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COMPARISON OF PAHS, NITRO-PAHS ANDOXY-PAHS ASSOCIATED WITH AIRBORNEPARTICULATE MATTER AT ROADSIDEAND URBAN BACKGROUND SITES INDOWNTOWN TOKYO, JAPANYuki Kojima a , Koji Inazu b , Yoshiharu Hisamatsu c , Hiroshi Okochi a

, Toshihide Baba d & Toshio Nagoya aa Department of Resources and Environmental Engineering, School ofScience and Technology , Waseda University , Shinjuku-ku, Japanb Department of Chemistry and Biochemistry , Numazu NationalCollege of Technology , Numazu, Japanc Field Science Center , Tokyo University of Agriculture andTechnology , Fuchu, Japand Department of Environmental Chemistry and Engineering,Interdisciplinary Graduate School of Science and Engineering , TokyoInstitute of Technology , Midori-ku, Yokohama, JapanPublished online: 19 Nov 2010.

To cite this article: Yuki Kojima , Koji Inazu , Yoshiharu Hisamatsu , Hiroshi Okochi , Toshihide Baba &Toshio Nagoya (2010) COMPARISON OF PAHS, NITRO-PAHS AND OXY-PAHS ASSOCIATED WITH AIRBORNEPARTICULATE MATTER AT ROADSIDE AND URBAN BACKGROUND SITES IN DOWNTOWN TOKYO, JAPAN,Polycyclic Aromatic Compounds, 30:5, 321-333

To link to this article: http://dx.doi.org/10.1080/10406638.2010.525164

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Polycyclic Aromatic Compounds, 30:321–333, 2010Copyright C© Taylor & Francis Group, LLCISSN: 1040-6638 print / 1563-5333 onlineDOI: 10.1080/10406638.2010.525164

Comparison of PAHs,Nitro-PAHs and Oxy-PAHsAssociated with AirborneParticulate Matter at Roadsideand Urban Background Sites inDowntown Tokyo, Japan

Yuki Kojima1, Koji Inazu2, Yoshiharu Hisamatsu3, Hiroshi Okochi1,Toshihide Baba4, and Toshio Nagoya1

1Department of Resources and Environmental Engineering, School of Science and Tech-nology, Waseda University, Shinjuku-ku, Japan2Department of Chemistry and Biochemistry, Numazu National College of Technology,Numazu, Japan3Field Science Center, Tokyo University of Agriculture and Technology, Fuchu, Japan4Department of Environmental Chemistry and Engineering, Interdisciplinary Grad-uate School of Science and Engineering, Tokyo Institute of Technology, Midori-ku,Yokohama, Japan

Atmospheric polycyclic aromatic hydrocarbons (PAHs), nitro-PAHs and oxy-PAHs areemitted from primary sources. Some nitro-PAHs and oxy-PAHs can also arise fromsecondary formation in the atmosphere. To assess the relative importance of thesesources, the polycyclic aromatic compound (PAC) concentrations were determined at aroadside (Roadside site) and on a rooftop (Urban Background site) in downtown TokyoJapan. The concentrations of PAHs, 1-nitropyrene and oxy-PAHs at the Roadside sitewere higher than those at the Urban Background site, while 2-nitrofluoranthene levelswere the same at both sites. However, the mean ratios of concentrations at the UrbanBackground site to the Roadside site were in the order 1,8-naphthalic anhydride>9,10-anthraquinone>PAHs or 1-nitropyrene or acenaphthenequinone or benzanthrone. Thissuggests that in addition to vehicle emissions, a considerable fraction of some of theoxy-PAHs studied originates from another source, which might be secondary formationby atmospheric PAH degradation, and this contribution varied among the oxy-PAHs.

