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A comparative study of K-rich and Na/Ca-rich feldspar ice-nucleating particles in a nanoliter droplet freezing assay

Peckhaus, Andreas; Kiselev, Alexei; Hiron, Thibault; Ebert, Martin; Leisner, Thomas



Abstract (englisch): A recently designed droplet freezing assay was used to study the freezing of up to 1500 identical 0.2 nL water droplets containing suspensions of one Na/Ca-rich feldspar and three K-rich and one Na/Ca-rich feldspar particles. Three types of experiments have been conducted: cooling ramp, isothermal freezing at a constant temperature, and freeze–thaw cycles. The observed freezing behavior has been interpreted with the help of a model based on the classical nucleation theory (soccer ball model (SBM); Niedermeier et al., 2015). By applying the model to the different freezing experiments conducted with the same ice-nucleating material, the unique sets of model parameters for specific feldspar suspensions could be derived. The SBM was shown to adequately describe the observed cooling rate dependence, the ice-nucleating active sites (INAS) surface density ns(T) in a wide temperature range, and the shift of the freezing curves towards lower temperature with dilution. Moreover, the SBM was capable of reproducing the variation of INAS surface density ns(T) with concentration of ice-nucleating particles in the suspension droplets and correctly predicting the leveling-off of ns(T) at low temperature. The freeze–thaw experiments have clearly shown that the heterogeneous freezing induced even by very active ice-nucleating species still possesses a stochastic nature, with the degree of randomness increasing towards homogeneous nucleation. A population of the high-temperature INAS has been identified in one of the K-rich feldspar samples. The freezing of 0.8 wt % suspension droplets of this particular feldspar was observed already at −5 °C. These high-temperature active sites could be deactivated by treating the sample with hydrogen peroxide but survived heating up to 90 °C. Given a high mass concentration of these high-temperature active sites (2.9 × 108 g−1) and a very low value of contact angle (0.56 rad) the possibility of biological contamination of the sample was concluded to be unlikely but could not be completely ruled out. The freezing efficacy of all feldspar samples has been shown to reduce only slightly after suspension in water for over 5 months.


Zugehörige Institution(en) am KIT Institut für Meteorologie und Klimaforschung - Atmosphärische Aerosolforschung (IMK-AAF)
Publikationstyp Zeitschriftenaufsatz
Jahr 2016
Sprache Englisch
Identifikator DOI: 10.5194/acp-16-11477-2016
ISSN: 1680-7316, 1680-7324
URN: urn:nbn:de:swb:90-597769
KITopen ID: 1000059776
HGF-Programm 12.01.01; LK 01
Erschienen in Atmospheric chemistry and physics
Band 16
Heft 18
Seiten 11477-11496
Lizenz CC BY 3.0 DE: Creative Commons Namensnennung 3.0 Deutschland
Bemerkung zur Veröffentlichung Gefördert durch den KIT-Publikationsfonds
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