Formation of Nitro-PAHs from the Heterogeneous Reaction of Ambient Particle-Bound PAHs with N₂O₅/NO₃/NO₂

Abstract

Reactions of ambient particles collected from four sites within the Los Angeles, CA air basin and Beijing, China with a mixture of N2O5, NO2, and NO3 radicals were studied in an environmental chamber at ambient pressure and temperature. Exposures in the chamber system resulted in the degradation of particle-bound PAHs and formation of molecular weight (mw) 247 nitropyrenes (NPYs) and nitrofluoranthenes (NFLs), mw 273 nitrotriphenylenes (NTPs), nitrobenz[a]anthracenes (NBaAs), and nitrochrysene (NCHR), and mw 297 nitrobenzo[a]pyrene (NBaP). The distinct isomer distributions resulting from exposure of filter-adsorbed deuterated fluoranthene to N2O5/NO3/NO2 and that collected from the chamber gas-phase suggest that formation of NFLs in ambient particles did not occur by NO3 radical-initiated reaction, but from reaction of N2O5, presumably subsequent to its surface adsorption. Accordingly, isomers known to result from gas-phase radical-initiated reactions of parent PAHs, such as 2-NFL and 2- and 4-NPY, were not enhanced from the exposure of ambient particulate matter to N2O5/NO3/NO2. The reactivity of ambient particles toward nitration by N2O5/NO3/NO2, defined by relative 1-NPY formation, varied significantly, with the relative amounts of freshly emitted particles versus aged particles (particles that had undergone atmospheric chemical processing) affecting the reactivity of particle-bound PAHs toward heterogeneous nitration. Analyses of unexposed ambient samples suggested that, in nighttime samples where NO3 radical-initiated chemistry had occurred, heterogeneous formation of 1-NPY on ambient particles may have contributed to the ambient 1-NPY concentrations at downwind receptor sites. These results, together with observations that 2-NFL is consistently the dominant particle-bound nitro-PAH measured in ambient atmospheres, suggest that for PAHs that exist in both the gas- and particle-phase, the heterogeneous formation of particle-bound nitro-PAHs is a minor formation route compared to gas-phase formation.

Particulate pollutants in the Brazilian city of São Paulo: 1-year investigation for the chemical composition and source apportionment

“…They have been studied because of their carcinogenic properties (de Oliveira Seinfeld and Pandis, 2006). The nitrated and oxygenated PAHs (nitroand oxy-PAHs) are emitted as primary species or are formed in situ as secondary compounds (Kojima et al, 2010;Souza et al, 2014b;Zhou and Wenger, 2013;Zimmermann et al, 2013). They are potentially more mutagenic and/or carcinogenic than their PAH precursors (Franco et al, 2010).…”

Effects of Humidity and [NO3]/[N2O5] Ratio on the Heterogeneous Reaction of Fluoranthene and Pyrene with N2O5/NO3/NO2

“…1, 24,35,43 Additionally, this experimental result was also consistent with the observation reported by Zimmermann et al 24 They found that under actual ambient conditions where N 2 O 5 /NO 3 /NO 2 was present, very little possible formation of 1-NPY occurred in comparison with 2-NFL formation. 27 Thereby, we concluded that only small amount of 1-NPY may be formed through the heterogeneous processing of PY with atmospheric oxidants in the real atmosphere. Besides 1-NPY, 2-NPY, and a trace amount of 4-NPY were also observed in the heterogeneous reaction of PY under low humidity (0.5% RH).…”

Theoretical study on atmospheric reactions of fluoranthene and pyrene with N2O5/NO3/NO2

“…3-NFL and 1-NPY observed in the atmosphere possibly originate from primary emissions or heterogeneous reactions. In addition, because of the different reaction processes, the heterogeneous reactions of FL and PY with N 2 O 5 /NO 3 /NO 2 are quite different from the gas-phase reactions under atmospheric conditions, which produces 3-, 8-, 7-, 1-NFL, and 1-NPY as the major particulate nitration products [21]. However, 2-NFL is considered as the dominant particle-bound NPAH measured in ambient atmospheres, which possibly originates mainly from the gas-phase NO 3 reaction and condensation on the aerosol surface.…”

“…In addition, the rate constants of the NO 3 -initiated reaction (in the order of 10 −17 cm 3 molecule −1 s −1 ) were considered to be close to those of the N 2 O 5 reaction. More recent studies [12,21] have also suggested that 2-NFL and 2-/4-NPY are generated from the gasphase NO 3 -initiated reactions of FL and PY, respectively. Hence, the experimental results of the products and kinetics of FL and PY in the reaction with N 2 O 5 /NO 3 /NO 2 , as well as the postulated reaction mechanisms of N 2 O 5 with PAHs, need to be further confirmed theoretically.…”