Evaluation of Secondary Chemistry due to Disinfection of Indoor Air with Germicidal Ultraviolet Lamps

ZHE PENG, Shelly L. Miller, Jose-Luis Jimenez, University of Colorado Boulder

     Abstract Number: 357
     Working Group: Aerosol Science of Infectious Diseases: What We Have Learned and Still Need to Know about Transmission, Prevention, and the One Health Concept

Abstract
The disinfection of air using Germicidal Ultraviolet light (GUV) is a long-standing technique, which has received intense attention during the COVID-19 pandemic. GUV generally uses UVC lamps as its light source, which are known to initiate photochemistry in air. However, the impact of GUV on indoor air chemistry has not been investigated in detail, to our knowledge. In this study, we model the chemistry initiated by GUV at 254 or 222 nm (GUV254 or GUV222) in a typical room with poor or reasonable ventilation. GUV254 is irritating to skin and eyes, has an occupational exposure limit to people, and thus these fixtures typically irradiate a small volume near the ceiling. GUV222 is thought to be much less harmful to skin or eyes and can be used for the whole room volume. Results of our analysis showed GUV254 nm can photolyze O3 in significant amounts and efficiently generate OH radicals, which initiates the oxidation of indoor volatile organic compounds (VOCs). Common products of VOC oxidation, e.g., carbonyls and peroxides, can also be directly photolyzed by GUV254, which helps sustain the radical chemistry indoors. Secondary organic aerosol can be formed in µg/m3 and tens of µg/m3 in typical and polluted indoor spaces, respectively, as a product of VOC oxidation, with an estimated bulk VOC mass yield of the order of 1%. In contrast, GUV222 with the same effective virus removal rate makes a smaller impact on indoor air quality, mainly because of substantially less efficient O3 and carbonyl photolysis than GUV254. Increasing air exchange between the irradiated and unirradiated spaces in a room with GUV254 is recommended, since it reduces UV intensity needed to attain a certain virus removal rate and hence the impact on indoor air quality. Better ventilation can not only remove pathogens, but also limit the production of secondary indoor pollutants by GUV, and is thus also recommended when outdoor air is relatively clean.