Environ. Sci. Technol. 2000, 34, 356-360
Temporal Trends in and Influence of Wind on PAH Concentrations Measured near the Great Lakes DONALD R. CORTES,† ILORA BASU,† CLYDE W. SWEET,‡ AND R O N A L D A . H I T E S * ,† School of Public and Environmental Affairs and Department of Chemistry, Indiana University, Bloomington, Indiana 47405, and Illinois State Water Survey, Champaign, Illinois 61820
This paper reports on temporal trends in gas- and particle-phase PAH concentrations measured at three sites in the Great Lakes’ Integrated Atmospheric Deposition Network: Eagle Harbor, near Lake Superior, Sleeping Bear Dunes, near Lake Michigan, and Sturgeon Point, near Lake Erie. While gas-phase concentrations have been decreasing since 1991 at all sites, particle-phase concentrations have been decreasing only at Sleeping Bear Dunes. To determine whether these results represent trends in background levels or regional emissions, the average concentrations are compared to those found in “urban” and “rural” studies. In addition, the influence of local wind direction on PAH concentrations is investigated, with the assumption that dependence on wind direction implies regional sources. Using these two methods, it is found that that PAH concentrations at Eagle Harbor and Sleeping Bear Dunes represent regional background levels but that PAH from the Buffalo region intrude on the background levels measured at the Sturgeon Point site. At this site, wind from over Lake Erie reduces local PAH concentrations.
Introduction The Integrated Atmospheric Deposition Network (IADN) consists of five master sampling sites on the shores of the five Great Lakes. This joint United States/Canadian project has been in operation since 1990, and since that time, about 5000 measurements of the concentrations of polychlorinated biphenyls (PCBs) pesticides and polycyclic aromatic hydrocarbons (PAH) in air and precipitation have been made. These data have been interpreted in terms of temporal trends and loadings of PCBs (1-3) and in terms of temporal trends and agricultural sources of organochlorine pesticides (4, 5). The focus of this paper is on the temporal trends of PAH in both the gas- and particle-phases. PCBs and polychlorinated pesticides, on one hand, and PAH, on the other, have fundamentally different sources to the environment. PCB and the pesticides were manufactured and dispersed, in some cases intentionally and widely, in the environment. Most of these compounds were severely regulated during the 1970s and 1980s, and current levels in the Great Lakes region are primarily due to revolatilization * Corresponding author phone: (812)855-0193; fax: (812)855-1076; e-mail:
[email protected]. † Indiana University. ‡ Illinois State Water Survey. 356
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from terrestrial surfaces. PAH are not intentionally produced, rather they exist in the atmosphere as byproducts of the incomplete combustion of almost any fuel. As a result, atmospheric levels are primarily due to recent emissions. Previous measurements (2, 4) indicated that the atmospheric concentrations of PCBs and pesticides were declining significantly at the five IADN master sites over the last 5-7 years. However, it was not clear if this observation could be extrapolated to PAH, given the differences in the sources of these compounds. Long-term trends in atmospheric PAH concentrations are often inferred by comparing historical measurements, usually made by different researchers using different measurement methods (6). Some researchers have analyzed sediment cores and calculated long-term atmospheric fluxes of PAH to lakes (7, 8). However, to determine if atmospheric PAH concentrations are responding to recent improvements in pollution control technology and other pollution reduction efforts, long-term sampling and consistent methodology are needed. There are only a few such studies in the literature. Coleman et al. reported decreasing PAH concentration in urban atmospheric samples from 1991 to 1995 in England (9). Jacob et al. found that urban atmospheric PAH have been declining from 1991 to 1995 in Germany by using spruce sprouts and poplar and beech leaves as passive samplers (10). This paper examines the temporal trends in background PAH concentrations measured between 1991 through 1997 at the three United States IADN sites. The assumption that these are, in fact, background PAH levels is tested by comparing the concentrations measured at these three sites to those measured in other studies and by examining the influence of local wind direction on the PAH concentration measurements.
