How to find absolute humidity of air

How to find absolute humidity of air

The absolute humidity – this mass of water vapor which is in unit of volume of this gas, in other words, is density of water vapor. Depending on temperature this size can change. It can be measured, having received a dew point or to calculate through relative humidity.

It is required to you

  • - mercury thermometer;
  • - tight vessel;
  • - table of dependence of saturated water vapor on temperature;
  • - psychrometer.


1. For direct measurement of humidity, select test of air in a tight vessel and begin to cool it. At a certain temperature on walls of a vessel there will be a dew (steam is condensed), write down value of temperature at which it will occur. According to specially table find density of saturated steam at that temperature that it was condensed. It will also be absolute humidity of air which test was selected.

2. Take the sensitive mercury thermometer, wind a vial of mercury with fabric. Take readings from it after it comes to temperature equilibrium with air. Determine density of saturated steam by the table at a temperature which is shown by the thermometer. It will also be absolute humidity, but the value will be not really exact.

3. Calculate absolute humidity at the known relative humidity. This size is measured as a percentage and shows how much the actual density of water vapor in air is less sated at this temperature. For determination of absolute humidity take air temperature. Then, according to the table of density of saturated steam find this size for the taken temperature. To find absolute humidity, relative humidity φ increase by density of saturated steam at this temperature ρн and divide into 100% (ρ = φ ∙ ρн/100%).

4. An example Relative humidity at a temperature 20ºС is 45%. To receive absolute humidity, find density of saturated water vapor at a temperature of 20 ºС which air has. This size is 17.3 g/m³. After that apply a formula to calculation of absolute humidity ρ=45∙17.3/100=7.785 g/m³. It will also be absolute humidity of air.

Author: «MirrorInfo» Dream Team