Environ. Sci. Technol. 1997, 31, 2064-2070
Measurement of Oxygenated Polycyclic Aromatic Hydrocarbons Associated with a Size-Segregated Urban Aerosol J O N A T H A N O . A L L E N , †,‡ N A M E E T A M . D O O K E R A N , †,§ KOLI TAGHIZADEH,| ARTHUR L. LAFLEUR,| KENNETH A. SMITH,† AND A D E L F . S A R O F I M * ,† Chemical Engineering Department and Center for Environmental Health Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
Size-segregated atmospheric particles were collected in Boston, MA, using a micro-orifice impactor. The samples were analyzed for oxygenated polycyclic aromatic hydrocarbons (OPAH) using gas chromatography/mass spectrometry. Seven PAH ketones (1-acenaphthenone, 9-fluorenone, 11H-benzo[a]fluoren-11-one, 7H-benzo[c]fluoren7-one, 11H-benzo[b]fluoren-11-one, benzanthrone, and 6Hbenzo[cd]pyrene-6-one), four PAH diones (1,4-naphthoquinone, phenanthrenequinone, 5,12-naphthacenequinone, and benzo[a]pyrene-6,12-dione), and one PAH dicarboxylic acid anhydride (naphthalic anhydride) were identified. Seven additional compounds with mass spectra typical of OPAH were tentatively identified. OPAH were generally distributed among aerosol size fractions based on molecular weight. Compounds with molecular weights between 168 and 208 were approximately evenly distributed between the fine (aerodynamic diameter, Dp, < 2 µm) and coarse (Dp > 2 µm) particles. OPAH with molecular weights of 248 and greater were associated primarily with the fine aerosol fraction. Most OPAH were distributed with particle size in a broad, unimodal hump similar to the the distributions observed for PAH in the same samples. These results suggest that OPAH are initially associated with fine particles after formation by either combustion or gas phase photooxidation and then partition to larger particles by vaporization and sorption. Two OPAH were distributed in bimodal distributions with peaks at Dp ≈ 2 µm and Dp ≈ 2 µm. These bimodal distributions may be indicative of sorption behavior different from PAH and other OPAH.
Introduction Oxygenated polycyclic aromatic hydrocarbons (OPAH) are semivolatile organic air pollutants of concern because of their demonstrated genotoxic effects. Studies of OPAH in bacterial * Corresponding author phone: 801-585-9258; fax: 801-581-8692; e-mail:
[email protected]. † Chemical Engineering Department. ‡ Present address: Environmental Quality Laboratory, Mail Stop 138-78, California Institute of Technology, Pasadena, CA 91125. § Present address: HB 7000, Dartmouth Medical School, Hanover, NH 03755. | Center for Environmental Health Sciences.
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and human cell mutation assays have found some of these compounds to be mutagenic (1-7). In addition, OPAH are compounds characteristic of the semipolar fractions of atmospheric particulate extracts; fractions that are highly mutagenic in bacterial and human cells (5, 7, 8). OPAH have been identified in source samples from gasoline, diesel, coal, wood, and municipal waste combustion (9-11, 5, 6). Photooxidation of PAH has also been found to produce OPAH (12). Atmospheric sampling studies of OPAH have found concentrations in the approximate range of 0.110 ng/m3 for a number of species (11, 13-16, 5, 17, 6). A study of OPAH associated with size-segregated particles found approximately half of the benzanthrone and perinaphrenone (phenalen-1-one) associated with particles smaller than 3.0 µm in summer and two-thirds in winter (18). The environmental fate of particle-associated OPAH depends, in part, on the distribution of the compounds among the aerosol size fractions. Particle size affects the removal rate of particulate OPAH from the atmosphere by dry and wet deposition (19, 20). The mechanism and location of deposition of particulate OPAH in the lung are also affected by particle size. Large particles tend to impact on the upper regions of the lung while small particles tend to diffuse to the surface of the alveoli (21). Therefore measurements of OPAH association with different aerosol size fractions are necessary for a complete understanding of the environmental fate of and human exposure to these compounds. The objective of this work was to determine the distribution of OPAH with particle size in an urban aerosol. In this paper, OPAH includes ketones, diones, and dicarboxylic acid anhydrides of PAH. Particles were collected with a micro-orifice impactor (MOI) from an urban site in Boston. The OPAH were identified and quantified by gas chromatography/mass spectrometry (GC/MS). These results are compared with the results from PAH analyses of the same samples to elucidate the formation and partitioning mechanisms of OPAH in the urban atmosphere.
