The winter effect on formation of PCDD_Fs in Guangzhou by vehicles_ A tunnel study

The winter effect on formation of PCDD/Fs in Guangzhou by vehicles:A tunnel studyYunyun Deng a ,b ,Pingan Peng a ,*,Man Ren a ,Jianzhong Song a ,Weilin Huang caState Key Laboratory of Organic Geochemistry,Guangzhou Institute of Geochemistry,Chinese Academy of Sciences,Guangzhou 510640,China bShanghai Academy of Public Measurement,Shanghai 201203,China cDepartment of Environmental Sciences,Rutgers,The State University of New Jersey,14College Farm Road,New Brunswick,NJ 08901,USAa r t i c l e i n f oArticle history:Received 26August 2010Received in revised form 10February 2011Accepted 10February 2011Keywords:PCDDs/Fs VehicleWinter effect Emission factora b s t r a c tPrior studies showed that the polychlorinated dibenzo-p -dioxin and dibenzofuran (PCDD/F)concentra-tions in the atmosphere are much higher in the winter than in the summer.This so called winter effect was explained via meteorology-dependent factors such as dispersion,mixing and photo chemical degradation or home heating related formation of PCDDs/Fs.In this study,we took vehicle emission as an example to investigate winter effect on PCDD/Fs formation by fossil fuel combustion.We hypothesized that vehicle emission of PCDDs/Fs may be elevated in the winter season due to the promoted supplies of Cl À(via particular matter)in winter.We collected particulate and gaseous samples from the Pearl River Tunnel and its adjacent open air during spring/summer and winter seasons.Chemical analyses of the tunnel samples showed that the PCDD/F concentrations in the tunnel ranged from 18.6to 20.4pg m À3(1.28e 1.39pg I-TEQ m À3)in the winter,which were 3e 5times higher than in the spring/summer.In the open atmosphere adjacent to the tunnel,the PCDD/F concentrations were much lower than in the tunnel;e.g.,approximately one fifth of the tunnel air concentrations during the winter.The emission factors (EFs)calculated based on the tunnel data were 3440(or 230I-TEQ)and 1580(or 27.8I-TEQ)pg km À1vehicle À1in winter and spring/summer season,respectively.The much higher PCDD/F concentrations in the tunnel air and much greater EF value during the winter are likely related to higher content of Cl Àassociated with small size particulates.This suggests that the winter effect observed in the open atmosphere is not only caused by meteorology-dependent factors and home heating,but also may partly results from much greater PCDD/F formation rates during the combustion processes of fossil fuels such as gasoline-and diesel-fuel in the winter.Ó2011Elsevier Ltd.All rights reserved.1.IntroductionPolychlorinated dibenzo-p -dioxins and dibenzofurans (PCDDs/Fs)are mainly generated as unintended by-products during combustion processes.It is estimated that 96%of PCDDs/Fs in the environment is emitted firstly to the atmosphere (Smit et al.,2004).Municipal solid waste incineration (MSWI)and fossil fuel burning have long been regarded as major emission sources of PCDDs/Fs (Yu et al.,2006).Recent research suggested that emission from MSWI has gradually lessened due to the advancement of better controlled combustion technologies (Yu et al.,2006).Instead,automobiles may become an important emitter of PCDDs/Fs.Ballschmiter et al.(1986)detected PCDDs/Fs in used motor oil and thus provided the first evidence that PCDDs/Fs might be emitted by the combustion processes in gasoline-and diesel-fueled engines.Fuster et al.