozone exposure model t h a t can accomnodate t h e c a l c u l a t i o n of sequential h o u r l y exposures t o t h e p o l l u t a n t .
Thus, f u t u r e
835 EPA ozone exposure estimates may be d i f f e r e n t than those presented i n t h i s
paper. TABLE 6 Estimate o f t h e cumulative number o f heavy exercisers i n t h e U.S. urban population exposed t o one-hour average ozone d u r i n g t h e ozone season a t very heavy exercise under a l t e r n a t i v e a i r q u a l i t y scenarios (thousands o f people) A i r Qua1it y Scenario
03 Conc. Equaled o r Exceeded ( ppm 1
The Current Situation
A l t e r n a t i v e NAAQS ( i n ppm)
0.12
0.10
0.08
0 0 0 0 0
0 0 0 0 0
0.361 0.341 0.321 0.301 0.281
1.8 2.8
0 0 0 0 0
0.261 0.241 0.221 0.201 0.181
2.8 3.5 5.0 7.1 11.2
0 0 0 0 0
0 0 0 0 0
0 0 0 0 0
0.161 0.141 0.121 0.101 0.081
25.3 75.3 100.0 162.8 258.7
0 0 0 27.7 148.7
0 0 0 0 49.7
0 0 0 0
0.061 0.041 0.021 0.001 0.000
343.0 387.9 431.8 441.8 441.8
305.6 379.8 434.5 441.8 441.8
266.1 337.1 431.8 441.8 441.8
0
* *
*
154.1 349.2 426.2 437.4 441I8
*kewer than 1,000 people. Note: These a r e "best estimate" projections. REFERENCES
1
2 3 4 5 6
7 8
42 U.S. Code 7408-9 (Sections 108 and 109 o f t h e Clean A i r Act as amended ) U.S. EPA. "Revisions t o t h e National Ambient A i r Q u a l i t y Standards f o r 44 Fed. Reg. 8202 (February 8, 1979). Photochemical Oxidants." W.F. B i l l e r , e t a l . "A General Model f o r Estimating Exposures Associated Paper presented a t t h e 74th annual meeting o f w i t h A l t e r n a t i v e NAAQS." t h e A i r P o l l . Control Assoc.; Phila., June 1981. R.A. Paul, e t a l . National Estimates o f Exposure t o Ozone Under A l t e r n a t i v e National Standards. Durham, NC: P E I Associates, 1986. A. Ferdo. "Ozone Microenvironment Factors." Memo t o T. McCurdy; 1985. T. Johnson and J. Capel. The Use o f t h e EKMA Model f o r A d j u s t i n g Hourly Average Ozone Data t o Simulate Attainment o f Proposed A i r Q u a l i t y Standards. Durham, NC: P E I Associates, 1985. W. Ollison. L e t t e r t o T. McCurdy; October 14, 1987. Flaak; January 26, 1988. G. Morgan. L e t t e r t o A.R.
.
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T. Schneider et aL (Editors),Atmospheric Ozone Reeeorch and its Policy Z m p h t b n e 0 1989 Elsevier Science Publiihem B.V., Ameterdam -Printed in The Netherlands
837
RISK ANALYSIS AND EVALUATION FOR DEVELOPMENT OF AN OZONE CONTROL STMTEGY
K.R. KRIJGSHELD and S. ZWERVER Ministry of Housing, Physical Planning and Environment, Air Directorate, P.O. Box 450, 2260 ME Leidschendam, The Netherlands ABSTRACT A risk assessment is presented by comparing current concentrations of ozone in Europe with suggested "no-effect-levels" derived from the presently available effect data. Clearly, the prevailing ozone concentrations are at an unacceptable level. Very drastic reductions of more than 75% in both NOx and VOC emissions are needed in order to significantly reduce the ozone levels. INTRODUCTION The atmospheric ozone problem relates, on the one hand, to excessive ozone formation in the boundary layer and the free troposphere and, on the other hand, to ozone breakdown in the stratosphere. The risk evaluation in this paper is directed primarily at the increased ozone concentrations in the ambient air. The formation, prevalence and dispersion of ozone have been part of Dutch research into air pollution for more than 15 years. In the beginning much effort has been put into smog-chamber research concerning the mechanism of the chemical reactions. Later, the step was taken towards models for the open air; first a box model, then the EKMA model and finally the large-scale model for Europe which was used in the Dutch - West-German PHOXA project Ozone was monitored regularly at several locations in the Netherlands for a long time. In addition, ozone has been monitored systematically for the last ten years at 29 points in the dense air pollution monitoring network in the Netherlands. The availability of monitoring statistics is thus increasing rapidly.
.
838 In the Netherlands, inhalation-toxicological research of ozone also got off the ground several years ago. In addition, the impact of ozone on plants is receiving increasing attention as part of the Netherlands' acidification-related research program. Research in the area of effects has already led to a tightening of the levels at which negative effects on humans and the ecosystem must be feared. EXPOSURE ASSESSMENT Photochemical ozone formation Until1 recently, risk assessment has devoted attention primarily to 1-hour average peak concentrations. In the past few years, research into the effects of sub-acute and chronic exposure to ozone has provided sufficient reason, both for hurnan health and vegetation, to devote more attention to long term average concentrations. Therefore, it is good to realize that ozone formation takes place on various spatial and temporal scales (TABLE 1). The large-scale background of ozone is determined in the free troposphere. This ozone level is caused by emissions of NO, and low-reactive hydrocarbons, but also methane and carbonmonoxide. Ozone peak values during episodes arise from reactions in the mixing layer. Here the transport on the national and the European scale does play a role. The very reactive hydrocarbons may cause locally increased ozone concentrations.
TABLE 1 Photochemical ozone formation rpakl usla
tinw mala
pncum
LOCAL
HOURS
NO., , highly reactive VOC
REGIONAL (nationallEuropeen)
DAYS
MONDW
%Zzi
NO,, VOC
SEASON. YEARS
No,, Voc (vscy low -41. CO, CH,
839
Current concentrations Concentrations have exhibited a considerable increase in the course of this century, particularly in the years between 1950 and 1970 when NO, and VOC emissions also grew substantially. There has been no clear trend in peak ozone concentrations over the past ten years. This is generally explained by the increase of NO,emissions through which ozone is quenched or eliminated on the local scale. Fig. 1 presents the daily maximum ozone concentrations for the period 1980-1985 (ref.1). It is striking that the maximum 8-hour
Fig. 1. Frequency distribution of measured ozone concentrations for all Dutch monitoring stations (ref. 1). average concentrations are only slightly lower than the maximum 1-hour values. The 8-hour averages range from 190-350 pg/m3. The 1-hour averages range from 230-430 pg/m3. Even the ozone concentrations during the growing season in the Netherlands on average amounts to 80-95 pg/m3 (average of &hour values, between 9 a.m. and 5 p.m., over the period May-September). When looking at the frequency distributions of 1-hour values in the Netherlands, then the highest 98-precantiles for ozone are found in the southern part of the country. This is illustrated in F i g . 2 for the year 1985. However, the highest 50-percentiles are measured in the north, in relatively clean areas. A great part of the year winds come from northern directions. The ozone concentrations in the north, therefore, are determined preponderantly by the tropospheric background level, present in
840
Fig. 2. The 50 and 98 percentile for ozone Netherlands (Jan Dec 1985) (ref.2).
-
(pg/m3) in the
the air masses coming from overseas. The average concentration of ozone decreases towards the south of the country due to dry deposition and reaction with NO from polluted air. The occurrence of peak concentrations usually involves episodes lasting several days. The seriousness 05 effects will presumably be influenced by the average duration of a period during which a certain maximum 1-hour or 8-hour average concentration is exceeded. The number of consecutive days that a certain ozone
Fig. 3. Average length of a period (in days) during which a maximum 1 hr (---) or 8 hrs (-) average concentration of ozone has been exceeded (station Den Helder; 1980-1985) (ref.3).
84 1
level is exceeded will usually decrease with increases in the considered concentrations of ozone (Fig. 3). HEALTH EFFECTS
To make possible a risk assessment for ozone in the Netherlands the National Institute for Public Health and Environmental Hygiene (RIVM) recently drew up - by order of the Ministry - a criteria document for ozone (ref. 1). In the document the effects both on human health and on crops and vegetation have been evaluated. The most critical effects on humans evident from the epidemiological and clinical research are decreased lung function, increased airway reactivity and an increase in chance and severety of attacks among asthmatics. Based on research with laboratory animals, it is also likely that other effects can occur as a result of exposure to ozone, such as increased sensitivity to respiratory infections and structural lung damage with repreated or chronic exposure. Unfortunately, the information regarding the exposure-response relationships for ozone is still very inadequate, also because of the disproportionate attention there has been in the past to peak exposures. The need for a better insight into the exposureresponse relationships for ozone is emphasized by recent research. The factors that govern this relationship may be separated in factors related to dose, and factors related to the intrinsic sensitivity of exposed persons:
* dose: - ozone concentration - duration of exposure in - number of days exposed - level of exercise * intrinsic sensitivity: - "responders" (people
-
hours per day
exhibiting reaction to ozone) persons with respiratory problems
stronger
than
average
Based on the factors noted above, we can distinguish various risk groups in the population:
8 of Dutch population Risk qroup * Persons whose work involves physical 3.5 exercise in the open air * Children (up to and including 14 years) 20 * "Responders" 5-15 ( ? ) * Persons with respiratory problems 7
042 This means that an estimated 30 to 40 percent of the Dutch population will fall into one of these categories and thus, are potentially at risk for exposure to ozone. So-called no-effect-levels to protect human health have been derived in the ozone criteria document (Table 2). They agree with the recommendations drawn up recently by the World Health Organization (ref. 4). TABLE 2 No-effect levels for ozone in relation with human health Dutch crlterladocument marginal effect level
neeffect level
WHO guideline value
1 hour average
240 p g h 3
160 pglm3
150-200 kglrn3
8 hour average
160 pg/rn3
110 pg/rn3
100-120 pg/rn3
A safety margin of 1.5 was applied in deriving the no-effectlevel from marginal effect levels. This factor is fairly arbitrary, but - nevertheless - is necessary to cover a degree of uncertainty in a number of aspects, like extrapulmonary effects, the effects caused by combined exposure to ozone and other air pollutants, and sufficient protection of populations at risk. The possible carcinogenic, co-carcinogenic and/or promotor activity of ozone is still a matter of debate. For the time being, in the Netherlands, we are not considering ozone as a carcinogenic substance. ECOLOGICAL EFFECTS With respect to the effects of ozone on plants, one can also make a distinction between acute toxicity at short-term exposure (visible leaf injury) and harmful effects from prolonged exposure to lower concentrations (growth inhibition, yield reduction, and increased susceptibility to biotic and abiotic stress). Harvest reduction in the Netherlands resulting from air pollution in general was estimated at 5 percent in 1983. Ozone is considered the most important component of air pollution in this matter,
043
accounting for nearly 70 percent of the harvest reduction. The concern about acidification has provided in recent years an important impulse for further research into the effects of ozone on plants. It is very likely that ozone contributes significantly to the decline in forest vitality which is observed in the Netherlands and elsewhere in Europe. In the Dutch Criteria Document for Ozone no-effect-levels have also been derived for plants, forests and crops (Table 3). The desired ozone air quality in this case has been differentiated into 1-hour, &hour and growing season averages in order to do justice to the influence of the exposure pattern. TABLE 3 No-effect-levels for ozone in relation with vegetation, forests and crops.
RISK ASSESSMENT. In order to get a sense of the extent of the risks presented by current ozone concentrations, we can compare these concentrations to the advised no-effect-levels. As can be judged from figure 2 the maximum 1-hour and 8-hour average concentrations in the Netherlands amply exceed the respective no-effect-values. If we look at the average number of days per year that a no-effect-level is exceeded, we see that this occurs in five percent of the days when compared with the 1-hour limit value, on five to ten percent of the days for the &hour level related with human health effects, and on even more than 50 percent of the days, when comparing with the 8-hour no-effect-level for vegetation. The average concentration of ozone during the growing season, being
844 80-95 pg/m3, will exceed the suggested no-effect-level of 50 pg/m3 during the entire season. A similar picture emerges from model calculations for the European situation, as performed in the PHOXA-project. This project is a collaboration of the Netherlands and the Federal Republic of Germany. Up till now it has been directed at calculating European ozone concentrations during summer episodes. The Dutch research institute TNO participates in the project and some of their results will be discussed here. The data represent model calculations based on an episode that occurred in 1982. The curves shown in Fig. 4 and 5 show the cumulative frequency distribution for the percentage of the
Fig. 4. Calculated frequency distributions of exposure to ozone during an episode. population in the considered area, that is exposed above a certain ozone concentration. In these calculations exceedence of 240 pg/m3 as a 1-hour average - the current ambient air quality standard in the USA and also the provisional limit value in the Netherlands - appears to occur only limitedly (Fig. 4). The model tends to underpredict the observed ozone levels. T h i s is mainly due to the fact that the ozone concentrations have been calculated as an averaae over fairly large surface units, grids of 60 x 60 km. Local variations in ozone levels therefore don't become visible. For example, 240 pg/m3 was exceeded at almost all of the stations in the National Monitoring Network in the Netherlands during this particular period: the highest value measured even reached 430 microgram/m3.
845
However, the suggested no-effect-level of 160 pg/m3 (1-hour average) is being amply exceeded. Taken these calculated concentrations, it is estimated that this involves 9 percent of the total population, that is 23 million inhabitants, for the area under consideration. The 6-hour no-effect-level, again, appears to be much more critical than the 1-hour value. The calculations indicate at least in this episode about 140 million people, that is more than half of the total number of inhabitants in the area, are exposed at ozone concentrations above the 6-hour no-effect-level. Only one conclusion is possible: for ozone we clearly have come into the range of unacceptable concentrations. CONTROL STRATEGY To develop a control strategy to reduce ozone to acceptable levels, models like the one used in PHOXA can become an important tool. In the PHOXA-project calculations with 50 percent less NO,
Fig. 5. Calculated frequency distributions of exposure to ozone duriong an episode: effect of emission reductions. emissions, 50 percent less hydrocarbon emissions, and the combination of both were also carried out (fig. 5). At this stage results should be interpreted as very preliminary. The effect of emission reductions on the ozone concentrations occurs especially in the high concentration ranges. Limiting hydrocarbon emissions clearly has a positive effect. NO. reduction appears to have a negative effect. This is particularly the case in the areas of dense NO,-emissions, as in the Netherlands.
846
However, elsewhere in Europe, reduction has a positive effect.
in
less NO,
rich
areas,
NO,
Model calculations with a more limited design indicate that very large emission reductions are needed in order to reach the no-effect-level in the Netherlands (Table 4). Only the ozone concentration in the Netherlands has been calculated in these studies although emissions in all of Europe were included. Emission reduction of NO, and VOC on a European scale is needed to limit the 1-hour average peak concentrations; reductions on a global scale may be needed to limit the 8-hour average and are certainly needed to reduce the seasonal average.
TABLE 4 Emission reductions needed to prevent all adverse effects on human health and vegetation.
Despite the many uncertainties in model calculations, all available studies tend to the same conclusion that very high emission reductions are needed to cause a significant decrease in ozone levels. We have to be realistic, this can only be achieved in the long run. Therefore, setting an interim-goal will be helpful Thus, it makes sense to research the emission reductions necessary to prevent, in any event, the more serious human health and environmental effects (Table 5). The existing provisional limit value in the Netherlands, which is comparable to the current standard in the USA of 240 pg/m3 (1-hour average) can be
.
847
considered the marginal-effect-level. If we take this level as the point of departure, an emission reduction of 40% is required for both NO, and VOC, on a European scale (if exceedence is allowed 3 times per year). Similarly, the marginal effect-level for the 8hour average at least in relation with human health may be set at 160 pg/m3. The associated emission reduction then is 75% for both NO, and VOC. TABLE 5 Interim-goal for ozone ambient air quality, and related emission reductions, to prevent serious effects on human health and vegetation.
ozone is concerned, it would be too speculative to conclude on the basis of the presently available model calculations, what emission reduction of NO,, hydrocarbons, CO and/or CH, are necessary to arrive at lower ozone levels. As far as the growing season average for
CONCLUSIONS To conclude, it is evident there are still many uncertainties in the effects of ozone that need further clarification:
* * * *
the relationship between exposure pattern and the effects on human health; similarly the effects of chronic exposure on the environment; the risk for sensitive groups in the population; why are "responders" extra sensitive to ozone; the effects of combined exposure to ozone and other air pollutants.
1348
To properly assess the risk of occurring concentrations of ozone we need better knowledge regarding the extent of the actual human exposure. Personal monitoring and modelling of exposure, based on human aqtivity patterns both indoors and oudoors, have to provide more insight in this respect. Despite the uncertainties it is clear that actions should be taken to reduce the ozone concentrations, the more so since we must acknowlegde that: 1. effects occur at much lower ozone levels than has been assumed thus far, also due to the importance being attributed to 8hour average ozone concentrations, in addition to the 1-hour peak values. 2. the prevailing concentrations are at an unacceptable level. To arrive at a control strategy, the development and use of models is an important tool for ascertaining which factors have a determining influence. Also in this area it is clear that our knowledge is far from complete. Next to validation of the models, there is a need to expand the models to include long-term average ozone concentrations. A good international infrastructure for monitoring ozone would be very useful for this purpose. In addition, it is essential that we improve our information about the levels and emissions of ozone precursors. The models indicate that the effectiveness of NO, emission reductions is slight in areas with high NO, emissions. However, NO, emissions need to be reduced, on the one hand because NO,, in low NO, areas and in the free troposphere, is a driving force In ozone formation and on the other hand because of the role of NO, in acidification. It is clear that very drastic reductions of more than 755 in both NO, and VOC emissions are needed in order to significantly reduce the ozone concentrations. Reductions that are planned in the Netherlands at the moment for the year 2000 are 33% and 50% for NO, and VOC, respectively. These appear not sufficient. In the Netherlands, this year an evaluation will take place of the present policy concerning the acidification. Especially for NO, further reduction measures are under consideration. The large scale origin of the problem emphasizes the need to give - in addition to policy development on a national scale-
a49
also internationally high priority to abatement o f photochemical air pollution, on both the European and the global level. In this respect the development of protocols within the ECE containing agreements concerning emission reduction of NO, and VOC will mean an important step ahead. REFERENCES National Institute of Public Health and Environmental Protection, Integrated Criteriadocument on Ozone (report nr. 758474002): Bilthoven, September 1987. F.A.A.M. de Leeuw, in R. Guicherit, J. van Ham and A.C. Posthumus (Eds.) , Proceedings Symposium on ozone, Ede, The Netherlands, November 13-14, 1986, Kluwer, Deventer, 1987, pp. 40-44. J.W. Erisman, National Institute of Public Health and Environmental Hygiene, Report nr. 758474001: Bilthoven, June 1987. World Health Organization, Air Quality Guidelines for Europe. WHO regional publications, European series: No.23. WHO, Regional Office for Europe, Copenhagen, 1987.
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T. Schneider et al. (Editors),Atmospheric Ozone Research and its Policy Zmplicntions 0 1989 Elsevier Science Publishers B.V., Amsterdam Printed in The Netherlands
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051
A HEALTH RISK ASSESSMENT FOR USE I N SETTING THE U.S. PRIMARY OZONE STANDARD
S. R. Ha es,' A. S. Rosen aum,' Winkler,4 and H. Richmond
!
T. S. Wallsten,'
R. 6. Whltfielde3 R. L.
'Systems Applications, Inc., 101 Lucas Valley Road, San Rafael, C a l i f o r n i a (USA) 2L.L. Thurstone Psychometric Laboratory, University o f North Carolina, Chapel ill, North Carolina (USA) !Argonne National Laboratory, Decision Analysis and Systems Evaluation Section, Pgonne , I 111no1s (USA) Fuqua School o f Business, Duke University, Durham, North Carolina (USA) 'U.S. Environmental Protection Agency, O f f i c e o f A i r Q u a l i t y Planning and Standards, Durham, North Carolina (USA)
ABSTRACT This paper describes the r e s u l t s o f a U.S. assessment o f the ozone-induced acute pulmonary health r i s k s associated w i t h attainment o f three a l t e r n a t i v e 1hour average ozone standards: 0.12 pprn (current U.S. standard), 0.10 ppm, and 0.08 ppm. Risk r e s u l t s are presented f o r pulmonary function and r e s p i r a t o r y symptoms i n heavy exercisers, the group thought t o be a t highest r i s k t o acute ozone exposure. To examine two a l t e r n a t i v e d e f i n i t i o n s o f response adversity, ozone-induced pulmonary function change i s measured as F E V l decrements o f 210 and 220 percent; respiratory symptoms are characterized by cough, chest discomfort, o r lower respiratory symptoms as a group, a t two d i f f e r e n t severity levels--any (including mild) and moderatelsevere. Rlsk estimates are presented f o r up t o ten U.S. c i t i e s : Chicago, Denver, Houston, Los Angeles, M i a m i , New York, Philadelphia, S t . Louis, Tacoma, and Washington, D.C.
INTRODUCTION The Clean A i r Act requires periodic review and possible r e v i s i o n o f U.S.
pri-
mary (health-based) and secondary (welfare-based) national ambient a i r q u a l i t y standards (NAAQS) to' assure that standards are based on the l a t e s t s c i e n t i f i c information and t h a t primary standards protect p u b l i c health w i t h an adequate margin o f safety. During NAAQS review, t o evaluate whether a l t e r n a t i v e primary NAAQS provide such an adequate margin o f safety, the U.S. Environmental Protect i o n Agency (EPA) assesses such factors as the nature and severity o f the health effects associated w i t h p o l l u t a n t exposure, the degree o f t o t a l human exposure (both indoor and outdoor), and the r i s k s o f adverse health e f f e c t s when the
NAAQS Is attained.
To assist i n i t s review o f the primary NAAQS f o r ozone, the EPA Office of A i r Q u a l i t y Planning and Standards has sponsored an ozone health r i s k assessment. To date, the i n i t i a l p o r t i o n o f the r i s k assessment, which addresses acute ozoneinduced lung effects, based on c l i n i c a l response data from 1- and 2-hour cont r o l l e d human exposure studies, has been completed. Results are discussed by Hayes e t al. (ref.1) and the EPA's ozone s t a f f paper (ref. 2). which i n t e r p r e t s the standard-setting implications o f the e x i s t i n g s c i e n t i f i c data base (described i n the EPA's ozone c r i t e r i a document--ref. 3 ) . Results were reviewed by the U.S. Science Advisory Board's Clean A i r S c i e n t i f i c Advisory Comnittee ( r e f . 4). The EPA i s currently planning t o address subchronic (6-8 hour) and chronic (several month) ozone e f f e c t s i n subsequent phases o f the ozone NAAQS r i s k assessment, and t o examine the e f f e c t o f a l t e r n a t i v e d e f i n i t i o n s o f heavy exercise. The r e s u l t s o f the r i s k assessment w i l l be an important input t o the EPA's overa l l review o f the U.S. ozone primary standard.
RISK ASSESSMENT SCOPE This paper describes the r e s u l t s o f the acute pulmonary function and symptom portion o f the ozone NAAQS health r i s k assessment. Results are presented f o r the attainment o f three a l t e r n a t i v e 1-hour average ozone primary standards: 0.12 ppm (current U.S. Standard), 0.10 ppm, and 0.08 ppm, a l l o f the same s t a t i s t i c a l single expected-exceedance form as the current standard. Risk i s calculated f o r pulmonary function, as measured by FEV1* decrement, o r respiratory symptoms, as measured by cough, chest discomfort, and lower respiratory symptoms taken as a group. To compare a l t e r n a t i v e d e f i n i t i o n s o f response adversity, r l s k i s calculated f o r two response levels: f o r pulmonary function, F E V l decrements o f 210 and 220 percent; and f o r respiratory symptoms, any symptoms (mild, moderate, o r severe) and moderate o r severe only. Two d i f f e r e n t kinds o f r i s k are calculated: benchmark (the r i s k posed by e l evated ambient ozone levels, without reference t o the number o f people exposed) and headcount (the r i s k due t o actual personal exposures, accounting f o r indooroutdoor differences, population a c t i v i t y and m o b i l i t y patterns, and physical act i v i t y ) . I n a l l cases, r i s k r e s u l t s are f o r heavy exercisers, t h a t p o r t i o n o f the population thought t o be most a t r i s k due t o ozone exposure because o f high, exercise-induced v e n t i l a t i o n rates. Benchmark r i s k r e s u l t s are presented f o r 10 U.S. urban areas: Chicago, Denver, Houston, Los Angeles, M i a m i , New York, Philadelphia, St. Louis, Tacoma, and Washington D.C. Headcount r i s k r e s u l t s are pre*A standard spirometric measure o f lung function, the forced expiratory volume i n one second (FEVl) i s defined as the volume o f a i r t h a t can be expelled from the lungs i n the f i r s t second o f a maximal expiration.
053
sented f o r eight c i t i e s ( a l l but Chicago and New York, for which population exposure r e s u l t s were being refined by the EPA a t the time o f the r i s k assessment). Exposure-response relationships are developed from c l i n i c a l data obtained i n three controlled human exposure studies: Avo1 e t a l . (1984) (ref. 5), K u l l e e t al. (1985) (ref. 6), and McDonneli e t al. (1983) (ref. 7). These studies, which are selected from studies reviewed i n the EPA ozone c r i t e r i a document according t o c r i t e r i a described i n r e f . 1, measured acute pulmonary function and symptom response i n heavy exerci s e n . R I S K MODELS
Two types o f r i s k are calculated: benchmark ( r i s k posed by ambient a i r ) and headcount ( r i s k due t o personal exposure). The r i s k o f a harmful health e f f e c t as posed by ambient a i r (benchmark r i s k ) may be thought o f as a hazard (i.e., a source o f potential danger, a c l i f f f o r example). A hazard i s the presence o f a danger, without reference t o the number o f people who come i n contact w i t h it. The r i s k posed t o an individual by personal exposure t o ozone (headcount r i s k ) may be thought o f as the chance that, having encountered the hazard (elevated ozone levels i n t h i s case), a harmful health event w i l l occur (analogous t o a climber on the c l i f f f a l l i n g o f f ) . The development of the r l s k models used i n the r i s k assessment closely follows previous work by Feagans and B i l l e r (refs. 8 and 9). Benchmark r i s k model The benchmark r i s k model calculates the p r o b a b i l i t y t h a t upon j u s t a t t a i n i n g the ozone standard, ambient ozone levels w i l l occur s u f f i c i e n t t o t r i g g e r a health endpoint o f concern (e.g., an FEVl decrement o f 210 percent) i n a l e a s t a
**
specified excess f r a c t i o n (the most sensitive portion) o f the sensitive popul a t i o n (heavy exercisers), one o r mare times during the period o f i n t e r e s t (usua l l y the ozone season). Two sources o f uncertainty enter i n t o benchmark r i s k calculation: (a) uncertainty i n the concentration l e v e l C* t h a t would a f f e c t an
*t
The term "excess" i s used throughout t h i s paper t o r e f e r t o response i n excess o f that which would have occurred under background ozone a i r q u a l i t y conditions. Risk i s measured from t h i s baseline because (a) only concentrations above background are susceptible t o human control and (b) i t i s d i f f i c u l t , given c u r r e n t l y available c l i n i c a l response data, t o characterize the very small, hypersensitive fraction o f the population t h a t a l g h t respond a t ozone levels a t o r below background. While background ozone levels fluctuate during the day, from day t o day, and seasonally, f o r the purposes o f the r i s k assessment, i t i s assumed t h a t 0.04 p p i s a generally representative surrogate f o r the l e v e l o f background ozone.
854
R* excess f r a c t i o n o f the population and (b) uncertainty as t o the value o f the ambient concentrations t h a t would occur when the NAAQS i s j u s t attained. Combining these two sources o f uncertainty y i e l d s the equation used t o compute benchmark r i s k : B(S,R:K,N)
-
[hax 0
f(C*lR*)
P('ob
2 '** Or wre) dC* times i n N periods
where B i s the benchmark r i s k , C* i s the concentration t r i g g e r i n g the health endpoint o f concern i n an R* excess f r a c t i o n o f the sensitive population (heavy exercisers), cobs are the hourly ambient concentrations projected t o occur upon j u s t exactly a t t a i n i n g the standard, K i s the number o f times C* i s equalled o r exceeded during the period o f i n t e r e s t (N averaging periods, e.g., 8,760 hours i n a f u l l year o r less f o r the ozone season), S i s the concentration l e v e l o f the standard, and Cmax i s a concentration value chosen t o be c l e a r l y above the range o f observed values. The exposure-response r e l a t i o n s h i p i s expressed i n the benchmark model by the which i s determined from c l i n i c a l data conditional p r o b a b i l i t y density f(C*lR*), (see refs. 1 and 10). Ambient ozone a i r quality, under conditions o f exact NAAQS attainment, i s represented by the second p r o b a b i l i t y d i s t r i b u t i o n i n eqn. 1. The required d i s t r i b u t i o n i s derived from the time series o f hourly ambient concent r a t i o n values thought t o represent ozone a i r q u a l i t y under conditions o f exact NAAQS attainment, and considers ozone concentration autocorrelation and nonsta-
t i o n a r i t y . Ozone time series projected f o r exact NAAQS attainment are provided t o the r i s k assesment from the EPA's ozone NAAQS population exposure p r o j e c t by Paul e t al. (1986) ( r e f . 11). Headcount r i s k model The headcount r i s k model calculates the expected excess number o f additional health endpoint incidences, o r people affected, w i t h i n a specified period (usua l l y the ozone season). Calculation of headcount r i s k takes i n t o account persona l exposure as people move about, from indoors t o outdoors, and from one place t o another. Sources o f uncertainty entering i n t o headcount r i s k c a l c u l a t i o n i n clude uncertainty i n (a) the exposure-response relationship, (b) indoor and outdoor a i r quality, and (c) population a c t i v i t y and m o b i l i t y patterns. For r i s k assessment purposes, headcount r i s k i s expressed as expected headcount (see r e f .
1 f o r f u r t h e r discussion).
H
=
1'
N N p e 0
i ( C ) dE(CIS)
Expected headcount may be w r i t t e n as follows:
*
855
where i? i s the expected headcount, Np i s the number o f people i n the sensitive popu1a t ion (heavy exercisers), Ne i s the number o f possible exposures per person during the period o f i n t e r e s t (8,760 hours f o r a year, o r less f o r the ozone season), ii i s the expected excess exposure-response function obtained from c l i n i c a l response data (see refs. 1 and lo), and d i i s the nomalized population exposure d i s t r i b u t i o n expected when the area under consideration j u s t a t t a i n s the standard S and i s derived from population exposure d i s t r i b u t i o n s generated by the EPA's ozone NAAQS Exposure Model (03-NEM). Exposure d i s t r i b u t i o n s calculated with the 03-NEM model were developed i n the EPA's ozone NAAQS population exposure project by Paul e t al. (1986) (ref. 11). The OJ-NEM i s an urban-scale population exposure model t h a t calculates ozone exposure f o r up t o 54 d i f f e r e n t population groups, which are distinguished on the basis o f age, occupation, and conmuting patterns. Individual population subgroups, o r cohorts, which are defined on the basis of c o m n age-occupation group and home and work location, are tracked by the 03-NEH f o r the ozone season (9 months t o a year, depending on the urban area), as they move each hour among f i v e d i f f e r e n t microenvironments: indoors-residential, indoors-other, motor vehicle, outdoors near a roadway, and outdoors-other. To characterize uncertainty i n the expected headcount, 90 percent credible intervals about the mean value are estimated based on uncertainty I n the exposure-response relationship (see l a t e r discussion). Results are expressed i n two ways: (a) the number o f times that a response occurs i n heavy exercisers (with possibly more than one response per person) and (b) the number o f people affected (each person i s counted only once). EXPOSURE-RESPONSE RELATIONSHIPS
The EPA ozone c r i t e r i a document and s t a f f paper i d e n t i f y the following sensit i v e groups thought t o be p o t e n t i a l l y a t r i s k t o ozone exposure: (a) i n d i v i d u a l s with pre-existing respiratory disease and (b) the general population o f normal, healthy individuals, p a r t i c u l a r l y those who f o r reasons c u r r e n t l y unknown are unusually responsive t o ozone, and those whose a c t i v i t i e s out o f doors r e s u l t i n increased lung v e n t i l a t i o n (refs. 2 and 3 ) . With regard t o the f i r s t o f these groups, while a given decrement i n lung function may be more serious i n persons with already impaired lung function, the ozone c r i t e r i a document concludes t h a t available data indicate s i m i l a r response i n both healthy groups and those w i t h pre-existing respiratory disease (ref. 2). Therefore, f o r the purposes o f the r i s k assessment, notwithstanding the p o t e n t i a l l y greater seriousness o f a given lung function decrement i n those individuals w i t h chronic r e s p i r a t o r y disease, i t i s assumed t h a t the exposure-response behavior o f the more heavily studied
856
normal, healthy population (as characterized by FEVl decrement and respiratory symptoms) can be used to characterize the response of both groups. Further, the criteria document identifies exercise, which strongly affects 'lung ventilation and thus dosage rate, as an important factor Influencing the effects of ozone exposure. Thus, it is reasonable to presume that the individuals potentially most at risk from such exposure are those who exercise most heavily, with those heavy exercisers who are unusually responsive to ozone (so-called "responders") the most at risk. Applying criteria described in ref. 1, three controlled human exposure studies are judged sufficiently similar in terms of subject population, exercise level, and exposure protocol for use in the risk assessment: Avol et al. (1984) (ref. 5). Kulle et al. (1985) (ref. 6). and McDonnell et al. (1983) (ref. 7). All three studies are of healthy, heavily exercising adults. Avol et al. exposed 50 well-conditioned, mostly male (80 percent) athletes (competitive bicyclists), two of whom had histortes of mild asthma, to ozone concentrations of 0.00 ppm (clean air), 0.08, 0.16, 0.24, and 0.32 ppm. Forty-one subjects had never smoked regularly, 3 were current smokers, and 6 were ex-smokers. Data for 48 subjects were available to the risk assessment. Kulle et al. exposed 20 healthy, nonsmoking, male subjects to ozone concentrations of 0.00, 0.10, 0.15, 0.20, and 0.25 ppm. Eight of the 20 subjects were also exposed at 0.30 ppm. McDonnell et al. divided 135 healthy male subjects into six exposure groups o f approximately 20 subjects each, exposing groups to ozone concentrations of 0.00, 0.12, 0.18, 0.24, 0.32, or 0.40 ppm. In the Kulle and McDonnell studies, subjects were exposed for 2 hours under heavy, intermittent exercise (alternating 15-minute periods of exercise and rest) at 68 L/min (Kulle) and 65 L/min (McDonnell); subjects in the Avol study exercised continuously for 1 hour at 57 L/min. The Avol and Kulle studies exposed the same subjects at all concentration levels; McDonnell et al. exposed different subject groups at each concentration. Spirometric measurements (including FEV1) and symptom response were reported for each study. The Kulle and McDonnell studies reported Individual symptom data (e.9.. cough and chest discomfort), ranked as either none, mild, moderate, or severe. Avol et al. grouped symptoms as either lower respiratory (including cough and chest discomfort), upper respiratory, or nonrespiratory. Individual responses for each symptom within a group were recorded as none, mild but noticeable only upon questioning, mild, moderate, severe, or incapacitating. Responses were reported by symptom group score, which were obtained by sumning the ratings for individual symptoms within the group.
a57
Probabilistic exposure-response relationships are developed for risk assessment purposes according to a methodology described in ref. 1. The effects of ozone are isolated by correcting for the effect of exercise alone, using response data obtained during clean-air exposures. Exposure-response uncertainty is represented in terms of sampling error due to small siunple size using a beta probability distribution constructed according to Bayesian statistical methods (e.g., see ref. 12). Continuous exposure-response curves (with 90 percent credible intervals) are estimated by fitting constrained four-parameter logistic functions to the fractile values of the beta probability distributions. The distributions are forced through the origin since, by definition, ozone-induced response must be zero when the ozone concentration equals zero. Exposure-response uncertainty is represented In two ways. Interlaboratory differences are recognized by separate calculation of risk results f o r all three clinical data sets, with no averaging or other aggregation performed. Intralaboratory uncertainty is accounted for by statistical techniques for calculating sampling error due to small sample size as outlined above. Figs. 1 and 2 present probabilistic exposure-response relationships for acute ozone-induced pulmonary function response in heavy exercisers (FEVl decrements of 210 and 220 percent). Similar relationships for cough and chest discomfort (Kulle and McDonnell) and lower respiratory symptoms as a group (Avol) are contained in ref. 1 for two symptom severity levels: any (including mild) and moderatehevere. As a final step, the exposure-response relationships are adjusted for response under exposure at background ozone levels, taken to be 0.04 ppm. The figures demonstrate a range of response among the three clinical data sets. As shown in ref. 1, the differences among data sets are also present for respiratory symptoms, with the McOonnell subjects reporting systematically greater response than the Avol and Kulle subjects. Although response differences may represent intrinsic variation in subject populations or may be attributable to experimental protocol differences, the reasons for the response variation are currently unknown. RISK RESULTS AND FINDINGS Probabilistic exposure-response relationships are utilized in the benchmark model (risk due to ambient air) and the expected headcount model (risk posed by actual personal exposure) to estimate acute ozone-induced pulmonary function and respiratory symptom risk. Risk results are calculated (ref. 1) for three alternative 1-hour ozone standards (0.12, 0.10, and 0.08 ppm), for ten urban areas, for each o f three clinical data sets (Avol, Kulle, and McDonnell).
858 Benchmark r i s k r e s u l t s and findings I l l u s t r a t i v e benchmark r i s k r e s u l t s f o r FEVl decrements o f 210 and 220 percent are presented i n Fig. 3 f o r S t . Louis. Results for the three a l t e r n a t i v e standards are s i m i l a r t o those f o r S t . Louis across a l l the other n h e urban areas. Results are presented i n the form o f bar charts, w i t h three groups o f bars per figure, corresponding t o the three exposure-response data sets. Each group i s comprised o f four bars. One bar i s f o r as-is conditions, w i t h one each f o r the three a l t e r n a t i v e standards. Each bar i s i t s e l f subdivided i n t o three parts, each corresponding t o a d i f f e r e n t excess percentage o f the exposed heavy exercisers responding. The t o t a l height o f a bar i s the r i s k f o r the 1%-benchmark case, t h a t i s , the p r o b a b i l i t y t h a t a t least an excess 1 percent o f heavy exercisers would respond. It should be noted t h a t t h i s measure o f benchmark r i s k focuses on the r i s k posed by ambient a i r t o the most sensitive individuals. The top o f the v e r t i c a l l y shaded portion o f the bar corresponds t o the r i s k f o r the 5%-benchmark case, t h a t i s , an excess 5 percent o f exposed heavy exercisers responding; s i m i l a r l y , the top o f the slant shaded p o r t i o n corresponds t o the 10%-benchmark case. Interpretation o f the f i g u r e depends on s p e c i f i c a t i o n o f (a) endpoint d e f i n i t i o n (the severity o f health response thought t o be a matter o f regulatory concern, e.g., an F E V l decrement o f 210 o r 220 percent); (b) n%-benchmark d e f i n i t i o n (the minimum excess percentage o f the sensitive population [heavy exercise r s l that must exerience the designated health endpoint before i t becomes a matt e r o f standard s e t t i n g concern); and (c) degree o f r i s k (the magnitude o f the event p r o b a b i l i t y thought t o represent a l e v e l o f concern). The EPA has not endorsed any s p e c i f i c values f o r these three quantities. However, assuming f o r i 1 l u s t r a t i o n purposes only t h a t we are interested i n a 5%-benchmark (the chance o f an excess 5 percent o r more exposed heavy exercisers responding) and an 0.2 degree-of-risk (a chance o f a given health endpoint occurring no more o f t e n than once every f i v e years, on average), Table 1 presents the number o f urban areas whose projected degree o f r i s k i s less than o r equal t o 0.2, f o r each health endpoint, f o r as-is conditions and the three a l t e r n a t i v e standards. Based on the r e s u l t s i n Table 1, the following findings may be stated: (1) Importance o f decision parameters. As can be seen through examination o f Fig. 3 (also see r e f . 1 f o r a more comprehensive demonstration), t h e choice o f decision parameters (health endpoint, nX-benchmark, and degreeo f - r i s k ) i s c r i t i c a l l y important i n the i n t e r p r e t a t i o n o f benchmark r i s k results. (2) S i m i l a r i t y o f r e s u l t s f o r the >10 percent FEVl decrement and any-symptoms Jincludlng mild) cases. Benchmark r i s k r e s u l t s are roughly s i m i l a r f o r three health endpoints: 210 percent F E V l decrement, any (Including mild) cough, and any (including mild) chest discomfort. I n none o f the three
859 cases do many o f the ten urban areas studied achieve the degree-of-risk considered, upon the attainment o f a 0.12 ppm standard. A few additional areas do so upon a t t a i n i n g a 0.10 ppm standard; i n general, nearly a l l areas achieve the specified degree-of-risk f o r a 0.08 ppm standard. (3) S i m i l a r i t y o f r e s u l t s f o r the >20 percent FEVl decrement and moderate/severe symptoms case. Benchmark r i s k r e s u l t s are roughly s i m i l a r f o r the remaining three health endpoints: 220 percent FEVl decrement, moderate/ severe cough, and moderately/severe chest discomfort. I n contrast t o (2). many, i f not a l l , o f the ten urban areas are projected t o achieve the degree-of-risk considered f o r a l 1 three standards, including the current 0.12 ppm NAAQS (with the exception o f r e s u l t s f o r the McDonnell symptom exposure-response data sets, which y i e l d systematicaly higher cough and chest discomfort r i s k estimates than w i t h the Avol and K u l l e data sets). A number o f urban areas also achieve the specified degree-of-risk under as-i s conditions. Headcount r i s k r e s u l t s and findings Headcount r i s k i s characterized i n the r i s k assessment by expected headcount, the number o f people ( o r incidences) i n which a health endpoint i s expected t o occur during the ozone season, given t h a t the ozone standard i s j u s t attained. Expected headcount i s calculated by combining ozone exposure-response r e l a t i o n ships with ozone population exposure d i s t r i b u t i o n s generated f o r heavy exercisers by Paul e t al. (1986) (ref. 11) using the EPA's 03-NEM urban-scale ozone population exposure model. Fig. 4 presents the aggregate expected headcount f o r e i g h t o f the ten study c i t i e s . (Chicago and New York are omitted because EPA ozone exposure calculations f o r those urban areas were being refined a t the time o f the r i s k assess-
TABLE 1 Number o f urban areas (up t o 10) whose projected 5%-benchmark degree-of-risk i s less than o r equal t o 0.2, f o r d i f f e r e n t acute ozone-induced pulmonary effects, f o r as-is conditions and attainment o f alternative 1-hour ozone standards. Number o f urban areas achieving 0.2 degree-of-risk 0.08 ppm Health AS-IS 0.12 PDln 0.10 ppm Endpoint A K M A K M A K M A K M bFEVl
->10%
Cough
>20% Any
Chest discomfort
Mod/Sev Any M/Sev
_ _ _ _ _ _ --- 5 2 -- -- -7 5 --- -- -7 4 --
--
8 - 10 9
-- -- -10 10 --- -- -lo lo
where A = Avol, K = Kulle, and M = McDonnell;
--
--lo-4
10 10
1 -lo lo
3 3 10 10
"--" =
---
---
3 10 3 10 10 10 9 5 -10 10 --
lo lo
10 10
0 (for clarity).
