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Discussion papers
https://doi.org/10.5194/acp-2018-905
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2018-905
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 10 Sep 2018

Research article | 10 Sep 2018

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

Heterogeneous Ice Nucleation Properties of Natural Desert Dust Particles Coated with a Surrogate of Secondary Organic Aerosol

Zamin A. Kanji1, Ryan C. Sullivan2,3, Monika Niemand4, Paul J. DeMott2, Anthony J. Prenni2,a, Cedric Chou1, Harald Saathoff4, and Ottmar Möhler4 Zamin A. Kanji et al.
  • 1Department of Environmental System Sciences, Institute for Atmospheric and Climate Science, ETH Zürich, 8092, Zurich, Switzerland
  • 2Department of Atmospheric Science, Colorado State University, Fort Collins, CO 80523, USA
  • 3Center for Atmospheric Particle Studies, Carnegie Mellon University, Pittsburgh, PA 15213, USA
  • 4Institute of Meteorology and Climate Research, Karlsruhe Institute of Technology, 76344, Eggenstein-Leopoldshafen, Germany
  • anow at: Air Resources Division, National Park Service, Lakewood, CO 80228, USA

Abstract. Ice nucleation abilities of surface collected mineral dust particles from the Sahara (SD) and Asia (AD) are investigated for the temperature range 253–233K and for supersaturated humidity conditions in the immersion-freezing regime. The dust particles were also coated with a proxy of secondary organic aerosol (SOA) from the dark ozonolysis of α-pinene to better understand the influence of atmospheric coatings on the immersion freezing ability of mineral dust particles. The measurements are conducted on poly-disperse particles in the size range 0.01–3µm with three different ice nucleation chambers. Two of the chambers follow the continuous flow diffusion chamber (CFDC) principle (Portable Ice Nucleation Chamber, PINC) and the Colorado State University CFDC (CSU-CFDC), whereas the third was the Aerosol Interactions and Dynamics in the Atmosphere (AIDA) cloud expansion chamber. From observed activated fractions (AF) and ice nucleation active site (INAS) densities, it is concluded within experimental uncertainties that there is no significant difference between the ice nucleation ability of the particular SD and AD samples examined. A small bias towards higher INAS densities for uncoated versus SOA coated dusts is found but this is well within the 1σ (66% prediction bands) region of the average fit to the data, which captures 75% of the INAS densities observed in this study. Furthermore, no systematic differences are observed between SOA coated and uncoated dusts in both SD and AD cases, regardless of coating thickness (3–60nm). The results suggest that differences observed are mostly within the uncertainty of the measurements or differences in cloud chamber parameters such as size fraction of particles sampled, and residence time, as well as assumptions in using INAS densities to compare poly-disperse aerosol measurements which may show variable composition with particle size. In the atmosphere, coatings with similar properties to that of the SOA tested here for a thickness up to 60nm, the maximum thickness tested here, is not expected to impede or enhance the ice nucleation ability by immersion mode of mineral dust in the mixed-phase cloud regime.

Zamin A. Kanji et al.
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Zamin A. Kanji et al.
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The ice nucleation ability of two natural desert dusts coated with a proxy of secondary organic aerosol is presented for temperatures and relative humidity conditions relevant for mixed-phase clouds. We find that at the tested conditions, there is no effect on the ice nucleation ability of the particles due to the organic coating. Furthermore, the two dust samples do not show variability within measurement uncertainty. Particle size and surface area may play a role in any difference observed.
The ice nucleation ability of two natural desert dusts coated with a proxy of secondary organic...
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