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. Distinct diurnal and seasonal variations of mercury (Hg) have been observedin near-surface air at Concordia Station on the East Antarctic Plateau, butthe processes controlling these characteristics are not well understood.Here, we use a box model to interpret the Hg0 (gaseous elementalmercury) measurements in thes year 2013. The model includes atmospheric Hg0 oxidation (by OH, O3 , or bromine), surface snow HgII (oxidizedmercury) reduction, and air–snow exchange, and is driven by meteorologicalfields from a regional climate model. The simulations suggest that aphotochemically driven mercury diurnal cycle occurs at the air–snow interfacein austral summer. The fast oxidation of Hg0 in summer may be providedby a two-step bromine-initiated scheme, which is favored by low temperatureand high nitrogen oxides at Concordia. The summertime diurnal variations of Hg0 (peaking during daytime) may be confined within several tens ofmeters above the snow surface and affected by changing mixed layer depths.Snow re-emission of Hg0 is mainly driven by photoreduction of snow HgII in summer. Intermittent warming events and a hypothesized reductionof HgII occurring in snow in the dark may be important processescontrolling the mercury variations in the non-summer period, although theirrelative importance is uncertain. The Br-initiated oxidation of Hg0 isexpected to be slower at Summit Station in Greenland than at Concordia (due to theirdifference in temperature and levels of nitrogen oxides and ozone), which maycontribute to the observed differences in the summertime diurnal variationsof Hg0 between these two polar inland stations.

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