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| Titel |
Synoptic-scale meteorological control on reactive bromine production and ozone depletion in the Arctic boundary layer: 3-D simulation with the GEM-AQ model |
| VerfasserIn |
Kenjiro Toyota, John C. McConnell |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250057698
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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 capable of converting relatively stable bromine
species to photolabile Br2 via air-snowpack interactions. A "bromine explosion", by which
Br- retained in the snowpack is autocatalytically released to the atmosphere as a result of
dry deposition of HOBr and BrONO2, is assumed to occur on young, first-year (FY) sea ice
(or its overlying snowpack), whereas the snowpack on old, multi-year (MY) sea
ice and over land is assumed only to recycle a part (but up to 100%) of bromine
reservoirs lost via dry deposition back to Br2. Model runs are performed for April 2001
at a horizontal resolution of approximately 100Â km x 100Â km in the Arctic. The
model simulates temporal variations in surface ozone mixing ratios as observed at
stations in the high Arctic and the synoptic-scale evolution of enhanced BrO column
amounts ("BrO clouds") as seen from satellite reasonably well. The results strongly
suggest: (1) the ubiquitous source of reactive bromine exists on the FY sea ice during
the Arctic springtime; and (2) the timing of bromine release to the atmosphere
is largely controlled by meteorological forcing on the transport of ozone to the
near-surface air. Also, if reactive bromine in the Arctic boundary layer is supplied
predominantly from the surface snowpack, it should be capable of releasing reactive
bromine at temperatures as high as -10Â °C, particularly on the FY 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" associated with the
surface source of bromine in the high Arctic. Contrary to our original intention, the
present air-snowpack interaction scheme yields a majority of atmospheric bromine
input via Br2 release associated empirically with a dry deposition of ozone on the
snow/ice surface under sunlight to represent a trigger of bromine explosion. This
implies that the bromine explosion actually occurs in the interstitial air of snowpack
and/or is accelerated by heterogeneous reactions on the surface of wind-blown
snow in ambient air, both of which are missing in our model but could have been
approximated by a parameter adjustment for the yield of Br2 from the trigger. |
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