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Condensation nuclei (formerly Re: Money to burn?)



On Mon, 28 Jun 1999, Daniel L. MacIsaac wrote:

Condensation nuclei are required for cloud formation at saturation
(really, just above saturation). No argument there.

[snip]

Again, my concern about the demo is that it implies that "regular" air is
devoid of condensation nuclei.

You might check out "Clouds in a Glass of Beer: Simple Experiments in
Atmospheric Physics" by Craig Bohren (should be <$20 from Amazon), which is
a delightful read on this sort of thing. Bohren distinguishes heterogeneous
nucleation (where something else nucleates the cloud) from homogeneous
nucleation (where the molcules are cooled enough to "stick" in their collisions
and nucleate themselves. You get heterogeneous nucleation on the insides
of the beer glass or from salt or sand (uck) particles in beer. You get
homogeneous nucleation in the throat of the bottle when you uncap and
release pressure, dropping the temp to about -36C and making the cloud in
the neck of the bottle. This is my fave cloud making demonstration :^).

I really should read that book; especially since Craig Bohren was my
undergraduate advisor for a year. :)

For those who have read the book, does he say (or imply) that clouds in
the atmosphere are from homogeneous nucleation?

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| Robert Cohen Department of Physics |
| East Stroudsburg University |
| bbq@esu.edu East Stroudsburg, PA 18301 |
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