Atmospheric Mercury Isotope Shifts in Response to Mercury Emissions from Underground Coal Fires

Pollutant emissions from coal fireshave caused seriousconcernsin major coal-producing countries. Great efforts have been devotedto suppressing them in China, notably at the notorious Wuda Coalfieldin Inner Mongolia. Recent surveys revealed that while fires in thiscoalfield have been nearly extinguished near the surface, they persistunderground. However, the impacts of Hg volatilized from undergroundcoal fires remain unclear. Here, we measured concentrations and isotopecompositions of atmospheric Hg in both gaseous and particulate phasesat an urban site near the Wuda Coalfield. The atmospheric Hg displayedstrong seasonality in terms of both Hg concentrations (5-7-foldhigher in fall than in winter) and isotope compositions. Combiningcharacteristic isotope compositions of potential Hg sources and airmass trajectories, we conclude that underground coal fires were stillemitting large amounts of Hg into the atmosphere that have been transportedto the adjacent urban area in the prevailing downwind direction. Theother local anthropogenic Hg emissions were only evident in the urbanatmosphere when the arriving air masses did not pass directly throughthe coalfield. Our study demonstrates that atmospheric Hg isotopemeasurement is a useful tool for detecting concealed underground coalfires. Mercury isotope evidence shows that undergroundcoal firescould emit large amounts of Hg into the atmosphere and significantlyincrease nearby urban Hg levels.

Automated summary

Pollutant emissions from coal fires have caused serious concerns in major coal-producing countries, and China has made great efforts to suppress them. Recent surveys have revealed that although fires in the notorious Wuda Coalfield in Inner Mongolia have been nearly extinguished near the surface, they still persist underground. The impacts of Hg volatilized from underground coal fires remain unclear.