---
860 ment.) Results, which are aggregated by sumning the expected number o f people exposed across the eight urban areas, are presented f o r pulmonary function (represented by F E V l decrements o f 210 and 220 percent). Though not shown, expected headcount was also calculated f o r cough, chest discomfort, and lower resp i r a t o r y symptoms taken as a group. Mean expected headcount i s shown f o r each alternative standard, f o r each c l i n i c a l data set. Exposure-response uncertainty i s represented by 90 percent credible intervals, which are calculated on the basis o f sampling e r r o r introduced by small-sample size. The t o t a l number o f people l i v i n g i n the e i g h t areas i s approximately 25.9 million; the number o f individuals i n population groups exercising heavily enough t o reach the 03-NEM heavy exercise regime used (three o r more 10-minute periods i n an hour, a t heavy o r very heavy exercise) a t l e a s t once during the ozone season t o t a l 9.3 m i l l i o n (or about 36 percent). Primary headcount r i s k findings are as follows: (1) Number o f people responding under NAAQS attainment, aqgregated f o r e i g h t U.S. urban areas. As shown i n Table 2, while there i s p o t e n t i a l l y s i g n i f icant uncertainty i n the absolute value o f the r i s k estimates, a s i g n i f i TABLE 2 Range o f mean number o f heavy exercisers responding (millions) across c l i n i c a l exposure-response data sets * under NAAQS attainment (expected headcount), f o r various acute ozone-induced pulmonary effects, f o r a l t e r n a t i v e 1-hour ozone standards, aqqregated f o r 8 U.S. urban areas. Health Mean number o f people responding under attainment ( m i l l i o n s ) Endpoint AS-IS 0.12 ppm 0.10 ppm 0.08 ppm A F E V ~ 210% -*20% Cough Any Mod/Sev Chest Any discom- Mod/Sev
0.46 0.15 1.22 0.18 0.78 0.06
- 1.72
- 0.95 - 2.73 - 1.43 - 1.30 - 1.15
0.06 0.03 0.20 0.02 0.20 0.02
- 0.22 - 0.12 - 1.34 -- 0.26 0.61 - 0.51
0.05 0.02 0.14 0.01 0.14 0.01
- 0.21 - 0.08 - 1.07 - 0.18 - 0.50 - 0.40
0.04 0.01 0.05 0.01 0.05 0.01
-
0.15 0.05 0.75 0.10 0.36 0.28
TABLE 3 Range o f mean percentages o f heavy exercisers responding across 8 U.S. urban areas (expected headcount), under NAAQS attainment, f o r various acute ozoneinduced pulmonary effects, f o r a l t e r n a t i v e 1-hour ozone standards. Health Range of mean percentages respondinq under attainment 0.10 ppm Endpoint As-1~ 0.12 ppm 0.08 ppm 210% ->20% Cough Any Mod/Sev Chest Any discom- Mod/Sev
bFEVl
1.1 0.5 3.1 0.2 2.7 0.2
-
-
36.3 20.7 41.8 27.7 20.4 18.7
0.5 0.2 0.9 0.1 0.8 0.1
- 4.2 - 2.1 - 18.8 - 4.8 - 8.5 - 7.1
0.1 0.0 0.2 0.0 0.1 0.0
-
3.0 1.3
0.0
15.2 2.9
0.1 0.0 0.1 0.0
7.0
5.8
0.0
-
1.9 0.7 10.1 1.4 4.8 3.8
cant reduction i n the number o f heavy exercisers responding i s projected t o occur, going from as-is conditions t o NAAQS attainment, f o r any o f the three a1ternative standards examined including the current 0.12 ppm standard. (2) Percentages o f heavy exercisers responding under NAAQS attainment, across eight U.S. urban areas. As shown i n Table 3, consistent w i t h (1). a sign i f i c a n t reduction i n the percentage o f heavy exercisers responding i s projected t o occur going from as-is Conditions t o NAAQS attainment. (3) Comparabi 1 it y o f percentages o f heavy exercisers responding. The percentage o f heavy exercisers responding under as-is conditions ranges widely across the eight urban areas. However, f o r a given standard and c l i n i c a l data set, the percentage projected t o respond under attainment i s o f t e n comparable across urban areas. F u l l supporting data f o r t h i s f i n d i n g are provided i n ref. 1. APPLI CAB I LITY A number o f assumptions are made i n the r i s k assessment, each o f which should be kept i n mind when i n t e r p r e t i n g results. Extrapolation o f r i s k r e s u l t s f o r the Avol, Kulle, and McDonnell studies t o the heavily exercising population a t large i s affected by a number o f considerations, including the following: (1) Interaction between ozone and other pollutants. It i s assumed t h a t the health endpoints o f i n t e r e s t are due solely t o ozone. This i s consistent with the r e s u l t s o f Avol e t al. (1984) and conclusions i n the EPA ozone c r i t e r i a document. (2) Reproducibility o f ozone-induced responses. It i s assumed t h a t ozone-induced pulmonary responses are reproducible i n individuals. Such an assumption i s supported by the EPA c r i t e r i a document and analyses o f study data sets conducted by Hayes e t al. (1987b) (ref. 13). (3) @. The r i s k assessment i s assumed t o apply t o a l l heavily exercising individuals regardless o f age. However, research studies discussed i n the ozone c r i t e r i a document have reported pulmonary function decrement, b u t not symptomatic response i n children under ozone exposure. Therefore, headcount r i s k , which r e l l e s on exposure estimates t h a t include children, may overstate t r u e symptom r i s k . However, pulmonary function r i s k e s t i mates are not affected, nor does any lack o f symptoms necessarily i n d i cate t h a t the b i o l o g i c a l processes associated w i t h ozone symptoms i n adults are not also present i n children. (4) Sex. It i s assumed t h a t exposure-response data obtained i n the Avol, Kulle, and McDonnel1 studies apply t o both males and females. To the extent t h a t females are more responsive than males (there i s some l i m i t e d evidence t o t h i s e f f e c t f o r lung function impairment as measured by
862
the r i s k estimates may be understated i n r e l a t i o n t o the percentage o f heavy exercisers who are female. (5) Smoking status. The r i s k assessment i s assumed t o apply t o a l l heavy exercisers, regardless o f t h e i r smoking status. There i s some l i m i t e d e v i dence t h a t smokers may be less responsive t o ozone exposure than nonsmokers. To the extent t h a t t h i s i s SO, the r i s k estimates may be overstated i n r e l a t i o n t o the percentage o f heavy exercisers who are smokers. (6) Exercise group. The r i s k assessment assumes t h a t the exposure-response relationships obtained from the Avol, Kulle, and McDonnell studies apply t o a l l heavy exercisers. The ozone c r i t e r i a document defines heavy exercise as lung v e n t i l a t i o n rates o f 44-63 L/min and very heavy exercise as ->64 L/min. The Avol study (57 L/min) corresponds t o the mid-to-upper port i o n o f the heavy exercise range (54 L/min i s the midpoint). The McDonn e l l study (65 L/min) f a l l s j u s t i n the lowest p o r t i o n o f the very heavy exercise range, w i t h the K u l l e study (68 L/min) some 5 percent higher. To the extent t h a t exercise rates among any p a r t i c u l a r heavy exercisers are lower than i n the subject studies, pulmonary f u n c t i o n and symptom r i s k s m a y be less than estimated. The extent t o which t h i s i s the case i s unknown and must be regarded as an additional source o f uncertainty. To further address t h i s uncertainty, EPA plans i n subsequent work t o examine the e f f e c t o f a l t e r n a t i v e d e f i n i t i o n s o f heavy exercise on r i s k assessFEVl),
ment results. (7) Attenuation o f response. The r i s k assessment assumes t h a t ozone-induced
response i s not affected by previous ozone exposure history. The extent o f attenuation and/or enhancement o f ozone response due t o previous exposures cannot be addressed q u a n t i t a t i v e l y i n the r i s k assessment and must, therefore, be regarded as an additional uncertainty. ACKNOWLEDGMENTS The authors wish t o g r a t e f u l l y acknowledge the assistance, comnents, and suggestions o f a l l who contributed t o t h i s work, p a r t i c u l a r l y the following: a t EPA, Mr. Bruce Jordan, Mr. Thomas McCurdy, and O r . David McKee; health researchers, Drs. Edward Avol, Thomas Kulle, and William McDonnell, whose c o n t r o l l e d human exposure data are the basis o f the ozone exposure-response r e l a t i o n s h i p s used; an independent consultant t o EPA, O r . William B i l l e r : a t P E I Associates Inc., Mr. Roy Paul and Mr. James Capel; and a t Systems Applications, Or. C. Shepherd Burton, O r . Thomas Permutt, and Ms. Marianne Dudik.
863
REFERENCES S.R. Hayes, A.S. Rosenbaum, T.S. Wallsten, R.G. Whitfield, and R.L. Winkler, Assessment o f Lung Function and Symptom-Health Risks Associated w i t h Attainment o f Alternative Ozone NAAQS (Draft Final), Systems Applications, Inc., San Rafael , California, 1987 (SYSAPP-87/171).
U.S. Environmental Protection Agency, A i r Q u a l i t y C r i t e r i a f o r Ozone and Other Photochemical Oxidants, Research Triangle Park, North Carol ina, 1986 (EPA-600/8-84/020a-ef). U.S. Environmental Protection Agency, Review o f the National Ambient A i r Qua1i t y Standards f o r Ozone: Preliminary Assessment o f S c i e n t i f i c and Technical Information (Revised Draft), Research Triangle Park, North Carolina, 1987.
Clean A i r S c i e n t i f i c Advisory Cornittee, Transcript o f the December 1987 Meeting o f the Clean A i r S c i e n t i f i c Advisory Cornittee, U.S. Science Advisory Board, Washington, D.C., 1987. E.L. Avol, W.S. Linn, T.G. Venet, D.A. Shamoo, and J.D. Hackney, Comparative Respiratory Effects o f Ozone and Ambient Oxidant P o l l u t i o n Exposure During Heavy Exercise, J. A i r Pollut. Control Assoc., 34 (1984) 804-809.
T.J. Kulle, L.R. Sauder, J.R. Hebel, and M.D. Chatham, Ozone Response Relationships i n Healthy Nonsmokers, Am. Rev. Respir. Dis., 132 (1985) 36-41. W.F. McOonnell, D.H. Horstman, M.J. Hazucha, E. Seal, Jr., E.D. Haak, S. Salaam, and D.E. House, Pulmonary Effects o f Ozone Exposure During Exercise: Dose-response Characteristics, J. Appl. Physiol.: Respir. Environ. Exercise PhySiOl. , 54 (1983) 1345-1352. T.B. Feagans and W.F. B i l l e r , Risk Assessment: Describing the Protection Provided by Ambient A i r Q u a l i t y Standards, Environ. Profess., 3 (1981) 235-247.
T.B. Feagans and W.F. B i l l e r , A General Method f o r Assesslng Health Risks Associated w i t h Primary National Ambient A i r Q u a l i t y Standards, U.S. Environmental Protection Agency, Office o f A i r Q u a l i t y Planning and Standards, Research Triangle Park, North Carolina (May 1981 d r a f t ) . 10 S.R. Hayes, M. Moezzi, T.S. Wallsten, and R.L. Wlnkler, An Analysis o f Symptom and Lung Function Data from Several Controlled Ozone Exposure Studies, Systems Applications, Inc., San Rafael , Cal ifornia, 1987 (SYSAPP-86/120).
11 R.A. Paul, T. Johnson, A. Pope, and A. Ferdo, National Estimates o f Exposure t o Ozone Under Alternative National Standards (Draft), P E I Associates, Inc. , Durham, North Carolina, 1986. 12 R.L. Winkler, An Introduction t o Bayesian Inference and Oecisfon, Holt, Rinehart and Winston, New York, 1972.
13 S.R. Hayes, M. Moezzi, T.S. Wallsten, and R.L. Winkler, An Analysis o f Symptom and Lung Funciton Data from Several Controlled Ozone Exposure Studies, Systems Applications, Inc., San Rafael , California, 1987b (SYSAPP-86/120).
PROBABILISTIC EXP.-RESP. RELAT. (Kulle Data)
PROBABILISTIC EXP.-RESP. RELAT. (Avol Data) _-D(FEV1) >= 1% 1.01.
n
.
Heavy Exercise.Variws Credii Levels 3
__ D(FEV1)>= 10%. Heavy Exercise,Various CmdiMe Levels --
-
- O.%(upper)
- .!5O(middle)
n
E
-
0.4
w
U Y
U
2
%
h
e2
0
2
0.2
a U
U
0.1
0.00.0
0.0
0.1
0.2
0.3
.05(bWer)
0.6
IA
\L
0.4
OZO~CONCE~AlDN@pn)
0.2
0.3
PROBABILISTIC EXPrAESP. RELAT. (McDonnell Data) -- D(FEV1) >= 10%. Heavy Exercise, Various Credble Levels 1.O-r
0.0
0.1
0.2
P
0.3
0.4
OZONE COWCENTRATKm(ppm)
Fig. 1. Probabilistic exposure-response relationships (with 90 percent credible intervals) for acute ozone-induced pulmonary function change i n heavy exercisers (FEV1 decrement 2 10 percent).
0.4
PROBABILISTIC EXP.-RESP. RELAT. (4
__ D(FEV1)
>= 20%. Heavy Exercise. Various Cred
, Levels --
-- D(FEV1)>= 20%. Heavy Exercse. Various Credlble Levels --
I
I-
-
Y
.os(lOmw)
06
Y
0 0
01 0 2 03 OZONE C0NcEHTRATK)N @pm)
4
0.2
0.1
0.0
OZONE C
O
N
C
0.3 0.4 E (p(nn) ~ ~
PROBABILISTICEXPAESP. RELAT. (McDonnell Data)
-- D(FEV1) >= 209c. Heavy Emmse. Various Credible Levels -I
1.0,,
n
E Y Y U.
a
o.81 0.6
e Y
a
E 0.0
0.1 0.2 0.3 OZONE CONCENTRATION (ppm)
0.4
Fig. 2. Probabilistic exposure-response relationships (with 90 percent credible intervals) for acute ozone-induced pulmonary function change in heavy exercisers (FEV1 decremnt 2 20 percent).
866
BENCHMARK RISK => ( O X . Haavy Exarclma
-- D(fEV1)
Avo1
*Ul*
--
YcDonndl
Alhmattvr Ozona Standordm (ppm)
BENCHMARK RISK
-- D(TfV1)
I> Z O X , Haavy Erarclra
Arol
--
YcOonndl
Alkmaltvr Ozone Standard@(ppm)
St.Lou1r
Fig. 3. Benchmark risk in St. Louis for three alternative U.S. ozone standards, (probability of F E V l decrements of 2 10% and 2 20 percent occurring at least once during the ozone season If exposed under heavy exercise): for three clinical exposure-response data sets (Avo1 , Kul le, and McOonnell).
23.0
z
I
Am-b
L c4
2
20.0
X
W
I
c
3
tS.0
-
0
P
I
4.4
10.0
2
.I0
-
c
0
an T
.I1
a W
A#
d,
-
HEADCOUNT RISK (Pooplo)
-- D(FEV1) E> 20%. Weoq Enerclrr --
-
CI
0 X
W
c
C
au
U 0
I
P
c
e
n W
lull8
YcDonnall
Altomoth Ozone ttondordr (ppm)
Eight City Aggrogation
Fig. 4. Expected headcount for three a l t e r n a t i v e U.S. ozone standards, aggregated for eight U.S. urban areas, for FEVl decrements of 10 and 2 20 percent (number of heavily exercising people respondlng durlng the ozone season).
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T. Schneider et al. (Editors), Atmospheric Ozone Research and its Policy Implications 0 1989 Elsevier Science Publishers B.V., Am~terdam-Printed in The Netherlands
ESTIMATED ECONOMIC CONSEQUENCES OF OZONE ON AGRICULTURE: THE U.S.
869
SOME EVIDENCE FROM
R.M. Adams Department o f A g r i c u l t u r a l and Resource Economics, 220 B a l l a r d Extension H a l l , Oregon State University, C o r v a l l i s , Oregon 97331-3601 ABSTRACT Tropospheric ozone a t ambient l e v e l s reduces crop y i e l d s . These reduct i o n s imply economic costs t o society. T h i s paper r e p o r t s estimates o f the economic consequences o f ozone changes on U.S. a g r i c u l t u r e , using recent data and procedures from an i n t e g r a t e d assessment program. Results suggest t h a t reductions i n ozone w i l l l e a d t o economic b e n e f i t s o f from $1 t o $3 b i l l i o n U.S. d o l l a r s p e r year. I m p l i c a t i o n s f o r s t r a t o s p h e r i c ozone changes are also discussed. INTRODUCTION An adequate supply o f a g r i c u l t u r a l products i s fundamental t o t h e welfare o f most societies. I t i s n o t s u r p r i s i n g then t h a t p o t e n t i a l adverse e f f e c t s o f environmental change on a g r i c u l t u r e generates considerable i n t e r e s t . The e f f e c t s o f a c i d deposition, gaseous a i r p o l l u t a n t s , and s t r a t o s p h e r i c ozone d e p l e t i o n on a g r i c u l t u r a l p r o d u c t i v i t y are being evaluated i n t h e U.S., Europe and elsewhere. I n t h e U.S., t h e economic consequences o f such e f f e c t s are a l s o assessed as i n p u t i n t o the process o f r e g u l a t i n g a i r p o l l u t a n t s . The a g r i c u l t u r a l e f f e c t s o f tropospheric ozone were r e c e n t l y studied by t h e U.S. Environmental Protection Agency’s National Crop Loss Assessment Network (NCLAN). The structure, p r o t o c o l s and f i n d i n g s o f t h i s program are w e l l documented [see, f o r example, r e f . 1 and 21. Results i n d i c a t e t h a t tropospheric ozone i s one o f the major p o l l u t a n t s i n terms o f y i e l d losses. Related a r t i c l e s r e p o r t p r e l i m i n a r y estimates o f t h e economic e f f e c t s o f these y i e l d changes on U.S. a g r i c u l t u r e [ r e f . 31. Improved estimates o f the economic e f f e c t s o f troposphere ozone are now a v a i l a b l e , based on f i n a l f i n d i n g s from NCLAN research [ r e f . 41. The o v e r a l l o b j e c t i v e o f t h i s paper i s t o summarize these more recent NCLAN estimates o f t h e economic e f f e c t s o f ozone on U.S. a g r i c u l t u r e . Procedures, r e s u l t s and p o l i c y i m p l i c a t i o n s o f a1 t e r n a t i v e tropospheric ozone l e v e l s and standards are b r i e f l y discussed. These f i n d i n g s i n d i c a t e the economic e f f e c t s o f emissions o f ozone precursors i n t o t h e troposphere. There i s also a p o s s i b l e l i n k between s t r a t o s p h e r i c ozone depletion, tropospheric ozone l e v e l s and crop p r o d u c t i v i t y , which we explore a t t h e conclusion o f t h i s paper.
METHODOLOGY A bioeconomic assessment r e q u i r e s c r i t i c a l i n p u t from several d i s c i p l i n e s i n order t o l i n k physical and b i o l o g i c a l phenomenon t o an economic v a l u a t i o n model. The s t a r t i n g p o i n t i n t h i s assessment i s d e f i n i t i o n o f a l t e r n a t i v e scenarios concerning tropospheric ozone changes, and s p e c i f i c a l l y how changes i n ozone w i l l r e s u l t i n changes i n items t h a t people value, i.e., t h e q u a n t i t y and q u a l i t y o f food and f i b e r . T h i s i n f o r m a t i o n i s obtained from appropriate crop y i e l d response models t h a t l i n k y i e l d changes t o changes i n ozone. Such crop y i e l d changes were estimated from data generated i n t h e NCLAN program. The f i n a l step o f the assessment process i n v o l v e s applying an appropriate model t o measure t h e economic a f f e c t s o f these y i e l d changes. The assessment model used here i s an updated v e r s i o n o f t h e economic model used i n e a r l i e r economic analyses o f tropospheric ozone [ r e f . 3 1 . I n general, t h e model and i t s a p p l i c a t i o n i s conceptually s i m i l a r t o t h e numerous induced change analyses found i n t h e a g r i c u l t u r a l economics l i t e r a t u r e . S p e c i f i c a l l y , the economic model i s a s p a t i a l e q u i l i b r i u m model formulated as a mathematical programming problem t o represent production and consumption o f 24 primary a g r i c u l t u r a l commodities i n t h e U.S., i n c l u d i n g both crop and l i v e s t o c k products (see Table 1). Processing of a g r i c u l t u r a l products i n t o secondary commodities (e.g., d a i r y products, meat products) i s a l s o included. The production and consumption sectors a r e made up o f a l a r g e number o f i n d i v i d u a l s , each o f whom operates under c o m p e t i t i v e market conditions.
This
leads t o a model which maximizes t h e area under t h e demand curves l e s s t h e areas under t h e supply curves. T h i s area, known as economic surplus o r net s o c i a l benefit, i s an accepted measure o f s o c i a l w e l f a r e i n market o r i e n t e d economies. Both domestic and f o r e i g n consumption (exports) are considered. Exports (foreign consumption) are p a r t i c u l a r l y important f o r many U.S. crops, i n c l u d i n g maize, soybeans and o t h e r feed g r a i n s . The assumptions and p r o cedures of t h i s methodology are discussed i n more d e t a i l i n Adams, Hamilton, and McCarl [ r e f . 41. TABLE 1 Primary commodities included i n t h e economic model, Cotton Corn Soybeans Wheat Sorghum Oats Bar1ey Rice
Sugar Cane Sugar beets Silage Hay Milk Culled d a i r y cows Culled d a i r y calves Culled beef cows
L i v e heif e r s L i v e calves Nonfed calves f o r slaughter Fed calves f o r slaughter Calves f o r s l a u g h t e r Hogs f o r slaughter Feeder p i g s
871
The model consists of two components, a set of micro or farm level models integrated with a national (sector) level model. Producer level behavior is captured in production relationships that portray the physical and economic environment of agricultural producers in 63 homogeneous production regions, encompassing the 48 contiguous states. The farm level supply response generated from the 63 individual regions are linked to national demand through the sector model objective function which features demand relationships for various market outlets for the modeled commodities. The model simulates a long-run, perfectly competitive equilibrium as reflected in 19801983 economic and environmental parameters. EXDOSUre ResDonse Functions Yield response data are needed to predict crop yield changes from ozone changes. NCLAN ozone exposure-response experiments on cultlvars of 14 distinct crops are used to estimate response functions for eight major field crops; alfalfa, barley, corn, cotton, hay (a clover-fescue mix), sorghum, soybeans, and wheat. In addition, data from a non-NCLAN rice experiment were used to estimate yield effects for rice [ref. 51. Ozone levels are transformed into a seasonal 7- or 12-hour average exposures for each experimental treatment. Functional correspondence between seasonal exposures and yields is estimated using the Weibull function. The flexible, nonlinear Weibull function is biologically reasonable and captures aspects of plant response to ozone that linear forms do not, with important economic consequences [ref. 61. Response functions were obtained from field experiments for each cultivar and site for each crop, as well as combinations across crop cultivar experiments. The parameter estimates used in the analysis are presented in Table 2, along with the standard errors and correlations. For this analysis, only the aggregate of all sites and cultivars of a crop (e.g., soybeans) are used. It should be noted that the use of pooled response is conservative (understates yield effects) because slightly larger yield effects would result from a given reduction in ozone if producers shifted cultivars in the face of differential response to ozone. Ozone Data and AssumDtions Use of the NCLAN response functions requires estimates of ozone levels in agricultural areas consistent with the NCLAN exposure measure (7- or 12-hour daily maximum). Using EPA's Storage and Retrieval of Aerometric Data System (SAROAD) ozone readings for rural areas, Lefohn et al. [ref. 71 calculated monthly averages on both a "maximum seven hour' and a "maximum twelve hour' basis for a five-year period. This was accomplished through use of the kriging spatial interpolation procedure.
872
The estimated regional seasonal 7- and 12-hour mean ozone levels for each year define the actual base or benchmark level for use In the economic analysis. Since the model is intended to represent equilibrium behavior over a recent period, the average 1981-1983 ozone levels are used as the base ambient ozone. This base ozone level is then altered to develop changes in ozone for use in the response function, as described subsequently. TABLE 2 Weibull Model Parameter Estimatesa Cropb c A1 fa1 fa Corn Cotton Forage Soybeans Rice Sorghum Spring Wheate Winter Wheat
Ud 178 124 111 139 107 202 314 186 137
(28) ( 2) ( 5) (15) ( 3) (50) (162) (40) ( 5)
C
2.07 2.83 2.06 1.95 1.58 2.47 2.07 3.20 2.34
( .55) ( .23) ( .33) ( .56) ( .16) (1.10) (1.22) (1.86) ( .34)
aThe Weibull is y = a exp [-x/oIc. The a parameter is normalized to unity. bThe pooled responses of all crop cultivars have been used. c12 hour averages have been used except for rice, sorghum, spring wheat and winter wheat, which use 7-hour averaging times. dStandard errors are in parentheses. Erowina Windows The growing season for each crop and region is modeled to approximate crop exposure to ozone. Growing seasons vary because producers have flexibility on planting (and hence harvesting) dates. There are also phenological periods when plants are more sensitive to ozone, e.g., during flowering of soybeans, or when growth rates differ. This results in a distribution of plant growth (yield sensitivity) between the planting and harvesting dates. The development of differentially weighted growing windows explicltly accounts for the distribution of planting dates and growth rates for each crop in concert with the experimental details which give rise to the exposure-response relations. By adjusting these dates and weights on a state-by-state and crop-by-crop basis, the estimated ozone exposures provide a good approximation to real world conditions. Moisture Stress An important issue in analyzing pollutant stress on crops is the interaction with moisture stress, as moisture stress is one of the primary factors
a73 a f f e c t i n g crop y i e l d s . A number o f NCLAN experiments t e s t e d p o t e n t i a l i n t e r a c t i o n s between ozone and moisture stress. To address t h i s r e l a t i o n ship, King [ r e f . 81 modeled drought e f f e c t s w i t h a p l a n t process model f o r major crops (maize, soybeans, cotton, wheat, and forage) i n t h e Corn B e l t and adjacent areas. This simulation process p r o j e c t s diminished s e n s i t i v i t y t o ozone when y i e l d s are reduced concurrently by moisture stress. The d e t a i l s o f the procedure can be found i n Adams, Glyer and McCarl [ r e f . 41. Scenarios for Chanaes i n Ozone A l t e r n a t i v e ozone l e v e l s (scenarios) are r e q u i r e d t o simulate t h e economic e f f e c t s o f changes from c u r r e n t l e v e l s . Previous assessments use a range o f assumptions i n developing ozone changes, i n c l u d i n g p r o p o r t i o n a l changes (from a base year) and s p e c i f i c seasonal averages. I n t h i s analysis, both proport i o n a l changes and changes t i e d t o seasonal l e v e l s are evaluated. The proportional changes provide a comparison w i t h t h e r e s u l t s from previous studies. Seasonal standard scenarios are developed t o approximate a standard proposed by t h e U.S. EPA [ r e f . 91. The standard i s a seasonal average i n c o r p o r a t i n g a three-month average o f d a i l y 7-hour averages. The 7-hour average i s the d a i l y average o f the seven (consecutive) one hour periods i n a day w i t h the highest average. The three-month average i s t h e t h r e e consecutive months w i t h t h e highest average. Any proposed seasonal standard must recognize t h e s t o c h a s t i c nature o f a i r p o l l u t i o n and t h e weather and human elements which cause i t . Because o f p o l l u t i o n v a r i a b i l i t y , c u r r e n t standards f o r ozone i n t h e U.S. use t h e highest one hour average on t h e second highest p o l l u t i o n day. To a l l o w f o r t h i s v a r i a b i l i t y , scenarios need t o r e f l e c t d i f f e r e n t p r o b a b i l i t i e s t h a t the seasonal standard w i l l be exceeded i n a given year. Development o f these s t o c h a s t i c p r o p e r t i e s f o r each seasonal standard i s presented i n Adams, Glyer and McCarl [ r e f . 41. RESULTS AND IMPLICATIONS Successful v a l i d a t i o n provides one i n d i c a t i o n t h a t t h e economic model i s acceptable f o r evaluating t h e e f f e c t s o f ozone on a g r i c u l t u r e . To e s t a b l i s h t h a t t h e model i s a reasonable approximation t o t h e a g r i c u l t u r a l sector over t h e period o f i n t e r e s t , we t e s t the model outputs w i t h actual values f o r the base years, 1981-1983. Table 3 provides a comparison o f actual average p r i c e s and q u a n t i t i e s w i t h those determined by t h e model a t 1981 t o 1983 average ambient ozone and moisture s t r e s s conditions. As i s evident, t h e p r i c e s for a l l commodities match reasonably w e l l ( w i t h i n 5 percent) w h i l e the q u a n t i t i e s g e n e r a l l y understate actual l e v e l s by.5 t o 10 percent.
874 Levels and Seasonal Standards The economic e f f e c t s o f a l t e r n a t i v e ozone l e v e l s o r standards are captured by t h e chanqes i n t h e o b j e c t i v e f u n c t i o n values f o r each ozone scenario when compared with t h e base s o l u t i o n . Table 4 presents t h e changes i n economic value (economic surplus) from t h e base f o r 10, 25 and 40 percent changes i n ozone from 1981-1983 ambient l e v e l s . The t a b l e a l s o contains some example seasonal standards. TABLE 3 t!lodel
Prices and Ouanti t i e s vs. Actual: Prices Cornnod t Y Model Actual (S per u n i t ) 281.90 Cotton 284.97 Corn 2.68 2.68 5.73 5.65 Soybeans Wheat 3.56 3.50 Sorghum 2.53 2.50 Rice 8.13 8.01 Bar1ey 2.23 2.20 1.55 1.67 Oats 65.76 Hay 62.08
1981-1983
Ouantities ode1
Actual (nlillions)
10.24 6,452.28 2,018.02 2,260.78 662.00 120.00 425.18 503.04 76.82
11.79 6,839.00 1,915.00 2,419.00 730.00 145.00 498.00 526.00 82.00
1,283.61 139.38 135.81 87.60
1,359.80 151.70 156.25 18.37
..................................................................
Milk Pork Fed beef Wonfed beef
13.35 169.54 232.27 131.44
13.65 165.90 239.70 145.15
Prices f o r a l l crops are d o l l a r s per bushel, except f o r c o t t o n (S per 480 pound bale), r i c e (S per hundredweight), and s i l a g e and hay (S p e r ton). Meat p r i c e s are S per cwt. and are average r e t a i l p r i c e s f o r f i n i s h e d meat products. Source:
USDA, ERS, S t a t i s t i c a l B u l l e t i n No. 715, Washington, D.C. USDA, A a r i c u l t u r a l S t a t i s t i c s , 1984. Washington, D . C .
I n aggregate terms the economic e f f e c t s o f ozone changes are substant i a l . For example, when ozone i s reduced u n i f o r m l y by 25 percent i n a l l regions, t h e estimated economic b e n e f i t s are $1.890 b i l l i o n ( i n 1982 U.S.$) f o r t h e c u r r e n t assessment. The 40 percent ozone r e d u c t i o n increases benef i t s t o s o c i e t y t o $2.780 b i l l i o n . To place these values i n perspective, the n e t value o f a l l crops included i n t h e model was approximately $65 b i l l i o n (U.S.)
i n 1982. Thus, these changes i n economic value a r e from 3 t o 5
percent o f gross crop value. This study d i f f e r s from previous analyses by e v a l u a t i n g p o t e n t i a l seasonal standards f o r tropospheric ozone i n t h e U.S.
One seasonal stan-
dard used here represents ozone c o n d i t i o n s which would p r e v a i l i f s t a t e s d i d n o t exceed t h e seasonal standard most o f t h e time (95 percent, o r 19 years o u t o f 20).
By i n c l u d i n g t h e p r o b a b i l i s t i c aspects o f t h e standard, the
a75 analysis captures both average levels and year-to-year variability in ozone. The focus here is on a seasonal standard of 50 ppb (parts per billion). This standard falls midway in the range of potential seasonal standards 140-60 ppb) suggested by OAQPS [ref. 91. The 50 ppb standard is sufficiently high that some states do not violate the standard, while other states must reduce pollution levels. To test the sensitivity of the seasonal standard to the extent and nature of ozone reductions, the probability of compliance is also varied to represent both 90 and 50 percent compliance levels. The benefits of a 25 percent reduction and a 50 ppb standard with 95 percent compliance (50/95) are similar, $1.890 and $1.674 billion, respectively. In aggregate terms, producers gain relatively more with the seasonal standard than with the constant 25 percent rollback (46 vs. 30 percent of total benefits). This difference is due to the regions (and hence the crops) which are most affected. The distribution o f consumer gains is constant across the two scenarios, with domestic consumers obtaining over half (5659%) of the benefits. At the regional level the effects on producers differ markedly between the seasonal standard and the constant percentage reduction. Producers in higher ozone areas, especially those with greater variability, gain most with the 50/95 standard. This is due to relatively low ozone levels in these regions (and hence little yield improvement), while crop prices decline by the same amount across all regions. As noted before, the 50 ppb standard is a "midpoint" seasonal standard. Alternative seasonal levels can be tested by varying the compliance parameter. Referring back to Table 4, for 90 and 50 percent compliance with a 50 ppb standard (50/90, 50/50), respective increases in economic surpluses of $1.465 and 5.853 billion result. In all cases, the gains of small ozone reduction accrue mainly to producers (over half for the 50/90 standard), while greater reductions consistently favor consumers. Consumer benefits favor the domestic sector. An implication o f these evaluations is that the degree o f compliance is an important element in setting a standard. Ignoring year-to-year variability in implementing a seasonal standard would be similar to choosing a standard with only a 50 percent o f not exceeding that seasonal level. Further, from a regulatory perspective, it is unreasonable to assess the impact of a standard by assuming that all regions exactly equal the proscribed level. lmpact o f Ozone Reductions on the Cost of U.S. Farm P r o a r m Due to government intervention, the agricultural industry in the U.S. (and the EEC) typically responds to a mix of market and institutional signals. Since agriculture is also affected by other government policies such as air
876 TABLE 4 Changes i n Economic Surplus A r i s i n g from A l t e r n a t i v e Ozone Scenarios: Constant Percentage Reduction vs. Seasonal Standardsa
-10% -25% -40%
808 1,890 2,780
Producers’ Surol us S Millions 286 572 683
50/95b 50/90 50/50
1,674 1,465 853
769 738 63 1
Ozone tion
Total Surol us
Consumers’ SurDl us
Consumers ’ Sum1us Exoort Domest 1c
A
522 1,318 2,097
313 738 1,127
209 580 970
905 727 222
53 1 473 186
374 254 136
.........................................................................
“Changes i n economic surplus are t h e changes from t h e base s o l u t i o n . bThese numbers r e f e r t o scenarios f o r changes i n ozone l e v e l s . 50/95 i s a 50 ppb seasonal standard w i t h 95 percent p r o b a b i l i t y o f n o t exceeding the l e v e l i n any given year, as explained i n t h e t e x t . qua1 i t y standards, i t s s t a t u s as a revenue-supported i n d u s t r y has imp1 i c a t i o n t i o n s when examining e f f e c t s o f ozone changes. For example, i f ozone reduct i o n s increase crop y i e l d s and hence output, c o s t t o government farm support programs may increase. Past estimates o f b e n e f i t s from ozone reductions t y p i c a l l y have n o t included such farm program costs because o f t h e d i f f i c u l t y i n modeling i n t e r a c t i o n s between long-term environmental p o l i c i e s and t h e s h o r t term p r o v i s i o n s o f U.S. farm programs as w e l l as t h e complexities and y e a r - t o - y e a r v a r i a t i o n s i n farm support p r o v i s i o n s . The procedure we use t o address t h e e f f e c t s o f ozone r e d u c t i o n s on U.S. Farm Program costs c o n s i s t s o f t h r e e stages. I n t h e f i r s t stage t h e t a r g e t p r i c e s are introduced f o r crops covered i n t h e 1985 Farm Program (cotton, corn, wheat, r i c e , barley, sorghum and oats).
Producers are presumed t o use
t h e t a r g e t p r i c e s as t h e i r expected market prices. Stage two f i x e s t h e q u a n t i t i e s o f program crops i n t h e model a t t h e l e v e l s determined by producer response t o t h e t a r g e t p r i c e s i n t h e f i r s t stage. Market c l e a r i n g p r i c e s f o r these new q u a n t i t i e s r e s u l t from t h e Stage two s o l u t i o n . The d i f f e r e n c e between the t a r g e t p r i c e (Stage 1) and t h e market c l e a r i n g p r i c e (Stage 2), times t h e q u a n t i t y produced (Stage 2), i s equal t o t h e d e f i c i ency payment f o r each program crop. These steps are then repeated using the y i e l d adjustments associated w i t h changes i n ozone l e v e l s . Comparison o f the Farm Program solutions, i n c l u d i n g d e f i c i e n c y payments, b e f o r e and a f t e r t h e ozone adjustment provides an estimate o f t h e p o s s i b l e impact o f t h e 1985 Farm Program on t h e b e n e f i t s from changes i n ozone l e v e l s . The r e s u l t s o f i n c l u d i n g farm program costs are r e p o r t e d i n Table 5. These increased costs t o s o c i e t y reduce t h e b e n e f i t s o f ozone c o n t r o l reported i n Table 4 by 15 percent. This i m p l i e s t h a t t h e a g r i c u l t u r a l
077
b e n e f i t s t o s o c i e t y o f ozone c o n t r o l are reduced when farm programs are i n place. However, i t may be inappropriate t o ascribe t h i s r e d u c t i o n i n b e n e f i t s from ozone c o n t r o l t o the cost o f t h a t environmental c o n t r o l program
[lo]. Rather, i t i s t h e increased cost o f t h e c u r r e n t Farm Program under the new "techno1 o g i c a l 'I conditions. TABLE 5 I n t e r a c t i o n Between Ozone Reductions and 1985 U.S. Farm B i l l Provisions
Scenario
25x
Change i n Economic SurDl us IS m i l l i o n s )
With 1985 Farm B i l l
1,621
Without 1985 Farm B i l l
1,890
Chanqe i n Estimates
lsJwhsl 269
A With 1985 Farm B i l l
1,438
Without 1985 Farm B i l l
1,674
236
THE EFFECTS OF STRATOSPHERIC OZONE DEPLETION ON AGRICULTURE Stratosphere ozone d e p l e t i o n has the p o t e n t i a l t o adversely a f f e c t a g r i c u l t u r a l p r o d u c t i v i t y . Reduction i n s t r a t o s p h e r i c ozone increase u l t r a v i o l e t f l u x i n t h e "Bll range (UV-B), which reduces y i e l d s o f some c u l t i v a r s o f soybeans and wheat [ r e f . 111. I n addition, increased UV-B r a d i a t i o n w i l l increase tropospheric ozone formation (USEPA). Thus, s t r a t o s p h e r i c ozone reductions are l i k e l y t o impose a g r i c u l t u r a l costs t o s o c i e t y v i a some o f the same mechanisms discussed above. Using t h e same model as defined e a r l i e r , we explored t h e p o t e n t i a l economic e f f e c t s o f s t r a t o s p h e r i c ozone d e p l e t i o n on U.S. a g r i c u l t u r e . The d e t a i l s o f t h i s assessment are reported i n Rowe and Adam [ r e f . 121. While the b i o l o g i c a l data on UV-B e f f e c t s on crop y i e l d s a r e l e s s w e l l researched then f o r tropospheric ozone, y i e l d reductions have been observed a t UV-B enhancements 1i k e l y t o occur under a 15 percent s t r a t o s p h e r i c ozone reduct i o n . A 15 percent s t r a t o s p h e r i c ozone reduction i s a l s o expected t o g i v e r i s e t o a 13 percent increase i n tropospheric ozone l e v e l s . Together, these e f f e c t s w i l l r e s u l t i n a y i e l d reduction f o r soybeans o f up t o 10 percent. A 15 percent reduction i n s t r a t o s p h e r i c ozone i s evaluated by using estimated reductions f o r soybeans, corn and wheat y i e l d s from UV-B, along w i t h the e f f e c t s o f increased tropospheric ozone on o t h e r crops i n t h e economic model.
078
Under these yield changes, the estimated economic cost of a 15 percent stratospheric ozone reduction is $2.6 billion. Of this total, about $1.6 billion is from direct UV-B effects, while the remaining $1 billion is due to the 13 percent increase in tropospheric ozone. This link between stratospheric and tropospheric ozone points to the complexities involved in setting atmospheric pollution regulations. Specifically, regulating pollutants in isolation ignores the interactive aspects of most pollution phenomenon. Similarly, assessing the agricultural yield or economic consequences of only one pollutant ignores these interactions and potentially understates the benefits of controls, given that reductions of pollutant precursors are likely to have a range of indirect benefits that may equal or increase the direct consequences. CONCLUSION Results from our current assessments of ozone effects on U.S. agriculture indicate substantial economic costs. Specifically, increases in the yields of eight NCLAN crops associated with a 25 percent reduction in ambient ozone from 1981-1983 levels results in a benefit of approximately $1.9 billion (in 1982 U.S. dollars). Rollbacks of ozone by 40 percent reveal net benefits of almost $3 billion. Including the increased cost of Farm Program payments reduces the magnitude of these estimates by 15 percent. A unique feature of the analysis reported here is the evaluation of seasonal, rather than hourly, standards for vegetation that reflect alternative exceedance rates arising from the stochastic nature o f pollution events. Analysis of a seasonal standard indicates that the magnitude of potential benefits are similar to those achieved with constant percentage rollbacks but the distributional consequences are substantially different. For example, a seasonal standard of 50 ppb with 9 5 percent probability o f not exceeding the level in each region would produce approximately $1.7 billion (in 1982 dollars) in benefits, about the same amount as in the 25 percent rollback. However, the regional implications are quite different, with areas with the greatest air quality improvement realizing the greatest gain. Producers in areas already in or near compliance may actually lose due to a decline in crop prices nationally from increased supply. This suggests the importance of using economic models that capture effects across the many facets that make up economic markets, whether that be in case in the U.S. or EEC countries. Finally, a companion study of stratospheric ozone depletion effects on agriculture indicates that stratospheric ozone reductions of IS percent will have costs to society of about $2.6 billion. These costs arise from both the
079 d i r e c t e f f e c t o f UV-B r a d i a t i o n on crop y i e l d s and t h e increases i n tropospheric ozone a r i s i n g from increased UV-B r a d i a t i o n . T h i s 1inkage between t h e two ozone phenomenon p o i n t s t o t h e need f o r i n t e g r a t e d environmental assessments t h a t r e f l e c t t h e i n t e r a c t i o n between p o l l u t i o n emissions and t h e i r various e f f e c t s . REFERENCES
1 Heck, W.W.,
W.W. Cure, J.O. Rawlings, L.J. Zaragoza, A.S. Heagle, H.E. Heggestad, R.J. Kohut, L.W. Kress and P.J. Temple. "Assessing Impacts o f Ozone on A g r i c u l t u r a l Crops: I.Overview." J. A i r P o l l . Cont. A s s o ~ .
34(1984) :729-735. 2 Heck, W.W., W.W. Cure, J.O. Rawlings, L.J. Zaragoza, A.S. Heagle, H.E. Heggestad, R.J. Kohut, L.W. Kress and P.J. Temple. "Assessing Impacts o f Ozone on A g r i c u l t u r a l Crops: I.Crop Y i e l d Functions and A l t e r n a t i v e Exposure S t a t i s t i c s . " J. A i r P o l l . Cont. Assoc 34 (1984):810-817. 3 Adams, R.M.. S.A. Hamilton and B.A. McCarl. "The B e n e f i t s o f P o l l u t i o n Control: The Case o f Ozone and U.S. A g r i c u l t u r e . " Amer. J. Aari. Econ. 68[19861:886-893. ,- - - - ,.- - - - ... 4 Adams, R.M., J.D. Glyer and B.A. McCarl. "The NCLAN Economic Assessment: Approach, Findings and Implications." I n t e r n a t i o n a l Symposium on Assessment o f Crop Loss from A i r P o l l u t a n t s . Raleigh, N.C., October 25-
.
29, 1987. 5 Katz, G., P.J. Dawson, A. Bytnerowicz, J. Wolf, C.R. Thomson and D. Olszyk. " E f f e c t s o f Ozone o r S u l f u r Dioxide on Growth and Y i e l d o f Rice." Aari. Ecosvs and Envi r 14 ( 1985) :103-117. 6 Rawlings, J. and W.W. Cure. "The Weibull Function as a Model f o r Plant Response." Croo Sci. 1985. 7 Lefohn, A.S., H.P. Knudsen, J.A., J. Simpson, and C. Bhumralkar. "An Evaluation o f t h e K r i g i n g Method t o P r e d i c t 7-Hour Seasonal Mean Ozone Concentrations f o r Estimating Crop Losses." 3. A i r P o l l u t . Cont. Assoc.
.
.
37(1987) :595-602. 8 King, D. "Influence o f Moisture Stress on Crop S e n s i t i v i t y t o Ozone," 9
10 11
12
I n t e r n a t i o n a l Symposium on Assessment o f Crop Loss from A i r Pollutants, Raleigh, N.C., October 25-27, 1987. U.S. EPA, O f f i c e o f A i r Q u a l i t y Planning and Standards. 1986. Review o f t h e National Ambient A i r O u a l i t v Stand ards f o r O a n e : P r e l i m i n a r y Assessment o f S c i e n t i f i c and Technical I n f o r m a t i m . Research T r i a n g l e Park, N.C. Segerson, K. "Economic Impacts o f Ozone and Acid Rain: Discussion.' Amer. J. o f Aari. Econ. 69(1987):7900-791. "Current Understanding o f t h e E f f e c t s o f Increased Levels Teramura, A.H. of Solar U l t r a v i o l e t Radiation t o Crops and Natural Plant Ecosystems." Testimony before U.S. Senate. May, 1987. Rowe, R.D. and R.M. Adams. 1987. "Economic Impacts Lower Crop Yields Due t o Stratospheric Ozone." Final P r o j e c t Report t o USEPA. Washington, DC, September.
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801
ESTIMATING THE COSTS OF CONTROLLING AMBIEHT OZONE I N THE UNITED STATES
T. McCURDY1, W. BATTYEZ, M, SMITH2, and M. DEESE2 1Ambient Standards Branch, U.S. T r i a n g l e Park, NC 27711
Environmental P r o t e c t i o n Agency, Research
2A1 l i a n c e Technologies Corporation; Chapel H i l l , NC
ABSTRACT Under contract t o t h e U.S. Environmental P r o t e c t i o n Agency, a l e a s t cost model was developed t o estimate annualized s o c i e t a l costs associated w i t h a t t a i n i n g a l t e r n a t i v e n a t i o n a l ambient a i r q u a l i t y standards (NAAQSs) f o r ozone. Costs are c a l c u l a t e d separately f o r s t a t i o n a r y , mobile, and area sources f o r t h r e e time periods: 1990, 1995, and 2000. Study areas included i n t h e modeling e f f o r t a r e 192 metropolitan s t a t i s t i c a l areas (MSAs) having v a l i d ozone data. Because most ozone c o n t r o l s t r a t e g i e s are based on reducing VOC emissions, t h e a n a l y s i s focuses on v o l a t i l e organic compounds (VOC) controls. Nitrogen oxides (Nox) l e v e l s a r e assumed t o remain constant unless otherwise specified. Emission c o n t r o l options studied i n t h e model i n c l u d e "reasonably a v a i l a b l e " and "best a v a i l a b l e " c o n t r o l technology f o r p o i n t and area sources. For mobile sources, basic and enhanced i n s p e c t i o n and maintenance ( I I M ) programs and other t r a n s p o r t a t i o n c o n t r o l measures (TCMs) are studied. A mixed-integer least-cost program i s used t o s e l e c t c o n t r o l s t r a t e g i e s t o achieve t h e required VOC emission reduction. S t r a t e g i e s are selected t o minimize t o t a l annualized costs o f c o n t r o l f o r each study area, w i t h some constraints. The c o n s t r a i n t s on s t r a t e g y s e l e c t i o n are designed t o emulate d i f f e r e n t s t a t e r e g u l a t o r y strategies.
OVERVIEW The U.S. o f a NAAQS. currently
Clean A i r Act, as amended i n 1977, r e q u i r e s p e r i o d i c review
In accordance w i t h t h i s requirement, t h e NAAQS f o r ozone i s being reviewed.
As p a r t o f t h i s review procedure, h y p o t h e t i c a l
Impacts t h a t changes i n t h e standard would have on nationwide c o n t r o l costs and on ambient a i r q u a l i t y i n various m e t r o p o l i t a n areas are analyzed. While these impacts data are n o t used by EPA t o s e t a NAAQS, they are provided t o t h e p u b l i c as background i n f o r m a t i o n regarding t h e regulatory action.
882 Control costs required t o achieve t h e c u r r e n t and a l t e r n a t i v e NAAQSs are presented i n t h i s paper.
The a l t e r n a t i v e l e v e l s studied are 0.10 ppm and
0.08 ppm, d a i l y maximum one-hour averages.
Costs and a i r q u a l i t y impacts
are analyzed f o r 1990, 1995, and 2000, b u t o n l y 1995 impacts a r e shown below. U n l i k e many a i r p o l l u t a n t s , ozone i s n o t e m i t t e d t o t h e a i r as a primary p o l l u t a n t .
Rather, ozone i n t h e troposphere i s produced by a complex
chain o f photochemical reactions i n v o l v i n g oxygen, n i t r o g e n oxides (Nox), v o l a t i l e organic compounds (VOC),
and o t h e r c o n s t i t u e n t s i n ambient a i r
( r e f . 1). Thus, ozone concentrations cannot be modeled d i r e c t l y from emissions data.
However, given a s t a r t i n g ozone concentration, changes i n ozone
concentrations can be estimated using t h e Empirical K i n e t i c Modeling Approach (EKMA) from expected changes i n VOC and NOx emissions.
Current EPA p o l i c y regarding ozone reductions i s t h a t VOC c o n t r o l i s t h e p r e f e r a b l e strategy f o r a t t a i n i n g NAAQS l e v e l s ( r e f . 2).
Thus, t h e
analyses discussed i n t h i s paper focus on VOC c o n t r o l s . I n order t o estimate precontrol ozone concentrations i n t h e t h r e e years o f a n a l y s i s (1990, 1995, and 2000). f u t u r e VOC emissions a r e p r e d i c t e d u s i n g s t a t e - s p e c i f i c growth indices.
Except i n t h e South Coast A i r Basin o f C a l i f o r n i a , NOx emissions
and ambient l e v e l s are assumed t o remain constant i n t h e f u t u r e and t o be independent o f a l l VOC c o n t r o l s t r a t e g i e s studied. I f EKMA does not p r e d i c t attainment o f an a l t e r n a t i v e ozone NAAQS, VOC emission reductions needed t o a t t a i n a r e estimated.
VOC c o n t r o l s t r a t e g i e s
are selected using an approach designed t o emulate t h e S t a t e Implementation Plan (SIP) process, by which S t a t e s f o r m a l l y develop and adopt emission c o n t r o l strategies. For s t a t i o n a r y and area sources, p o t e n t i a l emission c o n t r o l s s t u d i e d i n t h e cost a n a l y s i s i n c l u d e "reasonably a v a i l a b l e " c o n t r o l technologies
(RACT) and "best a v a i l a b l e " c o n t r o l technology (BACT).
