The Chemistry of Acid Rain - American Chemical Society

Chapter 16

Comparisons of Wet and Dry Deposition: The First Year of THal Dry Deposition Monitoring Β. B. Hicks, R. P. Hosker, Jr., and J. D. Womack1

Downloaded by PURDUE UNIV on May 26, 2018 | https://pubs.acs.org Publication Date: September 3, 1987 | doi: 10.1021/bk-1987-0349.ch016

National Oceanic and Atmospheric Administration, Atmospheric Turbulence and Diffusion Division, Post Office Box 2456, Oak Ridge, TN 37831 A trial program has been initiated to t e s t i n f e r e n t i a l methods f o r measuring dry d e p o s i t i o n . Although present c a p a b i l i t i e s are very l i m i t e d , preliminary r e s u l t s f o r s u l f u r deposition at a few selected locations confirm expectations that submicron p a r t i c l e deposition contributes f a r l e s s s u l f u r than does s u l f u r dioxide gas exchange at the surface. O v e r a l l , average t o t a l deposition of s u l f u r by dry mechanisms appears to be much the same as by wet deposition in the northeast, although the short-term difference can be large (in e i t h e r d i r e c t i o n ) at any p a r t i c u l a r l o c a t i o n . There i s no s i m p l e d e v i c e w h i c h enables t h e measurement o f d r y d e p o s i t i o n i n a manner as c o n v e n i e n t as f o r wet d e p o s i t i o n . Instead, c o m p a r a t i v e l y l e s s d i r e c t methods must be u s e d , none o f w h i c h i s f u l l y proven as y e t . F o r p a r t i c l e exchange, l e a f - w a s h i n g and t h r o u g h f a l l t e c h n i q u e s ( 1 ) c a n p r o v i d e measurements o f t h e accumulated d e p o s i t on n a t u r a l s u r f a c e s . L i k e w i s e , a c c u m u l a t i o n on snow s u r f a c e s can be sampled, and s u b j e c t e d t o subsequent c h e m i c a l a n a l y s i s . I t i s e v i d e n t , however, t h a t such methods o n l y a p p l y i n c e r t a i n c i r c u m stances. Budget t e c h n i q u e s a r e sometimes a d v o c a t e d , such as i n t h e case o f c a l i b r a t e d w a t e r s h e d s , b u t these have r a r e l y d e l i v e r e d unequivocal r e s u l t s . The d i f f i c u l t y t h a t a r i s e s i s t h a t t h e d r y d e p o s i t i o n must n e c e s s a r i l y be computed as t h e d i f f e r e n c e between p o o r l y determined i n - f l o w and o u t - f l o w measurements. These, and, a wide v a r i e t y o f o t h e r e x p e r i m e n t a l methods, have been r e v i e w e d elsewhere ( 2 ) . Few such t e c h n i q u e s a r e a p p l i c a b l e i n t h e case o f t r a c e gas exchange; i n s t e a d , m i c r o m e t e o r o l o g i c a l methods have r i s e n i n popularity. I n c o n c e p t , such methods e v a l u a t e t h e f l u x a c r o s s a p l a n e above t h e s u r f a c e r a t h e r t h a n t h e d e p o s i t i o n a t t h e s u r f a c e itself. C o n s i d e r a b l e care i s n e c e s s a r y t o ensure t h a t t h e f l u x e v a l u a t e d above t h e s u r f a c e i s t h e same as t h a t a t t h e s u r f a c e . This c o n s t r a i n t i s t h e reason f o r t h e w i d e l y acknowledged m i c r o m e t e o r o l o g i c a l r e q u i r e m e n t s f o r u n i f o r m c o n d i t i o n s , s u r f a c e homogeneity, and terrain simplicity. The most common m i c r o m e t e o r o l o g i c a l methods a r e e d d y - c o r r e l a t i o n and t h e i n t e r p r e t a t i o n o f g r a d i e n t s ( 2 ) . Of t h e s e 1

On assignment from Oak Ridge Associated Universities This chapter is not subject to U.S. copyright. Published 1987, American Chemical Society

Johnson et al.; The Chemistry of Acid Rain ACS Symposium Series; American Chemical Society: Washington, DC, 1987.


