Environ. Sci. Technol. 1988, 22, 1079-1085
Kramer, W.; Buchert, H.; Reuter, U.; Boscoito, M.; Maul, D. G.; LeGrand, G.; Ballschmiter, K. Chemosphere 1984, 13, 1255-1267.
Tanabe, S.; Tanaka, H.; Tatsukawa, R. Arch. Environ. Contam. Toxicol. 1984,13, 731-738.
Sims, G. G.; Campbell, J. R.; Zemlyak, F.; Graham, J. M. Bull. Environ. Contam. Toxicol. 1977, 18, 697-705. Subramanian, B. R.; Tanabe, S.; Hidaka, H.; Tatsukawa, R. Arch. Environ. Contam. Toxicol. 1983, 12, 621-626. Calambokidis, J.; Peard, J.; Steiger, G. H.; Cubbage, J. C.; DeLong, R. NOAA Technical Memorandum NOS OMS 6; National Oceanic and Atmospheric Administration: Rockville, MD, 1984; 167 pp. Hidaka, H.; Tanabe, S.; Tatsukawa, R. Agric. Biol. Chem. 1983,47, 2009-2017.
Calambokidis,J.; Peard, J. In 1982 Fur Seal Investigations; Kozloff, P., Ed.; NOAA Technical Memorandum NMFS F/NWC; National Oceanic and Atmospheric Administration: Rockville, MD, 1983. (39) Zell, M.; Ballschmiter, K. Fresenius' 2.Anal. Chem. 1980, 300, 387-402. (40) Castelli, M. G.;Castelli, G. P.; Spagone, C.; Cappellini, L.; Fanelli, R. Chemosphere 1981,10, 291-295.
(41) Bruggeman, W. A.; Marton, L. B. J. M.; Kooiman, D.; Hutzinger, 0. Chemosphere 1981, 10, 811-832. (42) Matthews, H. B.; Dedrick, R. L. Annu. Rev. Pharmacol. Toxicol. 1984, 24, 85-103. (43) Hansen, L. G.; Tuinstra, L. G. M. Th.; Kan, C. A.; Strik, J. J. T. W. A,; Koeman, J. H. J. Agric. Food Chem. 1983, 31, 254-260. (44) Safe, S.; Safe, L.; Mullin, M. J. Agric. Food Chem. 1985, 33, 24-29. (45) Bush, B.; Snow, J.; Connor, S.; Koblintz, R. Arch. Environ. Contam. Toxicol. 1985, 14, 443-450. (46) Norstrom, R. J. In Hazards, Decontamination and Replacement of PCB's;Crine, J.-p.,Ed.; Plenum: New York, 1988 (in press). (47) Addison, R. F.; Brodie, P. F.; Zinck, M. E.; Sergeant, D. E. Environ. Sci. Technol. 1984, 18, 935-937. (48) Holden, A. V. ICES C.M. 1978/E-41; International Council for the Exploration of the Sea: Copenhagen, 1978. (49) Ballschmiter, K.; Zell, M. Chemosphere 1980, 302, 20-30.
Received for review February 9, 1987. Revised manuscript received September 24, 1987. Accepted March 29, 1988.
Vapor-Phase Concentrations of Arsenic, Selenium, Bromine, Iodine, and Mercury in the Stack of a Coal-Fired Power Plant Mark S. Germani" and Wllllam
H. Zollert
Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742
w A sampling and analysis procedure is described for determining vapor-phase concentrations of As, Se, Br, I, and Hg in the stack of a coal-fired power plant. The percentages of the total in-stack concentrations for these elements present in the vapor phase are as follows: Br, 98%; Hg, 98%; Se, 59%; As, 0.7-52%; and I, 199%. A lower limit of 99% was obtained for C1. The vapor-phase concentration of As appears to be dependent upon the in-stack or filter mass loading. This indicates that a vaporization-condensation mechanism may control the vapor-phase concentrations of As. The results for Se indicate that the efficiency of the electrostatic precipitator affects particle vapor-phase fractionation. The results obtained in this study are compared with previous mass balance calculations.
