[Zurück]

M. Kohn, O. Stetzer, B. Sierau, A. Welti, B. G. Pummer, H. Grothe, U. Lohmann:
"Immersion freezing of biological aerosol particles in the ZINC setup";
Vortrag: ESF-Workshop - Atmospheric Ice Nucleation, Wien; 06.04.2013 - 07.04.2013; in: "Workshop - Atmospheric Ice Nucleation - Book of Abstracts", (2013).

Biological aerosol particles, such as pollen and fungal spores, are constituents of the atmospheric aerosol population. Besides their health impacts, some of these particles are found to be active as ice nuclei (IN) for heterogeneous freezing and can thus initiate ice formation in clouds. This effect could lead to changes in cloud properties, thereby influencing earth's radiation budget and hence could also have an impact on our climate.
Pollen are amongst the largest aerosol particles found in the atmosphere. Since IN activity is considered to increase with particle size, these aerosol types are more likely to act as IN. In mixed-phase clouds ice nucleation in the immersion freezing mode is of major importance, because liquid cloud droplets are necessary for heterogeneous nucleation at warmer temperatures; in particular biological aerosol particles were found to have the ability to act as
IN at relatively warm temperatures [1]. In the same study pollen have been investigated to act as efficient IN for freezing modes where the liquid phase was involved.
In this study ice nucleation experiments with the Zurich Ice Nucleation Chamber (ZINC, [2]) and its immersion freezing extension IMCA (Immersion Mode Cooling Chamber, [3]) has been performed to investigate the IN ability of different pollen species in the immersion freezing mode. It has previously been reported [4, 5] that also water, in which pollen had been emulsified and subsequently removed by filtration, may contain IN. We also tested these so called pollen washing waters. For this purpose the washing water was nebulized by an atomizer and the produced droplets were dried and size selected for ZINC/IMCA measurements. First results show good agreement with previous measurements of droplet residues produced from pollen washing waters in terms of their IN-activity [4]. To gain further insights into the IN properties of pollen in the atmosphere, we develop a field instrument to study immersion freezing outside the laboratory. The presented data provide important information for the adaption of IMCA for the field, which will be coupled to the Portable Ice Nucleation Chamber (PINC, [6]). Results from subsequent field measurements could give a better idea of the importance for processes in mixed-phase clouds initiated by biological aerosol particles.

ice nucleation, pollen, flow tube