Characteristics and source apportionment of water-soluble inorganic ions in PM2.5 during a wintertime haze event in Huanggang, central China

Winter haze events are frequent occurrences in central China, however, their characteristics and formational mechanisms in the region are still poorly understood. In this study, we conducted continuous observations of PM2.5 during a haze event (from January 13 to 24, 2018) in Huanggang in central China to identify the characteristics of water-soluble inorganic ions (WSIIs) associated with PM2.5. The observation period was divided into the pre-haze episode (Pre-HE, January 13 to 14), haze episode (HE, January 15 to 21) and post-haze episode (Post-HE, January 22 to 24). The daily average PM2.5 mass concentration during the Pre-HE, HE and Post-HE was 51.7, 134.9 and 92.2 mu g m(-3), respectively. The WSIIs accounted for 57.3% of the total PM2.5 content throughout the entire observation period and were predominantly composed of nitrate, sulfate, and ammonium. During the HE, the major ions predominantly occurred in the form of (NH4)(2)SO4, NH4NO3, NH4Cl, and HCl. Moreover, the sulfur oxidation ratios and nitrogen oxidation ratios were relatively high, inferring the high contribution of secondary transformation. During the HE, homogeneous and heterogeneous reactions played an important role in the formation of nitrate and sulfate in PM2.5, respectively. The results of the principal component analysismultiple linear regression suggest that the major sources of WSIIs were secondary inorganic aerosols, combustion and dust. The results of the backward trajectory analysis and the potential source contribution function model infer the strong influence of both local and regional air masses on haze formation and dissipation in Huanggang.