= Cloud-droplet activation
An <aerosol> particle becomes a freely growing <cloud droplet> after crossing its <Köhler theory> growth barrier under the parcel's <atmospheric supersaturation> history. Counting particles whose <critical supersaturation> is below a specified peak gives an equilibrium-threshold estimate; calculating that peak requires cooling, <water vapor> depletion and condensational-growth kinetics. Neither total <aerosol> number nor dry size alone determines activation.
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