Indoor Air Quality Implications of Germicidal 222 nm Light

Abstract

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.

Effects of 222 nm Germicidal Ultraviolet Light on Aerosol and VOC Formation from Limonene

“…In contrast, secondary OH, produced from limonene ozonolysis, does not require the lamp to be on. As the ratio k LIM+OH [OH] / k LIM+O3 [O 3 ] is not strongly modulated by the GUV222 lamp, we conclude that most of the OH is secondary, which is consistent with the modeled OH and previous measurements. ,, …”

“…As the ratio k LIM+OH [OH] / k LIM+O3 [O 3 ] is not strongly modulated by the GUV222 lamp, we conclude that most of the OH is secondary, which is consistent with the modeled OH and previous measurements. 16,55,56 To further evaluate the production of primary OH radicals, chamber experiments exposing hexanal to 222 nm light were performed under humid conditions (Figure S6B). Hexanal reacts efficiently with OH but not with the eluate of O 3 .…”

“…In contrast, Barber et al (2023) found primary OH production to be more important at fluence rates about 18 times larger than the fluence rates in our experiments. 16 3.2. Formation of Secondary Organic Aerosol.…”

Quantification of Byproduct Formation from Portable Air Cleaners Using a Proposed Standard Test Method

“…For AC2 the driver of VOC byproduct formation is likely O 3 chemistry with about three times more O 3 ( E r = 1300 μg h –1 ) mass produced than VOC byproducts ( E r = 403 μg h –1 ). The VOC byproducts for AC2 likely come from O 3 -initiated surface or gas-phase chemistryincluding reactions of OH produced from O 3 oxidation of limonene. , …”

“…The VOC byproducts for AC2 likely come from O 3 -initiated surface or gas-phase chemistry� including reactions of OH produced from O 3 oxidation of limonene. 26,27 We emphasize that the measured E r values are specific to the conditions of our chamber and the test method. In real-world indoor environments, reactive VOCs, which could produce VOC byproducts, can be present at concentrations higher than in our test method and/or may have emission sources that provide a continuous source of reactive VOCs.…”