Diurnal cycles of interstitial gaseous mercury inside a sub-arctic snow-pack prior to and during snowmelt events

The snowpack is a medium that greatly interacts with a variety of atmospheric gases. Its role in the mercury depletion events in arctic and sub-arctic regions seems to be crucial though it is poorly understood. We studied an environmental component of mercury that is interstitial gaseous mercury (IGM) present in the air of the snowpack at Kuujjuarapik (55°N, 77°W), Quebec in April 2002. Our data demonstrate that the snow-pack plays a major role in the global mercury cycle. Indeed, IGM concentrations exhibit a well-marked diurnal cycle with uninterrupted events of Hg° depletion and production within the snowpack. During snowmelt episode, high IGM concentrations (∼20 ng/m 3 at a depth of 37 cm) have been recorded. This study gives us the confirmation that Hg° is involved in oxidation processes occurring in the snowpack. Additionally, we assume that the impressive production of Hg° during the daytime may be the results of photoreduction and photo-initiated reduction of Hg(II) complexes.