ATMOSPHERIC POLLUTION 1980
Studies in Environmental Science Volume 1 Atmospheric Pollution 1978 Proceedings of the 13th International Colloquium, held in Paris, April 25-28,1978 edited by M.M. Benarie Volume 2 Air Pollution Reference Measurement Methods and Systems Proceedings of the International Workshop, held in Bilthoven, December 12-16,1977 edited by T. Schneider, H.W. de Koning and L.J. Brasser Volume 3 Biogeochemical Cycling of Mineral-Forming Elements edited by P.A. Trudinger and D.J. Swaine Volume 4 Potential Industrial Carcinogens and Mutagens by L. Fishbein Volume 5 Industrial Waste Water Management by S.E. Jq5rgensen Volume 6 Trade and Environment: A Theoretical Enquiry by H. Siebert, J. Eichberger, R. Gronych and R. Pethig Volume 7 Field Worker Exposure during Pesticide Application Proceedings of the Fifth InternationalWorkshop of the Scientific Committee on Pesticides of the International Association on Occupational Health, held in The Hague, The Netherlands, October 9-1 1, 1979 edited by W.F. Tordoir and E.A.H. van Heemstra-Lequin
Studies in Environmental Science 8
ATMOSPHERIC POLLUTION 1980 Proceedings of the 14th InternationalColloquium, UNESCO Building, Paris, France, May 5-8,1980 Organised by the lnstitut National de Recherche Chimique AppliquGe, Vert-le-Petit, France, in associationwith the Commission on Atmospheric Environment of the International Union of Pure and Applied Chemistry (IUPAC) edited by
Michel M. Benarie Titular Member of the Commission on Atmowheric Environment of IUPAC
ELSEVIER SCIENTIFIC PUBLISHING COMPANY 1980 AMSTERDAM-OXFORD-NEW YO RK
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Library of Congress Cataloging in Publication Data
International Colloquium on Atmospheric Pollution, l b t h , P a r i s , 1980. Atmospheric pollution 1980. (Studies i n environmental science ; 8 ) 1. Air--Pollution--Congesses. I. Benarie, Michel M. 11. Paris. I n s t i t u t national de recherche chimique appliquce. 111. InternatiDnal Union of Pure and Applied Chemistry. Conmission on Atmospheric Euvironment. N, T i t l e . V. Series. TD881.1555 1980 363.7’392 80-12833
ISBN 0-444-41889-x
(U.S. ) (Netherlands)
ISBN C444-41889-X (Val. 8 ) ISBN: 044441696-X (Series) 0 Elsevier Scientific Publishing Company, 1980 All rights reserved. N o 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 Scientific Publishing Company, P.O. BOX330, 1000 A H Amsterdam, The Netherlands Printed in The Netherlands
V
PREFACE This volume c o n t a i n s a s e l e c t i o n o f t h e 81 papers presented a t the 14th I n t e r n a t i o n a l Colloquium on Atmospheric P o l l u t i o n h e l d i n P a r i s , UNESCO B u i l d i n g , from t h e 5 t h t o 8 t h May 1980. Organized every second year; o u r Colloquium has t h e aim o f covering a very wide area i n t h e f i e l d o f a i r p o l l u t i o n . We a l r e a d y s t a t e d i n t h e Prefaces o f previous r e p o r t s o f t h i s s e r i e s t h a t t h e volume i s purposedly heterogeneous. We i n t e n d t o show "what i s on" i n a i r p o l l u t i o n , i n a somewhat d i f f e r e n t way than i s usual i n the e s t a b l i s h e d s c i e n t i f i c j o u r n a l s . The purpose o f a colloquium r e p o r t i s d i f f e r e n t . A rough analogy o f t h e d i f f e r e n c e can be given as f o l l o w s . The s c i e n t i f i c j o u r n a l i s e q u i v a l e n t t o t h e s p e c i a l i z e d r e t a i l trade, w i t h i t s e s t a b l i s h e d and guaranteed brands, i t s l e i s u r e l y t i m i n g s , and so on. A colloquium r e p o r t i s modelled on t h e stock exchange, and i t s h e c t i c d e a l i n g i n stocks which a r e n o t a l l n e c e s s a r i l y b l u e . But t h e advantage o f the stock exchange i s t o e s t a b l i s h r a p i d l y t h e worth o f commodity. But l e t us l e a v e t h e f i e l d o f analogies and models and e x p l a i n t h e d i f f e r e n c e s as we see them. The f i r s t d i f f e r e n c e i s t h e quickness o f r e p o r t i n g . From t h e moment o f w r i t i n g t h e l a s t word of a s c i e n t i f i c paper, i t can take on t h e average 12 months i n a good j o u r n a l b e f o r e t h e f i r s t reader becomes aware o f t h e r e s u l t . The conference r e p o r t has shortened t h e i n t e r v a l between the l a s t word w r i t t e n and t h e f i r s t one read t o a mere four months. Therefore i t s nature i s nearer t o l a b o r a t o r y and i n s t i t u t e ( " g r e y " ) r e p o r t s . Here i s our second p o i n t . As s c i e n t i f i c progress advances these days, as views and scopes change, 12 months i s t o o l o n g f o r p u b l i c a t i o n . Therefore, much o f t h e e f f o r t and r e s u l t s o f research teams go i n t o annual r e p o r t s , s p e c i a l r e p o r t s t o t h e sponsoring agencies, and xeroxed t e x t s o f r e s t r i c t e d a v a i l a b i l i t y , i n a c c e s s i b l e t o a f r a c t i o n of t h e s c i e n t i f i c community and inadequately indexed by a b s t r a c t s . Some end up published, o t h e r s n o t . By o f f e r i n g s i m i l a r delays as t h e "grey" c i r c u l a t i o n , b u t a t t h e same time a g r e a t e r d i f f u s i o n , an adequate awareness v i a t h e i n d e x i n g and a b s t r a c t i n g s e r v i c e s and j o u r n a l s , we t h i n k t h e p u b l i c a t i o n should be o f r e a l use t o t h e s c i e n t i f i c community. This s h o r t e n i n g o f t h e delay has been made p o s s i b l e by an increased e d i t o r i a l e f f o r t , aided by a s p e c i a l g o o d w i l l o f t h e team i n charge a t t h e p u b l i s h i n g house and, l a s t l y , by l e s s e d i t o r i a l i n t e r f e r e n c e than i s usual w i t h s c i e n t i f i c j o u r n a l s .Instead o f m a i l i n g o u t t h e t e x t s f o r r e f e r e e i n g , two stages o f s e l e c t i o n have taken p l a c e on panel b a s i s . F i r s t t h e a b s t r a c t s and then the t e x t s were
VI
appraised. B u t the final assessment will be made by the reviewers, by the whole readership of the volume. This i s the t h i r d difference with the s c i e n t i f i c journals, where a f t e r acceptance by two referees, a "good brand" of research i s being offered t o the reader. And here the "stock exchange model" becomes useful. Official financial support, on which so much research nowadays depends, does not necessarily reach the s c i e n t i f i c a l l y most prominent, original , or competent workers. Here we p u t into the limelight pertinent research together with the inconsequential ; the creative together with the more routine report. Thus we hope t o raise the awareness of b o t h concerned parties: t h a t which allocates the funds and t h a t which uses them. In t h i s way we hope t o improve the cost-effectiveness of research funding. The usual weeding out by refereeing i n s c i e n t i f i c journals encourages the strong, b u t a t the same time, overprotects the weak. By not being publicly compared, by leaving the l e s s worthy a c t i v i t y i n the benevolent shade of the internal reports, a l o t of rather below-average research i s l e f t t o thrive on public funds, t h u s depriving others, m r e deserving, from t h i s benefit. In t h i s volume before you, readers are asked t o judge each paper on i t s own merits, independently from the past laurels of the laboratory o r other non-scientific considerations. W e see an added benefit i n the f a c t t h a t some papers rejected by journal referees may nevertheless contain valuable information. If t h i s i s relegated to some obscure "grey" report, the e f f o r t will sometimes be duplicated -t h a t much e f f o r t wasted. The authors have been asked t o keep their papers short. This may be astonishing a t a time when sponsoring agencies often evaluate research reports by t h e i r volume. B u t a well formulated, well executed endeavour can be related adequately i n n o t more than a few pages. Alas, n o t every paper i s equal t o Einstein's essay on general r e l a t i v i t y , which had a mere f i v e pages, b u t this k i n d of result-to-length r a t i o would be the ideal one. Without daring to say t h a t a l l long papers are necessarily bad, we may s t a t e that most of them would g a i n a l o t by being l e s s rambling and d i r e c t l y and clearly reporting the f a c t s . A short paper i s e i t h e r good as i t stands, o r lacks something which could be f o r In the l a t t e r case, the paper example, quality, o r i g i n a l i t y , l u c i d i t y , e t c i s bad, and the shorter i s the time the reader losses while browsing through i t . Unfortunately, t h e production process o f t h i s book makes the compilation of a subject index v i r t u a l l y impossible.
...
Michel Benarie
VII
ACKNOWLEDGEMENTS The enormous administrative work necessary for the organisation o f such a colloquium was t h i s time also expertly executed by Mme Monique Thavard, t o whom thanks are expressed herewith.
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IX
CONTENTS
..................................................................
Preface
V
MODELING Models and Modeling A. C. Stern ...........................................................
3
Modeling t h e t r a n s p o r t and d i f f u s i o n of a i r p o l l u t a n t s using a prognostic mesoscale model
R. T. McNider and R. A. Pielke
........................................
P a r t 1: Overview and t r a n s p o r t a t i o n module R. M. Patterson, P . B. Simmon and W. B. Petersen ......................
9
Commuter exposure modeling.
Commuter exposure modeling.
P a r t 11: Emissions and dispersion modules and
generation o f exposure s t a t i s t i c s P . B. Simmon, R. M. Patterson and W . B. Petersen APT
- A
13
......................
19
computer program f o r the numerical s o l u t i o n o f problems i n
atmospheric dispersion A. J . H. Goddard, A. Ghobadian, A. D. Gosman, C . Harter and G . D. Kaiser
25
The t r a n s p o r t , chemical transformation, and removal of SO2 and s u l f a t e i n t h e Eastern United S t a t e s G. R. Carmichael and L. K. P e t e r s .....................................
31
The atmospheric impacts o f evaporative cooling systems
J . E. Carson
..........................................................
37
Improvement of mathematical models f o r plume r i s e and d r i f t deposition from cooling towers
A. J . P o l i c a s t r o , R. A. Carhart, M. Wastag, S. Ziemer, K. Haake, W. E. Dunn and P. Gavin ...............................................
43
X The simple box model simplified M. M. Benarie
.........................................................
49
GAUSSIAN PLUME
Sensitivity analysis o f the gaussian plume model G. Neumann and G. Halbritter ..........................................
57
Development of a gaussian plume model appropriate t o an urban area
M. Bennett
............................................................
63
AIRFLOW AND DISPERSION
Physical theories o f turbulent diffusion B. E. A. Fisher
.......................................................
Dispersion experiments from the 213 m high meteorological mast a t Cabauw in the Netherlands H. van Duuren and F. T. M. Nieuwstadt
71
.................................
77
.....................................................
91
Dispersion around buildings
P. J . H . Builtjes
A carbon monoxide dispersion experiment in a built-up area H. Kolb, H. Mohnl, U. Pechinger and R. Werner
.........................
97
Real-time prediction of local wind by means of stochastic models C. Bonivento, G. Fronza and A. Tonielli
...............................
Air p o l l u t i o n impact in s t r e e t s with heavy t r a f f i c and the e f f e c t s of the dominant parameters H . Sobottka
...........................................................
105
109
ANALOG MODELING
Wind tunnel modelling of buoyant emissions
A. G. Robins
..........................................................
117
Flue gas dispersion in the vicinity of buildings: wind tunnel simulation and comparison with f i e l d measurements H. Sommers, J . Hoitz and R. Haupt
.....................................
125
XI
Comparison o f wind tunnel and f u l l s c a l e measurements t o i n v e s t i g a t e t h e d i s p e r s i o n o f v e h i c l e exhaust gases
P. Leisen
.............................................................
131
Use o f a water-analog model t o determine t h e optimum l a y o u t o f a highc a p a c i t y power s t a t i o n
J . Rigard and M. M i l h e
................................................
137
POLLUTANT FORMATION, TRANSFORMATION AND l'RANSPORT
Regional s c a l e t r a n s p o r t o f f i n e aersol c o n s t i t u e n t s from urban a i r p o l l u t i o n i n Eastern North America
J . W. Winchester, J . W. Nelson, A. C. D. L e s l i e , M. Darzi, L. C. S. Boueres and S. E. Bauman
.....................................
147
Atmospheric t r a n s p o r t o f p a r t i c u l a t e sulphate and ozone i n t o the Toronto r e g i o n and i t s c o r r e l a t i o n w i t h v i s i b i l i t y
K. G. Anlauf, M. Olson, H. A. Wiebe and M. A. Lusis
...................
153
A study o f t h e t r a n s p o r t o f t r a c e metals and s u l f u r i n t o Scandinavia
H. 0. Lannefors and H. C. Hansson
.....................................
159
Transport o f ozone i n I s r a e l
E. H. Steinberger
.....................................................
165
D i r e c t f o r m a t i o n o f NO2 i n combustion products
W. J . McLean, J. Y. Chen, F. C. Gouldin and M. 3. Oven The r a t e o f NO, C. W. S p i c e r
................
173
r e a c t i o n i n t r a n s p o r t e d urban a i r
..........................................................
181
COMPUTATIONS AND STATISTICAL REPRESENTATIONS
D e s c r i p t i v e a n a l y s i s o f t h e SO2 p o l l u t i o n i n Brussels: seasonal v a r i a t i o n w i t h r e f e r e n c e t o sampling s i t e l o c a t i o n
F. A. S a r t o r
..........................................................
189
The generation o f h o u r l y average wind v e c t o r s u s i n g a Markov process
J . W. Bacon and B. Henderson-Sellers
..................................
195
XI1
An e m p i r i c a l d e s c r i p t i o n o f t h e extreme values o f SO2 c o n c e n t r a t i o n i n an urban area G. Drufuca and M. G i u g l i a n o
..........................................
209
Random sampl ing a g a i n s t continuous m o n i t o r i n g f o r a i r qua1 it y m o n i t o r i n g networks
J . G. Kretzschmar and G. Cosemans
....................................
213
A I R CHEKSTRY AND FORMATION OF PARTICULATE MATTER
Photochemical aerosol f o r m a t i o n i n multi-component system c o n t a i n i n g pre-exi s t i n g p a r t i c l e s
..............................
M. Kasahara, K. Takahashi and S. Tohno
221
I n t e r f a c i a l physicochemical c h a r a c t e r i s t i c s o f a i r b o r n e soot p a r t i c l e s
F. de Wiest and P. M. B r u l l
........................................
227
The e f f e c t o f p a r t i c l e s i z e on t h e e x t e n t o f bromination o f p o l y s t y r e n e 1atex aerosol s
J . A. Spatola and J . W. Gentry
.......................................
233
Aerosol p a r t i c l e s i n a i r w i t h a g r a d i e n t o f h u m i d i t y
H. Straubel
.........................................................
239
Heterogeneous n i t r o g e n o x i d e - p a r t i c l e r e a c t i o n s G. M. Sverdrup and M. R. Kuhlman
....................................
245
P a r t i c u l a t e p o l l u t i o n o f t h e atmosphere due t o l i q u i d hydrocarbon f i r e s Pham Van Dinh and B. Benech
..........................................
249
AEROSOL PHYSICS AND bBASUREMNT CONCERNING THE SUSPENDED PARTICULATE MATTER
Measurement o f p a r t i c l e s i z e d i s t r i b u t i o n s o f f l u e d u s t by means o f cascade impactors
R . Wiedemann
........................................................
Measurement o f aerosols l e s s than 0.01 p m
-
257
a p p l i c a t i o n t o the n u c l e a t i o n
i n t h e atmosphere
M. L. P e r r i n , Y. C. B o u r b i g o t and G. J . Madelaine
....................
267
XI11
On the c o u n t i n g e f f i c i e n c y o f a continuous f l o w condensation n u c l e i counter
Y. Metayer and G. Madelaine R e a l i z a t i o n o f a d u s t tunnel
-
..........................................
273
response o f some a i r sampling instruments
used i n in d u s t r i a1 hygiene
J . F. Fabries and B. Carton
..........................................
279
P r e l i m i n a r y measurements of t h e soot Stokes-Einstein parameters i n an oxygen/acetylene blow-pipe by means o f d i f f u s i o n broadening spectrosCOPY
G. Gouesbet, P. Flament, G. Grehan and M. W e i l l
......................
285
The generation and measurement o f primary soot aerosols between 50 and
400
8, Y. 0. Park, J
C a r o l l a and J . W . Gentry
..............................
291
I n s i t u c h a r a c t e r z a t i o n o f soot aerosols by s c a t t e r i n g and absorption o f a l a s e r beam
J. Lahaye and
G. Prado
...............................................
297
The development o f t h e GCAF i n e r t i a l impactor f o r s e p a r a t i o n o f non-spherical p a r t i c l e s S. L i n , R. Preston and
J. W. Gentry
..................................
303
New i n e r t i a l p a r t i c l e s i z e c l a s s i f i c a t i o n techniques f o r aerosol sampling and measurement K. W i l l e k e , R. E. P a v l i k , W. C. Friedman, S. A. Haberman
J. D. Blanchard and
.......................................................
309
Some s p e c i a l problems concerning asbestos f i b e r p o l l u t i o n i n ambient a i r K. R. Spurny, W.
Stober, G. Weiss and H. Opiela
......................
315
Comprehensive methods f o r r a p i d q u a n t i t a t i v e a n a l y s i s o f a i r b o r n e p a r t i c u l a t e s by o p t i c a l microscopy, SEM and TEM w i t h s p e c i a l reference t o asbestos G. B u r d e t t , J . M. l e Guen, A. P. Rood and 5. J . Rooker
...............
323
Some a p p l i c a t i o n s o f t h e “ J e t i m e t e r ”
J. C. Guichard, A. G a i l l a r d and M. Lamauve
...........................
339
XIV MONITORING NETWORKS AND SURVEY RESULTS
The design of a i r quality monitoring networks u s i n g an information content measure E. E. Pickett and R. G. W h i t i n g ......................................
347
The Canadian a i r and precipitation monitoring network APN L. A. Barrie, H. A. Wiebe, K. Anlauf and P. Fellin ...................
355
Ambient a i r pollution from industrial sources M. J . Suess ..........................................................
361
Measurements of atmospheric e l e c t r i c a l parameters near an industrial plant - influence o f ionized plumes on the e a r t h ’ s e l e c t r i c a l f i e l d 0. Laurent and R. Peyrous ............................................
365
A comparison of v i s i b i l i t i e s in polluted and unpolluted areas H. Horvath
371
Relationship between c i t i z e n complaints of a i r pollution, meteorological data and immission concentrations J . E. Evendijk, P. J . W. M. Miiskens and T. J . R. M. de Jong ..........
379
Building ventilation and indoor a i r quality C. D. Hollowell, J . V. Berk, M. L. Boegel, R. R. Miksch, W. W . Nazaroff and G. W. Traynor
387
Measurement of nitrosamines i n the a i r of Paris by thermal energy analysis B. T. Chuong and M. Benarie ..........................................
397
Performances of a piezoelectric p a r t i c l e mass monitor J . Paulou ............................................................
401
...........................................................
.....................................
EFFECTS: ON MAN AND ON VEGETATION
The exposure of human populations t o a i r pollution R. E. Munn ...........................................................
409
xv Monitoring of the a i r quality by analysis of biological indicators and accumulators R. A. Impens, T. P i r e t , G. Kooken and A. Benko .......................
417
Patterns of fluoride accumulation in Boreal f o r e s t species under perennial exposure t o emissions from a phosphorus plant S. S. Sidhu ..........................................................
425
Contamination of edible parts of seven plant crops and s o i l s by heavy metals in urban area by a i r pollution i n Alexandria d i s t r i c t , Egypt I . H. Elsokkary ......................................................
433
Author index
.............................................................
439
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MODELING
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Atmospheric Pollution 1980, Proceedings of the 14th International Colloquium, Paris, France, May 5--8,1980, M.M. Benarie (Ed.), Studies in Environmental Science, Volume 8 0 Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
3
MODELS AND MODELING ARTHUR C. STERN U n i v e r s i t y o f N o r t h Carolina, Chapel H i l l , N.C.
USA
ABSTRACT The f i r s t hundred years o f a i r p o l l u t i o n modeling, from 1859 t o 1959, i n t r o duced t h e box model f o r urban p o l l u t i o n c o n c e n t r a t i o n and p o i n t source plume models.
I t ended w i t h t h e i n t r o d u c t i o n o f t h e e l e c t r o n i c d i g i t a l computer t o
modeling.
I n t h e n e x t decade, u n t i l 1969, urban models more s o p h i s t i c a t e d than
t h e box model became o p e r a t i o n a l and p o i n t source models f o r l e v e l t e r r a i n came t o maturity.
I n t h e most r e c e n t decade, t o 1979, new modeling concepts have been
introduced, keeping pace w i t h enhanced computer c a p a b i l i t y and speed; models have been developed f o r complex t e r r a i n and f o r chemical r e a c t i o n s among p o l l u t a n t s , and t h e r e has been i n t e n s i v e o p e r a t i o n a l use o f models.
THE FIRST HUNDRED YEARS
-
1859-1959
Gerald De M a r r a i s ' H i s t o r y o f A i r P o l l u t i o n Meteorology through 1969' t e l l s us t h a t f i r s t computation o f p r e d i c t e d p o l l u t i o n c o n c e n t r a t i o n was most l i k e l y t h a t by R. Angus Smith,2 i n 1859, o f carbon d i o x i d e over Manchester; and t h a t Sutton'
i n 1932 f o r m u l a t e d a t h e o r y o f eddy d i f f u s i o n i n t h e atmosphere a p p l i c a -
b l e t o d i s p e r s i o n from l a r g e p o i n t sources, which, i n 1936, was expressed as exp l i c i t formulae f o r computing concentrations downwind o f continuous p o i n t and 4 l i n e sources by Bosanquet and Pearson. 5 I n t h e 1940's and e a r l y 1950's, Sherlock and S t a l k e r showed how t o compute 6 7 downwash from chimneys; H o l l a n d and Davidson showed how t o compute plume r i s e ; 8 Bosanquet, Carey and H a l t o n gave formulae f o r p r e d i c t i n g dust d e p o s i t i o n from 9 stack plumes; and Strom and H a l i t s k y described t h e i r New York U n i v e r s i t y wind tunnel modeling f a c i l i t i e s t h a t were t o p l a y an important r o l e i n t h e l a t e 1950's and e a r l y 1960's, d u r i n g which t i m e users t r u s t e d wind t u n n e l s more than mathem a t i c a l models. 1955 was a key y e a r i n t h e h i s t o r y o f modeling.
I t saw t h e assignment t o t h e
A i r P o l l u t i o n Research Group a t t h e Robert A. T a f t S a n i t a r y Engineering Center o f t h e U n i t e d S t a t e s P u b l i c H e a l t h Service i n C i n c i n n a t i , Ohio, o f t h e cadre o f U n i t e d States Weather Bureau m e t e o r o l o g i s t s , charged, among o t h e r t h i n g s , w i t h
4
the development of a i r p o l l u t i o n f o r e c a s t i n g and modeling techniques. This cadre, subsequently relocated t o Research Triangle Park, North Carolina, has worked on t h i s t a s k continuously f o r the p a s t twenty-five years. 1955 was a l s o t h e y e a r of the publication of "Meteorology and Atomic Energy"" by the United S t a t e s Atomic Energy Commission--most probably t h e f i r s t book one could turn t o f o r a i r p o l l u t i o n formulae and models. Urban a i r p o l l u t i o n f o r e c a s t s s t a r t e d i n Los Angeles i n 1955," and Frenkiel" described t h e r e s u l t s of h i s mathematical mode l of a i r p o l l u t i o n i n Los Angeles. Although t h i s study did not use the e l e c t r o n i c computer, Frenkiel noted t h e a p p l i c a b i l i t y of computers t o mathematical modeling o f a i r p o l l u t i o n .
I remember 1955 well a s the y e a r t h a t the I n t e r n a t i o n a l Business Machine company s t a r t e d t o aggressively merchandise i t s IBM-650 computer. T h i s was the one with a r o t a t i n g magnetic drum memory which was programed numerically because a l phabetic computer "software" was j u s t being invented. There were t h r e e 6 5 0 ' s in Cincinnati; one a t the telephone company, one a t the University of Cincinnati t o t r a i n the l i k e s of me on i t s use; and one i n a downtown s t o r e f r o n t window of t h e IBM o f f i c e . We, a t t h e T a f t Center, used a l l t h r e e of t h e s e machines t o debug and eventually r u n our f i r s t d i g i t a l computer program f o r the archiving and anal y s i s of a i r q u a l i t y d a t a , including t h e computation of t h e parameters of one of the f i r s t s t a t i s t i c a l models--the log-normal d i s t r i b u t i o n of t h e s e data. TOOLING UP
-
1959-1969
The 1959-1969 decade was ushered in w i t h the development i n C a l i f o r n i a of t h e rollback m 0 d e 1 . l ~ This model was conceived as a r a t i o n a l e f o r s e t t i n g l i m i t s on emission of carbon monoxide and hydrocarbons from automobile exhaust, and l a t e r in t h e decade, was extended t o t h e s e t t i n g of l i m i t s f o r oxidants and oxides of nitrogen from motor v e h i c l e s .
Also during t h i s decade, Pooler14 i n 1961 published
one of t h e f i r s t urban a i r p o l l u t i o n prediction models; the procedures advanced by Pasquill15 and Gifford'' and t h e plume r i s e computation procedures of Briggs 17 were accepted a s the b a s i s f o r most point and l i n e source modeling. These procedures were made widely a v a i l a b l e i n 1967 in Turner's "Workbook of Atmospheric Dispersion Estimates"18 and i t s subsequent e d i t i o n s .
The Workbook a l s o discussed
t h e a p p l i c a t i o n of modeling p r i n c i p l e s t o area sources and the combination of m u l t i p l e p o i n t , line and area sources t h a t would be necessary f o r a m u l t i p l e source urban d i f f u s i o n model, and which were incorporated i n t h e several multiple source urban d i f f u s i o n models published i n t h e l a t e 1960's. I p a r t i c u l a r l y remember 1968 because i t was my l a s t year with t h e U.S. Public Health Service and my f i r s t y e a r a t the University of North Carolina.
The l a s t
chore I did f o r t h e Public Health Service was t o set up the c o n t r a c t s p e c i f i c a t i o n s , review the c o n t r a c t o r s ' proposals, and recomnend t h e c o n t r a c t s f o r what became, when published i n 1969, t h e Air Quality Display Model (AQDM)lg--the work-
5
horse of m u l t i p l e source models i n t h e e a r l y 1970's i n t h e United S t a t e s , where i t was used t o e s t a b l i s h t h e boundaries of the Air Quality Control Regions o f the nation and t o develop i t s S t a t e Implementation Plans. One of t h e f i r s t chores I did a t t h e University of North Carolina was t o organize i n 1968 t h e Symposium on Multiple Source Urban Diffusion Modelsz0 held i n Chapel H i l l , North Carolina, in 1969.
THE MODELING EXPLOSION - 1969-1979 De Marrais' History 1 ends w i t h 1969. However, we a r e f o r t u n a t e t h a t i n 1979, Turnerz1 and the E l e c t r i c Power Research I n s t i t u t e (EPRI)" have brought modeling h i s t o r y u p t o d a t e . Turner's updating was in h i s Air Pollution Control Associat i o n C r i t i c a l Review Paper, "Atmospheric Dispersion Model ing;"21 and t h a t of EPRI i n t h e i r five-volume pub1 i c a t i o n , "Mathematical Models f o r Atmospheric of which t h e f i f t h volume (Appendix 0) i s e n t i t l e d , "Available Air Quality Models." There has been so much ferment i n t h e modeling f i e l d , during t h i s decade, t h a t models have expanded t o include a broad d i v e r s i t y w i t h respect t o time, source, receptor, t e r r a i n and type. W i t h r e s p e c t t o time, t h e r e a r e models whose output i s in terms of hourly, d a i l y o r annual averaging time; and those t h a t t r y t o t e l l u p what w i l l happen next y e a r , o r , a s i n t h e case of t h e build-up of global carbon dioxide, next century. Models a r e classed i n terms of the source c a t e g o r i e s they can represent a s point o r s i n g l e source; l i n e o r highway source, area source, o r m u l t i p l e source. In terms of r e c e p t o r , we have S t r e e t Canyon, Airport, Shopping Center models, e t c . Models of the e a r l i e r decades were only f o r l e v e l t e r r a i n . We now have models f o r v a l l e y s and o t h e r forms of complex t e r r a i n , f o r land/sea and fumigation conditions. The d i v e r s i t y of types i s shown by t h e o u t l i n e below: I . Physical A. Wind Tunnel B. Liquid Flume C. Towing Tank 11. Mathematical A. Empirical - Deterministic 1. Box - Eulerian 2. S t a t i s t i c a l - Rollback B. Semi-Empirical 1. Gaussian Plume - Puff 2. Trajectory - Moving Cell C. Numerical - Reactive 1. Multibox - Lagrangian 2 . Grid - Eulerian - Finite Difference 3 . P a r t i c l e ; P a r t i c l e - i n - C e l l ; Marker and Cell D. Global - Pollution
6
E.
Visibility
F. Dosage - Exposure O f these, I w i l l comment o n l y on t h e l a s t o f these c a t e g o r i e s .
Although Dosage
and Exposure models have been used almost e x c l u s i v e l y t o assess human exposure, H o r i e and t h e author23 p o i n t e d o u t t h e i r p o t e n t i a l f o r much wider a p p l i c a t i o n t o o t h e r p o p u l a t i o n s (e.g.,
vegetation, m a t e r i a l s , s t r u c t u r e s , e t c . ) .
The U n i t e d S t a t e s Clean A i r Amendments o f 197724 have had a profound i n f l u e n c e on modeling.
F i r s t l y , by making t h e Prevention o f S i g n i f i c a n t D e t e r i o r a t i o n (PSD)
o f u n p o l l u t e d areas a l e g a l requirement, i t has f o r c e d t h e p o i n t source modeling o f a l l new major sources as a p r e c o n d i t i o n f o r t h e i r approval.
The d r a f t e r s o f
t h e a c t almost committed t h e a b s u r d i t y o f s p e c i f y i n g t h e model t o be used, b u t were persuaded i n s t e a d t o s u b s t i t u t e t h e f o l l o w i n g language i n t h e a c t : STANDARDIZED A I R QUALITY MODELING Sec. 320. ( a ) Not l a t e r than s i x months a f t e r t h e date o f enactment o f t h e Clean A i r Act Amendments o f 1977, and a t l e a s t every t h r e e years t h e r e a f t e r , t h e A d m i n i s t r a t o r s h a l l conduct a conference on a i r q u a l i t y modeling. I n conducting such conference, s p e c i a l a t t e n t i o n s h a l l be given t o approp r i a t e modeling necessary f o r c a r r y i n g o u t p a r t C o f t i t l e I ( r e l a t i n g t o prevention o f s i g n i f i c a n t deterioration o f a i r q u a l i t y ) . ( b ) The conference conducted under t h i s s e c t i o n s h a l l p r o v i d e f o r p a r t i c i p a t i o n by t h e N a t i o n a l Academy o f Sciences, r e p r e s e n t a t i v e s o f S t a t e and l o c a l a i r p o l l u t i o n c o n t r o l agencies, and a p p r o p r i a t e Federal agencies, i n c l u d i n g t h e N a t i o n a l Science Foundation; t h e N a t i o n a l Oceanic and Atmospheric A d m i n i s t r a t i o n , and t h e N a t i o n a l Bureau o f Standards. ( c ) I n t e r e s t e d persons s h a l l be p e r m i t t e d t o submit w r i t t e n comments and a v e r b a t i m t r a n s c r i p t o f t h e conference proceedings s h a l l be maintained. ( d ) The comments submitted and t h e t r a n s c r i p t maintained pursuant t o subs e c t i o n ( c ) s h a l l be i n c l u d e d i n t h e docket r e q u i r e d t o be e s t a b l i s h e d f o r purposes o f promulgating o r r e v i s i n g any r e g u l a t i o n r e l a t i n g t o a i r q u a l i t y modeli n g under p a r t C o f t i t l e I. Secondly, t h e s e c t i o n s o f t h e a c t on non-attainment areas, i . e . what must be done i n areas where t h e a i r q u a l i t y o f a p o l l u t a n t i s worse than t h e a i r q u a l i t y standard f o r t h a t p o l l u t a n t , i m p l i c i t y r e q u i r e t h e use o f m u l t i p l e source models t o o b t a i n f e d e r a l approval f o r what i s proposed t o be done, p a r t i c u l a r l y i f emission o f f s e t s are required. T h i r d l y , t h e r e a r e s e c t i o n s o f t h e a c t concerned w i t h p r e v e n t i o n o f degradation o f v i s i b i l i t y , which among o t h e r t h i n g s , has prompted our Environmental P r o t e c t i o n Agency t o i s s u e i n 1979, a pub1 i c a t i o n e n t i t l e d , "The Development o f Mathematical Models f o r t h e P r e d i c t i o n of Anthropogenic V i s i b i l i t y Impairment. F o u r t h l y , by o u t l a w i n g t h e use o f supplementary c o n t r o l systems f o r c o a l - f i r e d power p l a n t s , t h e a c t has denied t h e U n i t e d States t h e b e n e f i t o f t h e use o f f o r e c a s t i n g e f f l u e n t d i s p e r s i o n from such p l a n t s . THE MODELING DILEMMA
-
1980
Two decades ago--even one decade ago--we b e l i e v e d t h a t i f o n l y we had t h e programs, t h e program i n p u t s , and t h e computer c a p a b i l i t y t o r u n them, we c o u l d gain
7
understanding o f o u r a i r p o l l u t i o n problems. We b e l i e v e d t h a t modeling c a p a b i l i t y would p u t us i n t h e d r i v e r ' s seat i n o u r t h r u s t t o c o n t r o l p o l l u t i o n . Unfortunatel y , now t h a t we have achieved modeling c a p a b i l i t y , a t l e a s t i n t h e United States
i t has p u t t h e models i n t h e d r i v e r s ' seats and l e f t many o f us asking where they
a r e t a k i n g us. The r o l l b a c k model f o r motor v e h i c l e carbon monoxide as o r i g i n a l l y developed i n C a l i f o r n i a was a r a t i o n a l procedure and used d e f e n s i b l e i n p u t data.
However,
i n t h e two decades s i n c e i t s development, i t s a p p l i c a t i o n t o t h e s e t t i n g o f f e d e r a l motor v e h i c l e emission standards has become i n c r e a s i n g l y i r r a t i o n a l and i t s input data increasingly indefensible.
With t h e r o l l b a c k model i n t h e d r i v e r ' s
seat, i t has d r i v e n us t o expend b i l l i o n s o f d o l l a r s needlessly, and i t s a p p l i c a t i o n t o t h e c o n t r o l o f hydrocarbons and oxides o f n i t r o g e n emissions has n o t accomplished i t s intended o b j e c t i v e o f reducing smog. I n t h e a p p l i c a t i o n o f p o i n t , l i n e and m u l t i p l e source models t h e r e are substant i a l issues t h a t need r e s o l u t i o n . '-8mong them are:
t h e p r o p r i e t y o f modeling o n l y
worst-case s i t u a t i o n s , which would occur r a r e l y , i f ever, i n r e a l l i f e ; t h e use o f models based on s h o r t - t e r m exposure t o e s t a b l i s h compliance w i t h standards
based on long-term exposure; and t h e r e l i a b i l i t y o f i n s t r u m e n t a l measurements and c a l i b r a t i o n s which a r e a t o r c l o s e t o t h e lower l i m i t o f d e t e c t i o n o f such instruments.
Here again, d e c i s i o n s on model i n p u t data can r e s u l t i n costs f a r
exceeding t h e b e n e f i t s achieved.
A w e l l c o n s t r u c t e d model does one t h i n g s u p e r l a t i v e l y w e l l .
It t e l l s us t h e
s i g n and o r d e r o f magnitude o f t h e change i n o u t p u t f o r a g i v e n change i n an i n p u t parameter.
T h i s i s a v e r y u s e f u l t h i n g t o know when s i t i n g a source and de-
s i g n i n g i t s c o n t r o l system; when s i t i n g m o n i t o r i n g s t a t i o n s and i n t e r p r e t i n g t h e i r r e s u l t s ; and when s t u d y i n g atmospheric t r a n s p o r t a t i o n and t r a n s f o r m a t i o n processes. However, when we use a model t o g i v e a go o r no-go d e c i s i o n , we a r e asking t h a t i t p r e c i s e l y t e l l whether t h e ground l e v e l c o n c e n t r a t i o n i s g r e a t e r o r l e s s than
some s p e c i f i c number.
N e i t h e r t h e models n o r t h e i r i n p u t data are t h a t good o r
a r e ever l i k e l y t o be so.
I f we t r y t o use models as go o r no-go d i s c r i m i n a t o r s ,
we a r e f o r c e d t o make them more and more complex t o accommodate a l l p o s s i b l e pert u r b i n g i n f l u e n c e s ; b u t i f we use them t o show t h e magnitude and s i g n o f change, we can r e l y on s i m p l e r models. THE FUTURE
A i r p o l l u t i o n models have come o f age.
They a r e a v a i l a b l e o f f - t h e - s h e l f from
p r i v a t e c o n s u l t a n t s and governmental agencies (e.g., United States).*l
the
UNAMAP models i n t h e
There a r e s t i l l many problems w i t h t h e models themselves, t h e
way t h e y a r e r e q u i r e d t o be used and t h e way t h e y a c t u a l l y a r e used, which i t i s hoped t h i s decade w i l l h e l p r e s o l v e .
8
REFERENCES
1 G.A. 2 3 4 5 6 7 8 9 10
11
12 13 14 15 16 17 18 19 20 21
22 23 24 25
De M a r r a i s , A H i s t o r y o f A i r P o l l u t i o n M e t e o r o l o g y t h r o u g h 1969, NOAA T e c h n i c a l Memorandum ERL ARL-74, N a t i o n a l Oceanic and Atmospheric A d m i n i s t r a t i o n , S i l v e r S p r i n g , Md., 1979, 78 pp. R. Angus Smith, On t h e A i r o f Towns, Q u a r t . J. Chem. SOC. London, 11(1859), pp. 196-235. O.G. S u t t o n , A Theory o f Eddy D i f f u s i o n i n t h e Atmosphere, Proc. Royal S o c i e t y London A 135(826), pp. 143-165. C.H. Bosanquet and J.L. Pearson, The Spread o f Smoke and Gases f r o m Chimneys, Trans. Faraday SOC., 32(1936), pp. 1249-1263. R.H. S h e r l o c k and E.A. S t a l k e r , A Study o f Flow Phenomena i n t h e Wake o f Smoke Stacks, B u l l e t i n No. 29, Dept. o f E n g i n e e r i n g Research, U n i v e r s i t y o f Michigan, Ann A r b o r , Mich., 1941, 49 pp. J.Z. H o l l a n d , A M e t e o r o l o g i c a l Survey o f t h e Oak Ridge Area, ORO-99, Atomic Energy Commission, Oak Ridge, Tenn., 1953, 584 pp. ( p a r t i c u l a r l y pp. 554-559). W.F. Davidson, The D i s p e r s i o n and S p r e a d i n g o f Gases and Dusts f r o m Chimneys, 38-55. Trans. B u l l . No. 13, 1 4 t h Ann. Mtg., Ind. Hyg. F o u n d a t i o n (1949) p C.H. Bosanquet, W.F. Carey and E.M. H a l t o n , Dust D e p o s i t i o n f r o m C\\mney Stacks, Proc. I n s t . Mech. Eng., 162(1950), pp. 355-367. G.H. Strom and J. H a l i t s k y , I m p o r t a n t C o n s i d e r a t i o n s i n t h e Use o f Wind Tunn e l s f o r P o l l u t i o n S t u d i e s o f Power P l a n t s , A i r R e p a i r 4(1954), pp. 24-30. M e t e o r o l o g y and Atomic Energy, AECU 3066, U.S. Atom. Energy Comm., Washington, D.C., 1955, 169 pp. E.K. Kauper, R.G. Holmes and A.B. S t r e e t , M e t e o r o l o g i c a l V a r i a b l e s and Object i v e F o r e c a s t i n g Techniques R e l a t i n g t o t h e A i r P o l l u t i o n Problem i n Los Angeles, Tech. Paper No. 15, A i r P o l l u t i o n C o n t r o l D i s t r i c t , Los Angeles, C a l i f o r n i a , 1955, 15 pp. F.N. F r e n k i e l , Atmospheric P o l l u t i o n i n Growing Communities, Smithsonian I n s t i t u t e Report f o r 1956, Washington, D.C. (1957), pp. 269-299, ( f i r s t desc r i b e d i n paper b e f o r e A i r P o l l u t i o n C o n t r o l A s s o c i a t i o n i n 1955). J.A. Maga and G.C. Hass, The Development o f M o t o r V e h i c l e Exhaust Emission Standards i n C a l i f o r n i a , J . A i r P o l l . C o n t r o l Assn., 10(1960), pp. 393-396, 414. F. P o o l e r , A P r e d i c t i o n Model o f Mean Urban P o l l u t i o n f o r Use w i t h Standard Wind Roses, I n t . J . A i r Water P o l l . , 4 ( 1 9 6 1 ) , pp. 199-211. F. P a s q u i l l , The E s t i m a t i o n o f t h e D i s p e r s i o n o f Windborne M a t e r i a l , Met. Mag. 90( 1961), pp. 33-49. F.A. G i f f o r d , Jr., Uses o f R o u t i n e M e t e o r o l o g i c a l O b s e r v a t i o n s f o r E s t i m a t i n g Atmospheric D i s p e r s i o n , N u c l e a r S a f e t y , 2(1961), pp. 47-51. G.A. B r i g g s , Plume Rise, U.S. Atomic Energy Comm., Oak Ridge, Tenn., 1969, 8 1 PP. D.B. Turner, Workbook o f Atmospheric D i s p e r s i o n E s t i m a t e s , PHS Pub. No. 999-AP26, U.S. P u b l i c H e a l t h S e r v i c e , C i n c i n n a t i , Ohio, 1967, 84 pp. TRW Systems Group, A i r Q u a l i t y D i s p l a y Model, N a t i o n a l T e c h n i c a l I n f o r m a t i o n S e r v i c e No. PB189-194, (NAPCA C o n t r a c t PH-22-68-60) , U .S. Dept. o f Commerce, Washington, D.C., 1969. Symposium on M u l t i p l e Source Urban D i f f u s i o n Models (A.C. S t e r n , ed.) - AP-86, U.S. E n v i r o n m e n t a l P r o t e c t i o n Agency, Washington, D.C., 1970, 461 pp. D. Bruce T u r n e r , Atmospheric D i s p e r s i o n M o d e l i n g - A C r i t i c a l Review, J. A i r P o l l . C o n t r o l Assn., 29( 1979), pp. 502-525 and 927-941. Mathematical Models f o r Atmospheric P o l l u t a n t s , E P R I EA-1131, (118 p p . ) ; Append i c e s A ( 9 9 pp.); B ( 8 4 pp.); C (254 pp.); D (143 p p . ) , E l e c t r i c Power Research I n s t i t u t e , P a l o A l t o , C a l i f o r n i a , 1979. Y . H o r i e and A.C. S t e r n , " A n a l y s i s o f P o p u l a t i o n Exposure t o A i r P o l l u t i o n i n New York-New J e r s e y - C o n n e c t i c u t T r i - S t a t e Region," EPA-450/3-76-027, U.S. Env i r o n m e n t a l P r o t e c t i o n Agency, Research T r i a n g l e Park, N.C., 1976, 169 pp. P u b l i c Law 95-95, U.S. Government P r i n t i n g O f f i c e , Washington, D.C., 1977. The Development o f Mathematical Models f o r t h e P r e d i c t i o n o f Anthropogenic V i s i b i l i t y Impairment, EPA-450/1-78-110, a.b.c., 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., 1979, 778 pp.
Atmospheric Pollution 198O! Proceedings of the 14th International Colloquium, Paris, France, May 5--8,1980, M.M. Benarie (Ed.), Studies in Environmental Science, Volume 8 0 Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
9
MODELING THE TRANSPORT AND DIFFUSION OF A I R POLLUTANTS USING A PROGNOSTIC
MESOSCALE MODEL R.T.
McNIDER
Alabama A i r P o l l u t i o n C o n t r o l Commission, Montgomery, AL, USA R.A.
PIELKE
U n i v e r s i t y of V i r g i n i a , C h a r l o t t e s v i l l e , V A , USA
ABSTRACT The u s e o f a t h r e e - d im e n s i o n a l ,
p r i m i t i v e e q u a t i o n , mesoscale model is examined
f o r p r e d i c t i n g t h e t r a n s p o r t and d i f f u s i o n of a i r p o l l u t a n t s i n complex flow s i t u a t i o n s such as sea b r e e z e and mountain v a l l e y c i r c u l a t i o n s .
P o l l u t a n t con-
c e n t r a t i o n s from area s o u r c e s w i t h scales l a r g e r t h an t h e model g r i d sp aci n g can be a d e q u a t e l y modeled u s i n g t h e c o n s e r v a t i o n e q u a t i o n and g r a d i e n t t r a n s f e r theory.
The
modeling o f p o l l u t a n t c o n c e n t r a t i o n s from p o i n t s o u r c e s is, however, d i f f i c u l t i n c o a r s e g r i d mesoscale models because o f n u m e r ical damping and t h e t h e o r e t i c a l inadequacy o f K-theory f o r plumes which are small compared t o t h e t u r b u l e n t scales.
To
model p o i n t s o u r c e s , a s t a t i s t i c a l p a r t i c l e d i s p e r s i o n scheme is ex p l o r ed w i t h i n t h e mesoscale model framework.
INTRODUCTION
In
sea
b r eeze f l o w s o r mountain-valley f l o w s, s t a n d a r d Gaussian d i s p e r s i o n models
are i n a p p r o p r i a t e due t o t h e u n s t e a d y n a t u r e and s p a t i a l inhomogeneity of t h e s e l o c a l
circulations.
A p r o g n o s t i c mesoscale model h a s t h e p o t e n t i a l t o i n c l u d e t h e impor-
t a n t p h y s i c a l mechanisms f o r t h e s e complex c i r c u l a t i o n s and t h u s p r o v i d e a p h y s i c a l l y c o n s i s t e n t flow f i e l d t o examine t h e t r a n s p o r t o f p o l l u t a n t s .
.In t h e f o l l o w i n g
d i s c u s s i o n , t e c h n i q u e s are o u t l i n e d u t i l i z i n g a mesoscale model f o r a i r p o l l u t i o n applications.
DISCUSSION The U n i v e r s i t y of V i r g i n i a Mesoscale Model ( r e f . 1 ) h as been employed t o s i m u l a t e t hr e e - d i m en s i o n al sea b r e e z e and t o p o g r a p h i c c i r c u l a t i o n s .
F i g u r e 1 shows p a r t i c l e
s t r e a k l i n e s i n t h e f l o w f i e l d o v e r t h e S o u t h F l o r i d a P e n i n s u l a d u r i n g a sea breeze event.
P a r t i c l e s have been r e l e a s e d from v a r i o u s p o i n t s o v er t h e p e n i n s u l a ev er y t e n
10 minutes s i n c e t h e beginning of model i n t e g r a t i o n at s u n r i s e .
Although t h e general
s y n o p t i c flow is from t h e S o u t h e a s t , t h e p a r t i c l e s r e l e a s e d on t h e West Coast a r e caught w i t h i n t h e sea breeze flow and a r e a l t e r n a t e l y c a r r i e d i n s h o r e and offshore producing a h e l i c a l p a t t e r n .
F i g u r e 1.
P a r t i c l e s t r e a k l i n e s a t 1900 LST from 300 meter release h e i g h t s .
Although t h e mean wind f i e l d is important f o r determining t r a n s p o r t d i r e c t i o n and f o r producing l a r g e scale meandering of plumes, i n c l u s i o n of t h e t u r b u l e n t s t r u c t u r e
is necessary t o make p r e d i c t i o n s of p o l l u t a n t concentrations.
For l a r g e s c a l e area
s o u r c e s and f o r plumes whose size is large i n comparison t o t h e model g r i d s c a l e and t u r b u l e n t scale, t h e conservation equation, 11, can be u t i l i z e d ;
where K is a t u r b u l e n t exchange c o e f f i c i e n t .
I n t h e c u r r e n t model, t h e advection
component is solved using an upstream s p l i n e i n t e r p o l a t i o n technique which f o r r e s o l v e a b l e s c a l e s is a highly c o n s e r v a t i v e technique.
The v e r t i c a l exchange coef-
f i c i e n t s f o r t h e convective boundary l a y e r needed i n 1 ) a r e based on a cubic polyno-
mial formulation dependent on t h e p l a n e t a r y boundary h e i g h t and s u r f a c e s i m i l i a r i t y theory. F i g u r e 2. shows suspended p a r t i c l e t r a n s p o r t and d i f f u s i o n using t h e conservation equation 1) i n a two-dimensional v e r s i o n of t h e model through a cross-section of the F l o r i d a Peninsula.
An urban s t r i p over t h e East Coast and p a r t i c l e production over
t h e rest of t h e peninsula provide a r e a sources f o r production of p a r t i c l e s i n t o t h e model atmosphere.
A t 1330 l o c a l time, t h e p a r t i c l e s are e s s e n t i a l l y w e l l mixed
w i t h i n t h e model convective boundary l a y e r .
A t n i g h t , t h e upward v e r t i c a l d i f f u s i o n
i s suppressed i n t h e s t a b l e atmosphere; and by 0530 on t h e East Coast, t h e suspended p a r t i c l e s are c a r r i e d out t o sea i n a shallow land breeze.
11
4
3
E2 r4
1
Figure 2.
Contours of p a r t i c l e c o n c e n t r a t i o n s i n a two-dimensional v e r s i o n of t h e m e s o s c a l e model. S y n o p t i c f l o w i s from t h e east ( R ) .
P o i n t s o u r c e s o f p o l l u t i o n cannot be d i r e c t l y handled i n t h e c o a r s e g r i d
mesoscale model u s i n g 1 ) due t o n u m e r i c a l damping and t h e f a c t t h a t plumes small compared t o t h e t u r b u l e n t scale d o n o t d i f f u s e i n a g r a d i e n t f a s h i o n o r a t least r e q u i r e t h e e f f e c t i v e K t o b e a f u n c t i o n of t r a v e l d i s t a n c e .
Because of t h e h i g h l y
s h e a r e d environment and u n s t e a d y c h a r a c t e r of t h e l o c a l c i r c u l a t i o n s , t h e s u b g r i d
scale d i s p e r s i o n cannot be e a s i l y p a r a m e t e r i z e d u s i n g a n a l y t i c a l methods.
An a l t e r -
n a t i v e t h a t w e are c u r r e n t l y u t i l i z i n g is a c o n d i t i o n e d p a r t i c l e d i s p e r s i o n scheme ( r e f . 2 ) based upon T a y l o r s ' 1921 theorem for p a r t i c l e d i s p e r s i o n i n which t h e par-
t i c l e v e l o c i t y , "p is expressed by up
=
u +
u'
2)
where 5 is t h e mesoscale wind, u' is a t u r b u l e n t component g i v e n by u'(t
+ T)
=
u ' ( t ) R(T)
+ U"
3)
and utl is a random component dependent upon t h e t u r b u l e n t energy,U,, and t h e autoc o r r e l a t i o n f u n c t i o n R. The u s e of t h i s scheme r e q u i r e s a n estimate o f a , and R
12 c o n s i s t e n t w i t h t h e model boundary l a y e r .
T h i s is accomplished f o r t h e vertical
component by u s i n g
where A,
is t h e s p e c t r a l peak i n t h e v e r t i c a l component and
d i c t e d exchange c o e f f i c i e n t .
The parameter
A,
I$,,
is t h e model pre-
is r e l a t e d t o h e i g h t and i n t h e l i m i t
t o t h e model p r e d i c t e d boundary l a y e r h e i g h t i n t h e c o n v e c t i v e boundary. F i g u r e 3. shows modeled deduced Ow v a l u e s s c a l e d a p p r o p r i a t e l y f o r comparison with estimates of The results look promising, and it is f e l t t h a t t h e u s e of
from f i e l d o b s e r v a t i o n s .
t h e p a r t i c l e d i s p e r s i o n scheme a l o n g w i t h t h e p r o g n o s t i c mesoscale model c a n be u t i l i z e d t o examine p o l l u t a n t b e h a v i o r i n l o c a l c i r c u l a t i o n s .
Irwin 11919)
Model . Wangara 33 1400 LSl
.I
.5
1.0
WW.
F i g u r e 3.
Model e x t r a c t e d aw f r o m a s i m u l a t i o n of Day 33 of t h e Wangara experiment. W, i s t h e c o n v e c t i v e v e l o c i t y and Zi i s t h e p l a n e t a r y boundary h e i g h t . S o l i d l i n e and dashed l i n e are composites of f i e l d o b s e r v a t i o n s .
ACKNOWLEDGEMENTS The a u t h o r s would l i k e t o thank t h e i r c o l l e a g u e s a t t h e U n i v e r s i t y of V i r g i n i a and Dr. S t e v e n Hanna f o r t h e i r h e l p i n t h i s r e s e a r c h and Ms. Linda Geddie who typed t h e m a n u s c r i p t . T h i s r e s e a r c h sponsored through U.S. Grant No. R80627010.
Environmental P r o t e c t i o n Agency
REFERENCES 1 Mahrer, Y., and R. A. P i e l k e , The effects o f topography on t h e sea and l a n d b r e e z e s i n a two-dimensional n u m e r i c a l model.Mon. Wea. Rev., I&, (1977) 1151-
1162. J. 2 Hanna, S.R., Some s t a t i s t i c s of Lagrangian and E u l e r i a n wind f l u c t u a t i o n s , Appl. Meteor., l8, (1979) 518-531. 3 I r w i n , J.S., E s t i m a t i n g plume d i s p e r s i o n A recommended g e n e r a l i z e d scheme. F o u r t h Symposium on Turbulence, D i f f u s i o n and Air Q u a l i t y , American M e t e r o l o g i c a l S o c i e t y . Reno, Nevada, 1979.
-
AtmosphericPollution 1980, Proceedingsof the 14th International Colloquium,Paris, France, May 5-8,1980, M.M. Benarie (Ed.), Studies in Environmental Science,Volume 8 0 Elsevier Scientific Publishing Company,Amsterdam - Printed in The Netherlands
13
COMMUTER EXPOSURE MODELING PART 11: EMISSIONS AND DISPERSION MODULES AND GENERATION OF EXPOSURE STATISTICS P. B. SIMMON and R. M. PATTERSON SRI International, Menlo Park, CA 94025 (U.S.A.) and W. B. PETERSEN U.S. Environmental Protection Agency, Research Triangle Park, NC
2 7 7 1 1 (U.S.A.)
ABSTRACT A model methodology has been designed to compute commuter exposure statistics
through simulation of the traffic, vehicular emissions, and atmospheric dispersion of roadway-related air pollutants. A detailed description of the emissions and dispersion elements of the commuter exposure modeling methodology and a discussion of the results generated by the model are presented in this paper; the traffic
element of the methodology is discussed in a companion paper. The commuter exposure model's emissions module incorporates two emissions methodologies: a treatment based on average route speed, and one that considers the effects of driving mode changes. Dispersion of pathway emissions is simulated by two separate dispersion treatments, while dispersion from nonpathway sources is computed with the simple Hanna-Gifford model.
The model produces a number of statistics describing annual average or short-term worst-case exposure. INTRODUCTION
This is the second (Paper 11) of two papers describing the development of a computer model of commuter exposure to air pollution. The modeling methodology requires the model user to define the major commute corridors or "pathways" in a metropolitan area. The computer model reads traffic and roadway characteristics of the pathways, general information regarding traffic and emissions on the remainder of the roadway network, and various meteorological data. This information is used by the three major modules of the model to simulate traffic flow, compute vehicular emissions, and calculate the atmospheric dispersion of roadway-related air pollutants. Various statistics describing pathway exposures (concentration integrated with time over the length of the pathway) are the output of the model.
Paper I gives an overview
of the model methodology and describes the computer model's traffic flow computa-
tion module.
This paper continues the discussion with a description of the emission
14 rate computation module, the dispersion module, and the methodology used to generate exposure statistics. EMISSION RATE COMPUTATIONS Emission rates for each pathway segment and grid square are computed using one of two types of emission treatments:
a treatment based on the average route speed
and one that considers the effects of driving mode changes on emissions. The first treatment is the EPA methodology based on the Federal Test Procedure (FTP) (ref. 1). The second treatment is the "Automobile Exhaust Emission Modal Analysis Model," (ref. 2) or modal model.
Emissions modeling along pathways requires both treat-
ments; FTP-based emissions estimates are suitable for nonpathway sources. Emission rates (Q) for pathway segments that are freeways, expressways, or arterials outside the central business district (CBD) are found by multiplying an emission density, E, computed using the FTP methodology and chosen according to the average route speed on the segment, by the demand volume (V) on the segment. To compute the average emission rate over a segment having congested flow, it is convenient to break the emissions into two components:
those occurring during
normal flow, E, and the excess over normal flow emissions that occur during congested flow, E'-E,
where E' represents the emissions during congested flow. The
component of total emissions due to uncongested flow is given by Q, with E chosen according to the average route speed on the uncongested portion of the segment. The average emission rate over the pathway segment is the sum of the components due to uncongested (Q) and congested (Q')
flow, as given by:
where E' corresponds to an average route speed of 20 mi/h,
i is the number of
vehicles affected by the backup, L = segment length (m), Lq = backup length (m), and
+
is the duration (seconds) of the backup.
Travel on arterials within the CBD is characterized by interrupted flow and low speeds, and a modal emissions treatment should be used.
This is available
through an adaptation of EPA's modal model. The modal model determines an instantaneous emission rate, e(t>, which is a function of vehicle speed, v, and acceleration, a. Acceleration to or from a given speed is assumed to be a perturbation to the steady-state emission rate. For the commuter exposure model, simulation of the effects of modal emissions is facilitated through the introduction of the concept of excess modal emissions. Excess modal emissions are those that occur over and above those that would have
15 occurred had the vehicle not stopped. The total excess emissions, EE(g/m/s),
the
sum of idle emissions, and the acceleration and deceleration parts of the excess emission, Em, may be expressed as
Where N = number of vehicles in the backup; b10 = constant (g/s), D = delay
(s),
P = proportion of vehicles stopped for the signal, and Cy = signal cycle length
(s)
The cruise emissions that would have occurred had the vehicle not stopped are found by integrating the modal model expression for the steady-speed emission rate over 4 T. The cruise emissions component may be calculated by E = C
6 V/3600 v 1609.344/3600
(G
)
(3)
where 1609.344 is the number of meters in a mile. Once emissions are calculated with the modal treatment, they are averaged for each pathway segment. DISPERSION MODELING Dispersion of Pathway Emissions For the purpose of computing the dispersion of vehicular emissions on commute pathways, limited-access and nonlimited-access pathway segments are distinguished from segments located in a street canyon. The dispersion of pollutants emitted by vehicles on both limited-access and nonlimited-access roadways is computed using a technique taken from the CALINE 2 (ref. 3) dispersion model. The model formulation is based on the treatment of pollution dispersion as the vector sum of two components: dispersion occurring along the horizontal wind component oriented perpendicular to the roadway, and dispersion along the horizontal wind component parallel to the roadway. The parallel wind model assumes that the roadway is divided into a series of square area sources as wide as the roadway. The concentration downwind of the area source is computed as if the emissions originated from a virtual source located upwind of the area source, at a distance that forces the model to assume a uniform concentration within a mixing cell over the roadway. The equation used to compute the concentration from each area source is:
3 where X = concentration from parallel dispersion (g/m ) , U = wind speed (m/s), P Q k = line-source emission rate (g/m/s), W = roadway width (m), 8 = angle between
16
wind direction and roadway, y = perpendicular distance between receptor and roadway edge plus an initial dispersion parameter (m), z above grade-level (m),
0
Y
=
height of the receptor
= horizontal dispersion function (m), and o
= vertical
dispersion function (m). The concentrations from each area source are summed to give the parallel component, which is then corrected by a stability-dependent factor. The cross-wind or normal component of concentration is given by
xn
=
O
iexp [- (31I $
U
(5)
3
where X = concentration from normal dispersion (g/m ) n
.
The parallel and crosswind components are summed to give the total concentration when
€Iis
non-zero.
Dispersion on a roadway with tall buildings on both sides is greatly influenced by the presence of the buildings.
The street-canyon dispersion treatment used in
the commuter exposure model is based on the empirical street-canyon model developed by Johnson et al. (ref. 4 ) and modified by Ludwig et al. (ref. 5 ) .
For the commuter
exposure model, the concentration on the roadway (X) was assumed to be the average of the expressions for the concentrations on the windward and leeward sides of the street, as given by KQk
x=
2(U+0.5)
where Q,
=
(h
+
$)
line-source emission rate (g/m/s), K
=
empirically derived nondimensional
constant =2 m, and W = street width (m). Segment pollutant concentrations are summed for each pathway and integrated over travel time to yield pathway exposures. Dispersion of Nonpathway Source Emissions It is expected that the portion of the total pathway integrated concentration (exposure) that results from nonpathway sources will be small in comparison to the portion resulting from traffic on the commuter pathways themselves. Therefore, a very simple emissions and dispersion treatment is used. The line-source emissions on nonpathways have been aggregated into area-source emissions from grid squares. For each pathway segment a concentration is computed, according to the so-called Hanna-Gifford (ref. 6 ) dispersion treatment, at receptors
17 located at the endpoints and the midpoint of the segment. These concentrations
(X) are given by
where C
=
$ $&
;
Qo= emission rate of the grid square in which the receptor is located (g/m2 /s),
U
=
wind speed (m/s), D
=
city size, and a and b are stability-dependent constants.
The normalized integrated concentration over the segment (the exposure E) is found by performing a stepwise integration over travel time from one endpoint to the midpoint and the midpoint to the other endpoint of the segment. The model computes exposures for all segments of a pathway and sums the results to yield the pathway exposure resulting from nonpathway sources. On-Roadway/In-Vehicle Concentration Relationship The little information that exists about the relationship between the concentration on the roadway and the concentration within a vehicle indicates that concentrations of CO inside a vehicle are about equal to that on the outside. Therefore, the commuter exposure model assumes the concentrations at the two locations are identical. Generation of Commuter Exposure Statistics Exposures are computed for each pathway according to the meteorological conditions of the mode of model operation chosen by the model user.
If the short-term
mode is chosen, one exposure is computed for each pathway, for the input meteorological conditions and traffic information. If the model is operating in the annual mode, morning and evening exposures are computed for each pathway for 576 sets of meteorological conditions (each combination of 6 wind speeds, 16 wind directions, and 6 atmospheric stability classes).
These exposures are weighted according to
the frequency of occurrence of each set of conditions and summed for each pathway. I n ad-ditinr!to the exposures, the model stores the total travel time or times on
each pathway and the average number of commuters using the pathway. When the model is run in the short-term mode, the output includes a list of the exposure on each pathway for the input worst-case meteorological and traffic conditions and the average and standard deviation of pathway exposure. When the model is in the annual mode it lists the annual average exposure on each pathway and over the modeled region. For either mode, the model produces data for two histograms. For the short-term mode the data pertain to a single commute; for the annual mode, the data are representative of annual variations. First, the range of exposures
18 found on all pathways is divided into several classes. Then for each class, two parameters are listed:
the percentage of the commuting population (commuting
vehicles multiplied by the average number of commuters per vehicle) treated by the model that experience exposure levels in the class, and the probability of experiencing the exposure levels in the class (i.e., the percentage of time commuters are exposed to the levels of the exposure class). may be output at the user's discretion.
Subsets of these statistics
Finally, the model user may call for
model output in grahical form. For a summary of model output, the reader is referred to Part I, Overview. ACKNOWLEDGEMENTS This work was supported by the U . S .
Environmental Protection Agency under
Contract No. 68-02-2754. REFERENCES 1 Mobile Source Emission Factors, Final Document, Environmental Protection Agency, Office of Transportation and Land Use Policy, Washington, D.C., 1978. 2 Modal Program Guide, an update to Automobile Exhaust Emission Modal Analysis Model, U.S. EPA Report No. EPA-46013-74-005, 1974. 3 K.E. Noll, T.L. Miller, and M. Claggett, A Comparative Analysis of EPA HIWAY, California, and CALINE 2 Line-Source Dispersion Models, submitted to Transportation Research Board, Washington, D.C., 1976. 4 W.B. Johnson, W.F. Dabberdt, F.L. Ludwig, and R.J. Allen, Field Study for Initial Evaluation of an Urban Diffusion Model for Carbon Monoxide, Comprehensive Report, CRC and Environmental Protection Agency (EPA) Contract CAF'A-3-68 (1-69), SRI International, Menlo Park, CA, 1971. 5 F.L. Ludwig and W.F. Dabberdt, Evaluation of the APRAC-1A Urban Diffusion Model for Carbon Monoxide, Final Report, CRC and EPA Contract CAPA-3-68 (1-69), SRI International, Menlo Park, CA, 1972. 6 S.R. Hanna, A Simple Method of Calculating Dispersion from Urban Area Sources, J. Air Pollution Control Assoc. 21, pp. 774-777, 1971.
Atmospheric Pollution 1980, Proceedings of the 14th InternationalColloquium,Pans, France, May 5-8,1980,M.M. Benarie (Ed.),Studies in Environmental Science, Volume 8 0 Elsevier Scientific PublishingCompany,Amsterdam - Printed in The Netherlands
19
COMMUTER EXPOSURE MODELING PART I: OVERVIEW AND TRANSPORTATION MODULE
R. M. PATTERSON and P. B. SIMMON SRI International, Menlo Park, CA
94025 (U.S.A.)
and
W. B. PETERSEN U.S. Environmental Protection Agency, Research Triangle Park, NC
27711 (U.S.A.)
ABSTRACT Recent concern over commuter exposure to high levels of roadway-related air pollutants, the projected increase in the number of diesel-powered passenger vehicles, and the demonstrated inadequacy of fixed monitoring stations in replicating commuter exposure have prompted research in this area. This paper presents the development of new methodological tools for identifying, predicting, and analyzing commuter exposure to motor vehicle generated air pollutants.
Commuter exposure modeling is
of interest to those involved in regulation, monitoring, planning, and health effects research. The approach was to build a methodology based on three distinct modules treating traffic flow, emissions, and dispersion.
This paper deals in
detail with the first module; the second two are discussed in "Part 11:
Emissions
and Dispersion Modules and Generation of Exposure Statistics."
INTRODUCTION This is the first (Paper I) of two papers describing the development of a computer model of commuter exposure to air pollution.
Those concerned with air qualit:
assessment are increasingly recognizing the inadequacy of fixed point monitoring data for characterizing the pollutant exposure of various population groups. The spatial variation of concentrations over short distances is recognized to be sufficiently great for some pollutants that concentration measurements made at fixed locations are not necessarily representative of the concentrations to which people, as moving receptors, are exposed.
Since the objective of air quality
regulation in general is to protect the health of people, the air quality assessment community has realized that simulation modeling should be directed toward modeling pollutant concentrations at the locations where people spend time, and considering the amount of time spent at each location. Thus, it is being
recognized that the quantity of real concern is not concentration, but rather exposure, which implies the interaction of a concentration and a (human) receptor, and that the population group experiencing the highest potential exposure to automobile-related pollutants is commuters.
To assess commuter exposures, the
U.S. Environmental Protection Agency commissioned a study (ref. 1) to develop methodologies for modeling commuter exposure using both computer and manual techniques.
The result was a recommendation for a modularized treatment of traffic,
emissions, and dispersion that reflected the current state of the art, but which also lent itself to relatively easy revision as modeling sophistication advanced in each of the three modules. The key element was the computer model; the manual model would be based on the computer model and consist of a series of nomographs.
This paper, which presents
the computer modeling methodology, provides an overview of the commuter exposure model and a discussion of the traffic flow module.
The emissions and dispersion
modules are presented in a second, companion paper. OVERVIEW The commuter exposure model has been designed in a modular format to facilitate the understanding of the code, to reduce the possibility of coding error and ease debugging, and to make modification relatively easy for the user.
However, the
crux of the commuter exposure modeling problem is defining the modeling area, and the most critical aspect in defining the modeling area is choosing the appropriate commuter pathways.
The commuter exposures that are calculated and the statistics
that are derived all depend directly on the pathways that are defined.
Choosing
the pathways might then be considered as a fourth module of the commuter exposure model, and it is the first to be exercised. For the problem to be manageable, a reasonable number of major commuting routes or pathways must be defined.
The commuter exposure model is designed to accommodate
up to 25 pathways having the highest numbers of vehicle miles of travel (VMT) by commuters. While it is recognized that these pathways will not carry all commuters, they will include the commuters at risk of experiencing high exposures. Most of the extensive commuting will be done along the defined pathways, both i n time and distance, and the pathways will by definition carry high volumes of traffic. A l though their total number may be close to that on the pathways, the commuters "missed" will, on the average, be traveling shorter times and distances on less heavily traveled roads.
They are not considered to be at risk to high pollutant
exposures during their commute. Commuting trips are not begun (for a morning commute) on the commute pathways as defined here, but rather on local surface streets and "collectors."
To handle
21 t h e exposure d u r i n g t h e approach t o and d e p a r t u r e from t h e pathway, minor pathways a r e used t h a t a r e r e p r e s e n t a t i v e of t h e t r a v e l t o and from t h e r o u t e .
Likewise,
a t t h e end of a (morning) commute, ending r o u t e s a r e s p e c i f i e d t h a t a r e r e p r e s e n t a The p r o c e s s i s r e v e r s e d
t i v e of t r a v e l from t h e major pathways t o work l o c a t i o n s . f o r t h e evening commute.
T r a f f i c on roadways o t h e r t h a n pathways i s t r e a t e d by a l l o c a t i n g VMT on a g r i d square b a s i s ( r e f . 2).
T h i s approximation i s made because t h e major c o n t r i b u t i o n
t o p o l l u t a n t c o n c e n t r a t i o n s on a pathway i s made by t h e v e h i c l e s t r a v e l i n g on t h e pathway i t s e l f .
The g r i d d e d street network i s d i v i d e d i n t o t h e primary network,
which i n c l u d e s roadways f o r which t r a f f i c volume i s a v a i l a b l e , and t h e secondary network, which i n c l u d e s t h e remaining roadways.
The VMT on t h e secondary network
a r e assumed t o b e a f u n c t i o n of t h e primary network t r a f f i c and l o c a l e .
The
gridded t r a f f i c d a t a a r e s u p p l i e d by t h e u s e r . The model i s designed t o be used i n a s h o r t - t e r m mode s i m u l a t i n g a s i n g l e commute p e r i o d , and i n a n a n n u a l mode t h a t s i m u l a t e s a n a v e r a g e commute over a y e a r .
A number of d a t a a r e g e n e r a t e d f o r each mode of o p e r a t i o n .
For t h e short-term
mode t h e s e a r e A l i s t of exposures on each pathway.
The a v e r a g e and s t a n d a r d d e v i a t i o n of exposures on pathways i n t h e modeling region. The p e r c e n t a g e of commuters i n each of s e v e r a l exposure c l a s s e s . For t h e a n n u a l mode t h e y a r e The p e r c e n t a g e of commuters i n each of s e v e r a l exposure c l a s s e s f o r each pathway and f o r a l l pathways. The p r o b a b i l i t y of e x p e r i e n c i n g exposure l e v e l s i n each of s e v e r a l exposure c l a s s e s f o r each pathway and f o r a l l pathways. The pathway c o n c e n t r a t i o n a s a f u n c t i o n of m e t e o r o l o g i c a l c o n d i t i o n s . Pollution roses. The exposure on each pathway and o v e r modeled r e g i o n .
TRAFFIC MODULE The t r a f f i c module of t h e commuter exposure model h a n d l e s two s e p a r a t e t r a f f i c flow regimes:
u n i n t e r r u p t e d f l o w and i n t e r r u p t e d flow.
T r a v e l on expressways i s
g e n e r a l l y u n i n t e r r u p t e d , a l t h o u g h d u r i n g a backup t h e flow can become s e v e r e l y c o n s t r a i n e d t o t h e p o i n t of becoming " s t o p and go."
I n t e r r u p t e d flow d e s c r i b e s
t r a v e l on a r t e r i a l s w i t h t r a f f i c s i g n a l s a t t h e i n t e r s e c t i o n s .
(Intersections that
have s t o p s i g n s a r e n o t c o n s i d e r e d , s i n c e t h e y w i l l n o t b e p r e s e n t f o r t h e main t r a f f i c flow on a n a r t e r i a l , commuter pathway.) t h o s e elements t h a t d e s c r i b e t h e t r a f f i c flow.
The f o l l o w i n g d i s c u s s i o n d e t a i l s
22 U n i n t e r r u p t e d Flow The c h a r a c t e r i s t i c s of u n i n t e r r u p t e d f l o w can b e o b t a i n e d from two parameters: demand volume (V) and f r e e - f l o w c a p a c i t y (C) of t h e road segment. some form are r e q u i r e d i n p u t s .
Volume d a t a i n
Data i n t h e form of a v e r a g e d a i l y t r a f f i c (ADT) o r
a n n u a l a v e r a g e d a i l y t r a f f i c (AADT) are converted t o h o u r l y v a l u e s through d i u r n a l and s e a s o n a l d i s t r i b u t i o n s , which may b e s u p p l i e d by t h e u s e r o r obtained through d e f a u l t v a l u e s i n t h e model.
Capacity d a t a may a l s o b e u s e r - s u p p l i e d ,
otherwise
t h e model assumes d e f a u l t v a l u e s a p p r o p r i a t e t o t h e v a r i o u s t y p e s of roadways. T r a v e l speed i s i m p o r t a n t f o r e s t i m a t i n g v e h i c l e p o l l u t a n t emissions along t h e pathways and f o r c a l c u l a t i n g t r a v e l t i m e , which i s t h e n used i n t h e exposure and dose c a l c u l a t i o n s .
Again, speed may b e i n p u t by t h e u s e r .
I f i t i s n o t , t h e model
c a l c u l a t e s speed on each pathway segment a s a f u n c t i o n of volume, c a p a c i t y , and t h e t y p e of roadway. Freeway Backup When demand exceeds c a p a c i t y , a t r a f f i c backup may o c c u r .
For t h e purposes of
commuter exposure modeling, a simple model was developed t o e s t i m a t e t h e s i z e of a backup and t h e a v e r a g e d e l a y t h a t i t would c a u s e .
The s t a r t i n g p o i n t i s an
e x p r e s s i o n s t a t i n g t h a t t h e r a t e of growth of t h e backup e q u a l s t h e d i f f e r e n c e i n demand minus c a p a c i t y :
where n i s t h e number of v e h i c l e s i n t h e backup, t i s t i m e , and q and s a r e t h e demand and c a p a c i t y i n v e h i c l e s p e r u n i t t i m e .
The t o t a l number of v e h i c l e s a f -
fected is then
where N’
i s t h e t o t a l number a f f e c t e d w h i l e demand exceeds c a p a c i t y , and t h e expres
s i o n i s e v a l u a t e d a f t e r demand f a l l s below c a p a c i t y .
The a v e r a g e d e l a y i s c a l c u l a t
by D = - k NeL v N
(3)
where k i s t h e d i s t a n c e between v e h i c l e s , v i s t h e t r a v e l s p e e d , and k / v i s t h e time headway.
23 I n t e r r u p t e d Flow I n t e r r u p t e d f l o w p e r t a i n s t o t r a f f i c c o n d i t i o n s when movement i s r o u t i n e l y s t o p p e d , o r i n t e r r u p t e d , f o r a f i n i t e p e r i o d of t i m e .
For t h e commuter exposure
model, o n l y two c a u s e s of i n t e r r u p t e d f l o w need b e c o n s i d e r e d :
signalized inter-
s e c t i o n s and t o l l b o o t h s , where t r a f f i c goes through mode changes from c r u i s e t o d e c e l e r a t i o n , i d l e , a c c e l e r a t i o n , and back t o c r u i s e .
Emissions, and hence con-
c e n t r a t i o n s , and t i m e s of e x p o s u r e are i n f l u e n c e d by t h e s e mode changes. Because of v e h i c l e e m i s s i o n c h a r a c t e r i s t i c s , t h e a v e r a g e r o u t e speed methodology used f o r freeways i s u s e d f o r a r t e r i a l s o u t s i d e of t h e c e n t r a l b u s i n e s s d i s t r i c t (CBD)
.
A more thorough a n a l y s i s i s w a r r a n t e d f o r CBD pathway segments.
Calculations
must be made o f d r i v i n g mode c h a n g e s , t h e p r o p o r t i o n of v e h i c l e s changing modes, and t h e l e n g t h of t i m e s p e n t i n t h e d i f f e r e n t modes.
Basically, t h i s requires a
c a l c u l a t i o n of queue l e n g t h s and d e l a y a t i n t e r s e c t i o n s .
The p a r a m e t e r s r e q u i r e d
are demand volume, c a p a c i t y , and t h e t r a f f i c s i g n a l p a r a m e t e r s of c y c l e l e n g t h and l e n g t h of t h e g r e e n (go) p h a s e . o r have t h e model c a l c u l a t e them.
The u s e r may choose t o i n p u t t h e s i g n a l parameters Queue l e n g t h and d e l a y d a t a can t h e n be used t o
c a l c u l a t e modal e m i s s i o n s . Once c a p a c i t y , volume, and t h e s i g n a l p a r a m e t e r s a r e known, t h e p r o p o r t i o n of v e h i c l e s t h a t s t o p f o r a s i g n a l i s g i v e n by
P =
1-GICy l-V/Cs
(4)
where G i s t h e l e n g t h of t h e g r e e n p h a s e , Cy i s t h e s i g n a l c y c l e l e n g t h , V i s t h e h o u r l y demand volume, and C s i s t h e c a p a c i t y service volume p e r hour of green. The number (N) of v e h i c l e s s u b j e c t t o queueing d e l a y i s
N =
P
v cy 3600
(5)
w h i l e t h e maximum l e n g t h of t h e queue (Lq, meters) i s
where 8 i s t h e d i s t a n c e ( m e t e r s ) occupied by e a c h queued v e h i c l e and M i s t h e number of l a n e s i n t h e approach.
On t h e a v e r a g e , a s t o p p e d v e h i c l e w a i t s one-half
the
l e n g t h of the r e d ( s t o p ) p h a s e , s o t h e a v e r a g e d e l a y t o t h e s e v e h i c l e s i s
D = 0.5 (Cy-G)
.
(7 1
24
For toll booths, the methodology is different because and wait to be served.
vehicles must stop
The average number of vehicles waiting to leave a toll
booth is computed from classical queueing theory as
The queue length in meters is Lq
=
8N M
(9)
’
The average delay for vehicles at a toll booth is the queue length (vehicles) multiplied by the average service rate, or the inverse of capacity: N D = - 3600 . C
(10)
The methodology presented here has been demonstrated for air pollution work in a number of studies (refs. 3,4).
While there are other more complicated methods
of handling traffic flow modeling, the present approach has been found to be quite suitable for air pollution work.
The basic outputs of the traffic module--speed,
volume, travel time, and modal behavior--are those required by the emissions and dispersion modules to calculate commuter exposure. ACKNOWLEDGEMENT This work was supported by the U.S. Environmental Protection Agency under contract No. 68-02-2754. REFERENCES
1 P.B. Simmon and R.M. Patterson, Commuter Exposure Modeling Methodologies, Report No. EPA-600/4-79-010, U.S. Environmental Protection Agency, Research Triangle Park, NC 27711, February 1979. 2 F.L. Ludwig et al., Users Manual for the APRAC-2 Emissions and Dispersion Model, Final Report, EPA Contract No. 68-01-3807, SRI International, Menlo Park, CA 94025, 1977. 3 R.M. Patterson and F . A . Record, Monitoring and Analysis of Traffic and Carbon Monoxide Concentrations at Oakbrook, Report No. EPA-450/3-74-058, U.S. Environmental Protection Agency, Research Triangle Park, NC 27711, 1974. 4 R.M. Patterson, Air Quality Modeling at Signalized Intersections, Conference on State of the Art of Assessing Transportation-Related Air Quality Impacts, Transportation Research Board, National Academy of Sciences, Washington, D.C., October 22-24, 1975.
Atmospheric Pollution 1980, Proceedings of the 14th International Colloquium, Paris, France, May 5-8,1980, M.M. Benaxie (Ed.), Studies in Environmental Science, Volume 8 0 Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
APT
-
25
A COMPUTER PROGRAM FOR THE NUMERICAL SOLUTION OF PROBLEMS IN ATMOSPHERIC
DISPERSION
A J H GODDARD, A GHOBADIAN, AND A D GOSMAN, Mechanical Engineering Department, Imperial College, London. C HARTER AND G D KAISER, UK Atomic Energy Authority Safety and Reliability Directorate
ABSTRACT APT (Atmospheric rollution Transport) is a computer program for predicting the dispersal of non-buoyant plumes emanating from point or line sources in a two-dimensional turbulent boundary layer.
The governing partial differential
conservation equations are sblved by means of a marching finite-difference procedure and incorporate a second-order closure turbulence model, with allowance for anisotropy and thermal-stratification effects.
The methods adopted
are briefly described in this paper, as is the application of the code to an example problem involving dispersal over terrain with downwind changes in surface roughness and heat flux.
INTRODUCTION The Safety and Reliability Directorate of the United Kingdom Atomic Energy Authority has sponsored the Mechanical Engineering Depalrtment at Imperial College to develop and assess a method for the prediction of the atmospheric dispersion of radioactive material downstream of the source, using numerical schemes and physical models that had previously proved successful in several engineering applications.
This work has now been completed (ref.1) and it is felt that it
is appropriate to report on the present state of the project, including details of the method used, the applications and possible future improvements. The dispersion method has been incorporated into a computer program, APT (Atmospheric Pollution Transport), which may be used to predict the dispersal of passive plumes emanating from point or line sources in a two-dimensional turbulent boundary layer.
The method solves the governing time-averaged partial
conServation equations by means of a marching finite-difference procedure with the effects of turbulence simulated by way of a second-order closure turbulence model, which also allows for anisotropy and thermal-stratification effects on
26
on both the flow and concentration fields. The formulation of the equations is outlined as is the numerical finite-difference procedure for solving them. It is intended that APT should be used in nuelear safety studies in some circumstances in which it is not appropriate to employ a simplified Gaussian model such as is found in consequence modelling codes(ref.2).€n
particular APT can allowwind
speed, surface roughness and heat flux to change as a function of distance downwind and carries no restriction on the initial source height.
The code also contains pro-
vision for simulating deposition via a source depletion model, but this aspect will not be described in the present paper.
An example of these capabilities is given in
the form of a prediction of the release of a plume into a stably-stratified atmosphere over open countryside and its subsequent behaviour as it crosses increasingly rougher and hotter surburban, and then urban, terrain. In conclusion, a brief summary of the paper is given and other areas of application and possible further improvements are indicated.
OUTLINE OF METHOD Basic assumptions and restrictions In the interests of economy, two key assumptions were made at the outset of the development of the APT method, one being that the flow and dispersal processes are amenable to the usual time-averaging employed in turbulence theory, and the other that the flow behaves as a two-dimensional boundary layer.
The former assumption (which is
inherent in Gaussian models) allows direct calculation of the time-averaged behaviour and thereby reduces the computational burden: however, as discussed later it does imply the need for special practices to allow for long-term meteorological effects such as changes in mean wind direction.
As for the second assumption, this too considerabl)
reduces the computer requirements from what would otherwise be a three-dimensional flow calculation, but also at a price: thus, for example buoyant plumes cannot be represented in this context (although overall thermal stratification effects may,and are).
It should be emphasised however that neither assumption is essential and indeed
the consideration of buoyant plumes is already underway as part of a separate study.
Governing Equations Within the present framework the dispersion problem may be represented mathematically in terms of the governing equations of motion and thermal energy for a steady two-dimensional fully-turbulent boundary layer, viz:
a (,Pu~T) /ax, + a ( P U ~ T /ax3 )
=
-a (
P ~ T/ax3 )
(3)
27
and the conservation equation f o r the three-dimensional field of plume material: + a(Pu3c)/ ax3 =
a(Pu1c)/
- a ( P u i i ) /ax2 - a (PUT) / ax3
(4)
where: U,T and C stand for time-average values of velocity, temperature and plume concentration respectively and the lower-case versions represent fluctuations about these averages; subscripts 1,2 and 3 refer in turn to the downwind, lateral and vertical directions; p is the static pressure and p the air density; and the overbar denotes time averaging, A key feature of the method is the manner of determining the additional unknowns pu73,pu3T,pu3C and
prc 2
arising from the time-averaging process: these represent, re-
spectively, the turbulent fluxes of momentum, thermal energy and plume material in the vertical direction, and the counterpart of the latter in the lateral direction.
Un-
fortunately space does not permit details to be given here of tkdevelopment of the equations for these, nor can they be quoted, for they are lengthy.
All that can be
said is that the fluxes are deduced from mathematical models (refs 3-5) of the turbulent transport processes, which under the present circumstances, allow them to be calculated from solution of two additional differential transport equations of the general form of (3) above for the time-averaged turbulence energy k and its dissipation rate
E,
together with algebraic relations connecting the fluxes to these and
other dependent variables of the set (I) to (4).
An important aspect of the equations
is that the anisotropies of the turbulent diffusivities emerge naturally, as do likewise influences of thermal stratification. the cited references (ref.1)
Complete details are available in one of
.
Numerical Solution Procedure Since under the boundary-layer assumptions Ul is everywhere positive and diffusion in the windward direction is negligible by comparison with convection (the relevant diffusion terms therefore having been omitted from the foregoing equations) the system of equations to be solved is parabolic in the x i direction and consequently amenable to a downwind-marching finite-difference method of solution, which is the approach adopted in APT, With such methods, the differential equations are transformed by finite-difference analysis into algebraic versions which link the values of the dependent variables at the nodal points of a computational grid, of the kind shown in Fig.1, the resulting equations being typically of the form: D aCQC =zan+nD + + s
(5)
all n where
+
stands for any of the variables U1,U2, T I C, k and
E;
the superscripts D and
U respectively refer to a particular Downstream cross-sectional plane of nodes and its
Upstream neighbours; the -
subscript
C
stands for the Central node of a typical cluster
in either plane and the summation C is over its nearest neighbours; and the a’s and S contain the combined effects of convection, diffusion and internal sources. Given a
28
starting field of
$u's, the sets of simultaneous equations (5) written for each vari-
able at all nodes are easily solved for the
$ J ~ ' S ,and
the resulting solution is then
available as the 'upstream' field for the next forward step in the x1 direction; and
so on. The foregoing entirely conventional practices are followed in APT, as is also the,,practiceof adjusting the dimensions of the grids in the cross-stream plane during the marching process so as just to encompass the region of significant gradients in the $Is.
An
important novelty (ref.1) is however the use of a separate smaller embed-
ded grid for the plume concentration calculations, as indicated in Fig.1.
Thisis done
out of recognition that the plume dimensions are often significantly smaller than those of the atmospheric boundary layer, thus entailing quite different grid spacings for optimum accuracy and economy.
Interpolation is employed to transfer velocity and dif-
fusivity information from the large grid onto the smaller one. APPLICATION Example problem The example that has been chosen to illustrate some of the useful features ofthe
APT program is that of the transport of a radioactive plume over consecutive regions of rural, suburban and urban terrain, each exhibiting different characteristic values of meteorological roughness and ground sensible heat flux, This use of the code in this context serves to demonstrate the capability to simulate varying surface conditions and the importance of doing this is reinforced by a second calculation in which the rural conditions are imposed throughout, as might be done in the equivalent conventional Gaussian plume representation. The specific conditions imposed are as follows: the notional radioactive pollutant,is assumed not to decay and is released at a constant rate from a 100 m elevated source into a nominal 8 m/s wind which has developed from an initially neutral 1 km deep atmospheric layer (this specification providing the starting conditions for the calculations) over a 20 km upstream fetch of rural terrain with a ground heat flux of
-
lo W/m2 and roughness length of 0 . h .
These conditions give a stably-stratified
atmosphere corresponding to Pasquill weather category E, according to the curves derived by Smith (ref.6).
The surface conditions remain at the rural levels for a fur-
ther 2 km downstream of the source, at which point a 2 km stretch of suburban terrain is encounter.,d. Data for- typical UK cities (ref.7) show that appropriate levels for sensible heat flux and surface roughness over such terrain are 10 W/m2 and 0.5 m respectively.
Following on from this the levels are further increased, in accordance with
the same data source, to values of 40 W/m2 and 1.0 m appropriate to urban conditions and the calculations are terminated after proceeding a final 2 km. Results The solid curves of Fig. 2 show the predicted variations with downstream distance the heighth, of the location of concentration Cmax in the cross-section; the relative value of the ground level concentration maximum Cground/Cmax; and the locations of the
of,
29 upper (1,) Cma,:
and lower A(),
plume boundaries, defined as the locations where C is 50%
The dashed lines depict the same information for uniformly-rural conditions,
and show the plume developing in the manner characteristic of Gaussian models of elevated releases, with the centreline running roughly parallel with the ground and no dramatic change in rate of spread with downstream distance. By contrast.,the full rural/suburban/urban simulation shows the plume as being initially deflected upwards as it passes over the suburban region and then the lower boundary plummeting downwards shortly after the urban zone is encountered, a manifestation of the expected 'fumigation' effect.
Inspection of the detailed output of the
calculations reveals the initial upwards motion as being due to the upwards velocities provoked by the sudden retardation of the near-ground wind by the increased roughness, an effect which occurs again at the start of the urban zone.but is masked by other processes there.
However the increase in roughness and positive heat flux also pro-
mote the growth of an internal layer of high turbulence which propagates upwards and eventually causes fumigation to occur when it reaches the main plume, through both the augmentation of the diffusivities and the downwards velocities resulting from the consequent thinning of the boundary layer.
As can be seen, the full simulation therefore
produces significantly higher ground level concentrations once fumigation occurs than does the representation based on uniform meteorological conditions.
Side Elevation Figure 1 Illustration of the flow grid and the embedded plume grid, showing their adjustment during the marching process.
30 I
I I
I I
+
-
+
-
+
RURAL TERRAIN THROUGHOUT
I
I I I
b
I I
DOWNSTREAM DISTANCE (m)
heat flux and (below) position of plume centreline, 50% boundaries and relative ground level concentrations. ACKNOWLEDGEMENTS The important contributions made to the development of APT by Professor B.E.
Launder,notably in the area of turbulence,are hereby acknowledged.
REFERENCES 1 S. El Tahry, Turbulent Plume Dispersal, PhD Thesis, Imperial College, London, 1979. 2 L.S. Fryer and G.D.Kaiser, TIRION 4, a Computer Code for use in Nuclear Safety Studies, UKAEA Rep. SRD R/34 (1978). 3 B.E. Launder, G.J. Reece, and W. Rodi, Journal of Fluid Mechanics, (1975) 68, 537. 4 B.E. Launder, Heat and Mass Transport, Chapter 6 in Topics in Applied Physics (1976), Volume 12, Springer, Edited by P. Bradshaw. 5 M.M. Gibson and B.E. Launder, Ground effects on pressure fluctuations in the atmospheric boundary layer, Journal of Fluid Mechanics (1978), 86,491. 6 F.B.Smith, A Scheme for Estimating the Vertical Dispersion of a Plume from a source near Ground Level, Proc. 3rd Mtg. on Air Pollution Modelling, NATO/CCMS, 14, Brussels (1972), unpublished UK Meteorologiaal Office Report. 7 R.H. Clarke, National Radiological Protection Board Report, NRPB-R91, (1979). 8 S. El Tahry, A.D.Gosman and B.E. Launder,The Two-and-Three-Dimensional Dispersal Of a Passive Scalar in a Turbulent Boundary Layer. Imperial College, Mechanical Engineering Department Report (1979). To appear in 1nt.J. Heat Mass Transfer.
Atmospheric Pollution 1980,Proceedings of the 14th International Colloquium, Paris, France, May 5--8,1980, M.M. Benarie (Ed.), Studies in Environmental Science, Volume 8 0 Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
31
THE TRANSPORT, CHEMICAL TRANSFORMATION, AND REMOVAL OF SO2 AND SULFATE I N THE EASTERN UNITED STATES
GREGORY R . CARMICHAEL and LEONARD K. PETERS U n i v e r s i t y o f Iowa, Iowa City, I A and U n i v e r s i t y o f Kentucky, Lexington, KY (U.S.A.)
ABSTRACT
A r e g i o n a l model o f SOE and s u l f a t e t h a t includes a d v e c t i v e and d i f f u s i v e t r a n s p o r t , homogeneous and heterogeneous o x i d a t i o n , and d r y d e p o s i t i o n o f both species i s described. and wind f i e l d .
The model i n c o r p o r a t e s t e m p o r a l l y and s p a t i a l l y v a r y i n g m i x i n g l a y e r Studies on the dynamic response o f an e l e v a t e d plume t o daytime
v a r i a t i o n s i n v e r t i c a l m i x i n g show the s h i f t toward t h e surface o f the plume c e n t e r l i n e , t h e e x i s t e n c e o f a double maxima i n ground l e v e l concentration, and the t r a p p i n g o f p o l l u t a n t s i n t h e e a r l y evening.
INTRODUCTION S u l f u r d i o x i d e has l o n g been known t o be a major p o l l u t a n t , b u t s t u d i e s now i n d i c a t e t h a t t h e o x i d a t i o n product, s u l f a t e , may present a g r e a t e r h e a l t h hazard and produce a number o f adverse e c o l o g i c a l e f f e c t s ( r e f . 1 ) .
I t i s g e n e r a l l y accepted
t h a t most s u l f a t e i s formed i n t h e atmosphere by chemical conversion from SO2. Long range t r a n s p o r t models can be used t o t r a c e the sources o f SO2 and t o t e s t t h e o r i e s o f t r a n s p o r t , t r a n s f o r m a t i o n , and removal by comparing model p r e d i c t i o n s w i t h measurements from m o n i t o r i n g networks ( r e f . 2-7). I n a p r e v i o u s paper ( r e f . 8 ) , we presented a combined transport/chemistry/surface removal model t o d e s c r i b e t h e r e g i o n a l d i s t r i b u t i o n o f s u l f u r d i o x i d e and s u l f a t e w i t h i n t h e lower troposphere.
I n t h i s paper, we w i l l summarize t h a t development and
study t h e dynamic response o f an e l e v a t e d plume t o daytime v a r i a t i o n s i n v e r t i c a l m i x i n g u s i n g a subset o f t h e model. MODEL DESCRIPTION The r e g i o n a l t r a n s p o r t o f SO2 and s u l f a t e i s modeled w i t h i n an E u l e r i a n framework. The g r i d model i n c o r p o r a t e s chemical transformation,
dry deposition, spatial varia-
t i o n o f topography, and s p a t i a l and temporal v a r i a t i o n s o f m i x i n g l a y e r h e i g h t , wind f i e l d , eddy d i f f u s i v i t y , d e p o s i t i o n v e l o c i t i e s , and temperature and water vapor concentration profiles.
A photochemical SO2 o x i d a t i o n mechanism i s i n c o r p o r a t e d i n t o
32
t h e t r a n s p o r t model w i t h t h e r a t e p a r a m e t e r i z e d u s i n g d i u r n a l l y v a r y i n g r a d i c a l s p e c i e s c o n c e n t r a t i o n s and a f i x e d heterogeneous r a t e c o n s t a n t . The matheniatical a n a l y s i s i s based on t h e coupled, t h r e e - d i m e n s i o n a l a d v e c t i ond i f f u s i o n equations f o r ac
ack+ at
k= Lax.[ K
U J. ax.
J
SO2 and s u l f a t e
(71
j j ax.
J
+ Rk + Sk
(11,
where c k i s t h e c o n c e n t r a t i o n o f s p e c i e s k, u . i s t h e v e l o c i t y v e c t o r , K is the J jj eddy d i f f u s i v i t y t e n s o r (K. .=O f o r i f j has been assumed), Rk i s t h e r a t e o f forma1J
t i o n o r l o s s b y chemical r e a c t i o n , and Sk i s t h e e m i s s i o n r a t e . V a r i a b l e t o p o g r a p h y i s h a n d l e d by mapping t h e i r r e g u l a r v e r t i c a l r e g i o n i n t o a d i m e n s i o n l e s s r e c t a n g u l a r r e g i o n w i t h t h e t o p s e t a t 3000 m e t e r s .
There a r e t e n
v e r t i c a l g r i d s w i t h h i g h e r r e s o l u t i o n between t h e s u r f a c e and 450 meters which p e r m i t s s i m u l a t i o n o f t r a n s p o r t i n s t a b l e l a y e r s a l o f t and i t s subsequent r e - e n t r a i n ment i n t o t h e m i x i n g l a y e r . The dynamic model uses a G a l e r k i n method f o r t h e n u m e r i c a l s o l u t i o n o f t h e p a r t i a l d i f f e r e n t i a l equations ( r e f . 9).
A t t h e b o u n d a r i e s , two cases a r e i m p o r t a n t .
m a t e r i a l t r a n s p o r t i n t o t h e model r e g i o n , and t h e second i s o u t f l o w .
One i s
I n b o t h cases,
t h e b e s t estimate o f t h e f l u x i s obtained from t h e concentration gradient a t the previous time step. CHEMISTRY OF SO2 AND SULFATE
SO2 o x i d a t i o n mechanism i n c o r p o r a t e d i n t o t h e model i s i n s u f f i c i e n t d e t a i l t o p r e d i c t a r e a l i s t i c o x i d a t i o n r a t e o f SO2 w i t h i n an a c c e p t a b l e c o m p u t a t i o n t i m e . The
Furthermore, b o t h homogeneous and heterogeneous processes a r e i n c l u d e d i n conversion t o sulfate. Homogeneous gas phase c h e m i s t r y A homogeneous gas phase mechanism f o r
SO2 o x i d a t i o n was developed by e v a l u a t i n g
t h e r a t e s o f i n d i v i d u a l r e a c t i o n s f r o m a d e t a i l e d k i n e t i c m o d e l i n g of two smog chamb e r s t u d i e s ( r e f . 10, 1 1 ) .
The r e s u l t s from t h e d e t a i l e d model were t h e n used t o c o n -
s t r u c t a s i m p l i f i e d scheme.
T h i s d e t a i l e d mechanism i n c l u d e d 72 r e a c t i o n s , and a com-
p l e t e d e s c r i p t i o n can be f o u n d elsewhere ( r e f . 7 2 ) .
The o v e r a l l r e s u l t s o f t h a t
s t u d y showed t h a t t h e d e t a i l e d k i n e t i c mechanism s i m u l a t e d w e l l t h e
SO2 o x i d a t i o n
r a t e s o b t a i n e d i n t h e two s t u d i e s . Based on t h e r e s u l t s , t h e most i m p o r t a n t r e a c t i o n s were r e t a i n e d . degree o f accuracy, t h e
To a h i g h
SO2 r a t e e x p r e s s i o n can be s i m p l i f i e d t o
The c o n c e n t r a t i o n s o f OH and H02 show d i u r n a l v a r i a t i o n s . The r a t e e x p r e s s i o n f o r SO2 i s uncoupled f r o m t h o s e f o r
OH and H02 by u s i n g t h e
33
SO2 c o n c e n t r a t i o n a t t h e p r e v i o u s t i m e s t e p i n t h e c a l c u l a t i o n o f OH and H o p .
This
approach agrees w e l l w i t h t h e e x p e r i m e n t a l d a t a and t h e v a l u e s p r e d i c t e d b y t h e det a i l e d model.
The r e l a t i v e c o m p u t a t i o n t i m e s f o r t h e d e t a i l e d and s i m p l i f i e d m o d e l s
a r e a p p r o x i m a t e l y 40: 1. Heterogeneous c h e m i s t r y
I n t h e atmosphere, t h e heterogeneous o x i d a t i o n o f SO2 occurs v i a o x i d a t i o n by i n t h e absence o f c a t a l y s t , c a t a l y t i c o x i d a t i o n by 02, and o x i d a t i o n by 0 3 . p o r t e d r a t e c o n s t a n t s f o r t h e u n c a t a l y z e d o x i d a t i o n by d i s s o l v e d
O2
O2
The r e -
v a r y b y two o r -
d e r s o f magnitude, w i t h most r e p o r t s on t h e l o w end i n d i c a t i n g t h a t t h i s r e a c t i o n i s n o t e x t r e m e l y i m p o r t a n t i n t h e atmosphere.
The c a t a l y z e d o x i d a t i o n o f
SO2 i s most
i m p o r t a n t i n urban a r e a s and s t a c k plumes under c o n d i t i o n s of h i g h h u m i d i t y and h i g h c a t a l y s t concentrations;
i t i s u n l i k e l y t o be s i g n i f i c a n t i n r u r a l areas.
Recent
measurements o f t h e r a t e o f o x i d a t i o n o f SO2 b y d i s s o l v e d O3 a l s o d i f f e r by two o r d e r s o f magnitude.
I f t h e h i g h e r r a t e c o n s t a n t i s c o r r e c t , t h e n t h e o x i d a t i o n by
O3 i s i m p o r t a n t even a t a t m o s p h e r i c background ozone c o n c e n t r a t i o n s . Assuming o x i d a t i o n by d i s s o l v e d 0 3 ,
02,and m e t a l c a t a l y s t s o c c u r s i m u l t a n e o u s l y ,
t h e combined heterogeneous r a t e e x p r e s s i o n can be w r i t t e n as d [SO,2-]
h K = -1.5
dt
d[SO,] -
60 KIHv*
dt
[H'I
( h K P '3 '3 '3
+ - 02 [Hf]
+
kcatK2[M+I)Cso21
(3) >
i s i n ppm min-', [SO2] i n ppm, H i s H e n r y ' s l a w c o n s t a n t , v* i s t h e 5 aqueous volume p e r volume o f a i r , ho =1x10 -3.3x105L m o l - l s - ' , K - 2 . 2 ~ 1 0 - ~ m o l L - ~ a t m - ~
where d[S04'-]/dt
O3-8 L 2mol - 2 s -1, [M+] Po3 i s t h e O3 p a r t i a l p r e s s u r e , ho =36 ~ 1 O - ~ s -fl o r 3
By c h o o s i n g t y p i c a l r u r a l v a l u e s o f [03]d0ppb 1 a pH o f 4.6 f o r m o d e r a t e l y p o l l u t e d c o n t i n e n t a l c l o u d s , [M+]=5~1O-~mol R- ,
k -2x105R m o l - l s - ' , 03-
T=300°K,
,
and v * = ~ x ~ O - ~ ,Eq. ( 3 ) reduces t o
d[S021 - -3.69~1O-~[SO~] dt
--
(4).
The c o n t r i b u t i o n b y t h e ozone r e a c t i o n i s 92%, 5% by t h e u n c a t a l y z e d r e a c t i o n , and 3% by t h e m e t a l c a t a l y z e d o x i d a t i o n . METEOROLOGICAL DATA The f o l l o w i n g i n p u t m e t e o r o l o g i c a l d a t a a r e r e q u i r e d t o s o l v e t h e atmospheric d i f f u s i o n equation:
mean w i n d v e l o c i t y , eddy d i f f u s i v i t y , temperature, s o l a r r a d i a t i o n ,
p r e c i p i t a t i o n , d r y d e p o s i t i o n v e l o c i t i e s , and w a t e r vapor c o n c e n t r a t i o n .
The temper-
a t u r e p r o f i l e s and s o l a r r a d i a t i o n d a t a a r e used t o e s t i m a t e t h e atmospheric s t a b i l -
i t y and r e a c t i o n r a t e c o n s t a n t s .
P r e c i p i t a t i o n d a t a a r e used t o e s t i m a t e wet deposi-
t i o n processes, and t h e w a t e r vapor c o n c e n t r a t i o n i s an i n p u t t o t h e p h o t o c h e m i s t r y mechanism.
34
Wind f i e l d and eddy d i f f u s i v i t i e s
To provide a mass-consistent wind f i e l d , a v e r t i c a l v e l o c i t y component i s found by numerically solving t h e c o n t i n u i t y equation using an e x p l i c i t second-order f i n i t e d i f f e r e n c e procedure with t h e c o n s t r a i n t t h a t i = O a t p=O.Ol.
The procedure t o c a l c u l a t e eddy d i f f u s i v i t i e s c o n s i s t e n t with theory and observation i s based on the work of Myrup and Ranzieri ( r e f . 1 3 ) . This model estimates t h e Monin-Obukhov length scale based on s t a b i l i t y c l a s s , aerodynamic roughness length, and t h e evaporation r a t e a t the surface. The s t a b i l i t y c l a s s i s estimated from r o u t i n e l y measured meteorological v a r i a b l e s - s u r f a c e w i n d speed, cloud cover, and cloud c e i l i n g ( r e f . 14). The surface roughness and evaporation r a t e s a r e estimated from a map of land use, and mixing l a y e r height within the t r a n s p o r t model i s fusivity profile.
taken i n t o account via t h e eddy d i f As a r e s u l t , eddy d i f f u s i v i t i e s a r e c a l c u l a t e d a t three-hour
i n t e r v a l s t o t r e a t v a r i a t i o n s i n mixing l a y e r heights r e a l i s t i c a l l y . The horizontal d i f f u s i v i t i e s a r e c a l c u l a t e d a s multiples of t h e v e r t i c a l c o e f f i c i e n t s . Deposi t i on vel oci t i e s Dry deposition v e l o c i t i e s a r e c a l c u l a t e d a t three-hour i n t e r v a l s from estimates o f the aerodynamic and s u r f a c e r e s i s t a n c e s based on surface windspeed, surface roughness, evaporation r a t e , and s t a b i l i t y . The a v a i l a b l e data on dry deposition of SO2 t o grass indicated t h a t the s u r f a c e r e s i s t a n c e v a r i e s from 1 t o 3 s cm-l and can be correlated with s u r f a c e roughness ( r e f . 1 2 ) . Surface r e s i s t a n c e s f o r non-grass surfaces a r e estimated from a v a i l a b l e d a t a , and t h e s u l f a t e deposition v e l o c i t i e s a r e calculated a s a l i n e a r function of f r i c t i o n v e l o c i t y ( r e f . 1 6 ) . Average values of the calcul a t e d deposition v e l o c i t i e s ( a t 20-30m) throughout t h e modeling region f o r t h e period of July 4 - J u l y 10, 1974 a r e vS02=0.44cm s-l and vS04=0.26cm s-’. 9 9 MIXING LAYER DYNAMICS An important aspect of the long range t r a n s p o r t of SO2 and s u l f a t e s concerns the i n t e r a c t i o n of elevated plumes with t h e dynamics of t h e mixing l a y e r and the overall v e r t i c a l m i x i n g . These f e a t u r e s a r e included i n the long range t r a n s p o r t model and have been studied using an i s o l a t e d two-dimensional plume from an elevated source. The plume was i n f i n i t e l y wide so t h a t crosswind d i f f u s i o n could be neglected. Convection dominated in t h e d i r e c t i o n of the wind and v e r t i c a l mixing was s o l e l y due t o t u r b u l e n t d i f f u s i o n . The emissions a r e from a 500m e f f e c t i v e source height f o r the period from 8:OOAM t o 9:OOPM. The r e a c t i o n r a t e was fixed a t 3.5% h r - ’ and the depos i t i o n v e l o c i t y was lcm s-’.
The mixing l a y e r height was changed hourly. Carmichael, Yang, and Lin ( r e f . 17) have presented d e t a i l e d r e s u l t s of these calc u l a t i o n s . Concentration i s o p l e t h s f o r d i f f e r e n t times a r e shown in Figure l . Between 9:OOAM and 12:OOPM t h e mixing l a y e r was b e l w t h e source height, and ground level concentrations were correspondingly low. A t noon the mixing l a y e r height reached 600m with fumigation occurring and t h e ground level concentrations increasing. The mixing l a y e r height was maximum (1200m) a t 3:OOPM and then decreased.
M V N W l N D DISTANCE. K Y
F i g . 1. C o n c e n t r a t i o n i s o p l e t h s r e s u l t i n g f r o m e m i s s i o n s f r o m a 500m e l e v a t e d s o u r c e d u r i n g t h e growth and d i s s i p a t i o n o f t h e m i x i n g l a y e r a t t i m e s c o r r e s p o n d i n g t o a ) 9:59 AM, b ) 10:59 AM, c ) 1:59 PM, d ) 3:59 PM, e ) 5:59 PM, f ) 7:59 PM, and g ) 8:59 PM.
m
$m MVNWINO OISIANCE. K Y
F i g u r e s l c and l e show t h e c o n c e n t r a t i o n f i e l d s a t 1:59 and 5:59PM,
respectively.
A t t h e s e t i m e s t h e d i f f u s i v i t y p r o f i l e s were s i m i l a r , b u t t h e c o n c e n t r a t i o n f i e l d s were q u i t e d i f f e r e n t .
When mass reached h i g h a l t i t u d e s , i t remained a l o f t u n t i l
being advected from the region.
I n t h e r e g i o n above t h e m i x i n g l a y e r , s t a b l e atmo-
s p h e r i c c o n d i t i o n s and maximum w i n d v e l o c i t i e s o f t e n o c c u r , e s p e c i a l l y a t n i g h t . T h i s m a t e r i a l can r e m a i n a l o f t and be t r a n s p o r t e d l o n g d i s t a n c e s w i t h l i t t l e v e r t i c a l spread u n t i l f u m i g a t i o n o c c u r s t h e n e x t a f t e r n o o n .
This i s important i n the transport
o f secondary p o l 1 u t a n t s such as s u l f a t e s .
I n t h e e a r l y e v e n i n g ( s e e F i g u r e I f ) m a t e r i a l n e a r t h e s u r f a c e was t r a p p e d , and h i g h ground l e v e l c o n c e n t r a t i o n s p e r s i s t e d .
T h i s m a t e r i a l would remain u n t i l i t i s
removed by d r y d e p o s i t i o n , chemical r e a c t i o n , and/or h o r i z o n t a l c o n v e c t i o n .
The i n -
f l u e n c e o f d r y d e p o s i t i o n on plume geometry i s a p p a r e n t i n F i g u r e s l c and I d .
Mass
was t r a n s f e r r e d t o t h e s u r f a c e , w h i c h caused t h e plume c e n t e r l i n e t o s h i f t downward. C a l c u l a t e d ground l e v e l c o n c e n t r a t i o n s o f t h e p r i m a r y p o l l u t a n t a t d i f f e r e n t downw i n d l o c a t i o n s a r e shown i n F i g u r e 2 as a f u n c t i o n o f t i m e . curred a t a l l locations.
Note t h a t two maxima oc-
The f i r s t o c c u r r e d as t h e m i x i n g l a y e r h e i g h t i n c r e a s e d j u s t
above t h e s o u r c e h e i g h t , w h i l e t h e second one o c c u r r e d as t h e m i x i n g l a y e r h e i g h t r e turned t o t h a t l e v e l i n t h e l a t e afternoon.
The d e c r e a s i n g c o n c e n t r a t i o n s i n mid-
a f t e r n o o n were due t o d i l u t i o n caused b y c o n t i n u e d growth o f t h e m i x i n g l a y e r .
The
o c c u r r e n c e o f t h e second maximum was delayed, and t h e ground l e v e l c o n c e n t r a t i o n s a t 9:OOPM were h i g h e r a t t h e i n t e r m e d i a t e downwind l o c a t i o n s .
T h i s ground l e v e l concen-
t r a t i o n b e h a v i o r has been observed i n t h e f i e l d . W o l f f e t a l . ( r e f . 1 8 ) found ground l e v e l SO2 c o n c e n t r a t i o n p r o f i l e s s i m i l a r t o t h o s e i n F i g u r e 2. I n t h e i r work, a
36
E .7
-GROUND LEVEL CONCENTRATION\
1400
1300 Ix)o 1100 1000
900
z.
