Environ. Sci. Technol. 1984, 18, 962-967
Aerosol Sulfur Episodes in St. Louis, Missouri James J. Huntzlcker," Robert S. Hoffman, and Robert A. Cary
Department of Chemical, Biological, and Environmental Sciences, Oregon Graduate Center, 19600 N.W. Walker Road, Beaverton, Oregon 97006 Aerosol sulfur and volatilizable sulfuric acid were measured for 8 days in Aug 1979 in St. Louis, MO, by using a quasi-continuous, in situ particulate sulfur monitor. Two types of episodes were observed. The first, which occurred during the afternoons of Aug 4-8, was characterized by rapid increases in aerosol sulfur, sulfuric acid, and sulfur dioxide but no corresponding increases in light scattering. These were hypothesized to result from gas-phase oxidation of SOz in a point source plume with subsequent condensation onto preexisting particles or into new particles. The second type of episode occurred over several days and was characterized by a broad peak in both aerosol sulfur and light scattering, little or no volatilizable sulfuric acid, and essentially no relationship between the daily variations of sulfur dioxide and particulate sulfur. This episode was associated with the long-range transport of a polluted air mass. Introduction Sulfate aerosols and particularly acidic sulfate aerosols are recognized as important air pollutants and have been studied extensively. These aerosols result primarily from the oxidation of SO2,the principal source of which is the combustion of fossil fuels. The two most important oxidation routes are homogeneous gas-phase reactions involving free radicals such as HO. ( I ) and aqueous-phase reactions in cloud and aerosol droplets (2,3).In the absence of NH3 the product of these reactions would be HzS04, which at ambient temperatures and relative humidities is almost totally in the particulate phase. In the presence of sufficient NH3, however, the HzS04is rapidly neutralized to (NH4)2S04at rates approaching the gasphase mass transfer rate of NH, to the H2S04 droplets (4-7). Consequently, NH3 and sulfate acidity can exist only when the oxidation rate of SO2 is "fast" (a few percent per hour) and the ratio of SO2 to NH, is large or when the relative humidity is sufficiently high (280%) (6). For the latter case the coexistence of NH3 and sulfate acidity is the result of the high equilibrium vapor pressure of NH3 over deliquesced (NH4)$04 particles and the consequent loss of NH, from such particles. In this paper we report measurements of acidic sulfate aerosol made during an intercomparison study of quasi-real time particulate sulfur monitors in St. Louis, MO (8). The data are examined to provide information on the conditions which lead to the presence of sulfate acidity in the atmosphere. Experimental Section The field measurements were conducted during the period Aug 3-10, 1979, as part of the sulfur monitor intercomparison study. All instruments were located in a fourth floor laboratory on the Washington University campus in St. Louis. Further details concerning the intercomparison study are given by Camp et al. (8). The in situ particulate sulfur analyzer consisted of a Meloy SA-285 flame photometric detector, an aerosol pretreatment section, and associated electronics (Figure 962
Environ. Sci. Technol., Vol. 18, No. 12, 1984
1). The Meloy SA-285 was modified by shortening the air inlet line and minimizing the number of right-angle bends to maximize particle transmission into the flame. In addition, the signal processing electronics of the Meloy SA-285 were replaced by the microcomputer system described below. The aerosol pretreatment section accomplished four functions: thermal speciation of the acidic, ammonium, and refractory fractions of the sulfate aerosol; removal of sulfur-containing gases (SO2,HzS) in the diffusion stripper (denuder); conversion of any H2S04to (NH4)zS04 just prior to entering the flame photometer; measurement of the flame photometer base line. These functions and the need for them have been described in previous papers (6, 9). For field measurements two aspects of the thermal speciation process deserve special note. First, NH4HS04, (NH4)2S04,and