Concentration and speciation of mercury in atmospheric particulates in the Wuda coal fire area, Inner Mongolia, China

Coal-seam fire is a source of atmospheric mercury that is difficult to control. The Wuda Coalfield in Inner Mongolia, China, is one of the most severe coal fire disaster areas worldwide and has been burning for more than 50 years. To investigate atmospheric mercury pollution from the Wuda coal fire, gaseous elemental mercury (GEM) concentrations and atmospheric particulate mercury (PHg) speciation were measured using a RA-915+ mercury analyzer and the temperature-programmed desorption method. Near-surface GEM concentrations in the Wuda Coalfield and adjacent urban area were 80 ng m^-3 (65-90 ng m^-3) and 52 ng m^-3 (25-95 ng m^-3), respectively, which are far higher than the local background value (22 ng m^-3). PHg concentrations in the coalfield and urban area also reached significantly high levels, 33 ng m^-3 (25-45 ng m^-3) and 22 ng m^-3 (14-29 ng m^-3), respectively (p < 0.05). There is no clear evidence that PHg combines with organic carbon or elemental carbon, but PHg concentration appears to be controlled by air acidity. PHg mainly exists in inorganic forms, such as HgCl₂, HgS, HgO, and Hg(NO₃)₂·H₂O. This work can provide references for the speciation analysis of atmospheric PHg and the safety assessment of environmental mercury.