(2001)reported that,in Tar-ragona Province of Spain,the PCDD/F emission from MSWI may contribute about 0.04%whereas the emission from diesel motors accounted for 18%of the total PCDD/F emissions.Several prior studies showed that the PCDD/F concentrations in the atmosphere are much higher in the winter than in the summer,which is often called winter effect.Hovmand et al.(2007)measured combined PCDD/F concentration from 12-m high tower in one Danish rural forest sites.The ratio between winter (October e March)and summer (April e September)mean values of atmospheric I-TEQ concentrations was 3.90,calculated for the period 2002e 2004.Coutinho et al.(2007)found the average ratio of the combined PCDD/F concentrations between winter (October e March)and summer (April e September)was 3.30at most.Sin et al.(2002)measured 27ambient air samples in Hong Kong.The combined PCDD/F concentrations ranged from 0.03to 0.43pg I-TEQ m À3in winter months (January and March),and 0.018to 0.025pg I-TEQ m À3in the summer months (July and August).When compared*Corresponding author.E-mail address:pinganp@ (P.Peng).Contents lists available at ScienceDirectAtmospheric Environmentjournal homep age:www.elsevi/locate/atmosenv1352-2310/$e see front matter Ó2011Elsevier Ltd.All rights reserved.doi:10.1016/j.atmosenv.2011.02.022Atmospheric Environment 45(2011)2541e 2548with the same sampling location,the ratio of the combined concentrations in the winter to summer ranged from1.10to20.4.The observed winter effect is often explained via seasonally-controlled dominant factors for the emission and degradation of PCDDs/Fs and/or seasonal change in air mass movement(Hippelein et al.,1996;Duarte et al.,1997;Lee et al.,1999;Lohmann et al., 1999).The former generally refers to higher emission of home heating in the winter and faster PCDD/F degradation rates in the summer.The latter is related to the seasonal variation of the atmospheric boundary layer generally referred to as the mixing layer(Coutinho et al.,2007).In a typical region of mid latitude,the heights of the convective mixing layer are very different between summer and winter.During summer as more heating of daytime than cooling during shortened nights,the convective mixing layer starts shallow in the morning,but rapidly grows to its full extent in early afternoon.On the contrary,during winter as more cooling at night than heating during the shortened daytime,the convective mixing layer remains relatively stable(Coutinho et al.,2007). Hence,local emissions to the atmosphere will be less welldispersed during winter.This process is particularly effective for emissions that occur near ground level because a reduced height of the well-mixed atmosphere favors an accumulation of pollutants and result in increasing ambient concentrations.In this study,we hypothesized that formation of PCDDs/Fs may be elevated in the winter season due to the promoted supplies of ClÀ(via particular matter),hence contributing partly to the often observed winter effect.We took vehicles as an example and initi-ated a systematic study to quantify the emission factor of PCDDs/Fs for vehicles in the Pearl River Delta area using a tunnel method.The major focus of the work was to quantify seasonal changes of PCDD/F concentrations in both open atmosphere and the tunnel air.The results presented here are consistent with our hypothesis,indi-cating that the formation of PCDD/Fs in the winter of Guangzhou by vehicles is higher,which provides an alternative explanation for winter effect.2.Materials and methods2.1.Sampling sitesGuangzhou,the capital of Guangdong province,is a subtropical city with an area of7430km2and a population over6.40million.It was estimated that1890thousand tons of gasoline