14
Removal of Trace Contaminants from the Air Downloaded from pubs.acs.org by UNIV OF CALIFORNIA SANTA BARBARA on 09/21/18. For personal use only.
The
Fate
of
Nitrogen
Oxides
in
Urban
Atmospheres
☼
CHESTER W. SPICER, JAMES L. GEMMA, DARRELL W. JOSEPH, and ARTHUR LEVY Battelle, Columbus Laboratories, Columbus, Ohio 43201
Nitrogen oxides enter the atmosphere from a variety of sources, principally from automotive exhausts and power p l a n t combustion. Some n i t r o g e n s p e c i e s , such as ammonia r e s u l t i n g from the n a t u r a l decomposition of organic m a t e r i a l , are a l s o an eventual source of n i t r o g e n o x i d e s . Most of the n i t r o g e n oxides are converted i n t o n i t r o g e n d i o x i d e which, in t u r n , r e a c t s w i t h other species in the atmosphere producing n i t r a t e s and nitrites in both gaseous and p a r t i c u l a t e forms. However, the u l t i m a t e disposition of the n i t r o g e n oxides is unknown. The problem of uncovering the fate of n i t r o g e n oxides in the atmosphere is complicated by the continuous movement of a i r masses and the c o n t i n u a l input of m a t e r i a l i n t o the atmosphere. The current program was designed to measure a m u l t i t u d e of chemical and m e t e o r o l o g i c a l parameters in two urban atmospheres in order to determine the distribution and disposition of nitro gen compounds in the atmosphere and the f a c t o r s which i n f l u e n c e the n i t r o g e n oxides removal processes. The program described here c o n s i s t e d of three distinct phases: a n a l y t i c a l methodology development, field sampling, and data a n a l y s i s . The analytical development phase of the program has i n v o l v e d t e s t i n g s t a t e - o f - t h e - a r t techniques and in some instances development and validation of novel procedures for determining the f o l l o w i n g species during the field sampling phase of the program: NO, N0 , O , CH ONO , C H ONO , PAN, NH , HNO , mass l o a d i n g , p a r t i c u l a t e NO , particulate NO , partic ulate NH , and total C, H, and Ν in the p a r t i c u l a t e phase. Temperature, relative h u m i d i t y , wind speed, wind direction, and s o l a r intensity were a l s o monitored. Some rainfall and dustfall samples were c o l l e c t e d and analyzed for n i t r o g e n s p e c i e s . 2
3
3
2
-
3
2
5
2
3
-
3
2
+
4
The f i e l d s a m p l i n g p h a s e o f t h e p r o g r a m was c a r r i e d o u t i n t h e summer o f 1 9 7 3 , i n S t . L o u i s , M i s s o u r i , and West C o v i n a , *To whom c o r r e s p o n d e n c e s h o u l d be a d d r e s s e d .
159
160
R E M O V A L OF
California
TRACE CONTAMINANTS F R O M THE
( l o c a t e d 25 m i l e s e a s t o f downtown L o s
Angeles).
Experimental The a n a l y t i c a l methods employed i n t h i s i n v e s t i g a t i o n a r e l i s t e d i n T a b l e I . B o t h NO and NO2 w e r e m o n i t o r e d by chemiluminescence techniques. We have p r e v i o u s l y r e p o r t e d (1) on i n t e r f e r e n c e t o t h e c h e m i l u m i n e s c e n t d e t e r m i n a t i o n o f NO2 by a v a r i e t y o f o t h e r g a s e o u s n i t r o g e n s p e c i e s i n c l u d i n g PAN, H N O 3 , and a l k y l n i t r a t e s . Ozone was m o n i t o r e d by c h e m i l u m i n e s c e n c e methods. A d u a l c a t a l y t i c - c o n v e r t e r chemiluminscent instrument was u s e d t o m o n i t o r ammonia. Gas p h a s e o r g a n i c n i t r a t e s w e r e d e t e r m i n e d by e l e c t r o n c a p t u r e d e t e c t i o n gas c h r o m a t o g r a p h y . Two n o v e l methods f o r HNO3 d e t e r m i n a t i o n were d e v e l o p e d . One, a m o d i f i e d c o l o r i m e t r i c p r o c e d u r e ( 2 ) , y i e l d s i n t e g r a t e d HNO3 v a l u e s , w h i l e t h e o t h e r , b a s e d on c o u l o m e t r y ( 3 ) . g i v e s a c o n tinuous readout of atmospheric n i t r i c a c i d . Table I.
