6. Condensation/evaporation of liquid aerosols

In nature, the most important aerosol-forming process is the condensation of vapor into very small liquid particles. The opposite of condensation is evaporation. It is this process, for example, that enables the production of nuclei, such as NaCl nuclei in the atmosphere, from evaporated droplets. In aerosol metrology, these phenomena must be taken into account, as they can distort results.

Since the first observations by Coulier (1875) and Aitken (1888), it has been known that in humid air, it is impossible to obtain vapor condensation without the presence of very fine particles. If the air remains very pure, drops can only be obtained at very high levels of supersaturation, while the presence of ions enables drops to be obtained at lower saturations (C.T.R. Wilson, 1897).