;
:
- 2w 700
600 -0
400 300 200
3 z
R
e 2
100 0
Fig. 2. Calculated ground level concentrations a s a function of time of day a t d i f f e r e n t downwind p o s i t i o n s r e s u l t i n g from emissions from a 500m elevated source during t h e growth and d i s s i p a t i o n of the mixing l a y e r . s i n g l e p r o f i l e ( t h e i r Figure 2b) obtained by averaging nine days of observational data showed t h e presence of t h i s double maxima. ACKNOWLEDGEMENTS Computer time has been provided by the NASA Langley Research Center. The a s s i s tance of Dr. Henry G . Reichle, J r . i n making t h i s possible i s appreciated. REFERENCES 1 U.S. Dept. Ag., Proc. 1 s t I n t . Symp. Acid Precip. and Forest Ecosystem, USOA Forest Service Gen. Tech. Rep. WE-23, 1976. 2 M.C. MacCracken, Atmos. Environ., 12(1978) 649-659. 3 W.E. Wilson, Atmos. Environ., 12(1978)537-547. 4 R . M . Perhac, 2nd Plat. Conf. on Interagency EnergylEnviron. R & D Program, Washington, D . C . , June, 1977. 5 J.P. Bromberg and T.G. Fox, Intergovernmental cooperation in "up-valley'' pollut i o n t r a n s p o r t management, Final Rep. of Ohio River Valley Assembly, 1978. 6 5. O t t a r , Atmos. Environ., 12(1978)445-454. 7 G.M. Hidy, E . Y . Tong, P.K. Mueller, S. Rao, I . Thomson, F. Berlandi, D. Muldoon, D. McNaughton and A. Majahad, Design of t h e S u l f a t e Regional Experiment, PB-251701, 1976. 8 G . R . Carmichael and L . K . P e t e r s , Proc. 4th Symp. Turbulence, Diffusion, Air P o l l u t i o n , Reno, Nevada, January, 1979, Amer. Meteor. SOC. 9 G.R. Carmichael, T. Kitada and L . K . P e t e r s , Comp. and Fluids, (1980) in press. 10 W.C. Kocmond and J.Y. Yang, S u l f u r dioxide photooxidation r a t e s and aerosol format i o n mechanisms: A smog chamber study. Calspan Corp., PB-260-910, 1976. 11 J.W. B r a d s t r e e t , 66th Ann. APCA Meeting, Chicago, IL, June, 1973. 12 G.R. Carmichael, Development of a regional transport/transformation/removal model f o r SO2 and s u l f a t e in the Eastern United S t a t e s , Ph.D. D i s s . , Univ. of K Y , 1979. 13 L.O. Myrup and A.J. Ranzieri, A c o n s i s t e n t scheme f o r estimating d i f f u s i v i t i e s t o be used i n a i r q u a l i t y models, PB-272-484, 1976. 14 D.B. Turner, J . Air P o l l u t . Control Assoc., 11(1961)483-489. 15 G . C . Holzworth, Mon. Wea. Rev., 92(1964)235-242. 16 W . G . N . S l i n n , Symp. Atmospheric-Surface Exchange of P a r t i c u l a t e and Gaseous Pollut a n t s , Richland, Washington, 1974. 17 G . R . Carmichael, D-K Yang, and C . Lin, Atmos. Environ. (1980) s u b . f o r pub. 18 G.T. Wolff, P.R. Monson and M.A. Ferman, Environ. S c i . Tech., 13(1979)1271-1276.
Atmospheric Pollution 1980,Proceedings of the 14th InternationalColloquium,Paris,France, May 5-8,1980,M.M.Benarie (Ed.), Studies in Environmental Science,Volume 8 Elsevier Scientific Publishing Company,Amsterdam - Printed in The Netherlands
37
THE ATMOSPHERIC IMPACTS OF EVAPORATIVE C O O L I N G SYSTEMS J.E. CARSON Division of Environmental Impact Studies, Argonne National Laboratory, Argonne, Illinois 60439 (U.S.A.)
ABSTRACT The observed atmospheric-impacts resulting from the use of evaporative cooling systems are minor and usually environmentally acceptable. Although these impacts are also considerably smaller than those usually predicted a few years ago, regulatory agency requirements are such that these effects must be identified and quantified.
INTRODUCTION Once-through cooling is the most efficient (and usually the lowest cost) method of heat dissipation for large heat sources such as electrical generating plants.
However, water shortages, regulatory actions, and concern about the
biological effects of heated water will force most future power plants to use "closed-cycle'' methods for waste heat discharge. This paper will discuss the effects of the operation of natural-draft and mechanical-draft cooling towers, cooling lakes, and spray canals on the local atmosphere. These impacts include fogging, icing, shadowing, long visible plumes, cloud formation, and precipitation generation/augmentation.
Additional informa-
tion on these topics can be found in recent survey papers by Carson, Hanna, Englesson and Hu (refs. 1-3), the April 1974 issue of Atmospheric Environment, and proceedings of two recent symposia (Cooling Tower Environment-1974 and Cooling Tower Environment 1978 (refs. 4 and 5). NATURAL-DRAFT C O O L I N G TOWERS The primary atmospheric effect of natural-draft cooling towers (NDCTs) is the generation of long plumes that remain aloft. plumes may strike elevated areas.
In mountainous-terrain areas, these
Observations at operating NDCTs indicate that
downwash rarely, if ever, brings the plume to ground level.
Locally heavy snow
can fall from natural-draft and mechanical-draft cooling-tower plumes in cold weather (refs. 1, 2 and 6).
About 75% of the heat transfer in evaporative cooling towers is in the form of latent heat; this fraction varies from 60% in winter to 90% on hot, humid summer days. Part of the evaporated water in a natural-draft cooling system recondenses inside the tower.
When the effluent leaves the tower, it mixes with cooler
ambient air, and more of the water vapor condenses in the form of a visible cloud-like plume.
Under most meteorological conditions, the plume will continue
to rise because of its buoyancy and momentum, and the water droplets will evaporate within a few hundred meters of the towers.
Hanna (ref. 2) reports that the
median plume length for NDCTs with a heat load similar to that of a two-unit nuclear power plant is about 250 to 500 m in summer and 500 to 1000 m in winter; plumes as short as 50 m have been observed on sunny summer afternoons.
Under
other conditions (especially periods with low air temperatures, high humidity, moderate wind speeds, and a stable atmosphere), the visible plume may extend for many kilometers.
Under these conditions, the plume may rise one or more kilo-
meters before leveling off, typically below the base of an inversion aloft. Fog could be created downwind of NDCTs in two ways: downward dispersion of moisture from an elevated plume.
aerodynamic downwash and Due to the height of the
NDCTs and added plume rise due to buoyancy and momentum, downwash fog is a rare event in areas of level terrain.
No cases of ground-level fog caused by the
downward dispersion of humidity from NDCT plumes have been reported. A small fraction (estimated to be 0.002% or less for towers with modern drift
eliminators in good repair) of the cooling water is carried into the plume and discharged into the atmosphere as drift.
These droplets carry dissolved and
suspended solids in the circulating water and could cause impacts due to wetting, icing, and deposition of salts onto soil, plants, and structures. Most droplets fall from the plume and usually evaporate before reaching the %round close to the towers.
Some drift droplets do not evaporate before reaching the ground and are
deposited at varying distances from the tower, depending on drop size and atmospheric conditions.
Observations at dozens of modern NDCTs with state-of-the-art
drift eliminators in Europe and the United States show that most of the drops that reach the ground do so within 0.5 to 1.0 km of the towers and most of the predicted adverse drift impacts do not, in fact, occur (refs. 1-3). The visible plume from a cooling tower is an artificial cloud.
In addition,
clouds are sometimes observed to form in the updraft created by a cooling tower after the initial visible plume has evaporated.
A few occurrences of snow due to
cooling-tower plumes have been reported, but never liquid precipitation (refs. 1,
2, 3, 6 ) .
Cooling-tower plumes slightly reduce the amount of sunshine reaching
the ground in the immediate area, but no evidence is available to indicate that they significantly alter local weather conditions or generate thunderstorms (refs. 1-3).
39 The NDCT is a proven, effective, and economical way to dissipate large heat loads. The atmospheric impacts of such a tower using fresh water for makeup are minimal.
The primary adverse impact is visual--i.e., the structures and their
visible plumes; NDCTs rarely, if every, cause significant ground-level fog and icing, and drift impacts are negligible. MECHANICAL-DRAFT COOLING TOWERS
In a mechanical-draft cooling tower (MDCT), fans are used to pull air through the fill section.
The MDCT is the most widely used method for cooling both large
and small heat loads in the United States and Canada. towers have several advantages over NDCTs:
Mechanical-draft cooling
lower capital costs, greater flexi-
bility, greater control of cold-water temperature, better icing control, and smaller visual impact of the structures due to their lower profile.
Disadvantages
include higher costs of operation an& maintenance, and the use of fuel to operate the fans. The primary environmental disadvantage of MDCTs when compared to NDCTs is the much greater potential for ground-level fogging and icing, especially in winter. This is caused by the relatively low heights of discharge (15 to 25 m), with aerodynamic downwash the primary cause.
The experience at such towers indicates
that due to its buoyancy, downwash fog usually evaporates or lifts to become stratus clouds within a short distance (on the order of 100 to 300 m) of the cooling towers (refs. 1-3).
Downwash begins with a wind speed of 3-5 m/s, per-
pendicular to the tower axis.
There are no reports of fog or ice formation from
the downward dispersion of moisture from an elevated plume of a MDCT, a condition forecast by many mathematical models. Hanna and Perry (ref. 7) report that on rainy days with low overcast, the plumes from MDCTs may extend for tens of kilometers below the natural cloud layer.
Clouds can also form from the updrafts created by MDCT plumes after the
initial visible plume evaporates.
Light snow has been observed to fall from the
plumes of MDCTs. Because of higher exit speeds, drift rates from all types of MDCTs are usually higher than from NDCTs.
Observations at existing MDCT sites indicate that most
of the drift that falls to the ground does tower.
so
within a few hundred meters of the
Thick layers of dense glaze ice may form on vegetation near MDCTs in
winter if drift rates are high.
The drift rate will depend in large part on the
design and state-of-repair of the drift eliminators. The MDCT is an environmentally acceptable cooling alternative for most power plant sites using fresh water for makeup.
Although much more fogging and icing
occurs with these towers than with the NDCTs, most of the impacts occur within a few hundred meters of the towers.
COOLING PONDS In areas where sufficient level land can be purchased at reasonable prices, the cooling pond (CP) is an effective, economical, and environmentally acceptable heat sink.
Optimal area requirements for dissipation of waste heat via surface
effects from a cooling lake or pond are about 0.6 ha per MWe for light-water reactors and about 0.4 ha per MWe for fossil-power plants.
In areas of cold
winters, additional land is required in order to mitigate the effects of steam fogs and icing to offsite roads, buildings, etc.; a buffer zone of about 100 to 200 m around the lake is adequate.
Stands of coniferous trees in this zone
further mitigate the effects of the steam fog.
Usually about 70% of the heat is
dissipated by evaporation, with conduction of sensible heat to the atmosphere dissipating most of the remainder.
Since evaporation is less important with
cooling ponds than with wet cooling towers, less water is consumed by "forced" evaporation. However, lakes require large areas, and consequently natural evaporative losses due to solar heating on the water surface usually lead to total evaporative losses that are greater than those from cooling towers. Heat and water vapor are transferred to the atmosphere whenever relatively cool air moves over a water surface.
If conditions are proper (cold air over
very warm water), part o f the water vapor from the surface immediately recondenses when the air next to the water mixes with cooler, drier air aloft; the resulting mist is called "steam fog."
This fog is created by the same process
that allows one to "see his breath" or see "steam" from a kettle--i.e., the nonlinear relation between the saturation vapor content of air and air temperature. Further vertical mixing, favored by the cold air over a warmer surface, tends to reevaporate the steam fog droplets; thus, the process that creates the fog tends also to dissolve it. The primary meteorological effect of a cooling pond is the generation of steam fog over and near the pond.
Observations made at existing cooling ponds indicate
that steam fog is usually shallow, wispy, and in turbulent motion, and may penetrate inland 30 to 50 m or more before evaporating or dissipating. However, if the air is very cold (below - 1 8 O C )
and the pond very warm ( 1 5 O C t o 25"C), the fog
over the pond will be very dense and wind may carry this fog inland some distance. Dense steam fog over the pond is a trivial environmental impact; frequent dense fog over a nearby road or house is a severe impact. Observations of steam fog over cooling ponds in Illinois indicate that the inland penetration of dense fog is limited to areas 100 m or so downwind; the f o g then becomes much thinner, evaporates completely, or rises to form a stratus layer of clouds.
Observations show that because of the very large area of heat
and moisture release to the atmosphere, cooling ponds are not major sources of extensive steam fog, despite the release of heat and moisture at ground level.
41 In periods of subfreezing temperatures, thick deposits of low-density rime ice may form on objects within the zone of steam fog.
Because of the low weight and
crumbly nature of this ice, little damage is done to trees, vegetation, wires, and other structures.
Thick deposits are usually limited to areas within 50 to
100 m of the pond. SPRAY CANALS In a spray cooling system (SC), pumps are used to send a spray of heated water droplets into the atmosphere to increase the area of contact between water and air, thus increasing the rate of cooling by conduction and evaporation.
The
primary advantage of a spray system over a cooling pond is the much smaller water area needed to cool a given plant load.
However, to reduce recirculation and
ensure maximum cooling efficiency, the sprays should be spread over a large area, such as a meandering canal.
A s with cooling ponds, however, a buffer zone of
about 100 to 200 m is needed to confine most fogging and drift effects to the site. The potential for fog downwind of SCs is greater than that of CPs but lower than that from MDCTs.
Icing immediately downwind of spray canals can be severe,
and much of the icing is due to drift.
However, because of the low height of
release (5 m) of the drift particles, the range of dense ice may be only 100 to
200 m.
Small deposits of light, friable rime ice may be formed on elevated
objects further downwind due to recondensation droplets. DRY COOLING TOWERS
Because of lower thermal efficiency, power plants with dry cooling towers generate more waste heat and use more fuel to produce a unit of energy.
The
possibility exists that the updraft from a dry tower could release an existing atmospheric convective instability and create showers, thunderstorms, and severe storms.
Lee (1977) has developed a model for predicting cloud generation from
dry cooling-tower plumes.
He notes that updraft-producing forces (buoyancy and
vertical momentum) from dry cooling towers are about one order of magnitude larger than than those from an evaporative cooling tower of similar capacity. Lee concludes that
"
... under potentially unstable ambient conditions, and other
conditions favorable to natural formation of cumulus clouds, a large dry cooling tower has a higher potential for inducing convective clouds than a wet cooling tower
..."
The cloud building and precipitation augmentation of a cooling-tower
effluent are due mostly to the buoyancy and vertical momentum of the effluent, n o t the moisture content.
Observations and cloud models show that the bulk of
liquid water in any elevated cooling-tower plume comes from entrained air, not from the tower itself.
42 SUMMARY AND CONCLUSIONS
Evaporative cooling towers and cooling ponds are effective heat sinks that sharply reduce the impact of thermal discharges on water bodies, although they do create their own atmospheric impacts.
For a large, isolated site (such as
required for the exclusion area of a nuclear plant), however, these impacts are mostly rather minor and usually acceptable. One possible reason for the lack of information on significant negative impacts may be the fact that such effects may have occurred but have never been observed and reported. The generation of snow by natural-draft cooling towers was first observed in 1975, although such towers have been in use for decades (ref. 6).
The basic reasons for this are the distance between the tower and the
snow (many kilometers) and the fact that no one has been looking for it. ACKNOWLEDGEMENTS This work was supported by the U.S. Nuclear Regulatory Commission, Office of Nuclear Regulatory Research, Washington, D.C.
The document was prepared at
Argonne National Laboratory, Argonne, Ill., operated for the U.S. Department of Energy under contract W-31-109-Eng-38. REFERENCES
1 J.E. Carson, Atmospheric Impacts of Evaporative Cooling Systems, Argonne Natl. Lab. Rep. ANL/ES-53, Argonne, Ill., 1976, 48 pp. 2 S.R. Hanna, Atmospheric Effects of Energy Generation, ATDL Contrib. No. 7719, Air Resources Atmospheric Turbulence and Diffusion Laboratory, Oak Ridge, Tenn., 1978, 101 pp. 3 G.A. Englesson and M.C. Hu, Nonwater Quality Impacts of Closed-Cycle Cooling Systems and the Interaction of Stack Gas and Cooling Tower Plumes, EPA-600/ 7-79-090, Industrial Environmental Research Laboratory, Research Triangle Park, N.C., 1979, 214 pp. 4 Cooling Tower Environment-1974, CONF-740302, ERDA Symposium Series, U.S. Energy Research and Development Administration, Technical Information Center, Office of Public Affairs, Washington, D.C., 1975, 638 pp. 5 Cooling Tower Environment-1978, WRRC Spec. Rep. No. 9, Water Resources Research Center, University of Maryland, College Park, Md., 1978, 1 v. (various pagings) with Supplement. 6 M.L. Kramer, D.E. Seymour and M.E. Smith, Science, 193(1976)1239-1241. 7 S.R. Hanna and S.G. Perry, Meteorological Effects of the Cooling Towers at the Oak Ridge Gaseous Diffusion Plant. I. Description of Source Parameters and Analysis of Plume Photographs and Hydrothermograph Records, ATDL Contrib. No. 86, Air Resources Atmospheric Turbulence and Diffusion Laboratory, Oak Ridge, Tenn., 1973, 40 pp. 8 J.L. Lee, Atmos. Environ., 11(1977)749-759. \he submitted manuscript has been authored by a contractor of the U. S. Government under contract No. W-31.104ENG-38. Accordingly, the U. S. Government retains a nonexclusive. royalty-free license to publish or reproduce the published form of t h s contribution, or allow others to do so, for V. S. Government purposes.
Atmospheric Pollution 1980,Proceedings of the 14th International Colloquium, Pans, France, May 5-8,1980, M.M. Benarie (Ed.), Studies in Environmental Science, Volume 8 0 Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
43
IMPROVEMENT OF MATHEMATICAL MODELS FOR PLUME R I S E AND DRIFT DEPOSITION FROM COOLING TOWERS
A.J.
POLICASTRO, R.A.
CARHART, M. WASTAG, S. ZIEMER, AND K. HAAKE
Argonne N a t i o n a l L a b o r a t o r y , Argonne,
W.E.
Ill. USA
DUNN and P. G A V I N
U n i v e r s i t y o f I l l i n o i s , Urbana USA
ABSTRACT New models f o r plume r i s e and s a l t - d r i f t d e p o s i t i o n f r o m c o o l i n g towers a r e p r e sented.
F o r plume r i s e , assumptions a r e made which h e l p r e s o l v e t h e usual d i f f i c u l t y
o f c o r r e c t l y p r e d i c t i n g b o t h plume t r a j e c t o r y
and d i l u t i o n .
The m u l t i p l e - t o w e r plume
m e r g i n g method accounts f o r d i f f e r e n t r a t e s o f e n t r a i n m e n t depending on t h e o r i e n t a t i o n o f t h e m e r g i n g plumes w i t h t h e w i n d d i r e c t i o n .
Model c a l i b r a t i o n and v e r i f i -
c a t i o n have been made w i t h f i e l d and l a b o r a t o r y d a t a f r o m n a t u r a l - and mechanicald r a f t c o o l i n g towers. F o r s a l t - d r i f t d e p o s i t i o n modeling, new d r o p l e t breakaway and d r o p l e t e v a p o r a t i o n f o r m u l a t i o n s a r e developed.
The d r o p e v a p o r a t i o n t r e a t m e n t accounts f o r t h e u s u a l l y
important e f f e c t s o f droplet salt-concentration gradients.
The d r i f t model has been
v a l i d a t e d w i t h f i e l d d a t a t a k e n a t t h e Chalk P o i n t s i t e .
INTRODUCTION T h i s paper summarizes r e s u l t s o f an improvement program f o r mathematical models o f c o o l i n g - t o w e r plume r i s e and d r i f t d e p o s i t i o n . year study evaluating the state-of-the-art
T h i s work b u i l d s on an e a r l i e r two-
o f m o d e l i n g i n t h i s area ( r e f s . 1 - 3 ) .
The
b a s i s f o r model improvement was ( a ) c a r e f u l e v a l u a t i o n o f t h e t h e o r e t i c a l s u i t a b i l i t y o f assumptions commonly made i n e x i s t i n g models, and ( b ) f o r plume models, u t i l i z a t i o n o f a l a r g e d a t a base o f l a b o r a t o r y and f i e l d d a t a f r o m American and European sources f o r c a l i b r a t i o n o f unknown e m p i r i c a l c o e f f i c i e n t s .
PLUME RISE The d a t a base employed i n o u r model v a l i d a t i o n and improvement programs were m o s t l y f i e l d d a t a on v i s i b l e plumes f r o m s i n g l e towers a t Chalk P o i n t , Lunen, and Paradise, and f o r m u l t i p l e towers, Amos and Neurath.
The v i s i b l e - p l u m e o u t l i n e s p r o v i d e d by
44
these data give information on the trajectory of the plume as well as dilution (from the visible plume length and rise). To test the effect of competing model assumptions, we set up a generic model and used it as a research tool. This generic model was arranged to easily permit changes in basic assumptions: entrainment, drag, bentover plume assumption, etc. The combination of assumptions which provided the best trend with data was chosen for calibration of unknown coefficients to field and lab data. Verification with data not used i n calibration was employed to test the overall predictive capability of our calibrated model. The basic assumptions in our single tower NDCT plume are: (1 ) bent-over plume assumption (equivalent to infinite horizontal drag force) (2) entrainment function proposed by Chan and Kennedy (ref. 4) ( 3 ) spreading rate of momentum greater than the spreading rate for temperature. A smaller spreading rate for temperature than for momentum causes a smaller buoyancy force to be created which must accelerate the larger mass defined by the momentum radius. (4) the moisture radius is smaller than both momentum and temperature radii. Previous studies (ref. 1) had shown that use of full equilibrium moisture thermodynamics across the entire plume cross-section introduces too much conditional instability. A smaller moisture radius is used to account for plume cross-sectional inhomogeneities and has the added effect of reducing the energetic effects of condensation/evaporation conditional instability.
ANL MODEL (SINGLE TCWERl
k=i 5 -.I
W O
0-
0 0
s-
zo w R _I L d :
n.
0.0
300.n
900.0
600.0
IBSLkVF'D PLUME RISE.
~
I
1200.
I VETF:RS)
Fig. 1. Comparison of ANL Model Predictions of Visible Plume Rise and Length to 46 Sets of Visible Plume Data.
45
(5)
downwash was t r e a t e d e m p i r i c a l l y by a l l o w i n g a d d i t i o n a l entrainment t o t h e
plume r e s u l t i n g from t u r b u l e n t m i x i n g caused by wake turbulence.
An a d d i t i o n a l
v e r t i c a l f o r c e r e s u l t i n g f r o m plume/wake i n t e r a c t i o n was added. The above model was t h e n c a l i b r a t e d t o t h e a v a i l a b l e s i n g l e tower data ( r e f . 4). Model p r e d i c t i o n s , o v e r 46 cases ( F i g . l ) , a r e seen t o be balanced between overpred i c t i o n and u n d e r p r e d i c t i o n .
The x ' s i n t h e f i g u r e r e f e r t o cases w i t h which t h e
model was c a l i b r a t e d ( 3 9 d a t a s e t s ) ; t h e
0's
i n the f i g u r e r e f e r t o v e r i f i c a t i o n re-
s u l t s o f t h e model w i t h 7 new d a t a s e t s from t h e Gardanne and Chalk P o i n t towers.
It
i s noteworthy t h a t t h e v e r i f i c a t i o n r e s u l t s ( 0 ' s ) a l l l i e w i t h i n t h e envelope o f t h e c a l i b r a t i o n r e s u l t s ( x i s ) a l t h o u g h t h e ambient and tower data f o r t h e 0 ' s represent s i g n i f i c a n t l y d i f f e r e n t c o n d i t i o n s w i t h r e s p e c t t o tower power o u t p u t and ambient c o n d i t i o n s than were used f o r c a l i b r a t i o n . An advantage t o o u r model i s i t s a b i l i t y t o handle wake e f f e c t s from towers corr e c t l y w i t h respect t o l a b o r a t o r y data (Fig. 2).
Recent EDF l a b o r a t o r y (water flume)
data ( r e f . 6) r e v e a l e d t h a t t h e l a r g e r winds ( l a r g e r K, where K i s t h e r a t i o o f wind speed t o tower e x i t v e l o c i t y ) y i e l d more d i l u t e d plumes than expected due t o t h e e f f e c t of plume i n t e r a c t i o n w i t h t h e wake o f tower s t r u c t u r e .
As expected, none o f
t h e t h r e e p o p u l a r models shown e x h i b i t s t h i s t r e n d due t o t h e absence o f a downwash f o r m u l a t i o n i n those models.
9
,,,' ,,'
/
,,,' ,,,,' ,,' ,,'
/
/
/
// ,/ ~- OBSERVED
DATA ANL __._...~._ HANNA -~ - WIN1 A R S K I-FR ICK __ - SLAWSON-WI GLEY
0
0.0
1.0
2.0
3.0
4.0
5.0
K=UO/WO F i g . 2. V a r i a t i o n o f Downwind Distance X/D, EDF DATA AT/ATo = 0.1
...
w i t h K f o r C e n t e r l i n e L o c a t i o n where
46
The method of plume merging we employ in our multiple-tower model follows the work of Wu and Koh (ref. 7). In that method the merging logic involves treatment of plumes from each tower or cell as separate plumes until they begin to interact; then a merged cross-section occurs which is represented as a finite slot jet in its central part and two half round jets at both ends. The advantage to that method is mainly that it accounts for the effects of wind direction on entrainment in the merging process. Model trajectory and dilution are compared with lab data acquired by EDF (Fig. 3a-b) for a configuration of four towers located at the vertices of a parallelepiped. The lower predicted line in (Fig. 3a) represents the cross-sectionally averaged concentration whereas the top curve represents the model prediction if the lateral -vertical distribution is a double-Gaussian. The correct prediction should lie somewhere between those lines. Other satisfactory validation of the multipletower model exists for lab data (two and four towers and mechanical-draft configurations) and with field data at the Neurath and Amos towers. //
/”
/ EDF D o t o Fo=O. 8
4 Towers K=3.03
EDF D o t o Fo=O. 8
4 Towers
K=3.03
LEGEND
0 0
10.0
X/ D
25.0 3 0 .
0.0
5.0
10.0
15.0
X/
= Observed
= ANL
20.0
D
Fig. 3 . Comparison of ANL Model Predictions of (a) Centerline Dilution and (b) Centerline Trajectory to EDF Laboratory Data.
Model
25.0
30.
47 SALT-DRIFT DEPOSITION Rur e v a l u a t i o n s t u d y ( r e f . 3) o f t e n s a l t - d r i f t d e p o s i t i o n models r e v e a l e d l a r g e , sometimes order-of-magnitude, a b l e models. needed:
d i f f e r e n c e s i n p r e d i c t e d d e p o s i t i o n r a t e s among a v a i l -
Improvements i n each o f t h e f o u r components o f a d r i f t model were
i n plume r i s e ( d e s c r i b e d above), d r o p l e t breakaway f r o m t h e plume, d r o p l e t
e v a p o r a t i o n , and i n d e p o s i t i o n under ambient t u r b u l e n c e e f f e c t s ( n o t y e t i n c l u d e d ) . E x i s t i n g d r o p l e t e v a p o r a t i o n f o r m u l a t i o n s were l a r g e l y i n a c c u r a t e due t o ( a ) simp l i f y i n g assumptions c o n c e r n i n g t h e t e m p e r a t u r e o f t h e d r o p and ( b ) t o erroneous assumptions c o n c e r n i n g t h e process o f d e s i c c a t i o n o f s a l t w i t h i n t h e drop.
Experi-
mental d a t a show t h a t p r e c i p i t a t i o n o f s a l t b e g i n s on t h e d r o p s u r f a c e and t h a t t h e d r y p a r t i c l e i s a c t u a l l y a porous c o n g l o m e r a t i o n o f t i n y c r y s t a l s r a t h e r t h a n one l a r g e c r y s t a l formed a t t h e d r o p c e n t e r as t h e models assume.
S a l t concentration
g r a d i e n t s may be l a r g e and need t o be c o n s i d e r e d i n modeling.
As p a r t o f o u r p r o j e c t , we developed ( a t t h e U n i v e r s i t y o f I l l i n o i s / U r b a n a ) an imp r o v e d a n a l y s i s ( r e f . 8 ) o f d r o p dynamics and thermodynamics w h i c h served as a b a s i s f o r o u r d r i f t model.
Owing t o t h e f a c t t h a t t h e p r e d i c t e d f i n a l s t a t e i s now a porous
p a r t i c l e t h a t i s h o l l o w i n s i d e (an e f f e c t o f s a l t g r a d i e n t s w i t h i n t h e d r o p ) i n s t e a d o f a commonly-assumed s o l i d c r y s t a l l i n e p a r t i c l e , t h e d r o p model p r e d i c t s t h e p o i n t o f d e p o s i t i o n f o r t h e s e p a r t i c l e s f u r t h e r f r o m t h e tower t h a n any o f t h e o t h e r e x i s t i n g methods t e s t e d . Improvement i n t h e a r e a o f d r o p l e t breakaway was made a l s o .
I n t h a t area, f i v e
d i f f e r e n t breakaway methods 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 w h i c h one p r o v i d e d t h e model w i t h t h e b e s t performance w i t h Chalk P o i n t f i e l d data.
Our d r i f t model (ANL
plume r i s e model c o u p l e d w i t h U n i v . o f Ill.d r o p e v a p o r a t i o n model) was r u n w i t h each o f t h e s e f i v e d i f f e r e n t breakaway methods a g a i n s t Chalk P o i n t sodium d r i f t d e p o s i t i o n d a t a ( F i g . 4).
Methods 1, 2, 3, and 5 a r e commonly used i n e x i s t i n g models; Method 4
was developed by us. b e t t e r performance.
Methods 2 and 4 p e r f o r m b e s t w i t h Method 4 p r o v i d i n g o v e r a l l Method 2 f o l l o w s t h e d r o p l e t descent w i t h i n t h e plume u n t i l t h e
d r o p f a l l s a d i s t a n c e equal t o t h e plume r a d i u s f o r breakaway; Method 4 i s a v a r i a t i o n on Method 2 i n which plume p r o p e r t i e s a r e a l l o w e d t o v a r y i n t h e v e r t i c a l d i r e c t i o n . Our d r i f t model i n c l u d e s Method 4 f o r breakaway.
SODIUM DEPOSITION R A T E J H U D Y E DATA -- 1.0 KM JUNE 16-17,1977 (TOWER) OBSERVED DEPOS I TI ON
~
,A
~-
--
, t
\*
r
METHOD METHOD METHOD METHOD METHOD
-.........
-
1 2 3 4
5
\
2 o--
V c 7
yG- 2 0
3400 345.0 3500 355.0 0 0 ANGLE (DEGREES)
50
10.0
Fig. 4. Comparison of ANL Model Predictions of D r i f t Deposition t o Sodium Deposition Flux Measurements a t Fixed Locations Along a 1.0 km Arc. (Methods 1-5 r e f e r t o Drop Breakaway Assumptions Described i n Text. )
REFERENCES 1 A.J. P o l i c a s t r o , R.A. Carhart, S.E. Ziemer, and K. Haake, Evaluation of Mathematical Models f o r Single and Multiple Source Natural Draft Cooling Tower Plume Dispersion, Final Report t o t h e U.S. Nuclear Regulatory Commission, in press, 1979, p p . 493. 2 W.E. Dunn, G.K. Cooper, and P.M. Gavin, Evaluation o f Methods f o r Predicting Plume Rise from Mechanical-Draft Cooling Towers, Second Conference on Waste Heat Management and U t i l i z a t i o n , Miami Beach, December 4-6, 1978. A.J. P o l i c a s t r o , W.E. Dunn, M.L. Breig, and J.P. Ziebarth, Evaluation of Math3 ematical Models f o r S a l t D r i f t Deposition from Natural-Draft Cooling Towers, Final Report t o t h e U.S. Nuclear Regulatory Commission, in press, 1979, PP. 450. 4. T.L. Chan and J.F. Kennedy, Turbulent Nonbuoyant o r Buoyant J e t s Discharged i n t o Flowing o r Quiescent Fluids, Iowa I n s t i t u t e of Hydraulic Research, 1972, Report No. 140. 5 . R.A. Carhart, A.J. P o l i c a s t r o , S. Ziemer, M . Wastag, and K. Haake, Mathematical Model f o r Cooling Tower Plume Dispersion from Single Natural-Draft Cooling Towers, Argonne National Laboratory, Argonne, I l l i n o i s , Report t o E l e c t r i c Power Research I n s f i t u t e , i n press. P . V i o l l e t , Etude de J e t s des Courants T r a v e r s i e r s e t Dans des Milieux 6 S t r a t i f i e s , Doctoral Thesis, l ’ U n i v e r s i t 6 P i e r r e e t Marie Curie, P a r i s , 1977. 7 F.Y. Wu and R.C.Y. Koh, Mathematical Model f o r Multiple Tower Plumes, Report NO. KH-R-37, W.M. Keck Laboratory of Hydraulics and Water Resources, California I n s t i t u t e o f Technology, Pasadena, C a l i f o r n i a , J u l y 1977. 8 P.M. Gavin, Dynamics and Thermodynamics of an Evaporating Salt-Water Drop, Master’s Thesis, Department of Mechanical and Industrial Engineering, University of I l l i n o i s , Urbana-Champaign, 1978.
Atmospheric Pollution 1980, Proceedings of the 14th International Colloquium, Paris, France, May 5-8,1980, M.M. Benarie (Ed,), Studies in Enoironmentul Science, Volume 8 0 Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
THE SIMPLE BOX MODEL M.M.
49
SIMPLIFIED
BENARIE
I n s t i t u t N a t i o n a l de Recherche Chimique Appliquee VERT-le-PETIT (France)
ABSTRACT Experimental evidence a v a i l a b l e from p u b l i s h e d r e g r e s s i o n a n a l y s i s concerning urban areas does n o t f i t the assumption o f i n v e r s e p r o p o r t i o n a l i t y between p o l l u t a n t c o n c e n t r a t i o n and wind speed. I n case o f predominant convective mixing, advection ( t r a n s l a t i o n ) would n o t change t h e c o n c e n t r a t i o n a t a l l , hence wind v e l o c i t y should e n t e r the formula w i t h zero power. I f advective m i x i n g dominates, the
-
1 power should be c o r r e c t . Long-time
average urban p o l l u t a n t c o n c e n t r a t i o l a seem t o show t h e i n f l u e n c e o f both mechanisms, hence i n t e r m e d i a t e experimental values are found f o r t h e exponent. The paper presents s t a t i s t i c a l evidence from Rouen and Strasbourg, France, t h a t i n w i n t e r , t h e wind speed exponent i s around
-
0.25 and i n summer, near t o zero.
INTRODUCTION I t has been shown ( r e f . 1 ) t h a t t h e simple box concept represented by the formula :
X=CQAU
-1
, where
x
= an average p o l l u t a n t c o n c e n t r a t i o n
c
= constant
QA = the source s t r e n g t h p e r u n i t area u
= the l o c a l wind speed
may be a t t a i n e d by a t l e a s t f i v e independent ways. Any o f these deductions contains e x p l i c i t b o r i m p l i c i t l y t h e d i l u t i o n volume ( o r f l u s h i n g frequency) idea, r e q u i r i n g the wind speed u t o appear w i t h the exponent -1 e x a c t l y . Experimental evidence a v a i l a b l e from p u b l i s h e d regression a n a l y s i s concerning urban areas ( r e f . 1 p.217 and r e f . 2 ) does n o t f i t t h e assumption o f i n v e r s e proport i o n a l i t y between p o l l u t a n t c o n c e n t r a t i o n and wind speed. This paper i n v e s t i g a t e s the wind speed exponent and i t s seasonal v a r i a t i o n s on hand o f urban records.
50
THEORETICAL A l i m i t e d area source w i t h i n an i n f i n i t e , r e l a t i v e l y source-less plane requires, as explained above, t h e wind speed power o f -1. On the o t h e r hand, a wind v e l o c i t y exponent equal t o zero, i . e . t h e independence o f the concentration o f wind v e l o c i t y might be understood by considering an extended area over which a constant ground concentration r e i g n s . Observed a t any p o i n t w i t h i n the area, the t r a n s l a t i o n (by the wind) o f the constant concentration does n o t modify the observed concentration. Hence t o t a l independence o f wind speed and wind d i r e c t i o n . Obviously, such an extended, constant concentration f i e l d i s b u t the l i m i t i n g , i d e a l i z e d case f o r ( a ) very large, very u n i f o r m area sources, and ( b ) f o r two meteorological s i t u a t i o n s , which by themselves represent i d e a l i z e d l i m i t s . ( b l ) One o f these meteorological s i t u a t i o n s i s when v e r t i c a l mixing up t o the i n v e r s i o n l i d i s instantaneous and t o t a l . I n c i d e n t a l l y , t h i s s i t u a t i o n i s assumed and works w e l l i n most advective c e l l models. (b2) The second l i m i t i n g meteorological s i t u a t i o n would be when absolutely no mixing i s t a k i n g place and a t h i n p o l l u t e d l a y e r i s displaced l a t e r a l l y l i k e a sheet. Therefore, r e a l urban s i t u a t i o n s w i l l have an exponent between 0 and -1, depending on the e x t e n t o f t h e urban area, the s i t u a t i o n o f the s t a t i o n w i t h i n i t and the r e l a t i v e i n t e n s i t y o f v e r t i c a l mixing. The generalized expression b
x = c Q u
A
becomes i d e n t i c a l t o equation (1) when b = -1. We may look a t the product c Q, i n two ways. It i s e i t h e r obtained by t h e m u l t i p l i c a t i o n o f the e m p i r i c a l o r deductive constant c which has the dimension ( l e n g t h - I ) by QA (mass u n i t area -1 u n i t t i m e - I ) . The o t h e r way i s t o consider
c
Q,
=
k and t o c a l c u l a t e k from
k = X u-b
(3)
by t h e use o f observed x and u values. This has been G i f f o r d ' s ( r e f . 3 ) approach by which he p u t the box model on a statistical-empirical
, receptor
o r i e n t e d basis.
I f b = 0, then k must be dimensionally and numerically equal t o the (seasonal) average concentration. I f O< b< 1, then k i s the r e s u l t o f a computation and i t s physical dimension i s governed by t h e e m p i r i c a l l y obtained value o f b. The nearer t h e b value t o zero, the b e t t e r k must approximate concentration.
x,
the average seasonal
51
RESULTS Equation (2) has been solved by the l e a s t squares technique f o r optimal c and b values from seasonally grouped 24 h data provided by three years' record i n Rouen and two years' observations i n Strasbourg, both i n France. I n each representative s t a t i o n ( t h r e e i n Rouen and f i v e i n Strasbourg) two p o l l u t a n t s were measured: SO2 and "black smoke" ( r e f l e c t i v i t y ) .
Based on the data o f Rouen, because t h e r e the record was longer and the d i v e r s i t y among t h e s t a t i o n s more pronounced, t a b l e 1 shows t h a t the s t a b i l i t y o f t h e b values i s q u i t e s a t i s f a c t o r y from y e a r t o year. This means t h a t averaging has some sense and perhaps, w i t h more forthcoming evidence, we w i l l be able t o r e l a t e the averages t o the s i t e o f the observations o r t o o t h e r independent variables. TABLE 1 Seasonal wind speed exponent ( b ) values computed from the Rouen data. Station
Pollutant so2
City centre
Black smoke so2
Suburban
Black smoke so2
I n d u s t r i a1
Black smoke Table
summer 1970 -.01
winter 1969 1970 -.28 -.29
1971 -.32
1969 -.17
-.50
-.54
-.48
-.14
-.32
-.26
-.40
-.58
-.54
-.33
-.02
-.16
-.37
-.57
-.47
-.21
-.32
-.22
-.18
-.07
-.16
-.26
-.23
-.14
-.49
-.31
-.36
-.22
-.13
-.29
1971 -.11
2 presents the average seasonal k and b values as obtained from the regression
equation ( 2 ) . TABLE 2 Average k (with standard d e v i a t i o n s ) and b values computed by equation ( 2 ) from three years' d a i l y data o f t h r e e s t a t i o n s f o r Rouen and two years' d a i l y data o f f i v e s t a t i o n s i n Strasbourg : x i s t h e average observed concentration i n ug ~ n - ~ . Strasbourg X k Winter
S umme r
Rouen k
X
+ 22
77
2
22
72
134
Smoke
67
-+
19
54
56
2
19
41
so2
31
2
11 33
64
+ 27
63
Smoke
30
2
10
23
+
22
so2
a s t r o n g l y s i t e dependent.
28
7
122
b both c i t i e s
-0.3 t o
5
0.0
-
0.2
0.5 a
52
I t may be seen t h a t t h e average exponent f o r SO2 i n sumner i s 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 zero, thus c o n f i r m i n g t h e t h e o r e t i c a l i n f e r e n c e . The urban summer concentrations a r e never very f a r from t h e r u r a l background, thus advection by the wind i s almost w i t h o u t i n f l u e n c e . During t h e h e a t i n g season, t h e s p a t i a l average o f t h e exponent i n b o t h c i t i e s i s
-
0.25. There i s a v a r i a t i o n within the c i t y , w i t h
a c l e a r tendency f o r t h e exponenet t o be s m a l l e r i n absolute value i n the centre
-
and t o a t t a i n
0.5 i n more o u t l y i n g r e s i d e n t i a l suburbs.Obviously,
where a h i g h
c o n c e n t r a t i o n i s replaced by a low one from t h e country, o r vice versa, t h e v e l o c i t y o f t h i s t r a n s p o r t e x e r t s an i n f l u e n c e on t h e i n d i v i d u a l event, as i t has been shown by Venkatram ( r e f . 4 ) and consequently, may be observed as w e l l i n t h e terms o f t h e average c o n c e n t r a t i o n . For b l a c k smoke, t h e summer exponent i s near
-
0.3 t o
ce
-
-
0.2 and i n t h e w i n t e r , from
0.5. This can be understood as an expression o f t h e g r e a t e r d i f f e r e n -
f o r smoke than f o r SO2, between r u r a l background and urban concentration, i n
summer as w e l l i n w i n t e r . Without r u r a l background a t a l l , the exponent would o b v i o u s l y be
-
1.
It can be seen f u r t h e r t h a t t h e nearer b i s t o zero, the b e t t e r t h e f i t between k and
x.
T h i s i s a l s o i n accordance w i t h t h e theory.
APPLICATION Table 3 shows t h e d a i l y c o n c e n t r a t i o n f o r two randomly s e l e c t e d weeks o u t s i d e t h e development sample, computed on one hand by equation ( 2 ) , seasonal k and b values and t h e observed wind speed, and on t h e o t h e r hand, by equation (1) and the
same wind speeds. To do j u s t i c e t o equation ( l ) , seasonal k values were
computed and used i n t h e same way as f o r equation ( 2 ) , the o n l y d i f f e r e n c e being t h e imposed value o f b = -1. A n e g a t i v e exponent value near t o zero n o t o n l y gives a g e n e r a l l y b e t t e r f i t t o the observed data, b u t as t a b l e 3 shows, avoids the nonsensical h i g h concentrations y i e l d e d by e q u a t i o n ( 2 ) as wind v e l o c i t y approaches calm c o n d i t i o n s . Although table 3 i s a s e l e c t i o n meant t o i l l u s t r a t e t h i s p o i n t
w i t h o u t p r e t e n t i o n t o represent
a l l s i t u a t i o n s , i t can he seen t h a t equation ( 2 ) achieves acceotable (annual) means o n l y by averaging over
-
and u n d e r p r e d i c t i o n s .
Lowering t h e absolute value o f t h e wind speed power improves the general f i t between c a l c u l a t i o n and observation. Thus, w i t h equation ( 2 ) , t h e t y p i c a l w i n t e r 30-days' c o r r e l a t i o n c o e f f i c i e n t i s from 0.4 t o 0.5, w h i l e the a p p l i c a t i o n o f equation ( 2 ) y i e l d s o n l y 0.2 t o 0.3. That means an increase i n t h e s i g n i f i c a n c e from worse than 10% t o b e t t e r than 2%. I t should be noted, t h a t such agreement can be achieved by t h e box model, improved o r not, o n l y i n the case o f t r u e area sources, t h a t i s , when t h e i n f l u e n c e o f p o i n t sources may be neglected.
53
TABLE 3 Examples o f d a i l y average s u l p h u r d i o x i d e c o n c e n t r a t i o n ( p g
as c a l c u l a t e d
f r o m e q u a t i o n s (2) and (l), S t r a s b o u r g , France. Data Jan 14 1977
15 16 17 18 19 20 Aug 1 1977 2
Average 24-h wind v e l o c i t y
5.1 5.8 2.5 0.2 0.6 1.8 0.1 2.0 1.9 0.3 0.6 0.4 0.3
Observed conc.
64 52 70 111 120 110
118 18 28 33 22 18 16
Computed E q u a t i o n (2) E q u a t i o n (1)
51 49 61 120 86 67 143 30 30 35 33 34 34
26 23 53 778 208 76 1574 28 28 194 91 131 161
REFERENCES
1 M.M. B e n a r i e , Urban A i r P o l l u t i o n M o d e l l i n g . M a c m i l l a n , London and B a s i n g s t o k e , 1980, p.143-6. 2 M.M. B e n a r i e , The Simple Box Model R e v i s i t e d , A t m . E n v i r o n . 12, 1978, p. 1929-30. 3 F. G i f f o r d , The s i m p l e ATDL Urban A i r P o l l u t i o n Model. Proc. 4 t h Meet.North A t l a n t i c T r e a t y O r g a n i z a t i o n , E x p e r t Panel on A i r P o l l u t i o n Modeling, O b e r u r s e l , 28 t o 30 May 1973, p.XVI-1 t o XYI-18. 4 A. Venkatram, An E x a m i n a t i o n o f Box Models f o r A i r Q u a l i t y S i m u l a t i o n , A t m . E n v i r o n . 12, 1978, p . 2243-49
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GAUSSIAN PLUME
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Atmospheric Pollution 1980,Proceedingsof the 14th International Colloquium,Paris, France, May 5--8,1980,M.M. Benarie (Ed.), Studies in EnvironmentalScience,Volume 8 0 Elsevier Scientific Publishing Company,Amsterdam - Printed in The Netherlands
57
SENSITIVITY ANALYSIS OF THE GAUSSIAN PLUME MODEL
G. NEUMA”, G. HALBRITTER Kernforschungszentrum Karlsruhe, Abteilung fiir Angewandte Systemanalyse, Karlsruhe (F.R.G.)
ABSTRACT The relative sensitivity of the Gaussian plume model with respect to the input parameters was checked analytically. The influence of varying input parameters to the mean concentration of areas of different sizes was tested. It was found that the most important parameters are the mean wind speed and the emission height near the elevated source. Further downwind of the source, the influence of the source height can be neglected in comparison with the top of the mixing layer. The importance of the dispersion parameters u
a is small compared with the other parameY’ z ters considered. The same results are found in examining the long-term concentration
average of areas of different sizes as a function of varying input parameters.
IMTRODUCTION The Gaussian plume model is recommended in various official regulations on air pollution calculations. These regulations include different versions of the basic Gaussian plume model, different diffusion parameters and different formulas to calculate the mean wind speed and the effective emission height. The influence of the limited height of the mixing layer is nearly always neglected, although this parameter becomes more and more important further downwind of the source. In order to demonstrate the importance of the top of the mixing layer and in order to compare the results of calculations of the outdoor pollutant concentration with different input parameters it is important to analyse the sensitivity of the model with respect to its parameters.
In this paper, a sensitivity analysis is performed and the transferability of the results to calculations of the long-term concentration average is tested.
THE GAUSSIAN PLUME MODEL The Gaussian plume model describes the atmospheric pollutant concentration C downwind of a stationary source with the emission height H and the source strength Q under certain restrictive conditions. The pollutant is transported by the mean wind
58 speed U and the diffusion velocity. The horizontal and vertical diffusion of the
.
plume is described by the dispersion parameters a a The top of the mixing layer z Y’ and the ground constitute definite borders of the model at the height YM and z = o resp.. The concentration can be calculated as follows:
+ 1
+m
2
exp (-
(z-h+2*k-YM)
1
+
exp (-
(z+h+2 - k *YM)
2a
k=-m
k#O
2
2 ))
2a z
THE SENSITIVITY ANALYSIS Sensitivity is formally defined as the partial derivative of a system’s output with respect to its input. Instead of differentiating the equations analytically, a more practical definition which is often employed is the incremental change in output resulting from an incremental change in input. In this paper, besides the relative partial derivative of the concentration, a YM. the more practical 2’ y’ definition of sensitivity is used and the percentage change of the mean concentration
which is obtained analytically with respect to U, H, a
YM y’ is tested, because regulatory guides require the calculation of this mean concentra-
of an area due to percentage variations of the input parameters U, H, a
2’
0
tion value. The mean concentration is obtained by averaging the concentration assigned to each cell of an area for one atmospheric condition (short-term value). The variation of the input parameters is done from
2 10
% stepwise to up to
2
40 %,
and for all atmospheric stability classes ( 6 classes adapted from Klug/Manier) as well as for two areas of different sizes with a sector of
2 50 degrees around the
main wind direction and up to a distance of 5 and 40 km resp. downwind of the source. If the input parameters are not varied, the concentration is calculated for H for heights of the top of the mixing layer adapted from Klug (ref. 2).
=
100 m,
for dispersion
parameters (Jiilich, 100 m) (ref. l ) , and for the mean wind speed calculated from a reference value (6 = 2 m/s) according to the German regulations for calculating the radiological impact (ref. 1). Further, the long-term mean concentration is tested in the same way for the input
.
(J a It is obtained by averaging the concentrations assigned z’ Y to each cell of an area of 10 x 10 km and of 20 x 20 km resp. at each hour over a
parameters U, YM,
total period of 10 years.
59
RESULTS Theoretical considerations The relative partial derivatives of the concentration of the Gaussian plume model, which are obtained analytically (see equation I ) , demonstrate the sensitivity of the model with respect to its input parameters U, H, u
0 2’
and for k
’
- E c aH
Y
at a height z = o
= 0:
= - _H
2
Z
For distances x > x (if uz = YM then x = x ) the greatest importance is found for YM. Equation 1 can be approximated and then differentiated, so that the relative sensitivity of the model is as follows:
From equations 2 and 6 it follows that the relative sensitivity is negative and its absolute value is reduced with increasing parameters U, YM. From equations 4 and 5 it follows that the relative sensitivity is negative, if H < and y < 0 and Y positive, if H > uz and y > u The sensitivity of the model is negative, but its Y absolute value is increasing with increasing parameter H (see equation 3 ) .
.
Sensitivity of the short-term mean concentration Thp mean concentrations of two different areas were calculated to demonstrate YM on these valthe influence of variations of the input parameters U, H, %’ uY’ ues. Fig. 1 demonstrates the impact of the mean wind speed and the horizontal disper-
sion parameter on the mean concentration of an area up to a distance of 5 km, fig. 2 the influence of the parameters
0
z’
H. A comparison of the calculations done for
different parameters shows the dominating influence of the mean wind speed on the mean concentration for all stability classes except F, E, where the parameter H, which is second in importance, is more influential. The importance of
(5
is less
60
than that of H, but greater than that of
0 The sensitivity with respect to a Y' is positive for stable classes F, E, but negative for the rest.
\ \
s
\\
.-C
:
E
+LO.
\
\
--hwizontal dispersion parameter cI
+20-
'\
b >
Y
\ -20
C
0 .Y .-D
wind speed
---mean
+60
F, ED C . 0 . A
-&O1
Variation of the input parameter in %
Fig. 1. Effect of varying mean wind speed and horizontal dispersion parameter on the mean concentration of an area of up to 5 km downwind of the source. The results of further calculations for the parameters YM, H, and
oz,
calculating
the mean concentration for the area of up to a distance of 40 km downwind of the source, demonstrate the importance of taking into account the limited height of the mixing layer. The relative sensitivity with respect to YM is negative, its absolute value is decreasing with increasing parameter value YM, and strongest for classes E, A, weakest for stability classes C, D. The mean concentration value of class E varies between +65 % and -23 X due to a parameter variation of YM between
40 %.
In comparison to the mixing layer the influence of the emission height is much less pronounced. The influence of
a
is small compared to that of YM and H. When
enlarging the grid size, the impact of the parameters H,
0
on the mean concentra-
tion decreases. Sensitivity of the long-term mean concentration
In order to investigate the sensitivity of the long-term mean concentration as a a YM, U, the long-term concentration 2' y'
a function of varying input parameters
value was calculated for a source of 100 m height in areas of 10 x 10 km and 20
x 20 km resp. around the source with the joint frequency distribution of meteoro-
61
--- vertical dispersion parameter
uz
-emisslon haght
,I
-40
Variation of the input parameter in
YO
Fig. 2. Effect of varying emission height and vertical diffusion parameter on the mean concentration of an area of up to 5 km downwind of the source. logical data over a 10-year period from Hanover (West Germany). The results from the sensitivity tests are in accordance with the results of the previous tests of the short-term mean concentrations. However, the long-term mean concentrations are much less sensitive than the tested short-term values to variations of YM, u
2’
uy
(fig. 3 ) . The variations of the mean wind speed have the greatest impact on the long-term concentration. The sensitivity with respect to U is the same as for the does not influence the long-term Y mean concentration at all. The impact of YM on the long-term value increases with short-term value. The horizontal parameter u
increasing grid size.
Station : Hannover- Langenhagen H= IOOm -20x20 Krn grid ---lo x 10 Km grid
Variation of the input parameter in
YO
Fig. 3. Effect of varying mean wind speed, height of the mixing layer, and vertical dispersion parameter u z on the long-term mean concentration value of different grids of 10 x 10 and 20 x 20 km resp..
CONCLUSIONS The sensitivity of the Gaussian plume model is greatest to variations of the mean wind speed. Its influence is independent from the region considered. Near the source, the emission height is approximately of the same importance or greater for all stable classes. With increasing distance from the source, however, the influence of the emission height is reduced and the concentration is mainly determined by the height of the mixing layer for all atmospheric classes.
aY3 u z are of minor importance in comparison to U, H, YM. Because of the importance of the parameters U, H, efforts should be made to
achieve conformity in the calculations of these parameters in the various regulatory guides. Likewise, the top of the mixing layer should be taken into account for concentration calculations for larger distances from the source.
REFERENCES 1 Bundesministerium des Innern, Allgemeine Berechnungsgrundlagen fiir die Bestimmung der Strahlenexposition durch Emission radioaktiver Stoffe mit der Abluft, 1977, 21-22,
64-65.
2 W. Klug, Ein Verfahren zur Bestimmung der Ausbreitungsbedingungen aus synoptischen Beobachtungen, Staub-Reinhaltung Luft, 2 9 ( 1 9 6 9 ) , 143-147.
Atmospheric PoNution 1980, Proceedings of the 14th International Colloquium, Paris, France, May 5-8,1980, M.M. Benarie (Ed.), Studies in Environmental Science, Volume 8 0 Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
63
DEVELOPMENT OF A GAUSSIAN PLUME MODEL APPROPRIATE TO AN URBAN AREA
M. BENNETT Central Electricity Research Laboratories, Leatherhead, U.K.
ABSTRACT The modelling of pollutant dispersion over a city requires account to be taken of the change in the wind and turbulence fields as the air moves from a rural to an urban area due to heat and surface roughness. The paper describes an adaptation
of the Gaussian plume model which takes this feature into account.
Dispersion
formulae which have been developed within the CEGB have been used in applying the model to the London area. The treatment of fumigation is discussed and compared with other published calculations.
INTRODUCTION The mathematical description of atmospheric pollution levels in the London area and the correlation of observed levels with particular sources is a highly complex problem.
The conurbation extends over the Thames Basin and is bounded
by low hills inland and by the sea to the East.
This geographical setting combines
contributions from shoreline and urban meteorology. extend into central London.
Sea breeze effects can
There are urban effects on both wind speed and
direction (Ref. 1). Further, for easterly winds there is the possibility of both an urban and a shoreline internal boundary layer.
Apart from domestic emissions,
the main sources of sulphur dioxide are concentrated along the east-west line of the Thames and its estuary.
Hence for winds in this direction there is an
accumulation of sources with the possibility of eventual fumigation effects. A multi-source model is being developed which includes two-dimensional wind field and fumigation effects.
The present paper concentrates on the latter aspects.
SEGMENTED PLUME MODEL It will be assumed that dispersion from each contributing source obeys the conventional Gaussian formulation with dispersion coefficients based upon CEGB field survey data (Ref. 2 ) .
An
approach using the advection-diffusion equation
64 i s p r e f e r a b l e i n some ways b u t t h e r e a r e numerous numerical p i t f a l l s and i n s u f f i c i e n t d a t a t o u t i l i z e t h i s approach t o t h e f u l l .
Further, t h e r e a r e
p h y s i c a l e f f e c t s r e l a t e d t o plume meander which are neglected by g r a d i e n t t r a n s f e r t h e o r y b u t which can be e a s i l y included i n a semi-empirical Gaussian approach. The b a s i s of t h e d i s p e r s i o n model i s shown i n Figs.
1 and 2.
Wind and
t u r b u l e n c e f i e l d s a r e d e f i n e d on a square g r i d having dimensions 5km x 5km. each t i m e s t e p , A t ,
a source emits a marker p o i n t which d r i f t s downwind.
At
This
g e n e r a t e s a s t r i n g of marker p o i n t s , marking t h e l i n e of t h e plume t r a j e c t o r y (Fig. 1 ) . A segment of Gaussian plume i s used t o j o i n each p a i r of marker p o i n t s . Each marker p o i n t remembers t h e crosswind and v e r t i c a l spread of t h e plume and
i t s a p p r o p r i a t e source s t r e n g t h .
A s t h e marker p o i n t moves downwind t h e s e spreads
i n c r e a s e according t o l o c a l c o n d i t i o n s .
Acceptably smooth i n t e r p o l a t i o n i s obtained
by using a marker p o i n t spacing of A 1 = 9.5km.
A model using d i s c r e t e p u f f s a s
opposed t o segments d e f i n e d i n t h e above fashion would r e q u i r e many more p o i n t s . For t h e plume-spread w i t h i n t h e urban mixing l a y e r t h e semi-empirical formulation of Ref. 2 w i l l be used, where t h e v e r t i c a l variance i s given by 2
uz ( X I
= Ld(H)x
and t h e l a t e r a l v a r i a n c e by
u
2 2 (x) = uz(x) Y
+ B 2x 2 .
46 t
i
Fig. 1. Advection of a marker p o i n t through t h e wind f i e l d .
65
Point
Fig. 2. Segment of Gaussian plume between two marker points. at measuring point is + ( u l ~- .2 )A~/A~. z
.',
Vertical variance
-
Here Ld(H) is a dispersion length at plume height, determined from early measured meteorological parameters; x is the down-wind distance and B = 0.065 47T/u where -1 u(m-s ) is the windspeed at plume height and T(hours) is the averaging period. The second term in ( 2 ) models the changing of wind direction with time.
In finite
difference form, equations (1) and ( 2 ) become
Ld(H) and B may then take local values.
In particular, Ld(H) is zero above the
mixing layer. A scheme based on Ref. 3 is used to take account of reflection of pollutant from the ground and from the top of the mixing layer.
Expressions for plume rise
due to Moore and Lucas (Refs. 4 and 5) are used for the large sources. The region is divided into urban and rural areas and appropriate boundary layer properties Over the city, L is increased mechanically by the d greater surface roughness and thermally by artificial heat emissions. are estimated for each.
FUMIGATION We consider a plume emitted above the rural boundary layer which is entrained into a convective urban boundary layer (Lda H4l3) at distance xo from the emitter The depth of the urban boundary layer is assumed to equal the plume height, H, this being the worst case.
According to equation ( 3 ) , the plume variances at x
downwind of the point of entrainment are
66
C
0.4
I\ 0.3
ref. 7 (Well-mixed BL)
I-\
u = 7ms' I T = 1 Sensible surface heat flux 160 w Present Ca Iculat ion x,= 0
0.2
0.1
-
(Funligation) / /
0
200
400
600
ref. 8 (No Fumigation)
Present Calculation x, = 40 km
Hlm
Fig.3. Comparison of concentration factors according to different calculations.
u
2
Y
(x)
=
(4)
uz2 (x) + 8* (x + xo) 2.
Using the formula from Ref. 3 for the ground level concentration, it is then possible to find the maximum ground level concentration, xmax as a function of 2 x. Defining a concentration factor, C as uH xmaX/Q where Q is the rate of emission, we can plot C as a function of the plume height.
This is done in Fi9.3
together with the results of other published calculations (Ref. 7 and 8). The model used in Ref. 7 over-estimates ground level concentration by allowing the plume to mix instantaneously to the ground.
The present calculations indicate that:
(1) C increases with H because the boundary layer is purely convective with L d 4/3
proportional to H (2)
.
The turning of the wind greatly reduces mean concentration from distant
emitters. We have applied this calculation to power stations in the Thames Estuary.
For
67
Kingsnorth on full load (1920 MW, mixed fired, 50 km from central London) the maximum concentration in central London would be 200 pg-m of wind speed.
These calculations are broad
-3
, almost
independent
in agreement with observed values
derived from the Nanticoke study on the shore of Lake Ontario (Ref. 6). The latter are probably over-estimates for the London situation because the onset of the urban boundary layer is much less well defined than the shoreline case. point of maximum concentration moves rapidly laterally and along wind.
The
This makes
the time-dependence of the ground level concentration formally similar to that at the break-up of the nocturnal inversion.
When measurement data becomes available
from the monitoring network being set up in the Thames Estuary better comparisons will become available. Summarizing, a multi-source model for dispersion over an urban area has been developed and applied to cases where fumigation occurs.
Preliminary comparisons
with observations at Lake Ontario show reasonable agreement. Comparison with earlier calculations of the dependence of maximum ground level concentration on source height show significant differences in the most pessimistic case with a convective urban boundary layer and indicate the need for more measurement data.
REFERENCES D.O. Lee, A t m o s . Env., 13(1979)1175-1180 D.J. Moore, Proc. Inst. Mech. Engrs., 189(1975)33-43 R J Yamartino, J. Air Poll. Cont. Ass., 27(1977)467-469 D.J. Moore, Atmos. Env., 8 (1974)441-457 D.H. Lucas, Atmos. Env., l(1967)421-424 R.V. Portelli, "The Nanticoke Study : Experimental Investigation of Diffusion from Tall Stacks in a Shoreline Environment", 10th NATO/CCMS International Technical Meeting on Air Pollution Modeling and its Application. (1979) 7 W.A. Lyons and H.S. Cole, J. Appl. Met., 12(1973)494-510 8 H. van Dop, R. Steenkist and F.T.M. Nieuwstadt, J. Appl. Met., 18(1979)133-137
68
APPENDIX
:
EXPRESSIONS FOR MAXIMUM GROUND
LEVEL
CONCENTRATION DURING FUMIGATION
We consider a plume of height H in a boundary layer of depth H.
If the boundary
layer is uniformly dispersive, the pollutant concentration on the ground along the axis of the plume is given by the method of images as
where
Yamartino (Ref. 3 ) points out that the expansion in equation (6) can be related to a Jacobi function of the third kind and proposes a approximation scheme for
this function.
We have neglected the higher-order terms in his scheme (which
contribute less than 4% of the final value) and arrive at the following expression for the axial concentration:-
for az (x)> (2/3) H.
Inserting the expressions from equation ( 4 ) for the plume
spreads, and differentiating with respect to x, leads to a transcendental equation for the maximum ground level concentration. This can readily be solved numerically. The concentration factor,
C =
the dimensionless variables 5 and
CL
;10, C
xmaxuH2 /Q =
approaches 0.4604
TI
can then be seen to be a function only of 2 2 2 2 2 L x /(2H ) and a = n L / ( 2 8 H ) For 5 = 0 d d o 4/(en). 2
.
AIRFLOW AND DISPERSION
This Page Intentionally Left Blank
AtmosphericPollution 1980, Proceedineg of the 14th InternationalColloquium,Paris, France, May 6-6.1980, M.M. Benarie (Ed.), Studies in Environmental Science, Volume 8 0 Eleevier Scientific Publishing Company,Amsterdam -Printed in The Netherlands
71
PHYSICAL THEORIES OF TURBULENT DIFFUSION
B.E.A.
FISHER
Central Electricity Research Laboratories, Leatherhead, Surrey (U.K.)
ABSTRACT Various methods of approximating turbulent diffusion are reviewed in the simplest case of homogeneous, steady turbulence.
Amongst the methods considered are random
walk models, second order closure models, random force models and analytic theories based on the exact equations of motion describing dispersion of marked fluid.
All
the models are tractable in the limit when the 'diffusion' approximation applies and it is shown directly from the equations of motion why this should be so.
In two of
the cases reviewed, a new and more direct method of derivation is used.
INTRODUCTION Industry needs to have practical methods for calculating the height of chimneys. These depend either on theoretical or empirical descriptions of dispersion by atmospheric turbulence.
There are a number of theories of turbulent diffusion which
using simple physical ideas attempt to simplify the complicated processes and to introduce practical methods for calculating the dispersion of material in a turbulent fluid.
The purpose of this paper is to investigate a whole range of practical models
and to see what support they have on theoretical grounds.
Our conclusion is that
the 'diffusion' approximation remains the best working hypothesis. We consider the time-averaged vertical dispersion of a continuous plume in the atmosphere.
There is an upper limit to the timescale of eddies contributing to the
turbulence.
This means it is possible to choose an averaging time which is much
longer than the turbulent timescale and thereby ensure that the time-averaged plume is not dependent on averaging time.
If we were modelling dispersion in a horizontal
plane in the atmosphere no limit to the timescale of eddies exists and there is no reason for expecting that a 'diffusion' approximation approach would be satisfactory.
RANWM WALK MODEL OF TURBULENT DISPERSION
In this model the dispersion is based on consideration of the random movement of a series of particles.
It is an important model, as the ideas behind it lead to
Taylor's theorem for the mean square distance material has dispersed from its source in a steady, homogeneous turbulent fluid. from the origin (Taylor, 1921) is given by
The mean square displacement of particles
72
where T is the characteristic time for reversal of particles and w is the root mean
In the same limit the concentration of particles is given
square turbulent velocity. by the 'telegraph' equation 2 ac 2 +
at
2a2c
=
0
2
7 a t
az
It is well known that in a certain limit the 'telegraph' equation, which allows for the finite velocity of particles, is equivalent to the diffusion equation.
Then
the concentration satisfies
where K is the effective eddy diffusivity given by K = w
2
'1.
In this model and subsequent models, we shall express the concentration in terms
of the Laplace transform, with respect to time, and the Fourier transform, with respect to space, of the concentration, namely C(p,k)
=
1,
ikz
e-pt
e
C(t,z)dzdt
(4)
--m
This is in order to compare in a simple way the equations used to model the concentration field.
In each case we shall consider a unit release from a point z = 0 at
time t = 0. For the 'telegraph' equation, the initial conditions are lim C(z) = 6(z) a c w = 0, for which the transformed concentration is t-m at
diffusion equation the concentration is
-
1 2 2
p + k w r SECOND ORDER CLOSURE MODELS Equation ( 3 ) is one of several ways of closing a system of equations for the turbulent flux of material.
The principle of second order closure methods is to go
beyond a simple gradient transfer approach and allow a more general dependence of flux on concentration and derivatives of the concentration. The method assumes that the time-averaged concentration can be represented by a differential equation so that the expression for the flux is local in space and time. use the followinn closiirt= emiationq.
Firqtlv
Lewellyn and Teske (1976)
73
since this is the basic equation for conservation of mass; secondly, the following equation for the mass flux -aF =
-
at where v
w2
E+
v w
2
T
-a2F -2 az
AF T
and A are empirical constants.
This is just a generalization of the
'telegraph' equation, with the transformed concentration given by
with the initial conditions lim C(z) t* With vc = 0 and equation.
A =
= 6(2)
ac
and lim - = 0. t* at
1 this I s equation ( S ) , the solution from the 'telegraph'
The form of closure given by equation ( 8 ) involves two additional conand A , apart from the constants w and T used in the random walk model.
stants v
The main criticism of this approach is that it still does not provide a theoretically exact description of the turbulence in a homogeneous, steady turbulent fluid.
ANALYTICAL THEORIES OF TURBULENT DIFFUSION It is usual in analytic theories of turbulent dispersion to discuss the form of the probability density G(t,z;O,O) that a particle emitted at time t = 0 and z = 0, is at height z at time t.
G can be identified with the concentration in a plume
emitted from z = 0, the quantity C(t,z) discussed in earlier sections.
From the
'direct interaction' approximation, Roberts (1961) was able to develop an equation for G(t,z), which retains some of the essential nature of turbulence, and in
particular the non-local nature of turbulent interactions in space and time.
The
equation for C(t,z) is in Fourier space
The Laplace transform of equation (10) can be written C(p,k)
=
1
P + +2 Q(p,k) This has a formal similarity to the solution of the diffusion equation given by equation (6), but Q(p,k) itself depends on the dispersion of particles and has the form
74
is the Fourier transform of the Eulerian velocity correlation. Roberts (1961) mentions an alternative form for the transformed concentration suggested by Bourret, namely
which is local in space, but is still not a local function of time.
Neither equation
(11) nor equation (14) can be directly inverted by transform methods to give an expression for C(t,z). For long times, Roberts suggests Q(p,k) should be replaced by Q(0,O) which is 2 then formally equal to w T , so that we are back with diffusion equation. However equation (11) shows that when the diffusion approximation does not apply, because correlations are still important, the equation describing the concentration is not necessarily a simple differential equation, local in space and time.
Bourret's model
is equivalent, in an approximate sense, with the 'telegraph' equation.
DIRECTLY FROM EQUATIONS OF MOTION
DERIVATION OF FORM OF CONCE-TION
It can be seen that the form of solution for the concentration in each of the models considered so far, has a certain similarity. the equations of motion why this form exists. a diffusing molecule.
It can be shown directly from
We consider the equation of motion for
@(t,zlO,O) is the concentration distribution of marked fluid
particles for a particular realization of the flow, the particles being released from z = 0, at t = 0. Then as before C(p,k)
=
:1
e-pt lei*'
dzdt
and we need to consider the additional functions
and UL(p,k)
.
=
w(t,z) w(0,O) $(t,zlO,O) dzdt
The exact equations relating C, C
W
(p
+
Dk
2
C(p,k)
+
ik Cw(p,k)
=
1
and U are L
(15)
75 (19) where D is the molecular diffusivity, leading to
In the limits kw/W, p r 4 (whichareequivalent in real space to z >> w t and t >> T )
our exact expression, equation (201, takes the form
All the other models have the same functional form in this limit which is the limit in which the diffusion approximation applies. from this exact limit.
The problem remains of extrapolating
It is plausible that C(p,k) takes the form of an infinite
series and the most straightforward generalization is C(P,k)
1 %
(22)
2
P + k (D + UL(Prk)) which has a functional form similar to Roberts' and Bourret's models, but with U still to be determined. L
RANDOM FORCE MODELS The random force model is a simple generalization of the random walk models except that particles are assumed to be under the influence of random forces which take the place of random fluctuations in velocities in the random walk model.
The basic
equation satisfied by the displacement of a particle is
where B is a coefficient expressing the retarding effect of frictional forces on the particle, N 2 ( E
-
9_ *) p0 az
is the Brunt-Vaisala frequency which gives the frequency of
oscillation of particles in a stably stratified flow, and A is a random force, which is taken to be stationary and homogeneous.
On integration this leads to (Pearson,
Puttock and Hunt, 1978)
where O ( o ) is the power spectrum of the random force field. Provided the random force A(t) is not correlated with the velocity field, so that w(0) A(t) = 0 for t > 0, the fluctuation-dissipation theorem applies (Kubo, 1966) which states that O ( o ) = 2w
2
B ( w ) i.e.
that the systematic part of the force appearing
76 as friction is actually determined by the correlation of the random force with itself. If the correlation between the random forces is very short, then B ( w ) 1 equals a constant, -and in the limit of a neutral atmosphere equation (24) reduces to equation (1).
CONCLUSIONS The purpose of this paper is to review what practical methods are available to model turbulent diffusion in the simplest case of a homogeneous, stationary turbulent fluid.
It is clear that some methods go beyond the simple ‘diffusion’ approximation.
In particular, the ‘telegraph’ equation models the dispersion of material near to its source in a more realistic way. analytic theories.
It is also supported by arguments based on
Because there is no exact theory even in the simplest case,
these two equations are the only satisfactory working approximations in real situations provided they are applied with care.
REFERENCES R. Kubo, The Fluctuation-Dissipation Theorem, Rep. Prog. Physics, 29(1966)255-284 W.S. Lewellyn and M.E. Teske, Second-Order Closure Modelling of Diffusion in the Atmospheric Boundary Layer, Boundary-Layer Meteorology, 10(1976)69-90 H.J. Pearson, J.S. Puttock and J.C.R. Hunt, A Statistical Model of Fluid Element Motions and Vertical Diffusion in a Homogeneous Stratified Turbulent Flow, (1978) (private communication) P.H. Roberts, Analytical Theories of Turbulent Diffusion, J. Fluid Mech., 11 (1961)257-283 G.I. Taylor, Diffusion by Continuous Movements, Proc. Lond. Math. SOC., (2), 20(1921)196-212 ACKNOWLEDGEMENT
This work was carried out at the Central Electricity Research Laboratories and is published by permission of the Central Electricity Generating Board.
Atmospheric Pollution 1980, Proceedings of the 14th International Colloquium, Paris, France, May 6-8,1980,M.M.Benarie (Ed.),Studies in Environmental Science, Volume 8 0 Elsevier Scientific Publishing Company,Amsterdam - Printed in The Netherlands
77
DISPERSION EXPERIMENTS FROM THE 213 m HIGH METEOROLOGICAL MAST AT CABAUW IN THE NETHERLANDS H. van DUUREN KEMA Laboratories, Arnhem (The Netherlands)
and F.T.M. NIEUWSTADT
Royal Netherlands Meteorological Institute, De Bilt (The Netherlands)
ABSTRACT Because only few experimental data exist on the diffusion from high sources, a series of dispersion experiments was performed from a 213 m high meteorological mast. The tracer SF6, which was released at either 80 m or 200 m, was sampled at one measuring arc situated at 3
-
5 km from the mast. From the ground
level concentration distribution we obtained values for the dispersion coefficients
and Uz. These parameters are compared with the dispersion coeffiY cients of Pasquill-Gifford. They are also compared with the standard deviations U
of the wind direction fluctuations, measured at the source height. The results of fourteen experiments are discussed.
INTRODUCTION Ib the last decade a solution to the problem of maintaining a good air quality at ground level has been sought by building very tall stacks. Although these stacks do not lessen the impact of air pollution emissions on the total environment, they nevertheless reduce efficiently the local concentrations near the source. In order to estimate ground level concentrations dispersion calculations are needed. Unfortunately little experimental information is available on the dispersion from high sources, so that no adequate calculations can be made. For instance in the Dutch national model for long term averaged concentrations (ref. 1) no recommendations have been given with respect to the dispersion coefficients for very high sources. Recently some new data on the dispersion from high sources became available (refs. 2 and 3). Here we report on dispersion experiments with SF6 from the 213 m meteorological mast at Cabauw in The Netherlands. During the experiments a large number of meteorological parameters was measured including profiles of wind speed and temperature, turbulence data and
mixing height.
A
description of the measuring procedure, the sampling techniques
and the meteorological measurements is given. From the concentration distributions, which were sampled at ground level, we
.
and (I These coefficients are compared Y with the well-known parameters of Pasquill-Gifford (ref. 4). estimated the dispersion coefficients
0
The statistical theory for dispersion by homogeneous and stationary turbulence (ref. 5 ) predicts a relation between the dispersion coefficients and the standard deviations of the wind fluctuation. We will study here such relations empirically (ref. 6 ) . DESCRIPTION OF THE EXPERIMENTS Tracer For the tracer in these experiments we chose sulfur hexafluoride (SF6 1, because it is non-toxic and stable with respect to chemical reactions in the atmsphere. Its removal due to deposition at the ground is negligible. It can be measured in very low concentrations with high accuracy. Its natural background 3 concentration is very small (less than 10 ng/m 1. For these reasons SF6 is a commonly used tracer (ref. 7J. During an experiment SF6 was released either at 80 m or at 200 m depending on the meteorological conditions (e.9. height of the mixing layer). The source strength was determined by a dry gas meter. We estimate the inaccuracy in the observed source strength to be 5%. Air samples were taken at measuring points which were installed during each experiment at preselected locations along a public road. The distance between the mast and the measuring points varied between 3 and 7 km depending on their location along the road. The angular separation between the points was 1.5 arc degree. In most experiments we used 24 manually operated measuring stations which each could take two half hour samples. One upwind measuring station located near the mast was used to determine the background concentration. A measuring station consists of two specially constructed glass vessels. Each vessel has two compartments separated by a partition in which a capillary is mounted, as schematically drawn in Fig. 1. The upper compartment is completely filled with distilled water. By opening stopcock A the water flows through the capillary into the lower compartment and air is sampled. The flow rate of water and therefore the f l o w rate of air fs constant h e to a constant pressure drop (Ap) over the capillary. The sampling time is 30 min during which 3/5 of the upper compartment is filled with air. After sampling the lower compartment is completely filled with distilled water through the stopcocks D. This i s done to avoid suction of air from the lower into the upper compartment due to possible temperature differences during the transwrt of the vessel. In the laboratory
79
Fig. 1. Schematlc drawing of the sampling vessel (for an explanation of the symbols see text]. the sampled air is led into the gaschromatograph through stopcock B by filling
the vessel
with
water through stopcock
A.
The air samples were analyzed by means of a gaschromatograph with an electron capture detector (Table 11. From the peak area measured with an integrator (Hewlett Packard type 3370 EI, the a m m t of sF6 in the air sample
was
determined
with the aid of a calibration curve. TABLE 1 Details of the gaschromatograph (Hewlett Packard, type 5753) used for the SF6analyses runs 1
- 10
12
-
15
separating column: material length diameter carrier carrier gas temperature
copper 2 m 6.35 mm mol. sieve 5A, 45-60 mesh nitrogen, 55 cm /min 8OoC
copper 2 m 6.35 mm mol. sieve 5A, 60-80 mesh 3 nitrogen, 20 cm /min
2 mCi Ni 63 none 1 5 Q ps z3a0c
2 mCi Ni 63 nitrogen, 18 cm /min 150 us
1oo0c
electron capture detector: source purge gas pulse interval temperature
17OoC
80
The inaccuracy in the SF6 concentrations is due to errors in the determination of the calibration curves, errors in the calibration gas concentrations and errors in the analysis procedure of each sample. Variations in the calibration curve, when determined at different times, are caused by the sensitivity of the electron capture detector to small changes in the temperature, the flow rate and the composltion of the carrier gas. The resulting variations in the calibration curves are usually less than 5% over a period of 12 hours but may sometimes amount to 10
-
2 0 % . Therefore a calibration
curve is determined before and after the analysis of the air samples. Calibration gases are made by diluting a known quantity of SF6 in an evacuated gas cylinder which is then compressed with nitrogen. From this parent cali3
bration gas other calibration gases with concentrations in the range of 30-8000 ng/m are made by further dilution. The concentrations of these calibration gases are known within 5%. This figure has been checked by preparing calibration gases with an independent method using a permeation device filled with liquid SF6 (Metronics Dynacal wafer type).
In order to minimize the error during the analysis each air sample is analyzed two times. The average of the two results is used. From the variation in the results of the two analyses we conclude that the error in the analysis pro3
cedure is less than 5% for concentrations higher than 200 ng/m Taking all errors into account we estimate the inaccuracy in the cross-wind integrated concentration to be 15% and in the lateral standard deviation to be 5%.
Meteorological data The meteorological mast is situated in a region with an average roughness length of z = 0.2 m. An extensive description of the instrumentation is given in ref. 8 . Here we summarize the measurements that are of relevance for the dispersion experiments. Along the mast the profiles of several meteorological parameters are routinely measured. They include wind speed measured with cup-anemometers at 9 levels, wind direction measured with wind vanes at 6 levels and temperature measured with ventilated and shielded thermocouples at 10 levels. These profiles are averaged over periods of 30 minutes. The global and net radiation are observed at a height of 2 m. They are also available as 30 min averages. A monostatic acoustic sounder is continuously in operation. Its reglstration during the experiment was used to monitor the mi'xing height when this was limited to a few hundred meters. During the experiments also a special measuring program is executed. It consists of measurements of turbulent temperature and wind fluctuations at 3
to 6 levels. Measurements at the release height are always included. Turbulent wind fluctuations are measured by trivanes and turbulent temperature fluctuations by fast responding thermocouples (ref. 8). The turbulence data are sampled at 5 Hz and stored on magnetic tape. From these data standard deviations are calcu-
lated over periods of 30 minutes, which coincide with the half-hourly sampling periods of the air. During most experiments a radiosonde was launched before and after the
sam-
pling period. The elevation and azimuth angle of the radiosonde were observed by means of a theodolite. From the radiosonde data the profiles of temperature, wind speed and wind direction in the first few kilometers are obtained.
Measuring procedure An
experiment was planned when the meteorological forecast indicated a situa-
tion with no precipitation and with a persistent, favourable wind direction: Before the start of an experiment the equipment for turbulence measurements had to be installed along the mast. This took about two hours. During this time the wind direction at 20, 80 and 200 m was monitored on an analog recorder. From these traces a prediction of the direction of theplume axis was made. Based on this prediction the measuring stations were installed at preselected points along a public road. This installation took about one hour. If during this time a major change in the wind direction occurred it was possible to relocate some measuring stations. The turbulence was measured from about one hour before the start of the sampling until about one hour after its ending. The release of SF6 was stabilized at a constant strength about a quarter of an hour before the start of the sampling. The duration of the sampling was restricted to two consecutive periods of 30 minutes because of the limited number of sampling vessels available.
RESULTS
From April 1977 to October 1 9 7 8 fifteen experiments were carried out. In ten cases the source height was 200 m, while 80 m was chosen for the other cases. The stability class, which is calculated from global radiation and wind speed at 10 m (ref. 91, varied between
C
and D. In Table 2 we have collected some rel-
evant data of fourteen experiments (for one experiment no concentration data are available).'
A complete report containing all measured data is available from the authors upon request. +
82
TABLE 2
Data of the dispers2on experfments run la b 2a b 3a b 4a b 5a b 6a b
7a 8a b 9a b 10a b 12a 13a
b 14a b 15a b
H
X
200 200 200 200 200 200 200 200 80 80 80 80 200 200 200 200 200 200 200 200 80 80 80 80 80 80
3150 3160 3400 3310 3160 3160 3200 3230 3880 3880 3280 3250 3160 4100 4300 4250 4300 3250 3480 3850 4310 4250 4200 3950 3110 3200
h
S
>2000 >2000 540 590 370 420 500 500 250 250 900 900 1450 500 500 1580 1580 600 600 >2000 200 200 350 400 700 700
C C D D C C D D D D D D
c D D C C C D D C D C C C
c
aA
5.7 6.9 5.4 6.5 5.3 5.4 4.0 4.5 5.4 5.0 11.5 5.2 6.7 6.0 7.2 4.7 6.1
OE
5.9 6.4 3.2 3.4 4.0 4.5 2.5 2.6 2.7 2.8 4.3 3.6 9.3 3.6 3.5 8.7 8.2 4.2
6.0
6.6 4.6
4.2 6.7 6.8 5.2 7.0 11.3
3.5 4.3 5.1 4.5 6.4 7.6
U
U .H/Q Y' H
C
Oz
Y
-
315 228 195 238 212 188 166 221 198 209 185 206 367 210 401 330 333 178 247 376
416 135 135
-
76 107 162 166 416
-
-
312 488
-
293 109
87
184
-
355 283 373 202 243
87
-
257 514
0.78 0.34 0.39 0.39 0.63 0.48 0.02 0.04 0.52 0.45 0.35 0.34 0.34 0.34 0.21 0.37 0.30 0.23 0.49 0.27 0.48 0.68 0.48 0.52 0.23 0.12
B
= source height in m.
X
=
h
= mixing height in m.
S
= stability class according to Pasquill (ref. 9 ) .
U
= standard deviation in degrees, of the horizontal (azimuth) wind di-
A
distance to the source in m (see Fig. 21.
rection fluctuations at the source height. U
E
= standard deviation in degrees, of the vertical (elevation) wind di-
rection fluctuations at the source height. U
Y
= horizontal dispersion coefficient in m, determined from equation (2).
= vertical dispersion coefficient in m, determined from equation (5). OZ C U .H/Q = dimensionless cross-wind integrated concentration; C is the cross-
Y'
Y
wind integrated concentration determined from equation ( 4 ) , UH is the wind speed at the source height H and Q is the source strength.
83 Lateral concentration distribution For each experiment the ground level concentrations are known at measuring points, which are distributed along a public road (Fig. 2 ) . The first moment or median
y
of the concentration distribution is defined as
where c is the concentration and s the co-ordinate along the road. The line which connects the location of the source with
is defined as the plume axis indica-
ted by the co-ordinate x. The lateral concentration distribution is projected on a line y which passes through
y
and which is perpendicular to x. For most exper-
iments the angle between the y-axis and the road was lees than 25O. We will neglect here the errors in the concentration distribution along the y-axis due to the projection procedure. An
example of a measured lateral concentration distribution is shown in Fig. 3 .
We have fitted the observed data to a Gaussian distribution curve, which in this case gives a very good fit. Most of the measured concentration distributions are very well approximated by a Gaussian profile except for a few experiments in which the average wind direction changed appreciably during the sampling period. A
poor approximation to a Gaussian distribution is a l s o found for some runs dur-
ing instable conditions, in which no change of wind direction was observed. We assume that for these cases a 30 min average is too short to obtain a statistically stationary result. pg/m3 4 r , r
,
,
l
,
,
,
,
l
,
,
,
,
measuring
- - Gaussian
x sampling point
distribution -
Fig. 2
Fig. 2. Configuration of the source and the sampling points with respect to the co-ordinate system used for the description of the dispersion results. Fig. 3. An example of a lateral concentration distribution measured during run 3a.
84
When the lateral concentration distribution is taken to be Gaussian, it is completely determined by its standard deviation 0 which is defined as Y'
u
Y
=
Tm (y - ;)2.c.dy]/{
{
Tmc.dy).
(2)
The standard deviation 0 is known as the lateral dispersion coefficient. Y Many, usually empirical, data on the lateral dispersion coefficient are known.
A well-known set of dispersion coefficients has been given by Pasquill and Gifford (ref. 4). These parameters, however, are representative for a sampling time of 3 minutes (ref. lo), while our data pertain to a sampling time of 30 minutes. If we approximate the dependence of 0 on sampling time as toe2 (ref. Y ll), we find that the Pasquill-Gifford values should be multiplied by a factor 1.6 in order to obtain parameters representative for t
=
30 min.
The observed data of 0 are plotted in Fig. 4. They do not show any appreciaY ble depence on stability class. The corrected parameters of Pasquill-Gifford, also given in Fig. 4, are for corresponding stability classes consistently higher than the observed results. A correction for the influence of roughness, which in case of
0
Y
is not very well known, would probably enlarge this overpre-
diction because the representative roughness length for the Pasquill-Gifford parameters is z
=
0.03 m, whlle in our case z
=
0.2 m. The overprediction
noted here may result from the influence of the source height on the dispersion, because the Pasquill-Gifford parameters are taken to be representative for low level sources, while our data pertain to hlgh sources. A better method of describi'ng the dispersion coefficients is by applying the
results of the statistical theory of Taylor (ref. 5 ) , which connects the dispersion coefficients to wind fluctuatlons. This theory also provides the limiting behaviour for small diffusion times, where where 0
%
0.5
t
.
13 Q
t and for large diffusion times,
Starting from these results Draxler (ref. 6) proposed the inter-
polation formula
uA .X
u = Y
+
where ci
A
Oe9
[+-I
(3)
0.5
is the standard deviation of the horizontal wind direction fluctuations
at the source height, T is proportional to the Lagrangian time scale of the Y horizontal turbulent fluctuations and x is the distance to the source; UH is taken here as wind speed at the source height. Based on a comparison of relation ( 3 ) with a large number of experimental data Draxler recommends T Y
=
1000 s for
neutral and instahle conditions. In Fig. 5 we compare relation (3) with our experimental results. The agreement is very satisfactory. It can be estimated, that expression ( 3 ) explains about 50% of the variance in the observed values of U Y'
85
I
1
0
-
CabauwD CabauwC
0
1-
Cabauw Draxler (ref.6) Hanna et aL(ref.11)
---
hhh' 0
10
-
Fig. 4. The observed results of the lateral dispersion coefficient U and the Pasquill-Gifford coefficients corrected to a sampling time of 30 minztes (for details see text). Fig. 5. The ratio of 0 and the standard deviation UA of the horizontal wind direction fluctuations'as a function of distance. It is clear from Fig. 5 that the ratio Uy/UA according to equation ( 3 ) depends only weakly on UH. This suggests, that an approximate relation of the form .x) = F(x) might he applicable. Pasquill (ref. 11) has proposed an expresY A sion for F(x), which is also shown in Fig. 5. This expression slightly underes-
U /(U
timates the observations. A thorough discussion of the function F(x) has been recently given (ref. 12J
.
Cross-wind integrated concentratlon The cross-wind integrated concentratlon measured at ground level is given by C = 2c.dy Y
.
(4)
From C an estimation of the vertical dispersion coefficient Uz can be obtained, Y when the vertical concentration distribution is known. Usually the vertical concentration profile is represented by a Gaussian distribution. This leads to the following relations between C and Uz: Y
66
if
UZ
< 1.1 h
if
Uz
> 1.1 h
C
U
.H
Y ' = = H . Q h In equations (5) and (6) Q is the source strength, H the source height and h the height of the mixing layer. The expressions involve an approximation of the influence of the mixing height on the ground level concentration distribution (ref. 13). A value for
0
can only be obtained for uz < 1.1 h. In the case that
Uz
> 1.1 h,
the tracer is distributed uniformily across the mixing layer, so that a vertical dimension of the plume becomes meaningless. The relations given by (5) and ( 6 ) are shown in Fig. 6. It follows that for a fixed value of H/h no solution for
U
can be obtained when C .U .H/Q exceeds a Y
H
certain maximum value. This was the case for several of the experimental data given in Table 2 . Apart from experimental errors we must attribute this to a break-down of the assumption that the vertical concentration profile may be approximated by a Gaussian distribution. As clear from Fig. 6 a certain value of C .U .H/Q may sometlmes lead to two Y H solutions for Uz. In that case we took the, in our opinion, most plausible result. The values of
Uz,
which could be deterrmned, are shown in Fig. 7. It fol-
lows that they depend only slightly on stability class. A well-known set of vertical dispersion coefficients has been given by Pasquill and Gifford (ref. 4 ) . However, these parameters are representative for a roughness length of zo = 0.03 m (ref. lo), while our experiments pertain to z
0
= 0.2 m. Therefore we have corrected the Pasquill-Gifford curves to a rough-
ness length of 0.2 m following the method of Pasquill (ref. 14). These corrected values are shown in Fig. 7. The experimental data scatter between the Pasquill-Gifford curves for the stability classes B and D. However, one must remind that the Pasquill-Gifford coefficients are mostly based on data from ground level sources (ref. 11). Analogously to the lateral di'spersion coefficient we can connect
Uz
to the
vertical wind direction fluctuations. As a direct consequence of Taylor's theory a relation similar to equation ( 3 ) is proposed by Draxler (ref. 6 ) :
U,.X
Uz
r,
=
1
U
E
+ 0.9
]
-
[UH:Tz
(7) OS5
is the standard deviation of the vertical wind direction fluctuations. However, the application of equation (71 is not straightforward, because the
basic assumption of homogeneity, which underlies Taylor's theory, is essentially not met in the case of vertical dispersion. Therefore it must be expected that the agreement will be somewhat poorer than found for In Fig. 8 our observations of
U
Y
in Fig. 5.
/a are shown together with equation (7). For z E
U
the time scale TZ we have substituted TZ = 500 s, which has been recommended by Draxler based on a comparison of relation (7) with a large number of experimental data. As
expected the scatter is quite considerable. Nevertheless about 55% of the
variance in the observed values of 0 firms that a relation between
bz
is explained 6y expression (7). This con-
and UE is appropriate.
The value of Uz, which could be determined from the observations in an only limited number of cases, is mostly of secondary importance. In practice one is usually more directly interested in the cross-wind integrated concentration itself.
m
--
0
a
Cabauw D Cabauw C Pasquill-Glford (ref.4)
--
a Fig.6
OO
0.5
1.0
Fig.7
1.5
H +rnQz
Fig. 6. The solution of the Gaussian plume equation given by equations (5) and (6).
Fig. 7. The observed results of the vertical dispersion coefficient U and the Pasquill-Gifford coefficients corrected to a roughness length of 0.2 (for details see textl.
88 mlrad 10' -
--
0
I I I 1 I I l l ) Cabauw Draxler (ref.6)
I
I
I
-
6
Imll
I
I
1
r
I
/
I44
t i lo3
-
-
-
-
Id
I
I
I
I
I
,,I
I
I
I
I I
I , ,
lo2
0 N
1
X
Fig. 8 . The ratio of Uz and the standard deviation tion fluctuations as a function of distance.
UE
-[+IdC.
2
3
4 C U h
Flg.9 5
6
of the vertical wind direc-
Fig. 9. A comparison between observed and calculated values of the dimensionless cross-wind integrated concentration. Therefore we have compared in Fig. 9 the observed values of the cross-wind integrated concentration in dimensionless form with calculated values, which are obtained by applying expression (7) for
(7
in equation (5). In the dimensionless
form of C in Fig. 9 h is substituted in stead of A. Y The agreement between the calculated and the ohserved values is good. The lineair correlation coefficlent is equal to 0.86.
CONCLUSIONS
Dispersion experiments with SF6 have been performed from a 213 m high meteorological mast. A large number o f meteorological parameters have been measured simultaneously, among which the wind fluctuations at the source height. Stability classes calculated according to Pasquill (ref. 91 varied between
C
and D.
For most runs the lateral concentrati'on profile can be very well approximated by a Gaussian distribution. The observed values of the lateral dispersion coefficient 0 do not seem to Y depend on stability class. They are consistently lower than the Pasquill-Gifford coefficients, when the latter are corrected from a sampling time of 3 minutes to a sampling time of 30 minutes as used in our experiments. Based on Taylor's statistfcal theory of diffusion Draxler (ref. 6) proposed a relation between U and the standard deviation of the horizontal wind direcY tion fluctuations. This relation is confirmed by our experimental results.
By assuming that the verti'cal concentration distribution is Gaussian, the dispersion coefficient U
is estimated from the cross-wind integrated concentration
C for a limited number of experiments. The values of O z , which depend only Y slightly on stability class, scatter between the Pasquill-Gifford curves B and D. The Pasquill-Gifford coefficients are corrected from a roughness length of 0.03 m to a roughness length of 0.2 m representative for our experiments. A comparison of
U
with a relation based on Taylor's theory leads to somewhat
poorer results than in the case of
U
Y'
Nevertheless the standard deviation of
the vertical wind direction fluctuations explains about 55% of the variances in
Oz.
Estimates of the cross-wind integrated concentration, made with a Gaussian model, agreed very well with the observed data.
ACKNOWLEDGEMENTS The authors are grateful for the co-operation of the instrumental divisions of the Royal Netherlands Meteorological Institute and of the KEMA Laboratories. They are also indebted to their colleagues who assisted during the experiments, in particular Messrs. G.D. Krijt, A.J. Hasselton and R. Agterberg. REFERENCES F.T.M. Nieuwstadt, C.M. Verheul and J. Addicks, The validation of the Gaussian dispersion model for long-term average ground level concentrations in the Rijnmond region, Proceedings of the seventh international technical meeting on air pollution modeling and its application, NATO-CCMS, Airlie House, 1976, pp.169-218. S. Gryning, E.L. Pettersen and E. Lyck, Elevated source SF -tracer dispersion 6 experiments in the Copenhagen area, Tenth international technical meeting on air pollution modeling and its application, NATO-CCMS, Rome, 1979 (preprint). W.G. Hiibschmann, K. Nester and P. Thomas, Diffusion of atmospheric pollutants being emitted from tall stacks, Tenth international technical meeting on air pollution modeling and its application, NATO-CCMS, Rome, 1979 (prepsint). D.B. Turner, Workbook of atmospheric dispersion estimates, U . S . Department of Health, Education and Welfare, Public Health Service Publication No. 999-AP-26, 1970 ("PIS Pa-191 4821. G.I. Taylor, Diffusion by continuous movements, Proc. London Math. SOC., Ser. 2 (19761, 20. R.R. Draxler, Determination of atmospheric diffusion parameters, Atmospheric Environment 10 (1976J,99-105. J.L. Deuble, Atmospheric tracer gas technology, techniques and applications, Systems, Science and Software, La Jolla, Technical Bulletin 79-5. A.G.M. Driedonks, H. van Dop and W.H. Kohsiek, Meteorological observations on the 213 m mast at Cabauw in the Netherlands, Fourth symposium on meteorological observations and instrumentati'on, American Meteorological Society, Denver, 1978, pp.41-46. F. Pasquill, Atmospheric Diffusion, John Wiley & Sons Ltd, Chicester, 1974, fig. 6.13. (a), p.374.
90 10 F. Pasquill, Atmospheric dispersion parameters in Gaussian plume modeling, Part 11: Possible requirements for change in the Turner Workbook values, U.S.
11
12
13
14
Environmental Protection Agency, 1976, report nr. EPA-600/4-76-030b(NTIs PB-258 0 3 6 ) . S.R. Hanna, G.A. Briggs, J.W. Deardorff, B.A. Egan, F.A. Gifford and F. Pasquill, Meeting review AMS Workshop on stability classification schemes and sigma curves - summary of recommendation, Bulletin Am. Meteorological SOC., 58 (1977), 1305-1309. J.C. Doran, T.W. Horst and P.W. Nickola, Variations in measured values of lateral diffusion parameters. J. Appl. Meteor., 17 (1978), 825-831. F. Pasquill, The "Gaussian-plume'' model with limited vertical mixing, U.S. Environmental Protection Agency, 1976, report nr. EPA-600/4-76-042 (NTIS PB-258 732). F. Pasquill, Atmospheric Diffusion, John Wiley & Sons Ltd, Chicester, 1974, fig. 6.13(d), p.377.
Atmospheric Pollution 1980, Proceedings of the 14th International Colloquium, Paris, France, May 5-8,1980, M.M. Benarie (Ed.), Studies in Environmental Science, Volume 8 0 Elsevier Scientific Publishing Company, Amsterdam - hinted in The Netherlands
91
DISPERSION AROUND BUILDINGS P.J.H. Builtjes MT-TNO, Department of Fluid Flow Technology, Apeldoorn, The Netherlands
ABSTRACT As a r e s u l t of a l i t e r a t u r e review concerning dispersion experiments around one building using wind tunnels, some general rules concerning t h i s dispersion behaviour have been derived. An application of these rules t o more complex situations consisting o f groups of buildings showed t h a t also i n these situations the same rules can be applied t o determine the magnitude of concentration levels.
INTKODUCTION The dispersion from a f r e e standing stack can be calculated by the so-called Gaussian plume model. The concentration c a t groundlevel ( z = 0 ) , and on the axis o f the plume (y = 0 i s given by c(x,O,O;H)
=
Q . IT00
2 2 exp { - H 1 2 0 ~ 1
U
Y Z
x i s the mean flow direction, H the height of the stack including plume r i s e , Q the source strength, 0 the mean wind velocity and o and oZ the dispersion Y
coefficients in the y- and z-direction. For H < 0 . 4 oZ equation ( 1 ) can be approxi mated by c(x,O,O; H ) = Q/&
u
Y Z
(2)
However, often a stack i s situated close t o buildings. These buildings give r i s e t o higher turbulent i n t e n s i t i e s and complicated wake-like and cavity-like flow patterns. This will influence plume behaviour, and equations (1) and ( 2 ) cannot be applied. Investigation of the concentration patterns under such circumstances can be carried out by using a wind tunnel with a simulated atmospheric boundary
1ayer.
92
T h a t a s i m u l a t i o n i n a w i n d t u n n e l o f t h e d i s p e r s i o n f r o m a s t a c k i s p o s s i b l e has been demonstrated by s e v e r a l a u t h o r s ( f o r r e c e n t a r t i c l e s see r e f . 1 and 2 ) . However, t h e s i m u l a t i o n s h o u l d i n p r i n c i p l e be r e s t r i c t e d t o s t a c k s w i t h a h e i g h t l e s s t h a n a b o u t 200 m and t o d i s t a n c e s l e s s t h a n a few k i l o m e t e r s ( r e f . 2, 3 ) . WIND-TUNNEL EXPERIMENTS OF THE DISPERSION AROUND BUILDINGS, SOME GENERAL RULES Most d i s p e r s i o n e x p e r i m e n t s i n w i n d t u n n e l s have been d i r e c t e d a t t h e i n f l u e n c e o f one b u i l d i n g on t h e plume b e h a v i o u r . The f i r s t experiments o f t h i s k i n d were p e r f o r m e d b y H a l i t s k y ( r e f . 4). The i n v e s t i g a t i o n was c a r r i e d o u t u s i n g a c u b i c b u i l d i n g w i t h an e m i s s i o n f r o m t h e r o o f w i t h an e m i s s i o n v e l o c i t y s m a l l e r t h a n t h e mean w i n d v e l o c i t y a t t h a t h e i g h t . F o r t h e ground l e v e l c o n c e n t r a t i o n c l o s e t o t h e b u i l d i n g t h e f o l l o w i n g e q u a t i o n was suggested:
c =
Q/KAU
(3)
w i t h A b e i n g t h e f r o n t a l a r e a o f t h e b u i l d i n g and K a c o n s t a n t f a c t o r . The b a s i c i d e a b e h i n d i t i s t h a t t h e plume a r e a i s equal t o t h e f r o n t a l area o f t h e b u i l d i n g and t h a t t h e c o n c e n t r a t i o n i s homogeneously d i s t r i b u t e d across t h e c a v i t y c l o s e t o t h e b u i l d i n g . By c o n s i d e r i n g e q u a t i o n ( 2 ) and assuming t h e plume area t o be TO u t h e f a c t o r K i n e q u a t i o n ( 3 ) s h o u l d be o f t h e o r d e r o f 1. H a l i t s k y Y z' f o u n d i n d e e d K = 1, b o t h f o r an e m i s s i o n f r o m t h e r o o f and f o r emissions r e l e a s e d
equal t o
i n t h e c a v i t y b e h i n g t h e b u i l d i n g ( r e f . 5 ) . Yang ( r e f . 3 ) found K = 1.15,
Svmes
( r e f . 6 ) f o u n d K = 0.6 b e h i n d a c y l i n d e r ; f o r t h e r e l e a s e t h r o u g h a porous cube Robins ( r e f . 7 ) f o u n d K = 1.0 f o r d i s t a n c e s b e h i n d t h e cube up t o about 3 t o 4 t i m e s t h e cube h e i g h t ; W i l s o n ( r e f . 8) shows t h a t a l s o t h e c o n c e n t r a t i o n a t t h e w a l l s o f a b u i l d i n g can be d e s c r i b e d b y e q u a t i o n ( 3 ) w i t h K = 1. A d r a m a t i c change i n t h e v a l u e o f K o c c u r s i n case t h e w i n d d i r e c t i o n i s n o t p e r p e n d i c u l a r t o t h e f r o n t o f t h e b u i l d i n g , b u t t u r n s o v e r 45'. Thompson ( r e f . 9 ) f o u n d a K - f a c t o r o f a b o u t 0.17.
F o r t h a t case
The same v a l u e was found by
V i n c e n t ( r e f . lo), Robins ( r e f . 7 ) f o u n d a K - f a c t o r o f 0.25.
I t has been suggested
( r e f . 11) t h a t t h e s e h i g h c o n c e n t r a t i o n s a r e caused by t h e v o r t i c e s coming from t h e s h a r p edges o f t h e cube, w h i c h narrow t h e wake. I t s h o u l d be n o t i c e d t h a t t h e r e s u l t s g i v e n above h o l d o n l y f o r t h e i n f l u e n c e o f one c u b i c b u i l d i n g , f o r an e m i s s i o n v e l o c i t y d i v i d e d by t h e mean w i n d v e l o c i t y n o t l a r g e r t h a n 1.2 (which
means t h a t t h e e m i s s i o n t a k e s p l a c e i n t h e r o o f - s w i r l o r t h e c a v i t y ) and f o r d i s tances f r o m t h e b u i l d i n g l e s s t h a n about 4 t i m e s t h e b u i l d i n g h e i g h t , Hb. F o r c o n c e n t r a t i o n s f u r t h e r downstream i n t h e b u i l d i n g wake t h e f o l l o w i n q equat i o n has been suggested ( r e f . 1 2 )
93
I n t h i s equation the influence of t h e building given by K ' A has been separated from t h e Gaussian plume behaviour given by TO 0 Close t o t h e building i t can be Y 2' assumed t h a t TO 0 = K I A , which with K' = 0.5 leads t o formula ( 3 ) w i t h K = 1 i f Y Z t h e wind d i r e c t i o n i s perpendicular t o t h e f r o n t of the building. Far downstream from t h e building K ' A << ~5 o and the normal Gaussian plume equation ( 2 ) will Y 2' d e s c r i b e t h e concentration. Halitsky ( r e f . 13) found t h a t equation ( 4 ) w i t h K ' = 0.5 describes his r e s u l t s reasonably well. In h i s review Abbey ( r e f . 14) mentioned f o r K ' values between 0.5 and 2 , with an average value of 1. However, t h e r e i s a l s o a d i f f e r e n t method of describing the influence of a building. The measured concentration can be compared w i t h t h e normal Gaussian plume r e s u l t s using equation (1). In t h i s way an e f f e c t i v e o r v i r t u a l stack heiaht and d i s t a n c e can be determined ( r e f . 15, 7, 11, 16). B a r r e t t ( r e f . 11) gives r e s u l t s which show t h a t f o r s t a c k s from 1.0 t o 1.9 times t h e building height, and beyond 10 building heights d i s t a n c e from t h e s t a c k , the e f f e c t i v e source h e i g h t i s 0.9 times t h e real source height. For distances c l o s e r t o the building the e f f e c t i v e source h e i g h t i s a function of the r a t i o of source height t o building height and of the d i s t a n c e i t s e l f ( f o r more information, a l s o of o t h e r dispersion experiments, see r e f . 17). DISPERSION AROUND GROUPS OF BUILDINGS
I n p r a c t i c a l a p p l i c a t i o n s i t i s necessary t o determine concentration patterns around groups of buildings o r complicated shaped buildings. The question a r i s e s whether i t i s possible t o make use of the equations derived f o r t h e concentration p a t t e r n s around one cubic building f o r t h a t s i t u a t i o n . In most cases t h e main i n t e r e s t i s d i r e c t e d a t t h e h i g h concentration l e v e l s c l o s e t o buildings, o r even a t the s i d e s of buildings i n view of intake-points f o r a i r conditioning systems. Equation ( 3 ) describes the concentration c l o s e t o buildings. The background of t h i s formula i s t h e f a c t t h a t the concentration i s homogeneously dispersed in a region c l o s e t o the building. T h e width of t h i s 'concentration c a v i t y ' i s equal t o t h e f r o n t a l area of the building A , i t s length i s about 4 times t h e building height Hb. In case t h e wind i s blowing perpendicular t o t h e f r o n t of the building (0 = 0') t h e K-factor i s 1.0, when 0 = 45O, K = 0 . 2 which means an e f f e c t i v e decrease of t h e width of t h e concentration cavity. As has been s t a t e d e a r l i e r , these r u l e s hold f o r an emission i n s i d e the roof-swirl or c a v i t y . In t r y i n g t o apply equation ( 3 ) t o complex s i t u a t i o n s the following points have t o be considered: - Determination of t h e mean wind v e l o c i t y a t t h e height of t h e building
-
Determination of t h e f r o n t a l area Determination of the c a v i t y length
- Determination of t h e wind d i r e c t i o n r e l a t i v e t o t h e building
94
I n general, t h e mean wind v e l o c i t y can e a s i l y be determined. The value o f t h e f r o n t a l area, however, i s o f t e n n o t s e l f - e v i d e n t . I n s t e a d o f t h e f r o n t a l area i t i s b e t t e r t o use c a v i t y - w i d t h d e t e r m i n i n g area. I t t u r n e d o u t t h a t t h i s area can always be determined w i t h s u f f i c i e n t accuracy f o r t h e a p p l i c a t i o n o f equation (3). I n general, t h e c a v i t y l e n g t h i s 4 Hb. When t h e n e x t b u i l d i n g i s l e s s than 4 Hb downstream from t h e b u i l d i n g where t h e emission takes place, t h e c a v i t y l e n g t h i s shortened and t h e c o n c e n t r a t i o n has t o be increased by a m u l t i p l i c a t i o n f a c t o r equal t o 4 Hb d i v i d e d by t h e r e a l c a v i t y l e n g t h . The d e t e r m i n a t i o n o f the r e l a t i v e wind d i r e c t i o n i s very i m p o r t a n t because a change i n wind d i r e c t i o n from 0'
t o 45'
g i v e s an i n c r e a s e i n t h e c o n c e n t r a t i o n l e v e l by a f a c t o r o f 5. I n t h e atmospheric wind tunnel a t TNO-Apeldoorn d i s p e r s i o n experiments around b u i l d i n g s a r e c a r r i e d o u t f r e q u e n t l y . F i v e o f these experiments have been used t o i n v e s t i g a t e t h e usefulness o f equation ( 3 ) and t h e above given r u l e s . The measured c o n c e n t r a t i o n l e v e l s a t many p o i n t s have been used i n combination w i t h determined values o f
5
and A t o c a l c u l a t e t h e K - f a c t o r . T h i s K - f a c t o r can be compared w i t h
t h e values o f K = 1 and 0.2,
r e s p e c t i v e l y mentioned e a r l i e r . F i r s t l y a complex o f
4 cross-shaped b u i l d i n g s w i t h a maximum h e i g h t o f 40 m has been i n v e s t i g a t e d ( r e f . 18). For 0 = 0'
1.1 For 0 = 45'
t h e average K - f a c t o r found i s 1.5, w i t h a minimum value o f
t h e average K - f a c t o r i s about 0.5,
w i t h a minimum value o f 0.25.
The second experiment was performed on a very complex shaped b u i l d i n g w i t h many sharp edges and a maximum h e i g h t o f 35 m ( r e f . 19). The average K - f a c t o r was about 0.5,
w i t h a range o f 0.35
-
1.0. This low K - f a c t o r i s most probably caused
by t h e sharp-edged shape o f t h e b u i l d i n g . I n t h i s case a l s o t h e a v a i l a b l e c a v i t y l e n g t h was o f t e n s h o r t e r than 4 Hb and t h e c a l c u l a t e d c o n c e n t r a t i o n had t o be c o r r e c t e d . The t h i r d complex c o n s i s t e d o f r e c t a n g u l a r shaped b u i l d i n g s w i t h an i n n e r c o u r t ( r e f . 20). For 0 = 45'
an average K - f a c t o r o f 0.5 was found. For t h e
i n n e r c o u r t sometimes K = 0.5 was found f o r perpendicular wind f l o w also. This i s probably caused by t h e f a c t t h a t h a r d l y any m i x i n g w i t h w i t h surrounding a i r i s p o s s i b l e i n t h a t s i t u a t i o n . The f o u r t h i n v e s t i g a t i o n was performed on one s i n g l e t a l l b u i l d i n g w i t h an i n n e r c o u r t ( r e f . 21). On t h e average a K - f a c t o r o f 0.5 was found. However, a t two p o i n t s very l a r g e concentrations were measured r e s u l t i n g i n K = 0.05. T h i s i s probably caused by t h e f a c t t h a t f o r very d i s t i n c t wind d i r e c t i o n s t h e plume was n o t mixed i n t o t h e c a v i t y and consequently could reach t h e f r o n t o f t h e n e x t facade d i r e c t l y . The l a s t i n v e s t i g a t i o n was performed on a t a l l r e c t a n g u l a r b u i l d i n g w i t h a h e i g h t o f 55 m ( r e f . 22). I n t h i s case K = 1 was found f o r 0 = 0'
and K = 0.25 f o r 0 = 45'.
I n t o t a l about 200 c o n c e n t r a t i o n measurements have been used. The concentration c o u l d be found by u s i n g e q u a t i o n ( 3 ) and t h e a p p r o p r i a t e K - f a c t o r w i t h an accuracy o f a f a c t o r 2. The maximum c o n c e n t r a t i o n can be found by using K = 0.2,
only a t
two p o i n t s t h e measured c o n c e n t r a t i o n was h i g h e r than t h e c o n c e n t r a t i o n c a l c u l a t e d
95
by u s i n g K = 0.2.
CONCLUSIONS The formulas and r u l e s which d e s c r i b e t h e c o n c e n t r a t i o n c l o s e t o one cubic b u i l d i n g can be used t o determine t h e magnitude o f t h e c o n c e n t r a t i o n l e v e l s around complex b u i l d i n g c o n f i g u r a t i o n s . Consequently these r u l e s can be used f o r p r a c t i c a l a p p l i c a t i o n s i n o r d e r t o determine whether t o o h i g h c o n c e n t r a t i o n l e v e l s can be expected and a d e t a i l e d wind-tunnel study i s necessary.