"Lowest achievable emission r a t e " (LAER) technology i s n o t included i n t h e ozone c o s t analysis. For mobile sources, motor v e h i c l e i n s p e c t i o n and maintenance ( I & M ) programs and t r a n s p o r t a t i o n c o n t r o l measures (TCMs) are studied. Control s t r a t e g i e s a r e selected i n t h e c o s t model t o minimize t o t a l annu a l i z e d costs o f c o n t r o l f o r each study area, w i t h some c o n s t r a i n t s .
Controls
are not applied on an i n d i v i d u a l source basis, b u t are a p p l i e d t o e n t i r e source categories, as they would be under a t y p i c a l SIP.
Moderate-stringency
I&M can be applied before o t h e r c o n t r o l s t o simulate an EPA requirement t h a t I&M be i n s t i t u t e d wherever an area requests an extension o f time t o a t t a i n t h e ozone standard.
TCMs, such as d i f f e r e n t i a l p r i c i n g p o l i c i e s and increased
gasoline taxes, a r e assumed t o be applied as a l a s t r e s o r t a f t e r a p p l i c a t i o n o f a l l o t h e r p o t e n t i a l controls.
Controls i n s t a l l e d a t new p l a n t s t o meet New Source Performance Standards (NSPS) and c o n t r o l s required under t h e Federal Motor Vehicle Control Progam (FMVCP) are t r e a t e d as baseline c o n t r o l s i n t h e cost analysis.
Costs o f
these c o n t r o l s are considered t o be a t t r i b u t a b l e t o NSPS and FMVCP.
Reductions
i n gasoline vapor pressure and onboard emission c o n t r o l s f o r automobile refueling, which would be required under proposed gasoline marketing regulations, are a l s o t r e a t e d as p a r t o f t h e c o n t r o l baseline. The cost analysis covers 192 geographic study areas f o r which c u r r e n t ozone monitoring data are available.
These areas comprise 218 U.S.
Bureau Metropolitan S t a t i s t i c a l Areas ( B A S ) .
Census
Since t h e cost a n a l y s i s does
n o t cover t h e e n t i r e nation, i t i s p o s s i b l e t h a t t o t a l U.S. c o n t r o l costs have been underestimated, e s p e c i a l l y f o r more s t r i n g e n t NAAQS a l t e r n a t i v e s . The analysis described here i s explained i n more d e t a i l i n Ref. 3. THE COST METHODOLOGY
I n t h e ozone cost model, emission source categories are grouped together i n "cost pods;" a cost pod i s defined as a category o f emission sources t h a t have s i m i l a r emission c h a r a c t e r i s t i c s which can be c o n t r o l l e d by t h e same type o f c o n t r o l device. Cost pods correspond roughly t o source categories regulated under a t y p i c a l S I P .
I n analyzing VOC c o n t r o l scenarios, t h e cost
model applies c o n t r o l s a t a cost pod l e v e l .
Thus, w i t h i n a given study area,
a l l members o f a given pod are t r e a t e d equally, as they would be under a t y p i c a l SIP.
S t a r t i n g w i t h t h i s c o n s t r a i n t , and others t h a t can be s p e c i f i e d
by t h e analyst, t h e model i d e n t i f i e s t h e l e a s t expensive s e t o f c o n t r o l s t h a t would achieve t h e t o t a l VOC emission reduction t a r g e t f o r a given study area. Although some study areas cross S t a t e boundaries, i t i s assumed t h a t t h e same l e v e l o f VOC c o n t r o l would be a p p l i e d over t h e e n t i r e study area. Controls t h a t are applied t o e x i s t i n g sources w i t h i n a cost pod are a l s o applied t o a l l new sources i n t h a t pod t h a t might be b u i l t , even i f t h e study area i s projected t o a t t a i n an a l t e r n a t i v e NAAQS i n t h e year t h a t c o n s t r u c t i o n occurs. The c o s t model i s implemented on t h e Sperry-UNIVAC mainframe computer a t EPA's National Computer Center. The model comprises a number o f separate modules, each o f which performs a s p e c i f i c task. There a r e s i x major modules (besides j o b run c o n t r o l modules). 1. data i n p u t 2. growth p r o j e c t i o n s
3. baseline EKMA model 4. c o n t r o l costs 5. l e a s t - c o s t model 6. post-control EKMA model
They are:
The modules a r e interconnected as shown i n F i g u r e 1.
A b r i e f discussion o f
t h e modules follow. The main purpose o f t h e i n p u t module i s t o develop a data base o f emissions and c o n t r o l e f f i c i e n c i e s f o r t h e base y e a r o f analysis.
The base
year i s defined t o be t h e most recent year f o r which ambient ozone data a r e available.
The main source o f data on base year emissions and c o n t r o l s i s
t h e National Emissions Data System (NEDS).
The i n p u t module processes NEDS
data t o g i v e a s i m p l i f i e d f i l e o f e s s e n t i a l data f o r each s t a t i o n a r y , area, and mobile source category included i n the ozone c o s t model.
I n addition t o
base year emissions and c o n t r o l information, t h e i n p u t module modifies and s t o r e s i n f o r m a t i o n regarding source l o c a t i o n , production capacity u t i l i z a t i o n , emission source c l a s s i f i c a t i o n code (SCC),
and Standard I n d u s t r i a l C l a s s i f i -
c a t i o n (SIC) code.
INPUT MODULE
CONTROL COSTS MODULE
GROWTH PROJECTIONS MODULE
LEAST-COST MODULE (FMPS)
BASELINE EKMA MODULE
a
POST-CONTROL EKMA MODEL
Figure 1.
M a j o r modules comprising t h e ozone cost model.
885 The i n p u t module performs q u a l i t y assurance checks on S I C and emissions c o n t r o l information.
I n addition, depending on run c o n t r o l s p e c i f i c a t i o n s , a
S I P c o n t r o l f i l e " can be used t o a l t e r c o n t r o l l e v e l s given I n NEOS f o r
s t a t i o n a r y sources so t h a t they correspond roughly t o c u r r e n t S I P c o n t r o l levels.
S i m i l a r adjustments can a l s o be made t o r e f l e c t c u r r e n t I I M programs.
Source-specific base-year capacity u t i l i z a t i o n r a t e s a l s o are assigned i n t h e module, using a f i l e o f SIC-specific i n d u s t r y capacity factors.
Finally,
the i n p u t module performs a number o f f i l e management operations, such as assigning study area and cost pod numbers and aggregating VOC emissions f o r sources t h a t do n o t f a l l i n t o any defined cost pod. The growth p r o j e c t i o n module estimates changes i n t h e emission i n v e n t o r y over time. For t h e t h r e e analysis years, t h e module assesses growth i n emissions from e x i s t i n g sources, closure o f e x i s t i n g sources due t o market conditions, and new source construction. P r o j e c t i o n s are stored i n a new source growth f i l e and a f u t u r e baseline emissions f i l e .
The basis
f o r these p r o j e c t i o n s i s a set o f annual growth estimates from 1980 t o 2000 f o r each S I C group w i t h i n each State. (from various U.S.
These are based on external p r o j e c t i o n s
federal government agencies) o f population and employment
growth, but t h e p r o j e c t i o n s can be v a r i e d by an analyst using t h e cost model t o perform s e n s i t i v i t y analyses. Emissions and c o n t r o l data i n t h e f u t u r e baseline emissions f i l e correspond t o t h e baseline l e v e l o f c o n t r o l .
T h i s f u t u r e baseline i s defined as
t h e emissions s i t u a t i o n t h a t would be achieved i f e x i s t i n g c o n t r o l s a r e maintain a t t h e i r current level.
For t h e primary case, whose r e s u l t s are shown
below, i t i s assumed t h a t no a d d i t i o n a l VOC c o n t r o l s are i n s t a l l e d as p a r t of t h e f u t u r e baseline o t h e r than those i n h e r e n t l y associated w i t h FMVPC and NSPS. Baseline ozone concentrations a r e modeled using EKMA. The b a s e l i n e EKMA module i s run separately f o r each NAAQS a l t e r n a t i v e , year o f analysis, and study area.
Inputs t o t h i s module i n c l u d e t o t a l baseline emission
p r o j e c t i o n s f o r each study area (from t h e f u t u r e baseline emissions f i l e ) and a f i l e o f ozone c,oncentrations o r "design values" by study area, determined from recent ambient ozone data. A major output o f t h e baseline EKMA module i s a f i l e o f emission reduction requirements b y study area. I n addition, t h e module produces a f i l e o f f u t u r e baseline design values. The c o n t r o l cost module i s a l s o r u n f o r each year o f analysis. The module uses a f i l e o f cost equations t o c a l c u l a t e costs and emission reductions o f p o t e n t i a l add-on controls.
These a r e assigned t o each i n d i v i d u a l
s t a t i o n a r y source, area source, and mobile source c o s t pod based on t h e source o r group size. A c o n t r o l c r e d i t f i l e determines whether c o s t s of NAAQS c o n t r o l s applied i n a previous year o f a n a l y s i s a r e t o be c r e d i t e d toward
886 t h e cost o f any a d d i t i o n a l r e q u i r e d controls.
The c o n t r o l c o s t module outputs
a f i l e o f t o t a l pod-level costs and emission reductions f o r each study area and a f i l e o f i n d i v i d u a l source costs and emission reductions. The least-cost module uses a mixed i n t e g e r l i n e a r program t o i d e n t i f y t h e l e a s t c o s t l y s e t o f emission c o n t r o l s t h a t w i l l achieve a s p e c i f i e d emission reduction. The user can s p e c i f y c o n t r o l s t h a t are t o be a p p l i e d f i r s t , regardless o f cost, and c o n t r o l s t h a t are t o be a p p l i e d as a l a s t resort. For instance, I&M c o n t r o l s f o r motor vehicles are a p p l i e d i n t h e module b e f o r e a d d i t i o n a l s t a t i o n a r y source controls, t o r e f l e c t c u r r e n t EPA SIP-development policy.
Least-cost modellng i s conducted separately f o r each study area,
each year o f analysis, and each NAAQS a l t e r n a t i v e . Inputs t o t h e l e a s t cost module are t h e pod-level cost and emission r e d u c t i o n and emission reduction requirements f i l e s . The module output i s a f i l e o f l e a s t cost s o l u t i o n s f o r each study area. A f t e r s e l e c t i o n of emission c o n t r o l s i n t h e l e a s t c o s t module, t h e EKMA model i s re-run t o estimate post-control ozone concentrations t h a t may be achieved using a l l i d e n t i f i e d controls. post-control EKMA module.
T h i s i s accomplished i n t h e
LEAST-COST MODELING The least-cost model used i n t h e ozone cost a n a l y s i s i s t h e UNIVAC Functional Mathematical P r o g r a m i n g System (FMPS). It operates on a s e t o f pod-level annualized costs and emission reductions.
For each c o s t pod, t h e r e i s a t l e a s t one emission c o n t r o l o p t i o n t h a t w i l l achieve a given l e v e l
o f c o n t r o l a t a given cost.
When t h e l e a s t - c o s t model i s run, a t o t a l pod-
l e v e l annualized cost o f c o n t r o l and a corresponding pod-level emission reduction are i n p u t f o r each c o n t r o l o p t l o n w i t h l n a pod.
The pod-level t o t a l s i n c l u d e c o n t r o l costs and p o t e n t i a l emission reductions f o r a l l sources w i t h i n t h a t pod. For a given study area, t h e l e a s t - c o s t model i d e n t i f i e s t h e s e t o f c o n t r o l optlons t h a t h y p o t h e t i c a l l y achieves t h e t o t a l emisslon reduction t a r g e t a t t h e lowest t o t a l annual cost. Annual c o s t s used i n t h e model i n c l u d e annualized c a p i t a l costs, annual o p e r a t i n g and maintenance and insurance and taxes costs, and product- o r fuel-recovery c o s t c r e d i t s . basic a l g o r i t h m f o r t h e mixed-integer l e a s t - c o s t model can be w r i t t e n as follows: Minimize:
AjXj
Such t h a t :
EHjXj
The
(1)
2 ERT
(2)
aa7 A j = pod-level annualized c o s t o f c o n t r o l o f o p t i o n j, f o r a p a r t i c u l a r study area, a n a l y s i s year, and NAAQS a l t e r n a t i v e ($/year),
where:
X j = 0 i f option j i s n o t selected and 1 i f o p t i o n j i s selected, E R j = pod l e v e l VOC emission reduction f o r o p t i o n j (tonslyear), and,
t a r g e t t o t a l emission reduction f o r t h e study area.
ERT
Pod-1 eve1 annualized c o n t r o l costs, A j , a r e c a l c u l a t e d by adding annualized c o n t r o l costs f o r a l l sources, i, i n t h e study area using c o n t r o l o p t i o n j. Thus,
n Aj
Z Aij i=1
(3)
A i j f o r each source i s c a l c u l a t e d by adding o p t i o n - s p e c i f i c c a p i t a l costs ( C C j )
t o t y p i c a l - y e a r operating and maintenance (OMj) costs and s u b t r a c t i n g any product o r f u e l recovery c r e d i t (RCj), i f any.
Annualized c a p i t a l costs a r e
calculated from i n s t a l l e d r e t r o f i t equipment costs, a 10% f l a t i n t e r e s t rate, an equipment l i f e o f 10 t o 15 years (depending upon t h e cost pod i n question), and a y e a r l y charge f o r insurance and taxes equal t o 4% o f i n s t a l l e d c a p i t a l costs.
Therefore, f o r each source w i t h i n a pod:
The independent variables i n Eq. 3 a r e obtained from f i t t i n g l i n e a r o r m u l t i p l i c a t i v e regression equations ( o f t h e general form: and y = a
*
y = a + bx
xb, r e s p e c t i v e l y ) t o c o n t r o l c o s t data from various s i z e d plants.
These data come from EPA cost analyses o f NSPS and RACT regulations.
The
regression equations t a k e t h e f o l l o w i n g form, removing some s u b s c r i p t s
on t h e regression parameters t o simp1 i f y presentation:
S t a t i o n a r y Sources Capital Costs OPM Costs Recovery C r e d i t
a * (Ui**b) a * (Ui**b) a + (b * U i )
Area Sources a a a
* Ui * Ui
*
Ui
888 U i i s t h e u n c o n t r o l l e d VOC emissions l e v e l from source i ( i n c o n t r o l pod j,
of course).
The m u l t i p l i c a t i v e regression equation c o e f f i c i e n t , b, f o r area
sources i s assumed t o be 1.0,
and hence i s n o t shown.
EXAMPLE OF DATA FOR A COST PO0 There are over 40 cost pods i n t h e ozone cost model f o r p o i n t and area sources, More are belng developed. To i l l u s t r a t e t h e t y p e o f data developed f o r each o f t h e pods, Pod 1 w i l l be f u l l y described. Pod ID:
001.
Solvent Metal Cleaning
SCCs Included:
4-02-002-02 t o -06 4-01-002-97 4-01 -002-99
Associated SICs:
Oegreasing ( M u l t i p l e SICs)
Cost Documentation:
NSPS ( r e f . 4)
Control Options ( j ) : 1. CCI:
OM1: RC1:
Freeboard Cover, E f f i c i e n c y :
23%
a = b a = b a =
$2,033/ton = 0.418 $21.70/ton = 0.550 $0.25 b = $147/ton
2. R e f r i g. Freeboard; E f f i c i e n c y : 42% CC2: OM2: RC2:
a = b a = b a = b
$4,72O/ton = 0.451 f165lton = 0.496 $0.92 = $266/ton
3. Carbon Absorbers; E f f i c i e n c y 54% CC3: OM3: RC3:
a = 114,989lton b = 0.368 a = 62931ton b = 0.623 a = $3.62 b = $340/ton
RESULTS Results o f applying t h e cost methodology t o one set o f c o n t r o l s t r a t e g i e s appear i n Table 1. 1995.
For ease o f presentation, o n l y one year o f a n a l y s i s i s shown:
The a l t e r n a t i v e ozone NAAQS analyzed are t h e c u r r e n t 0.12 ppm standard and
two a l t e r n a t i v e s :
0.10 and 0.08 ppm. Costs are aggregated i n t o f o u r major categories: point, area, ( I & M ) , and t r a n s p o r t a t i o n c o n t r o l measures, which i n v o l v e
such programs as r i d e - s h a r i ng and t r a n s l t system improvements.
889
TABLE 1 Emission reductions and v a r i a b l e costs a t t r i b u t a b l e t o a l t e r n a t i v e NAAQS f o r 1995
Case
VOC Reduction
C a p i t a l Cost
Annual Cost
(1000 tons)
(f m i l l i o n )
(f million)
PRIMARY CASE (NAAQS = 0.12 ppm)
Point source c o n t r o l s Area source c o n t r o l s ISM Transportation c o n t r o l measures
456 1,144 303 78
3,794 17,686 1,400 384
909 4,699 704 (1,207)
Totals Residual Nonattainment Areas
1,982
23,264 37
5,105
P o i n t source c o n t r o l s Area source c o n t r o l s ISM Transportation c o n t r o l measures
602 1,595 430 126
5,621 25,634 2,039 619
1,336 6,796 994 (1,940)
Totals Residual Nonattainment Areas
2,753
33,913 90
7,178
Point source c o n t r o l s Area source c o n t r o l s ISM Transportation c o n t r o l measures
697 1,969 504 167
5,910 32,119 2,594 82 1
1,510 8 ,542 1,175 (2,583)
Totals Residual Nonattainment Areas
3,336
41,444 167
8,639
NAAQS = 0.10 ppm
NAAQS = 0.08 ppm
Associated w i t h each a l t e r n a t i v e analyzed i s t h e number o f r e s i d u a l non-attainment areas.
T h i s i s t h e number o f geographic areas
(%As
or
combinations o f contiguous MSAs) t h a t cannot a t t a i n t h e ozone NAAQS being analyzed using the s e t o f cost pods included i n t h e model.
The number o f residual
non-attainment areas increases d r a m a t i c a l l y as t h e a l t e r n a t i v e ozone NAAQS becomer tighter.
For instance, t h e cost model p r e d i c t s t h a t 167 o f t h e 192 areas analyzec
(87%) would not a t t a i n a 0.08 ppm ozone NAAQS i n 1995. S e n s i t i v i t y analyses have been undertaken on t h e model ( r e f . 3). As might be expected, varying t h e i n p u t s used and t h e assumptions made makes a l a r g e impact on model results.
The i n t e r e s t e d reader i s d i r e c t e d
t o Ref. 3 f o r a more thorough dfscussion of s e n s i t i v i t y analyses t h a t have been undertaken.
890 CAVEATS AND LIMITATIONS Despite t h e complexity and comprehensive nature o f the' c o s t model, EPA considers t h e work done t o date t o be p r e l i m i n a r y i n nature.
Significant
u n c e r t a i n t i e s remain regarding t h e baseline VOC emission i n v e n t o r y a v a i l a b l e from each S t a t e on EPA's computer system (i.e.,
NEDS).
Past analyses have
I n d i c a t e d t h a t NEDS can be d i f f e r e n t by 2 200% f o r aggregated source categories when compared t o supposedly more d e t a i l e d i n v e n t o r i e s done by i n d i v i d u a l S t a t e s f o r S I P development work ( r e f . 5).
Another source
o f considerable u n c e r t a i n t y I s t h e VOC/NOx r a t i o needed f o r t h e EKMA model. R a t i o data a r e d i f f i c u l t t o o b t a i n and are a v a i l a b l e f o r o n l y a few MSAs.
(A d e f a u l t r a t i o h a d ' t o be used f o r most MSAs.)
F i n a l l y , area-
s p e c i f i c (and n a t i o n a l l y aggregated) growth r a t e s a r e always a source o f u n c e r t a i n t y regarding f u t u r e conditions.
Growth r a t e s e n t e r t h e ozone
c o s t model f o r numerous p r o j e c t i o n s : population, c a r sales, i n d u s t r i a l growth (by S I C ) , and v e h i c l e miles traveled. Any one o f these items obviously a f f e c t s f u t u r e emission estimates due t o t h e compounding phenomenon. I n addition, i f one r a t e i s o f f r e l a t i v e t o another, a s i g n i f i c a n t imbalance among sectors included i n t h e model can occur. There i s no i n t e r n a l check a t present t o determine if such an imbal ance is occurring. I n sum, t h i s paper described t h e ozone c o s t model t h a t EPA has developed t o analyze s o c i e t a l costs o f a t t a i n i n g a l t e r n a t i v e NAAQS. The model i s considered t o be a p r e l l m i n a r y method a t present, and w i l l be developed f u r t h e r over t h e next two years p r i o r t o EPA's t a k i n g formal a c t i o n regarding t h e ozone NAAQS review.
REFERENCES Environmental C r i t e r i a and Assessment O f f i c e . A i r Q u a l i t y C r i t e r i a f o r Ozone and Other Photochemical Oxidants, Volume I. Research T r i a n g l e Park, NC: U.S. EPA, 1987. E.L. Meyer. Review o f Control S t r a t e g i e s f o r Ozone and T h e i r Effects on Other Environmental Issues. Research T r i a n g l e Park, NC: U.S. EPA, 1986. W.H. Battye, M.G. Smith, and M. Deese. Cost Assessment o f A l t e r n a t i v e National Ambient A i r q u a l i t y Standard f o r Ozone, D r a f t Report. Chapel H i l l , NC: A l l i a n c e Technologies Corporation, 1987. Emission Standards and Engineering Division. Organic Solvent Cleaners Background Information o f Proposed Standards. Research T r i a n g l e Park, NC: U.S. EPA, 1979. W.T. Harnett. "Memo: Comparison o f S I P and NEDS Emission Inventories." Chapel H i l l , NC: GCA Corporation, June 15, 1983.
T.Schneider et d (Editore),Atmospheric Ozone Research and ite Policy Zmplicotions 0 1989 Elsevier Science Publiehere B.V.,Amsterdam Printed in The Netherlande
-
891
ESTIMATED COSTS AND BENEFITS OF CONTROLLING CHLOROFLUOROCARBONS
DAVID DULL1, STEPHEN SEIDELl, and JOHN WELLS2 loffice of Air and Radiation, U.S. Environmental Protection Agency, ANR-445, 401 M Street, SW, Washington, D.C. 20460 (U.S.A.1 2The Bruce Company, Suite 410, 3701 Massachusetts Avenue, NW, Washington, D.C. 20016 (U.S.A.) ABSTRACT The Montreal Protocol on Substances that Deplete the Ozone Laver requires a 5 0 percent reduction in consumption of fullyhalogenated chlorofluorocarbons (CFCs) within ten years and a freeze on consumption of halons. In December 1987, the U.S. Environmental Protection Agency (EPA) proposed to implement the Protocol requirements by allocating production and consumption quotas to CFC producers and importers based on their 1986 market shares. The quotas would be reduced over time according to the staged reduction schedule in the Protocol. As the supply of CFCs is directly reduced by regulation, rising CFC prices would serve as the mechanism which would allocate CFCs to the highest valueadded end-uses. EPA has completed simulations of the costs of control of the Montreal Protocol in the United States1. In addition, it has estimated the benefits resulting from stratospheric ozone protection. EPA's benefit-cost comparison shows that the benefits of stratospheric protection are far greater than control costs. METHODOLOGY -- ESTIMATING CONTROL COSTS while economic theory would hold that such a market system would achieve the Protocol reductions at the least possible cost, significant economic effects would still be felt in terms of higher prices of final products that use CFCs (social costs), and transfer payments from CFC users to CFC producers. EPA recently estimated these costs in the Regulatory Impact Analysis which accompanied its regulatory proposal. EPA used a bottom-up approach in analyzing the costs of meeting the proposed regulation. Studies were initiated in eight major CFC and halon use categories -- flexible foam, rigid polyurethane foam, rigid non-urethane foam, refrigeration and air conditioning, aerosols, solvents, fire extinguishing, and miscellaneous uses. These groupings were then further divided
892
into 82 specific applications. For example, refrigeration was divided into 18 categories including retail food, home refrigerators, refrigerated transport, etc. Finally, cost and emission reduction estimates were developed for over 6 5 0 distinct control options covering the full range of use applications. The control options included engineering controls (such as improved design to reduce leakage), chemical substitutes (such as aqueous cleaning and HCFC-l34a), product substitutes (such as fiberglass), recovery and recycling, and work practices (such as use of alternative leak testing agents). Cost estimates were developed and included capital and operating expenses (including,where applicable, any energy penalty). Technologies were assessed in terms of the date at which they would become available (0-3 years, 4-7 years, or longer), and the rate and limits for achieving market penetration. Documentation of the control options was reviewed by industry sources and published in December 1987. The cost estimates for these Dptions were used as inputs into EPA’s Integrated Assessment Model (IAM) which provided estimates of the total cost of meeting a regulatory goal. The model operates by prioritizing the potential reductions on the basis of least cost and the judgment of EPA’s contractors based on discussion with industry representatives concerning the likely response of specific industry sectors to CFC limits. The model estimates the resulting CFC and halon price increases, and the costs associated with these price increases. Two types of costs are computed: social costs and transfer costs. Social costs represent the real resource costs involved in meeting regulatory requirements. Transfer costs represent the transfer of income from consumers of CFC-using products to other segments of society. In computing transfer costs, decreases in income to one sector of the economy are usually offset by increases in income to a competing sector. For example, a shift in electronic cleaning from CFC-113 to terpene-based solvents results in decreases in income to CFC-113 manufacturers, but this loss is offset by an increase in income to manufacturers of terpene-based solvents. IMPACT ANALYSIS COST ESTIMATES FROM EPA’S -0RY The aggregate demand for CFCs in the absence of regulatory controls is one important determinant of CFC prices. Based on
893
econometric and market-based studies of CFC demand completed for a series of UNEP workshops, EPA projected that in the absence of regulatory controls, demand for CFCs -11, -12, -114, and -115 would rise at approximately 2.5 percent per year until 2050 and remain constant thereafter. Demand for CFC-113 is projected to rise at 3.75 percent per year from 1986 to 2 0 0 0 ; 2.5 percent from 2000 to 2050; and remain constant thereafter. As our companion paper for this symposium discusses, the rate at which available controls are adopted plays a large role in determining total control costs. Early adoption of controls reduces aggregate demand for CFCs and thus moderates the CFC price rises that are induced by the reduced supply as quotas are tightened. Figure 1 shows the projected price rises for two sets of assumptions about the rate at which firms shift to alternatives. Figures 2 and 3 show the accompanying Social costs and transfer costs.
as :::: 0
14.0
W 0
a8
12.0
P
9 9 Y c
10.0
t
P f" E
O-O 4.0 2.0 0.0
$/
Fig. 1. Diagram showing the projected CFC price increases for Montreal Protocol implementation in the United States'.
894
1989 THROUQH2075
c
0
30
Leaat Coat
Moderate
Moderate/ Major Major Stretchout Ca8.8
Fig. 2. Diagram showing the estimated social costs for Montreal Protocol implementation in the United States1.
10 I
1988THROUQH207S
I
9
1 0
Leaat Coat
Moderate I
Moderate/ Major Malor I Stretchout Caaer
Fig. 3. Diagram showing estimated transfers to producers for Montreal Protocol implementation in the United Statesl.
895
The "least costg1scenario assumes that all reductions are taken as soon as they are technologically available and as soon as the cost of the CFCs or halons exceeds the costs of making the reduction. In the "least cost8tscenario, CFC price rises are minimal in early years, rise to $3.77 per kilogram around the turn of the century, and plateau around $5.48 per kilogram Well before 2075 when chemical substitutes have penetrated major markets. The low initial cost increases reflect the large quantity of CFC and halon reductions that are available with current technologies and which either will save firms money (e.g. through CFC recovery and reuse) or which are competitive. In the latter years of the analysis, the $5.48 price ceiling represents the anticipated costs of substitute chemicals (primarily HCFC-134a replacing CFC-12 and HCFC-123 replacing CFC-11 in foam applications). In the "least costll scenario, social costs were calculated to be $689 million through 2000 and $27 billion through 2075. Transfer costs were calculated to be $2.0 billion through 2000 and $6.2 billion through 2075 (social costs are discounted at 2 percent per year and transfer costs at 6 percent per year). While the "least costttsimulation assumes no resistance to technological change, the Ilmoderate stretch out^^ simulation contains a number of assumptions that slow the rate or extent to which available technologies would be adopted. The assumptions primarily involve slower penetration rates for new products and production processes into the marketplace. In addition, manufacturers of products for which CFCs comprise only a minor share of the final product price (e.g. mobile air conditioning) are assumed not to adapt to increases in CFC prices. Finally, switches to alternative chemicals are assumed to be much slower. The other simulations -- "moderate to major stretchout" and "major stretchoutll -- assume additional delays in introduction of CFC alternatives. The social costs for the stretchout scenarios ranges from $1.1 billion to $1.8 billion by 2000 and $7.15 billion to $9.4 billion by the year 2075. Transfer costs range from $2.5 billion to $5.7 billion by 2000 and $7.1 billion to $9.4 billion by 2075. Thus, the rate at which firms implement low cost reductions is an important determinant, particularly in the near-term, of the
896
costs and transfer payments involved in meeting the proposed regulation. METHODOLOGY -- ESTIMATING BENEFITS FROM REDUCTIONS In addition to estimating the costs of control, EPA’s latorv ImDact (RIA) contains a description of the potential benefits that would result from actions to limit the risks from ozone depletion. The response of stratospheric ozone to increases in CFC and halon emissions was estimated based on a parameterized version of a one-dimensional atmospheric model developed by the Lawrence Livermore National Laboratory (LLNL). A United Nations Environment Workshop (UNEP) workshop on atmospheric modelling in Wurzburg, Federal Republic of Germany, found that the LLNL parameterization produces results that are within the range of estimates of the more complex models, although slightly on the low side (1.e. underestimating ozone depletion) in some cases2. The projected ozone depletion for the ItNo Controlsttcase and a simulation of the Montreal PrOtoCO1 controls is shown in Figure 4 . Note that the Montreal protocol results in significantly less depletion. To compute the health and environmental benefits of this reduced depletion, EPA relied on the scientific analysis that was completed earlier for its comprehensive risk assessment3. This assessment was peer-reviewed and approved by EPA’s independent Science Advisory Board, and summarizes the scientific basis for EPA’s decisionmaking. Benefits are computed only in those areas in which sufficient research has been completed to provide a basis for a quantitative dose-response relationship. The strongest dose-response relationships have been developed for basal, squamous, and melanoma skin cancer; and for cataracts. Sufficient case studies have been completed to allow development of extrapolated doseresponse relationships for effects on plants, aquatics, outdoor materials, ground-level oxidants, and sea level rise. In several areas, however, quantification of benefits for the RIA was not possible. These areas include suppression of the human immune system and climate-related impacts on water resources, agriculture and forests.
897
Fig. 4 . Projected ozone depletion for No Controls and tne 2.7 Montreal Protocoll. Assumes baseline growth in CFCS of percent per year; and that 94% of developed and 6 5 % of developing nations join the Protocol. To express benefits in common terms with control costs, benefits were monetized and discounted at the rate of 1 percent per year. BENEFIT ESTIMATES FROM EPA’SM IP -A C T A N A L S Y IS Estimates of the economic benefits in the United States which would result from implementation of the Montreal Protocol are shown in Table 1. These benefits reflect the difference between the base case of no controls and the simulated implementation of the Montreal Protoco1. It should be noted that projecting benefits out to the year 2075 is a speculative exercise, but is required because of the long atmospheric lifetimes of CFCs and halons. The estimates are subject to substantial uncertainties both in the calculation of the dose-response effects and in the economic values placed on such effects. Due to this uncertainty, the benefits are expressed in ranges. The total benefits through the year 2075 are estimated to be between $29 billion and $340 trillion Based on this analysis, it would appear that the estimated benefits of the mntrea 1 protocol would far exceed the control costs under any reasonable Set of assumptions.
898
Effects Skin Cancer Cases Skin cancer Deaths Cataract Cases
154.43 million cases 3.14 million deaths 17.60 million cases avoided Monetarv Effects (S)
Skin Cancer Cases Skin Cancer Deaths cataract cases crop Damage from W - B Loss of Fish harvests Crop Damage from Smog Polymer Damage Sea Level Rise Damage to Major Ports Total Monetary Benefits
61.3 6.4 2.6 23.4 5.5 12.4 3.1 4.3
billion trillion billion billion billion billion billion billion
6.3 trillion
Assumptions: Shows value of avoided damage relative to "NO Controlsn for populations alive today and born before 2075. Valuation assumes a 2 percent discount rate. The value of life is assumed to be $3 million and is increased at 1.7 percent per year. Dose-response e timates are based on models summarized in EPA's risk assessment
1.
Table 1. Estimated economic benefits of the Montreal Protocol in the United States1
899 REFERENCES 1
U.S. Environmental Protection Agency (EPA), -to rv ImDact vsis: Protection of Stratomheric O z a , U . S . EPA, Washington, D.C., 1987.
2
United Nations Environment Programme, Bd Hoc s c i e n t m ina to ComDare M o d e l G e n e r a t e d o o f Ozone Laver ae for Various Stratecries for CFC Control, UNEP/WG.167/INE'.lf Wurzburg, Federal Republic of Germany, 910 April, 1987.
3
U.S. EPA, Assessins the m k s- of m T m e S t r a t o s m , EPA400/1-87/001, U.S, EPA, Washington, D.C., 1987.
. .
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T.Schneider et al. (Editors),Atmospheric Ozone Research and its Policy Implications 1989 Elsevier Science Publishers B.V.,Amsterdam - Printed in The Netherlands
COST-EFFECTIVENESS OF SPECIFIC CONTROL OPTIONS FOR VOC EMISSIONS OIL INDUSTRY ASSESSMENT
301
-A
EUROPEAN
R. J.Ellis CONCAWE, Babylon-Kantoren A, Koningin Julianaplein 30-9, 2595 AA The Hague (The Netherlands)
ABSTRACT The paper VOC emissions that could be VOC emissions
introduces the subject by briefly reviewing the significance of as an ozone precursor and suggesting general control policies followed. An overall European inventory of man-made and natural is included In order to put the subject into perspective.
Some possible control measures are identified for VOC emissions originating from motor gasoline during its manufacture, distribution, dispensing and use. The capital and operating costs and cost-effectiveness of a number of these measures are discussed including, reduction of storage tank losses, vapour recovery systems for primary distribution modes, on-board car systems for evaporative refuelling emissions, Stage I1 controls for refuelling emissions and fuel volatility controls. The results show significant differences in cost-effectiveness of some of the options. A form of presentation of the results is used which allows authorities a clear choice of options for control measures.
INTRODUCTION It is generally accepted that tropospheric ozone is created from chemical reactions involving largely nitrogen oxides (NO ) and volatile organic X
compounds (VOC). Ozone soformed, supplements that which has been transported down from the stratosphere. Ozone formation is a photo-chemical reaction and therefore it can only occur in daytime. Actual measurements of tropospheric ozone concentrations in Europe show that episodes of high concentrations occur frequently normally in the hotest summer months. Such peak concentrations can contribute to damage to forests, vegetation, material and human health, and impair visibility. There is still a lack of adequate scientific understanding of the relationship between emissions and their ultimate contribution to observed damages whether they be via acidification or ozone attack. No rigorous criteria exist on which to base emission, air quality or pollutant deposition standards. For this reason the proposals to reduce NO
X
and VOC emissions are of
an arbitrary nature, and can be seen as necessary insurance against irretrievable damage if action were delayed indefinitely to await a complete scientific understanding.
902 Against this background CONCAWE strongly supports the view that:
-
control policies are required but should be balanced with respect to the state of evidence available relating cause with effect effective control regulations should begin with the largest significant sources
-
adoption of specific control measures should be preceded by adequate evaluation of the various technologies available to identify the most cost-effective ones.
Accordingly with respect to VOC emissions CONCAWE has gathered together inventory, control technology and cost information to assist in assigning priorities in the development of any regulatory activities felt to be necessary. VOC EMISSIONS INVENTORY CONCAWE's best estimates of anthropogenic and natural source VOC emissions to the atmosphere in Western Europe 1986 are s h a m in Appendix 1. The data have been compiled from a combination of emission factors
-
calculated from well established formulae and from actual measurements e.g. in the case of evaporative emissions from vehicles. The VOC data reported exclude methane basically because of the lack of reliable data and because initially it was felt that the low reactivity of methane would not have a significant effect on ozone production. This view is now undergoing some change since the large amount of methane in the atmosphere still has a significant effect on background ozone formation. Looking to the data some clear conclusions can be drawn:
- VOC emissions from mobile sources represent about 41% of total anthropogenic VOC emissions which include 37% from gasoline vehicles.
- VOC emissions from solvents represent another 40%. - The
oil industry contribution is only 6.5% of which 1.7% is from
refineries and 3.1% from gasoline distribution.
- Emissions
from natural sources such as forests leaf litter and
pastures are estimated to be of the same magnitude as those from man-made sources. There is some considerable uncertainty about the size of natural emissions, a number of other studies quoting eignificantly lover totals. A recent study of the US situation (1) has produced a figure for natural emission in the USA somewhat higher than man-made emissions there. An important aspect is that the rate of natural emissions ie temperature dependant
60
that the maximum emiesion occurs in the summer. Recent modelling
studies (OECD sponsored) have highlighted the importance of natural emissions.
903 The mobile source sector being one of the largest VOC emitters, is analysed in more detail. Gasoline vehicles contribute three categories viz.
- Exhaust
- Evaporative
- Refuelling
2.5 million tlyr 1.0 million t/yr 0.18 million t/yr
GASOLINE ENGINED VEHICLE EXHAUST EMISSIONS Without controls, exhaust is the largest source of vehicle VOCs. Since 1970 exhaust emission limits for gasoline engined cars hsve been steadily tightened in Europe (2). The so-called ECE 05 regulations (Luxembourg Accord) can be met by a combination of engine modification,
agreed on 21.7.87
oxidation catalysts or three-way catalysts depending upon the car model. A further tightening of controls for csrs with engine capacity below 1.4 litres is under discussion. Even more severe exhaust controls could be envisaged 1.e. to meet the standards now current in the USA, Japan and Australia involving all cars equipped with advanced catalyst systems. CAR EVAPORATIVE EMISSIONS These VOC emissions originate from: 0
vehicle fuel systems (as a result of fuel evaporation through vents open to the atmosphere). They occur:
- during a
period when the vehicle is stationary with the engine hot
(hot-soak losses)
- when - when
being driven (running losses) standing and subjected to temperature changes (diurnal losses)
displacement of vapours during car refuelling Evaporative emissions can be controlled by three routes:
-
the use of small carbon canister system installed in the vehicle. These have already been fitted to vehicles throughout the USA for some time and are beginning to find their way on to cars in Europe. By enlarging these canisters the refuelling losses could be captured as well.
- Reduction
of gasoline volatility which affects both vehicle fuel
system and refuelling emissions.
- Vapour recovery during vehicle refuelling which involves the transfer of vapours displaced from the vehicle tank to the service station tank during refuelling by use of specially designed filling nozzles, hoses and lines (so-called Stage 2 controls). In order to evaluate the effect of some of these measures CONCAWE has carried out a number of studies including come experimental work.
904 The conclusions were:
- vehicle and fuel system design has the greatest influence on evaporative emissions from vehicles. Fuel volatility has a significant but smaller effect
- under
standard test conditions (26-3OoC) small carbon canisters reduce
evaporative emissions by some 90%
- enlarged carbon -
canisters would enable refuelling losses to be reduced
by more than 95% a reduction in vapour pressure (RW) of 10 kPa under the standard test conditions would only reduce emissions by some 23%. However, under typical ambient temperatures in the market, which are for a large part of the year below 26-30°C, a 10 kPa vapour pressure reduction would give a lower emission reduction and would lead to unacceptable low volatility if applied to the lower R W summer gasolines. A smaller reduction in RVP to the 60 kPa level in summer would only reduce emissions by 10%. Furthermore RVP controls would have little or no effect when VOC emissions control equipment such as carbon canisters are in place.
COST-EFFECTIVENESS ASPECTS CONCAWE has carried out a number of studies (3) to evaluate the costeffectiveness of a number of control measures applicable to VOC emissions. Most of the control options require capital investment for new equipment and some maintenance and operating costs are incurred. In line with common industrial practice the capital costs are converted into an annual capital charge which reflects the required return on capital, lifetime of equipment (technical and economical), taxation required and inflation
-
if any. A
capital charge of 25% is normally applied by CONCAWE for oil industry
-
investment. A more detailed account of these costing aspects is given in (4). The costs shown below are in 1986 USD i.e.
1 USD
-
2.5 NLG
-
2.2 DM
0.65 GBP
In principle the following controls could be applied to vehicle evaporative emissions. (a) enlarged carbon canister (b) RVP plus Stage 2 (c) small carbon canister plus Stage 2 Re. (a), there is a large range of costs being quoted for the enlarged carbon canister, ranging from USD 20 by EPA to USD 80 and even higher from US car industry. On the basis of a range of USD 20-80 per canister and a conservative estimate of 90% vapour retention the cost-effectiveness can be calculated at USD 335-1340/ton VOC recwered. The potential European recovery
905 is 1.1 million t/yr when the complete European car population is fitted out with the enlarged canister. Re. (b), reduction of gasoline RVP means removal of butaae which is a high octane component and replacing it by lower RVP components of the same octane number. This will mean a downgrading in value of butane, finding a new outlet for it and the installation or modification of gasoline upgrading capacity such as catalytic reforming. For a 10 W a RVP reduction to European summer gasoline to give an emission reduction of lo%, some 0.1 million t/pr, a cost-effectiveness of USD 2100/t VOC is calculated. Stage 2 vapour recovery of refuelling emissions at service stations means the installation of special delivery hoses and new dispensing nozzles. Based on US experience and an average of 6 nozzles for European service stations with a throughput of 1200 ms/yr, a cost-effectiveness of USD 5000/t VOC is calculated. This assumes a capital cost of USD 17 000 per service station and 902 recovery of refuelling emissions i.e. 0.16 million t/yr if all 150 000 European service stations would be equipped with Stage 2 equipment. This recovery rate is significantly more optimistic than the 56-86% efficiency quoted by EPA depending upon the levels of maintenance and enforcement. Clearly alternative (b) is much less attractive both from potential VOC recovery and cost points of view, also illustrated in Appendix 2. Re. (c). CONCAWE has considered this option at an early stage but has discarded it because of the high incremental costs of Stage 2 (USD 5000/t VOC) compared with the cost of enlarging the canister. EPA has estimated this cost to be USD 1460/t VOC (ex-refuelling) compared with USD 770/t VOC (ex-evaporation/refuelling) which is in the middle of the CONCAWE range. As mentioned already EPA considers Stage 2 to have a lower efficiency to recover VOCs than canisters. TRENDS ON EXHAUST AND EVAPORATIVE EMISSIONS FROM GASOLINE ENGINED CARS CONCAWE has developed a computer model which can prwide data on the potential of various VOC control strategies to reduce emissions over a time period when there is a growing European car population. The results of the application of such a model are shown in Appendix 3. Comparison of Case 1 (do nothing) and Case 2 highlights the benefits that have followed from the progressive implementation of ECE standards up to and including ECE 04. However, despite this progress, growth in car population beyond the mid 80s exceeds the ability of the ECE 04 regulations to restrict growth in VOC emissions.
306
The Implementation of ECE 05 regulations (Case 3) will prevent growth in VOC emissions but the effect of car population growth especially in the muall car sector limits the long term benefits. The addition of controls to reduce vehicle evaporative and refuelling emissions show that enlarged carbon Canisters (Case 5) give a significant further improvement overall. RVP plus Stage 2 (Case 4) is clearly less efficient for recovery of these emissions. Finally, the best result ie achieved by a combination of applying US standards to exhaust emissions and enlarged carbon canisters to vehicle evaporative and refuelling emissions (Case 6). REFINERY AND DISTRIBUTION EMISSIONS Refinery emissions from crude oil receipt, refining and product dispatch are discussed in (5). In the case of crude oil receipt, the changeover to segregated ballast with tanker fleet renewal over time (prescribed in the MARPOL 74/78 Convention) will have the complementary effect of virtually eleminating hydrocarbon emissions at crude oil discharge locations by the equivalent of 1.5% of the total 10 million t/yr from man-made sources. Refinery emissions, based on the study of a hypothetical refinery, represent 1.7% ot total emissions. Principal sources considered were:
- process plant fugitive emissions; - waste water treatment fugitive emissions; - crude oil and relevant component and product
tankage.
Available controls include formal programmes of monitoring and maintenance for process plant fugitives, floating covers for waste water separator bays, and the installation of rim-mounted secondary seals in selected floating roof tanks. These controls could reduce the total emissions of 0.17 million tlyr by 0.07. 0.02 and 0.02 million t/yr respectively at cost of 100, 500 and up to 3000 USD/t. Emissions in the distribution sector occur when discharges are made from tanks of road and rail cars, barges and ships, and also when tank filling occurs at depots and service stations. Control measures that can be taken depending upon the particular situation include vapour balanclng/collecting and avoidance of splash loading e.g. by bottom loading. A further step could be the installation of vapour recovery units at distribution depots. Discharge of gasoline into underground tanks at service stations gives rise to vapour loss. This can be contained by some 90% if the displaced vapours are returned to the bulk road tanker by an additional hose connection. These facilities are normally referred to in the USA as "Stage 1" vapour recwery at service stations. Retention of the VOCs is only effected if the
907
road tanker loading terminal has a vapour recovery system and therefore in Europe, Stage 1 is taken to include these facilities. The cost-effectiveness of Stage 1 controls has been estimated as USD llOO/t VOC for a recovery of 0.2 million t/yr. CONCLUSIONS The state of knowledge concerning the role of VOC emirsions as ozone precursors is sufficient to require that VOC control measures should be introduced. There is still debate concerning an acceptable level particularly when taking account of natural VOC emissions. The largest sources of man-made VOC emissions are from the gasoline vehicle sector and from solvents. Within the gasoline vehicle sector exhaust VOC emissions are the largest contributor. European legislation already in place will prevent a further increase in these VOC emissions from increasing vehicle population. A further drastic decrease could be obtained by applying US and Japanese type legislation, resulting in the extension of advanced catalyst systems to all cars in Europe. Such measures of course also reduce very significantly NOx and CO emissions. Vehicle evaporative and refuelling emissions, the next largest source, can most efficiently and at lowest cost be reduced by enlarging the carbon canisters which are already a well-proven trouble-free and cheap control for evaporative VOCs on vehicles. Other alternatives involving gasoline volatility controls and so-called Stage 2 controls have either a low recovery efficiency and/or a poor cost-effectiveness. Experience with Stage 2 controls in the USA has shown that enforcement of maintenance and upkeep of the equipment is essential if the claimed 90% VOC recovery rate is to be maintained, a formidable task in an European context of 150 000 service stations. VOC emissions from the refinery and gasoline distribution sectors represent only some 5% of man-made emissions. These emissions can be reduced by half by a combination of additional refinery maintenance and inspection measures and Stage 1 vapour recovery with a cost-effectiveness comparable to that of enlarged carbon canisters for reducing evaporative emissions.
903 REFERENCES
1.
A national inventory of biogenic hydrocarbon emissions. Lamb, Guenther, Gay and Westberg. Atmospheric Environment Vol 21, No. 8 pp. 1695-1705, 1987 (GB)
2.
CONCAWE Report No. 87/53 Trends in motor vehicle emission and fuel 1987 update. CONCAWE, The Hague. 1987 consumption regulations
3.
CONCAWE Report No. 6/87 Volatile organic compound emissions in Western Europe. Control options and their cost-effectiveness for gasoline vehicles, distribution and refining. CONCAWE, The Hague, 1987
4.