and2720 thousand tons of diesel oil were consumed in2005and about1.77 million cars are running on the roads of Guangzhou according to the Statistical Bureau of Guangzhou(2006).Recent studies con-ducted by our research group(Yu et al.,2006;Ren et al.,2007) indicated that the atmospheric depositionfluxes of total2,3,7,8-substituted PCDD/F congeners ranged from2.10to41.0(mean20) pg WHO-TEQ mÀ2dayÀ1in Guangzhou,and that the particle-bound PCDDs/Fs in the atmosphere of Guangzhou ranged from0.105to 0.769pg I-TEQ mÀ3.It is expected that the sources of PCDDs/Fs are very diverse as rapid industrialization in this region may have brought in a spectrum of emitters of PCDDs/Fs.As fast growing of privately owned vehicles may have outpaced any other emitters, quantification of the contribution of vehicles to the total emissions is urgent for source control of PCDDs/Fs in this region.This study targeted the Pearl River tunnel located in the central city of Guangzhou which connects Fangchun District and Liwan District(Fig.1).It has a length of1240m and height of8.10m with two lanes per bore.Each day approximately120,000vehicles pass the tunnel at an average speed40.0km hÀ1(Guangzhou Transport Planning Research Institute,2006,Annual Report of Transportation Development in Guangzhou).Four sampling sites were selected in this study(Fig.1).Site A and Site B are located respectively in the midpoint and the southbound exit of the tunnel.They were selected for sampling the gaseous and particulate-bound PCDD/F pollutants in the atmosphere influenced directly by the traffic within the tunnel.Site C and Site D are located in Liwan district in the vicinity of the tunnel.They were selected for monitoring background air quality in the central city of Guangzhou.Site C is near the Tunnel Management Station,which is located200m away from the tunnel exit(Site B).The samples taken from this site should represent a mixture of the background atmosphere in central city and the atmosphere exit from the tunnel.Site D is located in Shamian Park(north side of the tunnel)situated on an island of the Pearl River.The samples taken from the park likely represented background atmosphere within the central city.The geographical locations of the four sampling sites are shown sche-matically in Fig.1.2.2.Air sampling in tunnel and ambient atmosphereTwo samples for each site were taken in the spring(April 11e12th),summer(July10e12th)and winter(December10e12th) of2006respectively.Both gaseous and particulate samples were simultaneously collected with a high-volume air sampler(Tian-hong Intelligent Instrument Co,Wuhan).The gaseous samples were collected with polyurethane foam(PUF,90mmÂ65mm i.d.). Whatman glassfiberfilters(GFF,20.3cmÂ25.4cm)were pre-treated at450 C for6h before being used for collecting the total suspended particulates(TSP).The airflow rate passing through the sampler was calibrated before and after the sampling.After sampling,thesefilters and polyurethane foams were removed from the sampler and wrapped with aluminum foil.Thefilters were weighed after equilibrated for24h at25 C and50%relative humidity.At both Site A and B,the speed of airflow within the tunnel was monitored with an anemometer.The vehicleflux was counted on a video tape kindly provided by the Pearl River tunnel administration station.The recorded data are summarized in Table1.We checked PCDD/F concentrations in the two samples collected for each site and season.The discrepancy was minor; therefore,only one set of concentration data was reported in this paper.To investigate the influence of particle-bound ClÀand