REFERENCES
1 A.G.
Robins, J . o f Ind. Aerodynamics 4(1979)71.
2
Robins, Wind-tunnel m o d e l l i n g o f plume d i s p e r s a l , C.E.G.B.-rep.
A.G.
R/M/R
247( 1977). 3
B.T. Yang and R.N.
Meroney, Gaseous d i s p e r s i o n i n t o s t r a t i f i e d b u i l d i n g wakes,
AEC Rep. n r . COO-2053-3,
Colorado S t a t e Univ. (1970).
4
J . H a l i t s k y , Gas d i f f u s i o n near b u i l d i n g s , New York Univ. Rep. n r . 63-3(1963).
5
J . H a l i t s k y , Ind. Hygiene J . 26(1965)107.
6
C.R.
7
A.G.
8
D.J. Wilson, Atm. Env. 12(1978)1051. R.S. Thompson and D.J. Lombardi, D i s p e r s i o n o f r o o f - t o p emissions from i s o l a t e d
Symes and B.N. Meroney, Cone frustrums i n a shear l a y e r , AEC-Rep. n r .
COO-2053-4,
9
Colorado S t a t e Uni v. (1970).
Robins and I . P .
Castro, A t m . Env. 11(1977)291.
b u i l d i n g s , EPA-600/4-77-006(1977). 10 J.H.
Vincent, Atm. Env. 11(1977)765.
11 C.F. B a r r e t t , e.a.,
D i s p e r s i o n from chimneys downwind o f c u b i c a l b u i l d i n g s
NATO-CCMS, 9 t h I n t . Meeting, Toronto (1978). 12 F.H. G i f f o r d , Nuclear S a f e t y 2(1960)56. 13 J . H a l i t s k y , Atm. Env. 11(1977)577. 14 R.F. Abbey, Concentration measurements downwind o f b u i l d i n g s : previous and c u r r e n t experiments, U.S. Nuclear Ref. Com. (1977). 15 A.H.
Huber and W.H.
Snyder, B u i l d i n g wake e f f e c t s on s h o r t stack e f f l u e n t s
EPA-rep.(1977). 16 E.H.
1 7 P.J.H.
Lucas, I n t . J. o f A i r Water P o l l u t i o n 6(1962)94. B u i l t j e s , A l i t e r a t u r e survey concerning d i s p e r s i o n experiments i n
wind tunnels, TNO-Rep. 79-02866(1979). 18 P.E.J.
Vermeulen, Concentration measurements around t h e U n i v e r s i t y o f Utrecht,
TNO-Rep. 79-06968(1979).
96
19 G. T h . Visser, Concentration measurements around the Ministry o f Education, TNO-Rep.
79-012906( 1979). 20 G . T h . Visser, Concentration measurements around t h e I n s t i t u t e o f Geology, TNO-Rep. 77-011370(1977).
2 1 J.A. Leene, Concentration measurements around a bank, TNO-Rep. 79-014423(1979). 22 J.W. Pohlmann, Concentration measurements around a bank, TNO-Rep. 76-09503(1976)
Atmospheric Pollution 1980, Proceedings of the 14th International Colloquium, Paris, France, May 5-8,1980, M.M. Benarie (Ed.), Studies in Environmental Science, Volume 8 0 Elsevier Scientific Publishing Company, Amsterdam - minted in The Netherlands
A CARBON MONOXIDE DISPERSION EXPERIMENT I N A BUILT-UP
and H .
H.
KOLB1)
U.
PECHINGER2) and R.
97
AREA
MOHNL2) WERNER1)
ABSTRACT A f u l l scale e x p e r i m e n t o f CO-dispersion
from an a r t i f i c i a l l y
v e n t i l a t e d p a r k i n g house w i t h i n a b u i l t - u p area i s d e s c r i b e d . The c a r b o n monoxide c o n c e n t r a t i o n w i t h i n t h e plume w a s r a i s e d up t o a b o u t 2 0 0 0 ppm, t h u s f a c i l i t a t i n g immission measurements a t d i f f e r e n t p o i n t s o f i n t e r e s t on n e a r b y b u i l d i n g s . The i n t r o d u c t i o n o f c o l o r e d smoke i n t o t h e plume made s t u d i e s o f plume r i s e w i t h o p t i c a l methods ( i n s i t u measurements,
s l i d e s and movies) p o s s i b l e .
Comparison o f
p l u m e - r i s e measurements and immission v a l u e s w i t h t h o s e y i e l d e d by t h e o r e t i c a l f o r m u l a s and r u l e s of thumb are made.
INTRODUCTION
P r e d i c t i o n s o f e x p e c t e d c a r b o n monoxide c o n c e n t r a t i o n s i n t h e v i c i n i t y of p a r k i n g h o u s e s are n e c e s s a r y as a b a s i s f o r town p l a n n i n g . A s s u c h p a r k i n g h o u s e s a r e g e n e r a l l y needed i n b u i l t up a r e a s ,
d i s p e r s i o n e q u a t i o n s become v e r y complex and i n v o l v e many p a r a m e t e r s which c a n n o t be d e t e r m i n e d from r o u t i n e d a t a .
I n o r d e r t o check t h e
o r d e r of magnitude o f t h e r e s u l t s y i e l d e d by t h e r u l e s o f thumb found i n m e t e o r o l o g i c a l l i t e r a t u r e ,
a f u l l scale d i s p e r s i o n experiment
w a s launched. DESCRIPTION OF THE PROJECT From J u n e t o November 1979 a f u l l s c a l e d i s p e r s i o n e x p e r i m e n t w a s r u n i n Vienna t o s t u d y t h e e f f e c t s o f carbon-monoxide e m i s s i o n s of p a r k i n g h o u s e s on t h e i r s u r r o u n d i n g s .
)
2,
I n s p i t e of a l l t h e d i f f i c u l t i e s
I n s t i t u t f i i r M e t e o r o l o g i e und Geophysik, Hohe Warte 3 8 , A-I190 Wien, A u s t r i a Z e n t r a l a n s t a l t f u r M e t e o r o l o g i e und Geodynamik, Hohe Warte 3 8 , A-I190 Wien, A u s t r i a
98 c o n n e c t e d w i t h a f u l l scale e x p e r i m e n t i n t h e complex s i t u a t i o n o f a c i t y , it was f e l t t h a t an a t t e m p t t o g e t away from i d e a l i z e d s i t u a t i o n s was w o r t h w h i l e , even if t h e r e s u l t s s h o u l d be v e r y s p e c i f i c f o r t h e s i t e chosen. The programm i n c l u d e d s t u d i e s o f e m i s s i o n s and h e a l t h e f f e c t s , b u t o n l y m e t e o r o l o g i c a l and d i s p e r s i o n a s p e c t s a r e t o be d i s c u s s e d h e r e . A s t h e e v a l u a t i o n of t h e experiment is n o t y e t completed, o n l y f i r s t r e s u l t s can b e r e p o r t e d a t p r e s e n t . A s m a l l p a r k i n g house i n a d e n s l y p o p u l a t e d r e s i d e n t i a l area w i t h
o n l y l i g h t t r a f f i c i n t h e s u r r o u n d i n g s w a s chosen a s e m i s s i o n s o u r c e i n o r d e r t o e n s u r e low background l e v e l s o f carbon monoxide concentrat i o n s . C a r movement i n t h e p a r k i n g house was v e r y s m a l l d u r i n g t h e day, a s most o c c u p a n t s w e r e r e s i d e n t s u s i n g t h e i r p a r k i n g l o t o n l y a t n i g h t . C o n s e q u e n t l y , e m i s s i o n s w e r e v e r y s m a l l , and no s i g n i f i c a n t immissions c o u l d b e d e t e r m i n e d . During most of t h e r u n s carbon monoxide was t h e r e f o r e a r t i f i c i a l l y i n t r o d u c e d i n t o t h e mechanical v e n t i l a t i o n s y s t e m o f t h e p a r k i n g house i n o r d e r t o enhance emissions and raise immissions t o a l e v e l t h a t c o u l d r e a d i l y be measured. The m e c h a n i c a l v e n t i l a t i o n system was l a y e d o u t f o r 1 0 4 0 0 m3 a i r p e r h o u r , and t h e CO-emission was k e p t a t a l e v e l of 2 0 0 0 ppm. For a few of t h e r u n s , a s p e c i a l model s o u r c e was u s e d , c o n s i s t i n g of a f a n e n c l o s e d i n a c a s i n g f i t t e d w i t h an a i r i n t a k e and a v e r t i c a l l y o r i e n t e d a i r o u t l e t on which t u b e s up t o 6 m h i g h can be mounted. The e m i s s i o n o f t h i s movable s o u r c e was g e n e r a l l y a d j u s t e d t o 1500 m3/h w i t h 10000 ppm CO.
The o b j e c t o f d e v e l o p i n g and t e s t i n g t h i s
movable model s o u r c e was t o become i n d e p e n d e n t of b u i l t - i n v e n t i l a t i o n s y s t e m s i n f u t u r e e x p e r i m e n t s . I t a l s o allowed e x p e r i m e n t s on t h e e f f e c t o f d i f f e r e n t e m i s s i o n s i t e s on t h e immission f i e l d . The b u i l d i n g w i t h t h e p a r k i n g a r e a on t h e g r o u n d f l o o r and i n t h e
c e l l a r had a b o u t t h e same h e i g h t a s t h e s u r r o u n d i n g b u i l d i n g s
(?. 2 5
mi.
The e m i s s i o n p o i n t o f t h e v e n t i l a t i o n system o f t h e p a r k i n g house was i n r o o f l e v e l n e a r t h e n o r t h w e s t e r n c o r n e r of an a l m o s t s q u a r e complex o f b u i l d i n g s w i t h a c o u r t y a r d i n t h e c e n t e r . During t h e 15 r u n s o f t h e e x p e r i m e n t t h e e m i s s i o n was monitored with
an UH++S2 . For immission measurements an UNOR 4N
with s i x external
s e n s o r s was a v a i l a b l e f o r e v e r y r u n . F o r s e v e r a l of t h e r u n s a d d i t i o n a l i n s t r u m e n t s (UNOR 6 , UNOR 4 , a i r b a g s a m p l e r s ) w e r e employed. The b a s i c i n s t r u m e n t s r e g i s t e r e d CO-concentrations
every 2 minutes, t h e a i r
Lags p r o v i d e d h a l f h o u r means. The d u r a t i o n o f t h e r u n s v a r i e d between 30 and 9 0 m i n u t e s . I n t h e c o u r s e of t h e e x p e r i m e n t , 2 2 p o i n t s w i t h i n
a 90° s e c t o r w i t h a 4 0 m r a d i u s w e r e sampled. Only p e r i o d s w i t h s u i t a b l e wind d i r e c t i o n s w e r e
chosen f o r e x p e r i m e n t s . Four r e f e r e n c e
99
p o i n t s w e r e f i t t e d w i t h s e n s o r s f o r e v e r y r u n , whereas t h e o t h e r s v a r i e d a c c o r d i n g t o 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 . Immission measurements w e r e made i n r o o f - l e v e l and a l o n g a v e r t i c a l p r o f i l e i n t o t h e courtyard. P r e l i m i n a r y i n v e s t i g a t i o n o f t h e w i n d f i e l d i n r o o f - l e v e l showed s u r p r i s i n g l y u n i f o r m c o n d i t i o n s . The w i n d r e g i s t r a t i o n s from one s i t e w e r e t h e r e f o r e c o n s i d e r e d as r e p r e s e n t a t i v e of t h e whole a r e a . V e r t i c a l t e m p e r a t u r e and h u m i d i t y p r o f i l e s w e r e measured a t t h e b e g i n n i n g and t h e end o f e a c h r u n . By a d d i n g c o l o r e d smoke and v i s i b l e . Plume r i s e o i l f o g t o t h e e m i t t e d a i r , t h e plume was made
was e v a l u a t e d from t h e e l e v a t i o n a n g l e s measured from two s i d e s of the source. RESULTS I n t h e f o l l o w i n g , o n l y 6-minute-means
c a l c u l a t e d from t h e 2-
m i n u t e v a l u e s a r e d i s c u s s e d . F i g . 1 shows t h e immission v a l u e s f o r f o u r measuring s i t e s d u r i n g two r u n s on t h e same day (1979-11-02). The s e n s o r a t s i t e 9 was n o t r e a c h e d by t h e plume d u r i n g t h e f i r s t p e r i o d and t h u s c h a r a c t e r i z e s t h e background c o n c e n t r a t i o n i n roof l e v e l . The o t h e r s e n s o r s show s t r o n g , r a t h e r a r b i t r a r y v a r i a t i o n s , produced by t h e h i g h v a r i a b i l i t y o f plume d i r e c t i o n s . T h i s i s a p p a r e n t from t h e r e g i s t r a t i o n s of t h e s i t e s 7 and 1 6 , which were p o s i t i o n e d i n r o o f l e v e l on o p p o s i t e s i d e s o f t h e s o u r c e . T h i s v a r i a b i l i t y i s n o t r e f l e c t e d i n t h e measured wind d i r e c t i o n s . S i t e one, w i t h i n t h e c o u r t y a r d , a b o u t 2 m above ground, shows c o n c e n t r a t i o n s up t o 6 ppm. These a r e due t o downward t r a n s p o r t w i t h i n t h e c a v i t y z o n e of t h e b u i l d i n g . Although a l m o s t continuous
downward t r a n s p o r t was
o b s e r v e d d u r i n g a l l r u n s , a c c u m u l a t i o n of carbon monoxide i n t h e courtyard never occured. According t o t h e p o s i t i o n o f t h e s i t e s , t h r e e t y p e s of f r e q u e n c y d i s t r i b u t i o n s of c o n c e n t r a t i o n s w e r e d i s c e r n i b l e . One example of each i s given i n Fig. 2 :
-
Type a r e p r e s e n t s s i t e s i n roof l e v e l more t h a n 30 m from t h e s o u r c e . Low c o n c e n t r a t i o n s have a v e r y h i g h f r e q u e n c y a s t h e plume o n l y r a r e l y p a s s e s o v e r one s p e c i f i c p o i n t a t t h e d i s t a n c e . Due t o
d i l u t i o n e f f e c t s no c o n c e n t r a t i o n s above 8 ppm w e r e found. - Type b i s c h a r a c t e r i s t i c o f p o i n t s on r o o f l e v e l a t s m a l l e r d i s t a n c e s from t h e s o u r c e . The lower f r e q u e n c y o f c o n c e n t r a t i o n s below 1 pprn i s due t o t h e f a c t t h a t t h e plume u s u a l l y p a s s e s t h e s e c l o s e r s i t e s a t l e a s t once d u r i n g a 6-minute i n t e r v a l l . The maximum v a l u e r o s e t o 2 5 ppm i n t h i s c a t e g o r y .
100
CO
rw
I
I
-
10
a16 S -
2.5
7
I
m
m
m
I
12: 45
1
I
I
.
I
I
15:ll TIME
13r22 ?4:48
F i g . 1 . Measured 6-minute-means o f c a r b o n monoxide c o n c e n t r a t i o n s a t s i t e s 1 , 7, 9 and 1 6 w i t h c o r r e s p o n d i n g wind d i r e c t i o n and windspeed.
-
Type c s t a n d s f o r t h e s i t e s of t h e v e r t i c a l p r o f i l e . A s a r e s u l t
of mixing i n t h e c a v i t y z o n e c o n c e n t r a t i o n s w e r e c o n t i n u o u s l y h i g h and r a t h e r i n d e p e n d e n t of t h e d i r e c t i o n of t h e plume. The h i g h e s t v a l u e measured w a s 3 9 ppm. Comparison o f measured c o n c e n t r a t i o n s w i t h t h e v a l u e s c a l c u l a t e d by t h e S c o r e r - e q u a t i o n
( r e f . 1) S
s = 2 - Q L2U
Q
U L
... c o n c e n t r a t i o n
...
e m i s s i o n r a t e of CO
... windspeed ... d i s t a n c e from
source
101
.
a/.
rl
400
200
400
1 I
201)
II
400 200
F i g . 2 . Frequency d i s t r i b u t i o n s of c o n c e n t r a t i o n s t y p i c a l f o r d i f f e r e n t site locations. y i e l d d i f f e r e n c e s i n c o n c e n t r a t i o n o f one o r d e r of magnitude. Especially f o r sites near t h e source t h e calculated values a r e much h i g h e r t h a n any measured 2-minute-values. 2 0 m,
F o r d i s t a n c e s above
t h e c a l c u l a t e d v a l u e s a g r e e i n o r d e r of magnitude w i t h t h e
h i g h e s t 6-minute-means.
Half-hour-means
which u s u a l l y p r o v i d e t h e
b a s i s for d e c i s i o n m a k i n g , where h e a l t h e f f e c t s are
concerned, w e r e
d i s t i n c t l y o v e r e s t i m a t e d by t h e S c o r e r e q u a t i o n . Due t o h i g h plume r i s e w i t h low windspeeds, i t was e x p e c t e d t o f i n d low c o n c e n t r a t i o n s i n t h e c o u r t y a r d . Higher windspeeds w e r e e x p e c t e d n o t o n l y t o r e d u c e plume r i s e , b u t a l s o t o enhance t u r b u l e n t mixing i n t h e wake o f t h e b u i l d i n g s , t h u s l e a d i n g t o h i g h e r concent r a t i o n s . Measurements i n t h e c o u r t y a r d 2 m above ground g i v e o n l y
l i t t l e s u p p o r t t o t h i s t h e o r y (see F i g . 3 ) . A l a r g e r range of wind-
102
s p e e d s might b e n e c e s s a r y t o p r o v e t h e tendency.
co
[PP~J 10,o 0
0
0
0
0
0
5.0
0
80
0
0
0
0
0
0 0
0 0 0
0 0
0
0 0 %
O
0
00
'8 O
0
0
0
1.o
0
0
0
0
0
0
0
O
9
0
1
I
1
0
2
3
4
5
u
[m/s]
F i g . 3 . Carbon monoxide c o n c e n t r a t i o n s i n dependence of windspeed a t site I . I n F i g . 4 o b s e r v e d and c a l c u l a t e d plume r i s e v a l u e s a r e compared. C a l c u l a t i o n s w e r e made a c c o r d i n g t o t h e ASME-equation
f o r momentum
sources ( r e f . 2 ) ,
v A H = D ( S ) U
1.4
D
vs u
.... s t a c k d i a m e t e r ... e x i t v e l o c i t y o f .... windspeed
f l u e gas
As t h i s e q u a t i o n was n o t d e v e l o p e d f o r 6-minute-means o f plume r i s e , t h e r e a r e problems i n i n t e r p r e t i n g t h e comparison. I t s e e m s however, t h a t t h e e q u a t i o n h a s a t e n d e n c y t o u n d e r e s t i m a t e plume rise f o r h i g h e r windspeeds. T h i s might a l s o be p a r t l y due t o a b i a s i n t h e measurement o f low e l e v a t i o n a n g l e s .
103
H! Im.
I50
12.5
mo
. .
7.5
. ..
..
5.4
.. ..
..
. . . .... ...... .. . . .. . ..
2.5
..
I
F i g . 4 . C a l c u l a t e d (AHTh)
a g a i n s t o b s e r v e d (AHFe)
plume r i s e v a l u e s .
CONCLUSION The p r e l i m i n a r y r e s u l t s i n e v a l u a t i n g t h e complete d a t a sets p r e s e n t e d a r e n o t y e t v e r y s a t i s f a c t o r y and much e f f o r t w i l l have t o b e made t o f i n d a way of d e t e r m i n i n g plume d i r e c t i o n more a c c u r a t e l y . ACKNOWLEDGEMENTS T h i s p r o j e c t w a s f i n a n c e d j o i n t l y by t h e Bundesministerium fiir Gesundheit und Umweltschutz and t h e Kuratorium f u r Umweltschutz, Austria
.
104 REFERENCES
1 Recommended Guide for t h e P r e d i c t i o n of D i s p e r s i o n of A i r b o r n e E f f l u e n t s . The American S o c i e t y of Mechanical E n g i n e e r s , New York, Second E d i t i o n ( 1 9 7 3 ) 2 R . S . S c o r e r and C.F. B a r r e t t , Gaseous P o l l u t i o n from Chimneys. 1 n t . J . A i r Water P o l l u t i o n , Vol. 5 , N o . 2 , 1961.
.
Atmospheric Pollution 1980, Proceedings of the 14th International Colloquium, Paris, France, May 5--8,1980, M.M. Benarie (Ed.), Studies in Environmental Science, Volume 8 0 Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
REAL-TIME
C.
105
PREDICTION OF LOCAL WIND BY MEANS OF STOCHASTIC MODELS
BONIVENTO,
G.
FRONZA and A . TONIELLI
I n t e r n a t i o n a l I n s t i t u t e f o r Applied Systems Analysis, Laxemburg ( A u s t r i a )
ABSTRACT S t o c h a s t i c models of l o c a l
wind a r e i l l u s t r a t e d i n t h e paper. From each model
a r e a l - t i m e p r e d i c t o r i s d e r i v e d , namely a r e c u r s i v e r e l a t i o n s h i p which, a t t h e beginning of each hour, s u p p l i e s with f o r e c a s t s of f u t u r e wind values on t h e b a s i s of c u r r e n t and r e c e n t wind measurements. The f o r e c a s t performances of t h e d i f f e r e n t p r e d i c t o r s a r e compared i n a real case (wind a t t h e meteorological s t a t i o n i n Venice)
.
INTRODUCTION
D i f f e r e n t types of r e a l - t i m e p r e d i c t o r s of short-term ground l e v e l p o l l u t a n t c o n c e n t r a t i o n s have been r e c e n t l y developed i n a i r q u a l i t y l i t e r a t u r e ( r e f s . 1 - 4 ) . A l l such p r e d i c t o r s r e q u i r e a c e r t a i n number of r e l e v a n t meteorological v a r i a b l e s
t o be f o r e c a s t a p a r t a t each time s t e p . From t h i s view p o i n t , p a r t i c u l a r l y important (both i n urban and r u r a l p o l l u t i o n c a s e s ) i s t h e f o r e c a s t o f s i t e wind speed and d i r e c t i o n , which i s i l l u s t r a t e d i n t h e p r e s e n t work. S p e c i f i c a l l y , t h e aim o f t h e p r e s e n t paper i s performance compar i s o n o f t h r e e d i f f e r e n t s t o c h a s t i c p r e d i c t o r s of hourly wind ( a t a given h e i g h t ) The comparison i s made on a r e a l c a s e ( f o r e c a s t of wind a t t h e meteorological s t a t i o n i n Venice). The t h r e e p r e d i c t o r s a r e d e r i v e d from t h e following t h r e e s t o c a s t i c models (see for instance ref. 5 ) . ( i )An AutoRegressive (AR) model of wind speed.
According t o such mathematical re-
p r e s e n t a t i o n , average wind speed i n each hour i s expressed a s a l i n e a r combin a t i o n o f previous hourly wind speed v a l u e s p l u s white n o i s e ( = p u r e l y random
term). ( i i ) A b i v a r i a t e a u t o r e g r e s s i v e model of t h e wind components (western and southern)
i n t h e h o r i z o n t a l p l a n e . According t o such model, each hourly wind component
i s expressed a s a l i n e a r combination of previous values of both hourly components p l u s white n o i s e . ( i i i ) A b i v a r i a t e AutoRegressive Moving Average
( A m ) model
n o i s e t e r m , p r e c i s e l y with a moving average n o i s e ) .
(model with colored
106 The performance o f t h e t h r e e p r e d i c t o r s i n t h e Venetian case l e a d s t o t h e following conclusions.
- The use of t h e b i v a r i a t e model ii) y i e l d s a s i g n i f i c a n t improvement i n windf o r e c a s t w i t h r e s p e c t t o approach i ) . This means t h a t c r o s s c o r r e l a t i o n s b e t ween t h e two wind components a r e u s e f u l information t o be taken i n t o account.
- The i n t r o d u c t i o n o f a c o l o r e d n o i s e , namely t h e use of model iii) i n s t e a d of i i ) , does n o t supply w i t h a s i p i f i c a n t l y b e t t e r f o r e c a s t .
THE UNIVARIATE MODEL AND PREDICTOR
The meteorological s t a t i o n i n t h e c i t y of Venice i s l o c a t e d 15 meters above t h e ground. Hourly wind d a t a recorded i n the p e r i o d May 1 0 t h - August 4 t h ,
1978, have been considered. P r e c i s e l y t h e d a t a up t o June 25th, 1978 have been used f o r e s t i m a t i n g t h e parameters of t h e d i f f e r e n t s t o c h a s t i c models, while t h e remaining d a t a have been used f o r t e s t i n g t h e f o r e c a s t performance o f t h e p r e d i c t o r s d e r i v e d from t h e models. F i r s t , only t h e r e c o r d of hourly wind speed has been taken i n t o account. Such r e c o r d shows a s t r o n g d a i l y p e r i o d i c i t y ( t y p i c a l of a c o a s t a l a r e a ) , so t h a t t h e d a t a have been c y c l i c a l l y s t a n d a r d i z e d as follows ( A = 1 h o u r ) :
w(24k+r) = rW(24k+r)
-
ur]
/
OI
where W(24k+r) = hourly wind speed i n t h e r - t h hour ( r = 1 , 2 , ..., 24) of t h e k-th day, namely i n t h e i n t e r v a l = mean
or
pr,
,
l(r-l)A, r.A]
of t h e k-th day.
s t a n d a r d d e r i v a t i o n o f wind speed i n t h e r - t h hour of t h e day.
Then, t h e s t o c h a s t i c p r o c e s s { w ( t ) } h a s been d e s c r i b e d by t h e following autot r e g r e s s i v e model :
where { n ( t ) } t = white n o i s e ;
a
=
j The
model parameters.
most s u i t a b l e o r d e r h a s t u r n e d o u t t o be p=3. Moreover t h e parameters of
model ( 2 ) have been e s t i m a t e d by a s t a n d a r d l e a s t squares f i t t i n g technique. The real-time p r e d i c t o r d e r i v e d from eq. r e f . 5) :
( 2 ) i s given by ( s e e f o r i n s t a n c e
w(t+2[t)
=
+ a 2w ( t ) + a 3w(t-1)
a w(t+llt)
1
w(t+3(t) = a l w ( t + 2 ( t )
+
a 2w ( t + l / t ) + a 3w ( t )
w ( t + d \ t ) = a 1w ( t + 3 ( t )
+
a2w(t+2jt)
+
a 3w ( t + l l t )
where ( f o r f = 1, 2 , 3, 4 )
w ( t + f ( t ) = f o r e c a s t o f w ( t + f ) made a t t h e i n s t a n t Of course, i f
.
( t + f ) corresponds t o t h e r - t h hour of t h e day,
t h e v a r i a b l e of i n t e r e s t t u r n s o u t t o be ( s e e eq.
W(t+fl t) = p r
tD
+
t h e f o r e c a s t of
(1))
orG(t+flt).
(4)
The performance of p r e d i c t o r (3)-(4) i n correspondence with t h e Venetian Data June 26th-August 4 t h , 1978 i s summarized i n T a b l e 1, where t h e f o r e c a s t q u a l i t y of t h e t r i v i a l p e r s i s t e n c e p r e d i c t o r i s a l s o reported. TABLE 1
F o r e c a s t performance o f u n i v a r i a t e and p e r s i s t e n c e p r e d i c t o r . U n i v a r i a t e AR
f
Precisely, the table
Persistence
.81
.77
.64
-56
.55
.44
.52
-28
r e p o r t s t h e c o r r e l a t i o n s between p r e d i c t i o n s and observa-
tions for different forecast lags f .
THE BIVARIATE MODELS AND PREDICTORS
F i r s t l e t (T = v e c t o r t r a n s p o s i t i o n symbol)
w ( t )= t - t h 1 w (t) = t-th 2
( c y c l i c a l l y s t a n d a r d i z e d ) hourly western component of wind; ( c y c l i c a l l y standardizedlhourly
southern component of wind;
T
Consider t h e following a u t o r e g r e s s i v e b i v a r i a t e model of t h e wind v e c t o r stochas t i c p r o c e s s {w(t)}, P w(t+l) = b.w(t-j+l) j=1 3-
1
where
+ m(t)
(5)
108 { ~ ( t )=}white ~ noise b. 7
=
model parameters
The parameters of model ( 5 ) have a l s o been estimated by standard l e a s t squar e s f i t t i n g . The optimal o r d e r h a s turned o u t t o be p = 2 . The p r e d i c t o r d e r i v e d from model ( 5 ) i s q u i t e s i m i l a r t o eqs.
( 3 ) . 1 t s perfor-
mance i s shown i n Table 2 , t o g e t h e r with t h e corresponding q u a l i t y of t h e p e r s i TABLE 2
F o r c a s t performance of b i v a r i a t e and p e r s i s t e n c e p r e d i c t o r s Western component f
1
Biv. AR
Southern component
P e r s i s t e n c e Biv. AR
Persistence
.80
.76
-92
-89
2
.64
.52
.86
.76
3
.56
.36
.84
.62
4.
.53
-24
.82
.46
sistence predictors.
The improvement with r e s p e c t t o t h e r e s u l t shown i n Table 1 i s s i g n i f i c a n t (part i c u l a r l y f o r high v a l u e s of 2 ) . A b i v a r i a t e ARMA model
( m ( t ) = moving
average n o i s e i n eq. ( 5 ) ) has a l s o been
considered. However, t h e c o e f f i c i e n t s of t h e moving average term have turned o u t t o be s m a l l (namely m ( t ) i s a c t u a l l y white) and t h e f o r e c a s t performance has been p r a t i c a l l y c o i n c i d e n t w i t h t h e one of t h e b i v a r i a t e AR p r e d i c t o r .
REFERENCES
1. 2. 3. 4. 5.
G.Finzi, G . Fronza and S . R i n a l d i , Atmosph. Envir., 12 (1978) 831-838. G.Finzi, P . Z a n n e t t i , G. Fronza and S . R i n a l d i , Atmosph. E n v i r . , 13(1979) 1249-1255. G.Finzi, G. Fronza and A. S p i r i t o , J . A i r P o l l . Contr. A s s . ( i n p r e s s ) . P. Bolzern and G. Fronza, Proc. 10th I n t . Techn. Meet. on A i r . P o l l . Modell., Rome, 1979 ( i n p r e s s ) G.E.P. Box and G.M. J e n k i n s , Time Series Analysis, Forecasting and Control, Holden Day, S . F r a n c i s c o , 1970.
AtmosphericPollution 1980, Proceedings of the 14th InternationalColloquium,Paris,France, May 5-8,1980, M.M. Benarie (Ed.),Studies in Environmental Science,Volume 8 0 Elsevier Scientific PublishingCompany,Amsterdam - Printed in The Netherlands
109
AIR POLLUTION IMPACT IN STREETS WITH HEAVY TRAFFIC AND THE EFFECTS OF THE DOMINANT PARAMETERS H. Sobottka, Tf?J Rheinland, Cologne (FRG)
ABSTRACT The air pollution impact caused by gaseous pollutants is investigated by carrying out comprehensive measurements in the city area of Cologne. This paper deals with the effects of the dominant parameters on the pollutant dispersion in street canyons. The distribution of CO concentrations for typical traffic situations are shown as well as structural features and meteorological conditions both at curbside and at the surfaces of the buildings. INTRODUCTION Under contract to the German Federal Ministry for Research and Technology,
flV Rheinland carries out field measurements in the city area of Cologne and investigations in the atmospheric wind tunnel for the purpose of estimating the air pollution impact caused by motor vehicles in street canyons. Unlike the large-area pollutant dispersion, for describing the dispersion phenomena of vehicle exhaust gases in the vicinity of the source, there are no scientifically proven simulation models by means of which the air pollution impact resulting from gaseous pollutants can be characterised, e.g. by mean values and 95 percentiles. The objectives of this research programme are to collect the input data necessary for the development of the simulation models, to analyse these data and to transform them into mathematical models. MEASUREMENTS This paper deals with the dominant parameters affecting pollutant dispersion. They are acquired with the aid of 2 stationary and 2 mobile monitoring stations in operation since October 1976. Figure 1 shows a schematic representation of a stationary pollution monitoring station. All the parameters are monitored continuously and summarized in the form of half-hourly mean values. RESULTS The concentration field is dependent to a great extent on the flow field 111. Characteristic concentration levels are found for the different wind directions
110
w Fig. 1. CO-monitoring s t a t i o n (Venloer Strasse) prevailing i n the s t r e e t canyon 121. Figure 2 i l l u s t r a t e s an actual diurnal variation for the CO concentrations, the t r a f f i c , the wind v e l o c i t y and wind d i r e c t i o n for both
sides of the street. Traftic Load Pattern
Above Roof Level Wind Pattern
800 cars 0.5 h 600
4.00
mls
3.00
2
-
? 2.00
400g
-I
K
U
1.oo
200
20.00
ppm 15.00
-8 10.00 5.00
0
4
8
12
16
20 240 time CO-DiurnalPattern (out of town)
8
20 time CO-DiurnalPattern (into town)
4
12
16
Fig. 2. Diurnal pattern i n the Bonner Strasse; date 14,12,1977
:
111 At about 4 p.m. there is an abrupt change of the above roof level wind (ARL-Wind) from a parallel to a perpendicular direction to the street. Despite a simultaneous increase in the above roof level wind speed, there is a sudden rise in the absolute concentrations leeward (out of town) at all 3 sampling heights (4 m, 9 m and 15 m) with clear-cut CO gradients between the monitoring levels, while the concentrations windward (into town) decrease significantly and the CO gradients almost disappear, although there is a comparable traffic load on each side of the street. At the bottom sampling height, at 4 m, the concentration level leeward ( 20 ppm) is about twice as high as that windward ( 11 ppm). These effects are characteristic of the socalled leeward-windward circulation. They must be taken into consideration when assessing the air pollution impact in city streets and drawing up monitoring plans. Traffic Load Pattern (into town)
Traffic Load Pattern (out of town) f
I Q 0
0
4
8
12
16
20
24
time CO-DiurnalPattern (out of town)
I
I
1
I
I
1
I 16
1
20
I 24
I
1
1
4
8
12
CO-Diurnal Pattern (into town)
time
Fig. 3. Diurnal patterns averaged over one year for the Bonner Strasse; monitoring 17,10,1978 period: 17,9,1977
-
The actual diurnal pattern shown gives an impression of the non-stationary stochastic process of pollutant production and dispersion. By summarising the time series for the emissions, CO concentrations and the wind, the deterministic variations can be made visible, e.g. by taking diurnal patterns averaged over one year. By compiling the time series according to week days and times of day, we find similar frequency distributions for the working days Monday to Friday and for Saturdays and Sundays. From their mean value curves diurnal patterns averaged over one year can be represented. Figure 3 shows these specific patterns for the CO concentrations and the
112 t r a f f i c w i t h t h e working d a y s Monday t o F r i d a y being summarised. The s p e c i f i c d i u r n a l p a t t e r n s f o r t h e t r a f f i c and t h e c o n c e n t r a t i o n s show q u a s i - s t a t i o n a r y behaviour o f t h e non-stationary
parameters when t h e i r t i m e series a r e averaged over
long p e r i o d s . On comparison o f t h e p a t t e r n s we can see c l e a r l y t h e d i r e c t connectioi between t h e t r a f f i c and t h e c o n c e n t r a t i o n s p r e v a i l i n g a t a l l t h r e e monitoring level8 D e t a i l e d a n a l y s e s of t h e flow f i e l d s i n t h e streets under c o n s i d e r a t i o n show, foi example f o r Bonner StraBe, t h a t t h e leeward-windward
c i r c u l a t i o n i s t h e most
prominent f o r a flow d i r e c t i o n a t a n a n g l e o f between 45" and 75' t o t h e s t r e e t . When c l a s s i f y i n g t h e CO c o n c e n t r a t i o n s according t o t h i s above roof l e v e l wind s e c t o r and i t s s u p e r p o s i t i o n t o form mean d i u r n a l p a t t e r n s f o r t h e c o n c e n t r a t i o n s a1 c u r b s i d e and a t t h e b u i l d i n g s u r f a c e s , t h e f o l l o w i n g r e s u l t s a r e gained ( F i g u r e 4 ) . Leeward ( i n t o town), t h e c o n c e n t r a t i o n l e v e l s monitored a t t h e same h e i g h t (e.g.
4 m)
are h i g h e r a t t h e b u i l d i n g s u r f a c e s t h a n a t c u r b s i d e . The c o n c e n t r a t i o n g r a d i e n t between t h e p o i n t s a t a h e i g h t o f 4 m a t c u r b s i d e and a t t h e b u i l d i n g s u r f a c e i s almost t h e same as t h a t between t h e sampling h e i g h t s 4 m and 8 m a t c u r b s i d e . A
s i m i l a r t r e n d c a n be observed from t h e 8 m monitoring l e v e l . The c o n c e n t r a t i o n g r a d i e n t s between t h e sampling h e i g h t s o n t h e windward s i d e almost d i s a p p e a r , a s do t h o s e between t h e c u r b s i d e and b u i l d i n g s u r f a c e comparison p o i n t s . The c o n c e n t r a t i o n l e v e l s windward correspond approximately a t a l l sampling h e i g h t s t o t h e l e v e l of background c o n c e n t r a t i o n ( c o n c e n t r a t i o n s measured a t 26 m). These e f f e c t s were f i r s t e s t a b l i s h e d by means of flow and c o n c e n t r a t i o n measurements i n t h e atmospheric wind t u n n e l 131.
CO-Diurnal Pattern (into town)
CO-Diurnal Pattern (into town)
I
I
sampling height: ----9 m curbside
----
26 m fbackground
9.0 ppm
-8 4.5 0
4 8 12 16 20 24 time CO-Diurnal Pattern (out of town)
Fig. 4. Mean -diurnal p a t t e r n s fox oncoming flow from sector 60" 5.12.1979 Venloer Strasse; monitoring p e r i o d : 22.12.1978
-
2 15'
i n the
113
-
0
30,
Fig. 5. Dependency of the standardised concentrations and concentration gradients on the atmospheric stability (Jiilich stability classification)* in the Venloer Strasse; monitoring period: 19,10,1976 15,8,1977
-
Besides the advective transport in wind direction, the pollutant dispersion is determined by turbulent flow phenomena in the atmosphere. The influence of the atmospheric turbulence on the pollutant dispersion in street canyons is portrayed ** consisting of in Figure 5. The example of the standardised CO concentrations
-
the measured CQ concentration, the traffic, the above roof level wind and the street width
-
shows that, for the two selected directions with increasing atmospheric
stability, there is also an increase in the CO concentrations. The differences of the standardised CO concentrations between the various sampling heights do not show this dependency. This result can be generalised for the remaining above roof level wind directions. This indicates a dominance by the mechanical turbulence caused by the buildings and the traffic over the atmospheric turbulence. Detailed investigations have also shown that, owing to the low frequency of occurrence (pattern) of stability classes relevant to pollution, when considered over a period of one year, longterm mean values can be taken without consideration of the stability classes. However, when taking 95 percentiles as a further assessment criterion for air pollution impact these stability classes must be included / 4 / . Finally, Figure 6 shows the influence of the street geometry on the pollutant dispersion illustrated by the mean diurnal patterns for the CO concentrations and
***
Meteorological data from the German Weather Service See paper by Mr. Leisen
114 Traffic Load Pattern
I VenberStrasse I
U
I
I
I
I I
I 1
12
16
T r a m Load Pattern
I
I
I
I
I
1
Tiimbari Strasre
II
I
I
I
4
8
12
16
I
4
0
4
8
20 tima24
20 time 24
CO-Dlurnal Pattern
CO-Diumal Pattern
Fig. 6. Comparison of mean diurnal patterns of Venloer Strasse and Trimborn Strasse; monitoring period: 19,12,1978 21.2.1979
-
the traffic. The streets vary in their ratio building height to street width (H/W). The approximate ratio for Venloer Strasse is 1:l and for Trimborn Strasse 2:l. A characteristic result of the measurements is that the CO level in Trimborn Strasse is 1.3 times higher than in Venloer Strasse although the traffic load in Trimborn Strasse is only about a third as high. This points to a far worse ventilation in the Rimborn Strasse. This effect is also relevant for the air pollution impact and must be taken into consideration in the model design. For this reason further measurements according to street categories will be taken by mobile monitoring stations to gather further experimental input data. REFERENCES I. H. Sobottka in Abgasimmissionsbelastungen durch den Kraftfahrzeugverkehr, Verlag TffV Rheinland, 1978. pp. 125-149. 2. Johnson, W . B . . Ludwig, F.C., Dabbert, W.F. and Allen, R.J.: Final Report, Contract CAPA-3-68 (1-69). for CRC and EPA, Stanford Research Inst., Menlo Park, Calif. 1971, NTIS No. PB 203469 3. P. Leisen in Abgasimmissionsbelastungen durch den Kraftfahrzeugverkehr, Verlag TffV Rheinland, 1978. pp. 223-249 4. H. Sobottka. P. Leisen in 18. FH-Texte. Verkehrs- und StraSenbauseminar 1979, Schriftenreihe FH Aachen, pp. 121-173
ANALOG MODELING
This Page Intentionally Left Blank
Atmospheric Pollution 1980, Proceedingsof the 14th InternationalColloquium,Paris,France, May 5-8,1980, M.M.Benarie (Ed.),Studies in EnvironmentalScience,Volume 8 0 Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
117
WIND TUNNEL MODELLING OF BUOYANT EMISSIONS A . G . ROBINS
CEGB, Marchwood Engineering Laboratories, Southampton
SO4 4ZB
ABSTRACT The field study of plume rise and ground level concentration downwind of the Tilbury and Northfleet power stations provides the only adequate data source for use in investigating the accuracy of laboratory scale experiments. The TilburyNorthfleet site was modelled at a scale of 11500 in a 9.1 x 2.7 m wind tunnel and measurements of ground level concentration, plume rise and spread were made in a neutrally stable boundary layer for a range of wind speeds and power station operating conditions.
Diffusion studies for buoyant and passive emissions were a l s o
undertaken in undistrubed boundary layer flows. The applicability of various scaling laws for buoyant emissions was thus determined and the likely accuracy of model studies thereby illustrated.
INTRODUCTION Although it has become relatively common practice to study plume dispersion problems at laboratory scale there have been very few attempts to compare model and full scale observations.
In so far as buoyant emissions are concerned there
are no properly established scaling laws and the applicability of those laws which have been suggested has not been adequately investigated.
It was with these
observations in mind that the present work was undertaken. In order to model a buoyant emission (density, p S ’. diameter D into an external cross-flow (density, p ; conserve the following parameters:
ps/p,
of model and full scale wind speeds is:
speed, W) from a source of
speed U) it is necessary to 2
W/U, gD/U
, and,
R = U(model)/U
=
consequently,the ratio
&, where
E,
the geometric
scale ratio,is defined by the nature of the problem being considered and the dimensions of the available laboratory facility; typically it lies in the range from 1/2000 to 11200.
This comes about because it is necessary to model the lowest
kilometer or so of the atmosphere and to study the concentration field over a sufficient fetch to define the maximum ground level concentration. As all wind tunnels have a minimum operating speed there is thus an implied limit to the lowest wind speed which can be modelled by the above procedure and in order to lower this
118 wind speed it i s necessary to relax the scaling criteria. accomplished by combining the previous
This is usually
three parameters into two and discarding
correct modelling of the emission density and, perhaps, source diameter. However, there is considerable scope for choice in the selection of the combined parameters and it i s essential to define the limitations inherent in these 'relaxed' scaling techniques. The most noteworthy previous investigation is that by Isyumov and Tanaka (ref. 1) who concluded that, of the scaling laws tested, only complete scaling (i.e. conservation of p , / p ,
2
W/U, gD/U ) appeared satisfactory. From a much more limited
study Hoult et a1 (ref. 2) claimed that adequate reproduction of observed full scale plume rise downwind of a short rectangular stack (with strong entrainment effects) could be obtained by modelling the velocity ratio and densimetric Froude number. Not all scaling law forms were examined in these studies and, as a result, no definite recommendations can be made, though Isyumov and Tanaka's conclusion, in
so
far as releases near buildings are concerned, seems intuitively correct.
EXPERIMENTAL DETAILS The experiments were carried out in the Marchwood Engineering Laboratories' 24.0 x 9.1 x 2.7 m wind tunnel, in which a 1.2 m deep neutrally stable atmospheric boundary layer (abi) was simulated (ref. 3 ) .
The surface roughness length ( z ) of
the undisturbed flow was 4.1Ow4~ (H is the boundary layer depth) and the fric:ion velocity (u,)
was 0.05 U(H)
(U(H) being U at height H).
At a scale of 11500 the
wind tunnel flow corresponded to a 600 m atmospheric boundary layer above a surface of roughness length 20 cm.
In the undisturbed flow, experiments were
undertaken to study diffusion downwind of passive emissions concentrations being measured.
-
mean and fluctuating
In order to study scaling problems emissions from
a 0.20 m tall stack (100 m at full scale) were considered. The emissions were taken to be typical of a fossil fuel fired power station generating either 400 or 1000 MW of electricity.
(E W
=
=
The heat emitted from the stack was taken as E/6
station load) and the equivalent full scale conditions were: -1 (E = 400 MW), 53 ms-l (1000 Mw); 21 ms p , / p = 0.72; D = 6.4 m
The only adequate full scale experiment for present purposes is that undertaken downwind of the power stations at Tilbury and Northfleet, to the east of London (refs. 4 & 5).
The site is sketched in fig. 1, in which the positions of the
twenty-two sulphur dioxide measuring stations are shown, as are the extents of the regions modelled, at a scale of 11500, for use in the wind tunnel studies. Thus, at full scale, ground level concentrations (glc) could only be measured for winds from about S to SW, whereas plume rise could be measured for all wind directions. Approximately 5000 sets of mean hourly glc data were obtained and these have been categorised according to power station load, wind speed and atmospheric stability (ref. 6), meteorological information being obtained from a nearby 187 m tower and
119 from the Crawley radiosonde; plume rise measurements were categorised in the same manner.
The results revealed significant topographical effects influencing the
plume from Northfleet power station, and it was deduced that for winds which carried the plume across the river the effective stack height was 30 to 40 m less than the actual stack height.
Both power stations have twin stacks and operate with
emission temperatures of llO°C above ambient; for Tilbury A (oil burning):
E 5 360 MW, h(stack ht.)
=
101 m, D = 6 . 4 m
E 6 7 2 0 MW, h = 1 5 3 m, D = 7 . 4 m
for Northfleet (coal burning}:
In each case the heat emitted from the stacks was taken to be E / 6 . The wind tunnel techniques for mean concentration measurement are described in ref. 7 and the instrumentation used for studying concentration fluctuations in refs. 8 & 9. In the wind tunnel experiments averaging times
(T)
were chosen such
that the residual scatter in repeated measurements was no more than 10%; roughly speaking, this required: from about 30 (for U
=
T U / H = 4 0 0 , whereas at full scale this parameter varied
5 ms-')
to 150 (U = 25 ms
-1
) so that a degree of variance
must thereby result. Much more relevant sources of variance are unsteadiness in the mean flow and source conditions, even though results were only recorded when mean conditions were relatively steady over a period of one hour. None-the-less, in nominally similar conditions hourly average glcs between 0 times and 3 times the ensemble mean were observed (ref. 10). SCALING CONDITIONS (NEUTRALLY STABLE APPROACH FLOW) Assuming that the approach flow and surface conditions have been properly modelled it remains to model the emission and this requires conservation of the 2 following properties: p , / p ; W/U; gD/U This so called 'complete' scaling
.
condition will hereafter be designated condition C.
One approach to relaxing the
requirements is to consider the magnitudes of the important terms in the flow equations and this leads to a number of possible modelling conditions, i.e.: 2 2 2, 2, W/U or psW / P U and gD@/U2, where 8 = ( p - p ) / p and p is a reference density. These conditions will be abbreviated as FXY, where F denotes the conservation of the densimetric Froude number, X = V for conservation of the velocity ratio or M for the momentum ratio, and Y
2,
=
A if p
= p
or S for p,.
Another approach to
relaxing C scaling conditions follows from plume rise theory which gives the rise, 2 3 Az/D, as a function of x/D, psW /pU2 and g$DW/U The resulting conditions will
.
be abbreviated as BXY, where B denotes conservation of the nondimensionalised buoyancy flux. A variation on these methods can be derived from the specific form of plume rise formulae; eg. Briggs (ref. 11): 3 2 = a(p W2/pU2) x /D + b(g@DW/U )(x/D)
.
Modelling requires the reproduction of Az/h at given x/h and this may be achieved by conservation of:
p,/p,
2
3
DW/hU, gD W/hU ; i.e.
by distorting D/h - condition BMD.
Of course it is impossible to conserve the various Reynolds numbers of the
120 problem.
This is of little consequence in
far as the approach flow is concerned
so
(as it is a fully turbulent flow) providing the surface is fully rough (u,zo/v
3 0(1)),
and in the present case this implies U(H) 5 0.6 ms-'.
The internal
flow in the stack must be 'tripped' in order to reproduce an appropriate exit velocity profile and this was affected by the insertion of 'porous plugs' a few diameters below the stack tops - in the experiments WD/v stack Reynolds numbers were between whereas they exceeded
lo6
lo3 and
4.10
3
= LO3
4
to 10
.
The external
in the wind tunnel studies,
However, as entrainment into the
at full scale.
recirculating flow immediately downwind of the stack was not a significant feature of the problem this discrepancy was unimportant. RESULTS Isolated Stack in Undisturbed Flow That the flow within the wind tunnel was an adequate model of the neutrally stable abE, and that the behaviour of plumes resulting from passive emissions was acceptably modelled have already been established (refs. 3, 12 & 1 3 ) .
Figs. 2 & 3 show typical
results for buoyant emissions of the variation of maximum glc with wind speed nondimensionalised as CU(H)h Az/h.v. l/U(H).
2
/Q.v.U(H),
and plume rise with wind
speed, shown as
Q is the volume emission rate and the results have been converted
to equivalent full scale values, assuming
W
refer to full scale conditions of:
=
E
1/500. -1
=
21 ms
, ps/p
The data shown in fig. 2 = 0.72.
If any of the
relaxed scaling conditions are to be considered realistic then results obtained by their application must satisfy two conditions: a) they must be relatively insensitive to the choice of model scale emission density, b) they must agree tolerably well with the results obtained by complete scaling. It can be seen that, of the scaling conditions tested, only BMA and DMS are acceptable on the above basis.
It is interesting to note that although the BMA and
BMD scalings conserved the same parameters, enhancement of the source diameter
proves to be unrealistic. Measurements revealed that with BMD scaling the initial dimensions of the plume were considerably exaggerated and,
as
a result, the
development of the plume was not properly modelled. Tilburv-Northfleet Site
It was observed that the chief effect of the topography upwind of the stacks was to increase the lateral turbulence intensity (also, presumably, the scale). near linear plume lateral growth,
(r
agreement with the full. scale data.
Y
A
(x), was measured (fig. 4) which was in good
Observations revealed that the mean streamline
through the top of the Northfleet stack descended by 30 to 40 m in a 2 km fetch downwind;
this agreed with deductions from full scale plume rise data.
Measurements of plume rise and ground level concentration were consistent with those in the undisturbed flow in that conditions DMS and BMA produced plume
121 behaviour close to that observed for complete scaling, whereas the other methods (BMD was not used) did not.
Further experiments were undertaken to investigate
the possibility of even greater relaxation of complete scaling.
If it is assumed
that the plume is entirely buoyancy driven then it may be argued that it is only necessary to conserve the densimetric Froude number, or buoyancy flux parameter. It was found that this was indeed feasible providing the momentum ratio was not
greatly enhanced (say by no more than a factor of two).
However, it would perhaps
be unwise to recommend the adoption of such a technique as the exaggeration of emission momentum could have important consequences to the near field plume path which would result in under-estimation of entrainment effects etc. A major difficulty in model full scale comparisons arises because of the almost
inevitable scatter in field data.
In the present case this was compounded by the
relative sparseness of the SO measuring network in comparison with the wind tunnel 2 gas sampling system. None-the-less, it was possible to demonstrate reasonable -1 simulation of plume rise and vertical spread for wind speeds greater than 6 ms , by using scaling conditions C, DMS and BMA.
Fig. 5 is a comparison of the variation
of maximum glc with wind speed for emissions from Tilbury; the model data are a composite of the results obtained by C and DMS scaling. At first sight it appears as though the model overpredicts the glc, but this is not a correct interpretation since the field data refer to the mean maximum observed glc (i-e. at one o f the 22 monitoring sites) for all wind directions in which the plume passed over the network. The equivalent data can be derived from the wind tunnel measurements and this results in good model full scale agreement - this also holds for the position of the maximum glc.
An alternative approach is to attempt to derive centre-line glc
profiles from the field data and to compare the resulting maxima with the model results.
This procedure shows reasonable agreement between the model and the upper
range of the full scale data.
A l s o shown in the figure is the variation in maximum
glc due to changes in boundary layer height and load division between the two stacks. Concentration Fluctuations Wind tunnel measurements of concentration fluctuations in the Northfleet plume showed that DMS scaling produced the same fluctuation levels as C scaling (ref. 4 ) . Unfortunately, it was not possible to obtain adequate statistics from the full scale 3 minute mean data in order to attempt model-field comparisons. An interesting
feature to emerge from subsequent laboratory experiments was the importance o f initial source size in determining fluctuation levels (fig. 6).
This reinforces
the previous observation that stack diameter exaggeration is not a reliable scaling procedure because it results in incorrect initial plume geometry. DISCUSSION It has been demonstrated that adequate modelling can be obtained with C, DMS or
122 BMA scaling. This is not entirely consistent with previous less extensive studies (refs. 1 & 2), though the accuracy of BMA scaling has been demonstrated elsewhere (Prof. D. J. Wilson, private communication). In practice it is to be recommended that C and either DMS or BMA are used in conjunction and that some situations are modelled in both ways in order to demonstrate the performance of the relaxed scaling condition. The situation is less clear in
so
far as building entrainment and other
near-field studies are concerned and in such cases it seems prudent to use only C scaling (Prof. W. Melbourne, private communication).
A necessary preliminary is a
demonstration of the adequacy of the modelled boundary layer; velocity, turbulence and dispersion data are necessary for this.
Providing the above recommendations are
followed it is to be expected that reasonably accurate modelling of the behaviour of buoyant emissions in the neutrally stable abl is possible. ACKNOWLEDGEMENTS This work was undertaken at the Marchwood Engineering Laboratories and is published by permission of the Central Electricity Generating Board. REFERENCES 1 N. Isyumov & H. Tanaka, Proc. 5th Int. Conf. on Wind Engineering, Colorado S t a t e University, 1979 paper VIII-3. 2 D.P. Hoult, S.R. O'Dea, G.L. Touchton & R . J . Ketterer, J. Air Poll. Control Assoc. 27 (1977) 56-60. 3 A.G. Robins, J. Industrial Aero., 4(1979)71-100. 4 D.H. Lucas, K.W. James & I. Davies, Atmos. Environ. 1(1967)333-365. 5 D.J. Moore, Atmos. hnviron., 1(1967)389-410. 6 D . J . Moore ti P.A. Roberts, CEGB Report RD/L/M469 (1974). 7 A.G. Robins, Proc. Inst. Mech. Engrs., 189(1973)44-54. 8 J.E. Fackrell, J. Phys. E:Sci. Instrum., 11(1978)1015-1022. 9 J.E. Fackrell, CEGB Report R/M/N1056 (1979). 10 D.J. Moore, Proc. Inst. Mech. Engrs., 189(1975)33-43. 11 G.A. Briggs, USAEC (1969) TID-25075. 12 A.G. Robins, Atmos. Environ., 12(1978)1033-1044. 13 A.G. Robins & J.E. Fackrell, in C.J. Harris (Ed.) Mathematical Modelling of Turbulent Diffusion in the Environment, Academic Press. London, 1979, pp.55-114. 14 J.E. Fackrell, CEGB Report (1978) R/M/N1016. FIG. 1 Tilbury (T) Northfleet (N) site showing SO2 monitors (X) and model outline. Land over 100 ft shaded.
123
.
10 FIG. 2
UCH) m/s
a
- -
-
40
10
Maximum glc.v.wind speed; E = 400 MW. Shaded area is C scaling (p / p = 0.72), scatter typical of all data. Relaxed sczlings p / p = 0.27 ( A ) , 0.17 ( B ) .
DMA//BMD 28
0',0
a
0
// BMA
c
. I
C shaded area-shows scatter typical o f all results.
%
N
Q
u
0 FIG. 3
I/UCHI
s/m
0-1
Plume rise.v.wind speed at x = 1 0 h ; E = 1000 MW. For C scaling p / p = 0.72, otherwise 0.27.
124
Q
I
7
8
8
8
x
0 FIG. 4
m.
5000
Lateral spread downwind of Tilbury A
Full scale data mean f I stdv. Source 1360
-10 FIG. 5
UH)
D/H 0*029+ Ooof
0.003 0
+ I
0
m/s
30
Maximum glc.v.wind speed, Tilbury, E = 250 MW. Solid line is actual max.; 1, H = 600; 2, 300 m; 3 , single stack. Dashed line is max. observed at site of field SO2 monitors.
dn
1
0
FIG. 6
Fluctuating (rms) concentrations downwind of source at h/H = 0.2. c' is max. fluctuation and C is max. mean concentration in plane x = const.
Atmospheric Pollution 1980, Proceedings of the 14th International Colloquium, Paris, France, May 5-8,1980, M.M. Benarie (Ed.), Studies in Environmental Science, Volume 8 0 Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
125
FLUE GAS DISPERSION IN THE VICINITY OF BUILDINGS: WIND TUNNEL SIMULATION AND COMPARISON WITH FIELD MEASUREMENTS H. SOMMERS Ruhrgas AG, Essen (West Germany) J. HOITZ Gaswarme-Institut E.V. (GWI), Essen (West Germany) R. HAUPT formerly GWI, now Gutehoffnungshutte Sterkrade AG, Oberhausen (West Germany)
ABSTRACT On a scale model of a hospital from which field data were available, flue gas dispersion was simulated in an environmental wind tunnel. An analysis showed the considerable influence of the velocity profile and the turbulence level on flue gas dispersion and on the values of diffusion-critical Reynolds numbers. The tests confirmed that diffusion-critical Reynolds numbers exist, although the critical level was determined to be higher than the levels reported by other authors. The wind tunnel test data ,for overcritical Reynolds numbers were in acceptable agreement with the field data measured.
TEST CONFIGURATION Wind tunnel The aerodynamic tests made to study flue gas dispersion in the vicinity of sharp-edged buildings were carried out in the upstream part of a wind tunnel as shown by Fig. 1. The wind tunnel was installed in a large 600 m3 hall with vents. The air was taken from the room and exhausted into the open air through an air duct. Parallel flow at the inlet of the wind tunnel was achieved by a hexagonal honeycombed grid ( 9 x 1 2 mm2 honeycombs) of a depth of 6 0 mm. The straightened flow then passed through a rod-type grid designed according to Cowdrey (ref. 1 ) to generate the velocity profiles and turbulences desired.
126
Fig. 1. Wind tunnel arrangement Simulation of atmospheric near ground boundary layer The grid consisted of parallel rods of equal diameters to produce four patterns of flow differing with regard to speed and turbulence. The rods were spaced at equal intervals to generate velocity profiles of constant speed with height, while the spacing was irregular for exponential profiles. Both types of profiles may be expressed by the following power law:
06
o<
=
for flat country, while according to Davenport (ref. 2 ) , 0.28 for suburbs as in the case studied. = 0
The speed and turbulence distributions in the wind tunnel were recorded by a DISA constant temperature anemometer. Fig. 2 shows some centre tunnel data without the model. installed. The distributions measured were largely constant in the longitudinal and transverse directions. The grid with horizontal rods produced eddies in one direction only unlike real field conditions. It was, however, assumed that the correct turbulence pattern was obtained automatically as a result of the installation of a scaled-down model of the upwind buildings. This assumption is justified as studies made have shown that differences in turbulence only have a minor influence on concentration levels with wind profiles for urban areas.
127
4.0
z/z, 3.0
2.0
1.0
0
Fig. 2 . Vertical turbulence (left) and velocity profiles generated in a wind tunnel Model of the building studied and dispersion measurement techniques The building studied (ref. 3 1 , a hospital, is located at the southern edge of the centre of a small city. The vicinity of the hospital is flat. The nearby buildings are mainly one or two-storey houses. A plastic 1:250 model of the hospital buildings and the buildings located within a radius of approx. 250 m was built. The smallest detail modelled was 1 nun in the model scale. The boiler house stack (Fig. 3 ) emitted traces of methane. The gas needed for determining the concentration levels was sampled at the same locations as during the field measurements (Fig. 3 ) and additional locations through probes in the walls of the buildings and pumped through teflon piping to a flame ionization detector. Concentration coefficients (ref. 4 ) were calculated from the concentration levels measured (ci), the height of the building (H = 35 m),
128
N
Fig. 3 . Hospital buildings and location of probes the reference speed uH (upstream at the height of the building) and the flue stack emission ce . vE by means of the following equation: K = (ci
. uH
H
2
)
/(ce vE)
.
(2)
RESULTS Diffusion-critical Reynolds numbers Apart from the geometric configuration and the wind profiles, the Reynolds number was considered to be an essential criterion of the simulation. The flue gas buoyancy was not modelled. Fig. 4 shows the concentration coefficients at some locations of the hospital model as a function of the Reynolds number Re = uH H/G for two different near-ground boundary layers for the north west approach. The ratio of momentum flux densities was i g a 5= ( f . ~ ) ~ / j . u ) 1.~ .The ~ =right part of the Figure shows that as with prismatic bodies studied in earlier tests, diffusion-critical Reynolds numbers are not reached if turbulence is low and the velocity profile is constant with height ( & = 0). The critical Reynolds numbers in the left diagram are considerably higher than 11,ooo quoted by J. Halitsky (ref. 4 ) .
129
I
1
BN 0
3.1
EN 2.L
1
I
I
l-Gkk44 4
0
1
2
Rex
lo-'
0
1
RexlO-'
Fig. 4. Concentration coefficients at the hospital as a function of the Reynolds number (wind tunnel) Comparison of wind tunnel and field data Figs. 5 and 6 compare some wind tunnel concentration coefficients (ref. 6 ) and field concentration coefficients (ref. 3). K 35 and i 35 refer to the reference height of 35 m. The concentration coefficients for the reference height have been plotted as a function of the direction of the wind (Fig. 5) for the small range of 0 < i35 < 2 and as a function of the ratio of momentum flux densities (Fig. 6) for a narrowly limited wind direction. The left diagram shows the direct approach data while the diagram on the right shows the data for the same point for reverse flow. The positions of the probes have been indicated. All results are satisfactory. The results may be improved by a model incorporating buoyancy whose influence is currently being studied in a new research project. Tests of models of the same hospital buildings were carried out by Munich Technical University (ref. 7) and British Gas Corporation. A summary paper is being prepared.
130
WESTFACE: Bvz.1
NORTHFACE: BN2.1 100. 00
188.00
:*
K35
K,
10.00
1E.m p
*
80e
F * 6i*
0
u
1.00 = -
1.00
--
0
O
t FIELD I
YINDOIRECTION
8 o WINDTUNNEL
0 I
l
l
VINDDIRECTION
Fig. 5 . Concentration coefficients at the hospital for different wind directions (wind tunnel and field data) o 6 i35 G 2
Fig. 6 . Concentration coefficients at the hospital as a function of i35 for direct approach (left) and reverse flow (wind tunnel and field data) REFERENCES 1 C.F. Cowdrey, Report of the National Physical Laboratory, NPL Aero 1055 ( 1 9 6 7 ) . 2 A.G. Davenport, Symposium
3 4
5 6
7
on Wind Effects on Buildings and Structures, Teddington, Her Majesty's Stationary Office, London 1 9 6 5 , pp. 53 - 1 1 1 . Ruhrgas Aktiengesellschaft, report No. LuK 2 / 7 4 , Dorsten 1 9 7 4 J. Halitsky in D.H. Slade (ed.) Meteorology and atomic energy, U.S. Atomic Energy Commission Office of Information Service, 1968, pp. 2 2 1 - 2 5 5 . R. Haupt, J. Hoitz, H. Sommers, Fortschr.-Ber. VDI-2, series 15, No. 11 ( 1 9 7 8 ) . R. Haupt, J. Hoitz, W. Lorenz, report No. 4 8 7 5 , Gaswarme-Institut E.V., Essen, 1 9 7 8 . R. Frimberger, A. Pernpeintner, P. Schmid, report No. 7 8 / 1 2 , Institut fur Stromungstechnik, Technische Universitat Munchen, 1978.
Atmospheric Pollution 1980,Proceedings of the 14th International Colloquium,Paris,France, May 5-8,1980,M.M. Benarie (Ed.), Studies in EnvironmentalScience,Volume 8 0 Elsevier Scientific Publishing Company,Amsterdam - Printed in The Netherlands
131
COMPARISON OF WIND TUNNEL AND FULL SCALE MEASUREMENTS TO INVESTIGATE THE DISPERSION OF VEHICLE EXHAUST GASES P. Leisen mV Rheinland, Cologne (FRG)
ABSTRACT To examine the exhaust gas dispersion in street canyons a comparison between investigations carried out in the atmospheric wind tunnel and full scale measurements is made. For 2 streets a good compliance of results for various sampling points can be shown with the dependence of the pollutant concentrations from the wind direction being clearly illustrated. INTRODUCTION To investigate the dispersion of vehicle exhaust gases in street canyons m V Bheinland in Cologne carries out a comprehensive research programme under contract to the German Federal Ministry for Research and Technology. It comprises measurements in actual street canyons and parallel wind tunnel investigations with the aim to set up simulation models for pollutant concentrations prognosis. The wind tunnel investigations serve to supplement the full scale measurements. They allow to make precise parameter variations to investigate the most significant influencing factors. This is especially applicable to the flow direction and the adjacent buildings. The wind tunnel can be regarded as an analog computer that shows the alterations resulting from variations of the individual parameters in the pollutant concentrations. MEASUREMENTS The aim of the following explanations is to demonstrate the suitability of wind tunnel measurements for the investigation of vehicle exhaust gas dispersion in street canyons using the example of two actual streets in Cologne. The measurements in the streets were made with the help of two stationary monitoring stations. The pollutant component carbon monoxide was continuously measured at 3 monitoring heights of each street side and the 30 minutes mean value calculated.
(For more detaikd description of The wind tunnel investigations of TUV Rheinland (for description stability being investigated. For
the monitoring stations see ref. 1). were carried out in the atmospheric wind tunnel see ref. 2) with only the neutral atmospheric this purpose the two streets chosen for the
132 full scale measurements "Bonner Strasse" and "Venloer Strasse" are reproduced originally on a 1:200 scale in an area of 240 m diameter. The simulation of the vehicle exhaust gas emission is made using street level line sources from which carbon monoxide is emitted in defined quantities at various emission rates. By means of flush mounted sampling ports on the building faces and a special sampling device air to be monitored is sucked off in the cross section of the street and analysed by means of an infrared gas analyzer. Thus, the concentration field of the model street can be determined. A constant temperature hot wire anemometer serves to determine the flow velocity and turbulence. RESULTS First of all it has to be found out to what extent the wind tunnel investigations are able to reproduce the actual physical relations correctly. This can only be checked by comparing the values of the wind tunnel investigations to those obtained in measurements carried out in the actual streets. For this purpose a dimensionless concentration coefficient is introduced. C*
=
dimensionless concentration coefficient
C
=
measured concentration
U
=
wind velocity at the reference point
6
=
source strength of traffic
B
=
street width
a r e , a linear dependence of the pollutant concentration C on the source strength and the wind velocity is assumend. For the actual wind velocity measurement and that made in the model, decisive geometric points were chosen. Fig. 1 shows the dimensionless concentration coefficient C* for 6 sampling points each in the two streets. As C* and C are highly dependent on the direction the wind has to the street axle, for any sampling point the C* concentrations for 12 wind directions each with a sector width of 30" are compared. For the full
scale measurements the mean values were taken from the biennial measurements. To this end, only the values measured between 6 a.m. and 10 p.m. were used in order to have a sufficient vehicle exhaust source strength as the measured concentrations are a superposition of background concentration and pollutant concentrations produced by the vehicles in the street. The concentration can however only be standardised on the basis of the exhaust source strength of these vehicles. The wind tunnel investigations were devided in sectors of 10" each which were subsequently superposed to form 30" sectors to show the wind direction dispersion
of the sector in the full scale measurements. The illustration shows a satisfactory compliance of the wind tunnel measumrents with the street measurements.
133
VENLOER STRASSE out of town
-
into town
bottom 4 m
out of town *top 15m Arniddle 9 m -bottom 4 m
4m
r I
0
BONNER STRASSE I
I
C, 30 0
20
10
I
I .
into town 15 m 9m 4m
I
1
1
I
10
20
30
40
Fig. 1. Comparison of standardised concentrations C and wind tunnel (wt) measurements
*
between full scale (fs)
TABLE 1 Correlation coefficients of C* between full scale (fs) and wind tunnel (wt) measurements
I
MNLOER
~
mRk.-I
top
single sampling point single street
0.85
BONNER
d single sampling
1
into town out of town middle /bottom/ top rnidd*)bottom)
1
1
0.90
1
0.90
I
0.52
1
0.86
0.90
0-68
intotown
out of town
0.91
I
I
0.78
0.71
0.68
0.73
0.78
0.79
0.76
!
134 This compliance can also be gathered from the associated correlation coefficients in Table I. For Bonner Strasse the compliance is less satisfactory. It has to be noted that some sectors show comparatively low frequencies of occurence and very low wind velocities. In particular some distinct outlying values can be observed. Constant K2 of the regression equation includes among others the background concentration proportions which are contained in the full scale measurements in various proportions of the measured values dependent on the meteorological conditions and the individual sampling point. The wind tunnel measurements are free from background concentrations thus taking only that proportion of pollutant concentrations into consideration that is produced by the vehicles in the street. It can be assumed that there will be a better compliance if the background concentration proportion is eliminated in the full scale measurements. As the background concentration was not measured directly, the following approximation is made: for each monitoring interval (30 minutes) the smallest concentration value of the six monitoring points is chosen and this concentration deducted from all other values. For the wind tunnel measurements the minimum concentrations are deducted in the same way. In the full scale measurements the lowest value measured contains the background concentration and the additional concentration, in the wind tunnel measurements the lowest value measured only contains the additional concentration. This value is deducted from the residual concentrations. This allows to make a more carrect comparison of the occuring concentration differences A C = C*
-
Cmin. This is shown in Fig. 2 and Table 2 in compliance with
Fig. 1. A better compliance expecially for Bonner Strasse can be clearly seen in the graphic illustration of the measured values as well as in the correlation table. In the current research programme the monitoring stations were enlarged by a background concentration monitoring height at above-roof level so that a more detailed comparison can be made. The quality of a method for gas dispersion simulation can in particular be demonstrated by its ability to show also the wind direction dependent structure of the pollutant concentrations produced. As an example characteristic of Venloer * Strasse (see Fig. 3) the C concentrations for the 6 monitoring points in the street for 12 angle sectors each were illustrated in the comparison between full scale measurements and wind tunnel. To approximate the level, the wind tunnel measurements were converted using the linear transfer function of correlation Table 1. The comparison also shows the satisfactory angle-dependent compliance of the structure of pollutant concentration. Thus, the concentration decrease dependent on the height and the maximum concentration values (leeward case) dependent on the direction and the minimum values (windward case) are clearly illustrated. On a whole, a very satisfactory compliance of the wind tunnel measurements with the full scale measurements can be proved for the case of exhaust gas dispersion in street canyons. In this connection it has to be noted that for the full scale measurements no
135
VENLOER STRASSE
30
BO"ER STRASSE 1
I
outoftown *top llm A C ~ ~middb 7 m .bottom 4 m 20
intotown 15 m
I
intotown
outoftown
15 m = 2 L e9 m
9m
15 m 9m
10
0
10
2 0 A G 300
10
20
Fig. 2. Comparison of standardised concentration differencesAC*- C between full scale (fs) and wind tunnel (wt) measurements
TABLE 2 Correlation coefficients o f A C measurements
VENLOER STRASE single sampling point single street side I all sampling points
top
*
between full scale (fs) and wind tunnel (wt)
into town middle bottom
0.99
0.98
0.88
top 0.95
0.90
out of town middle bottom 0.95
I
0.91 AcOs = W % t +K2
K1 = 0.711 K2 = 2.24
side sampling points
0.77 A
0.97
0.93 I
all
- 'mi*n
= KIA C;,+ Kq
K1 = 0.438 K2 = 1.89
136
out of town
I
into town
3800
I I I
BOGOM I I
I
*
Fig. 3. Comparison of standardised concentrations C
as a function of f l o w direction
distinctions were made with regard to the atmospheric stabilities. This corroborates the statements (see paper of Mr. Sobottka) that for gas dispersion in street canyons atmospheric stability is of minor importance. Here, gas dispersion is mainly influenced by mechanic turbulences resulting from the eddy-like effect of the wind produced by the adjacent buildings and the vehicle movement. REFERENCES 1.
2.
H. Sobottka in Abgasimmissionsbelastungendurch den Kraftfahrzeugverkehr, Verlag mV Rheinland, 1978, pp 125-149. P. Leisen in Abgasimmissionsbelastungen durch den Kraftfahrzeugverkehr, Verlag TUV Rheinland, 1978, pp 223-249
Atmospheric Pollution 1980, Proceedings of the 14th International Colloquium, Paris, France, May 5-8,1980, M.M. Benarie (Ed.), Studies in Environmental Science, Volume 8 0 Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
137
USE OF A WATER-ANALOG MODEL TO DETERMINE THE OPTIMUM LAYOUT OF A HIGH-CAPACITY POWER STATION
J. RIGARD and M. MILHE NEYRTEC, Grenoble D i v i s i o n o f ALSTHOM-ATLANTIQUE
ABSTRACT
A water-analog model was used t o i n v e s t i g a t e a i r p o l l u t i o n around a highc a p a c i t y thermal power s t a t i o n . A number o f l a y o u t s o f t h e s t a t i o n b u i l d i n g s and chimney were t e s t e d and t h e l a y o u t l e a d i n g t o minimum a i r p o l l u t i o n i n and around t h e s i t e was selected. The study shows t h a t water-analog models take a l l o p e r a t i v e parameters i n t o account.
1. INTROOUCTION The problem i s t o determine t h e b e s t l a y o u t f o r t h e b u i l d i n g s o f a 2 x 300 MW coal-operated power s t a t i o n i n order t o ensure compliance w i t h t h e maximum permiss i b l e c o n c e n t r a t i o n s i n t h e environment (e.9.
S02, dust, e t c . ) b e a r i n g i n mind
numerous requirements imposed by t h e n a t u r e o f t h e s i t e , i n p a r t i c u l a r :
1.1 The presence o f a l a r g e town nearby, on t h e o u t s k i r t s o f which t h e power s t a t i o n i s l o c a t e d . T h i s imposes r e s t r i c t i o n s on t h e p o s i t i o n i n g o f c e r t a i n buildings. 1.2 The presence o f a nearby a i r p o r t , which r e s t r i c t s t h e h e i g h t o f t h e stack and c o o l i n g p l a n t t o a maximum mandatory value. 1.3 The v i r t u a l i m p o s s i b i l i t y o f r e d u c i n g t h e h e i g h t o f t h e b u i l d i n g s (by construct i n g them below ground l e v e l , f o r example), i n view o f t h e t e c h n i c a l problems i n v o l v e d and t h e r e s u l t i n g c i v i l engineering costs.
1.4 The v a r i o u s o p e r a t i n g modes o f t h e c o o l i n g tower: e i t h e r w i t h or w i t h o u t d i s charge i n t o t h e atmosphere, (summer/winter )
.
depending on whether heat recovery i s e f f e c t e d
1.5 I n a d d i t i o n t o these r e s t r i c t i o n s , t h e r e i s t h e problem o f a l l o w i n g f o r t h e l o c a l meteorological conditions, and speeds on t h e s i t e .
e s p e c i a l l y t h e most unfavourable wind d i r e c t i o n s
138 2.
EXPERIMENTAL METHOD
2.1
Test c o n d i t i o n s The
t e s t s were performed by means of a d i r e c t water analog technique,
as
follows :
2.1.1
The e n t i r e area covered by t h e study, w i t h t h e v a r i o u s discharge sources ( s t a c k , c o o l i n g tower) and main o b s t a c l e s i n t h e v i c i n i t y , a r e reproduced i n t h e form o f a r e l i e f - t y p e 1/1000 model, w i t h o u t any v e r t i c a l d i s t o r t i o n
i n scale. 2.1.2
The model i s then immersed i n a water tunnel,
which represents t h e l o c a l
atmospheric movements (wind speeds and d i r e c t i o n s , v e r t i c a l speed p r o f i l e , atmospheric turbulence, 2.1.3
etc.).
The v e l o c i t y (U) o f t h e discharged gases and t h e i r r e a l o u t p u t temperature
(€Is)a r e reproduced on t h e model as t h e emission f l o w - r a t e and discharge d e n s i t y w i t h t h e customary laws o f s i m i l i t u d e (Richardson)whi.ch ensure a c o r r e c t r e p r e s e n t a t i o n o f t h e thermal and k i n e t i c e f f e c t s o c c u r r i n g i n vapour plumes from r a i s e d s t r u c t u r e s . We have :
R i (actual)
Richardson's number : Where p and A p
= Ri R i =
(simulated),
Op P
*
with :
gD U2
The s p e c i f i c g r a v i t y o f t h e environment (atmosphere) and d i f f e r e n c e between t h e s p e c i f i c g r a v i t y o f t h e h o t gas discharge and t h e d e n s i t y o f t h e environment.
9
=
A c c e l e r a t i o n due t o g r a v i t y .
=
Dimension (diameter or h e i g h t o f stack, f o r example) and c h a r a c t e r i s t i c speed ( o f discharge o r o f wind).
U
The o t h e r i n v a r i a n t t o be complied w i t h on t h e model i s t h e r a t i o j j repres e n t i n g t h e speed o f discharge i n r e l a t i o n t o t h e wind v e l o c i t y . By ensuring e q u a l i t y between these two terms ( R i and the actual conditions,
U v)
f o r t h e model and
as w e l l as good t u r b u l e n c e i n t h e l i q u i d t e s t section,
i t i s ensured t h a t t h e geometry o f t h e plumes and d i s t r i b u t i o n o f t h e escape gases a r e respected. 2.1.4
The v a r i o u s p o l l u t e d areas and t h e p o l l u t i o n l e v e l s obtained a r e d e f i n e d by plan-view and c r o s s - s e c t i o n a l photographs o f t h e phenomena, and by conduct i v i t y and c o l o r i m e t r i c analyses o f specimens.
2.1.5
The q u a l i t a t i v e measurements made on t h e model r e v e a l t h e r a t e o f d i l u t i o n of t h e escape gases a t v a r i o u s p o i n t s of t h e plume and a t ground l e v e l . The d i l u t i o n r a t e s concern t h e v a r i o u s c o n s t i t u e n t s of t h e plume:
139 or dust ( f o r low sedimentation speeds) and p r o v i d e t h e a c t u a l SO2, NOx c o n c e n t r a t i o n s of these substances i n ppm or ug/m3 a t t h e v a r i o u s measurement points.
A comparison o f t h e r e s u l t s obtained w i t h t h e model a g a i n s t t h e per-
m i t t e d values i n d i c a t e s whether a g i v e n design v a r i a n t is acceptable or not. 2.2
Qualitative tests The study covered f i v e main guide p r o j e c t s comprising some 40 sub-variants corresponding t o v a r i o u s o p e r a t i n g modes o f t h e power s t a t i o n and d i f f e r e n t l o c a l meteorological conditions.
A l a r g e number o f p r e l i m i n a r y q u a l i t a t i v e t e s t s were c a r r i e d o u t t o make a p r e l i m i n a r y s e l e c t i o n o f t h e d i f f e r e n t v a r i a n t s proposed, i n f l u e n c e on t h e environment.
depending on t h e i r
O p t i m i z a t i o n o f these v a r i a n t s was then e f -
f e c t e d by subsequent q u a n t i t a t i v e t e s t s . The q u a l i t a t i v e t e s t s p r o v i d e a v i s u a l r e p r e s e n t a t i o n o f , f o r example : 2.2.1
The e x t e n t t o which descending gases a r e i n f l u e n c e d by t h e c o o l i n g tower and o t h e r major o b s t a c l e s e i t h e r i n s i d e t h e power s t a t i o n complex ( b o i l e r b u i l d i n g s ) or o u t s i d e t h e area (photo No. 1.).
1. V a r i a n t No. 1.1 West wind 6.5 m/s
2.2.2
The i n f l u e n c e o f t h e wind speed on t h e i n i t i a t i o n o f a i r s t r e a m e f f e c t s , l e a d i n g t o t h e p r e l i m i n a r y d e p o s i t o f p o l l u t a n t s on t h e ground (photos 2,
3 and 4). 2. V a r i a n t No. 2.1 West wind 4 m/s
140
3. V a r i a n t No. 2.1 West wind 6.5 m/s
4. V a r i a n t No. 2.1 West wind 9 m/s
2.2.3 The g e n e r a l l y very favourable i n f l u e n c e o f t h e o p e r a t i o n o f t h e c o o l i n g tower on t h e r a i s e d s t r u c t u r e and t h e good d i s t r i b u t i o n o f t h e gases discharged f r o m t h e stack,
(photos 1 and 5).
5. Variant No. 1.1 West wind 6.5 m/s Influence o f c o o l i n g tower ( c f photo No. 1)
2.2.4
Favourable e f f e c t s o f r e d u c i n g t h e h e i g h t o f c e r t a i n obstacles ( c o o l i n g tower), although t h i s may have adverse e f f e c t s i n o t h e r r e s p e c t s ( r e c y c l i n g o f a i r c o o l i n g tower o u t p u t i n t h e case o f s t r o n g winds,
f o r example),
(photo No. 8 ) .
6. V a r i a n t No. 1.3 West wind 6.5 m/s 120 rn c o o l i n g tower
141
7. V a r i a n t No. 1.3 West wind 6 . 5 m / s
80 m c o o l i n g tower
8. V a r i a n t No. 1.3 West wind 9 m/s
80 m c o o l i n g tower Risk o f i n t e r n a l recycling
I n f l u e n c e o f s t a c k when p o s i t i o n e d a t a d i s t a n c e from t h e main b u i l d i n g s o f
f.Z.>
t h e power s t a t i o n , e t c .
3.
QUANTITATIVE MEASUREMENTS
The p o l l u t a n t c o n c e n t r a t i o n s a r e measured a t about 1 5 metres above ground l e v e l , over a d i s t a n c e of up t o 2000 metres from t h e power s t a t i o n , and f o r p e r i o d s l a s t i n g about 30 minutes i n r e a l terms. The r e s u l t s a r e d i s p l a y e d i n t h e f o r m o f curves o r t a b l e s as shown below, which i n d i c a t e t h e c o n c e n t r a t i o n s a t ground l e v e l , depending on t h e v a r i o u s parameters analyzed : v a r i a n t o r sub-variant
s t u d i e d , wind speeds and d i r e c t i o n s , and o p e r a t i n g
modes o f t h e power s t a t i o n .
500
I
400
-
SO0
-
200 100
{-
Layout 9.2 West wind 12 m/s
-
0 .
Layout No. 9.1 West wind 9 m/s
50% of max. capacity I
I
,
meters
-
Distance (m)
600 900 1200 1750
X
max. c a p a c i t y 50% 100%
420 550 525 400
375 600 675 650
142 I n t h e f o l l o w i n g example, which concerns one o f t h e v a r i a n t s analyzed, t h e t e s t s indicate : a) The c r i t i c a l speed o f t h e wind, which i s r o u g h l y 10 - 1 2 m/s (measured a t a height o f 10 metres above ground l e v e l ) .
For each problem o f ground p o l -
500s
Layout 9 . 3
p /m3,so2
400
300- V=12rn/s 10,s m/s 200
-
100
-
0 1 0
-
400
-
6= West wind
/ 50°/0 of mox. capocity 7.5 m/s .
9 m/s
I
500
p / m : SO2 500
l u t i o n caused by gases discharged from a stack, t h e r e i s a c r i t i c a l wind speed a t which t h e concentrat i o n s measured a t ground l e v e l are maximum. This i s because a t low wind speeds, i n view o f t h e f a s t thermal ascension o f t h e gases, t h e r e i s l i t t l e o r no entrainment o f t h e gases i n t h e a i r s t r e a m o f the buildings.
300 -
50
100 -
100
I
I
lo00
meters
I 500
Same t y p e o f phenomenon as above: t h e simultaneous v a r i a t i o n i n the /----discharge r a t e s and i n t h e SO2 c o n t e n t o f t h e escape f l o w may l e a d t o increased p o l l u t i o n : t h i s i s u n f o r t u n a t e l y t h e case o f opera t i o n o f t h e power s t a t i o n a t the r a t e d value (80 76).
200
o
On t h e o t h e r hand, i n very strong winds, t h e r e i s much more depress i o n o f t h e gases, b u t t h e a i r stream e f f e c t s and turbulence o f t h e lower l a y e r s o f t h e atmosphere l e a d t o a g r e a t e r d i s p e r s a l o f the gases. This may r e s u l t i n lower p o l l u t a n t c o n c e n t r a t i o n s a t ground level.
metersm
143
500
tp'm'8so=
50% of max. capacity
V = 12m/s
0 irect ion
200.
This graph shows the predominantly unfavourable effect of the cooling tower (when not in operation) on the depression o f escape gases, since the stack is directly in the airstream of the cooling plant when the wind is a westerly one.
100.
0 1 0
I
500
I
1000
, meters I500
4. CONCLUSIONS This brief summary of the study shows the usefulness of the water analogue model in determining the optimum characteristics o r at least an acceptable combination of parameters with regard to environmental pollution. These tests are a typical example of the research studies rendered necessary in France by the law of 1 0 July 1976. The method employed constitutes a valuable tool not only f o r the administrative body concerned (i.e. Service d e s Mines, Ministry of the Environment) but also for the operator o r building contractor.
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POLLUTANT FORMATION, TRANSFORMATION, AND TRANSPORT
This Page Intentionally Left Blank
Atmospheric Pollution 1980, Proceedings of the 14th InternationalColloquium,Paris,France, May 54,1980,M.M. Benarie (Ed.),Studies in Environmental Science, Volume 8 0 Elsevier Scientific Publishing Company,Amsterdam - hinted in The Netherlands
147
REGIONAL SCALE TRANSPORT OF FINE AEROSOL CONSTITUENTS FROM URBAN AIR POLLUTION IN EASTERN NORTH AMERICA J. W. WINCHESTER1’2’t, 3 . W. NELSON3, A.C.D.
LESLIE‘
, M.
DARZI2, L.C.S. BOUERES2,
2
and S. E. BAUMAN
‘National Center for Atmospheric Research*, Boulder , Colorado 80307, U.S.A. ; and ’Dept, of Oceanography and 3Dept. of Physics, Florida State University, Tallahassee, Florida 32306, U.S.A.
ABSTRACT Elemental constituents, including sulfur, lead, zinc, and potassium, are often found in urban and nearby nonurban air at concentrations much greater than in the natural atmosphere and predominantly in fine particle size fractions, < 2 pm aerodynamic diameter.
Inasmuch as the human respiratory tract is vulnerable to
damage by inhaling fine particulate matter, high concentrations of air pollutants in submicrometer aerosols are of public health concern. Measurements by particleinduced X-ray emission (PIXE) analysis of cascade impactor and time sequence streaker filter samples in eastern North America and over the western North Atlantic Ocean indicate regional aerosol sulfur levels often 100 times greater than the remote Southern Hemisphere average of 50-100 ng Sfm3 measured using the same techniques. Patterns of concentration variation with time frequently show 10-fold fluctuations over a few hours, apparently the result of variations in chemical gas-to-particle conversion rates as well as in physical transport pathways.
Air masses containing pollution sulfur, derived from fossil fuel
combustion, also contain fine particle lead, zinc, potassium and other elements derived from fuel and industrial sources, and acidic or oxidative constituents which can react vigorously with the marine aerosol to volatilize chloride. The regional scale urban plume in eastern North America can be traced over more than 1000 km distance as a chemically reactive medium heavily loaded with fine aerosol pollutants.
tNCAR Visiting Scientist, August 1979-January 1980. Present address : Department of Oceanography, Florida State University, Tallahassee, Florida 32306, U.S.A.
*The National Foundation.
Center for Atmospheric Research is sponsored by the National Science
148 AEROSOL ELEMENTAL COMPOSITION CHARACTERISTICS I N POLLUTED ATMOSPHERES Aerosol p a r t i c l e s occur commonly i n t h e range 0 . 1 t o 10
lesser amounts i n smaller and l a r g e r s i z e s .
diameter, w i t h
Largest p a r t i c l e s tend t o be e a s i l y
removed from t h e atmosphere by s e t t l i n g , impaction, o r p r e c i p i t a t i o n scavenging, and t h e smallest tend t o c o a g u l a t e r e a d i l y t o form l a r g e r .
0.1-10
P a r t i c l e s i n the
pm range form a s t a b l e a e r o s o l which remain suspended f o r s e v e r a l days and
can be t r a n s p o r t e d over c o n s i d e r a b l e d i s t a n c e s b e f o r e u l t i m a t e deposition. Many n a t u r a l and anthropogenic source processes l e a d t o t h e formation of a e r o s o l p a r t i c l e s , b u t condensation of g a s e s and d i s p e r s i o n of s o l i d s o r l i q u i d s
are most important.
N a t u r a l a e r o s o l i s l a r g e l y t h e r e s u l t of t h e r a i s i n g of d u s t
by t h e a c t i o n of wind on s o i l s and of t h e formation of sea spray by t h e b u r s t i n g of a i r bubbles a t t h e air-water
interface.
Both processes cause t h e d i s p e r s i o n
of s o l i d and l i q u i d material p r i n c i p a l l y i n t o p a r t i c l e s of diameters l a r g e r than
1 pan; t h e g r e a t e r energy i n p u t needed t o form smaller p a r t i c l e s by t h e s e processes i s less commonly a v a i l a b l e i n t h e n a t u r a l atmosphere.
Some submicrometer
n a t u r a l a e r o s o l i s formed by t h e r e a c t i o n of i n o r g a n i c gases t o form s u l f a t e p a r t i c l e s and t h e conversion of p l a n t and o t h e r organic vapors i n t o organic p a r t i c u l a t e matter.
I n p o l l u t e d atmospheres, however, f i n e p a r t i c u l a t e m a t t e r i s
formed i n much g r e a t e r abundance, p r i n c i p a l l y as t h e r e s u l t of f u e l combustion, m e t a l l u r g i c a l , and o t h e r h i g h temperature and high energy processes. Among t h e most important of t h e c o n s t i t u e n t s of f i n e p o l l u t i o n a e r o s o l , from both environmental and human h e a l t h s t a n d p o i n t s , are s u l f u r , l e a d , and z i n c ; potassium i s a l s o abundant and serves as a u s e f u l i n d i c a t o r of f u e l combustion a s a source.
The f o u r elements may be introduced t o t h e atmosphere as high tempera-
t u r e vapors b u t on c o o l i n g may condense t o form p a r t i c l e s , t h e m e t a l s q u i t e r e a d i l y b u t t h e s u l f u r more g r a d u a l l y by o x i d a t i o n of SO
t o s u l f u r i c a c i d and
2
sulfates.
The f i n e a e r o s o l i s most abundant i n t h e 0.2-0.5
pm diameter range,
t h e most important f o r causing impairment of atmospheric v i s i b i l i t y , and remain a i r b o r n e long enough t o be t r a n s p o r t e d 1000 km o r more.
Thus t h e "urban" atmo-
sphere i n i n d u s t r i a l i z e d c o n t i n e n t a l a r e a s of Europe and North America i s regional i n e x t e n t , w i t h a e r o s o l c h a r a c t e r i s t i c s i n r u r a l areas o f t e n being s i m i l a r t o t h o s e i n c i t y c e n t e r s ( r e f s . 1, 2 ) .
AEROSOL INTERACTION W I T H THE HUMAN RESPIRATORY TRACT From an immediate human h e a l t h s t a n d p o i n t , t h e d e p o s i t i o n of f i n e p a r t i c l e s i n t h e b r o n c h i a l and pulmonary r e g i o n s of t h e lung may be of s e r i o u s consequence. O n b r e a t h i n g , both c o a r s e p a r t i c l e s and water s o l u b l e t r a c e gases are e f f i c i e n t l y removed by t h e n a s a l passages and t h e t r a c h e a from inhaled a i r p e r m i t t i n g only cleansed a i r t o e n t e r t h e a l v e o l i where gas exchange occurs a c r o s s d e l i c a t e membranes.
F o r t u n a t e l y , t h e n a t u r a l atmosphere c o n t a i n s very l i t t l e f i n e
p a r t i c u l a t e matter which may bypass t h i s n a t u r a l b a r r i e r and p r e s e n t a hazard t o
149 the lower respiratory regions.
In the polluted atmosphere, however, sulfuric
acid, metallic compounds, organics, and other substances may be at levels hundreds of times above the natural background of particles smaller than 1
diameter,
and it is these which may enter and be deposited in the pulmonary region and cause biological insult.
Experimental measurements of the characteristics of
pollution aerosol in exhaled human breath (ref. 3 ) verify theoretical and laboratory evidence that the efficiency of respiratory deposition of fine particles is a minimum at about 0.5 pm diameter and is greater at both smaller and larger sizes, in the lower and upper respiratory tract, respectively.
Therefore,
pollution aerosol constituents are often most abundant in the particle size range which can cause the most biological harm on inhalation. AEROSOL SAMPLING FOR ELEMENTAL ANALYSIS BY PARTICLE-INDUCED X-RAY MISSION (PIXE) A powerful experimental tool for the investigation of aerosol composition characteristics, both in ambient air and in human inhalation studies, is the method of PIXE analysis (ref. 4 ) .
In conjunction with this sensitive method for
the determination of small amounts of trace elements by detecting X-rays emitted during energetic proton bombardment, specialized aerosol sampling equipment has been developed for separation of particles according to size (ref. 5) and time (ref. 6).
Advantages of the method are that only small samples need to be
collected for analysis, thus permitting inexpensive and convenient sampling equipment to be used under field conditions, needing very little electric power for operation, and in human studies permitting individual human subjects to provide exhaled aerosol samples under typical working conditions for short times without physiological stress.
The method is also precise and rapid,
so
that
small composition differences can be compared in large data sets suitable for statistical evaluation. COMPARISON OF URBAN W I T H GLOBAL AEROSOL SULFUR CONCENTRATIONS Sulfuric acid and sulfate compounds often comprise half or more of fine particulate matter in large regions of Europe and North America and is attributed mainly to the gaseous SO2 from coal and oil combustion which is discharged into the atmosphere from tall smokestacks and is gradually converted to aerosol matter by oxidation as it is carried by air currents downwind from its sources, often many hundreds of km.
Recent studies of the composition of the atmosphere in
remote regions of the world (ref. 7) indicate that the natural concentration of aerosol sulfur at temperature latitudes, both in continental and maritime regions, may be in the range 50-100 nanograms of sulfur per cubic meter of air.
In con-
trast, even in the relatively clean western continental U.S.A. several hundred ng S/m3 are not uncommon (ref. 8). Such concentrations represent elevations of 100-fold above natural levels of fine sulfate aerosol, and the human exposure is
150 accordingly 100 t i m e s g r e a t e r . reasons:
Currently t h e s e c o n c e n t r a t i o n s are r i s i n g f o r two
(1) i n c r e a s e d f o s s i l f u e l combustion f o r energy-intensive technologies
l e a d s t o i n c r e a s e d SO emissions, e s p e c i a l l y i f f u e l s h o r t a g e s b r i n g about t h e 2 use of h i g h e r s u l f u r f u e l , and (2) t h e use of t a l l smokestacks f o r c o n t r o l of l o c a l SO c o n c e n t r a t i o n s near t h e s o u r c e s causes longer t r a n s p o r t d i s t a n c e s 2 b e f o r e removal a t t h e ground, hence a longer atmospheric r e s i d e n c e t i m e and a g r e a t e r degree of conversion of SO
t o s u l f u r i c a c i d a e r o s o l i n t h e atmosphere 2 which, i n t u r n , i s c a r r i e d f u r t h e r b e f o r e d e p o s i t i o n than would be t h e more r e a c t i v e SO2.
Because of t h e e f f i c i e n t s c a t t e r i n g of l i g h t by 0.2-0.5
pm diameter
p a r t i c l e s and t h e l a r g e r e l a t i v e abundance of s u l f a t e s i n t h e submicrometer s i z e range, t h e degradation of atmospheric v i s i b i l i t y i n i n d u s t r i a l i z e d a r e a s i s p r i m a r i l y due t o a i r p o l l u t i o n s u l f u r .
The human h e a l t h consequences are less
c l e a r l y observed b u t may be no less profound.
CHEMICAL CONVERSION OF GASEOUS SO2 TO H2S04 AEROSOL I N SOLUTION DROPLETS The e x t e n t of t r a n s p o r t of p o l l u t i o n s u l f u r through t h e atmosphere depends both on t h e p h y s i c a l motion of t h e a i r and on t h e r a t e of chemical conversion of SO2 t o H2S04, s i n c e t h e l a t t e r form d i f f u s e s more slowly t o t h e e a r t h ' s surface.
Consequently, we a r e i n t e r e s t e d i n understanding t h e d e t a i l s of chemical r e a c t i o n s i n t h e atmosphere which could a f f e c t t h e conversion rate.
The r a t e can be
influenced by many f a c t o r s , and several d i f f e r e n t r e a c t i o n mechanisms f o r t h e conversion may be o p e r a t i n g simultaneously i n t h e atmosphere, w i t h d i f f e r e n t
r e l a t i v e importance depending on atmospheric c o n d i t i o n s .
Thus, t h e conversion
may t a k e p l a c e by photochemical r e a c t i o n s , b o t h d i r e c t , by r e a c t i o n w i t h oxygen and w a t e r i n t h e presence of s u n l i g h t , and i n d i r e c t , w i t h t h e a i d of oxidants present i n polluted air.
It may t a k e p l a c e by chemical r e a c t i o n s i n l i q u i d water
d r o p s , w i t h and without t h e a i d of c a t a l y s t s such as m e t a l i o n s .
It may a l s o
t a k e p l a c e by o x i d a t i o n on c e r t a i n dry s u r f a c e s which may c a t a l y z e t h e conversion reactions.
It i s now understood t h a t o x i d a t i o n may take p l a c e w i t h i n l i q u i d
sulfuric acid droplets (ref. 9).
Evidence f o r t h e last of t h e s e conversion
p r o c e s s e s i s supported by measurements made i n nonurban e a s t e r n U.S. w i t h abundant r e g i o n a l s c a l e a i r p o l l u t i o n .
locations
A s t r o n g dependence of t h e H SO
2
4
formation rate on t h e abundance of atmospheric H 0 vapor i s a d i f f e r e n c e between 2 t h i s p r o c e s s and those p r e v i o u s l y mentioned. Liquid d r o p l e t s c o n t a i n i n g > 65% H SO
2
4
by weight have low e q u i l i b r i u m water
vapor p r e s s u r e s , PHz0, which decrease a s t h e 3.7-power
of i n c r e a s i n g m o l a l i t y ,
% so ,
i n d i c a t i n g a s t r o n g binding of H 0 by H SO and an i n h i b i t i n g of t h e 2 2 4 2 4 chemical p o t e n t i a l of H 0 t o e n t e r i n t o r e a c t i o n w i t h o t h e r c o n s t i t u e n t s i n 2 s o l u t i o n , such as SO and d i s s o l v e d o x i d i z i n g agents. Except a t very low rela2 t i v e h u m i d i t i e s , such s u l f u r i c a c i d d r o p l e t s w i l l absorb water vapor a t a
r a t e approximately p r o p o r t i o n a l t o t h e ambient water vapor mixing r a t i o (not
151 relative humidity).
The uptake of water by the droplets would increase the
chemical potential of H 0 for other reactions as the 3.7-power of the decrease in 2 However, reaction with SO2, consumes both S O and H 2 0 to produce
molality. H2S04.
2
Thus, the reaction rate may be effect determined by the rate of diffusion
of water vapor toward the droplets.
Small variations in ambient water vapor
concentrations result in large variations in the sulfuric acid formation rate and may account for the observed cubic dependence of aerosol sulfur concentrations on water vapor content in the eastern U.S. atmosphere. INTERACTION OF POLLUTION AEROSOL CONSTITUENTS WITH THE MARINE ATMOSPHERE A s pollution aerosol and gaseous constituents are carried over the ocean
downwind of an urban area, as occurs east of the U.S.A.,
both physical mixing
with natural constituents of the atmosphere and chemical reaction with them can occur.
In the first instance, fine particle S, Pb, Zn, and K have been measured
in the Atlantic marine atmosphere from shipboard about 1000 km from the eastern U.S. seacoast at concentrations far above natural levels (ref. 10).
The con-
centrations of these pollutants vary sympathetically in time, implying their transport from sources on the continent. Additional measurements at Bermuda show that most of the aerosol sulfur content is in the fine mode, exceeding the coarse mode sea spray sulfate abundance even though sulfate is a major sea salt constituent.
Air pollution has thus already substantially modified the composition
of the Atlantic marine atmosphere more than 1000 km from the nearest urban source regions. In the second instance, gaseous SO2 and other reactive air pollution gases can be absorbed by sea spray droplets and cause chemical changes. Measurements made directly over the ocean surface in the Gulf of Mexico (ref. 11) show a 213 deficit of C1, the most abundant anion in the ocean, which can be explained by volatility of HC1, released by reaction of sea salt with SO or its oxidation 2 product H2S0,+. The regional concentration of air pollution sulfur in the southeastern U.S.,
not a heavily urbanized area, is enough to change the mean com-
position of sea salt directly over the water surface.
Substantial C1 deficits
are also observed over the North Atlantic (ref. 10). These examples illustrate the extent of regional scale transport of fine aerosol constituents from urban air pollution in eastern North America.
In order
to understand the transport processes the research methods based on rapid and sensitive PIXE analysis have provided essential environmental information.
152 ACKNOWLEDGEMENTS This work was supported in part by the U.S. Environmental Protection Agency
for ambient aerosol studies, by the National Institute of Environmental Health Sciences for studies of human inhalation of aerosols and for the support of two of us (L.C.S.B.
and S.E.B.)
by traineeships in the program Environmental Health
Measurement and Statistics, all at Florida State University, and by the National Science Foundation for a sabbatical leave appointment for one of us (J.W.W.) at the National Center for Atmospheric Research. REFERENCES 1 John W. Winchester and J. William Nelson, Sources and Transport of Trace Metals in Urban Aerosols, U.S. Environmental Protection Agency report EPA-60012-79-019, March 1979. 2 R. Akselsson, C. Orsini, D. L. Meinert, T. B. Johansson, R. E. Van Grieken, H. C. Kaufmann, K. R. Chapman, J. W. Nelson, and J. W. Winchester, Application of proton-induced X-ray emission analysis to the St. Louis Regional Air Pollution Study, Advances in X-Ray Analysis, Vol. 18, W. L. Pickles, C. S. Barrett, J. B. Newkirk, and C. 0. Ruud, eds., pp. 588-597, Plenum Press, New York, 1975. 3 K. Roland Akselsson, Georges G. Desaedeleer, Thomas B. Johnasson, and John W. Winchester, Particle size distribution and human respiratory deposition of trace metals in indoor work environments, Annals of Occupational Hygiene, 19, 225-238, 1976. 4 Thomas B. Johansson, Rene E. Van Grieken, J. William Nelson, and John W. Winchester, Elemental trace analysis of small samples by proton induced X-ray emission, Anal. Chem., 47, 855-860, 1975. 5 R. E. Van Grieken, T. B. Johansson, K. R. Akelsson, J. W. Winchester, J. W. Nelson, and K. R. Chapman, Geophysical applicability of aerosol size distribution measurements using cascade impactors and proton induced X-ray emission, Atmospheric Environment, lo, 571-576, 1976. 6 J. W. Nelson, G. G. Desaedeleer, K. R. Akselsson, and J. W. Winchester, Automatic time sequence filter sampling of aerosols for rapid multi-element analysis by proton induced X-ray emission, Advances in X-ray Analysis, Vol. 19, R. W. Gould, C. S. Barrett, J. B. Newkirk, and C. 0. Ruud, eds., pp. 403-413, Kendall Hunt, Dubuque, Iowa, 1976. 7 Douglas R. Lawson and John W. Winchester, Atmospheric sulfur aerosol concentrations and characteristics from the South American continent, Science, 205, 1267-1269, 1979. 8 C E . Bauman, L. C. S. Boueres, S. L. Cohn, A. C. D. Leslie, S. W. Rheingrover, S. Tanaka, J. W. Winchester, and G. S. Young, Nonurban eastern U.S. sulfate concentration variability in relation to meteorological parameters, to be published, 1980. 9 John W. Winchester, A chemical model for sulfur dioxide oxidation in sulfuric acid droplets, to be published 1980. 10 W. W. Berg and J. W. Winchester, Organic and inorganic gaseous chlorine concentrations in relation to the particle size distribution of chloride in the marine aerosol, J. Geophys. Res., a;?, 5945-5953, 1977. 11 Michael Darzi and John W. Winchester, Terrestrial influences on aerosol composition over the western North Atlantic Ocean, to be published, 1980.
Atmospheric Pollution 1980, Proceedings of the 14th International Colloquium, Paris, France, May 5-8,1980, M.M. Benarie (Ed.), Studies in Environmental Science, Volume 8 0 Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
153
ATMOSPHERIC TRANSPORT OF PARTICULATE SULPHATE AND OZONE I N T O THE TORONTO REGION AND ITS CORRELATION W I T H VISIBILITY
K.G.
ANLAUF, M. OLSON, H.A.
WIEBE
Atmospheric Environment S e r v i c e , Downsview, Canada, M3H 5T4 and M.A.
LUSIS
O n t a r i o M i n i s t r y of Environment, Toronto, Canada
ABSTRACT Measurements of p a r t i c u l a t e s u l p h a t e , l i g h t s c a t t e r i n g c o e f f i c i e n t (b and ozone w e r e made d u r i n g t h e summer of 1976 i n t h e Toronto r e g i o n .
)
scat A meteo-
r o l o g i c a l and t r a j e c t o r y a n a l y s i s showed t h a t e p i s o d e s of h i g h s u l p h a t e and ozone c o n c e n t r a t i o n s w e r e g e n e r a l l y due t o long-range t r a n s p o r t of a i r masses from t h e s o u t h and southwest. and b
There was a h i g h d e g r e e of c o r r e l a t i o n between s u l p h a t e
The p a s s a g e of c o l d f r o n t s r e s u l t e d i n r e g i o n a l n o r t h e r l y flows and
scat’ y i e l d e d low s u l p h a t e s , bscat
and ozone.
INTRODUCTION E l e v a t e d atmospheric s u l p h a t e c o n c e n t r a t i o n s have become of concern i n Northe a s t e r n America s i n c e t h e i r d e p o s i t i o n i n t o a c i d - s e n s i t i v e ecosystems h a s l e d t o environmental problems such as i n c r e a s e d a c i d i f i c a t i o n of l a k e s .
Associated
problems i n c l u d e t h e r e d u c t i o n i n v i s i b i l i t y due t o formation of l i g h t s c a t t e r i n g sulphate aerosols.
The p r e s e n t s t u d y was c a r r i e d o u t i n o r d e r t o i n v e s t i g a t e
t h e atmospheric c o n c e n t r a t i o n s and t r a n s p o r t of p a r t i c u l a t e s u l p h a t e , ozone and t h e a t t e n d a n t v i s i b i l i t y a s measured by a nephelometer. During t h e p e r i o d Aug-Sept,
1976, d a i l y p a r t i c u l a t e samples w e r e c o l l e c t e d and
c o n t i n u o u s ozone and n i t r o g e n o x i d e s measurements were made a t two l o c a t i o n s i n t h e v i c i n i t y of Toronto, O n t a r i o .
One s i t e was l o c a t e d on a n i s l a n d p a r k , Toronto
C e n t r e I s l a n d , 2.9 km s o u t h of Toronto.
The o t h e r s i t e , Maple, was r u r a l , 29 km
n o r t h of t h e i s l a n d s i t e and a b o u t 1 0 km o u t s i d e of t h e n o r t h e r n edge of Metrop o l i t a n Toronto. P a r t i c u l a t e samples were c o l l e c t e d on 47 mm d i a . Whatman 40 c e l l u l o s e f i l t e r , enclosed i n a M i l lipore f i l t e r holder.
The f i l t e r s were analyzed f o r w a t e r s o l u b l e
s u l p h a t e , n i t r a t e and ammonium by means o f automated ion-exchange chromatography.
A nephelometer (MRI model 1550B) was used t o measure t h e l i g h t s c a t t e r i n g coefficient,
bscat’
a t the i s l a n d l o c a t i o n only.
154 RESULTS 'Episodes'
of h i g h s u l p h a t e c o n c e n t r a t i o n occurred f r e q u e n t l y .
This i s c l e a r l y
e v i d e n t from F i g u r e 1 which shows d a i l y p a r t i c u l a t e s u l p h a t e c o n c e n t r a t i o n s f o r For comparison, t h e upper p o r t i o n of t h i s f i g u r e shows
Toronto I s l a n d and Maple.
t h e r e s u l t s o f a n o t h e r s u l p h a t e s t u d y ( r e f . 1) c a r r i e d o u t d u r i n g t h e month of August a t o t h e r s o u t h e r n O n t a r i o l o c a t i o n s , covering a d i s t a n c e of 600 km along Lakes E r i e and O n t a r i o .
It i s seen t h a t t h e sulphate episodes c o r r e l a t e w e l l a t
a l l s i t e s and are g e n e r a l l y r e g i o n a l i n c h a r a c t e r .
r
- Windsor 0 Kingston
40
[1
+ Simcoe
1
O
+
x Pickering Orillia -Mount Forest 0
20
0 40
r Maple
"
40L 20
0 August
Fig. 1.
September
Daily p a r t i c u l a t e s u l p h a t e c o n c e n t r a t i o n s a t s e v e r a l S . O n t a r i o l o c a t i o n s .
For 'background' a i r , t h e p a r t i c u l a t e c o n c e n t r a t i o n s as measured a t t h e two Toronto l o c a t i o n s ranged from 0.6 t o 2 pg m-3 ammonium and 0.2-2
pg me3 f o r n i t r a t e .
f o r s u l p h a t e , 0.5-1.5 ug
IU-~
for
However, t h e measured n i t r a t e concentrations
may n o t n e c e s s a r i l y r e f l e c t t r u e p a r t i c u l a t e n i t r a t e .
There may b e a r t i f a c t
formation by gaseous n i t r o g e n o x i d e s and n i t r i c a c i d , and l o s s e s due t o v o l a t i l i t y
155
.
.,
E
rn
a.
10
20
30
9
August
19
29
September
F i g . 2. D a i l y measurements of bscat, p a r t i c u l a t e c o n c e n t r a t i o n ( s u l p h a t e and n i t r a t e ) and ozone a t Toronto I s l a n d .
of t h e c o l l e c t e d n i t r a t e . The s u l p h a t e e p i s o d e s c o r r e l a t e v e r y w e l l w i t h p e r i o d s of h i g h bscat visibility).
(low
This i s i l l u s t r a t e d i n F i g . 2 which shows t h e d a i l y 24-hour averaged
v a l u e s f o r t h e Toronto I s l a n d l o c a t i o n ( p a r t i c u l a t e n i t r a t e i s i n c l u d e d f o r com-
It i s e x p e c t e d t h a t s u l p h a t e and b
correlate since the scat l i g h t s c a t t e r i n g p a r t i c l e s as measured by a nephelometer a r e mainly due t o s u l p h a t e s
p a r i s o n purposes o n l y ) .
(ref. 2).
For o u r d a t a , t h e s e two p a r a m e t e r s have a 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
of 0.972 and are r e l a t e d by t h e e q u a t i o n :
x bscat
(m-l) = 0.06 x SOT (pg m-3)
+
0.47
It i s a p p a r e n t from F i g . 2 t h a t ozone a l s o c o l - r e l a t e s w e l l w i t h s u l p h a t e . This was a l s o observed a t t h e Maple l o c a t i o n ( d a t a n o t shown).
An i n t e r p r e t a -
t i o n o f t h e s e c o r r e l a t i o n s r e q u i r e s a c o n s i d e r a t i o n of t h e m e t e o r o l o g i c a l condi-
156 t i o n s and t h e t r a j e c t o r i e s of t h e sampled a i r masses.
For t h e e n t i r e study period,
four-day b a c k - t r a j e c t o r i e s based on six-hour i n t e r v a l s were c a l c u l a t e d f o r t h r e e l e v e l s : 1000 mb, 925 mb and 8 5 0 mb.
