Spatiotemporal characteristics of PM2.5 components in the Beijing-Tianjin-Hebei region and its surrounding areas during the heating seasons from 2018 to 2023

To mitigate the severe PM2.5 pollution, China established the National Atmospheric Particulate Chemical-Speciation-Network (NAPCSN) in 2016 and has been implementing more strict clean air policies since 2018. In this study, based on the data from the NAPCSN, we analyzed the spatiotemporal characteristics of PM2.5 chemical components in the Beijing-Tianjin-Hebei (BTH) region and its surrounding areas of China during the heating seasons (November 15-March 15) from 2018 to 2023. The results showed that PM2.5 and its chemical components exhibited distinct stage characteristics during the 2018-2023 heating seasons. From 2018 to 2020, a significant decline phase occurred, during which PM2.5 concentrations decreased by 27.4% and its components by 17.2%-58.4%, driven by targeted emission reductions of pollutants such as PM2.5, SO2, and NOx implemented under the Three-Year Action Plan for Winning the Blue Sky Battle. From 2021 to 2023, a slight fluctuation phase was observed, characterized by PM2.5 concentrations ranging from 63 to 66 mu g/m3 with minor interannual variations, the composition of components remaining largely stable, and component concentrations showing small declines or localized rebounds. These patterns likely reflected the diminishing marginal potential for emission reductions and unfavorable meteorological conditions. Notably, the disproportionate decreases across PM2.5 components led to a growing dominance of secondary aerosols, with nitrate (NO3-) emerging as a particularly significant contributor. NO3- and organic matter (OM) emerged as the dominant components, indicating that future mitigation efforts should focus more on the generation of secondary PM2.5. Additionally, PM2.5 chemical components exhibited distinct monthly variations largely due to changes in emission sources and meteorological conditions. For instance, elevated NO3- concentrations were observed in December and January, when NOx levels were high and relative humidity (RH) was elevated. OM was primarily influenced by secondary transformation of volatile organic compounds (VOCs), with concentration peaks occurring in November and March. Furthermore, although PM2.5 pollution in the BTH region and its surrounding areas exhibited regional characteristics, significant differences in pollution sources were still observed across different cities. Further analysis reveals that changes in PM2.5 and its major components were closely aligned with the significant reductions in emissions of key pollutants such as PM, NOx, and SO2. Therefore, the improvement in air quality in the BTH region and its surrounding areas is primarily driven by anthropogenic emission reductions. This study provides essential information for optimizing future pollution prevention and control strategies.