Atmospheric mercury observations from Antarctica: seasonal variation and source and sink region calculations
Long term atmospheric mercury measurements in the Southern Hemisphere\nare scarce and in Antarctica completely absent. Recent studies have\nshown that the Antarctic continent plays an important role in the global\nmercury cycle. Therefore, long term measurements of gaseous elemental\nmercury (GEM) were initiated at the Norwegian Antarctic Research\nStation, Troll (TRS) in order to improve our understanding of\natmospheric transport, transformation and removal processes of GEM. GEM\nmeasurements started in February 2007 and are still ongoing, and this\npaper presents results from the first four years. The mean annual GEM\nconcentration of 0.93 +/- 0.19 ng m(-3) is in good agreement with other\nrecent southern-hemispheric measurements. Measurements of GEM were\ncombined with the output of the Lagrangian particle dispersion model\nFLEXPART, for a statistical analysis of GEM source and sink regions. It\nwas found that the ocean is a source of GEM to TRS year round,\nespecially in summer and fall. On time scales of up to 20 days, there is\nlittle direct transport of GEM to TRS from Southern Hemisphere\ncontinents, but sources there are important for determining the overall\nGEM load in the Southern Hemisphere and for the mean GEM concentration\nat TRS. Further, the sea ice and marginal ice zones are GEM sinks in\nspring as also seen in the Arctic, but the Antarctic oceanic sink seems\nweaker. Contrary to the Arctic, a strong summer time GEM sink was found,\nwhen air originates from the Antarctic plateau, which shows that the\nsummertime removal mechanism of GEM is completely different and is\ncaused by other chemical processes than the springtime atmospheric\nmercury depletion events. The results were corroborated by an analysis\nof ozone source and sink regions.