D e t a i l s of t h i s t r a j e c t o r y model a r e found
i n ref. 3. The geographical a r e a encompassing a l l t r a j e c t o r i e s was divided i n t o equal s e c t o r s by using t h e e i g h t p r i n c i p a l compass d i r e c t i o n s with t h e c e n t r e a t Toronto.
Each computed t r a j e c t o r y ( r e p r e s e n t i n g t h e a i r mass sampled) was c l a s s -
i f i e d according t o t h e s e c t o r which i t t r a v e r s e d during t h e 48 hours p r i o r t o Complicated t r a j e c t o r i e s , r e p r e s e n t i n g 1 6 % of a l l c a s e s ,
a r r i v a l a t Toronto.
could n o t be c l a s s i f i e d according t o t h i s scheme.
Table 1 shows t h e r e s u l t s of
I t i s c l e a r t h a t during t h e summer
t h i s c l a s s i f i c a t i o n f o r s u l p h a t e and ozone.
of 1976, t h e t r a j e c t o r i e s w i t h i n t h e southwesterly quadrant predominated and
r e s u l t e d i n t h e h i g h e s t c o n c e n t r a t i o n s , whereas t h e n o r t h e r l y t r a j e c t o r i e s were a s s o c i a t e d w i t h t h e lowest c o n c e n t r a t i o n s .
Since t h e s o u t h e r l y t r a j e c t o r i e s
t r a v e r s e many high SO2 and O3 p r e c u r s o r source r e g i o n s , i t i s reasonable t h a t t h e s e would l e a d t o t h e h i g h e s t measured c o n c e n t r a t i o n s .
The a r e a s to t h e north
of Toronto a r e r e l a t i v e l y f r e e of i n d u s t r i a l emissions and t h e r e f o r e t h e n o r t h e r l y t r a j e c t o r i e s would l e a d t o t h e lowest measured c o n c e n t r a t i o n s .
However, t h e r e i s
one s i g n i f i c a n t SO2 source r e g i o n centred a t Sudbury, 320 km n o r t h of Toronto. Several of t h e t r a j e c t o r i e s passed over t h i s r e g i o n b u t only i n one case did i t r e s u l t i n an e l e v a t e d s u l p h a t e c o n c e n t r a t i o n (11 pg m-3).
I t was noted t h a t i n
t h i s i n s t a n c e , t h e a i r mass had s t a g n a t e d i n t h e Sudbury region p r i o r t o i t s t r a n s p o r t t o Toronto. TABLE 1
C o r r e l a t i o n of p a r t i c u l a t e s u l p h a t e and ozone c o n c e n t r a t i o n s w i t h t h e d i r e c t i o n of computed t r a j e c t o r i e s . SE-S
-
soI(pg m-3) 0 3 (pphm) bscat
-
(10-4 m-1)
-
E-SE
-
-
NE-E 2.2(2)* 3.5(2) 0.4(2)
N-NE 3.0(3) 2.9(3) 0.7(2)
NW-N 2.2(16) 2.4(16) 0.6(9)
W-NW 1.5(7) 2.7(8) 0.5(5)
SW-W 15.1(23) 6.4(23) 1.6(14)
s-sw
30.4(16) 8.0(13) 2.8(8)
"Numbers i n b r a c k e t s denote t h e number of c a s e s A c l o s e r examination of t h e s u r f a c e s y n o p t i c weather maps showed t h a t t h e
c o n c e n t r a t i o n s of s u l p h a t e and ozone were governed by c y c l i c a l meteorological conditions.
High c o n c e n t r a t i o n s were a s s o c i a t e d w i t h s o u t h t o southwesterly
flows on t h e western o r back s i d e of h i g h p r e s s u r e systems, and with s t a g n a t i o n of high p r e s s u r e systems over t h e lower Great Lakes.
Low c o n c e n t r a t i o n s were
a s s o c i a t e d w i t h n o r t h t o n o r t h w e s t e r l y flows on t h e e a s t e r n o r f r o n t s i d e of high p r e s s u r e systems, g e n e r a l l y a f t e r t h e passage of a cold f r o n t .
A marked
r e d u c t i o n of s u l p h a t e and ozone c o n c e n t r a t i o n s w a s observed a f t e r t h e passages
of c o l d f r o n t s (shown as arrows i n Fig. 2 ) a t Toronto ( c f . r e f s . 4 - 8 ) .
157
Fig. 3 . Four-day b a c k - t r a j e c t o r i e s ending a t Toronto a t 1900 EST on d a t e s shown. F u l l and open symbols r e p r e s e n t 850 and 1000 mb t r a j e c t o r i e s r e s p e c t i v e l y . The p e r i o d of August 16-29 w i l l b e used t o i l l u s t r a t e t h e above-mentioned observations.
F i g u r e s 3 and 4 show t r a j e c t o r i e s o f a i r masses a r r i v i n g i n t h e
s t u d y a r e a on s p e c i f i c d a y s w i t h i n t h i s p e r i o d .
August 1 6 , 24 and 29 were days
f o l l o w i n g t h e p a s s a g e of c o l d f r o n t s and t h e corresponding t r a j e c t o r i e s were t y p i c a l l y from t h e n o r t h t o n o r t h w e s t .
Low c o n c e n t r a t i o n s of s u l p h a t e were
measured a s i n d i c a t e d i n t h e i n s e r t of F i g s . 3 and 4 . averaged ozone c o n c e n t r a t i o n s were 1-3.5 pphm.
The corresponding d a i l y -
During August 18-21, a h i g h
p r e s s u r e system had s t a g n a t e d o v e r t h e lower Great Lakes l e a d i n g t o i n c r e a s e d s u l p h a t e and ozone c o n c e n t r a t i o n s ; t h e s e maximized on August 2 1 w i t h t h e d a i l y averaged ozone a t 9-12 pphm f o r t h e two l o c a t i o n s .
The t r a j e c t o r y f o r t h i s day
(Fig. 3 ) i s s e e n t o b e of l i m i t e d g e o g r a p h i c a l e x t e n t ( l e s s t h a n 270 km); however, t h i s t r a j e c t o r y i s somewhat u n c e r t a i n s i n c e l o c a l m e t e o r o l o g i c a l f a c t o r s would b e expected t o predominate.
August 2 2 and 27 were days of s o u t h e r l y flow on t h e
w e s t e r n s i d e of h i g h p r e s s u r e systems. s o u t h e r l y and r e s u l t e d i n h i g h s u l p h a t e , ( t h e d a i l y - a v e r a g e ozone w a s 5-8 pphm).
The corresponding t r a j e c t o r i e s were bscat
and e l e v a t e d ozone c o n c e n t r a t i o n s
158
F i g . 4. Four-day b a c k - t r a j e c t o r i e s ending a t Toronto a t 1900 EST on d a t e s shown. F u l l and open symbols r e p r e s e n t 850 and 1000 mb t r a j e c t o r i e s r e s p e c t i v e l y .
ACKNOWLEDGEMENTS W e are i n d e b t e d t o I s a a c Savdie and Denis J a c o b f o r a s s i s t a n c e i n t h e meteo-
r o l o g i c a l a n a l y s i s , t o K. Oikawa f o r computing t h e t r a j e c t o r i e s , t o A. Gaudenzi f o r t e c h n i c a l support during t h i s study.
REFERENCES L a f l e u r and D.M. Whelpdale, ' S p a t i a l D i s t r i b u t i o n of S u l f a t e s o v e r Eastern Canada d u r i n g August 1976, Paper 77-48.3 p r e s e n t e d a t t h e 7 0 t h Annual Meeting of t h e A i r P o l l u t i o n C o n t r o l A s s o c i a t i o n , Toronto, Canada, June 1977. A.P. Waggoner, L. Granat, C. Tragardh, N a t u r e , 261 (1976) 120-122. M.P. Olson, K.K. Oikawa and A.W. MacAfee, 'A T r a j e c t o r y Model Applied t o t h e Long-Range T r a n s p o r t of A i r P o l l u t a n t s ' , Report LRTAP 78-4, 1978, Atmospheric Environment S e r v i c e , Downsview, Canada. K.G. A n l a u f , M.A. L u s i s , R.D.S. S t e v e n s and H.A. Wiebe, i n K.H. Grasnick (Ed.), P r o c e e d i n g s of t h e J o i n t Symposium on Atmospheric Ozone, Dresden, August 9-17, 1976, I n t e r n a t i o n a l A s s o c i a t i o n of Meteorology and Atmospheric P h y s i c s , B e r l i n , 1977, Vol. 3, pp. 145-164. W.N. S t a s i u k , J r . , P.E. Coffey and R.F. McDermott, ' R e l a t i o n s h i p s Between Suspended S u l f a t e s and Ozone a t a Non-Urban S i t e ' , Paper 75-62.7 p r e s e n t e d a t t h e 6 8 t h Annual Meeting o f t h e A i r P o l l u t i o n C o n t r o l A s s o c i a t i o n , Boston, U.S.A., June 1975. F.M. Vukovich, Atmos. Env., 1 3 (1979) 255-265. Y.S. Chung, Atmos. Env., 12 (1978) 1471-1480. P . J . Samson, Atmos. Env., 1 2 (1978) 1889-1893.
1 R.J. 2
3
4
5
6 7 8
Atmospheric Pollution 1980, Proceedings of the 14th International Colloquium, Paris,France, May 5-8,1980, M.M. Benarie (Ed.), Studies in Enuironmentul Science, Volume 8 0 Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
159
A STUDY OF THE TRANSPORT OF TRACE METALS AND SULFUR INTO SCANDINAVIA H.0.
LANNEFORS AND H.C.
HANSSON
Department of Nuclear P h y s i c s , Lund I n s t i t u t e of Technology S a l v e g a t a n 14, S-223 62 LUND, Sweden
ABSTRACT The long range transport of air pollutants i n t o fractionated aerosol samples were collected at two The concentrations of s u l f u r and many heavy metals masses that had passed over the European continent from t h e North Atlantic region.
Scandinavia have been studied. Size coastal and one inland sampling station. were one order of magnitude higher i n a i r compared t o concentrations i n a i r masses
INTRODUCTION Long r a n g e t r a n s p o r t of a i r p o l l u t a n t s are probably r e s p o n s i b l e f o r a h i g h p r o p o r t i o n of t h e d e p o s i t i o n s of s u l f u r i n s o u t h e r n Scandinavia. E a r l i e r measurements (ref.
1) i n d i c a t e t h a t a dominating p a r t of t h e s u l f u r d e p o s i t i o n s i n s o u t h e r n Sweden
r e s u l t s from e m i s s i o n s i n h i g h l y i n d u s t r i a l i z e d p a r t s of Europe.
Based on measurements
of s u l f u r d i o x i d e and s u l f a t e s in t h e OECD-program on l o n g range t r a n s p o r t of a i r p o l l u t a n t s (LRTAP), a European s u l f u r budget h a s been made ( r e f . 2 ) . According t o t h i s budget a number of less d e n s i l y populated c o u n t r i e s i n w e s t e r n Europe i.e.
Austria,
F i n l a n d , Norway, Sweden and S w i t z e r l a n d r e c e i v e c o n s i d e r a b l y h i g h e r amounts of s u l f u r t h a n are e m i t t e d w i t h i n t h e c o u n t r i e s . So f a r not much d a t a h a s been produced c o n c e r n i n g t h e long range t r a n s p o r t of o t h e r elements of environmental and t o x i c o l o g i c a l i n t e r e s t , such as t h e heavy m e t a l s . Expected d r a m a t i c changes i n t h e energy p r o d u c t i o n w i l l r e s u l t i n s t r o n g l y i n c r e a s e d c o n c e n t r a t i o n s (and d e p o s i t i o n s ) of e s p e c i a l l y a number of t o x i c metals.
EXPERIMENTAL 'Ib c o a s t a l sampling sites were selected, one on the west and one on the south coast of Sweden. I n addition one inland site was used. The sampling locations can be discerned i n f i g 1. Elevated (5-20 m) sampling positions were used t o reduce the local contamination. Every t h i r d day during t h e main part of the winter, spring and summer seasons of 1977, 24 hour-samples were collected. Cascade impactors of t h e Battelle-type (ref. 3 ) c l a s s i f i e d the aerosol samples i n t o seven s i z e fractions. A Nuclepore f i l t e r with an overall efficiency >80% collected the f i n e s t p a r t i c l e s . Each s i z e f r a c t i o n was analysed by particle induced X-ray emission (PIXE) analysis (ref. 4 ) f o r s u l f u r and heavy metals a t t h e Pelletron accelerator laboratory a t t h e Department of Nuclear Physics, Lund I n s t i t u t e of Technology, Sweden.
160
RESULTS AND DISCUSSION M e t e o r o l o g i c a l i n f o r m a t i o n , i. e. a i r m a s s t r a j e c t o r i e s a t t h e 850 mbar l e v e l , c a l c u l a t e d by t h e Norwegian I n s t i t u t e f o r A i r Research and s u r f a c e weather maps from t h e Swedish M e t e o r o l o g i c a l and H y d r o l o g i c a l I n s t i t u t e , was used t o s e l e c t f o u r sampling days f o r a d e t a i l e d s t u d y which is r e p o r t e d i n t h i s paper. Each sampling day c o n t a i n e d t h r e e sets of impactor samples, one p e r sampling site.
Two of t h e f o u r s e l e c t e d sampling days c o n s i s t e d of samples c o l l e c t e d i n a i r masses which had passed over h i g h l y i n d u s t r i a l i z e d r e g i o n s of Europe. R e p r e s e n t a t i v e t r a j e c t o r i e s f o r t h e s e e p i s o d e s are shown i n f i g .
1.
770116 I
7
Fig.
.
770627
1. 48 hour a i r mass back t r a j e c t o r i e s a t t h e 850 mbar l e v e l f o r t h e s e l e c t e d
sampling days.
The sampling s i t e s A, B and C a r e i n d i c a t e d .
j The t r a j e c t o r i e s f o r t h e J a n u a r y 16 samples i n d i c a t e t h a t t h e a i r masses passing t h e two c o a s t a l sampling s i t e s have a s i m i l a r o r i g i n . However t h e i n l a n d impactor
1
sample is taken in a d i f f e r e n t a i r mass, o r i g i n a t i n g in t h e south e a s t e r n p a r t s of Europe. The January 25 samples a r e taken i n t h e same air masses. Surface weather maps support t h e t r a j e c t o r i e s . Only small amounts of p r e c i p i t a t i o n w e r e recorded during t h e s e two sampling days, probably having only minor e f f e c t s by wash-out on t h e elemental concentrations. A s r e f e r e n c e s two sampling days were s e l e c t e d when a i r masses o r i g i n a t i n g in t h e
n o r t h A t l a n t i c area e n t e r e d Scandinavia from n o r t h w e s t ( s e e f i g . 1 , January 7 and June 27). By combining information from a i r mass t r a j e c t o r i e s and s u r f a c e weather maps i t can be seen t h a t t h e January 7 a i r mass c a m e from t h e Artic passing south over
Greenland. The same sources of information f o r t h e June 27 samples y i e l d s a more w e s t e r l y a i r mass path south of Greenland. Occasionally showers occurred i n t h e a i r masses of both sampling days p r i o r t o and when e n t e r i n g Scandinavia. To l e a r n about t h e long range t r a n s p o r t of elements emitted i n p a r t i c u l a t e form,
o t h e r chemical components than s u l f u r have t o be studied. By comparing elemental c o n c e n t r a t i o n s obtained i n s o u t h e r l y a i r masses with those i n n o r h t e r l y a i r masses, an i n d i c a t i o n can be obtained of t h e impact of long range t r a n s p o r t from t h e European Continent on t h e Scandinavian a i r q u a l i t y . Large element concentration d i f f e r e n c i e s ( s e e t h e t a b l e ) are found between t h e two types of a i r masses a t a l l sampling s i t e s . Most of t h e elemental c o n c e n t r a t i o n s are h i g h e r in t h e s o u t h e r l y a i r masses, some by more than one o r d e r of magnitude. Chlorine is t h e only exception being higher in t h e n o r t h e r l y a i r masses. However, t h e c h l o r i n e values a r e u n c e r t a i n due t o i t s v o l a t i l i t y
in some chemical compounds, which means it can be l o s t during sampling and a n a l y s i s . Dominating source processes f o r each element can be i d e n t i f i e d from its s i z e d i s t r i b u t i o n . I n f i g . 2 a number of d i f f e r e n t s i z e d i s t r i b u t i o n s a r e shown. Fine p a r t i c l e o r i e n t e d s i z e d i s t r i b u t i o n s of t e n are t h e r e s u l t of anthropogenic high temperature processes followed by gas t o p a r t i c l e conversion and coagulation mechanisms.
In t h e s o u t h e r l y a i r masses many of t h e elements, i.e.
S, K , V , C r , Mn,
Ni, Cu, Zn, B r and Pb, are mainly found i n the accumulation mode ( p a r t i c l e s with a n aerodynamic diameter of 0.1
-
2 um) w i t h a s i z e d i s t r i b u t i o n resembling t h a t of Zn in
f i g . 2 B o r Cu (770125) in 2 C. Occasionally i n d i c a t i o n s of very f i n e anthropogenic p a r t i c l e s can be seen i n t h e elemental s i z e d i s t r i b u t i o n s ( s e e f i g . 2 D). Presumably t h e s e t r a c e s can be i d e n t i f i e d as c o n t r i b u t i o n s from l o c a l (anthropogenic) sources. Copper (770116) in f i g . 2 C has been s e l e c t e d t o r e p r e s e n t one of the few occasions i n t h e s o u t h e r l y air masses when a l o c a l source seems t o dominate the copper s i z e distribution. I n t h e n o r t h e r l y a i r masses which contain much lower elemental concentrations, e s p e c i a l l y of t h e anthropogenically derived elements, t h e coarse mode f r a c t i o n ( p a r t i c l e s w i t h a n aerodynamic diameter l a r g e r than 2 um) can be discerned more clearly.
I n f i g . 2 A a s i z e d i s t r i b u t i o n of s u l f u r c o l l e c t e d i n a n o r t h e r l y ai,r mass
a t the c o a s t a l s i t e B is shown. The s i z e d i s t r i b u t i o n is bimodal. The sea-spray
derived s u l f u r i n t h e coarse mode can be c l e a r l y d i s t i n g u i s h e d from t h e
TABLE. Elemental concentrations, total and the fraction <2pm. Unit ng/m3. The uncertainty is typically 10-20%.
w
a,
N
Sample El emen t S
c1 K
Ca
Ti V
Cr Mn
Fe Ni
cu Zn 5r Pb
Site A 770107 <2pm Total 150 490 42 46
330 2000 98 170
2.2 4.7 0.36 3.9
6.8 6.6 0.36 6.1
33 1.5 8.1 21
82 2.9 8.4 24
1.3 28
4.2 32
Site B 770107 <2pm Total 73 300 18 19
160 1100 40 80
0.80 0.35 6.3
0.59 0.80 0.35 7.6
Site C 770107 <2pm Total
Site A 770627 <2pm Total
Site B 770627 <2pm Total
Site C 770627 <2pm Total
46 59 130 240 12 16 8.1 8.1
95 130 11 150 4.3 17 22 55
34 110 26 470 5.1 44 2.9 52
160 190 59 300 7.0 17 18 42
0.35 0.31
0.59 0.31
1.0
0.63
0.74
0.35
-
2.4
-
12
2.2 -
2.4
-
-
-
-
11 14 0.53 0.53 0.43 0.43 4.3 4.3
3.5
-
4.3
-
0.98 30
2.6 -
4.3
1.0
7.1
-
0.16
0.17 0.16
3.7 0.76
3.7 1.7
0.11
0.11
1.8 0.12
4.5 0.12 0.20 0.70
8.7
66
-
-
0.42 0.89
1.7 0.89
3.0
4.3
-
-
Sample Element
Site A 770116 durn Total
Site B 770116 <2pm Total
Site C 770116 <2pm Total
Site A 770125 <2pm Total
Site B 770125 <21.lm Total
S
2100
1100 1100 7.1 21 60 68 38 93
1100 1200 8.2 28 71 83 18 40
5400 22 300 130
2600
c1 K
Ca
Ti V
Cr Mn Fe
-
110 43
17 2.7 2.7 13
2300 390 150 280 41 .3.0 3.4 16
Ni cu Zn
160 350 1.8 1.8 13 14 81 90
Br Pb
150
5.9
5.9 160
2.8 1.9
1 .o 6.6
4.4 1.9 1 .o 7.8
84 110 2.6 2.6 3.8 3.8 17 20 4.2 42
5.8 3.0 2.3 11
150 180 1.4 1.4 1.1 1.1 18 18
-
-
4.2 42
7.4 3.2 2.5 12
24
24
23 15 6.2 37
5500 110 340 250 42 15 6.2 39
280 400 6.4 7.7 12 12 140 140 11
11
130
130
-
-
-
120 17
2700 61 130 57
2.5 4.5 0.58 6.5
4.6 4.7 0.58 7.4
67 3.1 2.8 43
92 3.3 3.0 49
5.5 64
64
-
-
0.70
-
-
-
-
Site C 770125 < 2 ~ m Total 1700
1700 15
56 15
61
-
26
1.9 3.9
2.8 4.1
4.1
4.6
45 2.6 1.7 30
53 2.6 1.9 34
-
-
-
5.5 29
163 a n t h r o p o g e n i c a l l y d e r i v e d s u l f u r i n t h e accumulation mode. Other elements o f t e n having
a bimodal s i z e d i s t r i b u t i o n i n n o r t h e r l y a i r masses are K and Fe. The c o a r s e f r a c t i o n of t h e s e elements probably r e s u l t s from wind blown e r o s i o n products.
However some
samples seem t o c o n t a i n a combination of a n aged e r o s i o n a e r o s o l and an aged a n t h r o p o g e n i c a e r o s o l ( s e e T i i n f i g u r e 2 B) making i t d i f f i c u l t t o d i s t i n g u i s h between t h e s e two components. I n t h i s f i g u r e t h e T i s i z e d i s t r i b u t i o n a r e r e s o l v e d i n t o two p o s s i b l e components.
b MlAlogD
A.
Site B 770627
(ng/m3)A
4 Site A 770125
B.
A
C.
Site 6
20
c
f
>
-9
6
5 4 3 2 1 0
Site B 770116
1
D.
6
5 4 3 2 1 0
Fig. 2.
6 5 4 3 2 1 0
S e l e c t e d r e p r e s e n t a t i v e elemental s i z e
d i s t r i b u t i o n s , where t h e c o n c e n t r a t i o n M a r e p l o t t e d as a f u n c t i o n of t h e p a r t i c l e diameter D.
. denote t h e d e t e c t i o n l i m i t .
Dotted curves i n
f i g . 2B show t h e Ti s i z e d i s t r i b u t i o n r e s o l v e d i n t o a c o a r s e and a f i n e f r a c t i o n .
Impactor s t a g e
0 contains p a r t i c l e s with an equivalent
6 5 4 3 2 1 0
Impactorstage
aerodynamic diameter >gum, s t a g e 1: 4-8 um, s t a g e 2 : 2-4 um. s t a g e 3:l-2 um, s t a g e 4: 0.5-1 um, s t a g e 5: 0.25-0.5
um and s t a g e 6 <0.25 um.
The s i z e f r a c t i o n a t e d e l e m e n t a l c o n c e n t r a t i o n s make a comparison of accumulation mode c o n c e n t r a t i o n s i n a i r masses from t h e s o u t h w i t h t h o s e from t h e n o r t h possible. I n d i c a t i o n s of t h e magnitude of long range t r a n s p o r t of a n t h r o p o g e n i c a l l y derived elements can t h e r e f o r e be obtained. Such a comparison f o r sampling s i t e A r e v e a l s the l a r g e s t r e a l i v e c o n c e n t r a t i o n d i f f e r e n c e f o r s u l f u r . The metals Ti, C r , Mn, Fe, Zn and Pb are more abundant by a f a c t o r 5 o r more i n t h e s o u t h e r l y a i r masses. P o t e n t i a l s o u r c e s f o r t h e accumulation mode f r a c t i o n of t h e s e elements a r e m e t a l l u r g i c a l p r o c e s s e s , g a s o l i n e combustion, combustion of c o a l and o i l f o r power production e t c . From t h e s i z e d i s t r i b u t i o n s of S , V, N i p Cup and Pb (resembles f i g u r e 2 C, Cu 770116)
164 a l o c a l c o n t r i b u t i o n of very f i n e p a r t i c l e s on January 7 ( s i t e A) can be traced. ~
The same t y p e of comparison f o r sampling s i t e B r e v e a l s c o n c e n t r a t i o n d i f f e r e n c i e s of a f a c t o r 5 o r more f o r t h e elements: S , Fe, N i p Cu, Zn, and Pb. The i n l a n d sampling
s i t e C shows t h e l a r g e s t c o n c e n t r a t i o n d i f f e r e n c i e s when comparing n o r t h e r l y and s o u t h e r l y a i r masses (see t h e t a b l e ) . A f a c t o r of 10 o r h i g h e r c o n c e n t r a t i o n s a r e found i n t h e accumulation mode in t h e l a t t e r case f o r t h e f o l l o w i n g elements S , V, Mn, Fe, N i and Zn.
I
ConcwsIoNs The u s e of a s e n s i t i v e a n a l y t i c a l technique (PIXE) i n combination w i t h a s i z e f r a c t i o n a t i n g sampler has allowed i d e n t i f i c a t i o n of s o u r c e types of a number of elements.
I n a i r masses which have passed over i n d u s t r i a l i z e d areas of t h e European
Continent, h i g h c o n c e n t r a t i o n s of many heavy metals and s u l f u r were found. T h e i r size d i s t r i b u t i o n s w i t h most of t h e mass i n t h e accumulation mode i n d i c a t e t h e dominance of a n t h r o p o g e n i c emissions. Concentrations i n n o r t h e r l y a i r masses coming from t h e north
w e s t were o f t e n one o r d e r of magnitude lower t h a n i n a i r masses from t h e south. The few measurements p r e s e n t e d i n d i c a t e a very s t r o n g i n f l u e n c e on t h e s u l f u r and heavy
metal c o n c e n t r a t i o n s i n Scandinavia, d u r i n g e p i s o d e s of long range t r a n s p o r t .
To
estimate t h e i n c r e a s e i n d e p o s i t i o n s of elements r e s u l t i n g from long range transport f u r t h e r measurements a r e required.
ACKNOWLEDGEMENTS
we are i n d e p t e d t o K.R.
Akselsson f o r v a l u a b l e s u g g e s t i o n s on t h e manuscript.
Sampling a s s i s t a n c e w a s o f f e r e d by s e v e r a l i n d i v i d u a l s which is g r a t e f u l l y acknowledged.
T h i s work w a s supported by t h e N a t i o n a l (Swedish) Environment Protection
Board.
REFERENCES 1 Sweden's
Case s t u d y f o r t h e United Nations Conference on t h e human environment
1971: Air p o l l u t i o n a c r o s s n a t i o n a l boundaries. The impact on t h e environment of s u l f u r i n a i r and p r e c i p i t a t i o n .
Royal M i n i s t r y f o r f o r e i g n a f f a i r s ,
Stockholm, Sweden. 2 OECD. The OECD program on long range t r a n s p o r t of a i r p o l l u t a n t s .
Measurements and
f i n d i n g s . OECD, P a r i s , 1977.
3 R.I.
M i t c h e l l and J.M.
4 T.B.
Johansson, R.E.
47(1975), 855
- 860.
P i l c h e r . Ind. Eng. Chem. van Grieken, J.W.
-
1042.
Winchester.
Anal.
, 15(1959),
Nelson and J.W.
1039
Chem.,
Atmospheric PoZZution 1980, Proceedings of the 14th International Colloquium, Paris, France, May 5-8,1980, M.M. Benarie (Ed.), Studies in Environmental Science, Volume 8 0 Elsevier Scientific Publishing Company, Amsterdam -Printed in The Netherlands
TRANSPORT OF OZONE
165
IN ISRAEL
E. H. STEJNBERGER Dept. of Atmospheric Sciences The Hebrew University, Jerusalem, I s r a e l
ABSTRACT Evidence of ozone transport f r o m t h e coastal urban complex was found in Jerusalem.
The a r r i v a l of ozone f r o m the coast w a s manifested by a sudden
increase in ozone concentrations i n J e r u s a l e m during the early afternoon. The ozone increase was accompanied by a s i m i l a r sharp r i s e in the water vapor mixing ratio,indicating the a r r i v a l of a distinct air m a s s f r o m the coast. In this study t h r e e y e ars
' ozone
measurements w e r e analyzed.
The results
showed that transport phenomena w e r e frequent, especially during the summer months.
The most important meteorological factors determining transport were
wind velocity and the p r e s e n c e of low level inversions.
A correlation coefficient
of r = 0. 75 was found between ozone maxima in J e r u s a l e m and the height of the base of the inversion layer. I I -
INTRODUCTION Ozone is generated in the polluted atmospheres of urban centers, where adequate amounts of hydrocarbons and oxides of nitrogen a r e present, under the action of s o l a r radiation. The concentration of ozone at a given time and place will be determined by the r a t e s of production and destruction and by t r a n s p o r t ,
Production and destruction
depend on the concentrations of the participating molecular species and the r a t e constants of the appropriate chemical reactions and the only meteorological quantity involved is the available s o l a r flux. Transport processes, however, depend entirely on the prevailing meteorological conditions, such a s wind velocity and atmospheric stability. Ozone transport has been observed in various places located downwind of a n urban source. (Steinberper and Balmor, 1973, Cox et a l . , 1975, Coffey and
166
Stasiuk, 1975, Ganor et a l . , 1977). The influx of ozone into r u r a l regions may cause s e r i o u s damage to sensitive agricultural crops (Naveh et a l . , 1978). In I s r a e l about 50% of the population and over 60% of a l l vehicles a r e concen2
trated in a s m a l l a r e a measuring about 1 5 x 55 km , along the coast.
Fig. 1
shows a p a r t i a l map of I s r a e l and the relative locations of Jerusalem, and the c o a s t a l strip, including T e l Aviv.
Four main highways and numerous secondary roads, all with very high traffic densities, a r e a l s o contained within this a r e a .
Therefore
SEA
the rectangle drawn into Fig. 1. c a n be considered as a n extensive pollutant source, including ozone. Ozone concentrations w e r e monitored in Tel Aviv since 1 9 7 5 and the data show that the average hourly concentrations w e r e occasionally
f O
W
P
O
W
above 0.15 p. p . m . , often above 0. 1 p . p. m. (State of California one-hour standard) and frequently above 0. 08 p. p. m. (U.S. Federal
L,"
Fig. 1. P a r t i a l map of Israel. Matched a r e a s r e p r e s e n t urban c enters .
.
standard)
Since continuous ozone monitoring data for the last four y e a r s w e r e available only f o r
J e r u s a l e m and T e l Aviv, this study is based entirely on these results.
EXPERIMENTAL TECHNIQUES Ozone concentrations w e r e measured by commercial chemiluminiscent ozone meters, utilizing the gas-phase reaction of ozone with ethylene.
Both instruments
w e r e calibrated regularly and exhibited qood stability. The relevant meteorodogical variables,
a . e. wind velocities and upper-air
soundings w e r e obtained f r o m the I s r a e l Meteorological Service, in Beit Dagan, near T e l Aviv. Ozone concentrations, measured durinq the months April w e r e studied.
-
October 1 9 7 7 -1979
Concentrations a r e expressed in t e r m s of one-hourly averages,
in units of p a r t s p e r million, (p. p. m. 1.
RESULTS AND DISCUSSION The expected diurnal variation of ozone within a n urban site c a n be predicted if photochemistry and traffic pattern only a r e considered.
Ozone concentration
167
would be low i n the morning, r i s e to a maximum value soon a f t e r local noon, (between 12-13 h local standard t i m e and d e c r e a s e i n the afternoon to a low level again
0.07
8 6 1978
0.07 -
-
0
28 6 19P
D
14 6 197H
II I I
I / I I
0.06-
0.06 -
p,
-
0.05
' \ I \
-
I
0.04 Q.
-
d m
0.03
-
0
\
I
I
1
1
/
,'>\
I I
/
\
\
'-'
/
0.05
\
I
* -\
/
'
I'
0.02 0.01
0.02
-
n0
-
0.01 a
I
I
I
6
12
18
n
I
24 - 0
6
b I
I
I
12
18
24
L.S.T (hours) Fig.2 Diurnal ozone variation i n J e r u s a l e m on selected days. (a) No transport ( b ) Evidence of t r a n s p o r t
Frequently, however, a different p a t t e r n is found, ( F i p . 2., (b). H e r e two maxima c a n be observed; t h e f i r s t one between 1 2
-
1 3 h L. S. T . , and the second one,
which is usually considerably higher, two t o t h r e e hours l a t e r .
The sudden
i n c r e a s e in ozone concentrations i n the e a r l y afternoon is accompanied by a s i m i l a r s h a r p r i s e in the w a t e r vapor mixing ratio, w, thus indicating the a r r i v a l of a distinct air m a s s f r o m t h e coast.
Lastly, recent wind observations in
J e r u s a l e m have shown, that wind s p e e d s i n c r e a s e d and wind directions acquired
a w e s t e r l y component a l s o a t about 14 h.
These f a c t s indicate that the appearance
of ozone peaks in the e a r l y afternoon c a n be attributed to transport of polluted air f r o m the c o a s t a l a r e a . The relationship between ozone levels in J e r u s a l e m and T e l Aviv and the variation of w i n J e r u s a l e m a r e shown in Fig. 3 f o r a typical "transport day". -1 and wind On this day wind speed in J e r u s a l e m increased f r o m 8 to 18 k m h direction changed f r o m 120° (Em)to 300" (WNW) a t 14 h.
168
Tel Aviv
A Jerusalem 0 0 3 IJerusalem)
0.10
17.4. I977 /
\
#
0 3 Tel Aviv
0.08
‘,w, Jerusalerr
I 0.07 h
d 0.06
d v
m 0.05
0 0.04
0.03
b\
0.02
b
10
12
14
16
18
L . S . T (hours) Fig. 3. Ozone concentrations in J e r u s a l e m and T e l Aviv and w in Jerusalem on 17. 4.1977. The frequent incidence of transport phenomena is demonstrated in Fig. 4 where the average monthly diurnal ozone variation is given f o r July 1977, July 1978 and September 1978. It can be s e e n that the maximum ozone concentration occured in a l l c a s e s between 14 - 15 h.
Due to the high incidence of transport
days and to the large impact of the p r o c e s s of the pollution levels in Jerusalem, the meteorological conditions enhancing transport f r o m the coast w e r e investigated. During the 3 y e a r s studied 244 transport days occured. The highest incidence of transport w a s in July (71% of all days), the lowest in April (10% of all days).
The dependence of the daily maximum ozone concentration on selected meteorological variables w a s examined.
It was found that the mcs t important factors
w e r e wind direction and inversion height.
It has been shown previously (Halevy
and Steinberger, 1974), that low-level inversions occur on 87% of a l l summer
169
a July 1978 0
Sepi 1978
0.05
I
I
I
6
12
18
I 24
L .S .T ( hours ) Fig. 4.
Average monthly diurnal ozone variation f o r July 1977, 1978 and September 1978 days and the inversion layer penetrates inland to at least 50 km.
Due to the
r i s i n g t e r r a i n (to 800 m elevation) the base of the inversion above J e r u s a l e m is about the same a s on the coast,
This conclusion was recently reconfirmed
by a s e r i e s of simultaneous upper-air soundings in Jerusalem and in Beit Dagan. It should be noted that ozone transport c a n occur a l s o in the absence of inversions, but the ozone maxima w e r e lower and the frequency of occurrence smaller.
(Fig. 5. )
The dependence of ozone concentration on wind direction is shown in Fig. 5. It is s e e n that the largest concentrations w e r e measured for
6
= 320".
This
result is the direct consequence of the relative location of J e r u s a l e m and T e l Aviv.
(Fig. 1. 1. A linear correlation was found between ozone maxima and wind
direction, with a correlation coefficient r = 0. 90. The connection between ozone maxima and inversion base height, H, is shown in Fir?.. 6 . It c a n be s e e n that the highest ozone levels occur for the lowest inversion bases.
This behaviour c a n be explained by noting that when low
inversions a r e present, the vertical mixing in the atmosphere is inhibited,
170
ooo
inversion
00.
No inversion
40
doys 0
.' 0.
O
060
L *
A
050
30-
h
V
i
.
c
4
a Y
040
m
0
I
,030
180
210
240
Wind
270
330
330
360
direction , 8
Fig. 5. Frequency distribution of transport day by wind direction and the average ozone maximum f o r each direction.
'I"
It
0,. 480.5 1 (IOOO/H YZ6' r = 0.86
\o
.08-
E
-2
.06-
n
0 .04 0
,021
500
1000
H (m) Fig. 6 . Ozone maxima vs. inversion base height.
1500
2000
171 leading to i n c r e a s e d pollutant concentrations under the inversion l a y e r .
The
Gaussian dispersion models also p r e d i c t a s i m i l a r dependence of concentrations on H. Various r e g r e s s i o n equations w e r e t r i e d to r e p r e s e n t the data and t h e best f i t w a s obtained by using the equation:
0 3 = 0.047
1000
o*286
with a c o r r e l a t i o n coefficient r = 0. 75.
CONCLUSION
It has been shown that t r a n s p o r t of pollutants f r o m the coast is a r a t h e r frequent p r o c e s s in I s r a e l during the s u m m e r months.
Transport will be facilitated when
low-level inversions a r e present.
REFERENCES' 1 P.E. Coffeyand W.N. Stasiuk, Environ. Sci. Tech., 9, (1975) 59-61. 2 R.A. Cox, F.J. Eggleton, R.G. Derwent, J.E. Lovelock and D.H. Pack, Nature (London), 255 (1975), 118-121. 3 G. Halevy and E. H, Steinberger, I s r a e l J. E a r t h Sci. 23, (1974), 47-54. 4 E. Ganor, E. H. Steinberger a n d A. Donagi, P r o c . 8th Sci. Conf., I s r a e l Ecol. SOC., (1977), 230-241. 5 Z . Naveh, E. H. Steinberger and S. Chaim, Environ. Poll. 1 6 , (1978),249-262. 6 E. H. Steinberger and Y. Balmor, Nature (London), 241, (1973), 341 -342.
This Page Intentionally Left Blank
Atmospheric Pollution 1980, hoceedings of the 14th International Colloquium,Paris, France, May 5-8,1980, M.M. Benarie (Ed.), Studies in EnvironmentalScience, Volume 8 0 Elsevier Scientific Publishing Company, Amsterdam -Printed in The Netherlands
173
DIRECT FORMATION OF NO2 IN COMBUSTION PRODUCTS
W. J. McLEAN Sandia Laboratories, Livermore, California (USA)
J. Y. CHEN, F. C. GOULDIN, and M. J. OVEN Cornell University, Ithaca, New York (USA)
ABSTRACT It is noted that combustion devices may, under some operating conditions, produce NOX emissions containing a rather large fraction of NO2. A detailed chemical kinetic mechanism for such NO2 formation is presented, and the results of measurements on a laboratory combustor are described. It is concluded that NOz forms via the reaction NO + H02 + NO2 + OH in regions where combustion processes are rapidly quenched by mixing with excess air.
INTRODUCTION The oxides of nitrogen (NOX) represent one of the principal classes of primary pollutants of concern in urban environments. The term NOx is used to designate the sum of the concentrations of the two oxides of concern, nitric oxide (NO) and nitrogen dioxide (NO2). Nearly all NOx in urban atmospheres is produced in high temperature combustion devices, where small quantities of atmospheric nitrogen or the trace quantities of organic nitrogen in the fuel may be oxidized to NO. Nitrogen dioxide, the atmospheric end product of NOx emissions, is of concern both because its photochemical reaction products lead to ozone formation, and because health effects are associated with exposure to low levels of NO2. It has also been recently noted that NO2 can play a role in atmospheric reactions which form mutagenic nitro derivatives from polycyclic aromatic hydrocarbons (ref. 1). Although NO2 is the oxide of nitrogen of concern in the polluted atmosphere, combustion sources operating under most conditions usually emit most of their NOx as NO. Subsequent reactions and dispersion in the atmosphere detenine the ambient levels of NOz. The chemical dynamics of NO to NO2 conversion in the atmosphere are complex, but by now reasonably well understood (ref. 2). Ambient concentrations of ozone (03), the primary noxious atmospheric oxidant, are
174
established by a relatively rapid photochemical cycle involving NO2, NO, and 0 3 , which results in O3 concentrations proportional to the ratio of the concentrations of NOz to NO. The high NO2 to NO ratios necessary for attaining ozone levels typical of polluted atmospheres result from photochemically induced reactions of NO, NO2 and hydrocarbons. In brief, oxygen atoms produced by photolysis of NO2 react with hydrocarbons present in polluted atmospheres to produce organic peroxy radicals. These radicals in turn accelerate the required oxidation of NO to NOz. Such processes typically take several hours in urban atmospheres, so that peak ozone levels are usually observed sometime after peak NO emissions. The time interval between the peaks represents the time required for conversion of NO to NO2.
It has recently come to our attention that a number of different types of combustion systems, both practical devices and experimental laboratory combustors, produce NOx containing a large fraction of NO2 under some operating conditions. Although the regimes of high NOz/NOx fractions are in general associated with relatively low total NOx emissions, such direct NO2 emissions to the atmosphere are of concern. Atmospheric reaction cycles on small geographic scales could possibly be perturbed by such emissions. Also, plume visibility and health effects due to short term NO2 exposure would be increased by locally high NOz emission sources. It is also possible that the efficacy of exhaust treatment processes may depend upon the form of the oxide of nitrogen in the exhaust. The purpose of the present study is to summarize those conditions which lead to direct formation of NO2 in combustion systems and to elucidate the causes of such direct NO2 formation. The results of a detailed chemical reaction theory as well as measurements on a laboratory prototype gas turbine combustor are discussed. NOz EMISSIONS FROM COMBUSTION SYSTEMS In this section recent literature regarding measured NOz emissions from various combustion devices is briefly summarized. It should be noted that extreme care must be exercised in sampling and transfer of combustion products if reliable N02/NOx ratios are to be obtained. If samples are obtained near the combustion zone itself, conversion of NO to NOz during cooling in the sampling probe is almost unavoidable (refs. 3,4,5). Care must also be taken to avoid both transformation by heterogeneous reactions in sampling lines and dissolution of NO2 into condensed water vapor (refs. 6 , 7 ) . The measurements cited below were all taken at the exhaust of the combustion devices where reliable probe sampling could be assured. Samples were also carefully handled and conditioned to avoid transformation in sampling lines. Gas turbines are in widespread use both in aircraft engines and in various types of stationary power plants. In both applications gas turbine combustors
175
have been shown t o produce substantial fractions of t h e i r NOx emissions as NO2 under l i g h t load conditions (ref. 7 ) . Such d i r e c t NO2 emissions from large stationary gas turbines may have a d i r e c t influence on plume v i s i b i l i t y (ref.8), while a i r c r a f t emissions may contribute t o locally high NO2 levels which are of concern near a i r p o r t s (ref. 9 ) . NO, emission measurements on a gas turbine power s t a t i o n obtained by Johnson and Smith (ref. 10) perhaps typify gas turbine behavior. Their data are s m a r i z e d i n Fig. 1 where NO and NO2 emissions and the r a t i o N02/NOx is shown as a function of turbine load. Total NOx emissions decrease with load but the NO2 fraction rapidly increases.
1
Hilliard and Wheeler (ref. 11) have recently reported results of careful NO and NO2 measurements i n reciprocating piston engine exhausts. In spark
80-
ignition engines, the NO2 i s
P c
0
only about 1%of the t o t a l NO, over a wide range of operating conditions. However, i n the diesel engine the combustion process i s different and considerable NO2 i s found i n the exhaust.
60-
c w
20
40
60
8o
TURBINE LOAD (% FULL LOAD)
F i g . 1. NO and NO emissions from a gas turbine power plan$ as given i n r e f . 10.
loo
Here, as i n the gas turbine system, the peak NO2 values are attained under l i g h t load conditions, while the NO and t o t a l NOx increase as load increases. The percentage of NO2 i n t o t a l NOx is about 2 5 % a t l i g h t loads
and decreases t o l e s s than 5% a t one-half maximum load.
Concentrations of NO,
arein general about an order of magnitude higher i n diesel exhaust than i n gas turbine exhaust. MECHANISM FOR NO2 FORMATION The r e s u l t s c i t e d above indicate t h a t the formation of NO2 is somehow intimately related t o processes i n the combustion chamber, and not simply due t o NO oxidation i n the exhaust system. Otherwise it would be expected t h a t NO2 would follow trends similar to NO. I t i s generally agreed t h a t any NO2 observed is derived from NO i n i t i a l l y formed i n the high temperature primary combustion zone. I t i s also accepted t h a t the t e m l e c u l a r reaction 2NO + O2 + 2 NO2 is too slow t o account f o r the observed NO2 levels. NO2 formation i n practical systems and i n laboratory combustors (ref. 11) i s strongly associated with those operating
176
regimes where hot, NO containing products of partially complete combustion are cooled and chemically quenched by rapid mixing with surrounding excess air. Both gas turbines and diesels operating at light loads exhibit this type of combustion condition, because the low fueling rates produce smaller, less intense Combustion zones which quickly mix with large quantities of surrounding air. Evidently, under these conditions NO is formed in the primary combustion zone and subsequently oxidized to NO2 by chemical reactions which are enhanced by the quenching process. We have constructed a detailed elementary chemical reaction mechanism to help explain our observations of NO2 in a laboratory prototype gas turbine combustor, in which intense shear between co-flowing jets causes rapid quenching of the combustion process. The history of NO to NO2 transformation in combustion products has been calculated during a simulated quenching process. The details of the mechanism and the simulation analysis are reported elsewhere (ref. 3); the principal features are summarized here. The continued oxidation of partially burnt combustion products during the quenching process is simulated by the multistep methane oxidation mechanism represented by the first 43 reactions in Table I. Because it was of interest to examine processes taking place at moderate temperatures, this mechanism contains a number of reactions involving H02 and H202 which are not important during high temperature oxidation. Reactions 44-50 in Table I determine NO and NO2 concentrations, with reaction 48 governing oxidation of NO to NO2. Application of the mechanism of Table I to quenching conditions typical of those found in our laboratory combustor have been carried out, and the details have been reported elsewhere (ref. 3). In brief, combustion products containing 30 ppm NO are assumed to be mixed with unbumt reactants and cooled from 1900K to 700K in Sms. These conditions are determined from analysis of the composition, temperature, and velocity measurements made inside the combustor (ref. 1 2 ) . The results of applying the reaction mechanism under these conditions are shown in Fig. 2 where the species concentrations and temperature are shown as functions of time. The increasing CH4 mole fraction in Fig, 2 is due to the fact that, in this combustor, quenching results from mixing of hot burnt products with cold unburnt reactants containing CH4. With respect to NO and NO2, a detailed analysis of the calculations used to construct Fig. 2 indicates that NO is rapidly oxidized to NO2 by H02, which is produced during quenching by reaction 10. With unbumt CH4 present, sufficient H02 is produced to convert all the NO to NO2. If unburnt CH4 is not present during the quenching process, a much smaller increase in the H02 concentration is obtained, and only about 25% of the NO is oxidized to NO2. EXPER1ME.NP.L RESULTS As part of a continuing experimental program on gas turbine combustion, we have made NO and NO2 measurements in the exhaust plane of a laboratory prototype gas
177
100 80
60 V
40
a
L
20
0
OHxlO-l
1
2
3
4
5
TIME (ms)
Fig. 2.
Calculated species mole fractions during a simulated combustion quenching process.
BvANE SWIRLER
,-INTERJETSHEAR
LAYER
Fig. 3. Schematic drawing of swirl stabilized laboratory combustor.
178
turbine combustor. The experiments are fully described elsewhere (ref. 1 2 ) , and only briefly smarized here. A schematic of the swirl stabilized laboratory combustor is shown in Fig. 3. The combustor is composed of two confined coaxial jets, each having swirl. The inner jet contains premixed methane-air with swirl obtained by tangential air injection. Secondary air is supplied in the outer jet with swirl regulated by variable angle vanes. Both co - and counter - swirl conditions are possible. Combustion is stabilized by the recirculation zone formed immediately downstream of the jet entrance by the fluid dynamic phenemonon hown as vortex breakdown. Samples obtained from the exhaust plane of the combustor by a water cooled probe were analyzed for NO and NO2 by a chemiluminescent analyzer equipped with a stainless steel converter for differentiating between NO and NO2. Additionally a dual beam optical technique based on ultraviolet absorption in the y (0,0) band of NO was used to confirm concentration measurements. The relative difference between the NO mole fractions determined by the two instments was generally less than 10%. The NOx measurements were analyzed for NO2 formation in the cooling region of the probe by the reaction mechanism of Table I. It was concluded that in the exhaust plane temperatures below 1400K prevented significant NO to NO2 conversion during sampling under most conditions (ref. 3). I
I
I
1100
-80
- 'O -5
- 6o -
<2 5
: I-
-
4o
-
30
w A
Results of the NO, NO2 exhaust plane measurements for two different swirl conditions in the combustor are shown in Fig. 4,where NO and NO2 mole fractions are plotted as functions of the radial location in the exhaust plane. For the co-swirling jet condition, limited interjet mixing leads to high temperatures in the central core of the combustor. Combustion is nearly complete along the centerline and temperatures are high enough for substantial NO formation (ref. 12). Although about 10-15 ppm NO2 is measured in the outer annulus of the exhaust plane, our
EXHAUST PLANE RADIAL LOCATION (R/R,)
Fig. 4. NO and NO measurements in exhaust plane of laboratory combustor for two 2ifferent conditions, co-swirling flows and counter-swirling flows.
179
calculations indicate that it is likely that this NO2 is formed in the sample probe (ref. 3). In the counter-swirling jet condition, dramatically different NO and NO2 measurements are obtained. The overall NOx is many times lower than in the coswirl case, but now essentially all the NOx appears as NO2. Probe reactions were demonstrated not to be a factor in this case due to sufficiently low exhaust temperatures. In the counter-swirl condition, NO is formed in the hot primary combustion zone; however, the very intense mixing and cooling caused by the counter rotating jets limits NO formation and leads to incomplete combustion and nearly complete conversion of NO to NO2 via the mechanism of Table I. Thus the laboratory combustor data supports the theoretical model for NO2 formation via oxidation of NO during quenching processes. It is apparent that the physical and chemical details of the combustion process itself are important in determining the potential for direct formation of NO2 in combustion devices. SUMMARY
It has been shown that in both practical devices and laboratory experiments NO2 may form from NO via oxidation by the H02 radical. Conditions where flame quenching may occur by rapid mixing with surrounding cool air are especially favorable for such NO2 formation. Under these conditions increased concentrations of H02 are produced and NO reacts with H02 to form NO2. In diffusion controlled combustion systems, such as gas turbines and diesel engines, it is under the lighter load conditions where flame quenching processes take place and high fractions of NO2 are found, although total NOx is relatively low. We find it particularly interesting that the observations noted here seem to answer a question that arose a number of years ago during SST engine'testing, where there were reports of greatly increased reddish-brown coloring due to NO2 in the exhaust plume under afterburning conditions (ref. 13). These observations were puzzling at the time, but now seem to be explained by a process where incomplete combustion in the relatively cool afterburning region leads t o conditions favorable to oxidation of the NO frum the primary combustor to NO2 in the exhaust plume. We also note that widespread use of stratified charge spark ignition engines and diesel engines is anticipated because of the improved motor vehicle efficiency and increased fuel tolerance provided by these engines. It would appear that the nature of the combustion process in these systems could also lead to conditions favorable for NO2 formation. Emission measurements on these engines should carefully differentiate between NO and NO2' ACKNOWLEDGEMENTS This work was supported in part by the United States National Aeronautics and Space Administration by grant nunber NSG 3019 to Cornell University, and in part by the United States Department of Energy.
180
REFERENCES 1 J. N. Pitts, Jr., K. A. Van Cauwenberghe, D. Grosjean, J. P. Schmid, D. R. Fitz, W. L. Belser, Jr., G. B. Krrudson and P. M. Hynds, Science, 202(1978) 515-519. 2 J. H. Seinfeld, Air Pollution: Physical and Chemical Fundamentals, McGrawHill, New York, 1975, Chap. 4. 3 J. Y. Chen, W. J. McLean and F. C. Gouldin, The Oxidation of NO to NO2 During Combustion Quenching Processes, Paper No. 79-17,presented at Western States Section/The Combustion Institute, 1979 Spring Meeting, Provo, Utah, April 1979. 4 J. C. Kramlich and P. C. Malts, Comb. Sci. and Tech., 18(1978)91-104. 5 G. M. Johnson, M. Y. Smith and M. F. R. Wlcahy, Seventeenth Symposium (International) on Combustion, The Combustion Institute, Pittsburgh, 1979, pp. 647-660. 6 G. S. Samuelsen and J. N. Harman, 111, Transformation of Oxides of Nitrogen Composition while Sampling Combustion Products, Paper presented at First Chemical Congress of the North American Continent, American Chemical Society, Mexico City, December 1975. 7 N. P. Cernansky, Sampling and Measuring for NO and NO in Combustion Systems, in B. T. Zinn (Ed.), Experimental Diagnostics in Gas 6hase Combustion Systems, Progress in Astronautics and Aeronautics, 53(1977). 8 H. R. Gloria, G. Bradburn, R. F. Reinisch, J. N. Pitts, Jr., J. V. Behar and L. Zafonte, Air Pollution Control Assn. J., 24(1974)645-652. 9 B. C. Jordan and A. J. Broderick, Air Pollution Control Assn. J., 29(1979) 119-124. 10 G. M. Johnson and M. Y. Smith, Comb. Sci. and Tech., 19(1978)67-70. 11 J. C. Hillard and R. W. Wheeler, Nitrogen Dioxide in Engine Exhaust Paper No. 790691, Society of Automotive Engineers, Warrendale, Pennsylvania, 1979. 12 M. J. Oven, F. C. Gouldin and W. J. McLean, Seventeenth Symposium (International) on Combustion, The Combustion Institute, Pittsburgh, 1979, pp. 363-376. 13 L. B. Anderson, J. W. Meyer and W. J. McLean, A I M Journal, 12(1974)56-64.
TABLE I.
Elementary reaction mechanism used in calculations.
1. M + M 4 = CH3 + H + M 2. M4 + H = M3 + H 2 3. ( H 4 + O = M 3 + O H 4. M 4 + OH = Mj + H20 5. M4 + Ho2 = CH3 + H202 6. M 3 + 0 = 0: 0 + H 2 7. M3 + MI = M20 + H2 8. M3+ m2 = (H30 + OH 9. (H3 + o2 = (H 0 + 0 3 10. m 3 0 + o2 = m20+ m2 11. M + CH30 = (H 0 + H + M 2 12. M + (H20 = HCO + H + M 13. m2O + H = HCO + H 2 14. CH20 + 0 = HCO + OH 15. M 2 0 + OH = HCO + H20 16. (H20 + Ho2'= HCO + H202 17. M + HCO = H + CO + M
18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 2829. 30. 31. 32.
HCO + O2 = CO + m2 K O + H = CO + H2 HCO + 0 = 0 + OH HCO + OH = CO + HZO HCO + H02 = CH20 + O2 O2 + H2 = OH + OH H + O2 = OH + 0 H2 + 0 = OH + H 0 + H20 = OH + OH H + H20 = OH + H2 M + H2 = H + H + M O + O + M = O2 + M OH+CO=CO + H 2 CO + 0 + M = C02 + M co + o2 = co2 + 0
Ho2 = co2 +
33.
CO
34.
O+H+M=OH+M
+
OH
35.
H
36.
O+OH+M=H02+M
37. 38.
m2 +
39.
OH + Ho2
40. 42.
Ho2 + HO = H202 + O2 2 M + H O =OH+OH+M 2 2 H + H202 = H02 + H2
43.
H20Z + OH = H20
44.
O + N
45.
N
46.
No2
+
47.
H
NO2 = NO + OH
48.
H02 + NO = OH + NO2 ND + 0 = N + O2 NO + 0 + M = NO2 + M
41.
49. 50.
+
O2
+
M = H02
+
M
0 = o2 + OH H + H02 = OH + OH
+
+
2
=
H20
+
O2
+
H12
=NO+N
OH = NO
+
H
0 = No +
o2
Atmospheric Pollution 1980,Proceedings of the 14th InternationalColloquium,Paris,France, May 5-8,1980,M.M.Benarie (Ed.), Studies in Environmental Science, Volume 8 0 Elsevier Scientific Publishing Company,Amsterdam - Printed in The Netherlands
181
THE RATE OF NOx REACTION IN TRANSPORTED URBAN AIR CHESTER W. SPICER Battelle, Columbus Laboratories, Columbus, Ohio (USA)
ABSTRACT Airborne studies of nitrogen oxides reactions in transported urban plumes have been conducted in the vicinity of two isolated cities. Measurements o f NO 0 CO, x’ 3’ fluorocarbon-11, NMHC, C -C hydrocarbons, PAN, HN03, condensation nuclei, NO;, SO,; 1 5 and meteorological variables were made in a Lagrangian manner using a twin-engine research aircraft.
Results for Phoenix, Arizona, located in the southwestern U.S. -1 transformation/removal rate of less than 0.05 hr , while
desert, indicate an NO
X
data for the northeastern coastal city of Boston, Massachusetts show rates in the range 0.14-0.24
hr-l.
The low rate in Phoenix is at least partly attributable to
thermal decomposition of PAN and its analogs at the high ambient temperatures of the desert area. For Boston, the experimental results yield an average NO
lifetime of 5.8
hours under moderate photochemical smog conditions during the day.
INTRODUCTION The reactions of nitrogen oxides (NO )
*
emitted to the atmosphere by combustion
and other processes have been under investigation for a number of years but are still not completely understood.
Knowledge of NO
reactions is important for an
understanding of global nitrogen cycles as well as more localized photochemical smog manifestations.
Nevertheless, major uncertainties are evident in our knowledge of
the nature of the intermediate and final NOx reaction products, the rates of transformation, the factors which influence these rates, and the ultimate removal mechanisms for NO atmospheric NO
X
and reaction products.
The area in which our understanding of
chemistry is most deficient is the rate of NO
transformation to
products. This paper describes the results of field studies designed to provide data on the rate of transformation of NO transported urban plumes.
*
NOx
=
NO
-+ NOg.
to products and the nitrogen mass balance in
182 EXPERIMENTAL METHOD
To study NOx reactions in an urban plume it is important that the plume be isolated and that emissions to the plume be negligible after the air leaves the city.
To satisfy these requirements our studies have been performed in plumes
transported over the desert (Phoenix, Arizona) or over the ocean (Boston, Massachusetts).
As the polluted air leaves the city, NO
uents are diluted with surrounding air and NO
X
and other plume constit-
reactions begin.
Initially, NO is
converted to NO
via chain reactions, and once this process is nearly complete, 2 N02 can be chemically transformed to products or physically removed from the air by wet
and dry scavenging processes.
The change in NO
X
concentration during transport is
dominated by dilution, which consequently must be carefully accounted for in order to obtain information on the chemical and physical removal processes.
In our
studies, dilution is determined from the measured concentrations of the inert species CO, C2H2, and fluorocarbon-11 present in the urban air. of these dilution tracers, as well as NO
X’
The concentrations
must be corrected for the concentrations
already present in the dilution air. From the preceding discussion, the measurements needed to determine the rate of NO
X
removal from an urban plume include: NO
X
concentration in the plume; CO, F-11,
and C H concentrations in the plume; NOx, CO, F-11, and C H concentrations in the 2 2 2 2 F-ll/NOx, and C2H,/N0 background dilution air; the background-corrected CO/NO X’
ratios for the air leaving the city.
L
X
If these measurements are made sequentially
throughout the day on the same parcel of air as it is transported downwind of the city, NO
removal rates can be calculated.
To make these measurements in a Lagrangian fashion, we have employed an instrumented twin-engine research aircraft.
For most study days a specific air parcel,
e.g. the 0800 EDT air mass, was sampled just downwind of the city at midmorning and then periodically throughout the day by successive flights, The concentrations of NOx, in situ inert tracers (CO, C2H2, F-ll), PAN, HON02, C -C hydrocarbons, 1 5 O3 * and several other variables were determined shortly after the air parcel left the city and subsequently throughout the day.
The concentrations of these same species
were also determined in background air outside of the plume dilution.
The ratios of NO
X
to
correct for plume
to the inert tracers were then used (after correction
for background air dilution) in conjunction with reaction times to derive NO removal rates.
The removal rates include both physical removal and chemical
transformation. During the study, air mass trajectory analysis was used to predict the position of the selected air parcel in order to vector the aircraft to the area.
The plane
then bracketed the predicted position with plume traverses. Subsequent, more detailed, trajectory analysis based on wind data from several stations was used to determine the air parcel position more exactly and to select the plume traverse
183 data that most closely matched the time and position o f the specified air parcel. Further details of the experimental protocol may be found in reports by Spicer et al. (ref. 1, 2).
The air parcel trajectory and aircraft traverse positions for
the 0800 EDT Boston air mass of August 30, 1978, are shown in Figure 1 as an example of the data obtained during the field experiments described in this paper.
-7--
r
I
0
: 5
: 10
:
:
IS
M
:
,
25 30
Slolule Milet
Fig. 1. Air parcel trajectory and aircraft sample positions for Flights 37-39, August 30, 1978. In interpreting the data, the tracer/NO
ratios just downwind of the city
have been used with the tracer data from later downwind plume traverses to calculate the expected NO
concentration for each downwind traverse.
with the measured NO
X
Those values, together
concentrations and the reaction time between traverses, are
used to determine the rate of NO
removal from the air parcel.
RESULTS AND DISCUSSION Studies designed to define NO
X
transformation rate by Lagrangian airborne
measurements have now been conducted in two major urban areas. for study are Phoenix, Arizona and Boston, Massachusetts.
The cities selected
The Boston study is the
most recent and the techniques employed in that work are the most sensitive. Consequently, the Boston results are expected to be more reliable.
184 Phoenix, Arizona Airborne studies to define NO
X
in October, 1977.
transformation rate were conducted in Phoenix
Very hot dry weather persisted throughout the experiments.
The data from 29 separate monitoring flights were reduced as described above to yield information on the quantity of NO
X
removed from the air parcels.
Three
inert tracers were used in the calculations. Air mass trajectory analysis was used to determine the reaction time, or transport time, from the urban center to the point where the parcel was sampled. The data from all of the flights were grouped together and averaged over 1-hour time intervals. A plot of averaged "NOx l o s s " versus reaction time is shown in Figure 2.
For reaction times greater than
6 hours, the data are sparse and the averages should be viewed with caution. Up to
6 hours of reaction, the data in Figure 2 show no strong trends in NO removal x This suggests a
within the 5 5 ppb error limits of the experimental measurements.
very slow rate of transformation/removal of nitrogen oxides from the Phoenix plume, certainly less than 5 percent per hour. A slow rate of conversion of NO
X
to
reaction products is substantiated by the low concentrations of reaction products. The concentration of PAN (peroxyacetyl nitrate) within the urban plume never exceeded 2.1 ppb, which is about 30 times less than hourly PAN concentrations measured in the Los Angeles plume.
Nitric acid in the plume was never observed to
exceed the 5 ppb detection limit of the continuous instrument being used at the time. Particulate nitrate concentrations were also generally quite low.
10 13
a u)
4
0
X
0
0 Based on CO X Based on C2HZ 0 Based on F-ll
z
-10
- 20
I
0
Fig. 2. NO
X
2
3
4 5 6 Reaction Time, hours
7
l o s s averaged over all flights versus reaction time.
9
10
185 The high temperatures in the study area are expected to inhibit the apparent conversion of NO
X
to products due to the very temperature sensitive thermal
decomposition of species such as PAN, H02N02, and R02N02. We have employed a chemical kinetic model to investigate the effect of temperature on NOx transformations.
The modeling study indicated that, while higher temperatures do inhibit
the conversion of NO
X
per hour.
to products, nonetheless the rate should exceed 5 percent
At this time we have no convincing explanation of the low NO
removal rates in Phoenix. Boston, Massachusetts An investigation of NO
X
1978.
transformation rate was conducted in Boston in August,
Boston was selected for study because it is a strong emissions source whose
plume is transported eastward over the ocean by the prevailing winds.
Under this
condition, fresh emissions to the plume are negligible once it leaves the urban area. Four sets of flights in the Boston urban plume met all the conditions necessary for transformation rate analysis.
For these experiments, the expected concentration
of NOx, (NOx)e, has been calculated from the measured initial urban tracer/NO ratio and the measured tracer concentrations downwind, after correction for tracer and NO
X
concentrations in the dilution air.
The results were then plotted in the
integrated form of the first order rate equation, In
-versus
reaction time.
(NOx)e is the expected NOx determined by calculation and (NOx)t is the concentration of NO
actually measured at time t.
order plot is presented in Figure 3 .
For the flights shown in Figure 1, the first The slope of the straight line represents
the pseudo-first order rate constant for the removal of NO
X
from the plume.
plots were constructed for the other three Boston plume experiments.
Reaction Time, hours
Fig. 3 . First order plot for Boston plume flights of August 30, 1978.
Similar
186 During the early stages of NO net l o s s of NO
X'
plot.
X
transformation, NO is converted to NO2 with little
Such behavior is expected to cause curvature in the first order
For these experiments, however, the first plume traverse was always under-
taken 1-2 hours after the air parcel left the urban area. NO-to-NO
By this time the
conversion is largely complete, so that curvature is not observed in
2 the first order plots.
Based on these four sets of experiments, the rate of NO Boston air varied from 0.14 to 0.24 hr-'.
removal from the
These first ordzr removal rates trans-
in urban air in the range of 4 . 2 to -1 The average rate and lifetime for the four experiments were 0.18 hr
late to conversion (or l/e) lifetimes for NO 7.1 hours.
and 5.8 hours respectively. The average NO
half-life under these conditions is
4.0 hours. The reported values are applicable o n l y to daylight hours under sunny conditions with moderate photochemical smog (maximum O3 in the plume on these four days ranged from 90 to 140 ppb).
They obviously should be validated and extended by further
studies under both similar and different environmental conditions.
Such data
should prove very valuable in assessing the impact of nitrogen oxides and their reaction products on our air environment. ACKNOWLEDGMENT This work was supported by the U. S. Environmental Protection Agency and the Coordinating Research Council.
The contents do not necessarily reflect the
views and policies of these groups. REFERENCES
1 C.W. Spicer, D.W. Joseph and G.F. Ward, Investigation of Nitrogen Oxides Within the Plume of an Isolated City, Battelle-Columbus Final Report to Coord. Res. Council, 1978. 2 C.W. Spicer, J.R. Koetz, G.W. Keigley, G.M. Sverdrup and G.F. Ward, A Study of Nitrogen Oxides Reactions Within Urban Plumes Transported Over the Ocean, Battelfe-Columbus draft Final Report to U.S. Environ. Protec. Agency, Contract No. 68-02-2957, 1979.
COMPUTATIONS AND STATISTICAL REPRESENTATIONS
This Page Intentionally Left Blank
Atmospheric Pollution 1980, Proceedings of the 14th InternationalColloquium,Paris,France, May 5-8,1980,M.M. Benarie (Ed.), Studies in Environmental Science, Volume 8 0 Elsevier Scientific PublishingCompany,Amsterdam - Printed in The Netherlands
189
DESCRIPTIVE ANALYSIS OF THE SO2 POLLUTION IN BRUSSELS : SEASONAL VARIATION WITH REFERENCE TO SAMPLING SITE LOCATION F.A. SARTOR Environmental Toxicology Laboratory, State University of LiGge (Belgium)
ABSTRACT The daily SO2 concentration has been measured for 5 years in 27 different sites of the built up area of Brussels. These sampling sites have been scored for the presence or absence of four binary variables describing the seasonal variation of the SO2 pollution. A divisive method of classification shows that 25 sites cluster into four dissimilar groups as regards the seasonal variation.
These groups define areas in the agglomeration differing by the human activities pattern and, consequently, the urban structure.
INTRODUCTION In this paper, we investigate the relationship between the seasonal variation of the daily SO
2
distribution function and the location of the SO2 sampling
sites. MATERIAL AND METHOD The daily SO
2
concentrations under consideration have been measured conti-
nuously between Jan 1.1968 and March 31.1973 in 27 points of the built up area of Brussels (1,075,136
inh.), these data being provided by the Belgian air
pollution monitoring network. For each sampling site, a log normal distribution has been fitted to the SO
2
concentration observed in winter and summer periods
(Ref. 1). The probit value of the 50,90,95,98,99
and 99.726 th percentiles,
x , and the corresponding estimated log SO2 concentrations, y, have been used
to compute the slope and intercept of the linear regression y
=
ax + b.
The deviations between the winter and summer values of a and b have been respectively noted da = a - a and db = b - bs. Each site has been scored 1 w s W or 0 according to the presence or the absence of the following variables : Ida1 > 0.1,
ldbl > 1 ,
da > 0 and
db > 0. The 27 x 4 matrix of the attributed
characteristicshas been submitted to the association analysis (Ref. 2, 3).
190 RESULTS da > 0, db > 0 and
Idat > 0.1 are successively selected as significant
variables with this classification procedure : they split the initial set of the sampling sites into four dissimilar groups (Fig. 1, Table I ) . The location of sampling sites and the geographical effect of the clustering appear in Fig. 2.
The mean value and range of the 50 and 95th percentiles within groups, as well as their mean relative decrease during summer period, are given in Table 2.
11 18
I
1,
2 15. 23.
26.
12
In
I
I t
1
IV -1
Fig. 1 - Two-dimensional representation of the classification.
14
191 TABLE I Specific features of the seasonal variation within each group Groups
da >
I I1 111 IV
0 0
1 1
1
1 0
0
db
1
1 = presence or
> 0
Ida1
>
0.1
I 0 0 I
(a)
0 = absence of the feature for all sites of the group
(a) : with the exception of one site (site 4 3 ) TABLE 2 3
Mean values and range of the 5 0 and 9 5 t h percentile (in vg S02/m /day) and relative seasonal variation within group (S.V. in %) Percentile 50th
95th
Group or Site I I1 I11 IV
W i n t e r
S u m m e r
Mean
Range
Mean
197-323 177-384 166-299 113-146
28 32
257.7 267.3 215.3 139 98 81
71.7 104.6 91.8 87 64 42
I I1 I11 IV 28 32
512.9 517.4 423.1 328 286 199
393-680 395-680 339-546 292-316
173.9 214.6 179 164 181 124
-
-
S.V. (a)
Range 57-82 65-179 74-104 61-1 10
-
144-218 140-358 143-205 121-202
-
72.2 60.9 57.4 44.7
66.1 58.5 57.7 56.4
-
(a) : S.V. : mean relative decrease of the 5 0 and 9 5 t h percentile during summer period : xth winter
-
xth summer / xth winter (with x = 50 and 9 5 )
COMMENTS In the groups I (7 sites) and I1 ( 8 sites), the slope of the linear regression
log SO2
-
probit frequency is lower in winter for each site (Table 1 ) . The
magnitude of the deviation between the winter and summer slopes discriminates these two groups : for all sites of the group I, da is greater than 0.1,
in
absolute value, while this is not observed in the group 11. In the group I11 ( 7 sites), the slope of all the regressions is higher in winter. In the groups
I, I1 and 111, the intercepts are higher in winter. In the group IV ( 3 sites)
the slope is higher in winter while the intercept is lower : furthermore, the decrease of the slope in summer is greater than 0.1 for two sites. The Fig. 1 shows that the groups order with the decreasing magnitude of the seasonal variation : in groups I, 11, I11 and IV, the lowering of the mean 50th percentile in summer represents successively 7 2 . 2 , 6 0 . 9 , 57.4 and 44.7 % of the respective winter values (Table 2 ) . An analogous figure obtains
192
'
032
-
F ig. 2 - Geographical location of the sampling site in Brussels and areas speedway; defined by the classification : --- group boundaries;
-
main road.
with the 95th percentile. In winter, the groups I and 11, on the negative side of the da axis, have the highest mean 50 and 95th percentiles and the groups 111 and IV, which are on the positive side of the same axis, have the lowest mean values (Table 2 ) . In summer, the mean 50 and 95th percentiles decrease in the groups which are the most distant of the origin, both sides : the mean 50th percentile, for instance, decreases from 104.6 to 71.7 as regards the groups I1 and I and from 91.8 to 87 as regards the groups 111 and IV (Table 2). From the geographical point of view, the sites of the group I1 are located
193 in the inner city (site 7 excepted) : in this area, the intense administrative and commercial activity implies the daily migration of a lot of non-resident people (Fig.2). This strong human concentration and the consequent intensity of space heating appear as a significant factor in the increase of the SO pollution: 2 during the winter, the highest daily SO2 concentrations are indeed observed in this area. Comparatively to other groups, the summer SO2 concentrations are also higher in this commercial core although significantly reduced vs winter values (Table 2). The sites of the group I are located in the suburban area with the exception of site 2 which stands in an old popular part of the inner city. Data provided by the 1970 Belgian population census show that there are less old houses around the sites of the group I (Table 3). The density of coal heating equipments is nevertheless two fold higher in the "statistical sectors" (municipal subunits) of the group I : this factor may be thus determining in the high seasonal variation of the SO2 emission at the sites of this group. TABLE 3 Old houses and coal heating equipment density around the sampling sites of the groups I and I1 Groups
(a)
(b)
I I1
42.2
26.5 12.5
58.1
(a) : proportion of recorded houses built before 1919 in the statistical sectors around the sampling stations of the concerned group (in %) (b) : density of coal heating equipments in the statistical sectors around the
sampling stations of the concerned group (number of coal heated dwellings by hectare). The sites of the group I11 are located in an industrial area (sites 8, 20, 22), near smaller factories (sites 13 and 16) or on the West and East sides of the suburban area (sites 12 and 17) : in these sites, the topographic, microclimatic and technical features(height of stacks, for instance) seem to favor the pollutant dispersion and reduce, to a certain extent,the SO ground levels. The three 2 sites forming the group IV are located in areas where the building density is very low. The sites 28 and 32 have not been taken into consideration because of their very low SO
2
pollution (Table 2) : they are situated in residential areas.
CONCLUSION A set of 25 sampling points located in the agglomeration of Brussels
have been classified into four groups. The classification requires the computation of two indices from the daily winter and summer SO distribution functions. 2 It may be used to visualize the importance of the pollution seasonal variation,
194 the SO level concentrations according to the season and the urban location 2
of the sampling station. ACKNOWLEDGEMENTS This work was supported by a grant of the Municipal Authorities of Brussels and the National Center for the Study of Air Pollution by Combustion, Brussels, Belgium. We thank Prof. RONDIA D. for his encouragement during the course of this work. REFERENCES I L.M. Malet, A. Joukov, L. Van Der Auwera, H. De Sadeleer, MinistPre de l a Santd Publique et de la Famille, Institut d'HygiSne et d'EpidEmiologie -
MinistPre de 1'Education Nationale et de la Culture Fransaise, Institut Royal Mdtdorologique de Belgique, I.R.M. Publications, 1976, sdrie A, no 95 2 B. Everitt, Cluster analysis, Heineman Educational Books, London, 1974, pp 21-23 3 P.Dagnelie, Analyse statistique 2 plusieurs variables, Presses agronomiques de Gembloux, Gembloux, 1975, pp. 291-294
Atmospheric Pollution 1980, Proceedings of the 14th International Colloquium, Paris, France, May 5-8,1980, M.M. Benarie (Ed.), Studies in Environmental Science, Volume 8 0 Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
195
THE GENERATION OF HOURLY AVERAGE WIND VECTORS USING A MARKOV PROCESS
J.W.
BACON and 8 . HENDERSON-SELLERS
Department o f C i v i l E n g l n e e r i n g University o f Salford S a l f o r d MS 4WT
U.K.
ABSTRACT The s e r i e s o f h o u r l y mean w i n d v e c t o r s i s t r e a t e d as a b i v a r i a t e f i r s t o r d e r Markov P r o c e s s ,
Wind d i r e c t i o n and speed a r e b o t h c o n s i d e r e d as d i s c r e t e
v a r i a b l e s s i n c e t h e d a t a a r e o f t e n o n l y a v a i l a b l e t o t h e n e a r e s t 10' p e r second r e s p e c t i v e l y .
Arra ys o f t r a n s i t i o n p r o b a b i l i t i e s pCi,Jl
assuming t i m e homogeneity [ i . e .
t h e p(;,j)
for a l l
2,J
and m e t r e
are c o n s t r u c t e d
a r e c o n s t a n t w i t h i n each
c a l e n d a r month) and f u r t h e r t h a t t h e r e a r e n o l o n g t e r m s t r e n d s i n t h e t r a n s i t i o n p r o b a b i l i t i e s (over a time period o f the order o f a year]. a r r a y s a r e deduced: one f o r each month o f t h e y e a r ; f u n c t i o n arrays.
Twelve t r a n s i t i o n
and t h e n c e t w e l v e d i s t r i b u t i o n
Random s a m p l i n g w i t h pseudo-random numbers i s t h e n u s e d t o
s y n t h e s i s e s e r i e s o f w i n d v e c t o r s f r o m t h e s e d i s t r i b u t i o n f u n c t i o n a r r a y s which can t h e n be used as one i n p u t t o a s t o c h a s t i c model o f e f f l u e n t d i s p e r s a l f r o m a stack. T h i s g e n e r a l l y a p p l i c a b l e method f o r g e n e r a t i n g t r a n s i t i o n p r o b a b i l i t i e s f o r w i n d speed and d i r e c t i o n i s i l l u s t r a t e d b y a case s t u d y of t h e w i n d f i e l d f o r G r e a t e r Manchester i n t h e U n i t e d Kingdom.
INTRODUCTION
A i r p o l l u t i o n models o f t e n r e q u i r e dynamic m e t e o r o l o g i c a l d a t a as i n p u t , Observed m e t e o r o l o g i c a l c o n d i t i o n s r e p r e s e n t o n l y one s e r i e s o f e v e n t s w h i c h c o u l d happen i n a g i v e n a r e a .
A c c u r a t e average,
be more s u i t e d f o r i n i t i a l model v a l i d a t i o n : Shieh [ r e f .
1).
o r " c l i m a t o l o g i c a l " , d a t a may
a s e n t i m e n t s h a r e d b y S h i r and
T h i s p a p e r d e s c r i b e s a method o f g e n e r a t i n g s e r i e s o f h o u r l y
average w i n d v e c t o r s w h i c h are " t y p i c a l " o f an a r e a .
These v e c t o r s can t h e n be
used i n s i m u l a t i o n e x p e r i m e n t s w h i c h can g i v e p r o b a b i l i t y d i s t r i b u t i o n s o f a i r p o l l u t i o n concentrations,
o r plume t r a j e c t o r i e s ( e . g . r e f . 21.
196 F o r t a k ' s ( r e f . 3 ) model of a i r p o l l u t i o n c o n c e n t r a t i o n s i n t h e Eremen a r e a
o f Germany u s e s s i m u l a t i o n o f t h e w i n d v e c t o r , a l t h o u g h a t e a c h t i m e p e r i o d , t h e d i s t r i b u t i o n of t h e v e c t o r i s a s s u m e d t o be i n d e p e n d e n t o f p a s t e v e n t s .
Stewart
a n d E s s e n w a n g e r (ref. 4 ) p r o d u c e d d i s t r i b u t i o n s o f w i n d s p e e d s n e a r t h e s u r f a c e o f t h e e a r t h , w h i c h , a l t h o u g h u s e f u l f o r many a p p l i c a t i o n s , d o n o t i n c l u d e t h e wind speeds o f t h e p a s t .
T h e m e t h o d o f h o u r l y mean w i n d v e c t o r
g e n e r a t i o n u s i n g t r a n s i t i o n p r o b a b i l i t i e s ( d e s c r i b e d h e r e l . i s b a s e d on a s t o c h a s t i c a n a l y s i s o f w i n d d a t a , a n d g e n e r a t e s a s e r i e s of w i n d v e c t o r s f o r use i n s i m u l a t i o n m o d e l l i n g .
STOCHASTIC PROCESSES I n a d i s c r e t e p a r a m e t e r s t o c h a s t i c p r o c e s s ( w h i c h i s a c o l l e c t i o n o f random variables{X(nl,
1
n e T o v e r a n " i n d e x s e t " T. w h e r e t h e d i s t r i b u t i o n o f X(n1 i s
a f f e c t e d b y t h e d i s t r i b u t i o n of X [ n - t l ,
t > 0 1 t h e r a n d o m v a r i a b l e , X, may b e
u n i v a r i a t e o r m u l t i v a r i a t e , i.e.
[la)
or
X[nl
c
=
x l [ n l , x2(n1
........x k ( n l I
( w h e r e x ( n l i s a r e a l i s a t i o n o f t h e random v a r i a b l e X ( n ) I . The p r o c e s s may b e m u l t i d i m e n s i o n a l . i . e .
X(21
c
.
I
x ( n l l , x(nZ)........x(nR)
or
-X(nl
{::
=
..........x l ( n R 1 x 2 ( n 2 ) .........x Z [ n R 1 x k ( n 2 1 ..........
x ( n l l , xl(nZ1 x2(nll,
x (nll,
: }
:
xk[nR1
f o r t h e u n i v a r i a t e a n d m u l t i v a r i a t e cases r e s p e c t i v e l y .
Markov P r o c e s s e s A g e n e r a l d i s c r e t e p a r a m e t e r s t o c h a s t i c p r o c e s s , i n which p [ X ( n l = x [ n l l
d e p e n d s on x c n - 1 ) .
x(n-ZI......x(O),
i s s a i d t o b e a n R t h . order.
197 Markov P r o c e s s o r Chain i f p [ X ( n ) = x ( n l ] depends o n l y on t h e p r e c e d i n g R v a r i a b l e s , i . e . on x(n-11, x(n-21....
..x(n-Rl(e.g.
refs. 5, 6 ) .
Thus:
A f i r s t o r d e r Markov Chain is t h e r e f o r e d e f i n e d by:
Extending t h i s t o t h e b i v a r i a t e , b u t s t i l l one d i m e n s i o n a l c a s e g i v e s , f o r a f i r s t o r d e r process:
I f t h e random v a r i a b l e s X1X2
a r e confined t o d i s c r e t e values, corresponding t o
a number of p o s s i b l e s t a t e s , E a b ,
a,b=1,2....
and t h e i n d e x s e t i s t a k e n t o be
d i s c r e t e time u n i t s , t h e n t h e p r o c e s s can b e denoted a s b e i n g i n s t a t e ( a , b l a t
time n by:
Eab
- E'")
-i
where
=
(a,b)
-
I f t h e p r o b a b i l i t y o f a t r a n s i t i o n from E I n ' t o
a t t i m e n is w r i t t e n as:
t h e n t h e a r r a y of t r a n s i t i o n p r o b a b i l i t i e s a t time n i s :
W I N D DATA
T h e wind d a t a m u s t b e p r e s e n t e d [ f o r a n a l y s i s i n t h e computer program) i n
terms of h o u r l y a v e r a g e v a l u e s o f wind d i r e c t i o n , t o t h e n e a r e s t 10'. s p e e d , t o t h e n e a r e s t m e t r e p e r second.
and wind
( T h i s i s t h e s t a n d a r d format u s e d by
t h e United Kingdom M e t e o r o l o g i c a l O f f i c e ) .
I n t h i s form, both a r e d i s c r e t e
v a r i a b l e s , o v e r a d i s c r e t e index set (each h o u r ) .
Although t h e o r e t i c a l l y wind
198 speed may t a k e any ( d i s c r e t e i n t h i s c a s e ) v a l u e g r e a t e r t h a n o r e q u a l t o z e r o , f o r p r a c t i c a l p u r p o s e s i t may be r e g a r d e d as h a v i n g a f i n i t e maximum v a l u e . [ T o d e m o n s t r a t e t h e a p p l i c a b i l i t y o f t h e model, d a t a f r o m Manchester Weather C e n t r e w i l l be used. recorded a t t h i s s i t e , possible (ilea
The maximum w i n d speed o f 40 m/s was t h e h i g h e s t e v e r ( i n J a n u a r y 1 9 6 7 1 and is t a k e n h e r e t o be t h e maximum
t h a t o c c u r i n g w i t h n o n - n e g l i g i b l e p r o b a b i l i t y ] f o r model
v e r i f i c a t i o n using these s i n g l e s i t e data). a bivariate,
f i r s t o r d e r Markov Chain.
The w i n d v e c t o r may be r e g a r d e d as
A t r a n s i t i o n array f o r t h e wind vector
c a n t h e n be c a l c u l a t e d f o r each c a l e n d a r month,
using data f o r the r e l e v a n t
month f o r each p a s t y e a r f o r w h i c h d a t a a r a a v a i l a b l e . from the b i v a r i a t e state
t o the bivariate state
t h e number o f t i m e s t h a t t h i s t r a n s i t i o n i s made,
J
The t r a n s i t i o n p r o b a b i l i t y i s deduced b y o b s e r v i n g
T h i s method g i v e s an u n b i a s e d
maximum l i k e l i h o o d e s t i m a t e o f t h e t r u e t r a n s i t i o n p r o b a b i l i t y ( s e e Appendix f o r proof).
I t must be assumed t h a t t h e Markov Chain r e p r e s e n t i n g t h e w i n d
v e c t o r i s t i m e homogeneous w i t h i n each c a l e n d a r month,
P = -n
,P
for all
i.e.
n
(71
- the transition probabilities
do n o t change w i t h i n each month,
I t i s f u r t h e r assumed t h a t t h e p r o c e s s i s s t a t i o n a r y w i t h r e s p e c t t o a t i m e p e r i o d o f a year;
i.e.
f o r a g i v e n month, t h e t r a n s i t i o n p r o b a b i l i t i e s remain
t h e same o v e r a l l t h e y e a r s f o r w h i c h d a t a a r e a v a i l a b l e . A l t h o u g h i t i s now acknowledged t h a t c l i m a t i c change o c c u r s o v e r t h e c e n t u r i e s , o r even o v e r decades,
t h e g r e a t e r i n f l u e n c e on t h e urban w i n d f i e l d
may w e l l be [ o v e r a p e r i o d o f 1-20 y e a r s 1 t h e development o f mesoscale topography and t h e u r b a n h e a t i s l a n d .
( I n d e e d i t has been s u g g e s t e d [ r e f . 7 1 t h a t such
m e t e o r o l o g i c a l changes have c o n t r i b u t e d d i r e c t l y t o t h e d e c l i n i n g p o l l u t i o n l e v e l s i n t h e U n i t e d Kingdom s i n c e 1 9 5 6 ( t h e d a t e o f t h e Clean A i r A c t ) and t h a t t h e e f f e c t s o f t h e A c t i t s e l f have been f a r o u t w e i g h e d b y a c o m b i n a t i o n o f s o c i o economic t r e n d s (e.g.
ref.
81 and changes i n dominant w e a t h e r t y p e ) .
Thus,
a l t h ough t h e assumption o f s t a t i o n a r i t y w i t h r es pec t t o a t im e p e r i o d o f a year c a n n o t be s t r i c t l y j u s t i f i e d , t h e wind vector,
i n t h e absence o f a n a l y s i s o f s h o r t t e r m t r e n d s i n
t h e a s s u m p t i o n must be made.
I t s h o u l d be p o s s i b l e , however,
t o i n c l u d e a t r e n d i n t h e model a t a l a t e r d a t e , when s h o r t - p e r i o d v a r i a t i o n s a r e b e t t e r understood. Twelve t r a n s i t i o n a r r a y s a r e t h u s formed,
one f o r each c a l e n d a r month,
(The d a t a a r e a l r e a d y t a b u l a t e d w i t h i n months b y o b s e r v e r s a t Manchester Weather Centre].
Also,
i t was t h o u g h t t h a t a l o n g e r p e r i o d w o u l d produce u n a c c e p t a b l y
l a r g e errors i n t h e t r a n s i t i o n p r o b a b i l i t i e s o w i n g t o non-homogeneity and t h a t
a s h o r t e r p e r i o d w o u l d p r o d u c e l a r g e e r r o r s o w i n g t o an i n c r e a s e d v a r i a n c e o f the estimates o f t h e p r o b a b i l i t i e s .
199 SIMULATION OF SERIES OF WIND VECTORS To form s e r i e s o f h o u r l y a v e r a g e wind v e c t o r s , samples must be t a k e n from t h e t r a n s i t i o n a r r a y s , w h e r e e a c h t r a n s i t i o n a r r a y may be thought o f a s a c o l l e c t i o n of conditional frequency function a r r a y s ; t h e array element:
Sampling i s a c h i e v e d by u s i n g t h e c o n d i t i o n a l
p r o b a b i l i t y t e c h n i q u e [ r e f . 91
viz :
f o r a bivariate distribution.
I n t h e case of t h e conditional frequency functions,
t h i s is w r i t t e n :
Sampling fmm a b i v a r i a t e d i s t r i b u t i o n i s t h u s r e p l a c e d by sampling from two univariate (conditional 1 distributions.
T h e g e n e r a l method o f sampling from a d i s t r i b u t i o n i s t o form t h e i n v e r s e d i s t r i b u t i o n f u n c t i o n , F - l ( r ) o f a ( g e n e r a t e d ) random number r , such t h a t :
F o r e a c h t r a n s i t i o n a r r a y two c o n d i t i o n a l d i s t r i b u t i o n f u n c t i o n a r r a y s , ( t h e m a r g i n a l ' d i s t r i b u t i o n f u n c t i o n o f d i r e c t i o n and t h e c o n d i t i o n a l '
distribution
f u n c t i o n o f s p e e d ) a r e formed.
A random number, r l , i s g e n e r a t e d on [0,1]
and a v a l u e of d i r e c t i o n i s found
from i t s m a r g i n a l d i s t r i b u t i o n f u n c t i o n a r r a y ( s e e eqn. (1011. number, rz, i s t h e n g e n e r a t e d on
LO.11
A second random
and a v a l u e f o r speed found from i t s
c o n d i t i o n a l d i s t r i b u t i o n f u n c t i o n a r r a y [ c o n d i t i o n a l on t h e v a l u e o f d i r e c t i o n already produced).
'Although " m a r g i n a l " and " c o n d i t i o n a l " a r e used here as f o r a b i v a r i a t e d i s t r i b u t i o n , i t i s i m p l i e d t h a t b o t h m a r g i n a l and c o n d i t i o n a l d i s t r i b u t i o n s a r e a l s o c o n d i t i o n a l on ( i o ,Ill. t h e v a l u e o f . t h e wind v e c t o r d u r i n g t h e * p r e v i o u s t ime p e r i o d .
200
G e n e r a t i o n o f random numbers on TO,l] S i n c e , f o r t h e p u r p o s e o f e x p e r i m e n t a t i o n , i t would be an advantage t o r e p e a t any g e n e r a t e d s e r i e s of random numbers, pseudo-random numbers a r e used.
There
a r e s e v e r a l methods f o r g e n e r a t i n g these [ s e e e . g . r e f s . 1 0 , 111. a l t h o u g h one o f t h e most s t r a i g h t f o r w a r d , which a l s o produces l o n g s e r i e s w i t h o u t d e g e n e r a t i o n .
i s t h e r e s i d u e c l a s s method [ a l s o known a s t h e congruence method).
In this,
pseudo-random numbers, ri, a r e g e n e r a t e d by:
where
= a
pi
t
kZ
p o u s u a l l y e q u a l s 1, a l t h o u g h d i f f e r e n t s e r i e s may be o b t a i n e d by a l t e r i n g t h i s .
a , t , k , and z a r e s e l e c t e d c o n s t a n t s : r e f . 1 0 g i v e s k = 2 , z = 4 0 , a = 5 and
t
=
on
”
By t h i s method a d e t e r m i n i s t i c sequence o f numbers
17 a s s u i t a b l e values,
[0.11
is generated;
t h e numbers have no s i g n i f i c a n t d e v i a t i o n from randomness.
Top - h a t ” s amp 1i n g t e c h n i q ue
I n i t s s i m p l e s t form t h i s method c o n s i s t s o f having a number o f c o u n t e r s on e a c h o f which i s w r i t t e n a v a r i a t e v a l u e .
T h e number o f c o u n t e r s w i t h each
v a l u e i s i n p r o p o r t i o n t o t h e p r o b a b i l i t y of t h a t v a l u e . placed i n a top-hat
The c o u n t e r s a r e
( n a t u r a l l y ! ] and one i s drawn a t random.
on t h i s c o u n t e r i s t a k e n a s t h e sample from t h e d i s t r i b u t i o n . be r e p l a c e d i n t h e t o p - h a t
The v a r i a t e value The c o u n t e r may
and t h e p r o c e s s r e p e a t e d a s many t i m e s a s d e s i r e d .
T h i s method may b e automated [ s e e e . g .
r e f . 91.
Consider t h e d i s t r i b u t i o n
i n F i g . 1. Each s q u a r e i n t h e h i s t o g r a m i s l a b e l l e d a c c o r d i n g t o i t s v a l u e and a l s o g i v e n a s e r i a l number [shown i n Fig. 1 i n t h e t o p l e f t - h a n d c o r n e r ) . be s e e n a s s i m i l a r t o t h e r a t h e r c r u d e method o u t l i n e d above.
This
However, i n s t e a d
of p l a c i n g t h e s q u a r e s i n a t o p - h a t , t h e i n f o r m a t i o n i s f i r s t compressed Table 1, which g i v e s o n l y t h e ” c r i t i c a l ” p o i n t s o f t h e histogram.
TABLE
1
Compressed h i s t o g r a m i n f o r m a t i o n
Variate value,
v
1
2
3
4
5
S e r i a l number,
s
1
2
4
0
10
-
201
f
SET
x=v
STOP
.
202 T h e s e " c r i t i c a l " p o i n t s a r e t h e s e r i a l numbers o f t h e items a t which t h e
If a random i n t e g e r i s
v a r i a t e value changes, t o g e t h e r with t h e v a r i a t e value, t h e n s e l e c t e d from [l,lO]
t h e n t h e f l o w c h a r t ( F i g . 21 d e s c r i b e s t h e s e l e c t i o n o f
a v a r i a t e v a l u e from t h e d i s t r i b u t i o n .
I n essence t h i s method f i n d s t h e column
o f t h e h i s t o g r a m ( F i g . 11 i n w h i c h t h e s e r i a l number ( g i v e n by t h e random number1 belongs.
As may b e s e e n , t h i s i s a d i s c r e t e c a s e e x a m p l e o f t h e g e n e r a l method.
The method i s e q u i v a l e n t t o e q n . (111, b u t h a s t h e a d v a n t a g e t h a t no a n a l y t i c a l f o r m f o r t h e i n v e r s e d i s t r i b u t i o n f u n c t i o n n e e d be f o u n d .
COMPUTER MODEL Form o f i n p u t
The w i n d d i r e c t i o n d a t a f o r e a c h month, i n t h e f o r m o f a s e r i e s o f two d i g i t i n t e g e r s are i n p u t t o a c o m p u t e r f i l e , e a c h l i n e of which h o l d s t h e d a t a f o r a day.
C o r r e s p o n d i n g f i l e s f o r wind s p e e d are a l s o f o r m e d .
These f i l e s a r e r e a d
t o g e t h e r by t h e p r o g r a m , a n d f o r e a c h t r a n s i t i o n f r o m w i n d d i r e c t i o n and s p e e d i n o n e h o u r t o wind d i r e c t i o n a n d s p e e d i n t h e n e x t h o u r , t h e r e l e v a n t e l e m e n t of t h e t r a n s i t i o n a r r a y is incremented.
(However, i n o u r c a s e s t u d y t h e d a t a a r e
i n c o m p l e t e ; t h e r e are p e r i o d s f o r which t h e d i r e c t i o n , o r s p e e d , o r b o t h are c o d e d a s 9 9 , w h i c h means t h a t t h e wind was v e r y g u s t y d u r i n g t h a t h o u r and so no mean c o u l d be f o u n d .
Such d a t a p a i r s are i g n o r e d by t h e p r o g r a m ) .
A f t e r processing,
i n t h i s way, a l l t h e d a t a r e l a t i n g t o t h e month u n d e r c o n s i d e r a t i o n . a t r a n s i t i o n p r o b a b i l i t y a r r a y c o u l d be made by f o r m i n g :
where n [ i O i l , j, jl) i s t h e number of t r a n s i t i o n s f r o m d i r e c t i o n
t o d i r e c t i o n j, a n d s p e e d j,. t r a n s i t i o n s from iD, il,
The d e n o m i n a t o r i n e q n .
io a n d s p e e d il
[ 1 4 1 i s t h e sum o f a l l
However, since it is r e q u i r e d t o s a m p l e f r o m t h e
d i s t r i b u t i o n , t h e m a r g i n a l d i s t r i b u t i o n f u n c t i o n o f d i r e c t i o n i s formed d i r e c t l y , viz:
203
r=rmin s=smni
-
rmax
%ax
x'5r=r min
(151
n [ i O il,rsl
s=s min
and s i m i l a r l y , t h e c o n d i t i o n a l d i s t r i b u t i o n f u n c t i o n o f wind speed i s formed. i n accordance w i t h eqn.
[lOl. These d i s t r i b u t i o n f u n c t i o n arrays a r e then used
f o r sampling, u s i n g t h e methods p r e v i o u s l y described.
R e s u l t a n t s e r i e s o f wind v e c t o r s Although wind v e c t o r s are r e a l l y r e q u i r e d t o t h e nearest 10'
f o r d i r e c t i o n and
metre p e r second f o r speed [ t h e accuracy o f t h e raw data1 t h i s r e s u l t s i n t r a n s i t i o n s from a p o s s i b l e 36x41 s t a t e s t o 36x41 s t a t e s f o r the vector. very l a r g e d i s t r i b u t i o n f u n c t i o n a r r a y s would be r e q u i r e d s i m u l a t i o n [ r e f . 91.
Thus
- a major o b s t a c l e i n
However, i t i s suggested t h a t a f u n c t i o n a l approximation
may be made t o the i n v e r s e d i s t r i b u t i o n f u n c t i o n . e . g . :
F-l
[sl= A
+
Bs
+
Cs2
+
ufl-sI2 l o g s
where t h e c o e f f i c i e n t s A,
+
Bs2 l o g [l-sl
(161
8, C, a and f3 are determined by l e a s t squares methods.
The l o g a r i t h m i c terms may be removed from eqn.
[ 1 6 ) and a polynomial i n s f i t t e d ,
and although convergence is l i k e l y t o be less r a p i d than w i t h eqn. o f f u n c t i o n i s o f t e n e a s i e r t o f i t [ s e e e.g.
[ I 6 1 t h i s type
r e f . 121.
S t r a i g h t f o r w a r d storage and sampling may be used i f a coarser grouping o f t h e s t a t e s o f wind d i r e c t i o n and speed i s taken.
I t i s found t h a t t h e computer
storage requirement i s n o t p r o h i b i t i v e l y l a r g e i f d i r e c t i o n i s taken t o t h e n e a r e s t 20'
and speed t o t h e n e a r e s t two metres p e r second.
I t can be e a s i l y
shown, by a p p l i c a t i o n o f t h e p r o b a b i l i t y axioms, t h a t t h i s coarser grouping a l s o g i v e s r i s e t o a Markov Chain.
I n i t i a l l y t h i s a c t i o n o f t a k i n g a coarser grouping
has been adopted, w h i l e work continue w i t h t h e s i m u l a t i o n o f v e c t o r s t o t h e n e a r e s t 10'
and one metre p e r second u s i n g t h e curve f i t t i n g techniques o f Eqn.
[ 1 6 1 and o t h e r methods.
204 CONCLUSION I n o r d e r t o generate h o u r l y average wind vectors, wind v e c t o r and a number [ O , l ]
t h e model r e q u i r e s a s t a r t i n g
t o i n i t i a l i z e t h e random number generator.
The
l e n g t h o f series o b t a i n e d can be a r b i t r a r i l y selected,
as required.
v e c t o r s so generated may then be used as one i n p u t to,
f o r example, a model o f
a i r p o l l u t i o n d i s p e r s i o n (8.g.
ref. 1) o r a plume r i s e model Ie.g.
A series o f
ref. 21.
In
these models m e t e o m l o g i c a l data a r e used, b u t by use o f a generated s e r i e s of wind v e c t o r s many p o s s i b l e s e r i e s o f i n p u t s become possible,
thus g i v i n g g r e a t e r
f l e x i b i l i t y t o t h e model.
I t has been suggested ( r e f .
3 3 ) t h a t a measure o f atmospheric s t a b i l i t y should
be i n c l u d e d i n t h e generated s e r i e s .
U n f o r t u n a t e l y , the s t a b i l i t y i s o f t e n n o t
e x p l i c i t l y measured a t most U n i t e d Kingdom weather s t a t i o n s and so one must make an e s t i m a t i o n from e x i s t i n g data.
I t i s hoped t h a t i n the f u t u r e t h i s can be
i n c l u d e d so t h a t t h e model w i l l be capable o f producing comprehensive s t o c h a s t i c h o u r l y average i n p u t data f o r d i s p e r s i o n models.
205 APPENDIX
It i s shown h e r e t h a t t h e e s t i m a t e d t r a n s i t i o n p r o b a b i l i t i e s u s e d i n t h i s p a p e r a r e u n b i a s e d , maximum l i k e l i h o o d e s t i m a t e s of t h e p o p u l a t i o n p a r a m e t e r s .
refs. 11, 14) i s :
The l i k e l i h o o d f u n c t i o n [see e . g . N- 1
( 171
t=O
w h e r e t h e p r o d u c t i s t a k e n o v e r a l l t h e N t r a n s i t i o n s t h a t are made. [p[i,
J)It
corresponds t o t h e t r a n s i t i o n a t time t, i.e.
t r a n s i t i o n a r r a y element f o r a t r a n s i t i o n f r o m s t a t e
is t h e s t a t e a t time t , a n d J i s t h e s t a t e a t time t If t h e o b s e r v e d number of t r a n s i t i o n s f r o m s t a t e
i +
2
pCi,
JI
to state
is the
J, w h e r e
i
1 [t
J i s n ( i , $1
t h e n t h e l i k e l i h o o d f u n c t i o n becomes:
w h e r e t h e p r o d u c t i s now t a k e n o v e r a l l t h e
i,J. (191
T h i s m u s t be maximised, s u b j e c t t o t h e c o n s t r a i n t :
Using Lagrangian m u l t i p l i e r s :
(221
(231
where p(L,
a1 h a s
b e e n r e p l a c e d by
w h i c h s a t i s f i e s em. (221.
&
p ( i , J1
t o show t h a t t h i s i s an estimate
(241
This i s normalised t o g i v e A
p(i.
1) =
nu&.
1)
ZncL,
-j
(26 I
JI
Furthermore t h i s i s an unbiased e s t i m a t e o f p(&,
=
E[n(&.
P(LI
=
PCL. JI
5,3 N
,
I S nc
!:
where p ( i ) i s t h e p r i o r p r o b a b i l i t y
of b e i n g in s t a t e
2
I271
207
REFERENCES C.C. S h i r and L.J. S h i e h , J o u r n a l o f Applied Meteorology, 13[19741185-204. 0. H e n d e r s o n - S e l l e r s , E c o l o g i c a l Modelling. 9c1980143-56. H.G. F o r t a k , P m c . Symposium on M u l t i p l e - S o u r c e Urban D i f f u s i o n Models, 1970, USEPA, APCQ. Publ. No. AP86. 4 D.A. S t e w a r t and O.M. Essenwanger, J o u r n a l o f Applied Meteorology. 17(19781 1633-1642. 5 S. K a r l i n and H.M. T a y l o r , A F i r s t Course i n S t o c h a s t i c P r o c e s s e s , John Wiley and Sons I n c . , 1975. 6 L. Takacs, S t o c h a s t i c P r o c e s s e s [ t r a n s . P. Z a d o r l , Chapman and H a l l Ltd., 1978. 7 D.M. Elsom, L e c t u r e p r e s e n t e d t o t h e Royal M e t e o r o l o g i c a l S o c i e t y , Manchester, 6 t h Oec., 1979. 8 A. A u l i c i e n s and I. B u r t o n , Atmospheric Environment, 7(197511063-1070. 9 K.D. Tocher, T h e A r t o f S i m u l a t i o n , E n g l i s h Universities P r e s s Ltd., 1963. 10 0. Teichmw, American S t a t i s t i c a l A s s o c i a t i o n J o u r n a l , flarch(1965127-49. 11 M. Kendall and A. S t u a r t , T h e Advanced Theory o f S t a t i s t i c s , 3 r d Edn.. Vol.11. C h a r l e s G r i f f i n and Co. Ltd., 1973. 12 M. Kendall and A. S t u a r t , The Advanced Theory o f S t a t i s t i c s . 4 t h Edn., V o l . I , C h a r l e s G r i f f i n and Co. Ltd., 1977. 13 F.P. Williams, P e r s o n a l Communication, 1979. 1 4 P. Hoel. I n t r o d u c t i o n t o Mathematical S t a t i s t i c s , 4 t h Edn., John Wiley and Sons I n c . , 1979.
1 2 3
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Atmospheric PoElution 1980,Proceedingsof the 14th InternationalColloquium,Paris,France, May 5-8,1980, M.M. Benarie (Ed.), Studies in EnvironmentalScience,Volume 8 0 Elsevier Scientific Publishing Company,Amsterdam - Printed in The Netherlands
209
AN EMPIRICAL. DESCRIPTION OF THE EXTREME VALUES OF SO2 CONCENTRATION IN AN URBAN AREA G. DRUFUCA CSTS del CNR del Politecnico di Milano M. GIUGLIANO Istituto di Ingegneria Sanitaria del Politecnico di Milano, Via Gorlini 1 20151
- Milano
(Italia)
ABSTRACT In this work we have analyzed 21 time series of SO concentration for the winter 2 semester from 1 9 7 2 to 1 9 7 9 collected at 3 locations in the urban area of Milan, with the aim to investigate the behaviour of the probability distributions of SO2 concentration versus the integration time. We have found profitable to relate directly the quantiles to the various parameters among which the seasonal average concentration has been found to have a dominating role. It has been possible to obtain a simple and accurate descriptive model which computes the quantiles given the probability, the integration time and the seasonal average. Thus this model allows to obtain detailed and accurate informations about extreme values of concentration from a datum simple and easily obtained as the seasonal average concentration.
INTRODUCTION Air quality evaluation can be based usefully upon the extreme quantiles of the pollutant concentration (ref. 1).
Infact their measurement describes meaningfully
the most severe conditions of air quality, similarly to the maximum values, but the quantiles are less affected by statistical variability and by instrument malfunction, more so for low integration times. It is common to evaluate the quantiles from distribution models which in turn are derived from the data. We have found that this approach is not profitable for the evaluation of maximum values (ref. 2 ) , and also for the evaluation of the lower quantiles. Instead we have preferred to derive directly the quantiles from the data and to describe them through an empirical model which results to be simple and easy to use.
RESULTS It has been found by the authors that most of the statistics of SO2 concentrations
210 in an urban area depends upon the seasonal average concentration
(refs.2-4).
In particular the quantiles of the SO2 concentration distribution will depend upon the integration time as well. Therefore we try to describe the relation:
Q
=
Q (P, F ,
(1)
t)
where Q is the quantile in ppm, P is the probability defining the quantile in %,
-C is the winter semester (October-March)
average concentration in ppm and t is
the integration time in hours. Figs. 1, 2 and 3 show the observed quantiles versus ? for different values of P and t.
0.6
0.5
0.4
0.3
0.2
0.1
SIX-MONTH AVERAGE CONCENTRATION
__ F i g . 1.
E . ppm
The observed quantiles versus ? for three different values of P,for t
=
1 h.
The data are taken from 20 of the 2 1 time series of SO2 concentration for the winter semester from 1972 to 1979 collected a 3 locations in the urban area of Milan (the climatological meaning of these data is discussed in ref. 3.)From these figures it appears that the quantiles display a markedly linear dependance upon
-C and a regular Q
=
4 x P
-
O.+
dependence upon P and t. Linear regression allows to formulate:
- 0.056
Which i s represented by straigth lines in figs. 1-3.
(2)
211
0.05 SIX-MONTH
pip. 2 .
0.20
0.25
AVERAGE CONCENTRATION
E , ppm
0.10
The observed quantiles versus
0.15
for three different values of P and for t=4h
This model slightly overestimates the higher quantiles such as 50%. In this case can be more precise the alternative: 0.417 0.056 9 = 4.6 x P C x t (3)
-
-
-
It is interesting to note that a similar behaviour has been found for the maximum value of concentration CM in a semester (ref. 2 ) : CM
=
6.9 x
x t
- 0.232
(4)
212
SIX-YOIIIH NERAGE COWCENTRATION
Fig. 3.
The observed quantiles versus
E . pprn
for three different values of P and for t = 2 4 h
REFERENCES
1 L.J. Brasser, Proc. of 4th Int. Clean Air Congress, Tokio 1977, pp. 1061-1064. 2 Drufuca G. and Giugliano M., Atm. Environment, 12 (1978) pp. 1901-1905. 3 Drufuca G. and Giugliano M., Atm. Environment, 11 (1977) pp. 729-735. 4 Drufuca G., Giugliano M. and Torlaschi E., to be published on Atmospheric Environment.
Atmospheric Pollution 1980, Proceedings of the 14th International Colloquium, Paris, France, May 5--8,1980, M.M. Benarie (Ed.), Studies in Environmental Science, Volume 8 0 Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
213
RANDOM SAMPLING AGAINST CONTINUOUS MONITORING FOR A I R QUALITY MONITORING NETWORKS J.G. KRETZSCHMAR and G. COSEMANS
Nuclear Energy Research Centre, B 2400 Mol ( B e l g i e )
ABSTRACT Based on some mathematical m a n i p u l a t i o n s o f t h e p r o p e r t i e s o f t h e
lognormal
d i s t r i b u t i o n i t i s shown t h a t c e r t a i n sampling schemes can g i v e t h e most important p a r t o f t h e i n f o r m a t i o n one i s l o o k i n g f o r i n many a i r p o l l u t i o n m o n i t o r i n g n e t works.
The soundness of t h e t h e o r e t i c a l conclusions i s i l l u s t r a t e d by means o f
d i f f e r e n t p r a c t i c a l examples taken from e x i s t i n g non-automatic as w e l l as from automatic m o n i t o r i n g networks.
INTRODUCTION The continuous o p e r a t i o n o f automatic as w e l l as non-automatic m o n i t o r i n g n e t works i s r a t h e r expensive, t i m e consuming and l a b o u r i n t e n s i v e .
Although t h e
o b j e c t i v e s o f q u i t e a l o t o f m o n i t o r i n g networks impose a continuous operation, and sometimes even a continuous on-1 i n e data a c q u i s i t i o n and i n t e r p r e t a t i o n ,it i s a l s o t r u e t h a t a continuous o p e r a t i o n f o r c e r t a i n networks i s merely a waste o f time and money, e s p e c i a l l y when one r e a l i z e s t h a t q u i t e o f t e n o n l y a v e r y lim i t e d amount o f i n f o r m a t i o n i s o b t a i n e d from t h e a v a i l a b l e data.
As an example
one c o u l d mention t h e general survey networks wherein a l o t o f e f f o r t s a r e spent f o r t h e p r e c i s e d e t e r m i n a t i o n o f y e a r l y averages, w h i l e t h e "general survey purpose" does n o t a t a l l r e q u i r e such a p r e c i s i o n .
Another example i s u s i n g a l l
t h e a v a i l a b l e means t o o b t a i n a complete data s e t i n a s i n g l e s i t e , whereas
for
t h e purposes o f t h e survey t h e s p a t i a l v a r i a b i l i t y i n t h e area o r r e g i o n under i n v e s t i g a t i o n i s much more i m p o r t a n t than t h e temporal v a r i a b i l i t y i n t h a t specif i c point. The p r e v i o u s l y mentioned problems a r e n o t new and many d i f f e r e n t i n v e s t i g a t o r s a l r e a d y analysed
t h e advantages and shortcomings o f c e r t a i n sampling
214
schemes ( r e f s . 1 - 9 ) . I t is therefore not the purpose of t h i s paper t o repeat the excellent work t h a t has heen done, b u t t o remind people of the existence of these papers and t o show t h a t under certain circumstances (discontinuous) sampling shemes do work.
