Atmospheric Environment 55 (2012) 431e439

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Atmospheric Environment

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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

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 (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 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 (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 , 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 10 and nitro-PAH formation (Bamford and Baker, 2003, and references w6.9 1013 cm 3, respectively. Irradiations were per- therein; Reisen and Arey, 2005). formed at a light intensity corresponding to an NO2 photolysis rate 1 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- 2004, 2006). Surprisingly, the reported concentrations of the NTPs in tions of w2.6 1014 and w1.4 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 instance greater than (Ishii et al., 2001), those of 2-NFL. To further addition of w2.4 1014 molecule cm 3 of 2-methyl-2- 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. 1. PAHs used in chamber experiments: mw 202 fluoranthene (FL) and pyrene (PY), and mw 228 triphenylene (TP), benz[a]anthracene (BaA), and chrysene (CHR). Bolded numbers represent the dominant position for electrophilic nitration (Ruehle et al., 1985). K. Zimmermann et al. / Atmospheric Environment 55 (2012) 431e439 433 purified air, with volume sampled (L) ¼ 7000 [1 {(NOx after 2265, with the addition of 1-NPY-d9 and 6-NCHR-d11, was used to sampling and backfilling)/(NOx before sampling)}]. identify nitro-PAHs and calculate response factors for certain Prior to sampling, the filters (and front PUF plugs for the N2O5/ isomers. NO3 and NO3 reactions) were spiked with 500 mg each of FL-d10,PY- d10, BaA-d12, CHR-d12, and TP-d12 to investigate heterogeneous 3. Results formation of nitro-PAHs on the filters and PUF plugs during sampling. After sampling, the filters and PUF plugs were separately 3.1. Environmental chamber reactions Soxhlet extracted with dichloromethane (DCM) for w24 h. Extracts were eluted through a Supelco Discovery SPE DSC-Si Silica Tube Chamber experiments were performed to examine the mw 247 (10 g) with 150 mL of DCM, concentrated, and divided into two and 273 nitro-PAH products of the gas-phase OH, N2O5/NO3, and aliquots. The first 2 mL aliquot was analyzed for mw 247 nitro-PAHs NO3 radical-initiated reactions with FL, PY, BaA, TP, and CHR. In and corresponding mw 256 nitro-PAHs-d9, while the second previous studies of the reactions of OH and NO3 radicals with aliquot was concentrated to 200 mL and analyzed for mw 273 nitro- gaseous FL and PY, products were collected only on PUF plugs (Arey PAHs and corresponding mw 284 nitro-PAHs-d11. Analyses utilized et al., 1986; Atkinson et al., 1990). It has since been shown that gas - spectrometry with electron impact (EI) particles can pass through PUF plugs to be collected on a filter and negative chemical ionization (GC-MS/NCI) in select ion moni- downstream (Wang et al., 2007). In the present study, particle toring (SIM) mode using a 60 m DB-17 column, as well as GC-MS/ formation during the reactions was observed using the SMPS, and NCI using a 60 m DB-5 column. Nitro-PAH identification was hence nitro-PAH products were collected on, and separately based on matching retention times with those of standards, as well analyzed from, two upstream PUF plugs and a downstream filter. In as fragmentation patterns in EI mode. Integrated chromatographic general, the amounts of nitro-PAHs on the filters were greater than peak areas were corrected for response factors and the volume those on the PUF plugs, but since the amounts on the second PUF sampled to obtain isomer distribution patterns for each reaction. plug were always a small fraction (0e30%) of the total collected on Particle formation during the reactions was monitored using the PUF plugs, a reasonable collection efficiency of the PUF plug for a TSI 3936L72 scanning mobility particle sizer (SMPS). In addition, gas-phase species was indicated. Therefore, the presence of isomers to investigate possible desorption of wall-bound nitro-PAHs during on the front PUF plug suggested gas-phase formation, with their sampling, samples were collected from the chamber after flushing presence on the filter presumably being due to adsorption onto with purified air for >16 h after the OH radical reaction. Since only particles formed during the reactions and collected on the filter. In a trace of 1-NPY was observed, this suggested negligible interfer- addition, the filters and, for the NO3 and the N2O5/NO3 reactions, ence from wall-adsorbed nitro-PAHs to the isomer distribution the front PUF plugs were spiked with deuterated FL, PY, BaA, TP and patterns of the experiments. CHR and analyzed for the corresponding deuterated nitro-products to investigate heterogeneous reactions during sampling. For any 2.2. Ambient particulate samples and NIST SRM 1975 specific nitro-PAH isomer, the occurrence of heterogeneous formation needs to be considered if a significant amount of the Ambient filter samples collected in Riverside, CA, Tokyo, Japan deuterated nitro-PAH was observed on the filter (or PUF plugs) and Mexico City, Mexico were analyzed for mw 247 and 273 nitro- relative to the non-deuterated isomer. PAH (see Table S3 for sampling details). Filter samples were solvent extracted, fractionated by normal phase high-performance liquid 3.1.1. OH reaction chromatography (HPLC), and analyzed by GC-MS/NCI. The NIST The combined PUF plugs þ filter isomer distribution of mw SRM 1975, a diesel forklift particulate extract in DCM, was also 247 nitro-PAHs observed in the OH reaction (Fig. 2A) agrees with analyzed for ten nitro-PAHs. Complete details of sampling and previous reports of the gas-phase OH radical-initiated reactions analysis procedures are given in the Supplementary Information, of FL and PY in which 2-NFL > 2-NPY w 8-NFL w 7-NFL (Arey section S1. et al., 1986). A small amount of 1-NPY was also observed (1- NPY/2-NFL w0.001) after sample concentration. A 2-NFL/2-NPY 2.3. Chemicals ratio of 7 was obtained from analysis of the front PUF plug, also consistent with earlier data (Atkinson et al., 1990). Particles The chemicals used, with their stated purities, were: fluo- were formed during the reaction (Fig. S5) and hence collected on ranthene (98%), pyrene (99%), triphenylene (98%), chrysene (98%), the downstream filter, with a 2-NFL/2-NPY ratio of 25 from the and 2-methyl-2-butene (98%), Aldrich; benz[a]anthracene, East- combined PUF plugs þ filter extracts. It is likely that the differ- man; chrysene-d12 (99.7%), triphenylene-d12 (98.4%), and 6- ence between the 2-NFL/2-NPY ratios from the front PUF plug nitrochrysene-d11 (99.7%), CDN ; fluoranthene-d10 (99.2%), and the combined PUF plugs þ filter is due to sampling being MSD Isotopes; benz[a]anthracene-d12 (98%), KOR Isotopes; pyrene- performed during irradiation and hence as the reaction pro- d10 (98%), Cambridge Laboratories; 1-nitrotriphenylene and ceeded and particle formation occurred. Initially, gaseous FL and 2-nitrotriphenylene, Hayashi Pure Chemicals; and PY would react and the gas-phase nitro-products formed during dichloromethane, Fisher; and NO (99.0%), Matheson Gas Products. this first portion of the reaction would be sampled onto the front 2-Nitrofluoranthene-d9 and 1-nitropyrene-d9 had been previously PUF plug, with 2-NFL/2-NPY ¼ 7. As the reaction progressed, FL synthesized using N2O5 in CCl4 solution (Zielinska et al., 1986). 12- and PY would desorb from the chamber walls into the gas-phase Nitrobenz[a]anthracene (12-NBaA) and 1- and 2-NTP were synthe- and the NO2 concentration increased from 0.14 to 1.8 ppmv sized using the same procedure. 12-NBaA was confirmed by because of NO-to-NO2 conversion. Nishino et al. (2008) have 1 comparison of its 400 MHz H NMR and 2-D COSY spectra with that shown that the NO2 concentration at which OH-aromatic of Iversen et al. (1985). The NMR and GC-MS spectra of the synthe- adducts react equally with NO2 and O2 depends on the specific sized 1- and 2-NTP matched those of the samples from Hayashi Pure aromatic hydrocarbon. It is therefore possible that the formation Chemicals. Figs. S1eS4 and accompanying text (section S2) present yields of 2-NPY and 2-NFL have different dependencies on the our mass spectral and NMR data and interpretation for 12-NBaA and NO2 concentration, with the NO2 concentration at which the OH- 1- and 2-NTP. CH3ONO and N2O5 were prepared and stored as PY adduct reacts at equal rates with NO2 and O2 being lower than previously described (Atkinson et al.,1990). The NIST nitro-PAH SRM that for the OH-FL adduct (see Scheme S1 and section S3). In this 434 K. Zimmermann et al. / Atmospheric Environment 55 (2012) 431e439