Introduction Numerous studies have been done on physical properties and elemental and chemical compositions of particulate material produced by coal combustion (1-12). Studies of the elemental composition of coal ashes indicate that some elements are fractionated by the combustion process. The degree of fractionation is usually determined by calculating an elemental enrichment factor for the ashes relative to the input coal, EFc0,+ The chalcophilic elements, e.g., Zn, As, Se, Cd, and Pb, typically have the largest EFCod values on in-stack suspended particles. Data obtained from cascade impactor samples have shown that enrichments of these elements increase with decreasing particle size (4, 13). Failure to achieve closure for some elements, most notably C1, Br, I, Se, and Hg (2, 4 ) , with mass balance *To whom correspondence should be addressed at McCrone As-
sociates, Inc., 850 Pasquineli Dr., Westmont, IL 60559.
Present address: Department of Chemistry, University of Washington, Seattle, WA 98195. 0013-936X/88/0922-1079$01.50/0
calculations, indicates that at least a portion of these elements are present in the vapor phase upon release from the stack. A volatilization-condensation mechanism has been invoked to explain the observed behavior of enriched elements in coal-fired power plants. The mechanism involves the vaporization of volatile elements during coal combustion followed by condensation onto particle surfaces in the flue gas stream. Evidence for surficial enrichment of some elements has been obtained in surface studies of fly ash particles (14, 15). Some questions still exist, however, as to whether these enrichments are due to the volatilization-condensation mechanism described above or to surface segregation within particles (16-18). Data concerning vapor-phase concentrations of elements in a coal-fired power plant would be useful for better understanding the behavior of volatile elements during coal combustion. In addition, such data are needed to accurately assess the impact of coal combustion on the environment. For example, receptor models, such as chemical mass balances, require not only precise chemical conposition of particulate emissions from sources but also vapor-phase emissions, especially for elements that may condense onto particle surfaces before being sampled at a receptor site (19). Only a few studies have been done to measure vaporphase concentrations of elements produced during coal combustion. Billings and Matson (20) found that 90% of the Hg input to a coal-fired power plant was released to the atmosphere in the vapor phase. Less than 1% of the total in-stack Hg concentration was present on suspended particles. Anderson and Smith (21) observed that 97% of the Hg was released as the vapor. In both studies, Hg was assumed to exist in the elemental form. The particulate and vapor-phase concentration of Se was determined by Andren et al. (22) a t the inlet and outlet to the electrostatic precipitator of the Allen Steam Plant
0 1988 American Chemical Society
Environ. Sci. Technol., Vol. 22, No. 9, 1988 1079
Table I. Charcoal Collectors Used for Radiotracer Experiments
_c
A r Out
'
'2'
LN Radioiracer
(50 ml round bottom flask)
Charcoal Back-up
Figure 1. Diagram of apparatus used for radiotracer experiments. C-1 and C-2 are heated and unheated charcoal collectors, respectively.
in Memphis, TN. Results of this work indicate that 32% of the input Se is released as vapor. Also, only 7% of the Se is present after the precipitator in the particulate phase. Selenium was determined to exist as the element in both the particulate and vapor phases and to be present only on particle surfaces. Fogg and Rahn (23) determined that >99% of boron emitted from coal-fired power plants is in the vapor phase. Here, we describe a method for determining vapor-phase concentrations of As, Se, Br, I, and Hg in the stack of a coal-fired power plant. Data are presented from samples collected at the Chalk Point Electric Generating Station located in southeastern Maryland. Chalk Point was the site of a previous study by Gladney et al. ( 4 , 25) to determine chemical compositions of size-fractionated in-stack suspended particles. Results from our study are compared to those obtained by Gladney et al. to evaluate our sampling aiid analysis procedures.
