GEM fluxes and atmospheric mercury concentrations (GEM, RGM and [formula omitted]) in the Canadian Arctic at Alert, Nunavut, Canada (February–June 2005)

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Five months of gaseous elemental mercury (GEM), reactive gaseous mercury (RGM) and particle bound mercury ( Hg p ) concentrations as well as fluxes of GEM were measured at Alert, Nunavut, Canada above the Arctic snow pack. The study spanned February to June of 2005 to capture the effects of polar night, the transition period between night and day as well as polar day on the behaviour of mercury in the near surface atmosphere. A micrometeorological approach was used to infer the flux of GEM using a continuous two-level sampling system to measure the GEM concentration gradient. The required turbulent transfer coefficients were derived from meteorological parameters measured on site. The flux of GEM was approximately zero during atmospheric mercury depletion events (AMDEs) demonstrating that mercury is not being deposited as GEM to the snow pack. Following AMDEs, there was no evidence of a net emission of GEM. The highest depositional fluxes of GEM occurred during polar night and the largest emission occurred when the tundra was first visible, followed by significant emission and deposition fluxes during the snow melt. Fluxes continued until the snow had completely melted ( ∼ JD 170) before returning to near zero. Average concentrations of RGM ( 44.4 ± 49.8 pg m - 3 ) , Hg p ( 102.6 ± 124.9 pg m - 3 ) and GEM ( 1.0 ± 0.4 ng m - 3 ) were variable throughout the study due to the dynamic nature of atmospheric mercury during AMDEs. Increases in Hg p preceded elevated levels of RGM during AMDEs by 60 days, yielding peak levels at 694 and 344 pg m - 3 , respectively. Elevated concentrations of Hg p typically occurred when the specific humidity dropped below 0.75 g kg - 1 , winds were light ( < 3 m s - 1 ) and the air temperature dropped below - 20 ∘ C . Increased levels of RGM were also noted when the winds were light ( < 3 m s - 1 ) but when the temperature increased above - 10 ∘ C and the specific humidity was in the range of 1 and 3 g kg - 1 . As different environmental conditions were observed for the elevated concentrations of Hg p versus RGM at Alert, it suggests that the formation mechanisms for each species may be different but tied to the atmospheric temperature and water content. Total mercury (TM) levels in fresh snow measured approximately 5– 10 ng l - 1 during AMDEs and reached nearly 80 ng l - 1 outside of depletion events, suggesting that wet deposition may not be a significant removal mechanism of GEM during depletion events. An unusually high concentration of TM was measured during a non-depletion event which coincided with the transitional period where atmospheric loading of RGM exceeded levels of Hg p .