Condensation in aerosol dynamics

Condensation can be summarized as a phase transition from a gas to a liquid as vapor condenses on a pre-existing surface, the exact opposite of the transition from liquid to vapor which occurs in evaporation. Both condensation and evaporation are happening all the time; atmospheric conditions determine which of them dominates. When the vapor is condensing, the particles on which the vapor condenses will grow bigger, in the same way when vapor evaporates from a particle, it will shrink. This can be seen in the size distribution of aerosol. When the vapor is condensing, then the size distribution moves to bigger sizes: on the contrary, when the vapor is evaporating it moves towards smaller sizes. As the size distribution grows towards bigger or smaller sizes, the airborne mass concentration increases or decreases respectively. In the atmosphere, condensation by for example H₂SO₄ and organic compounds is the main growth mechanism.