Exposure to vehicle emissions at international border crossings has been a concern for many, including daily cross- border travelers and US Customs and Border Protection (CBP) officials. The proposed project will measure PM2.5 concentration at different hours of the day and locations within selected international border crossings (IBCs) to understand the potential amount of such pollutant in contact with (and breathable by) people waiting to cross the border in private vehicles or as pedestrians, as well as with CBP officials manning inspection booths. Furthermore, the project will attempt to find statistically significant correlations between these PM2.5 measurements and other variables, such as motorized traffic volume/congestion and its distance to the monitor locations, as well as ambient conditions. These correlations can potentially help predict the spatial concentration of PM2.5 within an IBC, and even help foresee mitigation strategies.