stoichiometries intermediate between these two cannot be distinguished by the thermal speciation technique because they exhibit essentially the same temperature dependence of volatilization (9). Second, for aerosols more acidic than NH4HS04the amount of HzS04 that can be volatilized depends on the state of mixing of the acidic and ammonium fractions of the aerosol. For internal mixing of the two fractions (Le., NH4+and H+ in the same particle) the signal decrease at 130 OC corresponds to the amount of acidity (as sulfur) in excess of NH4HS04stoichiometry. The titratable acidity of such an aerosol would include the NH4HS04 contribution, however. For externally mixed HzS04 droplets and (NH4)2S04or NH4HS04 particles (i.e., H2S04 and (NH4)&3O4 in separate particles) the signal decrease measures the total titratable acidity (as sulfur). Therefore, unless the state of mixing of the aerosol is known, the thermal speciation technique can provide only upper and lower limits to the titratable acidity, with the former corresponding to pure internal mixing of the acidic and ammonium components and the latter to pure external mixing (i.e., HzS04 droplets and (NH4)2S04particles), respectively. The thermal speciation system was similar to that used previously (6) except that it was controlled automatically by a microcomputer. By approxpriate positioning of the ball valve (Vl in Figure l),total particulate sulfur, total particulate sulfur minus volatilizable sulfuric acid, and refractory sulfur species were measured. During each of these measurements the photocurrent for the flame photometer was converted to a voltage and digitized. After a 2-min period following the change of valve position to allow for the flame photometer signal to stabilize, the digitized signal was integrated (i.e., accumulated and stored in a buffer) for a 2-min period. At the end of the four-part cycle the base line was subtracted from the integrals for the analytical channels, and the resultant values were linearized with a software technique. The base-line integral which was used for each channel was determined by interpolation between the base-line integral from the current cycle and that from the preceding cycle. The linearized values for the room temperature, 130 "C, and 250 "C channels were presented to a strip chart recorder in the form of a histogram, and the nonlinearized data for all four channels were stored on cassette magnetic tape.
0013-936X/84/0918-0962$01.50/0
0 1984 American Chemical Society
Table I. Concentrations of SO2, Sod2-, HzSO4, and O3 at Acid Episode Peaks (8/4-8/8)a [HzS041 date
time (CDT)
[SO21 ppbVb
wg (S)/m3
8/4/79 8/5/79 8/6/79 8/7/79 8/8/79
14-15 13-14 16-17 14-15 16-17
13 47 26 80 23
17 60 33 102 29
a
[s04'-1 (S042-)/m3 wg (S)/ma
wg (S04")/m3
nequiv (H+)/m3
[os] ppbVb
7.0 9.8 7.0 12 8.1
150 200 150 250 170
64 57 (53) 67 87
3.6 5.4 4.0 5.9 4.3
11 16 12 18 13
9
"Background concentrations have been subtracted from the SO4'- and SOz peaks. The acidic aerosol was assumed to be an internal mixture of HzSO4 and (NH4)zS04 The [O,] value for 8/6/79 was determined by interpolation because of a missing datum at the time of the peak sulfate concentration. ppbV, parts per billion, volume.
*
I
N H ~ Permeation tube
- 25 ST. LOUIS
8
U m e r Line
TOIOI
SO:
n
Flame Photometric Detector
. \ \\ \
//-Hr*
i-1 /
Microcomputer
1-1 I
Flgure 1. Schematic of in sltu sulfur analyzer. V1 is a five-port ball valve, and V2 Is a solenoid shutoff valve.
The complete analytical cycle required 18 min, the last 2 min of which were used to produce a distinguishable histogram on the strip chart recorder. The instrument was calibrated by generating polydisperse aerosols of (NH4&304 and sampling simultaneously with the in situ instrument and by filtration with Fluoropore 0.5-pm pore size filters. The filters were extracted in water, and sulfur concehtrations were measured by our version of the flash volatilization-flame photometric method (9). These results and those of other validation experiments are reported as supplementary material (see paragraph at end of paper regarding supplementary material).
