Date of Award

12-2005

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Civil Engineering

Major Professor

Gregory D. Reed

Committee Members

Wayne T. Davis, Terry L. Miller, Williams L. Seaver

Abstract

Air toxics are important health concern. The purpose of this research was to develop a protocol to predict exposure concentrations of air toxics and inhalation cancer and noncancer risk that come from different gasoline and diesel-fueled sources. The protocol was developed by linking the U.S. EPA’s Models-3/CMAQ model as the exposure model and toxicological and epidemiological evidence functions. The NEI version 3 for the year 1999 was used in this analysis for point, area, and non-road sources, whereas NMIM was used to create the on-road emissions. The year 2003 was used for meteorological data and as reference to compare the monitored concentrations to model performance. The modeling domain consisted of a 36 km domain. To demonstrate the system’s effectiveness, this study was performed on priority mobile sources air toxics (1, 3-butadiene, benzene, formaldehyde, acetaldehyde, acrolein, and DPM), and was applied to Nashville, Tennessee using available air toxics monitored data. Ten emissions scenarios were selected in this study to compare the main results.

This research on air toxics emission scenarios was based on relative analyses and estimates of absolute exposure concentrations and health risk values. 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. Eliminating emission source categories is clearly not a policy option, but rather helps gain a better understanding of the total magnitude of the health effects associated with these major sources of air toxics, principally of DPM. Higher formaldehyde and acetaldehyde exposure concentrations occurred in the summer season, while benzene and 1,3-butadiene occurred in winter. DPM did not show a strong seasonality exposure during the year 2003 in Nashville. DPM generated the higher lifetime cancer risk excess among the other air toxics in Nashville, 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 (DFS), the principal reductions were due to the DPM contributions generated by HDDVs rather than LDDVs. An evident positive synergism in the cancer risk reduction occurred when reducing diesel on-road and non-road source emissions simultaneously. 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 that did not consider 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, principally benzene and 1,3-butadiene. The scenario 2020 showed a DPM and 4HAPs health effect reductions of approximately 32.8 and 19.4 %, respectively in Nashville. Higher cancer and non-cancer risks occurred on Southeastern urban areas due to long-term exposure to DPM, principally in Atlanta, GA, followed by Nashville, TN, Birmingham, AL, Raleigh, NC, and Memphis, TN. This research provided strong evidence that reducing ambient DPM concentrations will lead to improvement in human health more than other air toxics in Nashville, indicating that better technologies and regulations must be applied to mobile diesel engines, principally, over non-road diesel sources.

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