Ž .The Science of the Total Environment 227 1999 57]67

Ž .Polycyclic aromatic hydrocarbons PAHs in Chicago air

Mustafa Odabasia, Nedim Vardarb, Aysun Sofuoglub, Yucel Tasdemirc,Thomas M. Holsenb,U

aDepartment of En¨ironmental Engineering, Dokuz Eylul Uni ersity, Faculty of Engineering, Buca, Izmir, TurkeybDepartment of Chemical and En¨ironmental Engineering, Illinois Institute of Technology, 10 W. 33rd Street, Chicago,

IL 60616, USAcDepartment of En¨ironmental Engineering, Uludag Uni ersity, Faculty of Engineering and Architecture, 16059 Gorukle,

Bursa, Turkey

Received 24 June 1998; accepted 13 December 1998

Abstract

Ambient air samples were collected in Chicago, IL between June and October 1995 as part of a study toŽ .investigate the dry deposition and air]water exchange of polycyclic aromatic hydrocarbons PAHs . A modified

Ž .high-volume sampler PS-1 sampler was used to collect airborne PAHs in both the particulate and gas phases. TheŽ . y3average total gasqparticulate S -PAH concentration was 428"240 ng m , similar to those previously observed14

in Chicago, IL and other urban areas. The particlergas phase distribution varied widely. The gas phase percentageranged from 1.1 to 99.4%, and generally decreased with increasing molecular weight. The amount of PAHsassociated with the particulate phase increased with decreasing temperature, probably due to the temperaturedependence of gasrparticle partitioning. Concentrations of PAHs with molecular weights between 154 and 202 werecorrelated well with phenanthrene concentrations while compounds with molecular weights higher than 202 had littleor no correlation with phenanthrene concentration, probably due to the different partitioning, transport and removalcharacteristics of low and high molecular weight compounds. Q 1999 Elsevier Science B.V. All rights reserved.

Keywords: PAHs; Particlergas phase distribution

U Corresponding author. Department of Civil and Environmental Engineering, Clarkson University, Box 5710, Potsdam, NY 13699,USA. Tel.: q1 315 2683851; fax: q1 315 2687636; e-mail: holsen@clarkson.edu

0048-9697r99r$ - see front matter Q 1999 Elsevier Science B.V. All rights reserved.Ž .PII: S 0 0 4 8 - 9 6 9 7 9 9 0 0 0 0 4 - 2

( )M. Odabasi et al. r The Science of the Total En¨ironment 227 1999 57]6758

1. Introduction

PAHs are formed primarily during incompletecombustion of fossil fuels and wood. Majorsources of PAH include residential heating, openburning, coke and aluminum production and mo-

Žtor vehicle exhaust Finlayson-Pitts and Pitts,.1986 . The Chicago metropolitan area has a large

volume of automobile traffic and there arenumerous steel and coke oven industries concen-trated at southeast Chicago. The results of the

Ž .study by Khalili et al. 1995 indicated that cokeovens, gasoline and diesel engine vehicles are themajor sources of measured ambient PAH concen-trations in the Chicago metropolitan area and twoand three ring PAHs are responsible for themajority of the total PAH emissions.

The atmosphere is a major pathway for thetransport and deposition of PAHs. The removal

Ž .rate of semivolatile organic compounds SOCs bywet and dry deposition is controlled in part bytheir distribution between particle and gas phasesŽ .Bidleman, 1988 . Since the mid-1980s it has beencommonly accepted that the impact of atmo-spheric deposition of SOCs to the Great Lakes is

Ž .significant Hoff et al., 1996 . Particle phase drydeposition fluxes of PCBs in Chicago were sig-nificantly greater than in rural areas, suggestingthat Chicago and other urban areas are major

Žsources of PCB deposition to nearby lakes Hol-

. Ž .sen et al., 1991 . Offenberg and Baker 1997have also reported that urban plume of Chicagoincreases atmospheric deposition of contaminantsto Lake Michigan.

Ambient PAH concentrations resulting fromurban and industrial emissions in Chicago areawere measured between June and October 1995as part of a study to investigate the dry depositionand air]water exchange of these compoundsŽ .Odabasi et al., 1998a,b . Here, we report theresults of these measurements and compare themto previously reported PAH concentrations forChicago and other urban areas.

2. Experimental

2.1. Sampling and analysis

Air samples were collected between June andOctober 1995 during the daytime when there was

Žno rain. Average sampling time was 24 h 2=12.h and sampling volume was approximately 1403 Žm . A summary of sampling information dura-

tion of sampling, meteorological conditions, and.date of sampling is provided in Table 1.

