mean zinc concentration of 530 pg/lOO ml in the population they studied. Figures 1, 2 , and 3 are frequency distributions for various concentration ranges of cadmium, lead, and zinc, respectively. Table I1 is a comparison of whole blood trace metal concentrations found in this study with the corresponding concentrations found in other studies. Correlations. Table I11 contains correlation coefficients, calculated by the Spearman rank order procedure ( I O ) along with the corresponding level of significance, for the three possible pairs of trace metals studied-zinc with cadmium, zinc with lead, and cadmium with lead. Strong positive correlations were found between cadmium and lead (p < 0.006) and between cadmium and zinc (p < 0.001), with a relatively weak negative correlation (p < 0.254) between zinc and lead. Since increased lead concentrations in blood are undoubtedly due to environmental contamination by lead, these correlations suggest that cadmium is being absorbed along with lead. In fact, the suggestion has already been advanced that cadmium may be present in lead-containing paints ( I I ) . Cadmium toxicity may therefore be a complicating factor in some cases of lead poisoning. However, the suspected increased absorption of cadmium is apparently also accompanied by an increased absorption of zinc. This is not surprising since zinc and cadmium are found together in nature, and zinc could be released during the process of refining cadmium and vice versa (12). Simultaneously ingested zinc could exert a protective effect against the toxicity of cadmium. Surprisingly, in the Delves et al. (6) study of trace metal burdens in children, no correlation (at the 0.05 level) was found between lead and cadmium or between zinc and cadmium.
In addition, since air is suspected as a source of trace metal absorption, data from the Environmental Protection Agency (13) survey were used to determine if correlations exist between cadmium, lead, and zinc concentrations in the atmosphere. The mean atmospheric concentrations of each trace metal for a specific year were compared with the mean concentrations of the other two metals for the same year. Strong positive correlations @ < 0.01) were found for the three pairs, cadmium-lead, zinclead, and zinc-cadmium, suggesting that the high degree of correlation in blood could, in part, be due to the breathing of air containing all three trace metals.
Literature Cited (1) Louria, D. B., Joselow, M. M., Browder, A. A. Ann. Intern.
Med., 76,307-19 (1972). (2) Hessel, D. W., Atomic Absorption Neusletter, 7 , 5 5 - 6 (1968). (3) Joselow, M. M., Bogden. J. D., ibid., 11,99-101 (1972). 14) Westerlund-Helmerson. U.. ibid., 9. 133-4 11970). ( 5 ) Kahnke, M. J., ibid , 5,7-8 (1966). (6) Delves, H . T., Clayton, B. E., Bicknell, J., Brit J Prev Soc M e d . , 27, 100-7 (1973). (7) Imbus, H. R., Cholak, J., Miller, L. H., Sterling, T., Arch. Enuiron. Health, 6,286-95 (1963). (8) Kubota, J., Lazar, V. A,, Losee, F., ihid., 16,788-793 (1968). (9) Bureau of the Census, Newark. N.J., “Census of Population and Housing: 1970 Census Tracts,” 1970. (10) Siege1 S , “Nonparametric Statistics,” pp 202-5, McGrawHill Book Co., New York, N.Y., 1956. (11) Challou. R. S.. ‘Veu, Enp. J Med , 284.970-971 11971). (12) U.S. De’partment of Health, Education and Welfare, Public Health Service, Raleigh, K.C., “Preliminary Air Pollution Survey of Cadmium and Its Compounds,” p 19, 1969. (13) U.S. Environmental Protection Agency, Research Triangle Park, N.C., “Air Quality Data for 1967,” pp 99, 109, 123, 1971. Received for review January 7, 1974. Accepted March 18, 1974.
