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| Titel |
Low sensitivity of cloud condensation nuclei to changes in the sea-air flux of dimethyl-sulphide |
| VerfasserIn |
M. T. Woodhouse, K. S. Carslaw, G. W. Mann, S. M. Vallina, M. Vogt, P. R. Halloran, O. Boucher |
| 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 ; 10, no. 16 ; Nr. 10, no. 16 (2010-08-16), S.7545-7559 |
| Datensatznummer |
250008704
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| Publikation (Nr.) |
 copernicus.org/acp-10-7545-2010.pdf |
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| Zusammenfassung |
| The emission of dimethyl-sulphide (DMS) gas by phytoplankton and the
subsequent formation of aerosol has long been suggested as an important
climate regulation mechanism. The key aerosol quantity is the number
concentration of cloud condensation nuclei (CCN), but until recently global
models did not include the necessary aerosol physics to quantify CCN. Here we
use a global aerosol microphysics model to calculate the sensitivity of CCN
to changes in DMS emission using multiple present-day and future sea-surface
DMS climatologies. Calculated annual fluxes of DMS to the atmosphere for the
five model-derived and one observations based present day climatologies are
in the range 15.1 to 32.3 Tg a−1 sulphur. The impact of DMS
climatology on surface level CCN concentrations was calculated in terms of
summer and winter hemispheric mean values of ΔCCN/ΔFluxDMS,
which varied between −43 and +166 cm−3/(mg m−2 day−1
sulphur), with a mean of 63 cm−3/(mg m−2 day−1 sulphur).
The range is due to CCN production in the atmosphere being strongly dependent
on the spatial distribution of the emitted DMS. The relative sensitivity of CCN
to DMS (i.e. fractional change in CCN divided by fractional change in DMS flux)
depends on the abundance of non-DMS derived aerosol in each hemisphere. The
relative sensitivity averaged over the five present day DMS climatologies is
estimated to be 0.02 in the northern hemisphere (i.e. a 0.02% change in CCN
for a 1% change in DMS) and 0.07 in the southern hemisphere where aerosol
abundance is lower. In a globally warmed scenario in which the DMS flux increases
by ~1% relative to present day we estimate a ~0.1%
increase in global mean CCN at the surface. The largest CCN response occurs in the
Southern Ocean, contributing to a Southern Hemisphere mean annual increase of
less than 0.2%. We show that the changes in DMS flux and CCN concentration
between the present day and global warming scenario are similar to
interannual differences due to variability in windspeed. In summary, although
DMS makes a significant contribution to global marine CCN concentrations, the
sensitivity of CCN to potential future changes in DMS flux is very low. This
finding, together with the predicted small changes in future seawater DMS
concentrations, suggests that the role of DMS in climate regulation is very
weak. |
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