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| Titel |
Longpath DOAS observations of surface BrO at Summit, Greenland |
| VerfasserIn |
J. Stutz, J. L. Thomas, S. C. Hurlock, M. Schneider, R. Glasow, M. Piot, K. Gorham, J. F. Burkhart, L. Ziemba, J. E. Dibb, B. L. Lefer |
| 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 ; 11, no. 18 ; Nr. 11, no. 18 (2011-09-27), S.9899-9910 |
| Datensatznummer |
250010102
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| Publikation (Nr.) |
 copernicus.org/acp-11-9899-2011.pdf |
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| Zusammenfassung |
Reactive halogens, and in particular bromine oxide (BrO), have frequently
been observed in regions with large halide reservoirs, for example during
bromine catalyzed coastal polar ozone depletion events. Much less is known
about the presence and impact of reactive halogens in areas without obvious
halide reservoirs, such as the polar ice sheets or continental snow.
We report the first LP-DOAS measurements of BrO at Summit research station in
the center of the Greenland ice sheet at an altitude of 3200 m. BrO mixing
ratios in May 2007 and June 2008 were typically between
1–3 pmol mol−1, with maxima of up to 5 pmol mol−1. These
measurements unequivocally show that halogen chemistry is occurring in the
remote Arctic, far from known bromine reservoirs, such as the ocean. During
periods when FLEXPART retroplumes show that airmasses resided on the
Greenland ice sheet for 3 or more days, BrO exhibits a clear diurnal
variation, with peak mixing ratios of up to 3 pmol mol−1 in the
morning and at night. The diurnal cycle of BrO can be explained by a changing
boundary layer height combined with photochemical formation of reactive
bromine driven by solar radiation at the snow surface. The shallow stable
boundary layer in the morning and night leads to an accumulation of BrO at the
surface, leading to elevated BrO despite the expected smaller release from
the snowpack during these times of low solar radiation. During the day when
photolytic formation of reactive bromine is expected to be highest, efficient
mixing into a deeper neutral boundary layer leads to lower BrO mixing ratios
than during mornings and nights.
The extended period of contact with the Greenland snowpack combined with the
diurnal profile of BrO, modulated by boundary layer height, suggests that
photochemistry in the snow is a significant source of BrO measured at Summit
during the 2008 experiment. In addition, a rapid transport event on 4 July
2008, during which marine air from the Greenland east coast was rapidly
transported to Summit, led to enhanced mixing ratios of BrO and a number of
marine tracers. However, rapid transport of marine air from the Greenland
east coast is rare and most likely not the main source of bromide in surface
snow at Summit. The observed levels of BrO are predicted to influence
NOx chemistry as well as impact HOx partitioning. However,
impact of local snow photochemistry on HOx is smaller than
previously suggested for Summit. |
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