Abstract
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.
Highlights
Polar regions are being increasingly studied for their important roles in global climate and atmospheric chemical cycles
The day–night experiments demonstrate the existence of a diurnal cycle in surface snow for Hg and iodine, indicating that these species are influenced by the daily solar radiation cycle
During the 2015 experiment under full-day conditions, the average air temperature ranged between −10 and −6 ◦C and the surface snow temperature range between −13 and −5 ◦C, showing a diurnal variability connected with changes in the incoming solar radiation (Fig. 2)
Summary
Polar regions are being increasingly studied for their important roles in global climate and atmospheric chemical cycles. Mercury is a heavy metal with a known toxicity present in the environment in several different chemical forms It is reactive in the environment and undergoes photochemical reactions that change its speciation and chemical behaviour (Dommergue et al, 2010; Durnford and Dastoor, 2011; Saiz-Lopez et al, 2018; Steffen et al, 2002). Several studies aimed at understanding the behaviour of iodine in the Arctic region from a paleo-perspective using ice core archives (Cuevas et al, 2018; Spolaor et al, 2016b), and field (atmospheric and snow) experiments (Frieß et al, 2010; Gilfedder et al, 2007). A few experiments have been carried out in the field, with the specific aim of understand-
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