Static Studies of Sulfur Dioxide Reactions Effects of NO2,C3H6,and H20 Jerome P. Smith and Paul Urone” Environmental Engineering Sciences Department, University of Florida, Gainesville, Fla. 3261 1
Static studies of sulfur dioxide dark and photochemical reactions a t 2 ppm in air in the presence of N02, propylene, and H20 are reported. The initial photochemical reaction rate of SO2 alone in air was 1.7 X ppm/min. In the presence of NO2, the rate increased when the SO2 to NO2 ratio was 1 or 2 but decreased a t a ratio of 0.6 or less. When propylene and NO2 were both present, the reaction rate increased one hundred fold depending upon the amount of propylene as well as the SO2 to NO2 ratio. At 50% relative humidity, the S02-NO2 reaction rate increased tenfold, but the S02-N02-C& was not affected. At 75% relative humidity, the SO2-~02-C3H6-H20 system reacted in the dark and showed erratic photochemical reaction rates. Generalized mechanisms are proposed which illustrate the complexity of atmospheric reactions. W
A number of authors have recently reviewed the reactions of sulfur dioxide in air (1-3). A wide range of reaction rates has been reported depending to a large extent upon the types of other substances present and the experimental conditions used (2, 4, 5 ) . This report covers the findings of recent studies that reveal new reaction mechanisms and rates (6).The reactions were studied a t SO2 concentra742
Environmental Science & Technology
tions of 2 ppm by both static and dynamic techniques. The data reported here were derived from the static studies. A second paper will report on the dynamic studies.
Experimental The experiments were carried out in carefully cleaned 2-liter borosilicate glass flasks described previously ( 7 ) . Gas mixtures were prepared in the dark in light-tight bags by a two-stage dilution technique from pure reactant gases and clean air. SOz was measured gas chromatographically with a flame photometric (FPD) detector (Tracor Inc.) using a method similar to that employed by others (8, 9). Propylene was measured using a Varian Aerograph Model 200 gas chromatograph with an FID detector. It was equipped with a tube-type sampling valve and a 4-ml sampling loop. A 5-ft lk-in. stainless steel column of Porapak Q was used a t 110°C. The photochemical reactor used in this study was a Srinivasan-Rayonet Griffin Reactor (The Southern N.E. Ultraviolet Co.). It contained 16 coated uv fluorescent bulbs with 90% of the spectral distribution centered a t 3500 A and a cutoff point a t 3000 A. Its photon flux was determined to be 4.3 x photons/cc sec by the method given by Calvert and Pitts ( I O ) . The reactor temperature equilibrated a t approximately 38°C within 5 min.
Reagents a n d Materials. The gases used were all obtained from lecture bottles (Matheson Co., Inc.). The SO2 was anhydrous and the propylene was CP grade. The NO2 from the lecture bottle contained relatively large amounts of water and NO. It was therefore purified by distilling several times into ice water traps. The air used in these studies was purified by a multistage purification train using a series of H2S04, silica gel, activated carbon, and molecular sieve traps.
Results and DLscussLon SO2 in Air System. Figure 1 shows a plot of the photochemical reaction of SO2 in the absence and presence of NOz. The reaction of SO2 in the absence of NO2 or in the presence of the higher NO2 concentrations is slow and seems to reach a state of little to no additional disappearance after long irradiation times. A similar behavior was observed by Katz 111) who described the reaction as a first-order equilibrium reaction. The data given in Figure 1 for SO2 in air without NO2 agree well with the data of Schroeder (12) who used the same photochemical reactor and found about 20970 reaction after 72 hr irradiation for a 0.1% (1000 ppm) mixture of SO2 in air. Several others have obtained photochemical reaction rates of SO2 of 0.1-0.6%/hr (7, 13, 24). The overall rate obtained in this study was about 0.26%/hr which agrees well with the former studies. The initial rate, however, was about 1.7 x ppm/min or about 0.55%/hr which is still in good agreement with the previous work. If it is assumed that the principal photochemical reactions of SO2 involve the following (13, 15):