Experimental Methods Radiotracer Experiments. The initial goal of this study was to develop a method, using an activated-charcoal sampler, to determine concentrations of vapor-phase As and Se emitted from high-temperature combustion sources such as a coal-fired power plant. It was later, during sample analysis, that we determined that the method could also provide data concerning vapor-phase concentrations of Br, I, and Hg. Radiotracer experiments were done to determine the optimum size and placement of a charcoal trap for collecting As and Se species from high-temperature gas streams. Collectors were tested at a temperature of 260 " C and a flow rate of 20 L min-l. No attempt was made to duplicate the chemical composition of a coal-combustion flue gas stream or to determine the actual collection efficiency for a given collector size. The experiments were designed only to determine if the collector should be placed inside or outside of the stack. Activated coconut charcoal (8-12 mesh, Fisher Scientific) was cleaned by using solutions of 5 M HN03. Onehalf kilogram of charcoal was placed in a beaker and enough 5 M H N 0 3 added to cover the charcoal. The solution was heated at 85 " C for 24 h. The solution was decanted, and a fresh solution was added. This procedure was repeatedly daily for 2 weeks. The charcoal was rinsed with distilled-deionized water. The same procedure was used to rinse the charcoal as was used to clean it. After rinsing for 10 days, the solution was filtered in a vacuum filtration apparatus. Finally, the charcoal was dried at 150 "C for 12 h and placed in clean polyethylene bags. Laboratory experiments were done with the apparatus shown in Figure 1. Radiotracers were prepared for As, AsZ03,Se, and SeOz. Approximately 10 mg of each com1080
Environ. Sci. Technol., Vol. 22, No. 9, 1988
experiment
C-1
E-1 E-2 E-3 E-4
empty 3g empty
1g
c-2 1g 1g 3g 39
pound was irradiated in a sealed quartz vial for 10 min at a neutron flux of 1 X 1013n cmz s-l at the National Bureau of Standards (NBS) reactor. After irradiation, the vial was opened and placed in a 50-mL round-bottom flask. The elements and oxides were chosen because they are the most likely chemical species to be present in the stack of a coal-fired power plant. It is possible that a change in chemical species could occur during irradiation because of prompt y-ray recoil. No provisions were made to correct for this possibility. The experimental sampling train consists of (1)an oven for vaporizing the radiotracer, (2) a 47-mm A1 filter holder containing a 5.0-pm pore-size Teflon filter, (3) a heated charcoal trap, (4)an unheated charcoal trap, and (5) a backup charcoal trap contained in liquid nitrogen. Two charcoal traps were tested. Each trap was made from 1.3 cm 0.d. X 0.8 cm i.d. stainless steel tubing. One trap was 3.8 cm long and contained 1 g of charcoal; whereas, the other was 10 cm long and contained -3 g of charcoal. Stainless steel retaining frits were used to contain the charcoal in the tube. The backup charcoal trap consisted of 4 g of charcoal placed in a test tube inside of a gaswashing bottle. A section of polyethylene screen was placed over the end of the test tube to retain the charcoal. Four experiments were performed for each radiotracer. The experiments differ only in the collector size used for C-1 and C-2 in Figure 1. The collectors used for each experiment are listed in Table I. The heating tape and pump were turned on for 1h until collector C-1 was at 260 "C. The flask containing the radiotracer was placed in the oven. The oven was turned on and set to a temperature which was dependent upon the species being tested. The oven temperature was kept at e180 "C to prevent condensation in the heated portion of the sampling train. Vaporization times ranged from 20 min to 2 h depending upon the radioactive species and the oven temperature. After a time, the oven was turned off and allowed to cool. The radiotracer was removed. After 15 min, the pump and heating tape were turned off. The sampling train was disassembled, and the filter and charcoal samples were placed in polyethylene vials. y-ray spectra were collected with a Ge(Li) detector coupled to a multichannel analyzer system (Canberra Industries Model 8100). An internal integration routine was used to determine the peak areas for As (559-keV y-ray of 76As) and Se (136-keV y-ray of 75Se). The relative amount of activity (expressed as a percent of total activity for all collectors in the sampling train) observed on each collector in the sampling train is given in Table 11. The best results were obtained for experiment E-4 by using a 3-g unheated charcoal collector. Sample Collection. Samples were collected from unit 1 of the Chalk Point Electric Generating Station. A description of the power plant is presented elsewhere ( 4 , 2 5 ) . In-stack samples were collected at a port in the duct work located after the electrostatic precipitator (ESP), but before the stack. This is the same location that Gladney et al. ( 4 )used. Samples were collected by a modified EPA sampling train. It consists of a 6 mm diameter isokinetic nozzle followed by a 47-mm filter holder. The nozzle and
-
Table 11. Radiotracer Experiment Results for As and Se Compounds (% )" compound As
V T = 150 =1
v,
As203 VT = 25 V, = 0.5
sample
E-1
PF C-1 c-2 BUC PF
99 99 >99 52 87 99 2.1 11
7/24/79 3
4
5
7/31/79 6
>99 99 >99 33 68 98
>99 99 99 29 NA“ NA
>99 99 99 7.5 90 59
>99 99 >99 2.0 90 88
5.0 23
2.8 11
8.9 33
3.4 18
element
Se Hg
8/1/79 9
10
11
>99 99 >99 13 NA NA 9.5 50
8/2/79 12
13
>99 99 >99 0.7 57 98
>99 99 >99 1.6 61 99
>99 99 >99 1.7 54 97
>99 99 >99 0.9 56 97
>99 99 >99 1.4 41 96
>99 99 >99 1.0 50 98
66 245
59 237
35 237
25 133
17 159
25 136
= not analyzed.
