Ice Nucleation of Snomax® Particles below Water Vapor Saturation: Immersion Freezing in Concentrated Solution Droplets

Abstract:

Heterogeneous ice nucleation in the atmosphere is important and has received an increasing amount of interest in the past years, as it initiates the ice phase in mixed phase clouds and, to some extent, also in cirrus clouds. The presence of ice influences cloud radiative properties and, for mixed phase clouds, also the formation of precipitation and cloud lifetime.

Immersion freezing has been in the focus of ice nucleation research in recent years. Here, we examine ice nucleation activity of biological ice nuclei (IN) derived from bacteria, namely of particles generated from a suspensions of Snomax®, both above and below water vapor saturation. Measurements were done with PINC (Portable Ice Nucleus Counter, Chou et al., 2011) during a measurement campaign at LACIS (Leipzig Aerosol Cloud Interaction Simulator, see e.g. Wex et al., 2014) in Leipzig. Immersion freezing measurements from PINC and LACIS were in agreement in the temperature regime for which both instruments operate reliably. Here, we will show that measurements done below water vapor saturation follow what would be expected for immersion freezing in concentrated solutions, similar to what was suggested for coated kaolinite particles in Wex et al. (2014).

Chou, C., O. Stetzer, E. Weingartner, Z. Juranyi, Z. A. Kanji, and U. Lohmann (2011), Ice nuclei properties within a Saharan dust event at the Jungfraujoch in the Swiss Alps, Atmos. Chem. Phys., 11(10), 4725-4738, doi:10.5194/acp-11-4725-2011.

Wex, H., P. J. DeMott, Y. Tobo, S. Hartmann, M. Rösch, T. Clauss, L. Tomsche, D. Niedermeier, and F. Stratmann (2014), Kaolinite particles as ice nuclei: learning from the use of different kaolinite samples and different coatings, Atmos. Chem. Phys., 14, doi:10.5194/acp-14-5529-2014.