Received 28 October 2009; accepted 14 April 2010Address correspondence to Y. Kojima, Department of Resources and Environmental En-gineering, School of Science and Technology, Waseda University, 3-4-1 Okubo, Shinjuku-ku 169-8555, Japan. E-mail: ykojima@aoni.waseda.jp

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Key Words: oxy-PAHs, nitro-PAHs, PAHs, airborne particulate matter, roadside

INTRODUCTION

Anthropogenic airborne particulate matter is released from various sources throughcombustion of organic compounds, such as in power plants, open burning, and auto-mobiles (1−3). In an urban area like downtown Tokyo, automobiles are the dominantsource of airborne particulate matter. The soluble organic fraction of airborne partic-ulate matter includes a number of organic compounds that are detrimental to humanhealth. Inhalation of airborne particulate matter can cause several diseases, such asasthma, allergies, or lung cancer (4−7). Polycyclic aromatic compounds (PACs), includ-ing polycyclic aromatic hydrocarbons (PAHs) and their derivatives such as nitro poly-cyclic aromatic hydrocarbons (nitro-PAHs), are well-known as mutagenic pollutantsassociated with airborne particulate matter. They are released to the atmosphere byincomplete combustion such as in diesel engines (1−3, 8−12). Some nitro-PAHs canalso form by OH or NO3 radical-initiated reactions of parent PAHs with NO2 (13−15).Recently, we found that the annual mean concentrations of the secondary nitro-PAHs 2-nitrofluoranthene and 2-nitropyrene had remained the same or increased over the past10 years in downtown Tokyo Japan, despite significant concentration decreases for theparent PAHs and NO2 (Kojima et al., 2010). This suggests that secondary PACs havean increased influence on the toxicity of airborne particulate matter.

Oxy-PAHs are major products of atmospheric oxidation of PAHs (2, 16−18). Forexample, it has been reported that phenanthrene can be degraded to several oxy-PAHssuch as 9,10-phenanthrenequinone, 9-fluorenone, dibenzopyranone (17, 18). Recently,oxy-PAHs have been reported to be mutagenic and carcinogenic (4−6, 19) and to en-hance allergic inflammation (7, 20−22). Allergic inflammation can occur when oxy-PAHs generate reactive oxygen species (ROS), which cause oxidative stress. Addition-ally, some oxy-PAHs are parent compounds of secondary nitro-PACs that are also toxic(23−26). For example, benzanthrone is reported to be a parent compound of the sec-ondary nitrobenzanthrones, which are strong direct-acting mutagenic compounds (25,26). Despite these concerns about oxy-PAHs, there are limited reports on the atmo-spheric occurrence of them (27−30), and particularly their sources. Oxy-PAHs couldbe expected to form not only primarily during incomplete combustion (9, 31, 32) butalso secondarily by PAH oxidation in the atmosphere. However, to our knowledge, thecontribution of secondary formation to the ambient burden has only been assessed for9,10-phenanthrenequinone (30). Thus, the most important purpose of this study was toinvestigate the relative contributions of secondary formation to oxy-PAHs.

In most previous reports, the simultaneous observation of atmospheric concentra-tions of nitro-PAHs at several sampling sites has been conducted at urban–suburbansites or roadside–residential sites that were at least a few kilometers apart (26, 33−35).These were used to investigate PAH nitration during long-term transport. In compari-son, the two sampling sites in this study were a roadside and the rooftop of an eighteen-story building that were separated by a linear distance of only approximately 170 m.These sites allowed us to investigate the atmospheric occurrences of PACs during theirdilution into the background atmosphere after emission from vehicles at the roadside.Furthermore, by comparing the samples collected at the two sites, we could clearly as-sess the relative contribution of primary sources versus secondary formation of PACs.This was possible due to the following assumptions: a) with no traffic on the road thenthe concentrations of both primary and secondary pollutants at the two sampling sites

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Roadside and Urban Background PAC Concentrations 323

should be almost the same because of the short liner distance between the two sites,and these could be regarded as the background concentrations; b) with heavy traffic onthe road, the concentrations of primary pollutants at the roadside should be equal tothe background levels plus those from direct vehicle emissions, whereas concentrationsof secondary pollutants at the two sites should be almost the same. This is described indetail in results and discussion.

In this study, PACs associated with airborne particulate matter were collected ata roadside and on the rooftop of an eighteen-story building in downtown Tokyo, Japan.The PAC concentrations were compared to investigate the relative contributions of pri-mary sources and secondary formation, with a focus on oxy-PAHs. Additionally, theconcentrations of gas-phase PAHs at the two sites were determined because most atmo-spheric formation of nitro- and oxy-PAHs has been reported to be through the reactionof gas-phase PAHs (14, 18).