Analytical Methods
Technique
Measurement NO, 0
N0 , 2
Ν0
Chemiluminescence
χ
Chemiluminescence 3
NH
Chemiluminescence
3
PAN
E l e c t r o n Capture
Gas
Chromatography
Alkyl
E l e c t r o n Capture
Gas
Chromatography
Nitrates
HNO3
Continuous
HNO3
Integrated Colorimetric
Coulometric
nh£
H i V o l . S a m p l i n g and Standard A n a l y s i s
NO3 NO2
T o t a l C, Η,
Ν
Wind Speed Wind D i r e c t i o n MRI, Relative
INC.
Weather S t a t i o n
Humidity
Temperature Sunlight
Intensity
Pyrohelimoter
A e r o s o l s a m p l i e s w e r e c o l l e c t e d on h i g h - p u r i t y q u a r t z -
AIR
SPICER E T A L .
Nitrogen
Oxides
in Urban
Atmospheres
Legend PAN 0.004 ppm H N 0 0.009 ppm Nitrogen oxides 0.070 ppm Ammonia 0.006 ppm 3
St Louis
Ozone 0.080 ppm Nitric oxide 0.040 ppm Nitrogen dioxide 0.040 ppm — — Nitrogen oxides 0.070 ppm
Hour of Day Legend
—
Figure
Global irradiance 0.900 cal/sq cm/min Wind speed 7.000 mph Temperature 30.000 Centigrade Relative humidity 100.000 percent
1. Average meteorological
diurnal air quality profile, St. Louis
and
162
REMOVAL O F TRACE CONTAMINANTS FROM
Table II.
T H E AIR
Summary of
Aerosol Mass Weather Conditions Date
Day
GeneraK*)
Temp, C
RHft
Loading
O3,
NO, Ν Ο ,
pg/m*
ppm
ppm
χ
ppm
7-18
W
S
28
75
114.1
0.049
0.012
0.061
7-19
Th
R.S
27
92
80.7
0.033
0.016
Ο.ΟΰΙ
7-20
F
S
29
79
51.5
0.027
0.013
0.047
7-22
Sun
S
27
82
32.6
0.072
0.019
0.037
7-23
M
S,R
26
84
42.8
0.041
0.005
0.034
7-24
Τ
S
27
86
37.0
0.037
0.011
0.048
7-25
W
S
27
80
53.9
0.044
0.021
0.056
7-26
Th
R,C
26
69
33.4
0.032
0.013
0.035
7-27
F
C
27
67
50.9
0.028
0.013
0.038
7-30
Ni
R
25
76
68.2
0.023
0.026
0.057
7-31
PC.R
24
72
39.2
0.032
0.015
0.034
8-1
Τ W
C
21
72
41.9
0.022
0.016
0.028
8-2
Th
C
22
66
43.5
0.022
0.014
0.034
8-3
F
S
23
61
53.7
0.034
0.011
0.035
8-4
Sat
S
25
68
79.9
0.052
0.007
0.033
6-5
Sun
S
26
63.0
0.045
8-6
M
PC
25
76 72
74.9
0.042
0.009 0.011
0.038 0.037
0.039
8-7
T
S
61.4
0.038
0.012
W
S
27 30
84
8-8
82
51.5
0.023
0.014
0.036
8-9
Th
R
24
95
47.9
0.004
0.024
0.051
8-10
F
S.R
24
82
66.4
0.041
0.015
0.041
8-12
Sun
S,R
26
85
40.6
0.037
0.026
0.047
8-13
M
R
23
93
63.3
0.016
0.026
0.054
8-14
T
R.S
21
82
42.0
0.035
0.013
0.029
8-15
W
PC
23
76
90.5
0.041
0.034
0.062
8-16
Th
R.S
23
83
79.6
0.029
0.016
0.044
(a) S « Sunny, R = Rain, C » Clear, PC « Partly Cloudy, C l = Cloudy, (b) Continuous Coulometric.
Table III.
