INVESTIGATION INTO THE KINETICS AND MECHANISM OF THE REACTION OF NO3 WITH CH3O2 AT 298-K AND 2.5-TORR - A POTENTIAL SOURCE OF OH IN THE NIGHTTIME TROPOSPHERE

The kinetics of the reaction CH3O2 + NO3 --> CH3O + NO2 + O2 (1) have been studied at 298 K and at pressures between 2 and 3 Torr of helium using the discharge-flow technique combined with laser-induced fluorescence detection of the methoxyl radical and measurements of the NO3 radical using visible absorption. Numerical modelling of the concentration-time profile of CH3O with or without NO3 and NO as a titrant has allowed us to show that CH3O is a product of reaction (1) and to derive a rate constant k1 = (1.0 +/- 0.6) x 10(-12) cm3 molecule-1 s-1, at 95% confidence limits. A comparison of the reactivities of NO3 and NO2 towards the species R, RO and RO2, where R = H or CH3, is given. The implication of reaction (1) in the possible production of OH in the atmosphere at night is discussed.