scope:

In connection with air pollution control, it is necessary to have knowledge of the temporal and spatial distribution of the meteorological parameters of the atmosphere. One of these parameters is the water vapour contained in the atmosphere, which is called air humidity.

Air humidity plays a major role in the physical and chemical conversion of air pollutants. For example, high humidity favours the formation and growth of aerosols which are responsible for an increased occurrence of haze and fog in polluted air and thus for a change in the radiation budget of the atmosphere. Air humidity also influences the chemical conversion of air pollutants dissolved in aerosol droplets. To describe the atmospheric stability or the dispersion in the atmosphere, it is necessary to determine the vertical gradient of humidity. Moreover, some methods for the measurement of ambient air quality are affected by humidity, so that it has to be measured in order to correct the results.

For these tasks, continuous humidity measurements with electrical sensors are useful. Therefore, capacitive sensors with remote transmission and electronic data processing are almost exclusively used in measuring networks. For vertical sounding, not only radiosondes (VDI 3786 Part 8), but also remote sensing methods (VDI 4210 Part 1) are used.