Summary of St. Louis Hydrocarbon D a t a 7-19-73
7-18-73
Oate Sample N u m b e r
(b)
1
2
1
4
3
( a )
2
3
4
Component Methane CO
2390 2053
2057 2326 2271
2235
1674 2008
1266
578
1405 1746 2134
1634
24
18
5
17
26
38
27
2420 2541
C H 2
2
21
C H
4
29
29
17
7
30
28
40
26
80
88
54
34
77
92
103
73
Nonmethane Hydrocarbons
570
454
452
140
295
435
555
424^
Ο,Η./α,Η.,
1.38 1.22 0.93 1.42
2
Olefins Aromatics
1.79 1.06 1.03 0.96
(a) Courtesy of the U.S. Environmental Protection Agency.
spiCER E T A L .
14.
Nitrogen
Oxides
in Urban
Atmospheres
163
A i r Quality Data, St. Louis
Pollutants 23-Hour Average
1-Hour Maximum
NH ,
PAN,
HN0 (b)
ppm
ppm
ppm
0.010
0.001
0.008
0.002
0.008
NO.
NO .
ppm
ppm
ppm
ppm
ppm
ppm
ppm
0.012
0.007
0.110
0.043
0.114
0.014
0.003
0.044
0,005
0.004
0.107
0.061
0.121
0.011
0.007
0.022
0.002
0,002
0.000
0.083
0.0.-V4
0.070
0.011
0.006
0.012
0.002
0.001
0.001
0.007
0 . 146
0.026
0.050
0.016
0.003
0.00
0.004
0.001
O.00G
0.009
0.086
0.020
0.067
0.0'Vi
0.055
0.00G
0.001
0.004
0.011
0.113
0.Ο.Ί0
0.031
0.011
0.004
0.016
0.005
0.001
0,002
0.002
0.
i:s
0.070
0 . 108
0.000
0.0'U
0.017
0.004
0.001
0,000
0.004
0.066
0.024
0.060
0.005
0.001
0.000
0.004
0.001
0.000
0.004
0.067
0.042
0.069
0.006
0.004
0.000
0.004
0.001
0.002
0.001
0.003
0.001
0.002 0.003
3
f
C
HN0 < >, 3
3
x
ΝII .
PAN,
0 ,
3
3
HNO3.
a
0.006
0.050
0.054
0.0S9
0.002
0.068
0.047
0.084
0.005
0.002
—
0.003
0.033
0.030
0.049
0.003
0.002
--
0.005
0.051
0.033
0.061
0.005
0.002
0.002
0.000
0.004
0.087
0.037
0.077
0.004
0.0 04
0.000
0.003
0.004
0.008
0.124
0.051
0.096
0.006
0.006
0.015
0.003
0.002
0.003
0.001
0.092
0.03-1
0.091
0.006
0.003
0.013
0.002
0.001
0.002
0.002
0.078
0.035
0.075
0.004
0.003
0.029
0.002
0.002
0.005
0.004
0.076
0.030
0.067·
0.005
0.004
0.020
0.003
0.002
0.003
0.004
0.043
n.031
0.059
0.006
0.004
0.021
0.003
0.002
0.001
0.000
0.011
0.060
0.0S9
0.007
0.004
0.011
0.002
0.005
0.004
0.002
0.163
0.083
0.106
0.004
0.019
0.024
--
0.003
0.001
0.007
0.138
0.101
0.133
0.006
0.005
0.005
0.002
0.008
0.000
0.058
0.051
0.094
0.008
0.004
0.042
0.002
0.002
0.000
0.000
0.063
0.021
0.059
0.004
0.004
0.004
0.003
0.003
0.009
0.001
0.096
0.103
0.147
0.009
0.009
0.0S)
0.002
0.003
0.003
0.000
0.065
0.042
0.078
0.005
0.008
0.017
0.001
(c)
Integrated Colorimetric.
(Hydrocarbon values in ppbC; carbon monoxide values in ppb.)
