Trends in long-term gaseous mercury observations in the Arctic and effects of temperature and other atmospheric conditions

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 Correspondence to: A. S. Cole (amanda.cole@ec.gc.ca) 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.

Atmospheric mercury speciation and mercury in snow over time at Alert, Canada

“…Finally, Fig. 2 shows that the previously reported decrease in [GEM] in March (Cole and Steffen, 2010) is concurrent with a notable increase in [PHg] followed by an increase in [RGM] in May.…”

“…We have no explanation for the elevated [PHg] for these years at this time. Cole and Steffen (2010) reported a relationship between air temperature particulate mercury (PHg-green) and reactive gaseous mercury (RGM-pink) from Alert, 2002Alert, -2011. GEM is in ng m -3 and PHg and RGM are in pg m -3 .…”

“…The origin of air masses travelling to Alert have been previously studied in depth and revealed that the large majority of mercury and ozone depletion events occur when the wind direction is between 315 • and 90 • (i.e. from over the Arctic Ocean) (Cole and Steffen, 2010) and from the North Pole to the Kara Sea (Bottenheim and Chan, 2006). Another study from Alert reported that the predominant wind direction in 2005 was from the south-southwest direction; yet, when depletion events occurred, the winds tended to emerge from the north (Cobbett et al, 2007).…”

“…Long-term atmospheric measurements of GEM have been undertaken since 1995 Cole and Steffen, 2010) and speciation data have been collected since 2002. The unique GEM annual signature from Alert has been previously published Steffen et al, 2005;Cobbett et al, 2007;Cole and Steffen, 2010) showing northern hemispheric background levels in the fall and winter, lower concentrations in the spring and higher concentrations in the summer. The lifetime of atmospheric mercury depends on its chemical form and is considered to be GEM PHg > RGM (Schroeder and Munthe, 1998).…”

Speciated mercury at marine, coastal, and inland sites in New England – Part 2: Relationships with atmospheric physical parameters

“…Six-year measurement datasets from Mace Head, Ireland and Zingst, Germany showed a strong positive correlation TGM bore with wind and dew point (Kock et al, 2005). Cole and Steffen (2010) found a positive correlation between Hg 0 and air temperature from their 12 yr (1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007) measurement data in Alert, Canada although it was not clear if temperature was the direct cause of the Hg 0 variability. Long-term measurements of speciated mercury have been conducted at inland, coastal, and marine locations in southern New Hampshire.…”