Effects of secondary formation of inorganic ions and low molecular weight organic acids and biomass burning in regional pollution of PM2.5 in Central China

Abstract

Regardless of many reports describing the formation of regional PM2.5 pollution, it remains unclear how and why regional vs. local characteristics differ among aerosol species especially low molecular weight organic acids (LMWOAs). Here, PM2.5 was sampled simultaneously at Wuhan (megacity site) and Dongting Lake (background site) in Central China, a typical polluted region, from September 2017 to August 2018. High levels of PM2.5 were found at both sites, with SO42--NO3--NH4+ contributing over 60%. Similarity was observed in PM2.5 compositions, despite a 200 km distance between the two sites. More specifically, secondary ions, biomass-burning-related ions (K+ and Cl−), and LMWOAs were dominated by regional contributions, whereas other ions were mainly of local origin. Such high regional contributions might be mainly driven by meteorological homogeneity and, to a lesser extent, by the homogeneity of gaseous precursors. The results highlight the roles of secondary formation of both organic and inorganic aerosols as well as meteorology in the evolution of regional PM2.5 pollution.