Samples were taken on a 1.6-m high platformŽ .on the roof of a four-storey building 12 m height

located on the campus of Illinois Institute ofTechnology, 5.6 km south of Chicago’s center and1.6 km west of Lake Michigan. The sampling site

Table 1Summary of sampling and meterological conditions

Sample Date Sampling Wind speed Air temp. RHŽ . Ž . Ž . Ž .No. time h mrs 8C %

1 14]19 June 71.9 2.9 28.8 49.62 29 June]6 July 61.0 3.6 23.7 53.63 8]13 July 66.5 3.0 26.9 57.44 14]21 July 64.8 3.7 30.1 53.65 25]30 July 62.0 2.9 29.1 64.36 5]12 August 78.3 2.8 29.1 67.07 15]23 August 71.6 2.8 27.3 62.98 24]31 August 75.9 2.8 27.7 68.29 6]14 September 82.0 3.6 19.3 57.1

10 15]25 September 88.5 3.3 15.8 53.911 4]13 October 76.9 3.2 20.6 47.612 15]23 October 63.8 4.5 14.8 44.5

Note. Wind speed, temperatures and relative humidity were averaged over the sampling period.

( )M. Odabasi et al. r The Science of the Total En¨ironment 227 1999 57]67 59

is in a mixed institutional, residential andcommercial area. There are landscaped areas,large parking lots and low-rise buildings around

Ž .the sampling site Odabasi, 1998 .Samples were collected by using a modified

Žhigh-volume sampler Model PS-1 General Metal.Works Inc. . Particles were collected on 11-cm

diameter glass fiber filters. The gas phase com-pounds were collected in a modified cartridgecontaining XAD-2 resin placed between layers of

Ž .polyurethane foam PUF .Glass fiber filters were wrapped loosely with

aluminum foil and baked in a muffle furnace at4508C overnight. Then they were allowed to cool

Žto room temperature in a desiccator Leister and.Baker, 1994; Franz, personal communication .

PUF and resin cartridges were cleaned by SoxhletŽextraction using a series of solvents de-ionized

water, methanol, dichloromethane, acetone].hexane mixture for 24 h each. After extraction,

cartridges were wrapped loosely with aluminumfoil and dried in an oven at 708C. Cleaned car-tridges were stored in glass jars capped with

ŽTeflon-lined lids Hornbuckle et al., 1994; Franz,.personal communication .

Cleaned and prepared glass fiber filters andPUF and resin cartridges were transported to thefield in their containers without allowing exposureto ambient air. After sampling PS-1 filters andPUF and resin cartridges were placed into theircontainers, brought back to the laboratory andstored in the dark at y208C until they wereanalyzed.

All samples were spiked with PAH surrogatestandards prior to extraction in order to de-termine analytical recovery efficiencies. Sampleswere Soxhlet extracted with a mixture of

Ž . Ž .dichloromethane DCM : petroleum ether PEŽ .20:80 for 24 h.

All sample extracts were concentrated andtransferred into hexane using a rotary evaporatorand a high purity stream of nitrogen. After volumereduction to 2 ml and transfer into hexane, sam-ples were cleaned up on an alumina-silicic acid

Ž .column containing 3 g silicic acid 3% water andŽ .2 g alumina 6% water . The column was pre-

washed with 20 ml DCM followed by 20 ml PE.The sample in 2 ml hexane was added to the top

of column and PAHs were eluted with 20 mlDCM. The solvent was exchanged into hexane,and the final sample volume was adjusted to 1 ml

Žby nitrogen blow-down Harner, personal commu-.nication .

ŽSamples were analyzed for 14 PAHs acen-aphthene, fluorene, phenanthrene, anthracene,

w xcarbazole, fluoranthene, pyrene, benz a anthra-w x w xcene, chrysene, benzo b fluoranthene, benzo k -w x wfluoranthene, benzo a pyrene, indeno 1,2-

x w x .cd pyrene and benzo g,h,i perylene using a HPModel 5890 Series II gas chromatograph and a

Ž .HP Model 5971A mass selective detector MSD .ŽAn HP-5 column 60 m=0.32 mm i.d., Hewlett

.Packard Corp. was used. Injections were splitlesswith split opened after 0.6 min and the injectortemperature was 2508C. The temperature pro-gram was 508C for 1 min, 258C miny1 to 1208C,hold time 12 min, 68C miny1 to 2008C, 28C miny1

to 2908C, hold time 15 min. The MSD was oper-ated in electron impact mode with electron ener-