EXPERIMENTAL

Sampling of Airborne Particulate Matter and Gas-phase PAHsAirborne particulate matter was sampled on a quartz fiber filter (20 × 25 cm2,

Pallflex Product, 2500QAT-UP) by a high-volume air sampler (HV-1000F, Shibata Co.,Tokyo, Japan) equipped with an impactor stage to eliminate any particles larger than 10µm in aerodynamic diameter. The sample flow rate was 0.5 m3 min−1. After collection,all the filters were stored at −30◦C until they were analyzed.

The sampling train for the gas-phase PAHs consisted of a filter holder with a quartzfiber filter (47 mm in diameter, Pallflex Product, 2500QAT-UP), a home-made glass car-tridge (35 mm i.d.) packed with 5 g of XAD-2 resin (Supelpak 2, Supelco Inc., Bellefonte,USA), and a pump with a flow rate of 20 L min−1. After collection, the XAD-2 resin car-tridges were also stored at –30 ◦C until they were analyzed.

Sampling was conducted at a roadside on Meiji-Street facing the Okubo Cam-pus (School and Graduate School of Science and Engineering, Waseda University) inShinjuku-ward in downtown Tokyo, and on the rooftop of a 70 m high eighteen-storybuilding on the campus, (represented by the Roadside site and Urban Background sitein Figure 1(b)). In the surrounding area there are many roads with traffic densities of>40,000 cars a day (represented by heavy gray lines in Figure 1 (a)), such as Meiji-Street. However, apart from vehicles there are no other strong primary PACs sources(e.g., incinerators or power plants) located within the surrounding few kilometers. Thehigh-volume air sampler on the sidewalk at the Roadside site was placed as close tothe roadway as possible. There were significant differences in the concentrations of theprimary pollutants such as PAHs and 1-NP between the two sites (This is described indetail in results and discussion). This indicates that, compared with the particles col-lected on the rooftop, the particles collected at the Roadside site contain a large amountof new particles that have just been emitted from vehicles on the road. Consequently,relative to the roadside site we considered the rooftop to be an “Urban Background site.”

Twenty-four-hour sampling campaigns were performed on February 12, 16 and 18,2009. Sampling was conducted in winter to minimize artifacts from PAC degradationby ozone (O3) during air sampling. The O3 concentrations during the sampling days(Table 1) were low enough that artifacts would not affect the PAC concentrations ac-cording to a previous report (36). For the four oxy-PAHs in our study we measured onlythe particle-phase concentrations, as reports indicate they exist almost exclusively inthe particle-phase in winter (37).

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Figure 1: The sampling locations in downtown Tokyo, Japan. The heavy gray lines in (b)indicate busy traffic roads with a traffic density of >40,000 cars per day.

MaterialsBenzo[a]pyrene (BaP), benzo[k]fluoranthene (BkF), and indeno[1,2,3-cd]pyrene (IP)

were obtained from Wako Pure Chemical Industries. Naphthalene (NA), acenaph-thalene (ACthy), acenaphthene (AC), anthracene (ANT), phenanthrene (PH), pyrene(PY), benzo[ghi]perylene (BghiP), perylene (PER), acenaphthenequinone (ACQ), 9,10-anthraquinone (9,10-AQ), 1,8-naphthalic anhydride (1,8-NA) and benzanthrone (BA)were obtained from Sigma-Aldrich Chemical Co. Fluoranthene (FL) and 1-nitropyrene(1-NP) were obtained from Tokyo Kasei Kogyo. 2-Nitrofluoranthene (2-NF) was ob-tained from Chiron AS (Trondheim, Norway). All the chemicals were used without fur-ther purification. The chemical structural formulas of selected oxy-PAHs in this studyare shown in Scheme 1.

Table 1: Meteorological data and the concentrations of ozone (Ox) and COduring the three sampling campaignsa.

Sampling date 2/12/09 2/16/09 2/18/09

Wind direction NNW NNW NNWWind speed [ m s−1] 2.4 3.7 2.4Temperature [ ◦C ] 10.4 10.4 6.2Sunlight intensity [ MJ m−3 ] 9.2 5.2 9.1R. H. [ % ] 50 47 37Ob

x [ ppb ] 11 17 13CO [ ppm ] 0.79 0.60 0.64aAverage value from 24 hourly data provided by a government pollution monitoring station(Shinjuku-ku Honcho Station) located close to the sampling sites.bOx concentrations were based on the ultraviolet absorption method (APOA-370, Horiba).