-- so, so, + so, so, + hv
'SO,
'SO,
,so* +
(1)
,SO,
(2)
0,
(3)
2s0, (4) where lSOz represents the singlet excited state, and 3 S 0 2 represents the triplet excited state resulting from direct excitation or from the singlet state through an intersystem transition (16). SO1 has not been observed directly, and Equation 4 may be considered to represent the reaction of an intermediate complex of unknown molecular composition in the oxidation of SO2. S02-NOZ-Air System. When NO2 is irradiated in air, an equilibrium is established with 0 2 , NO, and NO2 as the major species present (2). NO,
+
hv
-
NO
+
0
-
O+O,+M-O,+M
+
(6)
NO NO, + 0, Other possible reactions include the following: 0,
+ NO + M 0 + NO, + M 03 + NO, 0
-
-
+M NO3 + M
NO,
NO,
(5)
+
0,
(7)
The S02-0-atom reaction has been studied previously (20). The rate constant for the SOZ-0-atom reaction is smaller than the rate constant for the reaction of 0 atoms with NO2 and NO. If it can be assumed that the only additional route of photochemical SO2 removal in the NOzair system is the reaction of SO2 with 0 atoms: SO2 0 M SO3 + M , then the competition of SO2 and other species for the 0 atom formed by NO2 photolysis becomes important. It might be expected that the rate of SO2 oxidation would be accelerated a t higher S 0 2 / N 0 2 ratios and decreased to its value in air alone at lower S 0 2 / N 0 2 ratios. At 0.85 ppm NO2 and 1.7 ppm NO2 the rate of photooxidation of 2 ppm SO2 in air was about double that for SO2 in air alone. At higher concentrations of X02, however, the rate of photooxidation of SO2 didn't vary from that observed for SO2 in air alone (Figure 1). The dark reaction between SO2 and NO2 was also studied a t various concentrations of NOz. No measurable dark reaction was observed at any of the concentrations investigated (Figure 1).It must be remembered that for all the reactions under study, a reference flask of SO2 in air was kept in the dark and used to correct for the response of the FPD as well as for volume and slight instrumental changes. The reaction rates measured represent the difference between the reaction rate in question and that which might occur between SO2 and air in the dark. N o measurable reaction is known to occur between SO2 and air in the dark, therefore the latter was assumed to he negligibly slow. In considering the NOn-SOz-air system, the question of light intensity and spectral distribution again arises. Although the spectral distribution of the lamps used differs from that on noonday sunlight in the same spectral range, the quantum yield for the NO2 photolysis is very close to 1 in the region of 3000-4000 A. The absorption spectrum of NO2 is intense, and very broad, decreasing gradually in the region of 3000-3500 A (13, 19). The total number of photons available for the reaction: NO2 hu NO 0 should be approximately the same whether black-light fluorescent bulbs or noonday sunlight is used as long as NO2 absorbs strongly in this region and the total photon flux in the region of 3000-4000 A is approximately the same as that found in daylight. Laity (21) found that black lights caused only slight discrepancies in the reactions involved in NO2 photolysis for hydrocarbon systems. No gas phase products of the reaction of SO2 and NO2 in air were detected by the FPD. However, if SOs, H2SO4, NOHS04, or N ~ S 2 0 9 (12) were the principal products formed they would not elute from the chromatographic column used for SO2 analysis. They more probably would be adsorbed on the walls of the flask and go undetected. SO2-Propylene-Air System. Figure 2 shows the photochemical reaction of 2 ppm SO2 and 6 ppm propylene in
+
+
-
+
-
+
(8)
(9) (10)
When SO2 is also present in an NOZ-air mixture under irradiation, it can be expected that SO2 will react with one or more species that result from the photochemical reactions of NO2 in air. .Jaffee and Klein (17) studied the dark reaction of SO2 and NO2 in the absence of air and found it to be relatively slow. Wilson and Levy (18) proposed that KO3 or N 2 0 5 can rapidly oxidize S02. Whether appreciable amounts of NO3 would be formed in an NOZ-air system is not clear, since the NOZ-air system yields only low steady state O3 concentrations (19).
$140 NO2 PPM
I 2 0.