CONCAWE Report No. 88/51 Capital and operating cost estimating aspects of environmental control technology residue hydrodesulphurization as a case example. CONCAWE, The Hague, 1988
5.
CONCAWE Report No, 87/52 Cost-effectiveness of hydrocarbon emission controls in refineries from crude oil receipt to product dispatch. CONCAWE, The Hague, 1987
-
-
Appendix 1 Emissions of volatile organic compounds in Western Europe (OECD) (tonnes x lo3)
(X)
1010 180 2500
10.1 1.8 25.0
Mobile sources Gasoline vehicles
- Evaporative - Refuelling
emissions
- Exhaust
Sub total
Diesel vehicles Aircraft Railways Coastal and inland shipping
3690 300 40 40
3.0 0.4 0.4 0.1
10
Sub total
36.9
4080
40.8
Oil industry Production Marine transport and crude terminals Refineries Gasoline distribution
20 150 170 310
Sub total Solvents Manufacturing industry Natural gas (non-methane) Solid waste disposal Stationary combustion Total Anthropogenic Natural (Trees, etc.) Grand Total Note: -
All values exclude methane
0.2 1.5 1.7 3.1 650
6.5
4020 410 650 110
40.2 4.1 6.5 1.1
90
0.9
10 010 10 000 20 010
100
-F-
EVAPORATIVE LOSS CONTROL COST-tw tCTlVENESS AND RECOVERY POTENTIAL,
-1-
STAGY 2 ALONE
4600
s / t
R E C 0 V E R E
IARQE CARBON
D
1.1Mt
0.-
0.1Mt
0.1-
0.2Mt w
0 10
W.EUROPE HYDROCARBON EMISSIONS FROM MOGAS VEHICLES 7500 NO EEC CONTROLS
7Ooo
6100 (ooo
T SIQO 0 T5ooo A
4100 ECE UPTO 01
E M
a
I
f
3100 Kt 0s
I 0 N
s
ECEOS + RVP +SllAGE 2
2100 ECE 05 + URGE CANISTERS
loo0 CANISTERS
100
0 1970
1990
2010
T. Schneider et aL (Editors),Atmospheric Ozone Research and its Policy Implications 0 1989 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands
911
OPTIONS FOR VOC-REDUCTION I N THE MECHANICAL AND ELECTRICAL ENGINEERING INDUSTRY
J . Nobel Association o f the Mechanica Zoetermeer (The Netherlands]
and Electrotechnical Industries FME,
INTRODUCTION In this paper I will go into the situation regarding the control1 and reduction of the emissions of hydrocarbons in the mechanical and electrical engineering industries in the Netherlands. In the first place I will give attention to the origin and extent of the hydrocarbon emissions. Thereafter I will consider the technical process and corporate economical consequences of steps to reduce these emissions. These reduction measures can be split up between methods of prevention at the source (by means of the use of alternative raw materials) and alternately the use of control1 and purification techniques. Both of these methods of controll and prevention have advantages and disadvantages. It will become clear, that the choice between these methods is dictated by the extent to which the reduction or prevention has to be realised within the shorter or longer term. THE ASSOCIATION FIE The Association of the Uechanical and Electrotechnical Industries FIE is an independant, private law organisation of industrial enterprises. The FUE cares for the collective and individual social, economic and technical interests of her members. The membership of FUE consists of some 1 . 1 8 0 industrial enterprises that achieved a collective turnover in 1987 of some 60 billion guilders. The products manufactured by the members of the associatioh know a great diversity (for example aeroplanes, bicycles, electronical apparatous, ships, steel mills, trucks, etc.). A number of the members are engaged in the field of environmental equipment. number of employees
<
50
number of member corp. 469
number of employees in service with these corporations 11.400
50- 100
281
19.900
100- 500
367
69.700
500
66
178.000
total
1.183
279 .OOO
)
Fig. 1 . Table showing the constitution of membership per 1987.
912
Calculated in terms of the total number of employees in the service of her members, the Association FHE is representative of about 80% of the mechanical and electrical engineering industries and is as such the largest industrial sector organisation in the Netherlands. The author of this paper is in service of the associon in the capacity of management advisor for environmental affairs. THE EXTENT AND ORIGIN OF HYDROCARBON MISSIONS The sources of hydrocarbon emissions can be divided into five sectors. The following table gives, divided into sectors, an oversight of the total anthropomorphic emissions in the Netherlands (in k.tons per year) as well as a percentage of the total (source: Institute of Public Health and Environmental Affairs, years 1981, 1 9 8 5 ) .
source
I
emission in k.tons/year
share in % (1985)
1985
Uobile sources (traffic) Industrial sources Non-industrial sources Petrol fillingstations Combustion emissions
200
Total anthropomorphic
190
41%
120
150
32%
90
105
23%
10
10
2%
8
10
2%
428
465
100%
Fig. 2 . Oversight of the total anthromorphic emissions in the Netherlands and percentage of the total. In this context non-industrial sources mean: personal residences and small companies that are not classified as industrial activities. A further analysis of the industrial sources shows that the share of the metal industries amounts to 21% ( 3 2 k.tons). This corresponds with 7% of the total anthropomorphic hydrocarbon emissions in the Netherlands. In this regard the contamination due to transnational importation of air pollution has not been taken into account. The sources of the hydrocarbon emissions within the metal and electrical engineering industries are extreemly diverse and this hinders any standard
913
approach. The prime sources of origin are painting, degreasing and cleaning. In consequence we will now give extra attention to the emission of hydrocarbons during paint application because that process is responsible for the largest proportion of the emissions.
source Closed area paint application Open area paint application Degreasing Diverse Total
emission
(%)
52 16 16 16
loo
(=
32 k.tons)
Fig. 3. Table of hydrocarbon emissions of the mechanical and electrical engineering industries of the Netherlands. Other than at the suppliers of raw materials and paint, where the hydrocarbons are normally to be found in closed reactor vessels, drums, pipelines and the like, the painter applies the paint to the metal surface with the intention that the hydrocarbons evaporate during drying. A characteristic of this method of application is the large surface area (about 500 km') that is treated per year together with the evaporation that takes place at an enormous number of locations. With painting operations a distinction can be made between 'closed' and "open' procedures. Typical for this distinction is that in the case of 'open' applications (that is in the open air) the contaminated airstreems can not be controlled. In this regard we can think of, among others, painting or conservation of off-shore installations, bridges, cranes etc. In the case of 'closed' procedures the contaminated airstreens will mostly be controllable. In this regard we can think in terms of extracted air from painting cabins, drying ovens and the like. An undifined area can however be found in the case of very large cabins for use in spraypainting extreemly large items such as aircrafts, space shuttles and the like. The amount of air to be treated can, in these cases, grow to such a volume, that problems of scale will be encountered, such as that the treatment installations will not be large enough or that the hydrocarbon concentrations will be too low for effective or economic treatment.
914
REDUCTION OF HYDROCARBON MISSIONS (alternative raw materials) and D r e v e n w at the soThe present use of hydrocarbons can be explained by their (combination of) chemical and physical properties such as speed of evaporation, surface tension, boiling point, polarity, etc. Total or partial replacement by environmental friendly alternatives is as such no easy t a s k . A great deal of research into alternative solutions with the same properties is being conducted especially in the field of industrial paints. The achievement of an equivalent quality turns out to be a recurring problem. It is often not possible to make concessions with regard to specific properties, especially in the sort of situations whereby the paints primary purpose is that of corrosion prevention. When it comes to the exterior appearance of the painted surface, industry is often confronted with reserves regarding the acceptance in the market of the endproduct. For example it will take some time before the average Dutchman or American would buy a car with a matt finish. Never the less progress is slowly but surely being made on a number of fronts. Just as well because prevention is better than cure.
. .
.
u r V use of D This can in principle be compared with putting the cart before the horse. However, the application of add on or integrated purification techniques cannot be completely avoided, for example in the cases where hydrocarbon emissions cause a direct danger for public health or the environment. It should be remembered that the availability of suitable purification technologies for companies within the mechanical and electrical engineering industries is limited. In this regard it often concerns a great number of small sources of emission per company. The installation of charcoal filters, afterburners, biological filters etc. rapidly become steps out of all proportion to the problem. For a central treatmentpoint, of all the separate enissionpoints, the same applies. Other than the availability of purification techniques the nature of the emissions also complicates there elimination. Within the metal and electrical engineering industries the emissions are often characterised by: - great variation in concentrations (both qualitative and quantitative) ; - non-continuous production processes; - (often) high temperatures and concentrated Contamination with sticky particles (baking ovens), so that the application of a number of purification techniques require the use of pretreatment exhaust gas apparatous with the consequence that the chance is great that from an air pollution problem a water pollution problem will be created.
915
It will be apparent that this will be an insurmountable problem for many companies. On top of this it should be noted that both in Western Germany and Japan the installation of afterburning systems is on the return. The cause of this can be found in the corporate economical and technical production considerations. It is also the case that in these countries people are concluding that prevention at the source is the best long term solution. Summing up we can say that both for prevention at the source as well as the application of useable (and payable) purification techniques much further research is needed. Source prevention deserves the highest priority for Sofar that one seeks a rational long term solution. Corporate economical and technical process requirements give this vision a decisive priority motivation. CORPORATE ECONOMIC FACTORS With regard to the foregoing it can be stated that the sources of hydrocarbon emissions are extreemly diverse. This diversity is reflected in the preventative measures and the related costs. A generalisation regarding preventative costs in the mechanical and electrical engineering industries should be treated with reservation when it comes to the evaluation of specific cases. It is in any event clear that the annual costs of applying purification techniques are at least a factor ten greater than those of prevention at the source with the help of alternative raw materials. In this regard it should be noted that the applicat.ion of alternative raw materials (water based paints, powder coating, ultra violett finishing, electron beam etc.) necessitate a degree of production technological change. There is at this moment little to be said regarding the extent and complexity of these expected technological changes. With regard to the foregoing factor ten, we have also taken into account a gradual process technology change via replacement investment. The Association FIE has taken the stand that reasonable and necessary measures to limit emissions can in general be accepted but only if they are cost effective. This requires a reasonable spread of measures in terms of time, in line with measures in foreign countries (namely European), a reasonable expectation that reduction of the emissions of hydrocarbons could actually be achieved, and that all taking into account the transnational causes of air pollution. It is self evident that in evaluating the corporate economic consequences of special environmental protection measures, the total costs and effectivity for the ecological defence must be taken into account.
916 THE POSITION OF PAINT-APPLICATORS I would like to take a short look at the position of paint-applicators, that is to say the companies that, given their production process, are required to use hydrocarbon releasing raw materials. These are also the companies ment in the saying 'the polluter pays'. They are also the companies whom the government, in ever increasing intensity, places under pressure via a permit system to invest in prevention techniques, to relocate the factory etc. The position of the applicator has become most uncomfortable in the last years. On one hand they experience the increasing,pressure of environmental laws, but on the other hand they are dependant on their suppliers of raw materials and their customers for so far as it concerns the quality of raw materials and end product and as such for their economic position in the market. Last but not least they are the ones who become trapped between the differences between federal and local government policies and laws. It is not for nothing that the industry pleads for a national approach that takes into account developments in environmental affairs control1 in international context so that technical environmental measures can, given the state of the art in technology, be realised within the bounds of economic responsibility. CONCLUSIONS For the elimination of hydrocarbon emissions in the metal and electrical engineering industries, primary attention will have to be given to the reduction of the use of paints with a hydrocarbon content. Seen from the point of view of corporate economic and process-technical factors the use of low hydrocarbon content or hydrocarbon-free raw materials is the only rational method to achieve major emission reductions. The use of purification techniques should be limited to situations where one could speak of a direct threat to public health. The transnational air pollution from Western Germany and Belgiua (among others) and the effect on the Dutch competative trading position makes an international approach necessary.
317
SESSION XV
POLICY ISSUES AND CONTROL STRATEGIES
Chairmen
V.A. Newill G.J.R. Wolters
This Page Intentionally Left Blank
T. Schneider et al. (Editors),Atmospheric Ozone Research and its Policy Implications 1989 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands
EMERGING U.S.
POLICY REGARDING STRATOSPHERIC AND GROUND LEVEL OZONE
D.CLAY United States Environmental Protection Agency, 401 H Street S.W., 20460 Washington D.C. (USA)
INTRODUCTION I appreciate the opportunity t o speak today t o t h i s distinguished group o f s c i e n t i s t s and professionals about the ozone problem i n the United States and where our e f f o r t s t o deal w i t h it are headed. I believe that t h i s has been an: - important - successful - and, from my viewpoint, a very useful conference (not only from the technical papers presented but because o f the opportunity t o meet and t a l k with many o f you). I must confess, there are times when I wish science could provide us simple answers t o complex problems - but that i s j u s t wishful thinking. I have also been struck by: - the overlap bet'ween science and p o l i c y - the high degree o f international cooperation - the i n t e r r e l a t i o n o f the two ozone problems - how f a s t science i s moving i n t h i s area Let me t u r n f i r s t t o the groundlevel ozone problem. H ISTORY U.S. p o l i c y i n ozone has been shaped by the h i s t o r y o f regulation. I n the early 1970-s the problem o f "tropospheric ozone" was p a r t o f a broad set o f pollutants called "smog". There were predictions t h a t by 1973 there would be "smog disasters" w i t h hunderds o f thousands o f casulties. The 1970 Clean A i r Act (CAA) was a sign t h a t the U.S. was going t o conquer a i r pollution, j u s t as i t had succeeded i n going t o the moon. Clean a i r was going t o be achieved by 1975, even i f large scale l i f e s t y l e changes were required. A very ambitious agency was set out w i t h few t o o l s t o solve
919
920 the problem (and, a t t h a t time, a fundamental l a c k o f understanding about the problem). One o f the early lessons we learned was t h a t notwithstanding the 1970 CAA, Americans were not ready t o make the social s a c r i f i c e s t h a t would have been required t o r e a l l y a t t a i n an oxidants standard i n 1975. I f possible a t a l l , i t would a t a minimum have required such steps as l a r g e scale gasoline r a t i o n i n g and/or high taxes on car ownership I n most l a r g e c i t i e s . Even lesser steps, such as parking r e s t r i c t i o n s , bridge t o l l s , and l i m i t s on developments that attracted more cars, proved more than many areas would w i l l i n g l y accept.
-
-
-
-
-
-
I n response t o the problem, Congress amended the CAA i n 1977 by: extending the attainment deadlines a t l e a s t t o 1982 f o r a l l areas, and t o 1987 f o r the worst areas, and c a l l i n g f o r a new round o f planning (note i n our system, the Federal Government i s responsible f o r goals and standards t o be met nationwide, while s t a t e governments are responsible f o r developing plans t o achieve the goals); requiring t h a t EPA review the e x i s t i n g ambient standards; g i v i n g automobile manufacturers more t i m e t o meet mobile source standards ; s e t t i n g up more speoific i n t e r i m requirements f o r areas not a t t a i n i n g ambient standards, including the requirement f o r emissions tests (inspection and maintenance) o f p r i v a t e cars i n some areas; p r o h i b i t i n g EPA from using c e r t a i n tools, such as bridge t o l l s and review o f i n d i r e c t p o l l u t i o n sources t o promote attainment. But Congress also gave EPA more tools. These included: t i g h t e r control requirements on stationary sources. Areas were required t o apply "reasonably available control technology" t o e x i s t i n g hydrocarbon sources. EPA put out tough control technology guidance on j u s t what constituted "reasonably available controls"; new sources were required t o use technology which presented the "lowest achievable emissions rate. (LAER). I n addition, before new sources could be constructed, they had t o f i n d and acquire o f f s e t t i n g reductions which more than compensated f o r the new emissions which the source would put out; b e t t e r sanctions were provided t o use i n cases where s t a t e and l o c a l governments d i d not l i v e up t o t h e i r planning and i q l e n e n t a t i o n r e s p o n s i b i l i t i e s under the CAA. Examples o f these sanctions include a ban on the construction o f new major stationary sources and the withholding o f highway construction funds. While the use o f these i s always a subject
921
o f p o l i t i c a l controversy, i t i s f a i r t o say t h a t they have been a f a c t o r i n stimulating action by state and local agencies and by industry. So where are we now? How much progress has been made? We have made progress. This i s reflected i n a i r q u a l i t y and emissions data. Our best estimates (using improved monitoring networks t h a t have been put i n place since 1978) are that on nationwide average, ozone a i r q u a l i t y has improved by 13% and hydrocarbon emissions have decreased by 19% (from 1977 - 1986). PROBLEM Yet despite t h i s progress (including reductions i n peak exposures and numbers o f exceedances), we s t i l l have not met the goals we set f o r ourselves. Data f o r 1987 reveals t h a t 68 areas i n the United States d i d not a t t a i n the .12 ppm ozone standard. When we look f o r reasons why t h i s i s so, we f i n d that there i s no one simple answer. I believe the e f f o r t f a i l e d t o reach attainment everywhere because: - as i n 1970, the 1977 amendments d i d not allow much time f o r planning. I n some cases, t h i s hurried approach required the use o f planning assumptions such as VMT growth rates which subsequent experiences has shown were c l e a r l y wrong; - also the tools we use f o r predicting ozone formation and needed emissions reductions needed improvement and s t i l l do. Current empirical models are an improvement on proportional rollback, but f u r t h e r refinement i s s t i l l neeeded. We would l i k e t o make greater use o f photochemical g r i d modeling, including regional transport modeling, but these models are s t i l l expensive and take a long time t o set up and run; - i n retrospect, i t i s clear t h a t we s t i l l have a l o t o f work t o do on emissions inventories. Calculating needed percent reductions does not do you much good without a good idea o f what i s a c t u a l l y being emitted. I n some cases we believe that inventories developed f o r the post-1977 plans may have understated emissions because o f e r r o r s i n emissions factors o r other means used t o calculate emissions. I n other cases emissions from some types o f sources, such as waste disposalor wastewater treatment, may have been omi t t e d a1together. I n some cases, rules that were adopted by s t a t e and l o c a l governments have not produced the kinds o f redcutions we expected they would achieve. We allowed rules t o be estimated t o 100% effectiveness. Small area sources, such as solvents, paints and coatings, and other consumer products are a significant source o f VOC. Infact, we estimate t h a t 49% o f U.S. VOC emissions come from small area sources, versus 38% from
922
mobile sources and 13% from large point sources. These are inherently more d i f f i c u l t t o deal w i t h from a control standpoint. As a r e s u l t o f a l l these issues, we are now looking again a t how t o address the ozone nonattainment issue. A l l o f the complexities mentioned above are s t i l l w i t h us plus some additional ones: - one o f the problems we have with ozone i s the long range transportation i n our northeast ( i n Europe t h i s presents an international problem). Addressing long-range ozone transport w i l l c l e a r l y be necessary f o r some areas t o a t t a i n the standards, but then we are i n the p o s i t i o n o f making some areas bear costs while other areas derive the benefits; - the r o l e o f NO, control as a possible t o o l i n reducing ozone formation i s g e t t i n g increased attention. However, t h i s has t o be analyzed c a r e f u l l y on an area-specific basis, since available information indicates that NO, plays a dual r o l e as both a promoter and a scavenger o f ozone, and t h a t NO, controls can lead t o greater ozone concentrations i n some ocat ions as well as less ozone i n others. The one lesson I hope we have learned i s t h a t you can-t mandate attainment through the use o f a r t i f i c i a l l y short deadlines f o r act on. While progress has been made, i t i s important f o r us t o recognize t h a t t h i s problem i s going t o be w i t h us f o r a while even despite our best, most vigorous e f f o r t s t o reduce it. One important aspect o f the ozone problem, which I believe w i l l influence the solution, i s t h a t there i s not widespread acceptance o f the nature o f the problem i n the eyes o f the U.S. public. The average c i t i z e n does not accept what you believe, and discuss so eloquently here: t h a t ozone i s a serious health (and welfare) problem. U n t i l we have such acceptance, I believe i t w i l l be very d i f f i c u l t t o force the American c i t i z e n t o change h i s l i f e s t y l e , even though such change w i l l l i k e l y be required t o a t t a i n our current standard. There i s also the question o f whether our current standard i s adequate t o protect public health w i t h an ample margin o f safety. Based on discussions I have had a t t h i s meeting, many of you do not believe so and believe a new standard, perhaps using a longer time period, w i l l be requi red. I n s e t t i n g our standards under the CAA, the Administrator i s required t o consult w i t h the Clean A i r S c i e n t i f i c Advisory Committee (CASAC): - t h i s process i s underway; - CASAC w i l l be g i v i n g the Administrator t h e i r advice t h i s f a l l ;
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Administrator w i l l t h i n k about i t and propose any change f o r public conrnent he believes i s necessary; Administrator then makes a decision based upon the whole report; obviously the process w i l l take some time and i t w i l l be several years before a new standard could be f i n a l i z e d ( i f Thomas believes i t should be changed). So where does that leave us? extensive non-attainment o f current standards; pressure t o make the standard more stringent; two major attempts t o achieve the standards; non-acceptance by the public that ozone i s a 'real" problem (except perhaps 10s Angeles, CA) and an unwillingness t o change l i f e s t y l e t o achieve it; an increase number o f lawsuits t h a t require one t o take area specific action; and no real concensus o f what t o do now. So what are we doing?
CURRENT EFFORTS TO SOLVE THE PROBLEN We are working on Wree fronts: a. l i t i g a t i o n b. congressional c. administrative
Litlaatlnn Not much we can do here! except f i g h t a series o f lawsuits, which i n general, we have not been winning. Where we lose, we are usually required t o w r i t e a Federal Implementation Plan (FIP) f o r a l o c a l area. We do not l i k e t o - states and l o c a l do not want us t o but t h a t i s the way t h i s law is w r i t ten. I do not want t o dwell on t h i s p o i n t but i t i s important t o r a i s e because i t i s the default option i f Congress does not change the law o r i f EPA does not put out a p o l i c y t h a t would convince a judge t h a t i t i s b e t t e r than a FIP. Then the agency i s on a course t h a t w i l l increasingly i n v i t e our w r i t i n g plans a t the federal l e v e l f o r state and local areas.
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Conaressional We believe the best solution i s f o r the Congress t o act and t e l l us what i s i t they believe should be required. Congress i s considering several b i l l s a t t h i s t i m e but t h e i r passage t h i s year i s very uncertain - mainly
924 because i t i s an election year (there i s not much t i m e and ozone i s t i e d w i t h other controversial issues such as acid rain). B i l l s being considered i n both parts o f the Congress d i f f e r i n d e t a i l but generally include: - d i v i d i n g the non-attainment areas i n t o d i f f e r e n t groups (3-4) depending on the degree o f non-attainment; - d i f f e r e n t attainment dates; - d i f f e r e n t requirements (more stringent f o r d i f f e r e n t data); - requiring EPA t o w r i t e some more national standards; - tightening up on mobile sources emissions. However, as I said earlier, i t i s not c l e a r t h a t these amendments t o the CAA w i l l pass. I n the meantime, what i s the EPA doing?
Eebcrh EPA proposed a p o l i c y l a s t f a l l f o r how we would proceed i n the absence o f congressional action. We have been receiving comments on the p o l i c y (more negative than positive) and we have not reached any f i n a l decision. The key t h r u s t o f t h i s p o l i c y as proposed i s f o r states t o undertake a new round o f planning f o r those areas t h a t d i t not a t t a i n the standard by 1987. This planning w i l l have t o incorporate several considerations, including regular rates o f prrgess (3% reduction i n VOC emissions per year net o f growth beyond federal requirements i n areas t h a t are long-term nonattainment); improved emissions inventories and attainment demonstrations; correction o f deficiencies i n e x i s t i n g rules; and inplementation o f federal measures such as onboard and gasoline v o l a t i l i t y control. EPA has also proposed national rules on: - =line v o l a t i l i t r t o reduce the vapor pressure - worth about 3%o f our inventory; pnboard refuelina controls - worth about 8 , we are i n the middle o f r u l e making f o r the r u l e s as w e l l as the control o f emissions fee; pansfer. storaae and disDosal f a c i l i t i e s and other rules are being considered and our p o l i c y asks f o r c m n t s on the c r i t e r i a f o r choosing rules. However, as noted above, we believe t h a t most o f the e f f e c t i v e national rules have been w r i t t e n and t h a t we cannot achieve attainment by w r i t i n g a series o f national rules. I n any event, we w i l l wait t o see what Congress does before f i n a l i z i n g our policy. I f Congress were t o act, there may not be a need t o f i n a l i z e the p o l i c y . I n the meantime, i t i s our i n t e n t i o n t o s t a r t the next round o f planning i n the next three weeks.
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We plan t o issue SIP c a l l s t h a t w i l l be i n two parts: 1. noting the States t h a t have a problem: - requiring them t o f i x past items they had said they would do and have not done "leveling the playing f i e l d " ; - requiring them t o s t a r t developing a current, accurate emissions inventory; - we believe these are the minimum requirements t h a t would e i t h e r be required by us o r the Congress. 2. Depends on the Congress: - i f Congress were t o act, we would, o f course, implement the law as written; - i f Congress does not act t h i s year we w i l l f i n a l i z e our p o l i c y and implement p a r t two o f the SIP process (probably l a t e f a l l o r winter). This would (depending on how we f i n a l i z e our policy) requires States t o demonstrate attainment o f d i f f i c u l t rates depending on the severity o f t h e i r non-attai nment problem.
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So where does t h i s leave us? We have a serious health problem w i t h ozone (although i t i s c e r t a i n l y b e t t e r than i t was when we f i r s t started). Here a t t h i s conference, scientists are t e l l i n g me t h a t the ozone problem may be more serious than we think. We have no r e a l acceptance o f the problem by the public. We have a plan underway t o address the problem - hopefully, w i t h congressional action - but i f not, we w i l l go forward anayway.
STRATOSPHERIC OZONE Now l e t me t u r n t o the other h a l f o f the ozone issue - stratospheric ozone - "good" ozone. in This Symposium i s very timely given the recent successes international negotiations i n Montreal, which show t h a t global cooperation i s possible; and the recent advances i n science, which show t h a t global stratospheric ozone losses are occuring.
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Chlorofluorocarbons (CFC's) have been o f regulatory concern i n the U.S. since f i r s t linked t o potential ozone depletion i n 1974. Over a dozen years o f intensive international s c i e n t i f i c research has strengthened our knowledge t h a t CFC*s can deplete ozone. I n 1978, the United States, acting u n i l a t e r a l l y , banned the nonessential aerosol uses o f CFC-s. This action, however, was not widely imitated elsewhere i n the world.
326 Increasing i n our s c i e n t i f i c understanding on the problem coupled w i t h the rapid growth o f CFC consumption i n the mid 1980-s (CFC use has grown a t twice the r a t e o f overall economic growth), has brought t o the World's attention the need f o r international action t o control CFC use. I f no national o r international controls were put i n place, we would expect CFC use t o grow both i n the United States and abroad, w i t h large depletions o f ozone by the middle o f the 21st century (40% by 2075. Recognition o f t h i s s i t u a t i o n l e d i n 1986 t o the resumption o f serious international negotiations which culminated i n the b n t r e a1 Drotocol on substances t hat deDlete the ozone laver, signed i n Montreal on September 16, 1987. I believe t h i s i s t r u l y a remarkable achievement and i l l u s t r a t e s the t r u e international acceptance o f the problem. 31 nations have now signed the Montreal Drotocol This landmark t r e a t y requires nations t o freeze t h e i r use o f CFC-s i n 1989 and 1986 l e v e l s and t o reduce t h e i r use o f CFC-s by 50% w i t h i n ten years. Use o f halons, a separate class o f bromine bearing compounds, w i l l be frozen a t 1986 l e v e l s i n 1992. Several features o f the Montreal Drotoco1 are p a r t i c u l a r l y noteworthy: the a b i l i t y o f each nation t o t a i l o r i t s reduction program t o meet i t s own needs, the encouragement f o r developing nations t o participate, the e f f e c t i v e and f a i r trade provisions, and the protocol's f l e x i b i l i t y i n responding t o new information.
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A l l o f these measures are designed t o produce the maximum international p a r t i c i p a t i o n i n the agreement. Let-s look a t some o f these provisions i n more d e t a i l . Each nation i s subject t o an overall consumption l i m i t f o r CFC's and halons, but i s free t o achieve t h i s l i m i t by any means. This provision allows nations t o t a i l o r programs t o t h e i r own needs. For example, i n the United States we have decided t o pursue a system o f allocated quotas t o manufacturers and importers. Selling o r auctioning the permit t o manufacture CFC's was considered but rejected because many believe t h i s would require an amendment t o the CAA. Developing countries are encouraged t o j o i n the protocol. They are allowed increased use o f CFC i n the short term i n exchange f o r t h e i r long term participation. The r e s u l t : minimal environmental e f f e c t s i n the short term but s i g n i f i c a n t environmental benefits i n the long term as these countries are directed away frw dependence on CFC-s. The p r o t o c o l encourages trade among p a r t i e s t o share t h e i r new technologies t h a t do not use CFC-s. Trade w i t h non-parties however, w i l l be r e s t r i c t e d . One year after the protocol enters i n t o force, imports f r o m non-parties o f bulk CFC's and halons w i l l be banned. A t f u t u r e meetings,
927 the protocol parties w i l l discuss possible measures t o r e s t r i c t trade i n finished goods containing o r manufactured with CFC's and halons from nonparties. F l e x i b i l i t y i s b u i l t i n t o the Montreal Drotocol. It c a l l s f o r regular reassessments o f science and regular meetings t o evaluate and revise the scope and stringency o f controls. The lo&mal orotocol i s a l i v i n g document t h a t w i l l evolve t o meet our future needs. An early t e s t o f t h i s seems 1ikely.
Hhat i s the United States d o i n d The United States i s s o l i d l y behind .the orotocol and i s acting quickly and decisively. We signed the protocol i n September 1987, the Senate r a t i f i e d i t i n March 1988, and President Reagan completed our r a t i f i c a t i o n process i n A p r i l 1988. I n December 1987, our agency proposed domestic regulations t o implement
the. EPA*s proposed r u l e closely tracks the protocol requirements. I t allocates production and consumption quotas t o producers and importers based on t h e i r 1986 market shares. These quotas are expressed i n terns o f ozone depletion potential, permitting producers and importers t o f r e e l y switch between individual substances w i t h i n each control group (CFC's and halons). EPA has collected and reviewed data from a l l producers, importers and exporters, and w i l l publish allocations t o producers and importers i n August. To enhance economic efficiency, persons who hold r i g h t s t o production and import o f controlled substances can s e l l those r i g h t s i n the free market t o the highest bidder. Several recent issues have arisen as we have begun our process t o implement the protocol. These include: - The W r e sources o f atmo-ric c h l o r b Even under the protocol, concentrat ions o f atmospheric chlorine w i l l increase s i g n i f i c a n t l y Compounds which are not controlled by the protocol (methyl chloroform, HCFC-22, and carbon tetrachloride) are one major source o f chlorine. The degree o f international p a r t i c i p a t i o n t h a t i s achieved i s another important determinant o f future chlorine levels. - The timina of reductions i n CFC use. By 1989 when the protocol takes effect, CFC use w i l l have risen 25%, and the "freeze" a t 1986 l e v e l s w i l l require s i g n i f i c a n t reductions i n CFC use. Lowering aggregate CFC demand
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(which moderates r i s e s i n CFC prices), by achieving e a r l y reductions i n CFC use w i l l ease the regulatory burdens. The w o r t a n c e o f encouraaina technoloa i c a l innovatipn I n s t i t u t i o n a l barriers - such as building codes that encourage CFC blown insulation and m i l i t a r y procurement specifications t h a t require use o f CFC solvents must be i d e n t i f i e d and overcome t o encourage e a r l y reductions.
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The potential increase i n r e a c t i v i t y o f VOC t h a t may make the stratospheric ozone problem worse.
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We see other future oolicv issues concernina the Drotection of For example, s i g n i f i c a n t progress has occurred even since the M o n t r d protocol was signed i n September l a s t year. Recent s c i e n t i f i c findings may require more stringent protocol reductions. I n March 1988, an international trends panel coordinated by the National Aeronautics and Space Administration found t h a t depletion o f 2 t o 3% had been observed over the l a s t decade above northern l a t i t u d e s . A depletion o f t h i s magnitude had net been predicted by current models, and i s greater than the depletion projected t o occur even w i t h the b n t r e a l protocol reductions. How s i g n i f i c a n t were these findings? Following t h e i r release, the Dupont Corporation, which produces one-quater o f the world’s CFC-s, announced t h a t i t would completely phase out t h e i r production. Pressure i s b u i l d i n g i n the U.S. Congress t o go f u r t h e r than the protocol requires i n phasing out CFC’s.
w We believe our most important task i s achieving r a t i f i c a t i o n o f the W t r e a l DrotocoL. While 31 nations have signed, only the U.S. and Mexico have r a t i f i e d the LlQntreal Drotocd. Timely r a t i f i c a t i o n and entry i n t o force by January 1, 1989 i s our number one task. Uhat are we doing t o achieve t h i s ? - We have n o t i f i e d a l l nations o f the findings o f the ozone trends report. - We have held discussions w i t h several countries on t h e i r domestic imp1ementat ion. - We have sent p o l i c y and technical missions t o key countries. We believe alternatives t o CFC-s must be encouraged. I n the United States, we are involved i n several j o i n t projects w i t h industry t o promote research and t o remove barriers. For example, EPA f a c i l i t a t e d the voluntary
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phaseout of CFC-12 by fast food packagers and is working with the mobile air conditioning industry to develop standards for recycled refrigerants. We are also beginning to work with developing countries to assist their efforts toward economic growth without reliance on CFC-s. In response to the recent findings of the ozone trends panel, the EPA Administrator, Lee Thomas, wrote to Mustafa Tolba o f UNEP to urge that the assessment process called for in the Montreal orotocol be accellerated so that the parties can meet as soon as possible to discuss tightening the protocol provisions. The Bontreal Drotocol exists because of the recognition that only concerted international action can protect the ozone layer. We must maintain our momentum and achieve rapid entry into force following ratification by 11 countries representing 2/3 of global consumption. Called for by the protocol and undertake the 1990 assessment process to determine if further concerted international action is necessary. One nation acting alone cannot solve the problem. OVERALL SUMMARY As I said in the beginning, I believe this Conference has been a success. Clearly new data has been presented often in a manner that made it complemented older data. Science will make progress, and it is the job of the policy person to guide in broad areas, but more important, to translate the scientific findings into meaningful control actions that will protect the people. Thank you.
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T. Schneider et al. (Editore),Atmoepheric Ozone Research and its Policy Zrnplications 1989 Elaevier Science Publiehere B.V., Amsterdam -Printed in The Netherlands
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OZONE CONTROL POLICY IN THE NFIIIERLISNDS
G.J.R. WOLTERS, S. ZWERVER and K.R. KRIJGSHELD Ministry of Housing, Physical Planning and Environment, Air Directorate, P.O. Box 450, 2260 ME Leidschendam (The Netherlands) ABSTRACT To reduce adverse effects in relation to ozone (and the related subjects of acidification and climatic change) far-reaching measures are necessary at European and even global scales. The approach in the Netherlands comprises ongoing research (risk assessment, model development) and further reduction of emissions of the relevant substances on a national basis and the promotion of internationally coordinated measures (Montreal protocol, protocols on NOx and VOC within the ECE-framework). On a national level measures are being developed (e.g. agreements with the Dutch industry on VOC- and CFK-emission reduction) that may go beyond internationally agreed reductions. INTRODUCTION At first glance, it seems that ozone involves problems which differ greatly in nature. However, this is deceiving. In fact, there is a strong inter-relationship among the photochemical processes which lead to changes in atmospheric composition in the various layers of the atmosphere. But there is also quite a bit of overlap in the substances - the precursors - which give rise to
Fig. 1. Direct involvement of several precursors in photochemical processes and greenhouse effect, arranged by atmospheric level.
932 the individual sub-problems: nitrogen oxides, non-methane hydrocarbons, carbon monoxide and carbon dioxide, methane, laughing gas, and the chlorofluorocarbons (Fig. 1). The overlap among these sub-problems with respect to both the substances involved and their effects, compels us to take the whole picture into account in developing related policies. Possibly the only differences occur in the time and phasing of the approach of each individual problem. Many sources and activities of a widely divergent nature cause the emissions of the substances I mentioned (Fig. 2). We also see, then, that the emissions from the different categories of sources affect all the layers of the atmosphere, the boundary layer as well as the free troposphere and the stratosphere. And it is precisely the most fundamental activities in our current societysuch as energy provision, transportation and mobility, agriculture which are responsible for the problems. and livestock
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Fig. 2. Major anthropogenic sources of the various precursors involved in atmospheric ozone-related changes and/or greenhouse effect. The practical possibilities for reducing the emissions of the various substances differ so greatly that, for the time being, the approach is focused primarily on those substances for which abatement currently offers the most possibilities: nitrogen oxides, the non-methane hydrocarbons and the CFC'e. I would like to deal with the following sub-problems successively, in this paper: ozone in relation to climate, depletion of the stratospheric ozone layer from CFC's, and
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increased ozone concentrations, in the bOmarY layer.
CLIMATE CHANGES When one hears "greenhouse effect", one thinks immediately of CO,. However, this substance is estimated to be responsible for only half of the problem. Other substances, such as methane, N20, CFC's and also 0, , have a share in this effect. Ozone presumably has a 5-10 precent share at the present time and some researchers believe that it will grow considerably in the future. Few or no models contradict the expectation that the average atmospheric temperature will continue to rise until the end of the next century. In Fig. 3 the estimated temperature rise is shown, with no ( A ) , moderate (B) or far-going abatement (C) of emissions of CO,, N20, CFC's and methane. Even with a very stringent approach, an average temperature increase of 1 to 2 ° C is expected during the second half of the 218t century.
Fig. 3. Calculated increase in global average temperature, in equilibrium, at different abatement scenario's; no abatement ( A ) , moderate (B) and far-going abatement ( C ) (ref. 1). There is need for a clear strategy for an effective abatement policy but, internationally, it has received little priority as yet. A s a long term goal, it can be stated that disruptions in the atmosphere resulting in climate change must be stopped as soon as possible. a tabilization of the concentrations of trace gases in the atmosphere may serve as a mid-term goal. This implies that anthropogenic emissions of CO,, CH,, .N,O, and CFC's, among other substances, will have to be rolled back significantly.
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Furthermore, the natural sinks for substances from the atmosphere (the Oceans and the biosphere) should be maintained and where possible reinforced, for example through reforestation. We will have to face up to the fact, especially as it relates to the contribution of CO,, that there are limits on the uninhibited use of energy. On a global scale the victims of climate effects are frequently not the same people as those causing them. For one thing, they will affect future rather than present generations. In addition, the contribution of the OECD countries in,causing the greenhouse effect is certainly 70 percent, while the areas vulnerable to flooding from a rise in the sea level lie for 70 percent outside the OECD countries. The industrialized nations (East and West) will have to acknowledge the main responsibility for the problem. Promoting international awareness will be an important element to start with. In any event, we will be working on concrete measures to reduce relevant emissions, e.g. of CFC's, nitrogen oxide and VOC, as will be discussed later on.
THE STRATOSPHERE The damage which has been done to the stratospheric ozone layer is illustrative of the careless way we have dealt with the atmosphere in the past. Although ozone depletion from CFC's was already diagnosed in the early 1970's, until recently it proved very difficult to reach international agreements to limit CFC's. A n 85 percent reduction in CFC emissions (and thus in CFC use) is needed in order to stabilize atmospheric CFC concentrations. Even then, the amount of ozone will ultimately decrease by 2 percent. With a decrease of only 50 percent in CFC emissions, which is the lower limit of the Montreal Protocol, ozone depletion will still amount to 5 percent over 50 years. We can be satisfied with the Protocol as a step in the right direction, but it is nothing more than a first step. The ozone layer is still not being protected from human activities as prescribed in the Vienna Convention. Relatively seen, it is an advantage that CFC policy involves a reasonably well definable target group of industrial users and producers. Moreover, there can be no discussion about natural contributions to total emissions since these do not exist.
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Although the Montreal Protocol is directed at stabilizing 1986 emission levels by 1990 as a first step, in the Netherlands an agreement has been reached with aerosol manufacturers to limit CFC use in aerosols to essential applications in 1990. This agreement, together with other measures such as promotion of the development and use of emission control techniques, will make it possible to reduce CFC use in the Netherlands by 25 percent, relative to 1986, already in 1990. For the longer term, the Dutch government is striving after complete termination of the use of fully halogenated hydrocarbons by the late 1990's. This will presumably have to be accomplished by changing over to other, less harmful CFC's.
THE TROPOSPHERE In the troposphere we are confronted with an increased formation of ozone. Present ozone concentrations in Europe are at an unacceptable level. Effects occur on both human health and vegetation, including forests. Very large emission reductions are needed to arrive at the no-effect levels derived for ozone (ref. 2,3). These reductions involve emissions of nitrogen oxides, volatile organic compounds (VOC), carbon monoxide and methane at European and even global scales. These very large emission reductions will be very difficult to achieve, even in the long run. Given this fact, it is important to provide direction to the abatement policy that should be followed in the coming years. A provisional air quality objective for ozone was drawn up for this purpose in 1984. This objective is restricted itself to ozone's most serious effects on humans (240 micrograms as a 1-hour average). The results of recent effect-research, however, demonstrate that one should think of an 8-hour average air quality objective as well: 160 pg/m3 to prevent the more serious health effects (Table 1). It is estimated that at least emission reductions up to 75 percent for both nitrogen oxides and VOC (Volatile Organic Compounds) are needed on a European scale in order to achieve these levels. To protect vegetation and forests from increasing chronic exposure to ozone, presumably a stabilization is required in emissions not only of hydrocarbons and nitrogen oxides but also of carbon monoxide and methane on a global scale.
936 TABLE 1 Interim-goal for ozone ambient air quality to prevent serious effects on human health and vegetation.
The Netherlands' acidification policy has set in 1985 a provisional goal of reducing NO, emissions by more than 30 percent in the year 2000 compared to 1980, and VOC-emissions by 50%. An evaluation of the policy concerning acidification is currently taking place. At the one hand, it is already clear that a 30 percent NO, reduction will not be enough. On the other hand the picture emerges that the measures that were planned for both mobile and stationary sources will not be sufficient to reach the goal for reduction for NOx emissions in the year 2000. Therefore, a set of additional measures already has been proposed to make it possible to reach at least the original goal. Further measures are under development now, to obtain extra NO,-reduction. A distinction can be made between mobile and stationary sources of NOx and VOC. The measures relating to these two types of sources will be discussed separately in the following sections. Mobile sources With respect to mobile sources, Dutch policy follows three tracks (Fig. 4): a. tightening emission standards; b. limiting the growth in traffic; c. traffic measures in urban areas. The third track is of particular importance for Improving the air
937
Fig. 4. Three-track approach in Dutch environmental policy towards road traffic. quality in busy traffic situations, and is of less interest in relation to ozone formation. The so-called Luxemburg Agreement (1985) has been a first step towards more stringent emission-standards for all categories of vehicles. Because of the new EC standards' long implementation period, the Federal Republic of Germany and the Netherlands have decided to anticipate these standards by means of fiscal incentive measures. Although these measures have been a success, further tightening of the standards contained in the Luxemburg Agreement is necessary. The Netherlands, together with countries like the Federal Republic of Germany, Denmark and Greece, wants to move towards standards for passenger cars in the short term which are fully equivalent to the US-83 standards. Future U.S. standards will also be normative for the Netherlands to a significant degree, all the more so since in many cases these standards approach the limits of the technical possibilities. As a result of decision-making in the EC, the maximum considered feasible is that emissions from gasoline and LPG driven cars in the year 2000 will have been reduced by an average of around 75 percent for NO,, and 80-90 percent for VOC per vehicle. It must be possible to reduce emissions from truck traffic by an average of 40 to 50 percent per vehicle. However, trucks remain a major problem in Europe. Trucks account for 35 to 50 percent of the traffic-related NO,-emissions in Europe. The more stringent standards which have been planned in the U.S.A. do not go far enough for us as far as the NO, reduction is concerned. A sharp growth in both car ownership and car use is expected in
338 the Netherlands and also in other European countries (about 70 percent more kilometers in 2010 than in 1980). It appears that this growth will undermine the emission reductions obtained by the emission standards. Given the role of the car in modern society, drastic measures are required to limit growth substantially. The point of departure for those measures is the fact that considerable potential exists for satisfying mobility needs with public transport and bicycles. The growth of car use can probably be decreased by 25 percent by tightening parking policies and introducing a road-pricing system, but even then the question remains whether in the long run the emission reduction desired can be achieved.
Stationary sources For NO,, regarding both stationary and mobile sources, a protocol is being prepared in the Economic Commission for Europe. The protocol will be signed in late October of this year. In addition to a commitment to apply state-of-the-art control technology, the protocol also prescribes an emission freeze at 1987 levels. This should be realized before 1995. We sincerely hope that it will be possible for the United States to sign the protocol too. The obligations in this NO,-protocol do not go as far as the Netherlands would like. Our national abatement policy intends to go further. The Netherlands is one of the countries which will sign a declaration of intent to achieve an actual NOx-reduction of 30 percent (compared to 1985 emissions), not later than 1998. Other countries sharing this intention include the FRG, Denmark, Austria, Sweden and Switzerland. In the Netherlands, for power plants possibilities are investigated to reduce NOx-emissions by using in-furnace-NOxreduction (INFR), especially in power plants newly to be build. When the results will not meet the expectations, additional measures will be considered, like selective catalytic reduction (SCR). In the industry extra NOx-reduction will be sought in the use of lean burn gas engines, selective catalytic reduction (SCF!) in gasturbines, and SCR or INFR in new industrial boilers. Concerning hydrocarbon emissions, a Task Force on Volatile Organic Compounds has been established in the framework of the
339 Economic Comission for Europe (ECE) to prepare proposals for an international abatement strategy. A report to be submitted to the Executive Body, this autumn, is expected to serve as a basis for drafting a protocol on VOC. A number of European countries (France, Federal Republic of Germany and the Scandinavian countries) have already made known their desire for a concrete VOC abatement policy. The Netherlands very recently developed a strategy for achieving reductions in VOC emissions from industrial, nonindustrial and household activities (ref. 4). A reduction plan was drawn up over a two year period. Not only our Ministry, but also private industry, the Ministry of Economic Affairs and the local governments were represented in the project group which developed this strategy. The constituencies of each of these groups were involved and consulted as much as possible during the strategy development. For private industry, this involved a large number of different sectors (about 20). A s a result of this co-operative process, we hope we can count on widespread acceptance of the goals and far reaching commitment to achieve them. A reduction of more than 50 percent is possible in the year 2000 if the conditions for a number of measures can be met and if the uncertainties can be resolved (Table 2). TABLE 2 Expected VOC-emission reduction for industry and households.
I
1 certainly feasible
with
%ditions
I
12%
12 certainly feasible
I
24%
I
I
58%
TOUI
reduction
340
CONSIDERATIONS and CONCLUSIONS We cannot avoid the conclusion that, in the past, we have been irresponsible in the way we have treated our atmosphere. The CFC issue is a clear illustration of this, as are the levels of other anthropogenic emissions to the air. Table 3 provides an overview of the desired emission reductions and the reductions that have been set as goal in the Netherlands for the year 2000, at least for NOx, VOC and CFC's. The whole ozone problem brings to the foreground the necessity of setting international goals for ourselves; the problems cannot be solved by any one government acting alone. However, we are aware of the fact that you cannot make an appeal to others, when you do not show action in your own country to cut down emissions. In addition, exploring possibilities and realizing emssionreductions may stimulate and convince other countries as well. The agreements with industry in the Netherlands on limiting CFC's and reducing VOC emissions are examples. We are seeing comparable developments elsewhere in Europe and in the U.S.A.. TABLE 3
Desired emission reductions at European/global scale and planned reductions in The Netherlands.
