Laboratory and modelling studies of the reactions of peroxy radicals with XO (where X = Cl, Br or I).

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Halogen chemistry can play a vital role in controlling the budgets of ozone, NOx, NOy and HOx throughout the troposphere and the importance of these families in determining atmospheric composition, the earth's radiative balance and any future change in climate can not be over-emphasised. However, there is a major gap in the kinetic database, in that there is little or no data for sub ambient temperatures and where data is available the picture is far from clear, and thus does not allow the full atmospheric importance of the coupling of halogen chemistry with peroxy radicals to be assessed. An integrated programme of laboratory and modelling studies is proposed to study a key set of peroxy radical reactions, namely RO2 + XO. A state of the art experimental system, a turbulent flow chemical ionisation mass spectrometer, that enables direct experimental acess to atmospherically relevant teperatures and pressures will be used to determine kinetic and mechanistic parameters. The experimental results will be raionalised using state of the art ab - intio calculations and then be incorporated into a global atmospheric model which allows the atmospheric importance of the interacttion of peroxy radicals with XO radicals to be assessed. The proposed work will be invaluable for the rationalisation of the effect of halogen chemistry on atmospheric pollution and climate change