17 Sources of Airborne Calcium in Rural
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Central Illinois DONALD F. GATZ, G A R Y J. STENSLAND, and MICHAEL V . MILLER Atmospheric Chemistry Section, Illinois State Water Survey, P.O. Box 5050, Station A , Champaign, IL 61820 ALISTAIR C. D. LESLIE Department of Oceanography, Florida State University, Tallahassee, F L 32305 In a search for sources o f alkaline m a t e r i a l s i n r u r a l air and rain, we have sampled and performed multi-element analyses on ambient particulate matter and p o t e n t i a l source m a t e r i a l s . Ambient a e r o s o l s were sampled daily u s i n g s i n g l e N u c l e p o r e ™ filters or F l o r i d a State U n i v e r s i t y " s t r e a k e r s . " Samples of soil and unpaved road m a t e r i a l s were a l s o coll e c t e d and a n a l y z e d . The samples were analyzed by v a r i o u s multi-element methods, i n c l u d i n g i o n -and proton-induced X-ray emission and X-ray f l u o r escence, as w e l l as by atomic absorption s p e c t r o photometry. V i s u a l o b s e r v a t i o n s , as w e l l as airborne elemental c o n c e n t r a t i o n distributions with wind direction and elemental abundances in aerosols and source m a t e r i a l s , suggested that soil and road dust both c o n t r i b u t e to airborne Ca. F a c t o r a n a l y s i s was able to i d e n t i f y o n l y a "crustal" source, but a simple mass balance suggested that roads are the major source o f Ca in rural c e n t r a l Illinois in summer. The s o u r c e s o f p a r t i c l e s i n t h e a t m o s p h e r e a r e o f much current i n t e r e s t . T h i s i s t r u e from t h e v i e w p o i n t o f b o t h t h e g e o - a t m o s p h e r i c s c i e n t i s t and t h e p o l l u t i o n c o n t r o l specialist. For the atmospheric chemist o r geochemist, the i d e n t i t i e s and t h e r e l a t i v e c o n t r i b u t i o n s o f s o u r c e s a r e i m p o r t a n t f o r u n d e r s t a n d i n g 1) a t m o s p h e r i c e l e m e n t c y c l e s and b u d g e t s , and 2) t h e c h e m i c a l c o n t e n t o f p r e c i p i t a t i o n . The p o l l u t i o n c o n t r o l d e c i s i o n - m a k e r must know t h e r e l a t i v e c o n t r i b u t i o n s o f n a t u r a l and s p e c i f i c man-made s o u r c e s o f t o x i c m a t e r i a l s i n order to e s t a b l i s h c r i t e r i a f o r c o n t r o l regulations. The o b j e c t i v e o f t h i s work was t o i d e n t i f y c a l c i u m s o u r c e s and t h e i r r e l a t i v e c o n t r i b u t i o n s i n r u r a l c e n t r a l I l l i n o i s as a step toward understanding the r o l e o f a i r b o r n e a l k a l i n e 0097-6156/81/0167-0303$05.75/0 © 1981 A m e r i c a n C h e m i c a l Society
Macias and Hopke; Atmospheric Aerosol ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
ATMOSPHERIC
304
AEROSOL
materials i n l o c a l p r e c i p i t a t i o n chemistry. The a p p r o a c h was one o f f i e l d c o l l e c t i o n o f a m b i e n t a e r o s o l s and s o u r c e mat e r i a l s f o l l o w e d by measurement o f t h e i r c h e m i c a l c o m p o s i t i o n . The d a t a w e r e i n t e r p r e t e d u s i n g a v a r i e t y o f methods i n c l u d i n g examination of element c o n c e n t r a t i o n v a r i a t i o n s w i t h wind d i r e c t i o n , f a c t o r a n a l y s e s , and c h e m i c a l e l e m e n t b a l a n c e s .
