Purifying air in 2022
What previously played only a small role in Europe has developed into a lively market in the last two years. Since the beginning of the pandemic, the offers have increased by various methods and different devices, which all have one task: To rid air, or even air and surfaces, of pathogens in order to better protect people from infection - after all, we spend 80-90% of our lives indoors, which are home to particularly high concentrations of germs, especially in public spaces.
Active vs. passive air purification
Basically, two approaches can be distinguished: Air purification by filtering, i.e. "sorting out" the negative components of our indoor air, and air purification by actively adding substances with a germ-eliminating effect. The latter method is colloquially known as disinfecting the air.
Fogging everything: Can, but does not have to be useful
Especially when fogging disinfectants such as sodium hypochlorite, hydrogen peroxide or similar. Fluids" is a good description of "disinfection of air and surfaces". Complementary UV-C irradiation is also used to eliminate pathogens, on surfaces. However, these methods should not be used under any circumstances while people are in the room without protective clothing. The disinfection power in the air and on surfaces is very high and the effectiveness of these methods is known from factory farming.
Filtering is harmless
Completely harmless for use in the presence of humans, on the other hand, is the use of hepa, activated carbon or UV-C light filters - as long as the filters are safely installed in a device and can only be replaced and disposed of by trained personnel. Regular replacement of filters is important to prevent contamination of the discharged air. On surfaces, these passive systems do not have a disinfecting effect; here, manual surface disinfection is necessary.
One gas, one molecule, one radical - does it help?
Adding molecules to indoor air includes other systems such as hydroxyl generators, used by NASA as early as 1994, ozone generators or HOCl molecule generators. While hydroxyl and hypochlorous acid (HOCl) are harmless to humans, an ozone generator, like disinfectant nebulizers, should not be run in the presence of humans, as the gas has the same oxidizing effect on human cells as it does on pathogens. Hydroxyl radicals are a part of our atmosphere and clean it from pollutants. Unfortunately, the lifetime of these radicals is so short (<0.2 seconds) that reliable purification is only possible within a small radius around a generator. Molecular HOCl can travel much longer distances before degrading and, incidentally, has a positive effect on the immune system of humans. These three systems reliably eliminate pathogens in the air and on surfaces within their radius of action.
Last but not least, ventilation, the natural supply of air, is an effective way to reduce germ concentrations in the air. However, surfaces are not protected and the energy efficiency of buildings is significantly affected.