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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union

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Atmos. Meas. Tech., 10, 4639-4657, 2017
https://doi.org/10.5194/amt-10-4639-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
01 Dec 2017
Using depolarization to quantify ice nucleating particle concentrations: a new method
Jake Zenker1, Kristen N. Collier1, Guanglang Xu1, Ping Yang1, Ezra J. T. Levin2, Kaitlyn J. Suski2,a, Paul J. DeMott2, and Sarah D. Brooks1 1Department of Atmospheric Science, Texas A&M University, College Station, TX 77843, USA
2Department of Atmospheric Science, Colorado State University, Fort Collins, CO 80526, USA
anow at: Pacific Northwest National Laboratory, Richland, WA 99352, USA
Abstract. We have developed a new method to determine ice nucleating particle (INP) concentrations observed by the Texas A&M University continuous flow diffusion chamber (CFDC) under a wide range of operating conditions. In this study, we evaluate differences in particle optical properties detected by the Cloud and Aerosol Spectrometer with POLarization (CASPOL) to differentiate between ice crystals, droplets, and aerosols. The depolarization signal from the CASPOL instrument is used to determine the occurrence of water droplet breakthrough (WDBT) conditions in the CFDC. The standard procedure for determining INP concentration is to count all particles that have grown beyond a nominal size cutoff as ice crystals. During WDBT this procedure overestimates INP concentration, because large droplets are miscounted as ice crystals. Here we design a new analysis method based on depolarization ratio that can extend the range of operating conditions of the CFDC. The method agrees reasonably well with the traditional method under non-WDBT conditions with a mean percent error of ±32.1 %. Additionally, a comparison with the Colorado State University CFDC shows that the new analysis method can be used reliably during WDBT conditions.

Citation: Zenker, J., Collier, K. N., Xu, G., Yang, P., Levin, E. J. T., Suski, K. J., DeMott, P. J., and Brooks, S. D.: Using depolarization to quantify ice nucleating particle concentrations: a new method, Atmos. Meas. Tech., 10, 4639-4657, https://doi.org/10.5194/amt-10-4639-2017, 2017.
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Short summary
We have developed a new method which employs single particle depolarization to determine ice nucleating particle (INP) concentrations and to differentiate between ice crystals, water droplets, and aerosols. The method is used to interpret measurements collected using the Texas A&M Continuous Flow Diffusion Chamber (TAMU CFDC) coupled to a Cloud and Aerosol Spectrometer with Polarization (CASPOL). This new method extends the range of operating conditions for the CFDC to higher supersaturations.
We have developed a new method which employs single particle depolarization to determine ice...
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