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Procedures Samples o f a m b i e n t a e r o s o l and s o u r c e m a t e r i a l s w e r e c o l l e c t e d d u r i n g t h e summer and f a l l o f 1978 a t t h e W a t e r S u r v e y ' s a t m o s p h e r i c c h e m i s t r y s a m p l i n g s i t e , 10 km s o u t h w e s t o f Champaign-Urbana, I l l i n o i s . A map o f t h e i m m e d i a t e v i c i n i t y o f t h e s a m p l i n g s i t e i s shown i n F i g u r e 1. The g r o u n d s i t e i s a g r a s s y f i e l d , m e a s u r i n g 120 χ 240 m and s u r r o u n d e d by c o r n and s o y b e a n f i e l d s . The tower u s e d f o r s a m p l i n g i s 35 m h i g h and l o c a t e d 360 m t o t h e s o u t h e a s t of the ground s i t e . A l t h o u g h t h e two s i t e s a r e n o t c o i n c i d e n t , we e x p e c t c o n d i t i o n s on t h e t o w e r t o be r e p r e s e n t a t i v e o f t h o s e 35 m above t h e g r o u n d s i t e , e x c e p t on r a r e and b r i e f o c c a s i o n s when t h e t o p o f t h e t o w e r i s i n t h e plume f r o m a t r a c t o r engaged i n t i l l i n g o r h a r v e s t i n g o p e r a t i o n s . A m b i e n t A e r o s o l s . A e r o s o l s w e r e sampled b o t h c o n t i n u o u s l y , u s i n g F l o r i d a S t a t e U n i v e r s i t y " s t r e a k e r " s a m p l e r s ( 1 ) , and on a d a i l y b a s i s . The s t r e a k e r s a m p l e r s draw a i r t h r o u g h a s t r i p o f 0.4 ym p o r e d i a m e t e r N u c l e p o r e ™ f i l t e r e x p o s e d f a c e downward. The s a m p l e r u s e s a vacuum o r i f i c e w h i c h moves t h e l e n g t h o f t h e s t r i p o f f i l t e r a t a r a t e o f 1 mm h r " ^ , t h u s p r o v i d i n g one week's sample i n a " s t r e a k " 168 mm l o n g . We o p e r a t e d one s t r e a k e r s a m p l e r a b o u t 1 m above a g r a s s y f i e l d a t o u r g r o u n d s i t e ( F i g u r e 1) and a n o t h e r on t o p o f t h e t o w e r d e s c r i b e d a b o v e . Samples w e r e a n a l y z e d i n 2-hr t i m e i n c r e m e n t s u s i n g p r o t o n i n d u c e d X - r a y e m i s s i o n ( P I X E ) (2) a t F l o r i d a State University. D a i l y 1 2 - h r f i l t e r s a m p l e s w e r e c o l l e c t e d on p r e w e i g h e d 37 mm d i a m e t e r N u c l e p o r e ™ f i l t e r s w i t h 0.8 ym p o r e d i a m e t e r s . These f i l t e r s were r e - w e i g h e d a f t e r s a m p l i n g t o o b t a i n t o t a l p a r t i c l e mass. T o t a l mass was u s e d as t h e b a s i s o f t h e e l e m e n t a l mass f r a c t i o n s d e s c r i b e d l a t e r , and i s known t o w i t h i n a few percent. One s e t o f f i l t e r s was c o l l e c t e d f a c e down u n d e r an i n v e r t e d f u n n e l r a i n s h i e l d a b o u t 1.5 m above g r a s s . Another s e t was c o l l e c t e d i n a s p e c i a l l y - m a d e d e v i c e we c a l l a v a n e sampler. I t c o n s i s t s of a p l a s t i c ( p o l y v i n y l c h l o r i d e ) t u b e w i t h a g r a d u a l 90° bend and a c o n s t r i c t e d o p e n i n g designed to provide q u a s i - i s o k i n e t i c sampling of p a r t i c l e s a t w i n d s p e e d s o f a b o u t 4 m sec""^-. I t i s p r o v i d e d w i t h a t a i l f i n and i s f r e e t o r o t a t e a b o u t a v e r t i c a l a x i s , so i t a l w a y s f a c e s i n t o t h e w i n d . E l e m e n t a l a n a l y s i s o f t h e s e f i l t e r s was performed a t Crocker Nuclear L a b o r a t o r y , U n i v e r s i t y of
Macias and Hopke; Atmospheric Aerosol ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
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GATZ E T A L .
-WASHED
Sources
of Airbourne
Calcium
in
Illinois
305
GRAVEL-
, TAR & CRUSHED
h i CLOSED BRIDGE WEAK
/ U - T A R & CRUSHED
'/X TOWER SITE
LIMESTONE
I CRUSHED
'
ONE LANE
CONCRETE
ONE LANE
BLACKTOP
LIMESTONE
.CRUSHED
L .
"T TAR & WASHED
LIMESTONE
GROUND SITEi
LIMESTONE
ONE LANE CONCRETE, ONE LANE TAR & CRUSHED LIMESTONE
GRAVELl
-ONE
MILEx
T W O
LANES CONCRETE
Figure 1. Map of the sampling site and the surrounding area showing ground and tower sampling sites and road surface characteristics. During the growing season the area is planted exclusively in corn and soybeans.
