Abstract. Sunlit snow is highly photochemically active and plays a key role in the
exchange of gas phase species between the cryosphere and the atmosphere.
Here, we investigate the behaviour 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 atmospheric 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
and their interaction 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 sampling
campaigns conducted at an hourly resolution for 3 d each were carried out
near Ny-Ålesund (Svalbard) to study the behaviour of mercury and iodine
in surface snow under different sunlight and environmental conditions
(24 h darkness, 24 h sunlight and day–night cycles). Our results indicate a
different behaviour of mercury and iodine in surface snow during the
different campaigns. The day–night experiments demonstrate the existence of a
diurnal cycle in surface snow for Hg and iodine, indicating that these
species are indeed influenced by the daily solar radiation cycle.
Differently, bromine did not show any diurnal cycle. The diurnal cycle also
disappeared for Hg and iodine during the 24 h sunlight period and during
24 h darkness experiments supporting the idea of the occurrence (absence) of
a continuous recycling or exchange at the snow–air interface. These results
demonstrate that this surface snow recycling is seasonally dependent,
through sunlight. They also highlight the non-negligible role that snowpack
emissions have on ambient air concentrations and potentially on
iodine-induced atmospheric nucleation processes.