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| Titel |
The influence of snow grain size and impurities on the vertical profiles of actinic flux and associated NOx emissions on the Antarctic and Greenland ice sheets |
| VerfasserIn |
M. C. Zatko, T. C. Grenfell, B. Alexander, S. J. Doherty, J. L. Thomas, X. Yang |
| 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 ; 13, no. 7 ; Nr. 13, no. 7 (2013-04-02), S.3547-3567 |
| Datensatznummer |
250018564
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| Publikation (Nr.) |
 copernicus.org/acp-13-3547-2013.pdf |
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| Zusammenfassung |
| We use observations of the absorption properties of black carbon and
non-black carbon impurities in near-surface snow collected near the research
stations at South Pole and Dome C, Antarctica, and Summit, Greenland, combined
with a snowpack actinic flux parameterization to estimate the vertical
profile and e-folding depth of ultraviolet/near-visible (UV/near-vis)
actinic flux in the snowpack at each location. We have developed a simple
and broadly applicable parameterization to calculate depth and wavelength
dependent snowpack actinic flux that can be easily integrated into large-scale
(e.g., 3-D) models of the atmosphere. The calculated e-folding depths of
actinic flux at 305 nm, the peak wavelength of nitrate photolysis in the
snowpack, are 8–12 cm near the stations and 15–31 cm away (>11 km)
from the stations. We find that the e-folding depth is strongly
dependent on impurity content and wavelength in the UV/near-vis region,
which explains the relatively shallow e-folding depths near stations where
local activities lead to higher snow impurity levels. We calculate the
lifetime of NOx in the snowpack interstitial air produced by photolysis
of snowpack nitrate against wind pumping (τwind pumping) from
the snowpack, and compare this to the calculated lifetime of NOx against
chemical conversion to HNO3 (τchemical) to determine whether
the NOx produced at a given depth can escape from the snowpack to the
overlying atmosphere. Comparison of τwind pumping and
τchemical suggests efficient escape of photoproduced NOx in the
snowpack to the overlying atmosphere throughout most of the photochemically
active zone. Calculated vertical actinic flux profiles and observed snowpack
nitrate concentrations are used to estimate the potential flux of NOx
from the snowpack. Calculated NOx fluxes of
4.4 × 108–3.8 × 109 molecules cm−2 s−1
in remote polar locations and 3.2–8.2 × 108 molecules cm−2 s−1
near polar stations for January at Dome C and
South Pole and June at Summit suggest that NOx flux measurements near
stations may be underestimating the amount of NOx emitted from the
clean polar snowpack. |
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