Experimental Methods The samples discussed here are half of size-segregated aerosol samples collected in the summer of 1994. The other half of the samples were analyzed for PAH, and the details of sample collection, preparation, and analysis have been reported elsewhere (22, 23). The experimental methods are only summarized here. Air samples were collected from the roof of a National Ambient Air Quality Standards monitoring station operated by the Massachusetts Department of Environmental Protection at Kenmore Square, Boston, MA. This site is on a traffic island in the center of a divided 6-lane street near a major intersection. The sampling inlet was located 4 m above ground level. A bus station is located 170 m away. Five 24-h air samples were collected on alternate days in June 1994. A total of 188 m3 of air was sampled over 120 h. The sampling train consisted of an inlet tube and cascade impactor followed by a regulating valve, rotameter, and vacuum pump. The cascade impactor used was a microorifice impactor (MOI) manufactured by MSP Corporation (Minneapolis, MN) (24). Size-segregated aerosols were collected by impaction on nine stages with aerodynamic cutoff diameters of 19.2, 6.00, 3.38, 1.90, 1.07, 0.626, 0.343, 0.141, and 0.087 µm. An impaction medium of a polytetrafluoroethylene (PTFE) membrane with an aluminum foil underlay was placed on each stage of the MOI to collect particles. Each impaction medium was coated with dibutyl phthalate, which has been shown to reduce particle bounce (25). A quartz
S0013-936X(96)00894-2 CCC: $14.00
1997 American Chemical Society
TABLE 1. OPAH Selected Ion Monitoring Program eluting compounds time after injection (min) 15.2-22.8
internal standard phenanthrene-d10
OPAH 1,4-naphthoquinonea 1,2-naphthoquinonea 1-acenaphthenoneb
22.8-27.0
phenanthrene-d10
9-fluorenonea 1,2-naphthalic anhydrideb acenaphthenequinonea 2,3-naphthalic anhydrideb
27.0-31.8
pyrene-d10
anthraquinonea 1,8-naphthalic anhydridea phenanthrenequinonea
31.8-35.8
chrysene-d12
11H-benzo[a]fluoren-11-onec 7H-benzo[c]fluoren-7-onec 11H-benzo[b]fluoren-11-onec benzanthronea aceanthrenequinonea
35.8-40.0
perylene-d12
benz[a]anthracene-7,12-dionea 1,4-chrysenequinonea 5,12-naphthacenequinonea 6H-benzo[cd]pyrene-6-onec
40.0-47.0
dibenz[a,h]anthracene-d14
benzo[k]fluoranthene-7,12-dioned 13H-dibenzo[a,i]fluoren-13-onec 7H-dibenzo[c,g]fluoren-7-onec 7H-dibenz[de,j]anthracen-7-onec benzo[a]pyrene-6,12-dioned benzo[a]pyrene-1,6-dioned benzo[a]pyrene-3,6-dioned benzo[a]pyrene-4,5-dioned benzo[e]pyrene-4,5-dioned
monitored ions 102.05 130.05 140.05 158.05 164.10 168.06 126.05 152.05 154.05 180.05 182.05 188.15 198.05 126.05 152.05 154.05 180.05 198.05 208.05 212.15 176.05 202.05 204.05 226.05 230.05 240.15 248.05 254.05 258.05 264.15 176.05 202.05 204.05 226.05 230.05 248.05 254.05 258.05 264.15 200.05 226.05 228.05 252.10 254.05 272.05 280.10 282.05 292.20
a Aldrich Chemical Co. (Milwaulkee, WI). b Chemsyn Science Laboratories (Lenexa, KS). c PAH Research Institute (Griefenberg, Germany). d Midwest Research Institute (Kansas City, MO).
