Environ. Sci. Technol. 1989, 23, 1269-1278
Mobile Sources of Atmospheric Polycyclic Aromatic Hydrocarbons: A Roadway Tunnel Study Bruce A. Benner, Jr." and Glen E. Gordon
Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland
20742
Stephen A. Wlse
Organic Analytical Research Division, Center for Analytical Chemistry, National Institute of Standards and Technology, Gaithersburg, Maryland 20899 Suspended particulate matter samples were collected by high-volume samplers in a heavily traveled roadway tunnel to characterize the mobile source emissions (dieseland gasoline-fueled vehicles) for polycyclic aromatic hydrocarbons (PAHs). Liquid and gas chromatographic techniques were employed to isolate and quantify individual PAHs in dichloromethane extracts of Teflon and glass-fiber filters. Some vapor-phase samples were collected on polyurethane foam plugs (PUFs) positioned downstream of the Teflon filters. The PUF samples contained relatively large amounts of phenanthrene and methyl- and dimethylphenanthrenes (>60% of total) compared with the filters. Mobile-source PAH emission estimates were generated from the particle- and vaporphase samples collected in the tunnel and agree with emission estimates reported previously for roadway tunnels in Japan. Factor analysis of PAH concentrations from 47 filter samples yielded two factors; one which possibly represented the diesel-fueled vehicles (heavy-duty trucks) and the other, either gasoline-fueled vehicles or a composite of the gasoline and diesel sources.
weighted, representative composition pattern for mobile sources. Furthermore, direct emissions from tail pipes are so hot that the exhaust gases must be diluted and cooled before sampling in order to simulate the behavior of the volatile species after release into the air. Because of these difficulties, we collected particles and gases from the mix of traffic passing through the Baltimore Harbor Tunnel (Tunnel) and analyzed them for PAHs and related compounds. The -5-min residence time of air in the tunnel (6) and dilution of the exhaust by several hundred fold, prior to exhaust to the outside, probably simulates processes in the real atmosphere better than in a laboratory dilution chamber. Also, because of the low level of lighting in a tunnel, there is essentially no photochemical decomposition or reaction with OH radicals or 03.Some PAHs were collected in the vapor phase, and the vapor-to-particle distributions compared with those determined from a model equation. The vapor- and particle-phase PAH concentrations measured in Tunnel air were used in estimating emission factors for 23 PAH species.
~~~
Introduction All combustion processes produce polycyclic aromatic hydrocarbons (PAHs). Major anthropogenic sources of PAHs include heating (coal, oil, and wood), refuse burning, coke production, industrial processes, and motor vehicles (1). Motor vehicles are thought to be the major source of atmospheric PAHs in the United States, accounting for -36% of the yearly total (2). Aluminum production and forest fires each contribute 17%, followed by residential wood combustion, coke manufacturing, power generation, and incineration, which emit 12%, 1190, 7%, and 3%, respectively (2). Knowledge of sources and composition patterns of PAH emissions is important because some of these compounds are mutagenic. Furthermore, as discussed by Daisey et al. (3),the traditional atmospheric tracer elements for identifying motor-vehicle emissions in receptor models, Pb and Br, are rapidly disappearing with the phase-out of leaded gasoline. They suggested that PAHs may in the future serve as markers for emissions from various types of combustion sources. Before PAHs can be used as tracers, composition patterns for important sources must be established. Here we describe experiments in which PAHs from motor vehicles were collected and their concentrations determined. Much has been learned about emissions of PAHs and related compounds by studies of individual vehicles on test stands (4, 5). However, studies of huge numbers of individual vehicles would have to be performed to develop a properly
* Present address: Center for Analytical Chemistry, National Institute of Standards and Technology, Gaithersburg, MD 20899. 0013-936X189/0923-1269$01.50/0
Experimental Section Sampling Site. Particulate matter samples were collected in exhaust rooms of the Tunnel during three field trips in 1985 and one trip in 1986. The Tunnel is a 2042-m-long, two-tube system (two traffic lanes per tube), which runs from southwest to northeast under the Patapsco River in Baltimore, MD. Diagrams of the Tunnel have been published previously (7). The Tunnel is ventilated by exhaust rooms situated in buildings located at either end of the Tunnel. Fan speeds for the exhaust rooms are varied manually by Tunnel personnel to keep the CO levels in the tubes below -100 ppm. Most samples were collected in an operating exhaust room, and a few were obtained in a ventilation passageway between the two tubes. Intake air was also sampled during each field trip for comparison with the exhaust room samples. Sample Collection. High-volumeair samplers (General Metal Works, Cleves, OH) were used to collect particulate matter generated by motor vehicles in the Tunnel. Particles were collected on 20.3- X 25.4-cm Teflon filters (Microfiltration Systems, Inc., Dublin, CA), which had been preextracted for at least 12 h with chromatography-grade dichloromethane (DCM). Tare weights were obtained for most Teflon filters for determination of total suspended particulate matter (TSP) concentrations. Gas-phase PAHs were collected on 10-cm-diameter X 10cm-thick porous polyurethane foam plugs (density, 0.02 g/cm3, Read Plastics, Inc., Rockville, MD), which had been cut from a sheet with a hole saw. The polyurethane foam plugs (PUFs) were rinsed with distilled water, dried in an oven at 100 "C, and subsequently rinsed with hexane, dichloromethane, acetone, and methanol. The PUFs were
0 1989 American Chemical Society
Environ. Sci. Technol.. Vol. 23, No. 10, 1989
1269