Ž .gies of 70 eV. Selected ion monitoring SIMmode was used to detect the ions used for PAH

Ždetermination. Ions monitored were target, qual-. Ž .ifier : Acenaphthene-d 164 , acenaphthene10

Ž . Ž .153, 154 , fluorene 166, 165 , phenanthrene-d10Ž . Ž .188 , phenanthrene, anthracene 178, 176 , car-

Ž . Ž .bazole 167, 166 , fluoranthene, pyrene 202, 200 ,Ž . w xchrysene-d 240 , benz a anthracene, chrysene12

Ž . Ž . w x228, 226 , perylene-d 264 , benzo b fluo-12w x w xranthene, benzo k fluoranthene, benzo a pyrene

Ž . w x Ž .252, 253 , indeno 1,2-cd pyrene 276, 277 ,w x Ž .benzo g,h,i perylene 276, 137 .

2.2. Quality control

Ž .Polyurethane foam PUF has been extensivelyused for SOC air sampling for sample volumesranging from 300 to 600 m3. It has been shown bynumerous other researchers that breakthrough inthese samplers at comparable flow rates and sam-

Žple volumes is insignificant Yamasaki et al., 1982;Foreman and Bidleman, 1990; Gustafson and

.Dickhut, 1997; Simcik et al., 1998 . In this studyin addition to PUF, XAD-2 resin was used. Thiscombination increases adsorption capacity andminimizes post-collection volatilization problemsŽ .Winberry et al., 1988 .

( )M. Odabasi et al. r The Science of the Total En¨ironment 227 1999 57]6760

All samples were spiked with PAH internalstandards prior to extraction to determine analyt-ical recovery efficiencies. Recoveries of PAH in-

Ž .ternal standards were 64"14% ns128 forŽ .acenaphthene-d , 74 " 14% n s 131 for10

Ž .phenanthrene-d , 79"12% ns131 for chry-10Ž .sene-d , and 67"13% ns131 for perylene-d12 12

for all sample matrices. The recoveries of thefollowing internal standards were used to correctthe amounts of specific PAHs found in the sam-ples: Acenaphthene-d for acenaphthene and10fluorene, phenanthrene-d for phenanthrene, an-10thracene, carbazole and fluoranthene, chrysene-

w xd for pyrene, benz a anthracene and chrysene,12and perylene-d for benzofluoranthenes,12

w x w xbenzo a pyrene, indeno 1,2-cd pyrene andw xbenzo g,h,i perylene.

Blank filters and PUF cartridges were routinelyplaced in the field to determine if there was anycontamination during sample handling and prepa-

ration for the analysis. The amounts found in theblanks were generally -10% of the amount inPUFs, and ranged 0]47% in filters.

Quantifiable PAH amounts were determinedfrom sequential injections of diluted standard so-lutions, using a signal-to-noise ratio of 20. Thisratio was used because peaks with smaller ratios

Ž .can not be reliably integrated Allen et al., 1996 .The quantifiable amounts of PAHs ranged from

Ž . Ž0.015 ng for acenaphthene to 0.24 ng forw x .benzo g,h,i perylene .

Ž .The limit of detection LOD, ng was definedas the mean blank mass plus 3 standard devia-

Žtions Halsall et al., 1994; Liu, 1995; Cotham and.Bidleman, 1995; Falconer et al., 1995 . PAHs

w x w xbenz a anthracene through benzo g,h,i peryleneŽ .were not detected nd in blanks. LODs for PAHs

ranged from nd to 1016 ng for PS-1 filters and ndto 2013 ng for PUFs. The largest amounts foundin the blanks were for phenanthrene. In general,

Table 2a y3Ž .Average concentrations of PAHs ng m in air, Chicago and other cities

b c d e f g h i jPAH Chicago Chicago Chicago Chicago Boston Houston London Chicago

