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

Nichman, Leonid and Fuchs, Claudia and Järvinen, Emma and Ignatius, Karoliina and Höppel, Niko Florian and Dias, Antonio and Heinritzi, Martin and Simon, Mario and Tröstl, Jasmin and Wagner, Andrea Christine and Wagner, Robert and Williamson, Christina and Yan, Chao and Connolly, Paul James and Dorsey, James Robert and Duplissy, Jonathan and Ehrhart, Sebastian and Frege, Carla and Gordon, Hamish and Hoyle, Christopher Robert and Kristensen, Thomas Bjerring and Steiner, Gerhard and McPherson Donahue, Neil and Flagan, Richard and Gallagher, Martin William and Kirkby, Jasper and Möhler, Ottmar and Saathoff, Harald and Schnaiter, Martin and Stratmann, Frank and Tomé, António (2016) Phase transition observations and discrimination of small cloud particles by light polarization in expansion chamber experiments. Atmospheric Chemistry and Physics, 16 (5). pp. 3651-3664. ISSN 1680-7316.

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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.

Item Type:Article
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Gordon, Hamish0000-0002-1822-3224
Flagan, Richard0000-0001-5690-770X
Schnaiter, Martin0000-0002-9560-8072
Additional Information:© Author(s) 2016. This work is distributed under the Creative Commons Attribution 3.0 License. Received: 18 Sep 2015 – Published in Atmos. Chem. Phys. Discuss.: 10 Nov 2015. Revised: 03 Mar 2016 – Accepted: 03 Mar 2016 – Published: 17 Mar 2016. Special issue: The CERN CLOUD experiment (ACP/AMT inter-journal SI) We would like to thank CERN for supporting CLOUD with important technical and financial resources, and for providing a particle beam from the CERN Proton Synchrotron. We express great appreciation for the CLOUD collaboration and the volunteers for the night shifts. We would also like to thank Darrel Baumgardner for CASPOL data filtering advice and review of the manuscript. T. B. Kristensen gratefully acknowledges funding from the German Federal Ministry of Education and Research (BMBF) through the CLOUD12 project. This research has received funding from the EC Seventh Framework Programme (Marie Curie Initial Training Network “CLOUD-TRAIN” no. 316662) and Swiss National Science Foundation (SNSF) grant no. 200 021_140 663. The CAPS instrument used in this work was supplied by the National Centre for Atmospheric Science. The UHSAS was funded by NERC grant NE/B504873/1. Edited by: V.-M. Kerminen
Funding AgencyGrant Number
Bundesministerium für Bildung und Forschung (BMBF)UNSPECIFIED
Marie Curie Initial Training Network316662
Swiss National Science Foundation (SNSF)200 021_140 663
National Centre for Atmospheric ScienceUNSPECIFIED
Natural Environment Research Council (NERC)NE/B504873/1
Issue or Number:5
Record Number:CaltechAUTHORS:20160317-102043098
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Official Citation:Nichman, L., Fuchs, C., Järvinen, E., Ignatius, K., Höppel, N. F., Dias, A., Heinritzi, M., Simon, M., Tröstl, 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., McPherson Donahue, N., Flagan, R., Gallagher, M. W., Kirkby, J., Möhler, O., Saathoff, H., Schnaiter, M., Stratmann, F., and Tomé, A.: Phase transition observations and discrimination of small cloud particles by light polarization in expansion chamber experiments, Atmos. Chem. Phys., 16, 3651-3664, doi:10.5194/acp-16-3651-2016, 2016.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:65422
Deposited By: Irina Meininger
Deposited On:17 Mar 2016 19:15
Last Modified:09 Mar 2020 13:19

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