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| Titel |
Sensitivity of tropospheric chemical composition to halogen-radical chemistry using a fully coupled size-resolved multiphase chemistry–global climate system: halogen distributions, aerosol composition, and sensitivity of climate-relevant gases |
| VerfasserIn |
M. S. Long, W. C. Keene, R. C. Easter, R. Sander, X. Liu, A. Kerkweg, D. Erickson |
| 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. 7 ; Nr. 14, no. 7 (2014-04-07), S.3397-3425 |
| Datensatznummer |
250118565
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| Publikation (Nr.) |
 copernicus.org/acp-14-3397-2014.pdf |
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| Zusammenfassung |
| Observations and model calculations indicate that highly non-linear
multiphase atmospheric processes involving inorganic Cl and Br significantly
impact tropospheric chemistry and composition, aerosol evolution, and
radiative transfer. The sensitivity of global atmospheric chemistry to the
production of marine aerosol and the associated activation and cycling of
inorganic Cl and Br was investigated using a size-resolved multiphase coupled
chemistry–global climate model (National Center for Atmospheric Research's
Community Atmosphere Model (CAM) v3.6.33). Simulated results revealed strong
meridional and vertical gradients in Cl and Br species. They also point to
possible physicochemical mechanisms that may account for several previously
unexplained phenomena, including the enrichment of Br- in submicron
aerosol and the presence of a BrO maximum in the polar free troposphere.
However, simulated total volatile inorganic Br mixing ratios in the
troposphere were generally higher than observed, due in part to the overly
efficient net production of BrCl. In addition, the emission scheme for marine
aerosol and associated Br−, which is the only source for Br in the
model, overestimates emission fluxes from the high-latitude Southern Ocean.
Br in the stratosphere was lower than observed due to the lack of long-lived
precursor organobromine species in the simulation. Comparing simulations
using chemical mechanisms with and without reactive Cl and Br species
demonstrates a significant temporal and spatial sensitivity of primary
atmospheric oxidants (O3, HOx, NOx), CH4,
non-methane hydrocarbons (NMHCs), and dimethyl sulfide (DMS) to halogen
cycling. Globally, halogen chemistry had relatively less impact on SO2
and non-sea-salt (nss) SO42− although significant regional
differences were evident. Although variable geographically, much of this
sensitivity is attributable to either over-vigorous activation of Br
(primarily BrCl) via the chemical mechanism or overproduction of sea-salt
aerosol simulated under higher-wind regimes. In regions where simulated
mixing ratios of reactive Br and Cl fell within observed ranges, though,
halogen chemistry drove large changes in oxidant fields and associated
chemical processes relative to simulations with no halogens. However, the
overall simulated impacts of Br chemistry globally are overestimated and thus
caution is warranted in their interpretation. |
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