title: 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), 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.
authors.affiliation: Air Pollution Research Center, University of California , Riverside, California 92521, United States.
authors.forename: Kathryn
authors.initials: K
authors.lastname: Zimmermann
authors.forename: Narumol
authors.initials: N
authors.lastname: Jariyasopit
authors.forename: Staci L
authors.initials: SL
authors.lastname: Massey Simonich
authors.forename: Shu
authors.initials: S
authors.lastname: Tao
authors.forename: Roger
authors.initials: R
authors.lastname: Atkinson
authors.forename: Janet
authors.initials: J
authors.lastname: Arey
mesh_terms: D000327:Adsorption; D009589:Nitrogen Oxides / Q000737:chemistry*; D052638:Particulate Matter; D011084:Polycyclic Aromatic Hydrocarbons / Q000737:chemistry*; D013499:Surface Properties
chemical_list: D009589:Nitrogen Oxides; D052638:Particulate Matter; D011084:Polycyclic Aromatic Hydrocarbons