Results Hourly average concentrations for total aerosol sulfur and volatilizable sulfuric acid are given in Figure 2a. (Total aerosol sulfur results have also been given for the same period by Camp et al. (8) and Jaklevic et al. (lo).) Sulfur dioxide concentrations, which were measured at a St. Louis County monitoring site (station 9; see Figure 3) about 4 km west of the Washington University site, are plotted in Figure 2b. Two types of episodes are apparent. The first is characterized by relatively narrow peaks that occur simultaneously for total aerosol sulfur, volatilizable sulfuric acid, and SO2 during midafternoon; these will be termed acid episodes. At all other times the concentration of volatilizable sulfuric acid was at or below the noise level of 1-2 pg (So4")/m3. The second is a broad, multiday episode in which total aerosol sulfur and SOz are uncorrelated, which contains essentially no volatilizable sulfuric acid and which peaks shortly after midnight on Aug 10, 1979. This will be designated a haze episode for reasons discussed below. The acid episode occurring on Aug 8, 1979, was superimposed on the front end of the haze episode. Acid Episodes. The results of Figure 2 suggest that the acid episodes were superimposed on a regional-urban background. Accordingly, appropriate background con-
80
t
(b) so
Lo
-I
AUGUST Flgure 2. (a) Hourly average aerosol sulfur concentratlons at the Washington University she, Aug 1979. The upper line corresponds to total sulfur and the lower line to volatilizable sulfuric acid. (b) Sulfur dioxide concentrations at St. Louis County station 9. The abcissa is central daylight time.
Table 11. Aerosol Characteristics at Acid Episode Peaks"
date
particulate sulfur fraction
acid fraction
ammonium fraction
08/04/79 08/05/79 08/06/79 08/07/79 08/08/79
0.18 0.083 0.11 0.055 0.13
0.65 0.60 0.59 0.68 0.63
0.35 0.40 0.41 0.32 0.37
" Particulate sulfur fraction: [S04z-]/([S0,Z-] + [SO,]). Acid fraction: [H']/([H+] + [NH,']). Ammonium fraction: [",+I/ ([H'I + ["4+1). centrations were substracted from the sulfate and SO2 data to give results characteristic of the acid episodes. In addition, it was assumed that the acidic and ammonium Environ. Sci. Technol., Vol. 18, No. 12, 1984
963
Table 111. Solution Characteristics of Sulfate Aerosols at Acid Episode Peaks Assuming a Formal Internal Mixture of H2S04 and (NH,),SOd weight percent date 8/4/79 8/5/79 8/6/79 8/7/79 8/8/79
H2S04
37 38 37 40 37
("4hS04
27 34 35 25 29
molarity, mol/L
HZO 36 28 28 35 34
H2S04
5.6 5.7 5.6 6.0 5.6
("4)2S04
@04*-) total
re1 humidity, %
8.6 9.5 9.5 8.8 8.8
47 39 41 40 44
3.0 3.8 3.9 2.8 3.2
ST LOUIS AREA
10 km
Figure 3. St. Louis area. The numbers 1-5 in circles correspond to St. Louis City monitoring stations and 6 and 8-10 to St. Louis County monloring sttes. WU, Washington University: L, Labadle power plant. The graphical Inserts are SO, concentratlons (ppbV) at the indicated monitoring stations as a function of time (CDT) for Aug 6, 1979.
fractions of the acid episode sulfate were internally mixed; i.e., the aerosol consisted of partially neutralized sulfuric acid droplets. An equivalent representation is to consider the aerosol a formal internal mixture of HzS04 and ("JzS04. The results are summarized in Tables I and 11. Each acid episode occurred during a period of elevated ozone concentrations, and although there was no consistent temporal relation between the ozone and sulfate peaks, e.g., ozone peak first and sulfate peak second, the two always occurred approximately within 1 h of each other. Sulfur dioxide peaked simultaneously with the sulfate during the acid episodes, and only 5.5-18% of the sulfur was in the particulate phase. (Because SO2 and particulate sulfur were measured at different sites, only qualitative significance should be attached to these percentages.) However, a large fraction (59438%)of the sulfate was acidic; Le., the ratio [H+]/([H+]+ [NH4+])varied between 0.59 and 0.68. From these results and the values of relative humidity measured by the National Weather Service at the Lambert St. Louis International Airport, the phase diagram of Tang et al. (11)was used to calculate the solution concentrations in terms of weight percent of HzS04,(NH4)2S04,and H20. These results are given in Table 111. For such concentrations all sulfate species are completely dissolved. The weight percent concentrations were converted to molarities by measuring the densities of two of the solutions (corresponding to the 8/4/79 and 8/6/79 episodes) and using the average density (1.47 g/cm3) for the five episodes. These results are also given in Table 111. The pHs of the same two solutions were measured to be less than zero. In Figure 4 the sulfate aerosol concentration at the Washington University site and the light scattering coef964
Environ. Sci. Technol., Vol. 18, No. 12, 1984
' d
AUGrST 6 Z
A
U
G
r
S
T 7
2
Flgure 4. (a) Aerosol sulfur at Washington University site: (b) bSat at St. Louis County station 9. Aug 6-7, 1979. The abcissa is central daylight time.
