Chapter 22
Pollutant Deposition in Radiation Fog 1
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Jed M. Waldman , Daniel J. Jacob , J. William Munger, and Michael R. Hoffmann
Downloaded by CORNELL UNIV on September 5, 2016 | http://pubs.acs.org Publication Date: September 3, 1987 | doi: 10.1021/bk-1987-0349.ch022
Department of Environmental Engineering Science, California Institute of Technology (138-78), Pasadena, CA 91125
A. study of atmospheric pollutant behavior was conducted in the southern San Joaquin Valley of California during periods of stagnation, both with and without dense fog. Measurements were made of gas-phase and aerosol pollutant concentrations, fogwater composition, and deposition of solutes to surrogate surfaces. Deposition rates for major species were 5 to 20 times greater during fogs compared to nonfoggy periods. Sulfate-ion deposition velocities measured during fog were 0.5 to 2 cm s . Rates measured for nitrate ion were generally 50% below those for sulfate, except for acidic fog (pH3 d) for valley air. -1
D e p o s i t i o n d u r i n g fog e p i s o d e s can make a s i g n i f i c a n t c o n t r i b u t i o n to the o v e r a l l f l u x o f p o l l u t a n t s i n c e r t a i n e c o s y s t e m s . Further more, when a t m o s p h e r i c s t a g n a t i o n p r e v e n t s normal v e n t i l a t i o n i n a r e g i o n , f o g d e p o s i t i o n may become t h e m a i n r o u t e o f p o l l u t a n t removal. Fogs c a n c o n s e q u e n t l y e x e r t dominant c o n t r o l over p o l l u t a n t l e v e l s i n c e r t a i n environments. The s o u t h e r n San J o a q u i n V a l l e y ( S J V ) o f C a l i f o r n i a i s a
'Current address: Department of Environmental & Community Medicine, UMDNJ-Robert Wood Johnson Medical School, Piscataway, NJ 08854 Current address: Center for Earth & Planetary Physics, Harvard University, Cambridge, MA 02138
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0097-6156/87/0349~0250$06.00/0 © 1987 American Chemical Society
Johnson et al.; The Chemistry of Acid Rain ACS Symposium Series; American Chemical Society: Washington, DC, 1987.
22.
WALDMAN ET AL.
Pollutant
Deposition
in Radiation
251
Fog
r e g i o n prone t o w i n t e r t i m e e p i s o d e s o f atmospheric s t a g n a t i o n . These l e a d t o e l e v a t e d p o l l u t a n t c o n c e n t r a t i o n s and/or dense, widespread f o g s . Major o i l - r e c o v e r y o p e r a t i o n s p l u s widespread a g r i c u l t u r a l and l i v e s t o c k f e e d i n g activités a r e i m p o r t a n t sources o f S 0 , Ν€χ, and NH . i n t h e v a l l e y . A m u l t i - f a c e t e d program o f f i e l d m o n i t o r i n g was conducted i n t h e SJV d u r i n g t h e w i n t e r 1984-85, f o c u s i n g on a s p e c t s o f p o l l u t a n t scavenging and removal i n t h e f o g ladden atmosphere. C o n c e n t r a t i o n s o f major s p e c i e s were measured i n gas, d r y a e r o s o l , and fogwater phases. In a d d i t i o n , d e p o s i t i o n a l f l u x e s were m o n i t o r e d by s u r r o g a t e - s u r f a c e methods. These measure ments were employed t o d i r e c t l y assess t h e magnitude o f enhanced removal r a t e s caused by f o g . Downloaded by CORNELL UNIV on September 5, 2016 | http://pubs.acs.org Publication Date: September 3, 1987 | doi: 10.1021/bk-1987-0349.ch022
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METHODS F i e l d m o n i t o r i n g was conducted a t two SJV s i t e s , B a k e r s f i e l d A i r p o r t and B u t t o n w i l l o w . Fogwater was sampled by event u s i n g r o t a t i n g - a r m c o l l e c t o r s (RAC) w i t h sampling i n t e r v a l s o f 1 t o 2 h . L i q u i d water c o n t e n t (LWC) v a l u e s were a v e r a g e d o v e r t h e f o g w a t e r s a m p l i n g i n t e r v a l s , c a l c u l a t e d from t h e r a t e o f RAC c o l l e c t i o n . Atmospheric c o n c e n t r a t i o n s o f a e r o s o l , n i t r i c a c i d and ammonia were monitored u s i n g d u a l - f i l t e r methods. T o t a l a e r o s o l samples were c o l l e c t e d on open-faced T e f l o n f i l t e r s operated s i d e - b y - s i d e . N y l o n f i l t e r s and g l a s s - f i b e r f i l t e r s impregnated w i t h o x a l i c a c i d c o l l e c t e d HN0 (g) and N H ( g ) , r e s p e c t i v e l y . Samplers were r u n t w i c e d a i l y (0000 t o 0400 and 1200 t o 1600 P S T ) , except d u r i n g f o g e p i s o d e s , when they were r u n c o n t i n u o u s l y f o r 2 t o 4-h i n t e r v a l s . Further d e t a i l s of sampling methods and s i t e s a r e g i v e n elsewhere ( 1 , 2 ) . 3
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P o l y s t y r e n e p e t r i d i s h e s (154 cm ) w i t h t h e i r l i p (1.2 cm) upwards were deployed t o c o n t i n u o u s l y m o n i t o r f o g and d r y p a r t i c l e deposition. These were changed t w i c e p e r day (0800 and 1600 PST) d u r i n g nonfoggy p e r i o d s o r , more f r e q u e n t l y d u r i n g f o g , c o n c u r r e n t to f i l t e r sampling i n t e r v a l s . P e t r i d i s h e s (PD) were e x t r a c t e d w i t h 10 mL o f d i s t i l l e d , d e - i o n i z e d water immediately f o l l o w i n g t h e end of ambient e x p o s u r e . Subsequent e x t r a c t i o n s i n d i c a t e d t h a t complete r e c o v e r y (i.e.,>90%) was a c h i e v e d . S i d e - b y - s i d e sample comparisons were i n good agreement· The use o f s u r r o g a t e s u r f a c e s t o measure d e p o s i t i o n r a t e s remains c o n t r o v e r s i a l due t o t h e u n c e r t a i n t y i n e x t r a p o l a t i n g these r e s u l t s t o n a t u r a l surfaces, e s p e c i a l l y regarding deposition of gases o r submicron a e r o s o l ( 3 ) . The c o n d i t i o n s i n t h e SJV d u r i n g the f o g / a e r o s o l study a l l o w e d us t o a p p l y s i m p l i f y i n g assumptions regarding t h e dominant d e p o s i t i o n p r o c e s s e s . The v a l l e y i s u n i f o r m l y f l a t , and over 85% o f t h e s u r f a c e cover i s open c r o p l a n d or rangeland. There i s m i n i m a l canopy s t r u c t u r e , e s p e c i a l l y d u r i n g wintertime. On a r e g i o n a l s c a l e , t h e t e r r a i n i s r e l a t i v e l y sparse and r a t h e r i n e f f i c i e n t f o r i m p a c t i o n . Furthermore, winds i n the_SJV u n d e r s t a g n a n t c o n d i t i o n s a r e u s u a l l y q u i t e l i g h t (
