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| Titel |
Inclusion of polar sea-ice emissions and sea-salt aerosol recycling of bromine into the global CAM-Chem chemistry-climate model |
| VerfasserIn |
Rafael Pedro Fernandez, Carlos Ordóñez, Douglas Kinnison, Jean-Francois Lamarque, Alfonso Saiz-Lopez |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250072774
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| Zusammenfassung |
| The global CAM-Chem chemistry climate model has been updated by including a coupled
polar module with a full halogen chemistry mechanism and time-varying organic and
inorganic halogen emissions into the polar marine boundary layer. The baseline halogen
CAM-Chem setup has already been validated for the tropics and mid-latitudes and includes
natural sources of very short-lived (VSL) halocarbons from the oceans; reactive chlorine,
bromine and iodine species; related photochemical, gas-phase and heterogeneous reactions,
as well as wet and dry deposition for relevant species. The coupled polar module
considers i) time-dependent sea-ice emissions of Br2 and BrCl as result of recycling
over the deposited snow over sea-ice, ii) sea-salt aerosol recycling of BrONO2,
BrNO2 and HOBr in the polar boundary layer and iii) improved sea-salt recycling
efficiency over fresh sea-ice regions representing the contributions from blowing
snow.
The external brominated sources posses a 2-fold dependence on both solar zenith angle
and local sea-ice cover. The time/sea-ice dependent local Br2 flux was scaled to reproduce
observations of reactive bromine species over coastal Antarctica. This results in an Antarctic
mean sea-ice flux of ~200 Gg Br yr-1 with maximum emissions in late spring, as a
compromise between sea-ice coverage and intensity of radiation. Recycling of bromine over
sea-salt aerosol is the dominant factor controlling the tropospheric vertical column density
(VCD) of BrO and other inorganic bromine species. A monthly-dependent depletion factor is
introduced to account for the net fraction of Br in sea-salt that is released to the
atmosphere.
Model results have been validated locally against measurements of BrO performed at
several Antarctic stations, showing a good agreement both in the boundary layer
concentrations for the entire year and the springtime maximum BrO observed in October. The
seasonality and intensity of the BrO total and tropospheric columns are also in agreement
with BrO VCDs results reported from satellite platforms, showing a polar BrO cloud
distribution coincident with the Antarctic monthly sea-ice coverage. Further work will
quantify the contribution of halogen chemistry to the oxidation capacity of the polar
atmosphere. |
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