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Isomer Distributions of Molecular Weight 247 and 273 Nitro-Pahs in Ambient Samples, NIST Diesel SRM, and from Radical-Initiated Chamber Reactions

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Isomer Distributions of Molecular Weight 247 and 273 Nitro-Pahs in Ambient Samples, NIST Diesel SRM, and from Radical-Initiated Chamber Reactions Atmospheric Environment 55 (2012) 431e439 Contents lists available at SciVerse ScienceDirect Atmospheric Environment journal homepage: www.elsevier.com/locate/atmosenv Isomer distributions of molecular weight 247 and 273 nitro-PAHs in ambient samples, NIST diesel SRM, and from radical-initiated chamber reactions Kathryn Zimmermann a,1, Roger Atkinson a,1,2,3, Janet Arey a,1,2,*, Yuki Kojima b,4, Koji Inazu b,5 a Air Pollution Research Center, University of California, Riverside, CA 92521, USA b Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8502, Japan article info abstract Article history: Molecular weight (mw) 247 nitrofluoranthenes and nitropyrenes and mw 273 nitrotriphenylenes (NTPs), Received 27 December 2011 nitrobenz[a]anthracenes, and nitrochrysenes were quantified in ambient particles collected in Riverside, Received in revised form CA, Tokyo, Japan, and Mexico City, Mexico. 2-Nitrofluoranthene (2-NFL) was the most abundant nitro- 28 February 2012 polycyclic aromatic hydrocarbon (nitro-PAH) in Riverside and Mexico City, and the mw 273 nitro-PAHs Accepted 5 March 2012 were observed in lower concentrations. However, in Tokyo concentrations of 1- þ 2-NTP were more similar to that of 2-NFL. NIST SRM 1975 diesel extract standard reference material was also analyzed to Keywords: examine nitro-PAH isomer distributions, and 12-nitrobenz[a]anthracene was identified for the first time. Nitro-PAH fl Atmospheric reactions The atmospheric formation pathways of nitro-PAHs were studied from chamber reactions of uo- Ambient particles ranthene, pyrene, triphenylene, benz[a]anthracene, and chrysene with OH and NO3 radicals at room Nitrotriphenylenes temperature and atmospheric pressure, with the PAH concentrations being controlled by their vapor pressures. Sampling media were spiked with deuterated PAH to examine heterogeneous nitration. Comparing specific nitro-PAH ratios in ambient and diesel particles with those from our chamber experiments suggests that the low 2-NFL/NTPs ratios in Tokyo particulate matter are not a result of gas- phase radical-initiated chemistry since both gas-phase OH and NO3 radical-initiated reactions result in high 2-NFL/NTPs ratios. Comparisons of the relative formation of deuterated nitro-PAHs on the sampling media suggest that heterogeneous reactions with N2O5 on ambient particle surfaces also do not explain the nitro-PAH profiles of Tokyo particles. Thus, the source of NTPs in Tokyo remains unidentified. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction initiated atmospheric reactions of their parent PAHs (Arey, 1998, and references therein; Feilberg et al., 2001, and references Nitrated polycyclic aromatic hydrocarbons (nitro-PAHs) in therein). For the molecular weight (mw) 247 nitrofluoranthenes ambient atmospheres are a health concern because of their (NFLs) and nitropyrenes (NPYs), specific isomer distributions contributions to the genotoxicity of respirable ambient particu- have been used to estimate contributions from primary emis- late matter (Ishii et al., 2001; IPCS, 2003, and references therein). sions and/or atmospheric formation. The NFLs and NPYs in diesel Nitro-PAHs are present in ambient air because of primary emissions resemble those from electrophilic nitration of pyrene emissions (e.g., from incomplete combustion) (IARC, 1989,and (PY) and fluoranthene (FL), i.e., mainly 1-NPY and a lesser references therein) and in-situ formation from gas-phase radical- amount of 3-NFL (Bamford et al., 2003). In contrast, gas-phase radical-initiated reactions of FL and PY produce 2-NFL (from OH and NO3 radical reactions) and 2-NPY (only from the OH radical reaction at ambient NOx levels), respectively (Atkinson * Corresponding author. Tel.: þ1 951 827 3502. et al., 1990; Atkinson and Arey, 2007). 2-NFL and 2-NPY have E-mail address: [email protected] (J. Arey). not been observed in significant quantities from primary emis- 1 Also Environmental Toxicology Graduate Program. 2 Also Department of Environmental Sciences. sions, such as diesel exhaust particles (Bamford et al., 2003). 3 Also Department of Chemistry. Ambient measurements of NFLs and NPYs suggest that atmo- 4 Present address: Department of Resources and Environmental Engineering, spheric formation from gas-phase radical-initiated reactions of School of Science and Technology, Waseda University, 3-4-1 Okubo, Shinjuku-ku FL and PY dominates, with 2-NFL generally being the most 169-8555, Japan. 