Human exposure to air contaminants under the far-UVC system operation in an office: effects of lamp position and ventilation condition

The far-UVC (222 nm) system has emerged as a solution for controlling airborne transmission, yet its effect on indoor air quality, particularly concerning positioning, remains understudied. In this study, we examined the impact of far-UVC lamp position on the disinfection and secondary contaminant formation in a small office. We employed a three-dimensional computational fluid dynamics (CFD) model to integrate UV intensity fields formed by different lamp positions (ceiling-mounted, wall-mounted, and stand-alone types) along with the air quality model. Our findings reveal that the ceiling-mounted type reduces human exposure to airborne pathogens by up to 80% compared to scenarios without far-UVC. For all the lamp positions, O₃ concentration in the breathing zone increases by 4-6 ppb after one hour of operation. However, it should be noted that a high concentration zone (> 25 ppb) forms near the lamp when it is turned on. Moreover, ventilation plays a crucial role in determining human exposure to airborne pathogens and secondary contaminants. Increasing the ventilation rate from 0.7 h^-1 to 4 h^-1 reduces airborne pathogen and secondary contaminant concentrations by up to 90%. However, caution is warranted as higher ventilation rates can lead to elevated O₃ indoors, especially under conditions of high outdoor O₃ concentrations.