Health risk assessment posed by the mobile source air toxics on an urban to regional area

The purpose of this research was to develop a protocol to predict air toxics exposure concentrations and inhalation health risk that come from different mobile sources. The protocol was developed by linking the Models-3/CMAQ and health evidence functions. NMIM was used for on-road sources and the NEI 1999 for the other sources. The year 2003 was used for meteorological data and modeling performance. This study was performed on priority mobile sources air toxics and was applied to Nashville, Tennessee. Ten emissions scenarios were selected to compare the results.; This research was based on relative analyses and estimates of absolute exposure concentrations. The proposed protocol was demonstrated and can be used for decision makers in the quantitative assessment of new policies that will affect the public health and the air quality by air toxics. Diesel particulate matter generated the higher lifetime cancer risk excess among the other air toxics, posing a cancer risk that was 4.2 times higher than the combined total cancer risk from all other air toxics. Those high cancer risk levels were due mainly to non-road sources (57.9%). For the on-road diesel fueled sources, the principal reductions were due to the DPM contributions generated by HDDVs rather than LDDVs. The main cancer risk reductions from acetaldehyde, benzene, 1,3-butadiene, and formaldehyde (4HAPs) were due to the contribution of biogenic sources with 32.2%. This condition was followed for the scenario without on-road sources with a 27.5% of reduction. For non-road sources, the main reductions were due to the air toxics contributions generated by gasoline LDVs. The scenario 2020 showed a DPM and 4HAPs health effect reductions of approximately 32.8 and 19.4%, respectively. Higher cancer and non-cancer risks occurred on Southeastern urban areas due to long-term exposure to DPM, principally in Atlanta, followed by Nashville, Birmingham, Raleigh, and Memphis. This research provided strong evidence that reducing ambient DPM concentrations will lead to improvement in human health more than other air toxics, indicating that better technologies and regulations must be applied to mobile diesel engines, principally, over non-road diesel sources.