Germicidal UV could contribute to indoor air pollution

Germicidal ultraviolet (UV) is used to reduce the load of airborne pathogens in viruses, but new research has found it could be producing harmful compounds.

Researchers from the Massachusetts Institute of Technology (MIT), Aerodyne Research and Harvard University have discovered 222-nanometer UV lights may produce harmful compounds in indoor spaces; and are best used in conjunction with appropriate ventilation.

UV lights are used in germicidal air purifier systems to disinfect germs and bacteria in the air. The light acts as a germicide by damaging the molecules of the germs, and causing a harmless mutation to form.

MIT postdoc Victoria Barber, doctoral student Matthew Goss, Professor Jesse Kroll, and six others published their findings in Environmental Science and Technology. Kroll and his team began to focus on indoor air quality during the pandemic after they discovered devices cleaning indoor air using chemical methods or UV light could cause photochemical reactivity.

Kroll says when the oxidation is brought indoors it can trigger a potential cascade of reactions. When UV light interacts with oxygen it can form ozone, but there’s also a possibility for other oxidation reactions.

Depending on the material and nature of exposure, oxidising materials can cause various types of bodily harm.

Barber explains that if there are volatile organic compounds in the environment (which is the case in most indoor environments), these oxidants react with them.

“You make these oxidised volatile organic compounds, which in some cases turn out to be more harmful to human health than their unoxidised precursors,” she says.

The process can also lead to the formation of secondary organic aerosols, which are harmful to breathe.

The team observed the pollution-forming processes in a series of experiments. First they exposed clean air to the UV lights inside a controlled container, then added one organic compound at a time to see how they each affected the compounds that were produced. The formation of secondary products was clear.

The findings suggest devices such as KrCl excimer lamps are not a suitable substitute for ventilation. Kroll says these lights are not a replacement for ventilation, but rather a complement to it.

He explains that a lack of ventilation can cause a build up of bacteria and viruses.

“Maybe if you could just deactivate the viruses and bacteria indoors, you wouldn’t need to worry about ventilation as much,” he says.

“There may be a sweet spot in which you’re getting the health benefits of the light, the deactivation of pathogens, but not too many of the disbenefits of the pollutant formation because you’re ventilating that out.”

The team admits further testing needs to be done in a larger controlled environment.

“What we’re seeing is not necessarily directly comparable to what you would see in a real indoor environment, but it does give a pretty good picture of what the chemistry is that can happen under radiation from these devices,” says Barber.

The next step will be testing the reactions in a real indoor environment.

The full research paper is available to read here.