Precursor (atrnospherlc Issue)
Deaired reduction
NO,
(1,Z)
275%
VOC
(12.3)
>75%
CH,
(2.3,4)
high
co
(2)
high
cq
(3!4)
hlgh
NP
(3.4)
high
CFC's ($4)
100%
Major aourD.8
the
Planned In Netherlands In 2ooo
Irallic, combustion trafllc. industry, households, agricullure agnculture. canle. energy production mmc, combustion lrnflic. cambucrtion
33% 50% 7 7
7 7
100%
Internationally, we will have to provide ourselves with means that will enable us to act jointly against the threatening changes in the global atmosphere. The Dutch government wants to help
941
promote the realization of an international convention on the atmosphere. We consider such a convention an important step in the phase of internationally growing awareness in which we now find ourselves. Although the Netherlands does not think that the Montreal Protocol goes far enough, it 9 a first sign of international common sense. A convention on the atmosphere could, in imitation of the Vienna Convention for Protection of the Ozone Layer, contain agreements pertaining to general principles, research and the exchange of information. It could function as a starting point for further protocols to co-ordinate control measures internationally. However, it might also be possible to agree to international rules of law covering the export of air pollutants and climate disrupting substances to other countries. The legal principles formulated at the UN-conference in Stockholm in 1972 and also by the Brundtland Commission, offer a point of departure for this. The concept of sustainable development, presented by the Brundtland commission offers a perspective for the future. The seriousness of the effects arising from the ozone problems and from the related environmental problems such as acidification and climatic changes, warrants our maximum efforts. REFERENCES 1 H. de Boois, J. Rotmans and R.J. Swart, National Institute of Public Health and Environmental Hygiene, Report nr. 758471001; Bilthoven,l988. 2 K.R. Krijgsheld and S. Zwerver, this volume. 3 N. Stenstra, this volume. 4 National Institute of Public Health and Environmental Protection, Integrated Criteriadocument on Ozone (report nr. 758474002); Bilthoven, September 1987.
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T. Schneider et al. (Editors), Atmospheric Ozone Research and its Policy Implications 0 1989 Elsevier Science Publishers B.V., Amsterdam Printed in The Netherlands
-
COMMENT ON POLICY ISSUES AND CONTROL STRATEGIES OF U.S.
M.A.
943
EPA, OZONE NAAQS
MEHLMAN
M o b i l Environmental and H e a l t h Science L a b o r a t o r y , P.O. NJ 08540
Box 1029, P r i n c e t o n ,
ABSTRACT U n l i k e o t h e r atmospheric p o l l u t a n t s such as s u l f u r d i o x i d e , carbon monoxide, n i t r o g e n oxides, l e a d , v o l a t i l e o r g a n i c compounds and t o t a l suspended p a r t i c u l a t e s , ozone i s n o t a p r i m a r y p o l l u t a n t , b u t i s produced from a v a r i e t y o f sources. I t s c o n c e n t r a t i o n i n t h e atmosphere i s l a r g e l y dependent on t h e r a t i o o f v o l a t i l e o r g a n i c compounds (VOCs) t o n i t r o g e n o x i d e s i n t h e presence o f sunl i g h t . D e s p i t e r e d u c t i o n i n VOCs, t h e r e has been n o n - a t t a i n m e n t o f t h e proposed ozone s t a n d a r d i n more t h a n 60 m a j o r U.S. u r b a n areas. T h i s paper d i s c u s s e s t h e f o l l o w i n g : ( i ) EPA's post-1987 proposal f o r a t t a i n i n g t h e ozone s t a n d a r d , ( i i ) t h e use o f t h e Lowest Observed Adverse E f f e c t L e v e l [LOAEL] r a t h e r t h a n t h e Lowest Observed E f f e c t Level [LOEL] i n s e t t i n g t h e standard; and ( i i i ) EPA's framework f o r assessing a d v e r s i t y o f e f f e c t f o r a c u t e ozone exposure. S i g n i f i c a n t progress has been made s i n c e t h e passage i n 1970 o f t h e Clean A i r Act i n t h e U n i t e d S t a t e s .
Since 1970 t h e a i r i n t h e U.S.
i s cleaner.
The N a t i o n a l Ambient A i r Q u a l i t y Standards (NAAQS) i n e f f e c t s i n c e 1986 a r e shown i n Table 1. TABLE 1 N a t i o n a l ambient a i r q u a l i t y standards* (1986)
E m i s s ion
TS P so2
co NoX O3 Pb
Averaging Time
Standard L e v e l s and C o n c e n t r a t i o n s
Annual Geometric Mean 24-hour
75 pg/m3 260 pg/m3
Annual A r i t h m e t i c Mean 24-hour
3 0.03 ppm, (80 pg/m 1 0.14 ppm, (365 u g h 3 )
8- hour 1-hour Annual A r i t h m e t i c Mean
9 ppm, (10 mg/m3J 35 ppm, ( 4 0 mg/m 1 3 0.053 ppm, (100 pg/m )
Maximum D a i l y H o u r l y Average
0.12 ppm,
(235 u g h 3 )
Maximum Q u a r t e r l y Average
*From EPA P u b l i c a t i o n , EPA 450/4-88,
February 1988
From 1977 t o 1986, summarized i n Tables 2, 3, and 4, t h e r e has been a
344 TABLE 2 N a t i o n a l emission estimates* o f t o t a l suspended p a r t i c u l a t e s , SO2 and NOX f o r 1977 and 1986
TS P
Transportation Fuel Combustion Indus. Process Others Total % T o t a l Change
so2
NoX
1977
1986
1977
1986
1977
1986
1.4 2.5 4.0 1.2
1.4 1.8 2.5 1.1
0.8 21.5 4.7 0
0.9 17.2 3.1 0
9.5 10.4 0.7 0.3
8.5 10.3 0.6 0.2
9.1
6.8
26.9
21.1
21.0
19.3
25
* M i l 1i o n s m e t r i c t o n s l y e a r
21
-
8
From EPA pub1 i c a t i o n 450/4-88-001,
Feb.,
1988
TABLE 3 N a t i o n a l emission estimates* o f carbon monoxide and v o l a t i l e o r g a n i c compounds
for 1977 and 1986
voc
co Source Trans po r t a t i o n Fuel Combustion I n d u s t r i a l Process Others Total % T o t a l Change
* M i l l i o n s m e t r i c tons/year
1977
1986
1977
1986
61 5.1 7.3 8.4
42.5 7.2 4.5 6.7
10.0 1.4 9.3 3.5
6.5 2.3 7.9 2.8
81.8
60.9
24.1
19.5
26
-
19
From EPA P u b l i c a t i o n 450/4-88-001,
Feb.,
1988
945 TABLE 4 N a t i o n a l l e a d e m i s s i o n e s t i m a t e s * f o r 1977 and 1986 Year Sources
T97 7
1986
Transportation Fuel Combustion I n d u s t r i a1 Process S o l i d Waste
124.2 7.2 5.7 4.1
3.5 0.5 1.9 2.7
141.2
8.6
Total
94
% T o t a l Change
*In
lo3
m e t r i c t o n s / y e a r , From EPA p u b l i c a t i o n 450/4-88-001,
Feb. 1988
TABLE 5 Framework f o r assessing a d v e r s i t y o f e f f e c t s f o r a c u t e O3 exposure* Gradation o f response Change i n s p i rometry FEV1, FVC
Mild
Moderate
Severe
5-1 0%
10-20%
20-40%
Incapacitating
~~
Duration o f effect
Complete recovery i n <30 min
Complete recovery i n <6 h r
Complete recovery i n 24 h r
Symptoms
Mild t o moderate cough
M i l d cough, p a i n on deep inspiration, shortness o f breath
Repeated cough, p a i n , shortness o f breath, b r e a t h ing distress
Recovery i n '24 hours Severe ou h, p a i n , sEorBness o f b r e a t h , distress -
Limitation o f activity
None
Few choose t o discontinue a c t i v i t y
Some choose t o discontinue a c t i v i t y
* M o d i f i e d by Mark J . U t e l l , U n i v e r s i t y o f Rochester
Many choose t o discontinue activity
946 significant,decrease i n t o t a l p a r t i c u l a t e s emission (estimates i n m i l l i o n s o f m e t r i c t o n s p e r y e a r ) from 9.1 t o 6.8 (25%), s u l f u r d i o x i d e from 26.9 t o 21.2, (21%), NOx from 21.0 t o 19.3 ( a % ) , CO from 81.8% t o 60.9 (26%), v o l a t i l e o r g a n i c compounds from 24.1 t o 19.5 (19%), and l e a d i n thousands o f m e t r i c t o n s from 141.2 t o 8.6 which i s a 94% decrease.
W h i l e t h e TSP, SO2, CO, NOx and Pb
a r e t h e p r i m a r y generated p o l l u t a n t s , ozone i s n o t .
Ozone i s produced b y many
sources, one o f w h i c h i s e m i s s i o n o f v o l a t i l e o r g a n i c compounds (VOCs) i n t h e presence o f n i t r o g e n o x i d e s and s u n l i g h t .
T h i s problem i s f u r t h e r c o m p l i c a t e d
by t h e f a c t t h a t t h e r a t i o o f VOC/NOx p l a y s an i m p o r t a n t r o l e i n t h e r a t e o f ozone p r o d u c t i o n , and a l t e r a t i o n i n t h e r a t i o by imblance o f one component o r t h e o t h e r may g e n e r a t e h i g h e r l e v e l s o f ozone t h a n i s d e s i r e d .
The h i s t o r i c a l
focus i n r e d u c i n g t h e ozone l e v e l s has been on t h e r e d u c t i o n o f VOC. From 1977-1986 t h e VOC's ( i n m i l l i o n s o f m e t r i c t o n s l y e a r ) were reduced i n two m a j o r areas:
t r a n s p o r t a t i o n from 10.0 t o 6.5 (35%) and i n d u s t r i a l proces-
ses from 9.3 t o 7.9 (15%), f o r a t o t a l r e d u c t i o n f r o m a l l sources from 24.1 t o 19.5 (19%).
I n s p i t e o f t h e r e d u c t i o n o f VOC's, ozone remains a problem.
I t became c l e a r i n e a r l y 1970 t h a t t h e s t a t e s would n o t be a b l e t o a t t a i n
a i r q u a l i t y standards f o r ozone, t h u s t h e Clean A i r A c t Amendment o f 1977 s e t a new d e a d l i n e f o r a t t a i n m e n t by December 31 , 1982 and t h e n by December 31, 1987. However, i n s p i t e o f t h e s e e x t e n s i o n s o f d e a d l i n e s , more t h a n 60 m a j o r u r b a n areas i n a l l p a r t s o f t h e U.S.
s t i l l cannot a t t a i n t h e proposed n a t i o n a l h e a l t h
s t a n d a r d f o r ozone, and i t i s u n l i k e l y t h a t t h i s s t a n d a r d can be a t t a i n e d i n t h e n e x t decade, i f ever. The l o w e s t observed e f f e c t l e v e l (LOEL) f o r humans exposed t o ozone i n e n v i r onmental chamber s t u d i e s now s t a n d s a t 0.08 ppm (D. Horstman, EPA, 1988).
In
1979 i t was 0.15 ppm ( D ' L u c i a and Adams, J . A p p l i e d P h y s i o l o g y , V o l . 43, 1977). EPA has determined t h a t LOEL was n o t n e c e s s a r i l y t h e number t o be used i n s e t -
t i n g t h e standard.
I n s t e a d , t h e A d m i n i s t r a t o r s h o u l d use Lowest Observed
Adverse E f f e c t L e v e l (LOAEL) which accomplishes t h e p r o t e c t i o n i n t e n d e d i n t h e
.
NAAQS There have been numerous a t t e m p t s by s c i e n t i s t s t o d e f i n e what c o n s t i t u t e s an adverse h e a l t h e f f e c t f o r ozone, w h i c h has been i n t e r p r e t e d as s t a t i s t i c a l l y The frames i g n i f i c a n t changes i n l u n g f u n c t i o n such as a 2-10% change i n FEV1. work f o r a s s e s s i n g a d v e r s i t y o f e f f e c t f o r a c u t e ozone exposure has been p r o posed by s c i e n t i s t s a t EPA, where g r a d a t i o n o f responses were c l a s s i f i e d as m i l d , moderate, severe and i n c a p a c i t a t i n g .
These a r e summarized i n T a b l e 5.
947 The m i l d r e s p i r a t o r y e f f e c t s a r e n o t c o n s i d e r e d adverse h e a l t h e f f e c t s ,
such
as 5-10% changes i n FEVl o r FVC o f l e s s t h a n 30 m i n u t e s d u r a t i o n and m i l d t o moderate cough w i t h o u t l i m i t a t i o n t o a c t i v i t y .
To d a t e , ozone a t 0.12 ppm has
n o t been shown t o cause adverse h e a l t h e f f e c t s such as: 1.
I n c r e a s e i n l u n g cancer
2.
Permanent r e s p i r a t o r y i n j u r y .
3.
Progressive r e s p i r a t o r y dysfunction.
4.
Episodes o f r e s p i r a t o r y d i s t r e s s which i n t e r f e r e w i t h normal f u n c t i o n .
T h e r e f o r e , a p o l i c y d e c i s i o n t o use LOAEL as t h e b a s i s o f t h e ozone s t a n d a r d i s The a p p r o p r i a t e NAAQS w i l l need t o i n c l u d e some m a r g i n o f s a f e t y .
i n order.
I n d u s t r y s u p p o r t s some aspects o f t h e EPA's p o s t - 1 987 n o n - a t t a i n m e n t p r o p o s a l t h a t promote a t t a i n m e n t o f t h e ozone s t a n d a r d : l
1.
S p e c i f i c s t r a t e g i e s o f o r d e r l y improvement based on t h e c h a r a c t e r -
i s t i c s o f i n d i v i d u a l nonattainment areas. 2.
Deadlines f o r a t t a i n m e n t based on l o c a l c o n d i t i o n s and problems.
3.
Changes i n t h e p r e p a r a t i o n process o f s t a t e implemented p l a n s o r
programs (SIP'S), such as t h e r e q u i r e m e n t t h a t s t a t e s improve emissions i n v e n t o r i e s t o p r o v i d e t h e i n f o r m a t i o n necessary f o r p o l i c y d e c i s i o n s .
4. Use o f more s o p h i s t i c a t e d a i r models and s t a t i s t i c a l l y r o b u s t measurements t h a t a r e t i e d t o improvement i n a i r q u a l i t y and a t t a i n m e n t o f t h e ozone and carbon monoxide standards. We b e l i e v e t h a t EPA needs t o address c a r e f u l l y t h e f o l l o w i n g i n t h e i r p o s t 1987 proposal : o
Prepare a s t r a t e g y which l e a d s t o s t e a d y improvement o v e r a l o n g -
t e r m p e r i o d , r a t h e r t h a n immediate c r i s i s - t y p e d e c i s i o n s s a t i s f y i n g s h o r t periods only. o
Commence t h e strategy-development process w i t h comprehensive e v a l -
u a t i o n o f t h e e x i s t i n g SIP'S.
o
Concentrate on d e v e l o p i n g s t a t i s t i c a l l y r o b u s t c r i t e r i a f o r d e t e r -
m i n a t i o n o f a i r q u a l i t y progress and n o n a t t a i n m e n t s t a t u s . o
E v a l u a t e and assess u n c e r t a i n t i e s i n t h e h e a l t h e f f e c t s d a t a .
o
Develop a more r e l i a b l e and i n c l u s i v e d a t a base on e m i s s i o n i n v e n -
t o r i e s f o r a i r modeling. o
Determine a c c e p t a b l e r a t e s o f p r o g r e s s based on l o c a l c o n d i t i o n s .
o
Give g r e a t e r f l e x i b i l i t y t o s t a t e s t o d e t e r m i n e t h e b e s t program
mix f o r improving a i r q u a l i t y .
'API
comment t o EPA, C e n t r a l Docket S e c t i o n , Doc. #A-87-18,
March 28, 1988
948 o
Modify t h e sanction proposal.
( F o r example, c o n s t r u c t i o n bans
impede m o d e r n i z a t i o n o f e x i s t i n g e m i s s i o n c o n t r o l systems; r e s t r i c t i o n o f h i g h way funds exacerbate c o n g e s t i o n and t h u s s e r v e t o i n c r e a s e a u t o m o t i v e e m i s s i o n s per v e h i c l e m i l e t r a v e l e d . ) Thus, i n general, t h e programs and p o l i c i e s t h a t a r e i n i t i a t e d i n E P A ' s post-1987 proposal w i l l have a good chance f o r success s u b j e c t t o t h e above considerations. Acknowledgment
I would l i k e t o acknowledge t h e a s s i s t a n c e o f M r . W. M. O l l i s o n , American Petroleum I n s t i t u t e , f o r h i s a s s i s t a n c e i n p r e p a r i n g t h i s paper.
T. Schneider et al. (Editors),Atmospheric Ozone Research and its Policy Implications 0 1989 Elsevier Science Publishers B.V., Ameterdam -Printed in The Netherlands
949
THE OZONE LAYER DEPLETION AND EUROPEAN POLICIES MICHAEL J. SCOULLOS* European Environmental Bureau Maison Europkenne de l'Environnement, Rue du Luxembourg 20 B-1040 Brussels (Belgium) The major article in the January 1988 issue of 'Scientific American' with an impressive cover from the TOMS (Total Ozone Mapping Spectrometer) which is on board the National Aeronautics and Space Administration's Nimbus 7 satellite, provides the following concrete data (ref 1): In the spring time ozone "hole" over Antarctica (October 5 , 1987) the abundance of ozone is about half that of a decade ago which averaged about 300 Dobson. One month earlier (on September 5 ) ozone levels fell on one day by about 10 percent over an area of some three million square kilometers. Ten days later, on September 14-16, 1988, in "response" to that, the International Community concluded the Montreal Protocol on Substances that Deplete the Ozone Layer, which is undoubtedly an important step in facing the problem but clearly far from being a generous and complete solution. In fact the initiatives which led to the Vienna Convention and the Montreal Protocol have been repeatedly acknowledged by the EEB during the preparatory phase. It has been stated (ref 2,O.l that despite disappointments over slow procedures, hesitations and weak positions of certain Governments, the ozone depletion question may offer a unique example of an emerging problem which has received an anticipatory response from the International Community. However the final outcome of the negotiations is clearly less promising than many scientists and environmental NGOs expected. It should be remembered that EEB both independently and together with other International and National Environmental NGOs had requested in 1986 and during the April 1987 meeting of the ad hoc working group of Legal and Technical Experts for the Preparation of a Protocol on CFCs to Vienna Convention held in Geneva and elsewhere (ref. 5,8,9,10): A 30 percent reduction in emissions of CFCs (11,12,22,113,114 and 115), Halons (1211 and 1301) and chlorinated solvents (carbon tetrachlaride, methyl chloroform and methylene chloride) within 18 months. An 85 percent reduction in emissions of the listed compounds within five years. A near-complete phase-out within ten years which could be modified in light of developing scientific findings. It should be noted furthermore that the Executive Director of UNEP Dr. M.K. Tolba in his statement (ref. 6 ) in April 1987 has asked for a freeze in production levels of all substances by 1990, a 20% reduction in 1992 and another 20% every two years thereafter, with the aim of reaching zero by the year 2000. : University of Athens, Department of address *Permanent Chemistry, Division 111, 13A Navarinou st. Athens 10680, Greece.
350 Taking into account the aforementioned positions it becomes clear that the Montreal Protocol (providing only for a freeze of consumption on 1986 levels by 1992; a 20% reduction of consumption plus 10% increase by 1994 and a 50% reduction of consumption plus 15% increase by 1999) is inadequate and was formulated without seriously taking into account the gravity of the problem of the Antarctic ozone hole (ref 1,3,7). Despite concrete evidence, and comparative scientific results and consensus reached by the major ozone modellers from both side of the Atlantic in Wurzburg, FRG etc, along with the fact that climatic changes due to the greenhouse effect may accelerate ozone depletion and evidence that also the Arctic is a potential site of rapid ozone loss, the participants failed to reach the decision required. EEB, wishing to base its argument on scientific data, had organised in ;me 1987 in Brussels a very well attended international seminar on "Ozone Depletion and Climate Warming due to CFCs and the Role of the European Communities". In the seminar major recent results and developments on both sides of the Atlantic have been revized and the contracting parties were called upon to include also the Halons in the list and to reach a 50% reduction by 1994. Since then EEB has been closely monitoring the outcoming new data, much of which has been presented in the present International Symposium. In a recent report of the Ozone Trends Panel R. Watson of NASA stated: "There is undisputed observational evidence that the of source gases important in atmospheric concentrations controlling stratospheric ozone levels (chlorofluorocarbons, halons, methane, nitrous oxide, and carbon dioxide) continue to increase on a global scale because of human activities" (ref.15). From the data provided, EEB concludes that the implementation of the Montreal Protocol will not prevent a further depletion of the ozone layer. Recent calculations suggest that the current depletion by fifty percent compared to the 1975 levels will still increase to eighty percent if the Montreal Protocol is implemented without further initiatives. The depletion of the global ozone layer outside the polar regions, that is currently estimated at approximately two to three percent, may also increase. EEB considers the continuation of the relevant research projects an absolute priority of the international scientific community. Furthermore it has been recognised that the ozone hole has spurred on researchers to study atmospheric chemistry and dynamics and has revolutionised our approaches with positive consequences for our overall scientific knowledge. It is selfevident that the EEB, as the major European Environmental NGO bringing together more than 100 national organisations of the 12 EEC countries with more than 20 million members, is particularly concerned about the development of the European Community policies on ozone. The EEC is the major producer of CFCs today and accordingly carries a major share of responsibilities in this matter. EEB knows about the peculiarities of the EC market and the developments in substitutes and realises that several of them, existing both in US and Europe, might need some time to be properly tested for toxicity and other effects. However it considers the draft regulation implementing 'the Montreal Protocol (COM (88)58 fin.) is totally inadequate. In its recent comments (ref.13) EEB urged the Environmental Council to establish production and consumption targets stricter than the Montreal Protocol and repeated that an 8 5 % reduction in five years and a complete phase out of substances destroying the ozone layer by the year 2000 are .technically feasible and should be
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established as EC wide targets for regulation. EEB has advised the previous and present EC Presidencies (see ref.14) to adopt a regulation and not a directive proper as legal instrument for the ozone case and has expressed its appreciation to the Commission regarding this decision; however EEB strongly objects to two other aspects of the draft EC regulation. Firstly: It appears that the draft regulation puts a premium on slowness in technological advance, and is a disincentive for more environmentally acceptable policies. This follows from article 9 of the draft regulation. According to this article the efforts of member states that reduce their production or use beyond the targets of the Montreal Protocol, may be used to compensate for the failure of other member states to reach the targets of the Montreal Protocol. To the EEB this is unacceptable, since several EC countries already in advance in this matter are directly discouraged. In Denmark the ban of fully halogenated CFCs in aerosols took effect on January 1 , 1987 in appliance with a statutory order of November 1984 (ref.16). In the FRG a label "Environment" is granted to CFC-free cans and a resolution was unanimously adopted in May 1987 by the Bundesrat, asking for a ban of CFCs in aerosols and other uses when recycling or substitutes are avaliable, whereas the German Federation of Chemical Industry announced its intention to reduce up to 95% the use of CFCs in aerosols in three years. In the Netherlands, spray cans containing CFCs should provide a "warning" to the user, whereas the overall use of CFCs in aerosols has been reduced by up to 90% although there is no specific legislation banning CFCs. Taking these examples into account, the EEB urges the Council of Ministers to implement measures allowing the Commission to supervise that reduction in production and use in all member states, and not to grant compensation. Secondly: the draft regulation fails to address the major uses of chlorofluorocarbons and Halons. EEB feels that a major EC effort pertinent to the development and dissemination of alternatives to the use of substances causing ozone layer destruction is necessary for recovering and recycling ozone. In addition, the depletion of chemicals in the atmosphere is crucial for minimizing further depletion of the ozone layer in the short term. So far the EC has failed in this respect and the draft regulation fails to provide a new impetus for such efforts. The EEB objects to the trade of production rights included in the draft directive. It addresses not only the EC institutions but. also %he member states and the individual citizens. It has expressed its regret that Ireland and Spain (ref.13) have not signed the Vienna Convention and its Protocol, has criticised countries directly guided by their manifacturing industries and has asked all member states to speed up the ratification procedures if possible before October 1, 1988. Finally the EEB plans to campaign further through its member organisations and in cooperation with BEUC to encourage individual consumers to personally alter their buying habits in order to avoid non CFC-free aerosols and certain foam products such as polystyrene foam products, flexible foam products, rigid foam insulation etc and by calling for legislation that promotes CFC recylcing. In the ozone issue several questions are still waiting to be answered. However several things are certain: 1. Chlorofluorocarbons are capable of drastically depleting the ozone atmosphere and their concentrations increase in the
052
atmosphere due to anthropogenic activities. 2. Chlorine which has been introduced in the stratosphere will interact with ozone for several decades to come. 3 . The Antarctic ozone hole is "deepening". 4. Substitutes exist and for several applications (freezers, airconditioning) recycling has been demonstrated. 5. Reversible changes in the Planet cannot be repaired by whatever action and cannot be "paid" by whatever profit commercial, national or regional. 6 . We have only one Earth and it is very risky to gamble with it. REFERENCES l . R . S . Stolarski, Sc. Amer. (1988)258,1,20-26. 2.M.J.Scoullos, Comprehension and Problems of the Contemporary Environment; %he Role of Environmental Education: UNESCO/UNEP International Congress on Env. Educ. and Training. Moscow 17-21 Aug 1987 (UNESCO pub1 : ED-87/CON.402/5/COL4). 3.EEB "The sky is the Limit". Proc. Intern. Seminar on Ozone depletion and Climate warming due to CFCs: The role of the European Communities, Brussels June 22, 1987. Q.M.J.Scoullos, ibid pp 2-5 S.EEB, FJRDC, EDF. Sierra Club, NWF,FoE, SSCV (1986) "Ozone Depletion and Climate change: A statement on CFCs and related compounds by the International Environmental Community; Nov.18, 1986. The statement was signed and enclosed by 59 international and National Env. NGOs in Geneva, Switzerland on April 27, 1981. 6.M.K.Tolba Exec. Director IJNEP "Nowhere to Hide" Statement in the adhoc W.G. of Legal and Technical experts for the Preparation of a Protocol on CFCs to the Vienna Convention for the Protection of the Ozone Layer, Vienna Group 35 Session, Geneva April 27, 1987. 7.M. Oppenheimer "Global Lessons from the Ozone Hole". Environmental Defence Fund, New York, March 1988. 8.EEB, Press release c/104/PR/86;December 1986. " c/24/87; February 1987. 9.EEB , c/55/87; April 1987. 10.EEB , " c/83/87; June 1987. 11.EEB, " lZ.EEB/BEUC c/133/81; November 1987. 13.EEB.Comments on the Draft Regulation Laying Down Common Rules Applicable to certain Products which Deplete the Ozone Layer. 14.EEB, Memorandum to the German Presidency. Bonn, February 1988. lS.R.T.Watson, Executive Summary of the Ozone Trends Panel, NASA, Washington, March 1988. 16.Ministry of the Environment, Denmark, National Agency of Environmental Protection: "On the use of Propellants and Solvents in Aerosol Spray Cans". Statutory order No. 571. Nov. 2 9 , 1984. I,
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CHAIRMAN'S CONCLUDING REMARKS L e s t e r D.Grant, D i r e c t o r , Environmental C r i t e r i a and Assessment O f f i c e , US Environmental P r o t e c t i o n Agency, Research T r i a n g l e Park NC 27711, USA
So, we have come t o t h e end o f q u i t e an i n t e r e s t i n g symposium concerning
new ozone research f i n d i n g s and t h e i r i m p l i c a t i o n s f o r development o f p o l i c i e s and c o n t r o l s t r a t e g i e s .
My compliments and those o f my f e l l o w Co-Chairman,
M r . Wolters, t o our speakers, p a n e l i s t s , session chairmen, and rappateurs f o r t h e i r e x c e l l e n t c o n t r i b u t i o n s t o t h e success o f t h i s , t h e T h i r d U.S.-Dutch Symposium i n our c o n t i n u i n g s e r i e s on a i r p o l l u t i o n issues. I t i s impossible t o provide here a d e t a i l e d summary o f t h e e n t i r e v a s t a r r a y o f i n f o r m a t i o n presented and discussed d u r i n g our f i v e days together.
Nevertheless, t h e r e a r e
several key p o i n t s which should be h i g h l i g h t e d as emerging from t h i s Symposium. You may remember t h a t , a t t h e o u t s e t o f our meeting, Mr. Wolters noted i n h i s opening remarks t h e r e c e n t Rotterdam Marathon and t h e disappointment o f t h e runners i n t h e i r performance, p o s s i b l y due t o h i g h ozone l e v e l s d u r i n g t h e event. He a l s o mentioned t h a t t h e s t a r t i n g time f o r f u t u r e marathons i s t o be changed t o the morning t o h e l p a v o i d h i g h ozone periods l a t e i n t h e day.
This represents
b u t one example o f t h e kinds o f d i v e r s e impacts o f trophospheric ozone on our everyday l i v e s and t h e p o t e n t i a l adjustments, some s u b t l e and some perhaps n o t so subtle, t h a t may come t o be necessary i n our l i f e s t y l e s and s o c i a l a c t i v i t i e s t o cope w i t h elevated surface l e v e l ozone concentrations.
S i m i l a r l y , major
changes i n our use o f c e r t a i n chemicals and i n our l i f e s t y l e s w i l l a l s o l i k e l y be necessary t o t r y t o minimize f u t u r e s t r a t o s p h e r i c ozone d e p l e t i o n o r t o cope w i t h consequent e f f e c t s o f such upper-level ozone d e p l e t i o n processes on human h e a l t h and t h e environment.
Consequently, s t r a t o s p h e r i c and t r o p o s p h e r i c ozone
i n our atmosphere are b o t h subjects o f much research and p o l i t i c a l debate a t t h i s time.
The s t r a t o s p h e r i c ozone l a y e r has come t o be c a l l e d "good" ozone by
some, i n view o f t h e f a c t t h a t i t forms a p r o t e c t i v e s h i e l d a g a i n s t u l t r a v i o l e t - B (UV-6) r a d i a t i o n i n Sun l i g h t .
Trophospheric ( o r s u r f a c e l a y e r ) ozone, on t h e
o t h e r hand, r e s u l t s from photochemical a i r p o l l u t i o n i n t h e troposphere, and has come t o be termed "bad" ozone, due t o i t s negative e f f e c t s on human h e a l t h and t h e environment.
TROPOSPHERIC OZONE During our sessions here a t t h e T h i r d U.S.-Dutch
Symposium, much new
i n f o r m a t i o n was presented w i t h regard t o trophospheric ozone formation, i t s e f f e c t s on b o t h human h e a l t h and t h e environment, and t h e c o m p l e x i t y o f developing p o l i c i e s and s t r a t e g i e s f o r i t s c o n t r o l . W i t h regard t o human h e a l t h , extensive new d a t a now p o i n t toward pulmonary f u n c t i o n decrements and r e s p i r a t o r y t r a c t morphological/biochemical a l t e r a t i o n s o c c u r r i n g a t lower ozone concentrations than p r e v i o u s l y thought.
When c o n s i d e r i n g
ozone h e a l t h e f f e c t s , two general types o f e f f e c t s a r e t y p i c a l l y recognized as being o f p u b l i c h e a l t h concern:
(1) t r a n s i e n t e f f e c t s on r e s p i r a t o r y f u n c t i o n
associated w i t h s i n g l e o r occasionally-repeated,
acute short-term (i.e.
,
1-2 h r )
e p i s o d i c exposures t o ozone; and (2) o t h e r e f f e c t s on r e s p i r a t o r y t r a c t defense mechanisms and morphological s t r u c t u r e associated w i t h more c h r o n i c continuous exposures o r f r e q u e n t l y repeated short-term exposures.
With regard t o transient
e f f e c t s on human r e s p i r a t o r y f u n c t i o n , several p o i n t s can be emphasized. decrements i n l u n g f u n c t i o n (e.g.,
Both
reduced a i r f l o w r a t e s o r increased airway
r e s i s t a n c e associated w i t h neurally-mediated airway c o n s t r i c t i o n , lower f o r c e d e x p i r a t o r y volumes, e t c ) and c e r t a i n i r r i t a t i v e symptoms (e.g.,
coughing, wheezing
chest pain, shortnesses o f breath, e t c . ) a r e o f concern--as a r e t h e e x t e n t t o which consequent reduced oxygen uptake o r a v a i l a b i l i t y and personal d i s c o m f o r t r e s u l t i n l i m i t a t i o n s o f normal work o r s o c i a l / r e c r e a t i o n a l a c t i v i t i e s .
As noted a t t h i s Symposium. t h e n a t u r e and magnitude o r s e v e r i t y o f most ozone-induced r e s p i r a t o r y f u n c t i o n e f f e c t s a r e c r i t i c a l l y determined by b o t h t h e c o n c e n t r a t i o n (C)
and t h e d u r a t i o n o r t i m e (T) o f exposure t o ozone, i.e.,
they a r e dependent upon a "C" x 'IT" dose-response r e l a t i o n s h i p .
That i s ,
r e s p i r a t o r y f u n c t i o n decrements and symptoms increase i n magnitude o r s e v e r i t y as t h e o v e r a l l accumulated dose o f i n h a l e d ozone increases.
This means t h a t
h i g h e r concentrations are needed i n o r d e r t o induce c e r t a i n types o r magnitudes o f t r a n s i e n t r e s p i r a t o r y f u n c t i o n e f f e c t s o r symptoms w i t h more acute (1-2 h r ) short-term ozone exposures than a r e t h e c o n c e n t r a t i o n s necessary t o induce analogous e f f e c t s w i t h somewhat l o n g e r (6-8 h r ) exposures.
Also o f much
importance i s t h e f a c t t h a t t h e l e v e l o f e x e r c i s e o r p h y s i c a l a c t i v i t y o f i n d i v i d u a l s d u r i n g t h e i r exposure t o ozone i s a c r i t i c a l f a c t o r i n determining t h e s p e c i f i c C x T dose-response r e l a t i o n s h i p s f o r ozone-induced h e a l t h e f f e c t s . That i s , t h e h i g h e r t h e l e v e l o f p h y s i c a l a c t i v i t y and, t h e r e f o r e , t h e g r e a t e r t h e b r e a t h i n g r a t e and dose o f ozone d e l i v e r e d t o t h e lower r e s p i r a t o r y t r a c t , then t h e l a r g e r t h e t r a n s i e n t r e s p i r a t o r y f u n c t i o n o r symptomatic e f f e c t s seen
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a t any given ozone concentration.
With regard t o 1-2 h r ozone exposures,
pulmonary f u n c t i o n decrements i n h e a l t h y a d u l t s have been seen a t 0.15-0.16
ppm
ozone, and some data suggest such decrements a t 0.12 t o 0.15 ppm ozone w i t h heavy exercise, t h e average changes i n l u n g f u n c t i o n being g e n e r a l l y small (55-6%) a t those exposure l e v e l s .
However, wide i n d i v i d u a l v a r i a b i l i t y e x i s t s ,
such t h a t c e r t a i n "responders" c o n s i s t e n t l y show markedly larger-than-average decrements i n l u n g f u n c t i o n a t such exposure l e v e l s . Newly emerging data, as reviewed o r presented a t t h i s Symposium, p r o v i d e evidence f o r r e s p i r a t o r y f u n c t i o n e f f e c t s o c c u r r i n g a t ozone l e v e l s a t o r below 0.12 ppm w i t h more prolonged (6-8 h r ) exposures t o ozone t h a t b e t t e r mimic ambient exposure conditions.
Recent c o n t r o l l e d human exposure s t u d i e s have now
shown t h a t prolonged exposure o f young a d u l t s u b j e c t s t o 0.12 ppm ozone r e s u l t s i n p r o g r e s s i v e l y l a r g e r changes i n r e s p i r a t o r y f u n c t i o n and symptoms w i t h time. The changes i n lung f u n c t i o n a t t h e end o f exposure were s i m i l a r i n magnitude t o those p r e v i o u s l y observed i n h e a l t h y subjects performing a t very heavy l e v e l s o f exercise a t much higher ozone concentrations (>0.2 ppm) f o r much s h o r t e r durations (i.e.,
A d d i t i o n a l s t u d i e s r e p o r t e d a t t h i s Symposium have
62 h r ) .
confirmed t h e above f i n d i n g s a t 0.8 and 0.10 ppm, as w e l l as a t 0.12 ppm ozone, w i t h t h e 0.8 and 0.10 ppm exposures producing smaller changes t h a t a l s o p r o g r e s s i v e l y increased w i t h each succeeding hour o f exposure.
Thus, t h e t r a n s i e n t r e s p i r a t o r y
f u n c t i o n decrements seen w i t h ozone exposure worsen as a f u n c t i o n o f i n c r e a s i n g time o f exposure and can be observed a t lower concentrations (0.8,
0 . 1 ppm)
than the present EPA 1-hr 0.12 ppm ozone standard w i t h more prolonged exposure d u r a t i o n s (6 t o 8 h r ) .
These new f i n d i n g s are very i m p o r t a n t f o r c u r r e n t
evaluations o f ambient ozone standards o r g u i d e l i n e s , as a r e new f i n d i n g s from animal t o x i c o l o g i c a l s t u d i e s t h a t demonstrate a v a r i e t y o f e f f e c t s o f ozone on l u n g defense mechanisms and morphological s t r u c t u r e . Accumulating evidence from animal s t u d i e s reviewed d u r i n g t h i s Symposium p o i n t s toward m u l t i p l e d e l e t e r i o u s e f f e c t s being associated w i t h c h r o n i c ozone exposure.
The c o n s t e l l a t i o n o f e f f e c t s includes, f o r example:
changes i n
r e s p i r a t o r y f u n c t i o n ; airway inflammatory responses; a l t e r e d p a r t i c l e clearance; p e r s i s t i n g changes i n l u n g s t r u c t u r e p o s s i b l y associated w i t h l u n g f i b r o s i s and emphysema; slowed lung development; and reduced a b i l i t y t o fend o f f r e s p i r a t o r y infections.
Much s t i l l remains t o be e l u c i d a t e d w i t h r e g a r d t o many o f these
types o f e f f e c t s ; t h i s i n c l u d e s t h e C x T dose-response r e l a t i o n s h i p s t h a t may apply and r e l a t i v e e f f e c t i v e n e s s o f v a r i o u s ozone exposure p a t t e r n s i n producing various types o f e f f e c t s .
For some e f f e c t s , repeated h i g h e r l e v e l peak exposures,
956
analogous t o ambient episode c o n d i t i o n s , may be more d e l e t e r i o u s t h a n c h r o n i c continuous exposures. e.g.,
Also o f importance i s t h e f a c t t h a t some o f t h e changes,
e p i t h e l i a l damage and inflammatory responses, seem t o be cumulative and
are p e r s i s t e n t even i n animals t h a t have a t t e n u a t e d r e s p i r a t o r y responses. Also o f growing concern a r e new d a t a r e p o r t e d here based on ambient a i r m o n i t o r i n g and new human exposure models m i l l i o n s , o f members o f t h e U.S.
-
data which i n d i c a t e t h a t many, even
and Dutch p o p u l a t i o n a r e exposed t o ozone
concentrations found t o be associated w i t h i d e n t i f i a b l e h e a l t h e f f e c t s .
A l l of
t h i s accumulating new evidence p r o v i d e s a s t r o n g impetus toward c o n s i d e r a t i o n o f p o s s i b l e longer-term ozone standards, perhaps averaged over 8 hours, i n o r d e r t o p r o v i d e f u r t h e r p r o t e c t i o n f o r human h e a l t h beyond t h e c u r r e n t U.S. 1-hour ozone NAAQS.
The need f o r a longer averaging time standard and t h e
a p p r o p r i a t e l e v e l s , I am sure, w i l l be c a r e f u l l y considered i n b o t h t h e U.S. and t h e Netherlands i n t h e coming months o r years.
I n each case, t h e u l t i m a t e
determination o f what c o n s t i t u t e s s u f f i c i e n t a l t e r a t i o n s i n normal f u n c t i o n t o c o n s t i t u t e adverse h e a l t h e f f e c t s w i l l be a key i s s u e t o be d e a l t w i t h . We have a l s o learned much here about s u r f a c e l e v e l ozone e f f e c t s on a g r i c u l t u r a l crops, f o r e s t s , and n a t u r a l ecosystems.
When developing an ozone
c o n t r o l p o l i c y t o p r o t e c t a g a i n s t v e g e t a t i o n e f f e c t s , t h e long-term average ozone c o n c e n t r a t i o n appears t o be i m p o r t a n t , as w e l l as s h o r t - t e r m peak l e v e l s d u r i n g consecutive episode days.
P a r t i c u l a r l y d u r i n g t h e growing season,
r e l a t i v e l y low l e v e l s o f ozone appear t o cause a g r i c u l t u r a l crop l o s s by growth i n h i b i t i o n and increased s u s c e p t i b i l i t y o f v e g e t a t i o n t o a b i o t i d b i o t i c s t r e s s . I n a d d i t i o n , c h a r a c t e r i s t i c i n d i c a t o r s o f f o r e s t d e c l i n e observed i n Europe and North-America have been a l s o associated w i t h ozone exposure.
I t becomes
i n c r e a s i n g l y c l e a r e r t h a t economic losses due t o reduced c r o p p r o d u c t i v i t y and f o r e s t damage are q u i t e l a r g e and a r e o f growing importance i n determining a p p r o p r i a t e l e v e l s f o r ozone standards i n o r d e r t o minimize r e g i o n a l ozone impact.
For many developing c o u n t r i e s these types o f e f f e c t s may be o f even
g r e a t e r importance, where extensive d e f o r e s t a t i o n and inadequate a g r i c u l t u r a l p r o d u c t i o n due t o o t h e r f a c t o r s are already serious problems.
I t i s noteworthy
t h a t long-term ozone l e v e l s necessary t o minimize n e g a t i v e e f f e c t s on v e g e t a t i o n approach background t r o p o s p h e r i c c o n c e n t r a t i o n s o f t e n p r e s e n t over c o n t i n e n t s i n t h e Northern Hemisphere. We have a l s o heard extensive d i s c u s s i o n here w i t h regard t o e x t e n s i v e c o m p l e x i t i e s and d i f f i c u l t i e s i n developing e f f e c t i v e ozone c o n t r o l p o l i c i e s and s t r a t e g i e s .
L a t e s t modeling r e s u l t s and r e a l - w o r l d experience, as r e p o r t e d
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here, show that no simple solutions are at hand. Several factors complicate the situation. The formation of ozone (03) and other photochemical oxidants of importance in producing so-called urban smog effects involve photochemical (UV light-enhanced) reactions between hydrocarbons or volatile organic compounds (VOC) and inorganic (nitrogen oxides; NOx) air pollutants. The VOC and NO, emissions are associated with both stationary sources (e.g., electrical power generation plants and petrochemical facilities) and mobile sources (automobiles, trucks, and other transportation devices), especially those involving fossil fuel combustion or utilization of oil components in production of commercial products. Also of very major importance are numerous small, widely dispersed sources of hydrocarbon emissions that are associated with many different everyday human activities. Besides the multiplicity and diversity of emission sources, the relevant atmospheric processes are also extremely complex. Several notable developments with regard to our understanding of photochemical oxidant/ozone air pollution phenomena and their effects were highlighted: (1) Organic emissions differ widely in ozone-forming potential, a finding that has led to the concept of discriminate VOC control for ozone reduction; (2) Ozone and related air pollution problems are regional-scale (not just urban-scale) phenomena resulting from multi-day pollutant transport and precursor transformation enroute; and (3) the mechanisms of atmospheric chemical processes that produce ozone have been elucidated in great detail, with hundreds of elementary chemical reaction steps being necessary to describe the mechanisms as now understood. Overall, VOC controls are likely needed as one common measure for reducing ozone formation but NOx reduction may only be applicable in certain situations depending upon VOC/NOx ratios and other factors in given locations. These facts all point toward the need for much flexibility and care in developing control strategies appropriate for particular situations in various countries. The one clear generally mandatory element o f such strategies appears to be the use of catalytic converters on motor vehicles. These have been used, of course, f w many years in the United States, and the Netherlands is now well on the way toward implementing catalytic converter use as a major step toward reducing mobile source contributions to ozone formation. It is important that other nations in the European community do this and countries in other areas, as well - if control of surface level ozone as a regional air pollution problem that does not respect national boundaries is to be accomplished. Even with such technology-based control efforts, large increases in numbers o f motor vehicles
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may o f f s e t gains from c a t a l y t i c converters, so t h a t reduced c a r use may be needed. As f o r VOC-emissions from s t a t i o n a r y sources, t h e l a r g e v a r i e t y o f sources and substances i n v o l v e d hampers t h e development o f c o n t r o l p o l i c y .
Advances
were noted here i n NOx c o n t r o l technology f o r l a r g e combustion i n s t a l l a t i o n s , e.g.
low NOx burners, two stage combustion processes, and f l u e gas treatment.
There i s an i n c r e a s i n g understanding o f t h e chemistry i n v o l v e d i n NOx f o r m a t i o n as t h e r e s u l t o f combustion processes.
New data suggest t h a t a s i g n i f i c a n t
p a r t o f NOx-emissions i n many combustion processes may c o n s i s t o f N20 (up t o
25%).
This i s o f a d d i t i o n a l environmental s i g n i f i c a n c e , because N20, w i t h i t s
l o n g atmospheric l i f e t i m e , i s i n v o l v e d i n s t r a t o s p h e r i c ozone d e s t r u c t i o n and i n t h e s o - c a l l e d 'greenhouse e f f e c t " .
A t t h i s symposium, s p e c i a l a t t e n t i o n was
a l s o focussed on emissions from t h e use o f p a i n t s , b o t h i n i n d u s t r y and i n households.
I n t h e p a i n t i n d u s t r y , a l t e r n a t i v e products have a l r e a d y been
developed i n which organic s o l v e n t s a r e e l i m i n a t e d o r reduced. The c o s t s o f these and o t h e r c o n t r o l measures, as we have heard here, w i l l be l a r g e , b u t nevertheless necessary.
Also, as noted here by speakers
and p a n e l i s t s , our a b i l i t y t o e x p l a i n t o t h e p u b l i c t h e reasons f o r needing such c o n t r o l s and, p o s s i b l y , f o r a l t e r e d l i f e s t y l e s w i l l be one key t o our accomplishing t h e i r cooperation i n d e a l i n g w i t h t h e ozone problem.
Public
communication w i l l be an i n c r e a s i n g challenge f o r a l l o f us i n t h e coming years; and c r e a t i v e new approaches must be developed and t r i e d ( f o r example, t h e use o f i n c e n t i v e programs t o encourage cooperation w i t h ozone c o n t r o l programs).
The need t o accomplish b e t t e r t r o p o s p h e r i c ozone c o n t r o l takes on
even f u r t h e r importance i n view o f s t r a t o s p h e r i c ozone d e p l e t i o n b e i n g expected t o enhance surface l e v e l ozone f o r m a t i o n as one o f many n e g a t i v e e f f e c t s . STRATOSPHERIC OZONE Turning t o s t r a t o s p h e r i c ozone, d u r i n g t h i s Symposium we have heard much i n t e r e s t i n g b u t , also, very d i s t u r b i n g i n f o r m a t i o n r e g a r d i n g t h e d e p l e t i o n o f s t r a t o s p h e r i c ozone and i t s l i k e l y f u t u r e impacts.