Macias and Hopke; Atmospheric Aerosol ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
ATMOSPHERIC
306
AEROSOL
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C a l i f o r n i a - D a v i s , u s i n g i o n - e x c i t e d X-ray f l u o r e s c e n c e ( 3 , 4 ) . F u r t h e r d e t a i l s o f t h e d a i l y N u c l e p o r e ™ s a m p l i n g and a n a l y s i s p r o c e d u r e s w e r e g i v e n i n an e a r l i e r p u b l i c a t i o n ( 5 ) . H o u r l y w i n d d i r e c t i o n s w e r e o b t a i n e d f r o m measurements made by F e d e r a l A v i a t i o n A g e n c y p e r s o n n e l 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 W i l l a r d A i r p o r t , a b o u t 8 km e a s t o f t h e s a m p l i n g site. Source M a t e r i a l s . Two c a t e g o r i e s o f l o c a l s o u r c e m a t e r i a l s w e r e s a m p l e d - r o a d d u s t and s o i l . Samples o f b u l k s o i l w e r e removed f r o m t h e u p p e r 1 0 cm o f t h e s o i l c o l u m n a t 74 l o c a t i o n s o v e r p o r t i o n s o f t h e 1 km c e n t e r e d on t h e g r o u n d s i t e . A square g r i d s p a c i n g of 160 m ( 0 . 1 0 mi) between sampling l o c a t i o n s was u s e d . B e f o r e a n a l y s i s , the samples were a i r d r i e d , c r u s h e d , and s i e v e d t o remove t h e l a r g e r p a r t i c l e s (>53 ym d i a m e t e r ) w h i c h w o u l d n o t be l i k e l y t o be r a i s e d by t h e w i n d . Road m a t e r i a l s w e r e g a t h e r e d f r o m 9 l o c a t i o n s on u n p a v e d roads i n the v i c i n i t y of the sampling s i t e . At each l o c a t i o n , d u s t f r o m t h e r o a d b e d was s c r a p e d i n t o a p o l y e t h y l e n e s a m p l e bag f r o m 5 o r more s p o t s o v e r a 1 0 m a r e a . T h e s e m a t e r i a l s w e r e a l s o a i r d r i e d and s i e v e d i d e n t i c a l l y t o t h e s o i l m a t e r i a l s , but not crushed. V i s u a l i n s p e c t i o n s of the road s u r f a c e suggested t h a t samples from 8 of the 9 s i t e s were p r i m a r i l y c r u s h e d l i m e s t o n e r o c k . The r e m a i n i n g s i t e c o n s i s t e d p r i m a r i l y o f washed g r a v e l d e r i v e d f r o m g l a c i a l d e p o s i t s . An i n v e n t o r y o f u n p a v e d r o a d s u r f a c e m a t e r i a l s w i t h i n 5 km o f t h e s a m p l i n g s i t e i n d i c a t e d t h a t a p p r o x i m a t e l y 80% c o n s i s t e d o f c r u s h e d limestone. A n a l y s i s o f b o t h s o i l and r o a d d u s t f o r A l , S i , K, T i , and Fe was p e r f o r m e d a t t h e I l l i n o i s S t a t e G e o l o g i c a l S u r v e y , u s i n g X-ray f l u o r e s c e n c e techniques ( 6 ) . Ca and Κ w e r e d e t e r mined a t the Water Survey by a t o m i c a b s o r p t i o n s p e c t r o p h o t o m e t r y (AAS) f o l l o w i n g L 1 B O 3 f u s i o n t o d i s o l v e t h e s a m p l e Ç7, 8). The Κ a n a l y s e s e m p l o y e d a n a i r / a c e t y l e n e f l a m e , b u t i t was f o u n d n e c e s s a r y t o u s e ^ O / a c e t y l e n e f o r a c c u r a t e r e s u l t s on Ca. A s e r i e s of four standard s o i l s , which are c e r t i f i e d r e f e r e n c e m a t e r i a l s f r o m t h e Canada C e n t r e f o r M i n e r a l and E n e r g y T e c h n o l o g y , O t t a w a , was a n a l y z e d by t h e A A S / f u s i o n p r o c e d u r e t o a s s u r e t h a t i t gave s a t i s f a c t o r y r e s u l t s . Excellent a g r e e m e n t w i t h recommended v a l u e s was o b t a i n e d . I n t e r c a l i b r a t i o n o f t h e two l a b o r a t o r i e s u s e d f o r t h e s o u r c e m a t e r i a l s a n a l y s e s was a c c o m p l i s h e d b y t h e p a r a l l e l a n a l y s e s o f K. Again, e x c e l l e n t a g r e e m e n t was a c h i e v e d . 2
2
F a c t o r A n a l y s e s . A n a l y s e s were c a r r i e d o u t on e l e m e n t a l c o n c e n t r a t i o n s i n a i r (ng m~^), o r e l e m e n t a l a b u n d a n c e s ( p e r c e n t o f t o t a l mass). B o t h k i n d s o f d a t a were s t a n d a r d i z e d by sub t r a c t i n g t h e e l e m e n t mean f r o m t h e o b s e r v e d v a l u e and d i v i d i n g by t h e e l e m e n t s t a n d a r d d e v i a t i o n . Computations were c a r r i e d o u t u s i n g t h e f a c t o r a n a l y s i s p r o g r a m f r o m t h e BMDP B i o m e d i c a l
Macias and Hopke; Atmospheric Aerosol ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
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17.
GATZ E T AL.
Sources
of
Airbourne
Calcium
in
Illinois
307
Computer P r o g r a m s ( 9 ) . I n i t i a l f a c t o r s w e r e e x t r a c t e d u s i n g a p r i n c i p a l components s o l u t i o n . The number o f f a c t o r s t o be k e p t f o r r o t a t i o n t o a f i n a l s o l u t i o n was s e l e c t e d f r o m a p l o t o f t h e v a r i a n c e e x p l a i n e d by e a c h f a c t o r ( i t s e i g e n v a l u e ) v e r s u s i t s o r d i n a l number. U s u a l l y , f a c t o r s w i t h e i g e n v a l u e s l a r g e r t h a n a b o u t 1.0 w e r e k e p t . F i n a l s o l u t i o n s w e r e o b t a i n e d u s i n g Varimax r o t a t i o n s . R e s u l t s a r e p r e s e n t e d i n terms o f t a b l e s o f " l o a d i n g s . " L o a d i n g s a r e c o r r e l a t i o n c o e f f i c i e n t s b e t w e e n v a r i a b l e s and factors. T h u s , e l e m e n t s w i t h h i g h l o a d i n g s on t h e same f a c t o r t e n d t o v a r y i n a p a r a l l e l manner and may o f t e n be i n f e r r e d t o have common s o u r c e s . The sum, a c r o s s t h e f a c t o r s , o f t h e s q u a r e s o f t h e l o a d i n g s , i s c a l l e d t h e c o m m u n a l i t y , and i n d i c a t e s t h e f r a c t i o n o f an e l e m e n t s t o t a l v a r i a n c e t h a t i s a c c o u n t e d f o r by a l l t h e f a c t o r s . 1
Chemical Element general relationship
Balances.
