Heterogeneous Reactions of Particulate Matter-Bound PAHs and NPAHs with NO(3)/N(2)O(5), OH Radicals, and O(3) under Simulated Long-Range Atmospheric Transport Conditions: Reactivity and Mutagenicity

[Image: see text] The heterogeneous reactions of ambient particulate matter (PM)-bound polycyclic aromatic hydrocarbons (PAHs) and nitro-PAHs (NPAHs) with NO(3)/N(2)O(5), OH radicals, and O(3) were studied in a laboratory photochemical chamber. Ambient PM(2.5) and PM(10) samples were collected from Beijing, China, and Riverside, California, and exposed under simulated atmospheric long-range transport conditions for O(3) and OH and NO(3) radicals. Changes in the masses of 23 PAHs and 20 NPAHs, as well as the direct and indirect-acting mutagenicity of the PM (determined using the Salmonella mutagenicity assay with TA98 strain), were measured prior to and after exposure to NO(3)/N(2)O(5), OH radicals, and O(3). In general, O(3) exposure resulted in the highest relative degradation of PM-bound PAHs with more than four rings (benzo[a]pyrene was degraded equally well by O(3) and NO(3)/N(2)O(5)). However, NPAHs were most effectively formed during the Beijing PM exposure to NO(3)/N(2)O(5). In ambient air, 2-nitrofluoranthene (2-NF) is formed from the gas-phase NO(3) radical- and OH radical-initiated reactions of fluoranthene, and 2-nitropyrene (2-NP) is formed from the gas-phase OH radical-initiated reaction of pyrene. There was no formation of 2-NF or 2-NP in any of the heterogeneous exposures, suggesting that gas-phase formation of NPAHs did not play an important role during chamber exposures. Exposure of Beijing PM to NO(3)/N(2)O(5) resulted in an increase in direct-acting mutagenic activity which was associated with the formation of mutagenic NPAHs. No NPAH formation was observed in any of the exposures of the Riverside PM. This was likely due to the accumulation of atmospheric degradation products from gas-phase reactions of volatile species onto the surface of PM collected in Riverside prior to exposure in the chamber, thus decreasing the availability of PAHs for reaction.