Particles and gases emitted by diesel vehicles can be toxic to human health. Polycyclic aromatic hydrocarbons (PAHs) and nitrated-PAHs (NPAHs) can be used as tracers to identify the contribution of diesel exhaust to the atmosphere. Air samples were collected near the Peace Bridge in Buffalo, NY, where studies have shown an association between asthma patients and traffic on the Peace Bridge. Positive Matrix Factorization (PMF) was used to estimate the source profile and the relative contribution of unknown emission sources. Four PAH sources identified were regional-scale volatilization, vehicle particulate matter, tar/asphalt volatilization, and diesel exhaust. Three NPAH sources identified were NO3 radical reaction, diesel exhaust and mixed sources. Volatilization was the major source of PAHs and NO3 radical reactions were the largest source of NPAHs in Buffalo, NY. Diesel exhaust accounted for approximately 30% of PAH and 18% of NPAH at the sampling site closest to the Peace Bridge.