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).