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

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 quality and 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 typical indoor pollutant levels, and for different ventilation levels. GUV254 is irritating for skin and eyes, has an occupational exposure limit, and thus these fixtures typically irradiate a smaller volume near the ceiling, or inside ventilation ducts. In contrast, GUV222 is described by some as harmless to skin or eyes due to rapid absorption in a very thin external layer. Our analysis showed that GUV254 is able to significantly photolyze O3, generating OH radicals, which initiates the oxidation of all indoor volatile organic compounds (VOCs). While secondary organic aerosol (SOA) can be formed as a product of VOC oxidation, most of SOA in our case studies is produced through GUV-independent terpene ozonolysis. GUV254-induced SOA formation is of the order of 0.1-1 μg m-3. GUV222 with the same effective virus removal rate makes a smaller impact on indoor air quality, mainly because of the significantly lower UV irradiance needed and substantially less efficient O3 photolysis (for primary OH generation) than at 254 nm.