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| Titel |
A three-dimensional model study of methanesulphonic acid to non sea salt sulphate ratio at mid and high-southern latitudes |
| VerfasserIn |
H. Castebrunet, P. Martinerie, C. Genthon, E. Cosme |
| 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 ; 9, no. 24 ; Nr. 9, no. 24 (2009-12-16), S.9449-9469 |
| Datensatznummer |
250007802
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| Publikation (Nr.) |
 copernicus.org/acp-9-9449-2009.pdf |
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| Zusammenfassung |
| The Antarctic and sub-Antarctic methanesulphonic acid (MSA) to non sea salt
sulphate (nssSO4) ratio is simulated with the Laboratoire de
Météorologie Dynamique Atmospheric General Circulation Model including an
atmospheric sulphur chemistry module. Spatial variations of the MSA/nssSO4
ratio in different regions have been suggested to be mostly dependent on
temperature or sulphur source contributions. Its past variations in ice cores
have been interpreted as related to the DMS precursor source location. Our
model results are compared with available field measurements in the Antarctic
and sub-Antarctic regions. This suggests that the MSA/nssSO4 ratio in the
extra-tropical south hemisphere is mostly dependent on the relative
importance of various DMS oxidation pathways. In order to evaluate the effect
of a rapid conversion of dimethyl sulphoxide (DMSO) into MSA, not implemented
in the model, the MSA+DMSO to nssSO4 ratio is also discussed. Using this
modified ratio, the model mostly captures the seasonal variations of
MSA/nssSO4 at mid and high-southern latitudes. In addition, the model
qualitatively reproduces the bell shaped meridional variations of the ratio,
which is highly dependent on the adopted relative reaction rates for the
DMS+OH addition and abstraction pathways, and on the assumed reaction
products of the MSIA+OH reaction. MSA/nssSO4 ratio in Antarctic snow is
fairly well reproduced except at the most inland sites characterized with
very low snow accumulation rates. Our results also suggest that atmospheric
chemistry plays an important role in the observed decrease of the ratio in
snow between coastal regions and central Antarctica. The still insufficient
understanding of the DMS oxidation scheme limits our ability to model the
MSA/nssSO4 ratio. Specifically, reaction products of the MSIA+OH reaction
should be better quantified, and the impact of a fast DMSO conversion to MSA
in spring to fall over Antarctica should be evaluated.
A better understanding of BrO source processes is needed in order to
include DMS + BrO chemistry in global models. Completing the observations of
DMS, BrO and MSA at Halley Bay with DMSO measurements would better constrain
the role of BrO in DMS oxidation. Direct measurements of
MSA and nssSO4 dry deposition velocities on Antarctic snow would improve
our ability to model MSA and nssSO4 in ice cores. |
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