The air-purifying properties of plants can be measured by placing them in a closed room. Such a room is filled with the usual amount of pollutants. The time it takes for these pollutants to disappear is then measured (direct analysis with a gastomatograph mass spectrometer).
If you want to compare different plants, it is important to treat all plants equally (well), i.e. no coarse rearrangement, sufficient watering, always enough light, etc. The effects of stress on the air-purifying properties can also be measured in this way.
In practice, it is also possible to measure the reduction of pollutants in the natural environment of offices, classrooms, apartments and other rooms using active collectors.
The test tubes, which are usually equipped with activated carbon, are exposed to the ambient air over a defined period of time and then examined in the laboratory for the individual pollutants.
This measurement is usually carried out by building biologists and test laboratories and is the most cost-effective and most common variant for a before/after measurement when plants are used.