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Exploring the Mechanisms of Ice Nucleation on Kaolinite: From Deposition Nucleation to Condensation Freezing
Journal article

Exploring the Mechanisms of Ice Nucleation on Kaolinite: From Deposition Nucleation to Condensation Freezing

  • Welti, André Institute for Atmospheric and Climate Science, ETH Zürich, Zurich, Switzerland
  • Kanji, Zamin A. Institute for Atmospheric and Climate Science, ETH Zürich, Zurich, Switzerland
  • Lüönd, F. Federal Office of Metrology, Bern, Switzerland
  • Stetzer, Olaf Institute for Atmospheric and Climate Science, ETH Zürich, Zurich, Switzerland
  • Lohmann, Ulrike Institute for Atmospheric and Climate Science, ETH Zürich, Zurich, Switzerland
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  • 2013-12-27
Published in:
  • Journal of the Atmospheric Sciences. - American Meteorological Society. - 2013, vol. 71, no. 1, p. 16-36
Atmospheric Science
English Abstract
To identify the temperature and humidity conditions at which different ice nucleation mechanisms are active, the authors conducted experiments on 200-, 400-, and 800-nm size-selected kaolinite particles, exposing them to temperatures between 218 and 258 K and relative humidities with respect to ice (RHi) between 100% and 180%, including the typical conditions for cirrus and mixed-phase-cloud formation. Measurements of the ice active particle fraction as a function of temperature and relative humidity with respect to ice are reported. The authors find enhanced activated fractions when water saturation is reached at mixed-phase-cloud temperatures between 235 and 241 K and a distinct increase in the activated fraction below 235 K at conditions below water saturation. To provide a functional description of the observed ice nucleation mechanisms, the experimental results are analyzed by two different particle-surface models within the framework of classical nucleation theory. Describing the ice nucleation activity of kaolinite particles by assuming deposition nucleation to be the governing mechanism below water saturation was found to be inadequate to represent the experimental data in the whole temperature range investigated. The observed increase in the activated fraction below water saturation and temperatures below 235 K corroborate the assumption that an appreciable amount of adsorbed or capillary condensed water is present on kaolinite particles, which favors ice nucleation.
Language
  • English
Open access status
hybrid
Identifiers
Persistent URL
https://sonar.rero.ch/global/documents/134402
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