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| Titel |
Nitrogen and oxygen isotopic constraints on the origin of atmospheric nitrate in coastal Antarctica |
| VerfasserIn |
J. Savarino, J. Kaiser, S. Morin, D. M. Sigman, M. H. Thiemens |
| 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 ; 7, no. 8 ; Nr. 7, no. 8 (2007-04-18), S.1925-1945 |
| Datensatznummer |
250004908
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| Publikation (Nr.) |
 copernicus.org/acp-7-1925-2007.pdf |
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| Zusammenfassung |
| Throughout the year 2001, aerosol samples were collected continuously for 10
to 15 days at the French Antarctic Station Dumont d'Urville (DDU) (66°40' S,
l40°0' E, 40 m above mean sea level). The nitrogen and oxygen
isotopic ratios of particulate nitrate at DDU exhibit seasonal variations
that are among the most extreme observed for nitrate on Earth. In
association with concentration measurements, the isotope ratios delineate
four distinct periods, broadly consistent with previous studies on Antarctic
coastal areas. During austral autumn and early winter (March to mid-July),
nitrate concentrations attain a minimum between 10 and 30 ng m−3
(referred to as Period 2). Two local maxima in August (55 ng m−3) and
November/December (165 ng m−3) are used to assign Period 3 (mid-July to
September) and Period 4 (October to December). Period 1 (January to March)
is a transition period between the maximum concentration of Period 4 and the
background concentration of Period 2. These seasonal changes are reflected
in changes of the nitrogen and oxygen isotope ratios. During Period 2, which
is characterized by background concentrations, the isotope ratios are in the
range of previous measurements at mid-latitudes: δ18Ovsmow=(77.2±8.6)‰;
Δ17O=(29.8±4.4)‰;
δ15Nair=(−4.4±5.4)‰ (mean ± one standard
deviation). Period 3 is accompanied by a significant increase of the oxygen
isotope ratios and a small increase of the nitrogen isotope ratio to
δ18Ovsmow=(98.8±13.9)‰;
Δ17O=(38.8±4.7)‰
and δ15Nair=(4.3±8.20‰). Period 4 is
characterized by a minimum 15N/14N ratio, only matched by one
prior study of Antarctic aerosols, and oxygen isotope ratios similar to
Period 2: δ18Ovsmow=(77.2±7.7)‰;
Δ17O=(31.1±3.2)‰; δ15Nair=(−32.7±8.4)‰.
Finally, during Period 1, isotope ratios reach minimum values for
oxygen and intermediate values for nitrogen: δ18Ovsmow=63.2±2.5‰;
Δ17O=24.0±1.1‰; δ15Nair=−17.9±4.0‰). Based on the measured isotopic
composition, known atmospheric transport patterns and the current
understanding of kinetics and isotope effects of relevant atmospheric
chemical processes, we suggest that elevated tropospheric nitrate levels
during Period 3 are most likely the result of nitrate sedimentation from
polar stratospheric clouds (PSCs), whereas elevated nitrate levels during
Period 4 are likely to result from snow re-emission of nitrogen oxide
species. We are unable to attribute the source of the nitrate during periods
1 and 2 to local production or long-range transport, but note that the
oxygen isotopic composition is in agreement with day and night time nitrate
chemistry driven by the diurnal solar cycle. A precise quantification is
difficult, due to our insufficient knowledge of isotope fractionation during
the reactions leading to nitrate formation, among other reasons. |
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