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Roadside and Urban Background PAC Concentrations 325

Benzanthrone(BA)(BA)

9,10-Anthraquinone(9,10(9,10--AQ)AQ)

1,8-Naphthalic-Anhydride (1,8(1,8--NA)NA)

O OO O

Acenaphthene-quinone (ACQ)(ACQ)

O OO O OO

OO

O

O

O

O

Scheme 1.

AnalysisAfter collection of airborne particulate matter, each filter was thoroughly cut into

small pieces and put in a flask, and an internal standard added. Then particle associ-ated PACs were extracted ultrasonically for 20 min twice with dichloromethane (DCM).For gas-phase PAH analysis, each entire XAD-2 cartridge was directly extracted ultra-sonically for 20 min twice with DCM. The DCM extracts were filtered to remove anysolid material. The filtrates were concentrated to 500 µL under a N2 flow. Then theresidues were purified by SPE with a silica gel solid phase for PAH and oxy-PAH anal-ysis (Discovery SPE DSC-Si Silica) and alumina-acidic and alumina-basic solid phasesfor nitro-PAH analysis (Bond Elut JR-AL-A and JR-AL-B, Varian). The purified solu-tions were concentrated to 500 µL under a N2 flow, and submitted to HPLC or GC/MSanalysis.

Particle-phase PAHs were determined by HPLC with fluorescence detection. Thesystem consisted of a detector (RF-10AXL, Shimadzu), a pump (LC-10AD, Shimadzu), asystem controller (SCL-10A, Shimadzu), a degasser (DGU-20A5, Shimadzu), a columnoven (CTO-10Avp, Shimadzu), and a column (3.0 mm i.d. × 250 mm, Pegasil ODS, Sen-shu Pak). The mobile phase was acetonitrile/water (8/2, v/v). The flow rate was 0.5 mLmin−1. The fluorescence detector was set to the optimum excitation and emission wave-lengths for each target PAH.

Gas-phase PAHs and particle-phase oxy-PAHs were determined by GC/MS. GC/MSanalyses were performed on a 30 m DB-5MS column (0.25 mm i.d. and 0.25 µm filmthickness) using an HP6890 GC interfaced to an HP5973 MS detector. The initial col-umn temperature was 100◦C and this was increased at 6◦C min−1 to 300◦C and heldat this temperature for 10 min. MS detection was performed in selected ion monitoring(SIM) mode.

For nitro-PAH analysis, the in-line reduction and chemiluminescence detectionHPLC method was employed, following that previously reported (38). The system con-sisted of a chemiluminescence detector (CLD-10A, Shimadzu), four pumps (LC-10ADvpand LC-10ATvp, Shimadzu), a six-port switching valve (FCV-12AH, Shimadzu), a col-umn oven (CTO-10ACvp, Shimadzu), and a system controller (CBM-20A, Shimadzu).Two separation columns (3.0 mm i.d. × 250 mm, 201TP54, Vydac and 5C18-MS-II,Nacalai Tesque), a concentration column (2.0 mm i.d. × 5 mm, Cadenza CD-C18, Im-takt), and a reducing column (4.0 mm i.d. × 10 mm, NPpak-R, Jasco) were employed.The mobile phase for the first separation and reduction of nitro-PAHs was 75% ethanol-acetate buffer (pH 5.5), and that for the second separation was acetonitrile/imidazole-perchloric acid buffer (pH 7.6) (1:1, v/v). Each flow rate was 0.5 mL min−1. The mobilephase for concentration was 10 mM ascorbic acid in water, and the flow rate was 2 mLmin−1 when necessary. The chemiluminescence reagent solution was 8 mM H2O2 and0.64 mM bis(2,4,6-trichlorophenyl)oxalate in acetonitrile.

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RoadsideUrban Background (a)

(b)

020406080

100120

NA ACthy AC PH ANT PY FL

Gas

-Pha

se P

AH

s/ p

mol

m−3 (× 25)

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Part

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Figure 2. Atmospheric concentrations of (a) gas, (b) particle, and (c) gas + particle phasePAHs at the two sampling sites. Each column and error bar represents the mean andmaximum/minimum concentrations, respectively. NA concentrations are in 25 × pmol m−3

units.