ficient (bscat) at the nearby St. Louis County monitoring station (no. 9) are plotted for Aug 6 and 7. The principal features of the bscat plot are morning peaks that were probably associated with local sources such as traffic. During the period when the sulfate concentration peaked, there was no corresponding peak in bscat, however. This behavior was also observed for the other acid episodes. Although bscat and sulfate were measured at different locations, the simultaneous occurrence of an SO2 peak at the St. Louis County site and a sulfate peak at the Washington University Site implies that the acid episode occurred at both sites. Therefore, the lack of a simultaneous increase in bscat during the sulfate peaks suggests that the sulfate aerosol was in a particle size range which was too small to scatter light effectively. Thus, the principal features of the acid episodes were predominance of SO2 over sulfate (i.e., low particulate fraction), high acid fraction, and particle sizes that were inefficient at scattering light. These are all sugggestive of a relatively fresh sulfate aerosol produced by the atmospheric oxidation of SOz to H$04 and partial neutralization of the H2S04 by NH3. An unknown, but probably small, fraction of the sulfate could have resulted from SO3 produced directly in a combustion process followed by hydration to H2S04. Although detailed trajectories are not available, the most likely source of the SOzwas the plume from the 2400 MW
coal-fired Labadie power plant, which is at 225' (westsouthwest) from station 9. During the 7 h preceding and including the sulfate peak the surface wind direction at station 9 was 270' f 22' for the first 5 h but shifted to 236' and 225' for the last 2 h. The average surface wind speed was 6.9 f 0.4 km/h. In the hour following the peak the wind direction was 236') and the speed was 8.5 km/h. Although no information is available on the variation of wind speed and direction with height, the qualitative picture which emerges is that of a plume whose initial direction would take it to the south of stations 6 and 9 but which was swept northeasterly across several monitoring stations more or less simultaneously during midafternoon. The SOz concentration profiles shown in Figure 3 for Aug 6 at the various air-quality monitoring stations support this contention. Results for the other acid episodes also suggest the Labadie power plant as the source but are not as clear-cut as for Aug 6. Haze Episode. Inspection of Figure 2a shows that the sulfate aerosol concentration reached a minimum during the night of Aug 5. From that time on, exclusive of the acid episodes, the sulfate concentration rose gradually until about the afternoon of Aug 8. A t that time the concentration rapidly increased until it reached a maximum shortly after midnight on Aug 10 and declined rapidly thereafter. With the exception of the short-term acid episode on Aug 8, the concentration of volatilizable HzSO4 did not exceed the instrument noise level. Thus, the aerosol had a stoichiometry between NH4HS04 and (NH4)2S04. Throughout the episode (except as noted below), the sulfate and SOz concentration profiles were quite dissimilar, and most of the sulfur was in the particulate phase. At the peak of the episode the fraction of sulfur in the particulate phase (i.e., [S042-]/([S042-] + [SO,])) was 0.68. This is in sharp contrast to the acid episodes and suggests an aged aerosol. In Figure 5 the aerosol sulfate concentration (at Washington University) and bat are plotted for the period Aug 8-10. Because only fragmentary bscat data were available from St. Louis County station 9 for this period, data from station 6, which is in a rural-suburban location about 17 km southwest of Washington University, were used. For Aug 9 and 10 the general features of the sulfate and bscat plots match closely and indicate a 2-day period of reduced visibility or haze. The simultaneous peaks in sulfate and bacatat midday on Aug 9 were accompanied by a rather poorly defined SOz peak at station 9 (see Figure 2b) but no SOz peak at station 6. Thus, it is likely that the sulfate peak on Aug 9 was not associated with fresh aerosol but was a feature of the 2-day haze episode. In contrast, however, the midday sulfate peak on Aug 10, which occurred on the downside of the haze episode, was accompanied by a sharp SOz peak at station 9 but little or no volatilizable HzS04. The fraction of sulfur in the particulate phase at the peak was 0.26. These results suggest a point source plume, which was producing fresh sulfate aerosol, as the cause of the peak.