2418
1984
1570
1536 2047
594
390
882
1018
817
528
1010
1423
1113
930
27
23
12
10
12
14
4
4
15
21
13
12
24
30
15
11
20
18
8
9
20
26
17
15
75
100
60
39
73
53
35
36
66
74
62
41
2310
2445 2235 2094 2079
2107 2129
2285 2117
140
273
166
109
129
353
220
217
155
198
78
46
513
818
530
376
448
657
448
420
486
579
387
284
0.88
1.32
122
1.08
1.62
1.31
151
2.09
1.30
125
1.31
1.26
(b) Sample No. 1 » 6-8 a.m.; 2 = 8-10 a.m.; 3 » 10 a.m.-12 p.m.; 4 - 12-2 p.m
—
—
0.006
—
164
R E M O V A L OF
TRACE CONTAMINANTS F R O M THE
AIR
f i b e r f i l t e r s by two h i g h v o l u m e s a m p l e r s ^ C o n v e n t i o n a l wet c h e m i s t r y p r o c e d u r e s w e r e employed f o r NO3 and N 0 determina tion. Ammonium i o n was d e t e r m i n e d , a f t e r c o n v e r s i o n t o ammonia, by an ammonia g a s - s e n s i n g e l e c t r o d e . A combustion technique was u s e d f o r t o t a l C, Η, Ν a n a l y s i s . 2
Results M o n i t o r i n g o f c h e m i c a l and m e t e o r o l o g i c a l v a r i a b l e s was c a r r i e d o u t f o r 5 weeks i n S t . L o u i s , M i s s o u r i , and 5 weeks i n West C o v i n a , C a l i f o r n i a . S a m p l i n g i n b o t h c i t i e s was c o n d u c t e d on a 2 3 - h o u r - p e r - d a y b a s i s , f r o m 11:30 p.m. t o 10:30 p.m. A summary o f t h e a i r - q u a l i t y d a t a c o l l e c t e d i n S t . L o u i s i s shown i n T a b l e I I . The g a s - p h a s e d a t a a r e p r e s e n t e d a s b o t h 23-hour a v e r a g e s and as maximum 1-hour a v e r a g e s . A summary o f S t . L o u i s h y d r o c a r b o n and CO d a t a t a k e n 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 f o r s e v e r a l d a y s s i m u l t a n e o u s l y w i t h o u r measurements i s presented i n Table I I I . F i g u r e 1 d i s p l a y s the p r o f i l e s of the a v e r a g e d i u r n a l a i r q u a l i t y and m e t e o r o l o g y d u r i n g t h e S t . L o u i s f i e l d program. These p r o f i l e s a r e composites over the e n t i r e 5-week s a m p l i n g p e r i o d . The a v e r a g e d a e r o s o l r e s u l t s f r o m o u r S t . L o u i s s t u d y a r e g i v e n i n T a b l e I V f o r two p a r t i c l e - s i z e fractions. Table IV.
Aerosol Analysis
Weight P e r c e n t
St.
ΝΗ*
N0
4.4
-
0.63
19.0
3.6
4.6
0.55
0.001
2.65
14.6
1.8
1.5
4.7
-
1.7
19.4
3.8
5.3
0.001
4.8
12.6
1.8
2.2
2
NO3
Louis, Missouri
Average T o t a l A e r o s o l Composition L a r g e P a r t i c l e (>2.5 ym) Composition West C o v i n a ,
California
Average T o t a l A e r o s o l Composition L a r g e P a r t i c l e (>2.5 ym) Composition
0.63
A summary o f t h e a i r - q u a l i t y d a t a f o r t h e 29 s a m p l i n g d a y s i n West C o v i n a , C a l i f o r n i a , i s shown i n T a b l e V. The g a s - p h a s e d a t a a r e t a b u l a t e d a s b o t h d a i l y ( 2 3 - h o u r ) a v e r a g e s and maximum 1-hour a v e r a g e s . F i g u r e 2 p r o f i l e s the average d i u r n a l a i r q u a l i t y and m e t e o r o l o g y d u r i n g t h e f i e l d s a m p l i n g i n West C o v i n a The a v e r a g e a e r o s o l r e s u l t s f r o m o u r West C o v i n a s a m p l i n g a r e
spiCER E T
AL.
