The relation between Specific and Relative Humidity of Air

Calculate the specific humidity of moist air knowing the relative humidity, water vapor and air density

Humidity is the quantity of water vapor present in air. It can be expressed as an absolute, specific or a relative value.

If we know the relative humidity of the moist air and the water vapor density and density of the air, the specific humidity can be expressed as:

x = 0.622 φ ρ_ws / (ρ - ρ_ws) 100% (1)

where

x = specific humidity of air vapor mixture (kg/kg)

φ = relative humidity (%)

ρ_ws = density of water vapor (kg/m³)

ρ = density of the moist or humid air (kg/m³)

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