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| Titel |
Assessment of cloud supersaturation by aerosol particle and cloud condensation nuclei (CCN) measurements |
| VerfasserIn |
Mira L. Krüger, Stephan Mertes, Thomas Klimach, Yafang Cheng, Hang Su, Johannes Schneider, Meinrat O. Andreae, Ulrich Pöschl, Diana Rose |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250099020
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| Publikation (Nr.) |
 EGU/EGU2014-14758.pdf |
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| Zusammenfassung |
| Atmospheric aerosols consist of particles spanning a wide range of size and chemical
composition from various natural and anthropogenic sources. They can act as cloud
condensation nuclei (CCN) and affect climate by influencing the properties of clouds and
precipitation. The water vapor supersaturation at which aerosol particles are activated as CCN
depends on particle size, composition and mixing state.
Techniques for the direct measurement of cloud supersaturation are not available. Thus,
indirect methods have been developed to estimate the value of water vapor supersaturation in
a cloud, which determines the fraction of particles that are activated and form cloud
droplets.
In this study we show how size-resolved measurements of aerosol particles and cloud
condensation nuclei (CCN) can be used to characterize the supersaturation of water vapor in
a cloud. The method was developed and applied for the investigation of a cloud
event during the ACRIDICON-Zugspitze campaign (17 Sep to 4 Oct 2012) at the
high-alpine research station Schneefernerhaus (German Alps, 2650 m asl). Number
size distributions of total and interstitial aerosol particles were measured with a
scanning mobility particle sizer (SMPS), and size-resolved CCN efficiency spectra
were recorded with a CCN counter system operated at different supersaturation
levels.
During the evolution of a cloud, aerosol particles are exposed to different supersaturation
levels. We outline and compare different estimates for the lower and upper bounds (Slow,
Shigh) and the average value (Savg) of peak supersaturation encountered by the
particles in the cloud. For the investigated cloud event, we derived Slow - 0.19%
– 0.25%, Shigh - 0.90% – 1.64% and Savg - 0.38% – 0.84%. Estimates
of Slow, Shigh and Savg based on aerosol size distribution data require specific
knowledge or assumptions of aerosol hygroscopicity, which are not required for
the derivation of Slow and Savg from the size-resolved CCN efficiency spectra. |
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