Nitrogen
Oxides
in Urban
Atmospheres
/A /
Los Angeles
too 90 80 70 60 50
NH
40
3
PAN I e
Ν0
χ
L o s s , ppm
14.6 ± 3.2
14.6
0.000 ± 0.012
18.4 ± 0.6
14.3
0.035 ± 0.006
I t i s apparent from t h e d a t a i n Table V I t h a t t h e average Ν 0 l o s s i n S t . L o u i s , 0 . 0 0 0 ± 0 . 0 1 2 ppm, i s s m a l l i n compar i s o n w i t h t h e a v e r a g e c o n c e n t r a t i o n o f Ν 0 . The a v e r a g e sum of PAN and HNO3 o v e r t h e same t i m e p e r i o d was 0.007 ppm, w e l l w i t h i n t h e 0 . 0 1 2 ppm d e v i a t i o n . Thus, t h e average l o s s o f N 0 in St. Louis i s quite small. The u s e o f a c e t y l e n e a s a t r a c e r has a l s o c o n f i r m e d t h i s f i n d i n g ( 2 ) . The a v e r a g e c a l c u l a t e d Ν 0 l o s s i n West C o v i n a a s r e p o r t e d i n T a b l e V I , i s 0.035 ± 0.006 ppm. The 0.006 ppm d e v i a t i o n i s m e r e l y t h e s t a t i s t i c a l d e v i a t i o n about t h e s l o p e c a l c u l a t i o n . T h e r e a r e s e v e r a l o t h e r s o u r c e s o f e r r o r h o w e v e r , w h i c h may have a much g r e a t e r i m p a c t on t h e a c c u r a c y o f t h e " N 0 l o s s " χ
χ
X
χ
X
170
R E M O V A L OF
TRACE CONTAMINANTS F R O M T H E
AIR
c a l c u l a t i o n f o r West C o v i n a . F i r s t , t h e c a l c u l a t i o n d e p e n d s on e m i s s i o n i n v e n t o r i e s w h i c h w e r e o v e r two y e a r s o l d a t t h e t i m e o f t h i s s t u d y . S e c o n d , t h e CO d a t a f r o m West C o v i n a w e r e o b t a i n e d by NDIR, a p r o c e d u r e w h i c h i s l e s s s e n s i t i v e and more s u s c e p t i b l e t o i n t e r f e r e n c e t h a n t h e gas c h r o m a t o g r a p h i c p r o c e dures used i n S t . L o u i s . The e f f e c t o f t h e s e i n t e r f e r e n c e s i s p r e s u m a b l y l a r g e l y e l i m i n a t e d i n o u r c a l c u l a t i o n by t h e u s e o f t h e s l o p e o f t h e CO v s Ν 0 r e g r e s s i o n l i n e . The i n t e r c e p t o f t h e r e g r e s s i o n l i n e now c o n t a i n s a b a c k g r o u n d CO component and a component c a u s e d b y i n s t r u m e n t a l i n s e n s i t i v i t y and i n t e r ference. However, t h e computed N 0 l o s s i s s t i l l l i k e l y t o be o v e r e s t i m a t e d because of these sources of e r r o r . Thus we c a n n o t a t t h i s t i m e make an u n q u a l i f i e d j u d g m e n t as t o t h e b a l a n c e b e t w e e n Ν 0 r e a c t a n t s and p r o d u c t s i n West C o v i n a due t o t h e many f a c t o r s w h i c h may be i n f l u e n c i n g t h e a c c u r a c y o f t h e Ν0 loss" calculation. We c a n s a y h o w e v e r , t h a t t h e " Ν 0 loss" a p p e a r s t o be a s m a l l f r a c t i o n o f t h e t o t a l N 0 c o n c e n t r a t i o n i n West C o v i n a . A much more e x a c t d e t e r m i n a t i o n o f Ν 0 loss w i l l be c a r r i e d o u t i n t h e n e a r f u t u r e u s i n g CO d a t a c o l l e c t e d by gas c h r o m a t o g r a p h y i n West C o v i n a s i m u l t a n e o u s l y w i t h o u r study. One f i n a l v i e w o f t h e p r o b l e m c a n be g a i n e d by e x a m i n i n g t h e time dependence o f t h e composited N 0 l o s s p r o f i l e . This 5-week a v e r a g e d p l o t i s shown i n F i g u r e 3. The r e l a t i v e c o n c e n t r a t i o n shown on t h e o r d i n a t e s o f t h e s e p l o t s may be t h o u g h t o f as p a r t s p e r h u n d r e d m i l l i o n (pphm). I t s h o u l d be o b s e r v e d f i r s t o f a l l t h a t we h a v e a l l o w e d t h e d a t a t o f o r m t h e i r own baseline. Our d e t a i l e