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Measurements of the Size of Natural Cloud Nuclei by Means of Nuclepore Filters

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  • 1 Division of Radiophysics, CSIRO, Sydney, Australia
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Abstract

The size of cloud nuclei acting at 0.75% supersaturation was estimated by using varying flow rates through Nuclepore filters to discriminate between different sizes. The nuclei, sampled in clean continental and maritime air at Robertson, N.S.W., were found to be small, not much greater than the theoretical minimum radius of ∼1−6 cm permitted by nucleation theory.

This result agrees quite well with previous estimates of cloud-nucleus size from experiments carried out at Chesapeake Bay, Md. It is concluded that the atmospheric residence time of cloud nuclei cannot be more than a few days and that they must be composed entirely or partly of a water-soluble material since an insoluble particle of such a small size could not nucleate condensation at supersaturations of the order of 1% or less.

Abstract

The size of cloud nuclei acting at 0.75% supersaturation was estimated by using varying flow rates through Nuclepore filters to discriminate between different sizes. The nuclei, sampled in clean continental and maritime air at Robertson, N.S.W., were found to be small, not much greater than the theoretical minimum radius of ∼1−6 cm permitted by nucleation theory.

This result agrees quite well with previous estimates of cloud-nucleus size from experiments carried out at Chesapeake Bay, Md. It is concluded that the atmospheric residence time of cloud nuclei cannot be more than a few days and that they must be composed entirely or partly of a water-soluble material since an insoluble particle of such a small size could not nucleate condensation at supersaturations of the order of 1% or less.

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