UV Absorption Cross Sections of ClOOCl Are Consistent with Ozone Degradation Models

Abstract

Cl in the Sunlight A major assumption in the long-standing mechanistic model for halogen-induced degradation of stratospheric ozone is the steady generation of Cl atoms by photolysis of molecules such as ClOOCl by sunlight. Recently, however, laboratory data raised uncertainties in the ClOOCl absorption cross sections underlying this assumption. Chen et al. (p. 781 ) undertook precise mass-sensitive cross-section measurements to explore the discrepancy. Molecules were directly quantified before and after ultraviolet photolysis, avoiding interference from impurity or by-product absorptions that can plague more traditional detection schemes that measure attenuation of a light beam. The measured cross sections at two different ultraviolet wavelengths proved well within the margin necessary to support standard models of ozone degradation.