Controlling air quality has become an issue of ever increasing importance to society over the last decade. Air quality models are essential tools towards achieving this objective. These models are capable of predicting particulate matter, nutrient depositions, photochemical oxidants and other major pollutants. The objective of this research was the implementation of the CMAQ model to determine particulate matter in the El Paso-Juarez Airshed. The air quality model CMAQ was selected to perform a study of PM2.5 over the El Paso-Juarez Airshed for the contrasting seasons, summer and winter of 2006. The sensitivity to boundary conditions and the processes that most affect the pollutant concentration and variability were examined. Results of PM2.5 using the CMAQ model are presented, and compared against experimental data from a laser particle counter (Climet) and from the Texas Commission for Environmental Quality (TCEQ). Statistical analyses are performed to evaluate the models' forecasting capabilities for PM2.5 over the El Paso-Juarez Airshed. These studies will have an impact in pollution control strategies over a U.S region which is in non-compliance with U.S Standards for pollutant concentration.