As noted here, t h e n a t u r a l
d i s t r i b u t i o n o f ozone i n t h e E a r t h ' s atmosphere, concentrated most h e a v i l y i n a r e l a t i v e l y t h i n l a y e r i n t h e stratosphere, i s c r u c i a l i n h e l p i n g t o p r o t e c t humans, b i o l o g i c a l organisms, and man-made m a t e r i a l s from t h e harmful e f f e c t s o f c e r t a i n wavelengths o f Sun l i g h t .
S t r a t o s p h e r i c ozone e x e r t s i t s b e n e f i c i a l
e f f e c t s by p a r t i a l l y b l o c k i n g u l t r a v i o l e t r a d i a t i o n i n t h e 295 t o 320 nm (ultraviolet-6,
UV-6) range from reaching t h e E a r t h ' s surface.
Also, t h e
v e r t i c a l d i s t r i b u t i o n o f s t r a t o s p h e r i c ozone and t h e r e l a t i v e dryness o f t h e
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a i r i n the stratosphere help t o maintain the r a d i a t i v e balance o f t h e earth. Depletion of t h e s t r a t o s p h e r i c ozone l a y e r can, therefore, be expected t o l e a d t o damaging e f f e c t s on human h e a l t h and t h e environment: (1) d i r e c t l y by increased penetration o f UV-B r a d i a t i o n t o t h e E a r t h ' s surface and (2) i n d i r e c t l y by the influences o f changes i n t h e v e r t i c a l d i s t r i b u t i o n o f s t r a t o s p h e r i c ozone and water vapor t h a t c o n t r i b u t e t o global warming e f f e c t s and a l t e r e d c l i m a t i c conditions. Also, as we have learned here, many gases emitted due t o man's i n d u s t r i a l and a g r i c u l t u r a l a c t i v i t i e s can accumulate i n t h e atmosphere and u l t i m a t e l y c o n t r i b u t e t o a l t e r a t i o n s i n t h e v e r t i c a l d i s t r i b u t i o n and concentrations o f stratospheric ozone. Among the most important are t r a c e gases having long residence times i n t h e atmosphere, a l l o w i n g f o r t h e i r accumulation i n t h e troposphere and gradual upward m i g r a t i o n i n t o t h e stratosphere where they c o n t r i b u t e t o d e p l e t i o n o f s t r a t o s p h e r i c ozone. Trace gases o f p a r t i c u l a r concern include: (1) c e r t a i n l o n g - l i v e d chlorofluorocarbons ( o r CFC's) such as CFC-11, CFC-12 and CFC-113, t h a t have atmospheric residence times o f approximately 75 t o 110 years; (2) carbon t e t r a c h l o r i d e (CC14), w i t h a 50 year residence time; and (3) Halon-1301 and Halon-1211, w i t h 110 and 25 year residence times, respectively. Given t h e long periods o f time i n v o l v e d i n t r a n s p o r t o f these gases t o the stratosphere, t h e i r l o n g residence-times there, and slow removal processes, any e f f e c t s already seen on s t r a t o s p h e r i c ozone are l i k e l y due t o atmospheric loadings o f these t r a c e gases due t o anthropogenic emissions several decades ago; and those gases already i n t h e atmosphere w i l l continue t o e x e r t s t r a t o s p h e r i c ozone d e p l e t i o n e f f e c t s f a r i n t o t h e f u t u r e - - t h a t i s , w e l l i n t o the next century. That stratospheric ozone d e p l e t i o n i s f u r t h e r advanced than e a r l i e r p r o j e c t e d and c l e a r l y t i e d t o chlorofluorocarbon emissions became very evident as we heard speakers discuss the A n t a r c t i c ozone hole and t h e chemical/atmospheric processes underlying it. We a l s o heard information t h a t p o i n t s toward l i k e l y f u r t h e r spread o f the p o l a r ozone d e p l e t i o n and i t s expansion beyond t h e South P o l a r Region i n the coming decade; and o t h e r information p o i n t s toward t h e p o s s i b i l i t y of an analogous (though smaller) d e p l e t i o n zone developing over t h e North Polar Region. What are the types of e f f e c t s t h a t can be expected due t o s t r a t o s p h e r i c ozone depletion? The u l t i m a t e f u l l range of impacts cannot y e t be d e f i n i t e l y estimated. However, as heard a t t h i s Symposium, a t l e a s t some very major impacts on human h e a l t h and t h e environment can be reasonably p r o j e c t e d even now. Probably the best defined human h e a l t h e f f e c t s a r e increases i n s k i n
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cancer cases expected as t h e r e s u l t o f even small increases i n UV-B r a d i a t i o n reaching t h e E a r t h ' s surface. E x c e l l e n t summaries o f i n f o r m a t i o n on t h e subject have been provided as p a r t o f t h i s Symposium. O f various s k i n cancer types (non-melanoma and melanoma), t h e most d e f i n i t i v e evidence e x i s t s f o r nonmelanoma basal and squamous c e l l carcinomas o f the s k i n being l i n k e d t o UV-B r a d i a t i o n and, therefore, being l i k e l y t o increase due t o ozone l a y e r depletion. Cutaneous basal and squamous c e l l carcinomas occur most f r e q u e n t l y on sun-exposed body s i t e s of l i g h t - s k i n n e d Causasion peoples, and t h e i r incidences increase w i t h age. These and other data on geographic d i s t r i b u t i o n o f r a t e s f o r such cancers i n r e l a t i o n s h i p t o t h e e x t e n t o f l i k e l y sun exposure a l l suggest t h a t cumulative l i f e t i m e exposure t o Sun l i g h t p l a y s an e s s e n t i a l r o l e i n the i n d u c t i o n o f these s k i n cancers. Increases o f s k i n cancers d u r i n g t h e p a s t several decades i n t h e U.S. are probably p a r t l y due t o i n c r e a s i n g exposure t o both natural and a r t i f i c i a l sources o f UV-B r a d i a t i o n (e.g.
, with
more sunbathing
a t younger ages i n b a t h i n g s u i t s covering l e s s body surface and use o f u l t r a v i o l e t tanning salons, r e s p e c t i v e l y ) and g r e a t e r l o n g e v i t y a l l o w i n g f o r appearance o f such cancers a f t e r t y p i c a l long l a t e n c i e s (several decades) before t h e i r manifestation.
Given such l o n g latency associated w i t h UV r a d i a t i o n , i t i s
u n l i k e l y t h a t already observed increases i n s k i n cancer r a t e s can be a t t r i b u t e d t o any o f t h e small measurable decreases i n s t r a t o s p h e r i c ozone observed d u r i n g the p a s t decade o r so. Extensive other evidence e x i s t s , however, which permits f o r reasonable p r e d i c t i o n s t o be made o f l i k e l y increases i n basal and squamous c e l l s k i n cancer r a t e s (above higher r a t e s seen d u r i n g t h e p a s t few decades) i f s t r a t o s p h e r i c ozone d e p l e t i o n occurs a t an increasing r a t e .
As noted d u r i n g t h i s Symposium, i f s t r a t o s p h e r i c ozone i s depleted, t h e g r e a t e s t increase i n UV-B r a d i a t i o n w i l l be nearer t h e 295 nm versus the 310 upper end o f t h e a f f e c t e d wavelength range. The subject s k i n cancers are most a f f e c t e d by UV l i g h t around 300 nm, as w e l l demonstrated by experimental animal studies; and t h e percent incidence o f tumors i s a f u n c t i o n of dose (0) times exposure d u r a t i o n o r time (TI, i.e., D x T, w i t h no evidence f o r any threshold. That i s , t h e p r o b a b i l i t y o f cancer i n d u c t i o n
increases w i t h any degree o f exposure t o UV l i g h t (even low d a i l y doses can have strong effects) and t h e number o f new s k i n cancer p a t i e n t s can be p r e d i c t e d t o increase a t a greater-than-linear r a t e due t o several f a c t o r s . Such f a c t o r s include both (1) o p t i c a l a m p l i f i c a t i o n and (2) b i o a m p l i c a t i o n e f f e c t s . The o p t i c a l amplication e f f e c t s a r e p a r t l y geographically dependent, w i t h greater increases i n s k i n cancer r a t e s p r o j e c t e d i n human populations as a
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function o f t h e i r distance from t h e equator t o t h e poles due t o higher amounts of UV-B r a d i a t i o n expected t o reach the E a r t h ' s surface nearer the poles. Both o p t i c a l and b i o a m p l i f i c a t i o n f a c t o r s w i l l c o n t r i b u t e t o d i f f e r e n t i a l increases i n r a t e s f o r t h e two types o f non-melanoma s k i n cancers, although greater than proportional increases i n each are l i k e l y i n r e l a t i o n t o percentage ozone depletion. Thus, i f both a m p l i f i c a t i o n f a c t o r s are taken i n t o account, then the f o l l o w i n g q u a n t i t a t i v e consequences can be expected: (1) With a 1% decrease i n stratosphere ozone, e f f e c t i v e UV-B i r r a d i a n c e w i l l increase by 2% and, i n t u r n , lead t o increases i n t h e incidence o f basal c e l l carcinomas by 4% and o f squamous c e l l carcinomas by 6%; and (2) With a 5% decrease i n stratospheric ozone, increases can be expected i n incidences o f basal c e l l carcinoma by 22% and o f squamous c e l l carcinomas by 33%. The above p r o j e c t i o n s (combined with population s t a t i s t i c s and a d j u s t i n g f o r geographic gradients noted e a r l i e r ) l e a d t o estimates t h a t markedly increased numbers o f cases o f non-melanoma s k i n cancers w i l l eventually occur due t o s t r a t o s p h e r i c ozone depletion. The lighter-skinned White populations o f t h e w o r l d are expected t o be most affected, w i t h 70,000 new cases o f non-melanoma s k i n cancer per year (worldwide) p r o j e c t e d w i t h 1% s t r a t o s p h e r i c ozone d e p l e t i o n and 360,000 new cases annually w i t h 5% ozone depletion. I t was a l s o noted t h a t s u f f i c i e n t evidence e x i s t s f o r s u n l i g h t p l a y i n g a r o l e i n t h e much more dangerous ( o f t e n f a t a l ) melanoma forms o f s k i n cancer and t h e i r higher incidence i n persons w i t h non-melanoma tumors t o r a i s e t h e issue o f p o t e n t i a l f u t u r e increases i n melanomas due t o s t r a t o s p h e r i c ozone depletion. The key u n c e r t a i n t y i s t h e extent t o which UV-B r a d i a t i o n , versus o t h e r sun1 g h t components, may s p e c i f i c a l l y c o n t r i b u t e t o i n d u c t i o n o f cutaneous melanomas; and the l a c k u n t i l very r e c e n t l y o f any v i a b l e experimental animal model i n which t o study these l i g h t - a c t i v a t e d s k i n pigment c e l l cancers impeded resea ch progress. Two new animal study f i n d i n g s noted d u r i n g t h i s Symposium may, however, be harbingers o f f u t u r e advances i n t h i s area: (1) demonstration o f UV-B r a d i a t i o n increasing both squamous c e l l carcinomas and melanomas i n an animal model having photoactivated s k i n c e l l s and (2) o t h e r new data showing much greater growth o f ,melanomas transplanted i n t o skins o f UV-radiated animals , suggesting t h a t UV r a d i a t i o n may n o t o n l y t r i g g e r growth o f melanomas b u t a l s o have promotor e f f e c t s as w e l l . I t i s t h u s l y c l e a r t h a t appropriate c a u t i o n must be taken n o t t o prematurely r u l e o u t p o s s i b l e increases i n melanoma-type s k i n cancers due t o s t r a t o s p h e r i c ozone depletion. Another important h e a l t h endpoint 1i k e l y t o be a f f e c t e d by s t r a t o s p h e r i c ozone depletion--with p o s s i b l e much more extensive impacts on more diverse
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human populations o f t h e w o r l d than t h e s k i n cancer e f f e c t s - - i s immune suppression. As h i g h l i g h t e d d u r i n g t h i s Symposium, UV-B r a d i a t i o n appears t o be able t o modify immune f u n c t i o n i n several d i f f e r e n t ways, i n c l u d i n g changes o c c u r r i n g l o c a l l y a t t h e p o i n t o f s k i n i r r a d i a t i o n and o t h e r systemic e f f e c t s a t d i s t a l s i t e s away from exposed areas. L o c a l l y induced e f f e c t s i n c l u d e UV-B impairment of Langerhans c e l l s , those macrophage-like s k i n c e l l s mainly responsible f o r e n g u l f i n g antigens and presenting them t o helper T - c e l l lymphocytes i n v o l v e d i n mediation o f immune responses t h a t destroy antigens ( i . e . , f o r e i g n substances e n t e r i n g the body) and abnormal endogenous cancer c e l l s . A f t e r exposure t o UV-B r a d i a t i o n , Langerhans c e l l s no longer present antigens t o t h e helper T-lymphocytes and, when contact a l l e r g e n s a r e a p p l i e d t o UV-B exposed skin, no contact a l l e r g y ensues. Instead, suppressor lymphocytes a r e a c t i v a t e d which prevent any subsequent immune response t o t h e same antigen. UV-B r a d i a t i o n induced a c t i v a t i o n o f suppressor T - c e l l lymphocytes, which are normally i n v o l v e d i n r e g u l a t i o n o f the magnitude and d u r a t i o n o f immune responses, prevents devel opment o f n a t u r a l immune responses against UV-B induced s k i n cancers and thereby c o n t r i b u t e s t o t h e i r growth and spread t o o t h e r p a r t s o f t h e body. Besides the above e f f e c t s , c i r c u l a t i o n o f UV-B a c t i v a t e d suppressor lymphocytes throughout t h e body and an associated r e d u c t i o n i n numbers o f helper lymphocytes r e s u l t s i n a general, systemic suppression o f c e r t a i n immune functions. Thus, n o t o n l y do UV-B i r r a d i a t e d mice f a i l t o e x h i b i t c o n t a c t a l l e r g y responses t o chemicals a p p l i e d t o i r r a d i a t e d skin, b u t they a l s o have impaired a b i l i t y t o respond t o chemicals a p p l i e d t o non-radiated s k i n and decreased lymphocytemediated immune responses t o f o r e i g n substances i n j e c t e d under the s k i n ( i . e . , delayed h y p e r s e n s i t i v i t y reactions).
The systemic suppression o f immune
f u n c t i o n due t o UV r a d i a t i o n has been demonstrated t o occur i n several animal species, t o increase as a f u n c t i o n o f increasing UV-B dosage, and t o p e r s i s t beyond t h e i n i t i a l p e r i o d o f UV exposure. Very importantly, as noted d u r i n g t h i s Symposium, t h e above f i n d i n g s r a i s e the p o s s i b i l i t y t h a t suppression o f c e r t a i n lymphocyte-mediated immune responses by UV r a d i a t i o n may a l s o r e s u l t i n impairment o f analogous immune responses t o some i n f e c t i o u s agents. For example, t h e p a r a s i t e Schistosoma and t h e leprosy b a c i l l u s g a i n e n t r y v i a the skin, and such e n t r y o f these disease-producing organisms through UV-irradiated s k i n may l e a d t o a c t i v a t i o n o f suppressor lymphocytes and impaired immune r e a c t i o n s t h a t would otherwise counter the i n f e c t i o n s . Also, noted was t h e f a c t t h a t many o t h e r i n f e c t i o u s agents (e.g.
some viruses, b a c t e r i a , fungi, e t c ) produce s k i n diseases, and
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other organisms are normally h e l d i n check by delayed h y p e r s e n s i t i v i t y immune reactions.
I n each case, UV-6 induced immune suppression may increase s e v e r i t y of i n f e c t i o n s and impair development o f immunity against r e i n f e c t i o n . Consistent w i t h t h i s hypothesis are f i n d i n g s f o r t h e two i n f e c t i o u s agents s t u d i e d thus f a r :
(1) the demonstration t h a t i n j e c t i o n o f Herpes simplex v i r u s i n t o t h e s k i n o f mice exposed t o UV-B r a d i a t i o n r e s u l t e d i n suppressed immune response t o t h e v i r u s which l a s t e d f o r several months; and (2) t h e demonstration t h a t UV-6 i r r a d i a t e d mice i n f e c t e d w i t h Leishmania (a protozoan p a r a s i t e ) f a i l e d t o e x h i b i t delayed h y p e r s e n s i t i v i t y immune responses induced i n n o n - i r r a d i a t e d mice. The f u l l s i g n i f i c a n c e o f o f f i n d i n g s reviewed above f o r human h e a l t h remains t o be b e t t e r elucidated. However, evidence does e x i s t s f o r UV-B exposure i n humans producing analogous impairments i n immune system function, including:
(1) damage t o Langerhans c e l l s i n the s k i n and depressed a l l e r g i c
reactions t o f o r e i g n substances applied t o UV-irradiated skin; (2) decreases i n immune system k i l l e r c e l l a c t i v i t y and increases i n t h e number and a c t i v i t y o f suppressor lymphocytes w i t h human exposure t o UV-B r a d i a t i o n o r Sun l i g h t ; and (3) the persistence o f some o f these e f f e c t s beyond two weeks a f t e r exposure.
Thus, although much s t i l l has t o be learned through f u r t h e r research, prudence argues f o r viewing immune suppression e f f e c t s and any associated increased incidences o f some i n f e c t i o u s diseases as being l i k e l y t o occur w i t h s t r a t o spheric ozone depletion. Various o t h e r p o t e n t i a l h e a l t h e f f e c t s o f s t r a t o s p h e r i c ozone d e p l e t i o n l i k e l y t o be mediated v i a increased UV-B r a d i a t i o n were a l s o i d e n t i f i e d i n Symposium presentations. Probably most notably among these o t h e r e f f e c t s are adverse ocular e f f e c t s of UV-B r a d i a t i o n . One p o s s i b l y increased o c u l a r e f f e c t o f s o l a r UV r a d i a t i o n , snowblindness, i s t y p i c a l l y t r a n s i e n t ( i . e . , l a s t i n g f o r o n l y a few days); b u t i t s p o s s i b l e increase may be o f i n t e r e s t e s p e c i a l l y i n view of a n t i c i p a t e d greater UV-B i r r a d i a t i o n a t higher (snowier) l a t i t u d e s as t h e r e s u l t of ozone l a y e r depletion. O f much more concern, however, are t h e prospects o f increased incidence o f c a t a r a c t s cases.
New evidence i n d i c a t e s
t h a t small percentages o f UV-B r a d i a t i o n can penetrate i n t o t h e l e n s o f t h e eye and t h a t UV-6 r a d i a t i o n increases c a t a r a c t formation. The ozone l a y e r d e p l e t i o n would be expected t o increase t h e incidence o f c a t a r a c t s (a permanent clouding o f t h e lens o f the eye most o f t e n seen i n t h e e l d e r l y ) i n exposed populations, regardless of r a c i a l o r e t h n i c o r i g i n s . O f much concern i s t h a t , even i n developed countries where s u r g i c a l operations prevent most c a t a r a c t s from causing blindness, cataracts s t i l l remain as a leading cause o f blindness;
964
and, i n less-developed c o u n t r i e s w i t h much more l i m i t e d s u r g i c a l c a p a b i l i t i e s , c a t a r a c t s represent an even g r e a t e r t h r e a t . Human h e a l t h e f f e c t s a r e n o t t h e o n l y concerns associated w i t h s t r a t o s p h e r i c ozone d e p l e t i o n .
I n f a c t , as some speakers have noted d u r i n g t h i s Symposium,
t h e environmental e f f e c t s t h a t can be hypothesized as l i k e l y t o occur, may be even more d e v a s t a t i n g than t h e d i r e c t h e a l t h e f f e c t s .
Increased UV-B r a d i a t i o n ,
f o r example, can be p r o j e c t e d t o a f f e c t b o t h phytoplankton and zooplankton i n our oceans.
These microscopic a q u a t i c organisms, o f course, form t h e base o f t h e
food chain f o r many marine species and decreases i n t h e i r number would i n v a r i a b l y l e a d t o reduced commercially a v a i l a b l e s u p p l i e s o f e d i b l e f i s h and o t h e r seafoods, as w e l l as o t h e r negative e f f e c t s .
I t i s a l s o hypothesized
t h a t increased UV-B r a d i a t i o n i s l i k e l y t o reduce t h e y i e l d s o f many food crops (e.g.,
r i c e ) and a l s o t h a t i t may l e a d t o s e r i o u s f o r e s t and o t h e r t e r r e s t r i a
ecosystem damage.
L a s t l y , we have a l s o heard t h a t increased UV-B l e v e l s due t o
s t r a t o s p h e r i c ozone d e p l e t i o n can be l i k e l y expected t o exacerbate o r worsen tropospheric ozone f o r m a t i o n and associated h e a l t h and enviornmental problems. Appropriate steps t o be taken t o deal w i t h s t r a t o s p h e r i c ozone d e p l e t i o n were e x t e n s i v e l y discussed d u r i n g t h i s Symposium.
The general concensus a t t h i s
meeting was: (1) t h a t e f f e c t i v e i n t e r n a t i o n a l cooperation i s necessary t o reduce f u t u r e s t r a t o s p h e r i c ozone d e p l e t i o n and (2) t h a t r a t i f i c a t i o n and implementation o f t h e Montreal Protocol i s u r g e n t l y needed as a f i r s t i m p o r t a n t i n t e r n a t i o n a l cooperation step. However, t h e r e d u c t i o n o f CFC-use as planned under t h e Montreal Protocol (50% r e d u c t i o n by 1998) w i l l be i n s u f f i c i e n t t o p r e v e n t a t l e a s t some f u r t h e r d e t e r i o r a t i o n o f t h e ozone l a y e r .
Emission c u t s o f a t l e a s t 80-90% a r e
necessary and the c u r r e n t l y a v a i l a b l e maximum c o n t r o l p o t e n t i a l i s expected t o be about 50-70%.
I n t h a t case, several c o n t r o l approaches w i l l need t o be f o l l o w e d
The f i r s t p r i o r i t y i s t o f i n d s u b s t i t u t e s f o r t h e CFC's i n chemicals w i t h lower ozone d e p l e t i n g p o t e n t i a l .
I n a d d i t i o n , products and equipmen
developed t h a t r e q u i r e l e s s o r no CFC's.
have t o be
Also, t h e technology f o r emission
c o n t r o l i n p r o d u c t i o n processes, as w e l l as recovery and recyc i n g o f used CFC's need f u r t h e r development. CLOSING
These p o i n t s should be s u f f i c i e n t t o capture t h e general f l a v o r o f t h i s Symposium.
Both M r . Wolters and I have g r e a t l y enjoyed c o - c h a i r i n g t h i s meeting
and having t h e o p p o r t u n i t y t o see many o l d f r i e n d s and t o make many new ones. We l o o k forward t o seeing such f r i e n d s again i n t h e f u t u r e , b o t h a t t h e n e x t U.S.-Dutcl Symposium t o be planned f o r 1991 i n t h e U . S and i n t h e i n t e r v e n i n g years as w e l l .
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T. Schneider et al. (Editors),Atmospheric Ozone Research and its Policy Znplicatwns 0 1989 Elsevier Science PublishersB.V., Amsterdam - Printed in The Netherlands
967
OZONE AGGRAVATES HISTOPATHOLOGY DUE TO A RESPIRATORY INFECTION IN THE RAT
H. VAN LOVEREN, P.J.A. ROMBOUT, and J.G.VOS National Institute of Public Health and Environmental Protection, P.O.Box 3720 BA
1,
BILTHOVEN, The Netherlands,
INTRODUCTION Epidemiologic observations have suggested that exposure to air pollutants is linked with increased susceptibility to respiratory infections. Although definite
correlation
has
not yet been
shown
a
(1,8,9,15,32,43,45) the
association of air pollution with excessive hospitalization seems valid (3). The interpretation of this association as mediated through host defense mechanisms and pulmonary infection is however conjectural. In inhalation toxicological studies much emphasis has therefore been placed on animal infectivity models. In general, these models comprise exposure of laboratory animals to noxious gases or aerosols, and subsequent challenge of the animals with infectious agents causing only marginal mortality in non-exposed animals. Excess mortality or differences in bacterial growth in the lungs, induced by exposure to gases, are the indicators of adverse effects. Many animal species have been used in such studies, including mice, hamsters, squirrel monkeys (17) and rats (41). The infectious agents that have been used include bacteria such as U e D t o c W u s D V eO or~ a e b s i a D n e m (17), but also viruses such as Influenza A (48). With some exceptions (41,48), numerous studies using infectivity models have revealed that exposure to oxidant gases has an adverse influence on the host defense to respiratory infections (6,10,12,13,16-19,23,26,33.34). The infectivity models are therefore very useful to hosts
to
defend
show
the
inability of
the
themselves against opportunistic pathogens as a result of
exposure to noxious gases. However, although these models may aid in understanding how the defense mechanisms are affected, the models cannot discriminate between the various aspects of pulmonary defense mechanisms. Roughly, pulmonary defense mechanisms to pathogens can be divided into three main categories, comprising mechanic
defense mechanisms, non-specific
defense mechanisms (ingestion by phagocytic cells) and specific immunity. Exposure to oxidant gases can, dependent on concentration and duration of the exposure, impair ciliary activity (7) and ciliated cells (39). Suppression of
phagocytic activity of macrophages by
exposure
to
oxidant
gases has
been
reported (l), as well as suppression of the digestive activity of lysosomal enzymes (20,21,25,28), and of leakage of lysozomal enzymes into the cell
(5). Regarding specific immunity exposure to oxidant to interfere with the humoral immune response (11,35,36,42). The cellular immune response in the lung is important in that it regulates the magnitude of the humoral response to various antigens, and thus the efficacy of the humoral immune defense mechanisms (4). Moreover, it is also important in recruiting and activating alveolar macrophages (27). Effects of exposure to oxidant gases on cellular immune responses have not been studied very extensively. Hillam et al. (24) found that lymphocytes from lung draining lymph nodes from rats that were intratracheally immunized with sheep red blood cells showed an exaggerated reactivity to antigens when the rats were exposed to nitrogen dioxide. We have described experiments in the rat that were aimed to investigate the effect of exposure to ozone on the cellular immune response to Listerb monocvtonenes (47). Apart from mechanic defense mechanisms in the lung, the relevant mechanisms of defense against Listeria in the lung include phagocytosis by macrophages. and T cell dependent lymphokine production that enhances phagocytosis (30,31,37,44,46). Humoral immunity, in contrast to T cell dependent immunity, is not relevant in terms of protection against the infection in this Listeria model. We found an inhibitive effect of ozone exposure on the clearance of Listeria by the lungs and spleen of intratracheally infected rats. Besides effects of ozone on the capacity of alveolar macrophages to ingest and kill Listeria also effects on ratios of T and B cells in lung draining bronchial lymph nodes, on proliferative responses to Listeria antigen of lymphocytes from bronchial lymph nodes and spleen of immunized rats, and on delayed-type hypersensitivity responses to Listeria cytoplasm and gases has
tissue
been
reported
antigen in immunized rats were
found
(47).
Pathological
lesions
following
intratracheal infections with m c v t o eenea appeared as inflammatory foci, comprising macrophages and lymphoid cells. Since both cell types seem to be
affected by
exposure
to
ozone, we also studied the influence of ozone
exposure on these lesions. For this purpose rats were continuously exposed
to
0, concentrations ranging from 0.25 to 1.5 mg/ms for a period of 1 week. TIME COURSE OF HISTOPATHOLOGIC EFFECTS OF A PUIMONARY INFECTION WITH
LISTERIA
MONOCYTOGENES Lungs of rats were examined at various
time points
infection with
infection (10 bacteria instilled
after
a pulmonary
6
Listeria.
One
day
after
observed; diffusely in lung interstitial histiocytes and lymphoid cells were noted, and a slight
intratracheally) very mild pathological changes were the
969 increase of alveolar macrophages could
be
established.
These
lesions were
observed associated with bronchi or bronchioli, but not preferentially. By day 3 after infection multiple foci, consisting of lymphoid cells, accompanied by histiocytes,
and
occasionally
an
influx of neutrophilic granulocytes with
areas of local cell degeneration could be seen. These lesions did not show a clear association with bronchi or bronchioli. These foci sometimes included alveolar lumina, where also granulocytes could be located. By day 5 the histopathological alterations in the lung were similar to those found 3 days after infection, but more severe and also more or less diffuse. By day 7 the inflammation was somewhat less severe. By day 10 after infection the lung had practically recovered from the infection, illustrated by the absence of major histopathological lesions. Some foci of histiocytes and lymphoid cells were still present. By day 15 after infection only sporadically lesions
could
be
observed. EFFECTS OF OZONE EXPOSURE ON PATHOLOGICAL LESIONS DUE TO LISTERIA 8
The lesions, that were observed in rats that were exposed to 1.5 mg/m I3 ozone for one week prior to intratracheal infection with 10 Listeria were more pronounced as compared to those in unexposed animals. Especially at 5 days after infection, the lesions in ozone exposed rats were most severe. Diffusely throughout the lung large inflammatory
infiltrates were
observed,
that were characterized by predominantly lymphoid cells and to a lesser extent also by histiocytes. Locally cell degeneration could be observed, and the entire aspect of the lesions were suggestive of granulomatous alteration (Fig.
1). The cells involved seemed
to
spread
in
the
lung parenchyma.
In the
alveolar spaces many macrophages were present. In contrast to non-exposed rats, the lungs of rats exposed to ozone still showed these pathologic lesions at later time points after infection. Whereas 15 days after infection the inflammatory noduli had disappeared in lungs of non-exposed rats, in the interstitium of exposed rats increased numbers of inflammatory cells could still be noted, and in the alveolar lumina clusters of alveolar macrophages were still observed. There were only minimal differences between rats that belonged to the same group. DISCUSSION Ozone exposure of rats decreased the resistance
to pulmonary
infection
with Wsteria m o n o c v t o m (47). In part this decreased resistance was due to an impaired capacity of alveolar macrophages to ingest and kill Listeria. Decreased phagocytic and lytic activity of alveolar macrophages due to exposure to oxidant gases is in agreement with many other studies, using other models (1,19,20,21,28). Besides non-specific defense mechanisms, mediated by macrophages, a crucial &fenso mchanimr i n t a r u of protection to ud control of raopiratory
Fig. 1. Granuloma in lung of ?At, 5 day8 aftor king continilauly oxpoaed to 0, for 1 week and subsequently infoctod intratrachoally w i t h loe (HE x 400).
ia
infection with
wdiatod by
cellular
immunity
(30,31,37,44,46).We have shown that also tho d e w l o p a n t of Icell mdiated immunity to Listeria appears to be suppressed in ozone exposed rats (47). The conclusion, that ozone exposure can have an influence on development of T cell dependent immune responses to Listeria indicates that potentially
hazardous with
respect
to
ozone must
The pulmonary changes in the rat that can be well
documented
judged
bacterial, viral
challenges of the lung, where T cell dependent immunity is crucial role in the defense. levels are
be
(2,14,38). In
and neoplastic known to play a
induced by
ambient
ozone
those studies damage was mainly
restricted to the transition zone from terminal bronchiole to
alveolar
duct.
Here, desquamation of type I pneumocytes of the alveolar lining, having a denuded basement membrane, was followed by a proliferation of type I1 cells, urd
together with
an
influx of interstitial inflammatory cells resulted in
thickor proximal alvoolar aopta. h incream of alvmolar ucrophasoa
waa
the
971 alvoolar component of tho infl-tory roaction. Loss of cilia and hypertrophy of tho bronchiolar epithelium has been deacribed in the t e I d M 1 conducting
d A h 8 t C ~ h t Wrphological O rocovery Of oxidant-induced lesion8 illustrates the e x t o ~ i v erepair capacity of the rat lung tissue. airvAy8. Rapid
Within a recovery period of one week nearly all lesion8 induced by continuous a exposure to 1.6 mg/m 0 , (22) or 20 mg/m NO, (40) had disappeared. Gross and White (22) described a nearly complete recovery of morphological lesions in a
rat lung 4 weeks after a continuous exposure to 1.4 mg/m 0 , for 4 weeks. In our model we made similar observations (data not shown). Within 5 days after termination of a one week period of continuous ozone exposure the lungs had recovered; by
that time hardly any lesions could be found, except some minor
lesions in the lungs of rats exposed to the higher s
concentrations of ozone
.
used, i.e. 1.5 mg/m Pulmonary infection with mnocvtlesions, that were characterized by foci of
induced histopathological inflammatory cells such as
lymphoid and histiocytic cells, accompanied by local cell degeneration and influx of granulocytes. The maximal histopathological effects due to a Listeria infection were observed at 5 and 7 days after infection. If rats were exposed t o ozone for one week prior to infection, the lesions found 5 and 7 days after infection were much more severe than in non-exposed animals. At that time the changes by exposure to ozone itself, without an infection, would virtually have disappeared. This indicates therefore, that the increased severity of lesions due to infection with Listeria after prior exposure to ozone was not an addition of ozone lesions, but
induced lesions and Listeria
induced
rather represented synergism between effects of ozone and
Listeria. This was illustrated also by the fact that at 15 days after infection, and thus also 15 days after the end of a one week period of exposure to 1.5 mg/m
s
ozone, at a time that both challenges of
the
rat
lung
were no longer seen as histopathologic lesions, lesions could still be seen if the challenges occurred in the same rat. Besides the severity and duration of the histopathology after
infection, also
the quality of the lesions was
influenced by prior exposure to ozone. Nature granulomas were Listeria infected rats that were also exposed to ozone. We interpret these data by macrophages after ozone exposure
found in
the diminished phagocytic activity of and the diminished cellular immunity to
Listeria after ozone exposure. Infection with Listeria caused an influx of macrophages. These macrophages ingested and killed the bacteria, and also gave rise to induction of Listeria-antigen specific T cells, that could produce lymphokines that activated macrophages to more effectively ingest and kill the bacteria. These defense mechanisms were visualized in the lungs by the inflammatory sites, where macrophages (histiocytic cells) and lymphoid cells were localized. In ozone exposed animals, as a consequence of diminished activity of u c r o p h g o s and of tho collular
upocts of tho dofeme, the
972 numbers of bacteria that could be recovered from the lung after infection were increased, thus effective
leading
to
an
even more
pronounced attxaction of
-
less
-
inflammatory cells. The frustrated efforts of both macrophages and lymphocytes resulted in granuloma formation.
CONCLUDING REMARKS In conclusion this report shows that ozone exposure, by diminishing the cellular immune and non-specific defense mechanisms with
Listeria, can
greatly
add
to
pulmonary
infection
to the pathological alterations due to the
infection, and, as a consequence, enhance the loss of lung functions caused by the
pulmonary
infection. These findings are underscored by the results that
indicate that systemic effects of a respiratory infection with Listeria, i.e. alterations in the liver, were more profound after exposure of the rats to the oxidant gas ozone (47). REFERENCES 1. Acton, J.D. and Myrvik. Q.N. (1972). Nitrogen dioxide effects on alveolar macrophages. Arch. Environ. Health 24, 48-52. 2. Barry, B.E., Miller, F.J. and Crapo, J.D. (1985). Effects of inhalation of 0.12 and 0.25 ppm ozone on the proximal alveolar region of juvenile and adult rats. Lab. Invest. 52, 692-704. 3. Bates, D.V. and Sitzo, R. (1983). Relationship between air pollutant levels and hospital adminissions in Southern Ontario. Canad. J. Publ. Health &, 117-122. 4 . Bienenstock, J., Befus, A.D. and McDermott, M. (1980). Mucosal Immunity. 1-18. Monogr. Allergy. 5. Castleman, W.L., Dungworth, D.L. and Tyler, W.S. (1973). Lung acid phosphatase reactivity following ozone exposure. Lab. Invest. 2,310-319. 6. Coffin, D.L., Gardner, D.E. and Blommer, E.J. (1966). Time-dose response for nitrogen dioxide exposure in an infectivity model system. Environ. Health Perspect. Q, 11-15. 7. Dalhawn, T. and Sj6holm, J. (1963). Studies on SO,, NO, and NH,: Effect on ciliary activity in rabbit trachea of single vitrQ exposure and resorption in rabbit nasal cavity. Acta Physiol. Scand. 287-292. a . Dohan, F.C., Everts, G.S. and Smith, R. (1962). Variations in air pollution and the incidence of respiratory disease. J . Air Poll. Contr. ASS. u , 418-436. 9. Durham, W.H. (1974). Air pollution and student health. Arch. Environ. Health 2,241-254. 10. Ehrlich, R. (1966). Effect of nitrogen dioxide on resistance to respiratory infection. Bacteriol. Rev. Zp, 604-614. 11. Ehrlich, R., Silversteyn, E., Maigetten, R. and Fenters, J.D. (1975). Immunologic response in vaccinated mice during long-term exposure to nitrogen dioxide. Environ. Res. 217-223. 12. Ehrlich, R., Findlay, J.L. and Gardner, D.E. (1979). Effects of repeated exposure peak concentration of nitrogen dioxide and ozone on resistance to streptococcal pneumonia. J. Toxicol. Environ. Health 5, 631-642. 13. Ehrlich, R. (1980). Interactions between environmental pollutants and respiratory infections. Environ. Health Perspect. 89-100. 14. Evans, M.J., Johnson, L.V., Stephens, R . J . and Freeman, C. (1976). Cell renewal in the lungs of rats exposed to low levels of ozone. Exp. Mol. Pathol. &, 70-83. 15. French, J.C., Lowrimore. G., Nelson, W.C., Fincklea, J.F. and Hertz, M. (1973). Effect of sulfur dioxide and suspended sulfates on acute reapiratory disease. Arch. Environ. Health 2,129-133.
u,
x,
u,
z,
973 16. Gardner, D.E., Miller, F.J., Blomer, E.J. and Coffin, D.L. (1979). Influence of exposure mode on the toxicity of NO2. Environ. Health Perspect. 2,23-29. 17. Gardner, D.E. (1982). Use of experimental airborne infections for monitoring altered host defenses. Environ. Health Perspect. 41. 99-107. 18. Gardner, D.E. (1984). Oxidant-induced enhanced sensitivity to infection in animal models and their extrapolation to man. J. Toxicol. Environ. Health 2,423-439. 19. Goldstein, E., Eagle, C. and Hoepreich, P.D. (1973). Effect of nitrogen dioxide on pulmonary bacterial defense nechanisms. Arch. Environ. Health 26, 202-205. 20. Goldstein, E., Lippert, W. and Warshauser, D. (1974). Pulmonary macrophage. Defences against bacterial infection of the lung. J. Clinic. Invest. &, 519-528. 21. Goldstein, E., Bartlema, H.L., Van der Ploeg, H., Van Duyn, P., Van der Stap, J.G.M.M. and Lippert, W. (1978). Effect of ozone on lysozomal enzymes of alveolar macrophages engaged in phagocytosis and killing of inhaled S t a D h v w aurew J. Infect. Die. 299-311. 22. Gross, K.B. and White, H.J. (1986). Pulmonary functional and morphological changes induced by a 4 week exposure to 0.7 ppm ozone followed by a 9 week recovery period. J. Toxicol. Environ. Health 143-157. 23. Henry, M.C., Findlay, J., Spangler, J. and Ehrlich, R. (1970). Chronic toxicity of NO, on squirrel monkeys. 111. Effect on resistance to bacterial and viral infection. Arch. Environ. Health 2p, 566-570. 24. Hillam, P., Bice, D.E., Hahn, F.F. and Schnizlein, C.T. (1983). Effect of acute nitrogen dioxide exposure on cellular immunity after lung immunization. Environ. Res. =,201-211. 25. Holzman, R.S., Gardner, D.E. and Coffin, D.L. (1968). Jn vivQ inactivation of lysozyme by ozone. J. Bacteriol. 1562-1566. 26. Illing, J.W., Miller, F.J. and Gardner, D.E. (1980). Decreased resistance to infection in exercized mice exposed to NO2 and 0 , . J. Toxicol. Environ. Health 6, 843-851. 27. Keller, R.H., Fink, J.N., Lyman, S. and Pedersen, G.M. (1982). Immunoregulation in hypersensitivity pneumonitis. I. Differences in T cell and macrophage suppressor activity in symptomatic and asymptomatic pigeon breeders. J. Clin. Immunol. 2, 46-51. 28, Kimura, A. and Goldstein, E. (1981). Effect of ozone on concentration of lysozyme in phagocytizing alveolar macrophages. J. Infect. Dis. 247251. 29. Lawther, P.J. (1958). Climate, air pollution and chronic bronchitis. Proc. Roy. SOC. Med. 3, 262-267. 30. Mackaness, G.B. (1969). The influence of immunologically committed lymphoid cells on macrophage activity b vivQ. J. Exp. Med. 973-992. 31. McGregor, D.D., Hahn, H.H. and Mackaness, G.B. (1973). The mediator of cellular immunity. V. Development of cellular resistance to infection in thymectomized irradiated rats. Cell. Immunol. 6 , 186-199. 32. Melia, R.J.W., Florey, C.V., Altman, D.G. and Swan, A.V. (1977). Association between gas cooking and respiratory disease in children. Br. Med. J. 2, 149-152. 33. Miller, S. and Ehrlich, R. (1958). Susceptibility to respiratory infections of animals exposed to ozone. 1. Susceptibility to Klebsiella 145-149. pneumoniae. J. Infect. Dis. 34. Miller, F.J., Illing, J.W. and Gardner, D.E. (1978). Effect of urban ozone level on laboratory-incurred respiratory infections. Toxicol. Letters 2 , 163-169. 35. Osebold, J.W., Owens, S.L., Zee, Y.C., Dotson, W.M. and Labarre, D.D. (1974). Immunological alterations in the lungs of mice following ozone exposure. Changes in immunoglobulin levels and antibody containing cells. Arch. Environ. Health &, 258-265.
m,
.
u,
s,
m,
m,
m,
974 36. Osebold, J.W., Gershwin, L.J. and Zee, Y.C. (1980). Studies on the enhancement of allergic lung sensitization by inhalation of ozone and sulfuric acid aerosol. J. Environ. Pathol. Toxicol. 2, 221-234. 37. Pennington, J.E. (1985). Immunosuppression of pulmonary host defense. Adv. in Host Defense Mechanisms 4, 141-164. 38. Plopper, C.G., Chow, C.K., Dungworth, D.L., Brummer, M. and Nemeth T.J. (1978). Effect of low levels of ozone on rat lungs. 11. Morphological responses during recovery and reexposure. Exp. Mol. Pathol. 2,400-411. 39. Rombout, P.J.A., Dormans, J.A.M.A.,.Danse, L.H.J.C., Van Esch, E., Van Leeuwen, F.X.R. and Marra, M. (1982). Correlation between morphological and biochemical alterations in the rat lung exposed to nitrogen dioxide. In: Air pollution by nitrogen dioxides (Eds. Schneider, T., and Grant, L.). pp. 457-466. 40. Rombout, P.J.A., Dormans, J.A.M.A., Marra, M . and Van Esch, G.J. (1986). Influence of exposure regimen on nitrogendioxide induced morphological changes in rat lung. Environ. Res. 41, 466-480. 41. Sherwood, R.L., Kimura, A.. Donovan, R. and Goldstein, E. (1981). Effect of 0.64 ppm ozone on rats with chronic pulmonary bacterial infection. J. Toxicol. Environ. Health 893-904. 42. Schnizlein, C.T., Bice, D.E., Rebar, A.H., Wolff, R.K. and Beethe, R.L. (1980). Effect of lung damage by acute exposure to nitrogen dioxide on lung immunity in the rat. Environ. Res. u , 362-370. 43. Speizer, F.E., Ferris, B., Bishop, Y.M.M. and Spengler, J. (1980). Respiratory disease rats and pulmonary function in children associated with NO, exposure. Am. Rev. Respir. Dis. 3-10. 44. Takeya, U., Shimotori. S., Tanaguchi, T. and Nomoto, K. (1977). Cellular mechanisms in the protection against infection by u t e r i a -om in mice. J. Gen. Microbiol. ULp, 373-379. 4 5 . Thomson, D.J., Lebowitz, 1. and Cassell, E.J. (1970). Health and the urban environment. Air pollution, wheather and the common cold. Am. J . Publ.Health 731-739. 46. Van Loveren, H., Postma, G.W., Van Soolingen, D., Kruizinga, W., Groothuis, D.G. and Voe. J.G. (1987). Enhanced macrophage activity and s in nude rats. In: deficient acquired resistance to Immune-deficient animals in biomedical research. Eds. Rygaard, J . , BrUnner, N., Graem, N., Spang-Thomson, M., pp. 108-111. Y.Karger, Basel. 47. Van Loveren, H., Rombout, P.J.A., Uagenaar, Sj.Sc., Walvoort, H.C., Vos, J.G. Effects of ozone on the defense to a respiratory Listeria monocytogenes infection in rat, Suppression of macrophage function and cellular immunity and aggravation of histopathology in lung and liver during infection. Toxicol. Appl. Pharmacol, $&, in press, 1988. 48. Wolcott, J.A., Zee, Y.C. and Osebold, J.W. (1982). Exposure to ozone reduces influenza disease severity and alters distribution of influenza viral antigens in murine lung. Appl. Environ. Microbiol. &, 723-731.
n,
u,
a,
T.Schneider et al. (Editors),Atmpheric Ozone Research and ita Pollcy Implications 0 1989 Eleevier Science Publishers B.V.,Amstardam -Printed in The Netherlands
975
ADAPTATION UPON OZONE EXPOSURE IN KICE AND RATS
T.S. VENINGA Central Animal Laboratory, University of Groningen, Ant. Deusinglaan 50, 9713 AZ Groningen, The Netherlands
ABSTRACT Changes in the activity of the enzymes creatine kinase and glucose-6-phosphate dehydrogenase observed in blood plasma and alveolar macrophages (AM) respectively, as well as changes in AM adherence caused by 0, concentratiom of 40 pg/ms and higher reveal activation of this pulmonary defense system after 0, exposure. Such an activation creates a certain threshold. If the defence can fully cope with an offending irritant the state of adaptation may have been reached. INTRODUCTION Studying the effect of air pollutants on living organisms you may expect to observe 3 types of reactions: 1. defensive
2. injurious 3. reparative We examined 3 aspects of alveolar macrophage (AM) activity in mice and rats after exposure to ozone (0,) in concentrations of 0.02 to 0.4 ppm (40 to 800 pg/ms) namely: 1. AM adherence to nylonwool, 2. their intracellular glucose-6-phosphatedehydrogenase (G-6-PD)-activity, 3. activity of the enzyme creatine kinase (CK) in blood plasma, which is suggested to originate from AM'S (ref. 1).
METHODS Young adult male C57BL mice and young adult male Wistar rats were used. These conventional clean animals were bred in own facilities. Mice were housed 5 to a cage and rats 2 to a cage. The animals had free access to pelleted feed and acidified water. Feed was removed 8 h before and during 0, exposure. Experiments were performed according to a staggered schedule. The exposure facilities have been described previously (ref. 2). In all series of experiments a comparable number of control animals were exposed to filtered air. The exposure time for mice was 2.h, for rats either 2 h in the CK experiment or 16 h in the adherence and G-6-PD study. AM'S were isolated by
976 pulmonary lavage immediately after exporure. Only 2 washes were performed by intratracheal injection of physiological saline. These were treated separately. The An adherence was measured by counting the number of A n ’ s before and after passing 1 ml samples through a nylonwool column (ref. 2). C-6-PD was histochemically determined (ref. 3). The number of positively stained cells, counted under the microscope, was related to the number of cells present in small samples. Blood was taken by orbital puncture. Mice were punctured only after exposure, rats before and after exposure. Plasma CK was determined with CK test combinations of Boehringer (W. Germany) (refs. 4 - 5 ) . The determination of CK isoenzymes was performed by gelelectrophoresis (ref. 1). A range of 0, concentrations was used for each of the 3 variables studied. At each concentration at least 20 mice and in general at least 10 rats were used.