Experimental Section Sampling and Analytical Methodology. The samples in this study were taken at Eagle Harbor near Lake Superior (latitude 47°27′47′′; longitude 88°08′59′′), Sleeping Bear Dunes near Lake Michigan (latitude 44°45′38′′; longitude 86°03′30′′), and Sturgeon Point near Lake Erie (latitude 42°41′34′′; longitude 79°03′20′′). These sites were chosen to be representative of the atmospheric environment near the Great Lakes, while minimizing influences from local pollution sources. In addition to air samplers, each site is equipped with a meteorological tower that records average hourly wind speed and wind direction at 10 m elevation. Air temperature, solar radiation, and relative humidity are measured at 2 m elevation. A summary of sampling and analytical procedures is presented here, but full details are reported elsewhere (1114). Air was pulled through a modified Anderson high-volume air sampler (General Metal Works, model GS2310) at a rate that gave an 820 m3 sample in 24 h. Sampling events were 24 h long and occurred every 12 days. Particles were collected on quartz-fiber filters (Whatman QM-A). Gas-phase organic compounds were collected on XAD-2 (Sigma, Amberlite 2060 mesh) resin. Prior to May of 1992, polyurethane foam was used to collect gas-phase compounds. After sampling, the XAD-2 resin was Soxhlet extracted using 50% hexane in acetone for 24 h. The extract was reduced by rotary evaporation, exchanged to hexane, and then fractionated on 3.5% (w/w) water-deactivated silica gel to remove interferences. PAH were then eluted with 50% hexane in dichloromethane. The final extracts were concentrated under a stream of nitrogen and spiked with quantitation standards prior to analysis by gas chromatographic mass 10.1021/es9905851 CCC: $19.00
2000 American Chemical Society Published on Web 12/17/1999
TABLE 1. Phase Transition Energies (Section A) and Atmospheric Half-Lives of Gas-Phase PAH (Section B) Determined from Regression Parametersa Section A Sleeping Bear Dunes
Eagle Harbor
phenanthrene fluoranthene pyrene chrysene
∆H (kJ/mol)
rel std error (%)
P > | t|
∆H (kJ/mol)
35 28 43 21
10 13 10 21
0.0001 0.0001 0.0001 0.0001
n.s. n.s. 14 n.s.
38
Sturgeon Point
P > |t|
0.0112
∆H (kJ/mol)
rel std error (%)
P > | t|
15 15 19 11
27 28 29 53
0.0002 0.0004 0.0007 0.0616
Section B Sleeping Bear Dunes
Eagle Harbor
phenanthrene fluoranthene pyrene chrysene
rel std error (%)
t1/2 (yrs)
rel std error (%)
P > | t|
7.8 7.1 2.8 2.9
29 27 12 11
0.0007 0.0003 0.0001 0.0001
Sturgeon Point
t1/2 (yrs)
rel std error (%)
P > | t|
t1/2 (yrs)
rel std error (%)
P > | t|
8.2 9.3 3.7 3.2
45 54 24 19
0.0285 0.0668 0.0001 0.0001
6.9 6.9 2.6 2.2
36 37 18 15
0.0057 0.0070 0.0001 0.0001
a Values that are significant with >95% confidence are in normal font, those that are significant with 90-95% confidence are in italics, and those that are not significant with >90% confidence are indicated by “n.s.”. The number of data points ranged between 160 and 191, except for chrysene which ranged between 96 and 145 due to many nondetected concentrations.
