Gawler, Kate Susan; (2006) Kinetic studies of halogen oxide free radical reactions of importance in the atmosphere. Doctoral thesis , UCL (University College London).

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Abstract

The aim of this research was to characterise the kinetics of key gas phase reactions between free radicals which occur in the atmosphere. In particular, the reactions that have been focused on are reactions where uncertainties are apparent in the reported kinetics and are: CIO + CIO + M C1202 + M CIO + H02 -> HOC1 + 02 BrO + BrO -> Products In the atmosphere, subsequent production of halogen atoms (X = CI, Br) following these reactions leads to ozone loss. X + 03 XO + O2 and repetition of these radical reactions renders this ozone loss process catalytic. Under sunlit conditions the self or cross-reactions of CIO or BrO constitute the rate limiting step in the ozone loss process. Consequently, accurate knowledge of the rate coefficients and products of these reactions under appropriate atmospheric conditions is essential when assessing the extent of halogen-induced atmospheric ozone depletion. These reactions were studied using flash photolysis coupled with UV absorption spectroscopy. The spectroscopy incorporated charge coupled device (CCD) technology, which facilitated rapid timescale broad band data acquisition giving rise to accurate and unequivocal monitoring of multiple species. Classical or numerical models were used to simulate experimental data by optimising kinetic parameters. The improvements in both accuracy and precision of radical monitoring associated with the CCD studies have led to a considerable improvement in our understanding of the roles of these free radical reactions in the Earth's atmosphere.

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