UV Inactivation of Common Pathogens and Surrogates Under 222 nm Irradiation from KrCl* Excimer Lamps

Germicidal ultraviolet (UV) devices have been widely used for pathogen disinfection in water, air, and on food and surfaces. Emerging UV technologies, like the krypton chloride (KrCl*) excimer emitting at 222 nm, are rapidly gaining popularity due to their minimal adverse effects on skin and eyes compared with conventional UV lamps emitting at 254 nm, opening opportunities for UV disinfection in occupied public spaces. In this study, inactivation of seven bacteria and five viruses, including waterborne, foodborne and respiratory pathogens, was determined in a thin-film aqueous solution using a filtered KrCl* excimer emitting primarily at 222 nm. Our results show that the KrCl* excimer can effectively inactivate all tested bacteria and viruses, with most microorganisms achieving more than 4-log (99.99%) reduction with a UV dose of 10 mJ cm⁻². Compared with conventional UV lamps, the KrCl* excimer lamp exhibited better disinfection performance for viruses but was slightly less effective for bacteria. The relationships between UV sensitivities at 222 and 254 nm for bacteria and viruses were evaluated using regression analysis, resulting in factors that could be used to estimate the KrCl* excimer disinfection performance from well-documented UV kinetics using conventional 254 nm UV lamps. This study provides fundamental information for pathogen disinfection when employing KrCl* excimers.