The mass balance of mercury in the springtime arctic environment

The load of mercury in the Arctic environment is to a large extent controlled by atmospheric mercury depletion events. At Barrow, Alaska, these depletion events have been linked with the near-surface air formation of reactive gaseous mercury (Hg( II)) (RGM), to a much lesser extent in a particulate-bound form, and the accumulation of total mercury in the snow pack (> 100 ng/L in late Spring). This transport of Hg from atmospheric conversion, to deposition, to bio-available forms is likely to be the predominant pathway for mercury into Arctic biota. For the first time we combine flux rate measurements, atmospheric chemistry measurements, and air mass trajectories to give a comprehensive two-week window into the springtime dynamics and mass balance of Arctic mercury. We have conducted polar-sunrise to snowmelt mercury monitoring at Barrow from 1998 to 2004, and the time period March 25th - April 7th (Julian days 84 - 97), 2003 appears typical for this time of year. A clear link was observed between air of marine origin, the build-up of BrO together with removal of gaseous elemental mercury ( GEM)), and the formation of RGM. This provides the most direct evidence so far for Br and Hg chemistry as the direct source of RGM. The fluxes of RGM and GEM were determined and the net flux calculated.