Discussion Acidic sulfate aerosol has been previously observed in the St. Louis area by a number of investigators (12-18), and short-term acid episodes at the Washington University site have been reported by Delumyea et al. (16) and Cobourn et al. (17)during a 3-day period in July 1977. These acid episodes were superimposed on a regional haze episode characterized by elevated concentrations of sulfate aerosol and reduced visibility throughout the 3-day period. In contrast to the episodes described in this paper, however, the July 1977 acid episodes were accompanied by
L 0'
I
S
1
I
9
I
1 I
I
IO
AUGUST
Flgure 5. (a) Aerosol sulfur at Washington University site; (b) b,,, at St. Louis County station 6. Aug 8-10, 1979.
simultaneous increases in bsca. Cobourn et al. also observed other sulfate episodes during July and Aug 1977, but little or no volatilizable HzS04was present. These periods also included increased light scattering and were characterized as multiday haze episodes. The absence of a significant increase in light scattering during the Aug 1979 acid episodes can be interpreted in terms of gas to particle conversion mechanisms. Two mechanisms must be considered: condensational growth and droplet-phase reactions. The former involves the condensation of H2S04onto preexisting particles or into new particles. In this case the H2S04is produced either by the homogeneous, gas-phase oxidation of SOz or by the hydration of SO3 formed directly in the combustion process. The latter mechanism involves the liquid-phase oxidation of SOz in cloud, fog, or aerosol droplets. McMurry et al. (19) made measurements in the plumes from three coal-fired power plants (including Labadie) and found that the condensation growth law accounted for 80-100% of the new aerosol volume formed in the plumes and droplet phase growth for 0-20%. For those cases in which the droplet growth law was operating, an increase in aerosol volume was accompanied by a corresponding increase in bscat. However, in the one case (50 km downwind from the stack of the Widows Creek plant in Stevenson, AL) where the aerosol growth was determined to be solely by condensation, only a very small increase (0.03 X m-l) in bscat was observed for an increase of 7.5 Envlron. Sci. Technol., Vol. 18,
No. 12, 1984 985
pm3/cm3 in the aerosol volume concentration. If the aerosol is assumed to have been HzS04in equilibrium with the ambient relative humidity (- 50%), this is equivalent to a scattering efficiency of 0.7 mz/g(SOz-). Such a small scattering efficiency resulted because the condensational growth occurred primarily on particles too small to scatter light effectively. Smog chamber studies of aerosol sulfate growth by condensation also show the growth to occur predominantly on particles too small to produce significant light scattering. In an analysis of an experiment involving SOz, NO,, propylene, air, and sunlight, McMurry and Wilson (20) found that no aerosol growth occurred for particles larger than 0.2 pm in diameter. In contrast, the growth rate for droplet-phase reactions increases with increasing particle size, and new aerosol material produced in such a manner would scatter light efficiently. Thus, the lack of increased light scattering during the 1979 acid episodes suggests that condensation was the dominant mechanism for gas to particle conversion. For the July 1977 acid episodes the associated increase in light scattering could have resulted from the participation of droplet-phase growth in the gas to particle conversion process or from an aging process involving several mechanisms (e.g., condensation onto a preexisting, wellaged aerosol, hygroscopic growth, and coagulation). Other studies in the St. Louis area also indicate the complexity of the gas to particle conversion process and its effect on light scattering. In a July 1976 study of the Labadie plume McMurry et al. (19) found that droplet-phase growth contributed