The Earth¿s climate is strongly influenced by atmospheric aerosols. Organic surfactant films on these aerosols influences their size, optical properties and ability to act as cloud condensation nuclei, hence leading to climatic effects. The magnitude of the climatic effects depends upon the fate of the organic films following atmospheric oxidation. We propose to monitor the air-water interface when monolayers of oleic acid on salt solutions are oxidised by gaseous ozone. The objectives are:1) To determine the rate at which the film is destroyed 2) To investigate how the composition of the bulk phase affects the properties of the product interface. The experiment follows up very successful preliminary investigations where it was demonstrated that neutron reflection is a valuable tool to study novel climatic problems.