*+occ .+C85
_ _ MRK7 1 'ti
IO0
.+
34
ct 5 I at102 REACT'ON
1,000
2,000
3,000
4,000
5,000
TIME, MINUTES
Figure 1 . Photochemical and dark reactions of 2.00 ppm SO2 in the presence and absence of NOn Volume 8 , Number 8 , August 1974
743
air alone and in the presence of NO2. When only propylene was present, SO2 disappeared a t a rate slightly slower than the rate in air alone. Within experimental error, the propylene did not react. The quenching of 3S02 by olefins has been studied, and the suggested mechanisms involved the interaction of the r-electrons of the olefin with the 3S02 formed by irradiation. The slight decrease in the rate of reaction of SO2 may have been due to this interaction. Although the quenching constant for propylene is almost 103 times that for 0 2 ( 4 ) , its concentration in these studies is about 10-5 times less. Therefore a t the concentration used, olefin interaction with the 3 S 0 2 was considered to be of secondary importance with respect to the oxidation of S02. S02-NO2-Propylene-Air System. The addition of an olefin to the NOx-air system disrupts the equilibrium between S 0 2 , NO, and 0 3 .It promotes the accumulation of NO2 and O3 by helping oxidize NO to NO2 without the overall consumption of an equivalent amount of 0 3 (19). olefin products must inTo do this, the reaction: 0 volve a chain mechanism which produces a number of free radicals capable of oxidizing NO to NO2 (19). The interaction of the NO,-olefin-air system with SO2 should also result in an increased rate of disappearance of SO2 (22). In the present study, the photochemical reaction rate of SO2 was studied a t several concentrations of NO2 and several concentrations of propylene (Figure 3). The rate of reaction of SO2 is much faster in the S02-502-propylene-air system than in the S02-air system or the SOZNO2-air system (23, 24). The photochemical reaction rate is also very much dependent on the reactant concentrations ratios. Of special importance is the propylene/NOz ratio. It appears that the propylene is the limiting reagent since it was completely consumed in all cases except in the case of 0.85 ppm NO2 and 6 ppm propylene where a small amount of propylene was left. After all the propylene was consumed, the photochemical reaction rate of SO2 slowed considerably whether SO2 was present or not. The rate of propylene disappearance was much faster than the rate of SO2 disappearance in all reactions studied. Figures 4 and 5 show the initial rates of SO2 photochemical reaction as a function of the initial concentrations of propylene and NO2 in SO2-NOz-propylene mixtures. The initial rate was obtained from the rate of disappearance of SO2 during the first 30 min and is actually the average rate for the first 30 min of reaction. These figures show the same general relationships as those observed by Altshuller et al. (25) between oxidant and propylene and KO, concentrations. They. therefore, demonstrate that SO2 can react with intermediates or products in the NOx-propylene-air system. Free radicals have been shown to add readily to SO2 (26). Increasing the propylene concentration increases the number of free radicals and other reactive species formed and therefore increases the amount of SO2 that reacts. This is observed in Figure 4. NO2, on the other hand, plays a dual role. It provides 0 atoms through photolysis which can react directly or indirectly through ozone with the propylene to produce free radicals and several reactive species. But NO2 itself and its photochemical reaction product, NO, are both free radicals and could compete with SOz for the free radicals formed from propylene. Hence high concentrations of NO2 decrease the rate of oxidation of SO2 as is shown in Figure 5 . The appearance of compounds such as PAN and other organic nitrates. nitrites, and nitro compounds in the atmosphere demonstrates that many of the free radicals formed from hydrocarbons are consumed by reaction with the various oxides of nitrogen (15). All these observations can fit effectively into a generalized mechanism such as that proposed by
+
744
Hecht and Seinfeld (27). Fitting SO2 into their generalized mechanism is a simple matter. The following reactions are to be considered:
RO,.
+
+
-
SO,
0
(5)
RO,. etc.
(11)
NO
+ 0, + olefin
0
RO,.
-- +
+ hv
NO,
NO2
---)
PAN etc.
R02S02,SO3
+
(12)
RO.etc.
(13)
where Reactions 11-13, in this instance. are used to indicate a general class of reactions resulting in peroxy compounds and free radicals.
-
Environmental Science & Technology
I20
.-
NO2 PPM
IO0
*to00
ot5 I
to85
&+IO 2
.
tI 7
200
400 600 800 TIME, MINUTES
1000
1200
Figure 2. Effect of NO2 on the photochemical reaction of 2.00 ppm SO2 and 6.00 pprn propylene
2.
& t BPPM C,H.
