Indoor Air Quality Implications of Germicidal 222 nm Light

One strategy for mitigating the indoor transmission of airborne pathogens, including the SARS-CoV-2 virus, is irradiation by germicidal UV light (GUV). A particularly promising approach is 222 nm light from KrCl excimer lamps (GUV₂₂₂); this inactivates airborne pathogens and is thought to be relatively safe for human skin and eye exposure. However, the impact of GUV₂₂₂ on the composition of indoor air has received little experimental study. Here, we conduct laboratory experiments in a 150 L Teflon chamber to examine the formation of secondary species by GUV₂₂₂. We show that GUV₂₂₂ generates ozone (O₃) and hydroxyl radicals (OH), both of which can react with volatile organic compounds to form oxidized volatile organic compounds and secondary organic aerosol particles. Results are consistent with a box model based on the known photochemistry. We use this model to simulate GUV₂₂₂ irradiation under more realistic indoor air scenarios and demonstrate that under some conditions, GUV₂₂₂ irradiation can lead to levels of O₃, OH, and secondary organic products that are substantially elevated relative to normal indoor conditions. The results suggest that GUV₂₂₂ should be used at low intensities and in concert with ventilation, decreasing levels of airborne pathogens while mitigating the formation of air pollutants.