Exposure to ozone gas can cause inflammation of the airways and breathing difficulties. The initial reaction of ozone is thought to be predominantly with lipids present in the pulmonary surfactant. The main lipid component is the saturated lipid DPPC which does not react directly with ozone gas. Minor lipid components include unsaturated lipids such as POPC however not only react readily with gas phase ozone but our previous experiments at Isis revealed that the reaction of ozone with POPC can leads to the attack of the saturated species DPPC. The experiments to be performed in this proposal will probe the nature of the attack, in particular is it a minor pathway leading to the complete loss of some DPPC molecules from the interface when mixtures of DPPC:POPC are exposed to ozone, or, is it that the major pathway is leading to partial consumption of the acyl chains of DPPC.