Significant Production of Ozone from Germicidal UV Lights at 222 nm

Lamps emitting at 222 nm have attracted recent interest for germicidal ultraviolet disinfection (“GUV222”). Their impact on indoor air quality is considered negligible. In this study, ozone formation is observed for eight different lamps from five manufacturers, in amounts an order of magnitude larger than previous reports. Most lamps produce O₃ in amounts close to the first-principles calculation, with, e.g., a generation rate of 22 ppb h^–1 for Ushio B1 modules in a 21 m³ chamber. Much more O₃ is produced by lamps when optical filters are removed for tests and by an undesired internal electrical discharge. A test in an office shows an increase of ～6.5 ppb during lamp-on periods, consistent with a simple model with the O₃ generation rate, ventilation, and O₃ losses. We demonstrate the use of a photolytic tracer (CBr₄) to quantify the averaged GUV222 fluence rate in a room. An important consequence of O₃ production by GUV222 is particulate matter (PM) formation, which may have significant negative health impacts. To limit GUV222-created indoor pollution, new guidelines should be developed and lower fluence rates should be used if possible, especially under low-ventilation conditions. Low-cost sensors for O₃ and PM were not useful for investigating GUV222-induced chemistry.