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two, e d d y - c o r r e l a t i o n i s p r e f e r r e d because i t p r o v i d e s a d i r e c t measurement of the t u r b u l e n t f l u x , whereas g r a d i e n t methods r e l y on the a v a i l a b i l i t y of an eddy d i f f u s i v i t y i n o r d e r t o y i e l d the d e s i r e d answers. T h i s eddy d i f f u s i v i t y i s f r e q u e n t l y d i f f i c u l t t o d e r i v e . I n g e n e r a l , the t u r b u l e n t exchange of t r a c e gas and a e r o s o l p a r t i c l e s cannot always be assumed t o be downwards. For many t r a c e g a s e s , the s u r f a c e c o n s t i t u t e s b o t h a source and a s i n k , l e a d i n g t o wide t e m p o r a l v a r i a t i o n s i n b o t h the d i r e c t i o n and the magnitude of the net exchange. For some c h e m i c a l s p e c i e s , however, the s u r f a c e can be assumed t o be a c o n t i n u i n g s i n k . Such s p e c i e s i n c l u d e s e v e r a l c h e m i c a l compounds of c u r r e n t i m p o r t a n c e , such as s u l f u r d i o x i d e , n i t r i c a c i d v a p o r , and ozone. I n such i n s t a n c e s , dry d e p o s i t i o n f l u x e s t o n a t u r a l s u r f a c e s can be i n f e r r e d from a i r c o n c e n t r a t i o n d a t a , p r o v i d e d a c c u r a t e e v a l u a t i o n s are a v a i l a b l e of the e f f i c i e n c y w i t h w h i c h the s u r f a c e scavenges p o l l u t a n t s from the a i r t o w h i c h i t i s exposed. T h i s s i m p l e approach i s the f o u n d a t i o n f o r the s o - c a l l e d c o n c e n t r a t i o n m o n i t o r i n g o r i n f e r e n t i a l method f o r a s s e s s i n g d r y deposition. The i n f e r e n t i a l method r e l i e s upon the a v a i l a b i l i t y of a c c u r a t e c o n c e n t r a t i o n d a t a and c o r r e s p o n d i n g d e p o s i t i o n v e l o c i t i e s . However, knowledge of these p r o p e r t i e s alone does not p e r m i t the d e s i r e d d e p o s i t i o n d a t a t o be computed. As an e x t e n s i o n of dry d e p o s i t i o n r e s e a r c h programs, a t r i a l network has been s e t up t o t e s t the i n f e r e n t i a l method. Here, the s c i e n t i f i c b a s i s f o r the network o p e r a t i o n w i l l be d i s c u s s e d , and p r e l i m i n a r y d a t a w i l l be p r e s e n t e d . T h e o r e t i c a l Foundations F i g u r e 1 p r e s e n t s an example of eddy f l u x d a t a from a r e c e n t i n t e n s i v e f i e l d program. The d i u r n a l c y c l e w h i c h i s c h a r a c t e r i s t i c o f most d e p o s i t i o n phenomena i s c l e a r l y e v i d e n t . I f the g o a l i s t o d e r i v e weekly averaged v a l u e s of dry d e p o s i t i o n , so as t o p a r a l l e l the weekly averaged wet d e p o s i t i o n d a t a produced by the N a t i o n a l Trends Network, t h e n two o p t i o n s are a v a i l a b l e . E i t h e r concent r a t i o n s and d e p o s i t i o n v e l o c i t i e s must be d e r i v e d w i t h s u f f i c i e n t t i m e r e s o l u t i o n t o r e s o l v e the d i u r n a l c y c l e , l e a d i n g t o an assessment of the weekly average as an i n t e g r a l of the time v a r y i n g p r o d u c t , or b o t h p r o p e r t i e s must be averaged over a s u f f i c i e n t l y l o n g time t h a t the average v a l u e s have s t a t i s t i c a l u n c e r t a i n t y s m a l l i n comparison t o the d i u r n a l c y c l e . Because of the c o s t of c h e m i c a l a n a l y s i s , the second a l t e r n a t i v e i s p r e f e r r e d , i f i t can be a p p l i e d w i t h o u t g r e a t l o s s of p r e c i s i o n . I t i s p a r t l y f o r t h i s r e a s o n t h a t a n e s t e d network o p e r a t i o n has been i n i t i a t e d . F i g u r e 2 shows the t r i a l network as i t i s p r e s e n t l y c o n f i g u r e d , i n c l u d i n g the s u p p o r t i n g sub-network of more i n t e n s i v e measurements i n t e n d e d t o p r o v i d e benchmark d a t a f o r t e s t i n g the i n f e r e n t i a l methods. At s t a t i o n s of t h i s s p e c i a l sub-network (the "CORE" n e t w o r k ) , d a t a are r e c o r d e d w i t h f i n e r time r e s o l u t i o n , and d e p o s i t i o n f l u x e s are measured u s i n g more d i r e c t measurement t e c h n i q u e s whenever p o s s i b l e . Measurement of D e p o s i t i o n V e l o c i t y E s t i m a t i o n of a p p r o p r i a t e d e p o s i t i o n v e l o c i t i e s r e q u i r e s balanced c o n s i d e r a t i o n of a l l of the f a c t o r s c o n t r o l l i n g the t r a n s f e r of the