THEORETICAL BACKGROUND Based on some elementary s t a t i s t i c a l rules and properties i t can he shown ( r e f s . 1, 2 , 4 and 8) t h a t from the characteristics of a sample o f s i z e n , taken a t random and without substitution from a f i n i t e and lognormally distributed population of s i z e N , the 100 y % confidence interval f o r the Pth-percentile (X,) of the cumulative frequency distribution of the population can be calculated as follows : zp-B xg
<
ss
with :
xp
B = ta y =
1
-
zp+5
<
xg sg
J (N-n)/(N-l)(n-l) Za,
iZ
p/JT(FTJ
the conftdence level o r degree of certainty
ta = the " t - s t a t i s t i c " associated with ( N - l ) ( n - l ) / ( N - n ) dom and a ( I - a ) confidence level
degrees of free-
zp = value of the standard normal variable corresponding with the P t h percentile of a normal distribution (given in tables as a function of P ) and
x s
*
9' g '
sample geometric mean sample geometric standard deviation
X p : Pth-percentile of the population N : population s i z e
n : sample s i z e A s the geometric mean equals the 50th-percentile in a lognormal distribution i t
i s obvious t h a t equation (1) can also be used t o determine the confidence i n terval f o r the population geometric mean m namely : 9
215
SOME PRACTICAL EXAMPLES I n t h e B e l g i a n Network f o r Heavy ' l e t a l s d a i l y averages o f t e n d i f f e r e n t metals were determined on a continuous b a s i s d u r i n g t h e p e r i o d May 1972 (ref.10).
-
A p r i l 1977
Based on t h e a n a l y s i s o f these f i v e years i t was decided t h a t t h e gene-
r a l survey purposes o f t h e network c o u l d be met i f o n l y one o u t o f f i v e successive d a i l y f i l t e r s would be analysed.
Continuous o p e r a t i o n continued nevertheless i n
two o f t h e f i f t e e n s t a t i o n s i n o r d e r t o have t h e p o s s i b i l i t y t o check t h e r e a l lim i t a t i o n s o f t h e sampling scheme. As an example we t a k e t h e p o p u l a t i o n o f t h e d a i l y l e a d l e v e l s over a p e r i o d o f one year f o r one o f t h e two continuous m o n i t o r i n g s t a t i o n s .
Beginning w i t h res-
p e c t i v e l y t h e f i r s t , t h e second, t h e t h i r d , t h e f o u r t h and t h e f i f t h day o f t h e year,five
d i f f e r e n t samples based on t h e above mentioned sampling scheme o f one
f i l t e r every f i f t h day can be made. r e n t samples
For t h e population, as w e l l as f o r t h e d i f f e -
one assumes l o g n o r m a l i t y and c a l c u l a t e s t h e r e s p e c t i v e geometric
.
x ) and geometric standard d e v i a t i o n s (a means (m With these numbers and g' 9 9' t h e formulas (1) and (2) one c a l c u l a t e s t h e 90 % confidence i n t e r v a l s f o r t h e geom e t r i c means and t h e 9 8 t h - p e r c e n t i l e values o f t h e f i v e samples as represented on t h e l e f t s i d e o f f i g u r e 1.
I t i s c l e a r t h a t f o r each sample t h e geometric mean
and ( c a l c u l a t e d ) 9 8 t h - p e r c e n t i l e o f t h e p o p u l a t i o n a r e w i t h i n t h e s p e c i f i e d i n t e r v a l s. On t h e r i g h t h a n d s i d e o f f i g u r e 1 a r e represented t h e geometric mean o f t h e p o p u l a t i o n (m ) and t h e 9 8 t h - p e r c e n t i l e (X.gs) as determined from t h e a c t u a l d i s 9 t r i b u t i o n (by r a n k i n g t h e numbers), t h i s i n c o n t r a s t w i t h t h e c a l c u l a t e d 98thp e r c e n t i l e (assuming p e r f e c t l o g n o r m a l i t y ) on t h e l e f t , t o g e t h e r w i t h t h e a c t u a l values o f t h e geometric means and 9 8 t h - p e r c e n t i l e s determined i n t h e same way f o r t h e d i f f e r e n t samples (no l o g n o r m a l i t y r e q u i r e d ) .
It i s obvious t h a t i n f o u r o f
f i v e cases t h e sample values a r e much c l o s e r t o t h e p o p u l a t i o n values than could be expected from s t a t i s t i c a l c a l c u l a t i o n s based on t h e assumed lognormal i t y . The d e v i a t i o n from l o g n o r m a l i t y i s a l s o c l e a r l y i l l u s t r a t e d by t h e discrepancy between t h e c a l c u l a t e d 9 8 t h - p e r c e n t i l e f o r t h e p o p u l a t i o n ( F i g . 1, l e f t ) and t h e measured 9 8 t h - p e r c e n t i l e ( F i g . 1, r i g h t ) . For t h e proper i n t e r p r e t a t i o n o f t h e r e s u l t s o f t h e f i r s t example i t must be p o i n t e d o u t t h a t t h e sampling scheme i s n o t a random sampling i n " s t r i c t 0 sensu". I n a second example a p e r f e c t random sampling scheme has been used t o show t h e i n f l u e n c e o f t h e sample s i z e upon t h e d i f f e r e n c e s between t h e cumulative frequency d i s t r i b u t i o n o f t h e p o p u l a t i o n t i o n o f t h e samples.
and t h e cumulative frequency d i s t r i b u -
Over a p e r i o d o f s i x months 6832
v a l i d h a l f h o u r l y SO2-
averages were o b t a i n e d from an automatic m o n i t o r i n g s t a t i o n i n an i n d u s t r i a l area w i t h two i m p o r t a n t i n d u s t r i a l S02-sources ( r e f . 11). The cumulative frequency d i s t r i b u t i o n o f t h i s data s e t was determined by r a n k i n g t h e measured concentration
216
values. The r e s u l t i s represented -r’n f u l l l i n e (pop.) on Figure 2. From t h e same data s e t several random samples of size 50, 100 and 200 a r e taken. For each sample t h e cumulative frequency d i s t r i b u t i o n i s determined i n exactly the same way a s f o r t h e population and the results a r e given i n dotted l i n e s on Figure 2. I t can be seen t h a t t h e approxtmation r e a d i l y improves when going from a sample s i z e 50 t o 100 and t o a l e s s e r e x t e n t a l s o by doubling t h e sample s i z e again. For t h e l a t t e r case (n=20O out of N=6832) the overall deviation between the 70thp e r c e n t i l e and the 98th-percentile i s approximately 20 %, while t h e 50th-perc e n t i l e has always t h e exact value. This i s due t o the f a c t t h a t as well the population a s t h e samples have 50 % o r more values helow t h e detection l i m i t of t h e monitor. The a r i t h m e t i c averages of the samples with size 200 a r e within approximately 10 % of the population mean. From this example i t can be concluded t h a t w i t h only 3 % of t h e successive half-hourly values over a period of
*
s i x months i t i s r e a d i l y possible t o obtain an acceptable approximation f o r t h e s t a t i s t i c s of the complete population. CONCLUSION Based on the f i n d i n g s of some previously published work of d i f f e r e n t i n v e s t i g a t o r s i t has been i l l u s t r a t e d by means of two d i f f e r e n t examples t h a t s p e c i f i c sampling schemes could replace continuous monitoring without loosing much of the information one i s looking f o r .
REFERENCES 1 J.Juda and K . Budzihski, Staub-Reinhalt. Luft, 27(1967) 176-179. 2 J.Juda, Staub-Reinhalt. Luft, 28(1968)186- 192. 3 J.Juda, Staub-Reinhalt. Luft, 29(1969)399-403. 4 M.G. N a t r e l l a , Experimental S t a t i s t i c s , Handbook 21,NBS,U.S. Government P r i n t i n g O f f i c e , Washington D.C.,1966. 5 W.E.Hale, A t m . Env., 6(1972)419-422. 6 W.F.Hunt, J r . , J . Air P o l l u t . Control Ass., 22(1972)687-691. 7 D.E.Phinney and J.E.Newman, J . A i r P o l l u t . Control Ass., 22(1972)692-695. 8 J.G.Kretzschmar, The Science of t h e Total Env. , 2(1973)213-221. 9 H.G.MUller und H . Meinl, S t a t i s t i s c h e Methoden zur Beurteilung der Immissionsstruktur, Dornier System GmbH, Friedrichshafen, Dezember 1977. 10 J.G.Kretzschmar, I.Delespau1, Th.I;e Rijck and G. Verduyn, A t m . Env. ll(1977) 263-271. 11 J.G.Kretzschmar, H.Bultynck and H.Peperstraete, i n M.M.Benarie (Ed.), Studies in Environmental Science, Vol . 1, E l s e v i e r S c i e n t i f i c Publishing Company, Amsterdam , 1978, pp .3-6.
217
I 1800
1600
1400, 1200 ' Cr)
E
\
n
LL
,9
1000
2.05
cT
9
800.
2oo
T-
'.98
t I
I
1
2
sample I
I
I
3
4
5
//
//
sam ple I
I
I
I
I
1
2
3
4
5
b
F i g . 1 . Comparison between t h e geometric means and 98th-percentiles of a populat i o n o f s i z e N=365 and f i v e d i f f e r e n t samples o f s i z e n=73.
218
... 0
m
i...
+:
:..o i...
:
.......
............
..........
0 0
m ........I . . .
...........
... ,. . . : ZLi
:..o i...
1 !-; .......
...........
;!
i . . .
...........
........
aJ
R
7
v)
a E
aJ
r
0
c,
rc
n s
h
S
aJ
V
3 0-
F i g . 2. I n f l u e n c e o f t h e sample s i z e upon t h e d i f f e r e n c e s between 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 t h e sample and 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 t h e p o p u l a t i o n .
AIR CHEMISTRY AND FORMATION OF PARTICULATE MATTER
This Page Intentionally Left Blank
AtmosphericPollution 1980, Proceedings of the 14th International Colloquium,Paris,France, May 5--8,1980,M.M. Benarie (Ed.), Studies in Environmental Science,Volume 8 0 Elsevier Scientific Publishing Company,Amsterdam - Printed in The Netherlands
221
PHOTOCHEMICAL AEROSOL FORMATION IN MULTI-COMPONENT SYSTEM CONTAINING PRE-EXISTING PARTICLES
M. KASAHARA, K. TAKAHASHI and S. TOHNO Institute of Atomic Energy, Kyoto University, Uji, Kyoto (JAPAN)
ABSTRACT Photochemical aerosol formation in a heterogeneous multi-component system containing S O P , NO,,
hydrocarbon and pre-existing particles is studied both experi-
mentally and theoretically.
Experiments are conducted for clarifying the role of
pre-existing particles on photochemical aerosol formation by measuring the number concentration and the size distribution of particles. The most dominant gaseous reactant in photochemical aerosol formation is revealed to be SOz, and aerosol formation is affected by the surface area concentration of pre-existing particles. A kinetic model of aerosol formation is presented for the heterogeneous multicomponent system, and simulated calculations using the kinetic model support the experimental results.
INTRODUCTION Atmospheric aerosols consist of both primary and secondary particulate matters. Secondary particles are formed through gas-to-particle conversion in the atmosphere and play an important role in air pollution.
The photochemical aerosol formation
from SO2 is recognized especially important, and special interest has been attracted in this subject last few ten years.
Consequently it has been evidenced that a
mixture of S O 2 and humid air is very reactive for the photochemical aerosol formation. Several investigators have also studied the photochemical aerosol formation in the multi-component system containing S 0 2 , NO,, air pollutants.
and hydrocarbon(HC) which are more common
Some of them, however, show contradictory results as summarized
in our previous report (ref. 1).
Besides, only a few studies have been made on new
aerosol formation in the presence of pre-existing particles (refs. 2-6).
In this study, laboratory tests were conducted on photochemical aerosol formation in the heterogeneous multi-component system containing SO2, NO,, particles(PP),
HC and pre-existing
and numerical calculations were performed applying the kinetic model
of aerosol formation.
222
EXPERIMENTAL Experimental equipment and procedure The apparatus, except for the additional system of pre-existing particle generation, and experimental procedure were almost similar to those described previously (ref. 1). ends. for
The reaction chamber was a 2.5 i! Acrylite cylindrical cell having conical
The inside of the chamber was coated with thin Teflon film.
U.V.
irradiation consisted of four 20 W blacklights.
The light source
Average light intensity
was about 0.15 mW/cm2sr, and this value was roughly equivalent to 0.05 per hour of the specific absorption rate constant of S02. The sample was prepared by adding gaseous reactants and pre-existing particles to purified and humidityadjustedair stream.
SO2
and HC gases were supplied from
gas cylinders, and NO2 gas was generated by using a permeation tube.
Pre-existing
particles were generated using either an electric furnace for metallic fume or a modified Sinclair-LaMer type generater for di-ethyl hexyl sebacate(DEHS1 aerosol. The number concentration of aerosol particles was measured with a condensation nuclei counter(CNC, Environment/One, Model Rich 100) which responds to the particle with diameter lager than 0.0025 pm.
Particle size distribution of aerosols was
determined by an Electrical Aerosol Analyzer(EAA, Thermo-System Inc., Model 3030). Results and discussions The number concentration N of aerosol particles formed newly by
U.V.
irradiation
was measured for the irradiation time up to 500 sec in S02/N02/HC(t-2-butene) /preexisting particle system.
Fig.la depicts the time change of N for various surface
area concentration Spp of pre-existing particles.
Aerosol formation is hindered
by the addition of pre-existing particles and this hindrance effect increases with the increase of S p p .
Similar tendencies are found in the S02/pre-existing particle
system for both the time change of N and the hindrance effect by pre-existing particles as shown in Fig.lb.
This hindrance effect is thought due to the fact that
gaseous matter expected to form new particles may be consumed by condensation onto the pre-existing particles. The number concentration N50 of aerosol particles formed newly by 50 sec irradiation was measured at various concentration of Spp in order to investigate the hindrance effect of pre-existing particles.
The magnitude of Spp was changed by
varying the number concentration of pre-existing particles.
At the irradiation
time of 50 sec, aerosol formation is mostly in the process of "the early stage of reaction" (ref, 7) in which particle formation is considered to be dominant rather than growth as seen in Figs.la and lb.
This implys that the number concentration
in this stage is an indication of reactivity of aerosol formation.
In Fig.2, the relative number concentration of NS0 to
NO,so
is shown as a function
of the surface area concentration of added pre-existing particles, where
is
the number concentration o f newly formed aerosol particles by 50 sec irradiation
223
3 -
-
x 106
spp (vm2/cm3) 0 0
A
3
750 1300
2 h
m I
5
v
L
1
0 0
200
t a) S02(lppm)/N02(0.75ppm)/HC(t-2-CqHg, 3ppm) /PP (DEHS) system
400
600
(sec)
b) S02(lppm)/PP(DEHS)
system
Fig.1. Time change of number concentration of aerosol particles formed photochemically ;R.H.=60%, pre-existing particle=DEHS
- S02/N02/HC/PP --- SO2/PP
.........
system
system Kinetic model
-
O z n ;S = -019 .IO vm2/part. 3 runs ' average
a D E H S ; :=.010- .153 7 runs @Pb;T=.026-.072 5 runs @Pb ; 3 = .033 .067 3 runs
-
11
11
11
Fig.2. Hindrance effect of pre-existing particles on photochemical aerosol formation investigated both experimentally and theoretically ; S02=lppm, N02=0.75ppm, HC(t-z-C4Hg) =3ppm, R.H. = 6 0 % , t = 50sec.
224
in the system of pre-existing particle
x lo6
free. Each curve is the average for 3 to 7 runs in which average surface area S , i.e. particle size, of pre-
- 3
existing particles was changed between
8
0.010 pm2/particle and 0.15 pm2/par-
0
the size of added particles are altered
m
v
2
ticle.
2
Even though the material and
aerosol formation is markedly affected
0
y! z0
when Spp is increased from
lo2
pm2/cm3
to 5 x lo3 pm2/cm3 and almost disappears
1
in the range of S p p larger than 5x103 pm2/cm3.
This is a suggestive finding
of the inverse relationship which is I
# " . I
0 0
0.5
observed often between the number I
1
concentration of initial particles
2
and that of newly formed particles
so2 (PPm)
when the actual atmospheric air is irradiated in a smog chamber (ref. 8).
Fig.3 Effects of SO2 concentration of photochemical aerosol formation in SO21 NO2(0.75ppm)/HC(t-2-CqHg = 3ppm)/PP(Pb) system;R.H.= 6 0 % , t=50sec.
-0
SO,
R.H.
The effect of the concentration of reactant in a case of pre-existing particle either
No.50
N50 1 ppm = 60 %
Spp = 820 pm2]cm3 (Pb
Aerosols)
n
free or added were investigated by keeping S p p constant. In Fig.3, values of N50 and N50/ No,50 are shown as a function of SO2 concentration for various
magnitudes of S p p , and N50 increases remarkably with the increase of SO2 concentration. The effects of the concentration of NO2 and HC is shown in Fig.4 by three dimensional illustration with respect to the axes of N50 and the initial concentrations of NO2 and HC.
0
1.5
3
6
HCgt-2-butene (ppm)
Trans-2-butene is ranked in the highly reactive group of hydrocarbon in terms of the
Fig.4 Three dimensional illustration of photochemical aerosol formation in S02(lppm)/N02/HC (t-2-CqHg)/PP(Pb, S p p = 0 , 820 um2/cm3) system.
photochemical aerosol formation (ref. l), however, aerosol
225
particles are hardly formed by 50 sec irradiation in the system of N02(0.75ppm)/ HC(t-Z-butene=3ppm).
From Figs.2 and 3, SO2 is revealed to be the most dominant
reactant in photochemical aerosol formation as was found in the previous experiment for multi-component system (ref. 1) and for the system of the actual atmospheric air (ref. 8 ) . The magnitudes of N50 and No,so concentration of NO2 and HC.
are influenced in very complicated way by the
However, the value of N501No,50 have a tendency to
increase with the increase of N,,50
as shown in both Figs.3 and 4. This means that
N50/No,50 vs. Spp curve, shown in Fig.2, shifts to the right under the experimental
condition having larger magnitude of No 50.
It was also found, but not being here
illustrated in figure, that the value of N5o/NO,5o at a fixed magnitude of S p p was almost independent of relative humidity ranged from 3 0 % to 95%.
KINETIC MODEL The aerosol formation process was simulated by the kinetic model which is a combination of the photochemical simulation model for S02/NOx/HC system with the kinetic model of aerosol formation (ref. 9).
Sixteen principal reactions adopted
in the present model and their reaction rate constants are given in Table 1. The 14th and 15th reactions are quasi-quenching reactions on the oxidation of SO2, and their reaction rate constants were determined from the previous experimental work (ref. 1). It is assumed in the simulation that nucleation from H2SO4 (SO3)
-
H20 vapor
TABLE 1 Principal reactions adopted in photochemical simulation model for S02/NOx/HC system NOi+hv 0+(02)+(W
NO+Os HC+O
nc+oI
XOz+NO* ROz+NO HC+OH ROa+RO% NOs+OH+(M) SOz+O+(M) SOe+ROa
SOz+OHf(M) SOs+IIC SOs+NO2 SOp+hv
* t
---
NO+O Oa+(M) N02t01 axROl
K, =
/MIN Kz = 4.00E+06 / M I N Ks = 3.00E+01 / P P M / M I N K4 =(6.00E+03) / P P M / M I N -+ a ~ ~ ~ a Ks + =(1.40E-02) ~ 2 /PPM/MIN Ke = 1.00E+00 / P P M / M I N xs N O ~ + ~ X O H K, = ~ . O O E + O Z/ P P n i / m x + cXROz Ks =(6.00E+04) / P P M / M I N --t 22 Ks = 4.00E+03 / P P M / M I N + HNOs+(M) Kio= 1.20E+04 / P P M / M I N -+ SOs+(M) K I I = 2.80E+01 / P P M / M I N t SOs+RO Kiz= l.OOE+OO / P P M / M I N + HOSO*+(M) K n = 7.80Ei-02 / P P M / M I N + xxx Ku=(3.00E-01) / P P M / M I N YYY Klr= 2.00E-01 /PPM/MIN K,r= /MIN ----+ sos -+
-
* t
t
t
?
t f
reaction rate constants depend on light intensity inferential value reaction rate constants and coefficients a, b, and c are depend on the kind of HC; values in ( ) are for HC = 1-butene; in the present model, K4=2.5X104, K5=0.052, Kg=l.lX105, K14=0.3, a=2.5, b=1.25, c=O.95.
226 following the oxidation of SO2 is the dominant process “at the early stage of aerosol formation and that a pre-existing particle has a sink surface for H2SO4 vapor and a reflecting surface for other gaseous matters.
The condensation prob-
ability of H2SO4 vapor molecule onto the particle is an important factor in this simulation, and various values were tried to use for the condensation probability 6 in calculations.
The general tendency, such as the time change of N and the effect of pre-exsisting particles on the photochemical aerosol formation, can be well elucidated by the present kinetic model, but the order of magnitude of various factors depends significantly on the value of 6.
Some of simulated results for the experimental
condition of S0~(lppm)/N0~(0.75ppm)/HC(3ppm)/pre-existing
particles(Spp=variable)
are also drawn in Fig.2, and the value around 0.1 is considered to be most suitable as 6 to the experimental results.
CONCLUSION The photochemical aerosol formation in the heterogeneous multi-component system was investigated both experimentally and theoretically. The most dominant reactant in photochemical aerosol formation is revealed to be S02. The aerosol formation is influenced in very complicated way by concentrations of NO2 and HC.
The presence
of pre-existing particles has a hindrance effect on the aerosol formation and this
hindrance effect can be evaluated as a function of surface area concentration of pre-existing particles.
The kinetic model supports experimental results and may
be helpful in search of photochemical aerosol formation processes.
REFERENCES 1 M. Kasahara and K. Takahashi, in E.T. White (Ed.), International Clean Air Conference, Ann Arbor Science, Michigan, 1978, p.687. 2 K. Takahashi and M. Kasahara, in B.Y.H. Liu (Ed.), Fine Particle, Academic Press, New York, 1976, p.276. 3 K. Takahashi, M. Kasahara and M. Itoh, in K. Takahashi (Ed.), Studies on Particulate Air Pollutants, Report to Toyota Foundation, 1977, p.IC-78 (in Japanese). 4 P.T. Roberts and S.K. Friedlander, Environ. Sci. Tech., 10(1976),573-580. 5 D.L. Fox, M.R. Kuhlman and P.C. Reist, in M. Kerker (Ed.), Colloid and Interface Science, Vol. IC, Academic Press, 1976, p.185. 6 P. Middleton and C.S. Kiang, J. Aerosol Sci., 9(1978)359-385. 7 M. Kasahara and K. Takahashi, Atmospheric Environ., 10(1976)475-486. 8 M. Kasahara and K. Takahashi, Proc. of 20th Annual Meeting of Japan SOC. of Air Pollution, Kobe, Nov. 6-8, 1979, Japan SOC. Air Poll., 1979, p.426 (in Japanese). 9 K. Takahashi, M. Kasahara and M. Itoh, J. Aerosol Sci., 6(1975)45-55.
Atmospheric Pollution 1980, Proceedings of the 14th InternationalColloquium,Pans,France, May 5-8,1980, M.M. Benarie (Ed.), Studies in Environmental Science, Volume 8 0 Elsevier Scientific PublishingCompany,Amsterdam - hinted in The Netherlands
INTERFACIAL PHYSICOCHEMICAL CHARACTERISTICS OF AIRBORNE SOOT PARTICLES.
F. DE WIEST and P.M. BRULL Laboratory of Environmental Toxicology, University of Liege, Belgium
ABSTRACT We describe carbon black and combustion soots surface characteristics. This description may improve our conception of one interfacial structure of airborne soot particles.
INTRODUCTION Studies of airborne soot particles physicochemical reactions bdsorbed polynuclear aromatic hydrocarbon (PAH) photooxidation, interactions between air suspended soots and gaseous pollutants) often reveal complex phenomena (Ref. I ) . A model of the interfacial structure could be a useful reference tool for understanding and explaining these experimental observations. Based on the specific experiments summarized below, the purpose of this paper is to describe the major interfacial characteristics of soot particles. EXPERIMENTAL The following forms of particulate matter were considered : (a) samples of commercial microcrystalline carbon black (oil furnace black T H E W
FLOFORM; particle diameter : 0.25 pm); (b) incomplete natural gas and light fuel oil ( 0 . 4 % S) combustion soot samples prepared in this laboratory (particle diameter : < 0.1 pm). After benzenic extraction of the original T H E W FLOFORM carbon black (type C ) an easily chemically oxidizable sample (type C1) was obtained 0
in order to modify its initial interfacial nature (type C,). Specific surfaces of the samples were measured by low temperature N 2 - Dsbgen method).
adsorption (Haul
Fractional dosage of the original organic matter associated with the blacks and soots was made according to the procedure described by TABOR (Ref. 2)
227
228
Acidic surface groups on the carbon were neutralized with bases of -3 M); in this way, we
varying basicities (NaHC03; Na2C03; NaOH 5.10
differenciated the acidic groups with respect to their pKa values (Ref. 3, 4 ) . Electrochemical experiments were performed with slightly modified polarographic equipment and a bubbling microelectrode made of microcrystalline amorphous carbon whose characteristics closely resembled those of the combustion soots (Ref. 3). Measurement of the amount of water adsorbed on the soot samples was made after a 24-hour equilibrium in constant humidity atmospheres. RESULTS and DISCUSSION 2 The specific surfaces of the particulate samples were : (a) 10.5 m .g-' 2
-1
for the carbon black; ( b ) 156 m*.g-l(sample I ) and 180 m .g (sample 2) 2 for the natural gas soots; (c) 213 m .g-' for the fuel oil soots. F o l l o wing the same sequence, the concentrations of the total organic matter initially present on the particles were respectively : (a) 4mg.g-'; (b) 100 mg.g-l (sample l), 19.5 mg.g-l (sample 2); (c) 37.4 mg.g-l. The data summarized in table 1 give the compositbn of the organic matter associated with the combustion soots. We can see : 1 . that polynuclear aromatic hydrocarbons are the most important fraction; 2. that significant amounts of free aliphatic compounds
are not present; 3. that acidic and
polar compounds are initially present among soot organics; additional organic content analysis carried out on natural gas soots (undetailed in this paper) revealed that acidic and polar fractions consisted mainly of oxygenated PAH derivatives (phenols, diols, quinones). Therefore we can say that the organic matter of combustion soots is essentially of a polyaromatic nature. Carbon blacks and soots are rich in oxygenated groups strongly bonded to the surface of the carbon. Most important and best known among these surface heterogeneities on carbon are carboxyl, hydroxyl and carbonyl functional groups (Ref. 3, 4). Table 2 gives the concentrations of acidic surface groups present on the carbon blacks and soots considered. We can see that the data obtained before and after exhaustive extraction of organic matter do not significantly differ; these observations mean that the surface groups are not
229
TABLE 1 Composition of the organic matter adsorbed on the combustion soots Components
Natural gas soots Sample 1
Acidic Neutral
Fuel oil soots
Sample 2
(I)*
(2)*
13.7
13.7 %
(2) 28.7 %
(I) 5.6
(2) 16.9 %
(1)
6.3
PAH
64.2 64.2 % 8.9 45.6 % 18.9 Polar 22.1 22.1 % 5.0 25.7 % 12.2 Neutral Aliphatic Hydrocarbon 0.0 0.0 % 0.0 0.0 % 0.0 Total 100.0 100.0 % 19.5 100.0 % 37.4 + ( I ) : organic matter concentration in the soots (mg.g-1) * ( 2 ) : relative percentage within the organic matter
50.5 % 32.6 %
0.0 % 100.0 %
TABLE 2 Concentration of acidic surface groups on carbon blacks and combustion sods Particulate sample.
Fraction of the total surface occupied by the surface groups.
Concentration(mole.cm-2) G (a) 1
G2
G3
Carbon black TF Type c0( 1) b,
0 . 12X10-10
Type C l ( 2 )
0 . 1 2 ~ 1 0 - ~0 ~. 0 5 ~ 1 0 - 0~ .~1 4 ~ 1 0 - ~ ~
Oxidized carbon black TF Type C 2 ( 2 )
0.78X10-10
1 . 1 lxlO-lo 0 . 5 9 ~ 1 0 - ~ ~
0.74X1O-I0
1 . 2 0 ~ 1 0 - 0~. ~5 7 ~ 1 0 - ~ ~
Type C with 2 artificially adsorbed PAH(c) Natural gas soots Sample 1 ( I )
0.49
o- 10
0 . 0 3 ~ 1 0 - 0. ~ ~I ~ X I O - ~ ~
0 . 1 3 ~ 1 0 - I~. ~ 47~lO-~O
0 . 3 5 ~o- 10
0 . 2 9 ~ 1 0 - 1~ .~8 5 ~ 1 0 - ~ ~
Sample 2 ( 1 )
0 . 4 8 ~0-lo('
0 . 4 2 ~lo-"
(2) Light fuel oil soots
0 . 2 5 ~0
(2)
-10
A
(1)
0.04x 10- l a d
(2)
0.04x 10-l0
(c)
:
26.0 %
18.3 % 10.4 %
0.45~10-I0 ~.33~10-~~
'
'
o.~8x10-10 0.14x
(a) : G I : pKa 6 6 . 5 ; G2 : 6.5 < pKa 6 8 . 5 ; (b) : ( 1 )
0.36~ lo-'
2.8 %
2.0 %
lo-1o G3 : 8.5< pKa< 10.0
: before organic matter extraction (2) : after extraction
Pyrene, benzo(a)anthracene,
benzo(a)pyrene
:
6 5910 pg.g - 1
( d ) : Natural gas soots : surface groups with pKa< 2.5 : 0.07x10-10mole. -2 -2 cm ; fuel oil soots : 0 . 0 1 5 ~ 1 0 - I mole.cm ~ W2S04 and 0 . 0 4 ~ 1 0 - ~ ~ -2 mole.cm surface groups with pKa < 6.5
230 covered by the original organic matter. Further evidence is given by the oxidized carbon blacks artificially enriched with PAH; Table 2 shows that indeed the amounts of surface groups neutralized before and after PAH adsorption on these particles are very similar. Based on X-ray diffraction studies (Ref. 5 ) , it was shown that the structure of the microcrystalline carbons (such as carbon blacks and soots) consists of graphite-like layers of limited size stacked parallel to each other without further ordering. The various forms of microcrystalline carbon differ in the size of these graphite-like crystallites (from a few ten to a few hundred angstroms) and in their mutual orientation. Our experimental results derived from the carbon blacks and soots can be easily explained if we assume (a) that the oxygenated surface groups on the carbon are bonded only to the edges of the crystallites (peripheral carbon atoms of each graphite-like plane; (b) that the polycyclic compounds are only adsorbed onto the outside lamellar planes of the graphite-like crystallites. Further evidence for this interfacial model and more detailed data were obtained by studying microcrystalline carbon electrochemical reactivity. The results concerning oxygen electroreduction are listed in table 3 . TABLE 3 Factors influencing microcrystalline carbon electroactivity Electrode Processe Studied.
Experimental modifications.
Faradic oxygen discharge NaOH 1 M After benzo(b)pyridine adsorption 350 mv/SCE After CH2N2 treatment
-
of the surface groups id. HC104 0.1 M
-
450 mv/SCE
Cathodic pretreatment leading to the transformation of the surface quinone groups into hydroquinone groups Cathodic pretreatment after chemical destruction of the surface quinone groups with CH N and 2 2 NaBH4
Relative rate of oxygene electroreduction 1
0.8 0.05 1 5.1
No more activation
W e can see : (a) that the chemical transformation of functional
surface groups with specific reagents (CH2N2 acting on p-quinone, carboxyl and hydroxyl groups, NaBH acting on the carbonyl groups) 4
231 greatly affected electrode response; in other words and in a more extended sense we can say that microcrystalline carbon reactivity to foreign substances strongly depends upon the nature and amounts of functional surface groups bonded to the surface (Ref.3);
(b) that the adsorption of a
polycyclic surfactant (benzo(b)pyridine)
on the electrode does not signi-
ficantly modify electroactivity; these facts confirm that the surface groups on the carbon are not covered by the adsorbed organic matter. Taking into account the portion of the surface occupied by the acidic surface groups, it is now easy to estimate the depth of the organic film adsorbed on the combustion soots (assuming that the polycyclic compounds are flat adsorbed on the lamellar planes of the crystallites) : 0
(a) natural gas soots : 3-4 A (6 1 monolayer) for sample 2 and 12 A (3-4 flat polyaromatic layers) for sample 1 ;
(b) light fuel oil soots:
0
3-4 A (
1 monolayer).
The following data, related to water adsorption,
will complete this physico-chemical description of the interfacial structure of the soots considered. Under humidity conditions very similar to those normally encountered in ambiant atmospheres (average values of water vapor pressure : 5 to 6 . 4 mm Hg during the cold season (January-April); 12 mm Hg during the hot season (June-Augustus) ), the soots showed a surprising affinity for water (Table 4 ) . TABLE 4 Water adsorption on combustion soots Particulate sample
Water vapor pressure (mm Hg)
.,
5.6 14.1
Natural eas soots
t ("C)
Weight of adsorbed water (mg.g
7 20
-1
H,O/HPA(*) L
)
12.0 25.2
17 37
Fuel oil 5.6 7 10.4 soots 14.1 20 20.8 ( a ) : number of H 0 molecules for one HPA molecule.
6 12
2
The presence of water and very acidic components on soot particles (table 2
shows (a) that 6% of the total acidic surface groups on natural
gas soots have pKa below 2.5;
(b) that significant amounts of a strong
mineral acid (H SO ) are found on fuel oil soots) leads us to expect very 2
4
low pH values for the airborne soot particles interface (pH < 2 ) . These interfacial characteristics will influence the interactions and chemical pathways between airborne soots and gaseous pollutants. Moreover, low surface pH will favour the influence of catalytic oxidation cycles 2+
controlled by redox-coupled components such as Fe
/Fe3+ (metallic traces
on fuel oil soots) or quinone-hydroquinone (surface groups on natural
232
gas s o o t s ) (Ref. 3). ACKNOWLEDGEMENTS We are indebted to the Commission of the European Communities for this research carried out under contract no 162-77-I-Env. B. REFERENCES 1
2 3
4 5
F. De Wiest, Proceedings of the European Symposium on the PhysicoChemical Behaviour of Atmospheric Pollutants - I S P M 16th-18th October 1979 (in press) E.C. Tabor, T.E. Hauser, J.P. Lodge and R.H. Burttschell, A H A . Arch. Ind. Health, 17 (1968) 58-63 F. De Wiest, Contribution H l'gtude du comportement 6lectrochimique du carbone vitreux. Ph.D. Thesis, University of Brussels, March 1972 H.P. Boehm, Advan. Catal. 16 (1964) 179-274 J. Kakinoki, Acta Cryst. 13 (1960) 171
Atmospheric Pollution 1980, Proceedings of the 14th International Colloquium, Paris, France, May 5-8,1980, M.M. Benarie (Ed.), Studies in Environmental Science, Volume 8 0 Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
233
THE EFFECT OF PARTICLE SIZE ON THE EXTENT O F BROWNATION OF
POLYSTYRENE LATEX AEROSOLS
J.A. SPATOLA and J.J.I.
GENTRY*
United S t a t e s E n v i r o n m e n t a l P r o t e c t i o n Agency, E d i s o n , N e w J e r s e y , * I n s t i t u t e f o r P h y s i c a l S c i e n c e and Technology,
U n i v e r s i t y of
Maryland, C o l l e g e P a r k , Maryland 2 0 7 4 2
ABSTRACT Measurements o f t h e e x t e n t o f b r o m i n a t i o n o f p o l y s t y r e n e l a t e x aerosols i n d i c a t e t h a t t h e r e i s a s i g n i f i c a n t increase of the f r a c t i o n b r o m i n a t i o n w i t h d e c r e a s i n g p a r t i c l e s i z e and i n c r e a s i n g r a d i u s of curvature.
Infrared spectroscopy as w e l l a s desorption
measurements i n d i c a t e t h a t bromine r e a c t s w i t h r a t h e r t h a n a d s o r b s
on t h e a e r o s o l .
The amount o f b r o m i n a t i o n a s measured by x-ray
f l u o r e s c e n c e c o r r e s p o n d s t o a p e n e t r a t i o n o f s e v e r a l hundred Angstroms.
INTRODUCTION
One o f t h e m o s t i m p o r t a n t u n r e s o l v e d problems i n a e r o s o l c h e m i s t r y
i s t h e e f f e c t o f p a r t i c l e s i z e o r r a d i u s o f c u r v a t u r e on r e a c t i o n k i n e t i c s and e q u i l i b r i a .
Based on arguments a n a l o g o u s t o t h e Kelvin
e f f e c t on v a p o r p r e s s u r e , M i t t a s c h
( r e f . 1) s u g g e s t e d t h a t t h e s h i f t s
i n t h e e q u i l i b r i u m c o n c e n t r a t i o n s i n t h e decomposition of n i c k e l c a r b o n y l c o u l d be a c c o u n t e d f o r by a s i z e e f f e c t .
S i m i l a r l y , Defay
( r e f . 2 ) p r e d i c t e d s h i f t s i n t h e l o c a t i o n s o f a z e o t r o p e s and t r i p l e points with radius of curvature.
Unfortunately, q u a n t i t a t i v e
v e r i f i c a t i o n of these predictions a r e lacking. The d i f f i c u l t i e s i n making e x p e r i m e n t a l measurements t o v e r i f y t h e e f f e c t o f r a d i u s of c u r v a t u r e can b e summarized a s f o l l o w s :
1.
The n e c e s s i t y o f p r o d u c i n g a monodisperse a e r o s o l i n t h e s i z e
r a n g e from 0.005 2.
t o 0 . 5 pm.
The d i f f i c u l t y o f making s h o r t t i m e measurements
(1-100 msec)
which p r e c l u d e l i q u i d s y s t e m s w i t h moderate vapor p r e s s u r e .
3.
The c o m p l e x i t y o f t h e c h e m i s t r y o f many r e a c t i o n s y s t e m s
234
( i . e . p a r t i a l o x i d a t i o n o f hydrogenation of carbon a e r o s o l s ) . I n o r d e r t o minimize t h e s e d i f f i c u l t i e s , w e c o n s i d e r e d t h e bromination of p o l y s t y r e n e l a t e x a e r o s o l s .
Since t h e aerosols a r e
' s o l i d w i t h a v e r y narrow s i z e d i s t r i b u t i o n , t h e r e q u i r e m e n t o f a s t a b l e , monodisperse a e r o s o l i s m e t .
Bromine was s e l e c t e d b e c a u s e
it can be d e t e c t e d q u a n t i t a t i v e l y i n low c o n c e n t r a t i o n s by x - r a y f l u o r e s c e n c e o r n e u t r o n a c t i v a t i o n and b e c a u s e bromine i s s u f f i c i e n t l y r e a c t i v e t h a t it would r e a c t w i t h t h e v i n y l group i n t h e s t y r e n e monomer. EXPE R IFIEN TAL DE SI GN
The e s s e n t i a l f e a t u r e s o f t h e d e s i g n were t o c o n t r o l t h e a e r o s o l s i z e and c o m p o s i t i o n , t o c o n t r o l t h e c o n c e n t r a t i o n o f bromine i n t h e r e a c t i o n g a s m i x t u r e , t o l i m i t t h e e x p o s u r e o f t h e a e r o s o l t o bromine t o t h e r e a c t i o n chamber, t o measure unambiguously t h e p a r t i c l e conc e n t r a t i o n and t h e bromine c o m p o s i t i o n on t h e p a r t i c l e s , and t o c o n t r o l t h e t e m p e r a t u r e a t which t h e r e a c t i o n o c c u r r e d .
The a e r o s o l
was g e n e r a t e d from aqueous s u s p e n s i o n s o f p o l y s t y r e n e l a t e x a e r o s o l s u s i n g a C o l l i s o n (TSI 7330) n e b u l i z e r .
A f t e r h e a t i n g and d r y i n g t h e
a e r o s o l s t r e a m , i t was n i x e d w i t h a b r o m i n e - n i t r o g e n m i x t u r e ( 1 0 8 5 ppm b r o m i n e ) . W e t c h e m i c a l a n a l y s i s confirmed t h a t t h e concent r a t i o n o f t h i s m i x t u r e was s t a b l e . The g a s s t r e a m was mixed w i t h
t h e a e r o s o l s t r e a m y i e l d i n g t h e t e s t c o n c e n t r a t i o n s o f 1 0 0 and 2 0 0 ppm o f bromine.
The r e a c t i o n v e s s e l was a b a f f l e d , j a c k e t e d g l a s s v e s s e l w i t h a c a p a c i t y of 5 0 l i t e r s . a t e i t h e r 2 6 O C o r 60°C.
The t e m p e r a t u r e i n t h e v e s s e l was m a i n t a i n e d The f l o w r a t e i n t o t h e v e s s e l w a s m a i n t a i n e d
a t 6 . 2 5 l i t e r s / m i n u t e corresponding t o a residence t i m e of 8 minutes. The e x p e r i m e n t s w e r e a l l o w e d t o run f o r 1 5 m i n u t e s b e f o r e samples
w e r e c o l l e c t e d f o r x-ray f l u o r e s c e n c e . To p r e v e n t f u r t h e r r e a c t i o n w i t h t h e a e r o s o l and t o e l i m i n a t e t h e r e a c t i o n o f a d s o r p t i o n o f bromine on t h e c o l l e c t i o n f i l t e r , t h e bromine-aerosol denuders.
s t r e a m was p a s s e d t h r o u g h f o u r a c t i v a t e d c h a r c o a l
Theoretical c a l c u l a t i o n s ( r e f . 3 ) a s w e l l a s test runs
w i t h o u t a e r o s o l s i n d i c a t e d t h a t o n l y t r a c e amounts o f bromine p e n e t r a t e t h e denuders. The a e r o s o l was c o l l e c t e d on f l u o r o p o r e ( t e f l o n ) f i l t e r s w i t h p o r e
s i z e s less than t h e aerosol.
The samples were t h e n a n a l y z e d f o r
bromine c o n c e n t r a t i o n a t t h e Environmental S c i e n c e L a b o r a t o r y ( E P A ) a t Research T r i a n g l e P a r k , N o r t h C a r o l i n a . w e r e i n t h e r a n g e o f 1 0 0 ng/cm 2
.
Measured c o n c e n t r a t i o n s
The mass of p o l y s t y r e n e c o l l e c t e d
235
on t h e f i l t e r was d e t e r m i n e d from t h e p r o d u c t o f t h e number concent r a t i o n ( a s measured by a Royco 203) and t h e s a m p l i n g t i m e .
,
t h e mass o f a s i n g l e p a r t i c l e ,
The f i l t e r assembly c o n s i s t e d o f two f i l t e r s .
Only t h e f i r s t f i l t e r c o l l e c t e d p a r t i c l e s , and t h e measured c o n c e n t r a t i o n o f bromine on t h e b a c k i n g f i l t e r was found t o be negligible. ADSORPTION OR REACTION W e b e l i e v e t h a t t h e bromine r e a c t e d w i t h t h e p o l y s t y r e n e l a t e x
p r o b a b l y b r o m i n a t i n g t h e v i n y l g r o u p i n t h e s t y r e n e monomer.
In
o r d e r t o check t h i s h y p o t h e s i s , w e c o n s i d e r e d f i v e e x p e r i m e n t s : 1. Experiments where t h e b r o m i n a t i o n o f s u r f a c t a n t s h e l l s ( t h e p a r t i c l e s w e r e c e n t r i f u g e d from t h e system) was measured.
(Detectable
bromine c o n c e n t r a t i o n s w e r e less t h a n 2 ng/cm2 i n d i c a t i n g t h a t t h e s h e l l s were n o t b r o m i n a t e d . ) 2.
Brominated p o l y s t y r e n e s h e e t s w e r e s u b j e c t e d t o 2 4 h o u r s o f
vacuum a t 6OoC and t h e c o n c e n t r a t i o n o f bromine remeasured.
(Bromine
loss between measurements was found t o be l e s s t h a n lo%.) 3. Examination o f t h e i n f r a r e d s p e c t r a f o r brominated and c o n t r o l samples i n d i c a t e s i g n i f i c a n t changes p a r t i c u l a r l y a t 1 8 0 0 - 2 0 0 0 wave numbers. 4.
C a l c u l a t i o n s o f t h e number of absorbed l a y e r s n e c e s s a r y t o
produce t h e measured c o n c e n t r a t i o n gave v a l u e s of 30 l a y e r s f o r t h e s h e e t s and 60-300 l a y e r s f o r t h e a e r o s o l . [The Bachman ( r e f . 4 ) model o f 3 bromine atoms p e r 5 monomer u n i t s was u s e d . ] 5.
The mass o f bromine measured p e r u n i t s u r f a c e a r e a was n o t
constant f o r a l l aerosol sizes. Based on t h e s e measurements, w e have concluded t h a t a d s o r p t i o n can be n e g l e c t e d and t h e bromine r e a c t s w i t h t h e s t y r e n e monomer. EFFECT OF PARTICLE SIZE The p r i n c i p a l o b j e c t i v e o f t h i s s t u d y was t o d e t e r m i n e t h e e f f e c t o f p a r t i c l e s i z e ( r a d i u s o f c u r v a t u r e ) on t h e e x t e n t o f r e a c t i o n . P a r t i c l e s o f f i v e sizes--O.234 t o l u e n e ) --in
,
0.50,
0.80,
1.0,
and 2 . 0 2
(polyvinyl-
a d d i t i o n t o t h e p o l y s t y r e n e s h e e t s w e r e used i n t h e
s t u d y . Experiments w e r e run under f o u r c o n d i t i o n s - - c o r r e s p o n d i n g t o t h e c o m b i n a t i o n s o f two t e m p e r a t u r e s and two flow r a t e s . T y p i c a l o f t h e e x p e r i m e n t a l d a t a a r e t h o s e i n T a b l e 1 and Fig. 1 f o r t h e c o n d i t i o n s o f 2 6 O C and 2 0 0 ppm bromine.
From t h e d a t a
( n g B r 2 / p a r t i c l e ) p r e s e n t e d i n F i g . 1, it i s c l e a r t h a t t h e r e i s c o n s i d e r a b l e s c a t t e r i n t h e measurements.
The s t r a i g h t - l i n e
236 regression
( t h e polyvinyl t o l u e n e p o i n t s w e r e excluded) h a s a n
e x p o n e n t o f 2.15 s u p p o r t i n g a h y p o t h e s i s o f d i f f u s i o n i n t o t h e Based on t h i s model, t h e number of l a y e r s
p a r t i c l e with reaction.
r e a c t e d can be c a l c u l a t e d .
T h e r e a r e g i v e n i n column 5 o f T a b l e 1.
A l l t h e p a r t i c l e s show f a r g r e a t e r p e n e t r a t i o n o f bromine t h a n do
F u r t h e r m o r e , t h e s m a l l e s t p a r t i c l e s i z e , 0 . 2 3 6 pm,
t h e f l a t sheets.
shows by f a r t h e g r e a t e s t e x t e n t of r e a c t i o n . TABLE 1
Summary Experiment a1 Measurements ( Brominat i o n )
-
( G a s Composition
Particle Size
(w)
200 ppm B r 2 , Temperature 2 6 O C )
Experiments (Number)
Bromine Concentration ng/cm2 ~~
0.234 0.500 0.804 1.101 2 . 0 2 0 (polyvinyl toluene ) Sheet
==-
~
7 6 6 6 7
2 900 2100 1800 2300 3700
4
650
10
3
Bromine Concentrat i o n per Particle x 1015 qm/ uarticle ~~
4.9 16.9 36.1 87.2 4 87
Layers of Penetrat ion
Relative Penetration
~
249 119 a7 111 178
1 0.22 0.10
0.09 0.08
30
1
1 02 /
c
1Do
!
-1 10
'0 10
'I
10
0 1 AME T E R F i g . 1. C o n c e n t r a t i o n of bromine ( n g / p a r t i c l e ) p a r t i c l e s i z e (urn).
a s a f u n c t i o n of
237 The r e s u l t s f o r t h e o t h e r t h r e e c o n d i t i o n s show s i m i l a r b e h a v i o r . The exponent o f t h e c o n c e n t r a t i o n p e r p a r t i c l e a s a f u n c t i o n o f p a r t i c l e s i z e h a s an exponent between 2 and 3.
The g r e a t e s t
r e a c t i v i t y i s shown f o r t h e 0.236 pm p a r t i c l e s . Somewhat s u r p r i s i n g i s t h e e f f e c t o f t e m p e r a t u r e and B r 2 c o n c e n t r a t i o n on t h e e x t e n t o f b r o m i n a t i o n .
When t h e c o n c e n t r a t i o n
was i n c r e a s e d from 1 0 0 t o 2 0 0 ppm a t 26OC and when t h e t e m p e r a t u r e was i n c r e a s e d from 26OC t o 6 O o C a t 1 0 0 ppm, t h e bromine c o n c e n t r a t i o n increased.
However, t h e bromine c o n c e n t r a t i o n was l e s s a t 2 0 0 ppm
and 6OoC t h a n f o r e i t h e r 2 0 0 ppm and 2 6 O C o r 1 0 0 ppm and 60OC. same t r e n d s w e r e shown f o r a l l p a r t i c l e s i z e s .
The
Although t h e r e i s
c o n s i d e r a b l e e x p e r i m e n t a l s c a t t e r , it can be a s s e r t e d t h a t t h i s d e c r e a s e i s a t r u e phenomena w i t h i n 95% c o n f i d e n c e l i m i t s .
W e a r e p r e s e n t l y d e v e l o p i n g a model t o e x p l a i n t h i s phenomena. W e propose:
1.
That t h e d i f f u s i o n c o e f f i c i e n t o f bromine t h r o u g h p o l y s t y r e n e
l a t e x d e c r e a s e s a s t h e f r a c t i o n o f bromination i n c r e a s e s . 2.
T h a t t h e r a t e o f r e a c t i o n i n c r e a s e s w i t h t e m p e r a t u r e and
with c o n c e n t r a t ion. 3.
That i f t h e r e a c t i o n o c c u r s s u f f i c i e n t l y r a p i d l y , t h e n t h e
a e r o s o l w i l l c o n s i s t o f a s h e l l o f h e a v i l y brominated p o l y s t y r e n e surrounding a core of unreacted polystyrene. A computer code h a s been w r i t t e n t o t e s t t h i s h y p o t h e s i s .
CONCLUSION An e x p e r i m e n t a l p r o c e d u r e f o r d e t e r m i n i n g t h e e f f e c t of p a r t i c e s i z e on t h e r a t e o f b r o m i n a t i o n of p o l y s t y r e n e l a t e x a e r o s o l s has been developed and t e s t e d .
D e s o r p t i o n e x p e r i m e n t s and i n f r a r e d
s p e c t r o s c o p y i n d i c a t e a d d i t i o n o f bromine t o t h e s t y r e n e monomers Comparisons o f t h e e x t e n t o f b r o m i n a t i o n f o r t h e a e r o s o l t o p o l y s t y r e n e s h e e t s i n d i c a t e d t h a t t h e a e r o s o l s w e r e more r e a c t i v e . R e g r e s s i o n a n a l y s i s o f t h e e x t e n t o f b r o m i n a t i o n p e r p a r t i c l e gave an exponent between 2 and 3 i n d i c a t i n g more t h a n a s u r f a c e r e a c t i o n . There was a s i g n i f i c a n t i n c r e a s e i n b r o m i n a t i o n f o r t h e 0 . 2 3 4 pm aerosol. Experiments i n d i c a t e d t h a t b r o m i n a t i o n i n c r e a s e d w i t h i n c r e a s i n g t e m p e r a t u r e o r i n c r e a s i n g bromine c o n c e n t r a t i o n .
However, i f b o t h
w e r e i n c r e a s e d , a lower e x t e n t o f b r o m i n a t i o n w a s o b t a i n e d .
A
computer code b a s e d on t h e f o r m a t i o n o f a brominated s h e l l ( c h a r a c t e r i z e d by low d i f f u s i v i t i e s ) i s under development.
238 ACKNOWLEDGEMENT The a u t h o r s w i s h t o a c k n o w l e d g e t h e E n v i r o n m e n t a l P r o t e c t i o n Agency, R e s e a r c h T r i a n g l e P a r k , N o r t h C a r o l i n a f o r t h e i r u s e o f x-ray
fluorescence.
Science Foundation,
J . W. G .
w i s h e s t o acknowledge t h e N a t i o n a l
G r a n t No.
78 00738 A 0 1 .
REFERENCES 1 A. M i t t a s c h , Z . P h y s i k Chem., 4 0 ( 1 9 0 2 ) 39. 2 R. D e f a y , I. P r i g o g i n e , A . B e l l e m a n s a n d D . H . E v e r e t t , S u r f a c e T e n s i o n a n d A d s o r p t i o n , Longmans, G r e e n , 1 9 6 6 , pp.280-284. 3 P.G. Gormley a n d M. Kennedy, P r o c . Royal I r i s h A c a d . , 52A ( 1 9 4 9 ) 163-169. 4 G.B. Bachman a n d H. Helman, J. o f O r g a n i c Chem., 1 2 ( 1 9 4 7 ) 1 0 8 - 1 2 1 .
Atmospheric Pollution 1980, Proceedings of the 14th International Colloquium, Paris, France, May 5-8,1980, M.M. Benarie (Ed.), Studies in Environmental Science, Volume 8 0 Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
239
AEROSOL PARTICLES IN AIR hTTH A GRADIENT OP HUMIDITY H. STRAUBEL 8973 Vorderhindelang, (G.F.R. )
ABSTRACT The measurement accuracy of optical scattering devices for aerosols doesn't depend only on apparatus constants. It is supposed, the captured aerosol particles don't change their shape or mass on their way to the screening volume. However, this can be induced by variation of relative humidity (r.h.) in the surrounding air. Capillary condensation arises between the crystalline surfaces and in the gaps between them. Several substances are solved or crystallize. These possible changes expiring in a time of a few milliseconds, are recorded by a movie picture with a sequence of 5-18 pictures/second. They lead to considerable incorrections in sizing with optical devices. INTRODUCTION Aerosols, moving in a gradient of relative humidity, change their shape o r chemical structure. Leaving out chemical reactions, mass and shape of the droplets are influenced by these possible changes. Sizing methods for particles are well-known: sedimentation,centrifuge and cascade impactor. Densityg must be known for evaluating the mass of the particle. These methods are not tlspeedylt, their recording is time-consuming and the particles are lost after having passed the screening volume. Therefore it is impossible to reintroduce the same the same particles in the device for further investigations. ttRapidltmeasuring methods are i.e. various methods of optical light scattering. The results are recorded in a split second. The instrument is calibrated with latex spheres, therefore the result is only valid for spherical shape.(Flie-theory). The response of non-spherical particles may be described by an I1equivalent-diametertt.If refractive index n and densitypare known, too, the mass can be exactly calculated, spherical shape providet. The sizing accuracy seems to depend only on apparatus constants and physical properties o f the particle, more or less well-known.
240
However, it must be considered, that the particle’s way from the place of sucking to the optical sreening volume needs a time. Considerable errors in sizing are possible, because this space of time is great against the time of particles changing in air. EXPERIMENTS Varying i.e. the relative humidity or air pressure (in aerodynamic focussing) before reaching the screening volume, particle’s size and shape can be changed by uptaking water. These changes can be very fast. The speed of the growing process depends on the initial size of the particle and the relative humidity. (ref. 1). Therefore the accuracy of the scattering device is reduced, as it is impossible to foresee this event.
For analysing these details, crystalites of NH C1, lying on an thin 4 cover glass, are investigated in pre-experiments with variable r.h. The crystal o r the agglomerates were illuminated by a laser beam ( A = O , 6 3 2 5 m ) , the diffraction patterns were taken directly by a movie picture 18 x 24 mm, 5-18 pictures/second. Fig. 1.
evaporating Fig.
evaporating
dry
1. diffraction patterns produced by an NI14C1-crystal lying on
a cover glass. Breathing on the cover glass, changes develop slowly, however, the changes due t o evaporating water occur very quick (in less 1/20 s).
241
Unfortunately this changes are influenced by the cover glass (epitaxie).
To avoid this influence, single crystals of NH4C1 were freely suspended in a capacitor, described by the author previously. (ref.2) Fig. 2. In this device the voltages a.c. and d.c., connected with the capacitor work simultaneously as a balance. Changes of mass
a
Fig. 2. 3-plate-capacitor for levitating charged particles (condensation or evaporation o f water) can be recorded instantaneously. Movie pictures in Fig. 3 . A t first the dry crystal (a) uptakes water slowly (b), and at the end a sphere is build up. (c), saturated solution. After reducing relative humidity, the sphere gradually evaporates. (The reduced diameter results increasing frings distances). Beginning with a defined supersaturation, water is ejected like an explosion, a crystal rests, more o r less developped ( d ) . The process can be repeated very often with the same crystal,
b
C
Fig. 3 . diffraction pattern produced by a free suspended crystal of N H 4 C 1 in air o f variable humidity.
a
242
as there is no loss of electrical charge. Short time before ejecting water, the interference fringes of the sphere, hitherto very sharp, become blurred, caused by very small micro-crystals (seeds). The complete arrangement is seen in Fig. 2. Beside the film (below) there is a little photocell inside the capacitor (detector). It receives one part of the light, back-scattered from the particle. Uptaking water, the particle's mass and shape is changed too: the relation foreward / sideward - scattering is modified to a maximum if the shape of a droplet is perfect. (foreward scattering maximum, sideward scattering minimum).Fig. 4 shows the diminuishing of the 90' scattering intensity of a particle when uptaking water.
e
Fig. 4 90' scattering intensity of a crystal taking up water o o o 0 0 0 crystal evaporating water - - - gooscattering intensity o f spheres of pure water (calculated).
Fig. 5 slit-electrodecapacitor in a cage with gradient of relative humidity.
These fast processes cannot be accelerated with the device described in Fig. 2, as the filling of the capacitor with different moistened air needs some time, to avoid an intense air stream. Thise disadvantages are overcomed, if the particle in research is exposed to a steady gradient of moistened air. Fig. 5. Instead of the circular shaped electrodes of the capacitor used previously (horizontal plates), a slit shaped electrode is taken (vertical position), installed in a box with a vertical temperature gradient. The air - column is cooled below by a peltier couple.
-
243
-
An insulated wire mounted below and perpendicular to the slit electrode is connected with a variable d.c. voltage. Its charge is of the same sign as the particle. Due to the voltage on the wire, the particle will be levitated more or less inside the slit. (re3 3 ) . All the time it runs throughout the gradient of relative humidity without stirring the air inside the box. (particle diameter i.e. 10 - 3 O m , width of the slit 8 0 0 0 ~ ) AS . the slit-electrode operates only as a guidance for the particle without any vertical component, the undisturbed falling velocity of the particle can be used by sudden disconnecting the d.c. voltage on the wire. However, there is no loss of the particle, because it is automatically captured in the under part of the slit. During the particle’s ascending and descending its changes canbe recognized directly by the varying sideward scattering intensity. Providet a constant d.c. voltage on the wire, the high of the particle’s position in the slit corresponds directly to the change of its mass, as there no loss of the charge takes place. The slit capacitor may be calibrated with latex spheres of known size. As there is no movement at the at the stabilized particle’s high, the measuremend is independent of the shape. (no correction due of shape factor). In the circular electrode capacitor (Fig. 2), however, the knowledge of the particle’s shape is necessary for attenuation of vertical oscillations. In this case, some time the stabilizing a.c. voltage must be disconnected shortly for exact balancing. (clean Millikan measurement).
-
-
-
-
-
COITCLUSIONS Experiments with the circular capacitor (Fig. 2 ) as well as with the slit electrode have shown the output of a distinct amount of water during the conversion supersaturated sphere crystal. (ref. 4). In this cases no change of charge was observed, due to the small charge of the particle (ca. l o w 6 Amp.sec./g). Therefore the field strength on the particle’s surface remains small against the break down field strength of the surrounding air (30 kV / em).
-
-
-
-
-
In the circular plate capacitor (Fig. 2 ) the losses of charge on the particles are a minimum, due to the outer Millikan plates. These plates catch all chrges in the surrounding air , therefore there is no compensation of particles charge.
-
244
REFERENCES 1
Hiinel, G.
, Pageoph, Vol.
115 (1977)775-797
Birkhauser Verlag, Basel
Thudium, J.,Pageoph, Vol. 116 (1978) 131-148 Birkhauser Verlag, Basel Winkler,P. and Junge, C.E. J.Rech.Atmos.(Memorial Dessens) (1972) 617-638
2
Henri
Straubel, H., Staub-Reinhalt.Luft 33 (1973) 174-177 Straubel, H., Progress in Vacuum PIicrobalances Techniques (Ed. Eyraud and Escoubes) V o l . 3 (1975) 319-323 Heyden, London Straubel, H., Proc. of the 13th Internat.Col1. Paris, France tlAtmosphericPollutionft, Ed. M. Benarie Elsevier Amsterdam, (1978) 97-100
3 Straubel, H., Chemie-Ingenieur-Technik 43 (1971) 853-855
4 Straubel, H., Gesellschaft fur Aerosolforschung (G A F) Tagung in Dusseldorf 3.-5.
Oct. 1979
in press.
Atmospheric Pollution 1980,F’roceedingsof the 14th International Colloquium,Paris,France, May 5-8,1980, M.M. Benarie (Ed.),Studies in Environmental Science, Volume 8 0 Elsevier Scientific Publishing Company,Amsterdam - Printed in The Netherlands
245
HETEROGENEOUS NITROGEN OXIDE-PARTICLE REACTIONS G.M. SVERDRUP and M.R. KUHLMAN Battelle, Columbus Laboratories, Columbus, Ohio, U.S.A
ABSTRACT Experimental investigations of the rates and mechanisms of heterogeneous reactions involving nitrogen oxides and particles which are either co-emitted from power plants or are resident in the atmosphere are described. Results from experiments involving NO and NO
2
and particulate sulfuric acid,
ammonium sulfate, sea salt, and fly ash are presented.
INTRODUCTION The impact of nitrogen oxides (primarily NO
X
composed of NO and NO ) 2
emissions from fossil-fueled power plants on health, materials, visibility, and precipitation chemistry is very uncertain (ref. 1).
This uncertainty
stems from a lack of knowledge concerning the removal and transformation mechanisms of NO
X
in power plant plumes as well as the rates of NO
removal
and transformation. The need for a more complete understanding of NO
plume chemistry is
being addressed in a program at Battelle’s Columbus Laboratories for the Electric Power Research Institute. Key homogeneous and heterogeneous reactions involving nitrogen oxides and other materials which are either co-emitted from power plants or are resident in the atmosphere are being studied.
This paper addresses the heterogeneous nitrogen oxide-particle
reactions studied to date.
EXPERIMENTAL DESIGN Both the rates and mechanisms of heterogeneous nitroaen oxide-particle reactions are being studied. by determining the fraction,
Heterogeneous reaction rates are quantified
0, of gas molecule-surface collisions which
result in chemical reaction or disappearance of the gas molecule. reactions with
+
less than about
For
the particulate surface is exposed
to the gas specie a5 bulk material residing on a liner conformed to the
246 inner circumference of a 4.5 cm i.d. aluminum tube flow reactor. Values of $ are determined by comparing the l o s s of gas specie concentration down the flow reactor with theoretical results based upon the basic fluid mechanics model of Gosman et al. (ref. 2).
The model of the flow reactor is used to calculate
the spatial concentration of a reactive gas specie as a function of the flow Reynolds number, Schmidt number, and $. -4 For reactions with 9 greater than about 10 , the transport to the reactor
wall by diffusion and subsequent removal at the wall of a gas molecule is diffusion limited. Sufficient aerosol surface can be generated to study these reactions under non-diffusion limited conditions. Mechanisms of heterogeneous NO
transformations are being studied by
exposing particulate surfaces on reactor liners to gas species for extended periods of time. performed.
Chemical analyses of the particulate matter are then
A 200-liter, Pyrex, dynamic flow irradiation chamber is also
being used to study SO -NO -particle systems at several concentrations and 2 x steady state residence times. SO concentrations from 1 to 100 ppm with 2
SO :NO:NO ratios of 2:l:O.l have been used at dew points of -1 and 2 0 C to 2 2 investigate homogeneous and heterogeneous interactions at high concentrations.
PARTICULATE SURFACES The following particulate matter has been used in the experiments conducted to date:
oil- and coal-fired fly ash, sulfuric acid, ammonium sulfate, and
artificial sea salt.
The fly ash was collected from the stacks of two plants,
one burning No. 6 fuel oil derived from predominantly Venezuelan crude and the second plant burning pulverized eastern U.S. high sulfur coal. For the experiments reported here, fly ash surfaces were provided by aspirating the fly ash and collecting it uniformly on quartz filters.
Sulfuric acid surfaces were
prepared as bulk surfaces by saturating high purity quartz fiber filters with sulfuric acid. reactor.
The filter substrates were placed in Teflon sleeves in the flow
Sulfuric acid aerosols were generated by atomization and photochemically
in the 200-liter reactor. Ammonium sulfate and artificial sea'salt surfaces were prepared by atomization followed by collection on quartz filters. These materials were not tested as aerosols due to their low reactivity.
RESULTS The interaction of NO with sulfuric acid and oil- and coal-fired fly ash was found to be negligible, i.e., @
cent.
over the relative humidity (rh) range 10 to 90 per-
Previous research using a different experimental technique demonstrated that
the value for $ is less than acid surfaces (ref. 3 ) .
for collisions of NO and NO2 onto sulfuric
247
Similarly, the value of 4 for NO
collisions with sulfuric acid and ammonium 2-7 sulfate was found to be less than 10
.
The value of 4 for NO collisions with artificial sea salt was found to lie 2 -6 in the range 10 to depending upon the rh of the system. The lowest value of 4 was found for dry sea salt at 44 percent rh; the highest value was found at the highest rh tested, wet sea salt equilibrated at 88 percent rh. Based upon a two-component log-normal size distribution model of sea salt aerosol, the minimum lifetime (l/e) of NO2 in air containing 10 pg/m3 sea salt would be about 260 days at about 90 percent ambient rh, if the N02-sea salt reaction were the only removal mechanism.
During a three day transport period, a maximum
of about 0.03 pg/m3 sodium nitrate could be added to the atmospheric aerosol burden by means of this reaction assuming an NO2 concentration of 0.02 ppm. The interaction of NO2 with oil fly ash has been studied at high rh (90%) by with 0.015 ppm NO past a fly ash laden substrate with a 2 mean gas-surface contact time of 13.7 sec. Data from one such experiment are flowing 0.390 ppm NO
shown in Figure 1. The N02/NOxIn data indicate that 4 ranged from the diffusion-6 at the beginning of the experiment to about 10 at the
limited rate
end of the experiment.
Analysis of the fly ash by ion chromatography indicated
the presence of 151 pg nitrate in agreement with integration of the NOx deficit shown in the figure. The strong conversion of NO2 to NO is also evident in this experiment.
An additional experiment using a fly ash loading about one-sixth
of the first experiment yielded conversions to nitrate and NO in the ratio of the amount of fly ash. The oil fly ash composition was determined to be about 38 percent VOS04-3H20 with 7 2 percent of the ash water soluble (ref. 4).
NO
2
interactions with the
water soluble fraction gave essentially the same results as experiments with the entire fly ash under humid conditions. NO
interaction with the insoluble 2 fraction showed no more than 0.005 ppm NO formed although a substantial amount of NO
was removed. Experiments with NO and pure VOSO4*3H20 did not yield NO 2 2 formation; NO depletion was much less than for the water soluble fraction. 2 NO interactions with coal fly ash were studied at several relative humidities. 2 Essentially no NO was generated. Substantial NO was lost to the surface, but 2 most of it reappeared when the reactor was purged with clean air. Analysis of the fly ash revealed the amount of nitrate was below the analytical detection limit. No interaction between NO and the fly ashes was observed. Studies with fly ash are continuing in an attempt to assess the effect of heterogeneous reactions on NO
X
transformations in plumes.
248
Fig. 1. Concentration of NO, NO2 and NOx at the reactor outlet normalized to inlet NO
X
using an oil fly ash liner.
ACKNOWLEDGMENT This work was supported by the Energy Analysis and Environmental Division of the Electric Power Research Institute under contract RP 1369. REFERENCES 1 Workshop on Atmospheric Pollution by Trace Nitrogen Compounds, Prepared by Battelle, Columbus Laboratories for the Electric Power Research Institute, EPRI EA-986-SY, Palo Alto, CA, February, 1979. 2 A.D. Gosman, W.M. Pun, A.K. Runchal, D.B. Spalding and M. Wolfshtein, Heat and Mass Transfer in Recirculating Flows, Academic Press, New York, 1969. 3 A.C. Baldwin and D.M. Golden, Science, 206 (1979) 562-563. 4 Methods for Analyzing Inorganic Compounds in Particles Emitted from Stationary Sources, Battelle-Columbus Report to U.S. EPA, EPA-600/7-79-206, September, 1979, p. 40.
Atmospheric Pollution 1980, Proceedings of the 14th InternationalColloquium,Paris, France, May 5-8,1980, M.M. Benarie (Ed.), Studies in Environmental Science, Volume 8 0 Elsevier Scientific Publishing Company,Amsterdam -Printed in The Netherlands
249
PARTICULATE POLLUTION OF THE ATMOSPHERE DUE TO LIQUID HYDROCARBON FIRES PHAM VAN DINH and B. BENECH Institut et Observatoire de Physique du Globe du Puy de DGme Centre de Recherches Atmosphdriques, Campistrous 65300 Lannemezan (France)
ABSTRACT The pollution of the atmosphere by the particles of various kinds generated by fuel-oil fires has been studied experimentally in controlled conditions. I n cases involving heavy fuel fires, the size spectrum of carbon smoke particles
is centered on the 0.5-1 Um size class (with concentrations up to 7000 particles per cm3) ; in casesinvolving lighter fuels, the size spectrum exhibits a mode in the 0.25-0.5
pm class, with concentrations about two orders of magnitude larger than
the ambient aerosol. Cloud particles may also appear at the top of the smoke plume. Measurements of droplet populations do not show any significant difference between artificial and natural clouds through the 3-45 pm size range ; moreover, the cloud condensation nuclei concentrations have the same order of magnitude inside and outside the plume (=I000 ~ m - ~in ) spite of a high SO2 content (300-400 ppb).
INTRODUCTION In order to study the particulate pollutants released into the atmosphere by liquid hydrocarbon fires, two series of experiments were carried out using powerful, controlled fires. The first series simulated accidental fires, through burning a heavy fuel layer ("brut de Parentis") stretched over a 2000 mz area, and releasing a 2000 MW heat power (PROSERPINE Experiment) ; during the second series, a natural convection source was simulated by a 105 burners system ("MdtSotron"), which used a locally produced, lighter fuel TAquitaine C'? and released a 1000 MW heat power (COCAGNE Experiment). During both experiments, airborne measurements were carried out ; collected particles samples are later compared to samples collected right above a 10 MW burner using domestic fuel (One-Burner, Control Experiment). EXPERIMENTAL SET-UP Table 1 summarizes, for each of the three experiments, measurement techniques used to evaluate the smoke particles and other aerosol populations, as well as S02.
250
TABLE 1 Pollutant measurement techniques used in three controlled experiments Experiment
Fuel Darameters
Plume source uarameters
PROSERPINE “Brut de Parentis” (Ref. I ) , 1977
C H
67.17 ’Z 11.96 %
Fuel layer on the ground A = 2000 m2 Pth 2000 Mw
Smoke particles
Airborne sampling on Nuclepore filter/Electron microscopy
One-Burner Domestic fuel (Ref.Z), 1978
C = 84.43 ’Z H = 12.26 Z S = 0.37 ’Z
Fuel pulverized into droplets Point source Pth = 10 MW
Smoke particles ; Trace elements in smoke particles and fuel residue
Same as above, plus Mass spectroscopy
COCAGNE Aquitaine C (Ref.3), 1979
C = 86.6 ’Z H = 11.9 % S = 1.28 %
Organized combustion (105 burners) A = 15000 m2 Pth = 1000 MW
Smoke particles ; other aerosol; Cloud condensation nuclei (CCN); cloud droplets ;
Same as above, plus EAA, ROYCO ; Light scattering/ diffusion chamber ; ASSP (PMSI) ; FPD flame detector
s
= = =
1.1
’Z
Pollutants samoled
so2
Measurement techni alle
In situ measurements were made from a CESSNA 206 aircraft operated by the “Centre Adrien d’Etudes MStdorologiques” during the PROSERPINE experiment,and aboard a Douglas B23 research aircraft belonging to the University of Washington during the COCAGNE experiment. DATA ANALYSIS TECHNIQUES AND EXPERIMENTAL RESULTS Smoke particles were sampled on Nuclepore filters
,
and later sized and counted
by means of scanning electron microphotographs. The smoke aerosol consists of agglomerates of smaller particles with a spherical aspect and a diameter of about 0.1 pm ; many agglomerates exhibit a chain-like structure (Fig.2a).
20 10
I 4
DIAMETER(pm)
DIAMETER (pm)
%
The frequency distributions
50
e
C
20 10
L i
4 DlAME TER ( p m)
0.06 025
Fig. 1. Frequency distributions of smoke particles versus particle diameter class f o r a) “One-Burner“ experiment ; b) PROSERPINE experiment and c) COCAGNE experiment.
251
U-
102
I
PARTICLE
a
I
XT'
I
1
loo
SIZE D ( p m )
b
Fig. 2. Sampling and sizing of particles during the COCAGNE experiment : a) scanning electron microphotograph showing smoke particles (in white) collected on 0 , 2 um pore size Nuclepore filter (magnification 4000) ; b) example of aerosol size distributions obtained within the plume (P) and the ambient air (A) at the same height (2500 m) 0: 18 june 1979 ; ( X ) , (+), (@), (@) refer to EAA measurements while ( o ) , ( o ) , (A), (0) refer to ROYCO 1 measurements. versus particle size (Feret's diameter), etablished from numerous samples involving several thousands particles, show a mode at 0 . 3 7 5 pm both for the One-Burner and COCAGNE experiments, and a mode at 0.75 pm for the PROSERPINE experiment (Fig.1). No difference in size was noted between smoke particles collected at various plume
heights ; nevertheless, the concentration decreased from about 7 0 0 0 to 4000 particles per om3 when the flight altitude increased from 300 m to 500 m A . G . L .
in the plume
updraft column. In all cases, particles as large as 12 and 24 Um represent less than
252
CONCENTRATION ( I-’
DROPLET
0
W
0 D r
n -I
?! !
N
m
0 h
‘1=
3
Y
P
60
I
I
1
I
I
Fig. 3. Examples of droplet distributions of natural clouds (N1, N2) and plume generated clouds (Pi, P2) sampled at the same height between 14h30 and 15h30 on 14 june 1979 (“1000 m).
0.5 Z and 0.05 X , respectively, of the total concentration. During the COCAGNE experiment, the aerosol was analysed by various devices aboard the B23 aircraft ; data were collected and stored on floppy discs for later processing by a ground based computer. In this study, we use only measurements recorded by the Electrical Aerosol Analyser ( E M ) for the 0.01-0.8
pm size range and the (modi-
fied) model 220 Royco Optical Particle Counter (ROYCO I ) for the 0.3-11 pm size range. Preliminary results do not show any significant variation of the modal size for either number concentration or mass concentration between the plume and ambient air. On the other hand, when considering the concentration functions dN/dlogD and dV/dlogD for number and volume, fig.2 shows that through the modal region (20.3-0.5 pm),both functions are two order of magnitude larger inside the plume than in surrounding air. Very few particles over 5 Um were detected : electron microphotographs generally allowed us to assign to them a mineral origin (e.g. clay, sand...). The microphysical structure of clouds was investigated simultaneously, especially by means of the Knollenberg Axially Scattering Spectrometer Probe (ASSP or PMSI) which measured in situ the size distribution of clouds droplets from 2.8 to 65 pm diameter over fifteen size intervals, each about 4.4 pm wide. On some days -for example on 14 june 1979-,
cumulus clouds were induced by the
plume ; generally,natural clouds were also present in such cases. Both the condensation level and the cloud nature (strato-cumulus on this particular day) are similar.
253
Fig. 4. An example of SO2 content (A) measured within the plume (the (A) symbol size denotes the concentration level) and cloud condensation nuclei concentration sampled in the natural air (measurement at 1 % supersaturation ( x ) ) and within the plume (at 1 Z ( 0 ) and 0.5 % (0) supersaturation). The photograph shows the plume size and shape on 18 june 1979 ; plume contours may be also retrieved from photogrammetric data points ( i )within a vertical plane parallel to the wind direction. Nevertheless, artificial clouds were smaller than natural ones (1.5 km versus 3.5 km typical horizontal size, in our example). The droplet size distributions do not show any systematic difference between artificial and natural clouds (Fig.3). It is true that droplets larger than 45 pm are only detected inside natural clouds (Fig.3) ; since however measurements in artificial clouds were performed but a few minutes after cloud formation, droplets clearly did not have the time to grow to such sizes. Cloud condensation nuclei were also measured by means of a diffusion chamber using a diffusion light detector at 0.5 % and 1 % supersaturations : the plume and ambient air contain nearly the same CCN numbers, about 500 to 1500 cm-3 (Fig.4). In fact, our mass spectrography analysis reveals that smoke particles essentially consist of carbon (at 97 %),
while other elements (such as C1, Na, Ca, K... that are able to
form hygroscopic nuclei) are not more than traces (a few thousands of ppm) (Ref.2). Gaseous sulfur content was high (e.g. up to 400 ppb) inside the plume, while the ambient SO2 content was lower than 10 ppb (Fig.4).
Sulfate particles are efficient
CCN indeed ; however, according to Newman e t aZ. (Ref.5), the rate of oxydation of
254
SO2 to particulate sulfate is quite low (0.3-5 Z h-'),
so that gaseous sulfur is not
likely to contribute significantly to CCN formation in our case.
CONCLUSION In plumes generated by fuel-oil fires, particulate pollutants consist essentially of carbon smoke particles,with a 0.8 pm modal diameter for heavy fuels and a 0.4 pm diameter for lighter fuels. Cloud condensation nuclei concentrations are not increased significantly, in spite of the high SO2 content (300-400 ppb) ; a similar conclusion is reached for droplets populations. Therefore, it appears that artificial clouds must be primarily induced by the thermodynamical effect of the heat source. ACKNOWLEDGEMENTS The work is supported by a grant from Electricit6 de France, Division Etudes et Recherches. We wish to express our thanks to Dang, Comunay and Saur (Laboratoire d'0ptique Electronique du C.N.R.S., Toulouse) for their help in the electron microscopy analysis. REFERENCES 1 B. BQnech, J.-M. Brustet and Pham Van Dinh, in Opgration PROSERPINE, MinistSre de
l'int6rieur (Direction de la SQcurit6 Civile), Paris, 1977, pp.73-98.
2 Pham Van Dinh and B. Bznech. Etude sur la combustion du fuel-oil domestique 1 l'air libre. Note I.O.P.G. n048 (1978), Institut et Observatoire du Puy de Dame, Clermont Ferrand, 60 p. 3 B. Benech, J. Dessens, C . Charpentier, H. Sauvageot, A. Druilhet, M. Ribon, Pham Van Dinh, P. MQry, paper accepted for presentation at the third WMO Scientific Conference on Weather Modification (Clermont Ferrand, France 21-25 July 1980).
4 P.V. Hobbs and L.F. Radke, J. Aerosol Sci., 7(1976)195-211. 5 L. Newman, J. Forrest and B. Manowitz, Atmos. Envir., 9(1975)969-977.
AEROSOL PHYSICS AND MEASUREMENT CONCERNING THE SUSPENDED PARTICULATE MAlTER
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Atmospheric Pollution 1980, Proceedings of the 14th International Colloquium, Paris, France, May 5--8,1980, M.M. Benarie (Ed.), Studies in Environmental Science, Volume 8 0 Elsevier Scientific Publishing Company, Amsterdam,- Printed in The Netherlands
257
MEASUREMENT OF PARTICLE SIZE DISTRIBUTIONS OF FLUE DUST BY MEANS OF CASCADE IMPACTORS R. WIEDEMANN Lehrstuhl fur Thermische Kraftanlagen, Technische Universitat Miinchen, Munchen, Bundesrepublik Deutschland
INTRODUCTION This report deals with investigations on cascade impactors which were accomplished at an experimental plant of the Technical University of blunich and at some coal-fired power plants. These investigations were mainly orientated to practical applications. In the following some of the results and recornmodations will be shown.
Trajectory of a Particle to Small to Impact Lines
Impaction Plate
Trajectory of an Impacted Particle
Fig. 1. Schematic plot of a single impactor stage.
Glass Fiber Filter
258
An impactoris a device to classify flue dusts with respect to their aerodynamic diameter. A solid-gaseous two phase flow is accelerated in a nozzle stage and is diverted in front of a following impaction plate (stagnation point flow). Coarse particles with a high inertial mass cannot follow the divertion and are impacted on the impaction plate, whereas fine particles follow the stream lines. Theoretically in each impactor stage a seperation into two particle size distributions is achieved. (Figure 1 ) . By connecting several nozzle stages and by increasing the mean flow velocity the cut-off points can be shifted to finer and iiner particle diameters, so-called "equivalent cut-off diameters". This separating process is governed by a dimensionless inertial parameter, the STOKES number. According to theoretical calculations the STOKES number describing this process is fairly constant for different nozzle dimensions and for a wide REYNOLDS number region. 1 1 1 .
1 . MEASUREMENTS AT AN EXPERIMENTAL PLANT
At an experimental plant installed at the Technical University of Munich some commercially available impactors were tested with respect to their applicability to reproduce correctly the particle size distribution of known, polydisperse flue dusts. By change of the dust concentration, the dust material and the gas flow rate various working conditions can be realized in a vertical duct of the plant (figure 2). The following criterions of performance of the impactors were examined at the experimental plant: 1 . Measurements should be reproducible. 2. Measured particle size distributions of known flue dusts should be recorded independently of the dust concentration and the flow rate through the impactor. 3. A measured particle size distribution should coincide with the particle size distribution of a known flue dust dosed into the experimental duct. The size distribution of the dosedin flue dust was determined by sedimentation analysis according to the Andreasen method. This analysis provides an aerodynamic diameter as well. The ratios of mean particle diameters of several different size distributions measured in the experimental plant should correspond tothe ratios, measured by means of the sedimentation analysis.
259
4. A great value was set on easy handiness. 5. The amount of wall losses should be as low as possible.
Fig. 2. Experimental plant for dust sampling at the Technical University of Munich All the conditions mentioned above could not be satisfied totally by any of the tested impactors. For measurements in the exhaust gas flow of coal-fired power plants a six stage cascade impactor with integrated nozzle-impaction plates was chosen. The research work at the experimental plant brought a lot of additional results and handling concepts which were considered for the measurements in stacks of power plants:
260 1.
2.
3.
4.
5.
6.
The application of a pre-separator in form of a pre-impactor o r a pre-cyclone for the retardation of particles larger than 10 microns is essential, because coarse particles are reflected at the impaction plates and may be transported to the back-up filter. Because of this phenomenon a finer particle size distribution is faked. The application of a pre-separator shifts the size distribution curves to a coarser region. The comparison of the measured curves with those provided by the sedimentation analysis are pretty acceptable. Moreover a decrease of the wall losses could be observed by use of a pre-separator. F o r the measurements in stacks of power plants a pre-impactor was chosen because of its handiness and because of its low penetrability for particles larger 10 microns. The coating of the impaction plates with pretreated, punched-out glass fiber filter is recommended, expecially if the dust deposition will be physically or chemically examined afterwards. Generally speaking there is no significant change of results whether glas fiber filter are used o r not except the deposited dust has only a low adhesion to the uncoated impaction plates. The application of gooseneck probes is not recommended. Presumable in the bent of a gooseneck probe a preseparation of coarse particles occurs, and measured distributions are shifted to finer regions. The application of an impactor to measure the total amount of the dust concentration is not advisable because the wall losses may fluctate between 20 to 40 4, of the theoretically expected mass deposit. The wall losses of coarse particles are higher than those of fine particles. By a suitable design of the air intake funnel the wall losses can be reduced but at the same time a nonuniform loading of the first stages has to be taken into account. On the contrary to measurements of total dust concentrations isocinetic sampling conditions do not have to be strictly adjusted. The error made by non-isocinetic sampling becomes only significant for wide size distributions. On the other hand the impactor flow rate should be constant during sampling time, otherwise the magnitude of the "equivalent cut-off diameters" is changed permanently. The dust loading of a filter should not increase 8 mg, otherwise already impacted particles may be reintrained.
261 2 . MEASUREMENTS OF PARTICLE SIZE DISTRIBUTIONS
IN EXHAUST GASES OF
POWER PLANTS Description of the Measuring Positions Power Plant A: stone coal-fired Measurement were taken at a stone-coal fired power plant with an electrical power output of 320 MW. The measuring point was situated in the purified exhaust gas duct between the electro-static precipitor and the exhaust fan. The flow was directed vertically downwards. Disturbing obstructions, bents and pipebranchings were not in the vicinity of the measuring point. A second measuring point was situated in the crude exhaust gas duct just in front of the electro-static precipitor. 2 . 1 . 2 . Power Plant B: lignite-fired Power plant B was provided with a lignite fired Benson vessel and delivered a power output o f 600 MW. The position of the measuring point was similiar to those of power plant A, except that the flow was directed horizontally and the measuring point was situated very adversely with respect to the flow pattern just after a 90O-bent and in front of a pipe branching. Measurements in the crude exhaust gas were not taken. During measuring time both power plantswere operated under constant maximum electrical power output. In both cases measurements were taken only at some grid points of the cross sectional area. 2.1.
2.1.1.
Methode of Measurement The glass fiber filter for the coating of the impaction plates were submitted to following procedure: 1 . Dehydrating at a temperature o f 300 O C far two hours. 2 . Cooling off in a desiccating cylinder. 3. Weighing of the filter in weighing dishes. 4. Transport of the filter in weighing dishes and Petri bowls. After each measurement the impactor was washed in acetoneand cleaned. The impactor was run in a dust sampling train. A condensate collector and a drying tower were added to the impactor. The instantaneous flow rate was controlled by a flow meter; the sucked-off gas volume was recorded by a gas meter. As the flow rate was measured after passing the drying tower the humidity of the exhaust gas had to be taken in consideration for the adjustment of an isocinetic flow rate and for the evaluation of the results. Before starting the sampling train the impactor and pre-impactor were warmed up in the exhaust duct. After finishing the glass fiber filter were packed in weighing 2.2.
262
dishes, dehydrated at a temperature of 1 1 0 "C, cooled-off in a desiccating cylinder and weighed. Changes of filter mass due to chemical reactions of sulphur dioxide and hydrofluoric acid were ignored. Dust depositions of the pre-impactor were swabbed out into a weighing dish and submitted to the same procedure as the filter. 2 . 3 . Evaluation of the Results
After determiningthe filter loading by weighing the "equivalent cut-off diameters d were calculated by trial-and-error method P according to the following equation:
lStk'=0,343
3
Volumenstrom
d
Furtikeldurchmesser (porticle diameter)
9
Portikeldichte
(particle density)
rl
dynom. Viskositat
Idynom. viscosity)
C
Cunningham Foktor (Cunninghorn factor)
St k
Stokes -Zohl
D
Dusendurchmesser (Nozzle diameter 1
A
Dusenfloche
(Nozzle c.s.orea)
n
Dusenonzohl
(number of nozzles)
(volume flux)
(Stokes number)
The actual parameters are the particle density, the exhaust gas temperature and the impactor flow rate. The mean nozzle diameter
263
of each stage was measured with help of a microscope. As magnitude for the particle density the unity density was chosen, because in general the particle density is unknown. In the following figures the cumulative residue of the distributions was plotted logarthmically versus the particle diameter.
2.4. Results Impactor measurements in the crude and purified exhaust gas of the stone coal fired power plant could be compared to sedimentation analyses of flue dust deposited in the pre- and final cleaner of the electro-static precipitor. In this case the equivalent cut-off diameters of the purified exhaust gas were evaluated with the flue dust density of the pre-cleaner (figure 3). As expected a significant decrease of the mean particle diameter of the flue dust is observed when passing the electro-static precipitor. The particle size distributions measured in the crude exhaust gas show a wide fluctuation mainly due to short sampling timeswhichhad to be chosen because of the high dust concentration. On the other hand these distributions overlap with those gained from the pre- and final cleaner. The particle size distributions in the purified exhaust gas are shifted clearly to finer regions. Evaluating the results by neglecting the mass deposited in the pre-impactor for all measurements in purified exhaust gas a narrow fluctuation field can be observed (figure 4). The results obtained at the lignite-fired power plant show a large scattering of the plotted points (figure 5). Presumable this is due to the adverse flow pattern caused by duct obstructions and to high fluctations of the fuel composition. The mean particle diameter in the purified exhaust gas of the stone coal-fired power plant turned out to be 3 , L microns, those of the lignite-fired power plant to 2 , 0 microns provided that the particle density is unity. Neglecting the pre-impactor massasmall scattering of the plotted points can be obtained similar to the proceeding case (figure 6). The wide fluctation field observed when taking into consideration the preimpactor mass is therefore due to high fluctations of the coarse particle concentration.
264
0 10
20
o lmpactw
Purified Exhaust Gas
0 Impactor
Crude Exhaust Gas
30 LO 0,
5 50 u)
?I 60 > 0,
-3 70
5 80
0
90 %
10 Pm Porticle Diometer dp
100
Fig. 3. Power plant A : stone coal-fired; comparison of the particle size distribution of flue dust out o f the crude exhaust gaq, the pre-cleaner, the final cleaner and the purified exhaust gas.
Yo 100
Od
1
10 Pm Particle Diometer dp ‘pp 1.0 g/cm3 1
100
Fig. 4. Power plant A: lignite-fired, evaluation without preimpactor mass.
265
0 10
3
0
1 Day
Axis 3
20
30 LO 0
4 50 3 LX 60
-
V
9Ar-r 100
L
0.l
1
10 Pm Partide Diameter dp
-
100
I Q =~i.0g/cm31
Fig. 5. Power plant B: lignite-fired, measurements in the purified exhaust gas.
0 POWER PLANT E
10
20
0 1 Day
V
0
Lignite
Axis 3
ZDay 3Day
30
3 LO 2 u)
a"
50
060
> .c
5 70 E
5 80 90 VO
100
0.1
1
10 Pm Particle Diameter dp
0
(pP = l . ~ g / c r n ~ ) Fig. 6. Power plant B: lignite-fired, evaluation without preimpactor mass.
266
3. CONCLUSION
For measurements of particle size distributions of flue dust a cascade impactor is very suitable if no great strain is put on high accuracy. The results of impactor measurements represent a time-averaged value. The application of a pre-separator if particles larger than 10 microns are expected is highly recommended. The impactor should not be used to determine the total dust concentration in an exhaust duct.
REFERENCES
1
Marple, V. A.: A fundamental study of inertial impactors. Diss. Univ. of Minnesota
Atmospheric Pollution 1980, Proceedings of the 14th International Colloquium, Paris, France, May 5-8,1980, M.M. Benarie (Ed.), Studies in Environmental Science, Volume 8 0 Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
MEASUREMENT OF AEROSOLS LESS THAN 0.01 pm
-
267
APPLICATION TO THE NUCLEATION I N THE
ATMOSPHERE M.L. PERRIN, Y.C. Commissariat DPr/STEP/SPT,
a
BOURBIGOT, 6.3. MADELAINE
1'Energie Atomique, I n s t i t u t de P r o t e c t i o n e t de Sirrete Nucleaire, CEN/FAR B.P. 6, 92260 FONTENAY-aux-ROSES, FRANCE.
ABSTRACT
IJe use a d i f f u s i o n b a t t e r y coupled w i t h a condensation n u c l e i counter t o d e t e r mine the f i n e p a r t o f t h e urban atmospheric aerosol s i z e d i s t r i b u t i o n . The e s t i mation o f t h e n u c l e a t i o n r a t e s i n two cases a l l o w s t o j u s t i f y the presence, o r not, o f a " n u c l e a t i o n " mode which comprises p a r t i c l e s w i t h a diameter l e s s than 0.008 pm.
INTRODUCTION
The d i f f u s i o n b a t t e r y method (1) allowed us t o go deeply i n t o the knowledge o f f i n e p a r t i c l e s , and p a r t i c u l a r l y p a r t i c l e s w i t h a diameter l e s s than lo-'
pm.
Smog-chamber experiments showed t h e d i f f e r e n t process which govern the e v o l u t i o n o f f i n e aerosols, e i t h e r i n s t a n t a n e o u s l y , o r c o n t i n u o u s l y produced ( 2 ) . A f i r s t approach o f the r e a l phenomena was obtained.
Then, i t seemed i n t e r e s t i n g t o make
" i n s i t u " measurements. This paper concerns urban atmospheric measurements. One can o b t a i n several forms o f s i z e - d i s t r i b u t i o n s ,
according t o the time when sam-
p l i n g i s made, m e t e o r o l o g i c a l c o n d i t i o n s , s o l a r a c t i v i t y , e t c . . .The t r i m o d a l d i s t r i b u t i o n g i v e n by WHITBY ( 3 ) seems t o be c o r r e c t t o d e s c r i b e the p h y s i c a l nature o f the atmospheric a e r o s o l . With a d i f f u s i o n b a t t e r y , our study i s more s p e c i a l l y l i m i t e d t o p a r t i c l e s w i t h a diameter between 3.10-3 Um and 2.10-1
pm.
The d i f f u -
s i o n b a t t e r y i s e s t a b l i s h e d as u n a v a i l a b l e beyond t h i s s i z e . On the o t h e r hand, we take advantage o f r e c e n t developements i n t h i s method (1) t o j u s t i f y the presence, o r n o t , of the " n u c l e a t i o n " mode ( 3 ) (Comprised o f p a r t i c l e s w i t h diameter <0.08
urn)
which i s o f t e n submitted t o u n c e r t a i n t i e s o f d e t e c t i o n and measurement.
RESULTS Experiments a r e made o u t s i d e our l a b o r a t o r i e s , i n Fontenay-aux-Roses.
Two s e r i e s
o f measurements a r e shown, which a l l o w t o j u s t i f y t h e presence, o r not, o f the " n u c l e a t i o n " mode.
268
Absence o f the " n u c l e a t i o n mode" We study the e v o l u t i o n o f the n a t u r a l a e r o s o l , i n t h e beginning o f t h e day, the most i n t e r e s t i n g p e r i o d being the s u n r i s e ( 4 ) a t 04:30 a.m.
-
Number s i z e d i s t r i b u t i o n s obtained
( l o c a l t i m e ) , 07:30 a.m. and 09:OO a.m. a r e shown on F i g . 1.
dN dlogD 105
104
103
102
F i g . 1. E v o l u t i o n a g a i n s t t h e time o f t h e atmospheric aerosol s i z e d i s t r i b u t i o n measured i n Fontenay-aux-Roses w i t h a d i f f u s i o n b a t t e r y and a condensation n u c l e i counter - Absence o f t h e " n u c l e a t i o n " mode.
A t 04:30 a.m.,
so j u s t b e f o r e the s u n r i s e (05:OO a.m.),
i s 0.07 pm and t h e standard d e v i a t i o n 1.35
-
t h e geometric mean diameter
A t 07:30 a.m.,
so about two hours
a f t e r t h e s u n r i s e , t h e number o f p a r t i c l e s w i t h a diameter l e s s than lo-* pm i n creases, because new p a r t i c l e s are brought by the photochemical r e a c t i o n . A t 09:OO a.m.,
t h e number o f these p a r t i c l e s i s decreasing, w h i l e t h e one o f par-
t i c l e s between lop2 pm and 3.10-'
pm i s i n c r e a s i n g
-
Table 1 shows t h e "nucleation"
r a t e s QNn ( 3 ) measured a t several times, and t h e r a t i o o f t h e volume dVn o f new
269 p a r t i c l e s appearing i n the " n u c l e a t i o n " mode t o the v a r i a t i o n o f the t o t a l volume o f aerosol (dVT).
TABLE 1 t ( l o c a l time)
QNn (number. ~ m - s~- l. )
dVn/dVT
04:30
0.30 0.030
6.
06: 30 07: 30
6. 2.10-5 7, 7.10-7
1 0.036 0.040
08:OO 09:oo
One can n o t e t h a t a s h o r t number o f p a r t i c l e s appears i n t h e " n u c l e a t i o n " mode. The condensation process seems t o be predominant i n the s t u d i e d aerosol e v o l u t i o n . It uses t h e a v a i l a b l e n u c l e a n t vapour and t h e formation o f new u l t r a f i n e p a r t i c l e s
by homogeneous n u c l e a t i o n i s so n e g l i g i b l e . These p a r t i c l e s , as soon as they are generated, coagulate on t h e "accumulation" mode ( 3 ) p a r t i c l e s which number i s g r e a t e r . The i m p o r t a n t surface and number o f t h e p a r t i c l e s present a t the sunrise ( F i g . 1) favour
t h e aerosol e v o l u t i o n by c o a g u l a t i o n and condensation.
Presence o f the " n u c l e a t i o n " mode Sometimes, i t may be completely d i f f e r e n t . For example, measurements made on the
79.4.24,
always o u t s i d e o u r l a b o r a t o r i e s i n Fontenay-aux-Roses,
show t h a t u l t r a f i n e
p a r t i c l e s appear i n t h e m i d d l e o f t h e day ( F i g . Z ) , maybe due t o a l o c a l p o l l u t i o n .
F i g . 2' : E v o l u t i o n a g a i n s t t h e time o f the atmospheric aerosol s i z e d i s t r i b u t i o n measured i n Fontenay-aux-Roses w i t h a d i f f u s i o n b a t t e r y and a condensation n u c l e i counter - Presence o f the " n u c l e a t i o n " mode.
\
-11
:oo
270
Experimental r e s u l t s (number c o n c e n t r a t i o n N, t o t a l volume V , t o t a l surface area A, geometric number mean s i z e , geometric standard d e v i a t i o n , " n u c l e a t i o n " r a t e s ) a r e g i v e n i n t a b l e 2. TABLE 2 t ( l o c a l time)
N
11:oo 11:45 12: 35 13: 15
7.00 7.76 1.76 2.3
2 V ( p ~ n ~ . c m - A(pm ~) . ~ m - ~ ) Dg (pm)
(4) (4) (5) (5)
3.71 1.67 1.31 1.5
308 173 149 175
0.035 0.025 0.023 0.020
QNn cm-3. s - 1 1.84 1.92 1.82 1.45
0.61 10 47 90
One can n o t e t h e g r e a t values o f t h e " n u c l e a t i o n " r a t e s QNn. I t seems t h a t t h e nuc l e a t i o n process i n f l u e n c e s s t r o n g l y t h e s t u d i e d aerosol e v o l u t i o n : between 11:45 a.m and 13:15 ( l o c a l t i m e ) , t h e t o t a l s u r f a c e area and volume a r e about c o n s t a n t because t h e generated u l t r a f i n e p a r t i c l e s c o n t r i b u t e v e r y l i t t l e t o t h e i r increase ( 5 ) . C o n t r a r y t o t h e p r e v i o u s case, one can n o t e t h a t t h e a v a i l a b l e s u r f a c e area a t 1 1 : O O i s small, so t h a t a g r e a t f o r m a t i o n o f n u c l e i i s p o s s i b l e (63. Because o f t h e g r e a t number o f these generated n u c l e i , a p a r t of them do n o t coagulate on t h e p r e s e n t "accumulation" mode, b u t
coagulate between them t o make t h e " n u c l e a t i o n " mode we can
measure t h i s day. The " n u c l e a t i o n " r a t e s QNn g i v e n i n t a b l e 2 a r e comparable t o t h e one abtained i n a smog-chamber when 0.1 ppm o f SO2 i s photolysed i n f i l t e r e d a i r ( 5 ) . I n t h i s case,
5
a maximum number c o n c e n t r a t i o n o f 3.7 x 10 p a r t i c l e s
i s o b t a i n e d a f t e r two
hours o f i r r a d i a t i o n , corresponding t o an a p p a r i t i o n r a t e o f 82 new p a r t i c l e s
s-'.
CONCLUSION The f i n e p a r t o f t h e urban atmospheric aerosol, measured i n t h e day i n Fontenay-aux-Roses w i t h a d i f f u s i o n b a t t e r y , has t h e f o l l o w i n g c h a r a c t e r i s t i c s :
-
an "accumulation" mode w i t h p a r t i c l e s between
- a " n u c l e a t i o n " mode w i t h p a r t i c l e s l e s s than
vrn and 2.10-1
pm.
pm, t h e presence o f which
depends on 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 and t h e importance i n number and s u r f a c e area o f t h e "accumulation" mode. A g r e a t s u r f a c e area favours t h e condensation o f t h e vapour molecules, and a g r e a t number causes t h e c o a g u l a t i o n of t h e generated nuclei. I t i s an evidence t h a t these f i r s t r e s u l t s do n o t g i v e a complete s i g h t o f t h e atmospheric a e r o s o l dynamics. Nevertheless, they show t h a t t h e d i f f u s i o n b a t t e r y method, coupled w i t h o t h e r t e c h n i c s ( a s E l e c t r i c a l Aerosol Analyser, spectrophotometer,
...)
may be u s e f u l t o go on t h e knowledge o f t h e f o r m a t i o n and e v o l u t i o n
271 o f n a t u r a l and anthropogenic p a r t i c l e s .
ACKNOWLEDGEMENTS T h i s work was p a r t i a l l y sponsored
by t h e U.S.
Environmental P r o t e c t i o n Agency
and t h e M i n i s t e r e de 1'Environnement e t du Cadre de Vie.
REFERENCES
1 J.P. Maigne, These de D o c t o r a t d ' E t a t , P a r i s , 1968. 2 6 . 3 . Madelaine, M.L. P e r r i n , A, Renoux, Formation and e v o l u t i o n o f u l t r a f i n e p a r t i c l e s produced by r a d i o l y s i s and Phobolysis, CAGCP Symposium on Trace Gases and Aerosols i n t h e Atmosphere, Boulder, Colorado, 1979 - To be p u b l i s h e d i n JGR Oceans and Atmospheres. 3 K.T. Whitby, Atmospheric Environment, 12(1978)135-159. 4 R.B. Husar, K.T. Whitby, B.Y. L i u - J. C o l l o i d I n t e r f a c e Sci., 39(1972)211-224. 5 G.J. Madelaine, M.L. P e r r i n , A. Renoux J. Aerosol S c i . 10(1979)202. 6 S.K. F r i e d l a n d e r - J . Aerosol S c i . 10(1979)198.
-
This Page Intentionally Left Blank
Atmospheric Pollution 1980, Proceedings of the 14th International Colloquium, Paris, France, May 5-8,1980, M.M. Benarie (Ed.), Studies in Environmental Science, Volume 8 0 Elsevier Scientific Publishing Company,Amsterdam -Printed in The Netherlands
273
ON THE COUNTING EFFICIENCY OF A CONTINUOUS FLOW CONDENSATION NUCLEI COUNTER Y. METAYER and Laboratoire de Dbpartement de Commissariat 2
G. MADELAINE Physique des Abrosols, Service de Protection Technique, Protection, Institut de Protection et de SQretd NucBbaire, 1'Energie Atomique, 92260 Fontenay-aux-Roses, France.
ABSTRACT The response of a continuous flow condensation nuclei counter has been determined as a function of particle size by means of monodisperse aerosols. The counting efficiency has been found to depend also on the particles chemical nature. The results can be explained on the basis of Fletcher's theory, which predicts the effect of the size and the "wettableness" of the nuclei upon the nucleation rate.
INTRODUCTION In the condensation nuclei counters (CNC), particles grow by condensation of a vapor on their surface, so they give a detectable amount of scattered light. The growth can be caused either by an adiabatic expansion or by circulation of the sampling, previously saturated with a condensable vapor, in a cooled pipe (1). The latter method, developed in continuous flow counters, is more and more used : particles concentration is monitored continuously and the instrument can be operated in conjunction with diffusion battery, where steady air flow is essential. In the expansion counters, the pressure drop is adjusted to obtain a supersaturation of the order of 300 P; and the minimum detectable particle radius is about rm = 0.001um, calculated theoretically from Kelvin's equation : 2 a m Ln S =
m
where S is the saturation ratio, m is the molecular weight of the vapor, u the surface tension, p the density of the liquid, Rg is the universal gas constant, T is the absolute temperature, and R the
274
particle radius. However, several investigators (2) ( 3 ) have shown that the counting efficiency decreases for particles diameters smaller than 0.01 vm, for all expansion counters, including the Nolan-Pollak, considered until then as a calibration standard ( 4 ) . After Kassner and a1 ( 5 ) , equation ( l ) , based on ideal assumptions, gives only a poor thermodynamic description : the adiabaticity is disturbed by the heat and vapor diffusion from the walls. 1 1 The recent analysis of Hollander and Schumann ( 6 ) , has shown that, during the growth of polydisperse highly concentrated aerosols, the smaller nuclei can be inhibited by the larger ones. But these considerations are not sufficient to explain the observed particle size detection limits, investigated by means of highly monodisperse aerosols. The continuous flow counters areneither absolute instruments ; Agarwal and Sem (7) have presented evidence that not all particles larger than the theoretical minimum detectable size are counted in the Thermo-System Incorporated CNC. The experiments described below show an influence of the chemical nature on the loss of count, for the TSI CNC. EXPERIMENTS The monodisperse test aerosols were generated by the electrical technique of Liu and Pui ( 8 ) .
da ca
Fig. 1
ca = compressed air f = filter ne = nebulizer n = neutralizer da = dilution air ec = electrostatic classifier e = electrometer
- Schematic diagram of the monodisperse aerosols generator
The method, schematically described in fig. 1 , consists of first generating a polydisperse aerosol by nebulization. The droplets are dried and a radioactive source of 85Kr brings the nuclei to a state of Boltzmann charge equilibrium.
215
The particles are then classified electrostatically by mobility in a cylindrical condenser. The corresponding current, measured by a sensitive electrometer, is proportionnal to particles concentration. The device can be used to generate aerosols in the size range from 5 -3 0.01 um to 0.3 vm at concentrations up to 10 p.cm . For smaller sizes, the fraction of charged nuclei decreases rapidly, so the concentration numbers never exceed 104 p.cm -3 , Aerosols of several alkali halides solutions (NaC1, NaBr, KC1) were first generated. To produce insoluble particles needed in the calibration experiments, the basic apparatus had to be modified : an ultrafine aerosol of vanadium oxyde (V2 05 ) was formed, after replacing the atomizer by a tube furnace. In a second set of experiments, a reaction vessel containing a radioactive source of 210Po was put on the compressed air stream and the addition of a small amount of SO2 allowed the production of a constant concentration of radiolytic nuclei composed of sulfuric acid, like the smaller particles of the atmospheric aerosol. The uniformity of the submicron particles produced by this method was carefully checked. Sodium salts aerosols were measured by a Sartorius flame photometer : vanadium oxyde nuclei were collected with a thermal precipitator and examined with the electron microscope. The test aerosols size distribution is characterized by a standard deviation ug < 1,3 ; the concentration accuracy is about 5 % . The calibration has been determined by comparing the actual concentration, exiting from the electrostatic classifier,with that indicated by the CNC. RESULTS AND DISCUSSION The response of the TSI counter to monodisperse, singly charged particles is shown in fig. 2. The counting efficiency, defined as the ratio of the indicated concentration NCNC to the input concentration, measured by the aerosol electrometer, NIE, decreases sharPly below 0.01 um, and the l o s s of count depends on particles nature, as already deduced by Cooper and Langer The efficiency decrease appears for a smaller size than in most of the expansion counters, surelybecause the thermodynamic conditions are quite different. Moreover, water is here replaced by N-butyl-Alcohol which has a smaller coefficient of diffusion, so that sufficient cooling can occur before too much vapor is lost on the walls.
.
276
7
NAE
'
Fig. 2 - Counting efficiency of the TSI CNC as a function of particles diameter.
Q 7 : : r 5 7 3 0 D4NaCi 05 025
"205
-
I
I
I
I
I
2
4
6
8
I
Particle Diameter, Supersaturation is an important factor, but is not likely to justify the effect of particles chemical nature. A possible explanation relates to the nucleation theory itself. Kelvin's equation makes the simplifying assumption that every particle of radius larger than rm is spontaneously covered with a thin liquid film, by adsorption of vapor molecules and therebybehaves as a droplet, growing by condensation. The Volmer's theory predicts that, in a saturated environment, the impacted vapor molecules diffuse along the surface and then gather into embryos, by heterogeneous nucleation. During this first step, the free energy involded in the solid-liquid and liquid-vapor interfaces cannot be neglected. Fletcher (9) derived an expression taking into account the size and surface properties of the nucleating particle. The nucleation rate on a particle of radius R , is : J = 4 . r r ~ K ~exp - AG"
[
where K is a kinetic coefficient ; AG", critical embryo, may be written as :
.'
AG" =
4 7
.rr
ur
::2
f (cos 0 , x)
free energy of formation of
a
(3)
in which ois the surface tension of the liquid, r is the radius of a critical embryo ; 0 is the contact angle between the substrate and tHe embryo, defined after Young's relation. The nucleation rates for some values of the contact angle are plotted as a function of particle size in fig. 3 . In the case under consideration, the number of critical embryos required to cover a particle of a given size can be estimated ; for a given value of the air flow through the saturated region, a minimum
277
nucleation rate is calculated.
1,
5-1
/
Fig. 3 - Nucleating rates versus particles radius, computed after Fletcher's formu1as
1
I
0.001
. -1 0.01
particle diameter I
0.1ym
By comparing with the values of the rates deduced from Fletcher's formulas, a detection threshold is established. When J is smaller than limit. Jmin the particle is below the size detection This type of analysis could explain qualitatively the influence of the particles nature upon the counters response. V205 is hydrophobic, H2S04 and NaCl are known to be highly hydrophilic ; since no numerical data are available, it seems reasonable to assume that the surface properties are comparable for water and N-butyl-Alcohol, both polar solvents. CONCLUSION The results of the above study show that condensation nuclei measurements are subject to large uncertainties. On the other hand, the experimental calibration curves are very useful for interpreting size distribution data obtained with the TSI CNC operated in conjunction with diffusion battery. For a complete understanding of the continuous flow counters, more experiments on heterogeneous nucleation are greatly needed as well as a theoretical approach of the thermodynamic processes.
REFERENCES 1 J.K. AGARWAL, G.J. SEM and M. POURPRIX - Procedings of the Ninth International Conference on Atmospheric Aerosols, Condensation and
218
Ice Nuclei, Galway, Ireland, September 1 9 7 7 , to be published. 2 B.Y.H. LIU and C.S. K I M - Atmospheric Environment, 11 ( 1 9 7 7 ) 1 0 9 7 1100.
3 G. COOPER and G. LANGER
-
J. Aerosol Sc, 9 ( 1 9 7 8 ) 6 5 - 7 5 . J. of Applied Met, 1 4 ( 1 9 7 5 ) 4 6 - 5 1 .
et al. et al. - J. of Atmospheric Sc, 25 ( 1 9 6 8 ) 9 1 9 - 9 2 6 . I 1 6 W. HOLLANDER and G. SCHUMANN - J. of Coll and Interface Sc, 7 0 ( 1 9 7 9
4 B.Y.H. LIU
5 J.L. KASSNER 475-482.
7 G.J. SEM and J.K. AGARWAL
- Presented at the second Symposium on
advances in Particulate Sampling and Measurement. Daytona Beach, USA, October 1 9 7 9 , to be published in J. of Aerosol Sc. 8 B.Y.H. LIU and D.Y.H. PUI - J. of Coll and Interface Sc, 4 7 ( 1 9 7 4 a ) 155-171. 9 N.H. FLETCHER
- J. of Chemical Physics,
29 3 ( 1 9 5 8 ) 572-576.
Atmospheric Pollution 1980, Proceedings of the 14th International Colloquium, Paris, France, May 5-8,1980, M.M. Benarie (Ed.), Studies in Environmental Science, Volume 8 Q Ehevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
R E A L I Z A T I O N OF A D U S T TUNNEL
279
- R E S P O N S E O F SOME A I R S A M P L I N G
I N S T R U M E N T S U S E D IN I N D U S T R I A L H Y G I E N E
J.F. F A B R I E S and B . C A R T O N l n s t i t u t N a t i o n a l de R e c h e r c h e et de S G c u r i t 6 p o u r l a p r e v e n t i o n des a c c i d e n t s du t r a v a i I et des maladies p r o f e s s i o n n e l l e s C e n t r e de R e c h e r c h e de N a n c y 5 4 5 0 0 V A N D O E U V R E ( F r a n c e )
ABSTRACT A dust tunnel i s d e s c r i b e d , which c a n r e p r o d u c e total dust c o n c e n t r a t i o n s r a n g i n g f r o m about 3 mg/m3 t o about 100 mg/m3 in an a i r f l o w w h e r e low v e l o c i t i e s a r e p r e v a i l i n g (maximum of 3 0 c m / s ) .
T h e u t i l i z a t i o n of a tyndallometer L E l T Z TM D i g i t a l as a r e f e r e n c e
i n s t r u m e n t for m e a s u r i n g the dust c o n c e n t r a t i o n i s investigated. The experimental equipment was a p p l i e d t o the study of the b e h a v i o u r of a s m a l l f i l t e r - h o l d e r used in p e r s o n a l a i r sampling at a w o r k p l a c e and an automatic r e s p i r a b l e mass m o n i t o r GCA
- 301.
