Humidity dependence of the rate coefficient of the OH + NO2 reaction has been studied. The rate coefficients, measured at the H2O partial pressures (P-H2O) of 29.1 and 3.7 hPa and at 298 K are (1.15 +/- 0.02) x 10(-11) and (1.40 + 0.10) x 10(-11) cm(3) molecule(-1) s(-1) (+/- 2 sigma), respectively. The equilibrium constant of the NO2-(HO)-O-2 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. (c) 2005 Elsevier B.V. All rights reserved.