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 (GUV(222)); this inactivates airborne pathogens and is thought to be relatively safe for human skin and eye exposure. However, the impact of GUV(222) 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 GUV(222). We show that GUV(222) generates ozone (O-3) 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 GUV(222) irradiation under more realistic indoor air scenarios and demonstrate that under some conditions, GUV(222) irradiation can lead to levels of O-3, OH, and secondary organic products that are substantially elevated relative to normal indoor conditions. The results suggest that GUV(222) should be used at low intensities and in concert with ventilation, decreasing levels of airborne pathogens while mitigating the formation of air pollutants.