The method i s b a s e d on
the
P. = Σ p.. C. ι . i j J
, (1) 1 N
w h i c h e x p r e s s e s t h e p e r c e n t a g e P^ o f any e l e m e n t i i n t h e a e r o s o l as a sum o f t e r m s i n v o l v i n g P j 4 , t h e p e r c e n t o f e l e m e n t i i n t h e p a r t i c u l a t e m a t t e r e m i t t e d by s o u r c e j , and C j , t h e f r a c t i o n o f the t o t a l a e r o s o l c o n t r i b u t e d by s o u r c e j . F o r a d d i t i o n a l d i s c u s s i o n o f t h e method, s e e ( 1 0 ) . We assume h e r e t h a t s o i l and r o a d s a r e t h e o n l y n o n - n e g l i g i b l e s o u r c e s o f Κ and Ca a t o u r r u r a l s i t e , so t h a t P
P
Ca
Ca,
soil
C
soil
+
p
Ca,
C
roads
roads
and P
K,
soil ^soil
+
P
K,
roads
C
roads
!
We h a v e measured t h e P s and t h e p ' s , so we may s o l v e t h e s i m u l taneous e q u a t i o n s f o r C ^ and C j . The p e r c e n t c o n t r i b u t i o n o f s o i l t o t h e a i r b o r n e Ca i s t h e n 100 p i i Csoil/ Ca. T h i s method, a l t h o u g h s i m p l e , i s j u s t i f i e d i n t h i s c a s e b e c a u s e the two s o u r c e s c o n s i d e r e d a r e t h e o n l y m a j o r o n e s , and b e c a u s e the a b u n d a n c e s o f Ca and Κ a r e s i m i l a r , r e q u i r i n g no n o r m a l i z a t i o n , as i s sometimes n e e d e d ( 1 0 ) . Once t h e C s h a v e b e e n computed, t h e y may be u s e d w i t h t h e m e a s u r e d p's o f o t h e r e l e m e n t s t o compute t h e P's f o r t h o s e elements. These may by compared t o o b s e r v e d v a l u e s as a c h e c k on t h e r e s u l t s . The o b s e r v e d s o u r c e c o m p o s i t i o n s ( p ' s ) u s e d i n t h e c a l c u l a t i o n s , and t h e mean e l e m e n t a l a b u n d a n c e s ( P ' s ) o f t h e 36 a e r o s o l s a m p l e s f o r w h i c h C's w e r e computed s e p a r a t e l y , a r e g i v e n i n T a b l e 1. s o i
r o a c
s
p
C a
s
o
f
Macias and Hopke; Atmospheric Aerosol ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
ATMOSPHERIC
308 Table I .
Mean a b u n d a n c e s o f c r u s t a l e l e m e n t s i n a e r o s o l s , s o i l , and r o a d d u s t i n a r u r a l a r e a n e a r Champaign, I L . p
i
p-L,
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soil
p
roads*
i 5
%
%
5.1
1.30
% Al
1.8
Si
6.7
Κ
0.78
1.75
Ca
2.2
0.70
Ti
0.24
0.42
0.08
1.3
2.2
1.29
Fe
AEROSOL
13.1
35
*Assuming a l l unpaved road
0.52 25
surfaces are crushed
limestone
Results D i s t r i b u t i o n o f C o n c e n t r a t i o n s b y Wind D i r e c t i o n . The good t i m e r e s o l u t i o n o f t h e s t r e a k e r d a t a means t h a t s i n g l e 2 - h r t i m e segments o f t e n r e p r e s e n t a v e r y n a r r o w r a n g e o f w i n d d i r e c t i o n s . This i s p o t e n t i a l l y important f o r source i d e n t i f i c a t i o n , s i n c e i t a l l o w s one t o examine v a r i a t i o n s o f c o n c e n t r a t i o n s a s a f u n c t i o n of wind d i r e c t i o n . T a b l e I I shows o v e r a l l mean c o n c e n t r a t i o n s o f t h e c r u s t a l e l e m e n t s Ca, A l , S i , and Κ f o r f o u r s a m p l i n g p e r i o d s i n 1 9 7 8 , and F i g u r e s 2 t o 5 show v a r i a t i o n s of c o n c e n t r a t i o n w i t h wind d i r e c t i o n during these p e r i o d s . F i g u r e 2 shows r e s u l t s a t t h e g r o u n d s i t e f o r a one-week p e r i o d i n J u n e , when c r o p s ( c o r n and s o y b e a n s ) w e r e s h o r t enough t o a l l o w t h e g e n e r a t i o n o f s o i l a e r o s o l s t h r o u g h c u l t i v a t i o n and w i n d e r o s i o n . F i g u r e 3 shows r e s u l t s f r o m t h e t o w e r s a m p l e r f o r a two-week p e r i o d i n J u l y when c r o p s w e r e m a t u r e . C u l t i v a t i o n s h o u l d h a v e b e e n a b s e n t , and w i n d e r o s i o n very l i m i t e d , during t h i s period. F i g u r e 4 and 5 show r e s u l t s f o r a p e r i o d d u r i n g and a f t e r h a r v e s t , i n O c t o b e r and November, 1978. G e n e r a t i o n o f s o i l a e r o s o l by t i l l i n g was o b s e r v e d , and w i n d e r o s i o n was p o s s i b l e , d u r i n g t h i s p e r i o d because o f the removal of the crop cover f r o m t h e s o i l s u r f a c e . F i g u r e 4 shows r e s u l t s o f t h r e e weeks o f s a m p l e c o l l e c t i o n f r o m t h e g r o u n d s i t e , and F i g u r e 5 shows r e s u l t s f r o m f o u r weeks o f s a m p l i n g on t h e t o w e r .
