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Discussion papers | Copyright
https://doi.org/10.5194/acp-2018-557
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 14 Jun 2018

Research article | 14 Jun 2018

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

Ice nucleation abilities of soot particles determined with the Horizontal Ice Nucleation Chamber

Fabian Mahrt1, Claudia Marcolli1, Robert O. David1, Philippe Grönquist2,3, Eszter J. Barthazy Meier4, Ulrike Lohmann1, and Zamin A. Kanji1 Fabian Mahrt et al.
  • 1Department of Environmental System Sciences, Institute for Atmospheric and Climate Science, ETH Zurich, 8092 Zurich, Switzerland
  • 2Department of Civil, Environmental and Geomatic Engineering, Institute for Building Materials, ETH Zurich, 8093 Zurich, Switzerland
  • 3Department of Functional Materials, Applied Wood Materials, Empa, 8600 Dubendorf, Switzerland
  • 4Scientific Center for Optical and Electron Microscopy, ETH Zurich, 8093 Zurich, Switzerland

Abstract. Ice nucleation by different types of soot particles is systematically investigated over the temperature range from 218 to 253K relevant for both mixed-phase (MPCs) and cirrus clouds. Soot types were selected to represent a range of physicochemical properties associated with combustion particles. Their ice nucleation ability was determined as a function of particle size using relative humidity (RH) scans in the Horizontal Ice Nucleation Chamber (HINC). We complement our ice nucleation results by a suite of particle characterization measurements, including determination of particle surface area, fractal dimension, temperature dependent mass loss, water vapor sorption and inferred porosity measurements. Independent of particle size, all soot types reveal absence of ice nucleation below and at water saturation in the MPC regime (T>235K). In the cirrus regime (T235K), soot types show different freezing behaviour depending on particle size and soot type, but the freezing is closely linked to the soot particle properties. Specifically, our results suggest that if soot aggregates contain mesopores (pore diameters of 2–50nm) and have sufficiently low water-soot contact angles, they show ice nucleation activity and can contribute to ice formation in the cirrus regime at RH well below homogeneous freezing of solution droplets. We attribute the observed ice nucleation to a pore condensation and freezing (PCF) mechanism. Nevertheless, soot particles without cavities of the right size and/or too high contact angles nucleate ice only at or well above the RH required for homogeneous freezing conditions of solution droplets. Thus, our results imply that soot particles able to nucleate ice via PCF, could impact the microphysical properties of ice clouds.

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Short summary
The ice nucleation ability of different soot particles in the cirrus and mixed-phase cloud temperature regime is presented. The impact of aerosol particle size, particle morphology, organic matter as well as hydrophilicity on ice nucleation is examined. We propose ice nucleation proceeds via a pore condensation freezing mechanism for soot particles with the necessary physicochemical properties, that nucleated ice well below water saturation.
The ice nucleation ability of different soot particles in the cirrus and mixed-phase cloud...
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