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F i g u r e 1. An example o f a time sequence o f eddy f l u x measurements o f submicron s u l f a t e p a r t i c l e s , o b t a i n e d d u r i n g a r e c e n t s t u d y over a d e c i d u o u s f o r e s t a t Oak Ridge, TN. Note t h a t n e g a t i v e v a l u e s i n d i c a t e f l u x e s d i r e c t e d towards t h e ground, i . e . , d e p o s i t i o n .

F i g u r e 2. The NOAA d r y d e p o s i t i o n t r i a l network. Additional s t a t i o n s w i t h s i m i l a r g o a l s but w i t h expanded emphasis on a i r c h e m i s t r y a r e p r e s e n t l y b e i n g s e t up by 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, w i t h an i n i t i a l c o n c e n t r a t i o n o f e f f o r t i n the n o r t h e a s t .



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m a t e r i a l of i n t e r e s t . For some c h e m i c a l s p e c i e s t h a t a r e c a p t u r e d e f f i c i e n t l y upon c o n t a c t w i t h any n a t u r a l s u r f a c e ( s u c h as n i t r i c a c i d v a p o r ) , these f a c t o r s are l a r g e l y aerodynamic. Most d i s c u s s i o n of the s u b j e c t i d e n t i f i e s two major a t m o s p h e r i c r e s i s t a n c e components i n f l u e n c i n g t r a c e gas and submicron p a r t i c l e t r a n s f e r : an aerodynamic r e s i s t a n c e w h i c h i s c o n t r o l l e d by wind speed, s u r f a c e roughness, and a t m o s p h e r i c s t a b i l i t y , and a q u a s i - l a m i n a r boundary l a y e r r e s i s t a n c e w h i c h i s determined by s u r f a c e f r i c t i o n and the m o l e c u l a r d i f f u s i v i t y of the substance i n q u e s t i o n . B i o l o g i c a l r e s i s t a n c e s are i m p o r t a n t i n the case of gases l i k e s u l f u r d i o x i d e , w h i c h e n t e r p l a n t biomass through storoata. S u l f u r d i o x i d e i s known t o be t r a n s f e r r e d t o m e s o p h y l l i c t i s s u e i n much the same way as carbon d i o x i d e ( 3 ) . The p h o t o s y n t h e t i c a l l y - m e d i a t e d exchange p r o p e r t i e s of p l a n t s a r e t h e r e f o r e c r i t i c a l l y i m p o r t a n t . F i e l d experiments have shown t h a t n i t r o g e n d i o x i d e and ozone a r e t r a n s f e r r e d s i m i l a r l y , a l t h o u g h q u e s t i o n s c o n c e r n i n g the s o l u b i l i t y of these s p e c i e s and the c o r r e s p o n d i n g d i f f i c u l t i e s w i t h w h i c h they e n t e r moist m e s o p h y l l i c t i s s u e remain t o be answered. A l l of the many b i o l o g i c a l t r a n s f e r p r o c e s s e s combine t o determine a net s u r f a c e r e s i s t a n c e t o t r a n s f e r . E m p i r i c a l r e l a t i o n s h i p s can be used t o i n f e r s t o m a t a l r e s i s t a n c e from d a t a on p h o t o s y n t h e t i c a l