Atmospheric Reactions of PAHs Including Formation of Nitroarenes

The effect of phase distribution on the atmospheric fates of the PAHs, the important atmospheric loss processes, and the resulting atmospheric lifetimes of the PAHs are discussed. Gasphase PAH reactions are emphasized because it is these reactions which control the in-situ formation of nitroarenes in ambient atmospheres. Results from laboratory studies of PAH reactions and data on ambient nitroarene profiles are presented. Hydroxyl (OH) radical-initiated reactions of gas-phase PAHs generally limit their atmospheric lifetimes to less than 1 day. Both daytime OH radical-initiated and nighttime nitrate (NO₃) radical-initiated reactions of gas-phase PAHs lead to the formation of nitroarenes, which depending upon their vapor pressures may become particle-associated. Two classes of PAH atmospheric reaction products, nitroarenes and nitroarene lactones, have been found to contribute significantly to the mutagenic activity of ambient atmospheres suggesting that comprehensive risk assessments for atmospheric PAHs should include the potential health effects of their atmospheric reaction products.