Environ. Sci. Techno/. 1995, 29, 2782-2789
Polycyclic Arematic HylkacarBgis and P o l y c k l e m Biphenyls in Air at an Urban and a Rural Site near Lake Michigan WILLIAM E. COTHAM+ AND TERRY F . BIDLEMAN*mt Department of Chemistry and Biochemistry, university of South Carolina, Columbia, South Carolina 29208, and Atmospheric Environment Service, ARQP,4905 Dufferin Street, Downsview, Ontario M3H 5T4, Canada
Air samples were collected at an urban (Chicago, IL) and a rural (University of Wisconsin at Green Bay, UWGB) site during February 1988 to determine concentrations and particle/gas distributions of polycyclic aromatic hydrocarbons (PAHs) and potychlorinated biphenyls (PCBs). Geometric mean ZPAHs of molecular weights 2166 were 195 ng/m3 in Chicago and 14 ng/m3 at UWGB. Ratios among PAHs suggested that some labile compounds were depleted during atmospheric transport. Geometric mean CPCBs (45 congeners) were 1.3 ng/m3 in Chicago and 0.13 ng/m3 at UWGB. PCB profiles of most samples in Chicago and all at UWGB were skewed toward the lower molecular weight congeners, as in mixtures of Aroclors 1242 and 1254. Two Chicago samples showed a heavy PCB profile similar to Aroclor 1260. Apparent particle/gas partition coefficients (K,) were well correlated with liquid-phase vapor pressures ( P O L ) within a class of compounds (PAHs or PCBs). PAHs were sorbed to a greater degree than PCBs for compounds of the same volatility. Slopes of log Kp vs log POL plots deviated from the expected value of -1 in Chicago, suggesting nonequilibrium effects. Aerosols at UWGB appeared to be closer to equilibrium with the gas phase, as indicated by slopes close to -1. Measured particulate percentages in the t w o locations were within a factor of 2 of those predicted by the Junge-Pankow adsorption model.
Introduction Atmospheric deposition is a major contributor of organic contaminants to the upper Great Lakes and other large water bodies. Relative loading estimates indicate that wet and dry deposition supply 58-89% of polychlorinated biphenyl (PCB) and 80-96% of benzo[a]pyreneinputs to lakes Superior,Michigan, and Huron (1). Dry particlefluxes of PCBs in Chicago were up to 3 orders of magnitude greater +
University of South Carolina.
t Atmospheric Environment Service.
2782 1 ENVIRONMENTAL SCIENCE &TECHNOLOGY / VOL. 29, NO. 11. 1995
than in rural areas, suggesting that Chicago and other urban centers are major sources of PCB deposition to nearby lakes (2, 3). Atmospheric loadings of polycyclic aromatic hydrocarbons (PAHs) and PCBs to Chesapeake Bay were estimated at 2300 and 38 kglyr, respectively. Wet fluxes of PCBs to the bay were similar to those in the upper Great Lakes (4). The distribution of semivolatile organic compounds between the particle and gas phases in the atmosphere controls their rate of removal by wet and dry deposition (5-10) and mechanisms of uptake by vegetation (11). Assignment of an aerosol-bound fraction is a key step in modeling dry deposition of PCBs and PAHs to the Great Lakes (12)and accounting for the deposition of chlorinated dioxins and dibenzofurans to grass in an air-to-cattle food chain model (13). Determiningthe particle-bound fraction of organic compounds is an ongoing challenge. The highvolume sampler, which employs a glass fiber filter to collect aerosols followed by an adsorbent trap for gas-phase compounds, is subject to artifactsthat includevolatilization lossesfrom particles on the filter and adsorption of gaseous compounds to the filter itself (14-18). To avoid these problems, several designs of denuders (19-24) as well as a diffusion separator (25) have been developed. This work was undertaken to measure ambient air concentrations and operational particlelgas distributions of PCBs and PAHs in an urban (Chicago)and a rural (Green Bay) site near Lake Michigan. Few attempts have been made to compare the phase distributions of different compound classes in the same sampling event. The measurements described here are for samples taken in February 1988. Some of these samples and additional ones from June 1989 were used to investigate the particle/gas distributionof PCBs having different o-chlorine substitution patterns (26).
Experimental Section sample Collection. Samples were taken in Chicago from February 16-22, 1988, in the southeast part of the city, a heavily industrialized area with steel mills, incinerators, landfills, coke ovens, and other polluting facilities. The location is described and shown on a map by Sweet and Vermette (27). Sampling in Green Bay was done February 24-29 on the University of Wisconsin Green Bay (UWGB) campus approximately 8 km from downtown Green Bay and within 2 km of the lake. Collection data are given in Table 1. Air volumes of 260-390 m3 were drawn at 0.5 m3/min through two 20 x 25 cm Gelman AE binderless glass fiber filters followed by two 7.6 cm diameter x 7.5 cm thick polyurethane foam plugs. Cleanup procedures for foam plugs and filters and details of the sampling method have been described previously (28). The back filter was used to correct for adsorption of gaseous organic compounds to the fdter itself (16-18). The back foam plug served as an indicator of breakthrough of gaseous compounds through the front plug. Sampling was restricted to 9-13 h during day or night to avoid the large diurnal changes in air temperature in an attempt to minimize volatilization artifacts from particles on the filter. After sampling, foam plugs were stored in glass jars with aluminum foil-lined lids. Filters were wrapped in solvent-rinsedaluminum foil.
