Measurement of the rate coefficient for the OHÂ +Â NO2 reaction under the atmospheric pressure: Its humidity dependence

Humidity dependence of the rate coefficient of the OH + NO2 reaction has been studied. The rate coefficients, measured at the H2O partial pressures (PH2O) of 29.1 and 3.7 hPa and at 298 K are (1.15 ± 0.02) × 10−11 and (1.40 ± 0.10) × 10−11 cm3 molecule−1 s−1 (±2σ), respectively. The equilibrium constant of the NO2-H2O system estimated using ab initio calculations is too small to explain the retardation of the reaction under our experimental conditions. Thus, we conclude that the NO2-H2O cannot contribute significantly to the OH + NO2 reaction in the atmosphere near the ground surface.