Table VI. Average In-Stack Particulate and Vapor-Phase Concentrations of C1, I, Br, As, Se, and He
Clb I* Br As
8
7
particle
15000 >IO00 1300 f 90 7f8 20 f 7 121 f 30
Table VII. Binary Correlation Coefficients ( r )for Particulate Br, As, Se, Hg, Al, and Fe with In-Stack Mass Loading
% vapor
total
>15000 >loo0 1310 f 90 140 f 80 33 f 5 124 f 30
phase >99 >99 99 f 13 f 59 f 98 f
element 7c 19 14 gC
“Samples 5, 6, and 7 have been excluded from the average. Vapor-phase concentrations given as lower limit (see text). Error represents analytical uncertainty not standard deviation.
limit of 400 mg m-3 is obtained. This value is an order of magnitude higher than the largest concentration determined for any of the charcoal collectors, i.e., 33 mg m-3 for sample 13. This result is consistent with the observation that C1 is “breaking through” the charcoal collectors. Iodine. The distribution of I in the charcoal collectors is similar to that of C1 for most samples. However, for samples 5 and 6 there was a definite decrease of the I concentration in the collector. The I distribution for sample 6 is given in Figure 3. An estimate of the efficiency of a collector can be determined by calculating the percentage of total vapor-phase I found on the first four sections of the collector. Based on this criterion, only samples 5 and 6 have greater than a 90% collection efficiency, i.e., 95% and 92%, respectively. These two samples were collected at a flow rate of 10 L m i d compared to 17 L min-l for the other samples. The lower flow rate increases the residence time of the gases in the collector which increases the collection efficiency. Lower limits are reported for the vapor-phase I concentration for the other samples (Table V). Bromine. Bromine was quantitatively collected by all of the charcoal traps (Figure 4). The least efficient collection, based on the criterion used for I, was obtained for sample 12, i.e., only 8% of the total Br is found on the last section of the trap. Ninety-nine percent of the total instack Br concentration is present in the vapor phase. Gladney (25) was able to account for only 2.3% of the Br, using a mass balance calculation. Correcting his mass balance calculation to take into account vapor-phase Br yields a 100% closure. The average particulate, vapor-phase, and total in-stack concentration for Br is given in Table VI. Samples 5, 6, and 7 were excluded from the average, since they were collected during minimum-load operation and 1 day after the unit was shut down. Effects of the shutdown and the subsequent minimum-load operation are evidenced by a higher Br concentration in the precipitator ash for that
Br As Se
in-stack mass loading 0.67 (11)” 0.97 (12) 0.58 (10)
element
in-stack mass loading
Hg Alb Feb
-0.34 (10) 0.91 (10) 0.99 (IO)
nNumber in parentheses is number of samples used in the correlation. A1 and Fe values are included for comparison. They are nonvolatile elements and should be highly correlated with in-stack mass loadings.