0013-936x/95/0929-2782$09.00/0
0 1995 American Chemical Society
TABLE 1
Collection Data, TSP, Total PCB, and Total PAH Concentrations, Chicago and UWGB av TSPb YO EPCBs EPAHs RH' (pg/d)TCc (ng/m3) (ng/d)
date m3 av sample Feb 1988 of air tamp 1 2 3 4 5 6 7 8 9 10 11
16-17 17 17-18 18 18-19 19 19-20 20 20-21 21 21-22
Chicago 70 261 3.1 84 97 1.8 69 312 93 329 -0.2 85 74 3.7 66 295 114 0.9 89 327 169 2.3 78 324 46 2.4 86 318 76 266 -4.2 59 62 328 -10.0 60 30 268 -5.3 58 34 1.6 72 312
1 2 3 4 5 6 7 8 9
24-25 25 25-26 26 26-27 27 27-28 28 29
361 -12.2 256 -8.2 389 -7.2 2.9 291 342 -1.9 342 -1.1 310 -4.0 1.7 298 304 -3.0
19 21 25 23 18 22 17 31 31 22 NMd
1.7 2.5 1.5 1.1 1.9 9.9 1.0 0.3 2.0 0.32 0.34
918 NM 841 184 286 555 76 1410 251 78 75
NM NM NM NM NM NM NM NM NM
0.21 0.13 0.14 0.37 0.26 0.06 0.11 0.12 0.04
38 19 27 22 13 10 14 NM 7.3
UWGB NM NM NM NM NM NM NM NM NM
31 31 31 31 31 31 17 17 17
*
a Relative humidity. TSPvalues at UWGB were obtained from two samples taken Feb 24-27 and Feb 27-29. These were considered to be representativeof all PAH samplescollected within these dates. Total carbon. NM, not measured.
Recovery spikes were prepared in the field by pipetting 1.0 mL of a solution containing 500-2000 ng of individualPAHs onto clean foam plugs and storing them as for samples. Unused foam plugs and filters from the samplingtrip were analyzed as procedural blanks. Plugs and filterswere placed in ice-fiUedcoolers immediatelyafter sampling,transported on ice, and frozen at -10 "C. A separate filter-foam plug train was used to collect total suspended particles (TSP, pg/m3) for each Chicago event. The plugs from this train were not analyzed since they served only to maintain the same flow rate as for the organics sampler. Because of the lower particle concentrations at UWGB, the TSP collector was operated for 2-3day periods to obtain a single sample. Extraction and Cleanup. Foam plugs and filters were extracted as previously described (28). Portions of urban air particulate matter reference material [200 mg, SRM1649, National Institute of Standards and Technology (NIST), Gaithersburg, MD] were extracted in precleaned cellulose thimbles for 8-10 h with &chloromethane. Extracts were concentrated and transferred into hexane or isooctane by rotary evaporation and blown down with a stream of nitrogen that had been precleaned by passing through a Tenax-GC trap. Samples were cleaned up and fractionated on an alumina-silicic acid column (29). Fraction 1 containing PCBs was concentrated to 5 mL, shaken on a vortex mixer with metallic mercury to remove elemental sulfur, and then shaken with 18 M sulfuric acid. Fraction 2 containing PAHs was analyzed without further cleanup. The final samplevolume was adjusted by nitrogen blow-down into isooctane. Analytical Methods. PAHs were determined using a Hewlett-Packard 5890 GC with a 5970 mass selective detector operated in the selected ion monitoring mode, using a DB-1301 bonded-phase column (30 m x 0.25 mm
i.d., 0.25 pm film, J&WScientific,Folsom, CAI. PCBs were determined by capillary GC with 'j3Ni electron capture detection (GC-ECD) using aVarian 3700 instrument, using an HP-5 or equivalent column (25 m x 0.25 mm i.d., Hewlett-Packard Corp.) Instrument operating conditions, ions for PAH determination, and methods for quantifying PCB congeners have been previously specified (29). Filters used for TSP determinations were desiccated -8 hover anhydrous calcium sulfate (drierite)before and after samplingand weighed to obtain particle masses. Sections of the filters were cut with a 1-cm diameter cork borer, ground a uniform color and consistencyinan agate mortar, and analyzed for total carbon by dry combustion (Desert Analytics, Inc., Tucson, AZ).
