Photochemical modeling and analysis of field data have been used to evaluate the effect of convective clouds on tropospheric trace gas chemistry. Observations were made during a 1985 field campaign over the rural south-central United States. Meteorological data and measurments of CO, NO, NOy, O3, and hydrocarbons were collected in air surrounding and inside clouds during and immediately following cloud convection. A one-dimensional photochemical model has been used to calculated O3 production potential before and after cloud redistribution of O3 precursor gases. Four distinct types of convective events have been analzyed. Fair weather cumulus clouds increase O3 production in a layer (to 4 km in the case studied). Outflow from deeper convection can cause enhanced O3 production in the upper troposphere hundreds of kilometers downstream from the clouds. A comparison of trace gas profiles measured in and around a large cumulonimbus during dissipation shows O3 production in the upper trosphere may be increased fourfold by convection relative to undisturbed air. Convection enhancement of O3 production for the entire tropospheric column is about 50%. Compared to nonurban continental regions with no convection, the rate of O3 production potential in air processed by convection is up to 3--4 times greater. Catalysis of O3 production becomes more efficient when NO becomes more dilute after being transported from the boundary layer to the free troposphere. Free tropospheric NO may also be enhanced by lightning, adding to O3 production, particularly when sufficient hydrocarbons are transported to such locations. ¿American Geophysical Union 1990