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| Titel |
How relevant is the deposition of mercury onto snowpacks? – Part 2: A modeling study |
| VerfasserIn |
D. Durnford, A. Dastoor, A. Ryzhkov, L. Poissant, M. Pilote, D. Figueras-Nieto |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 12, no. 19 ; Nr. 12, no. 19 (2012-10-11), S.9251-9274 |
| Datensatznummer |
250011504
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| Publikation (Nr.) |
 copernicus.org/acp-12-9251-2012.pdf |
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| Zusammenfassung |
| An unknown fraction of mercury that is deposited onto snowpacks is
revolatilized to the atmosphere. Determining the revolatilized fraction is
important since mercury that enters the snowpack meltwater may be converted
to highly toxic bioaccumulating methylmercury. In this study, we present a
new dynamic physically-based snowpack/meltwater model for mercury that is
suitable for large-scale atmospheric models for mercury. It represents the
primary physical and chemical processes that determine the fate of mercury
deposited onto snowpacks. The snowpack/meltwater model was implemented in
Environment Canada's atmospheric mercury model GRAHM. For the first time,
observed snowpack-related mercury concentrations are used to evaluate and
constrain an atmospheric mercury model. We find that simulated
concentrations of mercury in both snowpacks and the atmosphere's surface
layer agree closely with observations. The simulated concentration of
mercury in both in the top 30 cm and the top 150 cm of the snowpack,
averaged over 2005–2009, is predominantly below 6 ng L−1 over land
south of 66.5° N but exceeds 18 ng L−1 over sea ice in
extensive areas of the Arctic Ocean and Hudson Bay. The average simulated
concentration of mercury in snowpack meltwater runoff tends to be higher on
the Russian/European side (>20 ng L−1) of the Arctic Ocean
than on the Canadian side (<10 ng L−1). The correlation
coefficient between observed and simulated monthly mean atmospheric
surface-level gaseous elemental mercury (GEM) concentrations increased
significantly with the inclusion of the new snowpack/meltwater model at two
of the three stations (midlatitude, subarctic) studied and remained constant
at the third (arctic). Oceanic emissions are postulated to produce the
observed summertime maximum in concentrations of surface-level atmospheric
GEM at Alert in the Canadian Arctic and to generate the summertime
volatility observed in these concentrations at both Alert and Kuujjuarapik
on subarctic Hudson Bay, Canada. We find that the fraction of deposited
mercury that is revolatilized from snowpacks increases with latitude from
39% between 30 and 45° N, to 57% from 45 to 60° N,
67% from 60 to 66.5° N, and 75% polewards of
66.5° N on an annual basis. Combining this latitudinal gradient with the
latitudinally increasing coverage of snowpacks causes yearly net deposition
as a fraction of gross deposition to decrease from 98% between 30 and
45° N to 89% between 45 and 60° N, 73% between 60
and 66.5° N, and 44% within the Arctic Circle. The yearly net
deposition and net accumulation of mercury at the surface within the Arctic
Circle north of 66.5° N are estimated at 153 and 117 Mg,
respectively. We calculate that 58 and 50 Mg of mercury are deposited
annually to the Arctic Ocean directly and indirectly via melting snowpacks,
respectively. For terrestrial surfaces within the Arctic Circle, we find
that 29 and 16 Mg of mercury are deposited annually directly and indirectly
via melting snowpacks, respectively. Within the Arctic Circle, multi-season
snowpacks on land and over sea ice gained, on average, an estimated 0.1 and
0.4 Mg yr−1 mercury, respectively, from 2000–2005. The developed snowpack/meltwater
model can be used for investigating the impact of climate change on the
snowpack/atmosphere exchange of mercury. |
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