EXCHANGES OF MERCURY BETWEEN THE SNOW PACK AND ATMOSPHERE AT CONCORDIA STATION ANTARCTICA

Surface snow samples were collected over three sampling campaigns during the Austral summer from the clean sampling area upwind of Concordia station on the Antarctic plateau. During the first campaign a snow pit was also dug to gain an idea of the stability and temporal profile of mercury in the snow pack in the high Antarctic. In the last campaign (Austral summer 2015-16) a 72 hour experiment was carried out that collected surface snow and precipitation on an hourly basis for comparison with atmospheric measurements to evaluate surface recycling in connection with diurnal solar radiation changes. Sample analysis was carried out for 202Hg and 79Br using a Thermo Electron Element 2 sector field ICP-MS and an Agilent Technologies 7500cx ICP-MS. Samples were left unacidified for Br, I, Ca, K, Na, and were acidified with 100 ?L of ultrapure HCl before mercury analysis.We conducted three sampling campaigns at Dome C, in the austral summers of 2013-2014, 2014-2015, and 2015-2016, during which snow and atmospheric mercury concentrations (TGM) we measured. The three campaigns had different metereological conditions that heavily affected mercury deposition processes. In the absence of snow deposition (including diamond dust) the surface mercury and atmospheric concentration remained stable without any particular trend. During and after snow deposition, mercury concentrations undergo marked changes. In the 2015-2016 field campaign, several snow deposition events occurred strongly affecting the surface snow Hg abundance. Fresh snow deposits were collected from a bench elevated above ground level to reduce wind blown snow collection, and the concentrations detected (around 100 pg g-1) suggest/confirm the capacity of snow as a mercury atmospheric scavenger. These high concentrations decreased rapidly to 10-20 pg g-1 on average within days of being deposited, influencing the atmospheric TGM concentrations. Apart from this variation, during the high resolution experiment, no diurnal variations in surface snow concentrations ware seen. Preliminary results from this sampling campaign give us important indications for evaluating mercury cycling on the central Antarctic plateau. The connection between Br and Hg in snow does not show any particular correlation or trend during the high resolution experiment (72h). The connection is more pronounced over time. We found a correlation of R2=0.59 in the snow pit samples. Higher deposition of mercury in surface snow seems connected with an increase in Br suggesting an intrusion of humid air from the coast bringing reactive Br that interacted with mercury.