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| Titel |
Aerosol cloud activation in summer and winter at puy-de-Dôme high altitude site in France |
| VerfasserIn |
E. Asmi, E. Freney, M. Hervo, D. Picard, C. Rose, A. Colomb, K. Sellegri |
| 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. 23 ; Nr. 12, no. 23 (2012-12-04), S.11589-11607 |
| Datensatznummer |
250011648
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| Publikation (Nr.) |
 copernicus.org/acp-12-11589-2012.pdf |
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| Zusammenfassung |
| Cloud condensation nuclei (CCN) size distributions and numbers were measured
for the first time at Puy-de-Dôme high altitude (1465 m a.s.l) site in
Central France. Majority of the measurements were done at constant
supersaturation (SS) of 0.24%, which was also deduced to be representative
of the typical in-cloud SS at the site. CCN numbers during summer ranged from
about 200 up to 2000 cm−3 and during winter from 50 up to
3000 cm−3. Variability of CCN number was explained by both particle
chemistry and size distribution variability. The higher CCN concentrations
were measured in continental, in contrast to marine, air masses. Aerosol CCN
activity was described with a single hygroscopicity parameter κ. Range
of this parameter was 0.29 ± 0.13 in summer and 0.43 ± 0.19 in
winter. When calculated using SS of 0.51% during summer, κ of
0.22 ± 0.07 was obtained. The decrease with increasing SS is likely
explained by the particle size dependent chemistry with smaller particles
containing higher amounts of freshly emitted organic species. Higher κ
values during winter were for the most part explained by the observed aged
organics (analysed from organic m/z 44 ratio) rather than from
aerosol organic to inorganic volume fraction. The obtained κ values
also fit well within the range of previously proposed global continental
κ of 0.27 ± 0.21. During winter, the smallest κ values
and the highest organic fractions were measured in marine air masses. CCN
closure using bulk AMS chemistry led to positive bias of 5% and 2% in
winter and summer, respectively. This is suspected to stem from size
dependent aerosol organic fraction, which is underestimated by using AMS bulk
mass composition. Finally, the results were combined with size distributions
measured from interstitial and whole air inlets to obtain activated droplet
size distributions. Cloud droplet number concentrations were shown to
increase with accumulation mode particle number, while the real in-cloud SS
correspondingly decreased. These results provide evidence on the effects of
aerosol particles on maximum cloud supersaturations. Further work with
detailed characterisation of cloud properties is proposed in order to provide
more quantitative estimates on aerosol effects on clouds. |
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