Photoreducible Mercury Loss from Arctic Snow Is Influenced by Temperature and Snow Age

Abstract

Mercury (Hg) is an important environmental contaminant, due to its neurotoxicity and ability to bioaccumulate. The Arctic is a mercury-sensitive region, where organisms can accumulate high Hg concentrations. Snowpack mercury photoredox reactions may control how much Hg is transported with melting Arctic snow. This work aimed to (1) determine the significance of temperature combined with UV irradiation intensity and snow age on Hg(0) flux from Arctic snow and (2) elucidate the effect of temperature on snowpack Hg photoreduction kinetics. Using a Teflon flux chamber, snow temperature, UV irradiation, and snow age were found to significantly influence Hg(0) flux from Arctic snow. Cross-correlation analysis results suggest that UV radiation has a direct effect on Hg(0)flux, while temperature may indirectly influence flux. Laboratory experiments determined that temperature influenced Hg photoreduction kinetics when snow approached the melting point (>-2 °C), where the pseudo-first-order reduction rate constant, k, decreased twofold, and the photoreduced Hg amount, Hg(II)red, increased 10-fold. This suggests that temperature influences Hg photoreduction kinetics indirectly, likely by altering the solid:liquid water ratio. These results imply that large mass transfers of Hg from snow to air may take place during the Arctic snowmelt period, altering photoreducible Hg retention and transport with snow meltwater.

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

“…Nighttime elevated GEM in snow air was observed at Station Nord, Greenland, likely a result from dark formation of reducing radicals (e.g.,HO 2 q ) (Ferrari et al, 2004). Temperature is another factor enhancing Hg emission from snow by changing the solid and liquid water ratio (Mann et al, 2015a). Hg 0 flux from snow surface in the temperate regions has rarely been investigated (Faïn et al, 2007).…”

Atomistic View of Mercury Cycling in Polar Snowpacks: Probing the Role of Hg2+ Adsorption Using Ab Initio Calculations

“…Mercury (Hg) is of significant concern as a global pollutant, and its behavior and fate in the environment have been intensively studied for several decades [1][2][3][4][5][6][7][8][9][10][11]. The snowpack in polar regions serves as a natural sink in the global biogeochemical cycles of trace elements as long as it remains frozen [2].…”

“…When Hg 0 is oxidized to reactive gaseous mercury (RGM, Hg II ), however, it can be readily incorporated with particles to form particulate Hg (P Hg ), whose deposition causes a substantial increase (decrease) in Hg concentration in the surface snow (near-surface air) [6,8,11]. However, it has been proposed that the deposited Hg mostly returns to the atmosphere via a photochemically induced reduction of P Hg to Hg 0 [3,10,12]. Depending on the balance between deposition and reemission, the snowpack alternates its role in Hg cycling between a sink and a source from diurnal to seasonal time scales [11].…”

“…The lifetime of P Hg deposited in surface snow is estimated to be 4-24 h under solar ultraviolet (UV) radiation, but it is observed that a minor fraction of P Hg remains in the polar snowpack for a prolonged period in resistance to photochemical reemission and is sequestered from air-snow Hg cycling [3,6,10,12]. Since reducible Hg would mostly return to the atmosphere, P Hg resistant to reemission represents the major Hg form in the deep snowpacks.…”

“…Halides have also been proposed as potential stabilizers of P Hg in other studies ( [1] and other references therein). Laboratory and field experiments have found that the incident angle, and wavelength, intensity of solar radiation, and ambient temperature could affect the photochemical reemission flux [8][9][10]13], but explanations for P Hg production and the detailed reaction pathways of Hg reemission have been sparse or descriptive in nature. The main difficulties in experimental studies may lie in reproducing the natural air-snow interaction or in changing controlling factors in the laboratory or the field.…”