l y a c t i v e r a d i a t i o n , water s t r e s s , temperature, a t m o s p h e r i c h u m i d i t y and carbon d i o x i d e l e v e l s . The r e s u l t i n g net s u r f a c e r e s i s t a n c e has been c o u p l e d w i t h m a t h e m a t i c a l d e s c r i p t i o n s of aerodynamic and b o u n d a r y - l a y e r r e s i s t a n c e s i n a " b i g l e a f " model d e r i v e d on the b a s i s of a g r i c u l t u r a l and f o r e s t meteorology l i t e r a t u r e ( 4 ) . At p r e s e n t , the b i g - l e a f model i s r e l a t i v e l y c o a r s e , p e r m i t t i n g a p p l i c a t i o n o n l y t o areas dominated by maize, soybeans, g r a s s , deciduous t r e e s , and c o n i f e r s . I n p r a c t i c e , t h i s b i g - l e a f s u r f a c e r e s i s t a n c e model i s an e n g i n e e r i n g t o o l designed f o r r o u t i n e a p p l i c a t i o n . A c o n s i d e r a b l y more s o p h i s t i c a t e d , m u l t i l e v e l canopy model has been developed f o r comparison purposes and t o guide the f u t u r e development of the b i g - l e a f component. D e t a i l s of b o t h the e n g i n e e r i n g b i g - l e a f model and the subcanopy model a r e p r e s e n t e d elsewhere ( 4 , 5 ) . Measurement of C o n c e n t r a t i o n A c c u r a t e measurement of a i r q u a l i t y i s a demanding but r e l a t i v e l y s t r a i g h t f o r w a r d c h e m i c a l t a s k . I n the p r e s e n t c o n t e x t , the measurement program i s c o m p l i c a t e d by the need t o o b t a i n d a t a i n remote l o c a t i o n s where c o n c e n t r a t i o n s a r e low. C o n c e n t r a t i o n s must be measured w i t h an a c c u r a c y s i m i l a r t o the d e r i v a t i o n of d e p o s i t i o n v e l o c i t i e s ( i . e . , p r o b a b l y of the o r d e r of ± 30%). There a r e , of c o u r s e , o t h e r uses f o r the c h e m i c a l d a t a f o r w h i c h g r e a t e r a c c u r a c y i s c e r t a i n l y warranted. As a c o n v e n i e n t g o a l t o guide the c h e m i c a l measurement program, an a c c u r a c y of ± 10% has been t a r g e t e d . S e v e r a l i n t e g r a l measurement methods were e v a l u a t e d i n the e a r l y s t a g e s of t h i s program. The w e t - c h e m i s t r y b u b b l e r system deployed i n Europe f o r remote measurement purposes cannot d i s t i n g u i s h d i f f e r e n t c h e m i c a l s p e c i e s . S i n c e the d e p o s i t i o n v e l o c i t y i s v e r y s p e c i e s dependent, c l e a r d i s t i n c t i o n among d i f f e r e n t c h e m i c a l s p e c i e s i s r e q u i r e d t o d e r i v e d r y d e p o s i t i o n r a t e s . F i l t e r p a c k methods have l i m i t a t i o n s as w e l l . At the 1982 T e c h n i c a l Committee meeting o f the N a t i o n a l Atmospheric D e p o s i t i o n Program, conducted i n S t . L o u i s , a


