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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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Volume 18, issue 13
Atmos. Chem. Phys., 18, 9393-9409, 2018
https://doi.org/10.5194/acp-18-9393-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Atmos. Chem. Phys., 18, 9393-9409, 2018
https://doi.org/10.5194/acp-18-9393-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 05 Jul 2018

Research article | 05 Jul 2018

The efficiency of secondary organic aerosol particles acting as ice-nucleating particles under mixed-phase cloud conditions

Wiebke Frey1,a, Dawei Hu1, James Dorsey1, M. Rami Alfarra1,2, Aki Pajunoja3, Annele Virtanen3, Paul Connolly1, and Gordon McFiggans1 Wiebke Frey et al.
  • 1Centre for Atmospheric Science, School of Earth and Environmental Sciences, The University of Manchester, Manchester, UK
  • 2National Centre for Atmospheric Science (NCAS), The University of Manchester, Manchester, UK
  • 3Department of Applied Physics, University of Eastern Finland, Kuopio, Finland
  • anow at: Leibniz Institute for Tropospheric Research (TROPOS), Leipzig, Germany

Abstract. Secondary organic aerosol (SOA) particles have been found to be efficient ice-nucleating particles under the cold conditions of (tropical) upper-tropospheric cirrus clouds. Whether they also are efficient at initiating freezing under slightly warmer conditions as found in mixed-phase clouds remains undetermined. Here, we study the ice-nucleating ability of photochemically produced SOA particles with the combination of the Manchester Aerosol Chamber and Manchester Ice Cloud Chamber. Three SOA systems were tested resembling biogenic and anthropogenic particles as well as particles of different phase state. These are namely α-pinene, heptadecane, and 1,3,5-trimethylbenzene. After the aerosol particles were formed, they were transferred into the cloud chamber, where subsequent quasi-adiabatic cloud activation experiments were performed. Additionally, the ice-forming abilities of ammonium sulfate and kaolinite were investigated as a reference to test the experimental setup.

Clouds were formed in the temperature range of −20 to −28.6 °C. Only the reference experiment using dust particles showed evidence of ice nucleation. No ice particles were observed in any other experiment. Thus, we conclude that SOA particles produced under the conditions of the reported experiments are not efficient ice-nucleating particles starting at liquid saturation under mixed-phase cloud conditions.

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The coupled system of the Manchester Aerosol Chamber and Manchester Ice Cloud Chamber was used to study the ice-forming abilities of secondary organic aerosol particles under mixed-phase cloud conditions. Given the vast abundance of secondary organic particles in the atmosphere, they might present an important contribution to ice-nucleating particles. However, we find that in the studied temperature range (20 to 28 °C) the secondary organic particles do not nucleate ice particles.
The coupled system of the Manchester Aerosol Chamber and Manchester Ice Cloud Chamber was used...
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