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| Titel |
Global oceanic emissions of very short-lived (VSL) halocarbons in a chemistry-climate model |
| VerfasserIn |
Carlos Ordóñez, Jean-Francois Lamarque, Douglas E. Kinnison, Simone Tilmes, John Orlando, Gabriela Sousa Santos, Elliot Atlas, Donald R. Blake, Guy Brasseur, Alfonso Saiz-Lopez |
| 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 |
250047316
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| Zusammenfassung |
| The global CAM-Chem chemistry-climate model contains parameterisations of
stratospheric and tropospheric chemistry. Its scope has been extended to include halogen
chemistry in the troposphere. This comprises 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. We have derived an emission inventory for VSL bromocarbons
(CHBr3, CH2Br2, CH2BrCl, CHBrCl2, CHBr2Cl) and iodocarbons (CH2ICl, CH2IBr,
CH2I2) using a compilation of aircraft campaigns and more sparse observations in the
marine boundary layer (MBL), respectively. Emissions for methyl iodide (CH3I) in
CAM-Chem are based on the inventory from a previous modelling study while the
longer lived methyl bromide (CH3Br) and organochlorides are set as lower boundary
conditions.
Reported correlations between the abundance of bromocarbons and areas of high primary
productivity (as indicated by SeaWiFS satellite data for chlorophyll-a concentration) have
been used to constrain the emission fields for most VSL halocarbons over the tropical oceans
(defined as 20Ë S - 20Ë N). These emission sources have been extended to the mid- and
high-latitude oceans, where we consider latitudinal variation in addition to 2.5 higher
emission fluxes over the coastal areas to account for the stronger sources there
compared to the open ocean. Observed concentration ratios among bromoform
(CHBr3) and other bromocarbons as well as subsequent comparisons of modelled
bromocarbon mixing ratios with a composite of aircraft observations have been exploited
to derive their total emission fluxes. Overall, these are in good agreement with
emission magnitudes determined by previous model studies. The simulated vertical
profiles of bromocarbons and methyl iodide, which have atmospheric lifetimes (~
7 to 150 days) long enough for them to be transported to the upper troposphere
within deep convection areas, are similar in magnitude and vertical distribution to
airborne observations in the troposphere. The total emission fluxes of the remaining
iodocarbons (CH2ICl, CH2IBr, CH2I2) and molecular iodine (I2), with shorter lifetimes
on the order of a few hours to seconds and therefore more relevant as sources of
reactive halogens in the MBL, have been determined following previous reports
from the scientific literature and comparisons with available observations in the
MBL.
Further work will quantify the potential of bromine and iodine chemistry to influence the
oxidation capacity of the atmosphere. |
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