Synoptic condition and boundary layer structure regulate PM2.5 pollution in the Huaihe River Basin, China

Abstract

Huaihe River Basin is an open plain area in eastern China, experiencing frequent heavy PM2.5 pollution events during the last decades. The physical mechanisms underlying the pollution have not yet been well understood. In this study, we investigated the variations of PM2.5 pollution in the Huaihe River Basin and its associated meteorological processes. Long-term PM2.5 measurements from 2015 to 2019, as well as multi-scale meteorological observations, reanalysis data, and air quality simulation data were analyzed. As a regional mean, the PM2.5 concentration shows the highest pollution level in winter and lowest in summer, influenced by both the annual cycle of emission rate and the variations of planetary boundary layer (PBL) structure. Wintertime PM2.5 pollution episodes showed synchronous variation in multiple cities in this region, characterized by weak winds, humid, and strong thermal stratifications within the PBL. Two synoptic patterns associated with winter heavy regional pollution were identified. One was characterized by the elevated warm advection from the southwest, which can suppress the development of the PBL. Another was controlled by a high pressure in the west, causing effective transport of pollutants from the north to the basin. The alternating occurrence of these two synoptic modes is critical to the frequent regional pollution in the Huaihe River Basin.