The Effect of Vapor Depletion on Ice Nucleus Measurements with Membrane Filters

Paul J. Huffman Dept. of Atmospheric Resources, University of Wyoming, Laramie 82070

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Gabor Vali Dept. of Atmospheric Resources, University of Wyoming, Laramie 82070

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Abstract

The depletion of water vapor during humidification of filter samples, which introduces complications in the determination of ice nucleus concentrations, is considered in detail. A complete solution of the problem appears beyond reach because of the dependence of the depletion effect on the activation spectrum of nuclei; these spectra cannot be determined independently.

Measurements showed that depletion by activated nuclei is more important than by hygroscopic particles. A simple “area-of-effect” model was found to fit the observations relatively well. A generalized correction factor was derived with which the true concentrations of nuclei can be found from measured concentrations.

Abstract

The depletion of water vapor during humidification of filter samples, which introduces complications in the determination of ice nucleus concentrations, is considered in detail. A complete solution of the problem appears beyond reach because of the dependence of the depletion effect on the activation spectrum of nuclei; these spectra cannot be determined independently.

Measurements showed that depletion by activated nuclei is more important than by hygroscopic particles. A simple “area-of-effect” model was found to fit the observations relatively well. A generalized correction factor was derived with which the true concentrations of nuclei can be found from measured concentrations.

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