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f i l t e r p a c k method was recommended, p r o v i d e d m o d i f i c a t i o n s c o u l d be made t o r e s o l v e s e v e r a l p e r c e i v e d d i f f i c u l t i e s . The d e s i r e d f i l t e r p a c k system would p e r m i t s i m p l e measurement of submicron a e r o s o l p a r t i c l e s u s i n g a T e f l o n f i l t e r , d e t e c t i o n of n i t r i c a c i d vapor u s i n g a subsequent n y l o n f i l t e r , and measurement of s u l f u r d i o x i d e u s i n g a f i n a l f i l t e r doped w i t h p o t a s s i u m c a r b o n a t e ( o r a l t e r n a t i v e l y , p o t a s s i u m b i c a r b o n a t e , sodium c a r b o n a t e , or sodium bicarbonate). I t was recommended t h a t l a r g e p a r t i c l e s be e x c l u d e d f r o m the s a m p l i n g system, s i n c e t h e i r d e p o s i t i o n cannot be w e l l a d d r e s s e d u s i n g the i n f e r e n t i a l methods as they are now employed. A h o r i z o n t a l i n t a k e tube i s p r e s e n t l y b e i n g used t o p e r m i t l a r g e p a r t i c l e s t o s e t t l e b e f o r e the f i r s t f i l t e r of the f i l t e r p a c k i s e n c o u n t e r e d . A h e a t i n g element a l o n g t h i s tube r a i s e s the temperature of the a i r p a s s i n g t h r o u g h the t u b e , so as t o m a i n t a i n a n e a r - c o n s t a n t temperature a t the f i l t e r f a c e s ( t y p i c a l l y about 25 C). T h i s has e s s e n t i a l l y e l i m i n a t e d o c c a s i o n s of f i l t e r l i q u e f a c t i o n . I t i s acknowledged t h a t h e a t i n g the i n c o m i n g a i r s t r e a m w i l l have adverse consequences i n the case of some c h e m i c a l s p e c i e s . In p a r t i c u l a r , i t i s f e a r e d t h a t apparent n i t r i c a c i d c o n c e n t r a t i o n s w i l l be a f f e c t e d by the consequences of v o l a t i l i z a t i o n of ammonium n i t r a t e p a r t i c l e s , s h o u l d such p a r t i c l e s e x i s t i n the a i r b e i n g sampled. As y e t , t h e r e are i n s u f f i c i e n t d a t a t o address t h i s q u e s t i o n d i r e c t l y . The s e l f - r e g u l a t i n g h e a t e r a p p l i e s the g r e a t e s t temperature increment d u r i n g the c o l d e s t c o n d i t i o n s , so t h a t the t h e r m a l d i u r n a l c y c l e t o w h i c h the f i l t e r s are exposed i s s u b s t a n t i a l l y reduced. I n the c o n t e x t of n i t r i c a c i d vapor measurement, i t i s not y e t c l e a r whether the h e a t e r i s a net p o s i t i v e o r n e g a t i v e i n f l u e n c e . From the v i e w p o i n t of the v a l i d i t y of the s u l f u r d i o x i d e c o n c e n t r a t i o n s t h a t are o b t a i n e d , t h e r e i s no such doubt; the h e a t e r i s an advantage. S i t e Operations The c h e m i c a l sampler d e s c r i b e d above i s o p e r a t e d a t each of the s i t e s i n F i g u r e 2, a l o n g w i t h a s e t of m e t e o r o l o g i c a l and s u r f a c e s a m p l i n g d e v i c e s s e l e c t e d t o p r o v i d e d a t a from w h i c h d e p o s i t i o n v e l o c i t i e s can be d e r i v e d . The methods by w h i c h t h e s e d a t a are a n a l y z e d and d e t a i l s o f the measurements b e i n g made are g i v e n elsewhere ( 4 ) . I n p a r t i c u l a r , s e n s o r s have been d e p l o y e d t o d e t e c t when d e w f a l l , r a i n , e t c . cause the f o l i a g e t o be m o i s t e n e d . When the canopy i s wet, i t i s known t o be an improved s i n k f o r s u l f u r d i o x i d e . However, the magnitude of the e f f e c t on d e p o s i t i o n v e l o c i t y i s not y e t w e l l known. F i e l d s i t e o p e r a t o r s a r e r e q u i r e d t o s e r v i c e the equipment once e v e r y week, a t the same time as r e q u i r e d by wet d e p o s i t i o n n e t w o r k s . A t the time of t h i s w r i t i n g , d i s c u s s i o n s are t a k i n g p l a c e c o n c e r n i n g p o s s i b l e m o d i f i c a t i o n s t o b o t h the i n s t r u m e n t a t i o n and s a m p l i n g p r o t o c o l s used i n the i n i t i a l s t a g e s o f t h i s t r i a l network o p e r a t i o n . Results F i g u r e s 3, 4, and 5 i l l u s t r a t e month by month comparisons between wet and dry d e p o s i t i o n of s u l f u r , as d e r i v e d from the dry d e p o s i t i o n o p e r a t i o n d e s c r i b e d here and f r o m the p u b l i s h e d r e c o r d s of the MAP3S p r e c i p i t a t i o n c h e m i s t r y network. For the dry d e p o s i t i o n , i n f e r r e d v a l u e s of the d e p o s i t i o n of s u l f u r as s u l f u r d i o x i d e have been added