5 Present address: Department of Chemistry and Biochemistry, Numazu National abundant particle-bound nitro-PAH (Ciccioli et al., 1996; Marino College of Technology, 3600, Ohoka, Numazu 410-8501, Japan. et al., 2000; Feilberg et al., 2001; Bamford and Baker, 2003; 1352-2310/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.atmosenv.2012.03.016 432 K. Zimmermann et al. / Atmospheric Environment 55 (2012) 431e439 Kameda et al., 2004; Reisen and Arey, 2005). The atmospheric 2. Experimental radical-initiated reactions are postulated to proceed by initial addition of either the OH radical (present during daytime) or the 2.1. Gas-phase nitration of PAHs via OH or NO3 radical-initiated NO3 radical (present during evening and nighttime) to the reactions position of highest electron density, followed by ortho addition of NO2, and subsequent loss of H2OorHNO3 (Supplementary Experiments were performed in a w7000 L collapsible Teflon Information Scheme S1)(Arey, 1998). Based on OH radical- chamber in dry purified air at w297 K and w740 Torr total pres- initiated reactions of gas-phase FL and PY (Atkinson et al., sure. The chamber contains two parallel banks of blacklamps 1990), ambient 2-NFL/2-NPY ratios 10 indicate dominance of (l > 300 nm) for irradiation and a Teflon-coated fan for mixing of OH radical-initiated nitro-PAH formation (Bamford and Baker, reactants during their introduction. The following reactions were 2003, and references therein; Reisen and Arey, 2005). Because performed: (1) an OH radical-initiated reaction, (2) an N2O5/NO3 2-NPY is not formed from the NO3 radical-initiated reaction at reaction, and (3) an NO3 radical reaction. OH radicals were gener- ambient NO2 levels and 2-NFL is formed in high yield from the ated from the photolysis of CH3ONO in the presence of added NO NO3 radical reaction (Atkinson et al., 1990), high ambient 2-NFL/ (to suppress formation of O3 and therefore of NO3 radicals), with 14 2-NPY ratios indicate that NO3 radical chemistry dominates initial CH3ONO and NO concentrations of w1.3 Â 10 and À nitro-PAH formation (Bamford and Baker, 2003, and references w6.9 Â 1013 molecule cm 3, respectively. Irradiations were per- therein; Reisen and Arey, 2005). formed at a light intensity corresponding to an NO2 photolysis rate À1 Recently, 1- and 2-nitrotriphenylene (1- and 2-NTP) have been of 0.14 min for 4.7 min, and the NO and initial NO2 concentrations observed in the atmospheres of Tokyo and Osaka, Japan, and it was were monitored with a chemiluminescence NOeNOx analyzer. NO3 postulated that these isomers were formed from atmospheric radicals were generated from the thermal decomposition of N2O5 in reactions of triphenylene (TP) (Ishii et al., 2000, 2001; Kameda et al., the presence of NO2 (Atkinson et al., 1990), with initial concentra- À 2004, 2006). Surprisingly, the reported concentrations of the NTPs in tions of w2.6 Â 1014 and w1.4 Â 1014 molecule cm 3, respectively. Japan were often comparable to (Kameda et al., 2004), and in one The NO3 reaction differed from the N2O5/NO3 reaction by the À instance greater than (Ishii et al., 2001), those of 2-NFL. To further addition of w2.4 Â 1014 molecule cm 3 of 2-methyl-2-butene after investigate the sources and formation of these mw 273 nitro-PAHs, 2 min of reaction, but prior to sampling, in order to scavenge we have conducted laboratory radical-initiated reactions of FL, PY, unreacted NO3 radicals and hence N2O5 and thereby limit possible TP, benz[a]anthracene (BaA), and chrysene (CHR) (Fig. 1), and heterogeneous reactions involving N2O5 during sampling (see determined the resulting nitro-PAH isomer distributions. FL and PY Table S1). were included because, as noted above, their gas-phase radical- Approximately 10 mg each of FL, PY, TP, BaA, and CHR in initiated reactions have previously been studied, and ambient methanol were introduced into the chamber for each reaction using concentrations of NFLs and NPYs have been measured worldwide. an atomizer. The chamber was then flushed with dry purified air for BaA and CHR were included in part to investigate heterogeneous 4e7 h to remove methanol. Equilibrium of each PAH between the reactions since they are isomeric to TP and hence have similar walls of the chamber and the gas-phase was assumed to be volatilities, and their nitro-isomers have also been reported in reached, with the relative abundance of each PAH in the gas-phase ambient particulate matter (Bamford and Baker, 2003). We also being controlled by their vapor pressures (Table S2). Hence gas- report measurements of the mw 247 and 273 nitro-PAHs in ambient phase concentrations and specific nitro-PAH formation yields particle samples from southern California, Tokyo, and Mexico City, as could not be determined. Following each reaction, 3500e5700 L of well as in the National Institute of Standards and Technology (NIST) air were sampled from the chamber using a modified high-volume SRM 1975 diesel standard reference material. Comparisons of the sampler with two polyurethane foam (PUF) plugs in series relative abundances and isomer distributions of these nitro-PAHs in upstream of a Teflon impregnated glass fiber (TIGF) filter. Sample the ambient samples with those from our chamber reactions were volumes were calculated from the NOx concentrations measured utilized to investigate atmospheric formation of NTPs. before sampling and again after sampling and backfilling with 1 2 1 3 2 8 4 7 LF YP 2 1 2 1 1 3 2 11 12 4 3 10 4 9 5 5 8 7 6 6 PT BaA RHC Fig.
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