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MSc defence: Jesper Kamp Jensen

Flux measurements of gaseous elemental mercury in High Arctic

2016.06.07 | Susanna Pakkasmaa

Date Mon 20 Jun
Time 13:00 15:00
Location Aarhus University, Ny Munkegade 116, Aud. F (1534-125)

Photo Jesper Kamp Jensen

Flux measurements of gaseous elemental mercury in High Arctic by Jesper Kamp Jensen

Mercury (Hg) is primarily entering the Arctic through long-range transport from human sources at lower latitudes. Mercury entering the food web is a problem concerning human health for the Arctic population due to their traditional diet. One way that Hg becomes bio-available is during atmospheric mercury depletion events (AMDEs). The hypothesis in the literature is that gaseous elemental mercury (GEM) is oxidized to reactive forms of Hg that is deposited on the snow surface. Within days, deposited Hg is reduced and reemitted to the atmosphere as GEM. These events occur throughout the Arctic but the knowledge about the mechanisms involving in the depletion of atmospheric Hg is not well known.

Mercury exits in several forms in the atmosphere but the most abundant form is GEM thus surface exchange of GEM is important to look into because most Hg transport is in the form of GEM. The micrometeorological method relaxed eddy accumulation (REA) is used to measure GEM flux at Villum Research Station (Station Nord) in Northeastern Greenland.

Sequential sampling has been used with REA in previous studies, but none of the studies has validated this application. Sequential sampling for REA is simulated with CO2 flux data from Villum Research Station (Station Nord, Greenland), Young Sound (Greenland) and Sorø (Denmark). Results of the simulations presented in this thesis clearly show that the method is erroneous compared to eddy covariance (EC) and REA. These findings lead to a setup with traditional REA measurements of GEM, where CO2 flux is measured, which allow data filtration and determination of the b-coefficient for the REA flux of GEM.

Measurements took place from April 23 to May 7, 2016 at Villum Research Station (Station Nord) during periods with AMDEs. The results of the flux measurements support the theory of deposition of reactive gaseous mercury (RGM) onto the snow, which is followed by photo reduction and reemission of GEM. The filtered results show nearly no depositional fluxes and during the period, there is a net emission. There a two pronounced trends regarding the GEM emission. First, the GEM emissions are increasing with increasing temperatures above about -15°C. Second, there is a correlation between wind speed and GEM emission, this correlation is more pronounced as the stability range get nearer to neutral. Furthermore, there is an anti-correlation between the fluxes of GEM and CO2 as function of wind speed. The reasons for these correlations and trends are not known at the moment and further studies are necessary to gain more knowledge.

Overall, this study reveals correlations between GEM flux, temperature and wind speed that support the know theory about deposition and reemission of Hg during AMDEs. It further highlights the necessity of further studies to understand the mechanisms involved in exchange processes associated with AMDEs to gain a better understanding of Hg availability in the ecosystem and the global fate of Hg.

Arctic Research Centre