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| Titel |
Model study of multiphase DMS oxidation with a focus on halogens |
| VerfasserIn |
R. Glasow, P. J. Crutzen  |
| 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 ; 4, no. 3 ; Nr. 4, no. 3 (2004-04-14), S.589-608 |
| Datensatznummer |
250001700
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| Publikation (Nr.) |
 copernicus.org/acp-4-589-2004.pdf |
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| Zusammenfassung |
| We studied the oxidation of dimethylsulfide (DMS) in the marine
boundary layer (MBL) with a one-dimensional numerical model and
focused on the influence of halogens. Our model runs show that there
is still significant uncertainty about the end products of the
DMS addition pathway, which is especially caused by uncertainty
in the product yield of the reaction of the intermediate product methyl sulfinic acid
(MSIA) with OH. BrO strongly increases the importance
of the addition branch in the oxidation of DMS even when
present at mixing ratios smaller than 0.5pmol mol-1. The
inclusion of halogen chemistry leads to higher DMS oxidation
rates and smaller DMS to SO2 conversion
efficiencies. The DMS to SO2 conversion efficiency is
also drastically reduced under cloudy conditions. In cloud-free model
runs between 5 and 15% of the oxidized DMS reacts further to
particulate sulfur, in cloudy runs this fraction is almost 100%.
Sulfate production by HOClaq and HOBraq is
important in cloud droplets even for small Br- deficits and
related small gas phase halogen concentrations. In general, more
particulate sulfur is formed when halogen chemistry is included. A
possible enrichment of HCO3- in fresh sea salt aerosol would
increase pH values enough to make the reaction of S(IV)*
(=SO2,aq+HSO3-+SO32-)
with O3 dominant for sulfate production. It leads to a shift
from methyl sulfonic acid (MSA) to non-sea
salt sulfate (nss-SO42-) production but increases the
total nss-SO42- only somewhat because almost all available
sulfur is already oxidized to particulate sulfur in the base
scenario. We discuss how realistic this is for the MBL. We found the
reaction MSAaq+OH to contribute about 10% to the
production of nss-SO42- in clouds. It is unimportant for
cloud-free model runs. Overall we find that the presence of halogens
leads to processes that decrease the albedo of stratiform clouds in the
MBL. |
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