spectrometry. Instrumentation used over the course of the study included a Hewlett-Packard 5890 gas chromatograph with a 5970A mass spectrometer, a Hewlett-Packard 5890 gas chromatograph with a 5985 mass spectrometer, and a Hewlett-Packard 6890 gas chromatograph with 5973 mass spectrometer. Separation was achieved using 30 m × 250 µm i.d. (film thickness 0.25 µm) DB-5 and DB-5MS columns. Extensive quality control was performed to monitor the analytical process (15). Extraction efficiencies were monitored by including a matrix spike for all PAH with each extraction batch (approximately 10 samples). Perdeuterophenanthrene was added to each sample prior to extraction as a surrogate standard. Average matrix spike recoveries were between 60% and 100% with standard deviations of approximately 20% for all PAH reported in this study (15). Site-specific and matrixspecific field blanks usually contained less than 20% of the sample mass. Laboratory blank values were usually below the method detection limit, and blank corrections were not performed. Data Analysis. Data from December 1991 through December 1997 were used for the Sleeping Bear Dunes and Sturgeon Point sites; data from November 1990 through December 1997 were used for Eagle Harbor. In most cases, to enhance detection, two or three filters, each representing a 24-h sampling event and taken 12 days apart, were composited prior to sample extraction and analysis. Concentrations in air were determined by dividing the total mass measured by the total air volume collected during the 24-h sampling period. Partial pressures were calculated using the ideal gas law, which incorporates the molecular weight of the compound and the average air temperature during the sampling period. If a concentration was below the detection limit, it was not included in the determination of temporal trends. The reported values for chrysene include triphenylene, because these PAH cannot be chromatographically resolved. Acenaphthene, acenaphthylene, and fluorene were not reliably eluted during the silica gel fractionation; therefore, these concentrations are not reported here.
Results and Discussion Temperature Dependence. For the gas-phase components, we used the multiple linear regression technique developed in previous IADN studies (1, 4, 5) to determine the effect of atmospheric temperature on the PAH concentrations and to
obtain environmental half-lives for these compounds. In brief, this statistical technique fits the natural logarithm of the partial pressure (ln P) of a given compound (as the dependent variable) to the reciprocal atmospheric temperature and time (as two independent variables)
ln P ) a0 + a1
(T1) + a time
(1)
2
where T is the atmospheric temperature (in K) and time is the day number (in relative Julian days) of each sample. The parameters a1 and a2 represent -∆H/R from the ClausiusClapeyron equation and -k (a first-order elimination rate constant), respectively. Incorporating both temperature and time in the regression equation reduces bias in the temporal trends caused by variations due to temperature effects. These effects depend on the phase-transition and desorption enthalpies of the specific PAH, temperature-dependent physical processes (such as air-water transfer), and human activities that are correlated with temperature (such as seasonal fuel use). Obviously, there are direct sources that are not correlated with temperature, and trend biases due to these sources will not be removed by this technique. The environmental temperature effect on gas-phase PAH concentrations is quantified by ∆H, which can be calculated by multiplying the a1 term in eq 1 by -R. These values, which are often compared to laboratory-measured enthalpies of vaporization, are given in Table 1, section A. At Eagle Harbor these values are less than half of the laboratory values (16); at Sturgeon Point, the values are about one-quarter of the laboratory values; while at Sleeping Bear Dunes, temperature dependence was observed for pyrene only. Clearly, enthalpy of vaporization does not adequately describe the behavior of PAH at these sites. The low values are probably due to the many current sources of PAH that are not temperature dependent. Temporal Trends. Plots of the concentrations of pyrene (gas-phase) and benzo[a]pyrene (particle-phase) are shown in Figure 1. Note that the pyrene concentrations often peak in the summer months, but the benzo[a]pyrene concentrations do not. This observation indicates the importance of including both the atmospheric temperature and time in the regression (see eq 1). The environmental half-lives for the gas-phase compounds were determined by dividing the rate VOL. 34, NO. 3, 2000 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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FIGURE 1. Gas-phase pyrene (top) and particle-phase benzo[a]pyrene (bottom) concentrations (in pg/m3) as a function of time at Eagle Harbor (top), Sleeping Bear Dunes (middle), and Sturgeon Point (bottom). The arrows indicate July 1 of each year. constants (-a2 from eq 1) into the natural logarithm of 2. The half-lives, nearly all of which are significant at the 99% confidence level, are given in Table 1, section B. The halflives are about the same among the three sites: about 8 years for phenanthrene and fluoranthene and about 3 years for pyrene and chrysene. It is not yet clear what causes this 2-fold clustering. Atmospheric temperature could not be included in the regression for particle-bound PAH because each filter sample was a composite of two to three samples taken 12 days apart. Hence, the regression equation was reduced to
