Atmospheric mercury over sea ice during the OASIS-2009 campaign

Abstract

Measurements of gaseous elemental mercury (GEM), reactive gaseous mercury (RGM) and particulate mercury (PHg) were collected on the Beaufort Sea ice near Barrow, Alaska, in March 2009 as part of the Ocean-Atmosphere-Sea Ice-Snowpack (OASIS) and OASIS-Canada International Polar Year programmes. These results represent the first atmospheric mercury speciation measurements collected on the sea ice. Concentrations of PHg averaged 393.5 pg m⁻³ (range 47.1–900.1 pg m⁻³) and RGM concentrations averaged 30.1 pg m⁻³ (range 3.5–105.4 pg m⁻³) during the two-week-long study. The mean concentration of GEM during the study was 0.59 ng m⁻³ (range 0.01–1.51 ng m⁻³) and was depleted compared to annual Arctic ambient boundary layer concentrations. It is shown that when ozone (O₃) and bromine oxide (BrO) chemistry were active there is a positive linear relationship between GEM and O₃, a negative one between PHg and O₃, a positive correlation between RGM and BrO, and none between RGM and O₃. For the first time, GEM was measured simultaneously over the tundra and the sea ice. The results show a significant difference in the magnitude of the emission of GEM from the two locations, with significantly higher emission over the tundra. Elevated chloride levels in snow over sea ice are proposed to be the cause of lower GEM emissions over the sea ice because chloride has been shown to suppress photoreduction processes of RGM to GEM in snow. Since the snowpack on sea ice retains more mercury than inland snow, current models of the Arctic mercury cycle may greatly underestimate atmospheric deposition fluxes because they are based predominantly on land-based measurements. Land-based measurements of atmospheric mercury deposition may also underestimate the impacts of sea ice changes on the mercury cycle in the Arctic. The predicted changes in sea ice conditions and a more saline future snowpack in the Arctic could enhance retention of atmospherically deposited mercury and increase the amount of mercury entering the Arctic Ocean and coastal ecosystems

Atmospheric mercury speciation and mercury in snow over time at Alert, Canada

“…Other aerosols such as sea salts and ice crystals are also common during the spring at Alert. Both these aerosols are effective scavengers of RGM and have been associated with elevated levels of PHg and Hg in the snow (Rutter and Schauer, 2007a;Douglas et al, 2008;Malcolm et al, 2010;Steffen et al, 2013). Coarse particle Na + , mostly sea salt derived, is elevated in February and at the beginning of March at Alert (Leaitch et al, 2014) but decreases in April.…”

“…Many studies have reported the decrease in GEM and a concurrent increase in oxidized mercury (PHg and RGM) and the connection of this chemistry to spring time ozone and halogen chemistry (Lindberg et al, 2001;Lindberg et al, 2002;Aspmo et al, 2005;Kirk et al, 2006;Cobbett et al, 2007;Simpson et al, 2007;Dastoor et al, 2008;Steffen et al, 2008;Steen et al, 2011). While atmospheric mercury speciation data in the Arctic air have been collected at several sites Kirk et al, 2006;Skov et al, 2006;Cobbett et al, 2007;Steen et al, 2011;Moore et al, 2012;Cole et al, 2013;Steffen et al, 2013;Brooks et al, 2006), few longterm (more than 5 years) mercury speciation measurements at temperate regions have been published and the Alert data set is the only such Arctic data set .…”

Global observations and modeling of atmosphere–surface exchange of elemental mercury: a critical review

“…The reduction rate was found to be linearly correlated with UV intensity (Lalonde et al, 2002;Mann et al, 2015b), while Cl − showed an inhibiting effect on the photoreduction (Sect. 3.3) (Steffen et al, 2013). Oxidation and reemission of Hg 0 occurred simultaneously with the presence of oxidants (e.g., q OH, q Cl and q Br) formed through photolysis .…”

Mercury in arctic tundra snowpack: temporal and spatial concentration patterns and trace–gas exchanges

“…The snowpack plays an important role for the cycling of Hg, including for atmospheric deposition, photochemical oxidoreduction reactions, and associated phase changes between solid and gaseous Hg that can volatilize Hg to the atmosphere (Douglas et al, 2008;Faïn et al, 2013;Mann et al, 2014;Steffen et al, 2013). In particular, many temperate and arctic studies have shown that the snowpack can serve as sinks or sources of Hg 0 gas , whereby photochemical reduction of snow-bound Hg II …”