DARK
12
0.81
T
0
2
4
8
6
IO
12
14
16
18
20
TIME, HOURS
Figure 3. Effect of propylene (C3H6) on the photochemical and dark reactions of 2.00 ppm SO2 and 1.7 pprn NO2
O i
X
I
0
20
40
60
. C,H,
80
100
120
PPM
Figure 4. Initial rate of the photochemical reaction of 2.00 ppm SOz and 1.7 ppm N O n as a function of propylene (C3Hs) concentration
Using the steady state approximation on all reactive intermediates, one can derive the following:
M[h&NO,)
+ h&NO) + h&O2)]1
This expression essentially has two terms. The first represents the competition of SO2 and NO2 for the free radicals formed. The second term shows the competition for the 0 atom formed by NO2 photolysis. This competition involves olefin, 0 2 , N02, and NO. In this scheme the Os-olefin reaction has been neglected but including it would lead to essentially the same result. I t should be kept in mind that this is not a detailed mechanism. Each reaction in the scheme actually represents a class of reactions where several reactive intermediates are involved and where several products could be formed. The simplified reaction scheme, however, has the advantage that the effect of varying initial conditions can be seen easily. From the simplified scheme the relative rates of disappearance of reactants and appearance of products can be predicted, and the observed dependence of the reaction rate of SO2 on the propylene and NO2 concentrations conforms to the predictions of the equations. S02-N02-H20-Air System. Photochemical and dark reactions of 1.7 ppm NO2 and 2 ppm SO2 in air were studied a t 50 and 75% relative humidity. The results for 50% relative humidity are plotted in Figure 6. N o measurable dark reaction was observed. The photochemical reaction rate of 1.7 ppm NO2 and 2 ppm SO2 in 50% relative humidity air was about 10 times that observed in dry air. However, the reaction was much slower than the dry NO2 -SOz-propylene-air photochemical reaction. At 75% relative humidity, a strange effect was observed for the NOZ-SOZ-water-air system. Approximately 25% of the SO2 disappeared before irradiation. An accurate mea-
::
I!
x
Ii
surement of the initial concentration of the flask contents could not be made since so much of the SO2 reacted before an analysis could be performed. After the rapid initial reaction, the SO2 concentration leveled off. If the flask were then irradiated, SO2 was consumed a t a very rapid rate. The data were poor and are not presented, but the dark reaction before irradiation consumed approximately 0.5 ppm SO2 out of 2 ppm while the photochemical reaction was rapid but too erratic to measure. Sulfur dioxide alone in air, however, does not react a t relative humidities as high as 90% (7, 12). And since no reaction of SO2 in the dark occurs in any combination and at relative humidities u p to, and including, 50% relative humidity, it is more probable that the high humidity reaction takes place with NO2 in solution in a liquid layer or in freshly formed aqueous aerosols. The surface of the flask could become coated with HzO and promote the oxidation of SO2 by NO2 and 0 2 from the air, or the same reaction can occur in aqueous aerosols. The reaction would level off because of the high acidity developed by the reaction products and the low solubility of SO2 in highly acidic solutions. SO2-NOz-Propylene-HzO-Air System. The photochemical and dark reactions of 1.7 ppm NO2, 6 ppm propylene, and 2 ppm SO2 were also studied a t 50 and 75% relative humidity. At 50% relative humidity, no dark reaction was observed for any of the reactants measured. The photochemical reaction consumed SO2 and propylene a t approximately the same rate as that observed a t 0% relative humidity showing that water vapor does not play an important part in such systems. Again a t 75% relative humidity, a dark reaction was observed that consumed about 0.5 ppm SOz. Little or no propylene was consumed by the dark reaction, and the SO2 concentration leveled off as above. If the flask was irradiated, both SO2 and propylene were consumed rapidly. The data again were very poor and are not presented other than describing the reactions qualitatively. However, whenever the NO2 or propylene was completely reacted. the rate of disappearance of SO2 slowed down considerably. The increase in the S02-NO2 reaction in the presence of HzO could be explained by the following reaction scheme for the production of HO radicals (26, 28):
\.
NO1
+
0,
\
NO,
i
+
20
40
60
80
100
120
NO, PPM
Figure 5 . Initial rate of the photochemical reaction of 2.00 ppm
SOn in the presence of 6.00 ppm propylene as a function of NO2
0
M -03
0 3
0
HONO
+
HOSOz
s: 1 2 IO81
HOS0,02 HOSOiO
o\3‘
,
(5) (6) (15)
2 OH
(16)
2 HONO
(17)
NO
(18)
The HO radicals from the above or similar reactions can then react with SO2.
