Abstract
Abstract. Gaseous elemental mercury (GEM) measurements at Alert, Canada, from 1995 to 2007 were analyzed for statistical time trends and for correlations with meteorological and climate data. A significant decreasing trend in annual GEM concentration is reported at Alert, with an estimated slope of −0.0086 ng m−3 yr−1 (−0.6% yr−1) over this 13-year period. It is shown that there has been a shift in the month of minimum mean GEM concentration from May to April due to a change in the timing of springtime atmospheric mercury depletion events (AMDEs). These AMDEs are found to decrease with increasing local temperature within each month, both at Alert and at Amderma, Russia. These results support the temperature dependence suggested by previous experimental results and theoretical kinetic calculations on both bromine generation and mercury oxidation and highlight the potential for changes in Arctic mercury chemistry with climate. A correlation between total monthly AMDEs at Alert and the Polar/Eurasian Teleconnection Index was observed only in March, perhaps due to higher GEM inputs in early spring in those years with a weak polar vortex. A correlation of AMDEs at Alert with wind direction supports the origin of mercury depletion events over the Arctic Ocean, in agreement with a previous trajectory study of ozone depletion events. Interannual variability in total monthly depletion event frequency at Alert does not appear to correlate significantly with total or first-year northern hemispheric sea ice area or with other major teleconnection patterns. Nor do AMDEs at either Alert or Amderma correlate with local wind speed, as might be expected if depletion events are sustained by stable, low-turbulence atmospheric conditions. The data presented here – both the change in timing of depletion events and their relationship with temperature – can be used as additional constraints to improve the ability of models to predict the cycling and deposition of mercury in the Arctic.
Highlights
Mercury in the Arctic is of particular interest for two reasons
Based on research to date, these atmospheric mercury depletion events” (AMDEs) are believed to be due to chemical oxidation by halogen radicals of long-lived gaseous elemental mercury (GEM, or Hg0) to much more quickly deposited reactive gaseous mercury compounds (RGM) and particle-bound mercury (PHg), and are estimated to contribute as much as 30–55% of the total atmospheric mercury deposited to the Arctic annually (Ariya et al, 2004; Christensen et al, 2004; Skov et al, 2004; Dastoor et al, 2008)
A previous analysis up to 2005 showed no significant long term trend in the annual Gaseous elemental mercury (GEM) concentration at Alert (Temme et al, 2007), but in this paper we extend the analysis in time, use an alternative statistical method, and look at seasonal behaviour in order to isolate the springtime AMDE chemistry
Summary
Mercury in the Arctic is of particular interest for two reasons. From a health perspective, mercury is found in high levels in Arctic wildlife and in some populations despite there being no major mercury sources nearby. For atmospheric scientists, monitoring of atmospheric mercury revealed unusual “atmospheric mercury depletion events” (AMDEs) in which mercury concentrations drop precipitously on timescales of a few hours (Schroeder et al, 1998). This interest has led to a great deal of research on mercury cycling in polar regions in recent years (see Steffen et al, 2008; Nguyen et al, 2009; and references therein). As the Arctic undergoes dramatic change due to reduced sea ice and warming temperatures (Cosimo, 2006), it is crucial to understand how climate change may affect the frequency and magnitude of AMDEs in the future in order to predict future inputs of mercury to polar regions
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