Kinetics of the HO2 + NO2 Reaction: On the impact of new gas-phase kinetic data for the formation of HO2NO2 on HOx, NOx and HO2NO2 levels in the troposphere

The rate coefficient for the reaction HO2 + NO2 has been measured using a turbulent flow technique with high pressure chemical ionization mass spectrometry for the detection of reactants. The rate constant was measured between 75 and 700 Torr and at 298, 223 and 200 K. This work represents the first experimental evaluation of this rate coefficient at temperatures below 219 K. The kinetic data has been evaluated in both a global 3-dimensional atmospheric chemistry model of the troposphere and in a steady-state model. These new data improve the agreement between the steady-state model and field measurements but an unresolved discrepancy remains. Field measurements suggest that some pernitric acid may persist in the upper troposphere and if this background is taken into consideration together with these new kinetic data, good agreement between steady-state models and measurements emerge. Global model runs show that on average HO2NO2 levels are reduced by 30-40% in the upper troposphere and 20-30% in the free troposphere. This reduction in HO2NO2 leads to increases in HOx and NOx in the upper troposphere, most notably a rise of 1-12% in OH and around 5% in NOx. (C) 2011 Elsevier Ltd. All rights reserved.