Soxhlet-extracted with acetone and DCM, both for 18-24 h, and air-dried prior to storage in g h jars. This clean-up procedure was necessary due to the large amounts of solvent-extractable material present in polyurethane foam (8). The PUFs were positioned after the filter in the "throat" of the high volume samplers. Thirteen 20.3-cm X 25.4-cm glass-fiber filter samples were collected during the December 1986 trip. Since these filters were fragile, they were not preextracted with solvent, but were thermally treated at 500 "C for 18 h prior to use to remove organic contaminants. Samplers were calibrated before and after sampling trips by using a calibration orifice (General Metal Works, Cleves, OH), a rotameter, and a water manometer (9). The PUFs decreased air-flow rates nearly in half, from 1.4 m3/min without the PUF to 0.8 m3/min with the PUF in place. Face velocities through the filter and PUF were typically 26 and 190 cm/s, respectively, at a total flow rate of 0.8 m3/min. A soot sample was obtained from the walls of an exhaust room at the Tunnel. This sample ("exhaust room soot") was used for analytical methods development and for comparison with fresh suspended particulate matter collected by air samplers described above. Sample Extraction. The particle-loaded Teflon filters were equilibrated for 2 h in the hood used for tare-weight determinations and weighed for TSP measurements. The filters were subsequently cut in half with a stainless-steel scalpel and inserted into a Soxhlet extractor. A known volume of a standard DCM solution containing phenanthrene-dIo, l-n-butylpyrene, and l-nitropyrene-d9 was added as the internal standards to each filter prior to extraction for 18-24 h with chromatography-grade DCM. A standard solution consisting of known amounts of 17 PAHs dissolved in DCM was prepared and spiked with the same internal standards as the filter samples and processed through the extraction and isolation procedure. After extraction, samples were concentrated to 1 mg/m3 (sample BO), and the TSP for a background sample of Baltimore air (sample BC) was 100 pg/m3. These two extreme cases of TSP concentrations, relative to the typical Tunnel samples, yielded vapor-to-particle ratios that tracked well with Yamasaki's predictions. The consistency of temperature during the collection of the Tunnel samples (*2 "C), allowed us to observe the importance of TSP in defining the vapor/particle partitioning for the Tunnel and background samples. The importance of TSP in the Yamasaki equation may depend upon the composition of the particles (carbonaceous vs siliceous), which would affect the strength of the interaction between the species and the carrier. Wehry et al. (23)found that PAHs preferentially sorb to the carbonaceous fraction of coal fly ash. Perhaps there is strong sorption of PAHs on diesel soot, given the relatively high carbon content of that substrate compared to that of particles from other combustion processes. Alkylphenanthrene Concentrations. Alkyl-substituted phenanthrenes in the Tunnel samples had relatively high concentrations compared with those of the parent compound. Several groups (12, 24-28) have suggested relationships between the ratios of concentrations of the substituted and unsubstituted species and the sources of the particulate matter. Lee et al. (25) observed greater relative concentrations of alkylated PAHs in particulate matter from coal combustion than from that of either wood or kerosene. Yu and Hites (29)noted that concentrations of alkylphenanthrenes in extracts of diesel particulate matter were comparable to those for phenanthrene. Jensen and Hites (26)investigated relationships between dieselengine operating parameters and the relative levels of parent and alkyl-substituted species. Concentrations of the alkylated species increased relative to that of the parent compound as the exhaust temperature decreased. Low-temperature formation (petrogenesis) of PAHs produces mixtures enriched in alkyl-substituted PAHs and
-
Vapor-phase uncertainties represent a propagation of an estimated f10% uncertainty in the analysis and a f 2 0 % uncertainty in the sampling volumes. Particle-phase uncertainties represent a propagation of an estimated *lo% uncertainty in the analysis and a 120% Uncertainty in the samdina volumes.
the GC-FID analyses. This suggests that the majority (>99%) of PAHs with molecular weights 1228 amu were collected in the particle phase and that a negligible fraction of particles passed through the filter. Comparisons of the observed vapor-to-particle PAH ratios and those calculated by the Yamasaki relationship above are shown in Table IV for the PAHs collected on the PUF plugs. Predicted and observed ratios for the six PAHs generally agreed within a factor of 2, with a trend toward higher ratios calculated by the Yamasaki equation. Better sample-to-sample agreement between predicted and observed ratios was observed for 3-methylphenanthrene, fluoranthene, and pyrene than for the other species. The chromatographic system used by Yamasaki and co-workers to determine the coefficients A and B could not resolve phenanthrene from anthracene nor the individual alkylated phenanthrenes from each other, so A and B were determined from the combined peaks of those groups of PAHs. The GC column used in our study separated phenanthrene from anthracene, and from most of the methyl-substituted phenanthrenes/anthracenes. This may explain why our ratios for fluoranthene and pyrene agree with the theoretical values, whereas those for phenanthrene, anthracene, and 2-methylanthracene did not correlate as well with those calculated by using the Yamasaki
Table IV. Comparison of Observed" and Predictedb PAR Vapor/Particle Ratios
TSP, sample
rg/m3
BO BN BD BE BI BG BB BF BL BC'
1328 709 635 532 424 349 330 276 198 96
phenanthrene obs pred
anthracene obs pred
3-methylphenanthrene obs pred
3.1 10.2 6.6 6.5 8.2 9.8 7.4 7.4 12.8 29.3
1.7 5.8 4.2 4.9 9.9 7.1 6.5 4.1 14.8 19.4
2.9 5.3 3.8 3.2 5.4 5.1 5.3 4.1 5.7 25.7
3.7 7.0 7.8 9.8 13 16 13 20 28 51