ln P ) a0 + a2time
(2)
The environmental half-lives for particle-bound PAH are given in Table 2. Most of the trends at Eagle Harbor and Sturgeon Point are not significant, indicating that particlebound PAH concentrations are not declining at a rate that is detectable given the current length of study. In contrast, there is a significant downward trend for nearly all of the particulate bound PAH at Sleeping Bear Dunes, with halflives averaging 5.3 years (SD ) 1.5 yr). The most curious observation is that the PAH concentrations in the gas-phase decrease over time at all sites, but the PAH concentrations in the particle-phase decrease only at Sleeping Bear Dunes. There are two likely causes for this seeming anomaly: First, the particle-phase concentrations are lowest at the Eagle Harbor site (see Table 3), and thus, the relative errors of these concentrations are probably highest at this site. A relatively high error may limit our ability 358
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to find a statistically significant temporal trend in these Eagle Harbor data. Second, as we will show later, the Sturgeon Point PAH concentrations are influenced by wind direction during sampling. In this case, the effect of wind direction may confound the effect of time on the particle-phase PAH concentration regression at this site. Regional vs Remote PAH Sources. The IADN sampling sites were chosen to measure background levels of pollutants; however, it is difficult to find regions not affected by continuous PAH emissions. Thus, it is important to know whether the observed trends in PAH concentrations are trends in background concentrations or trends in regional emissions. Two approaches were taken to answer this question. First, the levels of PAH at the IADN sites were compared with levels measured at “urban” and “rural” locations in other studies. Second, the influence of local wind direction on pollutant concentration was examined. We assumed that, if PAH were coming from regional sources (within about 50 km), these sources should influence the measured PAH concentrations. The average atmospheric concentrations of PAH measured in this study are presented in Table 3. PAH concentrations at Sleeping Bear Dunes are slightly higher but similar to those observed at Eagle Harbor, while the concentrations at Sturgeon Point are 4-7 times higher. The concentrations at Eagle Harbor and Sleeping Bear Dunes compare well with PAH concentrations at other “rural” locations (6, 17, 20). Although the Sturgeon Point concentrations are greater than the rural locations, they are lower than concentrations found at “urban sites” (6, 10, 21-25). Thus, comparison of the PAH concentrations with the literature suggests that background levels are being observed at Eagle Harbor and Sleeping Bear Dunes, while the levels at Sturgeon Point are somewhat greater than background concentrations. While Sturgeon Point is not located in an urban area, Buffalo, NY is urban, and it lies about 20 km northeast across Lake Erie. Correlating wind directions with pollutant concentrations is complicated because the 24-h samples collected in this study do not correspond with only one primary wind direction due the presence of the diurnal lake/land breeze. The method used here incorporates hourly wind directions measured at each site in a linear regression model. Hourly wind roses for the three sampling sites are presented in Figure 2. Four sectors were selected based on the predominant wind patterns at each site. Infrequent wind directions are not included in any sector in order to prevent PAH associated with atypical wind patterns from interfering with the overall analysis. The four wind sectors were included in the following regression equation
conc ) a0 + a1fwd,1 + a2fwd,2 + a3fwd,3 + a4fwd,4
(3)
where conc is the total of the gas-phase PAH concentrations for the 24-h sampling period (see Table 1 for the four gasPAH included in this total) and fwd,i is the fraction of the 24-h period during which the wind was blowing from sector i. The fitted parameters (the ai values) were estimated using the general linear models routine in Statistical Analysis Software (SAS Institute Inc., Cary, NC). Because multiple filter samples were composited prior to analysis, the particle-phase PAH were not included in this analysis. The model statistics and fitted parameters for each site are presented in Table 4. The mean concentration is slightly different from that given in Table 3 because the samples associated with incomplete meteorological data are not included. The model is significant only for the Sturgeon Point site, where wind direction alone explains 29% of the variance in gas-phase PAH concentrations. This indicates that regional PAH sources are present. The model indicates that wind direction is not a significant variable for Eagle Harbor or Sleeping Bear Dunes sites.
