The Paso del Norte (PdN) region is one of the largest metropolitan areas along the U.S.-Mexico border. Different emission regulations between the two countries, particularly with respect to on-road vehicle and domestic burning, have impacted the regional concentration and human exposure of air toxics (e.g., metals, polycyclic aromatic hydrocarbons [PAHs], and carbonyls). Comprehensive air quality measurements were conducted using a mobile monitoring system at two urban-scale sites within El Paso, Texas in December 2008 as a pilot study to understand aerosol and air toxics exposure and sources in the PdN region. The measurements show clear diurnal variations due to traffic emissions and a major pollution episode likely caused by both motor vehicles and domestic burning. Wind analysis further confirms the importance of cross-border transport on elevated pollutant concentrations at the monitoring sites. The traffic-dominated periods are characterized by high fractions of black carbon, particle-bound PAHs (p-PAHs), and carbonyls in comparison with dust-related periods. During the particular pollution episode, high levels of elemental chlorine and vinyl chloride were observed that might relate to unregulated domestic burning of polyvinyl chloride (PVC) products. Although most pollution indicators show a substantial improvement in air quality over the last decade, short-term exposure to some p-PAHs, e.g., benzo[a]pyrene, is still close to the health effects screening level. Bi-national efforts are required to further reduce air toxics emissions.