after-filter downstream of the impactor was used to collect particles not collected on the impactor stages. Prior to extraction, the sampling media were spiked with 40 ng of eight deuterated PAH internal standards: naphthalene-d8, acenaphthene-d10, phenanthrene d10, pyrene-d10, chrysene-d12, perylene-d12, dibenz[a,h]anthracene-d14, and coronene-d12. The sampling media were covered with dichloromethane and sonicated for 30 min. The OPAH fraction of the samples was separated from dibutyl phthalate and other pollutants by high-performance liquid chromatography (HPLC) (26). The OPAH fraction of the HPLC effluent was collected and concentrated to 5 µL. One microliter of the sample solution was injected onto the GC/MS. OPAH were identified and quantified with an Hewlett Packard GC/MS system. At least three duplicate GC/MS injections were made for each sample. The MSD was run in selected ion monitoring (SIM) mode. The SIM program was designed to monitor the molecular
ion, M+, and prominent fragmentation ions of a group of OPAH that elute at times near one of the deuterated PAH internal standards. Prominent fragmentation ions were (M - CO)+ for ketones, (M - CO)+ and (M - 2CO)+ for diones, and (M - CO2 )+ and (M - CO2 - CO)+ for dicarboxylic acid anhydrides. The ratios of molecular to fragmentation ions were experimentally measured for authentic OPAH reference standards. Table 1 shows the SIM program and OPAH detected in each time window. Only OPAH for which reference standards were available are listed. OPAH were identified by comparing ion ratios and retention times with those of reference standards. Each OPAH was quantified by comparing the peak area for its molecular ion to the peak area for the molecular ion of an internal standard. Phenanthrenequinone, which had a weak molecular ion response, was instead quantified using the (M CO)+ ion. OPAH to deuterated PAH response factors, RF, were determined by triplicate injections of standards containing 3 ng/µL OPAH and deuterated PAH. RF values ranged
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TABLE 2. OPAH Identified in Kenmore Square Samples fraction with aerosol modes
a
OPAH
MW
concn with aerosol (ng/m3)
ultrafine
accumulation
coarse
1,4-naphthoquinone 1-acenaphthenone 9-fluorenone 1,8-naphthalic anhydride OPAH-208a phenanthrenequinone OPAH-208b 11H-benzo[a]fluoren-11-one 7H-benzo[c]fluoren-7-one 11H-benzo[b]fluoren-11-one benzanthrone 5,12-naphthacenequinone OPAH-248a OPAH-254a 6H-benzo[cd]pyrene-6-one OPAH-272a OPAH-280a benzo[a]pyrene-6,12-dione OPAH-280b
158 168 180 198 208 208 208 230 230 230 230 258 248 254 254 272 280 282 280
identified 0.264 ( 0.017a 2.072 ( 0.088 1.766 ( 0.081 0.379 ( 0.017 0.427 ( 0.035 0.041 ( 0.003 1.026 ( 0.037 0.372 ( 0.021 0.852 ( 0.036 1.176 ( 0.060 0.323 ( 0.022 0.058 ( 0.004 0.059 ( 0.005 1.337 ( 0.070 0.049 ( 0.004 0.143 ( 0.013 0.096 ( 0.009 0.284 ( 0.018
0.043 0.050 0.084 0.048 0.000 0.000 0.091 0.109 0.115 0.246 0.151 0.351 0.187 0.362 0.498 0.194 0.080 0.161
0.383 0.385 0.487 0.462 0.343 0.516 0.633 0.644 0.690 0.674 0.724 0.649 0.779 0.600 0.502 0.776 0.850 0.837
0.574 0.565 0.429 0.491 0.657 0.484 0.276 0.247 0.195 0.080 0.125 0.000 0.034 0.038 0.000 0.030 0.070 0.002
One standard deviation.
