| dc.description.abstract | Air pollution in Taiwan exhibits significantly different spatiotemporal characteristics across various seasons, making it a critical scientific issue that the people of Taiwan must face together. Air pollution can be classified into domestic and external sources. In addition to domestic sources, such as industrial, mobile, and other pollution sources, pollutants from upstream regions of East Asia can be transported over long distances to Taiwan during favorable meteorological conditions, leading to a decline in environmental quality and causing negative impacts on human health and ecosystems. To predict future pollutant concentration trends in advance, the CMAQ (Community Multiscale Air Quality) model employs reliable data and standardized procedures during simulations, which aids in enhancing Taiwan′s ability to manage and control air pollution. However, the model′s accuracy is not only related to meteorological fields and resolution, but also to the actual emission trends of pollution sources. The East Asian emission inventory currently used in the model is the MIX 2010, which is relatively outdated, leading to larger errors in simulating recent cross-border pollution transport events.
This study uses TROPOMI satellite observations and the Decoupled Direct Method (DDM) provided by the CMAQ model to capture the nonlinear relationship between pollutants and emissions, enabling the estimation of anthropogenic nitrogen oxide (NOx) emissions at the surface level. An average estimation of East Asian emissions was conducted for the period from January 1 to March 5, 2023. Additionally, three significant cross-border pollution events affecting Taiwan during the experimental period were selected to evaluate the benefits of emission reductions.
Case one occurred from January 18 to January 22, 2023. The atmospheric conditions during this period were characterized by the prevailing northeast monsoon. On January 18, a cold high-pressure system gradually moved eastward from Mongolia to North China, causing pollutants from North China to be transported to Central China, worsening air pollution in that region. On January 19, anthropogenic pollutants from the upwind areas of North and Central China were transported to the interior of Taiwan, and at this point, foreign pollution had begun to affect air quality across various regions in Taiwan.
Case two represented the most significant incident of foreign pollution among the three cases. On February 18, a cold high-pressure system gradually moved eastward from Siberia, and strong winds carried a large amount of pollutants from the industrial areas of North and Central China over the sea. On February 19, these pollutants reached northern Taiwan, deteriorating air quality in the northern region. The pollutants brought in also triggered a series of photochemical reactions in the weak wind area of the northeast monsoon′s tailwind in central and southern Taiwan, exacerbating air quality conditions in that area. In Case Three, from February 28 to March 2, two cold high-pressure centers moved eastward from East Asia to the sea near Korea. On February 28, the overall atmospheric environment was characterized by weak synoptic conditions, so Taiwan mainly experienced domestic pollution. On March 1, the high-pressure center moved southeastward, causing the environmental wind field to shift from easterly to northeasterly, changing the pollution trend to transboundary pollution. The different wind directions of the high-pressure systems also led to varying pollutant distributions between coastal and inland areas in central and southern Taiwan.
Overall, using the revised East Asia emission data to simulate the impact of foreign transport on Taiwan showed improvements, particularly in the case of nitrates brought in from abroad. The pollutants generated from photochemical reactions of the imported pollutants also demonstrated significant simulation effectiveness within the revised emission quantities. | en_US |