I N T R O D U C T IO N The measurement o f dust c o n c e n t r a t i o n at the w o r k p l a c e i s of p r i m a r y importance f o r the d e t e r m i n a t i o n of the r i s k l e v e l in i n d u s t r i a l hygiene. T h i s i s u s u a l l y made b y u s i n g a i r sampl i n g d e v i c e s f o r the e x t r a c t i o n o f a f r a c t i o n of the s u r r o u n d i n g atmosphere and f o r the c o l l e c t i o n of a i r b o r n e p a r t i c l e s on a f i l t e r f o r f u r t h e r a n a l y s i s . Indeed a l a r g e v a r i e t y of a i r sampling i n s t r u m e n t s a r e a v a i l a b l e , and i t i s important to know t h e i r response when they a r e exposed t o r e f e r e n c e c o n c e n t r a t i o n s . F o r t h i s study w e r e a l i z e d a dust tunnel f o r the r e p r o d u c t i o n of experimental conditions of a i r f l o w and dust c o n c e n t r a t i o n , w i t h i n the l i m i t s c u r r e n t l y encountered in i n d u s t r y .
E X P E R I MENTAL E QUIPMENT F l o w c o n t r o l and f i l t r a t i o n s e c t i o n T h e a i r f l o w i s obtained b y a c e n t r i f u g a l fan mounted on the r o o f of the l a b o r a t o r y ; the f l o w r a t e i s measured u s i n g the p r e s s u r e d r o p t h r o u g h a diaphragm (d) ( F i g . 1 ) . The f i l t r a t i o n o f the dust laden ai r i s achieved b y a f i r s t polyurethane foam p r e f i l t e r (f l ) , then b y a second f i l t e r ( f 2) and f i n a l l y b y an absolute f i l t e r ( f 3) S o f i l t r a 1506-12. A r e g u l a t i o n v a l v e (V) mai n t a i n s the f l o w r a t e at a constant value whatever the dust r e t e n t i o n o n the o u t l e t f i l t e r s i s ; i t c a n b e v a r i e d a p p r o x i m a t e l y f r o m 100 up to
6 0 0 rn3/h.
Experimental area
I n t h i s a r e a a i r v e l o c i t y and dust c o n c e n t r a t i o n a r e a p p r o x i m a t e l y constant, t h i s a r e a i s l o c a t e d in t h e m i d d l e p a r t o f the tunnel and i s a c c e s s i b l e f r o m the outside b y a d o o r which a l l o w s s a m p l i n g d e v i c e s and o t h e r s c i e n t i f i c equipments to b e p o s i t i o n e d . The square c r o s s s e c t i o n a r e a i s one s q u a r e m e t e r .
#I 4
1 mcfcr
F i g . 1 D u s t tunnel
T h e v e l o c i t y p r o f i l e was measured f o r a f i x e d value o f the total f l o w r a t e (283 m3/h) with a heated w i r e p r o b e T S I 1610 ( w i t h a l i n e a r i z e r model 67), connected w i t h a time-domain a n a l y z e r S O L A R T R O N JM 1 86 0 g i v i n g time a v e r a g e d values. The r e s u l t s a r e r e p o r t e d in F i g . 2, they do not v a r y w i t h the a l t i t u d e in the e f f e c t i v e w o r k i n g area. T h e v e l o c i t y range v a r i e s f r o m about 6 cm/s t o 3 0 cm/s w i t h the b a s i c equipment. T h e i n t e n s i t y of turbulence was measured w i t h a f a s t r e s p o n s e anemometer D l S A ( b r i d g e 55M10 w i t h p r o b e 5 5 P l 1 , linearizer
55M25) at the same f l o w r a t e ; i t was found t o b e c l o s e to 10%in both c o - c u r r e n t
and c r o s s - c u r r e n t d i r e c t i o n s .
F i g . 2 A i r v e l o c i t y p r o f i l e i n s i d e t h e experimental section. T o t a l f l o w r a t e = 283 m3/h. ( t ) tyndallometer
(h) honeycombs (9)g r i d .
281 D u s t g e n e r a t i o n and f l o w s t a b i l i z a t i o n Ambient a i r of the l a b o r a t o r y i s sucked in b y the f a n through an absolute f i l t e r ( f ) (Fig. 1) t o e l i m i n a t e any u n d e s i r a b l e contaminant. D u s t i s i n t r o d u c e d i n t o the f l o w just a f t e r the f i l t e r , i t i s generated f r o m a f l u i d i z e d b e d apparatus " P u l d o u l i t mod6le A " made b y IRCWA ( r e f s . 1 ,2). A r a d i o a c t i v e s o u r c e of 8 5 K r i s used to eliminate most e l e c t r i c c h a r g e s . F l o w s t a b i l i z a t i o n i s achieved in the s e c t i o n located between the experimental a r e a and the dust g e n e r a t o r o u t l e t , t h i s s e c t i o n i n c l u d e s : a two m e t e r s l o n g c y l i n d r i c a l duct, a p e r f o r a t e d cone (c) f o r homogeneizing the dust laden t u r b u l e n t a i r s t r e a m , and a t h r e e m e t e r s l o n g p y r a m i d a l s e c t i o n t e r m i n a t e d b y a 6 rnm mesh honeycombs (h) and a
0.75 mm mesh g r i d (9).
C o n c e n t r a t i o n measurement A t y n d a l l o m e t e r L E l T Z T M D i g i t a l i s p l a c e d i n the experimental a r e a , f o r measuring c o n t i n u o u s l y the c o n c e n t r a t i o n . The analog output i s connected w i t h a d i g i t a l voltmeter
FLUKE 8502 A w i t h l o w f r e q u e n c y option, g i v i n g f o r each d i g i t a l r e a d i n g a time averaged v a l u e UM, d u r i n g a time i n t e r v a l
T.
T h e r e l a t i o n s h i p between UM and the average c o n c e n t r a t i o n CM d u r i n g the mentioned time i n t e r v a l t h a s t o b e f o u n d . A d r i f t was detected in the output voltage r e c o r d of the tyndallometer
, due
t o p a r t i c l e d e p o s i t i o n on the o p t i c a l p a r t s of the dust chamber;
following expression f o r
UM
the
was s t u d i e d :
K (1) w h e r e A and 6 a r e adjustable p a r a m e t e r s , i and
K subscripts
r e l a t i v e to successive measure-
ments ( f r o m t = 0 UP t o t = k-r f o r the kth measurement); 6 i s a r e s i d u a l voltage obtained when t h e r e i s no dust in the tunnel. P a r a m e t e r s A and
B have to b e d e t e r m i n e d to c a l i b r a t e
the tyndallorneter. T h e c a l i b r a t i o n p r o c e d u r e c o m p r i s e s m s u c c e s s i v e steps a ( a = 1 , Z , .
. . . ,m)
during
which dust laden a i r i s sampled t h r o u g h a 37 mm d i a m e t e r f i l t e r - h o l d e r M i l l i p o r e MAWP
0 3 7 A 0 w i t h p r e - w e i g h t e d f i b e r g l a s s f i l t e r Whatman G F / C , at a f l o w r a t e of 2 0 I/mn.
It
c a n b e shown that the p r e v a i l i n g c o n d i t i o n s e n s u r e h i g h sampling e f f i c i e n c y , a c c o r d i n g to D a v i e s ( r e f . 3), w i t h the r e s t r i c t i o n f o r the sampling head t o b e c o n s i d e r e d as a thin-walled tube. T h e r e f o r e each c a l i b r a t i o n step a y i e l d s experimental a v e r a g e values
P
P
--(a)
uM
E =
c
j = 1
and
UMia)/p
and
C M( a ) E
=
c
j = l
J
( a.)
CMj%P J
w h e r e UM.(0) and CM. a r e v a l u e s a v e r a g e d d u r i n g time i n t e r v a l s 7. I f f o r each step J J fhe c o n c e n t r a t i o n i s s t a t i o n a r y , the f o l l o w i n g r e l a t i o n can b e deduced f r o m E q u a t i o n ( 1 ) :
282 F o r g i v e n A and residuals r
r
(a)
=
(a) .
6,m values $(a)
may be c a l c u l a t e d f r o m equation (3) and then m
.
( a )E UM
- (a) - M ‘
a = 1,2,
..., m
(4)
A least s q u a r e method c a n b e a p p l i e d f o r c a l c u l a t i n g p a r a m e t e r s , b y m i n i m i z i n g o v e r a l l e x p e r i m e n t s the sum S :
A s in equation (3) the a v e r a g e output v o l t a g e
rM(a) i s a l i n e a r f u n c t i o n of p a r a m e t e r s ,
the method g i v e s d i r e c t l y A and B without any i t e r a t i o n . A and
B b e i n g known,
the actual
may b e c a l c u l a t e d at any time f r o m equation (11, i f the p r e c e e d i n g values
concentration C
MK a r e s t o r e d in memory.
RESULTS A c a l i b r a t i o n p r o c e d u r e was a p p l i e d f o r c o n c e n t r a t i o n s r a n g i n g f r o m 0 to about 3 0 mg/m3 f o r a test p o w d e r
$:
w i t h the f o l l o w i n g c o n d i t i o n s : f i v e experiments ( n =
measurements p e r step ( p = 1 l ) , s i x steps f o r each experiment (m = 6) T=
51, eleven voltage
,
6 = 1,38 mV and
163 s . ( c o r r e s p o n d i n g to 215 voltage measurements p e r d i g i t a l r e a d i n g on the voltmeter).
T a b l e 1 g i v e s the obtained p a r a m e t e r s and the root-mean s q u a r e d e v i a t i o n s (RMS) between
( a ) o v e r a l l experiments.
the experimental and c a l c u l a t e d v a l u e s of
TABLE 1 C a l i b r a t i o n of the t y n d a l l o m e t e r L e i t z T M D i g i t a l Number of a d j u s t e d p a r a m e t e r s
A(mV m3mg-’ s - ’ )
3 B(mV m mg-’)
R ~ v ~ S ( $ () ~) % ’
1
0
9.16503
8.3
2
2 . 0 0 7 8 5 ( 1 0-4)
8.07008
4.6
I t c a n b e n o t i c e d that t h e i n c o r p o r a t i o n of the d r i f t f a c t o r A i n t o equations ( 1 ) and (3) i m p r o v e s the r e p r e s e n t a t i o n of the c o n c e n t r a t i o n . T h e b e h a v i o u r of a i r s a m p l i n g f i l t e r - h o l d e r s Gelman 1107 at a f l o w r a t e of 2 l/mn was studied, a s they a r e o f t e n used f o r d e t e r m i n i n g average dust c o n c e n t r a t i o n at a workplace,
in the b r e a t h i n g a r e a o f a w o r k e r . S u c h a model w a s e q u i p p e d w i t h a 25 mm diameter glassf i b e r f i l t e r Whatman GF/A, connected w i t h a Du P o n t P - 4 0 0 0 pump, and d i r e c t e d in d i f f e r e n t p o s i t i o n s r e l a t i v e l y t o the a i r f l o w in the tunnel. Ogden and Wood ( r e f .
4) measured the
c o l l e c t i o n e f f i c i e n c y of s m a l l s a m p l i n g f i l t e r - h o l d e r s in v a r i e d c o n d i t i o n s of n,ind speed and s u c t i o n r a t e . F i g . 3 shows the o b t a i n e d r e s u l t s , i t appears that i f the r e l a t i v e p o s i t i o n
A l o x i t e 5 0 f r o m E t s . M E R C I E R , median volume diameter = 3.2 urn, a = 2 . 5 0 urn. T h e s i z e 9 d i s t r i b u t i o n i n s i d e the tunnel was not found t o be d i f f e r e n t f r o m that of the o r i g i n a l powder. Y
283 of the f i l t e r - h o l d e r and the a i r f l o w does affect s t r o n g l y the measured c o n c e n t r a t i o n s , the sampling c o n d i t i o n s underestimate s l i g h t l y the r e a l concentration. F i g . 4 i n d i c a t e s the r e s u l t s obtained w i t h an automatic r e s p i r a b l e dust m o n i t o r GCA RDM-301, based on beta-ray a b s o r p t i o n f o r d e t e r m i n i n g the mass of the dust deposit obtained on an impaction p l a t e . T h e 4 mm diameter s u c t i o n o r i f i c e was p l a c e d p e r p e n d i c u l a r y to the f l o w . I t can be seen that the mass m o n i t o r u n d e r e s t i m a t e s s t r o n g l y the r e a l dust concentration. These r e s u l t s a r e t o b e compared w i t h those obtained b y s e v e r a l a u t h o r s ( r e f s .
RfFERENCE
Fig. 3
5,6).
10 10 CONCENTRATION ( MG/M31
Fig. 4
C O N C L U S IO N T h e d u s t tunnel designed b y the I N R S c a n r e p r o d u c e dusty atmospheres w i t h low a i r vel o c i t i e s and w i d e l y v a r i a b l e c o n c e n t r a t i o n s . T h e tyndallometer L e i t z TM D i g i t a l connected w i t h a d i g i t a l v o l m e t e r a l l o w s the f i n e measurement of dust c o n c e n t r a t i o n and can s e r v e as a r e f e r e n c e f o r the study of a i r s a m p l i n g i n s t r u m e n t s .
ACKNOWLEDGEMENTS T h e a u t h o r s w i s h t o e x p r e s s t h e i r g r a t i t u d e to M r . WROBEL and M A I E Z Z A f o r t h e i r technical c o n t r i b u t i o n in the r e a l i z a t i o n o f the equipment and experiences.
REFERENCES
1 I R C H A N o t i c e d'emploi P u l d o u l i t "modGle A " (1975) 2 J . C . G u i c h a r d , A e r o s o l G e n e r a t i o n u s i n g F l u i d i z e d B e d s , F i n e p a r t i c l e symposium sponsored b y E P A . Minneapolis (May 1975) 3 C . N . D a v i e s , Brit. 4 T.L. Ogden, J.D. 5 V.A.
J.
Appl. P h y s . (J. Phys.D.1,
Wood, Ann. occup. H y g . ,
S e r 2, 1 (1968) 921-932
17 (1975) 187-195
M a r p l e , K . L . Rubow, Am. Ind. H y g . A s s o c .
J.,
39 (1978) 17-25
6 J . C . V o l k w e i n , P . T . Behum, Am. I n d . H y g . Assoc. J., 39 (1978) 945-951
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Atmospheric Pollution 1980, Proceedings of the 14th International Colloquium, Paris, France, May 5--8,1980, M.M. Benarie (Ed.), Studies in Environmental Science, Volume 8 0 Elsevier Scientific Publishing Company, Amsterdam -Printed in The Netherlands
285
PRELIMINARY MEASUREMENTS OF THE SOOT STOKES-EINSTEIN PARAMETERS IN AN OXYGEN/ACETYLENE BLOW-PIPE BY MEANS OF DIFFUSION BROADENING SPECTROSCOPY
G. GOUESBET, P. FLAMENT, G. GREHAN and M. WEILL Laboratoire Associ6 au CNRS no 230 ; BP 6 7 ; 76130
MONT SAINT AIGNAN
ABSTRACT Environmental concern has been recently more and more directed towards the emission o€ soot particles from engines and flames, because of the carcinogenic properties of such particulates which are carried deeply inside the lungs. New methods of in situ measurements of soot diameters are thus desired in order to study the phenomenon of soot growing or to continuously control emission from various devices. Such measurements carried out by means of Diffusion Broadening Spectroscopy (DBS) are here reported.
INTRODUCTION Benedeck gave in 1969 (ref. 1) a comprehensive "status of the art" of Diffusion Broadening Spectroscopy for motionless systems. Hinds and Refst examined in 1972 the feasibility of the method for flow situations (ref. 2). Penner et a1 again considered flow situations and provided an extensive theoretical analysis, as well as some preliminary measurements for soot diameters (ref. 3). More soot diameter results are available from Driscoll et a1 (ref. 4 and 5) and Gouesbet et a1 (ref. 6 ) . Furthermore, it is feasible to simultaneously measure soot concentrations (and number-densities), and fluid velocities (ref. I and 8). New results are here given. Although the authors call them "preliminary", they show new interesting features. EXPERIMENTAL SET-UP AND BASIC THEORY The experimental set-up will serve to briefly explain the basic theory of DBS-systems (see fig. 1). A 3!Dbo argon laser beam FL (power : lW, on the X = 514,5 nm-line) converges in the flame under study. The control volume M is viewed by the photomultiplier PM through
286
where k is the Boltzmann constant, T the fluid temperature and p its dynamic viscosity. For monodisperse aerosols without velocity gradients in the control volume, the expression (1) reduces to :
=e nJ
S(W)
2D
laz
(3)
A,
where involves all the variables which do not interest the present paper. This spectrum is Lorentzian : its half-width at half-height (hw) determines the Stokes-Einstein coefficients. Knowing the ratio ( T / p ) , the diameters d are deduced from the Stokes-Einstein coefficients using the relation (2). In a first step, the ratio (T/)1) could be measured in situ by seeding the flame with particles larger than the soot particles to measure and using the same DBS-system : this has not been done here, but is being planned. RESULTS Measurements have been made on the axis of the blow-pipe flame (coordinate z ) . The photograph 1 shows a typical Lorentzian spectrum (note that the HP3582A actually displays the square root of the power spectrum). If fluid velocity gradients in the control volume cannot be neglected, the maximum of the spectrum is no more at zero frequency (see relation 1). We indeed observed such spectra when the control volume was located at about 2 cm of the burner exit (photograph 2 ) . The Stokes-Einstein coefficients have been determined versus z by means of the relation ( 3 ) . The soot being polydispersed, we thus actually measure "mean" coefficients. The hw was not taken from the experimental spectrum but from the Lorentzian spectrum corresponding to the same total frequency power as the experimental one. The results are shown in figure 2. No results are here given for z < 5 cm because the spectra had a displaced maximum. we From realistic values of T and )1 (T 5 2000 K, )1 ^I 7.11I-~J.s/m~), obtained values for the soot diameters. For instance, if D lo-'' S. I units, we have d 500 nm. This is consistent with Driscoll's results (same order of magnitude). We could not in the present situation measure D for z as m a l l as in Driscoll's experiments because the spectra were not Lorentzian (displaced maximum) as mentioned above. Nevertheless, let us note that Driscoll could not observes displaced spectra since data were high-pass filtered at 1 kHz before digitalization.
287
the collecting optics (lens L and diaphragm D). The interferential filter IF limits the parasitic light. In the present situation, the flame was an oxygen/acetylene blow-pipe containing soot particles. The incident light is a Dirac peak in the frequency domain (for the ease of discussion, no assessment is made for the temporal multi-mode character of the wave). The light scattered by the particles is shifted on the whole due to Doppler effect corresponding to the motion of the fluid (in the present situation, the flame was not turbulent ; furthermore, in this non-mathematical treatment of the involved phenomena, the fluid velocity is assumed to be uniform in the control volume). The optical scattered spectrum is also broadened through the random Doppler effect due to the brownian motion of the soot particles. The optical signal is changed to an electronic signal through the photomultiplier which is a quadratic detector. So, only the beating frequencies will appear in the electronic spectrum, obtained by a "folding operation'' each frequency in the optical spectrum is allowed to beat with aL1 the other frequencies. The electronic signal has been processed by a HP 3582 A spectrum analyzer : the width of the spectrum is linked to the brownian velocities of the soot particles, thus to their diameters. The mathematical analysis leads to the following expression for the electronic power spectrum (the aerosol is polydispersed, velocity gradients exist in the control volume ; the shot noise and the Dirac peak at zero frequency do not appear in the formula) :
This integral-formalism is a generalization of the summation-forma+ lism used by Penner (see ref. 3 and 8). is a constant. k is the scat4ll e tering vector defining the scattering geometry. We have = sin E(d) is the real amplitude of a wave scattered by a particle having a -+ + diameter equal to d ; n(d, v.).dd.dv is the number of particles present 3 1 in the control volume I having a diameter between d and (d+dd)and a non+ random velocity between v and ($.+d;.). Finally, D(d) is the Stokesj 3 7 Einstein coefficient defined by :
ZONCLUSION Preliminary measurements of Stokes-Einstein coefficients (and diameters) of soot particles in an oxygen/acetylene blow-pipe by means of Diffusion Broadening Spectroscopy have been reported. The feasibility of the method is demnstrated. It can be used for soot particle study with emphasis on pollution problems, between other subjects of interest. Because of the lack of morn available, the authors were not able to extensively point out assumptions and problems connected with this new method. There are indeed many important questions to answer. Probably, one of the most exciting questions is : what is to be done if the flame was turbulent 9 Consequently it is thought that DBS-systems for flow situations will have in the future a tremendous development. REFERENCES 1 G. B. Benedek, Optical Mixing Spectroscopy, with applications to problems in physics, chemistry, biology and engineering. “Polarisation, Matigre et Rayonnernent”. Presses Universitaires de Prance (1969) 49-84. 2 W. Hinds and P. C. Reist, Aerosol measurement by Laser Doppler Spectroscopy, Aerosol Science, 3 (1972) pp 501-514, 515-525. 3 S. S. Penner, J. M. Bernard and T. Jerskey, Power spectra observed in laser scattering from moving, polydisperse particle systems in flames. Acta Astronautica, (1976) pp 69-91, 93-105. 4 J. F. Driscoll and D. M. Mann, Submicron particle size measurements in an acetylene/oxygen flame. Proceedings of the Third International Workshop on Laser Velocimetry [LV-111) held at Purdue University, July 11-13 (1978). 5 J. F. Driscoll, D. M. Mann and Mc Gregor W. K., Submicron particle size measurements in an acetylene/oxygen flame. Combustion Science and Technology, 20 (1979) pp 41-47. 6 G. Gouesbet, G. GrBhan, P. Flament et M. Ledoux, MBthodes optiques en cours de dBveloppement 2 Rouen pour application 5 des problgmes de mBtrologie des dispersions. Comptes Rendus des JournBes sur les mBthodes optiques appliquges a la mgcanique des fluides (Orsay, 26 et 27 novembre 1979). To be published. I G. Gouesbet, Mesures simultanees de vitesses, fluctuations de vitesse et diam6tres de particules submicroniques dans un fluide par v6locirnBtrie-granulomBtrie laser-Doppler spectrale (VGLDS). Brevet franqais d6posB par l‘ANVAR, le 27 fBvrier 1979. 8 G. Gouesbet, P. Flament, M. Weill, Diffusion broadening spectroscopy : a way to simultaneously measure diameters, concentrations and number-densities of submicronic particles in flows. Internal Report TTI/GFW/79/11/15.
289
Fig. 1: Basic experlmental set-up
*
tothe electmlcs
2
-
pP"k
095!5
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PHOTOGRAPH :1
PHOTOGRAPH :2
Atmospheric Pollution 2 980, Proceedings of the 14th International Colloquium, Paris, France, May 5-8,1980, M.M. Benarie (Ed.), Studies in Environmental Science, Volume 8 0 Elsevier Scientific Publishing Company, Amsterdam - hinted in The Netherlands
291
THE GENERATION AND MEASUREMENT OF PRIMARY SOOT AEROSOLS BETWEEN
50 AND 4 0 0 A' Y . O . PARK, J. CAROLLA and J . W . GENTRY* Department o f Chemical E n g i n e e r i n g , * I n s t i t u t e f o r P h y s i c a l S c i e n c e
and Technology, U n i v e r s i t y o f Maryland, C o l l e g e P a r k , Maryland 2 0 1 4 2
ABSTRACT The development o f methods f o r t h e g e n e r a t i o n and measurement of p r i m a r y s o o t a e r o s o l s i n t h e s i z e r a n g e 5 0 - 4 0 0 A'
a r e described.
I n o r d e r t o c o n d u c t t h e s e measurements c o n t i n u o u s l y , a new instrument--the developed.
v a r i a b l e pressure d i f f u s i o n battery--has
been
The d e s i g n , c a l i b r a t i o n , and d a t a i n t e r p r e t a t i o n f o r
t h i s instrument are described.
INTRODUCTION
Among t h e i m p o r t a n t u n r e s o l v e d q u e s t i o n s i n a e r o s o l p h y s i c s i s t h e e f f e c t o f p a r t i c l e s i z e on a d s o r p t i o n e q u i l i b r a and r e a c t i o n kinetics. Of p a r t i c u l a r i n t e r e s t i s t h e e x t e n t o f a d s o r p t i o n and d e s o r p t i o n o f p o l y n u c l e a r a r o m a t i c h y d r o c a r b o n s on combustion aerosols.
The o b j e c t i v e s o f t h i s p a p e r a r e t o p r e s e n t a d e s c r i p t i o n
o f t h e p r o c e d u r e s f o r g e n e r a t i n g and measuring a s o o t a e r o s o l which
i s f r e e of agglomerates, c o n s i s t i n g o n l y o f primary p a r t i c l e s i n t h e s i z e r a n g e from 50-250 A'. S o o t a e r o s o l s c o n s i s t i n g p r i m a r i l y o f c a r b o n a c e o u s m a t e r i a l can b e formed e i t h e r by t h e p a r t i a l combustion o f h y d r o c a r b o n s ( a c e t y l e n e , benzene,
h e p t a n e , e t c . ) or by t h e t h e r m a l d e c o m p o s i t i o n o f a c e t y l e n e .
A t p r e s s u r e s n e a r o r g r e a t e r than one b a r ,
agglomerates c o n s i s t i n g o f 1 0 2 - 1 0 6 p r i m a r y p a r t i c l e s a r e formed f o r b o t h p r o c e s s e s . For combustion a e r o s o l s , Holmann
( r e f . 1) and Spurny ( r e f . 2 ) showed
t h a t an a g g l o m e r a t e f r e e a e r o s o l c o u l d be produced when t h e cornbustion
i s c a r r i e d o u t a t 50-200 t o r r .
The f o r m a t i o n of o n l y p r i m a r y p a r t i c l e s
when s o o t i s g e n e r a t e d by t h e t h e r m a l d e c o m p o s i t i o n o f a c e t y l e n e h a s n o t been d e m o n s t r a t e d . For a e r o s o l s l e s s t h a n 500 A',
the particle size distribution
292
can be measured i n d i r e c t l y - - e i t h e r
by a Condensation N u c l e i Counter
(CNC) o r w i t h an E l e c t r i c a l A e r o s o l A n a l y z e r (EAA) i n combination
with a diffusion b a t t e r y .
For b o t h i n s t r u m e n t s , r e l i a b l e measurements
r e q u i r e atmospheric pressure.
Consequently, t h e c r i t i c a l design
problem i s t h a t combustion o r a e r o s o l f o r m a t i o n must be c a r r i e d o u t a t s u b a t m o s p h e r i c p r e s s u r e b u t t h a t t h e measurement must be a t atmospheric pressure. I t is necessary t o increase t h e pressure w i t h o u t loss o r r e a g g l o m e r a t i o n o f t h e p r i m a r y p a r t i c l e s . By no means i s t h e i n v e r s i o n o f p e n e t r a t i o n measurements t o determine t h e s i z e d i s t r i b u t i o n s e t t l e d ( r e f s . 3 - 4 ) .
Below, t h e
a p p l i c a t i o n o f an i n v e r s i o n a l g o r i t h m based on t h e l i m i t i n g b e h a v i o r o f t h e a p p a r e n t d i f f u s i o n c o e f f i c i e n t ( r e f . 5 ) which h a s t h e a d v a n t a g e o f r e q u i r i n g few measurements and i t s a p p l i c a t i o n a r e discussed. COMBUSTION CHAMBER P r e v i o u s i n v e s t i g a t i o n s have shown t h a t o n l y primary p a r t i c l e s would be formed i f t h e combustion was c a r r i e d o u t a t low p r e s s u r e s and i f t h e flame was r a p i d l y d i s p e r s e d .
C o n s e q u e n t l y , t h e chamber
was d e s i g n e d so t h a t b o t h t h e chamber p r e s s u r e and r a t e o f d i s p e r s a l c o u l d be v a r i e d .
I n a d d i t i o n , t h e c o m p o s i t i o n and f l o w r a t e of
b o t h t h e f u e l and t h e d i s p e r s a l g a s c o u l d b e v a r i e d i n d e p e n d e n t l y . The chamber i t s e l f was a g l a s s c y l i n d e r ( 5 . 4 4 l i t e r volume, l e n g t h ) c l o s e d w i t h vacuum O-ring s e a l s a g a i n s t 0 . 9 5 c m .
2 5 cm.
aluminum f l a n g e s .
F u e l , d i s p e r s i o n g a s , e l e c t r i c a l l e a d s , and
p r e s s u r e probes w e r e introduced through t h e f l a n g e s . The f l o w r a t e o f t h e f u e l ( a c e t y l e n e ) was c o n t r o l l e d by a Nu-Pro M e t e r i n g Valve. The f u e l e n t e r e d t h e chamber t h r o u g h a Dilution o r custom b u i l t n o z z l e ( 0 . 0 5 c m . ) and was i g n i t e d . d i s p e r s i o n g a s was metered i n t o t h e chamber t h r o u g h t h e o p p o s i t e flange. I n o u r e x p e r i m e n t s , t h e o x i d a n t was p r o v i d e d by t h e d i s p e r s i o n gas and t h e f u e l w a s a c e t y l e n e . I t was p o s s i b l e t o mix a c e t y l e n e w i t h oxygen or i n e r t g a s b e f o r e e n t e r i n g t h e chamber.
c m . t u b e which can The d i s p e r s i o n r a t e was c o n t r o l l e d by t h e d i s t a n c e from t h e n o z z l e t o t h e sampling t u b e The p r e s s u r e i n and by t h e r a t i o o f d i l u t i o n g a s (02) t o t h e f u e l . t h e chamber was c o n t r o l l e d by t h e r a t e which g a s was removed t h r o u g h I t was n e c e s s a r y t o i g n i t e t h e a c e t y l e n e a t one t h e sampling tube. b a r and g r a d u a l l y r e d u c e t h e system p r e s s u r e so t h a t s t a b l e f l a m e s c o u l d be e s t a b l i s h e d a t 50 t o r r . The combustion g a s was removed t h r o u g h a 0 . 6 4 be moved from 2 0 t o 0 . 5 c m . from t h e n o z z l e .
293
A f t e r t h e s y s t e m p r e s s u r e had been s t a b i l i z e d , a sample was drawn t h r o u g h a 0.4 um NPF. The f i l t e r s w e r e examined u s i n g a s c a n n i n g e l e c t r o n microscope (Model ISI-60).
The c o n t r o l l a b l e
v a r i a b l e s f o r t h e s e measurements w e r e chamber p r e s s u r e (50-760 t o r r ) , d i l u t i o n r a t e o r 02:C2H2
r a t i o , and t h e d i s t a n c e between sampling
.
t u b e and flame n o z z l e 2.5 t o 25 c m . ) The SEM measurements showed t h a t i f t h e d i s t a n c e between flame and s a m p l i n g t u b e was a p p r o x i m a t e l y 2.5 c m . and i f t h e system p r e s s u r e was less t h a n 350 t o r r , t h e a e r o s o l c o n s i s t e d o f primary particles. CONTINUOUS MEASUREW3NT Although SEM microscopy i s n e c e s s a r y t o d e m o n s t r a t e t h e a b s e n c e of a g g l o m e r a t e s , i t i s i n a d e q u a t e a s t h e p r i n c i p a l measurement technique.
The s o o t a e r o s o l s i n o u r e x p e r i m e n t s w e r e n e a r t h e l i m i t
of r e s o l u t i o n f o r SEM. Secondly, t h e measurement and c o u n t i n g t e c h n i q u e s w e r e t e d i o u s and p r e c l u d e d measurements i n r a p i d l y c h a n g i n g systems. The p r i m a r y e x p e r i m e n t a l problem i n c o n t i n u o u s measurements is t o i n c r e a s e t h e p r e s s u r e t o a t m o s p h e r i c . The approach adopted h e r e
i s a semi-batch p r o c e d u r e i n which t h e r e p r e s s u r i z e r c o n s i s t e d of a 4 6 c m . p o r o u s t u b e [ a s i m i l a r t u b e was used by Ranade ( r e f . 6 ) t o a v o i d w a l l l o s s i n a s a m p l e r ] s u r r o u n d e d by a c o n s t a n t p r e s s u r e reservoir. The r e p r e s s u r i z a t i o n c y c l e i s a s f o l l o w s : 1. The p o r o u s t u b e and r e s e r v o i r a r e e v a c u a t e d . 2.
The porous t u b e i s opened t o t h e combustion chamber and
t h e r e s e r v o i r p r e s s u r e i s set e q u a l t o t h a t o f t h e chamber. 3. The p o r o u s t u b e i s c l o s e d t o t h e chamber and t h e r e s e r v o i r p r e s s u r e i s i n c r e a s e d t o o n e atmosphere. 4. The p o r o u s t u b e i s opened t o t h e c o n d e n s a t i o n n u c l e i c o u n t e r . The a d v a n t a g e o f t h i s d e s i g n f o r t h e r e p r e s s u r i z e r i s t h a t r e a g g l o m e r a t i o n and c o n d e n s a t i o n o f w a t e r vapor on t h e p a r t i c l e s a r e unlikely.
Wall l o s s t o p o r o u s t u b e s h o u l d b e s m a l l .
SEM
m i c r o g r a p h s o f a e r o s o l s b e f o r e and a f t e r r e p r e s s u r i z a t i o n show no c h a n g e s i n p a r t i c l e s i z e and a g g l o m e r a t e f o r m a t i o n ( F i g . 1-2). P r e l i m i n a r y measurements u s i n g a 1 0 0 0 t u b e d i f f u s i o n b a t t e r y w i t h an Environment One CNC m o d i f i e d w i t h an e x t e r n a l l a s e r a s a l i g h t s o u r c e [ H o l l a n d e r ( r e f . 711 gave v a l u e s of 350 A o f o r a p r e s s u r e o f 1 2 0 t o r r and 380 A'
f o r a p r e s s u r e o f 350 t o r r .
s i z e s are c o n s i s t e n t w i t h t h e p a r t i c l e s observed by SEM.
These
' F i g . 1. Soot a e r o s o l b e f o r e and a f t e r r e p r e s s u r i z e r x 55,000).
(120 torr;
C o n v e n t i o n a l d i f f u s i o n b a t t e r i e s - -char a c t er i z ed by segments o f d i f f e r e n t l e n g t h s and number o f c h a n n e l s o r by o p e r a t i o n a t d i f f e r e n t flow rates--have
a number o f a m b i g u i t i e s and u n c e r t a i n t i e s i n t h e
measurement o f u l t r a f i n e a e r o s o l s , e s p e c i a l l y e n t r a n c e e f f e c t s f o r e a c h o f t h e segments and t h e s e n s i t i v i t y o f g e n e r a t o r s o f u l t r a f i n e a e r o s o l s t o changes i n t h e flow r a t e .
The v a r i a b l e p r e s s u r e d i f f u s i o n
b a t t e r y was d e s i g n e d t o minimize t h e s e d i f f i c u l t i e s a s w e l l a s a l l o w i n g measurements t o b e made o v e r t h r e e o r d e r s of magnitudes of d i f f u s i o n c o e f f i c i e n t s . The p r i n c i p l e o f t h e i q a t r u m e n t i s t h a t f o r a e r o s o l s w i t h d i a m e t e r s below 1 0 0 0 A a , t h e d i f f u s i o n c o e f f i c i e n t h a s a s t r o n g p r e s s u r e dependence e x p r e s s e d by t h e Cunningham-Stokes c o r r e c t i o n . Our prototype c o n s i s t s of ten 0 . 6 3 cm. brass tubes i n p a r a l l e l . Needle v a l v e s a f t e r and b e f o r e t h e t u b e s can a r b i t r a r i l y a l t e r t h e system p r e s s u r e measured by a McLeod gauge. r e p r e s s u r i z e d t o atmospheric pressure.
The p a r t i c l e s t r e a m i s t h e n The a e r o s o l c o n c e n t r a t i o n
i s measured w i t h e i t h e r a c o n d e n s a t i o n n u c l e i c o u n t e r o r an e l e c t r i c a l aerosol analyzer.
The d a t a c o n s i s t o f measurements o f p e n e t r a t i o n
a s a function of system pressure. DATA INVERSION
The g e n e r a l problem o f f i n d i n g t h e s i z e d i s t r i b u t i o n f u n c t i o n
F(D*) from p e n e t r a t i o n measurements i s t o s o l v e t h e i n t e g r o d i f f e r e n t i a l equation:
295
5
m
(Q) =
Pt
D*,Q) F(D*) dD*
(1)
0
and P t a r e t h e e x p e r i m e n t a l and t h e o r e t i c a l p e n e t r a t i o n s ,
where
i s t h e f l o w r t e , and D* i s t h e i n d e p e n d e n t v a r i a b l e ( d i f f u s i o n c o e f f i c i e n t ) . The p r i n c i p a l d i f f i c u l t y i n t h e i n v e r s i o n o f Q
e q u a t i o n 1 i s t h a t P t i s a v e r y b r o a d f u n c t i o n o f D*; and consequently, t h e value of the d i s t r i b u t i o n function i s s e n s i t i v e t o e x p e r i m e n t a l error. Our a l g o r i t h m , e x p l a i n e d i n d e t a i l e l s e w h e r e ( r e f . 5 ) , i s based on t h r e e i d e a s : 1.
The n a t u r a l v a r i a b l e f o r t h e d i s t r i b u t i o n f u n c t i o n i s t h e -.
diffusion coefficient. 2. The d i s t r i b u t i o n f u n c t i o n can b e e x p r e s s e d w i t h a l o g normal f u n c t i o n . 3.
The p a r a m e t e r s o f t h e d i s t r i b u t i o n - - m e a n
diffusion coefficient
(D*) and s t a n d a r d d e v i a t i o n u--are d e t e r m i n e d from t h e l i m i t i n g 1 behavior of t h e apparent d i f f u s i o n c o e f f i c i e n t . S p e c i f i c a l l y , o u r a l g o r i t h m i s based on t h e e x p r e s s i o n s : Ln DT =
$',
Ln
E* d
and
?rumericai s i r n u i a r i v n s
ueiiiuIisc;Ldc-eu uiac
c o u l d b e o b t a i n e d unambiguously.
cue pa~airiece b ~u
~ I I UL J -
1
The a l g o r i t h m was found t o be
r e l a t i v e l y i n s e n s i t i v e t o s m a l l random e r r o r s i n t h e p e n e t r a t i o n measurements. SUMMARY
Soot a e r o s o l s c o n s i s t i n g o f p r i m a r y p a r t i c l e s - - 1 0 0
t o 4 0 0 A'--
w e r e produced by p a r t i a l o x i d a t i o n o f s o o t . I f t h e system p r e s s u r e was l e s s t h a n 350 t o r r and i f t h e flame was r a p i d l y d i s p e r s e d , a g g l o m e r a t e f o r m a t i o n was s u p p r e s s e d .
In order t o carry out
c o n t i n u o u s measurements, a r e p r e s s u r i z e r was developed (and t e s t e d f o r p r e s s u r e s down t o 1 2 0 t o r r ) . A v a r i a b l e p r e s s u r e d i f f u s i o n b a t t e r y h a s been s p e c i a l l y d e v e l o p e d t o minimize e n t r a n c e e f f e c t s . I n o r d e r t o i n t e r p r e t t h e measurements, an a l g o r i t h m based on t h e l i m i t i n g b e h a v i o r o f t h e a p p a r e n t d i f f u s i o n c o e f f i c i e n t h a s been d e v e l o p e d and t e s t e d .
296
ACKNOWLEDGEMENT J.W.G.
would l i k e t o acknowledge t h e s u p p o r t of t h e N a t i o n a l
S c ienc e Foundation, Grant No.
78 00738 A01, a n d t h e S t a t e o f Maryland
Department of N a t u r a l R e s o u r c e s . REFERENCES
1 K.H. Holmann, Agnew. Chem., 80 (1968) 425. 2 K.R. Spurny, H.P. B a u m e r t , H. O p i e l a and G. Weiss, Z b l . Bakt. Hyg. Abt. I. O r i g . B . , 1 6 5 ( 1 9 7 7 ) 139. 3 J . P . Maigne, P.Y. T u r p i n , G. M a d e l a i n e and J. B r i c a r d , J . A e r o s o l S c i . , 5 ( 1 9 7 4 ) 339. 4 S.C. Soderholm, J. A e r o s o l S c i . , 1 0 ( 1 9 7 9 ) 1 3 6 . 5 Y.O. P a r k , W.E. King a n d J . W . G e n t r y , I &EC P r o d u c t R/D, 1 9 ( 1 9 8 0 ) . 6 M.B. Ranade, D.K. W e r l e a n d D.T. Wasan, J. C o l l o i d a n d I n t e r f a c e S c i e n c e , 56 ( 1 9 7 6 ) 4 2 . 7 W. H o l l a n d e r , J. Schtlrmann a n d G. Schumann, A t m o s . E n v i r o n . , 1 3 ( 1 9 7 9 ) 743.
Atmospheric Pollution 1980, Proceedings of the 14th International Colloquium, Paris, France, May 5-8,1980, M.M. Benarie (Ed.), Studies in EnvironmentalScience, Volume 8 0 Elsevier Scientific Publishing Company, Amsterdam -Printed in The Netherlands
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IN SITU CHARACTERIZATION OF SOOT AEROSOLS BY SCATTERING AND ABSORPTION OF A LASER BEAM J . LAHAYE and G. PRADO Centre de Recherches sur la Physico-Chimie des Surfaces Solides, C.N.R.S. 24, avenue du President Kennedy 68200 MULHOUSE (France)
ABSTRACT Soot is a very pol luting by-product of combustion of carbonaceous materials. I t s characterization-volume fraction, number and average s i z e of aggregates-can be carried out by an i n situ optical method (scattering and absorption of a LASER beam). Results are i n good agreement w i t h those obtained by probing and observation of sample with an electron microscope. Different v a r i e t i e s o f "carbons" may be formed by heat treatment of carbonaceous materials. None of these i s pure carbon ; besides carbon, they contain heteroelements such as hydrogen, oxygen, nitrogen and s u l f u r as well as different metals (1). Soot o r carbon black consists o f aggregates of pseudospherical p a r t i c l e s having diameters o f a few tens of nanometers. Each aggregate i s formed by a few t o a few tens of p a r t i c l e s . Phase contrast electron microscopy points out t h a t carbon layers are continuous through several adjacent particles. Therefore, soot dimension i s often characterized by the s i z e of aggregates rather than the diameter of individual particles. In order t o avoid a misunderstanding i n terminology, i t is important to note t h a t carbon black o r soot is ?ilwvrs_ produced from the gas phase. I f the i n i t i a l carbonaceous material i s l i q u i d o r s o l i d , only the part capable to v o l a t i l i z e e i t h e r by phase change or by decomposition i s l i a b l e to give soot. Mechanisms of soot production are not completely c l a r i f i e d ( 2 , 3 ) . In the domain o f temperature o f soot formation i n relation with a i r pollution, i t i s usually admitted t h a t polycyclic aromatic hydrocarbons (P.C.A.H.) are intermediate species between carbonaceous precursors and soot p a r t i c l e s . In pyrolytic system ( i n the absence o f oxygen) soot i s formed from P.C.A.H. through liquid droplets. In flame, further experimental evidence is s t i l l necessary t o allow conclusion ; i n this casethe role of ions i n soot nucleation might be important (4,5). The purpose of the paper is not t o give information on mechanism of soot
298
production b u t t o describe techniques o f observation and c h a r a c t e r i z a t i o n o f soot aerosols.
I . Experimental methods D i f f e r e n t techniques can be used f o r the c h a r a c t e r i z a t i o n o f soot aerosols. We s h a l l mention : probing
-
c o l l e c t i o n on wires i n s i t u o p t i c a l technique.
1.1. F%bjng-;ectn~que Probing has been e x t e n s i v e l y used a t the l a b o r a t o r y . The c o l l e c t e d soot i s observed w i t h an e l e c t r o n microscope (JEOL 100 B ) . On the micrographs, the average s i z e and s i z e d i s t r i b u t i o n a r e determined w i t h a semi-automatic s i z e meter Zeiss TGZ3. This technique combined w i t h measurement o f the weight o f soot c o l l e c t e d
g i v e the s i z e and number o f i n d i v i d u a l p a r t i c l e s i n the c o l l e c t e d sample. I t has, however, a few disadvantages : i n usual q u a r t z o r metal probe, a l a r g e p r o p o r t i o n o f soot s t i c k s t o the w a l l and consequently i s n o t c o l l e c t e d on the f i l t e r l o c a t e d a t the probe e x i t . A
.
m o d i f i e d probe has been developped which avoid such deposition : a very small p r o p o r t i o n o f water o f the j a c k e t i s introduced i n t o the pipe. Besides the quenching r e s u l t i n g from v a p o r i z a t i o n o f a p a r t o f the water, the formation o f a t h i n f i l m
o f water on the i n s i d e w a l l o f the probe might be responsible f o r the absence o f deposit i n s i d e the probe.
. a probe, whatever i t s s i z e , d i s t u r b s the system i n which i t i s introduced. . probing and observation o f s o o t by e l e c t r o n microscopy are time consuming. 1* *
*
colle_~_tlon-on-a-tung~t~n-~l~~
Soot p a r t i c l e s deposit on a w i r e introduced i n t o a flame. A f t e r a few seconds, t h e w i r e i s withdrawn and the sample i s characterized by e l e c t r o n microscopy. I n t h i s technique the weight o f soot c o l l e c t e d i s meaningless because i t cannot be r e l a t e d t o a known volume o f the gas phase. I.3.
Is_sltu_oetlcal_tech~~q~e_
O p t i c a l techniques are w e l l adapted t o f a s t phenomena ( a few milleseconds i n the case o f s o o t formation). Moreover, conducted w i t h some precaution, i t does n o t d i s t u r b the system.
A technique we used f o r the study o f polymer combustion
(6)
has been developped. The p r i n c i p l e o f such a measurement f o l l o w s : l e t us consider a given volume o f s o o t i n suspension i n a gas phase ; the number and average s i z e o f aggregates per u n i t volume are noted N and D, r e s p e c t i v e l y . The wavelength o f i n c i d e n t beam i s A .
299
2~rD<<1, which i s a reasonable assumption f o r soot i n flames, Provided A computations can be carried out according t o Rayleigh approximation. T h u s ,
where Qvv : s c a t t e r efficiency (the subscripts vv indicate t h a t incident and scattered
l i g h t s are v e r t i c a l l y polarized) Kext : e x t i nc t i on coeff ic i e n t m : complex refractive index of soot. From equation (1) and ( Z ) , N and D can be computed. I t can be noticed t h a t the extinction c o e f f i c i e n t i s proportional to volume fraction of soot i . e . the volume of soot per u n i t volume of aerosol. For these determinations, the 514.5 nm wavelength of a 5 w ionized-argon LASER has been used. The incident beam i s chopped, and a lock i n amplifier tuned t o the frequency of the chopper s e l e c t s t h a t part of the signal received by the detector which i s in constant phase w i t h the reference input. The spatial resolution of such a device i s 0.01 mm3. In order t o make c l e a r the usefulness of t h i s technique, we shall give some r e s u l t s obtained w i t h premixed sooty flames. 11. Soot produced i n premixed methane/oxygen and propane/oxygen flames. A n atmospheric hydrocarbon/oxygen flame i s obtained w i t h a burner made of a sintered brass p l a t e . The flame i s protected with an annular flow of nitrogen. In such a system the following parameters can be controlled : - fuel equivalence r a t i o ; i n the case of propane/oxygen flame, i t has been varied from 2 . 1 t o 3 ( 2 . 1 corresponds t o the beginning of soot formation ; above 3 , the flame becomes turbulent). - i n i t i a l cold gas velocity ; i t i s a convenient way t o modify the temperature as the energy released increases w i t h gas velocity while energy transfer i s hardly affected. For example, f o r a fuel equivalence of 2.5 i n a propane/air flame, the temperature determined by the Kurlbaum method goes from 1600" to 1800°C when the i n i t i a l cold gas velocity goes from 3.92 t o 6.26 cm/s.
* I -1. _ c o m e a r l s ~ n _ o _ f - r e _ s u l t s - o b _ _ t ~ l n _ ~ ~ - ~ ~ -.e ~ ~ ~ ~ n _ ~ - ~ n ~ When a probe i s introduced a t a given distance d above the burner, a volume of the flame of Ad thickness i s collected. This thickness can be determined by measuring the variation of scattered l i g h t i n the zdRe close t o the nose of the
300
probe. W i t h the microprobe used a t the laboratory d i s equal t o 3 mn. Therefore, f o r comparing r e s u l t s obtained by probing and optical techniques, s h i f t i n probing determination has to be taken i n t o consideration. In table I , a r e compared the r e s u l t s obtained w i t h a probe located a t 5,lO and 15 mm with those given by scattering/absorption of l i g h t a t 3,8 and 14 mn. TABLE I . Volume fraction f v and s i z e of soot p a r t i c l e s , determined by probing (individual p a r t i c l e s ) and i n situ (aggregates) techniques.
distance to burner
2.65 x
f Probing
cnidi6
\--) Cn.d. In situ technique (LASER)
fV
3 mm
'I3
nm
8 mm
2.7 x
-
20.5
2.45 x lo-'
3.0 x lo-'
7.6
38.5
14 mm 6.2 x 21.6
5.8 x 67
Considering the poor s p a t i a l resolution i n probing soot, the agreement between volume fractions f v determined by both techniques i s excel l e n t . Soot concentrations in a flame can be computed w i t h a good accuracy from the extinction coefficient, which i s an easy and f a s t way t o proceed. The r a t i o of mean diameters as determined by optical and by probing increases, which corresponds t o an aggregation of individual soot p a r t i c l e s . Another comparison has been carried o u t i n collecting s o o t on a tungsten wire of 0.3 mm diameter, s e t horizontally a t 6 , 12 and 15 mn above the burner. Mean diameters of samples have been obtained by measuring the diameters o f 2,000 p a r t i c l e s . By comparison w i t h optical technique (figure 1) i t i s clear t h a t , a t 6 mm, the agreement between the two determinations i s good : individual p a r t i c l e s d i d not agglomerate. Later on, the mean diameter of individual p a r t i c l e s remains constant and close t o 20 nm, while the s i z e of aggregates increases. The agreement between diameters of individual p a r t i c l e s collected w i t h a probe (Table I ) and deposited on wire ( f i g u r e 1) i s satisfactory. These preliminary experiments lead t o the following procedure f o r characterization of soot aerosols : the volume fraction i s computed from extinction coefficient of a LASER beam s i z e and number of aggregates are determined from extinction coefficient and s c a t t e r efficiency of the same LASER beam s i z e s of individual p a r t i c l e s are determined by deposition on a tungstene wire and subsequent characterization by electron microscopy. For problem related t o
. . .
301
a i r pollution t h i s determination i s generally unnecessary.
Cnidi6 '13 F i g . 1. Comparison of mean diameters a =(-) as function of height above 1 1 m electron microscope (individual burner : 0 optical method (aggregates) ; p a r t i c l e s ) . Premixed CH4/02 flame (fuel equivalence P = 2.54 ; i n i t i a l cold gas velocity v = 7.4 cm/s)
.
I1
.*. Aeellcatlcn- of-cet_ica1-an_Li-~ro_b_ g!I _ r l l e _ t _ h _ o d s _ _ t o _ _ a - e ~ ~ l ~ ~ L-flams i _ e ~ ~. e a ~ ~ ~ ~
The above methode has been applied t o a premixed propane/oxygen flame. Table I1 shows the influence of temperature of the flame on the different c h a r a c t e r i s t i c s of s o o t aerosols. Volume fraction f v , s i z e and number of aggregate are determined by optical method, s i z e and number of individual p a r t i c l e s by probing, weighing and observation by electron microscopy. I t appears t h a t volume fraction, s i z e and number of aggregates decrease. This behavior i s d i f f e r e n t from what i s obtained i n a thermal system ( i n the absence of oxygen). I t points o u t the larger e f f e c t of a temperature increase on the kinetics of oxidation of intermediate species as compared t o pyrolysis. T h i s observation agrees w i t h a wellknown property of flame : soot can be reduced by increasing temperature e.g. in preheating gases before introduction i n the burner. I t can a l s o be noticed t h a t the number of particles per aggregate decreases when temperature increases.
302
TABLE I1
Premixed propane/oxygen flame Distance to burner : 10 mm.
-
Fuel equivalence : 2.5
CONCLUSION Characterization of soot aerosols by the techniques described i n the present paper i s very v e r s a t i l e . I t i s particularly well adapted t o system in which the characteristics o f soot aerosol are constant a l l along the l i g h t p a t h . Indeed, the extinction c o e f f i c i e n t integrates informations collected on the t o t a l i t y of the l i g h t path. This i s the case of soot i n the exhaust gases of engines o r in gas flows of chimneys. In a diffusion flame where soot concentration i s not constant in the e n t i r e volume, a method described by Jagoda e t a1 ( 6 ) can be applied. RE FE RENCES
1 J . Lahaye and G. Prado, Water, Air and Soil Pollution 3, 473-81 (1974). 2 H . Gg Wagner, Seventeenth Symposium (International) on Combustion, The Combustion I n s t i t u t e (Pittsburgh, Pennsylvania), 3-19 (1978). 3 J . Lahaye and G . Prado, Chemistry and Physics of Carbon, e d i t . P . L . Walker J r and P.A. Thrower (M. Dekker, N.Y.), 167-294 (1978). 4 B.L. Wesborg, A . C . Yeung and J.B. Howard, Fifteenth Symposium (International)
on Combustion, The Combustion I n s t i t u t e (Pittsburgh, Pennsylvania), 1439-1448 (1975). 5 K.H Homann, Ber. Bunsenges Phys Chem. 83, 738-745 (1979). 6 J . Jagoda, G. Prado and J . Lahaye, CombusTTon and Flame, 36 (1978). 229-235 (1978). 7 G. Prado, J . Jagoda and J . Lahaye, Fire Research,
.
.
.
1,
Atmospheric Pollution 1980, Proceedings of the 14th International Colloquium, Paris,France, May 5-8,1980, M.M. Benarie (Ed.), Studies in Environmental Science, Volume 8 0 Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
303
THE DEVELOPMENT OF THE GCAF I N E R T I A L IMPACTOR FOR SEPARATION O F
NON-SPHERICAL PARTICLES S.
LIN,
R.
PRESTON and J.W.
GENTRY*
Department o f Chemical E n g i n e e r i n g ,
" I n s t i t u t e f o r P h y s ical Science
a n d Technology, U n i v e r s i t y of Maryland, C o l l e g e P a r k , Maryland 2 0 7 4 2
ABSTRACT An i n s t r u m e n t d e s i g n e d t o p r e f e r e n t i a l l y s e p a r a t e f i b e r s from s p h e r i c a l p a r t i c l e s c o n s i s t i n g of a m u l t i p l e s t a g e impactor has been developed.
Each s t a g e c o n s i s t s o f t w o s e c t i o n s - - t h e
f i r s t section
b e i n g a f i l t r a t i o n s t a g e , a n d t h e s e c o n d s e c t i o n b e i n g an i m p a c t i o n stage.
D e s c r i b e d i n t h i s p a p e r a r e t h e e x p e r i m e n t a l d e s i g n and
calibrations with isometric aerosols.
S i m u l a t i o n s o f t h e performance
o f t h e f i l t r a t i o n state with non-spherical
p a r t i c l e s a r e presented.
INTRODUCTION
The m a j o r p r o b l e m i n a n a l y s i s f o r a s b e s t o s f i b e r s i s t h e r e l a t i v e abundance o f i s o m e t r i c p a r t i c l e s t o f i b e r s ( 3 . 1 ~ 1t ~o 1 ) .
The
o b j e c t i v e s o f t h i s r e s e a r c h program a r e t o d e v e l o p an i n s t r u m e n t f o r enrichment o f t h e a e r o s o l i n c r e a s i n g t h e c o n c e n t r a t i o n of f i b e r s . Our a p p r o a c h i s b a s e d upon t h e e x p e r i m e n t a l e v i d e n c e t h a t : 1.
The p e n e t r a t i o n o f f i b e r s t h s o u g h n u c l e p o r e f i l t e r s and
Anderson i m p a c t o r s i s g r e a t e r t h a n f o r i s o m e t r i c p a r t i c l e s o f t h e
.
s a m e a e r o d y n a m i c d i a m e t e r s ( r e f . 1) 2.
There i s a tendency f o r f i b e r s t o a l i g n i n flow f i e l d s
c h a r a c t e r i z e d by g r a d i e n t s i n t h e f l o w f i e l d
(ref. 2 ) .
D e s c r i b e d i n t h i s p a p e r a r e t h r e e d e v e l o p m e n t s which c a n b e regarded as e s s e n t i a l s t e p s i n t h e development of t h e instrument:
1.
The d e s i g n o f t h e i m p a c t o r and t h e d e s c r i p t i o n o f t h e
experimental design.
2.
Measurements o f t h e c o l l e c t i o n e f f i c i e n c y u s i n g m o n o d i s p e r s e ,
s p h e r i c a l aerosols. 3.
The s i m u l a t i o n o f t h e b e h a v i o r o f n o n - s p h e r i c a l
t h e g l a s s c a p i l l a r y a r r a y f i l t e r s (GCAF).
particles in
304
IMPACTOR DESIGN
The impactor was designed t o i n c o r p o r a t e a membrane f i l t e r and an i n e r t i a l impactor i n each s t a g e .
Specifically, the principal
f e a t u r e s i n t h e s t a g e are: 1. A cover p l a t e w i t h an o r i f i c e diameter (Do) constructed of b r a s s o r a nuclepore f i l t e r sets t h e j e t diameter.
2.
A glass capillar y array f i l t e r
( 1 0 , 2 5 o r 50 u m ) i s placed
d i r e c t l y below t h e cover p l a t e . 3.
An impaction p l a t e l o c a t e d e x a c t l y 0.254 Dm below t h e s u r f a c e
of t h e GCAF. The design used f o r t h e impactor i s v e r s a t i l e i n t h a t a Mercer impactor ( r e f . 3 ) (removal o f t h e GCAF) and membrane f i l t e r (removal of impaction p l a t e ) r e p r e s e n t l i m i t i n g c a s e s f o r t h e impactor.
O-ring s e a l s a r e used t o seal t h e s t a g e t o t h e impactor housing and t o a s s u r e a t i g h t s e a l around t h e GCAF.
Because t h e r e a r e a l a r g e 5
number of pores below t h e cover p l a t e (103-10 1, t h e v e l o c i t y p r o f i l e a c r o s s t h e j e t i s more n e a r l y uniform o f f e r i n g t h e p o t e n t i a l f o r higher c o l l e c t i o n e f f i c i e n c i e s f o r f i b e r s than conventional impactors The c a l i b r a t i o n experiments were c a r r i e d o u t with 0 . 4 8 and 0 . 7 9 u m polystyrene l a t e x a e r o s o l s nebulized with a Dautrebande
generator. was 0.32 c m . conditions :
In t h e f i r s t experiments, t h e o r i f i c e i n t h e cover p l a t e Experiments were c a r r i e d o u t under t h e following
1.
N o cover p l a t e and no GCAF ( t o e v a l u a t e t h e wall l o s s ) .
2.
Coverplate, GCAF, but no impaction p l a t e ( t h e e f f e c t of t h e
GCAF a l o n e ) .
3.
Coverplate, impaction p l a t e , but no GCAF (Mercer i n e r t i a l
impactor). 4. Coverplate, GCAF, and impaction p l a t e . I n each c a s e , t h e GCAF were checked by scanning e l e c t r o n micro-
scope before u s e , t h e impaction p l a t e coated with s i l i c o n e oil, and t h e p r e s s u r e drop a c r o s s t h e s t a g e measured. The c o l l e c t i o n e f f i c i e n c y was determined from t h e r a t i o of a e r o s o l concentrations before and a f t e r t h e impactor s t a g e a s measured by a Phoenix JM-4000 D u s t Photometer. EXPERIMENTAL RESULTS
From t h e experimental measurements of p r e s s u r e drop and f r a c t i o n a l p e n e t r a t i o n , it was found t h a t : 1. 0.48
There was a s u b s t a n t i a l q u a l i t a t i v e d i f f e r e n c e between t h e and 0 . 7 9 pm a e r o s o l s .
305 2.
The p r e s s u r e d r o p a c r o s s t h e p o r e s was d e s c r i b e d by t h e
H a g e n - P o i s e u i l l e l a w and w a s u n a f f e c t e d by t h e p r e s e n c e o f t h e i m p a c t i o n p l a t e o r by t h e p r e s e n c e o f p a r t i c l e s .
3.
Examination o f t h e a e r o s o l d e p o s i t i o n p a t t e r n on t h e
i m p a c t i o n p l a t e ( a NPF w i t h o u t s i l i c o n e o i l was used a s t h e c o l l e c t i o n s u r f a c e ) s u g g e s t s a uniform a e r o s o l c o n c e n t r a t i o n i n t h e nozzle. 4.
The c o l l e c t i o n e f f i c i e n c y f o r t h e GCAF a l o n e was h i g h e r f o r
t h e 0.48 ym p a r t i c l e s t h a n f o r t h e 0.79 pm. I n F i g . 1, t h e p r e s s u r e i s p l o t t e d a s a f u n c t i o n o f v e l o c i t y f o r a l l t h r e e p o r e s i z e s (DF)
of GCAF.
A t t h e h i g h e s t flow r a t e s t u d i e s ,
t h e p r e s s u r e d r o p was s t i l l l i n e a r w i t h flow r a t e w i t h a s l o p e g i v e n by t h e r e l a t i o n :
AP = 128 ~ I L
Agreement of e x p e r i m e n t and t h e o r y w e r e w i t h i n t h e l i m i t s o f u n c e r t a i n t y i n t h e p o r e d i a m e t e r DF, L.
t h e p o r o s i t y E, and t h e pore t h i c k n e s s These p r e s s u r e d r o p measurements w e r e i m p o r t a n t i n t h a t t h e y
e s t a b l i s h t h e f l o w w i t h i n t h e p o r e s are l a m i n a r .
There i s no
i n d i c a t i o n from t h e p r e s s u r e d r o p measurements t h a t t h e p r e s e n c e o f t h e i m p a c t i o n p l a t e d i s t u r b s t h e f l o w p r o f i l e above o r w i t h i n t h e pores. A
E
No lciosol
0m
.79 urn
0 0
4 a urn
Y
a. 0 p:
150
D Y
p:
=
VI
vr Y
p:
a
O n ""
V E L O C I T ~ :miter
F i g . 1. P r e s s u r e d r o p ( c m H 2 0 ) as a f u n c t i o n o f v e l o c i t y ( m / s e c ) . I n Fig. 2 , t h e c o l l e c t i o n e f f i c i e n c y i s p l o t t e d a s a function of f l o w r a t e f o r 0.48 um f o r t h e c a s e o f t h e GCAF a l o n e ( 0 ) and t h e c a s e o f t h e GCAF w i t h t h e i m p a c t i o n p l a t e .
For e x p e r i m e n t s where
306
t h e GCAF was removed, c o l l e c t i o n e f f i c i e n c y was l e s s t h a n 5%.
For
t h e s e e x p e r i m e n t s , c o l l e c t i o n a p p e a r s t o be c o m p l e t e l y d e t e r m i n e d by t h e p r o p e r t i e s o f t h e GCAF w i t h peak e f f i c i e n c i e s f o r 50% f o r t h e 25 pm p o r e s and 35% f o r t h e 5 0 pm p o r e s .
0 0
25 urn G C A F
8
50 urn G C A F
Fig. 2. C o l l e c t i o n e f f i c i e n c y a s a function of particles
f o r 0.48 wrn
.
I n Fig.
3, t h e e x p e r i m e n t a l measurements a r e r e p e a t e d b u t w i t h
0 . 7 9 pm p a r t i c l e s .
F o r t h e GCAF a l o n e , t h e e f f i c i e n c i e s w e r e l e s s
than f o r t h e smaller p a r t i c l e s . ( 1 0 % f o r 50 pm and 2 0 % f o r 2 5 u m . ) However, when t h e i m p a c t i o n p l a t e was added, a s t e e p l y i n c r e a s i n g c o l l e c t i o n e f f i c i e n c y curve i s obtained.
The c u r v e s w e r e s h i f t e d
toward h i g h e r f l o w r a t e s when a l a r g e r p o r e s i z e o r n o GCAF was used.
Here o n e o b t a i n s a c l a s s i c a l impaction c u r v e w i t h t h e
i n c r e a s e c o r r e s p o n d i n g t o a S t o k e s number o f 0 . 0 1 , than i s u s u a l l y observed ( r e f . 4 ) .
a lower v a l u e
The e s s e n t i a l p o i n t i s t h a t a s
t h e p a r t i c l e s i z e s h i f t s from 0 . 4 8 t o 0 . 7 9 pm,
t h e mechanism s h i f t s
from removal by t h e GCAF t o i m p a c t i o n .
'"1
00
25 urn GCLF
8
5 0 u m GCAF
I 00
fL . -125
,250
Isrlc
F i g . 3. C o l l e c t i o n e f f i c i e n c y a s a f u n c t i o n o f particles.
f o r 0.79 um
307 Although e x p e r i m e n t a l measurements
( r e f . 5 ) showing s i g n i f i c a n t
i m p a c t i o n a t low S t o k e s numbers are w e l l documented, w e were skeptical of our r e s u l t s .
Measurements were made r e p l a c i n g t h e
Phoenix p h o t o m e t e r w i t h a Model 2 0 3 Royco y i e l d i n g t h e same r e s u l t s . A sample of a e r o s o l w a s c o l l e c t e d and examined f o r a g g l o m e r a t e s ;
e x c e p t f o r an o c c a s i o n a l d o u b l e t , t h e r e w e r e none.
A l l of our
measurements s u g g e s t t h a t t h e i m p a c t o r d e s i g n i s more e f f i c i e n t i n removing a e r o s o l s a t low S t o k e s number t h a n e x p e c t e d . I t i s somewhat s u r p r i s i n g t h a t t h e GCAF are more e f f i c i e n t a t
removing t h e 0 . 4 9 pm a e r o s o l t h a n t h e 0 . 7 9 urn p a r t i c l e s .
Theoretical
c a l c u l a t i o n s s u g g e s t d i f f u s i o n t o t h e p o r e w a l l s s h o u l d be l e s s than 5%.
I t i s o u r c o n j e c t u r e t h a t t h e i n c r e a s e d c o l l e c t i o n i s due
t o turbulence a t t h e entrance.
T h i s h y p o t h e s i s w i l l be i n v e s t i g a t e d
by u s i n g a e r o s o l s w i t h d i a m e t e r s between 0 . 5 Um and 0 . 7 5 urn i n o r d e r t o i n v e s t i g a t e t h e t r an s i t i o n between dominant mechanisms
.
NUMERICAL SIMULATIONS
I n e s t i m a t i n g t h e e f f i c i e n c y o f t h e GCAF t o remove f i b e r s , c o g n i z a n c e o f s e v e r a l u n c e r t a i n t i e s must be c o n s i d e r e d :
1.
The a n a l o g o f t h e Cunningham-Stokes e q u a t i o n f o r f i b e r s i s
n o t known.
2.
There i s u n c e r t a i n t y i n a c c o u n t i n g f o r f i b e r o r i e n t a t i o n i n
determining t h e diffusion c o e f f i c i e n t f o r f i b e r s . 3.
Entrance e f f e c t s f o r f i b e r s a s w e l l a s isometric p a r t i c l e s
are n o t u n d e r s t o o d a l t h o u g h t h e r e i s e v i d e n c e i n d i c a t i n g t h a t f i b e r s have g r e a t e r p e n e t r a b i l i t y .
4.
The e f f e c t o f p o l y d i s p e r s i t y on c o l l e c t i o n e f f i c i e n c i e s f o r
f i b e r s is i n c o m p l e t e l y u n d e r s t o o d . W e have d e v e l o p e d a computer code ( r e f . 6 ) t o examine t h e i n f l u e n c e
of p o l y d i s p e r s i t y . 1.
Our c o d e shows t h e f o l l o w i n g f e a t u r e s :
The dynamic s h a p e f a c t o r s ( o r aerodynamic d i a m e t e r s ) a r e
c a l c u l a t e d assuming randomly o r i e n t e d s p h e r o i d s 2.
-
One d i m e n s i o n ( d i a m e t e r € o r f i b e r s and t h i c k n e s s f o r p l a t e l e t s )
i s c o n s t a n t , t h e s e c o n d dimension i s d i s t r i b u t e d l o g - n o r m a l l y . 3.
G r a v i t a t i o n a l s e d i m e n t a t i o n and d i f f u s i o n a r e c a l c u l a t e d
assuming l a m i n a r f l o w w i t h i n t h e p o r e s . 4.
Entrance e f f e c t s are neglected.
5.
P a r a m e t e r s t h a t c a n b e v a r i e d i n t h e code i n c l u d e f l o w r a t e ,
o r i f i c e diameter, porosity, length,
and d i a m e t e r o f t h e WAF, and
t h e p a r a m e t e r s of t h e f i b e r s i z e d i s t r i b u t i o n . I t i s i m p o r t a n t t o emphasize t h a t o u r e x p e r i m e n t s r u l e o u t
308 explaining t h e e n t r a n c e effects with expressions accounting f o r i n t e r c e p t i o n b a s e d on e x p e r i m e n t s w i t h n u c l e p o r e f i l t e r s .
Numerical
s i m u l a t i o n s i n d i c a t e t h a t n e i t h e r d i f f u s i o n or sedimentation
(the
i m p a c t o r was mounted v e r t i c a l l y ) c o u l d a c c o u n t f o r t h e p a r t i c l e
loss o b s e r v e d i n o u r e x p e r i m e n t s . CONCLUSION A new i n e r t i a l i m p a c t o r - - p o t e n t i a l l y
with t h e c a p a b i l i t i e s of
s e p a r a t i o n o f f i b e r s from i s o m e t r i c p a r t i c l e s - - h a s
been d e s i g n e d ,
c o n s t r u c t e d , and t e s t e d w i t h isometric p a r t i c l e s .
The i n s t r u m e n t
a p p e a r s t o b e a m o r e e f f e c t i v e i m p a c t o r t h a n o n e would e x p e c t from t h e o r y , w i t h i m p a c t i o n b e i n g t h e dominant mechanism a t S t o k e s numbers n e a r 0.01.
F o r smaller p a r t i c l e s ,
i s s i g n i f i c a n t c o l l e c t i o n by GCAF.
impaction i s n e g l i g i b l e but t h e r e The p r i n c i p a l c o l l e c t i o n
mechanism i s v e r y s e n s i t i v e t o p a r t i c l e s i z e . ACKNOWLEDGEMENT
The a u t h o r s would l i k e t o acknowledge t h e s u p p o r t o f t h e E n v i r o n m e n t a l P r o t e c t i o n Agency u n d e r c o n t r a c t number EPAR 80651801 REFERENCES
1 K . R . S p u r n y , J . W . G e n t r y and W. S t B b e r , i n D. Shaw ( E d . ) , F u n d a m e n t a l s o f A e r o s o l S c i e n c e , Wiley, N e w York, 1 9 7 8 , p.257. 2 J. G e n t r y and K . R . S p u r n y , J. C o l l o i d S c i . , 6 5 ( 1 9 7 8 ) 1 7 4 . 3 T.T. Mercer and R.G. S t a f f o r d , Ann. Occup. Hyg., 1 2 ( 1 9 6 9 ) 4 1 . 4 V.A. Marple a n d K. W i l l e k e , i n B . Y . H . Liu (Ed.), Fine P a r t i c l e s , Academic P r e s s , N e w York, 1 9 7 5 , p.411. 5 K.M. C u s h i n g , J . D . McCain and W.B. S m i t h , Env. S c i . & T e c h . , 1 3 ( 1 9 7 9 ) 629. 6 L . J . C o l c o r d and e t . a l . , N o n - s p h e r i c a l P a r t i c l e s : Effect of P o l y d i s p e r s i t y on P e n e t r a t i o n , EPA R e p o r t , 1980.
Atmospheric Pollution 1980, Proceedings of the 14th International Colloquium, Paris, France, May 5-8,1980, M.M. Benarie (Ed.), Studies in Environmental Science, Volume 8 0 Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
309
NEW INERTIAL PARTICLE SIZE CLASSIFrCATrON TECHNrQUES FOR AEROSOL SAMPLING AND MEASUREMENT
K. WILLEKE, R.E.
PAVLIK*, W.C.
FRIEDMAN, J.D, BLANCHARD and S , A . HABERMAN
Aerosol Research Laboratory, I n s t i t u t e o f Environmental Health, U n i v e r s i t y o f C i n c i n n a t i , C i n c i n n a t i , Ohio 45267 (U.S.A.)
ABSTRACT Three new p a r t i c l e s i z e c l a s s i f i c a t i o n techniques are described:
1.
An aerosol-laden a i r j e t i s d i r e c t e d against a c o - a x i a l l y opposed clean a i r j e t , so t h a t t h e o r i g i n a l s i z e d i s t r i b u t i o n i s separated i n t o two a i r b o r n e aerodynamic s i z e f r a c t i o n s .
2.
A p a r t i c l e - l a d e n annular a i r s t r e a m i s c e n t r i p e t a l l y accelerated a t an
angle thus forming a cone-shaped j e t which enters a downstream o r i f i c e w i t h h i g h - i n e r t i a p a r t i c l e s overshooting the o r i f i c e and eliminated from t h e airstream.
3.
An aerosol-laden j e t i s impacted onto a t i l t e d p l a t e several nozzle diameters from t h e j e t nozzle, This degrades the impaction e f f i c i e n c y thus s i m u l a t i n g r e s p i r a b l e c u t - o f f c h a r a c t e r i s t i c s .
INTRODUCTION When one evaluates a i r environments f o r p a r t i c u l a t e matter, i t i s g e n e r a l l y d e s i r a b l e t o o b t a i n samples c l a s s i f i e d i n t o s i z e ranges so t h a t the region o f p o t e n t i a l i n s u l t i n t h e r e s p i r a t o r y t r a c t may be determined through reference t o t h e aerodynamic s i z e d i s t r i b u t i o n o f t h e p a r t i c l e s .
Three new p a r t i c l e s i z e
c l a s s i f i c a t i o n techniques a r e described.
RESULTS Opposing-jet p a r t i c l e s i z e c l a s s i f i c a t i o n
A j e t o f p a r t i c l e - l a d e n a i r i s d i r e c t e d against an e q u a l l y strong axisyrnParticles with sufficient
metrically-opposed j e t o f clean a i r ( r e f s . 1-4).
i n e r t i a d e v i a t e from the a i r streamlines and cross t h e f l u i d i n t e r f a c e between 4-
Present address: U.S.
Navy Regional Medical Center, San Diego, C a l i f . 92134, U.S.A.
310
Fig. 1. Schematic o f t h e opposing-jet p a r t i c l e - s i z e c l a s s i f i e r , t h e j e t s , w h i l e smaller p a r t i c l e s continue on w i t h t h e o r i g i n a l a i r stream,
As
seen i n Fig. 1, a t h i n s o l i d p l a t e i s placed between the opposing j e t s , The p l a t e has a c i r c u l a r c u t o u t which i s a l i g n e d w i t h the c e n t e r l i n e o f t h e opposing j e t s and separates t h e impinging a i r f l o w i n t o two streams t h e upper one containing
-
t h e l o w - i n e r t i a p a r t i c l e s , and t h e lower one containing the h i g h - i n e r t i a p a r t i c l e s . Once separated, the two p a r t i c l e f r a c t i o n s can be ducted t o any desired l o c a t i o n f o r f u r t h e r s i z e c l a s s i f i c a t i o n o r f o r any desired method o f a n a l y s i s direct-reading,
-
including
continuous instrumentation.
Experiments have shown sharp p a r t i c l e - s i z e c l a s s i f i c a t i o n s i m i l a r t o t h a t o f s o l i d p l a t e impactors. However, p a r t i c l e losses are s t i l l q u i t e h i g h and are the focus o f present research.
As seen i n Fig. 2, a separation hole H which i s 25%
l a r g e r than t h e j e t w i d t h W r e s u l t s i n sharp p a r t i c l e s i z e c l a s s i f i c a t i o n , whereas f o r a l a r g e r hole s i z e r e l a t i v e l y l i t t l e s i z e c l a s s i f i c a t i o n occurs,
We have
a t t r i b u t e d t h i s t o t h e onset o f t h e edgetone e f f e c t which i s a fluid-dynamic i n s t a b i l i t y o c c u r r i n g when t h e l a t e r a l l y d e f l e c t e d t h i n a i r j e t impinges onto the i n n e r r i m o f t h e separation p l a t e .
I t produces transverse o s c i l l a t i o n s which
generate a sound f i e l d a t t h e same frequency as t h e f l u i d o s c i l l a t i o n s ,
It degrades
the c l a s s i f i c a t i o n which may have been achieved by the process o f i n e r t i a l impaction since t h e p a r t i c l e s contained i n t h e l a t e r a l l y - d e f l e c t e d airstream are a l t e r n a t e l y d e f l e c t e d along w i t h t h e airstream t o t h e upper o r lower chambers,
311
Fig. 2. Particle-size classificatton for dtfferent separatton-plate hole sizes. In our present research effort we have designed a rectangular opposing jet classifier in which the nozzle is rectangular in shape and the aerosols are deflected to one side only. This facilitates the study of critical separation Plate distances and of means of suppressing fluid-dynamic oscfllations. The rectangular geometry also permits relating the observed oscfllations to studies undertaken on reed instruments such as flutes and organ ptpes.
LOW-INERTIA PARTICLE
Ffg. 3.
Schematic o f centripetal particl e-size classification,
d " ' ~ 0.5" * . " 1.0. ~ "
I
NOZZLE-TO-CUP/NOZZLE DIAMETER. S/W,
Fig. 4.
Mean p a r t i c l e p e n e t r a t i o n e f f i c i e n c y f o r d i f f e r e n t diameters o f o l e i c
acid t e s t particles. Centripetal particle-size c l a s s i f i c a t i o n The i n l e t c o n s i s t s o f a plunger separated by distance H from a concave p l a t e w i t h a c e n t r a l primary o r i f i c e o f diameter W1
, see
Fig. 3.
The aerosol f l o w i s c e n t r i p e t a l l y accelerated i n t h e annular channel a t angle 0 perpendicular t o the
centerline.
The cone-shaped j e t between t h e surfaces o f t h e plunger and t h e
o r i f i c e p l a t e converges and passes down i n t o a c o l l e c t i o n o r i f i c e o f diameter W2 which i s c o a x i a l w i t h the primary o r i f i c e and l o c a t e d a t a distance S from i t . H i g h - i n e r t i a p a r t i c l e s overshoot t h e c e n t e r l i n e and the c o l l e c t i o n o r i f i c e and impact onto t h e t o p surface o f the c o l l e c t i o n cup w h i l e l o w - i n e r t i a p a r t i c l e s enter t h e c o l l e c t i o n cup w i t h t h e airstream. The p a r t i c l e p e n e t r a t i o n e f f i c i e n c y , shown i n Fig, 4, i s decreased as the p a r t i c l e s i z e i s increased.
I t r i s e s t o a maximum value a t an S/W1 distance l e s s
than 0.5, then decreases and approaches a plateau w i t h i n c r e a s i n g S/W1 distance. The p e n e t r a t i o n e f f i c i e n c y depends on t h e diameter r a t i o o f t h e two o r i f i c e s . (Ref. 5). I f one r e p l o t s t h e p a r t i c l e p e n e t r a t i o n e f f i c i e n c i e s f o r S/W1 = 0.25 as a f u n c t i o n o f p a r t i c l e size, t h e measure o f spread o f t h a t curve i s comparable t o t h e one used f o r r e s p i r a b l e sampling.
One o f t h e p o t e n t i a l a p p l i c a t i o n s o f t h i s
technique, therefore, i s i n t h e design o f i n l e t s f o r r e s p i r a b l e dust samplers,
313
A
Fig, 5.
Schematic of inclined-surface impaction
Respirable p a r t i c l e samplinq throuqh lncl Ined-surface impaction Aerosol-laden a i r i s drawn t h r o u g h a nozzle of diameter W and throat length T, and is then directed as a j e t against an inclined plate a t distance S from the nozzle e x i t plane, The impaction efficiency plotted in Fig. 6 i s the r a t i o of the p a r t i c l e count a f t e r impaction divided by the p a r t i c l e count w i t h the impaction plate removed, When the aerosol j e t i s impacted onto a 90° p l a t e , the measured impaction efficiencies f o r S/W = 0.5 t o 4.0 a r e close t o the theoretically predicted and experimentally verified values, As the jet-to-plate distance increases, the 50 per cent cut diameter and the measure of spread of the impaction efficiency curve increase. A t S/W = 10 t o 15 and 8 = 90°, the impaction efficiency curve achieves a measure of spread comparable t o the respirable penetration curve defined by the American Conference of Governmental Industrial Hygienists (A.C.G.I.H.). As the impaction angle i s decreased from 90°, the impacted flow becomes asymmetrically deflected giving r i s e t o a greater measure of spread so t h a t the A.C.G.I.H. curve i s simulated a t smaller S/W distances ( r e f . 6 ) . When the throat length i s increased from T/W = 3.1,as shown i n Fig. 6 , t o T/W = 25, the velocity profile a t the nozzle e x i t plane becomes more varied as a function of radial distance from the j e t axis. T h i s r e s u l t s i n an increased measure of spread. However, the measure of spread i s not s u f f i c i e n t t o simulate the A.C.G.I.H. curve, unless the jet-to-plate distance i s increased t o an S/W value o f about 10,
314
i n which case s h o r t e r t h r o a t lengths w i l l suffl’ce.
AERODYNAMIC PARTICLE DIAMETER. Irm
Fig, 6. Impactor performance f o r s h o r t t h r o a t l e n g t h w i t h v a r i a b l e impaction angle and nozzle-to-plate distance. Fixed t h r o a t l e n g t h T/W = 3.1. ACKNOWLEDGMENTS This m a t e r i a l i s based upon work which was p a r t i a l l y supported by the U.S, Environmental P r o t e c t i o n Agency under Grant No, R805971010 and the U.S. National Science Foundation under Grant No, ENG77-04667. We thank A. Fodor f o r h i s expert machining and J. S v e t l i k f o r h i s t e c h n i c a l assistance. REFERENCES
1, K. W i l l e k e and R.E. P a v l i k , Environ. Sci. Technol., 12 (1978) 563-566. P a v l i k and K. Willeke, Am, Ind. Hyg. Assoc. J , , 39 (1978) 952-957. 3. K. W i l l e k e and R.E. P a v l i k , J. Aerosol Sci., 10 (1979) 1-10. 4. K. W i l l e k e and R.E. P a v l i k , i n K. W i l l e k e (Ed.), Generation o f Aerosols and 2 . R.E.
F a c i l i t i e s f o r Exposure Experiments, Ann Arbor Science, Ann Arbor, Mich., 1980, Ch. 20, 4 2 7 - 4 4 0 . 5. K. W i l l e k e and J.D.
Blanchard, C e n t r i p e t a l P a r t i c l e Size C l a s s i f i c a t i o n ,
Environ. Sci. Technol. 6. K. W i l l e k e and S.A.
, 14
(1980),in press.
Haberman, Inclined-Surface Impaction f o r Respirable P a r t i c l e
Sampling, Atmospheric Environment, 14 (1980), i n press.
Atmospheric Pollution 1980, Proceedings of the 14th International Colloquium, Paris, France, May 543,1980,M.M. Benarie (Ed.), Studies in Environmental Science, Volume 8 0 Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
315
SOME SPECIAL PROBLEMS CONCERNING ASBESTOS FIBER POLLUTION IN AMBIENT AIR K.R. Spurny, W, Stober, G. 1.JEISS and H. OPIELA FraunhoferInstitut fur Toxikologie und Aerosolforschung 5948 Schmallenberg 1 1 - Grafschaft (G.F.R.)
ABSTRACT Two different sources of atmospheric asbestos fibre pollution were investigated: the weathering of asbestos-cement tiles and the atmospheric contamination by asbestos emitted from quarries. Measurements in ambient air and in quarries as well as measurements on surfaces of new and "wheathered" asbestos-cement tiles have shown that, in both cases, asbestos fibres are released into the atmosphere. Methods for sampling in ambient air and on different surfaces were developed and are described. Scanning electron microscopy and electron microprobe analysis were used for identifying asbestos in the samples. We have also tried to estimate and evaluate the emissions of these sources quantitatively or at least semiquantitatively. INTRODUCTION At present, reliable data on the distribution of asbestos sources or on asbestos emissions factors are rather limited, although the world consumption of asbestos amounts to more than 5 megatons per year (Western Europe approx. 0.8 megatons/yr; U.S.A. approx. 3.5 megatons/yr.) and is steadily increasing (ref. 1 ) . Man-made sources of airborne asbestos fibres may comprise industrial operations like mining and milling of asbestos materials, milling and processing of metal ores containing asbestos, and manufacturing of more than 3000 different commercial products involving asbestos. Further sources may be the consumption and wear of many asbestos-containing products such as vehicle brake linings and roof tiles, the demolition of asbestos-containing structures, the use of asbestos products in the building industry, the disposal of asbestos waste material, and the transportation of asbestos and asbestos products. To date, little consideration has been given to the fate of asbestos wasFes which \
316
may amount, on a g l o b a l scale and by o r d e r o f magnitude, t o one megaton/yr. T h i s waste m a t e r i a l can e a s i l y p o l l u t e s o i l , w a t e r and f o o d , as w e l l as ambient a i r . our i n v e s t i g a t i o n f o c u s s e s on t h e problem o f s u r f a c e changes and " w e a t h e r i n g " of a s b e s t o s - c e m e n t p l a t e s , such a s r o o f i n g t i l e s , and on t h e problem of a s b e s t o s o c c u r r i n g i n q u a r r i e s . I n b o t h c a s e s , a s b e s t o s f i b r e s can c o n t a m i n a t e t h e whole e n v i r o n m e n t - s o i l ,
water
and ambient a i r . The p u r p o s e was t o o b t a i n some p r e l i m i n a r y d a t a on t h e s e two p o t e n t i a l s o u r c e s of a s b e s t o s a i r p o l l u t i o n . WEATHERING O F ASBESTOS-CEMENT PLATES
A s b e s t o s cement p l a t e s , s u c h a s r o o f t i l e s , c o n t a i n a s much as 15 t o 2 0 % o f c h r y s o t i l e a s b e s t o s . There i s a s u s p i c i o n t h a t t h e c o n t i n u e d
e x p o s u r e t o m e t e o r o l o g i c i n f l u e n c e s , such a s r a i n , s u n s h i n e , wind, f r o s t , e t c . , a s w e l l as t o a t m o s p h e r i c p o l l u t a n t s l i k e H 2 S 0 4 ,
H CO
2 3' e t c . , t h e s u r f a c e of a s b e s t o s - c e m e n t p r o d u c t s may c o r r o d e and weather.
Thus, cement p a r t i c l e s , a s b e s t o s f i b r e s and a g g l o m e r a t e s o f p a r t i c l e s and f i b e r s may be r e l e a s e d from t h e p l a t e s u r f a c e and such d i s p e r s e d i n t h e a i r and t h e r a i n w a t e r . I n o u r p r e l i m i n a r y i n v e s t i g a t i o n , measurements o f a s b e s t o s f i b r e s
w e r e made n o t o n l y on samples o f ambient a i r drawn i n t h e v i c i n i t y of b u i l d i n g w a l l s f a c e d w i t h 17 y e a r s o l d asbestos-cement t i l e s , b u t also on t h e s u r f a c e s o f new and wheathered t i l e s , on t h e r o o f s t i l e d w i t h s u c h p l a t e s , on r a i n w a t e r sampled n e x t t o b u i l d i n g s w i t h such t i l e s and on r a i n w a t e r sampled from g u t t e r s of r o o f s t i l e d w i t h new asbestos-cement p l a t e s . 0.4
Atmospheric samples w e r e t a k e n w i t h Nuclepore f i l t e r s ( p o r e diam. pm) and e v a l u a t e d by a r e l i a b l e e x i s t i n g method ( r e f . 1 ) . F i b e r
c o n c e n t r a t i o n s o f c h r y s o t i l e f i b r e s a s h i g h a s 103 p e r c b m w e r e measured a t a d i s t a n c e of 50 c m from t h e w a l l f a c e d w i t h a s b e s t o s cement t i l e s ( 1 7 y e a r s o l d ) and l o 2 c h r y s o t i l e f i b e r s p e r cbm were found a t d i s t a n c e s o f 100 m from t h e same w a l l . A s i m p l e method was d e v e l o p e d f o r s a m p l i n g f r e e f i b r e s d i r e c t l y from t h e s u r f a c e s of a s b e s t o s - c e m e n t t i l e s . The method i s shown s c h e m a t i c a l l y i n F i g u r e 1. The s u r f a c e s o f b o t h a new p l a t e E ( 1 ) and a w e a t h e r e d p l a t e E ( I 1 ) a r e r i n s e d w i t h a m i x t u r e of d i s t i l l e d w a t e r and e t h a n o l ( 2 : l ) s p r i n k l e r A. The wash-off f i l t e r s ( p o r e diam. 0 . 1
l i q u i d i s f i l t e r e d t h r o u g h Nuclepore
m)
F and t h e f i l t e r sample i s e v a l u a t e d by
means o f a s c a n n i n g e l e c t r o n m i c r o s c o p i c a l method EM.
317
Fig. 1. A schematic diagram and electron micrographs showing the procedure for sampling and evaluation of fibrous material washed off the surface of asbestos-cement plates (Description in text) Number concentrations of chrysotile fibres between l o 3 and 104/cm2 were measured on the surfaces of new asbestos-cement tiles, and chrysotile fibre numbers ranging from lo2 to 5. lo3 could be found on the surfaces of weathered tiles. A similar method was used for the analysis of rain water and of gutter rain water. In gutter rain water sampled during the first rain after the roof was tiled with new asbestos-cement plates, fibre concentrations ranging from lo6 to lo7 fibers per liter could be measured. In the rain water sampled next to the investigated building, asbestos fibre concentrations of about 5 10 fibres/liter were found. In rain water sampled far from buildings and villages, fiber concentrations were assessed to be below 105 fibres/liter.
318
F i g . 2 . Scanning e l e c t r o n m i c r o g r a p h s of t h e s u r f a c e of a new b l a c k asbestos-cement t i l e ( E t e r n i t e ) .
Scanning e l e c t r o n m i c r o s c o p i c i n v e s t i g a t i o n s o f t h e s u r f a c e of
, and w e a t h e r e d ( F i g u r e 3 ) asbestos-cement p l a t e s , a s w e l l as t h e i n v e s t i g a t i o n s o f t h e i n n e r p l a t e s t r u c t u r e ( F i g u r e 4 ) d i d c o n f i r m , t h a t f r e e f i b e r s c a n be found on t h e p l a t e s u r f a c e s . A p p a r e n t l y , new p l a t e s have p o r e s i n t h e i r b l a c k s u r f a c e c o a t i n g , where a c h e m i c a l c o r r o s i o n can e a s i l y i n i t i a t e . Thus, t h e s u r f a c e l a y e r of w e a t h e r e d p l a t e s i s d e s t r o y e d and c h r y s o t i l e f i b r e s can be new ( F i g u r e 2 )
p i c k e d up by t h e wind. The p i c t u r e s of t h e i n n e r s t r u c t u r e ( a r u p t u r e o f t h e t i l e ) show t h a t no good l i n k a g e d o e s e x i s t between c h r y s o t i l e f i b r e s and cement i n t h e t i l e m a t e r i a l .
319
F i g . 3 . Scanning e l e c t r o n m i c r o g r a p h s of t h e s u r f a c e of a weathered ( 1 7 y e a r s old) asbestos-cement p l a t e .
F i g . 4 . Scanning e l e c t r o n m i c r o g r a p h s of a r u p t u r e of a weathered asbestos-cement t i l e .
320
Conclusions New asbestos-cement tiles and plates are heavily coated with free asbestos fibres. They should be washed by the producer before dispatching them for sale. Corrosion and weathering effects on asbestoscement plates were shown to be common. Wind can disperse chrysotile fibres from the plate surface in to ambient air. The fibers can also contaminate rain water, surface water and soil. A quantifitation of these corrosion and weathering effects was not possible by means of the described procedure. Further laboratory investigations are needed (ref. 2 ) .
AKTINOLITE ASBESTOS IN QUARRIES In some quarries in the US, asbestos minerals, mainly chrysotile and tremolite, were reported to be found in crushed rocks between 1 9 7 6 and 1 9 7 8 (ref. 3 ) . A similar situation was detected in West Germany, were actinolite asbestos was found in the diabase rock of a quarry (ref. 4). The gravel produced from the rock is used for road paving (Figure 5 ) .
Fig. 5. Photographs of some pieces of rock with fibrous actinolite (taken from the gravel in the quarry). Fibre measurements in ambient air, drinking and surface water were carried out in the vicinity of the quarry and indicated actinolite fibres to be present in all samples. The ambient air concentrations of actinolite fibres were lower than in industrial cities,but higher than in other places of that rural region (ranges between 50 to 1 0 0
321
fibres/m3 1 . Actinolite fibre concentrations in potable water were of the order of 106 to l o 7 fibres/liter while the surface water from the diabase quarry showed concentrations as high as lo9 fibres/liter. Concentrations of actinolite fibres in the atmosphere of the working places in the quarry were not measured. Fine fibres of actinolite from the quarry (Figure 6 ) were prepared and used in animal experiments (ref. 4 ) . In these experiments (intraperitoneal applications) the fibrous actinolite proved to be carcinogenic like other fibrous asbestos minerals and very fine glass fibres. The environmental analytic data indicated no significant danger to the public in the vicinity of the quarry. However, a general assessement of the health risk of asbestos contents of quarry products requires further investigations.
Fig. 6. Scanning electron micrographs of actinolite fibres used in animal experiments.
322 REFERENCES
1 K.R.
SPURNY, W.
STBBER, H.
O P I E L A and G . WEISS,
Sci. Total Environ.,
11 ( 1 9 7 9 ) 1-40. H.
O P I E L A and G.
WEISS, Staub-Reinhalt. Luft 3 9 ( 1 9 7 9 ) .
2 K.R.
SPURNY,
3 A.N.
Science, 1 9 6 ( 1 9 7 7 ) 1 3 1 9 - 1 3 2 2 . SPURNY, F. P O T T , H. HUTH, G . WEISS and H. O P I E L A , Staub-Reinhalt. ROHL, A.M.
LANGER and I . J . S E L I K O F F ,
4 K.R. Luft, 3 9 ( 1 9 7 9 ) 3 8 6 - 3 8 9 .
Atmospheric Pollution 1980, Proceedings of the 14th International Colloquium, Paris, France, May 5-8,1980, M.M. Benarie (Ed.), Studies in Environmental Science, Volume 8 0 Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
323
COMPREHENSIVE METHODS FOR RAPID QUANTITATIVE ANALYSIS OF AIRBORNE PARTICULATES BY OPTICAL MICROSCOPY, SEN AND TEN WITH SPECIAL REFERENCE TO ASBESTOS G. BURDETT, J.M. LE GUEN, A.P. ROOD
& S.J.
ROOKER
THE HEALTH AND SAFETY EXECUTIVE, THE OCCUPATIONAL MEDICINE AND HYGIENE LABORATORIES, 403 EDGWARE ROAD, LONDON NW2 6LN
ABSTRACT Comprehensive methods are described for the rapid investigation of material collected on membrane filters or by high volume electrostatic samplers, with special reference to asbestos. These methods permit the use of scanning and transmission electron microscopy, as well as phase-contrast optical microscopy. Novel methods of sample preparation, together with a critical assessment of the quantitative aspects of measurements made are presented. Mass losses during sample preparation are shown to be less than 25% for two methods in particular. The effects of sonication on asbestos, and the application of these results to the routine measurement of chrysotile in the occupational and non-occupational environment are discussed. Preliminary work on image analysis suggests that asbestos fibres may be identified automatically, although oversizing can often occur.
INTRODUCTION The choice of a sampling technique for the measurement of airborne concentrations of a specific particulate is invariably a compromise between various factors. These include (a)
requirements of the analytical technique
(b)
collection efficiency of the sampler
(c) ease of use and maintenance of the sampler (d) availability and cost of analytical technique and/or sampler. Sampling techniques based on membrane or glass fibre filters offer the advantages of high collection efficiency, cheapness and ease of use in the field, and they can be used in battery powered personal or static samplers. The increasing popularity of such techniques on these counts means that analytical techniques must be geared (primarily) to their use. A summary of alternative sampling and analytical techniques which have been used for
324
asbestos is given in Table 1. TABLE 1
Principle of method
Example of instrument
Analysis Technique
Settling
Horizontal Elutriator
Gravimetric
Impaction
Konimeter Owen's Jet Counter
Microscopic examination
192-5
Sartorius UC 25
p
6
Midget Impinger
Microscopic examination
Impingement
Ref 1
absorption 1,397, 8
Inertial Separation Precipitation (1) Electrostatic
Cyclones
1
Gravimetric
9
microscopic examination
7
High Volume Sampler
X-ray diffraction or microscopic examination
22
(ii) Thermal
Thermal precipitator
microscopic or gravimetric
193,7, 10
Filtration
(i) Glass fibre filter (ii) Membrane filter
Chemical analysis Optical microscopy
3.7,9
(iii) Nuclepore filter
Scanning electron microcopy
12
Royco particle counter
Integration of light
3,7
Light scattering
T.S.I. Balance T.S.1 Sampler
Gravimetric or chemical analysis
Fibrous aerosol monitor scattered by particles
The examination of chemically treated membrane filters by phase contrast microscopy has become the standard method of assessing asbestos levels in the workplace (14). Certain deficiencies exist; it is not possible to distinguish asbestos from non-asbestos fibres nor consistently to detect fibres of diameter
0.3 pm.
193, 10,n
13
325
,
Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) when combined with energy dispersive X-ray analysis, provide a rapid means of
elemental analysis of individual fibres, while selected area electron diffraction with TEM provides information about crystalline structure. Direct analysis of samples by SEM is severely limited by the fibrous nature of the membrane filter. This has prompted the use of Nuclepore filters, which, apart from the pores, offer an essentially flat and featureless surface. Serious disadvantages have been encountered however, these include: low collection efficiencies for particles of diameter less than the nominal pore size (12,15), high preesure drops and low flow rates consequent on the use of small pore sizes, and particle losses during transport (16). Spurny et a1 (17) reported in 1976 that no satisfactory method existed for the sampling and analysis of asbestos and recommended the use of Nuclepore filters. The Environmental Protection Agency (EPA) has given a provisional methodology for the TEM examination of airborne asbestos collected on Nuclepore filters (18). Chatfield et a1 (19)investigated various methods of preparation from Nuclepore and membrane filters; these methods involved the dissolution of 0 the filter by either condensation washing or the use of a Jaffe wick to leave the particles on a carbon coated grid. They compared particle losses for Nuclepore filters (carbon coated) and membrane filters (uncoated) and found losses of up to 80% during the dissolution of the latter. It is worth noting that prior to this work Zumwalde & Dement (20) and Ortiz & Isam (21) had avoided these high losses by exposing membrane filters to acetone vapour which caused partial dissolution of the filter to leave a smooth surface with particles embedded in the upper layer; this was then coated with carbon before dissolution. Ortiz & Isam claim fibre losses of <3% but this seems optimistic unless all fibres are sufficiently well exposed at the coating stage. Both the condensation washing and Jaffe)wick methods are severely limited by their long preparation times, of the order 2L-48 hours. Alternative approaches have been adopted for low concentrations of airborne and waterborne asbestos. Rickards (22) used a Litton high volume sampler to collect airborne chrysotile. The asbestos suspension was filtered onto a membrane filter which was ashed at high temperature, the residue was then redispersed in a small amount of distilled water and sonicated for a minimum of four hours. A drop of suspension was allowed to dry on a carbon coated grid and the mass was obtained by measuring the length of small fibres per unit area on the assumption that sonication produced a 'fibril' of uniform
326
diameter. Mudroch & Kramer ( 2 3 ) concentrated small amounts of waterborne asbestos by filtration. The filter was placed in a small volume of water and sonicated to remove the fibres. A little of the asbestos suspension was placed in a centrifuge tube containing a carbonised-parlodion TEM grid; this was preferred to the evaporating drop method which gave an uneven distribution of fibres. Brief reference has also been made to the use of a centrifuge for airborne and waterborne asbestos by Chatfield ( 2 4 ) but again no indication was given of this method's efficiency. This paper describes several rapid sample preparation techniques f o r microscopical examination of airborne asbestos collected on membrane filters or by high volume electrostatic samplers.
SAMPLE PREPARATION FOR SEN AND TEM
(1)
HIGH VOLUME AIRBORNE SAMPLE SAMPLER , ~ i ~ dm a t l o nsuf;jtePn:ion
'
MANUAL SIZING/ IMAGE ANALYSER
MEMBRANE FILTER collapse and etch
ash filter
centrt f uge
CONTRAST ( 2 b) MICROSCOPY MANUAL SIZING/ IMAGE ANALYSER
(7) FIG 1
FLOW DIAGRAM FOR SAMPLE PREPARATION
Centrifugation for the TEN Three techniques based on the ultra-centrifugeare described by which asbestos can be prepared for quantitative measurement in the transmission electron microscope. High volume samples can be centrifuged directly, but samples collected on
327
membrane filters must first be ashed and centrifuged, or alternatively centrifuged as part of a two phase system. Treatment of material collected by a high volume electrostatic sampler involves sonication of the suspension with a probe (Dawe Instruments 'Soniprobe operating at 70W), for a period of 20 mins. Adding 1%" of surfactant (e.g. Decon 90 or Manoxol OT) prior to this treatment produces a well dispersed suspension.
For direct centrifugation, the suspension can be diluted to any chosen value with 10% acetone in distilled water, especially if the concentration of sampled material is high. The addition of acetone reduces surface tension and allows the supernchant liquid to drain evenly from the TEM grid. A dilution of one to five is commonly used in this Laboratory. Samples are spun at 13,000 r.p.m. (giving a relative acceleration of 27,600 g) for a period of ten minutes in a modified Dupont-Sorvall RC-5B centrifuge tube shown in Fig. 2; the sample volume is typically 0.w. At the end of this time, the supernatant liquid is carefully drawn off by means of a Pasteur pipette with its tip just below the TEN grid sitting on the stainless steel mesh. The grid is then removed and allowed to dry for several minutes in a filtered air cabinet before examination.
If a membrane filter is used as a starting point, two possible centrifuge routes are available. The first technique involves the complete ashing of the filter in a low temperature plasma oven (19);a Nanotech Plasmaprep PlOO has been used in this Laboratory. This ash can then be sonicated and centrifuged onto a TEM grid. An alternative technique is the novel use of a two phase system for handling membrane filters. A slightly larger centrifuge tube has been machined from PTFE to sit directly in the centrifuge bucket as shown in Fig. 2. The filter (0.5 Prn Millipore EH for example) is dissolved in 50ml of mixture of 40% methyl ethyl ketone- 60% cyclohexanone, and treated with the ultra-sonic probe for 20 mins. lml of this suspension is then pipetted slowly onto the surface of 2 tetrahydrofuran water mixture (1.5 : 1) covering the base of the centrifuge tube. Centrifugation is then applied in exactly the same way as for the single phase system. In removing the supernatant liquid, however, care must be taken to remove the upper phase first, and then to use a clean pipette to drain the lower phase prior to drying and examination. Optical and SEM Five types of membrane filter have been prepared successfully for optical examination, and the clearing solutions for each are given below.
328
TABLE 2 Filter Gelman Millipore 'Celotate'
Pore size
(p)
Clearing solution
0.45 0.80
1
DM800
EG EH EH
0.20 0.50 1.00
50% dioxan
DM450
) ) )
35% dioxan 67% cyclohexanone 50% cyclohexanone 70% dioxan
30% cyclohexanone
60-891 of clearing solution is smeared onto a microscope slide to an area a b d t h e size of the filter. The filter, sample face upwards can then be quickly positioned, care being taken not to trap any air bubbles. Excess solution can be removed with a tissue at this stage. The filter and microscope slide are left in a dust f r e e environment for 3-5 mins and may then be dried in an oven at 60-80°C for 10 mins. During this time the filter collapses to about 15% of its original thickness leaving the fibres in the upper layer with minimal distortion. For further examination, the collapsed filter must be etched in a plasma oven (Nanotech Plasmaprep PlOO) for 7 min with an oxygen flow of 8ml/min and forward and reflected powers of lOOW and <2W respectively. These parameters have been established by trial and error to expose most of the fibres without leaving fibres exposed on ridges of unetched filter, such as occur with longer times. Blank filters prepared under these conditions have flat and featureless surfaces. For optical examination a drop of trichloroethene is placed on the etched filter and a coverslip applied. Trichloroethene is suitable for two reasons. Firstly, it has a refractive index of 1.48 and so mimics the conditions given by Galvin Le Guen (14) for clearing Millipore RA filters for counting and sizing by phase contrast microscopy. Secondly, it is very volatile and can be easily removed without disturbing the particles on the filters. &
By evaporating the trichloroethene naturally, or by warming in an oven at about 6OoC the coverslip may be removed, and the filter freed from the microscope slide with the aid of a scalpel. For SEM observation the filter can then be secured to stub with 'silver dag' and coated with gold, titanium or carbon in the usual way. If the filter is not to be optically examined, it may be prepared directly on an SEM stub. Direct transfer from membrane filters to TEM This is an extension of the method used to prepare membrane filters for the
SEN. The specimen holder and the three stages of preparation are shown diagram-
329
matically in FIG 3(A), (B) and (C). The holder is constructed of aluminium in three sections labelled I, I1 and 111; aluminium is preferred to brass which is slowly attacked by the oxygen plasma, and the geometry has been established by trial and error. The holder produces up to five samples from one membrane filter, and of those investigated, Millipore 'Celotate' EH (pore size 0.5pm) and EG (pore size 0.2pm)have proved particularly satisfactory. Sample preparation is identical for each: (A) 80-100p1 of cyclohexanone is smeared out over the upper surface of section I and each brass peg on which is placed a 400 mesh TEM grid (see Fig.3A). The pegs are a good fit to minimise seepage of solvent into the central area of Section I. The membrane filter, sample face downwards, is quickly and carefully placed on the specimen holder. Any excess solvent is removed with a tissue, and the whole assembly is placed in an oven at 80-1OO0C for about 15mins. During this time the filter collapses and the solvent evaporates to leave a thin transparent film with particles embedded in the bottom layer. To aid evaporation of solvent which seeps into the central cavity, small holes have been drilled in the side of I. The assembly is removed from the oven and allowed to cool until the plastic film hardens. The brass pegs are partially unscrewed, leaving the film intact with grids attached. The top section I is separated from 11, inverted and placed in a plasma oven (Nanotech Plasmaprep P100) for 15 mins with an oxygen flow rate of
(B)
8ml/min with a forward and reflected RF power of lOOW and (5W
respectively.
It can then be transferred to a vacuum evaporator and coated with 150-250 A of titanium (see Fig. 3 B ) . The etching time is sufficiently long to expose the particles on the surface of the filter, and the titanium film acts as a transparent support medium for subsequent Twexamination. The specimen holder is reassembled as for A, and a thin plate secured on top by two small bolts. The whole assembly is placed in a plasma oven (International Plasma Corporation IPC 1000) with an oxygen flow rate of 400ml/min and reflected RF powers of l30W and <2W respectively. The filter is left to ash completely leaving a clean titanium film with particles embedded in it,.
(C)
The time for complete ashing is 2 hours for EH filters, and 3 hours for EG filters. Fibre sizing and mass determination with the TEM Fibres are identified by means of a Phillips W O O T microscope fitted with
330
an Edax SW9100 energy dispersive system. Mass is determined by recording visually the length and breadth of fibres at a calibrated magnification of
10K directly from the TEZ screen or from photographic negatives. The mass per unit area is calculated, assuming a cylindrical morphology and a suitable density for fibres in the field. From a knowledge of the total mass precipitated by the centrifuge, the concentration existing in the original suspension can be readily calculated (a small correction can even be applied for the thickness of the stainless steel mesh supporting the TEM grid in the centrifuge methods if necessary).
LIFTING ARM/
/ BUCKET
S PACER
STAl N LESSSTEEL MESH
TUBE
SINGLE FIG 2
PHASE CENTRIFUGE
TWO PHASE TUBES
Ti
FIG3
SPECIMEN HOLDER FOR DIRECT TRANSFER
331
RESULTS The effects of sonication on chrysotile The effects of sonication of chrysotile have been examined by photographing cenhifuged samples of the material that had been agitated for 3, 10, 30 and 120 minutes with a probe operating at 70W. A sample was also given two days sonication at 50W as a further check on the extent of fragmentation of the material to component fibrils. FIGS 6, 7, 8, 9 and 10 show the extent of fragmentation at these respective times. FIG 10 indicates that even after extended sonication some material remains undispersed. Agglomerates of material were found to be sufficiently reduced in 10 to 30 minutes to give a reasonably uniform preparation of chrysotile on the TEM and after centrifugation. Centrifuge efficiency Two practical tests of the centrifuge efficiency were carried out. In the -6 Canadian chrysotile B was first a suspension of 5 x 10 g/ml of U.I.C.C.
.
precipitated by the previously described technique The supernatant liquid was then withdrawn and recentrifuged onto a clean TEM grid. FIGS 4. and 5 show a representative field of view of the sample at each stage. The many hundreds of fibres in the first field are in marked contrast to the few remaining fibres in the second (equivalent to less than
@g
in suspension).
A quantitative tests was carried out by again preparing standard chrysotile suspensions and applying the centrifuge technique as described. From manual sizing of the fibres on the TEM screen the results for two concentrations of the asbestos are shown in TABLE 3. The results are based on the random examination of
5 and 10 grid apertures respectively, and only fibres (or parts
of fibres) within these openings were recorded. Calibration of the two phase centrifugation system proceeded in a similar manner, with the results also shown in TABLE 3. In both cases a uniform distribution was noted over the TEM grid. TABLE 3 Total number of fibres Single phase (chrysotile)
162
Two phase (chrysotile)
50
4.0
Measured conc. dml) 1.1 x 1 0 : ; 1.3 x 10 1.1
68
8.0
1.7
150
Standard conc. ( g/ml)
1.6 1.6 x
FIG 13 shows chrysotile centrifuged from the two phase system
332 A n investigation of the limits of detection of the combined TEN/centrifuge technique was based on blank samples prepared with 'Analar' laboratory reagents,
a filtered air cabinet for specimen preparation, and filtered distilled water. This study indicated that background contamination sets a lower limit of detection at between 10-10 and g/ml for fibrous conponents. Use of image analyser A Joyce-Loebl 'Magiscan' image analyser (25) with a programme specifically
written for handling fibre images from photographic negatives has been used; fibres are identified according to certain parameters specified by the operator (for example aspect ratio or contrast above background). The programme is able to deal with crossing fibres, and with ones that may be partially obscured by associated debris. and breadth.
A mass is again calculated from measurements of length
FIGS. 11 and 12 show representative fields of chrysotile and amosite fibres presented to the image analyser.
A preliminary count was performed on photographs of standard suspensions of chrysotile and U.I.C.C. amosite with the 'Magiscan' image analyser; the results are shown below in TABLE 4. TABLE 4
Total number of fibres Single phase (chrysotile) Single phase (amosite)
521 225 227 217 188 133
Standard conc. ( g/ml)
Measured conc. ( g/ml)
1.0 x 1012 5.0 x 1.0 x 10
5.0 x
1.0 x 1012
5.0 x 1.0 x 10
-6
2.7 x
1.9 x 10 1.4 x 101; 7.0 x 2.5 x 10
Comparison between optical microscopy and SEM FIGS 14 and 15 show identical fields as seen by the optical microscope and the SEN. A comparison of the two micrographs (and others not illustrated) show that no particles are lost during the etching and coating process. Since it is unlikely that particles are lost during the clearing stage, it has been concluded that particles losses for the overall process are negligible. Direct transfer method (TEM) FIG 16 shows a typical field of view by the TEM. The contrast between the titanium film and fibres is good, with little structure in the support film.
333
If the filter is not left in the oxygen plasma sufficiently long, small spheres of unetched filter may remain on the support film or attached to fibres. The method is an extension of the SEN technique, and particle losses would be expected to be small.
To assess this, a mass equal to 4.0 x 10-7g of mildly sonicated chrysotile was filtered onto an EH filter and prepared for TEM examination. Negatives of thirty grid squares (taken at 3.7 K) gave 284. fibres, the sizes of which were accurately determined visually. This gave a mass of 2.8 x g, in good agreement with the mass on the filter.
It should be noted that while sonication is useful way of obtaining uniform preparations, some clumps of chrysotile fibres do occur. Indeed, one such clump contributed 50% of the measured mass.