3.7 7.0 7.8 9.8 13 16 13 20 28 51
1.9 3.5 3.9 4.9 6.5 7.9 6.9 10 14 26
2-methylanthracene obs pred 1.4 2.6 1.5 1.2 4.8 2.0 1.8
1.5 4.7 8.1
1.9 3.5 3.9 4.9 6.5 7.9 6.9 10 14 26
fluoranthene obs pred
pyrene obs pred
0.3 1.5 0.8 1.0 1.4 1.0 0.8 0.8 1.9 3.7
0.3 1.6 0.8 0.9
0.3 0.7 0.7 0.9 1.3 1.5 1.2 1.9 2.7 4.9
1.2 1.0
1.0 0.8 1.7 3.9
0.3 0.5 0.6 0.7 1.0 1.2 1.0 1.5 2.1 3.7
"Results from filter and PUF samples collected in Baltimore Harbor Tunnel on December 17, 1986. *Predicted from the Yamasaki equation (ref 8). 'Background air particulate matter sample. Environ. Sci. Technoi., Vol. 23, No. 10, 1989
1273
Table V. Fractions of Phenanthrene and Methylphenanthrenes in Baltimore Harbor Tunnel, Diesel and Air Particulate Matter Samples % total phenanthrenes 3M2M- 9+4M+4H1MPHEN" PHEN* PHEN' PHENd PHEN'
sample Baltimore Tunnel (n = 48) exhaustroom sootf mean intake8 diesel particulateh air particulate Washington, DC' St. Lou&
25f5
19f225f2
18f2
13f1
21 f 2
19 f 2
20 f 2
14 f 1
37 f 10 13 f 7 23 f 11 22f3 2 3 f 3 3 0 f 5
16 f 8 11f2
11 f 6 144~2
61 f 5
8 f 1 11 f 1
13 f 1
6.4
59 f 5
10 f 1 13 f 1
12 f 1
6.8f 0.7
26 f 3
f
0.7
Phenanthrene. 3-Methylphenanthrene. 2-Methylphenanthrene. 9- and 4-methylphenanthrene and 4H-cyclopenta[deflphenanthrene. e 1-Methylphenanthrene. 'Sample collected from wall of exhaust room at the Baltimore Harbor Tunnel. #Mean fractions for four intake air samples. Standard reference material 1650 (diesel particulate matter). Standard reference material 1649 (urban dust/organics, Washington, DC). jStandard reference material 1648 (air particulate matter, St. Louis, MOL CI
other kinetically favored compounds, whereas high-temperature processes (combustion and pyrolysis) encourage the generation of unsubstituted (thermodynamically favored) compounds (27). Garrigues and co-workers (12) reported significant concentrations of methyl- and dimethylphenanthrenes in coal and shale oil samples, using the relative concentrations of the more stable dimethylphenanthrenes as indicators of the maturity of the samples. The fractions of phenanthrene and six monosubstituted derivatives, with respect to the sum of concentrations of the species, are listed in Table V for several types of samples. The Tunnel samples, exhaust-room soot, and SRM 1650 yielded significantly greater fractions of 3methylphenanthrene than the background samples and the air particulate matter SRMs (1648 and 1649). Exhaust room soot yielded relative concentrations of the methylphenanthrenes similar to those of the Teflon filter samples, suggesting that the concentration pattern of phenanthrene and its derivatives is preserved despite aging of the soot on the walls. The SRMs 1648 and 1649 had significantly lower lower fractions of 2- and 1-methylphenanthrene than the background samples, with correspondingly greater fractions of the parent PAH. Diesel particulate matter (SRM 1650) yielded relative concentrations similar to those of the Tunnel samples, for all methylphenanthrenes except 9-methyl- and 4-methylphenanthrene and 4H-cyclopenta[deflphenanthrene, which were depleted in the SRM. The Tunnel samples, SRM 1650, and the exhaust room soot were also enriched in dimethylphenanthrenes (MW
= 206) compared to the background sample and the two air particulate SRMs. Fractions of phenanthrene and six dimethylphenanthrenes for Tunnel, background, exhaust room soot samples and three SRMs are listed in Table VI. Comparison of the mean relative concentrations of phenanthrene and dimethylphenanthrenes in the Tunnel samples with those from the background samples, exhaust room soot, and the diesel particulate matter (SRM 1650), yielded similar fractions of these species from the different types of samples. Exhaust room soot was slightly depleted in C2-PHEN(2), but moderately enriched in C2-PHEN(3) as compared with the other samples. The SRM 1650 has nearly the same relative concentrations of phenanthrene and dimethylphenanthrenes as the Tunnel samples. In general, the background samples contained more phenanthrene than the mean results of the Tunnel samples. The background samples may have contained a higher proportion of motor-vehicle emissions than typical for the Baltimore area if the plume from the Tunnel ventilation building was forced downward, so that the motor-vehicle emissions would have been collected by the background sampler. Standard reference materials 1648 and 1649were depleted in dimethylphenanthrenes compared to the parent compound. Despite the varying traffic compositions expected for the different sampling periods, the fractions of phenanthrene and the alkylated phenanthrenes do not change markedly from sample to sample. This suggests that either both types of vehicles emit particles enriched in methyl- and dimethylphenanthrenes or that particulate emissions from diesel-fueled trucks, known to have significant concentrations of methyl- and dimethylphenanthrenes (29,30), dominate the loading in the Tunnel at all times. T h e latter explanation is supported by the remarkable similarities of the phenanthrene and alkylphenanthrene distributions of SRM 1650 and the Tunnel samples. Particle-phase concentrations of phenanthrene and its alkylated derivatives do not appear to differentiate between emissions from diesel- vs gasoline-fueled vehicles. PAH Emission Rates. In 1983, the National Research Council (NRC) presented a report (31) which included PAH emission factors for gasoline- and diesel-fueled motor vehicles. They noted the paucity of data on PAH emissions from various types of motor vehicles and the large uncertainties associated with the data. In determining these emission rates, they assumed that the relative amounts of different PAHs (the PAH profiles) emitted by the wide variety of vehicle in operation (diesel and gasoline cars and trucks) were the same. Our Tunnel samples are appropriate for estimating PAH emission rates, as particulate matter from hundreds of vehicles was sampled in hourly periods. Actual PAH emission data were obtained directly, instead of basing estimates on combinations of single-vehicle data.