about 10% of the new aerosol volume. In the same experiment Cantrell and Whitby (21) found that increased light scattering always accompanied the formation of new aerosol material in the plume. In a study of the Labadie plume during the summers of 1974 and 1976, Husar et al. (22)found considerable variability in the ratio of excess bscatin the plume to excess particulate sulfur. If all the excess light scattering in these measurements was from sulfate aerosol formed in the plume, the minimum observed light scattering efficiency was 1.6 mz/g(S0,2-), which is also small relative to values generally observed for sulfate aerosol (see, for example, ref 23). Qualitative insight into the relationship between atmospheric sulfur chemistry and air mass character can be gained by considering the prevailing weather conditions during the study period. During the first 5 days of the measurement period a stationary cold front was several hundred kilometers south of St. Louis, and the eastern half of the United States was under the influence of high pressure. Surface winds in St. Louis were light and generally from the southwest. Daytime temperatures were high (up to 36 "C), and absolute humidity was high (dew point -20 "C). These conditions are representative of maritime tropical air masses, and it was under these conditions that acidic sulfate was observed. As noted by Vanderpol et al. (14),such air masses are likely to be deficient in ",-a situation which favors the retention of aerosol acidity. Similar associations of aerosol acidity with maritime tropical air masses have been observed by Pierson et al. (a), and Weiss et al. (25). Cobourn et al. By the morning of Aug 9 the western half of the cold front had curled toward the southeast, and the high pressure system had moved in the same direction. This motion continued through the morning of Aug 10. As a result of this motion St. Louis was on the western or trailing edge of the high pressure system, and during this period high aerosol sulfur concentrations with only modest diurnal variations and little or no volatilizable acidity
(In,
966
Environ. Scl. Technol., Vol. 18,No. 12, 1984
occurred, as noted above. The passage of the cold front during the afternoon of Aug 10 and the resultant influx of clean air from the northwest produced a rapid decline in sulfate concentrations and bscst. Previous studies (e.g., see ref 26-31) have attributed such broad maxima to a combination of long-range transport and the accumulation of both primary (e.g., SOz,NH3) and secondary (e.g., SO?-, 0,) pollutants in the slow moving, anticyclonic air mass. Wolff et al. (30, 31) have studied the Aug 1-10 episode in detail and formed their conclusions from an analysis of surface weather maps, 850-mbar wind fields, visibility measurements at 250 National Weather Service stations, O3data from 200 state and local monitoring sites, and measurements at their own instrumented van located in southern Louisiana. From these data they showed that the haze episode originated over Kansas and western Missouri on Aug 1and moved eastnortheasterly to western Ohio by Aug 3. During this period the episode was characterized mainly by elevated O3 concentrations, but by Aug 3 haze had begun to develop. A second area of haze and high O3developed in the Atlantic coastal area between Boston and South Carolina. Subsequently, these areas merged, and the polluted air mass moved clockwise around the center of high pressure. The polluted air arrived in southern Louisiana on Aug 7 and moved northeastward from there, reaching St. Louis on Aug 9 as indicated by our sulfate data. Summary
