Kinetic study of the OH and Cl-initiated oxidation, lifetimes and atmospheric acceptability indices of three halogenated ethenes

Abstract

The gas-phase kinetics for the reactions of OH radicals and Cl atoms with (E/Z)-CHClCHF, (E/Z)-CFClCFCl, and CCl₂CF₂ were investigated at room-temperature and atmospheric pressure. A conventional relative-rate technique was used to determine the rate coefficients k(OH + (E/Z)-CHClCHF) = (6.3 ± 1.2) × 10⁻¹², k(OH + (E/Z)-CFClCFCl) = (1.6 ± 0.2) × 10⁻¹², k(OH + CCl₂CF₂) = (5.0 ± 0.7) × 10⁻¹², k(Cl + (E/Z)-CHClCHF) = (11 ± 2) × 10⁻¹¹, k(Cl + (E/Z)-CFClCFCl) = (5.4 ± 1.3) × 10⁻¹¹, and k(Cl + CCl₂CF₂) = (6.3 ± 1.5) × 10⁻¹¹ cm³ per molecule per s. These rate coefficients were compared with previous literature data to analyze the effect of halogen substitution in ethenes on the reactivity towards OH and Cl, and used to estimate the global atmospheric lifetimes for the studied haloethenes. The calculated lifetimes, using average global concentrations of OH radicals and Cl atoms, indicate that the atmospheric loss of these compounds is determined by the OH-initiated oxidation. Also, the atmospheric implications of the halogenated ethenes studied were evaluated by estimating acceptability indices such as the global warming potential (GWP) and the ozone depletion potential (ODP). From these potentials, the contribution of (E/Z)-CHClCHF, (E/Z)-CFClCFCl, and CCl₂CF₂ to radiative forcing of climate change and to ozone layer depletion is expected to be negligible.