Macias and Hopke; Atmospheric Aerosol ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
17.
GATZ
ET
Table
Sources
AL.
II.
of
Airbourne
in
Illinois
309
Mean c o n c e n t r a t i o n s o f f o u r i m p o r t a n t c r u s t a l e l e m e n t s i n f o u r a e r o s o l sample g r o u p s .
e
periods June, ground Downloaded by UNIV OF MASSACHUSETTS AMHERST on May 26, 2018 | https://pubs.acs.org Publication Date: October 13, 1981 | doi: 10.1021/bk-1981-0167.ch017
Calcium
Mean C o n c e n t r a t i o n s , ng Ca
Al
Si
m' Κ
82
1930
780
3600
730
J u l y , tower
169
640
160
810
350
Fall,
ground
249
1990
520
1850
620
Fall,
tower
332
1800
490
1420
610
N o t e i n F i g u r e 2 t h a t SSE w i n d s p r o d u c e d t h e maximum Ca c o n c e n t r a t i o n s , w i t h s m a l l e r v a l u e s f r o m t h e SSW, a t g r o u n d l e v e l i n J u n e , w h e r e a s t h e o r d e r was r e v e r s e d f o r t h e o t h e r three c r u s t a l elements. This suggests a d i f f e r e n t primary s o u r c e f o r Ca t h a n f o r A l , S i , and Κ d u r i n g t h i s p e r i o d . The l i m e s t o n e g r a v e l r o a d 1 km SE ( s e e F i g u r e 1 ) , w h i c h we observed to p r o d u c e a d e n s e w h i t e c l o u d o f l i m e s t o n e d u s t f r o m v e h i c l e t r a f f i c i n d r y w e a t h e r , i s a l i k e l y Ca s o u r c e . The l i m e s t o n e g r a v e l r o a d t o t h e w e s t i s n o t a p p a r e n t i n F i g u r e 1, p e r h a p s b e c a u s e o f l e s s t r a f f i c due t o a weak b r i d g e . The most o b v i o u s f e a t u r e o f t h e J u l y t o w e r d a t a i n F i g u r e 3 i s the o v e r a l l drop i n the c o n c e n t r a t i o n s of a l l f o u r elements. This i s c o n s i s t e n t w i t h the i d e a t h a t t a l l crops i n h i b i t wind e r o s i o n or c o l l e c t eroded m a t e r i a l w i t h i n the crop canopy. It i s a l s o c o n s i s t e n t w i t h a decrease i n concentration w i t h height, w h i c h w o u l d be e x p e c t e d f o r m a t e r i a l s h a v i n g t h e i r s o u r c e a t t h e surface. However, t h e d e c r e a s e was much more t h a n was observed b e t w e e n t h e g r o u n d and t o w e r s i t e s i n t h e f a l l ( F i g u r e s 4 and 5 ) , and t h u s w o u l d a p p e a r t o h a v e an a d d i t i o n a l c a u s e b e s i d e t h e e l e v a t i o n d i f f e r e n c e . I n J u l y ( F i g u r e 3) t h e maximum c o n c e n t r a t i o n s a p p e a r e d f r o m t h e SE ( t h e d i r e c t i o n o f t h e n e a r e s t l i m e s t o n e g r a v e l r o a d ) f o r Ca and two o f t h e o t h e r t h r e e c r u s t a l elements. (K c o n c e n t r a t i o n s w e r e q u i t e u n i f o r m a r o u n d t h e com p a s s . ) T h i s s u g g e s t s t h a t r o a d s may be an i m p o r t a n t s o u r c e o f S i and A l , as w e l l as o f Ca, when m a t u r e c r o p s a r e l i m i t i n g t h e mechanisms o f s o i l e r o s i o n ; i . e . , w i n d and tilling. F i g u r e s 4 and 5 show r e s u l t s o f s a m p l i n g o v e r a b o u t one month i n t h e f a l l : m i d - O c t o b e r t o mid-November 1978. This p e r i o d i n c l u d e d h a r v e s t a c t i v i t i e s as w e l l as p o s t - h a r v e s t p l o w i n g and o t h e r t i l l i n g o p e r a t i o n s . These a c t i v i t i e s w e r e v i s u a l l y o b s e r v e d t o m o b i l i z e a c o n s i d e r a b l e amount o f s o i l material. This i s r e f l e c t e d i n the i n c r e a s e d c o n c e n t r a t i o n s over t h o s e o f J u l y ( T a b l e I I ) . M o r e o v e r , mean c o n c e n t r a t i o n s d u r i n g t h e f a l l p e r i o d a p p r o a c h e d , and i n one c a s e e x c e e d e d , t h o s e o f J u n e , when t i l l i n g and w i n d e r o s i o n w e r e a l s o a c t i v e . F i g u r e 4 shows r e s u l t s f o r t h e g r o u n d l e v e l s a m p l e r . The maximum c o n c e n t r a t i o n s o f a l l f o u r c r u s t a l e l e m e n t a l s o c c u r r e d
Macias and Hopke; Atmospheric Aerosol ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
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310
ATMOSPHERIC
AEROSOL
Figure 2. Distribution of mean concentrations with wind direction for 4 crustal elements measured on a streaker sampler at ground level during one week in June 1978. Radial bars indicate ±1 standard error of the mean. The numbers at the end of the bars indicate the number of 2-h samples from each direction.
