FATE OF MERCURY IN THE ARCTIC Michael Evan ... - COGCI

Fate of Mercury in the Arctic 108
Gaseous elemental mercury is approximately 95% of the total gaseous mercury in the
atmosphere, TGM, (Schroeder and Munthe, 1998). Much of the GEM is oxidised RGM (e.g.
Schroeder et al., 1998, Lindberg et al., 2002) during an AMDE. Thus RGM is likely subject to
subsequent fast dry deposition to the Arctic snow surface during an AMDE (Schroeder et al., 1998).
Therefore this work developed a method to quantify the deposition during an AMDE, so that the
data could be used for further flux measurement development and model calibration and
verification.
Given the challenges encountered with the micrometeorological system, it is worth reviewing
options considered for measuring RGM flux. Flux measurements could be as “simple” as setting a
small environmental chamber over the snow surface, however this would give limited information
as to the pattern and exclude natural processes and deposition. A chamber is not able to fully
measure representative exchange rates, and there has not been a chamber method developed yet, for
the flux of reactive gaseous mercury in the Arctic. Development of a chamber method for RGM is
hindered by the need to have a warm KCl coating, if KCl is used as the active surface for RGM.
This heating will liquefy the snow surface.
The work instead chose a micrometeorological method, REA.
REA has been used for the determination of elemental mercury flux (Cobos et al., 2002). REA
allows for a covering a relatively large area, known as the fetch, i.e., the fetch is approximately =
100 x height of system; in this case 300 m; since the system was set up 3 m above the snow pack
surface.
However, as discussed below, there are also drawbacks with using REA to investigate mercury
depletion events in the Arctic, particularly that weather conditions favourable for the system, i.e.,
high turbulence, are not favourable for mercury depletion events to occur, and are the exception to
stable weather normally encountered on a flat Arctic coastal plane.