d c a l c u l a t i o n i n d i c a t e s t h a t t h i s b a s e l i n e may be o b s c u r i n g an a p p a r e n t 20 ppb Ν 0 l o s s w h i c h r e m a i n s c o n s t a n t w i t h t i m e (shows no d i u r n a l v a r i a t i o n ) . This apparent 20 ppb l o s s may be due t o Ν 0 r e m o v a l b y d r y d e p o s i t i o n p r o c e s s e s , i t may r e p r e s e n t i n a c c u r a c i e s i n t h e e m i s s i o n s i n v e n t o r i e s , o r i t may r e p r e s e n t some o t h e r s o u r c e o f u n d e f i n e d error. The f a c t t h a t i t i s c o n s t a n t h o w e v e r , i n d i c a t e s t h a t , i f i t i s indeed a r e a l l o s s , i t i s probably not photochemical i n nature. Of t h e two p r o m i n e n t humps d i s p l a y e d i n t h e "NO loss" c u r v e , t h e s e c o n d one c a n be a c c o u n t e d f o r e n t i r e l y by t h e sum o f PAN and H N O 3 . T h i s i s i l l u s t r a t e d by t h e p r o f i l e i n the lower p o r t i o n of the f i g u r e . We c a n s a y , t h e r e f o r e , t h a t t h e mechanism o f a f t e r n o o n l o s s o f Ν 0 i s p h o t o c h e m i c a l l y r e l a t e d and t h a t t h e m a g n i t u d e o f t h e l o s s c a n be c o m p l e t e l y a c c o u n t e d f o r by m e a s u r e d Ν 0 r e a c t i o n p r o d u c t s . The e x p l a n a t i o n f o r t h e a p p a r e n t e a r l y m o r n i n g l o s s o f Ν 0 i s u n c l e a r at t h i s time. O b v i o u s l y , f o r the " Ν 0 l o s s " to i n c r e a s e as shown i n t h e f i g u r e , t h e ( C 0 / N 0 ) m r a t i o i n E q u a t i o n ( 2 ) must i n c r e a s e . S i n c e t h i s e a r l y morning i n c r e a s e i n the " N 0 l o s s " c u r v e a p p e a r s a t t h e same t i m e t h a t t h e CO and N 0 e m i s s i o n s s o u r c e s a r e u n d e r g o i n g t h e i r most d r a m a t i c change o f the day, the p o s s i b i l i t y e x i s t s t h a t the e a r l y morning " l o s s " χ
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i s a r t i f i c i a l . The r a t i o n a l e i s a s f o l l o w s : A m a j o r i n c r e a s e i n t h e a u t o e x h a u s t c o n t r i b u t i o n t o t h e a i r mass o c c u r s b e t w e e n 5:00-8:00 a.m., j u d g i n g from the average N0 p r o f i l e i n F i g u r e 2. S i n c e a u t o e x h a u s t has a c o n s i d e r a b l y h i g h e r C 0 / N 0 r a t i o t h a n t h e n o r m a l L o s A n g e l e s b a s i n m i x t u r e ( a p p r o x i m a t e l y 24 v e r s u s 1 4 . 3 ) , t h e m o r n i n g "N0 l o s s " peak may o n l y be t h e r e s u l t o f a d i f f e r e n t e m i s s i o n s m i x d u r i n g p e a k t r a f f i c h o u r s and n o t t r u l y r e f l e c t removal of Ν 0 f r o m t h e a i r mass. I n d e e d , i f t h e a d d i t i o n a l m o r n i n g a u t o e x h a u s t b u r d e n ( a t a C 0 / N 0 r a t i o o f 24) r a i s e s t h e n o r m a l CO/NO e m i s s i o n s r a t i o f r o m 14.3 t o 16.5, t h e n t h e 6:00 a.m. a p p a r e n t N0 l o s s " peak w o u l d be c o m p l e t e l y eliminated. A t t h i s t i m e t h e r e i s no s u r e way t o i n c o r p o r a t e a v a r i a b l e e m i s s i o n i n v e n t o r y r a t i o i n t o our c a l c u l a t i o n s , a l t h o u g h i t seems v e r y l i k e l y t h a t t h e e m i s s i o n s r a t i o must v a r y d u r i n g t h e day due t o t r a f f i c p a t t e r n s and v a r i a t i o n s i n other emissions sources. A t t h i s p o i n t we c a n o n l y s u g g e s t t h e v a r i a t i o n i n t h e C 0 / N 0 e m i s s i o n s r a t i o as a p r o b a b l e c a u s e o f the apparent morning N0 loss. X
