The Earth¿s climate is strongly influenced by clouds. The oxidative processing of pollutants in clouds affects cloud droplet size and optical properties, important climatic effects. Common cloud pollutants are naturally occurring organic surfactants forming organic films on the droplet. The magnitude of climatic effects depends upon the fate of the organic films following atmospheric oxidation. In this work we will measure the oxidation rate of OH radical with stearic acid as a function of temperature. Specifically:-(a) Measure the temperature dependence of the film oxidation rate for typical atmospheric conditions.(b) Determine the activation energy and pre-exponential factors and determine the sources of the activation barrier and describe the transition state.(c) Support an STFC/NERC case award student who will be based at ISIS 2008-2009.