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

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Nichman , L , Fuchs , C , Järvinen , E , Ignatius , K , Hoeppel , N F , Dias , A , Heinritzi , M , Simon , M , Trostl , J , Wagner , A C , Wagner , R , Williamson , C , Yan , C , Connolly , P J , Dorsey , J R , Duplissy , J , Ehrhart , S , Frege , C , Gordon , H , Hoyle , C R , Kristensen , T B , Steiner , G , Donahue , N M , Flagan , R , Gallagher , M W , Kirkby , J , Moehler , O , Saathoff , H , Schnaiter , M , Stratmann , F & Tome , A 2016 , ' Phase transition observations and discrimination of small cloud particles by light polarization in expansion chamber experiments ' , Atmospheric Chemistry and Physics , vol. 16 , no. 5 , pp. 3651-3664 . https://doi.org/10.5194/acp-16-3651-2016

Title: Phase transition observations and discrimination of small cloud particles by light polarization in expansion chamber experiments
Author: Nichman, Leonid; Fuchs, Claudia; Järvinen, Emma; Ignatius, Karoliina; Hoeppel, Niko Florian; Dias, Antonio; Heinritzi, Martin; Simon, Mario; Trostl, Jasmin; Wagner, Andrea Christine; Wagner, Robert; Williamson, Christina; Yan, Chao; Connolly, Paul James; Dorsey, James Robert; Duplissy, Jonathan; Ehrhart, Sebastian; Frege, Carla; Gordon, Hamish; Hoyle, Christopher Robert; Kristensen, Thomas Bjerring; Steiner, Gerhard; Donahue, Neil McPherson; Flagan, Richard; Gallagher, Martin William; Kirkby, Jasper; Moehler, Ottmar; Saathoff, Harald; Schnaiter, Martin; Stratmann, Frank; Tome, Antonio
Contributor: University of Helsinki, Department of Physics
University of Helsinki, Department of Physics
University of Helsinki, Helsinki Institute of Physics
University of Helsinki, Department of Physics
Date: 2016
Language: eng
Number of pages: 14
Belongs to series: Atmospheric Chemistry and Physics
ISSN: 1680-7316
URI: http://hdl.handle.net/10138/163785
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 50aEuro-mu m, 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.
Subject: ATMOSPHERIC ICE CRYSTALS
SCATTERING PROPERTIES
ALPHA-PINENE
AEROSOL SPECTROMETER
TROPICAL TROPOPAUSE
SIMULATION CHAMBER
SUBVISIBLE CIRRUS
ORGANIC-COMPOUNDS
CLUSTER-ANALYSIS
BETA-PINENE
114 Physical sciences
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