Articles | Volume 16, issue 7
Atmos. Chem. Phys., 16, 4423–4438, 2016

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

Atmos. Chem. Phys., 16, 4423–4438, 2016

Research article 11 Apr 2016

Research article | 11 Apr 2016

Observation of viscosity transition in α-pinene secondary organic aerosol

Emma Järvinen1, Karoliina Ignatius2, Leonid Nichman3, Thomas B. Kristensen2, Claudia Fuchs4, Christopher R. Hoyle4,8, Niko Höppel1, Joel C. Corbin4, Jill Craven5, Jonathan Duplissy6, Sebastian Ehrhart7, Imad El Haddad4, Carla Frege4, Hamish Gordon7, Tuija Jokinen6, Peter Kallinger9, Jasper Kirkby7,10, Alexei Kiselev1, Karl-Heinz Naumann1, Tuukka Petäjä6, Tamara Pinterich9, Andre S. H. Prevot4, Harald Saathoff1, Thea Schiebel1, Kamalika Sengupta11, Mario Simon10, Jay G. Slowik4, Jasmin Tröstl4, Annele Virtanen12, Paul Vochezer1, Steffen Vogt1, Andrea C. Wagner10, Robert Wagner1, Christina Williamson10,13,14, Paul M. Winkler9, Chao Yan6, Urs Baltensperger4, Neil M. Donahue15, Rick C. Flagan16, Martin Gallagher3, Armin Hansel17, Markku Kulmala6, Frank Stratmann2, Douglas R. Worsnop18, Ottmar Möhler1, Thomas Leisner1, and Martin Schnaiter1 Emma Järvinen et al.
  • 1Karlsruhe Institute of Technology, Institute for Meteorology and Climate Research, P.O. Box 3640, 76021 Karlsruhe, Germany
  • 2Institute for Tropospheric Research (TROPOS), 04318 Leipzig, Germany
  • 3School of Earth, Atmospheric and Environmental Sciences, University of Manchester, Manchester, M13 9PL, UK
  • 4Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, Villigen, Switzerland
  • 5California institute of technology, department of chemical engineering, Pasadena, CA 91125, USA
  • 6Helsinki Institute of Physics and University of Helsinki, Department of Physics, Helsinki, Finland
  • 7CERN, 1211, Geneva, Switzerland
  • 8WSL Institute for Snow and Avalanche Research SLF, Davos, Switzerland
  • 9Faculty of Physics, University of Vienna, Vienna, Austria
  • 10Institute for Atmospheric and Environmental Sciences, Goethe-University Frankfurt am Main, Campus Riedberg Altenhöferallee 1, 60438 Frankfurt am Main, Germany
  • 11University of Leeds, School of Earth and Environment, LS2-9JT Leeds, UK
  • 12Department of Applied Physics, University of Eastern Finland, Kuopio, Finland
  • 13NOAA Earth Systems Research Laboratory (ESRL), Chemical Sciences Division, 325 Broadway, Boulder, Colorado 80305, USA
  • 14Cooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado Boulder, UCB 216, Boulder, Colorado 80309, USA
  • 15Center for Atmospheric Particle Studies, Carnegie Mellon University, 5000 Forbes Ave., Pittsburgh, PA 15213, USA
  • 16California Institute of Technology, Division of Chemistry and Chemical Engineering, Pasadena, California 91125, USA
  • 17Institute for Ion and Applied Physics, 6020 Innsbruck and Ionicon Analytik GmbH, 6020 Innsbruck, Austria
  • 18Aerodyne Research, Inc., Billerica, MA 08121, USA

Abstract. Under certain conditions, secondary organic aerosol (SOA) particles can exist in the atmosphere in an amorphous solid or semi-solid state. To determine their relevance to processes such as ice nucleation or chemistry occurring within particles requires knowledge of the temperature and relative humidity (RH) range for SOA to exist in these states. In the Cosmics Leaving Outdoor Droplets (CLOUD) experiment at The European Organisation for Nuclear Research (CERN), we deployed a new in situ optical method to detect the viscous state of α-pinene SOA particles and measured their transition from the amorphous highly viscous state to states of lower viscosity. The method is based on the depolarising properties of laboratory-produced non-spherical SOA particles and their transformation to non-depolarising spherical particles at relative humidities near the deliquescence point. We found that particles formed and grown in the chamber developed an asymmetric shape through coagulation. A transition to a spherical shape was observed as the RH was increased to between 35 % at −10 °C and 80 % at −38 °C, confirming previous calculations of the viscosity-transition conditions. Consequently, α-pinene SOA particles exist in a viscous state over a wide range of ambient conditions, including the cirrus region of the free troposphere. This has implications for the physical, chemical, and ice-nucleation properties of SOA and SOA-coated particles in the atmosphere.

Final-revised paper