Macias and Hopke; Atmospheric Aerosol ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
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17.
GATZ E T AL.
Figure 3.
Sources
of
Airbourne
Calcium
in
Illinois
Same as Figure 2, except for a 2-week period on the tower during 1978.
Macias and Hopke; Atmospheric Aerosol ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
311
July
ATMOSPHERIC
AEROSOL
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312
Figure 4.
Same as Figure 2, except for 3 weeks at ground level in the fall, 1978.
Macias and Hopke; Atmospheric Aerosol ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
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17.
GATZ
Figure
ET
5.
AL.
Sources
Same as Figure
of
Airbourne
Calcium
in
Illinois
2, except for 4 weeks on the tower in the fall,
Macias and Hopke; Atmospheric Aerosol ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
313
1978.
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314
ATMOSPHERIC
AEROSOL
i n w i n d s f r o m SSE t h r o u g h W. F o r e a c h e l e m e n t t h e r e was a l s o a s e c o n d a r y peak f r o m t h e NNE. The l a c k o f a d i f f e r e n c e i n d i r e c t i o n a l d i s t r i b u t i o n b e t w e e n Ca and t h e o t h e r e l e m e n t s s u g g e s t s a common p r i m a r y s o u r c e f o r a l l , and t h i s i s c o n s i s t e n t w i t h t h e o b s e r v a t i o n s o f l a r g e amounts o f s o i l and a e r o s o l from a g r i c u l t u r a l f i e l d a c t i v i t y d u r i n g t h i s p e r i o d . C o n c e n t r a t i o n s measured on t h e t o w e r d u r i n g t h e f a l l p e r i o d a r e shown i n F i g u r e 5. Compared w i t h c o n c e n t r a t i o n s a t t h e g r o u n d , t h e s e a r e s l i g h t l y s m a l l e r ( s e e T a b l e I I ) and more u n i f o r m a r o u n d t h e compass, b u t s t i l l q u i t e s i m i l a r e l e m e n t t o element. Nothing here suggests d i f f e r e n t primary sources f o r these c r u s t a l elements, but the s e a s o n a l v a r i a t i o n s i n conc e n t r a t i o n and o c c a s i o n a l d i f f e r e n c e s i n d i r e c t i o n a l r e s p o n s e s o f t h e summer and f a l l s a m p l i n g p e r i o d s s u g g e s t t h a t b o t h r o a d s and s o i l a r e i m p o r t a n t s o u r c e s , a t l e a s t f o r Ca. Abundances. A d d i t i o n a l evidence of p o s s i b l e m u l t i p l e s o u r c e s comes f r o m an e x a m i n a t i o n o f t h e mass p e r c e n t a g e s (abundances) o f c r u s t a l elements i n a e r o s o l samples. Figures 6 t h r o u g h 11 show a b u n d a n c e s f o r A l , S i , K, Ca, T i , and F e . The f i g u r e s a l s o show measured a b u n d a n c e s i n l o c a l s o i l and road dust sources f o r comparison. Except f o r S i , the e l e m e n t a l abundances i n t h e a e r o s o l s u g g e s t a c o m b i n a t i o n o f r o a d and s o i l s o u r c e s . The Ca r e s u l t s a r e i m p o r t a n t t o t h i s o b s e r v a t i o n b e c a u s e o n l y f o r Ca were t h e a b u n d a n c e s i n a e r o s o l s c o n s i s t e n t l y l e s s than those i n road d u s t , but g r e a t e r than those i n s o i l . From t h e o t h e r e l e m e n t s , one c o u l d r e a s o n a b l y c o n c l u d e t h a t roads were the major s o u r c e . The S i a b u n d a n c e s i n t h e a e r o s o l g e n e r a l l y f a l l b e l o w t h o s e o f b o t h r o a d s and s o i l , b u t t h e y a r e much c l o s e r t o t h o s e o f r o a d s . As w i l l be shown l a t e r f r o m o t h e r e v i d e n c e , t h e r e i s r e a s o n t o b e l i e v e t h a t S i abundances a r e d i m i n i s h e d i n a e r o s o l r e l a t i v e to b u l k s u r f a c e m a t e r i a l s . This i s consistent with o u r k n o w l e d g e t h a t S i i s a m a j o r component o f t h e l a r g e r p a r t i c l e s o f o u r s o i l s a m p l e s , w h i c h a r e e i t h e r t o o b i g t o become a i r b o r n e , o r , i f r a i s e d by t h e w i n d , t e n d t o f a l l o u t q u i c k l y . F a c t o r A n a l y s e s . I n an a t t e m p t t o i d e n t i f y s o u r c e s o f t h e v a r i o u s e l e m e n t s , f a c t o r a n a l y s e s were c a r r i e d o u t s e p a r a t e l y on two d a t a s e t s r e p r e s e n t i n g 1) f i l t e r s e x p o s e d f a c e down u n d e r an i n v e r t e d f u n n e l r a i n s h i e l d , and 2) f i l t e r s e x p o s e d i n a v a n e sampler c o n t i n u o u s l y f a c i n g i n t o the wind. W i t h i n each d a t a s e t , s e p a r a t e f a c t o r a n a l y s e s w e r e p e r f o r m e d on t h e d a t a e x p r e s s e d as 1) c o n c e n t r a t i o n s i n a i r (ng m~^) and 2) a b u n d a n c e s ( p e r c e n t of t o t a l m a s s ) . R a i n amount, r a i n d u r a t i o n , and s o i l m o i s t u r e d a t a were i n c l u d e d i n e a r l y a n a l y s e s , but these parameters were l a t e r d r o p p e d f r o m t h e d a t a s e t s b e c a u s e t h e y had no s i g n i f i c a n t r e l a t i o n s h i p t o any o f t h e e l e m e n t s . Wind d i r e c t i o n f r e q u e n c i e s were i n c l u d e d i n t h e d a t a s e t s t h r o u g h o u t t h e a n a l y s e s , h o w e v e r . D i f f e r e n t r e s u l t s were o b t a i n e d f o r c o n c e n t r a t i o n d a t a
Macias and Hopke; Atmospheric Aerosol ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
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GATZ
ET
AL.
Sources
of
Airbourne
Figure 6. Frequency distributions of Al ples, summer, 1978. Source abundances bars on the source abundances indicate source
Calcium
LIMESTONE
i
Figure 7.
L6_
Illinois
315
abundances from 2 sets of aerosol samfor Al are shown for comparison. The ±1 standard deviation of an individual sample.
ROAD DUST
_J
in
8 10 12 14 ABUNDANCE, PERCENT
|,
16
'
B
RULÎ^IL U
L
K
34
S
0
I
L
,|
36
Same as Figure 6, except for Si
Macias and Hopke; Atmospheric Aerosol ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
316
ATMOSPHERIC
LOCAL LIMESTONE ROAD DUST
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AEROSOL (VANE SAMPLER)
ζ
R
2
J U L
0
AEROSOL (FUNNEL SAMPLER)
0
0.2
0.4
0.6
Figure 8.
0.8 1.0 1.2 1.4 ABUNDANCE, PERCENT
1.8
2.0
2.2
Same as Figure 6, except for Κ
LOCAL BULK SOIL L U t
1.6
L
0
C
A
L
LIMESTONE ROAD DUST
A L
1
* —
1
i 1
1
1
.
1
AEROSOL (VANE SAMPLER) Ν = 36
if
i
1
Λ
ZI
Ik
ABUNDANCE, PERCENT
Figure 9.
Same as Figure 6, except for Ca
Macias and Hopke; Atmospheric Aerosol ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
AEROSOL
17.
GATZ E T AL.
Sources
of Air bourne
Calcium
in
Illinois
LOCAL LIMESTONE ROAD DUST
AEROSOL (VANE SAMPLERl
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Τ - Π
J 0
0.05
1 0.10
0.15
Figure 10.
I, ,„..i
I
0.20 0.25 0.30 0.35 0.40 ABUNDANCE, PERCENT
L 0.45
* 0.50
* 0.55 0.60
Same as Figure 6, except for Ti
LOCAL LIMESTONE ROAD DUST BULK SOIL L
Figure 11.
