Understanding mercury oxidation and air–snow exchange on the East Antarctic Plateau: a modeling study

Shaojie E Song (1) , Hélène Angot (2) , Noelle E Selin (1) , Hubert Gallée (2) , Francesca Sprovieri (3) , Nicola Pirrone (3) , Detlev Helmig (4) , Joel Savarino (5) , Olivier Magand (6) , Aurélien Dommergue (2)

1 MIT - Massachusetts Institute of Technology
2 IGE - Institut des Géosciences de l’Environnement
3 IIA - Institute of Atmospheric Pollution Research
4 INSTAAR - Institute of Arctic Alpine Research [University of Colorado Boulder]
5 UGA [2016-2019] - Université Grenoble Alpes [2016-2019]
6 EDYTEM - Environnements, Dynamiques et Territoires de Montagne

Distinct diurnal and seasonal variations of mercury (Hg) have been observed in near-surface air at Con-cordia Station on the East Antarctic Plateau, but the processes controlling these characteristics are not well understood. Here, we use a box model to interpret the Hg 0 (gaseous elemental mercury) measurements in thes year 2013. The model includes atmospheric Hg 0 oxidation (by OH, O 3 , or bromine), surface snow Hg II (oxidized mercury) reduction, and air-snow exchange, and is driven by meteorological fields from a regional climate model. The simulations suggest that a photochemically driven mercury diurnal cycle occurs at the air-snow interface in austral summer. The fast oxidation of Hg 0 in summer may be provided by a two-step bromine-initiated scheme, which is favored by low temperature and high nitrogen oxides at Concordia. The summertime diurnal variations of Hg 0 (peaking during daytime) may be confined within several tens of meters above the snow surface and affected by changing mixed layer depths. Snow re-emission of Hg 0 is mainly driven by photoreduction of snow Hg II in summer. Intermittent warming events and a hypothesized reduction of Hg II occurring in snow in the dark may be important processes controlling the mercury variations in the non-summer period, although their relative importance is uncertain. The Br-initiated oxidation of Hg 0 is expected to be slower at Summit Station in Greenland than at Con-cordia (due to their difference in temperature and levels of nitrogen oxides and ozone), which may contribute to the observed differences in the summertime diurnal variations of Hg 0 between these two polar inland stations.

Domains: Ocean, Atmosphere

Shaojie E Song, Hélène Angot, Noelle E Selin, Hubert Gallée, Francesca Sprovieri, et al.. Understanding mercury oxidation and air–snow exchange on the East Antarctic Plateau: a modeling study. Atmospheric Chemistry and Physics, 2018, 18 (21), pp.15825-15840. ⟨10.5194/acp-18-15825-2018⟩. ⟨hal-02350377⟩