day and a lower vapor-phase Br concentration. The average EFcoal value for particulate Br (Table IV) is slightly higher than that reported by Gladney but within the range of the standard deviations for each value. The result obtained in this study has a larger relative standard deviation. This is because of the greater range of in-stack mass loadings encountered in this work (11-245 mg m-3, Table V) which are not well correlated (r = 0.67, Table VII) with particulate Br concentrations. Gladney (25) does not report in-stack mass loadings; however, they can be estimated from his A1 concentrations and the Al/mass found in this study, that is [Al]/[mass] = 0.16 f 0.04 By using this datum, the in-stack mass loadings based on four cascade impactor runs are 35,83,58, and 22 mg m-3. Arsenic. Arsenic was quantitatively collected by all of the charcoal traps (Figure 4). Large variations are observed for percent vapor-phase As (Table V) ranging from 52% (sample 2) to 0.7% (sample 8). No other element exhibits such a wide variation. Particulate As is highly correlated with in-stack mass loading (r = 0.97, Table VII). Particulate As is also highly correlated with filter mass loadings ( r = 0.95). Percent vapor-phase As is inversely correlated with filter and in-stack mass loadings, rlog = -0.93 and -0.96, respectively. Two mechanisms could account for the observed As behavior. Both mechanisms assume that an irreversible reaction is occurring a t the particle surfaces, converting vapor-phase As406to a nonvolatile form that remains on the particles. The two mechanisms differ only with regard to where this reaction occurs, i.e., on the particles in the stack or on the particles on the filter. Arsenic oxide is assumed to be the vapor-phase As species instead of the elemental form because combustion would tend to produce the oxide and the equilibrium-saturated vapor pressure concentration for As406 is greater than the largest vapor-phase concentration obtained for any of the samples. Environ. Sci. Technol., Vol. 22, No. 9, 1988
1083
For example, the saturated vapor pressure concentration for a stack temperature of 363 K is 1900 pg m-3 for As406 and 0.6 pg m-3 for As4 (26). The largest observed vaporphase As concentration is 22 pg m-3 for sample 2. For the first mechanism (M-l), the amount of As406in the vapor phase is dependent upon in-stack mass loading. We assume that an increase in in-stack mass loading represents only a change in the total number of particles not in the particle size spectrum. An increase in in-stack mass loading would represent a proportionate increase in the amount of particulate surface area available for a reaction to occur, with a subsequent decrease in the amount of As present in the vapor phase. This mechanism is consistent with the fact that in-stack mass loading is inversely correlated with percent vapor-phase As. Note the values obtained for samples 2 and 5. The in-stack mass loading was the same for both samples (11mg m-3); however, the percent vapor-phase As is lower for sample 5 (Table V). The stack gas velocity for sample 5 was less (-5 m s-l) than that for sample 2 (-9 m s-l). This would allow more time for a surface reaction to occur and may account for the decrease in percent vapor-phase As. For the second mechanism (M-2), the amount of As406 present in the vapor phase is dependent upon the particulate loading on the in-stack filter, as the reaction occurs as the gases pass the particles on the filter. An increase in the filter loading would represent an increase in the available surface area, such as was described for M-1, and a decrease in vapor-phase As. The fact that percent vapor-phase As is inversely correlated with filter mass loading supports this mechanism. The As data for samples 2 and 5 can also be explained by this mechanism. Samples 2 and 5 have approximately the same filter loading, i.e., 2.1 and 2.8 mg, respectively, but different percent vapor-phase As results. The lower sampling velocity used for sample 5 could account for the decrease in vapor-phase As, based on the reasoning used for M-1. In order to differentiate between M-1 and M-2, data are needed for samples collected at a constant in-stack mass loading and a range of filter loadings. The greatest difference