Cu on the formation of PCDDs/Fs,six particle sizes of aerosols(<0.49m m, 0.49e0.95m m,0.95e1.5m m,1.5e3.0m m,3.0e7.2m m,and7.2e10m m) in Site D were further collected in the summer and winter of2009. Particulates were collected with an Andersen sampler(modelSA235)Fig.1.Locations of the sampling sites.Y.Deng et al./Atmospheric Environment45(2011)2541e2548 2542at an airflow of1.13m3minÀ1.Quartzfilters(Environmental Tisch TE-230QZ)were used as impaction substrates(slotted14.3Â13.7cm)for the collection of thefive size fractions and rectangular backup quartzfilters(20.3Â13.7cm)for thefinest size fraction.The quartzfiberfilters were pretreated at450 C for5h before use.2.3.Sample analysis2.3.1.Reference standards and chemicals for cleanupAll13C12-labeled PCDD/F standards were purchased from Cam-bridge Isotope Laboratories Inc.(Boston,USA).All solvents and reagents used in this study were all pesticide grades or higher purchased from Merck,Germany.These solvents included meth-anol,acetone,dichloromethane(DCM),toluene,and n-hexane. Silica gel(70e230mesh)and basic alumina used in cleanup procedure were purchased from Merck,Germany.2.3.2.Clean-up procedureThe US EPA Method1613was followed for the analysis of PCDDs/Fs.The detailed procedure can be found in Ren et al.(2007). In brief,thefilters or foams were spiked with a stock solution (10m l)of13C12-PCDD/F internal standards,which includedfifteen PCDD/F compounds.Thefilters and foams were Soxhlet extracted with toluene(250ml)for48h.The extracts were cleaned sequentially with acid silica gel bed,multi-layer silica gel column and basic alumina column following the procedures briefed below. Each sample extract wasfirst cleaned in aflask containing20g of 40%H2SO4/silica gel and100ml of hexane.After stirred for2h,the content of theflask wasfiltered through a funnelfilled with glass wool and10g of Na2SO4.Hexane(100ml)was used to rinse the flask and the slurry.The hexanefiltrates were further cleaned on a multi-layer silica gel column eluted successively with20ml of hexane(discarded)and100ml of3%dichloromethane/hexane (retained).The later solvent mixture was loaded on a10-g basic alumina column,which was eluted sequentially with20ml of hexane(discarded),80ml of2%dichloromethane/hexane(dis-carded)and100ml of dichloromethane e hexane mixture (v:v50:50)(retained).The last solvent mixture was concentrated to 1ml on a rotary evaporator,which was then transferred to a1.5-ml teardrop vial.Before analysis,injection standards(10m l)consisted of13C12-labled1,2,3,4-TCDD and13C12-labled1,2,3,7,8,9-HxCDD were added into the vial and thefinal volume was reduced to 20m l on an N2blower.Cu contents in the samples were determined using the following procedures.A part of quartzfilter charged in a platinum crucible was completely dissolved in a mixture of HNO3,HF and HClO4.After dryness,the residue was dissolved with8M HNO3(2ml)and finally diluted to100ml with pure water for subsequent Cu determination using ICP-MS.ClÀcontents in the samples were determined by rinsing quartz filter with Milli-Q ultra pure water and then analysis with ion chromatography.2.3.3.Instrumental analysisPCDDs/Fs were identified and quantified using high-resolution gas chromatography coupled with high-resolution mass spec-trometry(HRGC/HRMS)(Trace GC2000and Thermo Electron Fin-nigan MAT95XP;GC column:J&W Scientific,CA,60mÂ0.25mm i.d.