TABLE 3. OPAH Tentatively Identified by GC/MS OPAH
retention index
secondary ion
relative abundance
OPAH-208a
351.7
OPAH-208b
369.9
OPAH-248a
435.8
OPAH-254a OPAH-272a
440.3 488.2
OPAH-280a OPAH-280b
488.6 500.5
180 152 180 152 204 176 226 228 200 252 252
0.087 0.151 0.130 1.581 1.280 1.294 0.183 1.272 1.474 0.155 0.427
from 0.09 to 0.74 and were repeatable, with relative standard deviations less than 20%. A RF of 1.0 was assumed for OPAH for which a reference standard was not available. One blank sample was carried to the field, and three additional method blanks were made up in the laboratory. All reported OPAH concentrations have been blank-corrected by subtracting the mean blank concentration from the sample concentration and summing the sample and blank variances. The minimum quantifiable amount of deuterated PAH was approximately 30 pg in a 1-µL injection. Because ≈10% of the total sample was injected for each GC/MS run, the limit of quantification for OPAH, assuming RF ) 0.3, in a 200 m3 air sample was ≈5 pg/m3 in each aerosol size fraction sample. Compounds were considered identified in the whole aerosol sample if they were quantifiable in at least one aerosol size fraction sample. OPAH were considered quantified in the whole aerosol sample if the sum of blank-corrected concentrations over all impactor stages was positive by at least 2 SD.
Results OPAH found in the urban size-segregated aerosol sample are listed in Table 2. Compounds listed in Table 1 but not in Table 2 were not found in the sample. OPAH for which authentic reference standards were available are listed by their chemical name. GC/MS peaks that were tentatively identified as OPAH in the absence of reference standards are designated OPAH-xy, where x is the mass of the proposed molecular ion and y is a designation to distinguish isomers. Because the MSD was operated in SIM mode, data are available on the abundance of only a few ions; this makes the
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tentative identification dione of MW 178 PAH dione of MW 178 PAH dicarboxylic acid anhydride of MW 178 PAH ketone of MW 240 PAH dicarboxylic acid anhydride of MW 202 PAH ketone of dibenzofluorene ketone of dibenzofluorene
identification less positive than if complete MS scan data were available. Table 3 lists all the tentatively identified OPAH found and the available GC/MS data. The fraction of OPAH collected on stage 8 and the afterfilter (aerodynamic diameter, Dp, < 0.14 µm) is referred to as the ultrafine fraction in Table 2. OPAH collected on impactor stages 4-7 (0.14 < Dp < 1.9 µm) is the accumulation fraction. The sum of ultrafine and accumulation fractions is referred to as the fine fraction. OPAH collected on stages 1-3 (1.9 < Dp < 19 µm) is the coarse fraction. PAH Ketones. Seven PAH ketones (1-acenaphthenone, 9-fluorenone, 11H-benzo[a]fluoren-11-one, 7H-benzo[c]fluoren-7-one, 11H-benzo[b]fluoren-11-one, benzanthrone, and 6H-benzo[cd]pyrene-6-one) were identified by comparison with reference standards and quantified (see Table 2). In addition, three compounds were tentatively identified as PAH ketones in the absence of reference standards. OPAH-254a may be an isomer of 6H-benzo[cd]pyrene-6-one. OPAH-280a and OPAH-280b were present as minor peaks in the 7Hdibenzo[c,g]fluoren-7-one reference standard and are therefore assumed to be isomers of this PAH ketone. Figure 1 shows the normalized distributions of molecular weight 230 PAH ketones with particle size. Dashed lines at Dp ) 0.14 and 1.9 µm show the ultrafinesaccumulation and accumulationscoarse fraction divisions. The error bars show 1 SD from the mean analysis results. The lower limit of particle size collected on the after-filter, Dp ) 0.01 µm, has been arbitrarily selected. (Similar figures for five tentatively identified OPAH not presented here are available as Supporting Information.)