A mw 247 nitro-PAHs C mw 273 nitro-PAHs

N2O5/NO3 N2O5/NO3



7-NBaA or 7-NBaA-d 1-NFL or 1-NFL-d9 8-NFL or 8-NFL-d9 11 12-NBaA or 12-NBaA-d11 2-NFL or 2-NFL-d9 1-NPY or 1-NPY-d9 1-NTP or 1-NTP-d11 3-NFL or 3-NFL-d9 2-NPY or 2-NPY-d9 2-NTP or 2-NTP-d11 7-NFL or 7-NFL-d9 4-NPY or 4-NPY-d9 6-NCHR or 6-NCHR-d11

mw 284 nitro-PAHs-d B mw 256 nitro-PAHs-d9 D 11

N O /NO N2O5/NO3 2 5 3

NO NO3 3


Fig. 2. Nitro-PAH isomer distributions for (A) mw 247 NFLs and NPYs, (B) mw 256 NFLs-d9 and NPYs-d9, (C) mw 273 NBaAs, NTPs, and NCHR, and (D) mw 284 NBaAs-d11, NTPs-d11, and NCHR-d11. Approximate amounts of the most abundant isomer observed in (A) N2O5/NO3: 2-NFL ¼ 30 mg; NO3: 2-NFL ¼ 90 mg; OH: 2-NFL ¼ 5 mg, (B) N2O5/NO3: 1-NPY- d9 ¼ 150 mg; NO3: 1-NPY-d9 ¼ 20 mg; OH: negligible formation, (C) N2O5/NO3: 7-NBaA ¼ 0.5 mg; NO3: 7-NBaA ¼ 0.7 mg; OH: 1-NTP ¼ 0.1 mg, (D) N2O5/NO3: 1-NTP-d11 ¼10 mg; NO3:1- NTP-d11 ¼1 mg; OH: negligible formation.

