| dc.description.abstract | PM2.5 (particulate matter with aerodynamic diameter less than or equal to 2.5 μm) plays a significant role in the environment and public health. This study analyzed the data collected at the Banqiao, Zhongming, Douliu, Chiayi, Xiaogang, and Hualien stations in the “2015-2016 PM2.5 chemical composition monitoring and analysis study” and “PM2.5 chemical composition monitoring and analysis study” in 2017. The objectives included the investigations on the variation trends of PM2.5 mass and metal element concentrations, potential sources of metal elements, differences of metal element proportions in high and low PM2.5, and the assessments of the health risk of metal elements. Additionally, this study executed source apportionments using Positive Matrix Factorization (PMF) and verified local source contributions by coupling Conditional Probability Function (CPF) with wind direction.
The results showed that the Banqiao and Hualien stations were with the highest PM2.5 seasonal concentrations in spring, while the Zhongming station was in autumn and the Douliu, Chiayi, and Xiaogang stations were in winter. In contrast, the lowest PM2.5 seasonal concentration was in autumn for the Banqiao station and summer for other stations. Among the six stations, Al, Fe, Na, Mg, K, Ca, and Zn belonged to the high concentration group. Major contribution sources of these metal elements can be derived from crustal material (Al, Fe, and Ca), sea salt (Na and Mg), transportation activities (Fe, Na, Ca, and Zn), steel refinery (Fe and Zn), and waste incineration (Al, Fe, Ca and Zn). The metal elements in the medium concentration group were mostly associated with anthropogenic activities, for example, coal and oil burning related industrial sources and transportation activities. For the metal elements in the low concentration group, industrial boilers and fossil fuel burning were major contributing sources. The highest concentration of vanadium (V) in all stations and seasons was at the Xiaogang station. Consequently, the Xiaogang station is under the influence of emissions of oil burning significantly in all stations, as V is the tracer element of oil burning.
Among the analyzed metal elements, Ni, Cr, Cd, and As are classified into group 1 and group 2B human carcinogens for Pb by the International Agency for Research on Cancer. This study computed the human exposure via inhalation pathway to find that Pb exposure was the highest followed by Ni and Cr in all stations. The exposure of Ni, Cr, and Cd ranked the highest at the Xiaogang station, while As and Pb reached the highest at the Chiayi station. The cancer risk of the elements lied in the range from 10-7 to 10-5. The Xiaogang station is noted to have the highest cancer risk among all stations.
The combination of PMF with CPF on source apportionment of metal elements resulted in identifying sources of oil (coal) burning, transportation activities, industrial discharge, crustal materials, and sea salt. Comparing high PM2.5 concentration (>35 μg m-3) with low concentration (<35 μg m-3) samples, Ba was the sole metal element with slightly greater PM2.5 proportion. The sources of Ba included tire and brake wearing, steel-making, and crustal materials. In contrast, Na, Mg, Ca, Ti, Mn, Ni, and V were with greater PM2.5 proportion in the low PM2.5 samples. They are tracers of industrial pollution and crustal materials.
Although metal elements are low in PM2.5 mass proportion, they tend to carry over polluting source characteristics and few of them are carcinogens. Therefore, the analysis of PM2.5 metal elements is of importance. | en_US |