FIGURE 1. Distributions of molecular weight 230 PAH ketones with particle size in an urban aerosol. The distributions of the benzofluorenones are nearly identical, and the distribution of benzanthrone is slightly shifted to smaller particles. Unique among the PAH ketones, benzanthrone appears to have a bimodal distribution with one peak at Dp ≈ 0.1 µm in the ultrafine mode. Similar peaks in the ultrafine mode were observed for PAH (22). The size distributions of other PAH ketones are shown in Figure 2. The PAH ketones tend to be distributed with particle size based on molecular weight, with lower molecular weight compounds associated with larger particles. The tentatively identified PAH ketones have distributions with particle size similar to those for positively identified PAH ketones of similar molecular weight. PAH Diones. Four PAH diones (1,4-naphthoquinone, phenanthrenequinone, 5,12-naphthacenequinone, and benzo[a]pyrene-6,12-dione) were identified by comparison with reference standards. In addition, two compounds were tentatively identified as PAH diones in the absence of reference standards. OPAH-208a and OPAH-208b may be diones of phenanthrene or anthracene. Five of these six were quantifiable (see Table 2). The normalized distributions of the identified PAH diones with particle size are shown in Figure 3. Benzo[a]pyrene6,12-dione has a unimodal distribution with a peak at Dp ≈ 0.6 µm. The distribution of 5,12-naphthacenequinone, which has a lower molecular weight than benzo[a]pyrene-6,12dione, appears to be shifted toward smaller particles than that of benzo[a]pyrene-6,12-dione. This is in contrast to the general trend observed here, that lower molecular weight species are associated with larger particles. Phenanthrenequinone was distributed differently from most other OPAH found in this study; it was found predominantly in two narrow size ranges centered at Dp ≈ 0.2 and 2.5 µm. OPAH-208b was also distributed with bimodal peaks at these particle sizes. Possible causes of these unusual distributions are discussed below. PAH Dicarboxylic Acid Anhydrides. One PAH dicarboxylic acid anhydride (PAH DCAA), 1,8-naphthalic anhy-
dride, was identified by comparison with a reference standard and quantified (see Table 2). In addition, two compounds were tentatively identified as PAH DCAA in the absence of reference standards. Both tentatively identified PAH DCAA, OPAH-248a and OPAH-272a, matched compounds identified in an urban particulate matter reference material (NIST SRM 1649) by others in our laboratory using the same GC/MS system (27). They operated the MSD in scan mode and obtained complete mass spectra for these compounds. The mass spectra were consistent with DCAA of PAH with 178 and 202 molecular weights, respectively. Therefore these compounds are less tentatively identified than others for which reference standards were not available. The normalized distributions of these compounds with particle size are shown in Figure 4. Following the trend observed for other OPAH, lower molecular weight PAH DCAA were associated with larger particles. In contrast to most PAH ketones and diones, large fractions of the higher molecular weight PAH DCAA were found in the ultrafine fraction.
