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

Abstract

Abstract. Ten years of atmospheric mercury speciation data and 14 years of mercury in snow data from Alert, Nunavut, Canada, are examined. The speciation data, collected from 2002 to 2011, includes gaseous elemental mercury (GEM), particulate mercury (PHg) and reactive gaseous mercury (RGM). During the winter-spring period of atmospheric mercury depletion events (AMDEs), when GEM is close to being completely depleted from the air, the concentration of both PHg and RGM rise significantly. During this period, the median concentrations for PHg is 28.2 pgm−3 and RGM is 23.9 pgm−3, from March to June, in comparison to the annual median concentrations of 11.3 and 3.2 pgm−3 for PHg and RGM, respectively. In each of the ten years of sampling, the concentration of PHg increases steadily from January through March and is higher than the concentration of RGM. This pattern begins to change in April when the levels of PHg peak and RGM begin to increase. In May, the high PHg and low RGM concentration regime observed in the early spring undergoes a transition to a regime with higher RGM and much lower PHg concentrations. The higher RGM concentration continues into June. The transition is driven by the atmospheric conditions of air temperature and particle availability. Firstly, a high ratio of the concentrations of PHg to RGM is reported at low temperatures which suggests that oxidized gaseous mercury partitions to available particles to form PHg. Prior to the transition, the median air temperature is −24.8 °C and after the transition the median air temperature is −5.8 °C. Secondly, the high PHg concentrations occur in the spring when high particle concentrations are present. The high particle concentrations are principally due to Arctic haze and sea salts. In the snow, the concentrations of mercury peak in May for all years. Springtime deposition of total mercury to the snow at Alert peaks in May when atmospheric conditions favour higher levels of RGM. Therefore, the conditions in the atmosphere directly impact when the highest amount of mercury will be deposited to the snow during the Arctic spring.

Chemical cycling and deposition of atmospheric mercury in polar regions: review of recent measurements and comparison with models

“…In addition, Toyota et al (2014) provided the temperature dependence of these reactions, which needs to be verified experimentally. Based on 10 years of data, Steffen et al (2014) also reported higher levels of mercury in the snow when the atmospheric conditions favored the formation of RGM. This springtime shift from the predominance of Hg(p) to RGM in AMDEs likely directly impacts the amount of mercury deposited onto the snowpack.…”

“…This shift has already been evidenced at Churchill, Manitoba (Kirk et al, 2006), ALT (Cobbett et al, 2007), and NYA (Steen et al, 2011) and has been shown to repeat year after year at ALT . Steffen et al (2014) suggested that this shift is due to temperature and particle availability. Using a detailed air-snowpack model for interactions of bromine, ozone, and mercury in the springtime Arctic, Toyota et al (2014) proposed that Hg(p) is mainly produced as HgBr 2− 4 through uptake of RGM into bromine-enriched aerosols after ozone is significantly depleted in the air mass.…”

Pan-Arctic aerosol number size distributions: seasonality and transport patterns

“…The nearby Lincoln Sea typically remains frozen year-round. The aerosol number size distribution in the range of 10 to 500 nm is measured with a TSI 3034 SMPS that is calibrated on site (Leaitch et al, 2013;Steffen et al, 2014).…”

Mercury in the Arctic tundra snowpack: temporal and spatial concentration patterns and trace gas exchanges

“…In our study, we did not have sufficient temporal resolution of snow sampling during the period of AMDEs to closely track the fate of Hg deposition during AMDEs and subsequent re-emissions. However, we find that snow Hg enhancements during AMDEs were much lower than at coastal sites (e.g., Steffen et al, 2014), but a coarse temporal sampling could just have missed peak snow Hg levels at this site. We also found that after AMDEs, snow Hg diss in surface snow declined to levels as was observed prior to AMDEs, and no concentration enhancements were observed deeper in the snowpack.…”

“…The lack of consistent statistically significant associations between major ions and Hg diss across the entire snowpack depth (Table 2a) further suggests that initial snowfall Hg content was maintained and largely unaltered after deposition, with no clear accumulation or depletion zones as found in other snowpacks (Ferrari et al, 2005;Poulain et al, 2004;Steffen et al, 2014). We found a small relative enrichment of alkaline earth elements in snowpack samples compared to surface snow, which indicates some additional contributions of local mineral dust, yet this did not result in a measurable increase in snowpack Hg levels.…”