Aerosol sulfur and sulfuric acid were measured in St. Louis for the period Aug 3-10,1979. During that period two types of sulfate aerosol episodes were observed. The first was characterized by sharp midafternoon increases in aerosol sulfur of which volatilizable HzS04constituted a significant fraction. Notably, corresponding increases in aerosol light scattering did not occur. These acid episoses were attributed to point source plumes in which SOz was being oxidized to HzS04by homogeneous, gas-phase reactions followed by condensation of the H2SO4both onto preexisting particles and into new particles with partial neutralization by NH,. The lack of light scattering from this aerosol was hypothesized to result from the newly formed particulate matter being in particle sizes too small to scatter light efficiently. The second type of episode was a multiday haze episode which was characterized by a broad peak in both the aerosol sulfur concentration and the light scattering coefficient but little or no volatilizable HzS04. This episode was attributed to sulfate production in a polluted air mass transported over very long distances. Acknowledgments
The continuing support and encouragement of Robert
K. Stevens of the US.Environmental Protection Agency throughout this research are very much appreciated. We also thank R. B. Husar, J. Djukic-Husar, and W. G . Cobourn for their help during the field study and Warren White for obtaining the St. Louis County and City air quality data and for his critical reading of the manuscript. Supplementary Material Available Results of calibration and instrument validation experiments (4 pages) will appear following these pages in the microfilm edition of this volume of the journal. Photocopies of the supplementary material from this paper or microfiche (105 X 148 mm, 24X reduction, negatives) may be obtained from Microforms Office, American Chemical Society, 1155 16th St., N.W., Washington, DC 20036. Full bibliographic citation (journal, title of article,
Environ. Sci. Technol. 1904, 18, 967-972
(15) Cunningham,P. T.; Johnson, S. A. Science (Washington, D.C.) 1976, 191, 77-79. (16) Delumyea, R.; Macias, E. S.; Cobourn, W. G. Atmos. Environ. 1979, 13, 1337-1338. (17) Cobourn,W. G.; Djukic-Husar,J.; Husar,R. B. J , Geophys. Res. 1980,85, 4487-4494. (18) Cobourn, W. G.; Husar, R. B. Atmos. Environ. 1982,16, 1441-1450. (19) McMurry, P. H.; Rader, D. J.; Stith, J. L. Atmos. Environ. 1981,15, 2315-2327. (20) McMurry, P. H.; Wilson, J. C. Atmos. Environ. 1982, 16, 121-134. (21) Cantrell, B. K.; Whitby, K. T. Atmos. Environ. 1978,12, 323-333. (22) Husar, R. B.; Patterson, D. E.; Husar, J. D.; Gillani, N. V.; Wilson, W. E., Jr. Atmos. Enuiron. 1978, 12, 549-568. (23) White, W. H. Nature (London)1976,264, 735-736. (24) Pierson, W. R.; Brachaczek, W. W.; Truex, T. J.; Butler, J. W.; Korniski, T. J. Ann. N.Y. Acad. Sei. 1980, 338, 145-173. (25) Weiss, R. E.; Waggoner, A. P.; Charlson, R. J.; Ahlquist, N. C. Science (Washington, D.C.)1977,195, 979-981. (26) Samson, P. J.; Ragland, K. W. J. Geophys. Res. 1977,16, . . 1101-1106. (27) Hidy, G. M.; Mueller, P. K.; Tong, E. Y. Atmos. Environ. 1978,12,735-152. (28) Vukovich, F. M. Atmos. Enuiron. 1979, 13, 255-265. (29) King, W. J.; Vukovich, F. M. Atmos. Environ. 1982, 16, 1171-1181. (30) Wolff, G. T.; Kelly, N. A.; Ferman, M. A. Science (Washington, D.C.) 1981,211, 703-705. (31) Wolff, G. T.; Kelly, N. A,; Ferman, M. A. Water, Air, Soil Pollut. 1982, 18, 65-81.
author, page number) and prepayment, check or money order for $7.50 for photocopy ($9.50 foreign) or $6.00 for microfiche ($7.00 foreign),are required. Registry No* "2, 7446-09-5; '3, 1002815-6; H2S049 7664-93-9; (NH4&304,7783-20-2; ammonium, 14798-03-9. Literature Cited Calvert,J. G.; Stockwell,W. R. Enuiron. Sci. Technol. 1983, 17,482A-443A.
Beilke, S.; Gravenhorst, G. Atmos. Environ. 1978, 12, 231-239.
Hegg, D. A.; Hobbs, P. V. Atmos. Environ. 1978, 12, 241-253.
Robbins, R. C.; Cadle, R. D. J. Phys. Chem. 1958, 62, 469-471.
Cadle, R. D.; Robbins, R. C. Discuss. Faraday SOC.1961, 30,155-161.
Huntzicker, J. J.; Cary, R. A.; Ling, C.-S. Environ. Sci. Technol. 1980, 14, 819-824.
McMurry, P. H.; Takano, H.; Anderson, G. R. Environ. Sei. Technol. 1983, 17, 347-352.
