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| Titel |
Analysis of reactive bromine production and ozone depletion in the Arctic boundary layer using 3-D simulations with GEM-AQ: inference from synoptic-scale patterns |
| VerfasserIn |
K. Toyota, J. C. McConnell, A. Lupu, L. Neary, C. A. McLinden, A. Richter, R. Kwok, K. Semeniuk, J. W. Kaminski, S.-L. Gong, J. Jarosz, M. P. Chipperfield, C. E. Sioris |
| 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. 8 ; Nr. 11, no. 8 (2011-04-28), S.3949-3979 |
| Datensatznummer |
250009660
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| Publikation (Nr.) |
 copernicus.org/acp-11-3949-2011.pdf |
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| Zusammenfassung |
| Episodes of high bromine levels and surface ozone depletion in the springtime
Arctic are simulated by an online air-quality model, GEM-AQ, with gas-phase
and heterogeneous reactions of inorganic bromine species and a simple scheme
of air-snowpack chemical interactions implemented for this study. Snowpack on
sea ice is assumed to be the only source of bromine to the atmosphere and to
be capable of converting relatively stable bromine species to photolabile
Br2 via air-snowpack interactions. A set of sensitivity model runs
are performed for April 2001 at a horizontal resolution of approximately
100 km×100 km in the Arctic, to provide insights into the effects
of temperature and the age (first-year, FY, versus multi-year, MY) of sea ice
on the release of reactive bromine to the atmosphere. The model simulations
capture much of the temporal variations in surface ozone mixing ratios as
observed at stations in the high Arctic and the synoptic-scale evolution of
areas with enhanced BrO column amount ("BrO clouds") as estimated from
satellite observations. The simulated "BrO clouds" are in modestly better
agreement with the satellite measurements when the FY sea ice is assumed to
be more efficient at releasing reactive bromine to the atmosphere than on the
MY sea ice. Surface ozone data from coastal stations used in this study are
not sufficient to evaluate unambiguously the difference between the FY sea
ice and the MY sea ice as a source of bromine. The results strongly suggest
that reactive bromine is released ubiquitously from the snow on the sea ice
during the Arctic spring while the timing and location of the bromine release
are largely controlled by meteorological factors. It appears that a rapid
advection and an enhanced turbulent diffusion associated with strong
boundary-layer winds drive transport and dispersion of ozone to the
near-surface air over the sea ice, increasing the oxidation rate of bromide
(Br−) in the surface snow. Also, if indeed the surface snowpack does
supply most of the reactive bromine in the Arctic boundary layer, it appears
to be capable of releasing reactive bromine at temperatures as high as
−10 °C, particularly on the sea ice in the central and eastern
Arctic Ocean. Dynamically-induced BrO column variability in the lowermost
stratosphere appears to interfere with the use of satellite BrO column
measurements for interpreting BrO variability in the lower troposphere but
probably not to the extent of totally obscuring "BrO clouds" that originate
from the surface snow/ice source of bromine in the high Arctic. A budget
analysis of the simulated air-surface exchange of bromine compounds suggests
that a "bromine explosion" occurs in the interstitial air of the snowpack
and/or is accelerated by heterogeneous reactions on the surface of wind-blown
snow in ambient air, both of which are not represented explicitly in our
simple model but could have been approximated by a parameter adjustment for
the yield of Br2 from the trigger. |
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