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
Received: 07 Nov 2015 – Discussion started: 18 Dec 2015
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.
Revised: 16 Apr 2016 – Accepted: 09 May 2016 – Published: 27 May 2016
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.
Ignatius, K., Kristensen, T. B., Järvinen, E., Nichman, L., Fuchs, C., Gordon, H., Herenz, P., Hoyle, C. R., Duplissy, J., Garimella, S., Dias, A., Frege, C., Höppel, N., Tröstl, J., Wagner, R., Yan, C., Amorim, A., Baltensperger, U., Curtius, J., Donahue, N. M., Gallagher, M. W., Kirkby, J., Kulmala, M., Möhler, O., Saathoff, H., Schnaiter, M., Tomé, A., Virtanen, A., Worsnop, D., and Stratmann, F.: Heterogeneous ice nucleation of viscous secondary organic aerosol produced from ozonolysis of α-pinene, Atmos. Chem. Phys., 16, 6495-6509, doi:10.5194/acp-16-6495-2016, 2016.