Ozone Generation by Ultraviolet Lamps^†

The COVID-19 pandemic has generated a great deal of interest in ultraviolet germicidal irradiation (UVGI) as an important means to disinfect air and surfaces. The traditional lamp employed for UVGI has been the low-pressure mercury-discharge lamp that emits primarily at 254 nm in the ultraviolet photobiological band UV-C (100-280 nm). The recent development of even shorter-wavelength UV-C lamps, such as the Krypton-Chloride, 222-nm lamp, has led to greater concerns about the UV-C generation of ozone. It is well known that wavelengths below 240 nm more readily generate ozone. However, there is a great misunderstanding with regard to the actual generation and dissipation of ozone molecules by UV-C lamps. A review of this subject is much warranted. An overview of the ozone generation of various UV-C light sources is presented to give users a better understanding of risk and how to assure control of ozone when employing UV-C lamps.