Temperature and pressure dependence of the rate coefficient for the reaction between ClO and CH3O2 in the gas-phase

Abstract

A temperature and pressure kinetic study for the CH₃O₂ + ClO reaction has been performed using the turbulent flow technique with a chemical ionisation mass spectrometry detection system. An Arrhenius expression was obtained for the overall rate coefficient of CH₃O₂ + ClO reaction: k₁₀(T) = (1.96^+0.28_−0.24) × 10⁻¹¹ exp[(−626 ± 35)/T] cm³ molecule⁻¹ s⁻¹ where the uncertainty associated with the rate coefficient is given at the one standard deviation level. Over a range of pressure (100–200 Torr) and temperature (298–223 K) no pressure dependence is observed. The smaller rate coefficients measured at lower temperatures compared with both previous low temperature studies are believed to arise through the reduction of secondary chemistry and greater sensitivity in terms of reactant detection (hence much lower initial concentrations were employed). These new data reduce the effectiveness of ozone loss cycles involving reaction of CH₃O₂ + ClO in the polar stratosphere by around a factor of 1.5 and restrict the importance of the reaction to the tropical and extra-tropical clean marine environments in the troposphere.