To understand the impact of fine particulate matter (PM2.5) on public health in Tainan City, this study conducted ambient PM2.5 collection and chemical analysis to estimate the possible PM2.5 sources and their contributions by a receptor model. It also investigated the PM2.5 concentration data, public health and disease data of recent years in Tainan metropolitan area to establish the concentration effect relationship for health risk assessment. This study further simulated and estimated risks for the analysis on variables and uncertainty. Based on the results, this study promoted the PM2.5 regulatory framework, and proposed control strategy by working with Air Quality Integration Management Plan in Tainan City.
The direct-reading PM2.5 measurement suggested that, the concentration of PM2.5 at traffic intersections was relatively higher during the morning and the afternoon rush hour, while the PM2.5 concentration was lower at noon (off-hour period). The PM2.5 concentration in the underpasses and tunnels of the motor vehicle lanes were relatively higher due to lack of proper ventilation facilities. In indoor environments when the air conditioning system was not on, PM2.5 concentrations were higher.
The sampling of summer PM2.5 component concentrations suggested that, the total carbon content of PM2.5 in summer and autumn as measured in Station Jhongshan Junior High School (Station Jhongshan) is the highest with an average level of 42.7%, followed by water-soluble ions at 36.9%, total metal content at 8.1% and unidentified content at 12.3%. Regarding the PM2.5 contents, as measured in Station Anshun Elementary School (Station Anshun), water-soluble ions account for the highest percentage at 31.7%, followed by total carbon content at 28.1%, total metal content at 5.4% and unidentified contents at 34.7%. The carbon contents are mainly of OC (organic carbon) and the majority of ion contents are SO42-. Ca, Fe and Na have the highest percentage among all the crustal metal elements, and Zn and Cu account for the highest percentage of man-made pollution elements.
In this study, health risks associated with exposure to PM2.5 for Tainan’s population were assessed based on an epidemiological study for populations from different cities in Taiwan. Results show that, for long-term health effects, percent of increases in total mortality and mortalities caused by cardiovascular diseases, cerebrovascular diseases, and pneumonia and influenza resulted from PM2.5 exposure were 9.1, 14.3, 18.3 and 26.4%, respectively. For the short-term effect resulted from the daily exposure, an increase in total daily mortality was 7.8%. If based on proportional rollback method stated in the USEPA’s guideline, and assuming an annual standard of 15 μg m-3and a daily 24-hr standard of 35 μg m-3 have been achieved, percent decreases in total mortality and mortalities caused by cardiovascular diseases, cerebrovascular diseases, and pneumonia and influenza will be decreased 5.2, 7.8, 9.7, and 13.3%, respectively, assuming a PM2.5 background level of 5 μg m-3.
Furthermore, this study also utilized Chemical Mass Balance (CMB), which is a receptor model, to analyze the contributions of PM2.5 sources. The main pollution source measured in Station Jhongshan is traffic (contribution percentage in the range of 30.6~60.5% in summer and of 67.9~76.5% in autumn), followed by ammonium sulfate due to by photochemical reactions and long-distance transportation (contribution percentage in the range of 24.2~29.6% in summer and of 18.0~21.7% in autumn), and the third pollution source of biomass burning (contribution percentage around 7.4~15.9% in summer and 17.5~11.4% in autumn). The crustal elements is the fourth contribution source in summer (contribution percentage in the range of 2.2~13.2%), while nitrate is the fourth contribution source in autumn (contribution percentage in the range of 2.6~6.8%). Similarly, the main pollution source measured in Station Anshun is traffic (contribution percentage in the range of 43.8~45.1% in summer and of 47.2~71.8% in autumn), followed by ammonium sulfate due to photochemical reactions and long-distance transportation (concentration percentage in the range of 18.1~24.2% in summer and of 20.6~22.0% in autumn). The third pollution source is biomass burning (contribution percentage in the range of 7.4~8.4 % in summer and of 8.4~10.6% in autumn). Nitrate is the fourth contribution source (contribution percentage in the range of 3.8~6.3%). This result indicates that the summer PM2.5 pollution contribution sources are mainly subjected to traffic and photochemical reaction products.
To assess 12% decrease of PM2.5 concentration in Tainan metropolitan area, this study recommends in order of importance the strengthening of the projects on construction engineering controls, washing and sweeping of road dust, emission restriction on restaurant and dining, burning centralization of ghost-money, reducing outdoor biomass burning, and inspection and control of stationary sources of air pollution and, then, to select the strategic combination with the lowest cost using linear programming and cost benefit analysis.
