Dominant Synoptic Patterns and Their Relationships with PM_2.5 Pollution in Winter over the Beijing–Tianjin–Hebei and Yangtze River Delta Regions in China

This paper concerns about the episodes of PM_2.5 pollution that frequently occur in China in winter months. The severity of PM_2.5 pollution is strongly dependent on the synoptic-scale atmospheric conditions. We combined PM_2.5 concentration data and meteorological data with the Hybrid Single Particle Lagrangian Integrated Trajectory model (HYSPLIT4) to investigate the dominant synoptic patterns and their relationships with PM_2.5 pollution over the Beijing–Tianjin–Hebei (BTH) and Yangtze River Delta (YRD) regions in the winters of 2014–17. The transport of PM_2.5 from the BTH to YRD regions was examined by using cluster analysis and HYSPLIT4. It is found that the level of PM_2.5 pollution over the BTH region was higher than that over the YRD region. The concentration of PM_2.5 in the atmosphere was more closely related to meteorological factors over the BTH region. The episodes of PM_2.5 pollution over the BTH region in winter were related to weather patterns such as the rear of a high-pressure system approaching the sea, a high-pressure field, a saddle pressure field, and the leading edge of a cold front. By contrast, PM_2.5 pollution episodes in the YRD region in winter were mainly associated with the external transport of cold air, a high-pressure field, and a uniform pressure field. Cluster analysis shows that the trajectories of PM_2.5 were significantly different under different weather patterns. PM_2.5 would be transported from the BTH to the YRD within 48 h when the PM_2.5 pollution episodes were associated with three different kinds of weather patterns: the rear of a high-pressure system approaching the sea, the high-pressure field, and the leading edge of a cold front over the BTH region. This suggests a possible method to predict PM_2.5 pollution episodes based on synoptic-scale patterns.