Feedback mechanisms between snow and atmospheric mercury: Results and observations from field campaigns on the Antarctic plateau

The Antarctic Plateau snowpack is an important environment for the mercury geochemical cycle. We have extensively characterized and compared the changes in surface snow and atmospheric mercury concentrations that occur at Dome C. Three summer sampling campaigns were conducted between 2013 and 2016. The three campaigns had different meteorological conditions that significantly affected mercury deposition processes and its abundance in surface snow. In the absence of snow deposition events, the surface mercury concentration remained stable with narrow oscillations, while an increase in precipitation results in a higher mercury variability. The Hg concentrations detected confirm that snowfall can act as a mercury atmospheric scavenger. A high temporal resolution sampling experiment showed that surface concentration changes are connected with the diurnal solar radiation cycle. Mercury in surface snow is highly dynamic and it could decrease by up to 90% within 4/6 h. A negative relationship between surface snow mercury and atmospheric concentrations has been detected suggesting a mutual dynamic exchange between these two environments. Mercury concentrations were also compared with the Br concentrations in surface and deeper snow, results suggest that Br could have an active role in Hg deposition, particularly when air masses are from coastal areas. This research presents new information on the presence of Hg in surface and deeper snow layers, improving our understanding of atmospheric Hg deposition to the snow surface and the possible role of re-emission on the atmospheric Hg concentration.

Volatile organic compounds in Arctic snow: concentrations and implications for atmospheric processes

The role of volatile organic compounds (VOC) in the snowpack for atmospheric oxidation, gas-particle transfer and aerosol formation remains poorly understood, partly due to a lack of methodology and unavailable data. We deployed solid phase micro-extraction (SPME) gas chromatography with flame ionization detection for measurement of halogenated, aromatic and oxygenated VOC in the snow pack in Alert, NU, Canada, a High Arctic site. Maximum concentrations in snow were 39 ± 6 μg L(-1) (styrene), indicating a potential VOC contribution to atmospheric oxidation and aerosol formation. Concurrently sampled air had concentrations of up to 1.0 ± 0.3 ng L(-1) (trichloroethene). Back trajectory data showed a change of air mass source region during a depletion event of several VOC in snow (e.g., trichloroethene and benzene). Snow profiles showed an enrichment of most compounds close to the surface. During a second study in Barrow, AK, USA VOC were quantified in snow and frost flowers in the Montreal lab. In Barrow work was carried out as part of the extensive OASIS (Ocean-Atmosphere-Sea Ice-Snowpack) field campaign. Maximum VOC concentrations were up to 1.3 ± 0.1 μg L(-1) (acetophenone). Bromoform in frost flowers averaged 0.19 ± 0.04 μg L(-1), indicating the potential to contribute to bromine generation through photolysis.