Photocatalysis air purifier: a solution or a threat?
A photocatalysis air purifier is a device that uses photocatalytic oxidation technology to purify indoor air. It uses a photocatalyst and UV light to produce oxidizing agents that can destroy organic pollutants in the air. The purified air is then released back into the room. They can be effective at removing many common indoor pollutants, but may not be as effective at removing larger particles such as dust and pollen... Overall, do they really keep their promises? In this article, we analyse this air purification technology.
What is photocatalysis?
Photocatalysis is the decomposition and the degradation of pollutants through the use of light rays on the surface of a catalyst, generally titanium dioxide. It can eliminate VOCs, inorganic pollutants and microorganisms. The process results in water and carbon dioxide.
Photocatalysis air purifier efficiency has not been proven
Most photocatalysis air purifier manufacturers assert that their air purifiers eliminate 99% of all VOCs, PAHs, viruses, and bacteria up to a size of 0,01 µm. There is an accumulation of research findings conducted in laboratories that confirm the depolluting properties of this technology. But tests under real-life conditions call into question that efficiency. According to the ADEME, photocatalysis is efficient only under certain conditions. Experiments reveal performance gaps depending on mixtures of air pollutants and airflows.
Under real-life conditions, photocatalysis-based air purifiers' efficiency depends on a variety of factors :
- The environmental conditions : temperature and humidity
- The parameters of the lights: power, spectrum:(UV-A, UV-C)
- The nature of the photocatalyst
- The wear of the photocatalyst
- The number of passages of the air that has to be cleaned on the active surfaces
- The nature and the concentration of pollutants
Photocatalysis air purifier safety questioned by experts
Manufacturers most often use titanium dioxide (TiO 2 ) as a catalyst. It is known to be effective against VOCs, gas, odors, mold, fungus, bacteria, and viruses. According to the International Agency for Research on Cancer, titanium dioxide is also a carcinogen. Results from animal studies (ARC, 2006 & Yamashita et al, 2011) indicate that titanium dioxide causes lung cancer and impedes fetal development.
Above all, degradation mechanisms involve dangerous by-products. It is difficult to guarantee that the photocatalytic reaction will be complete, as indicated in the picture. The factors listed can lead to a partial reaction and the emission of toxic by-products. Among them, are ketones and aldehydes have irritant and toxic properties.
For more information, click here and read an excellent French article by Corinne Mandin and Séverine Kirschner.
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