Phase transition observations and discrimination of small cloud particles by light polarization in expansion chamber experiments

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DOI	Resolve DOI: https://doi.org/10.5194/acp-16-3651-2016
Author	Search for: Nichman, Leonid; Search for: Fuchs, Claudia; Search for: Järvinen, Emma; Search for: Ignatius, Karoliina; Search for: Höppel, Niko Florian; Search for: Dias, Antonio; Search for: Heinritzi, Martin; Search for: Simon, Mario; Search for: Tröstl, Jasmin; Search for: Wagner, Andrea Christine; Search for: Wagner, Robert; Search for: Williamson, Christina; Search for: Yan, Chao; Search for: Connolly, Paul James; Search for: Dorsey, James Robert; Search for: Duplissy, Jonathan; Search for: Ehrhart, Sebastian; Search for: Frege, Carla; Search for: Gordon, Hamish; Search for: Hoyle, Christopher Robert; Search for: Kristensen, Thomas Bjerring; Search for: Steiner, Gerhard; Search for: Mcpherson Donahue, Neil; Search for: Flagan, Richard; Search for: Gallagher, Martin William; Search for: Kirkby, Jasper; Search for: Möhler, Ottmar; Search for: Saathoff, Harald; Search for: Schnaiter, Martin; Search for: Stratmann, Frank; Search for: Tomé, António
Format	Text, Article
Abstract	Cloud microphysical processes involving the ice phase in tropospheric clouds are among the major uncertainties in cloud formation, weather, and general circulation models. The detection of aerosol particles, liquid droplets, and ice crystals, especially in the small cloud particle-size range below 50 μm, remains challenging in mixed phase, often unstable environments. The Cloud Aerosol Spectrometer with Polarization (CASPOL) is an airborne instrument that has the ability to detect such small cloud particles and measure the variability in polarization state of their backscattered light. Here we operate the versatile Cosmics Leaving OUtdoor Droplets (CLOUD) chamber facility at the European Organization for Nuclear Research (CERN) to produce controlled mixed phase and other clouds by adiabatic expansions in an ultraclean environment, and use the CASPOL to discriminate between different aerosols, water, and ice particles. In this paper, optical property measurements of mixed-phase clouds and viscous secondary organic aerosol (SOA) are presented. We report observations of significant liquid–viscous SOA particle polarization transitions under dry conditions using CASPOL. Cluster analysis techniques were subsequently used to classify different types of particles according to their polarization ratios during phase transition. A classification map is presented for water droplets, organic aerosol (e.g., SOA and oxalic acid), crystalline substances such as ammonium sulfate, and volcanic ash. Finally, we discuss the benefits and limitations of this classification approach for atmospherically relevant concentrations and mixtures with respect to the CLOUD 8–9 campaigns and its potential contribution to tropical troposphere layer analysis.
Publication date	2016-03-16
Publisher	Copernicus Publications on behalf of the European Geosciences Union
In	Atmospheric Chemistry and Physics 16, no. 5: 3651–3664.
Language	English
Peer reviewed	Yes
NRC publication	This is a non-NRC publication "Non-NRC publications" are publications authored by NRC employees prior to their employment by NRC.
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Record identifier	8242a715-744b-4256-a562-8b322b26eb1f
Record created	2019-10-18
Record modified	2020-05-30

Date modified:: 2024-04-19