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

The heterogeneous reactions of ambient particulate matter (PM)-bound polycyclic aromatic hydrocarbons (PAHs) and nitro-PAHs (NPAHs) with NO sub(3)/N sub(2)O sub(5), OH radicals, and O sub(3) were studied in a laboratory photochemical chamber. Ambient PM sub(2.5) and PM sub(10) samples were collected from Beijing, China, and Riverside, California, and exposed under simulated atmospheric long-range transport conditions for O sub(3) and OH and NO sub(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 sub(3)/N sub(2)O sub(5), OH radicals, and O sub(3). In general, O sub(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 sub(3) and NO sub(3)/N sub(2)O sub(5)). However, NPAHs were most effectively formed during the Beijing PM exposure to NO sub(3)/N sub(2)O sub(5). In ambient air, 2-nitrofluoranthene (2-NF) is formed from the gas-phase NO sub(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 sub(3)/N sub(2)O sub(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.