ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-10-313-2010 Single ice crystal measurements during nucleation experiments with the depolarization detector IODE Nicolet M. 1 Stetzer O. 1 Lüönd F. 1 Möhler O. 2 Lohmann U. 1 Institute for Atmospheric and Climate Science, ETH Zurich, 8092 Zurich, Switzerland Institute for Meteorology and Climate Research, Forschungszentrum Karlsruhe, Germany 18 01 2010 10 2 313 325 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/10/313/2010/acp-10-313-2010.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/10/313/2010/acp-10-313-2010.pdf

In order to determine the efficiency of different aerosol particles to nucleate ice, an Ice Optical DEpolarization detector (IODE) was developed to distinguish between water droplets and ice crystals in ice nucleation chambers. A laser beam polarized linearly (power: 50 mW, wavelength: 407 nm) is directed through the chamber. The scattered light intensity from particles is measured at a scattering angle of Θ=175&deg; in both polarization components (parallel and perpendicular). The ratio between the perpendicular intensity over the total one yields the depolarization ratio δ. Single particle detection is possible, using a peak detection algorithm. For high particle concentrations, a real-time signal averaging method can also be run simultaneously. <br><br> The IODE detector was used in connection with the Zurich ice nucleation chamber during the ICIS 2007 workshop where ice nucleation experiments were performed with several aerosol types. In presence of ice crystals, a depolarization ratio could be measured on a particle-by-particle basis. Mean values of δ ranged from 0.24 to 0.37 and agree well with theoretical calculations.

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