case, the 2-NFL/2-NPY ratio would increase with NO2 concen- 3.1.2. N2O5/NO3 and NO3 reactions tration (to a plateau value), and hence the ratio would increase The nitro-PAH isomer ratios from the NO3 versus N2O5/NO3 as the reaction progressed and as particles were formed. The reactions, as well as the presence or absence of nitro-PAHs on the initial lower 2-NFL/2-NPY ratio would then be more applicable front PUF plug and of deuterated nitro-PAHs on the PUF plugs and/or to ambient conditions since our initial NO2 concentration of filters, were useful in investigating gas-phase formation of nitro-PAH 0.14 ppmv was at or above typical polluted ambient air NO2 (Table 1). In the NO3 reaction, 2-methyl-2-butene was added prior to concentrations. Note that 2-NFL/2-NPY ratios of 2e6were sampling to scavenge NO3 radicals and hence N2O5, thus decreasing observed in Mexico City (see Table 2). any heterogeneous reaction of N2O5 with filter-adsorbed PAHs Confirming that 2-NFL, together with smaller amounts of 7- and during sampling. The NO3 reaction proceeded for approximately 8-NFL and 2-NPY, are products of the gas-phase reactions of FL and twice as long as the N2O5/NO3 reaction, leading to higher gas-phase PY with the OH radical is the lack of the corresponding deuterated nitro-PAH formation. Additionally, because of the longer reaction nitro-PAH isomers on the filter (Fig. 2B). Only 1-NPY-d9 was formed time, the NO3 reaction would be expected to have more HNO3 during sampling on the deuterated PAH spiked-filter and, although production from N2O5 hydrolysis on surfaces, with the potential for very little 1-NPY-d9 was formed, it was greater than the corre- HNO3 to desorb back into the gas phase (Tuazon et al., 1983). sponding 1-NPY (1-NPY-d9/1-NPY ¼ 2.5). Thus the formation of 1- In both the NO3 and N2O5/NO3 reactions, 2-NFL was the principal NPY-d9 and 1-NPY are attributed to heterogeneous nitration, nitro-product (Fig. 2A). Consistent with formation of 2-NFL by gas- probably by HNO3/NO2,onthefilter (see Supplementary phase reaction of FL with NO3 radicals, 2-NFL was the only NFL Information, sections S4.1 and S4.2). isomer on the front PUF plug (Table 1), and 2-NFL-d9 was not As shown in Fig. 2C, 1- and 2-NTP and 7-NBaA were formed in observed in the NO3 reaction (Fig. 2B). Because only a small amount of similar amounts from the OH radical-initiated reaction, with 2-NFL-d9 was observed in the N2O5/NO3 reaction (Table 1,footnoted), a lesser amount of 12-NBaA. Comparable formation of 1- and 2-NTP we conclude that, relative to the gas-phase 2-NFL formed, hetero- is consistent with the previous study of Kameda et al. (2006) of the geneous formation of 2-NFL was negligible. Consistent with gas- OH radical-initiated reaction of TP. 2-NFL, the dominant mw 247 phase formation, the amount of 2-NFL formed in the NO3 reaction gas-phase nitration product, was formed in w35-fold higher was a factor of w3 greater than that formed in the N2O5/NO3 reaction abundance than the SNTPs. If the relative gas-phase concentrations (Fig. 3AandTable 1). Similar evidence suggests that 2-NPY was of FL and TP in our chamber were similar to the ratios of their vapor formed from the gas-phase reaction of PY with NO3 radicals in these pressures (Table S2), then the formation yield of the NTPs from reactions. Thus, the front PUF plug for each reaction contained 2-NPY, OH þ TP would be approximately the same as that for formation of no heterogeneously formed 2-NPY-d9 was observed in either reac- 2-NFL from OH þ FL under our experimental conditions. Although tion (Fig. 2B), and 2-NPY was formed in larger amounts in the NO3 no NTPs or NBaAs were observed on the front PUF plug, the absence reaction than in the N2O5/NO3 reaction (Table 1). Although 2-NPY of mw 284 deuterated nitro-PAHs (Fig. 2D) suggests that the small was formed in both reaction systems at initial NO2 concentrations amounts of observed 1- and 2-NTP and 7- and 12-NBaA were not of w1.4 1014 molecule cm 3 (w6 ppmV, much higher than formed on the filter during sampling and may be due to gas-phase ambient), previous data suggest it will not be formed from the NO3 OH radical-initiated reaction. radical-initiated reaction of PY at ambient NO2 concentrations K. Zimmermann et al. / Atmospheric Environment 55 (2012) 431e439 435

Table 1

Analysis of isomers formed in the NO3 and N2O5/NO3 reactions (see text for description of these reactions). The N2O5/NO3 reaction is denoted as N2O5 in the table below for clarity. Ratios are calculated from integrated peak areas based on identification on a 60 m DB-17 column with appropriate response factors and are normalized to chamber volume sampled. Compound abbreviations are NFL (nitrofluoranthene), NPY (nitropyrene), NBaA (nitrobenz[a]anthracene), NCHR (nitrochrysene), NTP (nitrotriphenylene).

1-NFL 2-NFL 3-NFL 7-NFL 8-NFL 1-NPY 2-NPY 4-NPY 7-NBaA 12-NBaA 1-NTP 2-NTP 6-NCHR aa On front PUF, NO3 No Yes No No No Yes Yes Yes No No No reaction? b bb On front PUF, N2O5 No Yes No No No Yes Yes No No No reaction? c ccc NO3 3.0 13.6 6.6 2.1 2.4 1.5 0.47 0.45 6.8 N2O5

