Significant Production of Ozone from Germicidal UV Lights at 222 nm

Abstract

AbstractLamps 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 O3in amounts close to the first-principles calculation, with e.g. a generation rate of 22 ppb h-1for Ushio B1 modules in a 21 m3chamber. Much more O3is produced by lamps when optical filters were 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 O3generation rate, ventilation and O3losses. We demonstrate the use of a photolytic tracer to quantify the averaged GUV222 fluence rate in a room. Low-cost electrochemical O3sensors were not useful below 100 ppb. Formation of O3increases indoor particulate matter (PM), which is ∼10-30 times more deadly than O3per unit mass, and which is ignored when only considering O3threshold limit values. To limit GUV222-created indoor pollution, lower fluence rates should be used if possible, especially under low-ventilation conditions.TOC graphic