Relative Saturation (Relative Humidity)

If the partial pressure of a vapor in the gas mixture is less than the vapor pressure of the liquid at the existing pressure, the gas mixture is partially saturated. The ratio of the partial pressure of the vapor to the vapor pressure of the liquid at the liquid at the existing temperature, expressed in percentage, is termed relative saturation.

The term ‘humidity’ is used if the vapor is water and the gas is air.

\[\text{Relative saturation} = \frac{P_A}{P^{\text{sat}}_A}\times 100\] where

\(P_A\) = partial pressure of the vapor (\(A\)) in the gas mixture
\(P_A^{\text{sat}}\) = vapor pressure of component \(A\).