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

• Published in: Environmental science & technology Vol. 47; no. 15; pp. 8434 - 8442
• Main Authors: Zimmermann, Kathryn, Jariyasopit, Narumol, Massey Simonich, Staci L, Tao, Shu, Atkinson, Roger, Arey, Janet
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 06-08-2013
• Subjects: Adsorption; Applied sciences; Atmospheric pollution; Exact sciences and technology; Nitrogen Oxides - chemistry; Particulate Matter; Pollutants physicochemistry study: properties, effects, reactions, transport and distribution; Pollution; Polycyclic Aromatic Hydrocarbons - chemistry; Surface Properties; California; Asia; United States; North America; China; America; Nitro compound; Megacity; Pollutant formation; Nitrates; Urban area; Polycyclic aromatic compound; Mutagen; Free radical reaction; Persistent organic pollutant; Carcinogen; Nitrogen pentoxide; Atmospheric chemistry; Aerosols; Air pollution; Nitrogen dioxide; Organic compounds; Inorganic radical anion; Heterogeneous reaction
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/es401789x

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.