condensation,deposition of aliquid or asolid from its vapour, generally upon asurface that is cooler than theadjacentgas. A substance condenses when thepressure exerted by its vapour exceeds thevapour pressure of the liquid or solidphase of the substance at thetemperature of the surface where condensation occurs.Heat is released when a vapour condenses. Unless this heat is removed, the surface temperature will increase until it is equal to that of the surrounding vapour.

1 of 2

2 of 2

If air were free of tiny particles, calledaerosols, condensation would only occur when the air was extremelysupersaturated withwater vapour. In theatmosphere, however, there is an abundant supply of aerosols, which serve as nuclei, calledcondensation nuclei, on which water vapour may condense. Some are hygroscopic (moisture-attracting), andcondensation begins on them when therelative humidity is less than 100 percent, but other nuclei require some supersaturation before condensation begins.

In the atmosphere the relative humidity of the air is increased, and condensation results when air temperature is reduced to thedew point or when sufficient water vapour is added to saturate the air. Condensation accounts for the formation of dew,fog, andclouds. Forrain to occur, other physical processes are required.

Britannica Quiz

Water and its Varying Forms