ACT 45 72 24.1 22.8 2.1 76.9"46.2FLN 138 102 93 53.6 36.2 24.2 13.4 74.8"43.7PHE 150 116 160 101.0 50.1 76.1 200.3"104.8ANT 104 61 15 7.6 3.0 1.4 5.0 14.1"11.9CRB 6.1"5.1FL 67 43 56 46.6 16.7 10.2 7.4 44.1"24.0PY 58 45 36 23.6 8.4 7.9 6.8 24.6"14.7BaA 11 9 15 3.0 0.9 0.6 0.8 2.1"1.3CHR 22 151 14 5.2 1.0 0.6 1.5 3.6"1.5BbF 9 12 26 1.1 0.5 1.1 2.3"1.4BkF 15 8 1.0 1.9"1.2BaP 25 8 9 3.0 0.4 0.2 0.6 1.6"1.0IcdP 5 9 10 3.9 0.5 0.2 1.2"0.7BghiP 8 8 3.3 0.6 0.3 4.4 1.1"0.7SPAH 649 644 442 150 194 119 120 428"240

a Values are the sum of particulate and gas phase concentrationsb Ž . Ž . Ž . Ž . Ž . Ž . Ž .Acenaphthene ACT , fluorene FLN , phenanthrene PHE , anthracene ANT , carbazole CRB , fluoranthene FL , pyrene PY ,

w x Ž . Ž . w x Ž . w x Ž . w x Ž .benz a anthracene BaA , chrysene CHR , benzo b fluoranthene BbF , benzo k fluoranthene BkF , benzo a pyrene BaP ,w x Ž . w x Ž .indeno 1,2,3-cd pyrene IcdP , benzo g,h,i perylene BghiP .

c Ž . Ž .Khalili 1992 Summer 1990 .d Ž . Ž .Khalili 1992 Fall 1990 .e Ž . Ž .Cotham and Bidleman 1995 Winter 1989 .f Ž . Ž .Pirrone et al. 1995 Summer 1991 .g h Ž . Ž .and Lewis et al. 1991 Summer 1991 .i Ž . Ž .Halsall et al. 1994 Annual average, 1992 .j Ž .This study Summer]Fall 1995 , average"S.D.

( )M. Odabasi et al. r The Science of the Total En¨ironment 227 1999 57]67 61

PAH amounts in the samples were substantiallyhigher than LODs. However, for some samples,amounts found on PS-1 filters were near LOD.Sample quantities exceeding the LOD were quan-tified and blank-corrected by subtracting the meanblank amount from the sample amount.

The analytical method used for samples wastested by analyzing three aliquots of NIST Stan-

Ždard Urban Dust Reference Material SRM-.1649 . Concentrations of PAHs in SRM-1649, as

the percent of NIST certified values, were:w x w xbenz a anthracene 96%, benzo a pyrene 88%,

w xbenzo g,h,i perylene 96%, fluoranthene 106%,w xand indeno 1,2-cd pyrene 117%.

3. Results and discussion

PAH concentrations are reported in two dif-ferent ways: Total PAH concentration and S -14PAHs. The total PAH concentration refers to thesum of the particulate and gas phase concentra-tions of an individual compound while S -PAHs14refers to the sum of the concentrations of the 14measured compounds.

Ž .S -PAHs gasqparticulate ranged from 15914to 863 ng my3 with an average of 428"240 ng

y3 Ž .m Fig. 1 . The concentrations in Fig. 1 are theŽ .averages of 24 h 2=12 h samples taken during

Ž .each sampling period ;3 per sampling period .By comparison, the S -PAHs measured by oth-14

y3 Ž .ers in Chicago, IL was 644 ng m Khalili, 1992 ,y3 Ž .442 ng m Cotham and Bidleman, 1995 , 150 ng

y3 Ž . y3 Žm Pirrone et al., 1995 , 48]550 ng m Simcik. y3 Žet al., 1997 , in London 120 ng m Halsall et al.,

. y31994 , in Boston, MA 194 ng m and, in Hous-y3 Ž . Ž .ton, TX 119 ng m Lewis et al., 1991 Table 2 .

Approximately two orders of magnitude lowerambient PAH concentrations were measured in

Žrural and non-urban areas Cotham and Bidle-.man, 1995; Pirrone et al., 1995 . Higher ambient

PAH concentrations measured in urban areas,such as Chicago, Boston and Houston are likelydue to the proximity of local sources. Althoughwashout, dry deposition and mixing decrease theconcentration of PAHs in the atmosphere duringtransport from urban areas, decomposition ofthese compounds via photo-oxidation is also sus-pected to reduce levels reaching non-urban areas

Ž .Fig. 1. S -PAH concentrations gasqparticulate and temperature fluctuations.14

( )M. Odabasi et al. r The Science of the Total En¨ironment 227 1999 57]6762

ŽLeister and Baker, 1994; Cotham and Bidleman,.1995; Pirrone et al., 1995 .

