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| Titel |
Bromine and iodine chemistry in a global chemistry-climate model: description and evaluation of very short-lived oceanic sources |
| VerfasserIn |
C. Ordóñez, J.-F. Lamarque, S. Tilmes, D. E. Kinnison, E. L. Atlas, D. R. Blake, G. Sousa Santos, G. Brasseur, A. Saiz-Lopez |
| 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 ; 12, no. 3 ; Nr. 12, no. 3 (2012-02-07), S.1423-1447 |
| Datensatznummer |
250010638
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| Publikation (Nr.) |
 copernicus.org/acp-12-1423-2012.pdf |
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| Zusammenfassung |
| The global chemistry-climate model CAM-Chem has been extended to incorporate
an expanded bromine and iodine chemistry scheme that includes natural
oceanic sources of very short-lived (VSL) halocarbons, gas-phase
photochemistry and heterogeneous reactions on aerosols. Ocean emissions of
five VSL bromocarbons (CHBr3, CH2Br2, CH2BrCl,
CHBrCl2, CHBr2Cl) and three VSL iodocarbons (CH2ICl,
CH2IBr, CH2I2) have been parameterised by a biogenic
chlorophyll-a (chl-a) dependent source in the tropical oceans (20° N–20° S).
Constant oceanic fluxes with 2.5 coast-to-ocean emission ratios
are separately imposed on four different latitudinal bands in the
extratropics (20°–50° and above 50° in both hemispheres).
Top-down emission estimates of bromocarbons have been derived using
available measurements in the troposphere and lower stratosphere, while
iodocarbons have been constrained with observations in the marine boundary
layer (MBL). Emissions of CH3I are based on a previous inventory and
the longer lived CH3Br is set to a surface mixing ratio boundary
condition. The global oceanic emissions estimated for the most abundant VSL
bromocarbons – 533 Gg yr−1 for CHBr3 and 67.3 Gg yr−1 for
CH2Br2 – are within the range of previous estimates. Overall the
latitudinal and vertical distributions of modelled bromocarbons are in good
agreement with observations. Nevertheless, we identify some issues such as
the reduced number of aircraft observations to validate models in the
Southern Hemisphere, the overestimation of CH2Br2 in the upper
troposphere – lower stratosphere and the underestimation of CH3I in the
same region. Despite the difficulties involved in the global modelling of
the shortest lived iodocarbons (CH2ICl, CH2IBr, CH2I2),
modelled results are in good agreement with published observations in the
MBL. Finally, sensitivity simulations show that knowledge of the diurnal
emission cycle for these species, in particular for CH2I2, is key
to assess their global source strength. |
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