Characteristics and Control Priority of Hazardous Air Pollutants in the Metropolitan Areas : A Case Study in Tainan, Taiwan

This research investigated the hazardous air pollutants (HAPs), also known as air toxics, emission profiles and the potential health risks in Tainan City in Taiwan. Emission profiles of HAPs were derived by source test data and speciation data bank. Emissions from stationary source, mobile source, and area source were estimated in this study. Airborne concentration of target HAPs had been simulated by Models-3/CMAQ simulation and followed by cancer risk assessments for control priority assessment.

Five species of air toxics were selected as target component in this study, which included benzene, formaldehyde, acetaldehyde, acrolein, and 1,3-butadiene, by weighting the emissions and toxicity factors. Emission estimation indicated that these target air toxics were released by stationary sources with 34.5, 35.0, 5.0, 72.3, 94.5 %, respectively. Emissions of these 5 air toxics from mobile sources were 62.8, 45.4, 94.7. 27.5, 3.5 %, respectively. Area sources contributed less fraction in the city. The simulated annual average concentrations of target air toxics indicated the hot zone of various HAPs present in different location in the city. The airborne concentration of benzene and acetaldehyde in hot zone were mainly caused by mobile source emissions. Concentrations of formaldehyde in hot zone was caused by various sources. Airborne concentrations of acrolein and 1,3-butadiene in hot zone were mainly caused by area sources. The potential health risk assessment imposed by these target air toxics were evaluated by simulated exposure concentrations and with inhalation unit risk factor (cancer risk) and reference concentration level (non-cancer risk), respectively. The results showed 1,3-butadiene would pose the highest carcinogenic potential in the city which were mainly released by area sources. Acrolein had the highest non-carcinogenic potential. The cancer burden, by considering population density and exposure concentration, was higher in downtown area. Formaldehyde was the critical HAP which would impose the highest impacts on people caused by dense emission from mobile sources.