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I have done the cloud in a bottle experiment (Youtube video) with a thermometer probe in the bottle to show the temperature increase and decrease. I am interested in the nature of the changes as the cloud nuclei get covered with water and then as the water evaporates (almost instantly) with the increased pressure as you squeeze the bottle.

For those unfamiliar with the subject, evaporation of a cloud droplet absorbs energy and the formation of a droplet releases energy. I find it interesting (and counter intuitive) that when you release pressure, cloud droplets form (meaning that the droplets themselves are releasing energy). Why are they releasing energy in a system that is already going to a lower energy state? Seen as a part of the system, as a speck of smoke at the start of the pressure drop, they have no energy to begin with!

I would also like to see a theory about this. Where the things that happen are related to how catalysts work. Smoke is a catalyst in this case. And where the condensation nuclei are acting almost like "buffers" in acid base theory. A buffer in acid base acts as a proton donor or proton acceptor to reduce pH fluctuations. Maybe the condensation nuclei can be seen as doing the same thing to reduce temp, and pressure changes in the cloud?

So, anyways, a cloud droplet forms around a condensation nucleus. Energy is released, while water vapor is absorbed from the gas around the nucleus. As the droplet falls into lower humidity air, it releases droplet water as water vapor with absorption of energy. On the one hand, more water vapor is more volume, but on the other hand, the lower temperature as the droplet absorbs energy as the water vapor is released causes lower pressure. I do not know where the balance lies.

Here is my attempt (Youtube video) to provide questions and maybe answers

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  • $\begingroup$ The CCN acts to reduce local evaporation allowing drops to grow at lower RH than possible without. I can take a stab at an answer when I find time. It would be helpful to know your thermo background. $\endgroup$ – casey Feb 16 '16 at 2:55

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