Abstract

Halogen oxide radicals, XO (where X = Cl, Br, I), are known to self- and cross-interact in cycles leading to catalytic depletion of atmospheric ozone in both the troposphere and the stratosphere. The former affects the atmospheric oxidative capacity, and hence the lifetime of pollutants including greenhouse gases. This perturbation of oxidants may also have implications for regional air quality. The latter, stratospheric ozone loss, affects solar UV radiation.

But, whilst the self- and cross-reactions of halogen oxide free radicals are important, their interactions with other species, notably peroxy radicals formed through HOx and VOC degradation chemistry are far less well characterised. These reactions of XO + RO2 (R = H or CH3 ) are key, since they control the effect of XO chemistry on atmospheric ozone in regions where the halogen oxide concentration is not especially elevated.

This talk will show results from some of our recent studies of the XO + RO2 reactions in the laboratory. Aside from the fundamental kinetics of these processes, we have also assessed the branching ratios, which dictate the extent that these reactions contribute to the destruction of ozone and their subsequent consequences.