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Discussion papers
https://doi.org/10.5194/acp-2018-1271
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2018-1271
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 11 Jan 2019

Research article | 11 Jan 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

Ice nucleation properties of K-feldspar polymorphs and plagioclase feldspars

André Welti1,a, Ulrike Lohmann1, and Zamin A. Kanji1 André Welti et al.
  • 1ETH Zurich, Institute for Atmospheric and Climate Science, Zurich, 8092, Switzerland
  • anow at: Finnish Meteorological Institute, Helsinki, FI-00101, Finland

Abstract. The relation between the mineralogical characteristics of size selected feldspar particles from 50–800nm and their ability to act as ice nucleating particles (INPs) in the immersion mode is presented. Five polymorph members of K-feldspar (two microclines, orthoclase, adularia and sanidine) and four Na/Ca- rich feldspar samples (three labradorites and a pericline sample) are tested. Microcline was found to be the most active INP in the immersion mode consistent with previous findings. Samples are selected for their differences in typical feldspar properties such as crystal structure, bulk and trace elemental composition and ordering of the crystal lattice. The mentioned properties are related to the temperature of feldspar crystallization from the melt rocks during formation. Properties characteristic for low temperature feldspar formation coincide with an increased ability to nucleate ice. Ice nucleation is most efficient on the crystallographic ordered, triclinic K-feldspar species microcline, while the intermediate and disordered, monoclinic K-feldspar polymorphs orthoclase and sanidine nucleate ice at lower temperatures. The ice nucleation ability of disordered, triclinic Na/Ca-feldspar is comparable to disordered K-feldspar. The conditions of feldspar rock formation also leave a chemical fingerprint with varying abundance of trace elements in the samples. X-ray fluorescence spectroscopy analysis to determine metal oxide and trace elemental composition of the feldspar samples revealed a correlation with median freezing temperatures (T50) of the K-feldspar samples allowing to sort them for their ice nucleation efficiency according to the abundance of specific trace elements. A pronounced size dependence of ice nucleation activity for the feldspar samples is observed, which also depends on mineralogical characteristics. In particular, microcline exhibited immersion freezing even for 50nm particles which is unique for heterogeneous ice nucleation of mineral dusts. This suggests that small microcline particles that are susceptible to long-range transport can affect cloud properties via immersion freezing far away from the source. The measurements generally imply that temperatures at which feldspars can affect cloud glaciation depends on the transported particle size.

André Welti et al.
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Short summary
The ice nucleation ability of singly immersed feldspar particles in suspended water droplets relevant for ice crystal formation under mixed phase cloud conditions is presented. Effects of particle size, crystal structure, trace metal and mineralogical composition, are discussed by testing up to 5 different diameters in the sub-micron range and 9 different feldspar samples at conditions relevant for ice nucleation in mixed-phase clouds.
The ice nucleation ability of singly immersed feldspar particles in suspended water droplets...
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