TABLE 2. Atmospheric Half-Lives of Particle-Phase PAH Determined from Regression Parametersa Eagle Harbor
Sleeping Bear Dunes
rel std error (%)
t1/2 (yrs)
rel std error (%)
P > | t|
t1/2 (yrs)
9.6 5.7 4.9 5.6 4.0 4.9 5.4 4.6 4.9 6.1 3.3 5.0 5.2
55 41 35 38 30 29 31 28 33 42 24 34 42
0.0357 0.0038 0.0010 0.0008 0.0001 0.0008 0.0022 0.0005 0.0001 0.0039 0.0001 0.0003 0.0076
n.s. n.s. n.s. n.s. n.s. n.s. n.s. 9.5 n.s. n.s. 4.2 n.s. 5.3
t1/2 (yrs) n.s. n.s. 8.9 n.s. 7.4 n.s. n.s. n.s. n.s. n.s. 8.4 n.s. n.s.
phenanthrene fluoranthene pyrene benz[a]anthracene chrysene benzo[b]fluoranthene benzo[k]fluoranthene benzo[e]pyrene benzo[a]pyrene indeno[1,2,3-cd]pyrene dibenz[a,h]anthracene benzo[ghi]perylene coronene
P > | t|
46
0.0456
35
0.0095
54
0.0409
Sturgeon Point rel std error (%)
P > | t|
61
0.0713
24
0.0001
35
0.0032
Values that are significant with >95% confidence are in normal font, those that are significant with 90-95% confidence are in italics, and those that are not significant with >90% confidence are indicated by “n.s.”. The number of data points ranges between 71 and 100, except for dibenz[a,h]anthracene and coronene, which ranged from 42 to 91 due to many nondetected concentrations. a
TABLE 3. Average PAH Concentrations with Relative Standard Deviation Eagle Harbor av (pg/m3)
rsd (%)
Sleeping Bear Dunes av (pg/m3)
Sturgeon Point
rsd (%)
av (pg/m3)
rsd (%)
87 94 100 118 89
3600 840 360 44 4800
78 84 95 120 81
74 79 78 84 82 90 78 82 76 84 94 79 84 81
89 190 110 40 120 200 59 83 57 110 16 88 47 1200
72 74 71 70 80 87 91 81 81 80 73 80 78 79
Gas-Phase PAH phenanthrene fluoranthene pyrene chrysene total gas-phase
650 110 75 13 850
98 99 180 85 105
910 180 74 15 1200
Particle-Phase PAH phenanthrene fluoranthene pyrene benz[a]anthracene chrysene benzo[b]fluoranthene benzo[k]fluoranthene benzo[e]pyrene benzo[a]pyrene indeno[1,2,3-cd]pyrene dibenz[a,h]anthracene benzo[ghi]perylene coronene total particle-phase
21 30 19 5 17 25 8 11 7 15 4 13 10 190
130 130 120 70 81 83 73 71 73 82 105 77 84 98
28 48 32 10 29 46 15 19 15 28 6 23 17 310
The model parameters indicate how the wind direction influences gas-phase PAH concentrations. For example, to determine the concentration at Sturgeon Point, one starts with an intercept concentration of 6700 pg/m3. Then, one multiplies the fraction of the day when the wind was from 30 to 89 degrees by 3400 pg/m3 and adds this to the intercept. Repeating this procedure for each of the three other wind directions produces an estimate of the concentration measured over the 24-h sampling period. Wind that is consistently from the Buffalo region (30-89 degrees) produces a concentration of 10 000 pg/m3. Wind consistently off the lake produces a concentration of 3000 or 1600 pg/m3, depending on if the wind is westerly or northerly (200-330 degrees). Simcik et al. similarly found that the PAH concentrations over Lake Michigan increase by a factor of 12 when the wind is from the Chicago region (26). Our results indicate that wind from the Buffalo region (see Figure 2) is a source of PAH to Sturgeon Point. The large negative values for parameters a3 and a4 at Sturgeon Point indicate that wind blowing off of Lake Erie significantly reduces the local concentration of PAH at Sturgeon Point. Incidentally, it is