F1G.L
1
FIG. 5
334
335
FIG. 12
FIG. U
FIG. 16
FIG. 13
FIG. 15
336
DISCUSSION In much of this work of ultrasonic probe has been found useful at some stage of the specimen preparation. However, the production of an 'ultimate fibril' (22) has not proved possible for chrysotile even after 48 hours of strong agitation. Twenty minutes of agitation does noticeably reduce aggregates of material not only for chrysotile, but for other forms of asbestos. The centrifuge route, step 1 in FIG. 1, has been found an extremely and efficient means of producing uniform TEM samples. The fibre losses small from accurate manual counting ( 25$ in mass terms), and the time to examine a high volume sample is less than one hour. Steps 2a and 2b
rapid appear taken covering
the use of phase contrast and polarised light microscopy have been previously discussed (14,26) and the techniques are widely used for the routine assessment of asbestos in the occupational environment. The examination of collapsed and etched filters in the SEM (step 3) can provide a cheap (relative to TEM) method of investigating fibres that may be below the resolving power of the optical microscope, and often make a significant contribution to the total amount of asbestos in the non-occupational environment. Energy-dispersive X-ray analysis in the SEM is a valuable means of identification over and above the simple criterion of morphology. SEM images tend to be low in contrast, and are not always ideal for subsequent use with an image analyser. The resolving power of the SEM is also lower than that of the TEM, which can make observation of very small fibres difficult if specimen preparation is deficient. The direct transfer process (step 4 ) and two-phase centrifugation (step 6) are both rapid means of handling material sampled on membrane filters directly by transmission electron microscopy. The first preserves spatial information, and direct comparison with optical and scanning microscopy is possible. The advantage of two-phase centrifugation is that specimen preparation time is again less than one hour, as compared with several hours for the direct transfer method. From mass measurements on standard chrysotile suspensions, the direct
transfer process gave small losses (approximately 25%); with the two phase technique the losses appear higher by a factor of two or three, probably because the small chrysotile fibres fail to cross the phase boundary.
337
Preliminary work on presenting the various microscope images to the 'Magiscan' image analyser indicates that provided a reasonable level of contrast exists between the fibre and the background, and that overlapping debris is minimal, fibre sizing may be aktempted. The results in Table 4 show an overestimation of total mass except in two cases for chrysotile which is characterised by its large number of very small diameter fibres. The results suggest that such small fibres are sometimes missed by 'Magiscan' with the present algorithm. Work is in progress on an improved version of this aspect of the programme. CONCLUSION The direct centrifuge method of preparing samples from the high volume electrostatic sampler for TEM, and the direct transfer method for membrane filters, are quick quantitative techniques for airborne asbestos, with mass losses of less than 25%. The two-phase centrifugation technique is a useful adjunct when less rigorous but more rapid treatment of membrane filters is required. XEFERENCES 1.
R.E.G. Rendall and G.C.H. Sittert, Proc. Int. Cont. on Pneumoconiosis, Johannesburg 1969, Oxford University Press, 1970, p74.
2.
R.S.J.
3.
C.G. Addingley, Ann. Occ. Hyg., 9(1966)73.
4.
E. Walter, Staub, 26 (1966)422.
5.
A.M. Kesting, Staub, 26(1966)419.
6.
W. Coenen, Staub, 33(1973)97.
7.
Du Toit, ibid, p13
R.E. Lane, J.M. Barnes, D.E. Hickish, J.G. Jones, S.A. Roach and E. King, Ann. Occ. Hyg., 11(1968)47-69.
8.
J.E. Lynch and H.E. Ayer, J. Occ. Med., 10(1968)21.
9.
J. Simecek, Staub, 27(1967)484.
10. S. Holmes, Ann. N.Y. Acad. Sci., 132(1965)288.
11. G.H. Edwards and J.R.
12 *
K.R.
Lynch, Ann. Occ. Hyg., ll(1968)l.
Spurny, W. St'dber, E.R.
Ackerman, J.P. Lodge and K. Spurny, J.
Air Pollution Control Assoc., 26(1976)496-498.
338
13.
-
P. Lilienfield, P.B. Ellerman and P. Baron, Am. Ind. Hug. Assoc. J., J. , 4.0(1979)270-282.
14
S. Galvin and J.M.M. Le Guen, to be published, Ann. Occ. Hyg.
15.
B.Y.H. Liu and K.W. Lee, Envir. Sci. Tech, 10(1976)345-350.
16.
I.M. Stewart, Symp. on Electron Microscopy of Microfibres, Pennsylvania State University, 1976, p93.
17.
K.R. Spumy, W. StEber, J. Opiela and G. Weis, Proc. 12th Int. Coll. on Atmospheric Pollution, Paris, May 5-7, 1976, Elsevier, Amsterdam, 1976,
-
~~459-469 18.
A.V. Samudra, C.F. Harwood and J.D. Stockham, U.S. Envir. Protection Agency, EPA-600/2-77-178 , 1978.
19.
E.J. Chatfield, R.W. Glass and M.J. Dillon, U.S. Envir. Protection Agency, EPA-600/4-78-011, 1978.
20.
R.D. Zumwalde and J.M. Dement, Syrnp. on Electron Microscopy of Microfibres, Pennsylvania State University, 1976, p139.
21.
L.W. Ortiz and B.L. Isom, Proc. 32nd EMSA Meeting, St. Louis, Miss.,
1974, p554. 22.
A.L. Rickards, Anal. Chem., 45(1973)809-811.
23.
0. Mudroch and J.R. Kramer, Proc. 32nd EMSA Meeting, St. Louis, Miss.,
1974, p526. 24*
E.J. Chatfield, ibid, p.528.
25.
R.N. Dixon and C.J. Taylor, in press, Scanning Electron Microscopy.
26.
J.M.M. Le Guen, S.J. Rooker and N.P. Vaughan, to be published.
Atmospheric Pollution 1980, Proceedings of the 14th International Colloquium, Paris, France, May 5-8, 1980, M.M. Benarie (Ed.), Studies in Environmental Science, Volume 8 0 Elsevier Scientific Publishing Company, Amsterdam -Printed in The Netherlands
SOME APPLICATIONS
J.C.
339
OF THE "J ETIMETER"
GUICHARD, A. GAILLARD arid
M.
LAMAUVE
I n s t i t u t National de Recherche Chimique Appl iqu@e
-
VERT-le-PETIT (France)
ABSTRACT The j e t i m e t e r i s a device f o r measuring p a r t i c u l a t e concentrations between 1 mg/m3 and 1 g/m3 on a continuous basis. I t was developed mainly f o r i n d u s t r i a l purposes, nevertheless i t i s a l s o a l a b o r a t o r y instrument. This apparatus i s easy t o use, o f small s i z e and l i g h t w e i g h t . Consequently i t s a p p l i c a t i o n s are varied b u t here we r e p o r t o n l y about those t e s t e d i n t h e f i e l d . We s h a l l t r y a l s o t o describe b r i e f l y t h e j e t i m e t e r and i t main p r o p e r t i e s which are e s s e n t i a l f o r i t s use.
INTRODUCTION The d e s c r i p t i o n o f the Jetimeter. The main p a r t o f t h e device ( f i g u r e 1) i s a s t a i n l e s s s t e e l c y l i n d e r (1) o f 3 cm diameter and 15 cm height. A t i t s hemispherical basis a small hole i s connected t o a tube ( 2 ) by which t h e aerosol i s drawn i n a t a f l o w r a t e around 29 l/min.An a i r e j e c t o r connected t o ( 3 ) assures t h e s u c t i o n . The hemisperical basis contains a bed o f m e t a l l i c spheres which i s e.g.
50 g o f bronze beads w i t h diameter between 400 and
500 p, o r 45 g o f t i n beads w h i t h diameter between 500 and 630 p. When the a i r flows a t a convenient r a t e , a spouted bed appears. Around the c y l i n d e r ( l ) , t h e r e i s another s t a i n l e s s s t e e l c y l i n d e r ( 5 ) (diameter 5 cm) which c o n s t i t u t e s a Faraday cage t o avoid e x t e r n a l i n t e r f e r e n c e on the measuring p a r t (1). The coaxial r i g i d cable ( 6 ) e s t a b l i s h e s connection between (1) and the operational The s i g n a l r e s u l t i n g from t h e e l e c t r i c charges
amplifier (7).
generated i n s i d e the c y l i n d e r ( I )
i s a m p l i f i e d and sent t o any p o t e n t i o m e t r i c recorder; most i n d u s t r i a l recording devices are usable. We j u s t described the most elementary form o f the j e t i m e t e r . Two o t h e r versions are o f i n t e r e s t . For t h e f i r s t o f them, a h e a t i n g tube (1,5
cm diameter and 20 cm l e n g t h )
400 W heats the aerosol t o around 120°C b e f o r e i t enters the j e t i m e t e r . I n a second
version, we use two j e t i m e t e r s i n p a r a l l e l with, i f needed, a heater preceeding each o f them. The spouted beds are d i f f e r e n t i n nature, g e n e r a l l y o f bronze f o r one and t i n
for the other. The electrometer head i s replaced by a d i f f e r e n t i a l a m p l i f i e r .
340
Working p r i n c i p l e . Consider an aerosol g o i n g through t h e spouted bed. We observe t h a t t h e i n p u t and o u t p u t c o n c e n t r a t i o n s a r e equal and, i n f a c t , i t i s p o s s i b l e t o send l a r g e q u a n t i t i e s o f d u s t w i t h o u t c l o g g i n g t h e bed. This i s n o t a s t r a i g h t f o r w a r d
passage and t h e r e i s
a two-step mechanism a t work. F i r s t t h e p a r t i c l e s a r e captured by t h e beads, l a t e r they a r e r e e m i t t e d i n aerosol form. When t h e p a r t i c l e i s separated from t h e bead, c o n t a c t o r s e p a r a t i o n e l e c t r i f i c a t i o n g e n e r a t e e l e c t r i c charges whether o r n o t i n s u l 1 a t i n g s u r f a c e s are i n v o l v e d . The o u t f l o w i n g aerosol becomes charged and a compensation charge f l o w s f r o m t h e bed towards t h e a m p l i f i e r i n p u t . This d e s c r i p t i o n i s o n l y a rough b u t u s e f u l one, ment t o understand t h e b a s i c principle o f the jetimeter.
I n f a c t , more complicated phenomena are i n v o l v e d when the
aerosol adheres and then leaves t h e spouted bed. MAIN PHYSICAL,PROPERTIES OF THE JETIMETER On can separate t h e p h y s i c a l p r o p e r t i e s o f t h e j e t i m e t e r i n two c a t e g o r i e s . I n the f i r s t we f i n d t h e response o f t h e device when aerosol i s introduced; the aerosol b e i n g c h a r a c t e r i z e d by i t s c o n c e n t r a t i o n , p a r t i c l e s i z e d i s t r i b u t i o n and i t s i n t r i n s e c physico-chemical p r o p e r t i e s . To t h e second category belong " i n f l u e n c e parameters" t h a t i s parameters which may modify t h e e l e c t r i c a l response, i n s p i t e o f t h e f a c t t h a t i t would be d e s i r a b l e t h a t t h i s response should o n l y be c o r r e l a t e d w i t h t h e aerosol c o n c e n t r a t i o n . The main i n f l u e n c e parameters a r e :
-
i n i t i a l e l e c t r i c charge o f t h e aerosol
r e l a t i v e h u m i d i t y o f t h e gaseous phase - s u r f a c e contamination o f t h e p a r t i c l e s
The c a l i b r a t i o n curve o f t h e j e t i m e t e r I n absence o f a t h e o r e t i c a l b a s i s , t h e c a l i b r a t i o n curves are e m p i r i c a l l y established. As we a r e i n t h e f i e l d o f aerosol measurement and because i n d u s t r i a l goals a r e involved, we do n o t seek a g r e a t p r e c i s i o n and t h e f o l l o w i n g r e l a t i o n s a r e t r u e w i t h i n a 10% l i m i t . With a w e l l d e f i n e d aerosol, t h e e l e c t r i c a l response i s p r o p o r t i o n a l t o t h e mass concentration according t o V = k C a where V i s t h e s i g n a l a t t h e o u t p u t o f t h e e l e c t r o m e t e r head C t h e mass c o n c e n t r a t i o n
k and a two constants
a i s o f t e n somewhat l e s s t h a n 1, near 0,9. N e i t h e r k n o r a depends s i g n i f i c a n t l y on t h e s i z e d i s t r i b u t i o n i n t h e range 1 p ( f o r s m a l l e r s i z e , t h e c a p t u r e e f f i c i e n c y decreases) t o 100 p (above p a r t i c l e s a r e n o t a d m i t t e d ) . We conclude t h a t t h e mean charge g i v e n t o any p a r t i c l e i s p r o p o r t i o n a l t o i t s w e i g h t o r , r a t h e r t o i t s volume as we w i l l see l a t e r . As f o r any i n s t r u m e n t u s i n g t r i b o e l e c t r i s a t i o n , t h e c e n t r a l problem i s t h e r o l e
341 played by t h e physico-chemical p r o p e r t i e s o f t h e p a r t i c l e ( m o d i f i c a t i o n o f t h e f a c t o r k ) . We s h a l l t r y t o g i v e a p a r t i a l answer s t a r t i n g from experimental r e s u l t s obtained w i t h well-known powder ( t e s t powder f o r example) o r d u s t samples gathered i n t h e i n d u s t r y . I t i s u s e f u l t o d i s t i n g u i s h here between m e t a l l i c p a r t i c l e s (we suppose t h a t t h e i r s u r f a c e i s c l e a n ) and semi-conductors o r i n s u l a t o r s ( i n t h i s category we i n c l u d e m e t a l l i c p a r t i c l e w i t h o x i d i s e d s u r f a c e s ) . We observe t h a t t h e s i g n and value o f t h e e l e c t r i c a l response v a r i e s g r e a t l y w i t h the m e t a l l i c nature o f t h e p a r t i c l e s . But pure m e t a l l i c aerosols a r e r a r e i n p r a c t i c e and we are mainly concerned w i t h semi-conductors and i n s u l a t o r s . I n t h i s case t h e c u r r e n t generated by the same aerosol i s d i f f e r e n t f o r a spouted bed c o n t a i n i n g e i t h e r bronze o r t i n beads. The response o f t h e d i f f e r e n t i a l model expressed i n terms o f volume concentration, f o r many d i f f e r e n t powders, remains i n the same range w i t h i n
2
50 % around the mean. For
i n d u s t r i a l purposes, i t i s p o s s i b l e t o measure t h e c o n c e n t r a t i o n o f an unknown aerosol using the d i f f e r e n t i a l model and the c a l i b r a t i o n curve f i g u r e 2. I t i s f u r t h e r p o s s i b l e t o deduct, i f r e q u i r e d , t h e c a l i b r a t i o n curve o f t h e j e t i m e t e r working f o r example w i t h t i n beads.
FIGURE 1
section of the jhtirnater
FIGURE 2
I n f l u e n c e parameters. The i n i t i a l e l e c t r i c charge o f t h e aerosol may p a r t i a l l y be t r a n s f e r r e d t o the beads d u r i n g t h e i r c o n t a c t . There are two s o l u t i o n s t o a v o i d t h i s p e r t u r b i n g e f f e c t . I n the l a b o r a t o r y , t h e s i m p l e s t way i s t o b r i n g aerosol t o Boltzman
e q u i l i b r i u m using a
Kr-85 source. For most i n d u s t r i a l a p p l i c a t i o n s , i t i s more convenient t o use the
342
d i f f e r e n t i a l model which eliminates the i n i t i a l charge by substracting the resulting
currents. The r e l a t i v e humidity of the gaseous phase yields an adsorbed layer of water molecules on the p a r t i c l e surface. In this case e l e c t r o l y t i c potentials play a role d u r i n g the e l e c t r i f i c a t i o n between particules and beads. The solution i s t o operate above 100°C. Surface contamination, particularly ionic contamination, i s a troublesome parameter. Working above 100°C reduces t h i s e f f e c t . On the other hand, the differential model gives an approximate solution because we p a r t i a l l y cancelled out the unwanted currents by substracting one from the other. In conclusion, we may say t h a t the most general form of the jetimeter i s the d i f f e r e n t i a l version, operating above 100°C. Nevertheless, i t i s possible, f o r most practical applications, t o take i n t o account particular circumstances which allow the use of the simple model, more easy t o use and cheaper.
SOME APPLICATIONS There are numerous applications of the jetimeter, b u t here we l i m i t ourselves t o those which were tested under operational conditions. Application t o the emission of a cement plant. The in-stack application was our primary goal from the outset of the research. Due t o the kindness of the "Ciments FranGais" we had the opportunity t o experiment under real conditions i n a stack of the cement p l a n t of Guerville (near Mantes). The j e t i m e t e r , f i l l e d w i t h bronze beads, was mounted on a s u p p o r t 2 m length allowing i t s introduction and fixation inside the stack. The a i r ejector was fed with compressed a i r from a compressor. A bimetal thermometer was attached t o the jetimeter to switch off the power of the compressor i f the temperature would f a l l below 100°C within the stack. The jetimeter was normally working around 130°C i n t h i s stack b u t i t could happen d u r i n g a stop of the production, t h a t the inner temperature would f a l l w i t h the risk of formation of droplets. Such water droplets are a poison f o r t h e spouted bed. industrial instrument. The Figure 3 shows a typical r e s u l t recorded with an mean concentration i s r e l a t i v e l y s t a b l e , i n the range 30 t o 50 mg/m3. The jetimeter was working well during s i x months and we had only t o change the paper of the recorder from time t o time. A t the time being, we a r e trying to define the conditions required f o r a one-year function without any maintenance because that seems to correspond t o the industrial needs. Application to industrial hygiene. The simplicity and v e r s a t i l i t y of the jetimeter i s of i n t e r e s t i n this f i e l d where one wants t o known the s p a t i a l d i s t r i b u t i o n of the aerosol and i t s variations w i t h time. Using a long time constant or some k i n d of integrator, i t i s possible t o record mean concentrations. For application t o industrial hygiene, we sample generally ambient air
343
and i t i s recomnended to use a heating tube t o avoid spurious response due t o changes i n r e l a t i v e humidity. A jetimeter was used during two months in a woodworking shop. Figure 4 shows a typical example of the recording. The time when the workshop i s a t r e s t i s clearly indicated by an unmeasurable low dust concentration. We see also dust clouds corresponding to basic operations as cutting, p o l i s h i n g e t c ... B u t the d u s t i s rapidly eliminated by the ventilation a t the end of each dusty operation. Operation i n coal mine. In m i n i n g a c t i v i t y , people are more and more interested by concentrations in term of "total dust" and by the variations i n space and time. B u t a coal mine offers an adverse environment to the use of any measuring device. The s o l i d i t y of the jetimeter and i t s good i n t r i n s i c security, allowed t o think t h a t i t could be useful i n t h i s application. B u t i t was necessary t o make real test before having a definite opinion. The "Charbonnages de France'' and the "CERCHAR" were interested by project and kindly accepted t o help us. We operated during one week i n the coal mine of La Mure (near Grenoble) which has the advantage of being free of methane. For t h i s application a battery fed converter was added t o the electronic pack. B u t another problem was t o solve. In a coal mine the humidity i s generally h i g h , greater than 95 %.I t was necessary to heat the aerosol b u t not with the usual system because o f a too high demand on the b a t t e r i e s and also f o r security reasons. We solved t h i s problem using a Ranque tube. This device i s able t o divide a compressed airflow i n two parts : one of colder a i r and another of h o t a i r around 70°C. This hot a i r was sent i n a rough exchanger and increased the aerosol temperature by ten degrees In these conditions the r e l a t i v e humidity decreases t o 75 % i f the primary a i r i s nearly saturated. A special calibration curve f o r coal dust a 75 % relative humidity was obtained i n the laboratory. The jetimeter was i n s t a l l e d downwind of a large crusher. Figure 5 shows the dust clouds corresponding t o the crushing operation. The good ventilation o f the gallery cleans rapidly the atmosphere and the dust concentrationsreach background conditions which are of few mg/m3. Miscellaneous applications. A jetimeter was mounted on a tank AMX i n view of h a v i n g an equipment t o measure the dust concentration of the a i r admitted by the ventilation system o f the tank when used in dusty countries. The experience showed that i t was possible t o make continuous e discovered measurement when the inclination against the vertical was l e s s t h a n 15". W that f o r a jetimeter f i l l e d with t i n beads the vibrations of the t a n k added to those of the motor generated a background noise of around 50 mV. This value corresponds approximatively to 10 mg/m3. The dust concentrations higher t h a n this level were measurable. The jetimeter was useful in our laboratory in problems of detection and control. For aerosols used on a r e p e t i t i v e basis ( f o r example t e s t dust f o r a i r f i l t e r s ) i t i s
344 p o s s i b l e t o o b t a i n an accurate c a l i b r a t i o n curve and the j e t i m e t e r become a s h o r t response-time measuring device. CONCLUSION Laboratory s c a l e s t u d i e s allowed t o understand t h e main p h y s i c a l p r o p e r t i e s o f t h e j e t i m e t e r . B u t t h e i n d u s t r i a l a p p l i c a t i o n s described here show t h a t t h e j e t i m e t e r c o u l d be an i n d u s t r i a l device, w e l l s u i t e d f o r easy
and r a p i d measurements o f
aerosols, o r f o r continuous r e c o r d i n g o f aerosol concentrations
, if
a great precision
i s n o t needed, I t s good performances i n adverse environmental c o n d i t i o n s are remarkable.
Fig. 3
Fig. 4
Fig. 5
MON ITORlNG NETWORKS AND SURVEY RESULTS
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Atmospheric Pollution 1 980, Proceedings of the 14th International Colloquium, Paris, France, May 5-8,1980, M.M. Benarie (Ed.),-Studies in Environmental Science, Volume 8 0 Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
347
THE DESIGN OF A I R QUALITY MONITORING NETWORKS U S I N G AN INFORMATION CONTENT IEASURE.
E.E.
PICKETT AND R.G.
WHITING
Dept. o f I n d u s t r i a l Engineering, I n s t . f o r Environmental S t u d i e s , University of Toronto, Toronto, O n t a r i o , Canada.
M5S 1A4
ABSTRACT A s t a t i s t i c a l design methodology based on s i g n a l d e t e c t i o n i s proposed f o r
t h e design of a i r q u a l i t y monitoring networks.
The information c o n t e n t displayed
by a given network c o n f i g u r a t i o n is d e f i n e d and suggested a s a v a l i d o b j e c t i v e f o r optimal network design. work of SO
2
Application o f t h e methodology t o an e x i s t i n g n e t -
monitors i s demonstrated, and a comparison i s made with an a l t e r n a t e
s t a t i s t i c a l design c r i t e r i o n .
INTRODUCTION The problem o f a i r q u a l i t y monitoring network design h a s received considerable attention i n t h e recent l i t e r a t u r e .
A s a r e s u l t , a wide v a r i e t y of approaches
and techniques c o n f r o n t t h e network d e s i g n e r (see, f o r example, r e f . 1 ) . T h i s i s p a r t i c u l a r l y t r u e of t h e class o f s t a t i s t i c a l network design philosophies, which i n c l u d e s t h e methodology d e s c r i b e d h e r e .
The problem o f s e l e c t i n g a design
technique can be s i m p l i f i e d , however, i f an a c c e p t a b l e measure o f ' o p t i m a l i t y ' i n network design can b e found.
Consideration can then be l i m i t e d t o those
techniques which can e f f e c t i v e l y and e f f i c i e n t l y provide t h i s measure f o r a l l f e a s i b l e network c o n f i g u r a t i o n s . The measure of o p t i m a l i t y used h e r e i s t h e following:
t h e 'optimal' network
design i s t h a t which meets t h e monitoring program o b j e c t i v e s with acceptable r e l i a b i l i t y and a t l e a s t c o s t .
R e l i a b i l i t y r e f e r s t o t h e a b i l i t y o f a network
c o n f i g u r a t i o n t o provide t h e information a p p r o p r i a t e t o t h e program o b j e c t i v e s a c c u r a t e l y and r o b u s t l y . The s t a t e m e n t o f a well-understood program o b j e c t i v e i s a fundamental requirement o f t h e design p r o c e s s . optimality.
An attempt
Such a statement i s e x p l i c i t i n our measure of
i s made h e r e t o q u a n t i f y t h e notion t h a t a p a r t i c u l a r
network c o n f i g u r a t i o n should b e p r e f e r r e d t o another i f it provides more 'independent' information r e g a r d i n g t h e space and t i m e p a t t e r n s of p o l l u t a n t
To t h i s end we have defined a measure
c o n c e n t r a t i o n s over t h e r e g i o n of i n t e r e s t .
of information c o n t e n t of network a network c o n f i g u r a t i o n ( r e f s . 2 - 3 ) .
OVERVIEW OF THE DESIGN METHODOLOGY AND DATA REQUIREMENTS An
e s s e n t i a l requirement f o r t h e design methodology i s t h e a v a i l a b i l i t y of a
d a t a base of 'observed'concentrations of t h e p o l l u t a n t i n question over a network of ' p o t e n t i a l ' monitoring s i t e s .
I n t h e example p r e s e n t e d h e r e , d a t a from an
e x i s t i n g network of f i f t e e n permanent monitors were a v a i l a b l e , and a reduction i n network s i z e was t h e design o b j e c t i v e .
However, d a t a from d i f f u s i o n - t r a n s p o r t o r
o t h e r models may be used as o b s e r v a t i o n s .
I n t h i s c o n t e x t , t h e p o t e n t i a l monitor
s i t e s may be no more than p o i n t s on a map.
The n a t u r e and q u a n t i t y of t h e a v a i l a b l e
d a t a s t r o n g l y i n f l u e n c e t h e r e l i a b i l i t y of t h e network design, a s w i l l be discussed later.
This d a t a s e t i s employed i n two d i s t i n c t phases.
In the f i r s t , identification
and e s t i m a t i o n of a dynamic s t a t e - s p a c e model i s perfonred, where c u r r e n t p o l l u t i o n c o n c e n t r a t i o n s a t each p o t e n t i a l monitoring s i t e a r e r e l a t e d t o p a s t concentrations a t a l l p o t e n t i a l s i t e s (and t o c u r r e n t meteorological and source emission d a t a ) . This model i s an estimate of t h e " s i g n a l " which i s i d e n t i f i a b l e from t h e d a t a . I n t h e second phase, t h e o b s e r v a t i o n d a t a s e t i s regarded as a n o i s e corrupted sample of t h e s i g n a l d e s c r i b e d by t h e model. A l t e r n a t i v e f e a s i b l e network c o n f i g u r a t i o n s can be a s s e s s e d within t h i s framework by using t h e o b s e r v a t i o n s from those sites which are monitored t o d e t e c t t h i s signal.
The combination of monitored s i t e s which performs t h i s b e s t
i s t i c a l sense
-
-
i n a stat-
can be regarded as o f f e r i n g t h e most information concerning the
space and t i m e behaviour of t h e observed p o l l u t i o n c o n c e n t r a t i o n s . I t e r a t i o n of an a p p r o p r i a t e Kalman f i l t e r ( r e f . 4 ) i s t h e procedure used here t o perform t h e s i g n a l d e t e c t i o n r e q u i r e d i n t h e second phase.
The s t e a d y - s t a t e Kalman
f i l t e r e s t i m a t e s are e q u i v a l e n t t o t h e minimum v a r i a n c e , one-sided f i l t e r of t h e observed d a t a , where t h e o b s e r v a t i o n s are regarded as noise corrupted samples from t h e modelled s i g n a l (see, f o r example, r e f . 5 ) .
I s s u e s r e l a t e d t o implementation
and network o p t i m i z a t i o n with t h i s technique are d i s c u s s e d i n t h e n e x t s e c t i o n .
S I G N A L DETECTION AND NETWORK DESIGN
The f i r s t phase of t h e design procedure r e q u i r e s an e x p l i c i t and unbiased des-
c r i p t i o n of t h e space time dependencies of t h e p o l l u t i o n c o n c e n t r a t i o n s within the r e g i o n and d u r i n g t h e t i m e horizon o f t h e a n a l y s i s . I t i s assumed t h a t t h e dynamics of t h e c o n c e n t r a t i o n f i e l d a r e adequately repres-
e n t e d as a m u l t i v a r i a t e a u t o r e g r e s s i v e p r o c e s s of o r d e r p which i n c l u d e s a d e t e r ministic input. Let
X(t)
be an npxl v e c t o r denoting t h e ' t r u e ' p o l l u t i o n c o n c e n t r a t i o n s a t t h e n th t-p+l ( s o t h a t j n + k
p o t e n t i a l monitoring l o c a t i o n s f o r t i m e p e r i o d s t,t-1,
...,
349
...,
element of X(t) is the concentration of site k in time period t-j, where j=O 1, p-1 and k=1,2,
X(t)
=
...,n).
A x(t-1)
+
Then we have:
C c(t)
...,T, where A
f o r t=l,
+ v(t)
1)
is an np x np transition matrix; C is an np x h matrix of
coefficients multiplying c(t), an h x 1 vector of deterministic input variables at time t; and v(t) is np x 1 vector random variable with zero mean and covariance vV-
The justification of the use of a multivariate representation as in equation (1) rests upon its ability to adequately describe the space and time correlations exhibited by atmospheric pollutants over an urban scale region. A number of techniques are available for the identification and estimation of the model in equation (1) (see, for example, ref. 6). The next section provides an illustration of a simple iterative multiple regression procedure which produced adequate estimates in practice. In the second phase of the design procedure, the observed pollution concentrations (denoted by {Y(t)}, a sequence of n x 1 vectors; t=l,. ..,T) are regarded as noise corrupted samples of the true concentrations, which are modelled in equation (1). This can be represented by M(z(t) + w(t))
Y(t) =
(2)
for t=l,...,T, where
is the np x 1 state vector in equation (l), w(t) is an np x 1
vector random variable with zero mean, covariance matrix V W
'measurement' matrix.
,
and M is an n x np
The matrix M has the partitioned structure M = (I 0 0
where I and 0 are n x n identity and null matrices, respectively.
...0)
Equation (2)
will be referred to in the following as the observation model. The covariance matrices V
V
and V
of the vector random variables appearing in
W
equations (1) and ( 2 ) , respectively, share the partitioned structure
L' I:
v = v where
(3)
np np n x n covariance matrix and the diagonal and off-diagonal matrices are
v' is a
appropriately dimensioned null matrices. The structure of V' is assumed to be W
V' = W
2
Ow I
(4) 2
where I is then x n identity matrix, and aw the common variance of the uncorrelated observation noise. The selection of Vw in equation (2) completes the prerequisites for the signal detection phase.
The signal is that represented by the model, equation (l), and
the available data are regarded as noise-corrupted samples of this signal. We X(t)) which is a linear combination of seek the minimum variance estimator (say, -
350 c u r r e n t and p a s t o b s e r v a t i o n s , { Y ( t ) ) ie. t h e one-sided f i l t e r .
This e s t i m a t o r can
be r e a l i z e d i n p r a c t i c e by c o n s t r u c t i n g a n e s t i m a t e of t h e s t e a d y - s t a t e Kalman filter
.
The e q u a t i o n s f o r t h e f i l t e r are provided i n ( r e f . 4 ) .
A key component of
t h e s e e q u a t i o n s i s t h e np x np m a t r i x , P ( t \ t ) , which i s t h e covariance m a t r i x of t h e Kalman f i l t e r e s t i m a t e ,
X(t\t).
Under s u i t a b l e c o n d i t i o n s of o b s e r v a b i l i t y and
c o n t r o l l a b i l i t y (see, f o r example,
w i l l exist.
( r e f . 7)
,a
s t e a d y - s t a t e v a l u e ( P ) of P ( t l t)
The corresponding Kalman f i l t e r e s t i m a t o r i s e q u i v a l e n t t o
X(t)
Evaluation of a l t e r n a t e network c o n f i g u r a t i o n s i n t h e c o n t e x t of t h i s s i g n a l d e t e c t i o n procedure w i l l be accomplished using an e s t i m a t e of t h e s t e a d y - s t a t e cov a r i a n c e matrix, p. The o b s e r v a t i o n d a t a s e t corresponding t o a p a r t i c u l a r network c o n f i g u r a t i o n i s s p e c i f i e d by an a p p r o p r i a t e choice of t h e measurement m a t r i x , M.
Corresponding t o
each f e a s i b l e network c o n f i g u r a t i o n i s a v a l u e of P which can be approximated by i t e r a t i n g t h e Kahnan f i l t e r equations.
The r e s u l t i n g P m a t r i c e s r e f l e c t t h e value
o f t h e o b s e r v a t i o n s o b t a i n e d from t h e corresponding monitoring networks i n e s t i m a t i n g t h e s i g n a l d e s c r i b e d by t h e model i n equation ( 1 ) . I t i s important t o recognize t h a t t h e s i g n a l d e t e c t i o n i s performed i n each case f o r
all p o t e n t i a l
monitoring l o c a t i o n s
n o t j u s t t h o s e d i r e c t l y sampled. The information c o n t e n t possessed by a given monitoring c o n f i g u r a t i o n i s defined t o be l / t r ( P ' ) ,
where P i s t h e covariance m a t r i x of t h e s i g n a l d e t e c t i o n e r r o r ( i . e .
t h e covariance m a t r i x of
X(t)),
t h e f i r s t n rows and n columns
t h e prime ( ' ) ' d e n o t e s t h e sub-matrix obtained from ( c f . equation ( 3 ) ) , and "tr" denotes t r a c e .
Defining t h e measure of information c o n t e n t i n t h i s way has s e v e r a l important advantages.
The v a l u e of t h e o b s e r v a t i o n s from each sampled s i t e a r e a s s e s s e d i n
t h e c o n t e x t of t h e space and t i m e dependencies e x h i b i t e d by t h e e n t i r e s e t of p o t e n t i a l sites.
This i s i n c o n t r a s t t o many e x i s t i n g s t a t i s t i c a l design techniques
which do n o t account f o r t i m e dependencies i n t h e d a t a , and o f t e n do n o t attempt t o e x p l a i n d a t a v a r i a t i o n i n terms of a v a i l a b l e meteorological and source emission data. Evaluating network performance by e x p l i c i t l y attempting t o recover t h e observed p o l l u t i o n c o n c e n t r a t i o n p a t t e r n s a t l o c a t i o n s t h a t are p r a c t i c a l design approach.
not
d i r e c t l y sampled is a
I f t h e d a t a s e t which has been analyzed i n t h i s fashion
i s t y p i c a l o f f u t u r e behaviour, t h e r e s u l t i n g optimal network w i l l o f f e r t h e most independent information from which t o i n f e r f u t u r e r e g i o n a l p a t t e r n s . This l a s t p o i n t raises t h e important i s s u e o f r e l i a b i l i t y of a monitoring network, which w a s e x p l i c i t i n our 6 e f i n i t i o n of optimal network design.
I n t h e c o n t e x t of
t h e design procedure o u t l i n e d h e r e , r e l i a b i l i t y can b e s t be i n s u r e d by r e p l i c a t i o n of t h e a n a l y s i s over d a t a sets r e p r e s e n t i n g a wide range of c o n d i t i o n s . p a r t i c u l a r l y important f o r d a t a a r i s i n g from s i m u l a t i o n models.
This i s
The r e s u l t s can
351 be easily pooled by totalling the measures of information content from each replication. One further issue of a technical nature which arises from this design approach is ensuring that the steady-state filter estimates are indeed optimal, i.e. that valid signal detection is performed.
This can be ensured by examining the innovations
sequence (ref. 8) arising from the steady-state filter when the full network is monitored.
If the model in equation (1) has been properly validated, then any
significant time dependencies in the innovations sequence (in the Kalman filter applied to the system of equations (1) and the model noise covariance matrix, V'. V
(2)) may be removed by re-estimation of
This problem may not arise in practice if a
relatively small value of the observation noise convariance matrix, V;,
is selected
initially. APPLICATION TO AN EXISTING NETWORK In this section, an example illustrating the application of the methodology using data from an existing network is presented. The design objective involves reducing the network from the current fifteen stations to one of thirteen stations displaying maximum information content. The network in this example (see Fig. 1) is located in the vicinity of a largefossil-fuel generating station.
The monitors are operated by the Thermal Generation
Division of Ontario Hydro (see (refs. 9-10)) and provide measurements of the average hourly
SO2
concentration.
Data representing two months, February and July, were
available for each of the fifteen locations, as well as meteorological and source emission data (including wind speed and direction, ambient temperature, and station load data). An
iterative multiple regression procedure was employed in estimating the co-
efficients and order of the autoregressive process (equation (1)) describing the time and space dependencies in the observation data set.
The technique involves in-
creasing the order of the estimated model until the residuals display properties of white noise (ref. 11). Initial attempts to apply the technique to the data in its raw form indicated a fairly high order model would be required.
To reduce the model order, four-hour
averages of the raw data were used. Model validation indicated a second order model to be adequate for both the February and July transformed data (ref. 12). The second phase of the design methodology was implemented using a value of 10 for
u
Wr
the observation noise variance.
Analysis of the innovations sequence from the
resulting steady-state Kalman filter indicated the hypothesis of white noise could be rejected for only one site (site 3 , fig. 1).
Reestimation of V', the model noise V
covariance matrix, was not performed; rather, site 3 was included in all networks in the subsequent optimization. Table l(a) summarizes the results of the network reduction for the two months. A
s e q u e n t i a l procedure f o r dropping t h e s i t e s from t h e network w a s used ( r e f . 1 2 ) . The r e s u l t s from t h e February and J u l y r e p l i c a t i o n s were combined i n performing t h e network reduction.
Note t h a t s i t e 1, a s well a s s i t e 3 , has been included i n a l l
network c o n f i g u r a t i o n s i n t h e a n a l y s i s .
I t e r a t i o n of t h e f i l t e r equations d i d not
r e s u l t i n convergence when t h i s s i t e was dropped, implying t h a t c o n d i t i o n s of obs e r v a b i l i t y are not met i n t h i s case.
S i t e 1 i s t h e most w e s t e r l y l o c a t i o n i n t h e
network, and appears t o be t h e f i r s t t o d e t e c t l e v e l s of S O 2 i n t h e p r e v a i l i n g southwest winds. S i t e s 4 and 5 a r e s e l e c t e d by t h i s procedure f o r removal i n t h e optimal t h i r t e e n s i t e network.
These s i t e s may be regarded a s providing redundant information, i n
t h e sense t h a t they c o n t r i b u t e l i t t l e towards explaining t h e observed space and t i m e dependencies i n Lhe d a t a . To emphasize t h e use of o t h e r s t a t i s t i c a l design c r i t e r i a may r e s u l t i n q u i t e d i f f e r e n t optimal network c o n f i g u r a t i o n s , an a l t e r n a t e procedure w i l l be i l l u s t r a t e d using t h e same d a t a . The use of p r i n c i p a l components a n a l y s i s and r e l a t e d techniques i n network design has been suggested by a number of authors ( s e e , f o r example, ( r e f . 1 ) ) . The b a s i c i d e a i s t o e x p l a i n most of t h e v a r i a t i o n i n t h e observed p o l l u t i o n concentrations v i a a few orthogonal l i n e a r combinations (components) of the readings taken a t each site.
Those monitor l o c a t i o n s with t h e v a r i a t i o n i n t h e i r observed p o l l u t i o n l e v e l s
b e s t explained by t h e s e components a r e r e t a i n e d i n t h e network design process. This approach was a p p l i e d t o t h e two d a t a s e t s used i n t h e previous a n a l y s i s . Three components were r e t a i n e d i n each c a s e , explaining 8 0 % and 68% of t h e v a r i a t i o n i n t h e February and J u l y d a t a r e s p e c t i v e l y .
The v a r i a t i o n i n t h e observed concen-
t r a t i o n s a t each s i t e t h a t was explained by t h e s e t h r e e components were ranked i n increasing order.
The r e s u l t s appear i n Table 1 ( b ) .
have high rankings f o r both months.
Note t h a t s i t e s 4 and 5
These two s i t e s would be r e t a i n e d using t h i s
design procedure. The fundamental d i f f e r e n c e between t h e two methodologies i s i n t h e way they regard independent v a r i a b i l i t y i n t h e observed c o n c e n t r a t i o n s .
If the variation a t a
s i t e i s n o t w e l l explained by t h e model, equation (l), it w i l l be r e t a i n e d i n t h e optimal network produced by t h e s i g n a l d e t e c t i o n method proposed here.
Variation
n o t explained by t h e p r i n c i p a l components method forms t h e b a s i s f o r r e j e c t i o n of a s i t e i n performing network r e d u c t i o n .
This c o n f l i c t i n g behaviour i n t h e two
approaches s e r v e s t o emphasize t h e importance of formulating an e x p l i c i t statement of program o b j e c t i v e s p r i o r t o any design a n a l y s i s . To summarize, a network design objective--maximizing
information content--has
been
proposed, and a methodology presented which can e f f e c t i v e l y provide t h i s measure i n practice.
The technique a s s e s s e s t h e information c o n t e n t i n a given network config-
u r a t i o n based on t h e space and time c o r r e l a t i o n s observed over t h e e n t i r e region t o be monitored.
353
NANTICOKE GS AIR POLLUTION SURVEY AREA
( " , . I . I"
.C.LI
. , W . 1 , " ' 1
FIG. 1 L
TABLE 1
a)
R e s u l t s of Network O p t i m i z a t i o n f o r I n f o r m a t i o n C o n t e n t O b j e c t i v e s ( t a b u l a r v a l u e s are r a n k i n g s o f r e s u l t i n g network i n f o r m a t i o n c o n t e n t s , largest to smallest)
STEP 1
I
STEP 2
2
4
5
Feb. 1 6 July 11 Feb. & J u l y 8
1 6
5
Feb.
July Feb.
b)
Feb. July
&
1*
6 4
3 5 3
2 1 0 2 5
4 D 5 3 1 0 D 2 9 July 6 D 1* 4
SITE DROPPED 8 9 10 11 2 7 8 13 8 1 2 3 9 4 10 6 12
7
2
5
1
6 2
3
8
13 12
4
13 13
7
9 1 1 4 1 2
7 1 2 3 8 5 11
6 1
1
12 10
7
12
14 9 7 9
15 111 1 11
8 1 0 7 1 9 10
Results of Network Optimization for Alternative Design Objective (tabular values are rankings of each site according to the variance explained for that site, smallest to largest)
1 4 13
2 10 7
4 5 14 11 14 8
6 7 8 12 2 6
* Denotes site to be dropped. prior iteration.
SITE DROPPED 8 9 10 2 13 6 4 1 12
1112 3 5
13 9
14 7
10
3
5
9
15 1 11
"D" implies site has been previously dropped in a
354
mFEF33NCES
f R.E. tlunn, The Design o f A i r Quality Monitoring Networks, I n s t i t u t e f o r Environmental S t u d i e s , Univ. o f Toronto pub. NO. EE-7, 1978. 2 E.E. P i c k e t t and R.G. Whiting, An Information Content Measure t o Evaluate SpaceT i m e Tradeoff i n Environmental Monitoring Network Design, WP 78-007, Dept. of Ind. Eng., Univ. o f Toronto, 1978. 3 E.E. P i c k e t t and R.G. Whiting, Sensor I o c a t i o n and Measurement Scheduling i n t h e o p t i m a l Design of Environmental Monitoring Networks, WP 78-008, Dept. of Ind. Eng., Univ. o f Toronto, 1978. 4 R.E. Kalman, A New Approach t o Linear F i l t e r i n g and P r e d i c t i o n Problems, J . Basic Eng., 820 (1960), 35-46. 5 E . J . Hannan, Multiple Time S e r i e s , John Wiley & Sons, 1970. 6 R.C.K. L e e , Optimal I d e n t i f i c a t i o n Estimation and Control, Research Monograph No. 28, MIT Press, Cambridge, Mass., 1964. 7 A.H. Jazwinski, S t o c h a s t i c Processes and F i l t e r i n g Theory, Academic P r e s s , New York, 1970. 8 R.K. Mehra, On t h e I d e n t i f i c a t i o n o f Variances and Adaptive Kalman F i l t e r i n g , IEEE Trans. on Automatic Control, V o l . AC-15, No. 2 , 1970, pp. 175-184. 9 Ontario Hydro, Nanticoke GS 1976 Air Quality Data, Environ. P r o t . Dept., Cent. Thermal S e r v i c e s , Report CTS-07012-15, 1977. 1 0 O n t a r i o Hydro, Nanticoke GS A i r Q u a l i t y Monitoring Program and 1976 R e s u l t s , Environ. P r o t . Dept., Cent. Thermal S e r v i c e s , Report CTS-07012-6, 1977. 1 1 K . J . Astrom and P. Eykhoff, System I d e n t i f i c a t i o n - - A Summary, Automatica. 7 (1971), 123-162. 1 2 R.G. Whiting, Design o f Air Q u a l i t y Monitoring Networks: A S t a t e Estimation Approach, Unpublished M.A.Sc. t h e s i s , Dept. o f Ind. Eng., Univ. o f Toronto.
Atmospheric PoNution 2980, Proceedings of the 14th International Colloquium, Paris, France, May 5-8,1980, M.M. Benarie (Ed.), Studies in Environmental Science, Volume 8 0 Elsevier Scientific Publishing Company, Amsterdam -Printed in The Netherlands
355
THE CANADIAN AIR AND PRECIPITATION MONITORING NE’IWORK AF” L.A. BARRIE, H.A. WIEBE, K. ANLAW and P. FELLIN Atmospheric Environment Service, Damsview, Canada (M3H 5T4)
ABSTRACT A five station network of air and precipitation monitors was established in November 1978 in eastern Canada as part of the Canadian Long Range Transport of Air Pollutants Program (LRTAP). Its purpose is to provide information on the spatial and temporal variation of ambient concentrations and denosition rates of potentially acidic trace constituents. The chemical constituents of event precipitation samples as well as the daily average concentration of SO2 and particulate major ions are determined routinely. Aspects of the network’s operation such as sampling methodology, analysis and data handling are described in detail. The discussion is based on the results for November 1978 - June 1979.
INTRODIJCTION The Air and Precipitation Monitoring Network (APN) (ref. 1) was established in late 1978 to investigate regional scale pollution phenomena associated with acidic wet and dry deposition. It is operated within the framework of the Canadian Long Range Transport of Air Pollutants Program. At present, efforts are concerned with obtaining a record of the spatial and temporal variation of the concentration o f selected acid-related substances in air and precipitation. Twenty-four-houratmospheric particulate samples are analyzed for sulphate, nitrate, chloride, sodium, potassium, ammonium and gaseous sulphur dioxide. Daily precipitation samples are analyzed for sulphate, nitrate, chloride, hydrogen, ammonium, sodium, potassium, calcium, magnesium and total phosphorous ions. The network consists of five regionally representative sites located east of the Ontario - Manitoba border (Fig. 1). Presently, it is this part of the country in which acidic precipitation and its associated effects are causing qreat concern. Data generated by the network will be utilized to: (i) give estimates of the atmospheric contribution of major ions to terrestrial and aquatic ecosystems; (ii) assess the frequency and magnitude of elevated regional pollution episodes; (iii) iwrove LRTAP model predictions of pollutant concentrations in air and precipitation.
356
FIG. 1. Locations of APN sites and 1000 mb back-trajectories f o r ELA February 16-19, 1979 (crosses mark 24-h intervals). SAMPLING METHODOLOGY
Atmospheric p a r t i c u l a t e matter and gaseous sulphur dioxide are collected i n a f i l t e r h o l d e r containing a Whatman 40 particulate f i l t e r , followed by an SO2 absorbent Whatman 4 1 paper impregnated with potassium carbonate - glycerol solution. Approximately 30 cubic metres of a i r are sampled a t a height of 1 0 metres during a 24-hour period beginning and ending a t 1200 C2-V. The f i l t e r s are analyzed by ion chromatography and the Thorin method. The detection l i m i t s are 0.2 and 0.8 ug mm3 for particulate major ions and sulphur dioxide, resPrecipitation is collected using a Sangmo wet-only collector.
pectively.
Daily samples a r e analyzed f o r pH and major ions within s i x weeks of collection AMBIENT AIR CONCENTR4TIONS
Daily particulate sulphate and gaseous sulphur dioxide concentrations for the period November 1978 to June 1979 a t the Experimental Lakes Area (EM) s i t e a r e shown i n Fig. 2. A detailed meteorological analysis has revealed t h a t the large concentration fluctuations a r e due t o the alternating presence of clean background air and of a i r polluted by large SO2 sources i n the Lower
357
I97EV 1 374
FIG. 2
Daily-ylphate and sulphur dioxide concentrations i n a i r a t EM (ug m 1.
Great Lakes area.
The data f o r February 1979 i l l u s t r a t e s these conclusions.
Sulphur concentrations were close t o background for the first half of the month. On February 1 7 , ambient concentrations increased and f o r about two weeks remained
high with a maximum of 20 ug m-3 f o r SOz.
This period was associated with an
extensive high pressure system centred south of the Great Lakes and covering most of eastern North America. Three-dimensional four-day back-trajectories of a i r parcels (1000 mb) arriving a t ELA a t 0 Gh.rT on February 16, 1 7 and 18 are shown i n Fig. 1. For
3 58
February 16, the trajectory is c l e a r l y from northern Canada and low concentrations were measured. During the succeeding days, as the centre of the high pressure system moved progressively eastward, the computed t r a j e c t o r i e s s h i f t markedly southward i n t o the United States. The particulate and sulphur dioxide concentrations increased from a m i n i m on February 16 cO.76 pg m -3 SOi and 1.1 pg m-3 SO2) t o maximum values on February 18 and 19 (4-9 ug m-3 SOT and -3 18 - 20 pg m S O 2 ) . On February 19, a t the beginning of the sampling period (1200 GPU) the trajectory (dashed l i n e i n Fig. 1) passed over the industrialized lower Lake Michigan region.
However, a t 2400 Mythe a i r mass trajectory is
from the southwest (could may have been sampled f o r Pollution episodes are a far days of one another
not be shown i n Fig. 1) and somewhat cleaner a i r the remainder of the day. occasionally observed a t ELA and Chalk River within even though the two s i t e s are 2000 km apart. For the February 18 episode a t ELA discussed above was observed a t
instance, Chalk River two days l a t e r . Trajectories show that as the centre of the same high pressure system passed Chalk River, a regional flow developed on the western
99
FIG. 3. Cumulative frequency F distribution of daily sulphate concentrations a t APN sites and a t sites i n the northeastern United States ( r e f . 2 ) .
3 59
side of the anticyclone. This brought about the long-range transport of polluted air, high in sulphur concentrations, to Chalk River from SO2 source regions south of the lower Great Lakes. The log-normal cumulative frequency distributions of sulphate concentration at APN sites are shown in Fig. 3. The geometric mean concentrations for ELA and Chalk River are 1 and 1.8 pg m-3, respectively; these are lower than those for Long Point (5.4 ug m-3) and Toronto (4 pg m-3) , or than those in the northeastern United States (5.8 - 10 pg m-3) (ref. 2). Sulphate distributions are broader at APN sites than at EPRI-SURE1 and NYC CHAMP stations in t h e northeastern United States. Geometric standard deviations at the Canadian and American sites are 3.3 and 2.3, respectively. Particulate pollution episodes, defined as situations in which daily sulphate concentrations exceed 10 ug m-3, occur 2 5 , 15, 6 and 2% of the time at Long Point, Toronto, Chalk River and ELA, respectively. PRECIPITATION (HEMISTRY Monthly precipitation-amount-weighted-manconcentrations of hydrogen (expressed as pH), sulphate and nitrate ions are summarized in Table 2. Table 2. Ebnthly mean of precipitation-amount-weightedpH, sulphate and nitrate at APN sites in 1978/79 (site locations in Fig. 1). Nov.
Dec.
Jan.
Feb.
Mar.
Apr.
- May
June
!!?I
EL4
-
CHALK RIVER LONG POINT KEJIMKUJIK
4.3
4.2
4.4
5.0
5.0
4.9
-
4.3
4.1
-
4.1 4.2
4.2 4.1 4.7
-
Sulphate ELA CHALK RIWA LONG POINT KEJIMKUJIK
0.9 2.1 3.2
Nitrate ELA CHALK RIVER LONG POINT KEJIMKUJIK
1.2 2.2 2.5
1.3 2.0 3.0
2.4 0.7 4.3
1.9 1.8 2.6
1.5 4.3 5.1
2.6 2.1 -
1.1 4.9 6.7
-
-
1.9 2.6 2.0
1.0
0.6 2.4
1.0 4.6 1.9
1.5 4.6 4.3
1.4 1.6
-
1.3 2.4 3.3
-
1.9 6.0 10.2 1.5 2.0 2.4 4.0 0.5
360
The s i t e most remote from pollution sources, EM, received the least acidic precipitation (mean pH 4.9 - 5.01. During the three spring months, April t o June 1978, 28 daily precipitation samples were collected; 47% were above pH 5.6, 21% were between pH 5. 5 and 5 and 32%were below pH 5. Long Point and Chalk River, being mre exposed to polluted a i r masses, showed tee most acidic precipitation. The episodicity of acidic deposition so characteristic of Scandinavia (ref. 3) was a l s o observed a t EM. For instance, r a i n on two successive days i n June, 1979 represented only 2 of 13 events. Yet, i t deposited 54%of the t o t a l r a i n f a l l and 88% of the hydrogen ion input t o the area by r a i n during that month. Precipitation sulphate concentrations a t Chalk River and Long Point increased two t o three fold fromwinter t o l a t e spring (Table 1) suggesting a summer-time m a x i m so frequently observed i n the northeastern United States (ref. 4 ) . No sulphate trend was evident a t EM. trend a t any of the s t a t i o n s .
Precipitation n i t r a t e did not show seasonal
SUMMARY The f i r s t e i g h t months of APN data indicate t h a t the frequency and magnitude
of high sulphur episodes i s greatest i n southern Ontario where monthly mean prec i p i t a t i o n pH i s .., 4 . 2 . Episodes also occur a t a remote s i t e i n northwestern Ontario where mean precipitation pH is 4.9 but are l e s s frequent and severe.
-
High sulphur concentrations a t t h a t s i t e a r e associated with distant anthropogenic sources south of the Great Lakes. ACKNOWLEDGEPENT
This work was supported by the Atmospheric Environment Service of Canada. The authors thank M r . J. Kovalick f o r h i s support i n preparing t h i s report. REFERENCES
1. L.A. Rarrie, H.A. Wiebe, P. F e l l i n and K . Anlauf, APN the Canadian A i r And Precipitation Monitoring Network: A Description And Results For November 1978 t o June 1979, 1980, REP. AQRB-80, 4905 Dufferin S t . , Downsview, Ont. 2. P.K. Mueller, G.M. Hidy, T.F. Lavery, K. Warren and R.L. Baskett, Proc. 4th Symp. Turbulence, Diffusion And A i r Pollution, Reno, Nevada, Jan. 15-18, 1979, pp 322-329, h e r . Met. SOC. 3. F.B. Smith and R.D. Hunt, Atmos. Envir., 1 2 (1978), 461-478. 4 . J . M . Hales and M.T. Dana, Atmos. Envir., 13 (1979), 1121-1132.
Atmospheric Pollution 1980, Proceedings of t h e 1 4 t h International Colloquium, Paris, France, May 5-8,1980, M.M. Benarie (Ed.), Studies in Environmental Science, Volume 8
361
0 Elsevier Scientific Publishing Company, Amsterdam - Printed in T h e Netherlands
AMBIENT A I R POLLUTION FROM INDUSTRIAL SOURCES
M.J.
SUESS
World H e a l t h O r g a n i z a t i o n , R e g i o n a l o f f i c e f o r E u r o p e , Copenhagen,
Denmark
The l o n g r a n g e programme o f t h e World H e a l t h O r g a n i z a t i o n (WHO) i n c l u d e s a number o f r e g i o n a l p r o j e c t s a i m e d a t r e d u c i n g t h e damage t o h e a l t h a n d t h e e n v i r o n ment f r o m a i r p o l l u t a n t s .
W i t h i n t h e a r e a s e r v e d by t h e R e g i o n a l O f f i c e f o r
E u r o p e (EURO), r e c e n t U n i t e d N a t i o n s Development Programme s u p p o r t e d c o u n t r y p r o j e c t s i n C z e c h o s l o v a k i a , Greece, P o l a n d , Romania, S p a i n a n d T u r k e y h a v e d e a l t w i t h a i r p o l l u t i o n problems.
I n t e r n a t i o n a l c o o p e r a t i o n on a i r p o l l u t i o n i s c a r r i e d o u t
w i t h i n t h e framework o f t h e U n i t e d N a t i o n s E n v i r o n m e n t Programme, t h e G l o b a l E n v i r o n m e n t a l M o n i t o r i n g S y s t e m (GEMS), a n d w i t h v a r i o u s i n t e r n a t i o n a l g o v e r n m e n t a l and non-governmental
o r g a n i z a t i o n s , s u c h a s Economic Commission f o r E u r o p e , C o m m i s -
s i o n o f E u r o p e a n C o m m u n i t i e s , O r g a n i s a t i o n f o r Economic C o o p e r a t i o n a n d Development, and I n t e r n a t i o n a l Organization for Standardization.
The l i s t i s n o t e x , h a u s t i v e and
i s c i t e d o n l y t o g i v e a n i d e a o f t h e b r e a d t h o f t h e programme.
I n r e s p o n s e t o t h e n e e d a n d i n s u p p o r t o f v a r i o u s p r o j e c t s , EURO p r e p a r e d a n d p u b l i s h e d i n 1 9 7 6 t h e manual o n u r b a n a i r q u a l i t y management.
T h i s manual i s con-
c e r n e d w i t h g e n e r a l p r i n c i p l e s f o r t h e a b a t e m e n t and c o n t r o l of a i r p o l l u t i o n and
i t s l e g a l , a d m i n i s t r a t i v e , a n d e c o n o m i c a s p e c t s , m e t e o r o l o g y , town a n d c o u n t r y planning, urban a i r p o l l u t a n t s , source inventory, a i r q u a l i t y c r i t e r i a standards, s u r v e i l l a n c e , and m o n i t o r i n g sy ste m s. A n o t h e r p h a s e o f t h e programme i s t h e p r e p a r a t i o n of a manual on a m b i e n t a i r p o l l u t a n t s from i n d u s t r i a l s o u r c e s . the Association
To t h i s e n d WHO h a s r e a c h e d a n a g r e e m e n t w i t h
o f German E n g i n e e r s (VDI) i n D b s s e l d o r f , F e d e r a l R e p u b l i c o f
Germany, t o c a r r y o u t t h e w o r k .
The V D I i s t h e l a r g e s t t e c h n i c a l s c i e n t i f i c o r g a n i -
z a t i o n o f i t s k i n d i n E u r o p e a n d s i n c e i t s f o u n d a t i o n i n 1 8 5 6 h a s made a d e c i s i v e c o n t r i b u t i o n t o t h e d e v e l o p m e n t o f r e s e a r c h a n d t e c h n o l o g y , a l s o i n t h e f i e l d of environmental protection.
The p r o j e c t , w h i c h i s f i n a n c e d by t h e F e d e r a l R e p u b l i c
o f Germany, was s t a r t e d i n November 1 9 7 7 .
During t w o m e e t i n g s i n J a n u a r y and
November 1 9 7 8 , t h e s t r u c t u r e , c o n t e n t s , s i z e a n d l i m i t a t i o n o f t h e manual were reviewed and supplemented.
The s e c o n d d r a f t o f t h e work h a s b e e n c o m p l e t e d by
e x p e r t s from e l e v e n E u r o p e a n c o u n t r i e s .
The d r a f t w i l l b e s e n t t o i n d i v i d u a l
experts and institutions for review, as well as to ministries of industry, planning, environment, forestry, national resources, etc.
It is expected that the preparatory
work will be completed at the end of 1980, at which time the VDI will submit the final manuscript in English, ready for editing and publication by WHO/EURO.
The objectives of the manual The manual is to serve governmental agencies, and other organizations concerned with the control of environmental pollution, and to assist public health personnel, managers, planners, legislators, environment administrators, and pollution control engineers in the process of planning and decision-making.
It is intended to provide
comprehensive information and references on the present international state-of-theart, which will familiarize the reader with the acute health problems of air pollution caused by industry, and ways to control them. The manual is designed to supplement the first manual on urban air quality measurement, and to provide specific information on the nature and comparative quantities of pollutants emitted by industry, the respective health effects, ways in which they are produced, and the technologies available for dealing with them. It is designed to serve as a guide for planners who can then refer to available engineering handbooks for details.
The aspects of air pollution in contained
atmospheres and the health and safety of workers inside a factory are touched on only to the extent that measures to protect workers may reduce air pollution outside the plant. The manual deals with measurement technology as it is involved in the presentation of problems of industrial air pollution.
Maximum permissable concentrations of air
pollutants change with local legislation and available technology, and vary widely between areas and with time and are, therefore, unsuitable for inclusion in the present manual.
As a publication of EURO, the manual refers primarily to situations which exist in the industrialized areas of Europe and North America.
Much of the material,
however, is of general interest and applies equally well to centres of industrialization in developing countries throughout the world.
Costs are limited to qualitative
comparison and are not tied to any currency or economic systems.
The emphasis is on
the health implications and control of those air pullutants which arise from industry that affect large areas and a great part of the population.
Organization of the manual The manual consists of three parts, with further breakdown into chapters.
It is
made clear in the general introduction that only particularly harmful substances,
363 t h e most i m p o r t a n t b r a n c h e s o f i n d u s t r y e m i t t i n g t h e s e s u b s t a n c e s , and modern p o l l u t i o n a b a t e m e n t t e c h n i q u e s are covered.
-
Part I
Harmful g r o u p s o f s u b s t a n c e s and t h e i r e f f e c t on h e a l t h
I n t h i s p a r t of t h e manual c h o s e n g r o u p s o f p o l l u t a n t s , e m i t t e d by i n d u s t r i a l p l a n t s i n t o t h e a t m o s p h e r e , which might be harmful t o t h e h e a l t h o f t h e p o p u l a t i o n on a l a r g e s c a l e , a r e d e a l t w i t h .
The c r i t e r i a f o r i n c l u s i o n of a p o l l u t i n g sub-
s t a n c e c o m p r i s e i t s t o x i c i t y , i t s q u a n t i t a t i v e i n c i d e n c e , and t h e p r o p o r t i o n of t h e p o p u l a t i o n f o r which i t c o n s t i t u t e s a h a z a r d o r a n annoyance. C h a p t e r s i n t h i s p a r t a r e d e v o t e d t o p a r t i c u l a t e matter, i n c l u d i n g a s b e s t o s f i b r e s ; S&
and s u l f a t e s ;
carbons;
N 4 , and o x i d a n t s ;
heavy m e t a l s and o d o u r s .
c a r b o n monoxide;
halogens;
ammonia;
hydro-
The e f f e c t s o f c a r c i n o g e n i c , mutagenic and t e r a t o -
g e n i c s u b s t a n c e s a r e t r e a t e d i n o n e c h a p t e r , and t h e combined e f f e c t s o f s p e c i f i c pollutants i n another.
B e s i d e s t h e i s o l a t e d and combined e f f e c t s o f t h e s p e c i f i c
p o l l u t a n t g r o u p s on t h e h e a l t h of t h e p o p u l a t i o n , a n a d d i t i o n a l c h a p t e r w i l l b r i e f l y o u t l i n e t h e e f f e c t s on f l o r a , f a u n a , and m a t e r i a l s of c o n s t r u c t i o n . i n t e r a c t i o n s i n t h e eco-system,
More complex
s u c h a s t h e i n d i r e c t consequences of damages t o f l o r a
and f a u n a a f f e c t i n g human h e a l t h must a l s o be t a k e n i n t o c o n s i d e r a t i o n . The g e n e r a l s t r u c t u r e of t h e c h a p t e r s f o l l o w s a s t a n d a r d i z e d f o r m a t l i s t i n g major c h e m i c a l and p h y s i c a l p r o p e r t i e s and t h e p u b l i c h e a l t h s i g n i f i c a n c e of s u b s t a n c e s w i t h i n t h e group;
s o u r c e s and e x p o s u r e , i n c l u d i n g , when a p p r o p r i a t e , c o n c e n t r a t i o n s
o b s e r v e d i n t h e ambient a i r , f a t e of s u b s t a n c e s i n t h e organism; and c r i t i c a l r e s p o n s e l e v e l s
health effects;
and t h e g r o u p s a t r i s k .
The p h i l o s o p h y which governed t h e s e l e c t i o n of t h e g r o u p s o f harmful s u b s t a n c e s discussed includes:
d o s e / e f f e c t and d o s e / r e s p o n s e r e l a t i o n s ;
e x p e r i m e n t a l and
epidemiological d a t a ;
d o s e and body burden a s measures of r i s k ;
adaptation;
a c t i o n and s y n e r g i s m ;
and t h r e s h o l d l i m i t s , emergency e x p o s u r e l e v e l s and r i s k
inter-
estimation. The major e m p h a s i s i n t h i s p o r t i o n of t h e work i s t o p r o v i d e i n f o r m a t i o n t o s u p e r v i s i n g a u t h o r i t i e s , p l a n n e r s o f new i n d u s t r i a l p l a n t s , s a n i t a r y b o a r d s and o t h e r r e s p o n s i b l e p e r s o n s i n s t a t e and s o c i e t y , a b o u t t h e p o s s i b l e consequences o f a i r The c e n t r a l p o i n t o f i n t e r e s t i s t h e p u b l i c h e a l t h r a t h e r t h a n occupa-
pollution.
tional health considerations.
Part I1 This
-
Industrial pollution sources
p a r t of t h e manual d e a l s w i t h a b o u t a dozen i n d u s t r i a l b r a n c h e s , which a r e
m a i n l y r e s p o n s i b l e f o r i n t e r r e g i o n a l a i r p o l l u t i o n and t h e h a z a r d s f o r p u b l i c h e a l t h .
Major
i n d u s t r i e s and o p e r a t i o n s d i s c u s s e d i n c l u d e :
e n e r g y p r o d u c t i o n and i n c i n e r a -
364 tion; metals; quarrying and the treatment of mineral products; forestry products; pulp and paper; coal and mineral oil; food and processing; and the chemical and petrochemical industries. Specialty chemicals and other small industries including discharges from processes designed to reduce pollution are also included in this part.
Part I11
-
Control technology
This part describes various types of equipment which may be used for the control of gaseous emissions.
Removal of dust;
treatment of organic vapours by combustion,
catalysis, adsorption and biological filtration are dealt with, together with safety techniques and emergency procedures.
Each of the procedures mentioned is appropriate
under particular circumstances and the complete list, with obvious combinations and modifications, should be sufficient to deal with any aspect of air pollution arising from industrial discharges, with the possible exception of certain radioactive isotopes. Criteria to guide the selection of the most favourable purification procedure, including economics as well as secondary effects on the environment, are given in a separate chapter.
Measures which are or should be integrated into the production
process are also covered. Accident-prevention techniques and measures to be taken in emergencies are presented as a completion of the topic "Control technology" in the last two chapters of this part. It is hoped that this manual will repeat the success of its predecessor - the manual on urban air quality - and that the two together will be especially valuable in helping to prevent the repetition of some of the air pollution mistakes of an earlier period of industrialization.
Atmospheric Pollution 1980, Proceedings of the 14th InternationalColloquium,Paris,France, M.M.Benarie (Ed.), Studies in Environmental Science, Volume 8 May 5--8,1980,
365
0 Elsevier Scientific Publishing Company,Amsterdam - Printed in The Netherlands
MEASUREMENTS OF ATMOSPHERIC ELECTRICAL PARAMETERS NEAR AN INDUSTRIAL PLANT INFLUENCE OF IONIZED PLUMES ON THE EARTH'S ELECTRICAL FIELD D. LAURENT d d
and R. PEYROUS
**
CIRN/Laboratoire Pollution
-
B.P 11'23
- 6 4 1 7 0 ARTIX (France)
*Groupe Electricits - Facult6 des Sciences
-
6 4 0 0 0 PAU (France)
INTRODUCTION A study of the behaviour of atmospheric electrical parameters indicatesthat electrical phenomena accompany pollutant fall-outs during various meteorological situations. Systematic observations from a fixed observation post, over several months, have shown that a pollutant fall-out is accompanied by a negative space charge and an inversion of the earth's electric field (D. LAURENT, 1 9 7 8 ) . Generalization of this phenomenon has been verified by successive measurements on various sites (LACQ, PARDIES-NOGUERES and PORCHEVILLE complexes and TURBIGO
electric plant in Italy). The electric field inverses when travelling under the plume or i n the plume (fall-out). This confirms the presence of negatively charged aerosols in the plume near the chimney exits. The area over which the phenomenon extends is a function of the wind-speed. The experimental results obtained on various sites will be discussed in the first part.
In the second part we will develop a theoretical study of the behaviour of the electric field created by ionized plumes, using the charged line concept. From electric field values measured on the ground it is possible, by calculations, to determine the altitude and the mean-charge of the plume. EXPERIMENTAL RESULTS Detection of charged aerosol sources and location of the plume The measuring apparatus placed on the laboratory-van roof is a "field-mill" or rotative flux meter developed by E.D.F. to measure the electric field at ground level. The continuous recording of the electric field is synchronised to the laboratory-van speed limited to 30km/h. Cross-sectional measurements of the electric field are represented by black drawings on the maps(D. LAURENT, 1 9 8 0 ) Measurements on the site of LACQ The main activity of the LACQ complex is the exploitation and refining of natu-
366 ral gas (S.N.E.A (P)). When the wind direction is constant and the wind-speed high, it is possible to locate the plume at great distances from the exit point. The plume altitudes calculated for various cross-sections permitted the determination of a probable fallout zone between 3 and 5 km from the source on 12/12/78. Confirmation of such fall-out was given by the SO2 concentrations measured at the control-station of AUDEJOS (see 0. LAURENT, 1980). Measurements on the site of NOGUERES The main industrial plant of this site is a factory producing aluminium by melted alumina electrolyses (PECHINEY). The electric field inversions measured around this complex are more important than those recorded on the site of LACQ. This is not a comparison criterion of the pollution emitted by the two complexes since the difference in the electric field values is dependant on the charge of the plumes which depends, in the first place, on the fabrication process used. The range limit at which an inversion zone can be located is a function of the plume charge and of the wind-speed. The plume emitted by the factory of PARDIESNOGUERES during meteorological conditions similar to those for LACQ
can be tra-
ced to a distance of about 6km from the chimney. The calculated plume height from various cross-section made that day, showsa rising plume stabilizing at an altitude of 17Om which corresponds with an inversion layer at 2OOm altitude (D. LAURENT 1980).
Measurements on the site of PORCHEVILLE These results were significantly generalized by measurements made at PORCHEVILLE with the participation of ECOPOL. The industrial complex consists of a cellophane factory, a cement factory and a thermal power station having a fuel and a coal unit. Figure 1 shows simultaneous results obtained with a "field-mill" (electric field measurement) and with a BARRINGER-COSPEC (SO2 measurement). All the industrial plumes were detected by the "field-mill" whilst the BARRINGER detected only the fuel powered unit. Measurements on the site of TURBIGO in Italy During a teledetection run organized by C.E.E., with the collaboration of E.D.F., measurements were made near TURBIGO (north Italy) on the site of a thermal power station. A l l the results of this run which confirm the measurements made at PORCHEVILLE
will form the subject of a C.E.E. report.
367 Results From the results obtained on the sites of LACQ and PARDIES-NOGUERES, we have estimated the mean recombination coefficient between positive and negative charges to be 1,2 10-6 cm2/s, and the mean negative ion mobility k in the plume to be 5.10-5
m2Is.V.
For the site of LACQ a good correlation was found between our calculations of plume altitude and HOLLAND'S rising formula. Studies in fall-out zones Measurements of electrical parameters at a fixed station Measurements of electrical parameters at a fixed station permit the recording of the plume when it passes vertically over the shed
containing the measuring
apparamses (electric-field modification only) as well as the recording of pollutant fall-out (electric field and ionization modifications at ground level). As the wind-direction varies during the day, one records plumes passing overhead either coming from the LACQ complex (west-wind) or from PARDIES-NOGUERES (E.S.E. wind) these results have already been published (D. LAURENT & R. PEYROUS, 1979). Measurements of electrical parameters from a mobile laboratory Figure 2 confirms results obtained at a fixed station and shows the behaviour of various parameters. THEORETICAL STUDY We consider the plume as a uniformely charged line, without taking into account atmospheric turbulence. However, the concept of a charged line cannot be used at great distances from the source because of electrostatic auto-repulsion effects and of electric image forces as well as ion recombination. Calculation of the electrical field created at ground level by the plume We determine the polar coordinates (R,Q,
,z) of
the electric field created at
point A at a certain distance from the chimney exit
s.
xis the electric charge
per unit length. h = height of the chimney Only the vertical component
Ez is measured (Fig. 3
)
Calculations of the electric field created by a charged line whose charge diminishes regularly with the distance As a result of atmospheric diffusion the pollutant concentration per unit v o lume diminishes as the plume moves away from the source, furthermore, owing to
368 recombination phenomena between the charged particules, the charge is continuaIly modified.
In the plume axis for a wind speed ofuand at a distance
X
from the source,
the charge is :
X where
=
XO
-x
D =
-jj-
exp
U Prl
(2)
D is a constant with a length dimension,P = number/m3 of positive charges.
q = mean recombination coefficient between positive and negative charges.
From equation ( I ) ,
replacing A
by this value, we obtain the expression of the
electric field created by a line whose charge varies with the distance from the source. Ez =
o
exp(-RID)
2 TEO
h
(
I +
(3)
(R2+h2) ' I 2
Determination of the altitude of a charged line Consider a uniformly
charged line situated at an altitude a and parallel to
the ground. Then, taking into account the electrical image placed symetrically with regard to ground level, the vertical componant of the field p will be :
where @ is the angle under which one sees the charge q at
z.
Case of a plume (Fig.3) The value at ground-level, of the vertical componant of the earth's electric field falls as one approaches the influence zone, crosses zero and becomes negative. After passing through a maximum negative value under the plume axis, the process is reversed as one leaves the influence zone. Knowing the field values at the point P(Ep) and O ( E 0 ) and the distance
OP
(Fig.3) it is possible to calculate the approximate altitude of the charged line using the ratio
Ep/Eo.
Numerous crossings, perpendicular to the wind direction
(X
axis), make it pos-
sible to calculate the plume altitude at each intersection, to determine the electric charge and, taking each inversion width as the plume width, to determine the particle mobility using the relationship defined by JONES & HUTCHINSON (1976). CONCLUSION Realization of electric field maps on various sites (LACQ, PARDIES-NOGUERES, PORCHEVILLE & TURBIGO) under various plumes (natural gas refinery plant, aluminium factory by electrolysis, petrochemical complex and thermal power-station) have shown up an important modification of the earth's electric field in the presence
369
of ionized plumes. The phenomenon seems to be general. The detection of chimney plumes (whatever their chemical composition) from ground level by the measurement of the vertical componant of the earth's electric field allows one to follow their displacement and spread as well as, to calculate their charge and altitude and to determine the maximum fall-out zones. This method can be regarded as complementary to measurements made with a BARRINGER COSPEC. With more numerous apparatuses to measure the earth's physical parameters one could envisage :
- a study of the charge separation mechanisms at source level
-
a study of ion recombination and diffusion
- a check of the theoretical formulae, that permit the calculation of plume rising and diffusion. The field mill can fonction by day or night and rain is the only element that prevents its use. The presence of fog does not disturb measurements, plumes can be located under such conditions and strong pollution situations which are often associated with fog can be studied. The distance from the emission point at which significant measurements of the plume can be made depends on the quantity of electric charge emitted. A t TURBIGO with a wind speed of 2m/s, the plume could be detected at 16km from the emission point. With a single field mill making several crossings under the plume, in a reasonably short time, it is possible to calculate the geometrical position and shape of the plume as well as the distribution of the charge along the plume. REFERENCES 1 D. Laurent, Mesure des paramStres physiques accompagnant les retombges de polluants sur le site de LACQ, ThCise de 3Sme Cycle, Pau (Janvier 1 9 7 8 ) 2 G.D. Jones and S.G. Jennings, Atmospheric Environment, 2 (1977) 1197-1207
3 D. Laurent and R. Peyrous, Measurement of physical parameters accompaning polluant fall-out on the site of LACQ. Studies of the correlations between the different phenomena with a view to predicting pollution, Proceed 13th Inter.Col1. in atmospheric pollution, M. BENARIE (Ed.) Elsevier, Paris (avril 1978) 4 J . A . Chalmers, Atmospheric Electricity, 2nd edition Pergamon Press, Oxford (1967) 5 G.T. Csanady, Turbulent diffusion in the Environment, D. Reidel (1973) 6 D, Laurent and R. Peyrous, Behaviour of the electrical parameters of the atmosphere near an industrial plant situated in a rural site, The Science of the Total Environment, Elsevier Scientific publishing company, 13 (1979) 55-70. 7 D. Laurent, Influence des panaches ionis& sur le champ Glectrique terrestre The Science of the Total Environment (1980) (In publication)
370
ELECTRIC FIELD 1
Fig.
PORCHEVILLE le 03.07.79
so2
-
9h42-9h53
I
cellophane factory
2
cement factory
3
power plant : fuel unity
4
power plant : carbon unity
TOTAL VERTICAL CHARGE
Fig.
2
Recording of electrical parameters during a fall-out with the laboratory-van
n-+
:
N?:
:
large ions
E,
:
vertical electric field
----
:
ground level away from plume
small ions
Fig.
3
371
Atmospheric Pollution 1980,Proceedings of the 14th International Colloquium, Paris, France, May 5-8,1980, M.M. Benarie (Ed.), Studies in Environmental Science, Volume 8 0 Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
A COMPARISON OF VISIBILITIES I N POLLUTED AND UNPOLLUTED AREAS H. HORVATH
I n s t i t u t f u r Experimentalphysik der U n i v e r s i t a t Wien, Vienna ( A u s t r i a )
ABSTRACT
A comparative study has been performed i n an u n p o l l u t e d area i n an a r i d (Arizona, USA),
zone
i n an area near a l a r g e town (Boulder near Denver, USA) and
i n several towns ( S t . Louis, USA, Vienna, L i n z , A u s t r i a ) . I n a l l cases t h e c o n t r a s t r e d u c t i o n o f d i s t a n t t a r g e t s has been measured w i t h a telephotometer over the s p e c t r a l range o f t h e v i s i b l e l i g h t . The e x t i n c t i o n c o e f f i c i e n t and thus t h e v i s i b i l i t y can be d e r i v e d from these data. V i s i b i l i t i e s i n unpopulated, a r i d
areas
reach f r e q u e n t l y values o f Zoo km o r more, b u t may be d i s t u r b e d by l o c a l and d i s t a n t sources. The v i s i b i l i t i e s i n an i n d u s t r i a l town may be as low as 2 km. The v i s i b i l i t y n o r m a l l y shows l a r g e v a r i a t i o n s w i t h meteorological c o n d i t i o n s . I n and near towns t h e p o l l u t i o n i s n o r m a l l y d i s t r i b u t e d inhomogeneously, t h e r e f o r e the v i s i b i l i t y i n d i f f e r e n t d i r e c t i o n s may vary. The e x t i n c t i o n c o e f f i c i e n t o f t h e aerosol i s a f u n c t i o n o f wavelength and n o r m a l l y decreases w i t h i n c r e a s i n g wavel e n g t h . Under c o n d i t i o n s o f low p o l l u t i o n t h e decrease i s by a f a c t o r o f 5 t o l o over the s p e c t r a l v i s i b i l e range, whereas i n heavy i n d u s t r i a l p o l l u t i o n no change i n e x t i n c t i o n c o e f f i c i e n t w i t h wavelength has been observed.
INTRODUCTION V i s i b i l i t y i s c l o s e l y r e l a t e d t o atmospheric p a r t i c u l a t e matter, and except f o r areas w i t h predominant R a y l e i g h s c a t t e r from a i r molecules i . e . v i s i b i l i t i e s l a r g e r than Zoo km i t i s m a i n l y t h e p a r t i c l e s which determine the v i s i b i l i t y . Increased p a r t i c u l a t e p o l l u t i o n causes reduced v i s i b i l i t i e s , thus t h e v i s i b i l i t y i s a good and simple i n d i c a t o r f o r a i r q u a l i t y . The a b i l i t y t o see something i s based m a i n l y on t h e f a c t , t h a t a d i f f e r e n c e i n b r i g h t n e s s and/or c o l o r between t h e p a t t e r n t o be recognized and i t s background e x i s t s . When t h i s p a t t e r n i s l o c a t e d somewhere i n t h e atmosphere and i s moved f u r t h e r away b o t h i t s d i f f e r e n c e i n b r i g h t n e s s and c o l o r decreases, s i n c e t h e atmosphere reduces l i g h t coming from t h e p a t t e r n and adds s c a t t e r e d l i g h t t o t h e l i g h t coming from t h e t a r g e t ; t h e f u r t h e r t h e p a t t e r n i s away, t h e l e s s l i g h t from the t a r g e t and t h e more s c a t t e r e d l i g h t reaches t h e observer, thus t h e background
372 and t h e t a r g e t approach t h e b r i g h t n e s s and c o l o r o f t h e atmospheric s c a t t e r e d l i g h t . A t a c e r t a i n d i s t a n c e t h e d i f f e r e n c e i n b r i g h t n e s s between t h e p a t t e r n and t h e background has reached a v a l u e t h a t i t i s j u s t d i s c e r n a b l e . T h i s d i s t a n c e i s c a l l e d t h e visibility. A s i m p l e v i s i b i l i t y f o r m u l a has been d e r i v e d by Koschmieder ( r e f . 1); i f a v i s i b i -
to Co i t s background, t h e v i s i b i l i t y v i s r e l a t e d t o t h e e x t i n c t i o n c o e f f i c i e n t b o f t h e
l i t y t a r g e t i s assumed t o have a r e l a t i v e b r i g h t n e s s d i f f e r e n c e ( c o n t r a s t )
a e r o s o l by
V = (-ln With
I E ~+
I n I C o / )/b
(1)
t h e c o n t r a s t t h r e s h o l d o f t h e human eye. A l t h o u g h
person, i t u s u a l l y i s assumed t o be -0.02.
E
may v a r y f r o m person t o
The e x t i n c t i o n c o e f f i c i e n t o f t h e
atmosphere u s u a l l y v a r i e s w i t h wavelength, and t h u s a c e r t a i n wavelength has t o be chosen f o r t h e e x t i n c t i o n c o e f f i c i e n t i n (1). N o r m a l l y t h e wavelength o f t h e maximum s e n s i t i v i t y o f t h e eye (590 nm) i s used, b u t l a b o r a t o r y experiments have shown, t h a t l o n g e r wavelengths (580 nm) a r e more a p p r o p r i a t e ( r e f . 2 ) . D e t e r m i n a t i o n o f V i s i b i l i t i e s . The u s u a l method f o r v i s i b i l i t y d e t e r m i n a t i o n uses s e v e r a l t a r g e t s a t d i f f e r e n t d i s t a n c e s . An o b s e r v e r t r i e s t o l o c a t e t h e s e t a r g e t s and t h e d i s t a n c e o f t h e t a r g e t w h i c h can be f u r t h e s t seen i s c a l l e d t h e v i s i b i l i t y .
A c o n s i d e r a b l e number o f t a r g e t s i n t h e same h o r i z o n t a l p l a n e as t h e o b s e r v e r a r e needed.This method i s w i d e l y used i n r o u t i n e m e t e o r o l o g i c o b s e r v a t i o n , and when performed w i t h c a u t i o n i t w i l l g i v e r e l i a b l e r e s u l t s . There a r e some drawbacks o f t h i s method, e s p e c i a l l y i f i t i s i m p o s s i b l e t o have t a r g e t s i n t h e same h o r i z o n t a l p l a n e , o r i f t h e t a r g e t s have d i f f e r e n t b r i g h t n e s s o r c o l o r . O t h e r methods f o r v i s i b i l i t y d e t e r m i n a t i o n use t h e e x t i n c t i o n c o e f f i c i e n t , s c a t t e r i n g c o e f f i c i e n t o r t h e c o n t r a s t r e d u c t i o n . The e x t i n c t i o n c o e f f i c i e n t can be d e t e r m i n e d e.g. by means o f t r a n s m i s s o m e t e r w h i c h i s e s p e c i a l l y s u i t a b l e f o r small visibilities (
2 km)., i t i s o b t a i n e d f r o m t h e e x t i n c t i o n c o e f f i c i e n t by means
of ( 1 ) . F o r l a r g e v i s i b i l i t i e s t h e t r a n s m i s s i o n measurement becomes i n a c c u r a t e , u n l e s s a l o n g l i g h t p a t h i s used, which c r e a t e s a s e r i o u s a l i g n m e n t problem. Since l a r g e v i s i b i l i t i e s o n l y o c c u r i n c l e a n atmospheres, and t h e n t h e p a r t i c l e s show v e r y s m a l l l i g h t a b s o r p t i o n , t h e measurement o f t h e e x t i n c t i o n c o e f f i c i e n t can be subs t i t u t e d by t h e d e t e r m i n a t i o n o f t h e s c a t t e r i n g c o e f f i c i e n t by means o f a nephelometer ( r e f . 3 ) . S i n c e t h e c o n t r a s t r e d u c t i o n o f a t a r g e t due t o atmospheric s c a t t e r i n g i s t h e p r i m a r y cause f o r t h e v i s i b i l i t y r e d u c t i o n , t h e measurement o f t h e c o n t r a s t a l t e r a t i o n can be used f o r v i s i b i l i t y d e t e r m i n a t i o n s . A d i s t a n t t a r g e t i s viewed t h r o u g h a t e l e p h o t o m e t e r , and i t s c o n t r a s t r e l a t i v e t o t h e h o r i z o n i s determined. The i n t r i n s i c c o n t r a s t o f a s i m i l a r t a r g e t c l o s e by i s a l s o determined, t h u s p e r m i t t i n g
373 t h e d e t e r m i n a t i o n o f t h e e x t i n c t i o n c o e f f i c i e n t . W i t h t h e known i n t r i n s i c c o n t r a s t , t h e d i s t a n c e , t h i s t a r g e t can be seen i s computed e a s i l y . Telephotometer f o r v i s i b i l i t y d e t e r m i n a t i o n .
It c o n s i s t s o f an a s t r o n o m i c t e l e -
scope where t h e o c u l a r i s r e p l a c e d by a p h o t o m e t r i c measuring u n i t ( r e f . 4 ) , c o n s i s t i n g o f an a d j u s t a b l e s t o p , i n t e r c h a n g e a b l e i n t e r f e r e n c e f i l t e r s and a sens i t i v e p h o t o c e l l . The p h o t o c u r r e n t i s p r o p o r t i o n a l t o t h e b r i g h t n e s s o f t h e t a r g e t . L e t us d e n o t e t h e p h o t o c u r r e n t when measuring t a r g e t and h o r i z o n w i t h I1 and
I 0'
S i n c e b r i g h t n e s s and p h o t o c u r r e n t a r e p r o p o r t i o n a l , t h e c o n t r a s t C b e i n g t h e r e l a t i v e b r i g h t n e s s d i f f e r e n c e between o b j e c t and background) i s :
c
= 11/1
0
-
1
The c o n t r a s t o f a t a r g e t a t d i s t a n c e x i s g i v e n by ( r e f . 5 ) : C = Co exp ( b . x )
(3)
I n order t o o b t a i n t h e e x t i n c t i o n c o e f f i c i e n t b, t h e i n t r i n s i c c o n t r a s t Co(contrast of t h e t a r g e t a t d i s t a n c e z e r o ) has t o be known. W i t h i n reasonable a c c u r a c y t h i s can be d e t e r m i n e d b y measuring t h e b r i g h t n e s s o f c l o s e b y s i m i l a r t a r g e t s . L e t us denote t h e measured p h o t o c u r r e n t o f t h e c l o s e b y t a r g e t w i t h I1. Then t h e i n t r i n s i c c o n t r a s t Co i s
co
=
12/11
-
1
(4)
and t h e e x t i n c t i o n c o e f f i c i e n t can be d e t e r m i n e d by
from t h i s t h e v i s i b i l i t y o f t h e b l a c k t a r g e t i s given by VB = 3.9/b
The v i s i b i l i t y o f a t a r g e t o f i n t r i n s i c c o n t r a s t Co i s V = (3.9 + I n Cg)/b
(7)
I n t h e f o l l o w i n g r e s u l t s f r o m t e l e p h o t o m e t e r ( v i s i b i l i t y ) measurements a t d i f f e r e n t l o c a t i o n s w i l l be d i s c u s s e d . The d a t a a r e p r e s e n t e d s t a k i n g w i t h remote areas and ending w i t h h e a v i l y p o l l u t e d l o c a t i o n s .
374
V i s i b i l i t i e s i n Northern Arizona. A s e r i e s o f measurements were performed i n Northern Arizona i n June and J u l y 1979. T h i s area i s known f o r i t s e x c e l l e n t v i s i b i l i t i e s and b e a u t i f u l v i s t a s . The telephotometer was s e t up a t a p o i n t , which perm i t t e d t h e view w i t h i n a t l e a s t 180 degrees, and several t a r g e t s were measured. The t a r g e t s were e i t h e r mountains covered w i t h c o n i f e r s o r l a r g e r o c k formations. W i t h i n t h e immedeate v i n c i n i t y o f t h e telephotometer t h e i n t r i n s i c b r i g h t n e s s o f c o n i f e r s and rocks were a l s o determined. I n o r d e r t o o b t a i n an average value o f t h e brightness o f c l o s e by t a r g e t s , t h e telephotometer was s l i g h t l y defocussed f o r these measurement s . The data o b t a i n e d from these measurements u s u a l l y show very s i m i l a r behaviour. As an example t h e c o n t r a s t o f t h e t a r g e t , t h e i n t r i n s i c c o n t r a s t and t h e e x t i n c t i o n c o e f f i c i e n t a t wavelength from 400 t o 800 nm a r e shown f o r one s p e c i f i c measurement i n f i g . 1. The e x t i n c t i o n c o e f f i c i e n t was c a l c u l a t e d from c o n t r a s t , i n t r i n s i c cont r a s t and distance, u s i n g ( 5 ) . The v i s i b i l i t y o f t h e b l a c k t a r g e t i s obtained by using t h e e x t i n c t i o n c o e f f i c i e n t a t 575 nm i n eq. ( 6 ) , i n t h i s case i t was 268 km, the observed t a r g e t would have been v i s i b l e f o r 261 km which i s s l i g h t l y l e s s , due t o i t s i n t r i n s i c c o n t r a s t beeing n o t much d i f f e r e n t from t h e b l a c k t a r g e t . v
I
I
E
E
Y
4
c
'E s I
m 4
r4
9
=?
s
9
nm
\
6
\
600 WAVELENGTH
400
F i g . 1. c o n t r a s t C o f a t a r g e t l o c a t e d 32.2 km form t h e telephotometer. The c o n t r a s t o f a s i m i l a r rock l e s s than loo m ( C ) and t h e e x t i n c t i o n c o e f f i c i e n t (b? o f t h e atmosphere.
\
7M)
500
800
nm
F i g . 2 E x t i n c t i o n c o e f f i c i e n t s o f the atmosphere i n f l u e n c e d by c l o s e and d i s t a n t sources ( f . . f o r e s t f i r e , s . . smog). The v i s i b i 1it y c a l c u l a t e d from t h e e x t i n c t i o n c o e f f i c i e n t was loo and 92 km. For comparison t h e e x t i n c t i o n coefficient figure 1 i s also plotted.
.
375 The v i s i b i l i t i e s thus measured showed a g r e a t v a r i a b i l i t y both i n time and t o some extend a l s o i n space. During t h e measuring p e r i o d a smog episode i n Los Angeles (700
km west o f t h e measuring s i t e ) and f o r e s t
f i r e s caused decreased v i s i b i l i t i e s .
The v a r i a t i o n i n e x t i n c t i o n c o e f f i c i e n t s f o r a p a r t i c u l a r t a r g e t a r e shown i n f i g . 2. V a r i a t i o n s o f t h e v i s i b i l i t y i n d i f f e r e n t d i r e c t i o n s were u s u a l l y very small. Measurements o f v i s i b i l i t i e s near a town. V i s i b i l i t y data were gathered a t Boulder/ Colorado. The measuring s i t e was l o c a t e d a t a h i l l , which p e r m i t t e d the determination o f c o n t r a s t s o f t a r g e t s a t d i r e c t i o n s n o r t h e a s t and south.Measurements towards the west were n o t possible, s i n c e t h e Rocky Mountains were a t a much higher e l e v a t i o n as t h e measuring s i t e , and thus the path o f s i g h t would have been i n c l i n e d , making i t impossible t o measure t h e h o r i z o n . Boulder i s l o c a t e d approx. 45 km
NW o f Denver,
which probably i s t h e major aerosol source i n t h i s area. An example o f measured c o n t r a s t o f a d i s t a n t t a r g e t , i t s i n t r i n s i c c o n t r a s t and t h e e x t i n c t i o n c o e f f i c i e n t i s shown i n f i g . 3. The t a r g e t was a n e a r l y completed water tower a t t h e o u s k i r t s o f Denver, t h e i n t r i n s i c b r i g h t n e s s was determined from a sample p i e c e o f s t e e l . Generally t h e e x t i n c t i o n c o e f f i c i e n t s are h i g h e r than those observed i n Arizona, they a l s o showed v a r i a t i o n s i n space and time.
loo km F i g . 3. Example f o r a v i s i b i l i t y measurement i n Boulder. The t a r g e t used was a n e a r l y completed water r e s e r v o i r a t Denver.
F i g . 4. V A r i a t i o n o f V i s i b i l i t i e s i n d i f f e r e n t d i r e c t i o n s . The town o f Denver i s l o c a t e d approx.SE o f t h e measuring s i t e . The arrows g i v e t h e v i s i b i l i t i e s , the c i r c l e s the distance o f the targets.
376
Usually t h e e x t i n c t i o n c o e f f i c i e n t ( v i s i b i l i t y ) was higher (lower) in t h e d i r e c t i o n of Denver ( S E ) , as shown in f i g . 4 . Under s t a b l e and dry weather t h e r e was only a small d a i l y v a r i a t i o n of the e x t i n c t i o n c o e f f i c i e n t (curve A, f i g . 5 ) . During the measuring period frequently f a i r l y high r e l a t i v e humidity occured, and e s p e c i a l l y under these conditions t h e e x t i n c t i o n c o e f f i c i e n t s showed considerable d a i l y v a r i a t i o n s (curve B , f i g . 5 ) . Extremely h i g h e x t i n c t i o n c o e f f i c i e n t s were measured during fog o r r a i n ( f i g . 6 ) . In t h e r a i n t h e e x t i n c t i o n c o e f f i c i e n t i s p r a c t i c a l l y independent of wavelength wheras i n t h e o t h e r cases i t decreases with increasing wavelength.
.E
Y
WAVELENGTH
TIME
Fig. 5. Daily v a r i a t i o n of e x t i n c t i o n coef f ic i e n t a t 550 nm.
10
500
600
..9
nm 700
800
Fig. 6 . Extinction c o e f f i c i e n t in r a i n , fog and on a c l e a r day with e x c e l l e n t v i s i b i 1 i ty.
V i s i b i l i t i t e s i n towns. V i s i b i l i t y measurements were performed i n several towns, as an example measured c o n t r a s t , i n t r h s i c c o n t r a s t , and e x t i n c t i o n c o e f f i c i e n t f o r a day with e x c e l l e n t v i s i b i l i t y i n S t . Louis i s shown i n f i g . 7 . The t a r g e t was a brick building i n t h e downtown area. The measured e x t i n c t i o n c o e f f i c i e n t i s about l o times higher than under good v i s i b i l i t y conditions i n Arizona and a l s o shows a decrease with increasing wavelength. The photometer was located a t the c i t y border upwind of t h e t 8 r g e t ; t h e r e f o r e i t could be assumed, t h a t the aerosol measured by the photometer was most probably t h e "background" aerosol o f this area.
317
Near l a r g e sources t h e e x t i n c t i o n c o e f f i c i e n t can be much h i g h e r . An example f o r t h i s i s shown i n f i g . 8. The t h r e e c u r v e s a r e e x t i n c t i o n c o e f f i c i e n t s measured i n t h e i n d u s t r i a l a r e a ( m a i n l y s t e e l and chemical i n d u s t r y , c u r v e A), n o r t h o f t h e i n d u s t r i a l a r e a ( c u r v e B), and t h e suburban area ( c u r v e C ) . As expected t h e e x t i n c t i o n c o e f f i c i e n t decreases w i t h i n c r e a s i n g d i s t a n c e f r o m t h e source, and c u r v e C c o u l d a l r e a d y be c o n s i d e r e d as a background a e r o s o l f o r t h i s a r e a .
c
'YE
I
r
1979 0806
9hC8
X
W
WAVELENGTH 0
LOO
500
600
700 nm
, 400
F i g . 7. Measured c o n t r a s t , i n t r i n s i c c o n t r a s t f o r a b r i c k b u i l d i n g , and e x t i n c t i o n c o e f f i c i e n t c a l c u l a t e d from t h e c o n t r a s t measurements
I
500
Mw)
700 nm
F i g . 8. E x t i n c t i o n c o e f f i c i e n t a t t h r e e d i f f e r e n t l o c a t i o n s i n Linz, Austria. W i t h i n t h e i n d u s t r i a l area (A) a h i g h e x t i n c t i o n c o e f f i c i e n t was o b t a i n e d , and a g r a d u a l decrease towards t h e r e s i d e n t i a l a r e a ( B and C ) can be ssen.
The c o r r e s p o n d i n g v i s i b i l i t i e s would be 2.6, are subject t o large fluctuations,e,g,
WAVELENGTH
8 . 1 and 12.2 km. V i s i b i l i t i e s i n towns
i n Vienna d u r i n g t h e summer o f 1978 t h e
s m a l l e s t v i s i b i l i t y d e t e r m i n e d was 11 km, t h e l a r g e s t was loo. km. ( O n l y c l e a r days were c o n s i d e r e d ) . L a r g e v i s i b i l i t i e s a r e o n l y observed, when a change o f a i r mass has o c c u r e d 1 o w ; v i s i b i l i t i e s can have s e v e r a l causes
l i k e l a r g e p a r t i c l e numbers,
h i g h humidity o r others. R o u t i n e measurements w i t h t h e t e l e p h o t o m e t e r i n d i f f e r e n t d i r e c t i o n s and t o t a r g e t s a t d i f f e r e n t d i s t a n c e s p e r f o r m e d i n Vienna showed i n most cases, t h a t t h e e x t i n c t i o n c o e f f i c i e n t has i t s h i g h e s t v a l u e i n t h e downtown area. Depending on t h e wind d i r e c t i o n , t h e e x t i n c t i o n c o e f f i c i e n t was l o w e r i n c e r t a i n p a r t s o f t h e o u t s k i r t s and h i g h e r i n o t h e r s . The d i f f e r e n c e was more d i s t i n g u i s h e d i n cases o f l o w winds, and
378 h i g h e r e x t i n c t i o n s were always found downwind o f t h e c i t y center, thus suggesting, t h a t t h e p o l l u t i o n produced by t h e town i s blown by t h e winds i n t h i s d i r e c t i o n . Conclusion. When comparing t h e v i s i b i l i t i e s i n remote and i n d u s t r i a l areas, i t i s obvious, t h a t human
a c t i v i t i e s cause reduced v i s i b i l i t i e s . But even i n an urban
environment i t i s sometime p o s s i b l e t o observe v i s i b i l i t i e s o f 150 km. These v i s i b i l i t i e s a r e o n l y obtained, when t h e a t r masses, g i v i n g r i s e t o a l a r g e v i s i b i l i t i e s , had a very s h o r t residence time over populated areas. Therefore these v i s i b i l i t i e s a r e n o t r e p r e s e n t a t i v e . I n Europe even i n " c l e a n areas" the v i s i b i l i t y u s u a l l y i s l e s s than 70 km. This i s caused by numerous aerosol sources which a f t e r d i s p e r s i o n cause a g e n e r a l l y lower l e v e l o f v i s i b i l i t y as compared t o l a r g e areas w i t h low p o p u l a t i o n . Therefore v i s i b i l i t y d e t e r m i n a t i o n can be used as an i n d i c a t o r f o r p o l l u t i o n . Background measurements g i v e i n f o r m a t i o n o f an average o f t h e p a r t i c u l a t e p o l l u t i o n o f a l a r g e area ( s e v e r a l hundreds o f km) whereas data obtained near a source g i v e an average o f t h e p o l l u t i o n from t h i s source. ACKNOWLEDGEMENTS This work was supported by t h e Environmental P r o t e c t i o n Agency, NOAA and a Grant o f t h e Fonds zur Forderung der w i s s e n s c h a f t l i c h e n Forschung, Grant N r . 3453. REFERENCES
1. Koschmieder H., B e i t r . Phys. A t m . 12 (1924) 33 - 53, 172 - 181 2. Horvath H., J. Aer. Sci., 6 (1975), 73-95 3. Radke L . F . , Hobbs P.V. J.Atmos. S c i . 26 (1969) 281-299 A h l q u i s t N.C., Charlson R.J. J . A i r P o l l u t . Control Ass. 17 (1967) 467 -469 4. Horvath H., P r e s l e G. Appl. O p t i c s 17 ( 1978 ) 1303-1304 5. M i d d l e t o n W.E.K. V i s i o n through t h e Atmosphere. U. Toronto Press, Toronto, 1968
Atmospheric PoNution 1980, Proceedings of the 14th International Colloquium, Paris, France, May 5 4 , 1 9 8 0 , M.M. Benarie (Ed.), Studies in Enuironmentai Science, Volume 8 0 Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
379
RELATIONSHIP BETWEEN CITIZEN COMPLAINTS OF AIR POLLUTION, METEOROLOGICAL DATA AND IMMISSION CONCENTRATIONS
J. E. EVENDIJK, P.J.W.M. MfiSKENS and T.J.R.M.
DE JONG
Central Environmental Control Agency of Rijnmond, Schiedam (The Netherlands)
ABSTRACT Since many years an alert system has come into operation in the highly industrialized Rijnmond area of The Netherlands. The object of issuing alerts is to achieve a temporary reduction of the normal industrial emission pattern during periods of increased air pollution in order to reduce or prevent nuisance. To develop objective criteria for issuing alerts a study has been started on the relations between citizen complaints, meteorological parameters and immission concentrations. Correlations are discussed between a number of meteorological variables and the corresponding number of complaints and measuring data from three living centres around the industrial area. The data refer to daily averages of the year 1978. It is shown that citizen complaints give rise to higher correlations with immission concentrations than with meteorological variables. The correlations are greatly affected by wind direction. Owing to the poor correlation with the parameters mentioned, citizen complaints contribute essentially to a better understanding of air quality. From all meteorological data, temperature and from all measuring data, hydrocarbons, give the highest correlation with the total number of citizen complaints.
INTRODUCTION The Rijnmond area is considered the most highly industrialized area of The Netherlands, including not only the world's largest Port of Rotterdam, but also five oil refineries with a joint refining capacity of 85 million tons a year, thus forming the basis of the biggest petrochemical centre of Western Europe. More than 1 million people (i.e. 8 per cent of the population of The Netherlands) live in Rijnmond, which covers 1.6 per cent of the country's surface. It is not surprising, then, that as a result of industrial activities, the population in Rijnmond has to put up with inconveniences and nuisance. In case of unfavourable weather conditions the concentrations of air pollutants may increase, sometimes causing many complaints from the population. In such circumstances the Central
380 Environmental Control Agency of Rijnmond will issue alerts to the industry, which will take measures to reduce their emissions voluntarily. Several factors play a role in issuing alerts to industry, such as weather conditions, measuring results and the pattern of complaints (ref.1). Unfortunately no pat formula is available for issuing and withdrawing alerts. Although some subjectivity may never be excluded, at the moment an investigation is being made to create more objective criteria for issuing and withdrawing alerts. One of the aspects of this investigation is the relation between citizen complaints on one hand, and measuring results and meteorological parameters on the other. This will be discussed in this paper.
BASIC MATERIAL All data have been converted into daily figures and refer to the year 1978. Meteorological data The parameters used are: wind direction, wind speed, mixing height, cloudiness, temperature, potential temperature difference between 500 m and ground level and AVA-index. The hourly data regarding wind direction and wind speed have been obtained from a weather station in the centre of the industrial area (Fig. 1) and have been converted into daily averages. The wind rose has been divided into 8
Fig. 1. Industrial area of Rijnmond with sampling stations, located in urbanized areas (I = Maassluis, Rozenburg; II = Schiedam; I11 = Hoogvliet).
381 sectors of 40 or 50 degrees. When 11 or'14 hourly observations of one day respectively come into one sector, the wind direction is said to be characteristic. In the year under consideration there are 236 days with a characteristic wind direction. It has been assumed that on the remaining days a variable wind direction prevailed. The hourly data concerning cloudiness and temperature have been taken north-east of the area. The remaining meteorological parameters have been calculated for the Rijnmond area in particular. The AVA-index is a measure for the accumulating capacity of the atmosphere, and ranges from 0 (high dispersion) to 100 (low dispersion). For 1978 the average value was 29, the maximum value 95. The index is based on the maximum mixing height, potential temperature difference and wind speed (ref. 2).
Measuring results The hourly values of NO, NO2, including
C5
03,
paraffins and olefins, both C2 up to and
minus acetylene, have been converted into daily averages. They have
been determined at the three stations which are located in Rotterdam suburbs, each of them bordering the most important industrial area (Fig. 1). Daily values of SO2 and standard smoke have been measured at these stations. For all components regional daily average values have been determined from the daily averages at the above stations.
Complaints from the population Whenever people complain by telephone, their names, addresses, the time of complaining and details about the nature of the complaints are noted. Complaints about air pollution can be described in 28 different ways. However, in this investigation the complaints have been divided each day into 6 main classes: nuisance from soot or dust, stench, chemical smell, oily smell, irritating smell or smog and other complaints. One of the starting-points of the investigation in question is the absence of time delay between the occurrence of nuisance and the time of complaining.
An
inquiry, held in September/October, 1978, proved that 60 per cent of the people who complain, do so within less than an hour after experiencing the nuisance; about 80 per cent of them do so within 6 hours. As the complaints refer to various causes, two master files have been made: one of all complaints received per day, and one of these complaints excluding the ones referring to incidents.
ANALYSIS OF COMPLAINTS Nearly 7000 complaints about air pollution were registered in 1978 from a population of about 1 million inhabitants. The areas I, I1 and I11 (Fig. I), in which the three measuring stations are located, hold 38,000, 82,000 and 26,000
382
nll
t
number of cornplaints
episode oct./nov '71
incidents,
Fig. 2. Citizen complaints per month with moving average inhabitants respectively. The city of Rotterdam, from which the majority of complaints are received, is situated east of the area on the map. To get an idea of the relation between the number of complaints received in 1978 and those of previous years, the number of complaints per month is given in
figure 2. The wavy line represents the moving average, indicating the influence of the so-called structural air pollution, to a greater or less extent always present due to "normal" emissions from heating activities, traffic and industry. In superposition are the complaints resulting from periods of increased air pollution and serious incidents, such as break-downs, fires and explosions. The peaks in relation to the periods of increased air pollution are due to stagnant weather conditions. Table 1 indicates the nature of the complaints received in 1978. In the last four columns of the table the complaints resulting from incidents have been excluded. The ureatest number of Complaints registered on one day was 151; a fire at a chemical plant gave rise to 146 complaints about soot nuisance in area 111. Impact of the industrial area on complaints and measuring results When the wind is blowing from the industrial area to one of the three areas under consideration (down wind), in the area concerned higher measuring values and a greater number of complaints per day are found than when the wind direction is just the reverse (up wind), as can be seen in table 2. The impact of the source area on the complaints is obvious. For the areas I, I1 and 111, 80, 84 and 89
383
TABLE 1 Number of complaints about air pollution in 1978 Class of complaints
Including incidents
Excluding incidents
whole area
whole area
area area area I
soot/dust stench chemical smell oily smell smog other complaints
564 1551 1732 1635 494 985
58 108 116 227 50 39
total
6961
598
I1
I11
39
area area area I
11
I11
186 130 48 96
158 103 109 119 22 47
356 1522 1421 1456 494 985
49 108 116 196 50 39
39 111 130 127 48 91
12 103 109 119 22 47
588
558
6234
558
529
412
111
TABLE 2 Mean values of the number of complaints per day and immission concentrations found in areas I, I1 and I11 ~~
Area I down wind
Area I1 up wind
down wind
Area I11 up wind
down wind
up wind
~~~~~~
Complaints per day (~100) 5 38 62 89 9 20
10 6 7 9 5 4
39 130 60 15 28
5 12 5 6 4 4
5 39 45 48 11 20
3 7 2 2
224
41
230
36
168
18
86
No2 (pg/m3) paraffins (ppb) olefins (ppb)
94 22 13 44 42 56 19
34 36 13 40 37 48 15
57
33 46 28 9
18 51 8 11 28 6 2
11 18 43 56 15
47 36 13 24 48 25 10
number of days
55
81
109
81
112’
124
soot/dust stench chemical smell oily smell smog other complaints total
10
0 2
Measuring results so2 (pg/rn3) 0 3 (pg/m3)
15
stand.smoke (vg/m3) 14 NO (pg/m3)
51
per cent respectively of the average number of complaints received per day, are due to the presence of the industrial area. With the exception of ozone, a similar impact is represented by the measuring results, be it to a less extent. Furthermore, the impact of the industrial area on the number of complaints per inhabitant proves to decrease according as the residential areas are more distant.
384 CORRELATIONS BETWEEN COMPLAINTS AND METEOROLOGICAL PARAMETERS When the number of complaints increases or decreases linearly with the meteorological parameters, the correlation can be indicated by single or multiple correlation coefficients. In the latter case the correlation is determined by
..., where y
y = a+bxl+cx2+dx3
is the number of complaints and x i , x2, x3
...
are the meteorological variables. Of the variables mentioned in "Measuring results", temperature usually gives the highest correlation with the total number of complaints ( R
=
0.25
for the
whole area). The multiple correlations for the areas under consideration are given in table 3. TABLE 3 Multiple correlation coefficients ( ~ 1 0 0 )between number of complaints (excluding incidents) per day, and all parameters mentioned in "Measuring results", with the exception of the AVA-index Complaints
Area I all
soot/dust stench chemical smell oily smell smog
24 27 21 17 36
total
25
-:
Area I1
up wind
down wind
29
43 24 29
all
up wind
down wind
all
up wind
down wind
16
29 21 41 29 32
-
-
-
17
17
19
20
-
19 21
16 19 29
37
24
17
22
44
-
28
39
16
19 17 15 34 18
35
31
20
18
30
-
Area I11
18
25 22
correlation i s not significant ( 9 5 per cent)
The correlation usually is higher on days with a wind direction from the industrial area - down wind
-
to the area concerned.
CORRFLATION BETWEEN COMPLAINTS AND IMMISSION CONCENTRATIONS In the areas I and 111 the correlations between the total number of complaints and hydrocarbons prove to be highest; so does the correlation with sulphur dioxide in area 11. Furthermore the numbers of complaints about stench and oil give the highest correlations with hydrocarbons. The relation between complaints about soot/dust and standard smoke is poor, just like complaints about smog and ozone. The multiple correlation coefficients between complaints and measuring results are shown in table 4. When the wind direction is from the industrial area to area I, the correlation coefficient for complaints about oily smell proves to be higher than when the wind direction is just opposite. Probably other industrial areas (which are not indicated in figure 1 ) where considerable quantities of oil are stored, play a role. Table 5 shows which measured variables have the greatest impact on the number of complaints in area I.
385 TABLE 4 Multiple correlation coefficients ( ~ 1 0 0 )between the total number of complaints per day and all daily averages of S02, 0 3 , NO, N02, paraffins, olefins and standard smoke Complaints
Area I
Area I1
Area I11
all
up wind
down wind
all
up wind
down wind
all up wind
down wind
soot/dust stench chemical smell oily smell smog
20 51 39 38 50
26
20 17 24 27 26
34 24 34 20
45 42 57 42 62
29 30 35 25
-
72 38
31 47 46 44 58
30 29 33 36
total
44
59
41
30
23
58
39
20
37
36
19
27 19 54
-
36
-: correlation is not significant ( 9 5 per cent)
TABLE 5 Relation between number of complaints per day and measured immission values in area I, irrespective of wind direction ComplaintS
SO2
03
soot/dust stench chemical smell oily smell smog
V
A
Standard NO smoke
NO2
Paraffins Olefins Multiple correlation coefficient (XIOO)
A
a
A
A A A A
20 51 39 38 50
A
A
44
A A
v
total
A
A positive correlation
V negative correlation
to multiple correlation
Of all measurements paraffins and olefins obviously are most indicative for
the number of complaints, except for those about soot/dust and smog. Though to a less extent, this conclusion can also be applied to the other two areas. The multiple correlations between complaints on one hand and immissions as well as meteorological parameters on the other, prove to be only a little higher (for the areas I , I1 and 111, 0.47,
0.37 and 0.44 respectively1 than those between
complaints and immissions.
