Photoactive roofs ensure clean air: Photoactive roof tile surfaces are effective against harmful nitrogen oxides (NOx) from exhaust gases in the air. For this purpose a special titanium dioxide (TiO2) photocatalyst is imbedded in the mineral surface. The photocatalyst is not affected or changed by the reactions and thus remains active the whole building material's life.
Photocatalysis is based on a sequence of physical and chemical reactions, which occur on the surface of the catalyst with the aid of light. The conversion of the nitrogen oxides results in harmless nitrates, which are rinsed off with the rain water from the roof and usually are fed back into the natural cycle as nutrients. Thus, photoactive roofing materials contribute to fighting air pollution e. g. as elements of the municipal Clean Air Policy and Planning.
Besides converting these air pollutants photoactive roof tiles are self-cleaning. They reduce the amount of organic compounds such as mosses, lichens and algae by degradation. The residues are flushed away by rain. This self-cleaning effect is - considering the preservation of values - a worthwhile aspect of choosing roof building material.