A conceptual model of O3 pollution in El Paso, TX, was developed to examine factors associated with O3 pollution in the El Paso metropolitan area and in the greater Paso del Norte (PdN) region, which includes El Paso County, TX southern Dona Ana County, NM, and Ciudad Juarez, Chihuahua, Mexico. The model follows guidelines established by EPA for developing attainment demonstrations for the 2008 8-hr O3 NAAQS. Both surface and upper air meteorology influenced high O3 days in El Paso. Wind statistics were very similar at monitoring stations along the El Paso-Juarez border where high O3 levels were often reported. High O3 concentrations were strongly associated with winds coming from the southeast and northwest octants. South and southeast winds dominated the wind field with a higher percentage of calm conditions during high O3 episodes. Emissions from external regions extending from the Gulf of Mexico to the east and Baja California to the southwest contributed to deteriorated air quality in the PdN region. Factors that favored O3 formation include atmospheric stability, calm breezes, ambient NOx, and total non-methane organic carbon. Emissions inventories underreported precursor pollutants. Improvements in the air quality in the PdN region were elucidated. This is an abstract of a paper presented at the 105th AWMA Annual Conference and Exhibition 2012 (San Antonio, TX 6/19-22/2012).