FIGURE 2. Hourly wind roses for the (A) Eagle Harbor, (b) Sleeping Bear Dunes, and (C) Sturgeon Point IADN sites. Measurements were made continuously from the beginning of sampling at each site through 1997; n ) 57 000, 49 000, and 33 000, respectively. VOL. 34, NO. 3, 2000 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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TABLE 4. Model Statistics and Wind Direction Parameters for Eq 3 Sturgeon Point
ΣPAH (gas-phase)
n mean (pg/m3) relative std error (%) Pr > F r2
144 4980 65 0.0001 0.290
a0 a1 a2 a3 a4
hourly wind direction (°)
av overall wind speed (m/s)
av overall temp (°C)
concn (pg/m3)
intercept 030-089 150-189 200-269 270-329
6700 6.5 ( 4.1 6.1( 3.9 6.4 ( 4.1 6.8 ( 4.3
10 5.5 ( 10.0 10.4 ( 10.2 8.8 ( 10.8 6.7 ( 10.5
0.0001 3400 -1350 -3690 -5060
rel std error (%) Pr > |t| 22 53 19 15
0.0728 0.4360 0.0079 0.0025
important to note that the northeasterly winds associated with the highest PAH concentrations are also associated with the lowest air temperatures. Thus, the influence of wind direction on PAH at Sturgeon Point is not an artifact of the Clausius-Clapeyron effect. The observation that wind from over the lake actually lowers PAH concentrations at Sturgeon Point has important implications to the PAH loading rate estimates for Lake Erie (3, 28, 29). These estimates assume that the concentration of PAH measured at Sturgeon Point is the same as the air over the lake. Using the concentrations measured at Sturgeon Point could overestimate the loadings of PAH to Lake Erie. Application of the model provided in this paper may provide a more accurate estimate of the atmospheric loadings to Lake Erie. Based on the above analysis, the gas-phase PAH concentrations observed at Eagle Harbor and Sleeping Bear Dunes are regional background levels. The gas-phase PAH concentrations observed at Sturgeon Point are strongly influenced by northeasterly winds from the Buffalo region, and thus, this site does not represent PAH concentrations for the entire Lake Erie region.
Acknowledgments The authors thank Team IADN and the U.S. Environmental Protection Agency and the Great Lakes National Program Office for funding (Grant GL995656).
Literature Cited (1) Hillery, B. R.; Basu, I.; Sweet, C. W.; Hites, R. A. Environ. Sci. Technol. 1997, 31, 1811-1816. (2) Simcik, M. F.; Basu, I.; Sweet, C. W.; Hites, R. A. Environ. Sci. Technol. 1999, 33, 1991-1995. (3) Hillery, B. R.; Simcik, M. F.; Basu, I.; Hoff, R. M.; Strachan, W. M. J.; Burniston, D.; Chan, C. H.; Brice, K. A.; Sweet, C. W.; Hites, R. A. Environ. Sci. Technol. 1998, 32, 2216-2221. (4) Cortes, D. R.; Basu, I.; Sweet, C. W.; Brice, K. A.; Hoff, R. M.; Hites, R. A. Environ. Sci. Technol. 1998, 32, 1920-1927.
