This project conducts routine PM2.5 sampling and chemical composition analysis at six Environmental Protection Administration air quality monitoring stations in northern, central, southern, and eastern Taiwan (Hualien, Banqiao, Chungli, Douliu, Chiayi, and Xiaogang stations) every nine days. The project, ongoing since 2017, has accumulated seven years of long-term observational data. Over the seven-year period, the results of PM2.5 and chemical composition analyses indicate a decrease in PM2.5 and major chemical component mass concentrations across Taiwan. Particularly significant is the reduction in SO42-, while NO3- shows relatively less reduction. NO3- is the highest contributing chemical component in PM2.5 high concentration events and visibility reduction (IMPROVE method). Therefore, the control of NO3- and its precursor pollutants will be a future focus. PMF analysis identified ten potential pollution factors, with the "Oil combustion" factor at each station significantly decreasing in 2020 Q1, likely influenced by global sulfur restrictions on ship fuel. The "industrial heavy metal pollution" factor did not exhibit a noticeable decrease over the past seven years, prompting the need to evaluate whether controls on heavy metal emissions are necessary to reduce health risks. Environmental perimeter sampling in the Taichung region, combined with stack sampling for key pollution sources, revealed that CPM's contribution to PM2.5 is far greater than that of FPM, emphasizing its significance. Additionally, DEHP appeared in various stack samples, raising questions about its association with the use of solid recovered fuel (SRF), requiring ongoing tracking and clarification. To enhance the temporal resolution of PM2.5 pollution distribution in the future, this project compared the results of PM2.5 chemical composition analysis between high-volume samplers and standard method samplers (low-volume). In general, most component mass concentrations were consistent; however, some differences in specific components need further clarification.

PM2.5 long-term monitoring, PM2.5 source apportionment, CPM identification