HO
4-,14a
M
0 2
HO
hv
concentration
DARK
+
0
+
H,O
NO
I
0
NO
hv
H,O
0 0
+ + + + + - + +
+ +
--
SO1
+
0,
NO RH
-
HOSO,
(19)
HOSOzOz
(20)
+ HOS0,O HOSOzOH + R NO,
(21) (22)
,Lo.
where RH represents an organic compound or radical. Water did not cause a significant increase in the reaction rate of the NOz-S02-propylene-H20-air system, because the reaction of 0 atoms. 0 3 , and NO2 with propylene produce so many free radicals and other species that consume SO2 that the HO radicals produced in the reactions of NO2 with HZO are probably insignificant. Volume 8, Number 8 , August 1974
745
Table I . Initial Rate of Photochemical Reaction of S O pin S02-N0,-Air System Concentration, p p m SO2
2.00 2.00 2.00 2.00 2.00 2.00 2.0@ a
Initial rate of SO1 reaction, pprn/rnin X 104
NO?
0
1.71. 0.3 3 . 3 1 0.3 2 . 9 1 0.3 1 . 6 + 0.3 1 . 7 1 0.3 1 . 8 1 0.3 1 5 i 2c
0.85 1.7 3.4
5.1 10.2
1.7a
50% relative humidity.
Table II. Initial Rate of Photochemical Reactionin SOpN 0 *-Prop y Ie ne-A i r System Concentration, pprn SO2
2.00 2.00 2.00 2.00 2.00 2.00 2.00 2 . OG“ Q
NO2
0
0.85 1.7 5.1 10.2 1.7 1.7 1.7a
Initial rate of reaction, pprn/rnin
Propylene
6.00 6.00 6.00 6.00 6.00 3.00 12.00 6.001
SO? X lo3
Propylene X 102
0 . 1 3 1 0.03 1 5 13 1 2 13 5.6k 0.1 3 . 7 1 0.1 6 . 6 ; 0.1 2113 1 2 1 30
0 9 . 0 1 0.5 1 3 11 1 2 11 8 . 3 3 ~0 . 5 6 . 6 1 0.5 23i1 11 i lQ
W i t h H ? 0at 50% relative humidity.
Summary, Generalized Mechanism, and Comparison of Systems. Tables I and I1 give the data obtained for the photochemical reactions of SO2 for all the systems studied. We can now summarize the importance of various parameters on the rate of SO2 removal. The photochemical reaction of SO2 in air results in an initial rate of SO2 disappearance of about 1.7 x ppm/min. The addition of NO2 can increase the rate of SO2 disappearance to about 3.0 x ppm/min a t an NO2 concentration of 0.85 ppm or 1.7 ppm relative to an SO2 concentration of 2 ppm. The excess rate is about the same as the rate of photooxidation of SOz in air alone, and is attributed to the reaction of SO2 with 0 atoms produced from NO2 photolysis either directly, or indirectly, through higher oxides of nitrogen. At 50% relative humidity, the rate of the photooxidation of SO2 is increased tenfold to 1.5 x 10-3 ppm/min. This result has been explained by assuming that HZO contributes OH radicals to the system through reactions of the type shown in Equations 16 through 21. The dark reaction observed a t 75% relative humidity may be a homogeneous liquid reaction between SO2 and NO2 or, more simply, the old lead chamber reaction for the formation of sulfuric acid in the presence of NOz. The reaction is not well characterized from the data obtained from these studies. The largest effect observed was caused by the addition of propylene to the NO2-Son-air system. Depending on the relative concentrations of YO2 and propylene, the rate of disappearance of SO2 can be increased by two orders of magnitude or more over that observed in air alone. The propylene/NOz ratio is important in determining the fraction of reactive intermediates available to react with the SO2. Gas chromatographic analysis of the aerosols formed a t high concentrations in these reactions showed more than 40 peaks. A polymerization process is definitely indicated, and there is reason to believe that the polymers include sulfur dioxide as a copolymer. Extrapolation of the results given here to atmospheric conditions would be difficult. The concentrations of SO2 746
.-**(
Environmental Science & Technology
.......
and NO2 used in this study are from one to two orders of magnitude greater than those found in polluted air. The SO2 and NO2 might happen to be a t approximately the same concentration in a polluted atmosphere; however, the hydrocarbon concentration is usually much higher than either the NO2 or SO2 concentrations. There are many different substances present in a polluted atmosphere. Each has its own characteristic reactivity and its own set of reactions. Temperature and humidity vary greatly. Light intensity changes with time of day and season of the year. Pollutants are continually being emitted from a wide variety of sources. However, the general trends observed in this study can be of value in predicting certain conditions. Hydrocarbons contribute an important mechanism of SO2 removal, and high or very low concentrations of NO, inhibit SO2 removal. Water vapor can contribute to SO2 removal, particularly at high relative humidities. It can be seen, therefore, that the complex relationship among multiple pollutants must be understood before an intelligent control scheme can be derived.