NO3 1-NFL-d9 2-NFL-d9 3-NFL-d9 7-NFL-d9 8-NFL-d9 1-NPY-d9 2-NPY-d9 4-NPY-d9 7-NBaA-d11 12-NBaA-d11 1-NTP-d11 2-NTP-d11 6-NCHR-d11 d e N2O5 0.16 0.13 0.12 0.11 0.14 0.94 0.08 0.25 0.10 0.16 0.18 f -d9/-h9 -d9/-h9 -d9/-h9 -d9/-h9 -d9/-h9 -d9/-h9 -d9/-h9 -d9/-h9 -d11/-h11 -d11/-h11 -d11/-h11 -d11/-h11 -d11/-h11 NO reaction 3 g 0h 16 39 g 4.5 0h 1.3 0.65 0.38 30 25 6.4 f d9/-h9 ed9/-h9 -d9/-h9 -d9/-h9 -d9/-h9 -d9/-h9 -d9/-h9 -d9/-h9 -d11/-h11 -d11/-h11 -d11/-h11 -d11/-h11 -d11/-h11 N O reaction 2 5 g 0.02 gg952 444 0h 2.8 21 2.2 150 75 246

a 7-NBaA and 12-NBaA were present on the front PUF, which was also spiked with the five deuterated PAH. Since similar amounts of the corresponding deuterated nitro- PAHs were also present, heterogeneous formation on the PUF plug cannot be ruled out. b 1-NPY, 7-NBaA and 12-NBaA were present on the front PUF, which was also spiked with the five deuterated PAH. Since similar or higher (in the case of 1-NPY-d9) amounts of the corresponding deuterated nitro-PAHs were also present, heterogeneous formation on the PUF plug cannot be ruled out. c None, or only trace amounts formed, S(1-, 3-, 7-, 8-NFL)/2-NFL ¼ 0.003 and 0.001 in the NO3 and N2O5 reactions, respectively (Fig. 2). d No 2-NFL-d9 was observed in NO3 reaction; in N2O5 reaction 2-NFL-d9/2-NFL ¼ 0.02 (Fig. 2). e No 2-NPY-d9 was observed in NO3 or in N2O5 reaction. f -d9/-h9 refers to, for example, the ratio of 1-NFL-d9/1-NFL. g Only deuterated isomer observed. h No deuterated isomer observed.

(Atkinson et al., 1990). The 2-NFL/2-NPY ratios of 180 and 80 for the In both the N2O5/NO3 and NO3 reactions, 4-NPY was observed N2O5/NO3 and NO3 reactions, respectively, are significantly greater on the front PUF plug (no 4-NPY-d9 was present on the PUF plugs) than those for the OH radical reaction, consistent with the data of and the total formation of 4-NPY was greater in the NO3 reaction Atkinson et al. (1990). than in the N2O5/NO3 reaction (Table 1), suggesting gas-phase formation of 4-NPY. If 4-NPY was formed only by gas-phase reac- tion, then essentially no 4-NPY-d9 would be expected and although A mw 247 mw 256 some 4-NPY-d9 was observed from these reactions (Fig. 2B), the 4- 20,000 2-NFL NPY-d9/4-NPY ratios were relatively low (Table 1). Thus the evidence suggests that gas-phase formation accounts for some, or 1-NPY-d9 Σ most, of the observed 4-NPY, consistent with Atkinson et al. (1990). 15,000 1-, 3-, 7-, 8-NFL-d9 It has previously been reported that heterogeneous reaction of PY with N O gives 1-NPY and reaction of FL gives 1-, 3-, 7- and 8-

ume sampled) 2 5 10,000 NFLs (Pitts et al., 1985). In contrast to 1-NPY-d9 and 1-, 3-, 7- and 8- NFL-d9, whose formation in the N2O5/NO3 reaction was about an order of magnitude greater than in the NO3 reaction (see Table 1), 5,000 similar amounts of 4-NPY-d9 were observed in the N2O5/NO3 and NO3 reactions suggesting that heterogeneous formation of 4-NPY- d9 by N2O5 reaction was about equal to its nitration by HNO3/NO2 in Nitro-PAH (area/vol the NO3 reaction. Because heterogeneously formed 1-NPY-d9 was NO3 N2O5 NO3 N2O5 the most abundant deuterated nitro-isomer in both the NO3 and N2O5/NO3 reactions (Figs. 2 and 3), the small amounts of 1-NPY B mw 273 mw 284 observed in these reactions are not attributed to gas-phase NO3 52 000,3 radical reaction (see Supplementary Information, section S4.3, for Σ

Σ Σ NTP-d NTP NTP-d11 additional discussion). 2,500 20 As seen on Fig. 2C and D, in contrast to the NFLs and NPYs (Fig. 2A

11 and B) the same isomers were observed for the mw 273 nitro- 2,000 (area/volume sampled) products and their corresponding mw 284 deuterated products, 15 making it more difficult to distinguish between gas-phase and 1,500 heterogeneous formation of mw 273 nitro-PAHs. The observation of 10 on the filters shows that heterogeneous nitration 1,000 1- and 2-NTP-d11 of TP-d12 occurred and, consistent with heterogeneous reactionwith 5 500 N2O5, the formation of both 1- and 2-NTP and of 1- and 2-NTP-d11

