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Abstract: Impact of the excited nitrogen dioxide (NO2 ∗) chemistry on air quality in the U.S. is examined using the Community Multiscale Air Quality (CMAQ) model for a summer month. Model simulations were conducted with and without the NO2 ∗ chemistry. The largest impact of the NO2 ∗ chemistry in the eastern U.S. occurred in the northeast and in the western U.S. occurred in Los Angeles. While the single largest daily maximum 8-h ozone (O3) increased by 9 ppbv in eastern U.S. and 6 ppbv in western U.S., increases on most days were much lower. No appreciable change in model performance statistics for surface-level O3 predictions relative to measurements is noted between simulations with and without the NO2 ∗ chemistry. Based on model calculations using current estimates of tropospheric emission burden, the NO2 ∗ chemistry can increase the monthly mean daytime hydroxyl radicals (OH) and nitrous acid (HONO) by a maximum of 28% and 100 pptv, respectively. [Copyright &y& Elsevier]

Predictions of nitrous acid from the Community Multiscale Air Quality modeling system are compared with the measurements from the 2001 Northeast Oxidant and Particle Study. Four different sources of nitrous acid were considered in the study: gas-phase reactions, direct emissions, a heterogeneous reaction, and a surface photolysis reaction. When only gas-phase reactions were considered in the model, the diurnally averaged mean bias, the normalized mean bias, the root mean square error, and the normalized mean error of the model were −1.01ppbv, −98%, 1.05ppbv, and 98%, respectively. However, the diurnally averaged mean bias, normalized mean bias, the root mean square error, and the normalized mean error of the model improved to −0.42ppbv, −41%, 0.45ppbv, and 41%, respectively, when all sources were considered. Model results suggest that the heterogeneous reaction and the surface photolysis reaction are the most important sources of nitrous acid in the atmosphere, accounting for about 86% of the predicted nitrous acid. Emissions and the gas-phase reactions were relatively minor sources and accounted for only 14% of the predicted nitrous acid. Model predictions suggest that the heterogeneous reaction is the most significant source of nitrous acid at night, while the surface photolysis reaction is the most significant source during the day. The addition of these sources increased the diurnally averaged hydroxyl radicals and ozone by 10% and 1.4ppbv, respectively. [Copyright &y& Elsevier]

Estimates the indoor hydroxyl radical concentrations with the use of an emerging indoor air quality model which employs an atmospheric chemistry model to simulate indoor homogenous reactions. Comparison of results with those taken from previous studies; Results of base case application; Effects of indoor alkene emission rates on indoor hydroxyl radical concentrations.