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F i g u r e 3. A comparison between d r y and wet d e p o s i t i o n r a t e s o f s u l f u r , as computed from t h e t r i a l d r y d e p o s i t i o n d a t a r e p o r t e d here and from r e c o r d s o f MAP3S p r e c i p i t a t i o n c h e m i s t r y network, f o r Oak R i d g e , Tennessee. Data a r e r e p o r t e d as average weekly v a l u e s , computed f o r each month.

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F i g u r e 4. As i n F i g u r e 3, b u t f o r S t a t e C o l l e g e ,

Pennsylvania.



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F i g u r e 5. As i n F i g u r e 3, b u t f o r W h i t e f a c e Mountain, New York.

F i g u r e 6. A comparison between weekly s u l f u r d e p o s i t i o n a s s o c i a t e d w i t h submicron p a r t i c l e s and t h e c o r r e s p o n d i n g d e p o s i t i o n r e s u l t i n g from s u l f u r d i o x i d e uptake a t t h e s u r f a c e .



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onto the v a l u e s deduced f o r the d e p o s i t i o n o f s u l f u r as submicron sulfate. F o r the wet d e p o s i t i o n , the t o t a l s u l f u r content of the p r e c i p i t a t i o n samples i s u s e d . Values are r e p o r t e d as the average weekly d e p o s i t i o n f o r each month. As y e t , the d a t a do not p e r m i t a c l e a r p i c t u r e o f the comparison between wet and d r y d e p o s i t i o n of s u l f u r . F o r some p e r i o d s , i t i s e v i d e n t t h a t d r y d e p o s i t i o n g r e a t l y exceeds w e t , but f o r o t h e r p e r i o d s the o p p o s i t e i s t r u e . A t t h i s t i m e , g e n e r a l i z a t i o n i s not p o s s i b l e , nor are the dry d e p o s i t i o n v a l u e s computed w i t h enough c o n f i d e n c e to w a r r a n t extended d i s c u s s i o n . I n p a r t i c u l a r , the d e r i v a t i o n of d r y d e p o s i t i o n assumes, f o r the moment, t h a t s u r f a c e s when w e t t e d behave as i f they were w e t t e d by r a i n f a l l ( t y p i c a l l y c o n t a i n i n g d i s s o l v e d S O 2 as a consequence o f t h e i r f a l l t h r o u g h the l o w e r atmosphere and hence a poor r e c e p t o r f o r d e p o s i t i n g S O 2 m o l e c u l e s ) , whereas i n r e a l i t y w e t t i n g by d e w f a l l w i l l cause an i n c r e a s e i n the s u l f u r d i o x i d e d e p o s i t i o n r a t e s . F o r t h i s r e a s o n , the d r y d e p o s i t i o n v a l u e s p l o t t e d i n F i g u r e s 3, 4, and 5 a r e viewed as u n d e r e s t i m a t e s , l i k e l y t o be i n c r e a s e d somewhat as the r e s u l t o f r e s e a r c h p r e s e n t l y under way. F i g u r e 6 i s a p l o t of p a r t i c u l a t e s u l f u r d e p o s i t i o n v e r s u s the gaseous component. I t i s o f t e n c l a i m e d t h a t the d e p o s i t i o n o f s u l f u r as submicron p a r t i c l e s i s s m a l l i n comparison t o the d e p o s i t i o n as gaseous s u l f u r d i o x i d e . I n s p e c t i o n o f the diagram r e v e a l s t h a t the p r e s e n t d a t a and a n a l y s i s are i n support of t h i s common c o n t e n t i o n . Conclusions I n the absence of some g e n e r a l t e c h n i q u e s u i t a b l e f o r m o n i t o r i n g d r y d e p o s i t i o n , i n f e r e n t i a l methods p r o v i d e a s o l u t i o n . The t r i a l network p r e s e n t l y i n p l a c e appears t o be o p e r a t i n g as e x p e c t e d . Weekly d a t a produced by t h i s network a l r e a d y r e v e a l the expected importance of d r y d e p o s i t i o n as a major c o n t r i b u t o r t o the net i n p u t o f a t m o s p h e r i c s u l f u r t o t e r r e s t r i a l ecosystems, and show the e x p e c t e d dominance o f gaseous i n p u t o v e r submicron p a r t i c l e d e p o s i t i o n . Acknowle dgment s T h i s work was supported by the N a t i o n a l Oceanic and A t m o s p h e r i c A d m i n i s t r a t i o n as a c o n t r i b u t i o n t o the N a t i o n a l A c i d P r e c i p i t a t i o n Assessment Program.

Literature Cited 1. Lindberg, S. L . , and R. C. Harriss, Water, Air and Soil Pollut. 16, 13 (1981). 2. Hicks, B. B., M. L. Wesely, and J. L. Durham, Critique of Methods to Measure Dry Deposition, EPA Workshop Summary, NTIS PB81-126443 (1980). 3. Chamberlain, A. C., Chapter 22 of "Atmospheric Sulfur Deposition," Ann Arbor Science, Ann Arbor, Michigan (1980). 4. Hicks, B. B., D. D. Baldocchi, R. P. Hosker Jr., B. A. Hutchison, R. T. McMillen, and L. C. Satterfield, NOAA Technical Memorandum, ERL/ARL-241 (1985). 5. Baldocchi, D. D., Β. B. Hicks, and P. Camara, ATDL 85/7, Atmos. Environ., in press (1986). RECEIVED May 13, 1987


The Chemistry of Acid Rain - American Chemical Society

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