NTP (area/volume sampled) decreased in the NO3 reaction compared to the N2O5/NO3 reaction Σ (Fig. 3B and Table 1). If heterogeneous nitration by N2O5 dominated, the ratio of the NTPs produced in the NO reaction compared to the NO3 N2O5 NO3 N2O5 3 N2O5/NO3 reaction would be expected to be w0.1 (based on the data Fig. 3. The relative amounts of nitro-PAHs formed in the NO3 and N2O5/NO3 reaction in Table 1 for 1-NPY-d9 and 1-, 3-, 7-, and 8-NFL-d9). As shown in (termed N O here) for (A) 2-NFL, 1-NPY-d , and S(1-, 3-, 7-, and 8-NFL-d ), and (B) 2 5 9 9 Fig. 3, this is the case for the NTPs-d11 (SNTPs-d11 in the NO3 reaction sum of NTPs and corresponding deuterated NTPs. The Y-axes represent the integrated versus the N O /NO reaction ¼ 0.12) but not for the NTPs (SNTPs in chromatographic peak areas adjusted for response factors and volumes sampled 2 5 3 ¼ during the reaction. the NO3 reaction versus the N2O5/NO3 reaction 0.46). Thus, it is 436 K. Zimmermann et al. / Atmospheric Environment 55 (2012) 431e439 possible that both gas-phase reaction with NO3 radicals and consistently the highest measured nitro-PAH in each ambient heterogeneous reaction with N2O5 result in NTP formation in our sample. The mw 273 isomers measured include 7- and 12-NBaA, 1- chamber reactions, and it has previously been reported that gas- and 2-NTP, and 6-NCHR (Fig. 4 and Table 2). 7-NBaA was the phase reaction of TP with NO3 radicals forms 2-NTP (Kameda et al., dominant mw 273 isomer observed in the majority of samples, and 2006). However, formation of 2-NFL dominated over that of the 6-NCHR was found in consistently lower concentrations than the SNTPs by w240 for the N2O5/NO3 reaction and by w1500 for the NO3 other nitro-PAH isomers (Table 2 and Fig. S6). While the lowest and reaction (Fig. 3), with the large increase in the 2-NFL/SNTPs ratio highest concentrations of 2-NFL were from Mexico City, with those when N2O5 was largely scavenged suggesting that a majority of the from Tokyo and Riverside falling between these, Tokyo had the two NTPs formed were from heterogeneous N2O5 reaction. The [N2O5]/ highest concentrations of 1- and 2-NTP, consistent with previous [NO3] ratios in our chamber experiments greatly exceeded the cor- reports of high concentrations of NTPs in Tokyo and Osaka, Japan responding ratios in the ambient atmosphere because of the high (Ishii et al., 2000, 2001; Kameda et al., 2004, 2006). Although 12- NO2 concentrations present in the chamber experiments compared NBaA was identified for the first time in southern California to ambient, and hence our chamber N2O5/NO3 reaction had a higher particulate matter, its quantification is uncertain due to use of an potential for heterogeneous N2O5 reactions than could be the case in estimated NCI response factor. ambient. Even based on the 2-NFL/SNTPs ratio in the N2O5/NO3 The NIST diesel SRM 1975 was analyzed for ten nitro-PAHs of 1 reaction, the NTPs yield from NO3 þ TP appears to be much lower mw 247 and 273, and the quantitative results (in mg kg )are than that of 2-NFL from NO3 þ FL (taking into account the likely reported in Table S4 together with previously reported values. As relative concentrations of gaseous TP and FL; see section 3.1.1). shown in Fig. 4, the relative abundances and isomer distributions of Fig. 3 shows that with the same amounts of PY-d10, FL-d10, and mw 247 and 273 nitro-PAHs in the NIST SRM 1975 are different TP-d12 coated onto the filter, heterogeneous formation of 1-NPY-d9 from those found in ambient atmospheres, but are similar to those and S(1-, 3-, 7-, 8-NFL-d9) each dominated over SNTPs-d11 expected from electrophilic nitration, with 1-NPY dominating formation by a factor of >6 for both the N2O5/NO3 and NO3 reac- (Nielsen, 1984). A small amount of 2-NFL was identified in the tions. The higher reactivity of the more volatile FL and PY is extract, with 2-NFL/3-NFL <0.05. 7-NBaA and 6-NCHR dominated consistent with a previous study of the reaction of filter-adsorbed the mw 273 nitro-PAHs, and our measured concentration of 2-NTP PAH with gaseous N2O5 in which PY and FL gave more nitro- in the NIST SRM 1975 agrees with that reported by Kameda et al. products than BaA and CHR (Pitts et al., 1985). (2006). See the Supplementary Information for a discussion on the data for 6-NCHR and 7-and 12-NBaA formation (section S4.3). As dis- 4. Discussion cussed, it is possible that 12-NBaA is formed by gas-phase NO3 radical-initiated reaction of BaA. While 2-NFL was consistently the dominant nitro-PAH in each ambient particulate sample, ratios of 2-NFL/2-NPY and 2-NFL/1- 3.2. Nitro-PAH concentrations in ambient samples and NIST SRM NPY varied (Table 2), suggesting different contributions from OH 1975 radical formation, NO3 radical formation, and direct emissions. Our chamber studies suggest that the use of 2-NFL/2-NPY ratios 10 as The concentrations of particulate mw 247 and 273 nitro-PAHs indicative of the dominance of OH radical chemistry in their from analyses of Riverside, Tokyo, and Mexico City ambient filter ambient formation is appropriate. The insignificant 2-NFL relative samples are given in Table 2. Seven of the eight possible NFL and to 1-NPY in the diesel SRM and the lack of any evidence for gas- NPY isomers were identified together with five mw 273 nitro-PAHs. phase 1-NPY formation in the OH or NO3 radical-initiated reac- Fig. 4 shows GC-MS/NCI analyses of the Riverside Nighttime #3 and tions suggests that the use of 1-NPY as one marker of direct emis- Tokyo 24-hour Winter samples, and the NIST diesel SRM 1975, sions is also reasonable. Low 2-NFL/2-NPY ratios (10) indicative of showing resolution of all nitro-PAH isomers. 2-NFL was OH radical-initiated formation were observed for the Tokyo Winter

Table 2 Ambient concentrations of filter associated nitro-PAHs (pg m 3)a: see Supplementary Information for details on sample collection.