Â0.25mmfilm thickness).Helium was used as the carrier gas at aflow rate of0.8ml minÀ1.The sample(1m l)was injected with a splitless injection mode.The temperature of GC was programmed to increase to90 C,stayed for1min,then increased to200 C at 76 C minÀ1and stayed at200 C for7min,then to275 C at 1.2 C minÀ1andfinally to300 C at 1.7 C minÀ1.The injector temperature was kept at250 C and the HRGC/HRMS interface temperature was held at250 C.The HRMS was operated in the EI positive(electric impact ionization)and LOCK MID mode with a mass resolution of10,000(313.9839,perfluorotributylamine).The electron impact ionization energy was55eV with a source temperature of250 C.Cu measurement was performed using an Elan6000ICP-MS spectrometer(Perkin e Elmer,USA).Instrumental conditions are listed as the following.Rf power,1050W;Plasma gasflow rate, 15l minÀ1;Intermediate gasflow rate,1.2l minÀ1;Nebulizer gas flow,0.83l minÀ1;Auto lens,On;Measurement mode,Peak hopping;Sweeps/reading,8;Reading/replicate,1;Dwell time, 100ms.The identification and quantification of chlorine ions were performed by a Dionex ICS900IC(Dionex,Sunnyvale,CA,USA), equipped with a RFIC IonPacAS19analytical column(250mmÂ4mm id),a RFIC IonPacAG19guard column(50mmÂ4mm id)and a conductivity detector.The mobile phase,containing20mM KOH was pumped at aflow rate of1.0ml minÀ1.The injection volume was200m l.Quantification of ClÀwas performed by external calibration.2.3.4.Quality assurance and quality control(QA/QC)Standard procedures were employed during sampling,extrac-tion and quantification of target contaminants for QA/QC purpose. Before sampling,all glassfiberfilters were heated at450 C for6h to remove possible background organic contaminants.The poly-urethane foams were Soxhlet extracted sequentially with methanol, DCM,toluene,and acetone for4Â24h,vacuum dried,and kept in pre-cleaned amber glass jars.The air samplers were calibrated in thefield before and after each sampling event.During extraction and chemical analysis in the lab,afield blank and a method blank were used for every batch of twelve samples.During extraction,all samples and blanks were spiked with15kinds of internal13C12-labeled PCDD/F standards to trace the recovery efficiency of theTable1Background information of the four sampling sites.Sampling date Sampling time(min)Sampling volume(m3)Temperature( C)Vehicle volume(vehicles duringthe sampling)TSP(mg mÀ3)Site A(Middle of tunnel)2006-4-1141384.252216,726 1.72 2006-7-11259102.953111,204 1.172006-12-1142396.871919,466 1.48Site B(Outlet of tunnel)2006-4-1127252.872011,016 1.89 2006-7-1125886.993211,164 2.592006-12-1141589.11918,837 1.93Site C2006-7-11720201.6330.295 2006-12-11664183.26200.49Site D2006-7-11630155.82310.225 2006-12-11600128.82190.228Y.Deng et al./Atmospheric Environment45(2011)2541e25482543method.According to the surrogate standards run in parallel to the samples,the recovery ef ficiency ranged from 63to 97%,which meets the limit of 32e 123%given in US EPA Method 1613.The detection limits of the method were ca.0.1pg for 2,3,7,8-TCDF,0.2pg for 2,3,7,8-TCDD,and 0.8pg for OCDD.3.Results and discussion3.1.PCDD/F concentrations in the Pearl River TunnelTable 1lists the background data of the gaseous and particulate samples taken inside and outside of the tunnel.Table 2summarizes the concentrations of individual 2,3,7,8-substituted PCDD/F congeners in both gaseous and particulate samples taken at Site A and B of the tunnel.As shown in Table 1,the average concentrations of the particulate materials in the tunnel were 1.81,1.88and 1.71mg m À3in spring,summer and winter,respectively.These total particulate concentrations remained fairly constant for the three sampling times,but they were 4e 6times higher than those from the atmosphere outside the tunnel,which were collected on the