Atmospheric mercury (Hg) is a globally pervasive and toxic pollutant. Atmospheric Hg is operationally defined in three different forms: gaseous elemental mercury (GEM or Hg0), gaseous oxidized mercury (GOM), and particulate-bound mercury (PBM). (1) Mercury directly emitted into the atmosphere, whether from anthropogenic or natural sources, is predominantly in the form of Hg0. (2) However, the proportion of divalent Hg (HgII) emitted from anthropogenic sources has gradually increased in recent decades. (3,4) Although the total Hg emissions from anthropogenic sources were gradually decreasing due to the implementation of a number of pollution control measures, (5) the increase in the proportion of HgII in flue gas may partly offset the impact of reduced Hg emissions in a local-scale environment because of the faster deposition rate of GOM and PBM than GEM. (6) The deposited Hg in terrestrial and aquatic ecosystems has the potential to undergo methylation by microorganisms to form methylmercury (MeHg), a species that can be bioaccumulated in the food chain and poses a health threat to ecosystems and human health. (7,8) Hence, a comprehensive understanding of the sources, transport processes, and fates of speciated atmospheric Hg is crucial for assessing Hg impacts on ecosystem and human health.

Coal-fired power plants (CFPPs) and cement plants (CPs) are the predominant sectors of anthropogenic Hg emissions in China. (3,9,10) In 2015, cement production emerged as the largest source of Hg emission in China, emitting 144 Mg Hg, (11) while CFPPs constituted the second largest source, emitting 73 Mg Hg. (12) Up to 84.5% and approximately 25% of the total Hg emission amounts mentioned above are in the form of HgII from cement production and CFPPs, respectively. (11) This implies that Hg deposition from CPs is much higher than that from CFPPs in China due to higher cement-related HgII emissions. Considering that the sum of atmospheric Hg emissions from CFPPs and CPs accounted for approximately 42% of the national total emissions, (3,10) it is essential to gain a complete understating of the speciated Hg emissions from these two source sectors to comprehensively assess the subsequent environmental impacts.