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(5) Cortes, D. R.; Hoff, R. M.; Brice, E. A.; Hites, R. A. Environ. Sci. Technol. 1999, 33, 2145-2150. (6) Smith, D. J. T.; Harrison, R. M. Atmos. Environ. 1996, 30, 25132525. (7) McVeety, B. D.; Hites, R. A. Atmos. Environ. 1988, 22, 511-536. (8) Simcik, M. F.; Eisenreich, S. J.; Golden, K. A.; Liu, S.-P.; Lipiatou, E.; Swackhamer, D. L.; Long, D. T. Environ. Sci. Technol. 1996, 30, 3039-3046. (9) Coleman, P. J.; Lee, R. G. M.; Alcock, R. E.; Jones, K. C. Environ. Sci. Technol. 1997, 31, 2120-2124. (10) Jacob, J.; Grimmer, G.; Hildebrandt, A. Chemosphere 1997, 34, 2099-2108. (11) Gatz, D. F.; Sweet, C. W.; Basu, I.; Vermette, S.; Harlin, K.; Bauer, S. Great Lakes Integrated Atmospheric Deposition Network (IADN); Data Report 1990-1992; Illinois State Water Survey: Champaign, IL, 1994. (12) Sweet, C. W.; Harlin, K.; Gatz, D. F.; Bauer, S. Great Lakes Integrated Atmospheric Deposition Network (IADN); Data Report 1993-1994; Illinois State Water Survey: Champaign, IL, 1996. (13) Cortes, D.; Brubaker, W. Instrumental Analysis and Quantitation of Polycyclic Aromatic Hydrocarbons; Indiana University: Bloomington, IN, 1997. (14) Basu, I. Analysis of PCBs and Pesticides in Air and Precipitation samples, IADN Project Standard Operating Procedure; Indiana University: Bloomington, IN, 1995. (15) Basu, I.; Manire, A.; Cortes, D. R.; O’Dell, M. Quality control report 1994-1996; Indiana University: Bloomington, IN, 1998. (16) Hinckley, D.; Bidleman, T. F.; Foreman, W. T.; Tuschall, J. R. J. Chem. Eng. Data 1990, 35, 232-237. (17) Halsall, C. J.; Barrie, L. A.; Fellin, P.; Muir, D. C. G.; Billeck, B. N.; Lockhart, L.; Rovinsky, F. Y.; Kononov, E. Y.; Pastukhov, B. Environ. Sci. Technol. 1997, 31, 3593-3599. (18) Weather and Climate of the Great Lakes Region; Eichenlaub, V., Eds.; The University of Notre Dame Press: Notre Dame, 1979. (19) Honrath, R. E.; Sweet, C. I.; Plouff, C. J. Environ. Sci. Technol. 1997, 31, 842-852. (20) Wenzel, K.-D.; Weiflog, L.; Paladini, E.; Gantuz, M.; Guerreiro, P.; Puliafito, C.; Schuurmann, G. Atmos. Environ. 1997, 34, 25052518. (21) Halsall, C. J.; Coleman, P. J.; Davis, B. J.; Burnett, V.; Waterhouse, K. S.; Harding-Jones, P.; Jones, K. C. Environ. Sci. Technol. 1994, 28, 2380-2386. (22) Greenberg, A.; Darack, F.; Harkov, T.; Lioy, P.; Daisey, J. Atmos. Environ. 1985, 19, 1325-1339. (23) Baek, S. O.; Golstone, M. E.; Kirk, P. W.; Lester, J. N.; Perry, R. Sci. Total Environ. 1992, 111, 169-199. (24) Keller, C. D.; Bidleman, T. F. Atmos. Environ. 1984, 18, 837845. (25) Hoff, R. M.; Chan, K.-W. Environ. Sci. Technol. 1987, 21, 556561. (26) Brook, J. R.; Dann, T. F.; Burnett, R. T. J. Air Waste Manage. Assoc. 1997, 47, 2-19. (27) Simcik, M. F.; Zhang, H.; Eisenreich, S. J.; Franz, T. P.; Environ. Sci. Technol. 1997, 31, 2141-2147. (28) Eisenreich, S. J.; Strachan, W. M. J. Estimating atmospheric deposition of toxic substances to the Great Lakes; an update; Gray Freshwater Biological Institute: Burlington, Ontario, 1992. (29) Hoff, R. M., Strachan, W. M. J.; Sweet, C. W.; Chan, C. H.; Shackelton, M.; Bidleman, T. F.; Brice, K. A.; Burniston, D. A.; Cussion, S.; Gatz, D. F.; Harlin, K.; Schroeder, W. H. Atmos. Environ. 1996, 30, 3505-3527.
Received for review May 24, 1999. Revised manuscript received October 11, 1999. Accepted November 2, 1999. ES9905851
