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| Titel |
On the origin of the occasional spring nitrate peak in Greenland snow |
| VerfasserIn |
L. Geng, J. Cole-Dai, B. Alexander, J. Erbland, J. Savarino, A. J. Schauer, E. J. Steig, P. Lin, Q. Fu, M. C. Zatko |
| 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 ; 14, no. 24 ; Nr. 14, no. 24 (2014-12-16), S.13361-13376 |
| Datensatznummer |
250119242
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| Publikation (Nr.) |
 copernicus.org/acp-14-13361-2014.pdf |
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| Zusammenfassung |
| Ice core nitrate concentrations peak in the summer in both Greenland and
Antarctica. Two nitrate concentration peaks in one annual layer have been
observed some years in ice cores in Greenland from samples dating
post-1900, with the additional nitrate peak occurring in the spring. The
origin of the spring nitrate peak was hypothesized to be pollution transport
from the mid-latitudes in the industrial era. We performed a case study on the
origin of a spring nitrate peak in 2005 measured from a snowpit at Summit,
Greenland, covering 3 years of snow accumulation. The effect of
long-range transport of nitrate on this spring peak was excluded by using
sulfate as a pollution tracer. The isotopic composition of nitrate
(δ15N, δ18O and Δ17O) combined with
photochemical calculations suggest that the occurrence of this spring peak
is linked to a significantly weakened stratospheric ozone (O3) layer.
The weakened O3 layer resulted in elevated UVB (ultraviolet-B)
radiation on the snow surface, where the production of OH and NOx from
the photolysis of their precursors was enhanced. Elevated NOx and OH
concentrations resulted in enhanced nitrate production mainly through the
NO2 + OH formation pathway, as indicated by decreases in δ18O and Δ17O of nitrate associated with the spring peak.
We further examined the nitrate concentration record from a shallow ice core
covering the period from 1772 to 2006 and found 19 years with double nitrate
peaks after the 1950s. Out of these 19 years, 14 of the secondary nitrate
peaks were accompanied by sulfate peaks, suggesting long-range transport of
nitrate as their source. In the other 5 years, low springtime O3
column density was observed, suggesting enhanced local production of nitrate
as their source. The results suggest that, in addition to direct transport
of nitrate from polluted regions, enhanced local photochemistry can also
lead to a spring nitrate peak. The enhanced local photochemistry is probably
associated with the interannual variability of O3 column density in the
Arctic, which leads to elevated surface UV radiation in some years. In this
scenario, enhanced photochemistry caused increased local nitrate production
under the condition of elevated local NOx abundance in the industrial
era. |
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