same day.Note that relative constant meteorological condition and single vehicle emission source may have resulted in similar concentrations of particulates in the tunnel air.One striking feature of the data listed in Table 2is that,for the two sampling sites within the tunnel,the particulate-bound PCDD/F concentrations were approximately 1e 10times higher in the winter than in the spring and summer,suggesting an strong winter effect on the overall concentration of the particulate-bound PCDDs/Fs.As shown in Table 2,the particulate-bound PCDD/F concentrations ranged widely from 2.25to 19.6pg m À3(or 0.114e 1.30pg I-TEQ m À3),and there is no appreciable difference between the spring and summer,which had the average concentrations of 3.05and 3.40pg m À3(or 0.217and 0.127pg I-TEQ m À3)respectively.The particulate-bound PCDD/F average concentrations in the winter were 18.4pg m À3(or 1.24pg I-TEQ m À3).Such a winter effect was much less for the gaseous PCDD/F concentrations,which ranged narrowly from 0.715to 1.54pg m À3(or 0.091e 0.22pg I-TEQ m À3)for all the three sampling times at the two tunnel sites.Table 1also showed no signi ficant difference of the total suspended particulate (TSP)concentrations between spring/summer and winter.Therefore,it is unlikely that the observed winter effect is related to the concentrations of particulate materials in the air.To our knowledge,no prior publications reported the winter effect from the tunnel studies.Wevers et al.(1992)reported that the combined (gas þparticulate)PCDD/F concentrations in a Belgium tunnel were approximately 0.0803pg I-TEQ m À3.Geueke et al.(1999)conducted PCDD/F sampling of diesel engine at a constant load rate with about 30%of its nominal power.The emission concentrations were from 0.21to 58.0pg I-TEQ m À3.Chang et al.(2004)reported the total PCDD/F concentrations of 0.0473(outlet)and 0.0571(midpoint)pg I-TEQ m À3for a tunnel of northeastern Taipei,Taiwan.All these published data are in general comparable to our data summarized in Table 2.Further inspection of the data in Table 2indicated that,for the same sampling trip,the PCDD/F concentrations measured at Site B (exit)(4.55e 20.4pg m À3or 0.218e 1.39pg I-TEQ m À3)were slightly higher than those at Site A (midpoint of the tunnel)(3.79e 18.6pg m À3or 0.207e 1.27pg I-TEQ m À3).The higher concentra-tions measured at the exit of the tunnel were likely due to the so called piston effect,referring to the forced air flow inside a tunnel caused by moving vehicles.The air pollutants were pushed out of the tunnel by the cars,leading the higher concentrations at the exit (Chang et al.,2004).Table 3presents the PCDD/F concentrations of open atmosphere (Site C and D)in the summer and winter;they were collected on the same days as the samples from the tunnel.The combined partic-ulate-bound and gaseous PCDD/F concentrations measured at Site C were 3.59pg m À3(0.186pg I-TEQ m À3)and 16.1pg m À3(1.17pg I-TEQ m À3)respectively in July and December.The combined concentrations measured at Site D were 3.08pg m À3(0.186pg I-TEQ m À3)and 9.23pg m À3(0.247pg I-TEQ m À3)respectively in July and December.These values were all lower than those within the tunnel.Note that the difference of the combined I-TEQ concentra-tions between inside and outside the tunnel was insigni ficant in summer,but signi ficant in winter.The combined I-TEQ concentra-tions within the tunnel (Site A and B)were 1.14times higher than the background I-TEQ concentrations (Site D)in the summer,but they were 7.16times as high as the background I-TEQ concentra-tions (Site D)in the