Inter-annual variability in fine particulate matter pollution over China during 2013-2018: Role of meteorology

Based on the long-term observed fine particulate matter (PM2.5) data obtained from the Ministry of Environmental Protection of China, the present study focused on the analysis of annual and seasonal trends of PM2.5 over the polluted areas in China from 2013 to 2018. The MODIS-derived aerosol optical depth (AOD) data was used as an auxiliary data to supplement the analysis with surface measured PM2.5. The emission source inventory and meteorology datasets are also used and analyzed to examine the causes of changes in trends of PM2.5. The results revealed that the annually averaged values of AOD and surface PM2.5 concentrations over the high-polluted areas are decreasing year-by-year, with stable values found over the Pearl River Delta (PRD) region. The decreasing trends of PM2.5 concentration and fine particle pollution frequency over the Beijing, Tianjin, and Hebei (BTH) area are most obvious. Over the PRD region, PM2.5 concentration maintains below the annual air quality standard (35 mu g/m(3)) with low fine particle pollution frequency. The decreasing trend of averaged PM2.5 in each region is closely related to the reduction of anthropogenic PM2.5 emissions. However, the fluctuated features in different season are mostly influenced by the meteorological conditions. Based on the weather type classifications observed from the COST733 model, the weather types under uniform pressure and eastern high pressure more likely resulted in the occurrence of fine particulate pollution over China. When the weather under the bottom with high pressure occurs, Northeast China (NEC) and BTH regions are most likely to be polluted, which is more likely to lead to heavy fine particle pollution events. The air pollution in the Yangtze River Delta (YRD) area is the most serious when the uniform pressure field weather occurs in winter.