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https://doi.org/10.5194/acp-2020-671
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2020-671
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  05 Aug 2020

05 Aug 2020

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This preprint is currently under review for the journal ACP.

Comparative Study On Immersion Freezing Utilizing Single Droplet Levitation Methods

Miklós Szakáll1, Michael Debertshäuser1, Christian Philipp Lackner1, Amelie Mayer1, Oliver Eppers2, Karoline Diehl1, Alexander Theis1, Subir Kumar Mitra2, and Stephan Borrmann1,2 Miklós Szakáll et al.
  • 1Institute for Atmospheric Physics, Johannes Gutenberg University, Mainz; J.-J.-Becherweg 21, D-55128 Mainz, Germany
  • 2Department of Particle Chemistry, Max Planck Instute of Chemistry, Hahn-Meitner-Weg 1, D-55128 Mainz, Germany

Abstract. Immersion freezing experiments were performed utilizing two distinct single-droplet levitation methods. In the Mainz vertical wind tunnel (M-WT) supercooled droplets of 700 μm diameter were freely floated in a vertical air stream at constant temperatures ranging from −5 °C to −30 °C where heterogeneous freezing takes place. These investigations under isothermal conditions allow applying the stochastic approach to analyze and interpret the results in terms of the freezing or nucleation rate. In the Mainz acoustic levitator (M-AL) 2 mm diameter drops were levitated while their temperature was continuously cooling from +20 °C to −28 °C by adapting to the ambient temperature. Therefore, in this case the singular approach was used for analysis. From the experiments, the densities of ice nucleating active sites (INAS) were obtained as function of temperature. The direct comparison of the results from two different instruments indicates a shift of the freezing temperatures towards lower values that was material dependent. As ice nucleating particles, seven materials were investigated, two representatives of biological species (fibrous and microcrystalline cellulose), four mineral dusts (feldspar, illite NX, montmorillonite, and kaolinite), and natural Sahara dust. Based on detailed analysis of our results we determined a material dependent temperature correction factor for each investigated particle type. The analysis allowed further classifying the investigated materials as single- or multiple-component. From our experiences during the present synergetic studies, we listed a number of suggestions for future experiments regarding cooling rates, determination of the drop temperature, purity of the water used to produce the drops, and characterization of the ice nucleating material. The observed freezing temperature shift is significantly important not only for the intercomparison of ice nucleation instruments with different cooling rates but also for cloud model simulations with high speed ascents of air masses.

Miklós Szakáll et al.

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Immersion freezing of a liquid drop in the Mainz Acoustic Levitator Miklos Szakall and Amelie Mayer https://doi.org/10.5446/46729

Miklós Szakáll et al.

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Latest update: 21 Oct 2020
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Short summary
A comparative study of the immersion freezing abilities of different aerosol types utilizing the Mainz vertical Wind Tunnel and the Mainz Acoustic Levitator is presented. We show that the freezing temperature of droplets containing the aerosols depends on the employed cooling rate of the instrument and the aerosol material. This finding is important not only for the intercomparison of ice nucleation instruments but also for cloud model simulations with high speed ascents of air masses.
A comparative study of the immersion freezing abilities of different aerosol types utilizing the...
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