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Conclusions S e v e r a l t e n t a t i v e c o n c l u s i o n s c a n be drawn f r o m o u r r e s u l t s . S i n c e d e t a i l e d d i s c u s s i o n s of the d a t a s u p p o r t i n g each of these c o n c l u s i o n s has b e e n p r e s e n t e d e l s e w h e r e ( 2 ) . we w i l l s i m p l y s t a t e o u r m a j o r o b s e r v a t i o n s and c o n c l u s i o n s h e r e : (1) B a s e d on o u r "N0 L o s s " c a l c u l a t i o n s i t a p p e a r s t h a t t h e mechanisms by w h i c h t h e n i t r o g e n o x i d e s a r e removed f r o m t h e a t m o s p h e r e i n v o l v e r e l a t i v e l y slow processes. (2) I n West C o v i n a , t h e g r e a t e s t l o s s of n i t r o g e n o x i d e s was o b s e r v e d d u r i n g m i d a f t e r n o o n on h i g h p h o t o c h e m i c a l smog d a y s . This portion o f t h e Ν 0 L o s s " p r o f i l e was h i g h l y c o r r e l a t e d w i t h ozone c o n c e n t r a t i o n . I f c e r t a i n assumptions are accepted, the afternoon or photochemical l o s s of n i t r o g e n oxides appears t o be l a r g e l y a c c o u n t e d f o r by t h e sum o f t h e PAN and n i t r i c a c i d c o n c e n t r a t i o n . (3) T h e r e was some e v i d e n c e t h a t n i t r i c a c i d i s removed f r o m t h e a i r by a l k a l i n e - s u r f a c e g l a s s - f i b e r f i l t e r s , b u t n o t by h i g h - p u r i t y q u a r t z - f i b e r f i l t e r s . I f t r u e , t h i s would mean t h a t much p a r t i c u l a t e n i t r a t e d a t a c o l l e c t e d o v e r t h e y e a r s may have b e e n s t r o n g l y i n f l u e n c e d by g a s e o u s n i t r i c a c i d . (4) T h e r e was some i n d i c a t i o n f r o m our d a t a t h a t ozone i s advected i n t o the S t . L o u i s r e g i o n d u r i n g e a r l y morning hours. While the source of t h i s ozone i s not y e t c l e a r , t h e r e i s some e v i d e n c e t h a t PAN and p o s s i b l y X
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n i t r i c acid are associated with the nighttime ozone. The p r o g r a m i s c o n t i n u i n g and t h e s e c o n d y e a r e f f o r t w i l l be d e v o t e d i n p a r t t o f u r t h e r v a l i d a t i o n and d o c u m e n t a t i o n o f o u r n i t r i c a c i d measurements a n d i n p a r t t o f u r t h e r a n a l y s i s and i n t e r p r e t a t i o n o f o u r f i r s t - y e a r f i e l d r e s u l t s . Acknowledgments The w o r k r e p o r t e d h e r e was s u p p o r t e d b y t h e C o o r d i n a t i n g R e s e a r c h C o u n c i l , I n c . , and t h e 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 A g e n c y . We w o u l d l i k e t o a c k n o w l e d g e t h e v a l u a b l e c o n t r i b u t i o n s t o t h i s s t u d y made b y t h e members o f t h e CRC-APRAC c o m m i t t e e , CAPA-9-71; E. S. J a c o b s , J . J . B u f a l i n i , E. H. B u r k , W. A. G l a s s o n , R. Hammerle, and t h e l a t e D. H u t c h i n s o n .
Literature Cited 1.
S p i c e r , C. W. and Miller, D. F., "Nitrogen Balance in Smog Chamber Studies", to be published in J. A i r Poll. C o n t r o l A s s o c . ; presented at 67th Annual M e e t i n g , Air Poll. C o n t r o l A s s o c . , Denver, 1974.
2.
S p i c e r , C. W., "The Fate of Nitrogen Oxides in the Atmo sphere", Battelle-Columbus r e p o r t to EPA and CRC, September, 1974.
3.
Miller, D. F. and S p i c e r , C. W., "A Continuous Analyzer for D e t e c t i n g Nitric Acid", to be published in J. Air Poll. C o n t r o l A s s o c . ; presented at the 67th Annual M e e t i n g , Air Poll. C o n t r o l A s s o c . , Denver, 1974.
