DIURNAL VARIATION OF HG ABUNDANCE IN SURFACE SNOW IN CONNECTION WITH ATMOSPHERIC AND METEOROLOGICAL CONDITIONS

Mercury deposition and re-emission from surface snow in the polar regions is an important part of the global mercury cycle. Mercury can be deposited during the polar winter and accumulate in the snow pack. During spring time the increasing solar radiation as well as the increase in oxidant species in the atmosphere can interact with the mercury present in the surface snow and increase emission of gas phase mercury from the surface. Dommergue et al. in 2014 suggested that atmospheric mercury above the Antarctic Plateau (Total gaseous mercury TGM) can undergo to a daily concentration cycle. Two 72 hours experiments were carried out in the proximity of Ny-Alesund research station, Svalbard. The two experiments were performed to evaluate the changes in concentration of Hg and other possible reactive elements in surface snow. The first experiment was conducted between the 27th and the 1st of May 2015 under 24h Sun irradiation conditions and the second was between the 7th and the 10th of April 2016 when a day and night cycle still occurred. The experiment was performed with high temporal resolution to investigate the possible changes in Hg, Br, major ions include nitrate, ammonia and I and trace elements. Surfaces samples have been collected every hour for 3 consecutive days, aimed at the study of the effect of solar radiation, snow events, deposition and meteorological conditions on surface snow chemical composition and evolution. The results obtained were integrated with the meteorological data collected by the Amundsen-Nobile Climate Change Tower and compared with the TGM measured as part of the EMEP program at the Mt. Zeppelin Observatory in Ny-Alesund. The results show two different trends. During the period with continuous solar presence, no diurnal variations in surface snow were detected for Hg and other elements that can undergo photochemical processes. For the experiment conducted during the day and night cycle, Hg and I showed appreciable diurnal cycles with maximum concentrations during the night and lower concentrations during the daytime. During the 24h solar presence experiment, the surface snow mercury did not show any correlation with atmospheric mercury while with a cycle of light and dark conditions we detect a negative correlation between the two measurements. In both experiments snow deposition events occurred during the surface snow sampling. In both cases the Hg concentration in the snow increase markedly suggesting a primary role of snow deposition as a mercury scavenger from the atmosphere.