Air cleaning systems creating harmful new pollutants, study finds

Posted on Thursday 31 July 2025

While germicidal ultraviolet (GUV) lights are increasingly used for disinfecting indoor air, the new research has examined their potential to affect indoor air chemistry - leading to the formation of indoor air pollution.

Harmful secondary pollutants

Researchers have found that GUV lights can have negative impacts on human health through the formation of harmful secondary pollutants.

The study, led by researchers from the University of York in collaboration with institutions including the University of Colorado Boulder, Johns Hopkins University, Rutgers University and NHS Tayside, used a sophisticated indoor air chemistry model to simulate the effects of GUV lights in typical indoor environments like classrooms and kitchens.

The research highlights the need for a comprehensive assessment of GUV technology, balancing its benefits for pathogen removal with its impact on air quality.

Crucial insights

Dr. Toby Carter, the lead author from the University of York, said: “Our findings underscore the importance of looking beyond the pathogen removal capabilities of UVC lights. We need to fully understand their impact on the air we breathe indoors to ensure these technologies truly benefit public health. Although GUV lamps can remove biological pathogens like the COVID-19 virus, they can produce chemical pollutants as they do so.”

“We hope this research provides crucial insights for policymakers, manufacturers, and consumers to make informed decisions about implementing GUV air cleaning technology.”

The research found that 222 nanometre GUV lamps, often marketed as “far-UVC” and safe for human exposure, can lead to a notable increase in indoor ozone concentrations.

Harmful to health

This ozone can then interact with surfaces, including human skin, to form secondary chemicals like nonanal, decanal, and 4-oxopentanal, which are potentially harmful to human health at high concentrations. Conversely, 254 nm GUV lamps, which are commonly used in upper-room disinfection systems, caused a less significant rise in ozone levels.

The authors emphasise that while GUV devices are effective at removing airborne pathogens, their impact on indoor air chemistry is relatively underexplored. They are now calling for a quantitative comparison of the long-term health benefits of GUV disinfection against the potential harms from GUV-induced air pollution to enable a more complete understanding of this technology.

Real world impacts

Dr Carter added: “The impact of air pollutants can be particularly harmful for vulnerable people - that is why our study examined real world situations such as classrooms in schools.” 

The study, “The Impact of UVC Light on Indoor Air Chemistry: A Modelling Study,” has been published in the Journal Environmental Science & Technology.