RESULTS AND DISCUSSION

Meteorological data and O3 and CO concentrations during the sampling campaign(Table 1) were provided by a government pollution monitoring station (Shinjuku-kuHoncho Station) located close to the sampling sites. O3 concentrations were based onthe ultraviolet absorption method (APOA-370, Horiba). PAC concentrations at the sam-pling sites could be affected by meteorological conditions, particularly the wind direc-tion and speed. However, no relationship was found between meteorological conditionsand PAC concentrations in this study.

Figures 2(a) and (b) show the atmospheric concentrations of gas- and particle-phasePAHs, respectively, at the two sampling sites. Gas-phase PAHs with more than fiverings were not detected in the XAD-2 resin samples. Particle-phase PAHs with eithertwo or three rings are highly volatile, and mostly exist in the gas-phase in the atmo-sphere (8, 37). These PAHs are not discussed in this study because their volatility wouldlead to large artifacts in the data due to their loss during filtration sampling, and thiscould undermine the credibility of any conclusions. Remarkable decreases in concen-tration from the Roadside site to the Urban Background site were observed for all gas-and particle-phase PAHs (Figures 2(a) and (b)). This indicates that primary emissionfrom vehicles was the main source of PAHs in the surrounding area, and that atmo-spheric dilution of PAHs occurred dramatically from the road to the urban backgroundatmosphere in Tokyo. To assess the magnitude of the decreases in concentration, the ra-tios of PAH concentrations at the Urban Background site to those at the Roadside site(CUB/CRS ratio) were calculated (Figure 3). A low ratio indicates that a significant de-crease occurred in the concentration of PAHs from the Roadside site to the Urban

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Roadside and Urban Background PAC Concentrations 327

0.0

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thy

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BkF

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iP IP PY FL

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B /

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T R

atio

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Gas-Phase PAHs Particle-Phase PAHs total PAHs(Gas + Particle)

(a) (b) (c)

Figure 3. The ratios of concentrations of (a) gas- and (b) particle-phase PAHs at the UrbanBackground site to those at the Roadside site (CUB/CRS). Each column and error barrepresents the mean and maximum/minimum ratios, respectively.

Background site. Overall, the ratios for gas-phase PAHs (average 0.36) tended to belower than those of particle-phase PAHs (average 0.49). The ratios for PY in the gas-phase (average 0.32) on all three sampling days were also lower than those in theparticle-phase (average 0.51). The main reason for the lower ratios might be a highergas-phase PAH degradation rate than the heterogeneous gas-particle reaction duringtransport in the atmosphere. Differences in the dilution rate from the road into the ur-ban background atmosphere between gas- and particle-phase PAHs could also affect theratio. However, the mean ratio for the gas-phase varied depending on the compounds,and that for ACthy (0.14) was the lowest of all the PAHs studied. In previous laboratoryexperiments (39), the rate constant for the gas-phase reaction of ACthy with hydroxylradicals, nitrate radical and O3 was reported to be highest of the PAHs selected forour study. Thus, this might have contributed to ACthy having the lowest ratio in ourresults.

1-NP is a representative primary nitro-PAH (3, 11, 33–35). As might be expected,we found its concentration associated with particulate matter was also significantly de-creased from the Roadside site to the Urban Background site (Figure 4 (a)). It had anaverage CUB/CRS ratio of 0.43, which was also on the same level as that of the particle-phase PAHs at 0.49 (Table 2). In contrast, no remarkable differences were found be-tween the 2-NF concentrations at the two sites, and its average CUB/CRS ratio was closeto 1 at 0.97. This result indicates that 2-NF was not directly emitted from vehicles. Thisis consistent with previous reports that 2-NF is formed in the atmosphere via an OHor NO3 radical-initiated reaction of FL with NO2 (13, 14, 33−35), and it is not detectedin particulate matter emitted directly from sources such as auto and diesel exhausts(3). The particles collected at the Roadside site consisted of two particle types. The firstof these were background particles that had a relatively long residence time in the at-mosphere. These were equivalent to those collected at the Urban Background site dueto the short distance between the two sampling sites. The background particles couldbe expected to contain a significant amount of secondary pollutants such as 2-NF. Theother particles were new ones that had just been emitted from vehicles on the road fac-ing the sampling site in this study, and these had short residence times of less than a

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328 Yuki Kojima et al.

