The presence of a monolayer of surfactant material at the air-water interface of the lung is crucial for respiratory function. It is well known that exposure to the ubiquitous pollutant ozone damages this surfactant layer but the details of the process are still poorly understood. We propose to study monolayers of freshly extracted neat bovine lung surfactant and the purified natural proteins (SP-B and SP-C) at the air-water interface during exposure to very low levels of ozone gas. Our preliminary experiments reveal dramatic changes to the surface tension when natural surfactant is exposed to ozone. The key objectives are to determine if the lipids and/or the proteins initially leave the interface when damaged by ozone, are removed following successive compression/expansion cycles or remain at the interface and thus alter its surface properties.