Temperature and sunlight controls of mercury oxidation and deposition atop the Greenland ice sheet
1NOAA ATDD, 456 S. Illinois Ave, P.O. Box 2456, Oak Ridge, TN 38731, USA
2University of Maryland Center for Environmental Science, Appalachian Laboratory, Frostburg, MD 21532, USA
3University of Houston, Department of Earth and Atmospheric Sciences, 312 Science & Research Building 1, Rm. 312, Houston, TX 77204, USA
4Georgia Institute of Technology, School of Earth & Atmospheric Sciences, Atlanta, GA 30332, USA
Abstract. We conducted the first ever mercury speciation measurements atop the Greenland ice sheet at Summit Station (Latitude 72.6° N, Altitude 3200 m) in the Spring and Summer of 2007 and 2008. These measurements were part of the GSHOX campaigns investigating the importance of halogen chemistry in this remote environment. Significant levels of BrO (1–5 pptv) in the near surface air were often accompanied by depletions of gaseous elemental mercury (GEM) below background levels, and in-situ production of reactive gaseous mercury (RGM). While halogen (i.e. Br) chemistry is normally associated with marine boundary layers, at Summit, Greenland, far from any marine source, we have conclusively detected bromine and mercury chemistry in the near surface air. We suggest that the fate of the formed mercury-bromine radical (HgBr) is further oxidation to stable RGM (HgBr2, HgBrOH, HgBrCl, etc.), or thermal decomposition. These fates appear to be controlled by the availability of Br, OH, Cl, etc. to produce RGM (Hg(II)), verses the lifetime of HgBr by thermal dissociation. At Summit, the availability of Br appears to be controlled by J(Br2), requiring a sun angle of > 5 degrees, while the formation of RGM from HgBr requires a temperature < −15 °C. The majority of the deposited RGM is readily photoreduced and re-emitted to the air as GEM. However, a very small fraction becomes buried at depth. Extrapolating to the entire Greenland ice sheet, we calculate an estimated net annual sequestration of ~ 13 metric tons Hg per year, buried long-term under the sunlit photoreduction zone.