Effect of NO₂ concentration on dimethylnitronaphthalene yields and isomer distribution patterns from the gas-phase OH radical-initiated reactions of selected dimethylnaphthalenes.
Dimethylnitronaphthalene (DMNN) formation yields from the reactions of 1,7- and 2,7- dimethylnaphthalene (DMN) with OH radicals were measured over the NO(2) concentration range 0.04-1.4 ppmv. The measured DMNN formation yields under conditions that the OH-DMN adducts reacted solely with NO(2) were 0.252 ± 0.094% for Σ1,7-DMNNs and 0.010 ± 0.005% for Σ2,7-DMNNs. 1,7-DM-5-NN was the major isomer formed, with a limiting high-NO(2) concentration yield of 0.212 ± 0.080% and with equal reactions of the adduct with NO(2) and O(2) occurring in air at 60 ± 39 ppbv of NO(2). The reactions of the OH-DMN adducts with NO(2) must therefore result in products other than DMNNs. Although the yields of the DMNNs are low, ≤0.3%, the DMNN (and ethylnitronaphthalene) profiles from chamber experiments match well with those observed in polluted urban areas under conditions where OH radical-initiated chemistry is dominant. Daytime OH radical and nighttime NO(3) radical reactions appear to account for the alkylnitronaphthalenes formed and their observed profiles under most urban atmospheric conditions, with profiles reflecting daytime OH chemistry modified by contributions from isomers formed by any NO(3) radical chemistry that had occurred. Since the formation yields and NO(2) dependencies for the formation of a number of alkylnitronaphthalenes have now been measured, the effect of NO(x) emissions control strategies on their atmospheric formation can be quantitatively assessed, and the decrease in formation of these genotoxic species may provide a previously unrecognized health benefit of NO(x) control.