Nitro-PAH Riverside nighttime Riverside daytime Tokyo 24 h Mexico City

#1 #2 #3 #4 #1 #2 #3 #4 Summer Winter #1 #2 #3 #4 #5 7-NFLb NDc 0.1 0.01 NDc NDc 0.1 0.06 0.01 NDc NDc 0.2 0.1 0.5 0.2 0.9 2-NFL 216 171 46 127 49 99 56 76 80 137 37 14 156 62 325 3-NFL 0.2 0.5 0.2 0.2 0.5 0.6 0.3 0.4 1.0 13 0.3 0.3 0.2 0.5 1.0 4-NPY 0.9 0.7 0.3 0.2 0.2 0.2 0.1 0.2 0.5 1.3 0.5 0.4 1.4 0.9 2.1 8-NFLb 0.3 0.7 0.1 0.2 1.2 0.7 0.3 0.3 0.6 12 0.7 0.3 2.0 1.1 3.9 1-NPY 2.7 6.3 3.0 2.7 2.5 7.4 4.3 5.5 21 34 4.1 5.3 14 5.2 23 2-NPY 3.0 6.2 0.9 2.0 4.8 5.2 2.3 4.8 4.8 20 7.6 2.4 73 24 83

2-NFL/2-NPY 72 28 51 63 10 19 24 16 17 7 56234 2-NFL/1-NPY 80 27 15 47 20 13 13 14 4 4 9 3 11 12 14

12-NBaAb 0.8 1.9 0.3 0.6 0.3 0.7 0.2 0.7 1.0 3.4 1.0 0.2 4.7 2.5 1.0 7-NBaA 3.7 6.2 1.1 2.3 1.2 0.9 0.4 1.0 13 28 5.9 1.0 35 16 6.1 1-NTP 0.6 1.8 0.8 0.2 1.7 0.6 1.5 0.3 9.3 33 0.4 0.1 0.8 0.4 0.3 6-NCHR 0.07 0.1 0.03 0.02 0.1 0.1 0.05 0.04 0.2 0.4 NDc NDc NDc NDc NDc 2-NTP 0.9 0.8 0.2 0.1 1.1 0.9 0.3 0.2 6.2 17 0.3 0.2 0.6 0.3 0.4

2-NFL/SNTPs 144 66 46 423 18 66 31 152 5 3 53 47 111 89 464 1-NPY/SNTPs 1.8 2.4 3.0 9.0 0.9 4.9 2.4 11 1.4 0.7 5.8 18 10 7.4 33

a Quantification was done using a 30 m DB-17 column. b Concentrations were calculated using an assumed response factor of 1. c ND: not detected, below detection limit. K. Zimmermann et al. / Atmospheric Environment 55 (2012) 431e439 437

mw 247 mw 273

3 5 6 8 9 10 11 A 7-NBaA 21 4 12 x1 x4



2 6 B 2-NFL 1 34 5 7 12-NBaA 7-NBaA x20 x250



C 2-NFL 1-NTP x140 x140 12-NBaA 3-NFL

1-NPY 4-NPY 7-NBaA 2-NTP 8-NFL 2-NPY

Fig. 4. Comparison of GC-MS/NCI ion chromatograms for mw 247 and 273 nitro-PAHs using a DB-17 column for (A) diesel NIST SRM 1975; (B) Riverside Nighttime #3; and (C) Tokyo Winter. The identification of isomers are: (1) 7-NFL, (2) 2-NFL, (3) 3-NFL, (4) 4-NPY, (5) 8-NFL, (6) 1-NPY, (7) 2-NPY, (8) 12-NBaA, (9) 7-NBaA, (10) 1-NTP, (11) 6-NCHR, and (12) 2- NTP. Note that in (A), 1-NPY is off-scale (see Table S4 for concentrations). It is important to note the low sensitivity for 2-NPY and 2-NTP when using GC-MS/NCI. Isomer iden- tifications were confirmed using a DB-5 column. sample, all Mexico City samples, and Riverside Daytime #1 (Fig. 5). High 2-NFL/2-NPY ratios were observed for the Riverside nighttime 80 0.4 fi samples, suggesting a signi cant contribution of NO3 radical 70 chemistry to nitro-PAH formation. The lower 2-NFL/1-NPY ratios

(Table 2) observed in Mexico City and Tokyo suggest higher 60 0.3 Σ NTPs/2-NFL contributions of direct emissions to the observed nitro-PAH levels, 50 while higher ratios in Riverside suggest a greater impact from atmospheric formation. 40 0.2 It has previously been suggested that 1-and 2-NTP in particulate 30 samples could arise from atmospheric formation from radical- 2-NFL/2-NPY initiated reactions of triphenylene (Ishii et al., 2001; Kameda 20 0.1 et al., 2004, 2006). As seen in Fig. 5, the highest ambient SNTPs/ 10 2-NFL ratios occurred in the Tokyo samples. For gas-phase radical- initiated reactions to produce a SNTPs/2-NFL ratio approaching 0.4 0 0.0 R R R R R R R R T T M M M M M > i i i i i i i i o o as seen in the winter Tokyo sample, or 1 as previously reported by v v v v v v v v k k e e e e e e e e e e e e e y y x x x xi x r r r r r r r r o o ic ic ic c ic Ishii et al. (2001), would require either significantly more gas-phase s s s s s s s s o o o o o id id id id id id id id 2 2 e e e e e e e e 4 4 C C C C C - - i i i i i TP than FL and/or a higher yield from the OH or NO3 radical- N N N N D D D D h h ty ty ty ty ty i i i i a a a a o o fi g g g g y yt y y u u # # # # # initiated formation of the NTPs than of 2-NFL, or a signi cantly h h h h t t t r r 1 2 3 4 5 tt tt tt tt im im im im S Wi im im im im u shorter lifetime for particle-phase 2-NFL than for the NTPs. While e e e e m n e e e e # # # # t fl # # # # 1 2 3 4 m e ambient concentrations of PAHs are in uenced by emissions and 1 2 3 4 e r meteorology, the profiles of FL, PY, BaA, CHR, TP (or CHR þ TP) on r the filters were all generally similar for the sites studied, with Fig. 5. 2-NFL/2-NPY ratios from ambient filter samples from each site (left axis, open S þ S þ þ > (FL PY) (BaA CHR TP) and FL TP (Table S5). Thus, there circles) are compared to the corresponding SNTPs/2-NFL (right axis, filled bars). The was no evidence on a relative basis that TP concentrations in Tokyo dashed line represents the approximate maximum 2-NFL/2-NPY ratio which is were higher than in Riverside or Mexico City. Furthermore, the consistent with formation of nitro-PAHs via OH radical-initiated reactions (10). While majority of ambient FL and PY would not be collected on filters (see the OH radical is ubiquitous in sunlit atmospheres, the presence of the NO3 radical is more episodic and occurs at night since NO3 radicals photolyze rapidly. Note that the Table S6 for Mexico City data from PUF plugs located downstream lifetime of particles is sufficiently long that “carryover” from day to night and vice of filters), and the gas-phase concentrations of FL or PY in Riverside, versa can occur. 438 K. Zimmermann et al. / Atmospheric Environment 55 (2012) 431e439

