Air humidity & Temperature

Humidity of air

Air, depending on its temperature, is able to absorb and store an amount of water vapour. The content of water vapour stored in the atmosphere is called air humidity

The amount of the water vapour in the atmosphere with a maximum of 4 vol. % is comparatively low. The water vapour content of the air varies considerably. The water vapour is one of the most effective meteorological elements. Therefore the air humidity is of great importance. At the same time a lot of chemical, physical and biological processes are caused or influenced by the content of water vapour in the atmosphere so that the moisture content in the surrounding air is an important factor in many cases of process engineering.

Important figures of humidity measurement
Methods of humidity measurement
Mollier chart for humid air


The temperature describes the thermal state of the atmosphere. At the same time the temperature is a measure of the mean kinetic energy of the air molecules. At the absolute temperature-zero the molecules are not in motion. Readings of temperature are normally given in °C (degrees centigrade). Differences between any two temperatures (readings or calculated) are given in K (Kelvin). The only difference between the centigrade and the Kelvin scale are the zero points. The following is valid: t [°C] = T [K]-273.15 

Temperature and uv radiation balance

For exact measurements of the temperature it is necessary that the sensor and the surrounding air are in an thermal balance. Every thermally closed system reaches with the time such a thermal balance. Therefore the measurement of the temperature of the atmosphere is accompanied by difficulties as the measurement is influenced by direct and diffuse radiation.

The used definition of temperature in meteorology should only describe the mean kinetic energy of the air molecules and not the energy of the radiation. To determine the air temperature both is necessary the thermal balance and an effective protection against uv radiation.

By international agreements the temperature is measured two meters above soil. Temperature readings are always given as shade temperatures.

« back
to overview