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 night-time troposphere?

Abstract

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)× 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.