Secondary Organic Aerosol Production from a 222 nm Germicidal Lamp

MATTHEW GOSS, Victoria Barber, Lesly Franco Deloya, Lexy LeMar, Yaowei Li, Erik Helstrom, Manjula Canagaratna, Frank Keutsch, Jesse Kroll, MIT

     Abstract Number: 266
     Working Group: Aerosol Science of Infectious Diseases: Lessons and Open Questions on Models, Transmission and Mitigation

Abstract
The Covid-19 pandemic has accelerated the need to reduce the levels of airborne pathogens within indoor spaces. One novel mitigation strategy, the use of KrCl excimer lamps (222 nm) for ultraviolet disinfection, has recently gained attention since it effectively inactivates pathogens while posing little risk via direct skin and eye exposure. However, the effect of 222 nm light on indoor air chemistry is poorly constrained. Here we carry out a set of experiments in which VOCs are added to a 150 L environmental chamber and exposed to 222 nm light. Gas-phase species are monitored using an ozone monitor, Vocus (H₃O⁺-CIMS), and PTR3 (NH₄⁺-CIMS), and particle-phase products are measured using an aerosol mass spectrometer and scanning mobility particle sizer. We find that 222 nm lamps can produce substantial levels of ozone and OH; when VOCs are present, these oxidants react to form oxidized VOCs and secondary organic aerosol (SOA). This work examines the amount and composition of the SOA formed from 222 nm photooxidation of three VOCs (hexanal, cyclohexene, and limonene). Results are extrapolated to realistic indoor conditions, enabling estimates of SOA concentrations in indoor environments as a function of ventilation and 222 nm light intensity.