Camp, D. C.; Stevens,R. K.; Cobourn, W. G.; Husar, R. B.; Collins, J. F.; Huntzicker,J. J.; Husar, J. D.; Jaklevic, J. M.; McKenzie, R. L.; Tanner, R. L.; Tesch, J. W. Atmos. Environ. 1982, 16, 911-916. Huntzicker,J. J.; Hoffman, R. S.; Ling, C.-S. Atmos. Environ. 1978, 12, 83-88. Jaklevic, J. M.; Loo, B. W.; Fujita, T. Y. Enuiron. Sei. Technol. 1981,15, 687-690. Tang, 1. N.; Munkelwitz, H. R.; Davis, J. G. J. Aerosol Sei. 1978,9, 505-511.
Charlson, R. J.; Vanderpol, A. H.; Covert, D. S.; Waggoner, A. P.; Ahlquist, N. C. Science (Washington,D.C.) 1974,184, 156-158.
Charlson, R. J.; Vanderpol, A. H.; Covert, D. S.; Waggoner, A. P.; Ahlquist, N. C. Atmos. Environ. 1974,8,1257-1267. Vanderpol. A. H.; Carsey, F. D.; Covert, D. S.; Charlson, R. J.; Waggoner, A. P. Science (Washington, D.C.) 1975, 190, 510.
Received for review January 23,1984. Accepted June 14,1984. This research was supported in part by US.Environmental Protection Agency Grant R804750 and by Cooperative Agreement CR807654. The paper has not been subjected to EPA$ peer review and therefore does not necessarily reflect the views of EPA. Thus, no official endorsement should be inferred.
Acute Toxicity Screening of Water Pollutants Using a Bacterial Electrode Elalne J. Dorward and 6. George Barisas" Department of Chemistry, Colorado State University, Fort Collins, Colorado 80523 ~
~~
Escherichia coli electrodes were used in an instrumental
bioassay of the acute toxicity of substances in water. The method involves potentiometric measurement of C02 production by E. coli cells immobilized a t the surface of a C02-sensing electrode. The net rate of COz production by the bacteria reflects the complex series of biochemical reactions which constitute the respiratory processes of the cells. The inhibition of any part of the respiratory process by some pollutant will result in a measurable decrease in bacterial COz production. The E. coli electrode is able to measure the acute toxicity of a broad range of substances, including metals, anions, gases, and organic compounds. Dose-effect curves obtained with the E. coli electrode are compared with results reported for the Beckman Microtox bioassay and for rainbow trout 96-h LC50values. Acute toxicity values measured with the E. coli electrode for cadmium, lead, copper, cyanide, and arsenite are comparable to those obtained with the 1Bmin Microtox bioassay. Introduction
Water quality criteria for aquatic environments are based primarily on bioassays or toxicity tests. Acute toxicity tests are the first steps in determining, for a particular species, acceptable levels of a given chemical 0013-936X/84/0918-0967$01 SO10
substance. Many problems are associated with commonly used techniques for measuring acute toxicity. High cost, long experiment times, and requirements for specialized laboratories and much laboratory space are among the important problems. Quantitation of biological responses is another difficulty; the inherent variability of biological systems makes it difficult to measure chemical toxicity by purely biological means. To measure acute toxicity effectively, a system must provide a simple, sensitive, and rapid measurement of physiological parameters which are indicative of overall organism viability. Such parameters might be associated with a major metabolic process controlled by interdependent enzyme systems. Metabolic processes can be effectively monitored by electroanalytical techniques. For example, bioselective sensors, which use intact, living bacterial cells in place of isolated enzymes a t the surface of a membrane electrode ( I ) have been developed as extensions of enzyme electrodes. The measurement of L-glutamine in aqueous solutions and in human serum by a highly selective and sensitive potentiometric bacterial membrane electrode has been reported (1). Potentiometric bacterial membrane electrodes have been employed to measure L-aspartate (2),L-histidine (3),and L-arginine (4)
0 1984 American Chemical Society
Environ. Sci. Technol., Vol. 18, No. 12, 1984 967
