Comparison of Alkylnitronaphthalenes Formed in NO3 and OH Radical-Initiated Chamber Reactions with those Observed in Ambient Air

Nitrated polycyclic aromatic hydrocarbons (nitro-PAHs) are potential human carcinogens and it has been postulated that their abundance profiles in ambient air in polluted urban areas are influenced by formation due to radical-initiated gas-phase reactions of their parent PAR. In this work, the isomer distributions and yields of the nitroarenes formed from the gas-phase reactions of naphthalene and alkylnaphthalenes with NO3 radicals are reported. For the first time, a mixture of ethylnaphthalenes and dimethylnaphthalenes with relative abundances matching those observed in ambient air has been reacted with OH radicals and with NO3 radicals to generate isomer profiles of ethylnitronaphthalenes (ENNs) and dimethylnitronaphthalenes (x,yDMzNNs; where, for example, 2,7-dimethyl-4-nitronaphthalene = 2,7DM4NN) for comparison with ambient samples. The atmospheric formation rates of ENNs/DMNNs from NO3 radical reactions were calculated and the isomers with the highest mass formation rates are 2,7DM4NN, 1,2DM4NN, 2,6DM4NN, 2,6DM1NN, 1,6DM8NN, 2,7DM1NN, 1,6DM5NN, and 2-ethyl-4-nitronaphthalene. From a comparison of the chamber reaction product profiles with ambient air samples, the ratios of 2-methyl-4-nitronaphthalene/1-methyl-5-nitronaphthalene and of 2,7DM4NN/1,7DM5NN are proposed to be sensitive markers of nitroarene formation from NO3 versus OH radical chemistry.