Table VI. Fractions of Phenanthrene and Dimethylphenanthhrenes in Baltimore Harbor Tunnel, Diesel and Air Particulate Matter Samples (a) sample
PHEN
Baltimore tunnela mean intakeb exhaust room soot diesel particulatec air particulate Washington, DCd St. Louise
18.7 f 5.5 33 f 17 15.8 f 1.7 22.6 f 3.2
C2-PHEN(l) C2-PHEN(2) C2-PHEN(3) C2-PHEN(4) C2-PHEN(5) C2-PHEN(6) 13.9 f 0.9 11 f 5 10.7 f 1.0 14.2 f 1.9
9.2 f 0.7 10 f 5 3.2 f 0.3 8.6 f 1.3
25.6 f 2.6 18 f 9 30.0 f 3.1 25.9 f 3.6
13.2 f 1.3 10 f 5 15.8 f 1.7 12.3 f 1.7
10.3 f 0.9 11 f 6 13.2 f 1.4 8.3 f 1.1
77.5 f 5.9 72.6 f 6.6
3.8 f 0.5 5.2 f 0.3
2.1 f 0.3 3.2 f 0.2
7.9 f 1.0 9.3 f 0.9
5.7 f 0.5 5.5 f 0.6
3.1 f 0.5 4.3 f 0.4
9.2 f 1.0 6+3 11.4 f 1.3 8.1 f 1.2
Mean fractions from 48 Baltimore Harbor Tunnel samples; uncertainties represented by the standard deviations of the percentages of the 48 samples. bMean fractions for four intake air samples. cStandard reference material 1650 (diesel particulate matter). dStandard reference material 1649 (urban dust/organics, Washington, DC). e Standard reference material 1648 (air particulate matter, St. Louis, MO). 1274
Environ. Sci. Technol., Vol. 23, No. 10, 1989
Table VII. Mobile Source PAH Emission Rates from Particle- and Vapor-Phase Samples Collected in the Baltimore Harbor Tunnel and Those from Single-Vehicle Studies PAH
mean emissn rate, r g / h
phenanthrene anthracene 3-methylphenanthrene 2-methylanthracene 9+4M-PHEN/4H-CYC 1-methylphenanthrene C2-PHEN(1) C2-PHEN(2) C2-PHEN(3) C2-PHEN(4) C2-PHEN(5) C2-PHEN(6) fluoranthene pyrene benzo [ghi]fluoranthene cyclopenta[cd]pyrene benz [a]anthracene chrysenel triphenylene benzo[bJ+k]fluoranthrene benzo[e]pyrene benzo[a]pyrene indeno[1,2,3-cd]pyrene benzo[ghi]perylene
38 f 13 6f3 14 f 4 2 f l 12 f 4 8f3 5f2 3 f l 10 f 3 5 f l 3 f l 3 f l 8&3 8f3 2 f l 4f2 2 f 2 3f2 3f2 1f1 2 f l If1 2 f l
range, rcg/km 22-64 3-10 9-22 1-4 8-19 5-13 3-8 2-4 7-15 3-7 2-5 2-4 4-14 4-14 1-5 1-9 0.5-7 1-9 1-10 0.3-4 0.3-5 0.4-4 0.4-6
NRC sum," pg/km 224 55.5
Table VIII. Comparison of PAH Mobile Source Emission Rate Estimate (pghehicle-km) from the Baltimore Harbor Tunnel and Two Highway Tunnels in Japan" PAH
Baltimore
Nihonzaka
Tsuburano
PFene benz[a]anthracene chrysene/triphenylened benzo[a]pyrene benzo[ghi]perylene
8f3 2 f 2 3f 2 2 f 1 2f1
15: 32c 1.8: 1.9' l.l,b1.3c 1.2,b 1.9' 0.7,b 3.0'
47,b 91' 4.1: 4.3c 6.l,* 8.gC l.l,b2.6' 1.5,b3.3'
"See ref 33. Original emission rates were reported as pg/h and were converted to pg/vehicle-km assuming a typical vehicle speed of 88.7 km/h. Emission rate estimates from diesel-fueled vehicles using the tunnels. Emission rate estimates from gasoline-fueled vehicles using the tunnels. Estimates from Tunnel study included both chrysene and triphenylene, whereas the Japanese experimenta were based on the emission rates of chrysene alone. 117 149 61.2 5.8 27.9 17.1 8.0 6.9 4.8
Estimates from single-vehicle emission rates and 24-h passenger car/truck and bus counts (ratio of 81:ll) for December 17, 1986. Vehicle breakdown as follows: 57.1% light-duty (LD) spark with three-way catalyst; 21.1% LD with no catalyst; 9.3% heavyduty (HD) diesel; 6.3% LD spark with oxidation catalyst; 4.5% LD diesel; and 1.6% HD spark with no catalyst (32).
We built a simple model to convert observed PAH concentrations in the Tunnel exhaust room (ng/m3) to emission rates of individual PAHs (pg/vehicle-km). From knowledge of the Tunnel's dimensions and thus, its volume, and the 5-min air-exchange period, we could estimate the total air flow through the exhaust rooms to yield an expression for obtaining total vehicle PAH emissions from filter and PUF samples. This equation can be simply stated as
ERP*, = 4000[PAH,]/(Nveh X 1.2 km) where ERPAHz is the emission rate for PAH,, 4000 is the ratio of exhaust room flow to that of the high-volume air samplers, [PAH,] is the total mass of PAH, determined from filter and PUF measurements, Nvehis the total number of vehicles using the tube during the sampling periods, and 1.2 km is the length of this section of the Tunnel. Ranges of these emission rates for 25 PAHs determined in this study are shown in Table VII. A simulated traffic composition for the Tunnel was estimated from total passenger car and trucks/buses counts at the Tunnel for December 17,1986 (sampling for both particle- and vapor-phase PAHs). From the recommendations of Black et al. (32),the traffic composition was further defined as 57% light-duty spark-ignition (LDSI) three-way catalyst vehicles, 21 % LDSI vehicles without catalysts, 9% heavy-duty diesels, 6% LDSI with oxidation catalyst, 4 % light-duty diesels, and 2% heavy-duty spark-ignition vehicles without catalysts. These fractions of the different types of vehicles were multiplied by their respective single-vehicle PAH emission rates (NRC data, ref 31) to yield composite emission rates for comparison with the emission rates estimated from the Tunnel samples (Table VII).
