This paper reports results from the Southern Oxidants Study field campaign designed to characterize the formation and distribution of ozone and related species in the Nashville urban region. Data from several airborne platforms as well as surface observations on July 3 and 18 are examined to gain insight into the factors that control O3 formation rates and concentrations in the regional plumes. On both days, well-defined urban and power plant plumes were sampled. Utilizing both aircraft and surface data, a detailed kinetic analysis of the chemical evolution of the urban plume is performed to derive NOx lifetime, ozone production efficiency, OH concentration, HNO3 dry deposition rate, and the relative importance of natural and anthropogenic hydrocarbons to O3 production. Analysis of the urban plume data revealed a very active photochemical system (average ~1.2¿107 molecules cm-3) which consumed 50% of the NOx within approximately 2 hours, at an ozone production efficiency of 2.5 to 4 molecules for each molecule of NOx. Anthropogenic hydrocarbons provided approximately 44% of the fuel for ozone production by the urban plume. The dry deposition rate for HNO3 in the urban plume was estimated to be of the order of 5 to 7 cm s-1. ¿ 1998 American Geophysical Union