Literature Cited (1) Altshuller, A. P., Bufalini, J. J., Enuiron. Sci. Technol., 5 , 39 (1971). ( 2 ) Bufalini, M . , ibid., p 685. (3) Urone, P . , Schroeder, W. H., ibid., 3,436 (1969). (4) Sidebottom, H . W., Badcock, C. C., Calvert, J . G., Rabe, B. R., Damon, E. K . , J Amer. Chem. SOC.,93,3121 (1971). (5) Wilson, W. E., Levy. A,, Wimmer, D. B., J. Air Pollut. Contr. Ass.. 22,27 (1972). (6) Smith, J . P., PhD Thesis, University of Colorado, Boulder, Colo., 1973. ( 7 ) Urone, P . , Lutsep, H., Noyes, C . M., Parcher, J . F., Enuiron. Sci. Technol., 2, 611 (1968). (8) Crider, W. L., Anal. Chem., 3 i , 1770 (1965). (9) Stevens, R. K . , Mulik, J . D., O’Keeffe, A. E., Krost, K . J., ibid., 43,827 (1971). (10) Calvert, J . G.: Pitts, J. N., “Photochemistry,” pp 783-6, Wiley & Sons, New York, N.Y.1966. (11) Katz, M., Can.J. Chem. Eng., 48,3 (1970). (12) Schroeder, W. H., PhD Thesis, University of Colorado, Boulder, Colo., 1971. (13) Hall, T. C., PhD Thesis, University of California, Los Angeles. Calif., 1953. (14) Gerhard, E. R., Johnstone, H. F., Ind. Enp. Chem. 4 i , 972 (1955). (15) Leighton, P. A,, “Photochemistry of Air Pollution,” pp 20811,234-8, Academic Press, Kew York, N.Y., 1961. (16) Rao, T. N., Collier, S. S., Calvert, J . G., J. Amer. Chem. Soc.. 91,1609 (1969). (17) Jaffe, S . , Klein. F. S., Trans. Farada) Soc.. 62,2150 (1966). (18) Wilson, W. E., Levy, A,, J . Air Pollut. Contr. Ass., 20, 385 (1970). (19) Stephens, E. R., ibid., 19,181 (1969). (20) Mulcahy. M . F., Stevens, J. R., Ward, J . C., J . Phq‘s. Chem., i l , 2124 (1967). (21) Laity, J. L., Enoiron. Sci. Technol., 5,1218 (1971). (22) Altshuller, A. P., Kopcznyski, S. L., Lonneman, W. A , , Becker, T. L., Wilson, D. L.. ibid., 2, 696 (1968). (23) Groblicki, P. J . , Nebel, G. J., in “Chemical Reactions in Urban Atmospheres,” pp 241-69, C. S. Tuesday, Ed., Elsevier, New York, N.Y.. 1971. (24) Falgout, D. A , , PhD Thesis, University of Florida, Gainesville, Fla., 1972. (25) Altshuller, A. P., KoDczvnski. S. L.. Lonneman. W. A , . Becker, T. L., Slater, R.. &uGon. Sei. Technol., 1,899 (1967). (26) Calvert. J . G., Slater, D. H., Gall, J . W , , in “Chemical Reactions in Urban Atmospheres,” pp 133-54, C. S. Tuesday, Ed.. Elsevier, New York, N.Y., 1971. (2’7) Hecht, T . A,. Seinfeld, J. H., Environ. Sci. Techno/.. 6, 47 (1972j . (28) Calvert, J . G., Demerjian. K . L., Kerr, J. A,, International Symposium on Air Pollution, Tokyo, 1972.
Received for reuieu M a y 7, 1973. Accepted April 22, 1974. This work u‘as made possible by grants from the National Center for Air Pollution Control (AP-00357-07) and the National Science Foundation fGP-342381. Work u‘as in partial fuljillment of the PhD requirements off-campus for J . P. Smith, L’niuersitq‘ of Colorado.
