Extensive measurements of ozone and its photochemical precursors and coproducts were made in the 1990 Rural Oxidants in the Southern Environment (ROSE) program. Peroxy radical production, loss, and partitioning are described at a rural site in Alabama, showing the important role that biogenic organic compounds play in ozone production. Estimates of the peroxy radical concentration obtained by four methods along with the measured nitric oxide level are used to predict the instantaneous rate of photochemical ozone production at the site. The four methods agree on the diurnal behavior of peroxy radicals and ozone production rates, while consistent discrepancies between the methods generally are within their combined uncertainties. Selected aircraft measurements are used to derive ozone production rates above the ground site, with the highest rates occurring in the boundary layer and in industrial plumes. The dependences of peroxy radical concentration and ozone production rate on the level of nitrogen oxides exhibit good agreement between the various methods and are consistent throughout the lower troposphere. Surface deposition and entrainment are shown to be as important as photochemical production in determining the diurnal evolution of ozone at this site. ¿ 1998 American Geophysical Union