Because nowadays many houses and buildings are badly ventilated (e.g. to save energy) accumulation of gaseous compounds that potentially are harmfull may occur.
Fytagoras developed tests for the determination of the air purifying properties of plants using the clearance of chemcial indicator compounds from the air by the plant tested. The result is an objective air purification classification of each plant species tested.
In addition, this method can be used in research into optimizing the air purification properties of plants, from the perspective of cultivation as well as breeding possibilities.