Discussion Both direct emissions from combustors and photooxidation of PAH have been proposed as important sources of OPAH in the atmosphere (13, 28, 5, 17). In the case of combustion emissions, OPAH emitted would be initially released in the gas phase or associated with fine particles since combustors emit mainly fine particles (29). Combustion-generated OPAH would then be expected to have distributions with particle size similar to those of PAH, which are generated only by combustion. Photooxidation reactions to produce OPAH may occur in the gas phase, on solid particles, or in liquid particles. For condensed phase reactions, the rates of PAH photooxidation have been shown to be highly dependent on the nature of the sorbent particle or the composition of the solution (30, 31). Because detailed information on the nature of sorbent
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FIGURE 2. Distributions of (a) 1-acenaphthenone, (b) 9-fluorenone, (c) 6H-benzo[cd]pyrene-6-one, and (d) OPAH-280b with particle size in an urban aerosol. particles is not available, we focus on the partitioning of OPAH formed by gas phase photooxidation. Once formed by gas phase photooxidation, the products undergo mass transfer from the gas phase to particles. These products are initially distributed among particle size fractions in proportion to the mass transfer rate. The rate of mass transfer in the continuum regime is proportional to Dp. The initial distribution of photooxidation products is therefore in proportion to the first moment of the particle number distribution with Dp. The first moment of Whitby’s average aerosol distribution has a single peak at ≈ 0.1 µm (32). This is similar to the size distribution of combustion particles (33). Since the initial distributions of compounds generated by combustion and photooxidation are similar, the source of these compounds cannot be unequivocally determined by measurements of their distribution with particle size. The case of benzanthrone is interesting; this is the only OPAH to exhibit a peak in the distribution with particle size at Dp ≈ 0.1 µm. Similar, though less prominent, peaks are observed for PAH in the urban aerosol sample (22). This
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FIGURE 3. Distributions of PAH diones with particle size in an urban aerosol. intriguing observation encourages speculation that PAH and benzanthrone are emitted by the same combustion sources and that other OPAH have different sources than benzanthrone. Once associated with fine particles, OPAH formed by either combustion or photooxidation will migrate from the fine particles to coarse particles by volatilization and sorption. The rate of this flux is directly related to the gas phase concentration of OPAH. Because higher molecular weight OPAH generally have much lower vapor pressures, the time needed for them to partition to large particles is much greater than that for lower molecular weight OPAH. Therefore, high molecular weight OPAH generated by combustion or photooxidation tend to remain with the fine particles with which they were initially associated while lower molecular weight OPAH partition to other particles. OPAH formed by photooxidation of PAH will undergo vaporization and sorption at a rate substantially slower than the PAH reactants since the equilibrium vapor pressures of the photooxidation products are expected to be much less than those of the PAH reactants. For example, the sublimation
FIGURE 5. Fraction of PAH and OPAH associated with coarse particles (Dp > 1.9 µm) in an urban aerosol.
FIGURE 4. Distributions of PAH dicarboxylic acid anhydrides with particle size in an urban aerosol. pressures of fluorene and 9-fluorenone at 298 K are 7.9 × 10-2 and 1.6 × 10-2 Pa, respectively (34, 35). A useful measure of partitioning among aerosol size fractions is the mass fraction of a compound found with the coarse particles. Figure 5 shows the fraction of OPAH, by compound class and molecular weight, associated with coarse particles in the urban aerosol. The line shown is a curve fit to the PAH data (22). Like PAH, lower molecular weight OPAH are observed to associate to a greater degree with coarse particles. The relation between molecular weight and the fraction associated with the coarse particles for PAH ketones is remarkably similar to that for PAH. PAH diones seem to partition to coarse particles to a greater extent than PAH of the same molecular weight; PAH DCAA to a lesser extent. The differences in partitioning with molecular weight among compound classes can be explained by noting that partial pressure in the atmosphere, not molecular weight, will determine the flux by evaporation and sorption. The fraction of PAH in the gas phase has been shown to correlate with its pure component vapor pressure (36). Sublimation pressures at 298 K [pS(298 K)] for 9-fluorenone and benzan-
