| Summary: | Emission rates (fluxes) of gaseous elemental mercury (GEM) and concentration measurements of GEM, reactive gaseous mercury (RGM) and particle bound mercury (Hgp) were measured from different terrestrial surfaces in Canada in order to provide regional modelers with more reliable information on the behaviour of mercury in the environment during colder months. A micrometeorological flux gradient technique was used to infer the flux of GEM using a continuous two-level sampling system. Fluxes were measured from substrates (soils) containing low concentrations (< 1 [mu]g g-1) of mercury in the substrate but are representative of background levels in North America. In the Arctic, the highest depositional fluxes occurred during polar night and the largest emissions occurred when the tundra was first visible. The flux of GEM was approximately zero during atmospheric depletion events (AMDEs) demonstrating that mercury is not being deposited as GEM to the snow pack during these episodes. In Southern Ontario during the late fall, depositional fluxes of GEM were significantly elevated during a biosolids application event, although fluxes were only slightly increased during substantial rain events due to the surface soil moisture being near field capacity throughout the study. During the winter in Southern Ontario, GEM emission fluxes were 3 times higher during periods of snow cover than without. GEM fluxes were also significantly influenced by soil freezing, resulting in fluxes over 2 times greater when the freezing duration increased from 6 to 20 continuous days. Concentrations of RGM and Hgp in the Arctic were elevated during periods of low wind speeds. As the air temperature and specific humidity increased, higher levels of RGM were noted and colder temperatures with low specific humidities resulted in elevated Hgp concentrations. A biosolids application event during the fall in Southern Ontario resulted in elevated levels of RGM and He while harvesting of corn produced increased concentrations of Hgp and GEM. During ...
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