Tokyo, and Mexico City are expected to have significantly exceeded Agency, the results and the contents of this publication do not the gas-phase TP concentration. As discussed above, the 2-NFL/ necessarily reflect the views and the opinions of the Agency. Mr. SNTPs ratios observed in our chamber reactions provide no William P. Harger and Ms. Sara M. Aschmann are thanked for evidence for higher NTP yields than 2-NFL yields in these reactions. technical assistance. The limited literature data concerning the loss processes of particle-bound NTPs and 2-NFL (Fan et al.,1996a,b; Ishii et al., 2001) Appendix. Supplementary data suggest that the loss of particle-bound 2-NFL by photolysis and by S reaction with O3 is unlikely to explain the high NTPs/2-NFL ratios Supplementary data related to this article can be found online at observed in Tokyo (see Supplementary Information, section S5). doi:10.1016/j.atmosenv.2012.03.016. Unique loss processes for Tokyo resulting in decreased stability for 2-NFL in comparison with other cities also seems unlikely. References It does not appear that gas-phase OH radical-initiated chemistry S can explain the high NTP concentrations (and high NTPs/2-NFL Arey, J., Zielinska, B., Atkinson, R., Winer, A.M., Ramdahl, T., Pitts Jr., J.N., 1986. The ratios) observed in Japan. Consistent with this expectation, for formation of nitro-PAH from the gas-phase reactions of fluoranthene and pyr- Mexico City, a site dominated by OH radical chemistry based on the ene with the OH radical in the presence of NOx. Atmospheric Environment 20, e fi 2339 2345. 2-NFL/2-NPY ratios [and con rmed by observed alkylnitronaph- Arey, J., 1998. Atmospheric reactions of PAHs including the formation of nitroarenes. thalene isomer distribution patterns (Wang et al., 2010)], the ratios In: Neilson, A.H. (Ed.), The Handbook of Environmental Chemistry. PAHs and Related Compounds, vol. 3. Springer-Berlag, Berlin, Germany, pp. 347e385. Part I. of 2-NFL/SNTPs ranged from 47e464 (Table 2). In our chamber NO3 Atkinson, R., Arey, J., Zielinska, B., Aschmann, S.M., 1990. Kinetics and nitro-products and N2O5/NO3 reactions, 2-NFL formation far exceeded NTP of the gas-phase OH and NO3 radical-initiated reactions of -d8, formation (Fig. 3). Consistent with NO3 radical-initiated reaction fluoranthene-d10, and pyrene. International Journal of Chemical Kinetics 22, producing far more 2-NFL than NTPs, the Riverside nighttime 999e1014. Atkinson, R., Arey, J., 2007. Mechanisms of the gas-phase reactions of aromatic samples influenced by NO3 radical chemistry had ratios of 2-NFL/ hydrocarbons and PAHs with OH and NO3 radicals. Polycyclic Aromatic SNTPs ranging from 46e423 (Table 2). Thus, gas-phase NO3 radical- Compounds 27, 15e40. initiated chemistry also cannot explain the high NTP concentra- Bamford, H.A., Bezabeh, D.Z., Schantz, M.M., Wise, S.A., Baker, J.E., 2003. Determi- tions observed in Japan. nation and comparison of nitrated-polycyclic aromatic hydrocarbons measured in air and diesel particulate reference materials. Chemosphere 50, 575e587. As discussed above, our data suggest that the NTPs in the NO3 Bamford, H.A., Baker, J.E., 2003. Nitro-polycyclic aromatic hydrocarbon concentra- and N2O5/NO3 chamber reactions were formed partly, if not mainly, tions and sources in urban and suburban atmospheres of the Mid-Atlantic region. Atmospheric Environment 37, 2077e2091. by heterogeneous reaction of gaseous N2O5 with TP on the filter. In S Ciccioli, P., Cecinato, A., Brancaleoni, E., Frattoni, M., Zacchei, P., Miguel, A.H., our chamber reactions, (1-, 3-, 7-, and 8-NFL-d9) and 1-NPY-d9 Vasconcellos, P. de C., 1996. Formation and transport of 2-nitrofluoranthene and were formed heterogeneously on the filters in >6-fold higher 2-nitropyrene of photochemical origin in the troposphere. Journal of Geophysical Research (Atmospheres) 101, 19567e19581. abundance than 1- þ 2-NTP-d11 (Fig. 3). Therefore, if heterogeneous Fan, Z., Kamens, R.M., Hu, J., Zhang, J., McDow, S., 1996a. Photostability of nitro- formation of NTPs by reaction with N2O5 were important in polycyclic aromatic hydrocarbons on combustion soot particles in sunlight. ambient atmospheres, 1-, 3-, 7-, and 8-NFL and 1-NPY would be Environmental Science and Technology 30, 1358e1364. expected to be formed in greater abundance than the NTPs. Fan, Z., Kamens, R.M., Zhang, J., Hu, J., 1996b. Ozone-nitrogen dioxide-NPAH heterogeneous soot particle reactions and modeling NPAH in the atmosphere. Recognizing that 1-NPY is also directly emitted, the