winter.Meanwhile,the ratios of the combined concentrations between the samples of 11th December and 11th July were 1.33at Site D,but the ratios increased to 6inside theTable 2Concentrations (pg m À3)of 2,3,7,8-substituted congeners.CongenersTunnel Site A (Middle of tunnel)Tunnel Site B (Outlet of tunnel)2006-4-112006-7-112006-12-112006-4-112006-7-112006-12-11ParticulateGaseous Particulate Gaseous Particulate Gaseous Particulate Gaseous Particulate Gaseous Particulate Gaseous 2378-TCDF 8.40E-02 5.79E-01 1.92E-02 2.51E-01 1.45E þ00 1.87E-01 1.88E-01 4.67E-029.12E-027.09E-02 1.45E þ00 6.37E-0212378-PeCDF 1.40E-01 4.36E-01 5.97E-02 1.05E-01 2.06E þ00 5.87E-02 2.57E-01 3.82E-02 5.76E-027.39E-02 2.17E þ00 6.72E-0223478-PeCDF 1.77E-01 1.84E-01 1.09E-019.27E-028.53E-01 6.22E-02 3.06E-01 4.80E-02 1.40E-018.30E-029.50E-017.68E-02123478-HxCDF 6.39E-02 3.40E-02 1.01E-01 3.00E-02 1.58E þ008.59E-02 1.00E-01 4.98E-02 4.28E-02 2.12E-02 1.99E þ00 5.84E-02123678-HxCDF 4.53E-02 3.92E-027.77E-02 2.68E-027.97E-01 3.52E-02 1.02E-01 6.66E-02 2.60E-02 1.30E-029.57E-01 5.15E-02234678-HxCDF 1.11E-01 1.06E-02 1.17E-01 1.45E-02 6.56E-01 6.17E-02 2.44E-01 3.18E-02 1.11E-01 3.54E-027.58E-01 4.33E-02123789-HxCDF 5.10E-03 3.68E-03 4.25E-02 3.69E-03 4.19E-01 1.34E-02 1.12E-02 4.35E-03 6.78E-03 1.22E-02 4.90E-01 2.41E-021234678-HpCDF 3.00E-01 5.38E-02 3.83E-017.64E-02 2.33E þ00 1.66E-01 4.97E-018.42E-02 5.04E-01 4.64E-02 2.66E þ00 1.19E-011234789-HpCDF 6.45E-02 2.97E-03 4.82E-02 3.11E-03 5.27E-01 1.44E-02 4.88E-028.51E-03 2.77E-02 4.71E-03 6.09E-018.64E-03OCDF1.60E-01 1.28E-022.11E-013.05E-02 2.05E þ004.94E-02 2.54E-01 3.01E-02 2.95E-01 2.05E-02 2.34E þ00 3.77E-022378-TCDD 2.73E-03 2.52E-02 1.12E-03 2.17E-038.52E-037.19E-038.51E-03 3.22E-03 1.06E-02 1.22E-027.52E-03 1.17E-0212378-PeCDD 2.55E-02 2.31E-027.23E-03 1.09E-02 1.50E-01 2.02E-025.92E-02 1.06E-01 2.97E-02 4.83E-03 1.13E-01 1.48E-02123478-HxCDD 5.58E-03 3.32E-03 1.84E-020.00E þ00 5.97E-02 1.37E-029.46E-03 2.27E-030.00E þ000.00E þ00 1.12E-01 1.26E-02123678-HxCDD 9.50E-038.19E-03 2.45E-02 2.33E-03 1.17E-016.04E-02 1.17E-02 1.08E-02 2.47E-02 1.46E-02 1.57E-01 1.28E-02123789-HxCDD 8.66E-037.10E-04 2.48E-02 1.23E-039.11E-02 1.92E-02 2.67E-027.00E-03 1.15E-03 3.91E-03 1.46E-01 1.45E-021234678-HpCDD 1.91E-01 4.93E-02 3.05E-01 2.42E-028.49E-01 1.70E-01 3.40E-01 4.79E-02 3.66E-01 3.59E-029.50E-01 6.16E-02OCDD 8.57E-017.37E-02 1.40E þ00 1.17E-01 3.10E þ00 4.77E-01 1.37E þ00 1.30E-01 2.21E þ00 2.94E-01 3.76E þ008.60E-02TEQ(pg I-TEQ m À3) 1.51E-01 2.20E-01 1.14E-019.34E-02 1.17E þ00 1.03E-01 2.84E-01 1.06E-01 1.40E-017.81E-02 1.30E þ009.09E-02Total PCDDs/Fs2.25E þ001.54E þ002.95E þ007.92E-011.71E þ011.50E þ003.83E þ007.15E-013.94E þ007.47E-011.96E þ017.65E-01Y.Deng et al./Atmospheric Environment 45(2011)2541e 25482544tunnel (Site A and B).These ratios were consistent with other studies summarized in the Introduction Section.3.2.Homolog and congener pro filesFig.2illustrates the relative contributions of different homolog compounds to the combined gaseous and particulate phase PCDDs/Fs for the samples taken within the tunnel.It indicates that the greater is the degree of chlorination of the compounds,the higher is the combined PCDD concentration.However,the combined PCDF concentrations were not correlated well with the degree of their chlorination,which was different from the negative correlation revealed in a previous study by Lohmann and Jones (1998).Fig.2shows slightly different homolog distribution of the PCDDs/Fs between the winter and the spring e summer of the combined PCDD/F concentrations within the tunnel.In the spring e