INFLUENCE OF THE HETEROGENEOUS REACTION HCL+HOCL ON AN OZONE HOLE MODEL WITH HYDROCARBON ADDITIONS

Injection of ethane or propane has been suggested as a means for reduc ing ozone loss within the Antarctic vortex because alkanes can convert active chlorine radicals into hydrochloric acid. In kinetic models of vortex chemistry including as heterogeneous processes only the hydrol ysis and HCI reactions of ClONO2 and N2O5, parts per billion by volume levels of the light alkanes counteract ozone depletion by sequesterin g chlorine atoms. Introduction of the surface reaction of HCl with HOC l causes ethane to deepen baseline ozone holes and generally works to impede any mitigation by hydrocarbons. The increased depletion occurs because HCl + HOCl can be driven by HO(x) radicals released during org anic oxidation. Following initial hydrogen abstraction by chlorine, al kane breakdown leads to a net hydrochloric acid activation as the rema ining hydrogen atoms enter the photochemical system. Lowering the rate constant for reactions of organic peroxy radicals with CIO to 10(-13) cm3 molecule-1 s-1 does not alter results, and the major conclusions are insensitive to the timing of the ethane additions. Ignoring the or ganic peroxy radical plus ClO reactions entirely restores remediation capabilities by allowing HO(x) removal independent of HCI. Remediation also returns if early evaporation of polar stratospheric clouds leave s hydrogen atoms trapped in aldehyde intermediates, but real ozone los ses are small in such cases.