Among the ports of entry between the US and Mexico, the International Bridge of the Americas (BOTA) connecting El Paso, TX, and Ciudad Juarez, Chihuahua, Mexico, has the largest combined traffic of privately owned (mostly gasoline fueled) and commercially operated (mostly diesel fueled) vehicles. The air quality at the BOTA was studied in terms of particle mass, particle number, and benzene concentrations near the US customs inspection area at the BOTA. The results suggested that diesel emissions account for fraction of the variability of the total and particularly ultrafine particle number concentrations. Principle component analysis showed that the ultrafine particle (UFP) and benzene levels might be emitted by the same source, since component 3 showed correlations with both. The correlation analysis suggests that the impact of diesel traffic minimizes quickly with distance as southbound traffic was associated with PM2.5 levels at both sites while northbound traffic only correlated with PM2.5 levels at the Mexican site. This is an abstract of a paper presented at the 102nd Air & Waste Management Association Annual Conference and Exhibition (Detroit, MI 6/16-19/2009).