Behavior of mercury in snow from different latitudes

Deposition of Hg via snow fall may represent an important Hg flux to terrestrial and aquatic ecosystem of temperate and polar regions. We have conducted a series of field and laboratory experiments to better understand the post-depositional behaviour of Hg in snow. We found that: 1) a significant portion of the snow-to-air Hg evasion results from photoreduction of Hg in snow; 2) this photoreduction is mainly driven by UV-B radiation; 3) this photoreduction can be observed even in the presence of halogens in the snow, although we further found that these halogens favour the reverse photooxidation reaction; 4) laboratory experiments show that this photoreduction is likely mediated by organic reducing agents found in the snow matrix. These data will be incorporated in a global/regional Hg model. We propose that Hg falling inland in temperate and Arctic areas could be more rapidly re-emitted than Hg falling in coastal Arctic areas (where mercury depletion events occur).