Fig. 1 also shows the S -PAH concentrations14and temperature fluctuations during the samplingprogram. Although concentration fluctuationswere, in general, similar to the temperature fluc-

Ž 2 .tuations only a weak correlation r s0.14 wasobserved. This low correlation is probably due tovariations in wind direction and source strength

Ž . Žduring the long sampling periods 61]89 h Ta-.ble 1 . Easterly winds dilute the urban signal

bringing clean air off the lake while southerlywinds represent the contribution of the dispersed

Žurban signal and point sources steel and coke.industries located at south-east Chicago. Simcik

Ž .et al. 1997 reported over an order of magnitudevariation in daily SPAH concentrations inChicago, IL during July 1994, which was at-tributed to changes in wind direction. The lowestconcentrations were found when the wind was offthe lake and the highest concentrations were as-sociated with southwest winds.

SPAH concentrations were dominated by more

volatile compounds such as phenanthrene, fluo-Ž .rene and acenaphthene Fig. 2 and as a result,

the highest ambient concentrations of PAHs werepredominantly in the gas phase. Phenanthrenewas the most abundant compound measured inthis study. Phenanthrene, acenaphthene and flu-orene accounted for 46%, 18% and 17% ofSPAHs, respectively. These percentages were very

Žsimilar to the ones reported previously Lewis etal., 1991; Halsall et al., 1994; Cotham and Bidle-

.man, 1995 .In this study, gas and particulate phase S -14

PAH concentrations ranged from 144 to 853 and10]48 ng my3, respectively. Gas phase S -PAHs14accounted for ;91% of the total ambient con-

Ž .centration. By comparison, Simcik et al. 1997measured a range of 27]430 ng my3 for gasphase SPAHs accounting for approximately 90%of the total ambient concentrations at the samesite in Chicago in 1994.

Fig. 3 shows the variation of particulate and gasphase S -PAH concentrations with temperature.14Gas phase S -PAH concentrations generally in-14

Fig. 2. Mass percent contributions of individual compounds to S -PAHs in Chicago air.14

( )M. Odabasi et al. r The Science of the Total En¨ironment 227 1999 57]67 63

creased with temperature, however, the correla-Ž 2 .tion was weak r s0.19 . Similarly, increasing

gas phase SPAH concentrations with tempera-ture and weak correlations were reported recently

Ž .by Gustafson and Dickhut 1997 . A rise in atmo-spheric concentrations with increasing tempera-

Ž .ture was also reported by Simcik et al. 1997 forPCBs. The vapor pressure of PAHs increases withincreasing temperature. As a result, volatilization

Žfrom contaminated surfaces soils, roads, vegeta-.tion and atmospheric particles increases as the

Žtemperature rises Halsall et al., 1994; Gustafson.and Dickhut, 1997 . This is consistent with the

observed increase of both atmospheric total andgas phase SPAH concentrations with increasingtemperature. Since the total SPAH concentra-tions were dominated by relatively volatile com-pounds, variations of total and gas phase SPAHconcentrations with temperature were similar.

Particulate phase SPAH concentrations gener-Žally decreased with increasing temperature Fig.

.3 . The correlation between the particulate phaseS -PAH concentration and the temperature was14

Ž 2 .relatively good r s0.62 . A similar trend in par-

ticulate phase SPAH concentrations was re-Ž .ported by Gustafson and Dickhut 1997 . The

decrease in particulate phase S -PAH concen-14trations during warmer periods may be due to thetemperature dependency of vapor pressure whichcontrols particlergas partitioning.

The particlergas phase distribution variedŽ .widely Fig. 4 . The gas phase percentage gener-

ally decreased with increasing molecular weightand ranged from 1.1 to 99.4%. Three-ring PAHsŽacenaphthene, fluorene, phenanthrene and an-

.thracene were associated primarily with the gasŽ w xphase while six-ring PAHs indeno 1,2-cd pyrene,

w x .benzo g,h,i perylene were associated primarilywith the particulate phase. These results weregenerally consistent with the particlergas phase

Ždistributions reported in previous studies Ligockiet al., 1985; McVeety and Hites, 1988; Baek et al.,

.1991; Lewis et al., 1991 .Fig. 5 shows the fluctuation in gas phase per-

centages of PAHs throughout the sampling pro-gram. For ease of comparison, PAHs were di-vided into four groups based on their vapor pres-

Žsures because it controls their partitioning Group

Fig. 3. Variation in particulate and gas phase S -PAH concentrations with temperature.14

( )M. Odabasi et al. r The Science of the Total En¨ironment 227 1999 57]6764

Fig. 4. Average particlergas phase distributions of individual PAHs. Error bars represent 1 S.D.