0

50

100

150

1-NP 2-NF

Part

icle

-Pha

se N

itro

-PA

Hs

/ fm

olm

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RoadsideUrban Background

0.0

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9,10-AQ ACQ 1,8-NA BA

Part

icle

-Pha

se O

xy-P

AH

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(b)(a)

Figure 4. The atmospheric concentrations of (a) and nitro-PAHs (b) oxy-PAHs in theparticle-phase at the two sampling sites. Each column and error bar represents the meanand maximum/minimum concentrations, respectively.

few minutes. If significant secondary formation did not occur during the dilution of theprecursors into the roadside atmosphere after vehicular emission or the dilution fromthe roadside atmosphere to the urban background atmosphere, the concentrations ofthe secondary pollutants at the Roadside and Urban Background sites should be thesame. This is what we observed for 2-NF, where similar 2-NF concentrations betweenthe two sites suggested that secondary formation during the dilution of FL did not havea significant influence on 2-NF concentration levels.

The atmospheric concentrations of all oxy-PAHs decreased from the Roadside siteto the Urban Background site (Figure 4 (b)). This indicates that their atmospheric con-centrations are strongly affected by vehicle emissions, as was the case for PAHs and1-NP. However, the CUB/CRS ratios illustrated that the decreases for some oxy-PAHswere not as significant as those for PAHs and 1-NP (Table 2). The average ratios onthe three sampling days were in the order 2-NF at 0.97>1,8-NA at 0.69>9,10-AQ at0.63>gas- and particle-phase PAHs or 1-NP or ACQ or BA at 0.36−0.51. This indicatesthat some of the oxy-PAHs have an additional source besides primary emissions, andthis source might be secondary formation by atmospheric PAH degradation. Particu-larly, the ratios for 1,8-NA and 9,10-AQ were higher than those for the PAHs and 1-NPon all three sampling days.

If 1,8-NA and 9,10-AQ originate from both primary and secondary sources then theaverage percentage contributions from secondary formation at the Urban Backgroundsite can be calculated as 54% (1,8-NA) and 41% (9,10-AQ). The percentage of the sec-ondary oxy-PAH to the total oxy-PAH associated with airborne particulate matter wascalculated as

Ro − Rp

Ro(1 − Rp)× 100 . (1)

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Roadside and Urban Background PAC Concentrations 329

Table 2: The ratios of PAH, oxy-PAH, and nitro-PAH concentrations at the UrbanBackground site to those at the Roadside site (CUB/CRS).

CUB /CRS Ratio

Compounds 2/12/09 2/16/09 2/18/09 Average

Averaged gas-phase PAHs a 0.43 0.38 0.28 0.36Averaged particle-phase PAHs b 0.54 0.50 0.43 0.49Nitro-PAHs

1-NP 0.53 0.43 0.33 0.432-NF 0.96 1.06 0.91 0.97

Oxy-PAHs9,10-AQ 0.73 0.65 0.51 0.63ACQ 0.66 0.45 0.43 0.511,8-NA 0.82 0.67 0.57 0.69BA 0.46 0.37 0.27 0.37

aAverage value of the ratios of seven gas-phase PAHs (NA, AC, ACthy, PH, ANT, PY, and FL).bAverage value of the ratios of seven particle-phase PAHs (PY, FL, BkF, BaP, PER, BghiP, and IP).

where Ro and Rp are the CUB/CRS ratios of oxy-PAH and PAH, respectively. This cal-culation is based on the following assumptions: a) primary emission from vehicles andsecondary formation in the atmosphere are the only sources of oxy-PAHs; b) the atmo-spheric occurrences of primary oxy-PAHs and PAHs associated with airborne particu-late matter are the same, which could lead to the further assumption that the CUB/CRS