DISCUSSION
Although a causal relationship between meteorology and complaints (excluding those due to incidents) may be expected, the impact of the meteorological parameters proves to be rather small. Temperature and lapse rate have the greatest influence. The temperature effect may be a result of emissions increasing according
386 as temperature rises, e.g. due to vapour losses, or the fact that rising temperatures induce people to stay longer and more frequently out of doors, thus being more perceptible to air pollution. When forecasting the number of complaints by means of a meteorological index, which -according to the above- offers no great chance of success, temperature has to be taken into account anyway. The AVA-index is less appropriate for the above forecasting purposes. The concentration of pollutants, causing the complaints, is a function of the emitted quantities and the meteorological conditions. If the emissions are rather stable, the concentration of the pollutant responsible for the complaints, should be determined particularly by the meteorological conditions. Considering the above correlations, however, the conclusion can be drawn that the sources of the complaints vary widely. Between the measured immissions and the different sorts of complaints a direct causal relation can exist, e.g. between complaints about oily smell and measured saturated hydrocarbons. On the other hand, the measuring results may have been produced by an other cause (source, height of the source) than the complaints registered; in that case the complaints can be considered indicative for a pollutant which has been measured. From table 5 it is shown that
SO2
cannot be
considered a proper tracer in case of stench. Though the S02-level as well as the concentration of stench components in the atmosphere might be expected to increase with the accumulating capacity of the atmosphere, this is not the case. Against expectation, the correlation between complaints about soot/dust and standard smoke is not very high, apparently as a result of different sources. For the same reason there is no proper correlation between the number of complaints about smog/irritating air and ozone. As correlations between complaints and immissions are not very explicit, citizen complaints can be used complementarily when describing the air quality or the environmental air pollution on the basis of measuring results. The investigation described above was initiated only recently; as stated before, the results refer only to 1978. Long-term relationships are to be investigated as yet. An other time base may then be applied, and other meteorological parameters, such as radiation, stability class, humidity, may then be included. Furthermore, in stead of the linear model other techniques, such as pattern recognition, may be used. REFERENCES 1 J.E. Evendijk and P.A.R. Post van der Burg, Environ. Sci. Technol., 11 (1977) 450-455. 2 H. van Dop and A.P. van Ulden, Scientific Report WR 75-4, Royal Meteorological
Institute, De Bilt, The Netherlands (in Dutch).
Atmospheric Pollution 1980, Proceedings of the 14th International Colloquium, Paris, France, May 5-8,1980, M.M. Benarie (Ed.), Studies in Environmental Science, Volume 8 0 Elsevier Scientific Publishing Company, Amsterdam - hinted in The Netherlands
387
BUILDING VENTILATION AND INDOOR AIR QUALITY C.D. HOLLOWELL, J.V. BERK, M.L. BOEGEL, R.R. MIKSCH, W.W. NAZAROFF AN0 G.W. TRAYNOR Lawrence Berkeley Laboratory, University of C a l i f o r n i a , Berkeley, California 94720
ABSTRACT Rising energy p r i c e s , among o t h e r f a c t o r s , have generated an incentive t o reduce v e n t i l a t i o n r a t e s and thereby reduce the c o s t o f heating and cooling buildings. Reduced i n f i l t r a t i o n and v e n t i l a t i o n i n buildings may s i g n i f i c a n t l y increase exposure t o indoor contaminants and perhaps have adverse e f f e c t s on occupant health and comfort. Four indoor a i r contaminants -- carbon monoxide and nitrogen dioxide from gas appliances; formaldehyde from p a r t i c l e b o a r d , plywood, urea-formaldehyde foam i n s u l a t i o n , and gas appliances; and radon from building m a t e r i a l s , s o i l , and ground water -- a r e c u r r e n t l y receiving considerable a t t e n t i o n in the context of potential health risks a s s o c i a t e d with reduced i n f i l t r a t i o n and v e n t i l a t i o n r a t e s . W e have measured and analyzed these a i r contaminants i n conventi.ona1 and energy e f f i c i e n t buildings w i t h a view t o a s s e s s i n g t h e i r p o t e n t i a l health risks and various control s t r a t e g i e s capable of lowering p o l l u t a n t concentrations. Preliminary findings suggest t h a t f u r t h e r i n t e n s i v e s t u d i e s a r e needed i n order t o develop c r i t e r i a f o r maintaining acceptable indoor a i r q u a l i t y without compromising energy e f f i c i e n c y . Keywords:
a i r p o l l u t i o n , carhon monoxide, energy conservation, formaldehyde, h e a l t h , indoor a i r q u a l i t y , nitrogen dioxide, radon
The work described i n t h i s r e p o r t was funded by the Office of Health and Environmental Research, A s s i s t a n t Secretary f o r Environment and the Office of Buildings and Community Systems, A s s i s t a n t Secretary f o r Conservation and Solar Applicat i o n s of the U.S. Department of Energy under c o n t r a c t No. W-7405-ENG-48.
INTRODUCTION O u t of national concern about t h e a v a i l a b i l i t y of conventional energy resources, a major e f f o r t is c u r r e n t l y underway i n t h e United S t a t e s t o make buildings more energy-efficient. Various energy-conserving measures tightening the building envelope t o reduce e x f i l t r a t i o n and i n f i l t r a t i o n , improving i n s u l a t i o n , and reducing v e n t i l a t i o n -- a r e being devised t o reduce heating and cooling requirements.
--
388
U n f o r t u n a t e l y , r e d u c i n g i n f i l t r a t i o n and v e n t i l a t i o n r a t e s i n b u i l d i n g s can lead t o e l e v a t e d l e v e l s o f indoor-generated a i r contaminants which, i n excessive concent r a t i o n s , may i m p a i r t h e h e a l t h , s a f e t y and/or comfort o f t h e occupants. Indoor contaminants i n c l u d e gaseous and p a r t i c u l a t e chemicals from indoor combustion processes (such as cooking, heating, tobacco smoking), t o x i c chemicals and odors f r o r cooking and c l e a n i n g a c t i v i t i e s , odors and v i a b l e microorganisms from occupants and a wide assortment of chemicals released from i n d o o r c o n s t r u c t i o n m a t e r i a l s and f u r n ishings. I n conventional b u i l d i n g s , occupants a r e p r o t e c t e d from undesirable indoor a i r contaminants i n two ways: f r e s h a i r e n t e r s through cracks i n t h e b u i l d i n g envelope ( u n c o n t r o l l e d ) o r by t h e opening o f doors and windows o r v i a mechanical v e n t i l a t i o n systems ( c o n t r o l l e d ) , a l l o w i n g contaminants t o be d i l u t e d o r t o escape.
As i n f i l t r a t i o n i s reduced, c r i t e r i a must be developed f o r determining v e n t i l a t i o n requirements t h a t w i l l assure acceptable i n d o o r a i r q u a l i t y w i t h o u t s a c r i f i c i n g energy e f f i c i e n c y .
A t present, t h e r e i s l i t t l e agreement i n t h e U n i t e d States, o r
elsewhere, on t h e amount o f v e n t i l a t i o n a i r r e q u i r e d f o r t h e h e a l t h , s a f e t y and comfort o f b u i l d i n g occupants.
T h i s i n f o r m a t i o n gap i s due i n l a r g e measure t o the
complex b i o l o g i c a l , chemical and p h y s i c a l mix o f i n d o o r a i r p o l l u t a n t s .
Furthermore,
e a r l i e r s t u d i e s o f indoor a i r p o l l u t i o n have assumed t h a t i n d o o r p o l l u t i o n a r i s e s from and i s d i r e c t l y r e l a t e d t o outdoor sources, whereas i t i s now recognized t h a t numerous i n d o o r a i r contaminants have t h e i r sources i n t h e b u i l t environment i t s e l f . Four indoor-generated contaminants a r e of p a r t i c u l a r concern i n r e s i d e n t i a l b u i l d i n g s : carbon monoxide (CO), n i t r o g e n d i o x i d e (N02), formaldehyde (HCHO), and radon (Rn).
The h e a l t h r i s k s posed by exposure t o these contaminants i n conventional
houses, as w e l l as t h e added r i s k s engendered by reducing i n f i l t r a t i o n and v e n t i l a t i o n i n new c o n s t r u c t i o n and i n r e t r o f i t t e d houses a r e discussed below. DISCUSSION
Gas Appliance Emissions:
Carbon Monoxide, N i t r o g e n Dioxide and Formaldehyde
Several r e c e n t f i e l d and l a b o r a t o r y s t u d i e s conducted a t Lawrence Berkeley Labo r a t o r y (LBL) have focused on combustion-generated i n d o o r a i r p o l l u t i o n i n conventional residential buildings systems.
--
namely, a i r contaminants from gas stoves and heating
We have demonstrated t h a t l e v e l s o f several gaseous. a i r p o l l u t a n t s (CO,
NO, NO2 and HCHO) and r e s p i r a b l e p a r t i c u l a t e s a r e e l e v a t e d i n indoor environments where gas appliances a r e used’
y2.
I n t h e case o f CO, NO2 and HCHO, these l e v e l s
o f t e n approach or exceed ambient a i r - q u a l i t y standards adopted o r proposed i n t h e
U.S. and o t h e r c o u n t r i e s and, i n t h e case o f r e s p i r a b l e p a r t i c u l a t e s , t h e l e v e l s we have measured a r e o f t e n comparable t o those present outdoors on a very smoggy day.
Such h i g h l e v e l s a r e c l e a r l y unacceptable i n terms o f human h e a l t h , s a f e t y
and comfort, and a r e o f p a r t i c u l a r concern i n e n e r g y - e f f i c i e n t r e s i d e n t i a l s t r u c t u r e s
389
where i n f i l t r a t i o n i s reduced. Using an experimental room ( s i m u l a t i n g a k i t c h e n ) w i t h a volume o f 27 m3 (950 f t 3 ) and an air-exchange r a t e v a r y i n g from 0.25 t o 10 a i r changes per hour (ach), we have c h a r a c t e r i z e d t h e emissions from a new gas stove3.
Our r e s u l t s i n d i c a t e
t h a t gas stoves generate h i g h emissions o f carbon monoxide (CO), n i t r i c oxide (NO), n i t r o g e n d i o x i d e (NOz),
formaldehyde (HCHO), and r e s p i r a b l e aerosols ( s i z e < 2 . 5 pm),
and t h a t t h e c o n c e n t r a t i o n s o f these species become s i g n i f i c a n t when the air-exchange r a t e i s l e s s than 1 ach.
The r e s u l t s f o r CO, NO2 and HCHO a r e summarized i n Table 1.
P a r t i c u l a r l y noteworthy a r e t h e observations t h a t w i t h mechanical v e n t i l a t i o n a t 85 m3/hr (50 cfm) [ t h e upper l i m i t recommended by ASHRAE Standard 62-7314, CO concent r a t i o n s a r e maintained a t acceptable l e v e l s ; NO2 and HCHO concentrations, however, exceed a i r - q u a l i t y h e a l t h standards5 a t t h i s v e n t i l a t i o n r a t e . A t t h e lower v e n t i l a t i o n r a t e s recommended by ASHRAE Standard 90-756, even h i g h e r NO2 and HCHO concent r a t i o n s r e s u l t . To keep NO2 and HCHO c o n c e n t r a t i o n s t o l e v e l s w i t h i n t h e estab3 l i s h e d a i r q u a l i t y l i m i t s , a k i t c h e n v e n t i l a t i o n r a t e o f a t l e a s t 170 m / h r (100 cfm) i s required. TABLE 1 Contaminant c o n c e n t r a t i o n s i n a t e s t k i t c h e n
Ventilation Conditions No stove vent or hood Hood vent (with no fan) above stove Hood vent with fan at low speed
Contaminant Concentrationsa Mechanical CO NO2 HCHOb Ventilation Air Exchange Rate (m3/hr) Rate (ach) (mg/m3) (pg/m3) fpg/m3)
85 I50 cfm)
200 Typical Outdoor
Air Quality Concentration 40C 470d Health Standards Averaging Time 1 hour 1 hour ASHRAE Standards for Ventilation Requirements in Kitchens
120e maximum
51-85 m3/hr (30-50 cfm) (Standard 62-73) 34 m3/hr (20 cfm) (Standard 90-75)
a 1 hour average concentration in center of kitchen in which gas oven is operated at 180°C. (350°F.) b Calculated from measured emission rate for gas stoves
c EPA promulgated standard (1) d EPA recommended standard (1) e European standard (11
390
Further studies of CO and NO2 emissions from gas appliances were conducted a t an energy-efficient research house maintained by LBL i n Walnut Creek, California, where we measured the a i r quality in the kitchen, the l i v i n g room, a bedroom, and one outdoor location over a 24-hour period. Gas stove operation was based on consumption patterns determined as typical i n the United States by the American Gas Assoc i a t i o n7. . I n f i l t r a t i o n varied between 0.33 and 0.44 a i r changes per hour (ach) 3 3 during the course o f the study. The natural gas consumption was 0.170 m (6 f t ) 3 3 f o r both the breakfast and lunch meals and 0.425 m (15 f t ) f o r the dinner meal. As expected, the peak pollutant concentrations (averaged over one hour) occurred d u r i n g the dinner meal. The ambient air-quality standard proposed by the Environmental Protection Agency (EPA)for a one-hour exposure t o NO2 i s expected t o be 470 pg/m3 As shown i n Table 2 , NO2 levels i n both the kitchen and living room exexceed this standard and, i n the bedroom, NO2 levels a r e j u s t under this limit. The one-hour EPA standard f o r CO i s 40 mg/m3, and t h i s standard was n o t exceeded anywhere i n the house.
’.
TABLE 2 NO2 and CO concentrations i n EEB Research House
co
NO2 (clg/m3)
( mg/m3)
Peak 1-hour average Kitchen Living Room Bedroom Outside
850 750 440 130
27.8 24.1 17.8 0.5
24-hour average Kitchen Living Room Bedroom Outside
140 140 85 66
5.9 5.9 4.7 0.5
Air exchange rates (air changes per hour-ach) morning mid-day evening
0.43 0.33 0.34
391
A recent study i n England8 has compared the incidence r a t e s of respiratory i l l n e s s i n two groups of children: those living i n homes i n which natural gas stoves were used and those where e l e c t r i c stoves were used. The investigators concluded t h a t the increased levels of respiratory i l l n e s s found among children living in homes using gas stoves might be associated w i t h the elevated levels of nitrogen dioxide emitted by these appliances. A study i n progress i n s i x c i t i e s i n the United States has released i t s preliminary analyses which report similar conclusions 9 . Formaldehyde Formaldehyde (HCHO) is an inexpensive, high-volume chemical used throughout the world i n a variety of products, mainly i n urea, phenolic, melamine and acetal resins. These resins a r e present i n insulation materials, particleboard, plywood, t e x t i l e s , adhesives, e t c . , used i n large quantities by the building trades. Although particleboard and urea formaldehyde foam insulation have received the most attention, formaldehyde a l s o emanates from combustion processes (gas cooking and heating, tobacco smoking). The pungent and c h a r a c t e r i s t i c odor of formaldehyde can be detected by most humans a t levels below 100 pg/m 3 . Several studies reported i n the l i t e r a t u r e indicate t h a t concentrations in the range of 100 t o 200 vg/m 3 may be sufficient t o cause swelling of the mucous membranes, depending on individual s e n s i t i v i t y and environmental conditions (temperature, humidity, e t c . ) . Burning of the eyes, weeping, and i r r i t a t i o n of the upper respiratory passages can also r e s u l t from exposure t o r e l a t i v e l y low concentrations. High concentrations (>> 1000 pg/m 3 ) may produce coughing, constriction i n the chest, and a sense of pressure i n the head. There is concern t h a t formaldehyde may have serious long-term health e f f e c t s . Several countries are moving rapidly t o establish standards for formaldehyde concentrations i n indoor a i r . In July 1978, the Netherlands established a standard of 120 pg/m 3 as the maximum permissible indoor concentrationlo and Denmark, Sweden, the United States and West Germany a r e considering similar action. Indoor measurements of formaldehyde levels reported from Denmark, Sweden, West Germany and the U.S. were frequently found i n excess of the recommended indoor s t a n dards of 120 pg/m 3 and, i n several cases, exceeded the Threshold Limit Value (2430 3 pg/m ) f o r workroom a i r . In general, these studies showed t h a t several recently constructed residential buildings and mobile homes w i t h air exchange rates less t h a n 3 0.3 ach exhibited h i g h formaldehyde concentrations (>120 pg/m ) . Formaldehyde and total a l i p h a t i c aldehydes (formaldehyde plus other aliphatic aldehydes) have been measured by LBL a t several energy-efficient research houses a t Figure 1 shows a histogram of frequency of various geographic locations i n the U.S. occurrenceof concentrations of formaldehyde and t o t a l a l i p h a t i c aldehydes measured a t an energy-efficient house w i t h an a i r exchange r a t e of 0.2 ach. Data taken a t an energy-efficient house i n Mission Viejo, California, a r e shown i n Table 3. As shown,
392 Concentration ( DDb)
~ n u 7
i
Indoor,
1
HCHO
’7
I
ii
i 60
0
I20 Concentration (pg/m 3 1
I80
240
XBL795-14SIA
F i g . 1. Histogram of i n d o o r and outdoor formaldehyde and t o t a l a l i p h a t i c aldehyde c o n c e n t r a t i o n s measured a t an energy research house i n Maryland d u r i n g March and A p r i l 1979. The a i r exchange r a t e o f t h e house i s about 0.2 ach.
TABLE 3 Indoor/Outdoor Formaldehyde And Aliphatic Aldehyde Concentrations Measured at The Med-ll Residence August 1979
Number of Measurements
Condition
Sampling Time
Formaldehyde Aliphatic ( ~ g / m ~ ) ~ Aldehydes ( ~ g / m ’ ) ~
Unoccupied, without furniture
3
12
80f 9%
Unoccupied, with furniture
3
24
223f 7%
294f 4%
Occupied, dayC
9
12
261 ? 10%
2 7 7 t 15%
Occupied, nightd
9
12
140 f 31%
178 f 29%
a Determined using pararosaniline method (120 pg/m3 < 10 pg/rn3.
= 100 ppb).
90 i 16%
All outside concentrations
b Determined using MBTH method, expressed as equivalents of formaldehyde. All outside concentrations 20 pglrn3.
<
c Air exchange rate = 0.4ach. d Windows open part o f time; air exchange rate significantly greater than 0.4ach and variable.
393
when t h e house d i d n o t c o n t a i n f u r n i t u r e , formaldehyde l e v e l s were below t h e 120 vg/m3; when f u r n i t u r e was added, formaldehyde l e v e l s rose t o almost t w i c e t h e 120 pg/m
3
level.
A f u r t h e r increase was noted when t h e house was occupied, very
l i k e l y because o f such a c t i v i t i e s as cooking w i t h gas.
blhen occupants opened windows t o i n c r e a s e v e n t i l a t i o n , t h e formaldehyde l e v e l s dropped s u b s t a n t i a l l y .
Radon Radon and i t s decay daughters a r e known t o comprise a s i g n i f i c a n t p o r t i o n o f n a t u r a l background r a d i a t i o n t o which t h e general p o p u l a t i o n i s exposed.
Radon-222 i s
an i n e r t , r a d i o a c t i v e , n a t u r a l l y o c c u r r i n g gas which i s p a r t o f the uranium-238 decay chain.
Any substance t h a t c o n t a i n s radium-226, t h e precursor o f radon, i s a poten-
t i a l emanation source.
Since radium i s a t r a c e element i n most rock and s o i l , sources o f i n d o o r radon i n c l u d e b u i l d i n g s m a t e r i a l s , such as concrete o r b r i c k , and t h e s o i l under b u i l d i n g foundations.
Tap water may be an a d d i t i o n a l source i f taken
from w e l l s o r underground s p r i n g s . Scattered observations have shown t h a t indoor c o n c e n t r a t i o n s o f radon and radon daughters a r e t y p i c a l l y h i g h e r than outdoor concent r a t i o n s , presumably because t h e b u i l d i n g s t r u c t u r e serves t o c o n f i n e radon e n t e r i n g t h e i n d o o r environment from v a r i o u s sources.
Conservation measures, p a r t i c u l a r l y
reduced a i r exchange r a t e s , may exacerbate t h i s s i t u a t i o n . F i g u r e 2 summarizes and compares radon c o n c e n t r a t i o n s i n outdoor and indoor a i r a t d i f f e r e n t geographic s i t e s .
What becomes e v i d e n t from t h i s f i g u r e i s t h a t indoor
l e v e l s exceed outdoor l e v e l s i n each case presented, and t h a t houses b u i l t on phos11 phate-reclaimed l a n d i n F l o r i d a show radon l e v e l s above h e a l t h g u i d e l i n e s .
A simple p o p u l a t i o n s - a t - r i s k model based on the " l i n e a r hypothesis" t h a t r i s k i s d i r e c t l y p r o p o r t i o n a l t o dose suggests an added annual r i s k o f 50 t o 110 cases o f 3 12 l u n g cancer per m i l l i o n based on an average c o n c e n t r a t i o n o f 1 nCi/m o f radon
.
Based on t h e above estimates o f r i s k , l i f e - t i m e exposures t o a few nCi/m3, which m i g h t be t h e case w i t h low a i r exchange r a t e s (<0.3 ach), c o u l d y i e l d increased l u n g cancer i n c i d e n c e equal t o t h e observed r a t e f o r male non-smokers. Since we do n o t y e t know enough about t h e a c t u a l dose-response c h a r a c t e r i s t i c s of l o w - l e v e l r a d i a t i o n exposure, we cannot say w i t h c e r t a i n t y whether t h e r e i s any 3 . However, use o f a l i n e a r
added r i s k from a l i f e - t i m e exposure t o a few nCi/m
hypothesis model i s considered prudent f o r r a d i a t i o n p r o t e c t i o n purposes u n t i l we do have a b e t t e r understanding of t h e dose-response c h a r a c t e r i s t i c s o f r a d i a t i o n exposure. LBL has conducted measurements o f radon l e v e l s i n e n e r g y - e f f i c i e n t b u i l d i n g s throughout t h e U n i t e d States. For these studies, grab samples were taken w i t h a l l doors and windows closed, i n o r d e r t o s i m u l a t e worst-case c o n d i t i o n s .
Results
i n d i c a t e t h a t houses w i t h low a i r exchange r a t e s (e0.3 a i r changes p e r hour) o f t e n have h i g h e r radon c o n c e n t r a t i o n s than conventional houses (-0.75
a i r changes per hour).
394
Radon concentration (nCi/rn3) XBL 795-1659
C
Fig. 2. Radon concentrations i n a i r . The numbers f o r New York, Salzburg, and Florida a r e geometric means of the average f o r each s i t e sampled. The value given a s the uranium mines standard i s c a l c u l a t e d (assuming an equilibrium f r a c t i o n of 0.5) from the annual dose l i m i t f o r occupational exposures of 4 WLM. The health guidelines apply t o houses b u i l t on land reclaimed from phosphate s t r i p mining i n Florida, and ho es i n f o u r communities associated w i t h uranium mining and processing i n Canada.
Y2
Figure 3 i s a s c a t t e r p l o t of radon concentrations vs. v e n t i l a t i o n r a t e i n a number of e n e r g y - e f f i c i e n t houses. While t h e data show considerable s c a t t e r , a c o r r e l a t i o n between radon concentration and a i r change r a t e i s apparent. An a i r exchange r a t e o f approximately 0.5 ach i s required i n order t o maintain radon con3 c e n t r a t i o n s below 4 nCi/m , the maximum permissible concentration allowed by present U.S. health guidelines. Integrated measurements of l a r g e numbers of grab samples need t o be made under typical l i v i n g conditions and various c l i m a t i c conditions bef o r e we can reasonably estimate average exposures of building occupants. CONCLUSIONS Indoor a i r contaminant l e v e l s a r e s t r o n g l y a f f e c t e d by human a c t i v i t i e s and the manner i n which m a t e r i a l s a r e incorporated i n t o buildings, a s well a s o t h e r aspects of building design, p a r t i c u l a r l y t h e i n f i l t r a t i o n o r v e n t i l a t i o n r a t e s . Our work t o d a t e i n d i c a t e s t h a t indoor a i r pollution may a f f e c t human health and, i f t h i s assumption i s borne o u t by f u r t h e r studies, i t may ultimately have a l a r g e impact on energy conservation s t r a t e g i e s f o r buildings and on t h e need f o r more
395
0
0
0
0 0
0. 0 .
8
0
0
0
0.1 1 0.01
I
I
I I Illll
0.I
I
I
I I II I I I
I
I
I l l
I
1
Air change rate (hr-')
XBL 801-38
Fig. 3. Radon concentration vs. ventilation in energy efficient houses. stringent control of air pollution from indoor sources. There are several measures that might be adopted to limit increases in indoor air pollution in both conventional and energy-efficient buildings. Options include an informed selection of building materials; coating of various building materials with sealants to reduce emissions of potentially harmful pollutants; the use of mechanical ventilation/heat exchanger systems; and the use of contaminant control devices. REFERENCES 1 C.D. Hollowell, R.J. Budnitz, G.D. Case, and G.W. Traynor, Generation of Gaseous and Particulate Pollutants from Indoor Combustion Sources: I . =Measure-ments 8/75 - 10/75, Lawrence Berkeley Laboratory Report, LBL-44T6 ( J a n u a r y . 2 C.D. Hollowell , R.J. Budnitz and G.W. Traynor, "Combustion-Generated Indoor Air Pollution," in Proceedings of the Fourth International Clean Air Congress, Tokyo, Japan, May 16-20, 1977, pp. 684-7,theapanese Union of Air Pollution Prevention Associations, Tokyo, Japan (1977). 3 G.W. Traynor, D.W. Anthon, and C.D. Hollowell, "Indoor Air Quality: Gas Stove Emissions," Submitted to Atmospheric Environment (1980). 4 The American Society of Heating, Refrigerating, and Air Conditioning Engineers,
396
Inc. (ASHRAE), Standards f o r Natural and Mechanical Ventilation, 62-73 (1973). 5 C.D. Hollowell, J.V. Berk, and G.W. Traynor, "Impact of Reduced I n f i l t r a t i o n and Ventilation on Indoor Air Q u a l i t y i n Residential Buildings," ASHRAE Transactions, 85, Part 1,pp. 816-127 (1979). 6 The American Society of Heating, Refrigerating, and Air Conditioning Engineers, Inc. (ASHRAE), Energy Conservation i n New Building Design, 90-75 (1975). 7 D.W. DeWerth, Energy Consumption of Contemporary 1973 Gas Range Burners and P i l o t s Under T i c a l Cooking Hoods, American Gas Association Research Report NO. 1 4 9 m y k 8 R.J.W. Melia, C. du V. Florey, D.G. Altman, and A.V. Swan, "Association Between Gas Cooking and Respiratory Disease i n Children," B r i t . Med.J., 2 149 (1977). 9 F.E. Speizer, B. F e r r i s , J r . , Y.M.M. Bishop and J . Spengler, "HeTlth Effects of Indoor Exposure, Preliminary Results," Presented a t t h e American Chemical Society Meeting, Honolulu, Hawaii , April 1979. 10 R. Baars, "The Formal Aspects o f t h e Formaldehyde Problem i n t h e Netherlands," presented a t " I n t e r n a t i o n a l Indoor Climate Symposium," Copenhagen, Denmark (August 30-September 1 , 1978). In Indoor Climate, ed. P.O. Fanger and 0. Valnjorn, Copenhagen: Danish Building Research I n s t i t u t e , pp. 77-81 (1979). 11 "Indoor Radiation Exposure Due t o Radium-226 i n Florida Phosphate Lands; Radiation Protection Recommendations and Request f o r Comment." Federal Register, 44 NO. 128, pp. 38664-38670 ( J u l y 2 , 1979). 12 KJ. Budnitz, J.V. Berk, C . D . Hollowell, W . W . Nazaroff, A.V. Nero, and A.H. Rosenfeld, "Human Disease from Radon Exposures: The Impact o f Energy Conservation i n Buildings," Energy and 8 u i l d i n g s , 2 , 209 (1980).
Atmospheric Pollution 1980, Proceedings of the 14th International Colloquium, Paris, France, May 5-8,1980, M.M.Benarie (Ed.), Studies in Environmental Science, Volume 8 0 Elsevier Scientific Publishing Company,Amsterdam -hinted in The Netherlands
397
MEASUREMENT OF NITROSAMINES I N THE A I R OF P A R I S BY THERMAL ENERGY ANALYSIS B.T. CHUONG and M. BENARIE
'
I n s t i t u t N a t i o n a l de Recherche Chimique Appliquse
-
91710 VERT-le-PETIT (FRANCE)
ABSTRACT Results o f measurements o f nitrosamines u s i n g gas chromatography and thermal energy analyzer d e t e c t o r made a t two s i t e s i n P a r i s (FRANCE) a r e reported. N-nitrosodimethylamine (NDMA) and, a t sone
occasions
, N-nitrosodiethylamine
(NDEA) were found. N-nitrosodimethylamine i s encountered more f r e q u e n t l y i n w i n t e r than d u r i n g s p r i n g o r summer.
INTRODUCTION.
As nitrosamines are r e p u t e d l y carcinogenic, we a r e l o o k i n g f o r these compounds i n t h e a i r o f P a r i s s i n c e 1976 ( r e f . 1 ) . During t h i s measurement programme, the samples were c o l l e c t e d a t :
-
The b u i l d i n g o f t h e U n i v e r s i t y P a r i s V I , Quai St-Bernard, n e x t t o the
Seine r i v e r , f a c i n g the courtyard, a t 20 m h e i g h t above ground;
-
The Tour St-Jacques on R i v o l i S t r e e t , n e a r l y a t t h e m i d p o i n t o f the P a r i s
urban area, a t 10 m h e i g h t o v e r ground;
-
The C a f e t e r i a o f t h e U n i v e r s i t y P a r i s V I , a l s o Quai St-Bernard, where
simultaneous i n d o o r and outdoor samples were taken. EXPERIMENTAL The a i r was sampled a t t h e r a t e o f 2 1 mine' i n 60 m l
N KOH s o l u t i o n contained
i n 100 m l bubblers made of low a c t i n i c glass. The a l k a l i n e s o l u t i o n was e x t r a c t e d w i t h 30 m l dichloromethane;
o p e r a t i o n repeated t h r e e times. The u n i t e d s o l v e n t
f r a c t i o n s were f i l t r a t e d over Na2 SO4 and concentrated on a Kuderna-Danish eveporator t o 5 m l . A f t e r a d d i t i o n o f 0.2 m l n-hexane, the evaporation was continued u n t i l the f i n a l volume o f 0.2 m l . 10 ~1 o f t h i s f i n a l concentrate were t To whom correspondence should be adressed.
398
i n j e c t e d i n t o t h e GC-TEA ( r e f . 2 ) . The gas chromatographic column o f 6 m l e n g t h and 2 mm i . d . was f i l l e d w i t h Carbowax 20 M on Chromosorb WAW 100/200 mesh.
30 m l min-'
Argon f l o w r a t e Oven temperature
180°C
I n j e c t i o n temperature
210°C
D e t e c t o r : Thermal Energy Analyze (TEA) a t
425°C
-
Col d t r a p temperature Pression o f t h e r e a c t o r chamber
161°C 1.5 mm Hg
Absence o f a r t e f a c t s . I n t h e blanks prepared s i m p l y w i t h deionised water, about 40 ng o f NDMA and 100 ng o f NDEA c o u l d be detected. Therefore the water used i n the p r e p a r a t i o n
o f t h e KOH s o l u t i o n has been double d i s t i l l e d . J u s t b e f o r e sampling, t h e s o l u t i o n was b o i l e d d u r i n g one hour. I n such blanks, no n i t r o s a m i n e c o u l d be detected by TEA. S e n s i t i v i t y o f t h e method.
1 ng NDMA added t o t h e blank c o u l d be determined by TEA. Therefore we estimate t h e s e n s i t i v i t y o f t h e method sampling 3 m-3 a i r p e r day a t about 0.3 ng NDMA ~ n - ~ . The mention "n d" ( = n o t detected) among the r e s u l t s means a concentration i n f e r i o r t o t h i s value. RESULTS The r e s u l t s are condensed i n Table 1. The f i r s t p a r t o f t h i s t a b l e presents a t y p i c a l s e t o f consecutive measurements. The lower p a r t o f the t a b l e summarizes a l l measurements, w i t h o u t calendar d e t a i l s . Nitrosamines were present i n a l l samples from Tour St-Jacques and from t h e C a f e t e r i a . The h i g h e s t l e v e l was 9 ng mm3 NDMA a t Tour St-Jacques. NDMA was detected i n a l l p o s i t i v e samples, NDEA was present i n about a t h i r d o f the p o s i t i v e samples. I n d o o r r e s u l t s were always s u p e r i o r t o those found outdoor, l i k e l y due t o the presenceof cooked food and smokers. Concentrations found a t the Tour St-Jacques were g e n e r a l l y h i g h e r than those simul taneosly recorded a t t h e U n i v e r s i t y , the l a t t e r b e i n g more remote from than urban t r a f f i c . MEASURES DURING SPRING OF 1979.
A s e r i e s of measurements were made i n s p r i n g and e a r l y summer 1979 a t t h e Tour St-Jacques. Among t h e 16 a i r samples, o n l y 5 contained nitrosamines. The h i g h e s t l e v e l found was 4 ng from 1 p.m. (17°C).
t o 5 p.m.
NDMA and 3 ng m-3 NDEA i n the sane sample on June 13 This day was cloudy, the temperature low f o r t h e season
The o t h e r p o s i t i v e samples d i d n o t c o n t a i n more than 1 ng m- 3
.
399
TABLE 1 24- hour sampling, w i n t e r 1978-1979. A l l concentrations i n ng ~ n - ~I .n the f i r s t p a r t of t h e t a b l e , a t y p i c a l s e t o f t e n days' r e s u l t s . The l a s t l i n e s summarize t h e whole s e t . U n i v e r s i t y o f P a r i s VI Outdoor Cafeteria Indoor NDMA NDEA NDMA NDEA Wed Fri Sat Sun Mon Wed Thu Fri Sat Sun
31.1.79 2.2.79 3 4 5 7 8 9 10 11
n d n d n d n d n d 3 1 < 0.5 4 2
T o t a l number o f measurements
n n n n n n n
d d d d d d d 1 2 1
2 1 < 0.5 < 0.5 7 1 1 3 3
n d n d n d < 0.5 1 n d n d < 0.5 < 0.5
Tour St-Jacques R i vol i S t r e e t
NDMA
NDEA
9 1.5 1
< 0.5 n d n d
2
n d
17
36
13
NDMA i d e n t i f i e d
...
in samples NDEA i d e n t i f i e d in.. samples
25
.
17
13
13
Maximum l e v e l o f NDMA o r NDEA found (ng m-3)
4
4
6
6
1
7
9
1
CONCLUSION. Using GC-TEA, NDMA and NDEA were determined i n t h e a i r o f P a r i s . The average i n an area w i t h heavy automobile t r a f f i c i n w i n t e r , was about 2-3 ng
NDMA. The
maximum observed was 9 ng m-3 NDMA. Nitrosamines occur more f r e q u e n t l y i n w i n t e r than i n s p r i n g o r summer, probably due t o t h e p h o t o l y s i s o f nitrosamines by s u n l i g h t ( r e f .3). REFERENCES
1 B.T. Chuong and M. Benarie - Recherche d'une methode pour l e dosage de l a N-Nitrosamine dans 1 'atmosphere. S c i . Tot. Environ. 6 (1976) 181-193. 2 D.H. Fine, D.P. Rounbehfer, E. Sawicki and K. Krost - Determination o f D i methylnitrosamine i n A i r and Water by Thermal Energy Analysis : V a l i d a t i o n o f A n a l y t i c a l Procedures. Environ. S c i Tech. , 11 (1977) 577-580. 3 P.L. Hanst, J.W. Spence and M. M i l l e r - Atmospheric Chemistry o f N-Nitroso Dimethy lami ne Envi ron. Sci Tech. , 4 (1977) 403-405.
.
.
Acknowledgement
-
.
Support f o r t h i s research was provided by t h e M i n i s t e r e de 1' I n d u s t r i e . We would l i k e t o thank t h e " L a b o r a t o i r e de N u t r i t i o n e t des Maladies MGtaboliques de l ' U n i v e r s i t @ de NANCY I"f o r t h e e x e c u t i o n o f the GC-TEA analyses.
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Atmospheric Pollution 1980, Proceedings of the 14th International Colloquium, Paris,France, May 5-8,1980, M.M. Benarie (Ed.), Studies in Environmental Science, Volume 8 0 Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
401
PERFORMANCES OF A PIEZOELECTRIC PARTICLE MASS MONITOR
J. PAULOU Facult6 des Sciences, Laboratoire d'ElectricitG, Avenue Philippon 64000 PAU (France)
INTRODUCTION A piezoelectric particle mass monitor, using the "electric wind" created by the
discharge of an electrostatic precipitator, has been tested with various aerosols and under various operating conditions.
PRINCIPLE OF OPERATION AND DESCRIPTION OF THE INSTRUMENT A schematic diagram of the apparatus is drawn below (Fig.l)
Frequcncya i r outlet
t
converter
Fig. 1 . Schematic diagram of the apparatus 1 : teflon block ; 2 : platinum probe ; 3 : gold electrodes (diameter : 8mm, thickness 0,1 pm) ; 4 : quartz crystal (diameter : 14mm) ; 5 : tungsten needle (dFameter : lmm, radius of curvature : 15 pm) Ambiant air is sampled by the "ion drag pump" (electric wind), and the flow rate
Q is measured by means of a platinum probe, placed in a Wheastone bridge. Particles suspended in ambiant air are charged electrically and collected on
402
the quartz crystal electrode as a result of the electric field (about 10 kilovolts/cm) The frequency shift of the crystal, due to particle deposition during a time interval At, allows the calculation of the mass concentration of particles :
'
AF c = -100 -
r
s
Q At expressed in @.PI-3 or yg.1-1
where r = particle collection efficiency (percent) AF = frequency shift of the crystal (Hz) = sensitivity of the quartz crystal (Hz.I,J&-~)
s
Q
=
flow rate (m3 sec-1 or 1.sec-1)
At = sampling time (sec.)
The theoretical values of the sensitivity s , for crystal dimensions such as for a nominal frequency of 9 MHz, and 114 Hz~y-1 those in Fig. I are 368 Hz ).I&-1 for 5 MHz. The purpose of the present study are to measure particle collection efficiency and to compare theoretical and experimental sensitivities, as a function of different parameters, namely :
- distance between needle and - discharge current
quartz crystal
3
5<1<15 p4 0,35
-
flow rate
-
particle size, concentration and chemical composition. It should be noted that for a given distance d, Q is approximately proportio-
nal to I. Q can reach the value of 2 Ipm for d = 7mm, I
=
15pA.
PARTICLE COLLECTION EFFICIENCY (r) Overall particle collection efficiency (r) Overall efficiency has been measured by two means :
-
condensation nuclei counter (C.N.C.)
-
two cells in series with various aerosols
with room aerosol,
The results range from 80% to 90% according to the different operating conditions. Collection efficiency as a function of particle size The collection efficiency as a function of particle size has been measured by means of a spectrophotometer (ROYCO model 225) with room aerosol, and with an electrostatic aerosol analyser (T.S.I. model 3030) on a combustion aerosol. Results are plotted on Fig. 2a-2b. In the light of these measurements, we can conclude that the particle collection efficiency is independant of aerosol concentration and chemical composition (because of the good agreement between ROYCO and E.A.A. measurements, carried out under very different conditions). Furthermore, r increases as either I, d, or particle radius increases. Finally, we can say that r reaches correct values (>90%) for d > 5 m and I>5 yA for a wide range of particle sizes.
403
I
P
o dtrnml: 3 f (MA): 5
90.
O 3
5
A 5
A 7
15
5
15
5
~
Fig. 2a. Particle collection efficiency electrostatic aerosol analyser.
V.S.
particle diameter measured with an
Fig..2b. Particle collection efficiency optical counter.
V.S.
particle diameter measured with an
SENSITIVITY Combustion aerosol (concentration of about several pg 1 - 1 ) A previously calibrated beta jauge (SAPHYMOSTEL) was available to measure sensitivity as a function of the sampling flow rate. The operating conditions where
I = 10 VA and a nominal 5Mlz crystal frequency. The sensitivity depends on the flow rate and is a maximum for the value corresponding to the "electric wind" (similar results were obtained for I
=
5 uA). This phenomenon, depicted on Fig.3,
is due to cell geometry, producing different particle deposition patterns as the flow rate varies, since the collection efficiency does not change much ('93 5 r < 98%). The sensitivity is known to be a maximum for a uniform particle deposit over the whole crystal electrode surface. Other experiments were effected by weighing loaded and unloaded crystals by means of an electrobalance CAHN (precise to 2 pg). It appears from the results that the experimental sensitivity is 15% less than theoretical sensitivity for both the nominal frequencies of 9 and 5 MHz.
404
;m? d =
0-
7mm.
A
05 \ L
"electric
0
3 mm m . .
wind"
Fig. 3 .
0
I
I
1
50 flow
100
r a t e
1
(liters per hour)
Fig. 3 . Particle sensing efficiency (experimental sensitivity/theoretical sensitivity) as a function of the flow rate. Monodisperse aerosols Measurements have been made with :
- Polystyrene latex spheres ( 0 , I
-
1 - 5.7 - 25.7 pm diameter) ; humidity 2 3 0 %
comparisons were made with a beta gauge.
-
NaCl particles (0,047
-
0,055 - 0,069 - 0,08
-
0,103 pm diameter) every parti-
cle carrying one elementary charge, the total charge being measured by an electrometer ; humidity -4%.
- Fluoresceine particles ( 9 , 0 pn diameter) in Boltzmann equilibrium ; humidity ~ 4 % Particles deposited on the crystal are dissolved in an appropriate solution (H20, NH3) and measured using a fluorimeter.
With such aerosols, a very important decrease in sensitivity is found for particles larger than 5 pm in diameter (see Fig.4).
The saturation of the quartz
crystal occurs very rapidly for large particles (e.g. when 1 1-18of fluoresceine particles have been deposited) although the crystal can still oscillate for 100 pg of a polydispersed aerosol. The particle deposit takes the shape of an annulus, and this contributes to a decrease of sensitivity. It would seem that the sensitivity depends on the chemical composition of particles (and consequently on attractive forces between particles and the crystal
405
electrode) if we compare the results obtained for NaCl particles and latex spheres of 0 , l Um, though latex spheres of such a diameter cannot be generated, without a large amount of aggregates (2 or more particles) and would be considered as larger particles. Room aerosol A comparison has also been drawn (not a calibration) between our prototype and
the T.S.I. model 3203, for a room aerosol. The results show agreement to within 20% between the two instruments. CONCLUSIONS Results concerning sensitivity are summarised in Fig.4
p -
x U
room a e r o s o l
0’
/
0 ; 5 Mhz.
C
.-U
.-
fluoresceine p a r t icl e s
A
A
Fig. 4 .
:
9 Mhz.
U
L
L
-5
0
V
0
m
.-t
Y)
C
U Y)
0
-
t
I
n
I I l l
I
1
I
I I
I , ,
Fig. 4 . Particle sensing efficiency
V.S.
particle diameter.
It appears from this study that the location and the shape of the deposit are very important factors with regard to measurement accuracy. This shape could be improved by redesigning the system geometry, by reducing crystal electrode diameter to 6 m , needle diameter to O,Imm, and perhaps by changing the precipitation chamber geometry in order to obtain an air velocity profile which would deposite particles as uniformely as possible on crystal electrode. For this purpose, fur-
406
ther theoretical considerations are being studied. Furthermore, an auxiliary device such as an impactor, should prevent particles over 5 pm in diameter from entering the instrument, but would make the use of a mechanical pump necessary. Finally, due to its high sensitivity, such a device could be employed for monitoring respirable particle mass concentrations, and could be made to be entirely automatic, including the cleaning of the crystal. ACKNOWLEDGMENTS This study was supported by "le Minist&-e de 1'Environnement et du Cadre de Vie", le "Centre d'Infomation et de Recherches sur les Nuisances" (S.N.E.A (P) ; LACQ) le S.T.E.P.A.M. (Commissariat 2 1'Energie Atomique, Fontenay-aux-Roses) et le laboratoire d'Electricit6 de la Facultd des Sciences de Pau.
REFERENCES 1
2 3
4 5
6
Benjamin Y.M. Liu, Fine Particles, aerosol generation, measurement sampling and analysis, Academic Press. Inc. J. Bricard, Physique des aerosols, rapport C.E.A., R 4 8 3 1 , I & 2 R. Camps, Contribution 2 l'6tude d'un analyseur de poussisres par conjugaison de l'effet piezo6lectrique et de l'effet couronne, These Universitd de Pau, 1975 G.J. Sem, Ferformance of the piezobalance respirable aerosol mass monitor, Therno Systems Inc., presented at the 4th Meeting of the G.A.F., Gesellschaft fzr Aerosolfoschung. T.E. Carpenter, Monitoring aerosol concentrations with piezoelectric crystals, D.L. Brenchley, 16th A.E.C. Air Cleaning Conference, 720,823, 1. J.G. Olin, G.J. Sem, D.L. Christenson, Piezoelectric Electrostatic Aerosol Mass Concentration Monitor, Themo Systems Inc.
E FFECTS: ON MAN AND ON VEGETATION
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409
AtrnospSeric Pollution 1980, Proceedings of the 14th InternationalColloquium,Paris,France, May 5-8,1980, M.M.Benarie (Ed.),Studies in Environmental Science, Volume 8 0 Elsevier Scientific Publishing Company,Amsterdam - Printed in The Netherlands
THE EXPOSURE OF HUMAN POPULATIONS TO AIR POLLUTION R. E. MU"
Institute for Environmental Studies, University of Toronto, Toronto, Canada
ABSTRACT Urban air quality is usually monitored at fixed locations whereas people move about, often spending most of their time indoors.
The air pollution exposures
of human populations are therefore rather uncertain.
Portable air quality mon-
itors have been carried by volunteers in short-term studies.
However, the lar-
ger problem is to generalize these data so that exposures of large groups of people can be estimated for use in the development of dose-response relations. This requires information on:
(a) the population being sampled; (b) the life
styles of these people; and (c) indoor-outdoor relations in the absence and presence of indoor sources of pollution, for various kinds of buildings and meteorological conditions.
INTRODUCTION A recent monograph on the design of air quality monitoring networks (ref. 1) has emphasized the importance of specifying the objectives for monitoring and the tolerances to be permitted in achieving these objectives. For example, an objective might be to estimate the mean annual concentration of
SO2
within a
given area with sufficient accuracy that a downward trend of 5% per annum could be detected in 5 years with 95% confidence.
Considerations of this kind have
frequently been overlooked with the result that although networks may provide masses of information, they may be incapable of answering many of the questions put to them. Most urban air quality networks have been established by control agencies, whose main task is to ensure that pollutant concentrations do not exceed air quality standards.
In the absence of better information, epidemiologists often
use these data to determine whether air pollution has an effect on health. plicit in such analyses are the assumptions that:
Im-
(1) air quality as measured
by networks of stations is highly correlated with the exposures of the populations being sampled; ( 2 ) the pollutants being monitored are surrogates for the health-related components of air quality; and ( 3 ) the health-related indicators
being used are sensitive to gradations of air quality. is rather tenuous.
This line of reasoning
Yet it must be admitted that statistically significant cor-
relations are sometimes found between air quality data and various health indicators.
OUTDOOR AIR QUALITY Networks of air quality monitoring stations provide information on urban air quality patterns at outdoor sites with similar "representative" exposures. However, there are many local anomalies, e.g., at busy traffic intersections, or directly downwind of a short chimney. been well documented.
In the case of
CO,
these effects have
For example, Waldman Ual. (ref. 2) found that
CO
con-
centrations experienced by Washington bicyclists were correlated significantly with those experienced by motorists following the same routes, but were not correlated with those measured at a neighbourhood monitoring station.
Local anom-
alies with respect to other pollutants are not so well documented, although a general estimate could be obtained from knowledge of emission patterns and building geometries.
INDOOR AIR POLLUTION Indoor air quality may be different from that outdoors, and may vary greatly from building to building and from day to day because: (1) There are indoor sources of air pollution (stoves, cigarettes, fireplaces,
moulds, etc .) (2)
;
Ventilation and air conditioning systems sometimes provide purified envir-
onments (and sometimes recycle pollutants); (3)
The natural ventilation of structures varies, depending not only on the
type of construction and heating system but also on meteorological factors (windspeed, gustiness, indoor-outdoor temperature differences) and on life styles; (4) Buildings absorb pollutants, some materials having a much greater capacity
to do this than others. The net effect is likely to be different in summer (windows open) than in winter (windows closed).
Because of these many factors, the published literature on
indoor air quality tends to be anecdotal, with numerous case studies.
See, for
example, several recent reviews (refs. 3 - 6 ) . In the last century, houses were rather drafty, preventing a buildup of trace substances from indoor sources.
The present trend towards energy conservation
and airtight construction leads to indoor dead zones where pollution may accumulate (ref. 71, as well as contamination of an entire room or building if there is a breakdown in the ventilation system in conjunction with an indoor pollution
411 source (ref. 8). Major indoor sources of air pollution are: (a) Cigarettes: Numerous studies have demonstrated that concentrations of suspended particulates and CO are relatively high if there are smokers in a room (refs. 9, 10). (b) Gas stoves: Gas stoves emit significant amounts of NO
X
and CO, resulting
in high indoor concentrations of these gases at times when stoves are on (refs.
11, 12). (c) Human beings:
Human beings are sources of CO (human breath), particulates
(human skin) and various volatile organic compounds (hair sprays, deodorants, perfumes). (d) Other:
In addition, active young children cause house dust to fly about. Other sources of indoor air pollution include building materials
(various organic compounds and radon), the earth's surface (radon) and damp cellars (moulds). In the .absence of indoor sources, indoor concentrations of trace substances are generally 20 to 70% of those outdoors, depending on building ventilation characteristics, absorptivities and meteorological factors (refs. 13, 14). Several mathematical models have been proposed to predict indoor-outdoor air pollution relations (refs. 15, 16). Finally, it should be mentioned that other kinds of enclosed environments are of imporrance in air pollution epidemiological studies, e.g., occupational exposures (in mines, smelters, arc-welding shops, etc.), transportation exposures (in automobiles, buses, trains, etc.) and recreational and entertainment exposures (in theatres, ice hockey arenas, restaurants, etc.).
EPIDEMIOLOGICAL METHODS An
epidemiological study may be retrospective (using historical data sets) or
prospective (using new data sets obtained from existing and supplementary monitoring systems).
The approach may be exploratory (e.g., multivariate statisti-
cal analysis) or confirmatory (hypothesis-testing). Exposure times of interest may vary from a few hours to a few decades.
The main types of air pollution ep-
idemiological studies are: (1) Occupational studies (of traffic officers, taxi drivers, miners, etc.);
(2) Comparisons of mortality/morbidity rates in different cities or in different parts of the same city (cross-sectional studies); (3)
Comparisons of mortality/morbidity rates of people in the same age group
but born in different years or decades (longitudinal studies); (4) Day-by-day comparisons of mortality/morbidity rates in a city; (5)
Studies of rare events (e.g., the London 1952 smog, a taxi strike, an in-
dustrial strike in a single-industry town).
412 Health-related indicators used in air pollution studies include: mortality rates; mortality ratios (mortality rates normalized for age, sex, etc.); school, factory or office absenteeism; medicare data; hospital statistics; single questionnaires (re occupation, smoking habits, respiratory history, etc.); bi-weekly or monthly interviews (sometimes by telephone); daily diaries (re respiratory symptoms, etc.); ability to perform specific tasks; pulmonary function tests (using a spirometer); airway resistance changes from control levels (plethysmograph); measurement of elastic recoil of the lungs at different breathing rates; in the case of asthmatics, nose thermocouples to determine ratios of expiration (warm) to inspiration (cool) times and thus to monitor asthma attacks; for CO, alveolar air samples before and after CO exposures to estimate blood uptake, or venous blood samples to determine the carboxyhemoglobin (HbCO) levels (a good indicator of the time-weighted CO exposure over the previous 15 hours). The population to be studied must be chosen with care.
Some selection cri-
teria include the following:
1. The sample population should be sensitive (e.g., children, asthmatics, the elderly), and the control group relatively insensitive to the pollutant studied; 2.
The sample population should be exposed to relatively high pollution concen-
trations (e.g., inner-city residents, occupational groups, smokers) and the control group to relatively low concentrations; 3.
The effects of confounding influences should be minimized; e.g., the sample
should not include smokers, persons who are allergic to pollens and dusts, persons from different socioeconomic strata; 4.
The sample population should be relatively immobile, e.g., children, the
elderly, persons who live near their places of work. Having selected the population types, the space and time resolutions of the data sets should be chosen such that:
1. Air pollution exposures of each subgroup of people are relatively uniform; for example, the study might be limited to seasons when windows are open, and thus when indoor exposures are most likely to be similar to those outdoors; 2.
The space and time resolutions of the health-indicator data match those of
the air quality data; 3.
The sample size is likely to be sufficient to obtain statistically signifi-
cant results; 4. The sample is likely to be representative of a larger well-defined group of
people. Even if the investigator has considered these points carefully, he will still encounter the following difficulties:
1. After repeated exposures to poor air quality, populations may adapt, or sensitive individuals may move away;
413 2.
A person may react differently on different occasions to the same air pollu-
tion loading, even in a controlled chamber environment; 3.
Two people may react differently on the same occasion, even in a controlled
chamber environment;
4. The measured health effects may not be caused specifically by the pollutant being measured but by other trace substances, by combinations of trace substances, or by other environmental stresses, e.g., heat or dampness.
In some cases,
there are synergisms amongst the stresses; 5.
Some health effects take weeks or even years to become detectable; over such
long periods, the physical and even the socioeconomic environments of the persons being studied may change significantly; 6. For some pollutants, there may be several pathways to the body, and atmos-
pheric exposures may not be strongly correlated with health effects; 7.
Population exposures may be significantly different from air quality as
measured by networks of outdoor air quality stations.
LIFE-STYLE INDICATORS Two philosophies have emerged to the problem of characterizing population
movements for the purpose of estimating air pollution exposures. On the one hand, the behaviour patterns of the people being sampled are determined (from census data, surveys, diaries, etc.) and total exposures are obtained from a weighted average of the exposures for each environment. For example, Morgan and Morris (ref. 17) used U.S. census data to divide urban populations into seven subsets: (2)
people who live in the city, and (1) work indoors in the city (30.6%),
work outdoors in the city (0.5%), ( 3 ) work indoors in the suburbs (1.6%);
people who live in the suburbs, and (4) work indoors in the suburbs (59.2%), (5) work outdoors in the suburbs ( 0 . 8 % ) , (6)work indoors in the city (6.7%),
(7) and work outdoors in the city (0.4%).
The numbers in brackets are the per-
centages of the population in each subset in two cities in the northeastern United States. In the other general approach, the population studied is limited to those people exposed to poor air quality.
Parts of a city in which concentrations ex-
ceed designated values (usually the air quality standards) over designated time periods (usually 1, 3 , 8 or 24 hours) are determined, and, an attempt is made to estimate the numbers of people in these areas at these times (including persons at home, working, shopping or engaged in recreation) (refs. 18, 19). Of course, the population at risk could be limited to a subset like school children or asthmatics.
414
THE DESIGN OF SYSTEMS FOR ESTIMATING POPULATION EXPOSURES TO AIR POLLUTION (a) Introduction The preceding paragraphs were a necessary preamble.
It is now possible to
consider methodologies for estimating population exposures to air pollution. It is of course obvious that the methodology selected will depend on objectives and on the funds and technical support available.
It should also be emphasized
that the relevant physiological literature should be reviewed before making a decision; for example, daily average pollutant concentrations should not be used if high hourly concentrations have been found to produce detectable physiological changes. (b) CO:
a special case
Because the percentage of HbCO in the blood is a good indicator of timeweighted CO exposure, people can be used as their own CO monitors.
For example
in a comparative study of non-smokers in Chicago, Stewart et al. (ref. 20) found that:
1970
1974/75
Number of persons sampled
406
426
of blood samples exceeding the federal standard (1.5% HbCO)
74 %
42%
%
The data show that CO exposures decreased over the 4-year period, probably because of automobile emissions controls. (c) Other pollutants and groups of pollutants (1) Retrospective studies.
The air quality data available for retrospec-
tive analysis were collected for other than health-related purposes, and their relevance for epidemiological studies has not been established in many cases. However, it should be noted that improved design criteria can be expected in the next few years with the completion of several important studies, in particular the 6-city investigation in the United States (ref. 14) and the WHO/UNEP initiative in 5 or 6 urban areas in widely differing parts of the world (ref. 21).
Finally, it should be mentioned that day-to-day variations in air quality are sometimes greater than those from point to point.
In such cases and pro-
vided that the response times of the health-related indicators chosen for study are comparable, a single outdoor monitoring station may yield useful data. (2) Prospective studies.
test a model.
Prospective studies are usually designed to
The ultimate objective is to make useful predictions of air pol-
lution exposures and resulting health effects, preferably from the smallest possible number of supplementary data sets. Once the model has been validated, an optimal monitoring strategy might then have the goal of verifying that the model
415
is remaining in calibration rather than of attempting to measure small changes in health in the presence of great variability in nearly all of the factors included in the analysis. A useful tool to be included in a prospective study is a sensitivity analysis,
which is an attempt to estimate the cumulative effect of input errors on the outputs of the study.
For example, does it matter in estimating population ex-
posures if average times spent in the home, and/or ratios of indoor to outdoor pollution, are in error by
&
10, 20 or 30%?
Further, if population exposure is
in error by a designated amount, what is the effect on the numerical values of the health indicators being used, and is this within the limits of detection of the observing system? Considerations such as these have rarely been considered by epidemiologists.
CONCLUSION The importance of inter-disciplinary collaboration in health-related air pollution studies must be emphasized.
The epidemiologist, the human physiologist,
the air pollution chemist, the heating and ventilating engineer and the meteorologist can make significant contributions to our understanding of this important topic.
REFERENCES 1 R. E. Munn, The Design of Air Quality Monitoring Networks, Macmillan Press, London, 1980 (in press). 2 M. Waldman, S. Weiss and W. Articola, Final report, DOT-TES-78-001, Office of Env. Affairs, U.S. Dpt. Transportation, Washington, D.C., 1977, 226 pp. 3 F. B. Benson, J. J. Henderson and D. E. Caldwell, AP-112a. EPA, NERC, Research Triangle Park, N.C., 1972, 73 pp. 4 J. J. Henderson, F. B. Benson and D. E. Caldwell, AP-l12b, EPA, NERC, Research Triangle Park, N.C., 1973, 32 pp. 5 T. D. Sterling and D. M. Kobayashi, Env. Res., 13 (19771 1-35. 6 S. S. Morse and D. 3 . Moschandreas, EPRI EA-1025, Electric Power Res. Inst., Palo Alto, Cal., 1979, 169 pp. 7 G. R. Lundqvist, in N. Tanyolac '(Ed.), Theories of Odors and Odor Measurement, Rbt. College Res. Center, Bebek, Istanbul, Turkey, 1968, pp. 431-445. 8 J. S. Kelley and G. J. Sophocleus, J. Am. Med. Assoc., 239 (1978) 1515-i519. 9 R. E. Binder, C. A. Mitchell, H. R. Hosein and A. Bouhuys, Arch. Env. Health, 31 (1976) 277-279. 10 J. Sebben, P. Pimm and R. J. Shephard, Arch. Env. Health, 32 (1977) 53-58. 11 M. Benarie and A. Nonat, Sci. Total Env. 9 (1978) 53-58. 12 E. D. Palmes, C. Tomczyk and A. W. March, J. Air Poll. Control Assoc. 29 (1979) 392-393. 13 R. L. Derham, G. Peterson, R. H. Sabersky and F. H. Shair, J. Air Poll. Control Assoc. 24 (1974) 158-161. 14 J. D. Spengler, B. G. Ferris, D. W. Dockery and F. E. Speizer, Env. Sci. Tech. 13 (1979) 1276-1280. 15 F. H. Shair and K. L. Heitner, Env. Sci. Tech. 8 (1974) 444-451. 16 D. 3 . Moschandreas and J. W. C. Stark, EF-628, GEOMET Inc., 15 Firstfield Rd., Gaithersburg, Md., U.S.A., 67 pp. 17 M. G. Morgan and S. C. Morris, BNL 50637, Brookhaven Nat. Lab., Long Island, N.Y., 1977, 11 pp.
416 18 W. P. Darby, P. J. Ossenbrugqen and C. J. Gregory, ASCE 100 (EE3) (1974) 571591. 19 N. H. Frank, W. F. Hunt and W. M. Cox, Preprint 77-44.2, APCA 70th Annual Meeting, APCA, Pittsburq, Pa., 12 pp. 20 R. D. Stewart, C. L. Hake, A. Wu, T. A. Stewart and J. H. Kalbfleisch, Arch. Env. Health 31 (1976) 280-286. 21 WHO, EHE/ETS/79.5, World Health Org., Geneva (1979), 7 pp.
Atmospheric Pollution 1980, Proceedings of the 14th International Colloquium, Paria, France, May 5-8,1980, M.M. Benarie (Ed.), Studies in Environmental Science, Volume 8 0 Elsevier Scientific Pubhhing Company, Amsterdam - Printed in The Netherlands
417
MONITORING OF THE AIR QUALITY BY ANALYSIS OF BIOLOGICAL INDICATORS AND ACCUMULATORS R.A. IMPENS, T. PIRET, G. KOOKEN and A. BENKO Departement de Biologie VBgBtale, Facult6 des Sciences Agronomiques de l'Etat, Gembloux, B-5800 Belgique.
SUMMARY An
experimental network using indicator and accumulator plants for the recogni-
tion and monitoring of air pollutants effects was created in 1978.
Sixteen sites
were selected in three industrial areas (Liege, Charleroi, La Louviere) and in a rural area (Libramont) of Southern Belgium. The data on seven heavy metals (Pb, Cd, Ni, Zn, Fe, Mn, Cr) are given and interpreted from three points of view
-
:
variation of pollution levels, choice of plants as bioindicators, comparison between plant's reactions, heavy metals accumulation and the heavy metals' contents of deposit gauges.
INTRODUCTION Three different networks of permanent stations for monitoring air quality are established in Belgium. The oldest one was created by the Ministry of Public Health and is devoted to the survey of sulfur dioxide and smoke occurences.
It covers the territories of
Belgium and Luxembourg with about 2 3 0 stations ( 100 of them are located in big cities (ref. 1 ) . A second one is called as the National automatic air pollutants network, it is developed in the five biggest urban districts of Belgium. In 1972, a permanent network of continuously operating stations comprising 110 deposit gauges, distributed over 44 communes of the Meuse industrial basin, was set up by I.N.I.E.X.
(ref. 2 ) .
This initial network was later extended to other
industrial areas of Southern Belgium, with a programme including, as well as establishing the fall-out mass, the quantitative determination of certain marker or toxic substances in the deposited dust. In 1978, the Ministry of Public Health decided to study the methods for a biological surveillance o f air quality.
Our Laboratory was charged to create an
418
experimental network using indicator and accumulator plants for the recognition and monitoring of air pollutants effects. Plants as indicators are living objects, relatively sensitive to different compounds and they react in some more of less specific ways, showing very early and clearly internal and external changes, which may be relevant for other living organisms.
Examples of such networks in which indicator plants were exposed to
different situations on a national scale in the Netherlands prove that such method can be used to determine the pollution effect levels (ref. 3 ) . Our methods are based on rigorous standardization of plant material and cultivation conditions. Plants are proposed to be used as indicators in open air, to show acute injury by high concentrations of gaseous pollutants and some cultures in open air to accumulate heavy metals and fluorine compounds for analysis. This paper presents some of the results of the first two years of observation and analysis in three industrial regions (Liege, Charleroi and La Louviere) and in a rural area (Libramont) of Belgium.
EXPERIMENTAL METHODS The selected indicator plants present the following criteria
-
a high sensitivity to pollutants,
-
a good specificity of observed symptoms,
-
:
a great easiness to handle and to cultivate, an adequate period of vegetation, a short delay between exposition to air pollutants and the physiological reaction,
- well genetically fixed characters, etc. Seven species were choiced in 1978
-
:
Medicago sativa L. var. Du Puits (Lucern), Lolium multiflorum Lam, var. Optima (Italian rye grass), Zea mays L. (Corn) Anthriscus cerefolium (L.) (Hoffm.) (Chervil), Valerianella locusta (L.) (Betche) (Corn salad), Raphanus satins L. (Radish), Hypericum perforatum L. (St John's wort). These standardized and "same-age'' plants are grown in containers in a rural
area, and introduced in the 16 stations, where they will be exposed to air pollutants.
They are compared to soil seedlings of the same varieties.
The cultures follow one another every 28 days during the growth's season, in each of the 16 stations of the network.
Samples of leaves or roots are collected
419 at the end of each period of 28 days, before being analyzed (cfr. table 1) TABLE 1 Sample analysis Harvesting Drying Weighing Alcaline fusion
Calcination
Mineralisation
Automatic titration
Atomic absorption
Specific electrode
S
Pb, Cd, Zn, Fe, Mn, Ni, Cr
F-
RESULTS AND DISCUSSION In 1978, seven heavy metals (Pb, Cd, Ni, Zn, Fe, Mn, Cr) were analyzed during 8 periods of four weeks, giving about 5600 results.
from three points of view
The data were interpreted
:
- variation of pollution levels in the areas monitored by -
choice of plants as bioindicators,
-
comparison between plant
the network,
reactions, heavy metals accumulation and the data
collected in the Owen's gauges of the I.N.I.E.X. Results on SO2 effects and
S
network.
accumulation are reported in another paper (ref. 4)
as for Fluoride (ref. 5 ) . A. Pollution levels The first aims of ouc study is
-
:
to indicate the average contamination and recognize the predominating elements in each monitored site,
-
to warn us of any risk due to pollutant enrichment in the food chain. For each station and element, the average contaminations over a whole season
are reported as graphs (fig. 1 to 4 for Lolium multiflorum). These results show differences between the three industrial areas
:
with an im-
portant Pb, Zn and Cd contamination in the region of LiSge where zinc and cadmium factories are present (station E) and important concentration of Fe, (stations C and L) near iron smelters (Charleroi and La Louvisre).
Mn
and Cr
420
x lo3 b g Zn/g D.M.
‘g n.M.
P9
150
20
100
10
b C
50
I
x 11 r 0
kw
Ili
10
2
1
L0 rl
N e N
P 6i
m * m d ~ r n *m
w w wwwuuuvv
.+N m e
c-7 d A i l
-w
BB
r
t
rn ~q m ~N , m
crr0-m
w w ww wu u u u
m e
Ud 4 dil
Fig. 1 to 4. Average metal content of rye grass in the 16 stations o f the network.
The results with Pb are not so evident because of a general contamination due to the important traffic of vehicles in the different areas. B. Choice of plants We may compare the ability of our tested plant species as indicator or accumulator systems. Indicator plants show quickly clear and specific symptoms indicating the possible presence of some pollutant(s). termination of a pollutant.
The symptoms may lead to a qualitative de-
The reactions of the plants may also be measured
quantitatively to determine the effects intensities for monitoring. Accumulator species accumulate very easily air polluting compounds, which may be analyzed in the plant material, after an exposure's period, by physical or chemical methods, to get a recognition of the pollutant and a quantitative measurement of the pollution burden. The same plant species may be used as an indicator and a accumulator, both for fluorine compounds (e.9. tulips, gladioli and St Johns worts). We have compared our different tested plant species for their specific accumulation of heavy metals.
This accumulation is the resultant of uptake and
the mechanism of elimination, metabolism and internal transport. An accumulation's factor i.e. the ratio heavy metals content of plants in polluted or non polluted areas is calculated. For each contaminant one or two of our tested species are convenient, e.g. chervil is a good and quick accumulator of Cd. Another estimation of the accumulator's ability of these species is to compare the average content of each heavy metal in the different plant materials. By this way, Italian rye grass seems to be a good and faithfull accumulator, easier to handle than corn, Seeds are sown directly in the plant containers of the uniform cultivation system and plants are grown in non polluted area.
Cuttings are made regularly before
the grass cultures are exposed at the monitoring sites ( 2 plant containers per location).
After exposure period of 2 weeks, the rye-grass cultures are harvested
for analysis and replaced by new ones. Such systems using cultures of Italian rye-grass were used for the surveillance of fluoride and heavy metals in a monitoring network in the Ruhr area (ref. 6) and in the Meuse Valley (ref. 7).
422
C. Comparison between plants and Owen gauges In each of our 16 fields, there is a deposit gauge of the I.N.I.E.X. The following determinations are carried out on the gauge contents
- mass of the insoluble and -
network.
:
soluble matter,
mass of the cations of Fe, Cr, Zn, Pb, Cd, Ca and Hg in the insoluble matter, mass of the fluorides, nitrates, phosphates and sulphates in the soluble matter (ref. 2 ) . It seems interesting to find relationships between the results of these deter-
minations on rain water and the heavy metals and fluoride contents of plant tissues. As
an example, we find a good relationship between the contents of Zn in rain
water and in plant tissues (fig. 5).
Data for plants are the average contents
of Zn for the six plant species, in the 5 locations of the Meuse Valley.
But
the differences in the involved processes by the two methods of monitoring are great
:
gauges collect the general fall out, and plants react with selective ac-
cumulation of cations.
No strict correlation could be calculated between the
results of Owen gauges and the average accumulation of our six plant species (fig. 6). During the nextcoming months, we shall calculate, for each element and each location, a correlation between a global accumulator species (Italian rye grass) burden and the same results obtained by gauges.
Better correlations are
calculated for a given cation by its specific accumulator species (e.g. chervil for Cd).
x
Me RAIN
Me DUSTS
GAUGE
4
Me IN WATER
Me
Me
&
Absorption by leaves
PLANT
Leaching
Absorption by roots
4
Me IN PLANT TISSUE
Fig. 6. Comparison of Me (metals) contents in rainfull and i n plant-tissues.
423 WATER2
mg.m Zn 100
-1
.d
I
0
50
0
Fig. 5. Relationship between Zn content in rain water and in plants (Region of Liege). D. Discussion
In nearly all publications dealing with the technique of biological monitoring, plants are considered as an inexpensive and easy to handle substitute for chemical or physical methods.
However, the biological indicators could not survive in
the competition against the advantages of instrumental monitoring. Schonbeck et al. (ref. 8 ) , have been the first authors who stressed that effects observations cover a field of information, which by no other way can be provided. Biological indicators may give informations on
:
- the incidence of real effects of pollutants on living material,
-
the census of the potential emission's sources,
- the mapping of areas submitted to fall out and air pollution, - the prevention and the survey of pollutant enrichments in the food chain,
-
the calculation of damages caused to crops and live stock by accidental or chronical pollutions. We make a distinction between surveys in open country, the exposure of stan-
dards plants and the testing of immission samples in the laboratory. The use of the exposure of standards plants in regional surveys is practiced in three different industrial areas of Southern Belgium, it will be more efficient by the development and utilization of further indicators. Our aims should be to link up geographically with other Europeans partners (e.g. the Netherlands, Federal Republic of Germany and France), in order to obtain full area coverage on the pollution of ecosystems. REFERENCES 1 J. Bouquiaux et J. Grandjean. Le r6seau belge de mesure journaliGre de la pollution urbaine. OMS, in Colloque sur les climats urbains et la climatologie appliqu6e ii la construction. Bruxelles, octobre 1968, pp.12. 2 W. Duhameau and R. Noel. Five years of recording the atmospheric fall-out in the industrial region of Liige. Atmospheric pollution. Proc. 13rh Intern. C o l l . Paris, April 25-28 (1978) pp.29-32. 3 H. Floor and A.C. Posthumus (1977). Biological Erfassung von Ozon- und PANImmissionen in de Niederlanden (1973, 1974, 1975) VDI Berichte 270 : 183-190. 4 R. Impens, G. Kooken and E. Delcarte (19801. Etablissement et utilisation d'un reseau de plantes indicatrices de la pollution de l'air. Under press (Annales de Gembloux) 14 p. 5 R. Impens et R. Paul (1976). Mise en evidence d'une emission fluoree par observa*on et analyse de la vegetation. Mem. SOC. Roy. Bot. Belg. 7, 49-58. 6 G. Scholl (1974). Ermittlung iiber die Belastung der Vegetation durch Schwermetalle in verschiedene Immissionsgebieten. Staub-Reinhaltung der Luft 34, 89-92. 7 P. Mathy, T. Piret, G. Kooken and R. Impens (1979). Heavy metal contamination in the Meuse Valley (Belgium). In Intern. Conf. Management and Control of Heavy metal in the Environment. London (Sept.1979) : pp.226-229. 8 H. Schonbeck, M. Buck, H. Van Haut und G. Scholl (1970). Biologische Messverfahren fur Luftverunreinigungen. VDI-Berichte n0149 : 225-234.
Atmospheric Poftution 1980, Proceedings of the 14th International Colloquium, Paris, France, May 5-8,1980, M.M. Benarie (Ed.), Studies in Environmental Science, Volume 8 0 Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
425
PATTERNS OF FLUORIDE ACCUMULATION I N BOREAL FOREST SPECIES UNDER PERENNIAL EXPOSURE TO EMISSIONS FROM A PHOSPHORUS PLANT Sidhu
S.S.
Newfoundland F o r e s t Research Centre, Canadian F o r e s t r y Service, P.O.
Box 6028, S t . John's, Newfoundland, Canada, A1C 5x8
ABSTRACT The i n f o r m a t i o n i n t h i s paper r e l a t e s t o accumulation p a t t e r n s o f f l u o r i d e (F) i n f o l i a g e o f boreal f o r e s t species under p e r e n n i a l exposure t o emissions from a phosphorus p l a n t .
Regressional r e l a t i o n s h i p s o f f o l i a r F - l e v e l s t o long-term
average F-concentrations i n a i r a r e a l s o presented.
These r e l a t i o n s h i p s a r e used
t o p r e d i c t F - l e v e l s i n a i r corresponding t o f o l i a r F-accumulations which a r e cons i d e r e d s a f e f o r the h e a l t h o f p l a n t s and consuming animals. Accumulation o f f l u o r i d e i n balsam fir and o t h e r boreal c o n i f e r s reached i t s maximum a t the end o f second year o f exposure and f o l i a r F - l e v e l s s t a b i l i z e d thereafter.
P a t t e r n s and l e v e l s o f F-accumulation i n o t h e r boreal c o n i f e r s were s i m i l a r
t o those i n balsam fir.
A r e g r e s s i o n equation, Y = 1.89 X -1.41,
was d e r i v e d t o
express t h e r e l a t i o n s h i p o f F - l e v e l s i n f o l i a g e exposed f o r one year (X) t o those i n f o l i a g e exposed f o r 2 years ( Y ) .
T h i s d o u b l i n g o f f o l i a r F - l e v e l s i n 2 years
i s i m p o r t a n t t o be considered f o r e s t a b l i s h i n g a i r q u a l i t y standards s a f e f o r the 2 h e a l t h o f p l a n t s and consuming animals. An a i r c o n c e n t r a t i o n o f 37.4 p g F/dm / 30 days ( = 0.29 p g F/m 3 ) i s p r e d i c t e d t o r e s u l t i n 20 ppm o f F - l e v e l s i n f o l i a a e , r e p o r t e d t o be a s a f e l e v e l f o r p l a n t s and consuming animals.
This F - l e v e l i n a i r
compares reasonably w e l l w i t h t h e recomnended Canadian Standard o f 0.20 pg HF/m 3 average f o r 70-day exposure p e r i o d and 0.30 p g HF/m averaoe recormended by
3
IUFRO f o r one-year p e r i o d .
INTRODUCTION Excessive l e v e l s o f f l u o r i d e ( F ) accumulate i n f o l i a g e o f p l a n t s when exposed 3 t o above normal F-concentrations ( > 0.05 pg F/m ) i n a i r ( r e f . 1 ) . This phenomenon i s common i n t h e neighbourhood o f i n d u s t r i e s e m i t t i n g f l u o r i d e s from t h e i r stacks.
As a r e s u l t o f excessive f o l i a r accumulations,
i n j u r i e s ranging
from minor m e t a b o l i c d i s o r d e r s t o m o r t a l i t y i n p l a n t s have been r e p o r t e d ( r e f s .
2 & 3).
The accumulated f l u o r i d e becomes bound i n leaves which can be c o l l e c t e d and
426
analysed t o evaluate the F-concentration i n the a i r d u r i n g t h e i r exposure. The f o l i a r F-concentrations have been r e l a t e d d i r e c t l y t o the i n t e n s i t y o f damage t o vegetation, F - l e v e l s i n u r i n e and skeleton o f animals consuming vegetation growing under p o l l u t e d c o n d i t i o n s (refs. 4, 5, 6, 7, 8, 9). As a r e s u l t o f these r e l a t i o n s h i p s , a i r q u a l i t y standards safe f o r the h e a l t h and growth o f p l a n t s and consuming animals can be established. F l u o r i d e accumulations of 35-40 ppm ( d r y w t . basis) i n f o l i a g e are recommended t o be safe f o r consuming animals by S u t t i e ( r e f . 5) and Rose and Plarier ( r e f . 6 ) . However, based on a safe l e v e l o f 10 ppm of f l u o r i d e i n u r i n e ( r e f . 7), 20 ppm has been recommended as a safe l e v e l i n p l a n t s ( r e f s . 4 & 6 ) . I n most o f the s t u d i e s r e p o r t e d i n l i t e r a t u r e , r e s u l t s a r e based on short-term exposure o f p l a n t s t o F-polluted a i r .
The exposure o f f o l i a g e before harvesting was u s u a l l y s h o r t e r
than the maximum l i f e of the f o l i a g e ( u s u a l l y < 1 year).
The s i t u a t i o n i s e n t i r e l y d i f f e r e n t i n boreal f o r e s t s where the f o l i a g e o f dominant c o n i f e r s p e r s i s t s f o r 5-8 years and the same f o l i a g e i s exposed t o i n d u s t r i a l emissions year a f t e r year before i t s m o r t a l i t y o r n a t u r a l senescence.
I n v e s t i g a t i o n s were conducted on the f o l l o w i n g aspects: a ) F-accumulation i n f o l i a g e p e r e n n i a l l y exposed t o f l u o r i d e emissions, b) F-concentrations i n a i r a t which f o l i a r F-accumulations do n o t change s i g n i f i c a n t l y from c o n t r o l s under pere n n i a l exposure, and c ) F-concentrations i n a i r a t which f o l i a r F-concentrations do n o t exceed e s t a b l i s h e d o r proposed f o l i a r F - l e v e l s safe t o the h e a l t h o f p l a n t s and animals, and t h e r e s u l t s obtained a r e presented i n t h i s paper. METHODS Study area 2 An area o f approximately 700 km was included i n the study.
The f l u o r i d e
emission source was a phosphorus p l a n t l o c a t e d a t Long Harbour (47'26'N, Newfoundland.
53O47'W),
Major gaseous emissions from the p l a n t were hydrogen f l u o r i d e (HF) The f o r e s t s o f the area belong t o the Boreal
and s i 1 i c o n t e t r a f l u o r i d e ( S i F 4 ) .
F o r e s t (B.30, Avalon, Newfoundland) o f Rowe ( r e f . 10) dominated by balsam fir [Abies balsamea (L.) M i l l . ]
and black spruce [Picea mariana ( M i l l . ) ESP].
b i r c h [Betula p a p y r i f e r a Marsh.] and l a r c h
[ml a r i c i n a
minor component i n most f o r e s t stands i n t h e area.
White
(Du Roi) Koch] form a
D e t a i l s o f c l i m a t i c conditions,
vegetation, and i n d u s t r i a l emissions were published e a r l i e r ( r e f s . 8, 9, 11). F i f t e e n permanent a i r and f o l i a g e sampling p l o t s were located i n a sector northeast o f t h e emission source up t o
3
d i s t a n c e o f 20 km.
E a r l i e r study o f
F-accumulation i n a number o f p l a n t species revealed t h a t accumulation l e v e l s and p a t t e r n s a r e s i m i l a r i n balsam fir, black spruce, white spruce [Picea glauca (Moench) Voss],
l a r c h , w h i t e b i r c h and other deciduous species ( r e f s . 9, 10, 11).
Balsam fir was selected f o r d e t a i l e d s t u d i e s on the p a t t e r n s o f F-accumulation
421
because o f i t s dominance and wide d i s t r i b u t i o n i n the study area, d i s t i n c t development o f f l u o r i d e damage symptoms on i t s f o l i a g e and r e t e n t i o n o f i t s f o l i a g e on the t r e e s even a t h i g h F-accumulations. F i e l d sampling o f f o l i a g e and a i r samples Accumulation p a t t e r n over 4 years o f continuous exposure.
This p a r t o f the
study was r e s t r i c t e d t o 15 permanent p l o t s , 3 from each o f the 4 damage zones ( r e f . 12) and 3 from a c o n t r o l area. Ten t r e e s o f balsam fir were tagged f o r repeated c o l l e c t i o n o f f o l i a g e samples a t various i n t e r v a l s from 1974 t o 1977. A t each sampling time, 9 windward branches from 3 randomly selected trees i n each p l o t were sampled f o r 1974-foliage. Composite sample o f 27 branches was analysed f o r t o t a l f l u o r i d e and an average o f 3 p l o t s f o r each damage zone and a c o n t r o l area i s presented i n F i g u r e 1. A t a l l these permanent s t a t i o n s , F-concentrations i n a i r were monitored from 1 June t o 30 September a t weekly i n t e r v a l s d u r i n g 1976, 1977 and 1978, using Na-formate p l a t e s ( r e f . 9). D u p l i c a t e p l a t e s were hung from windward branches i n each p l o t f o r each sampling period. During the p e r i o d 1976 t o 1978, f o l i a g e exposed f o r one year and 2 years were c o l l e c t e d f o l l o w i n g the aforementioned procedure and analysed f o r t o t a l f l u o r i d e s . Comparison o f F-accumulations i n f o l i a g e exposed f o r 1 and 2 years.
Earlier
s t u d i e s i n the area ( r e f s . 8, 9) revealed doubling o f F-accumulations i n the f o l i a g e o f evergreens under continuous exposure t o F-emissions.
I n 1978, t o f u r t h e r t e s t
and c o n f i r m t h e hypothesis, 120 temporary f i e l d p l o t s were s e t up d i s t r i b u t e d 2 u n i f o r m l y over an area o f 700 km surrounding the emission source. A t each s t a t i o n , f o l i a g e exposed f o r 1 and 2 growing seasons (1977 and 1978-foliage) were sampled f o r chemical a n a l y s i s .
Bulk samples o f 27 branches from 3 sample trees
were c o l l e c t e d a t each s t a t i o n f o r each growth year separately. A i r a t these s t a t i o n s was monitored using Na-formate p l a t e s a t 30-day i n t e r v a l from June t o July, 1978. Chemical a n a l y s i s o f f o l i a r and a i r samples The f o l i a g e samples were d r i e d a t 7OoC a t l e a s t f o r 72 hours and ground t o pass through 40 mesh sieve. The ground samples were analysed f o r t o t a l f l u o r i d e s by methods used e a r l i e r by Sidhu ( r e f . 8).
One gram o f ground sample was s l u r r i e d
w i t h 2 m l o f 50% e t h y l alcohol and 0.02 g o f C a O ( a n a l y t i c a l grade) before subj e c t i n g t o ashing a t 475OC. I n t h e laboratory, exposed as w e l l as c o n t r o l unexposed Na-fomate p l a t e s were analysed f o r f l u o r i d e s ( r e f . 9 ) . The Na-formate p l a t e s data was expressed a s 2 3 ug F/dm /30 days and converted t o vg F/m u s i n g conversion equation established f o r t h e f i e l d c o n d i t i o n s by Sidhu ( r e f . 13).
428
RESULTS AND DISCUSSION F o l i a r F-accumulation under perennial exposure The r e s u l t s o f t h e study o f p a t t e r n s o f F-accumulation i n f o l i a g e o f balsam f i r exposed t o f l u o r i d e emissions continuously f o r 4 years a r e presented i n Figure 1. Over 58% o f the maximum f o l i a r F-accumulations a t the end o f 4-year exposure o f t h e same f o l i a g e t o f l u o r i d e emissions occurred d u r i n g the f i r s t growing season During the second year o f exposure, t h e r e was a 70-100%
(June t o September).
increase over the f i r s t year f o l i a r F-accumulations.
*
E!
250-
I-
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.
.
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.
.
.
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.
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.
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.
1974-1975
P
,
”
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.
.
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.
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.
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.
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.
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.
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1977BREAK
F i g . 1. Patterns o f f l u o r i d e accumulation i n 1974-foliage o f balsam fir from 4 damage zones ( r e f . 12) and a c o n t r o l area. L i t t l e change occurred i n t h e f o l i a r F - l e v e l s a f t e r the f a l l o f second year o f exposure o f balsam fir f o l i a g e and F-concentrations s t a b i l i z e d t h e r e a f t e r i n f l u o r i d e damaged as w e l l as c o n t r o l areas ( F i g . 1 ) . I n 1978, the average Fconcentrations were 273, 161, 79, 32 and 11 ppm i n the 1974-foliage o f balsam
f i r from damage zones 1, 2, 3, 4 and c o n t r o l areas r e s p e c t i v e l y . The p a t t e r n s o f accumulation i n o t h e r boreal c o n i f e r s were s i m i l a r t o t h a t i n For
balsam fir except t h a t the f i n a l f o l i a r F-concentrations were d i f f e r e n t .
example, f o l i a r F-concentrations were 10-30% lower i n black spruce and up t o 40% higher i n w h i t e spruce than i n balsam f i r .
However, the present study does
reveal t h a t maximum F-accumulation l e v e l s i n f o l i a g e o f boreal c o n i f e r s a r e reached a t t h e end o f second growing season under perennial exposure t o f l u o r i d e emissions.
The F-concentrations i n the 2-year exposed f o l i a g e was 1.9 times the
concentration i n f o l i a g e exposed f o r 1 year.
The process o f cumulative increase operated u n t i l t h e end o f second y e a r o f exposure. No s i g n i f i t a n t increase i n
429
f o l i a r F-levels occurred thereafter. The levels of accumulation in deciduous broadleaved species, such a s white birch, American ash [Sorbus americana Marsh.], speckled a l d e r [Alnus rugosa (Du Roi) Spreng.], sedges and grasses were maximum a t the end of f i r s t growing season and were 1.5 to 4 times the levels in balsam f i r ( r e f s . 8, 9 ) . This accumulation pattern i n deciduous boreal species i s similar t o t h a t in agriculture crops which a r e harvested 3-6 months a f t e r i n i t i a l exposure t o polluted atmosphere. The e a r l i e r studies by the author ( r e f s . 8, 9) indicated that increase i n Faccumulations from f i r s t t o second year was proportional t o levels of accumulation during the f i r s t year and F-concentration in the a i r . A comparison of the Faccumulation i n balsam f i r foliage exposed t o excessive fluorides i n a i r for 1 and 2 years i s presented i n Figure 2 and i s expressed i n the regression equation, Y = 1.89 X -1.41.
" r
--
1.89X 0.96
- 114
2.0 1.6
LOG
Y = 0.747
LOG
Y = 0.899
L O G V = 0.964
-
0.089X
(1976)
0.109 X
(1977)
0.111 X
(19781
3
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100
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200
FOLIAR F-CONCENTR&TION
250
-
300
350
400
I Y E I R EXPOSME
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-
4
6
DISTANCE
8
10
FROM
12
14
18
16
SOURCE
-
20
km
F i g . 2 . Relationship between F-concentrations (ppm, dry w t . basis) i n foliage of balsam f i r exposed f o r 1 and 2 years t o fluoride emissions from a phosphorus plant. 3 F i g . 3. Average F-concentrations in a i r ( u g F/m ) a t various NE-distances from the source i n years 1976 t o 1978.
Air Quality Standards s e t on the basis of accumulation patterns i n agriculture crops a n d deciduous vegetation need t o be re-examined in view of t h i s d o u b l i n g of accumulations in boreal conifers during the f i r s t 2 years of exposure to F-emissions. Based on the above regression equation, a i r quality standards s e t f o r presently accepted safe levels of 35 and 20 ppm ( r e f s . 4 , 5, 6, 14) will possibly r e s u l t in 65 and 36 pprn f o l i a r F-concentration i n conifers a f t e r 2-year or longer exposure t o F-polluted a i r . A serious consideration t o these findings on accumulation
430
patterns of fluoride i n conifers must be given f o r s e t t i n g u p Safe Air Quality Standards f o r fluoride emitting industries. Relationship between f l u o r i d e concentrations i n foliage and i n a i r Average F-concentration i n a i r from 1976 to 1978 did not a l t e r significantly (Fig. 3). The relationships between f o l i a r accumulations and a i r concentrations a r e presented i n Figures 4a and 4b.
~g W m ’
1.0
0.0
$
900’
UNITS O F X F/dml/30doy,
5 800.
P
r
700-
~ g F / d
a
5
-z
Y r
600-
0 >
Y
---
EQUATION 0.99 034X
+
0.96 0.99 0.96
+
44.04X
z 5 G
900
2.0
3.0
UNITS O F X 4 0 F/dml/30 days
000
40
Y r
5.0
6.0
8.0
7.0
--
EQUATION 0 6 6 X - 4.71 099
700
0
2
600
0 500-
e
400-
b
k
500 400
300
”z
200
0
100
Y
0 0 AV
200
400
(ZYRSI
F-CONC
800
600 IN AIR
-
*gF/dm2/30
1000 do*
Fig. 4 . Relationship between average F-concentrations in a i r and accumulation levels of fluoride i n foliage of balsam f i r a f t e r 1 and 2 con ecutive years of exposure to f l u 0 ide emissions from a phosphorus plant - p g F/m 3 values were derived from pg F/dm /30 days by equation reported e a r l i e r ( r e f . 13).
5
Solving f o r X, when Y1 year = Y2 years from regression equations in Fig. 4, one can conclude t h a t no significant difference i s expected in f o l i a r levels a f t e r exposure periods of one and two years a t an average a i r concentration of 2 3 18 p g F/dm /30 days ( = 0.15 pg F/m ) . A t this average F-concentration i n a i r , fluoride levels in f o l i a g e will remain a t levels comparable t o those in foliage from control samples, 7-8 ppm. Foliar fluoride levels have been variously related to v i s i b l e symptoms, a i r concentrations (dose), F-levels in urine, safe levels i n feed f o r c a t t l e and w i l d l i f e and defoliation i n plants ( r e f s . 2, 4, 5, 6 , 8, 10, 11, 15). Predicted values of F-concentrations i n a i r are given i n Table 1 f o r 3 f o l i a r fluoride levels recommended t o be safe f o r plants, f o r F-levels i n urine of c a t t l e and other e f f e c t s on consuming animals by various authors ( r e f s . 4, 5, 6 and 8 ) . Average F-levels of 20 and 35 ppm will accumulate in foliage of balsam f i r and
431
TABLE 1 Predicted values of f l u o r i d e concentrations i n a i r for three reported s a f e levels of f o l i a r F-accumulations.
Exposure Measure of period levels i n a i r
Predicted avg. a i r F-concentrations (+ C.L.)&’ f o r 3 s a f e levels!!/ of f o l i a r F-accumuTations 20 ppm 35 ppm 40 ppm
1 year
55.91 f.40.26
pg F/dm2/30 days 119 F/m3
2 years
pg F/dm2/30 days ug F/m3
0.43 f 0.31 37.44 t 2 3 . 6 8 0.29 2 0.18
100.03 f. 43.42 0.77
2
114.72 f 42.11
0.33
0.89 f 0.32
60.17 5 22.37 0.46 f 0.17
67.74 23.68 0.52 f 0.18
a ) C.L. = Confidence l i m i t s b) Based on references 4, 5, 6, and 8 o t h e r boreal c o n i f e r s f o r a 2-year exposure t o predicted a i r concentrations of 2 3 2 3 37.4 pg F/cbn /30 days ( = 0.29 pg F/m ) and 60.17 pg F/ch /30 days ( = 0.46 pg F/m ) r e s p e c t i v e l y (Table 1 ) . A d e t a i l e d examination of 2-year f i e l d data from pe‘rmanent monitoring s t a t i o n s with average concentrations of 5 0.29 pg F/m 3 revealed t h a t f l u o r i d e accumulations i n 2 years old balsam f i r needles were 5 20 ppm in f o l i a g e sample from 72% of these s t a t i o n s and between 20-35 ppm i n samples from the other 28% of s t a t i o n s . Considering a l l the s t a t i o n s where the f o l i a r F-accumulation 0.46 pg F/m 3 . levels were ( 3 5 ppm, average a i r concentrations were > 0.29 Results of a short-term (4-6 weeks) a i r and vegetation monitoring over 120 s t a t i o n s over an extensive f o r e s t area showed t h a t f o l i a r F-accumulations of 20, 35, and 40 ppm i n balsam f i r occurred a t F-concentrations i n a i r of 0.35, 0.95 and 1.15 3 pg F/m respectively. These values were considerably higher than those based on 2-year averages i n Table 1 and reminds us of the shortcomings and dangers of basing a i r q u a l i t y standards on short-term s t u d i e s . A t average F-concentrations of 37.4 pg F/m 3 ( = 0.29 ug F/m 3 ) f o r a 2-year exposure i n Table 1 , probably very l i g h t or no v i s i b l e F-damage symptoms will occur t o c o n i f e r s a s well a s deciduous boreal species. Average a i r concentrations a t 3 which no visual symptoms of F-damage occurred, were determined t o be 0.20 ug F/m for c o n i f e r s and 0.40 pg F/m 3 f o r deciduous species in an e a r l i e r study ( r e f . 8 ) . 3 The recommended Air Quality Standards of 0.20 pg HF/m f o r 70 days in Canada ( r e f . 15) and 0.30 pg HF/m3 f o r one year by IUFRO ( r e f . 16) compare well w i t h the predicted level of 0.29 pg F/m 3 ( = 0.30 pg HF/m 3 ) f o r 20 ppm of F-accumulation i n f o l i a g e f o r a 2-year exposure (Table 1 ) . These recommended l e v e l s a r e reasonably safe f o r the health and growth of plants and animals based on the information a v a i l a b l e a t this time.
432 REFERENCES 1 R.J. Thompson, T.B. McMullen and G.B. Morgan, J. A i r P o l l u t . Control Assoc., 2 1( 1 971 ) 484 -487. 2 L.H. Weinstein, 3. Occup. Med., 19(1977)49-78. 3 U.S. Nat. Acad. Sci., F l u o r i d e s , Comm. B i o l . E f f e c t s Atmos. P o l l u t . Div. Pled. Sci., Nat. Res. Council, Washington, 1971, 295 pp. 4 G.W. I s r a e l , Atmos. Environ., 8(1974)167-181. 5 J.W. S u t t i e , J. A i r P o l l u t . Control ASSOC., 19(1969)239-242. 6 Dyson Rose and J.R. Marier, Nat. Res. Council, Canada Publ. No. NRCC 16081(1977), 151 pp. 7 K.N. Burns i n C.F. M i l l s (Ed.), Trace Element Metabolism i n Animals, Proc. WAA/IBP I n t e r n a t . Symp. 1969, Scotland. Publ. by E. and S. Livingstone, London pp. 490-492. 8 S.S. Sidhu, Proc. 71st Ann. Meeting A i r P o l l u t . Control Assoc., June 25-30, 1978, Houston, Texas, Paper No. 78-24.7, p. 1-16. 9 S.S. Sidhu, Proc. 7 0 t h Ann. Meeting A i r P o l l u t . Control ASSOC., June 20-24, 1978, Toronto, Canada, Paper No. 30.2, p. 1-16. 10 J.S. Rowe. F o r e s t Regions o f Canada. Environ. Canada, Can. For. Serv., Publ. No. 1300, Ottawa, Canada. 1972. 11 L.K. Thompson, S.S. Sidhu and B.A. Roberts. Environ. P o l l u t . 18(1979)221-234. 12 S.S. Sidhu and B.A. Roberts, Environ. Canada, Can. For. Serv., Bi-Monthly Res. Notes, 32( 1976)29-31. 13 S.S. Sidhu, Environ. Canada, Can. For. Serv., Bi-Monthly Res. Notes 35( 1979) 10-1 1 14 R.M. Cooper, N.E. Cook, Jacques P i l o n and E.H. R e i l l y . A D i g e s t o f Environmental P o l l u t i o n L e g i s l a t i o n i n Canada, Canadian I n d u s t r i e s Ltd., Montreal, Canada, 1973. 15 Environment Canada, Canada Gazette Announcements - Clean A i r Act, Proposed N a t i o n a l Ambient A i r Q u a l i t y Objectives, P a r t I , Environ. Canada, Environ. P r o t e c t i o n Service, Ottawa, Canada, August 7, 1976. 16 IUFRO ( I n t . Union Forest. Res. Organizations), IUFRO NEWS 25(3/1979) supplement, S u b j e c t Group S2.09-00 R e s o l u t i o n on A i r Q u a l i t y Standards f o r t h e P r o t e c t i o n of Forests, IUFRO-Secretariat, Vienna, A u s t r i a .
.
Atmospheric Pollution 1980, Proceedings of the 14th International Colloquium, Paris, France, May 5-8,1980, M.M. Benarie (Ed.), Studies in Environmental Science, Volume 8 0 Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
433
CONTAMINATION OF EDIBLE PARTS OF SEVEN PLAET CROPS ANI) SOILS BY HEAVY METALS IN URBAN AREA BY A I R POLLUTION IN ALEXANDRIA DISTRICT, EGYPT
I.H. ELSOKKARY Soil & Water Sci. Dept., Faculty of Agric. Alexandria Univ.,Egypt.
ABSTRACT Contamination of the edible parts of wheat grains, roquette, radish, pepper, cabbage, parsley and jew's mallow grown in four soil site8 in Alexandria were investigated. The results showed high contamination of these plants and soils with Zn, Pb, Cd, Co and Hg. The sources of contamination are the vehicle exhaustes which acted along distance of 50 meter from roadside, and the industry fallout which was effective beyond 10 km from the source. Significat portions of these metals particulates were subject t o washing out from plants surfaces by water.
INTRODUCTION Work in recent years suggested marked accumulation of Cd, Ni, Pb and Zn in plants grown in soils close to heavily traffic highways (Ref. 2). That work drew the attention to the possibility of contamination of the environment with other heavy metals. The present work attempts a systematic investigation of the contamination of plants and soils by heavy metals at various cultivated sites in Alexandria district, Egypt. MATERIALS AND EYlETHGDS Plants and soils Alexandria district (Triticum sativum), (Raphanus sativus),
samples were taken from various sites in (Fig. 1). These plants included: wheat grains leaves of both roquette (Eruca sativa), radish cabbage (Brassica oleracea var capitata),
434
parsley (Petroselinum hortense) and Jew's mallow (Corchorus o l i t o r i u s ) and the fruit of pepper (Capsicum f r u t e s c e n s ) , Before a n a l y s i s , half of each plant sample was s i m p l y washed with tap water, then the two h a l f s were then separately dried a t 3 5 O C and digested w i t h HN03-HC104 acids mixture, Fe, Mn, Zn, Cu, Cd, Pb and Co were measured i n t h i s e x t r a c t by atomic absorption (Ref, 4). Hg was measured i n the HNO e x t r a c t by flameless atomic absorption. 3 Se w a s measured c o l o r i m e t r i c a l l y (Ref. 1). The DTPA-extractable metale from s o i l s were measured and defined as the available t o plants.
MEDITERRANEAN
SE
-
SCALE
0
1
1:lOO,OOO
-3 2
4-5km
Fig. 1- Location of the c u l t i v a t e d s i t e s i n Alexandria d i s t r i c t . RESULTS AND DISCUSSION
The mean values of metals i n the edible p a r t s of t h e plants grown i n s i t e 1 i n d i c a t e high l e v e l s of contamination by Zn, Pb, Cd, Co and H g and t o some extent w i t h Se (Table 1). The unwashed plants contained r e l a t i v e l y high l e v e l s of metals than those washed. Since a l l these p l a n t s a r e grown i n the same area, the data i n Table 1 give an idea about the effectiveness of t h e vehicle particul a t e deposition, which i s t h e main source of pollution i n s i t e 1,
435
on the c o n cen t ra t i o n of metals i n the various p l an t species. I n t h i s c as e , t h e s e p l a n t s showed d i f f e r e n t s u s c e p t i b i l i t y f o r metals abs o r p ti o n through t h e i r l e a v e s and consequently d i f f e r e n t r a t e s of metals accumulation c a p a c i t i e s. TABLE 1 The mean values of metals i n the p l a n t s ppm, a s influenced by ve hi cle exhaust ( S i t e 1).
P l a n t s p e c i e s and number of samples Metal
A
(9 )
cu
uw W uw W uw
zn
uw
Fe Mn
Pb Cd CO
W
W
uw W uw w uw W
-
31.4
27.3
20.2
0.9 0.19 0.38
10.3
Hg
uw W
0.023
Se
uw w
0.42
A: wheat g r a i n s
-
D: pepper G: Jew's mallow
D (12)
B (8)
C (7)
3650.0 1150.0 185.0 150.0
1350.0
260.0
1000.0
180.0
67.0 55.0 23.5 19.5 88.5 71.5 22.5 10.5 0.5
27.5 22.5 17.0 19.0 34.5 27.5 1.6
18.0
15.0 65.0 51.5 12.5 7.2 0.70
0.55 4 *3 1.6
-
-
B:
1.5
1.5
0.8
0.036 0.25
0.2
1.0 0.2 0.1
-
0.060
-0.12
ro q u e t t e
E: cabbage
UW: unwashed
E (10)
0.8
0.10
0.015
F
G
(12)
(20)
650.0 1750.0 180.0 55.0 45.0 65.0 35.0 47.5 13.8 19.0 17.0 8.8 52.0 80.0 65.0 36.5 14.5 38.0 8.0 19-0 0.65 0.35 0.20 0.45 0.4 1.9 1.3 0.1
460.0 400.0 78.0 69.0
0.15
0.020
-
0.055
-
0.28
22.0
20.5 35.0 32.0 10.5 6.0 0.25
0.10 1.1 0.5
0.25
0.060
C: r a d i s h F: p a r s l e y W: washed
The d a ta i n Table 2 suggest t h a t contamination of p l a n t s and s o i l s by Zn, Pb and Cd occur beyond a d i s t a n c e o f 50 meters from t h e highway ( s i t e 2 ) . Nearly 20-30!% of t h e deposited metals p a r t i c u l a t e s could be washed out from r a d i s h l eav es surfaces by water. Also, about 30-50$ of t h e s e metal p a r t i c u l a t e s a r e subjected t o washing from jew's mallow l e a v e s surfaces . Mostly, t h i s p o rt i o n i s h i g h i n p l a n t s grown a t d i s t a n c e c lo s e t o t h e roadside. Since these s o i l s a r e a l k a l i n e , i t i s expected t h a t t h e l e v e l s of a v a i l a b l e metals a r e below t h e adequate range req u i red by p l a n t s
436
(Ref. 3 ) . The d a t a i n Table 2 showed high l e v e l s of a v a i l a b l e a, Pb and Cd e s p e c i a l l y in soils c l o s e t o t h e roadside. This suggests t h a t t h e s e deposited metals p a r t i c u l a t e s on s o i l s u r f a c e could considered as a r e s e r v o i r for supplying p l a n t s w i t h metals even a t t h a t a l k a l i n e s o i l reaction. TABLE 2
The mean metal content i n t h e p l a n t s and DTPA-extratable-metala from t h e c u l t i v a t e d s o i l s i n r e l a t i o n t o t h e d i s t a n c e from roadside. Distance from road meters
S o i l DTPA-Metals PPm
Metals p l a n t c o n t e n t , ppm.
zn
uw
Pb
w
Cd
uw
w
uw
w
zn
Pb
Cd
32.0 30.0
24.0 20.0 19.5
0.80 0.60 0.50 0.52
0.55 0.50 0.40
0.25 0.12
0.07 0.06
0.11 0.06
0.03 0.01
14.5
0.45
2.8 2.7 1.4 0.6 0.5
0.05
0.01
18.0
0.65
0.20
16.5
0.40
10.4 11.0
0.40 0.35 0.30
0.05 0.05 0.04 0.01 0.01 0.01
Radish l e a v e s 100.0 100.0
5
10 20
88.5
77.5 75.0
30 40
82.5 81.0 80.0
71.0
72.0
22.5 16.5 14.5
14.5
0.45 0.35
Jew's mallow l e a v e s 5
125.0 121.5 85.0 72.0 60.0
10 20
30 40
57.0
50
85.4 85.0
80.6 68.0
5705 55.2
26.5 22.8 16.5 18.0
13.5 10.4
~--
17.0
17.5
0.45 0.35 0.30 0.40 0.20 0.25
0.45
3 .0 2.8 1.0
0.5 0.4 0.4
0.15 0.10 0.05 0.05 0.04 ~~
~~
I n t h e i n d u s t r i a l a r e a a t s i t e 3 (Table 31, a l l t h e jew's mallow Nearly samples a r e h i g h l y contaminated w i t h Zn, Fb, Cd and Co. 2O-3O% of metals p a r t i c u l a t e s a r e s u b j e c t e d t o washing out by water from jew's mallow l e a v e s surfaces. TABLE 3 The mean values of m e t a l s contents, ppm, i n 23 jew's mallow washed l e a v e s samples grown arround the i n d u s t r i a l c e n t e r i n s i t e 3.
zn -
UW W
57.5 43.0
- 99.8 - 81.5
Pb 12.5
9.0
- 47.5 - 32.0
co
Cd
0.35 0.15
- 0.80 - 0.65
0.90
0.75
-
-~
2.15
- 1.80
The d a t a i n Table 4 suggest t h a t contamination of p a r s l e y leaves w i t h Zn, Pb, Cd and Co could occur beyond a d i s t a n c e of about 10 lsm
437
from t h e e l e c t r i c power s t a t i o n . These metals a r e probably dispersed a s a e r o s o l s and are p o t e n t i a l l y capable of being transported over a g r e a t distance. High p o r t i o n of these metals p a r t i c u l a t e s a r e s u b j e c t t o washing o u t by water from p a r s e l y l e a v e s s u r f a c e s ( 40-6%)
.
TABLE 4
Metal c o n t e n t s , ppm, i n p a r s l e y p l a n t l e a v e s grown proximity an e l e c t r i c power s t a t i o n s a t s i t e 4 a s a f u n c t i o n of distance.
zn
Km
from E.P.S. 1
2
5 10
UW
86.0 90.0 76.5 84.5 60.0 72.0 52.0 48.0
Pb
co
Cd
W
uw
w
uw
w
uw
w
45.0
39.0 48.5
60.0 70.0 47.5
0.6 0.7 0.25 0.20 0.15 0.15 0.15 0.20
4.6 5.2 3.6 3.2 1.8 2.6 2.1 2.1
1.8
31.5 32.5 24.0
14.0 13.0 20.0
0.1
43.0
45.0 38.5 40.5
30.5 10.5 8.5
17.0 9.0 10.5 5.0 3.6
0.1 0.15 0.15 0.05 0.15
0.10 0.10
1.6 1.2 1.2 1.4 1.0 0.6 0.8
Generally, t h e r e s u l t s r e p o r t e d i n t h i s work show a marked accumulation of Zn, Pb, Cd, Co and Hg and t o some e x t e n t Se i n t o x i c l e v e l s t o p l a n t s (Ref. 3 ) . I n s p i t e of t h a t Fe, bfn, Zn and Cu d e f i c i e n c i e s i n p l a n t s grown i n s i m i l a r s o i l s a r e most common (Ref. 3 ) , air-borne p a r t i c u l a t e s from v e h i c l e o r i n d u s t r y could be considered r i c h s o u r c e s of some o r a l l of t h e s e metals. While t h e s e l a t e r f o u r metals are w e l l known t o be e s s e n t i a l f o r p l a n t s and human being, t h e o t h e r s : Pb, Cd, Coy Hg and Se a r e not known t o be e s s e n t i a l f o r most of l i v i n g organisms. Because these l a t e r metals a r e h e a l t h hazardous f o r human being, more s t u d i e s should be conducted. For example, t h e bread i s the most p r i n c i p l e food i n Egypt. Wheat grain6 c o n t a i n on t h e average 0.2 ppm Cd. A d a i l y d i e t of 500 gram wheat f l o u r could c o n t a i n n e a r l y 100 p g Cd. This r a t e of C d i n t a k e i n combination with those taken from o t h e r C d sources, i.e. vegetables, w i l l account f o r g r e a t e r d a i l y i n t a k e than the average (50 p g Cd p e r day) f o r i n d i v i d u a l s i n uncontaminated areas.
438
ACKNOWLEDGEMENTS The author wishes to express his thanks to Prof. Dr. S. LLg for his valuable suggestions and to the Norwegian Agency for International Development (NORAD) for the financial support of this work. REFERENCES 1. Elsokkary, I.H.
and A. Idien., Acta. Agric. Scand. 27 (1977)
2 85-288.
2. Elsokkary, I.H. Studies in Environ. Sci. Vol. 1. Atmos. Poll., 1.1. Benarie (Ed.), Proc., 13th, Inter. Collog., Paris. France,
April 25-28, 1978 Elsevier pp. 25-28. 3 . Elsokkary, I.H. and J. Llg. Beitrage Zur Trop. Landw. und Veterinarmedizin, In press (1979). 4. Oien, A. and K. Gjerdingen. Acta. Agric. Scand. 27 (1977) 67-70.
439 AUTHOR Anlauf K.G. Bacon J.K. B a r r i e L.A. Bauman S .E. Benarie M.M. Benech B. Benko A. Bennett M. Berk J.V. Blanchard J.D. Boegel M.L. Bonivento C. Boueres L.C.S. B o u r b i g o t Y.C. B r u l l P.M. B u i l t j e s P.J.H. B u r d e t t G. Carha rt R .A. Carmichael R.G. C a r o l l a J. Carson J.E. Carton B. Chen J.Y. Chuong B.T. Cosemans G. Darzi M. De Jong T.J.R.M. De Wiest F. Drufuca G. Dunn W.E. Elsokkary I . H . Evendi j k J. E. Fabries J.F. F e l l i n P. F i s h e r B.E.A. Flament P. Friedman W.C. Fronza G. G a i l l a r d A. Gavin P. Gentry J.W. Ghobadian A. G i u g l i a n o M. Goddard A.J.H. Gosman A.D. Gauesba t G. Gouldin F.C. Grehan G. Gui chard J. C. Haake K. Haberman S.A. Hal b r i t t e r G. Hansson H.C. H a r t e r C. Haup t R
.
Page 153,355 195 355 147 49,397 249 417 63 387 309 387 105 147 26 7 227 91 323 43 31 291 37 279 173 39 7 2 13 147 379 227 209 43 433 379 279 355 71 285 309 105 339 43 233,291,303 25 209 25 25 285 173 285 339 43 309 57 159 25
125
INDEX Page Henderson-Sel l e r s B. H o i t z J. H o l l o w e l l C.D. Horvath H. Impens R.A. K a i s e r G.D. Kasahara M. Kolb H. Kooken G. Kretzschmar J G. Kuhlman M.R. Lahaye J. Lamauve M. Lannefors H.O. Laurent D. Le Guen J.M. Leisen P. L e s l i e A.C.D. L i n S. Lusis M.A. Madelaine G. McLean W.J. McNider R.T. Metayer Y. Miksch R.R. M i l h e M. Mohnl H. Munn R.E. Muskens P.J.W.M. N a z a r o f f W .W. Nelson J.W. Neumann G. Nieuwstadt F.T.M. Olson M. Opiela H. Oven M.J. Park Y.O. Patterson R.M. Paulou J. P a v l i k R.E. Pechinger U. P e r r i n M.L. Peters K.L. Peyrous R. Petersen W.B. Pham Van Dinh P i c k e t t E.E. P i e l k e R.A. P i r e t T. P o l i c a s t r o A.J. Prado G. Preston R. Rigard J. Robins A.G. Rood A.P. Rooker S.J.
.
195 125 387 371 417 25 221 97 417 213 245 297 339 159 365 323 131 147 303 153 267,273 173 9 273 387 137 97 409 379 387 147 57 77 153 315 173 291 13,19 401 309 97 267 31 365 13,19 249 347 9 417 43 297 303 137 117 323 323
440
S a r t o r F.A. Sidhu S.S. Simmon P.B. Sobottka H. Sommers H. Spatola J.A. S p i c e r C.W. Spurny K.R. Steinberger E.H. S t e r n A.C. Stober W. Staubel H. Suess M.J. Sverdrup G.M. Takahashi K.
Page 189 425 13,19 109 125 233 181 315 165 3 315 239 361 245 221
Page Tohno S. T o n i e l l i A. Traynor G.W. Van Duuren H. Wastag M. W e i l l M. Weiss G. Werner R. Whiting R.G. Wiebe H.A. Wiedemann R. W i l l e k e K. Winchester J.W. Ziemer S.
221 105 387 77 43 285 315 97 347 153,355 257 309 147 43
