Assessment of cloud supersaturation by size-resolved aerosol particle and cloud condensation nuclei (CCN) measurements

• Main Authors: M. L. Krüger, S. Mertes, T. Klimach, Y. F. Cheng, H. Su, J. Schneider, M. O. Andreae, U. Pöschl, D. Rose
• Format: Article
• Language: English
• Published: Copernicus Publications 2014-08-01
• Series: Atmospheric Measurement Techniques
• Online Access: http://www.atmos-meas-tech.net/7/2615/2014/amt-7-2615-2014.pdf
• ISSN: 1867-1381; 1867-8548

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 during the ACRIDICON-Zugspitze campaign (17 September to 4 October 2012) at the high-Alpine research station Schneefernerhaus (German Alps, 2650 m a.s.l.). 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. <br><br> 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 (<i>S</i>_low, <i>S</i>_high) and the average value (<i>S</i>_avg) of peak supersaturation encountered by the particles in the cloud. A major advantage of the derivation of <i>S</i>_low and <i>S</i>_avg from size-resolved CCN efficiency spectra is that it does not require the specific knowledge or assumptions about aerosol hygroscopicity that are needed to derive estimates of <i>S</i>_low, <i>S</i>_high, and <i>S</i>_avg from aerosol size distribution data. For the investigated cloud event, we derived <i>S</i>_low &approx; 0.07–0.25%, <i>S</i>_high &approx; 0.86–1.31% and <i>S</i>_avg &approx; 0.42–0.68%.