throne are 1.6 × 10-2 and 2 × 10-5 Pa, respectively (35, 37). These values are close to the extrapolated sublimation pressures of PAH of similar molecular weight. The vapor pressures of 9-fluorenone can be compared with phenanthrene, pS(298 K) ) 1.6 × 10-2 Pa, and anthracene, pS(298 K) ) 7.9 × 10-4 Pa; that of benzanthrone can be compared with benz[a]anthracene, pS(298 K) ) 2.7 × 10-5 Pa, chrysene, pS(298 K) ) 1.2 × 10-6 Pa, and triphenylene pS(298 K) ) 4.2 × 10-6 Pa (34, 38). The similar correlation of sublimation pressures with molecular weights for PAH and PAH ketones leads to an identical dependence with molecular weight of the fraction of the compounds associated with coarse particles. One can hypothesize that PAH diones have higher vapor pressures than PAH of the same molecular weight and therefore are associated to a greater degree with large particles. Similarly, PAH DCAA may tend to be associated with smaller particles because their vapor pressures are lower than those of PAH of the same molecular weight. These results are consistent with the conclusion that OPAH are initially associated with small particles following generation by combustion or photooxidation. These compounds then partition to large particles by vaporization and sorption. For high molecular weight, low vapor pressure compounds, mass transfer by vaporization and sorption will be slow, and the compounds will not reach equilibrium partitioning in an urban aerosol. Two OPAH have size distribution profiles distinct from PAH and most other OPAH. These compounds, 9,10phenanthrenequinone and OPAH-208b, have bimodal distributions with peaks at Dp ≈ 0.2 and 2.5 µm. These compounds have lower molecular weights than 5,12-naphthacenequinone and benzo[a]pyrene-6,12-dione, both of which are observed to be associated with Dp ≈ 1.0 µm particles. Therefore, these compounds are expected to have vapor pressures sufficient to allow partitioning to other particle size fractions. That they do not indicates that these OPAH have very different equilibrium sorption behavior from PAH and other OPAH and therefore partition to a different aerosol fraction. The existence of chemically distinct aerosol fractions has been recently observed by analyses of single atmospheric particles (39, 40). The distributions of PAH and other OPAH with particle size are approximately unimodal, indicating that the aerosol faction with which they associate also has a unimodal distribution. In contrast, the aerosol faction with which 9,10-phenanthrenequinone and OPAH-208b associate may have a bimodal distribution. The present conclusion, that organic compounds distribute very differently among aerosol size fractions based on their sorption behavior, implies that to predict the environmental fate of and human exposure to semivolatile organics
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one must understand the equilibrium sorption behavior of these compounds to atmospheric particles. The simplistic assumption that all semivolatile organics partition equally among atmospheric particles based on surface area or volume must be revised to explain the complex, compound-dependent partitioning observed in these samples.
Acknowledgments We thank A. Rana Biswas for his assistance in assembling and testing the sampler. We thank John L. Durant for helpful discussions on OPAH identification. We also thank the staff of the Massachusetts Department of Environmental Protection for access to the sampling site. This research was supported by the National Institute of Environmental Health Sciences and the Environmental Protection Agency. One of us (J.O.A.) was partially supported by a grant provided by the S. C. Johnson Wax Company.
(9) (10) (11) (12) (13) (14) (15) (16) (17) (18) (19) (20)
Supporting Information Available Five figures plus their captions showing the distribution of OPAH-254a, -280a, -280b, -208a, and -208b with particle size in an urban aerosol (6 pp) will appear following these pages in the microfilm edition of this volume of the journal. Photocopies of the Supporting Information from this paper or microfiche (105 × 148 mm, 24× reduction, negatives) may be obtained from Microforms Office, American Chemical Society, 1155 16th St. NW, Washington, DC 20036. Full bibliographic citation (journal, title of article, names of authors, inclusive pagination, volume number, and issue number) and prepayment, check or money order for $16.50 for photocopy ($18.50 foreign) or $12.00 for microfiche ($13.00 foreign), are required. Canadian residents should add 7% GST. Supporting Information is also available via the World Wide Web at URL http://www.chemcenter.org. Users should select Electron Publications and then Environmental Science and Technology under Electronic Editions. Detailed instructions for using this service, along with a description of the file formats, are available at this site. To download the Supporting Information, enter the journal subscription number from your mailing label. For additional information on electronic access, send electronic mail to
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(21)
(22) (23) (24) (25) (26) (27) (28) (29) (30) (31) (32) (33) (34) (35) (36) (37) (38) (39) (40)
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Received for review October 18, 1996. Revised manuscript received March 3, 1997. Accepted March 11, 1997.X ES960894G X
Abstract published in Advance ACS Abstracts, May 15, 1997.
