Controlling air quality has become an issue of ever increasing importance to society over the last decade. Air quality models are a very important tool to help us achieve this. The air quality models WRF-Chem and CMAQ were selected to perform a study over the El Paso-Juarez Airshed for the summer and winter months of 2004. The sensitivity to boundary conditions and the processes that most affect the pollutant concentration and variability were examined. Results from both air quality models are presented and inter-compared against each other and against experimental data from the Texas Commission for Environmental Quality (TCEQ). Statistical analyses are performed to evaluate the models' forecasting capabilities 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.