in filter loadings for a constant in-stack mass loading in this study is found for samples 8 and 10. The filter loadings are 66 and 35 mg at an in-stack mass loading of 245 and 237 mg m-3, respectively. The percent vaporphase As for these samples are 0.7 (sample 8) and 1.7 (sample 10). These data indicate that the amount of vapor-phase As may be dependent upon filter loading (M-2). Whichever mechanism is occurring, the fact that As406can be removed from the vapor by coal-derived fly ash has been observed in a study by Wouterland and Bowling (27). The authors found that fly ash can remove As406 from the vapor even when the vapor is not saturated at 200 “C. They conclude that chemisorption or a chemical reaction is occurring. The average particulate and vapor-phase As concentrations are given in Table VI. The wide range of values observed are indicated by the large standard deviations for these values. This data cannot be compared with Gladney’s (25) mass balance calculation for As due to the uncertainty in the mechanism that is determining the vapor-phase As concentration. Selenium. Distributions of Se in the charcoal collectors indicate that it was quantitatively collected (e.g., Figure 4). Unlike the case of As, Se is not well correlated with in-stack mass loading (Table VII). Consequently, consistent results were obtained as indicated by the rather narrow range of values listed in Table V. An average of 59% Se was present in the vapor phase in the stack, less 1084
Environ. Sci. Technol., Vol. 22, No. 9, 1988
Poly Bag (---I Pnlyvial (-1
1 0
,
I
1
I
:------
correlated with in-stack mass loading (Table VII), and therefore, the EFCodvalue has a large relative standard deviation. Ninety-eight percent of the total in-stack Hg concentration is present in the vapor phase. According to Gladney's (25) mass balance calculation for Hg, only 43% of the Hg needs to be in the vapor phase to achieve 100% closure. The reason for the disagreement between the two studies is not known. A value of 98% is in agreement with results from other studies ( 1 , 2 0 ,21, 29).
Summary A sampling and analysis procedure is described for determining the vapor-phase concentrations of elements emitted from the stack of a coal-fired power plant. The results are compared with a previous study done a t the sampling site. The results for Br, Se, and Hg are in good agreement with previous mass balance calculations. The results for As indicate that the percent of As in the vapor phase is dependent upon either in-stack or filter mass loading. Consequently, the data obtained in this study could not be directly compared with previous mass balance calculations. The data for C1 and, in some samples, I indicate that these elements are not quantitatively collected by the charcoal samplers. A redesign of the sampling device may improve the collection efficiency for C1 and I. Similar charcoal collectors have also been used to determine the vapor-phase concentrations of F, C1, As, and Se from volcanoes (30) and copper smelters (31). Such data are very important for understanding the behavior of volatile chemical species from both natural and anthropogenic high-temperature atmospheric particle sources. Acknowledgments We thank Greg Barley, Jeff Fedderly, and Stu Hersh for their help in sample collection and G. Gordon and E. S. Gladney for their comments. Registry No. Na, 7440-23-5;Mg, 7439-95-4; Al, 7429-90-5;K, 7440-09-7;Sc, 7440-20-2;Ti, 7440-32-6;V, 7440-62-2;Cr, 7440-47-3; Mn, 7439-96-5;Fe, 7439-89-6;Co, 7440-48-4;Zn, 7440-66-6;Rb, 7440-17-7; Sb, 7440-36-0; Cs, 7440-46-2; Ba, 7440-39-3; La, 7439-91-0; Ce, 7440-45-1; Sm, 7440-19-9; Eu, 7440-53-1; Dy, 7429-91-6; Yb, 7440-64-4; Lu, 7439-94-3; Hf, 7440-58-6; Ta, 7440-25-7; W, 7440-33-7; Hg, 7439-97-6; Th, 7440-29-1; Clz, 7782-50-5;Br2, 7726-95-6;12, 7553-56-2;As, 7440-38-2;Se, 778249-2.
Literature Cited (1) Kaakinen, J. W.; Jorden, R. M.; Lawasani, M. H.; West, R. E. Environ. Sci. Technol. 1975, 9, 862-869. (2) Klein, D. H.; Andren, A. W.; Carter, J. A.; Emery, J. F.; Feldman, C.; Fulkerson, W.; Lyon, W. S.; Olge, J. C.; Talmi, Y.; Van Hook, R. I.; Bolton, N. Environ. Sci. Technol. 1975, 9,973-979. (3) Fisher, G. L.; Chang, D. P. Y.; Brummer, M. Science (Washington,D.C.) 1976, 192, 553-555.
