Single ice crystal measurements during nucleation experiments with the depolarization detector IODE M. Nicolet1, O. Stetzer1, F. Lüönd1, O. Möhler2, and U. Lohmann1 1Institute for Atmospheric and Climate Science, ETH Zurich, 8092 Zurich, Switzerland 2Institute for Meteorology and Climate Research, Forschungszentrum Karlsruhe, Germany
Abstract. 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° 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.
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.
Citation: Nicolet, M., Stetzer, O., Lüönd, F., Möhler, O., and Lohmann, U.: Single ice crystal measurements during nucleation experiments with the depolarization detector IODE, Atmos. Chem. Phys., 10, 313-325, doi:10.5194/acp-10-313-2010, 2010.