Event-Based Tracking of Spatiotemporally Contiguous PM2.5 Pollution Events in China

PM2.5 pollution events evolve continuously through spatiotemporal diffusion. However, their three-dimensional spatiotemporal variation characteristics are often overlooked, and the interactions among key characteristics (e.g., duration, maximum concentration) have not yet been systematically analyzed. This study established a three-dimensional (longitude, latitude, and time) spatiotemporal framework for identifying contiguous PM2.5 pollution events based on the high-resolution ChinaHighAirPollutants (CHAP) dataset (1 km spatial and 1-day temporal resolution). The framework applied the meteorological event tracking algorithm (i.e., the Forward-in-Time method) to track PM2.5 pollution events. Based on this framework, we systematically tracked and characterized the spatiotemporal evolution of PM2.5 events across China from 2013 to 2021, quantified the relationships among key event characteristics, and tracked their transport pathways. The results show that: (1) The combination of the FiT algorithm and CHAP dataset enables effective tracking and identification of the three-dimensional spatiotemporal evolution of PM2.5 pollution events across China. (2) Event PM2.5 totals, average totals per event and pollution events exhibit a distinct right-inclined “T”-shaped pattern, with hotspots located in Xinjiang, the Beijing-Tianjin-Hebei (BTH) region, Shandong, and Henan, where annual event frequency exceeds 15. (3) Event PM2.5 totals show strong correlations with average duration per event and average maximum concentration per event, particularly in heavily polluted areas where the Pearson correlation coefficient is close to 1. (4) PM2.5 pollution events are mainly characterized by short durations of 1 day or 2–3 days, accounting for over 80% of occurrences. Long-duration events are mostly concentrated in areas with severe pollution problems, and their persistence is closely linked to spatial coverage, terrain barrier effects, and meteorological conditions. (5) PM2.5 pollution events consistently exhibit a west-to-east transport pattern. Short-duration events propagate slower across the inland northwest, whereas long-duration events show a pronounced increase in meridional transport speeds along the eastern coastal areas. This study elucidates the continuous spatiotemporal evolution and intrinsic drivers of PM2.5 pollution events, offering scientific insights to support air quality improvement and the development of targeted management strategies.