ratio of a primary oxy-PAH is equal to the average CUB/CRS ratio for the seven particle-phase PAHs selected in this study; and c) concentrations of secondary pollutants at thetwo sites should be almost the same because of no contribution from vehicle emissions.Assumption (c) was supported by experimental data we obtained for the secondary-formed 2-NF (Figure 4 a). As mentioned above, PAH (fluoranthene) nitration in theatmosphere is a major contributor to secondary formation of atmospheric 2-NF. Thiscould lead to the further assumption that the CUB/CRS ratios for secondary oxy-PAHsare equal to 1, as is the case with 2-NF of our results. The calculated contributionson the three days were in the order 2/12/09>2/16/09>2/18/09 for both compounds. Forexample, those for 1,8-NA on the three days were 74%, 50% and 39%, respectively. Al-though these daily variations were not related to O3 concentrations (Table 1), which isone of the indicators of atmospheric photo reactivity, the percent contributions mightalso have been affected by OH or NO3 radical concentrations and the amount of primaryoxy-PAHs emitted in association with airborne particulate matter. In addition, this cal-culation is sometimes inadequate because these assumptions would not be completelyvalid in the real atmosphere. For example, although particulate phase PAHs were usedas an indicator of atmospheric occurrences of primary oxy-PAHs in particle-phase in as-sumption b) above, the CUB/CRS ratios might not be exactly the same between PAHs andoxy-PAHs, and this is evidenced by the average ratios on the three sampling days foran individual particle associated PAH ranging from 0.44–0.58 (Figure 3 (b)). Thus, thecalculated % contribution can only be used in a relative sense. However, these resultsdo give an indication that secondary formation might significantly affect the concen-tration of some oxy-PAHs like 1,8-NA and 9,10-AQ even in winter, while there mightbe no or low contributions of secondary formation for ACQ and BA. Furthermore, thecontribution in summer could be expected to be higher than that in winter.

The parent PAHs of individual oxy-PAHs need to be taken into consideration wheninvestigating the different source contributions among the oxy-PAHs. For example,

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there is no known stable parent-PAH for BA in the atmosphere, at least there is nonewith the same number of rings as BA. This suggests that the contribution of secondaryformation for BA should be quite low, and may explain its lower CUB/CRS ratio com-pared with the other oxy-PAHs in this study. In contrast to BA, the other oxy-PAHshave some known parent PAHs in the atmosphere, such as ANT for 9,10-AQ. 1,8-NAcan form by the oxidation of several PAHs such as AC and ACthy, and even from PAHswith more than three rings like benz[a]anthracene (40−42). This could lead to a highercontribution of secondary formation for 1,8-NA, and is consistent with the CUB/CRS ra-tio for 1,8-NA being the highest of the selected oxy-PAHs on each sampling day in thisstudy. One anomaly in the data was with ACQ, which has stable parent PAHs (ACand ACthy) and the potential for significant secondary formation. Additional factorsthat would have been expected to lead to a high secondary formation contribution forACQ were: the mean atmospheric concentration of ACthy (55 pmol m−3) was about 300times higher than that of ACQ (0.18 pmol m−3) at the Roadside site, and both previousreports and data from our study suggest that the atmospheric degradation rate of AC-thy would be high as mentioned above. However, the CUB/CRS ratio for ACQ was onlyat the same level as those for particle-phase PAHs, indicating minimal secondary for-mation. One possible reason for this discrepancy is that the most abundant product ofACthy oxidation in the atmosphere was not ACQ, as has been shown in previous labo-ratory experiments (40−42). Even if ACQ could be formed by atmospheric oxidation ofAC or ACthy, it might readily degrade to further oxidative products like 1,8-NA that isexpected to be more stable than ACQ, before it can aggregate to airborne particulatematter. However, further research is required to confirm this.

Further studies are needed to develop a better assessment of the contributions ofsecondary formation for oxy-PAHs. For example, the atmospheric degradation rate dif-ferences among particle-phase PAHs and oxy-PAHs were not considered in this study,and this might influence the contribution calculations. Similarly, differences in atmo-spheric formation rates between oxy-PAHs and nitro-PAHs were not discussed in thisstudy. However, the important findings of this study were: 1) secondary formation mightaffect the concentrations of oxy-PAHs in downtown Tokyo Japan, even in winter, and2) the contributions of secondary formation varied among the oxy-PAHs, even for thosethat have suitable parent PAHs with the same number of rings as seen with ACQ inthis study. In the future, it is important to examine the contribution of secondary forma-tion and its mechanism for individual toxic oxy-PAHs by both laboratory experimentsand real atmospheric observations.

ACKNOWLEDGMENTS

This paper is a part of the outcome of research performed under a Waseda UniversityGrant for Special Research Projects (Project number: 2009A-861).

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