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 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 O3 generation rate, ventilation and O3 losses. We demonstrate the use of a photolytic tracer to quantify the averaged GUV222 fluence rate in a room. Low-cost electrochemical O3 sensors were not useful below 100 ppb. Formation of O3 increases indoor particulate matter (PM), which is ~10-30 times more deadly than O3 per unit mass, and which is ignored when only considering O3 threshold limit values. To limit GUV222-created indoor pollution, lower fluence rates should be used if possible, especially under low-ventilation conditions. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement We thank the Balvi Filantropic Fund, the CIRES Innovative Research Program, and the Sloan Foundation (grant 2019-12444) for support of this work. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes All data produced in the present work are contained in the manuscript