Evaluation of updated nitric acid chemistry on ozone precursors and radiative effects

Abstract. This study shows that revising the reaction rate of NO₂ + HO^· → HNO₃ improves simulated nitrogen partitioning and changes the simulated radiative effects of several short-lived climate forcers (SLCF). Both laboratory and field study analyses have found that the reaction rate should be reduced by 13–30% from current recommendations. We evaluate the GEOS-Chem model over North America with and without the recommended update using observations from the Intercontinental Chemical Transport Experiment – North America (INTEX-NA) Phase A campaign. Revising the NO₂ + HO^· → HNO₃ rate coefficient improves model performance of oxidized nitrogen partitioning by increasing NO_x concentrations in the upper troposphere and decreasing HNO₃ throughout the troposphere. The increase in NO_x concentrations has a corresponding global increase in O₃ concentrations and local increases in sulfate aerosols, causing a perturbation in simulated radiative effects. These findings demonstrate the positive influence the mechanism update has on the partitioning of oxidized nitrogen species, the benefits it provides when compared to aircraft observations, and the simulated radiative effects that the reduction induces.