summer,the predominant homolog was OCDD,which constituted approximately 37.9%of the combined PCDD/F concen-trations.This is consistent with an EPA report of PCDDs/Fs for the total emissions from various combustion processes including unleaded gasoline combustion and diesel-fuel combustion (US EPA,2006).Other major homologs included PeCDF,HpCDF and HxCDF,which accounted respectively for 14.1,12.8and 9.61%of the combined PCDD/F concentrations.In the winter,however,HxCDF was the predominant compound which accounted for 20.5%of the total 2,3,7,8-substituted PCDD/F homologs.Other major homologs were OCDD,HpCDF and PeCDF,which accounted respectively for 19.1,16.5and 16.2%of the total 2,3,7,8-substituted PCDD/F concentrations.Congener pro files of the combined PCDD/F concentrations shown in Fig.3for the spring and summer samples indicated that OCDD was the largest contributor to the total PCDDs/Fs,accounting for 37.9%on average,whereas 1,2,3,4,6,7,8-HpCDF,2,3,7,8-TCDF,and 1,2,3,4,6,7,8-HpCDD were also found as the major congeners,accounting for 11.5,8.33and 8.06%of the total TCDDs/Fs,respec-tively.Meanwhile,the total PCDD contributions were slightly greater than the total PCDF concentrations.Our spring and summer data were consistent with the studies of Rappe et al.(1988),Wevers et al.(1992)and Gertler et al.(1998),both showing that OCDD,1,2,3,4,6,7,8-HpCDD,OCDF,and 1,2,3,4,6,7,8-HpCDF were the dominant congeners.During the winter,the congener pro files were slightly different.The dominant congeners were OCDD (19.1%),1,2,3,4,6,7,8-HpCDF (13.5%),OCDF (11.5%)and 1,2,3,7,8-PeCDF (11.2%),and theTable 3Concentrations (pg m À3)of 2,3,7,8-substituted congeners of open atmospheric samples in Shameen Park.Tunnel Management Station Site C Shameen Park Site D 2006-7-112006-12-112006-7-112006-12-11ParticulateGaseous Particulate Gaseous Particulate Gaseous Particulate Gaseous 2378-TCDF 1.90E-02 1.35E-01 1.32E þ00 1.04E-01 4.31E-02 1.24E-01 5.39E-02 6.29E-0212378-PeCDF 4.33E-02 1.04E-01 2.03E þ00 2.75E-02 3.52E-02 1.13E-018.64E-02 4.40E-0223478-PeCDF 6.25E-02 1.02E-018.08E-01 3.28E-02 5.76E-02 1.16E-01 1.18E-01 5.76E-02123478-HxCDF 1.18E-01 3.54E-02 1.71E þ00 1.77E-02 3.96E-02 1.37E-02 1.39E-01 2.78E-02123678-HxCDF 1.14E-01 4.35E-027.49E-01 2.27E-02 5.30E-02 1.35E-02 1.62E-01 4.97E-02234678-HxCDF 1.50E-01 1.97E-02 6.05E-01 1.57E-02 3.47E-02 1.78E-02 1.71E-01 4.47E-02123789-HxCDF 1.30E-02 2.33E-03 4.34E-01 4.72E-03 1.19E-027.57E-03 4.26E-02 1.40E-021234678-HpCDF 4.42E-01 2.94E-02 2.31E þ00 3.14E-02 4.61E-01 5.47E-02 6.62E-019.79E-021234789-HpCDF 4.75E-02 1.84E-03 5.49E-01 2.33E-03 2.07E-02 1.29E-028.27E-02 1.86E-02OCDF2.37E-01 6.20E-03 2.26E þ009.88E-03 2.14E-019.43E-03 4.52E-013.91E-022378-TCDD 1.29E-03 2.48E-039.17E-03 5.70E-03 6.29E-039.75E-03 1.81E-03 1.93E-0212378-PeCDD 1.07E-02 1.46E-02 1.39E-01 6.35E-03 1.62E-02 2.77E-02 2.89E-029.05E-03123478-HxCDD 1.09E-02 2.13E-037.34E-02 1.36E-03 2.60E-02 5.20E-03 2.41E-028.98E-03123678-HxCDD 2.40E-02 2.33E-03 1.09E-01 6.24E-039.11E-03 5.26E-034.90E-02 1.85E-02123789-HxCDD 1.24E-02 2.43E-039.94E-02 4.23E-03 1.75E-02 2.25E-03 4.05E-028.03E-031234678-HpCDD 2.66E-01 4.86E-037.12E-01 2.27E-02 3.41E-015.19E-02 5.95E-018.48E-02OCDD1.46E þ00 4.70E-02 1.87E þ00 1.44E-02 1.04E þ00 5.93E-02 5.75E þ00 1.64E-01TEQ(pg I-TEQ m 3)9.54E-029.05E-02 1.13E þ00 4.49E-027.79E-02 1.08E-01 1.67E-018.04E-02Total PCDD/DFs3.03E þ005.55E-011.58E þ013.29E-012.43E þ006.45E-018.46E þ007.69E-01Fig. 2.Relative abundance of 2,3,7,8-PCDD/F homologs of the different sites and seasons in tunnel.Y.Deng et al./Atmospheric Environment 45(2011)2541e 25482545。