Results and Discussion Quality Control. Because of low temperatures and short sampling times, breakthrough to the back foam plug was negligible. Loss of the most volatile analyte (fluorene) to the back plug was no more than 11%and averaged 4% of the front plug value. Recoveries of fluorene, phenanthrene, and 2-methylphenanthrene from spiked foam plugs were 55%,68%,rind 79%. These recoveries were taken into account when calculating sample quantities. No adjustmentswere made for recoveries of other PAHs, which were '84%. Extraction yields from SRM-1649 urban dust as the percent of NIST certified or information values (30, 31) were as follows: phenanthrene 147%,anthracene 40%,fluoranthene 104%, pyrene 115%, chrysene triphenylene 115%, benz[alanthracene 92%, benzo[b]fluoranthene + benzo[k]fluoranthene 112%, benzo[alpyrene 83%, indeno[l,2,3-cdlpyrene 85%, and benzo[ghzlperylene 82%. The NIST informationvalue for anthracene was reported with greater uncertainty (RSD = 34-107%, by GC and HPLC) than for the other PAHs (31). Although PCBs were not included in field spiking experiments, laboratory spikes of tri- through heptachlorobiphenyls gave recoveries of 89 & 13%from foam plugs and 72 f8%from filters (25). Our research group has also documented 67- 110%recovery of chlorinated pesticides and PAHs using the same extraction and analyticalmethods (29). Limits of detection (LOD, ng or pg) were defined as the mean blank plus three standard deviations. For ease of comparison, LOD values were also expressed on a concentration basis by dividing the LOD quantities by 300 m3, the average sample volume (Tables 2 and 3). Sample quantities exceeding the LOD (ng or pg) were blankcorrected and then divided by the volume of air to yield concentrations. PAHs in Air, Chicago and UWGB. The collection site in Chicago is in an area of heavy traffic and within 1-2 km of steel and coke plants (271. Stack emissions and flares were visible throughout the study period. It is therefore not surprising that PAH concentrations were high. The sum of 13 PAHs ranged from 75 to 1410 ng/m3, with arithmetic and geometric means of 507 and 195 ng/m3.By comparison, the XPAHs of molecular weight z 166 was 93 ng/m3in Denver, CO (32), 57 ng/m3 in Portland, OR (la, 43-56 ng/m3in Columbia, SC (33,34),and 87 ng/m3 in a combined data set from Minneapolis,MN, and Salt Lake City, UT (35). In this study, a positive correlation (r = 0.65) was obtained for regression of XPAHs vs the time that winds blew from the SW-NW sector, suggesting that the nearby industrial facilities to the west of the sampling site
+
VOL. 29, NO. 11, 1995 I ENVIRONMENTAL SCIENCE & TECHNOLOGY
2783
TABLE 2
Concentration@ of PAHs in Air, Chicago and UWGB (nslm3) UWGB
Chicago
FLE PH AN 2-m-PH F LA PY BaA CY+TP Bb+kF
BeP BaP lcdP BghiP EPAH
arith mean
arith SD
geom mean
arith mean
arith SD
geom mean
concn LODb
92 159 15 20 56 36 21 19 39 12 14 13 11 507
83 131 17 14 59 36 21 19 39 12 14 13 11 469
38 70 5.0 11 24 16 4.4 5.5 8.6 2.9 2.9 3.4 3.6 195
4.1 9.6 0.05 0.93 1.7 0.76 0.16 0.43 0.57 0.19 0.12 0.13 0.19 18.9
1.5 4.7 0.02 0.54 1.0 0.61 0.17 0.34 0.44 0.17 0.09 0.13 0.14 9.9
3.3 6.7 0.06 0.81 1.4 0.60 0.14 0.35 0.47 0.18 0.12 0.12 0.18 14.4
0,010 0.002 0.005 0.005 0.007 0.006 0.036 0.014 0.013 0,011 0.007 0.006 0.004
a Values are the sum of particulate and gaseous species. Abbreviations: fluorene (FLE), phenanthrene (PH), anthracene (AN), 2-methylphenanthrene (2-m-PH), fluoranthrene (FLA), pyrene (PY), benzlalanthracene (BaA), chrysene triphenylene (CP+TP), benzolblfluoranthene + benzo[k]fluoranthene (Bb+kF), benzo[elpyrene (BeP), benzoblpyrene (BaP), indeno[l,2,3-cdpyrene (IcdP), and benzolghilperylene (BghiP). b Concn LOD (ng/m3)= LOD/300 m3 of air; LOD = mean blank (ng) 3SD.
+
+
are major PAH contributors. Poor correlation was found between TSP and particulate PAH ( r * = 0.03) or between gaseous and particulate PAH ( r = 0.1). PAHs are enriched on aerosols
