Tropospheric and stratospheric sinks for halocarbons: Photooxidation, O(1D) atom, and OH radical reactions

Abstract

The photooxidation products of CCl4, CFCl3, CF2Cl2, and CHF2Cl at 184.9 nm have been determined to be COCl2, COFCl, COF2, and COF2, respectively, with quantum yields near unity measured for CCl4, CFCl3, and CF2Cl2. The same products are observed for the reaction Of O(1D) atoms with these halocarbons. Rate constants for the reaction of O(1D) atoms with CHF2Cl, CF2Cl2, CFCl3, CF2ClCF2Cl, CF2ClCFCl2, COF2, COFCl, CF4, and CCl4, relative to the rate constant for the reaction of O(1D) atoms with N2O, are 1.6, 2.4, 2.65, 1.5, 2.5, 0.29, 2.8, <0.1, and ≥3, respectively, and except for CF4 and COF2, approach collision frequency. The significance of these reactions and of OH radical attack as halocarbon loss processes in both the troposphere and the stratosphere is discussed. Thus O(1D) atom and/or OH radical reactions are shown to be major stratospheric loss processes for weakly absorbing species such as CHF2Cl.