RESULTS Typical dose-response relationships were obtained for all 3 variables (Fig. 1, 2 ) .
CK rats(.) Median in relation to control
CK mice(0) Mean : per cent of control
-40
- 20 -0
- -20
Fig. 1. Activity of the enzyme CK in blood plasma of rats and mice exposed to a range of 0, concentrations for 2 h. Solid line: activity in rats, dashed line: activity in mice.
977
I
A 02 05 01
Low200
02 WM
B
04
02 a5 01
02
ppn
0.4
800
urn m
wx)
pg/w
1)oo
Fig. 2. Activity of the enzyme G-6-PD in AM'S (solid lines) and adherence of A M ' S (dashed lines) of rats exposed to a range of 0, concentrations for 16 h.A. First wash A M ' S , B. second wash AM'S
Except for the adherence where the lowest concentration was not tested, the curves start with one or two values negative in relation to the controls, then rise to positive values and then show a decline to values as or below those of controls. Lavages contained 98 per cent A M ' S ; 96 per cent of the cells were vital as demonstrated by dye-exclusion. AM'S of first washes showed a somewhat greater adherence than AM'S of second washes. Morphological variations were present between first- and second wash AM'S (Fig. 3): the majority of the first-wash A M ' s were larger and more rounded, with a foamy cytoplasm; the majority of the
second-wash AM'S were compact cells with a dense cytoplasm. The percentage G-6-PD positive AM'S in the washes varied between 10 and 40. In contrast to adherence no difference was found between first- and second wash A M ' S . Regarding CK activity in blood plasma rats turned out to be less sensitive to 0, exposure than mice. CK-BB in murine plasma demonstrated significantly higher activity in 0, exposed animals. CK-MM showed no difference, whereas CK-
MB was absent. DISCUSSION AM's represent a pulmonary defence system which as shown in this study, is and lower. Concentraactivated by 0, in concentrations of 0.1 ppm (200 &ma) tions higher than 0.1 ppm lead to decreasing activity. This may point to a deficit in defensive capacity and therefore may be the consequence of a detrimental effect. All 3 variables studied react in a similar way and give rise to comparable curves. The observed increase of CK-BB may originate from the lungs
9 78
F i g . 3. First-wash (left) and second-wash (right) An's from non-exposed rats. May-Grilnwald Giemsa stain. Magnification 1000 x.
(ref. 6). CK is present in An's
(ref. 7); it is necessary for their mobiliza-
tion. Activated AM'S move to foreign substances and adhere (Fig. 4). As indicated previously AM adherence is an expression of their (increased) activity (ref. 2). Stimulation of G-6-PD supports the defensive potential of the cells. Also Rietjens et a1 (ref. 8) reported increased G-6-PD activity in rat An's grown in vitro after exposure to 1.5 0, for 4 days. We did not observe large amounts of neutrophils in the lavage fluid of rats
muma
exposed for 16 h to 0, as has been reported by others in this symposium. The reason might be that we lavaged the animals only twice. In general it is done serveral times in order to obtain larger numbers of An's. The presence in living organisms of defence systems wich become activated upon 0, inhalation, creates a threshold. If the defence becomes disabled no threshold will be observed. Activation of the defence may occur with some delay. Therefore, we can not exclude the possibility that even a small amount of 0, causes a lesion in the respiratory system beit of a minor order. Besides morphological it could be of biochemical on physiological nature. Such a lesion may be unnoticed because it is rapidly repaired and the defence systems
Fig. 4. Adherenco of M ' m to
A
foreign particle lavaged from a non-exposed rat.
have started their activity. In this relation distinction between defence and repair reactions is not always possible. Our results indicate that we observed elevated AM activity as an expression of an increased defensive capacity caused by 0, concentrations of 0.1 ppm (200
pg/ms) and lower. With 0, concentrations of 0.2 ppm (400 pg/ms) and higher the defensive capacity becomes deficient. We suggest that if the defence can cope with an offending stimulus like 0,, the state of adaptation is achieved. REFERENCES T.S. Veninga, Variations in pulmonary macrophage and enzymatic activity characteristics in animals exposed to photochemical oxidants, Proceedings Clean Air Congres, Sydney, 1986, 2 , pp. 293-299. T.S. Veninga and P. Evelyn, Activity changes of pulmonary macrophages after in vivo exposure to ozone as demonstrated by cell adherence, J . Toxicol. Environm. Health, 18 (1986) 483-489. C.J.F. Van Noordsn, I.M.C. Vogels, J. James and J. Tar, A sensitive cytochemical staining method for glucose-6-phosphate dehydrogenase activity in individual erythrocytes, Histochemistry, 75 (1982) 493-506. T.S. Veninga, J. Wagenaar and W.Lemstra, Distinct enzymatic reponses in mice exposed to a range of low doses of ozone, Environm. Health Persp., 39 (1981) 153-157. T.S. Veninga and V. Fidler, Ozone - induced elevation of creatine kinase activity in blood plasma of rats, Environm. Res., 41 (1986) 168-173. R.B. Coolen, D. Pragay, J . S . Nosanchuk and R. Belding, Elevation of brain type creatine kinase in serum from patients with carcinoma, Cancer, 44 (1979) 1414-1418. J . D . Loyke, V.F. Kozler and S.C. Silverstein, Increased ATP and creatine phosphate turnover in phagocytosing mouse peritoneal macrophages, J . Biol. Chem., 254 (1979) 9558-9564. I.M.C.M. Rietjens, L. Van Bree, M. Marra, M.C.M. Poelen, P.J.A. Rombout and G.M. Alink, Glutathione pathway enzyme activities and the ozone sensitivity of lung cell population derived from ozone exposed rats, Toxicol., 37 (1985) 205-214. ACKNOWLEGMENT The skilful technical assistance of R.A. Wieringa is gratefully acknowledged.
981
ORGANIZATION
SYMPOSIUM CHAIRMEN Environmental Protection Agency, United States o f America L. D. Grant M i n i s t r y o f Housing, Physical Planning and Environment, G.J.R.Wolters The Nether1ands
ORGANIZING COMMITTEE United Stat e s o f America S.D. Lee, chairman K. Barry B.Dimitriades L. D. Grant F.Mi 1l e r
PARTNERS PROGRAMME Mrs.M.Schneider-Ferrageau de S t .Amand
ADVISORY COMMITTEE
L.D.Grant, chairman G .Hueter B. Long V. A. Newi 11 J.O*Connor D.H. S t r o t h e r
REGISTRATION AND INFORMATION CENTRE Mrs.O.van Steenis
The Nether1ands T.Schneider, chairman J.van Ham, secretary Mrs .O. van Steen is Mrs P. W .A.M. Veni s-Pol s S. Zwerver
.
-
T.Schneider, chairman J.van Ham, secretary E .H Adema J .H. Blom L.J.Brasser N. C. van Lookeren Campagne G. Schaap C. J. E. Schuurmans J.F.van de Vate K.Verhoeff G. H. Von kernan W .H. J .M.Wi entjens S, Zwerver
.
INTERNATIONAL SECRETARY J.van Ham
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983
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School o f Veterinary Medicine
334 H. J e f f r i e s U n i v e r s i t y of North Carolina, Env.Sci. School o f Public Health EigPiL HILL NC 27514 USA
S.M. J o f f r e
Finnish Meteoroloaical I n s t i t u t e Sahaajankatue 22ESF-00810 HELSINK1 Finland telex: 124436 t e l : 358-0-7581320
W. B. Johnson National Center f o r Atmospheric Research BOULDER CO 80307 USA t e l : 303-497-1032 telex: 989764 P. E, Joost i n g Laan van Oostenburg 16 2271 AP VOORBURG The Netherl ands t e l : 070-869418 J. Kagawa Dep. o f Hygiene and Public Health, Tokyo Women’s Medical College 8 - 1 Kawada-cho, Shinjuku-ku TOKYO 162 Japan t e l : 03-353-8111
R.R. Kampen Kerkhofsweg 17 9995 PL KANTENS The Netherl ands t e l : 05995-1903
L.V. Karenlampi U n i v e r s i t y o f Kuopi P.0.Box 6 70211 KUOPI 21 Fin1and t e l : 971-163180
telex: 42218
A. Karpinen M i n i s t r y o f t h e Environment P.0.Box 399 SF-00121 HELSINKI Finland telex: 123717 t e l : 358-0-1991371 H.R. Kehrl US EPA, C l i n i c a l Research Branch MD-58 RESEARCH TRIANGLE PARK NC 27711 USA t e l : 919-966-6208
995
H. Kelder KNMI P.0.Box 201 3730 AE DE BILT The Netherlands t e l : 030-766472
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J.van der Kooy N.V. KEMA P.0.Box 9035 6800 ET ARNHEM The Netherl ands t e l : 085-562543 H.S.
t e l e x : 45016
Koren
US EPA. Health E f f e c t s Research Lab.
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telex: 510-927-1800
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R. Kroes National I n s t i t u t e o f Pub1i c Health and Environmental Protection P.0.Box 1 3720 BA BILTHOVEN The Netherl ands t e l : 030-742310 telex: 74215
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T. McCurdy US EPA, MD-12 RESEARCH TRIANGLE PARK NC 27711 USA t e l : 919-541-5658 M. McElroy Harvard U n i v e r s i t y , Department o f Earth and P1 anetary Sciences Pierce H a l l , 100 E CAMBRIDGE MA 02138 USA
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999 E.L. Meyer US EPA 10 Glenmore Drive DURHAM, NC 27707 USA t e l : 919-541-5594 J. Meyer RMNO P.O.Box 5306 2280 HH RIJSWIJK The Netherl ands t e l : 070-985880
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1000
J . Nobel Association o f the Mechanical and E l e c t r i c a l Engineering I n d u s t r i e s P.0.Box 190 2700 AD ZOETERMEER The Netherl ands t e l : 079-531334 S.L. Nolen US EPA, MD-61 RESEARCH TRIANGLE PARK NC 27711 USA t e l : 919-541-7607
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American Petroleum I n s t i t u t e 1220 L S t . NU WASHINGTON DC 20005 USA t e l : 202-682-8262
D. Onderdel 1nden
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R. Orthofer Austrian Research Centre Sei bersdorf A-2444 SEIBERSDORF Austria t e l : 02254-80-2166 telex: 014-353
J. Overton US EPA, MD 82 RESEARCH TRIANGLE PARK NC 27711 USA t e l : 919-541-5715 J . Pankrath
Unwel tbundesamt Bismarckplatz 1 0-1000 BERLIN 33 FRG t e l : 030-8903-375
FME
1001
R.T. Paul Motor Vehicle Manufacturers Association 300 New Center B u i l d i n g DETROIT, Michigan 48202 USA telex: 1009770 t e l : 313-872-4311
S.
Penkett U n i v e r s i t y o f East Angl ia, School o f Environmental Sciences NORWICH NR4 7TJ UK L. Perros L.P.C.E.University o f Paris X I 1 Avenue du General de Gaulle 94000 CRETEIL France t e l : 16-148989144 t e l e x : UPVM 211 752 F
A.C. Posthurnus Research I n s t i t u t e f o r Plant Protection Wageningen, Free U n i v e r s i t y Amsterdam Vossenwe 66 6721 BP OENNEKN The Netherlands t e l : 08370-19151 H. Puxbaum Technical U n i v e r s i t y Vienna Getreidemarkt 9 A-1060 VIENNA Austria M. Raizenne National Health and Welfare Tunney-s Pasture OTTAWA, ON KIA OL2 Canada S.T. Rao NYS, Department o f Environmental Conservation 50 Wolf Road, Room 134 ALBANY, NY 12233-3259 USA t e l : 518-457-3200 L. Reijnders Societv f o r Environmental Conservation Donkerhraat 17 3511 KB UTRECHT The Netherlands t e l : 030-331328 t e l e x : 70890
I.M.C.M. Rientjens A g r i c u l t u r a l U n i v e r s i t y , Department o f Biochemistry De D r e i j e n 11 6703 BC WAGENINGEN The Netherlands t e l : 08370-83723
1002
M.G.M. Roemer MT-TNO P.O.Box 217 2600 AE DELFT The Netherlands t e l : 015-693038 P.J.A. Rombout National I n s t i t u t e of Public Health and Environmental P r o t e c t i o n P.0.Box 1 3720 BA BILTHOVEN The Netherl ands t e l : 030-742238 J. Rotmans National I n s t i t u t e o f Pub1 i c Health and Environmental P r o t e c t i o n P.0.Box 1 3720 BA BILTHOVEN The Netherl ands t e l : 030-743323 t e l e x : 47215
R.A. Rykowski US EPA 2565 Plymouth Rd. ANN ARBOR M I 48105 USA t e l : 313-668-4339
J. Salleras Av. D i agonal 401 1-08008 BARCELONA Spain t e l : 93-217-8304
telex: 54595 i b x b e
6.S. Sanchez Centro de Investigaciones Energeticas, Medioambientales y Technologicas Avda.Com lutense 22 28040 MAgRID Spain t e l : 3466549 t e l e x : 23555 B. Sanchez Fernandez M i n i s t e r i o Sanidad y Consumo Paseo d e l Prado 20 MADRID 28014 Spain t e l : 4682455 t e l e x : 22608 msass-e 6. SchaaD
RAI Vereniging Europaplein 2 1078 GZ AMSTERDAM The Netherl ands t e l : 020-5491212
t e l e x : 12100
K.L. Schere US EPA M a i l Drop 80 RESEARCH TRIANGLE PARCK NC 27711 USA t e l : 919-541-3795 t e l e x : 510-927-1800
1003
B. Schmidl Warren Spring Laboratory Gunnels Wood Road STEVENAGE HERTS SG1 28X UK t e l e x : 82250 wsldoi g t e l : 0438-7411122 C. Schneider I n s t i t u t f u r Industriebetriebslehre und Indust r Prod. Herzstrasse 16 7500 KARLSRUHE FRG t e l : 0721-608-4458 telex: 721 166
.
T. Schneider National I n s t i t u t e o f Pub1 i c Health and Environmental P r o t e c t i o n P.O.Box 1 3720 BA BILTHOVEN The Netherlands t e l : 030-742696 t e l e x : 47215
M. Schneider-Ferrageau de St.Amand
Nassaupl antsoen 7 3761 BH SOEST The Netherl ands
D. Schuermann Vol kswagen AG Forschung Messtechni k D-3180 WOLFSBURG 1 FRG C.J.E. Schuurmans Royal Netherlands Meteorological Society P.O.8ox 201 3730 AE DE BILT The Netherl ands t e l : 030-766445 t e l e x : 47096
H. Scoullos European Environment Bureau, U n i v e r s i t y o f Athens, Dept. o f Chemistry 13 A.Navarinou Street ATHENS 10680 Greece H. Seesing Deutscher Bundestag Bundeshaus D-5300 BONN 1 FRG t e l : 0228- 169345
D. Simpson Warren S r i n g Laboratory Gunnels i o o d Road STEVENAGE, Herts. UK t e l : 0438-741122
1004
E. Smol ko Duke University, Medical Center 350 B e l l B u i l d i n g P.0.Box 3177 DURHAM NC 27710 USA t e l : 919-684-6266 O t t e l i e n van Steeni s National I n s t i t u t e o f Pub1 i c Health and Environmental P r o t e c t i o n P.0.Box 1 3720 BA BILTHOVEN The Netherl ands telex: 47215 t e l : 030-742970 N.J. Stenstra Lelie lein 4 3202 RE SPIJKENISSE The Netherlands t e l : 01880-12239 J.van Straaten DCMR s-Gravel andseweg 565 3119 XT SCHIEDAM The Netherl ands t e l : 010-4273246 telex: 25515
D. S t r o t h e r US EPA, European Program Manager A-106 401 M S t r e e t SW WASHINGTON DC 20460 USA t e l : 202-382-4892
telex: 892758
J. Swager VROM P.0.Box 450 2260 MB LEIDSCHENDAM The Netherlands t e l : 070-209367 telex: 32362 J.A. Terning CONCAWE Konin i n J u l i a n a p l e i n 30-9 DEN HAAG 2595 The Netherl ands telex: sipm 36000 t e l : 070-424500
h
G. Theis Lufthygieneamt bei der Basel, Lufthygieneaat CH-4410 LIESTAL Switzerland t e l : 061-966141
B.E. T i l t o n US EPA MD 52 , ECAO RESEARCSI T i i d G L E PARK NC 27711 USA t e l : 919-541-4161 telex: 510-927-1800
1005
D. Tingey US EPA 200 S.U. 35th Street CORVALLIS, O r 97333 USA
A.E.G. Tonneijck Research I n s t i t u t e f o r Plant Protection P.0.Box 9060 6700 GW UAGENINGEN The Netherl ands t e l : 08370-19151 telex: 45888 A.P.van Ulden KNMI P.0.Box 201 3730-AE DE BILT The Netherl ands t e l : 030-766441
telex: 47096
J.F.van de Vate Netherl ands Energy Research Foundation ECN P.0.Box 1 1755 ZG PETTEN The Netherl ands t e l : 02246-4460 telex: 57211 E.van Veen CONCAUE, c/o Shell Internationale Petroleum M i j . P.0.Box 162 2501 AA DEN HAAG The Netherl ands telex: 3600 shell n l t e l : 070-771787 C. Veldt TNO, Division o f Techn. o f Society P.0.Box 342 7300 AH APELDOORN The Netherl ands t e l : 055-173344 telex: 363395
T.S. Veninga Melkw 4 9306 RODEN The Netherlands t e l : 05908- 17501
#
P.U.A.M. Venis-Pols -TNO P.0.Box 186 2600 AD DELFT The Netherlands t e l : 015-696885 SCIW)
K. Verhoeff Directorate Agricultural Research P.O.Box 20401 2500 EK DEN HAAG The Netherlands t e l : 070-792130
1006 J.J. Verhoog Esso
P ~ O ~ E o7150 x 3000 HD ROTTERDAH The Netherl ands J.H.
IW
Visser
P.0.Eox 9060 6700 GW WAGENINGEN The Netherl ands t e l : 08370-19151
E.J. Vles Federation o f t h e Dutch Chemical Industry P.0.Eox 443 2260 AK LEIDSCHENDAM The Netherl ands t e l : 070-209233 6. Vonkeman I n s t i t u t e f o r European Environmental P o l i c y p/a Amalia van Solmslaan 47 3708 CM ZEIST The Netherl ands t e l : 03404-17140 J.de Vries Open U n i v e r s i t y , Natural Sciences P.0.Box 2960 6401 DL HEERLEN The Netherl ands t e l : 045-762624
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M.P. Walsh Consultant 2800 N.Dinwiddie S t r e e t ARLINGTON, VA 22207 USA t e l : 703-241-1297 t e l e x : 347-2315 W.P.G.M. Waque VROM P.0.Box 450 2260 MB LEIDSCHENDAM The Netherl ands t e l : 070-209367 t e l e x : 32362
1007
J.W. Weenink VROn
PYO..Box 450 2260 MB LEIDSCHENDAM The Netherl ands t e l : 070-209367 telex: 32362 W.H.J.M. Wientjens MT-TNO P.0.Box 217 2600 AE DELFT The Netherl ands t e l : 015-696185 J.van Wieringen Sealed i .r B.V. - .- . - - A . .. - . .. P.0.Box 271 6500 AG NIJMEGEN The Netherl ands t e l : 080-710111
telex: 48153
R.B. Wilson UK De artment o f the Environment Room i352, Romney House 43 Marsham Street LONDON SWlP 3PY UK t e l : 01-2126161 telex: 2222 A.de W i t R i j k s i n s t i t u u t voor Natuurbeheer P.O.Box 46 3956 ZR LEERSUM The Netherl ands t e l : 03434-52941 G.J.R. Wolters VROn P.0.Box 450 2260 MB LEIDSCHENDAM The Netherlands telex: 32362 t e l : 070-209367 F.C. Worrest US EPA 200 S.W. 35th Street CORVALLIS Oregon 97333 USA R. Ybema Troel strawe 52 6702 An WAG~NINGEN The Netherl ands t e l : 08370-10845
E. Yokoyama The I n s t i t u t e o f Public Health 4-6-1 Shirokanedai Minato-ku TOKYO Ja an te!: 03-441-7111
1008 K.H. Zierock EnviCon W i esbadenerstrasse 13 D-1000 BERLIN 41 FRG t e l : 030-8222111 B.C.J. Zoeteman National I n s t i t u t e o f Public Health and Environmental Protection P.0.Box 1 3720 BA BILTHOVEN The Netherlands t e l : 030-742045 F.C. Zuidema National Council f o r Agrieul t u r a l Research P.0.Box 407 6700 AK WAGENINGEN The Netherl ands t e l : 08370-19066 P.L. Zuldeveld K o n i n k l i j k e Shell Laboratorium, Dept. H.C.P. P.0.Box 3003 1003 A4 AMSTERDAM The Netherl ands telex: 11224 k s l a n l t e l : 020-303234 A. Zwart TNO- C IVO P.0.Box 360 3700 AJ ZEIST The Netherl ands t e l : 03404-52244
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SUBJECT INDEX
Adaptation Age Effects A i r Qua1it y Alfalfa Alveolar Macrophages Asthma Automobi 1it y
805 284 36, 127, 839 233 50 1 493 472
Basis Document Boundary Layer Brundtl and Conmi ssi on
573 608, 657 8
Carbon Cycle Catalytic Cycles Chi 1dren Climate Modification Control Options Strategies Cost -Effectiveness Crop Loss
61, 67 358 319 79 392, 565, 766, 774, 901 623, 660, 671, 683, 837, 845 891, 901 254
Direct Effects Dose-Effect Relationships Dosimetry Dry Depos it i on
240 51, 713, 851 281, 293, 319, 553 583
Economic Effects
869, 881, 891 564 302 57
EKMA Electrocardiography Elemental Cycle Emi s s i on CFC Diesel Evaporative Factors Inventories Mobi 1e Sources Reduction
103, 765, 777, 786, 891 43 1 406, 423, 675, 903 454, 944 85, 111, 637 87, 405, 443, 936 438, 443, 455, 567, 671, 779
1010
Refueling Environmental Protection EPA Exercise Exposure Acute Assessment Chronic Effects Index Indicators Model Population
554, 711 535, 301, 220 207, 825, 83 1
Fibrosis Forest Decline Free Troposphere
529, 750 47 60, 605
Glutathione Greenhouse Effect Guinea Pigs
520 14, 75, 368, 377 545
Hi stami ne Human Health Effects
550 12, 711, 745, 795, 803
Indicator Plants International Cooperation In Vitro
253 496 7, 16 514
Luminescence Lung Structure
264 26
Indomet hac in
413, 423 9 17 23, 345, 757 738, 759 738 321, 975 749, 883 855
Memorandum o f Understanding 3 Mi crodosimetry 287 380, 563, 589, 613, 623, 633, 647, 657, 825, Model simulation Monkey Montreal Protocol Motor Vehicles
869, 886 524 15, 16, 175, 785, 926, 949 387, 405
Nasal Cavity
525
1011 Neutrophil Nitrogen Cycle Oxides Non- a t t a i nment
65 102, 122, 141, 683 13
Ozone Background Episodes Forest Trees Formation Health Effects Toxicity Transport Trends Vegetation Effects Ozonides
127, 575, 607 633, 647 239 35, 130, 172, 579, 590 21, 311, 319, 331, 501, 513, 701, 759, 841 334 134 167, 174, 177, 195, 205 45, 219, 229, 251, 843, 875 518
751
Paint PAN Photochemistry Photosynthesis PHOXA Phytoplankton P1ant Hetabol ism Pol i c y Pollutant Interactions Potent ia t ion Pulmonary Function
691, 913 190, 368 35, 177, 589, 633 262 633 270 46 919, 931, 943, 949 49 24 289, 295, 313, 343, 483, 493, 537, 726, 733, 755, 975
Rat Respiratory Function Risk
301, 501, 536, 553, 723, 733, 967, 975 22, 348, 523, 547, 759, 967 336, 814, 837, 851
Scal es Scenario Skin Cancer Sol vents Spi r e t r y Standards Setting
5 311, 641 796 691 488 21, 701
1012 Stratospheric Ozone Depletion
355, 365, 765, 785, 877, 925, 934
Test Cycl e Threshold Trace Gases Troposphere
435, 461 33 1 73, 159 62, 935
Urban Areas US-Dutch Symposium UV-B Radiation Effects General Imnunesystern He1anoma
195, 206 4, 11 269, 795 18, 261, 803 799, 809 809, 813
Veget a t ion Effects Vitamin E
45 341
voc Emissions /NO, Ratio Volunteers
92, 123, 137, 667, 675, 901, 911 67, 139, 630, 641 311
Zooplankton
272
1013
PAPERS RECEIVED LATE
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T.Schneider et aL (Editore),Ahnospheric Ozone Research and its Policy Implicotiona 0 1989 Elaevier Science Publishem B.V.,Amsterdam-Printed in The Netherlands
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STATIONARY SOUIECE CXARACI'ERIZATION AND OONTROL Sl'RATEGIES FOR REACI'IVE VOLATILE ORGANIC COMPOUNDS
G.B.Martin, US EPA, Research Triangle Park NC 27711, USA
ABSTRACT Volatile organic conpounds (Mcs) are emitted t o the atmosphere from a variety of processes. These conpounds may react i n the lower atmosphere as part of the process leading t o ozone generation and/or may be classified as hazardous a i r pollutants (HAPS) which have direct health inpacts. This paper provides a brief overview of the sources of VOCB and of the control technologies which may be used t o control these emissions. INTRoDumroN
Volatile organic conpounds (Mcs) are emitted by a w i d e variety of stationary and mobile sources. The v a s t majority of mobile source VOC emissions are from highway vehicles. The stationary emission sources are extremely varied ranging from large point sources t o numerous relatively small area sources and fugitive emissions. The major stationary source classes of VOCB are: solvent uses; petroleum production; treatment, storage, and disposal f a c i l i t i e s ; combustion; and industrial processes. Solvent uses include: metal cleaning, consumer solvents, and a variety of surfacing coating. Petroleum production includes exploration, refinery processes, d i s t r i h t i o n , and marketing. Combustion includes numerous small fuel combustion processes and agricultural, forest or other open burning. Industrial processes include organic chemical manufacturing and manufacturing of a number of consumer products. The specific process w i t h i n these source categories w i l l determine the applicable control technology. Many of the area and fugitive sources require a collection system of some kind t o duct the VCC emission stream t o the control device.
CONTROL TECHNOLOGY SELECTION
The control technologies applicable t o control of VCC emissions are described i n "Control Technologies for Hazardous Air Pollutants" (ref. 1) and a methodology for matching a specific source w i t h a technology is discussed. Although the report deals w i t h hazardous organics, the discussion of organic control technologies is equally applicable t o a l l VOCB. VOC Emission Characteristics
The characteristics of the VOC emission stream are more inportant i n selection of the control technology than the type of source. These charac
1016
teristics can further be separated into two categories: stream characteristics and Mc characteristics. Stream characteristics. The characteristics of the VOC-containing stream are a primary consideration i n selecting the preferred control technology. The major stream characteristics are: 1. Organic content. The amount of VOC i n the emission stream w i l l determine whether the Mc can be economically recovered or if a destruction technology is preferred. I t may also determine which type of combustion technology is preferred t o most effectively and economically destroy the VOC. 2. Heat content. The heat content (Btu/SCF) of the stream is inportant primarily for those technologies where additional fuel may not be used i n the combustion process (e.g., boilers or f l a r e s ) . 3. Moisture content. This characteristic is of primary importance only for carbon absorption. 4. Flow rate. The various technologies have different limits on the amount of flow that they can effectively handle. Additionally some of the technologies can handle time variant flow rates more effectively. VOC characteristics. The characteristics of specific VOCs i n the stream are important primarily for removal techniques. Molecular weight and adsorption/desorption characteristics are important for carbon adsorption. Solubility i n water or other solvents is key for adsorbers. Vapor pressure as a function of tenperature is the governing characteristic for condensers. Control Technology Characteristics Several control technologies are available t o t r e a t specific VOC streams. These technologies can be divided into two categories: destruction techniques and removal techniques. Destruction techniques. A l l t h e currently available destruction techniques are based on combustion of the VOC stream either alone or w i t h supplementary fuel. By matching the characteristics of the stream t o the capabilities of the technologies, appropriate levels of control can be achieved a t reasonable costs. The characteristics of each technology are: 1. Thermal incineration. This technique is broadly applicable t o continuous VOC emission streams. It can achieve 95 t o over 99% destruction relatively independent of Mc characteristics. Only minor fluctuation i n flows can be tolerated and still maintain residence time and tenperature necessary for high destruction efficiency. Thermal incineration is typically applied t o d i l u t e
1017
l i m i t (LEI,) concentration; however, i f the VOC concentration is too
low, supplemental fuel may be required t o maintain the tenperature necessary for acceptable destruction efficiency. A potential advantage is that systems which recover heat may allow recovery of some economic value. 2. catalytic Incineration. This is another form of thermal incineration, which uses a catalyst t o promote VOC oxidation a t a lower temperature. It can achieve 90 t o over 99% destruction of VOCa for low VOC concentrations. ~ t applicability s is more restricted s i n c e VOC Characteristics have a greater influence on the efficiency of the catalyst than for thermal incinerators. A number of metals, as well as sulfur and halogens, can poison the catalyst and reduce its efficiency. Careful tenperature control is essential since the catalyst l i f e can also be significantly reaced by thermal aging. I n fact, catalyst l i f e is a key factor both i n maintaining control efficiency and i n determining the economic feasibility of the technique. I t has the advantage that the amount of supplemental fuel required may be rehced substantially. 3. Flares. Flares are typically used t o control intermittent emissions Qring process upsets and/or emergencies. Properly designed flares for high heat content waste stream 0300 Btu/SCP or 1.12 megaJoules per normal cubic meter) can achieve up t o 988 VOC control. For lower heat content stream, supplemental fuel may be required. A variety of f l a r e designs can accolrmodate a w i d e range of VOC stream characteristics and/or flow rates. 4. Boilers/Process Heaters. I n many cases existing plant equipment can be used t o destroy VOC streams and t o recover energy a t the same time. Destruction efficiencies of greater than 988 can be achieved. The limitation of the technology is the amount of a d i l u t e Mc w a s t e stream that can be incinerated w i t h o u t adversely affecting the equipment's primary function of supplying steam and/or heat t o the plant.
Removal techniques. These techniques can provide efficient removal of the VOC from t h e emission stream but do not change the chemical form of the VOC. This h a s the advantage that economic pro&ct recovery may be achieved i n addition t o p o l l u t i o n control. Unlike thermal destruction, these processes work on several different principles and can be strongly dependent on the VOC characteristics.
1018
1. carbon Adsorption.
The VOC is selectively removed from the
emission stream by a bed of activated carbon. Removal efficiencies of 50 t o 99% can be achieved for dilute mixtures of Mc and air. Inlet VOC concentrations are limited t o avoid exceeding the adsorption capacity of the bed and/or generating excessive bed tenperatures due t o t h e heat of adsorption. The maxinum concentration is about 10,000 ppmv, and higher concentrations may have t o be reduced by dilution. A further limitation may be placed on concentration of flammable organic vapors for safety reasons. These limits are 25% of LEL for most cases,, although 40 t o 50% of LEL may be acceptable i f proper monitors and controls are present. Furthermore, high molecular weight organics may be d i f f i c u l t t o remove from the bed once adsorbed, Therefore, the application of t h i s technique is generally limited t o conpounds with boiling points less than 400° F (200° C) and/or molecular weights less than 130. On the other hand, conpounds w i t h molecular weights below 50 are not efficiently removed. Finally, the removal efficiency decreases as relative humidity increases and, a t relative humidit i e s above 50%, efficiency may show a significant decrease. I n most systems one bed is used t o adsorb organics from the stream while a second bed is being regenerated t o recover a high VOC concentration stream. 2. Absorbers. This technique has limited applicability t o organic vapors, although removal efficiencies can exceed 99% for specific systems. The primary limitation is the availability of a suitable solvent t o remove the specific VOC. I n addition, disposal of the used solvent can present additional problems. 3. condensers. This technique is frequently used for recovery of raw materials and/or products from a process stream. Condensers are most suited t o streams w i t h more t h a n 5000 ppmv and can achieve removal efficiencies increasing from 50 t o 90% as VOC concentration increases. The VOC removal is limited by the VOC vapor pressure a t the available coolant temperature. H i g h removals require coolant tenperatures below normal water temperature. Condensers can be used as a preliminary resource recovery and pollution control device t o be followed by a destruction technique for high efficiency. These devices are typically applicable t o relatively low flow rates.
1019
Conplter Technique Based on the HAP manual (ref.21, the EPA and the New Jersey Department of Environmental Protection has complterized the design and cost calculations
for eight control devices for permit reviewers.
This program, called
IM conpatible Controlling Air Toxics (CAT), has been designed for use on B conputers. Information supplied on the permit application is entered into
the program, and design parameters and cost estimates are calculated. The program is designed t o easily perform what-if calculations, allowing the reviewer t o change parameters and quickly see the inpact on design and costs. REFERENCES
1 Control Technologies for Hazardous Air Pollutants, EPA/625/6-86/014, September 1986. 2. S. L. Nolen, T. Micai, G. Shareef, and M. T. Johnson, "Controlling Air Toxics, an Advisory System", paper 88-51.14, presented a t the 81st Annual Meeting of APCA, Dallas, TX, June 19-24, 1988.
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T. Schneider et al. (Editors),Atmospheric Ozone Research and its Policy Implications 1989 Elsevier Science Publishers B.V., Amsterdam -Printed in The Netherlands
1021
GLOBAL MODELING OF OZONE AND TRACE GASES
W.L.
GROSE, R.S.
ECKMAN, R.E.
TURNER, AND W.T.
BLACKSHEAR
Atmospheric Sciences Division, NASA Langley Research Center, Hampton, V i r g i n i a 23665-5225
ABSTRACT A three-dimensional, global atmospheric model f o r s i m u l a t i o n o f t h e d i s t r i b u t i o n o f ozone and other t r a c e gases i s described. The model extends from the surface t o 60 km, i n c l u d i n g a comprehensive formulation o f the r e l e v a n t chemistry. Simulated d i s t r i b u t i o n s o f some o f t h e c o n s t i t u e n t s important t o understanding the stratospheric ozone budget are presented and discussed w i t h respect t o degree o f agreement w i t h observations. The seasonal e v o l u t i o n o f t h e global d i s t r i b u t i o n o f t h e s t r a t o s p h e r i c ozone column i s discussed. The i n t e r a c t i o n between dynamical and chemical processes i s i l l u s t r a t e d during disturbed winter conditions i n t h e mid-stratosphere.
INTRODUCTION
For much o f t h i s century, s c i e n t i s t s have been engaged i n the study o f atmospheric ozone. However, during the past 2 decades, concern over the p o t e n t i a l d e p l e t i o n o f t h e ozone layer by nitrogen compounds i n h i g h - a l t i t u d e a i r c r a f t emissions, chlorofluorocarbons, and various other chemicals has provided the stimulus f o r a comprehensive program o f observations and t h e o r e t i c a l modeling ( r e f . 11. The d i s t r i b u t i o n s o f ozone and other constituents i n the Earth's atmosphere evolve as t h e r e s u l t o f the complex i n t e r p l a y among r a d i a t i v e , chemical, and dynamical processes.
Our
understanding o f these processes has been hindered by t h e lack o f simultaneous, long-term, global-scale measurements o f winds, temperature, and constituents. Hence, much o f our i n s i g h t must, o f necessity, r e l y upon atmospheric simulation models o f varying complexity. Substantial computational resources a r e required f o r modeling t h e chemistry o f the ozone l a y e r because o f t h e exceedingly l a r g e number ( i n excess of 100, e.g.
ref. 2) o f chemical r e a c t i o n s believed
relevant. For t h i s reason, most o f the modeling studies have been conducted w i t h one- o r two-dimensional models i n which the t r a n s p o r t i s h i g h l y parameterized.
These models r e l y upon various types o f parameterizations
( f r e q u e n t l y ad hoc) o f t h e t r a n s p o r t processes (e.9.
r e f . 3 and r e f . 1).
1022 Although the r a t i o n a l e f o r three-dimensional model studies o f s t r a t o s p h e r i c chemistry and t r a n s p o r t i s w e l l established (e.g. r e f . 1 and included references), r e l a t i v e l y fewer studies have been done w i t h t h e three-dimensional models because of t h e requirement f o r l a r g e computational resources even without i n c l u d i n g chemistry. A t t h e present time, long-term simulations w i t h a general c i r c u l a t i o n model which incorporates a comprehensive and f u l l y i n t e r a c t i v e treatment o f r a d i a t i v e , chemical, and dynamical processes a r e n o t f e a s i b l e and, indeed, may be unwarranted considering known d e f i c i e n c i e s i n our c u r r e n t understanding o f these processes ( r e f . 3). For these reasons, a v a r i e t y o f approaches t o modeling t h e ozone layer w i t h more s i m p l i f i e d three-dimensional models (e.g. see references and discussions i n r e f . 1 and r e f . 3) have developed over the years. Nearly 20 years ago, Hunt ( r e f . 4 ) studied the t r a n s p o r t o f ozone using a three-dimensional, hemispheric, p r i m i t i v e - e q u a t i o n GCM. Despite t h e s i m p l i f i e d nature o f t h e GCM and a much-abbreviated photochemical formulation, he achieved modest success i n t h a t the simulated ozone d i s t r i b u t i o n agreed qua1 i t a t i v e l y w i t h observations.
P a r t i c u l a r l y notable was t h e establishment o f a column
ozone maximum a t high latitudes--a r e s u l t c o n t r a r y t o what one would expect based upon p u r e l y photochemical considerations. Hunt's pioneering e f f o r t s were followed by a succession o f attempts t o model the s t r a t o s p h e r i c ozone l a y e r . An i n t e r e s t i n g example i s t h e study by Cunnold e t a l . ( r e f s . 5 and 61, who conducted a long-term simulation ( 3 years) w i t h a low-resolution quasigeostrophic model w i t h a much s i m p l i f i e d representation o f t h e ozone chemistry. Schlesinger and Mintz ( r e f . 7 ) adopted e s s e n t i a l l y t h e same representation o f t h e ozone chemistry as Cunnold e t al., b u t used a comprehensive p r i m i t i v e equation GCM. The usefulness o f t h i s study was somewhat compromised i n t h a t the s i m u l a t i o n extended o n l y s l i g h t l y more than a month. Mahlman e t a l . ( r e f . 8) studied ozone t r a n s p o r t using a p r i m i t i v e equation GCM extending t o t h e mid-stratosphere. They assumed ozone t o be i n photochemical e q u i l i b r i u m a t t h e t o p model l e v e l and i n e r t below.
This study
was notable i n i t s extensive diagnosis of t r a n s p o r t mechanisms. Examples o f a l t e r n a t e approaches are t h e studies o f Kurzeja e t a l . ( r e f . 91 and C a r i o l l e and Oeque ( r e f . 10). These two groups examined ozone t r a n s p o r t using three-dimensional c i r c u l a t i o n models, b u t adopted a l i n e a r i z e d f o r m u l a t i o n o f the ozone chemistry. Recently, Grose e t a l . ( r e f . 11) used an " o f f - l i n e " ( r e f . 12) t r a n s p o r t model w i t h a very comprehensive f o r m u l a t i o n o f the chemistry o f t h e stratosphere t o simulate t h e d i s t r i b u t i o n o f most o f the relevant cocstituents
.
1023 The present study extends the work of Grose et al. (ref. 11) describing the methodology used in constructing a model of the ozone layer and presenting preliminary results from an annual cycle simulation experiment. DESCRIPTION OF THE MODEL A global, primitive equation GCM (see refs. 11, 13, and 1 4 for details of the model) was used for the studies described herein. The model extends from the surface to approximately 60 km (12 levels) and includes the effects of forcing by orography and land-ocean thermal contrast. Time integration is accomplished with a semi-implicit technique using a 30-minute time step. Transport model simulations are performed with an "off-1 ine" technique (ref. 12) in which wind and temperature fields are generated separately by the GCM and then used as input to the set of mass continuity equations for the constituents. Formulation of the transport model is essentially identical to that of the GCM. A scale-selective, biharmonic diffusion term is included to parameterize horizontal, sub-grid-scale processes. Vertical sub-grid diffusion is not included, following Mahlman and Moxim (ref. 12). However, special attention is given to vertical transport in the model when negative mixing ratios are encountered. Early experiments with inert tracers indicated that vertical transport in the presence of strong gradients was the primary mechanism for producing negative mixing ratios. Generation of such negative mixing ratios resulting from the use of second-order central difference approximations to the vertical transport term was alleviated by switching to upstream differencing only when negative values occur. The switch to upstream differences is accomplished in a mass-conserving manner by addition of a flux divergence term equal to the difference between an upstream difference and a central difference approximation to the vertical advection term. The effectiveness of this technique for suppressing negative mixing ratios is a consequence of the positive definite advection property of this technique. Evaluation of the net chemical source (sink) term required during the integation requires consideration of a large number o f species and chemical reactions (39 and 115, respectively, in this version of the model). The complexity o f the chemistry makes explicit transport of each constituent an unwieldy and expensive option. Also, the extremely fast chemistry characteristic of some species would dictate integration time steps so small as to be impractical for conducting long-time simulations. To circumvent these difficulties, the "family" approach has been adopted i n which related species that undergo relatively fast chemical transformation are grouped into a family with a characteristic chemical lifetime much greater than for the component
1024 members--a concept f r e q u e n t l y used i n one- and two-dimensional models ( r e f . 2). I n t h e present version o f t h e model, mixing r a t i o s o f Ox L O 3 + O(’P) + O(’D)l, NOy [NO + NO;! + NO3 + N + HNOp + HNOkI, CEx [ C i + CgO + CtONOp + CeO2 + H O C i + HCel,
HzO;!,
HNO3, and N205 a r e determined by e x p l i c i t
i n t e g r a t i o n of t h e i r respective mass c o n t i n u i t y equations. Although n o t e x p l i c i t l y transported, t h e chemistry of t h e f a m i l i e s HOx [H + OH + H O 2 l and CHx [HCO + CH3 + CH20 + CH200H + CH30z + CH,OI
i s included i n t h e
formulation. P a r t i t i o n i n g f a m i l i e s for evaluation of t h e net source ( s i n k ) term i s accomplished through various e q u i l i b r i u m r e l a t i o n s h i p s .
I n order t o assess the
impact of using these r e l a t i o n s h i p s , d e t a i l e d production and loss analyses have been performed f o r various z e n i t h angles and l a t i t u d e s and intercomparisons made w i t h more complete mechanisms o f a one-dimensional model.
Largest d i f f e r e n c e s appear i n those i n d i v i d u a l species which have chemical l i f e t i m e s on
the order o f a day or so and deviate s i g n i f i c a n t l y from e q u i l i b r i u m due t o diurnal effects.
Invoking t h e e q u i l i b r i u m assumption f o r most o f these species
has l i t t l e impact on t h e net f a m i l y source term (e.g.
CeONO;!).
I n a r i g o r o u s evaluation o f p h o t o l y s i s r a t e s r e q u i r e d i n t h e chemical code, i t i s necessary t o perform i n t e g r a t i o n s w i t h respect t o wavelength o f t h e
products o f photodissociation cross section, quantum e f f i c i e n c y , and l o c a l solar f l u x . Evaluation o f these i n t e g r a l s numerically consumes a s i g n i f i c a n t f r a c t i o n o f t h e computational time i n a t y p i c a l chemical c a l c u l a t i o n .
As an
a d d i t i o n a l approximation f o r the chemical code used i n the model, a l l r e q u i r e d p h o t o l y s i s r a t e s are parameterized as a f u n c t i o n o f 0 2 and 03 absorber amounts. A s a t i s f a c t o r y degree o f approximation has been ensured by comparison w i t h values determined i n the r i g o r o u s c a l c u l a t i o n . Ordinary r a t e c o e f f i c i e n t s are taken from DeMore e t al. ( r e f . 15) Certain chemical species t r e a t e d i n the model include l o n g - l i v e d constituents, which are e s s e n t i a l t o the ozone problem i n t h a t they represent
Ce,, and odd hydrogen species. These chemicals (H20, H;!, CH,, N20, CH,Ce, CF2Ce3, CH3CCe3, and CO) are s p e c i f i e d as a f u n c t i o n o f a l t i t u d e , l a t i t u d e , and season (as appropriate) based on observations or t h e sources o f NOy,
two-dimensional model r e s u l t s o f Garcia and Solomon ( r e f . 16). D I S C U S S I O N OF RESULTS
The simulation discussed i n the f o l l o w i n g section consisted o f a I-year i n t e g r a t i o n i n i t i a t e d on model day January 1. I n i t i a l c o n s t i t u e n t f i e l d s were e i t h e r i n f e r r e d from monthly mean data (December 1978) from the Limb I n f r a r e d Monitor o f t h e Stratosphere (LIMS) experiment ( r e f . 1 7 ) o r from two-dimensional
1025 model simulations ( r e f . 16). Wind and temperature f i e l d s used i n t h e t r a n s p o r t model simulation were taken from a multi-year i n t e g r a t i o n of t h e GCM. Numerous p r e l i m i n a r y comparisons have been made w i t h observations, but t h e l i m i t e d scope o f the present paper allows o n l y a few i l l u s t r a t i o n s t o be presented.
The r e s u l t s a r e generally encouraging, b u t model/data comparisons
are d i f f i c u l t , a t best, because o f the s c a r c i t y o f simultaneous, g l o b a l data f o r the r e l e v a n t constituents and an incomplete understanding o f t h e interannual v a r i a b i l i t y o f the atmosphere. I n the f o l l o w i n g sections, some representative zonal mean d i s t r i b u t i o n s are discussed w i t h respect t o degree o f s i m i l a r i t y w i t h observations and/or two-dimensional model r e s u l t s i n order t o provide a broad, general perspective o f model performance. Next, t h e e v o l u t i o n o f t h e global, column ozone above 100 mb i s presented t o i l l u s t r a t e seasonal v a r i a t i o n s i n t h e s t r a t o s p h e r i c distribution.
V e r t i c a l p r o f i l e s o f the
CEO r a d i c a l and the temporary r e s e r v o i r
species C i O N O 2 are then presented as examples o f c o n s t i t u e n t s which are important i n the c a t a l y t i c d e s t r u c t i o n o f ozone by f r e e chlorine. F i n a l l y , pressure surface d i s t r i b u t i o n s o f 0% and N205 i n the mid-stratosphere are shown during a disturbed winter c o n d i t i o n t o demonstrate t h e i n t e r a c t i o n s between chemical and dynamical processes. Total column NO2 i s prese ted t o i n t e r p r e t the sequestering o f odd-nitrogen i n the polar night. Zonal mean d i s t r i b u t i o n s o f c o n s t i t u e n t s Zonal mean cross sections o f odd-oxygen (Ox),
t o t a l odd-n trogen (NO,
=
N t NO + NO2 t NO3 + HN03 + 2 x N205 + CiON02 + HN02 + HN04) n i t r i c a c i d (HN03), and hydrogen peroxide (H202) are presented f o r t h e m d-November p e r i o d
i n f i g . 1. These r e s u l t s were selected near the end o f t h e i n t e g r a t i o n period t o allow the c o n s t i t u e n t d i s t r i b u t i o n s t o adjust from t h e i r i n i t i a l s t a t e t o the model climatology. Throughout much o f the stratosphere, the odd-oxygen f a m i l y i s dominated l a r g e l y by ozone.
