Toxic air pollutants, also known as hazardous air pollutants, are those that are known or suspected to cause cancer or other serious health effects, such as birth defects or adverse environmental outcomes. The aim of this research was to predict air toxics related health risks due to different emission scenarios by linking Models-3/CMAQ and cancer risk assessments. To demonstrate the effectiveness of this approach, this study was performed on the priority mobile source air toxics (PMSAT) of benzene, 1,3-butadiene, formaldehyde, acetaldehyde, and diesel particulate matter (DPM), based on data from 2003. The analysis was carried out in the eastern US, and mainly in Nashville, TN. Ten emissions scenarios were examined, including a 2020 scenario with the effects of on-road mobile source regulations. The results show that DPM poses a cancer risk that is 4.2 times higher than the combined total cancer risk from all of four other PMSAT. These high cancer risk levels are mainly due to non-road sources (57.9%). The main cancer risk from acetaldehyde, benzene, formaldehyde, and 1,3-butadiene (4HAPs) is due to biogenic sources, which account for 32.2% of this risk, although these cannot be controlled. Excluding DPM, the main on-road cancer risk contribution was due to the air toxics generated by gasoline light duty vehicles (LDVs), principally benzene and 1,3-butadiene. The scenario for 2020 showed reductions in the adverse health effects related to DPM and 4HAPs of 32.8 and 19.4%, respectively. This research provides strong evidence that reducing ambient DPM concentrations will lead to greater improvements in human health than other air toxics, indicating that better technologies and regulations must be applied to mobile diesel engines, as these have more significant adverse health effects than non-road diesel sources.