(4) Gladney, E. S.; Small, J. A.; Gordon, G. E.; Zoller, W. H. Atmos. Environ. 1976, 10, 1071-1077. (5) Fisher, G. L.; Prentice, B. A.; Silberman, D.; Ondov, J. M.; Biermann, A. H.; Ragaini, R. C.; McFarland, A. R. Environ. Sci. Technol. 1978, 12, 447-451. (6) Coles, D. G.; Ragaini, R. C.; Ondov, J. M.; Fisher, G. L.; Silberman, D.; Prentice, B. A. Environ. Sci. Technol. 1979, 13,455-459. (7) Ondov, J. M.; Ragaini, R. C.; Biermann, A. H. Environ. Sci. Technol. 1979,13,598-607. (8) Ondov, J. M.; Ragaini, R. C.; Biermann, A. H. Environ. Sci. Technol. 1979, 13, 946-953. (9) Smith, R. D.; Campbell, J. A.; Nielsen, K. K. Environ. Sci. Technol. 1979, 13, 553-558. (10) Henry, W. M.; Knapp, K. T. Enuiron. Sci. Technol. 1980, 14,450-456. (11) McElroy, M. W.; Carr, R, C.; Ensor, D. S.; Markowski, G. R. Science (Washington, D.C.) 1982,215, 13-18. (12) Hansen, L. D.; Silberman, D.; Fisher, G. L.; Eatough, D. J. Environ. Sci. Technol. 1984, 18, 181-186. (13) Natusch, D. F. S.; Wallace, J. R.; Evans, C. A. Science (Washington, D.C.) 1974, 183, 202-204. (14) Linton, R. W.; Williams, P.; Evans, C. A.; Natusch, D. F. S. Anal. Chem. 1977,49, 1514-1521. (15) Campbell, J. A.; Smith, D. 0.;Davis, L. E. Appl. Spectrosc. 1978, 32, 316-319. (16) Hulett, L. D., Jr.; Weinberger, A. J.; Northcutt, K. J.; Ferguson, M. Science (Washington, D.C.) 1980, 21 0, 1356-1358. (17) Stinespring, C. D.; Stewart, G. W. Atmos. Environ. 1981, 15, 307-313. (18) Smith, R. D.; Baer, D. R. Atmos. Environ. 1983, 17, 1399-1409. (19) Kowalczyk, G. S.; Choquette, C. E.; Gordon, G. E. Atmos. Environ. 1978, 12, 1143-1153. (20) Billings, C. E.; Matson, W. R. Science (Washington,D.C.) 1972,176, 1232-1233. (21) Anderson, W. L.; Smith, K. E. Environ. Sci. Technol. 1977, 11, 75-80. (22) Andren, A. W.; Klein, D. H.; Talmi, Y. Environ. Sci. Technol. 1975, 9, 856-858. (23) Fogg, T. R.; Rahn, K. A. Geophys. Res. Lett. 1984, I, 854-857. (24) Germani, M. S.; Gokmen, I.; Sigleo, A. C.; Kowalczyk, G. S.; Olmez, I.; Small, A. M.; Anderson, D. L.; Failey, M. P.; Gulovali, M. C.; Choquette, C. E.; Lepel, E. A.; Gordon, G. E.; Zoller, W. H. Anal. Chem. 1980, 52, 240-245. (25) Gladney, E. S.Ph.D. Thesis, 1974, University of Maryland, College Park, MD. (26) Handbook of Chemistry and Physics, 48th ed.; Weast, R. C., Ed.; CRC: Cleveland, OH, 1967-1968, D140. (27) Wouterland, H. J.; Bowling, McG. K. Environ. Sci. Technol. 1979, 13, 93-97. (28) Pillay, K. K. S.; Thomas, C. C.; Sondel, J. A.; Hyche, C. M. Anal. Chem. 1971,43,1419-1425. (29) Lindberg, S.E. Atmos. Environ. 1980, 14, 227-233. (30) Germani, M. S.Ph.D. Thesis, 1980, University of Maryland, College Park, MD. (31) Germani, M. S.; Small, M.; Zoller, W. H.; Moyers, J. L. Environ. Sci. Technol. 1981, 15, 299-305.
Received for review July 8,1987. Accepted March 15,1988. This work was supported by the National Science Foundation R A " Program under Grants ENV 75-02667-A03 and PFR 7502667806.
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