The predicted composite emission factors (Table VII, NRC sum) are approximately 10 times greater than observed for fluoranthene, pyrene, and cyclopenta[cd]pyrene. Composite emission factors for other species ranged from 1 to 6 times greater than observed from the Tunnel samples. The use of these single-vehicle data for estimating atmospheric burdens from mobile sources seems to yield "worst casen approximations. Handa et al. (33)determined emission rates for six PAHs from diesel- and gasoline-fueled vehicles using two roadway tunnels in Japan. Table VIII compares emission rates from our Tunnel study for five species with those of Handa and co-workers. Good agreement was observed between the emission estimates from the two studies, especially with the diesel-emission rates from the Nihonzaka Tunnel and those from our experiment, supporting claims, above, regarding the dominance of the diesel emissions in the Baltimore Tunnel. Factor Analysis. Factor analysis (FA) was applied to the Tunnel composition data in an attempt to identify factors associated with different types of vehicles. Anthracene, 2-methylanthracene, cyclopenta[cd]pyrene, indeno[ 1,2,3-cd]pyrene, and coronene were not included in the FA because they were not detected in all Tunnel samples. Twenty particle-phase PAH concentrations from 47 samples were treated by the StatView (Brainpower, Inc., Calabas, CA) FA routine using principal-component analysis (PCA) followed by Varimax rotation. Two factors account for >92% of the data variance, so only two factors were retained. As shown in Table IX, communalities for most PAHs are very high, with the exceptions of those for phenanthrene, fluoranthene, benzo[ghi]fluoranthene and benzo[ghi]perylene. Most compounds are strongly associated with one factor or the other: the alkylphenanthrenes on factor 1and benz[a]anthracene, chrysene/triphenylene, benzo[b j + k ] fluoranthene, benzo [e]pyrene, and benzo[alpyrene on factor 2. The remaining compounds were less distinctly divided between factors. Samples collected in the Tunnel were expected to be composed of emissions from the two major types of mobile sources, diesel- and gasoline-fueled motor vehicles and, possibly, input from ambient air. If the two mobile sources emit particles with different distributions of PAHs, one might be able to resolve the diesel from the gasoline emissions. The distribution of PAHs in diesel particulate matter (DPM) is rich in the lower molecular weight PAHs and alkylated PAHs, as evidenced by PAH analysis of SRM 1650 and work by other groups (30,34). Factor 1 of the Varimax rotation was heavily loaded with the methyl- and dimethylphenanthrenes. Phenanthrene, pyrene, and benzo[ghi]fluoranthene also loaded significantly on factor Environ. Sci. Technol., Vol. 23, No. 10, 1989
1275
Table IX. Factor Analysis of Particulate PAH Concentrationsin Baltimore Harbor Tunnel (Varimax-Rotated Solutions for 47 Samples) compound
factor loadings av contrib obs/pred u, factor 1 factor 2 communalities ng/m3 comp 1 comp 2 corr (r2)
0.74 phenanthrene 0.99 3-methylphenanthrene 0.98 2-methylphenanthrene 9+4-methylphenanthrene/4H-cyclopenta[deflphenanthrene 0.97 l-methylphenanthrene 0.99 C2-PHEN(1) 0.99 0.99 C2-PHEN(2) C2-PHEN(3) 0.99 0.99 C2-PHEN(4) 0.98 C2-PHEN(5) 0.98 C2-PHEN(6) 0.27 fluoranthene 0.81 pyrene 0.74 benzo[ghi]fluoranthrene 0.07 benz[a]anthracene 0.26 chrysene/triphenylene -0.05 benzo[bJ+k]fluoranthene 0.12 benzo[e]pyrene 0.08 benzo[a]pyrene 0.13 benzo[ghi]perylene
1. These results suggest that the majority of the variations of the alkylated-PAH concentrations and those of the larger PAHs are explained by separate factors. Based on the PAH composition of DPM, and DPM’s high levels of alkylated PAHs, factor 1 probably represents emissions from diesel engines. High loadings of the larger PAHs on factor 2 suggests that those species are preferentially emitted by gasoline-fueled vehicles. Results of FA must be interpreted carefully because species can be loaded on the same factor because of any effect that imposes correlations, not just origin from a common source. Groupings of all methyl- and dimethylphenanthrenes on factor 1, for example, could have resulted from their similar volatilities, reactivities, or both. If this were the case, they could not be used for distinguishing emissions of diesel- from gasoline-fueled vehicles. If the PAHs were grouped with factors solely on the basis of volatilities, however, one would expect fluoranthene to load significantly on factor 1 instead of on factor 2 with the less volatile compounds. Also, benzo[ghi]fluoranthene loaded significantly on factor 1, but was not detected in the gas-phase samples, suggesting that factor 1 is not defined solely by PAH vapor pressures. Possibly, factor 2 does not represent gasoline-fueled vehicles, but light-duty diesels or background air contributions. The former would be more reasonable since the background TSP was usually a small fraction of the Tunnel TSP. Henry (35) proposed a way of obtaining relative concentrations of species from FA using the following proportionality: C j j = aijai,where Cij is the relative concentration of species i in the material accounting for factor j , ajj is the loading of species i on factor j , and ui is the standard deviation of the concentration of species i over the samples included in the factor analysis. We used this technique to obtain relative concentrations of the 20 PAHs in the two components (Table IX). All loadings were positive except for the small negative loading of benzo[bj+k]fluoranthene, which we set equal to zero in constructing the components. To test the validity of the components, we reconstructed the composition of each sample by use of multipliers that forced fits of the concentrations of C2-PHEN(l) and benzo[bj+k]fluoranthene, which are strongly associated with components 1 and 2, respectively. Results of the exercise, shown in Table IX, are excellent for most species, 1276
Environ. Sei. Technol., Vol. 23, No. 10, 1989
0.49 0.09 0.10
0.19 0.09 0.08 0.09 0.07 0.05 0.13 0.09 0.83 0.50 0.42 0.98 0.94 0.97 0.98 0.96 0.82
