Articles | Volume 16, issue 10
Atmos. Chem. Phys., 16, 6495–6509, 2016

Special issue: The CERN CLOUD experiment (ACP/AMT inter-journal SI)

Atmos. Chem. Phys., 16, 6495–6509, 2016

Research article 27 May 2016

Research article | 27 May 2016

Heterogeneous ice nucleation of viscous secondary organic aerosol produced from ozonolysis of α-pinene

Karoliina Ignatius1, Thomas B. Kristensen1, Emma Järvinen2, Leonid Nichman3, Claudia Fuchs4, Hamish Gordon5, Paul Herenz1, Christopher R. Hoyle4,6, Jonathan Duplissy7, Sarvesh Garimella8, Antonio Dias5, Carla Frege4, Niko Höppel2, Jasmin Tröstl4, Robert Wagner7, Chao Yan7, Antonio Amorim9, Urs Baltensperger4, Joachim Curtius10, Neil M. Donahue11, Martin W. Gallagher3, Jasper Kirkby5,10, Markku Kulmala7, Ottmar Möhler2, Harald Saathoff2, Martin Schnaiter2, Antonio Tomé12, Annele Virtanen13, Douglas Worsnop14, and Frank Stratmann1 Karoliina Ignatius et al.
  • 1Leibniz Institute for Tropospheric Research (TROPOS), 04318 Leipzig, Germany
  • 2Institute of Meteorology and Climate Research – Atmospheric Aerosol Research, Karlsruhe Institute of Technology, Karlsruhe, Germany
  • 3School of Earth, Atmospheric and Environmental Sciences, University of Manchester, Manchester, M13 9PL, UK
  • 4Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, Villigen, Switzerland
  • 5CERN, 1211 Geneva, Switzerland
  • 6WSL Institute for Snow and Avalanche Research SLF Davos, Davos, Switzerland
  • 7Department of Physics, P.O. Box 64, 00014 University of Helsinki, Helsinki, Finland
  • 8Massachusetts Institute of Technology, Cambridge, MA, USA
  • 9SIM/CENTRA and F. Ciencias, Universidade de Lisboa, Lisbon, Portugal
  • 10Goethe-University of Frankfurt, Institute for Atmospheric and Environmental Sciences, Altenhöferallee 1, 60438 Frankfurt am Main, Germany
  • 11Center for Atmospheric Particle Studies, Carnegie Mellon University, Pittsburgh, PA 15213, USA
  • 12SIM/IDL, Universidade da Beira Interior, Covilhã, Portugal
  • 13Department of Applied Physics, University of Eastern Finland, Kuopio, Finland
  • 14Aerodyne Research, Inc., Billerica, MA 08121, USA

Abstract. There are strong indications that particles containing secondary organic aerosol (SOA) exhibit amorphous solid or semi-solid phase states in the atmosphere. This may facilitate heterogeneous ice nucleation and thus influence cloud properties. However, experimental ice nucleation studies of biogenic SOA are scarce. Here, we investigated the ice nucleation ability of viscous SOA particles.

The SOA particles were produced from the ozone initiated oxidation of α-pinene in an aerosol chamber at temperatures in the range from −38 to −10 °C at 5–15 % relative humidity with respect to water to ensure their formation in a highly viscous phase state, i.e. semi-solid or glassy. The ice nucleation ability of SOA particles with different sizes was investigated with a new continuous flow diffusion chamber. For the first time, we observed heterogeneous ice nucleation of viscous α-pinene SOA for ice saturation ratios between 1.3 and 1.4 significantly below the homogeneous freezing limit. The maximum frozen fractions found at temperatures between −39.0 and −37.2 °C ranged from 6 to 20 % and did not depend on the particle surface area. Global modelling of monoterpene SOA particles suggests that viscous biogenic SOA particles are indeed present in regions where cirrus cloud formation takes place. Hence, they could make up an important contribution to the global ice nucleating particle budget.

Short summary
Viscous solid or semi-solid secondary organic aerosol (SOA) may influence cloud properties through ice nucleation in the atmosphere. Here, we observed heterogeneous ice nucleation of viscous α-pinene SOA at temperatures between −39 °C and −37.2 °C with ice saturation ratios significantly below the homogeneous freezing limit. Global modelling suggests that viscous biogenic SOA are present in regions where cirrus formation takes place and could contribute to the global ice nuclei budget.
Final-revised paper