Only i n the upper stratosphere and above does atomic oxygen
c o n t r i b u t e t o any s i g n i f i c a n t degree t o the t o t a l odd-oxygen abundance.
Hence,
odd-oxygen i s a s u i t a b l e proxy f o r ozone i n much o f t h e stratosphere. Figure l a shows the calculated zonal mean abundance o f odd-oxygen f o r mid-November. The d i s t r i b u t i o n i s g e n e r a l l y s i m i l a r t o observations f o r t h i s period, w i t h peak mixing r a t i o displaced southward from the Equator a t 10 mb. The peak mixing r a t i o i s s l i g h t l y i n excess o f 10 ppmv, w i t h i n t h e range o f values from s a t e l l i t e - d e r i v e d ozone climatologfes ( r e f . 18). Values i n t h e upper stratosphere e x h i b i t the we1 1-known discrepancy between theory and observations t y p i c a l l y seen i n one- and two-dimensional model simulations ( r e f . 1).
The calculated ozone l e v e l s are approximately 30 percent lower than
1026
(a)
,
"290
-60
-30
0
30
60
90
60
90
Latitude (deg)
-
O
10' n
n E
B3 0' v) u)
2 a 10'
lb)
10'
-90
-60
-30
0
30
Latitude (deg)
Fig. 1. Zonal mean f i e l d s f o r mid-November: .(a) Odd oxygen (ppmv); (b) Odd nitrogen (ppbv); ( c ) N i t r i c acfd (ppbv); (d) Hydrogen peroxide (ppbv).
1027
I ) ' - O 1' oo
1 o3
\
-90
I
I
I
I
I
-60
-30
0
30
60
90
Latitude (deg)
l
Latitude (deg)
Fig. 1 continued.
1028 observed values. Examination o f t h e seasonal e v o l u t i o n o f t h e ozone d i s t r i b u t i o n r e v e a l e d t h a t t h e l o c a t i o n o f t h e peak m i x i n g r a t i o t r a v e r s e d t h e Equator f r o m s o u t h t o n o r t h and back s o u t h a g a i n s i m i l a r t o observed b e h a v i o r (e.g.
SBUV r e s u l t s , r e f . 18).
T o t a l o d d - n i t r o g e n shown i n f i g . 20 ppbv a t a p p r o x i m a t e l y 6 mb.
l b e x h i b i t s a peak abundance i n excess o f
T h i s v a l u e i s w i t h i n t h e range o f c a l c u l a t e d
v a l u e s t y p i c a l o f two-dimensional models ( r e f . 1 ) and i n agreement w i t h s a t e l l i t e - and b a l l o o n - b o r n e o b s e r v a t i o n s o f t h e o d d - n i t r o g e n f a m i l y which a r e presently available.
Using LIMS d a t a , C a l l i s e t a l . ( r e f . 19) e s t i m a t e a lower
l e v e l f o r t o t a l o d d - n i t r o g e n of 22.5 k 4 b y summing HN03 and n i g h t t i m e NO2. P r e l i m i n a r y comparisons o f t h e s e r e s u l t s w i t h n i g h t t i m e LIMS NO2 o b s e r v a t i o n s show s u b s t a n t i a l areas o f agreement ( r e f . 1 1 ) . The seasonal e v o l u t i o n o f o d d - n i t r o g e n d i s p l a y s a wide range o f s p a t i a l and temporal v a r i a t i o n s .
In
November, t h e l o c a t i o n of t h e peak m i x i n g r a t i o i s s h i f t e d toward h i g h l a t i t u d e s i n t h e N o r t h e r n Hemisphere, b u t s h i f t s i n t o t h e Southern Hemisphere a f t e r s o l s t i c e i s reached. The HNOB d i s t r i b u t i o n shown i n f i g . l c has a l s o been compared w i t h r e s u l t s f r o m a v a r i e t y o f two-dimensional models and shows agreement b u t , l i k e t h e s e models, does n o t reproduce t h e h i g h - l a t i t u d e h e m i s p h e r i c asymmetry p r e s e n t i n t h e L I M S o b s e r v a t i o n s ( r e f . 20).
LIMS o b s e r v a t i o n s show an i n c r e a s e i n peak
HN03 m i x i n g r a t i o towards t h e w i n t e r p o l e , whereas models t e n d t o p r e d i c t n e a r l y c o n s t a n t m i x i n g r a t i o a t h i g h l a t i t u d e s i n w i n t e r . Based upon t h i s disagreement between o b s e r v a t i o n s and modeling s t u d i e s , A u s t i n e t a l . ( r e f . 21) conclude t h a t gas-phase c h e m i s t r y a l o n e i s n o t s u f f i c i e n t t o e x p l a i n t h e observed h i g h - l a t i t u d e b e h a v i o r i n w i n t e r , and suggest t h a t i n c o r p o r a t i o n o f heterogeneous processes may be r e q u i r e d . The H202 d i s t r i b u t i o n shown i n f i g . I d a l s o agrees w i t h two-dimensional model s i m u l a t i o n s and shows g e n e r a l agreement w i t h v a l u e s i n f e r r e d f r o m LIMS d a t a ( r e f . 22).
However, t h e v a r i o u s model p r e d i c t i o n s v a r y b y a r a n g e o f a
f a c t o r o f 2 o r l a r g e r over much o f t h e s t r a t o s p h e r e .
The H202 c o n c e n t r a t i o n
has a q u a d r a t i c dependence on t o t a l odd-hydrogen (HOx) and w i l l be s e n s i t i v e t o d i f f e r e n c e s i n HO, p r o d u c t i o n f o r t h e v a r i o u s models ( r e f . 1). O n l y 1 i m i t e d d i r e c t o b s e r v a t i o n s a r e a v a i l a b l e ( i n most cases e s t a b l i s h i n g o n l y upper l i m i t s , e.g. r e f . 23 and r e f . 241, so i t i s d i f f i c u l t t o make d e f i n i t i v e comparisons. S t r a t o s p h e r i c column ozone The e v o l u t i o n o f t h e m o n t h l y mean column ozone above 100 mb d u r i n g an annual c y c l e i s shown i n f i g . 2.
P r i o r comparisons o f an e a r l i e r model s i m u l a t i o n
w i t h LIMS r e s u l t s showed good agreement i n most r e s p e c t s .
However, t h e s p a t i a l
1029 90
60
-
30
cn 0,
-0
v
a
U
r
o
3
.c c
4
-30
- 60 -90 Month
Fig. 2.
Variation o f column ozone (Oobson Units) above 100 mb.
1
n
E
v
?
10
ffl ffl
!? a
100
Mixing Ratio (ppbv)
Fig. 3.
V e r t i c a l p r o f i l e o f chlorine monoxide a t (ppbv) 30.5N f o r mid-May.
1030 coverage (84N t o 645) and l i f e t i m e o f t h e LIMS experiment ( 7 months), together w i t h t h e d u r a t i o n o f t h e e a r l i e r simulation (4 months), permitted o n l y l i m i t e d comparison. The present r e s u l t s e x h i b i t a maximum i n s p r i n g a t h i g h l a t i t u d e s i n the Northern Hemisphere (N.H.1,
a lesser f a l l maximum a t h i g h l a t i t u d e s i n
and a minimum i n t h e e q u a t o r i a l region. These the Southern Hemisphere (S.H.), general features are i n reasonable agreement w i t h t h e 20-year average t o t a l column ozone d i s t r i b u t i o n presented by London ( r e f . 251, b u t d i f f e r i n some d e t a i l s . For example, the observed S.H. f a l l maximum shows a d i s t i n c t poleward progression w i t h time. The model r e s u l t s d i s p l a y a s i m i l a r tendency, b u t c e r t a i n l y much less pronounced. U n t i l 3-D model simulations o f s u f f i c i e n t d u r a t i o n (10 years o r more) become p r a c t i c a l and t h e model c l i m a t o l o g y can be developed, i t i s d i f f i c u l t t o assess the importance of some o f t h e d i f f e r e n c e s between models and observations. Constituent v e r t i c a l p r o f i l e s V e r t i c a l p r o f i l e s o f the CkO r a d i c a l and t h e temporary r e s e r v o i r species CEON02, important i n the c a t a l y t i c d e s t r u c t i o n o f ozone by f r e e c h l o r i n e , have been selected as i l l u s t r a t i o n s of species which are not e x p l i c i t l y p r e d i c t e d by the model, b u t are derived from the Ca, assumptions.
f a m i l y through e q u i l i b r i u m
For these species, t h i s assumption i s reasonable f o r most o f the
stratosphere w i t h the important exception t h a t CtONO2 becomes long-lived i n t h e polar n i g h t . The loss o f CaON02 occurs by p h o t o l y s i s i n t h e u l t r a v i o l e t and, t o a lesser extent, by r e a c t i o n w i t h atomic oxygen. For a i r parcels r e s i d e n t i n the polar n i g h t f o r extended periods, CaON02 forms by r e a c t i o n of CaO w i t h NOp.
P r o f i l e s o f CEO and CaON02 a t 30.5N f o r mid-May a r e presented i n f i g s . 3 and 4, respectively. This l o c a t i o n was chosen because i t i s t h e Gaussian l a t i t u d e i n the model c l o s e s t t o 30N, where recent data on these species are a v a i l a b l e . The CaO p r o f i l e i n f i g . 3 f o r l o c a l noon has peak mixing r a t i o o f approximately 0.6 ppbv a t 2 mb.
Waters e t a l . ( r e f . 26) have r e c e n t l y reported C a O
measurements taken a t Palestine, Texas, i n May 1985 and October 1986 using a microwave limb sounder. They present comparisons o f t h e i r data w i t h other observations and a range o f 2-D model p r e d i c t i o n s f o r summer conditions. The CEO p r o f i l e shown i n f i g . 3 i s w i t h i n the range predicted b y t h e various 2-D models. The May 1985 data o f r e f . 26 (average o f values from 2 hours before noon t o 3 hours a f t e r noon) are i n t h e middle o f t h e model range between 26-
30 km.
A t 34 and 38 km, the measured values are lower than the model Values
(both 2- and 3 4 1 , b u t e r r o r bar estimates overlap t h e lower h a l f o f t h e model range, Waters e t al. note t h a t w i t h i n 1-1/2 hours a f t e r sunset, C a O between 26 t o 34 km has v i r t u a l l y disappeared, w h i l e 38 km values are unchanged. This
1031
100
t\
I
_______~~
0
0.2
I
I
0.4
0.6
I
0.8
I
1
1.2
Mixing Ratio (ppbv)
F i g . 4.
V e r t i c a l p r o f i l e s o f c h l o r i n e n i t r a t e (ppbv) a t 30.5N f o r mid-May.
180
GM
F i g . 5. Ozone mixing r a t i o (ppmv) a t t h e 10 mb pressure l e v e l o f t h e Northern Hemisphere, February 7.
1032 r e s u l t i s consistent w i t h t h e d i u r n a l behavior displayed i n t h e present 3-0 model r e s u l t s . V e r t i c a l p r o f i l e s o f CtON02 a t l o c a l noon and noon plus 6 hours are shown i n f i g . 4. A peak mixing r a t i o s l i g h t l y exceeding 1 ppbv occurs a t 20 mb f o r t h e noon p r o f i l e . The p r o f i l e has decreased n o t i c e a b l y a t 10 mb and below w i t h i n 6 hours.
This behavior i s consistent w i t h t h e CEO behavior noted i n r e f . 26.
Measurements o f C l O N O 2 have been reported by Zander e t a l . ( r e f . 27) a t 31N f o r May 1985 f o r the Atmospheric Trace Molecular Spectroscopy (ATMOS) experiment. The observed p r o f i l e has peak mixing r a t i o s between 10-20 mb, w i t h decreasing values above and below, and it i s i n good q u a l i t a t i v e agreement w i t h the model The peak mixing r a t i o i s about 30 percent higher than t h a t f o r t h e
results.
model a t noon.
However, u n c e r t a i n t i e s o f 54 percent are quoted f o r t h e data
( r e f . 27). Mid-stratosphere d i s t r i b u t i o n o f c o n s t i t u e n t s The d i s t r i b u t i o n of 03 and N205 on t h e 10 mb pressure surface o f t h e Northern Hemisphere i s shown i n f i g s . 5 and 6 f o r e a r l y February conditions. These r e s u l t s are selected f o r a disturbed period t o i l l u s t r a t e t h e i n t e r a c t i o n between dynamical and chemical processes. The e v o l u t i o n o f a s t r a t o s p h e r i c sudden warming which occurred during t h i s period has been described by Blackshear e t a l . ( r e f . 131. Minimum ozone concentration ( 5 ppmv) occurs i n the p o l a r vortex, which i s displaced from t h e pole and elongated toward 9OW. The p o l a r vortex i s flanked on the l e f t by an i n t e n s i f y i n g Aleutian anticyclone and on the r i g h t by a weaker, secondary anticyclone over t h e A t l a n t i c .
The
r e g i o n o f low ozone concentration w i t h i n t h e p o l a r vortex has been drawn o u t and wrapped about t h e region where the anticyclone has i n t e n s i f i e d . Note t h e large m a t e r i a l tongue ( i n d i c a t e d by the darkened arrow on f i g . 5) being drawn d i r e c t l y across the pole between t h e main vortex and t h e f l a n k i n g anticyclone. Both t h e q u a l i t a t i v e features and the mixing r a t i o l e v e l s a r e c o n s i s t e n t w i t h t h e behavior noted i n LIMS observations f o r t h e January 1979 warming event b y Leovy e t a l . ( r e f . 28). I s e n t r o p i c diagnostic analysis o f these r e s u l t s has been conducted t o i n t e r p r e t the i n t e r a c t i o n s between chemistry and dynamics b y Turner e t a l . ( r e f . 29). I n the zonal mean, the ozone tendency increases during t h i s p e r i o d a t h i g h l a t i t u d e s (poleward o f 50N), p r i n c i p a l l y i n response t o h o r i z o n t a l advection w i t h weak opposition by chemical destruction. Three-dimensional diagnosis reveals t h a t the increase i n ozone concentration a t high l a t i t u d e s i s p r inc ipa 1l y associated w i t h quas i-hor izonta 1 (on isentropic s u r f aces ) transport, l a r g e s t i n the r e g i o n denoted by t h e darkened arrow ( r e f . 11).
1033
Fig. 6. Dinitrogen pentoxlde mlxing r a t i o (ppbv) a t the 10 mb pressure l e v e l o f Northern Hemisphere, February 7.
10
n
I
I
I
I
I
0
30
60
8
N I
E 6
Y) L
0 F
v
E
-0
4
0
N
0 Z
2
0 -90
-60
-30
Latitude (deg)
Fig. 7.
(10”
L a t i t u d i n a l v a r i a t i o n o f the column abundance o f nltrogen dioxlde 22.5E (Local noon), February 7.
CIII-*),
1034 The N2O5 d i s t r i b u t i o n shown i n f i g . 6 i s a l s o t h e r e s u l t o f t h e i n t e r a c t i o n between dynamics and chemistry.
I n c o n t r a s t t o ozone, however, N 2O5 has a much
shorter l i f e t i m e a t these l e v e l s of t h e stratosphere ( r e f . 2). The highl a t i t u d e d i s t r i b u t i o n o f N2O5 i s much influenced by t r a n s p o r t i n t o and o u t o f t h e p o l a r n i g h t . A i r parcels e n t e r i n g the confluence r e g i o n between t h e main vortex and t h e Aleutian anticyclone (near 70E) tend t o have a low l e v e l o f N2O5 as a r e s u l t o f p h o t o l y s i s i n the s u n l i t atmosphere. A i r parcels e n t e r i n g the confluence region subsequently c i r c u l a t e about t h e Aleutian anticyclone, experiencing increased production of N 205 i n t h e p o l a r n i g h t (note the maximum near 60N, 120W) or e l s e they c i r c u l a t e about t h e main vortex e v e n t u a l l y entering s u n l i g h t where much o f t h e N2O5 i s photolyzed. A t lower l a t i t u d e s , t h e d i s t r f b u t i o n is, t o a l a r g e extent, a f u n c t i o n o f t h e d i u r n a l photochemistry. Minimum mixing r a t i o s o f N2O5 I < 0.5 ppbv) occur near l o c a l sunset (approximately 101E). Mixing r a t i o s increase eastward and westward w i t h a maximum o f approximately 2.9 ppbv near 4 0 N , 4W o c c u r r i n g j u s t before sunrise. Solomon and Garcia ( r e f s . 30 and 31) have demonstrated t h a t the highl a t i t u d e production o f N2O5 i n t h e p o l a r n i g h t i s t h e key element i n t h e development o f the so-called "Noxon c l i f f " ( r e f . 32) i n which t h e column o f NO2 experiences a sharp decrease over a small l a t i t u d i n a l extent during winter. The NO2 column shown i n f i g . 6 corresponds t o the N 205 d i s t r i b u t i o n shown i n f i g . 7 f o r model day February 7. The NO2 column i s shown as a f u n c t i o n o f l a t i t u d e along t h e meridian a t 22.5E ( l o c a l noon). Note t h a t t h e sudden decrease i n t h e NO2 column poleward o f 4 0 N corresponds t o t h e increasing gradient i n N2O5 concentration a t these l a t i t u d e s (see f i g . 6 ) . Thus, N2O5 acts as a r e s e r v o i r f o r sequestering odd-nitrogen i n the p o l a r n i g h t . CONCLUDING REMARKS Some selected r e s u l t s from a three-dimensional, g l o b a l atmospheric chemistry/transport model have been presented f o r t h e s t r a t o s p h e r i c ozone layer. The r e s u l t s are g e n e r a l l y encouraging and compare favorably, i n most instances, w i t h both observations and 2-D models w i t h comparable treatments of t h e r e l e v a n t chemistry. The r e s u l t s suggest t h a t t h e o f f - l i n e t r a n s p o r t approach i s a useful, v i a b l e a l t e r n a t i v e t o a 3-0 model with f u l l y i n t e r a c t i v e r a d i a t i o n , chemistry, and dynamics. A complete assessment o f t h e v a l i d i t y o f such models i s d i f f i c u l t because o f t h e lack o f simultaneous, long-term, .global measurements o f the species and meteorological variables.
1035 REFERENCES World Meterological Organization, "Atmospheric Ozone 1985: Global Ozone Research and Monitoring Project." Report No. 16, (19861. 2. 6. Brasseur and S. Solomon, Aeronomy o f the Middle Atmosphere. D. Reidel and Co., Dordrecht, Holland. (19841. 3. D.G. Andrews, J.R. Holton, and C.B. Leovy, Middle Atmosphere Dynamics, Academic Press Inc., New York, NY, (19871. 4. B.G. Hunt, Mon. Wea. Rev., 97, (19691, 287-306. 5. 0. Cunnold, F. Alyea, N. P h i l l i p s , and R. Prinn, J. Atmos. Sci., 32, (19751, 170-194. 6. D. Cunnold, F. Alyea, and R. Prinn, PAGEOPH, 118, (19801, 329-354. 7. M.E. Schlesinger and Y. Mintz, J. Atmos. Sci., 36, (19791, 1325-1361. 8. J.D. Mahlman, H. Levy 111, and W.J. Moxim, J. Atmos. Sci., 37, (19801, 655-685. 9. R.J. Kurzeja, K.V. Haggard, and W.L. Grose, J. Atmos. Sci., 41, (19841, 2029-2051. 10. 0. C a r i o l l e and M. Deque, J. Geophys. Res., 91, (19861, 10825-10846. 11. W.L. Grose, J.E. Nealy, R.E. Turner, and W.T. Blackshear, i n 6. Visconti and R. Garcia (Eds.), Transport Processes i n t h e Middle Atmosphere, D. Reidel and Co., (19871, 229-250. 12. J. Mahlman and W. Moxim, J. Atmos. Sci., 35, (19781, 1340-1374. 13. W.T. Blackshear, W.L. Grose, and R.E. Turner, Quart. J. Roy. Met. SOC., 113, (19871, 815-846. 14. B.J. Hoskins and A.J. Simmons, Quart. J. Roy. Met. SOC., 101, (19751, 637-655. 15. W.B. DeMore, M.J. Molina, S.P. Sander, D.M. Golden, R.F. Hampson, M.J. Kurylo, C. J. Howard, and A.R. Ravishankara, JPL P u b l i c a t i o n 87-41, Jet Propulsion Laboratory Pasadena, CA, (19871. 16. R. Garcia and S. Solomon, J. Geophys. Res., 88, (19831, 1379-1400. 17. J.C. G i l l e and J.M. Russell 111, J. Geophys. Res., 89, (19841, 5125-5140. 18. J.M. Russell I 1 1 ( E d i t o r ) , MAP Handbook, 22, (19861. 19. L.B. C a l l i s , M. Natarajan, and J.M. Russell 111, Geophys. Res. Lett., 12, (19851, 259-262. 20. J.C. G i l l e , J.M. Russell 111, P.L. Bailey, E.E. Remsberg, L.L. Gordley, W.F.J. Evans, H. Fischer, B.W. Gandrud, A. Girard, J.E. Harries, and S.A. Beck, J. Geophys. Res., 89, (19841, 5179-5190. 21. J. Austin, R.R. Garcia, J.M. Russell 111, S. Solomon, A.F. Tuck, J. Geophys. Res., 91, (19861, 5477-5485. 22. L.B. C a l l i s , M. Natarajan, R.E. Boughner, J.M. Russell 111, and J.O. Lambeth, J. Geophys. Res ., 91, (19861, 1167-1198. 23. R.L. DeZafra, A. Parrish, J. B a r r e t t , and P. Solomon, J. Geophys. Res., 90, (19851, 13087-13090. 24. K.V. Chance and W.A. Traub, J. Geophys. Res., 89, (19841, 11655-11660. 2 5. J. London, i n M. N i c o l e t and A.C. A i k i n (Editors), Proc. o f t h e NATO Advanced Study I n s t i t u t e on Atmospheric Ozone: I t s V a r i a t i o n and Human Influences, Aldeia das Acoteias, Portugal, October 1979, U.S. Dept. o f Transportation, Washington, D.C., 1980, pp. 31-44. 26. J.W. Waters, R.A. Stachnik, J.C. Hardy, and R.F. Jarnot, Geophys. Res. Lett., 15, (19881, 780-783. 27. R. Zander, C.P. Rinsland, C.B. Farmer, L.R. Brown, and R.H. Norton, Geophys. Res. Lett., 13, (19861, 757-760. 28. C.B. Leovy, C.-R. Sun, M.H. Hitchman, E.E. Remsberg, J.M. Russell 111, L.L. Gordley, J.C. G i l l e , and L.V. Lyjak, J. Atmos. Sci., 42, (19851, 230244. 29. R.E. Turner, W.L. Grose, W.T. Blackshear, and R.S. Eckman, Proc. Quad. Ozone Symp., Gottingen, FRG, August 1988, (submitted f o r p u b l i c a t i o n ) . 30. S. Solomon and R. Garcia, J. Geophys. Res., 88, (19831, 5229-5239. 31. S. Solomon and R. Garcia, J. Geophys. Res., 89, (19831, 5497-5501. 32. J.F. NOxon, J. Geophys. Res., 84, (19791, 5067. 1.
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T.Schneideret al. (Editors),Atmospheric Ozone Research and its Policy Implications 1989 Elsevier Science Publishers B.V.,Amsterdam - Printed in The Netherlands
1037
CATALYTIC CONTROL OF HYDROCARBONS IN AUTOMOTIVE WHAUST
H. S. GANDHI and M. SHELEF Research Staff, Ford Motor Company, P . O . Box 2053, Dearborn, Michigan 48121 U.S.A.
ABSTRACT Hydrocarbons in the atmosphere participate in a series of complex reactions leading to the formation of oxidant and therefore their emission is subject to stringent environmental control. The principal means for the control of hydrocarbons from mobile sources is catalytic removal. The catalytic reactivity of hydrocarbons varies widely with their chemical structure, the exhaust composition and the composition of the catalyst. The paper describes the intricate relationship between these factors and explains the processes taking place on the catalyst surface. INTRODUCTION The control of oxidants in the atmosphere which are considered injurious to the environment is based principal
oxidant
generated by These
in
on
the
automotive vehicles
species
are
control of
the atmosphere
is
their precursors.
ozone.
The
The
ozone precursors
are hydrocarbons and nitrogen oxides.
participants
in
a
complex set
transformations which lead to the formation of ozone.
Of
of
atmospheric
these precursors,
nitrogen oxides are considered to be injurious to the environment in their own right as well, while the hydrocarbon emissions
because of
their
are subject
to control
involvement in atmospheric processes resulting in the
formation of photochemical smog and ozone. aromatic hydrocarbons, benzene on
It must
also be
noted that
the one hand and polycyclic aromatic
hydrocarbons on the other, are considered to be adverse to human health and their emissions are undesirable. There are
two sources of hydrocarbons emissions from vehicles equipped
with spark-ignited engines. The vented into
first
source are hydrocarbons
the atmosphere without passing
and are the result of fuel evaporation. controlled by
that are
through the combustion chamber The evaporative emissions are
making the fuel delivery system as leakproof as possible and
by installing absorbent traps which soak-up fuel vapors when the vehicle is at rest or during
idling.
These vapors
are redirected into the air-fuel
stream going to the engine when the vehicle is in a cruising or accelerating mode,
1038 The composition of the evaporative emission is reflective of the more volatile components of the fuel i.e. C4, C5 and c6 alkenes and single ring
aromatics i.e.
alkenes and
benzene, toluene, xylenes and trimethylbenzene
(ref. 1). The second source, of processes are
interest here, which is controlled by catalytic
the hydrocarbons
exiting
from
hydrocarbons originate in part from uncombusted the exhaust
stroke and partly from
residual hydrocarbons
stem
tailpipe.
fuel molecules
from
front in
emerging in
of the
emission system.
the unavoidable presence of small
spaces and other locations in the engine cylinder which are the flame
These
the transformation of these molecules
either in the engine cylinders or in the hot part These
the
inaccessible to
the combustion process such as crevices. oF1 films and in addition
Thus,
hydrocarbon species
in the fuel, the exhaust hydrocarbons introduced into
the catalyst will contain measurable
to
over
70 or
engine deposits.
amounts of
identifiable
so
lighter hydrocarbons not
present in the original fuel; methane, ethane, ethylene, acetylene, propane, propylene and of partially
oxygenated species.
mostly C1-C3 aldehydes and
benzaldehyde, with minute amounts of ketones. Because
of
the
removal of
equipped cars, oxygenated fuel octane enhancers.
These
are
lead
fuels designated for catalystincreasingly used as
tertiary C4 and C5 ethers and short chain
alcohols, mainly methanol and ethanol. operating on
from
additives have been
The catalyst feed gas
from vehicles
fuel containing oxygenated octane enhancers will contain such
species and somewhat elevated amount of aldehydes derived
from the alcohols
in the fuel. The task of the
catalytic converter
is to oxidize all the hydrocarbon
species, including partially oxygenated molecules, to
carbon
dioxide and
water as completely as possible under all operating conditions.
The present
emission standard in the U.S. for hydrocarbons is
(0.25 g/km)
which is
roughly equivalent to 90% reduction compared
vehicle in 1974. g/mile
0.41 g/mile
In present
day vehicles,
hydrocarbons when measured
Procedure driving cycle.
to an uncontrolled
the feed gas will
contain 2-3
over a specially designed Federal Test
Therefore, the overall catalyst
efficiency should
85-90% and be maintained over a long use of the vehicle, presently 50,000 miles (80.000 km).
be
upwards
of
Tightening of the standards to 0.25 g/mile has duty vehicles
been adopted
for light
in California for 1991, which makes the task of the catalyst
still more demanding.
1039 PRINCIPLES OF CATALYST OPERATION In early
catalyst-equipped cars, the removal of hydrocarbons and carbon
monoxide was accomplished in a exhaust by
an
large excess of
auxiliary air pump.
oxygen
supplied
The catalyst contained platinum and
palladium as the active elements, finely dispersed on a high support. mostly
1-Al2O3.
sensors and electronic
Modern catalyst-equipped cars are controlled by feedback to maintain the engine combustion at
the amount of oxygen required to
molecules to water and from
surface area
to stoichiometry, where the air supplied to the engine is
conditions close equivalent to
to the
the engine has
stoichiometry.
convert all
an overall composition which
The
is also close to
residual uncombusted hydrocarbons and
monoxide, which is a product of partial oxygen left over from
the fuel
As a result, the exhaust emerging
carbon dioxide.
the carbon
combustion, are balanced by the
the engine combustion and by nitric oxide formed at
high engine temperatures by the reaction of air nitrogen and oxygen. The present-day catalyst is conditions in order
nitric oxide to Cop, water condition of catalyst
designed
to
operate at
stoichiometric
to convert simultaneously the CO, hydrocarbons and
300-700.C
and molecular nitrogen.
the equilibrium
strongly accelerates the
rate
At
the operating
favors this conversion and the at which
this equilibrium
is
attained. The denomination of such a catalyst is three-way catalyst or TWC. In actual vehicle
operation, the air/fuel ratio oscillates about the
stoichiometric value at frequencies of 0.5-5.0 Herz. extends to
the
fuel-rich side of
partially removed by
When this oscillation
stoichiometry, the hydrocarbons are
reaction with water vapor
in the
exhaust (steam
reforming) which yields hydrogen and Cog. The hydrocarbon removal reactions are:
+ n)
4%
+
2%
+ 4d20
(4m
+
02 + 4mC02+ 2nH20 (oxidation) 2mC02
+
(4m
+
n) H2 (steam reforming)
(2)
The removal of carbon monoxide proceeds in parallel by oxidation to C02 and by
the water
gas shift reaction which is analogous to steam reforming
and leads also to C02 and hydrogen when stoichiometry.
Nitric oxide
the A/F
ration shifts rich of
is reduced either to molecular nitrogen, the
desirable product, or to ammonia by the small amounts of hydrogen present in the exhaust or generated by water-gas shift and steam reforming.
1040 The catalytically active noble metals in TWC's are platinum, palladium and rhodium in varying proportions which depends on the prospective application. The high surface alumina is modified by various stabilizers such as oxides of cerium, lanthanum and barium and other modifiers such as nickel oxide. The role
of rhodium
is mainly
to catalyze selectively the conversion of
nitric oxide to molecular nitrogen in the presence
of partial
pressures of
oxygen which usually exceed those of nitric oxide. The overall performance of the automotive TWC in the removal of oxidant precursors (hydrocarbons) will depend in a complex way on several variables: catalyst composition, residence
time, composition
of
the hydrocarbons,
presence of catalyst poisons, the redox potential of the gas,
inhibition by
other gas constituents, etc. EFFECT OF HYDROCARBON COMPOSITION The catalytic reactivity of hydrocarbons is atmospheric reactions which lead double
and
to
triple carbon-carbon
oxidant bonds
akin to their reactivity in formation. Hydrocarbons with
are
The hydrocarbons
hydrocarbons are less so.
reactive while
in
the
raw
saturated
engine exhaust
contain 20-30% saturated hydrocarbons, depending on fuel composition. reactivity of alkanes increases with chain length (ref. 2). most inert methane
is
species as not
it is
included
in atmospheric reactions.
in emission
standards
for
The
Methane is the For that reason, hydrocarbons
in
California. As a
consequence of
the differing catalytic reactivity of hydrocarbons,
their composition in the
tail pipe
differs considerably
from that
at the
inlet to the catalyst. The tailpipe contains proportionately less aromatics and olefins and more paraffins.
As the emissions standards have become more
stringent, the overall catalyst efficiency has risen and the proportion of saturated hydrocarbons has risen in parallel.
In the time span from 1975 to
1982, the weighted proportion of alkanes in tail pipe emission has increased from 46 to 708, the proportion of olefins has decreased that of
from 21
to 11% and
aromatics from 28 to 18%. The increase of methane was, as would be
expected, the steepest from 7.0 to
24%
(ref. 1).
Thus,
the
10-15% of
hydrocarbons that escape the catalytic treatment are the least reactive part and will accordingly contribute little vehicles designed to meet
0.25 g
methane can be expected to be with
fresh highly
active
hydrocarbons can attain
oxidant
formation.
In future
HC/mile, the proportion of non-reactive
still higher. catalysts,
- 50% (ref. 3).
the stringent regulations if the total hydrocarbons.
to
Indeed,
in vehicles equipped
the proportion of methane to total It will
be very
difficult to meet
the non-reactive methane is not excluded from
1041
The catalytic reactivity of benzene approximates that of the average catalytic reactivity of all exhaust hydrocarbons and its proportion in the tail pipe hydrocarbons remained fairly constant from 2.5 to 3.5% in vehicles from the 1975 model year
to
1982.
The catalyst
is very
efficient in
oxidation of polynuclear aromatic compounds. In the numerous investigations aimed at
the evaluation of automotive
catalysts, the reactive hydrocarbons are usually represented by
ethylene or
propylene and the non-reactive by propane. EFFECT OF CATALYST COMPOSITION in TWC, platinum, palladium
The three noble metals
and rhodium are all
quite active for the oxidation of olefins and aromatics under conditions prevailing
in automotive exhaust.
In one
the operating
study of olefin
oxidation (ref. 4), the specific activity series is given as Pt>Pd>Ir>Ru>Rh. The activity for the oxidation of the slow-burning Ci-Cg alkanes was studied by Yao (ref. 5), both on massive metallic surfaces in the form on supported catalysts.
Large crystallites of noble
supported catalysts are expected wires.
to behave
of wires and
metals in sintered
catalytically similar
to metal
On Pt the catalytic activity increases very sharply with the alkane
chain length in the C1-C4 range, approximately one each increase
in carbon number.
order of magnitude for
The reaction rate is inhibited by excess
oxygen in the reacting gas. Thus, at a large excess oxygen, the rate of methane is higher
than on
Pt wire.
length on Pd is less steep than on faster on
Pt.
oxidation of
Pd wire
Because the dependence of reactivity on chain Pt, propane
and butane
are oxidized
Rhodium wire behaves similarly to Pd wire but the activity Large excess of 02
for each hydrocarbon is lower by one order of magnitude. does not inhibit the reaction of Pd or Rh wires. The
strong effect
related to the metals.
of
oxygen excess
on
thermodynamic stability of
The surfaces
the activity of Pt surface is the
surface oxides
of noble
of Pd and Rh are covered by an oxide layer even at a
slight oxygen excess in the gas
phase and
this coverage
is independent of
increased oxygen concentrations. Platinum oxide is mush less stable and the extent of
the coverage of
Pt by
surface oxygen
concentration of oxygen in the gas phase. active than the metallic
increases with
is especially prominent
surface which
the
The oxidized surface is less in the
oxidation of the least reactive hydrocarbon, methane. It
can be
generalized
that, with
the possible
oxidation, the activity for oxidation of wires or
small
exception of methane
saturated hydrocarbons on
large supported metal crystallites is Pt>Pd>Rh. As mentioned, the
incorporation of rhodium is necessitated by its selectivity in the reduction
1042 of nitric oxide.
Its role in the removal of hydrocarbons is associated with
its high activity in the steam reforming reactions (ref. 6 & 7). EFFECT OF NOBLE KETAL DISPERSION The extent of dispersion of the noble metal over the support is dependent on the nature of
the metal
the surface area of
and support, the metal loading with respect to
the support, the treatment temperature and
the redox
potential of the gas phase at that temperature. It is
stability of the ionic species (higher oxidation
the thermodynamic
states) of the noble metals that determines the metals over
oxide supports.
The
stable higher oxidation states than Pt under
oxidizing conditions at high
dispersion of
and maintain
their high dispersion
temperature.
With increased metal
loading, the dispersion decreases. The metal crystallite under reducing conditions.
the noble
metals. Pd and Rh, have more
less noble
growth is faster
The modification of the support surface by the
addition of ceria to high-surface 7-Al203 stabilizes the highly dispersed. non-crystalline, ionic state of the noble metals. If the treatment under
oxidizing conditions, calcination, is carried out
below 600'C,
the dispersion of Pt and Pd, the noble metals responsible for
hydrocarbon
oxidation, is high
for both
metals.
At higher calcination
temperatures the Pd is still resistant to sintering while the dispersion of Pt
decreases and
metallic
crystallites are
stabilizes the dispersion of both
noble
formed.
metals with
Addition of ceria the effect
of the
stabilization of the Pd dispersion being larger than on Pt dispersion. It has been repeatedly noted in
the evaluation of hydrocarbon oxidation
activity that under the conditions of operation of automotive catalysts, the oxidation of
the fast-burning olefins and aromatics is not dependent on the
dispersion of the noble metals. species, it
is
advantageous to
practice the oxidation of
Therefore,
for
the oxidation of these
maintain a high dispersion.
reactive hydrocarbons
Thus, in
is "structure" insensitive
although at lower temperatures such sensitivity has been noted (ref. 8). The oxidation of short-chain saturated hydrocarbons is, on the other hand, very much dependent on catalysts (ref.
5).
the
dispersion of
the noble metal
in supported
The larger crystallites of noble metals have a higher
specific activity for the oxidation of C1-Cs paraffins.
Depending
on the
hydrocarbon, noble metal, and conditions, the crystallites or metal wires may have a specific activity exceeding that of highly-dispersed noble metals by several orders of magnitude.
Platinum crystallites are more active than
Pd or Rh crystallites parallelfng the activity
of metal
wires discussed
above. The effect
of increased metal dispersion on the oxidation of slow-burning
hydrocarbons is immediately apparent from Figure 1. The figure shows
1043
directly
that
the activity for
strongly inhibited by the addition of 3.7%
containing 0.07% Pt/-y-A1203 is ceria.
the oxidation of propane of a catalyst
The influence of ceria
is to maintain the high initial dispersion
and to prevent the agglomeration of Pt into discrete particles. would enhance
the structure-insensitive reactions such as oxidation of CO
and nonsaturated hydrocarbons, it does
strongly
saturated hydrocarbons.
al.
oxidation at 250'C particle
While this
Tokoro at
inhibit
the oxidation of
(ref. 9 ) . have studied propane
over supported Pt and simultaneously measured the average
size and
found out
that
':I
the increase
in particle
size
is
accompanied by a sharp rise in specific activity i.e. the turnover number. 0
Increasing the average particle size from 20
to
> 1000 A increases the
turnover number by two orders of magnitude.
Y 4 0
L
P 20
0 100
I
200
300
400
500
TEMPERATURE(-1
Fig. 1 Conversion of propane on a 0.07% Pt catalyst support on 1-Al2O3 with and without 3.7% ceria; 1000 ppm C3H8, 2% 02. If the temperature is lowered to permit the measurement of rates structure sensitivity is observed even burning propylene
(ref. 8).
At
130'
low reaction
for the oxidation of fast
the specific reaction rate for the
oxidation of propylene increases sharply when the average Pt particle 0
The absence of the effect of crystallite
size increases from 11 to 144 A.
size on the oxidation of olefins and aromatics above 250'C, range of
interest to
the temperature
automotive catalysis, is apparently due to the fakt
that at these temperatures, the intrinsic surface reaction for the oxidation of
fast burning hydrocarbons is
faster than transport processes such as
diffusion. The structure sensitivity of depends very
much on
the nature
the oxidation of
Saturated hydrocarbons
of catalyst and of the hydrocarbons.
The
1044
oxidation of
n-butane on
supported rhodium was found
to be structure in-
sensitive in contrast to the NO-H2 reaction (ref. 10). It is plausible that the structure sensitivity is
dependent more
on the
oxidation state of the noble metal particles than on their size per se.
As mentioned before, small noble metal
particles are
oxidized under strongly oxidizing conditions and that determines their lower activity. structure sensitivity
in hydrocarbon
it
More work oxidation
more likely to be
is
this circumstance
is needed
over
to study the
noble metals
as a
function of chain length, dispersion, and temperature. EFFECT OF EXHAUST COMPOSITION The exhaust gas composition will influence the oxidation of hydrocarbons in several ways. inhibits the
Firstly, the presence of carbon monoxide
oxidation of hydrocarbons by competing for active sites of the
hydrocarbons. The retarded by
and nitric oxide
oxidation of
the presence
slow-burning, saturated
of carbon monoxide, aromatics
hydrocarbons is
and olefins. The
temperature of removal of saturated hydrocarbons is pushed
upwards when the
more reactive species are also present in the gas stream.
This is important
for the light-off performance of the catalyst. the feedgas
to the
It is beneficial to control
catalyst for obtaining satisfactory conversion of the
slow burning hydrocarbons during light off. Nitric oxide is also adsorbing on atmosphere.
the
catalytic
sites
in
an oxidizing
The inhibition of propylene conversion by nitric oxide can be
very pronounced as seen in Fig. 2.
It is shown that a five-fold increase in
the concentration of nitric oxide shifts the conversion curve to much lower space velocities (ref. 11). oxidation of
Nitric
oxide
is
also
known
CO and hydrocarbons over Pt and Pd wires.
to
inhibit the
The effect of NO on
the light-off behavior of vehicle catalysts is small since during cold start NO concentrations are low.
Space Velocity, Literq(min)(gm cot.)
Fig. 2 Inhibition effect of nitric oxide on propylene conversion at 550'F.
1045
As
mentioned
above, under
reducing conditions the steam
reactions contribute to the conversion of reforming activity
is very
the TWC is active while Pt
the hydrocarbons.
reforming The steam
dependent on catalyst composition. Rhodium in and Pd
inactive (ref. 6).
are relatively
The
steam reforming activity is vulnerable to poisoning by traces of lead. The large amounts of water vapor and carbon dioxide have minimal effect. Excess oxygen accelerates the oxidation of reactive hydrocarbons noble metals and
on all
inhibits the oxidation of saturated hydrocarbons on Pt
crystallites and wires. Finally. the
small amounts of sulfur dioxide will
in generally inhibit
somewhat the oxidation of hydrocarbons on noble metals at temperatures below 500'C
(ref. 2).
The inhibition will be much more
other noble metals because
pronounced on
Pt than on
SO2 chemisorbs on platinum to a greater extent
than on other noble metals. The catalytic behavior is completely altered, however, when supported on an oxide
capable of
forming a
adsorbing sulfur trioxide. Both 1-Al2O3 and CeO2
surface
the Pt is
sulfate layer by
chemisorb sulfur trioxide
and form sulfate groups on the surface. These groups can cover a portion of the exposed surface of ?-A1 (ref. 12).
The catalytic oxidation of
SO2 to
SO3 is structure sensitive in a manner similar to the catalytic oxidation of small saturated hydrocarbons. Platinum has long been known to
be much more
active in SO2 oxidation than other metals (ref. 13) and it is the Pt present as crystallites (or massive metallic Therefore, the
surface of
a
form)
that
is catalytically active.
supported catalyst
is
sulfated much more
effectively if it contains Pt which is not very highly dispersed. It has been noted that the presence of gases containing
20 ppm
SO2 in mixture with other
saturated hydrocarbons, such as propane, and excess oxygen
reacting over a Pt
catalyst
oxidation of
saturated hydrocarbons
the
supported on 1-Al2O3 strongly promotes the (ref.
14).
This promotion is
associated with the creation of new catalytic sites on the junction between the Pt particles
and
the
surrounding sulfated surface of the 1-Al2O3.
Without sulfur dioxide in the gas stream the catalyst oxidizes propylene and propane in two distinct
steps, the propylene reacting at temperatures much
below those at which propane is oxidized. The addition of 20 ppm of
SO2 to
the gas
In the
stream equalizes
the reactivity of propylene and propane.
absence of SO2 there is a large disparity
in the
activity of
Pt catalysts
with different metal loadings for propane oxidation. Addition of SO2 levels out these
activity differences and strongly enhances the activity of all
catalysts (Fig. 3).
1046
Fig. 3 Percentage conversion as a function of temperature for C3Hg oxidation over three Pt/l-A1203 catalysts of different Pt concentrations. The surface aluminum sulfate and sulfur elevated temperatures and
trioxide itself are unstable at
low oxygen partial pressures.
606-C or so. the enhancing effects of SO2 on hydrocarbon catalysts may
not be
observable.
Therefore above
oxidation over Pt
Neither will the effect be noted on
catalysts with a very high metal dispersion. DE-ACTIVATION OF CATALYSTS FOR HYDROCARBON OXIDATION Because the oxidation of hydrocarbons, in particular the carbon number
oxidation of low
alkanes, is structure sensitive it is also more vulnerable to
deactivation by poisons than the oxidation of carbon monoxide (ref. 15).
As
the catalyst is gradually deactivated in prolonged use the activity for the oxidation of C1-C5 alkanes will be amounts of
residual lead
in the
lost
first.
fuel is
The
presence
of small
in particular injurious for this
activity (ref. 16). Here, again the ability of Pt crystallites to oxidize sulfur an indirect,
residual lead. The sulfur trioxide formed interacts with the lead sulfate.
lead to form
Small amounts of lead sulfate do not deactivate the surface
of a noble metal catalyst. an oxide
dioxide has
important effect on the catalyst resistance to deactivation by
or when
it forms
On the other hand, when the lead is
present as
an intermetallic compound with the noble metal,
the deactivation is severe (ref. 17). Due to their composition and their range susceptible to
deactivation by
of
operation, TWC's
residual lead.
When
are more
operating near
stoichiometry, the amount of oxygen present is small and the SO2
+
1/2
O2c*SO3
equilibrium
is
shifted to
formation probability of lead sulfate.
the
left, minimizing the
1047
As the regulations require long term durability at very high hydrocarbon conversion it is necessary to protect the catalyst from contamination. The noble metal composition, state of noble metal dispersion. composition of the high-surface area support will have an effect on the ability of the catalyst to remove the oxidant precursors from the exhaust and to achieve the goal of maintaining a desirable air quality. REFERENCES 1. J. E. Sigsby at al.. Environ. Sci. Technol., 21, 466 (1987). 2. J. T. Kummer, Prog. Energy Combust. Sci., 6, 177 (1980). 3. T. Kornieki. and J. Butler. Ford Motor Company, Private Communication (1988). 4. N. W. Cant, and W. K. Hall, J. Catal, J&, 220 (1970). 293 (1980). 5. Y-F Y. Yao, Ind. Eng. Chem. Prod. Res. Dev., 6. H. S. Gandhi. et al., SOC. Aut. Eng. Paper 770196 (1977). 7. C. J. Kim, J. Catal.. 12. 169 (1978). 8. L. K. Carballo and E. E. Wolf, T. Catal.. 2,366 (1978). 9. Y. Tokoro et al., Nippon Kagaku Kaishi u, 1646 (1979) C.A. 2:180367f. 10. H. C. Yao, Y-F Y. Yao, and K. Otto, J. Catal., Id, 21 (1979). 11. S. E. Voltz et al., Ind. Eng. Chem. Prod. Res. Develop., u, 294 (1973). 12. R. H. HamnerIe and K. Kikkor, SOC. Aut. Eng. Paper 750097 (1975). 13. G. C. Bond, "Catalysis By Metals", Academic Press, London and New York 1962. 14. H. C. Yao, H. K. Stepien and H. S. Gandhi, J. Catal., 62, 231 (1981). 15. H. Shelef, K. Otto and N. C. Otto, Adv. Catal., 2,311 (1978). 16. W. B. Williamson et al., Ind. Eng. Chem. Prod. Res. Dev., 21, 531 (1984). 17. H. S. Gandhi et al., Surf. Interf. Anal.. 6. 148 (1984).
u,
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