0.79 0.98 0.97 0.97 0.98
10.5 9.3 12.0 7.7 6.8
1.00
10.1
0.97 0.97 0.99 0.99 0.98 0.76 0.91 0.72 0.96 0.95 0.95 0.97 0.92 0.69
6.0 19.8 10.5 6.5 6.7 10.3 14.3 5.3 4.8 7.7 7.3 2.9 4.2 4.2
10.1 11.9 15.3 9.9 8.8 13.0 7.8 25.4 13.5 8.3 8.6 3.6 15.0 5.1 0.4 2.5 0.0 0.5 0.4 0.7
7.8 1.3 1.8 1.0 0.9 1.2 0.8 2.0 0.8 1.3 0.9 13.0 10.9 3.4 7.0 10.9 10.8 4.4 6.0 5.1
0.76 0.98 0.95 0.95 0.98 1.00 0.99 0.99 0.99 0.99 0.98 0.73 0.87 0.69 0.91 0.90 1.00 0.90 0.84 0.60
the exceptions being the four species with low communalities: phenanthrene, fluoranthene, benzo[ghi]fluoranthene, and benzo[ghi]perylene. If components 1and 2 are indeed associated with diesel trucks and gasoline-powered vehicles, respectively, one would expect the ratio of the strength of the former to that of the latter to be highest at times when diesel traffic is greatest, e.g., late at night and the middle of the day, and lowest during the morning and afternoon rush hours. Absolute strengths are not very informative because ventilation fan speeds are adjusted to maintain a CO level below 100 ppm. Although there is considerable fluctuation of the ratio, there is a tendency for component l/component 2 to be high when expected, but not clearly enough to confirm the source of component 2. Another point favoring the association of factor 2 with gasoline-fueled vehicles is that all of the PAHs observed by Fox and Staley (11)in the Tunnel in 1975 are strongly associated with our factor 2 except for pyrene, for which our resolution indicates only 40% arises from factor 2. All of these PAHs had much higher concentrations in the earlier study, which can be fitted rather well by increasing the strength of our component 2 in Table IX by a factor of 12. Unfortunately, Fox and Staley (11) did not measure any of the PAHs strongly associated with our component 1. Mass measurements were available for 33 of the 47 samples, which were also subjected to FA. Results for the PAHs were quite similar to those for the 47 samples, but the communality for TSP was only 0.5 and its loadings were 0.07 and 0.70 on factors 1 and 2, respectively. Thus, PAH concentrations do not appear to be strongly associated with mass contributions, of which they comprise a very small portion. Large portions of the TSP in a tunnel arise from crustal material carried in by vehicles (7, 36). The concentration of TSP contributed by this kind of material will depend on many variables such as the time since the tunnel roadway was last washed and rain or the lack thereof outside. Summary Absolute concentrations of several PAHs measured in the Baltimore Harbor Tunnel by Fox and Staley (11)in 1975 were lower by factors of 5-10 in 1985/1986, probably because of the use of catalytic convertors in most of the present fleet. Normalized concentrations of PAHs in the
Tunnel agreed well with those from other highway tunnel studies, although the other experimenters did not measure the methyl- and dimethylphenanthrenes determined in this work. Vapor-phase and "blow-off" PAHs in the Tunnel were conservatively collected on PUFs, and the distribution of species collected in the particle- and vapor-phases agreed surprisingly well with a model proposed by Y amasaki and co-workers (B), which required knowledge of the TSP concentrations, average temperature, and Yamasaki's coefficients for each PAH. Vehicle emission rates for particle- and vapor-phase PAHs were determined from filter and PUF concentrations, total vehicle counts, and Tunnel ventilation rates. Emission rates for five PAHs were comparable to those determined by Handa et al. (33) for a similar highway tunnel in Japan, but much lower than expected on the basis of data summarized by a NRC panel (31). Factor analysis of particle-phase PAHs concentration data from the Tunnel samples yielded two factors. The alkylated phenanthrenes all loaded significantly on factor 1,suggesting that it is the diesel source, while several of the higher molecular weight PAHs loaded on factor 2, which may implicate the gasoline-fueled emissions in the Tunnel.
Acknowledgments We are grateful to Thomas J. Fallon, Robert Alter, and Charles Racob of the Baltimore Harbor Tunnel Authority for their cooperation in allowing us to sample in the Tunnel. We thank Reuben Olp, Jeff Youngbar, and James Mercer of the Tunnel for their assistance during the field trips at the Tunnel. Many thanks also go to Willie E. May and Stephen N. Cheder of the National Iristitute of Standards and Technology for permitting use of laboratory facilities during the project. This work was included in a dissertation submitted in partial fulfillment of the requirements for the Ph.D. degree by B.A.B., Jr. at the University of Maryland, College Park, MD. Certain commerical equipment, instruments, or materials are identified in this report to specify adequately the experimental procedure. Such identification does imply recommendation or endorsement by the National Institute of Standards and Technology (formerly National Bureau of Standards). Registry No. Phenanthrene, 85-01-8; anthracene, 120-12-7; 3-methylphenanthrene, 832-71-3; 2-methylphenanthrene, 253184-2; 2-methylanthracene, 613-12-7; 9-methylphenanthrene, 883-20-5; 4-methylphenanthrene, 832-64-4; 4H-cyclopenta[defl phenanthrene, 203-64-5; 1-methylphenanthrene, 832-69-9; 2,6dimethylphenanthrene, 17980-16-4; 2,7-dimethylphenanthrene, 1576-69-8; 1,3-dimethylphenanthrene,16664-45-2; 2,lO-dimethylphenanthrene, 2497-54-3; 3,9-dimethylphenanthrene, 66291-32-5; 3,10-dimethylphenanthrene,66291-33-6; 1,6-dimethylphenanthrene, 20291-74-1; 2,9-dimethylphenanthrene, 17980-09-5;1,7-dimethylphenanthrene, 483-87-4; 2,3-dimethylphenanthrene, 3674655; fluoranthene, 206-44-0; pyrene, 129-00-0; benzo[ghi]fluoranthene, 203-12-3; cyclopenta[cd]pyrene, 2720837-3; benz[a]anthracene, 56-553; chrysene, 218-01-9; triphenylene, 217-59-4; 1-butylpyrene, 35980-18-8; benzo[ blfluoranthene, 20599-2; benzoulfluoranthene, 205-82-3; benzo[k]fluoranthene, 207-08-9; benzo[e]pyrene, 192-97-2; benzo[a]pyrene, 50-32-8; perylene, 198-55-0; indeno[ 1,2,3-cd]pyrene, 193-39-5; benzo[ghilperylene, 191-24-2; coronene, 191-07-1.
