Diurnal cycle of iodine and mercury concentrations in Svalbard surface snow

Sunlit snow is highly photochemically active and plays an important role in the exchange of gas-phase species between the cryosphere to the atmosphere. Here, we investigate the behavior of two selected species in surface snow: mercury (Hg) and iodine (I). Hg can deposit year-round and accumulate in the snowpack. However, photo-induced re-emission of gas phase Hg from the surface has been widely reported. Iodine is active in new particle formation, especially in the marine boundary layer, and in the destruction of atmospheric ozone. It can also undergo photochemical re-emission. Although previous studies indicate possible post-depositional processes, little is known about the diurnal behaviour of these two species in surface snow. The mechanisms are still poorly constrained and no field experiments have been performed in different seasons to investigate the magnitude of re-emission processes. Three high temporal resolution (hourly samples) 3-day experiments were carried out near Ny-A?lesund (Svalbard) to study the behaviour of Hg and I in surface snow under different sunlight and environmental conditions (24h-darkness, 24h-sunlight and day/night cycles). Our results indicate a clearly different behaviour of Hg and Iin surface snow during the different experiments. The 24h day/night experiments demonstrate the existence of a diurnal cycle in surface snow for Hg and I, indicating that these species are indeed influenced by the daily solar radiation cycle. Differently Br does not show any diurnal cycle. The diurnal cycle disappears during the 24h-sunlight period (and during the polar night) supporting the idea ofthe occurrence (absence) of a continuous recycling / exchange at the snow-air interface. These results demonstrate that this surface snow recycling is seasonally dependent. They also highlight the non-negligible role that snowpack emissions have on ambient air concentrations and potentially on iodine-induced nucleation processes.