Water vapour flow - Theory and regulation

Air is a gaseous mixture which contains several components in various proportions including hydrogen, nitrogen, oxygen, carbon dioxide, rare gases and water vapour. The atmospheric air, called polluted humid air is on its part composed of a certain number of gases, dusts and bacteria. By convention, dry air is defined as humidity-free and is thus an entirely theoretical concept and humid air contains a certain level of humidity. Physical quantities such as hair sensitivity to humidity allow for quantifying the static thermo-hygro state of the air and defining relative humidity and the dew point. Fick's law defines the transfer of water vapour between two different hygrothermal atmospheres and introduces the notion of permeance.