high 2-NFL/1- Environmental Science and Technology 30, 2821e2827. NPY ratios in the Riverside Nighttime samples (Table 2) suggest Feilberg, A., Poulsen, M.W.B., Nielsen, T., Skov, H., 2001. Occurrence and sources of that heterogeneous formation of 1-NPY and, by inference, NTPs by particulate nitro-polycyclic aromatic hydrocarbons in ambient air in Denmark. Atmospheric Environment 35, 353e366. N2O5 is much less important than formation of 2-NFL by gas-phase IARC monographs on the evaluation of carcinogenic risks to humans. In: Diesel and NO3 radical-initiated reaction. Therefore, the high NTP concentra- Engine Exhausts and Some Nitroarenes, vol. 46, 1989. World Health tions observed in Tokyo do not appear to be explained by hetero- Organization, International Agency for Research on Cancer, Lyon, France. geneous N O reactions, and this conclusion is consistent with that IPCS, 2003. Environmental Health Criteria 229: Selected Nitro- and Nitro-oxy- 2 5 polycyclic Aromatic Hydrocarbons. International Programme on Chemical reached by Kamens et al. (1990) from laboratory studies of PAH Safety, World Health Organization, Geneva, Switzerland. reactions with N2O5 on diesel particles. The absence of significant Ishii, S., Hisamatsu, Y., Inazu, K., Kadoi, M., Aika, K., 2000. Ambient measurement of 6-NCHR in the Tokyo samples (Fig. S6) also argues against hetero- nitrotriphenylenes and possibility of nitrotriphenylene formation by atmo- spheric reaction. Environmental Science and Technology 34, 1893e1899. geneous N2O5 reactions producing the NTPs observed in Tokyo (see Ishii, S., Hisamatsu, Y., Inazu, K., Aika, K., 2001. Environmental occurrence of Supplementary Information, section S6, for additional discussion). nitrotriphenylene observed in airborne particulate matter. Chemosphere 44, A 1-NPY/SNTPs ratio of w360 is obtained from the analysis of 681e690. S Iversen, B., Sydnes, L.K., Greibrokk, T., 1985. Characterization of nitro- the SRM 1975, while Kameda et al. (2006) reported a 1-NPY/ NTPs benzanthracenes and nitrodibenzanthracenes. Acta Chemica Scandinavica 39B, ratio of w5 for particles collected from a 1988 Nissan Civilian diesel 837e847. vehicle. Ambient 1-NPY/SNTPs ratios ranged from 0.7e33 (Table 2), Kameda, T., Takenaka, N., Bandow, H., Inazu, K., Hisamatsu, Y., 2004. Determination of atmospheric nitro-polycyclic aromatic hydrocarbons and their precursors at with the values from Tokyo being at the low end of this range. a heavy traffic roadside and at a residential area in Osaka, Japan. Polycyclic Although our chamber results confirm that atmospheric reactions Aromatic Compounds 24, 657e666. will produce NTPs, they also suggest that neither gas-phase radical- Kameda, T., Inazu, K., Hisamatsu, Y., Takenaka, N., Bandow, H., 2006. Isomer distribution of nitrotriphenylenes in airborne particles, diesel exhaust particles, initiated reactions nor heterogeneous N2O5 reactions of TP are and the products of gas-phase radical-initiated nitration of triphenylene. responsible for the high concentrations of NTPs observed in the Atmospheric Environment 40, 7742e7751. Tokyo ambient samples. Direct emissions of NTPs may be respon- Kamens, R.M., Guo, J., Guo, Z., McDow, S.R., 1990. Polynuclear aromatic hydrocarbon sible, and more work to identify the sources of these highly degradation by heterogeneous reactions with N2O5 on atmospheric particles. Atmospheric Environment 24A, 1161e1173. mutagenic (Ishii et al., 2001) NTPs is clearly warranted. Marino, F., Cecinato, A., Siskos, P.A., 2000. Nitro-PAH in ambient particulate matter in the atmosphere of Athens. Chemosphere 40, 533e537. Acknowledgements Nielsen, T., 1984. Reactivity of polycyclic aromatic hydrocarbons toward nitrating species. Environmental Science and Technology 18, 157e163. Nishino, N., Atkinson, R., Arey, J., 2008. Formation of nitro products from the gas- The authors thank the U.S. Environmental Protection Agency phase OH radical-initiated reactions of , naphthalene, and : (Grant No. R833752) and the University of California Agricultural effect of NO2 concentration. Environmental Science and Technology 42, 9203e9209. Experiment Station for supporting this research. While this work Pitts Jr., J.N., Sweetman, J.A., Zielinska, B., Atkinson, R., Winer, A.M., Harger, W.P., has been supported in part by the U.S. Environmental Protection 1985. Formation of nitroarenes from the reaction of polycyclic aromatic K. Zimmermann et al. / Atmospheric Environment 55 (2012) 431e439 439

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