Literature Cited (1) National Academy of Science Particulate Polycyclic Organic Matter; National Academy Press: Washington, DC, 1973.
(2) Bjarseth, A.; Ramdahl, T. In Handbook of Polycyclic Aromatic Hydrocarbons: Emission Sources and Recent Progress in Analytical Chemistry;Bjorseth, A., Ramdahl,
T., Eds.; Marcel Dekker: New York, 1985; pp 1-20. (3) Daisey, J. M.; Chesney, J. L.; Lioy, P. J.Air Pollut. Control ASSOC. 1986, 36, 17-33. (4) Lang, J. M.; Snow, L.; Carlson, R.; Black, F.; Zweidinger, R.; Tejada, S. SAE Trans. 1981, Paper 811186. (5) Westerholm, R. N.; Alsberg, T. E.; Frommelin, A. B.; Strandell, M. E.; Rannug, U.; Winquist, L.; Grigoriadis, V.; Egeback, K.-E. Environ. Sei. Technol. 1988,22,925-930. (6) Israel, G. W.; Whang, J. In Study of the Emissions from Major Air Pollution Sources and Their Atmospheric Interactions, Two-Year Progress Report. 1November 72-31 October 74; University of Maryland, Department of Chemistry and Institute for Fluid Dynamics and Applied Mathematics, College Park, MD. (7) Ondov, J. M.; Zoller, W. H.; Gordon, G. E. Enuiron. Sei. Technol. 1982,16,318-328. (8) Yamasaki, H.; Kuwata, K.; Miyamoto, H. Environ. Sei. Technol. 1982,16, 189-194. (9) Fed. Regist. 1982, 47, 234, 54896-54921. (10) Wise, S. A.; Cheder, S. N.; Hertz, H. S.; Hilpert, L. R.; May, W. E. Anal. Chem. 1977,49, 2306-2310. (11) Fox, M. A.; Staley, S. W. Anal. Chem. 1976,48,992-998. (12) Garigues, P.; Parlanti, E.; Radke, M.; Bellocq, J.; Willsch, H.; Ewald, M. J. Chromatogr. 1987, 395, 217-228. (13) Kebbekus, B.; Greenberg, A.; Horgan, L.; Bozzelli, J.; Darack, F.; Eveleens, C.; Strangeland, L. J. Air Pollut. Control Assoc. 1983, 33, 328-330. (14) Grimmer, G.; Naujack, K. W.; Schneider, D. In Polynuclear Aromatic Hydrocarbons: Chemistry and Biological Effects; Bjrarseth, A., Dennis, A. J., Eds.; Battelle Press: Columbus, OH, 1980; pp 107-125. (15) Handa, T.; Kato, Y.; Yamamura, T.; Ishii, T.; Matsusheta, H. J. Environ. Sei. Health, Part A 1980, 15, 573. (16) Daisey, J. M.; Butler, J.; Hering, S. V., unpublished data, cited in ref 3. (17) Coutant, R. W.; Brown, L.; Chuang, J. C.; Riggin, R. M.; Lewis, R. G. Atmos. Environ. 1988,22,403-409. (18) Bidleman, T. F.; Olney, C. E. Bull. Environ. Contam. Toxicol. 1974, 11, 442-447. (19) Keller, C. D.; Bidleman, T. F. Atmos. Environ. 1984, 18, 837-845. (20) You, F.; Bidleman, T. F. Environ. Sei. Technol. 1984,18, 330-333. (21) Bidleman, T. F.; Billings, W. N.; Foreman, W. T. Enuiron. Sci. Technol. 1986,20, 1038-1043. (22) McVetty, B. D.; Hites, R. A. Atmos. Enuiron. 1988, 22, 511-536. (23) Wehry, E. L.; Mamantov, G.; Dunstan, T. D. J.; Jinxian, Z.; Mauldin, R. F.; Sanders, J. K.; Hipps, A. D. Photodegradation of PAH Adsorbed on Coal Ash and Other Solid Substrates. Presented at the Eleventh International Symposium on Polynuclear Aromatic Hydrocarbns, Gaithersburg, MD, 1987. (24) Laflamme, R. E.; Hites, R. A. Geochim. Cosmochim. Acta 1978,42, 289-303. (25) Lee, M. L.; Prado, G. P.; Howard, J. P.; Hites, R. A. Biomed. Mass Spectrom. 1977,4, 182-186. (26) Jensen, T. E.; Hites, R. A. Anal. Chem. 1983,54594-599. (27) Youngblood, W. W.; Blumer, M. Geochim. Cosmochim. Acta 1975, 39, 1303-1314. (28) Wakeham, S. G.; Schaffer, C.; Giger, W. Geochim. Cosmochim. Acta 1980,44, 415-429. (29) Yu, M.-L.; Hites, R. A. Anal. Chem. 1981, 53, 951-954. (30) Williams, P. T.; Bartle, K. D.; Andrews, G. E. Fuel 1986, 65, 1150-1158. (31) National Research Council Polycyclic Aromatic Hydrocarbons: Evaluation of Sources and Effects; National Academy Press: Washington, DC, 1983. (32) Black, F.; Braddock, J.; Bradow, R. Environ. Int. 1985,11, 205-233. Environ. Sci. Technol., Vol. 23,
No. 10, 1989 1277
Environ. Sci. Technol. 1989, 23, 1278-1286
Handa, T.; Yamauchi, T.; Sawai, K.; Yarnamura, T.; Koseki, Y.; Ishii, T. Environ. Sci. Technol. 1984, 18, 895-902. Andrews, G. E.; Iheozor-Ejiofor, I. E.; Pang, S. W.; Oeapiptanukul, S. Znt. Conf. Combust. Eng., Inst. Mech. Eng. 1983, C73/83, 63-77. Henry, R., The Application of Factor Analysis to Urban Aerosol Source Identification. Preprint volume from The
Fifth Conference on Probability and Statistics, Las Vegas, NV, 1977. (36) Pierson, W. R.; Brachaczek, W. P. Aerosol Sci. Technol. 1983, 2, 1-40.