0
C
A
L
Same as Figure 6, except for Fe
Macias and Hopke; Atmospheric Aerosol ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
317
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318
ATMOSPHERIC
AEROSOL
t h a n f o r abundance d a t a , b u t d i f f e r e n c e s b e t w e e n s a m p l e r s ( v a n e v s . f u n n e l ) were m i n i m a l . Therefore, the r e s u l t s presented h e r e , f o r b o t h c o n c e n t r a t i o n s and a b u n d a n c e s , a r e f o r v a n e s a m p l e s only. T a b l e I I I shows t h e l o a d i n g s t a b l e b a s e d on c o n c e n t r a t i o n s . F a c t o r 1, w h i c h e x p l a i n s 44% o f t h e v a r i a n c e , i n c l u d e s a l l t h e u s u a l c r u s t a l e l e m e n t s a t h i g h l o a d i n g s p l u s Zn and Pb a t much w e a k e r l o a d i n g s . F a c t o r 2 i n c l u d e s Pb and S, b u t o n l y a t r e l a t i v e l y weak l o a d i n g s , a s s o c i a t e d w i t h SE w i n d s . This d i r e c t i o n i s c o n s i s t e n t w i t h the l o n g range t r a n s p o r t of s u l f u r f r o m t h e O h i o V a l l e y , b u t no o b v i o u s Pb s o u r c e s a r e a p p a r e n t i n t h e SE d i r e c t i o n . N o t e t h a t Ca i s p r e s e n t on o n l y one f a c t o r , w i t h a r e l a t i v e l y high l o a d i n g (0.87). The l o a d i n g s f o r t h e d a t a e x p r e s s e d as a b u n d a n c e s a r e shown i n T a b l e I V . Now f o u r f a c t o r s a p p e a r , b u t o n l y t h e f i r s t two c o n t a i n e l e m e n t s . F a c t o r 1 i s a c o m b i n a t i o n o f c r u s t a l e l e m e n t s and S, w i t h an i n v e r s e r e l a t i o n s h i p b e t w e e n t h e two. T h i s i s r e a s o n a b l e f o r m a j o r components o f t h e mass b e c a u s e when e x p r e s s e d as a b u n d a n c e s , any e x t r e m e l y h i g h v a l u e s o f one component a u t o m a t i c a l l y d e c r e a s e t h e o t h e r . As w i t h c o n c e n t r a t i o n s , no w i n d d i r e c t i o n s a r e i m p o r t a n t on f a c t o r 1. F a c t o r 2 c o n t a i n s t h e p o l l u t a n t m e t a l s Pb, Zn, and Mn, as w e l l as Ca and Fe a t weak l o a d i n g s , and t e n d s t o o c c u r w i t h NE w i n d s . T h i s s u g g e s t s p o l l u t a n t t r a n s p o r t from Champaign-Urbana. I n t h i s c a s e we do f i n d Ca s p l i t b e t w e e n s o u r c e s , b u t n o t t h e ones e x p e c t e d . The a p p a r e n t r o a d s o u r c e t o t h e SE, suggested i n the c o n c e n t r a t i o n d i s t r i b u t i o n s w i t h wind d i r e c t i o n , does n o t a p p e a r i n t h e f a c t o r a n a l y s i s r e s u l t s , no m a t t e r w h e t h e r b a s e d on c o n c e n t r a t i o n s o r a b u n d a n c e s . T h i s r e s u l t c o n t r a s t s w i t h those presented e a r l i e r , which suggested a combination o f r o a d and s o i l s o u r c e s , a t l e a s t f o r Ca. Chemical Element B a l a n c e . To h e l p r e s o l v e t h i s d i l e m m a , t h e r e s u l t s o f a s i m p l e c h e m i c a l e l e m e n t b a l a n c e b a s e d on Ca and Κ a r e u s e f u l . The c a l c u l a t i o n s w e r e p e r f o r m e d s e p a r a t e l y f o r e a c h o f t h e 36 v a n e s a m p l e s c o l l e c t e d , so a d i s t r i b u t i o n o f t h e r e s u l t s c o u l d be p r e s e n t e d . The i n p u t d a t a f o r t h e s e c a l c u l a t i o n s i n c l u d e d t h e mean a b u n d a n c e s o f t h e e l e m e n t s i n t h e s o u r c e m a t e r i a l s ( l o c a l b u l k s o i l and r o a d d u s t ) ( T a b l e 1) and t h e a e r o s o l e l e m e n t a b u n d a n c e s m e a s u r e d i n t h e 36 i n d i v i d u a l v a n e s a m p l e s . The d i s t r i b u t i o n s o f c r u s t a l e l e m e n t a b u n d a n c e s i n a e r o s o l s w e r e shown i n F i g u r e s 6-11 a l o n g w i t h the r e s p e c t i v e abundances o f the elements i n the s o u r c e materials. The d i s t r i b u t i o n s o f t h e c o n t r i b u t i o n s o f r o a d s and s o i l t o t o t a l s u s p e n d e d p a r t i c u l a t e m a t t e r (TSP) a r e shown i n F i g u r e 12. The f i g u r e shows t h a t s o i l c o n t r i b u t e d a mean o f 39% o f t h e TSP and r o a d s 12% d u r i n g t h e summer s a m p l i n g p e r i o d i n 1978. The d i s t r i b u t i o n s show t h a t on i n d i v i d u a l d a y s s o i l c o n t r i b u t e d up t o a b o u t 70% o f t h e TSP and r o a d s up t o a b o u t 30%.
Macias and Hopke; Atmospheric Aerosol ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
17.
GATZ
ET
Downloaded by UNIV OF MASSACHUSETTS AMHERST on May 26, 2018 | https://pubs.acs.org Publication Date: October 13, 1981 | doi: 10.1021/bk-1981-0167.ch017
Table I I I .
AL.
Sources
of
Airbourne
Calcium
in
Illinois
319
L o a d i n g s from f a c t o r a n a l y s i s o f vane sampler d a t a , b a s e d on c o n c e n t r a t i o n s . L o a d i n g s