1: acenaphthene through phenanthrene; Group 2:w xanthracene through pyrene; Group 3: benz a -

w xanthracene through benzo k fluoranthene; Groupw x w x .4: benzo a pyrene through benzo g,h,i perylene .

Fluctuations of the gas phase percentages andtemperature were generally similar, as the tem-perature increased the percentage in the gas phasealso increased. The phase distributions of PAHs

Žprimarily associated with the gas phase Group 1,. Ž93.4]99.6% and particulate phase Group 4,

.0]7.6% did not vary significantly with tempera-ture. However, the variation in the gas phasepercentages were significant for compounds in

Ž . Ž .Groups 2 63]97.6% and 3 6.3]47.4% , indicat-ing that partitioning of these medium volatilitycompounds was more sensitive to the change intemperature than it was for compounds havingrelatively higher or lower volatilities.

Since PAHs originate from fossil fuel combus-tion, ambient concentrations of PAHs are likely

Ž .to be correlated Leister and Baker, 1994 .w xPhenanthrene and benzo a pyrene were used pre-

viously as markers to investigate temporal andŽspatial variation of PAHs Leister and Baker,

.1994; Halsall et al., 1997 . In this study, the con-centrations of compounds acenaphthene through

Ž .pyrene MWF202 correlated well with phenan-Ž .threne concentration Fig. 6 . Concentrations of

Ž w xhigher molecular weight PAHs benz a anthra-w x .cene through benzo g,h,i perylene, MWG202

Ž 2 .had little or no correlation r s0.00]0.20 withthe phenanthrene concentration. However, con-centrations of these compounds were well corre-

w x Ž .lated with benzo a pyrene concentration Fig. 7 .The lack of correlation between the higher and

lower molecular weight compounds may be due todifferential gasrparticle partitioning, transportand removal in the atmosphere. Higher molecularweight compounds are associated primarily withparticles and likely to be removed by dry deposi-tion while lower molecular weight compounds arefound primarily in gas phase and are subject totransformation or removal by photochemicaldegradation.

Varying particle size distributions also effectremoval of PAHs during transport in the atmo-sphere. Other experimental studies have shownthat a greater fraction of the lower molecularweight PAHs are associated with coarse particlesrelative to the higher molecular weight com-

Žpounds Pistikopoulos et al., 1990; Baek et al.,1991; Aceves and Grimalt, 1993; Allen et al.,

( )M. Odabasi et al. r The Science of the Total En¨ironment 227 1999 57]67 65

Fig. 5. Gas phase percentages for different groups of PAHs.

.1996 . Therefore, PAHs with lower molecularweights have higher dry deposition velocities andconsequently are removed by dry deposition moreeffectively than the higher molecular weight com-pounds.

Another important mechanism for the removalof PAHs from the air is below-cloud scavenging.

Ž .Ligocki et al. 1985 investigated below-cloudscavenging ratios of particle and gas PAHs. Theyfound that PAHs of MWF202 had higher parti-cle scavenging ratios relative to the PAHs ofMWG202, probably because of their associationwith large particles. However, gas scavenging wasthe dominant scavenging mechanism for the PAHsof MWF228.

As a result of increasing vapor pressure,volatilization of PAHs from contaminated sur-

Ž .faces soils, roads, vegetation and atmospheric

particles increases as the temperature risesŽHalsall et al., 1994; Gustafson and Dickhut,

.1997 . This may increase gas phase concentra-tions of low molecular weight PAHs which havehigher vapor pressures.

Results of the regression analysis reportedabove and findings of other studies suggest thateven though all PAHs originate primarily fromcombustion sources, their contribution to SPAHconcentration may change significantly duringtransport from the source to the receptor.

Acknowledgements

We would like to thank Warawut Suadee forhis assistance in air sampling and Nasrin R. Khaliliof Illinois Institute of Technology for her supportduring the study.

( )M. Odabasi et al. r The Science of the Total En¨ironment 227 1999 57]6766

Fig. 6. Relationship between the concentrations of phenanthrene and compounds acenaphthene through pyrene.

w x w x w xFig. 7. Relationship between the concentrations of benzo a pyrene and compounds benz a anthracene through benzo g,h,i per-ylene.

( )M. Odabasi et al. r The Science of the Total En¨ironment 227 1999 57]67 67

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