Abstract
Abstract. Distinct diurnal and seasonal variations of mercury (Hg) have been observed in near-surface air at Concordia 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 Hg0 (gaseous elemental mercury) measurements in thes year 2013. The model includes atmospheric Hg0 oxidation (by OH, O3, or bromine), surface snow HgII (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 Hg0 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 Hg0 (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 Hg0 is mainly driven by photoreduction of snow HgII in summer. Intermittent warming events and a hypothesized reduction of HgII 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 Hg0 is expected to be slower at Summit Station in Greenland than at Concordia (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 Hg0 between these two polar inland stations.
Highlights
Mercury (Hg) is an environmental concern due to its health effects on humans and wildlife (Mergler et al, 2007)
We have computed ranges of atmospheric Hg0 oxidation rates for different schemes (O3, OH, and two-step Br), using the low and high rate constants listed in Table 2 and uncertainties of oxidant concentrations (Sect. 2.3)
In austral summer (November–February), the twostep Br oxidation scheme is more efficient than the O3 and OH oxidation schemes
Summary
Mercury (Hg) is an environmental concern due to its health effects on humans and wildlife (Mergler et al, 2007). 2016; Han et al, 2017; Spolaor et al, 2018) Most of these studies only measured atmospheric mercury in austral summer, whereas Angot et al (2016c) reported a year-round observational record at Dome C. The summertime photochemical mechanism of Hg0 oxidation in air is unknown but has been related to the high oxidizing capacity of the plateau, which is characterized by high concentrations of NOx, OH, and other oxidants within the Antarctic mixed layers (Eisele et al, 2008; Helmig et al, 2008a, b; Neff et al, 2008; Kukui et al, 2014; Frey et al, 2015) Such summertime diurnal variations of Hg0 have not been seen at the polar inland Summit Station atop the Greenland ice sheet (Brooks et al, 2011). In winter (May–August), as expected, the diurnal cycle of Hg0 disappeared, and a gradual decline of Hg0 was seen in nearsurface air
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