Received for review December 29,1988.Accepted June 21,1989.
Influence of Macromolecules on Chemical Transport Carl 0. Enfleld,*
st
Goran Bengtsson,$and Roland LIndqvlst§
R. S.Kerr Environmental Research Laboratory, U.S. Environmental Protection Agency, Ada, Oklahoma, and Department of Ecological Chemistry, University of Lund, Lund, Sweden Macromolecules in the pore fluid influence the mobility of hydrophobic compounds through soils. This study evaluated the significance of macromolecules in facilitating chemical transport under laboratory conditions. Partition coefficients between 14C-labeledhexachlorobenzene and three macromolecules [dextran, humic acid, and groundwater dissolved organic carbon (DOC)] were determined in a three-phase (water-macromolecule-soil) system. There were significant differences between the macromolecu1e:water partition coefficients, which ranged from 1 X lo3to 1 X 106. Soikwater partitioning for humic acid was demonstrated by using column breakthrough curves where the breakthrough curve for humic acid was retarded behind 3H20. Breakthrough curves for dextran and groundwater DOC demonstrated apparent size exclusion, as these compounds eluted from the soil column before the 3H20. The impact of the dextran was demonstrated under dynamic conditions by use of hexachlorobenzene, anthracene, and pyrene with and without macromolecules in replicated, biologically inhibited (sodium azide), saturated soil columns. The results may help explain the mechanism by which hydrophobic pollutants appear in deep groundwater aquifers.
Introduction The transport of organic pollutants in a saturated porous medium is determined by many physical, chemical, and biological processes. Mathematical models recently reviewed by Rao and Jessup ( I ) , Boeaten and Leistra (2))and Addiscott and Wagenet (3) describe the impact of dispersion, advection, sorption, and transformation on the movement of chemicals in soils. A fairly extensive literature (e.g., ref 4-11) has emphasized the linear relationship between sorption of nonpolar hydrophobic compounds, the organic carbon content of the soil, and the octano1:water partition coefficient of the sorbate. Roy and Griffin (12), in a review of methods of predicting soibwater partition coefficients from octanokwater and solubility relationships, suggested that soil organic carbon:water partition coefficients could be estimated within an order of magnitude if the octano1:water partition coefficient were known. This model of hydrophobic sorption as a linear phase equilibrium relationship has been challenged by laboratory measurements showing solid concentration induced nonlinearities (13). This observation has been attributed to slow desorption rates (14) and incomplete phase separaSoil Scientist, U.S. EPA.
tions (15, 16) due to nonsettling organic matter that remains in the aqueous phase, so that solute molecules can reside in three phases rather than two. The concept of two aqueous subphases is in agreement with earlier observations on the binding of hydrophobic compounds to humic macromolecules or colloids (17-21). In recent years, the partitioning between a solute and macromolecules in the aqueous phase has been addressed in a number of papers (22-29). Both concentration and chemical composition of dissolved organic material (DOM) may vary considerably in natural waters on a geographical basis, and structural differences between similar macromolecules may modify partition coefficients by a factor of 10 or more (25, 29-31). If hazardous chemicals partition to mobile macromolecules in subsurface environments, the current approaches of making environmental exposure and risk analysis, assuming partitioning between soil organic carbon and dilute aqueous solutions of the solute, may significantly underestimate the mobility of relatively immobile solutes. Enfield (32) suggested that macromolecules or immiscible substances moving with water may, under certain circumstances, enhance the movement of hydrophobic chemicals through soils. Enfield and Bengtsson (33) demonstrated that under some conditions macromolecules, on the average, will actually move faster through soils than water due to exclusion of the macromolecules from the smaller pores. Bengtsson et al. (34) showed that 500 mgL-' of a polysaccharide enhanced mobility of hexachlorobenzene by about 25% in a saturated sandy soil. The present study was conducted to further explore the theory for facilitated transport with solutes of different hydrophobicity and more heterogeneous macromolecules. The objective of this study was to propose a mathematical model that offers some insight into the mechanisms of facilitated transport and to test the predictions of the model by independently measuring the partitioning between selected hydrophobic compounds and macromolecules and their breakthrough curves in saturated soil columns. Theoretical Development
The movement of a contaminant through the soil in the presence of macromolecules or other nonreactive organic substances can be described by dividing the soil system into three phases: a liquid or aqueous phase, a solid phase-the soil, and a mobile organic phase-the macromolecule. The following equations can be written to describe the individual phases:
* Associate Professor, Dept. of Ecological Chemistry, University
of Lund. 8 Graduate student, Dept. of Ecological Chemistry, University of
Lund. 1278
Environ. Sci. Technol., Vol. 23, No. 10, 1989
0013-936X/89/0923-1278$01.50/0
0 1989 American Chemical Society
