Improving an In-Duct System for Bioaerosol Hazard Mitigation: Evaluating the Role of Particle Size and Relative Humidity in Ultraviolet Germicidal Irradiation Efficiency

Ultraviolet germicidal irradiation (UVGI) technology has garnered substantial attention in disinfecting airborne microorganisms during and beyond the COVID-19 pandemic. Given that UVGI inactivation performance varies in complex indoor environments, this study examines the effects of bioaerosol particle size and relative humidity (RH) on the inactivation efficiencies of an in-duct UVGI system. MS2 bioaerosol with phosphate-buffered saline as suspending media was used for this purpose. At any given RH condition (25%, 40%, or 60% RH), our data presented lower UV rate constants for larger bioaerosols (2.1–7 µm) in comparison to smaller ones (0.65–2.1 µm). In terms of humidity, the UV rate constant for MS2 initially increased and then decreased as RH increased from 25% to 60%, peaking at 40% RH, irrespective of the particle size. In conclusion, our findings suggest that a higher UV dose is required to mitigate hazards from larger bioaerosols in either dry or humid environments. In addition, this work proposes a comprehensive flowchart, a beneficial tool for engineers and designers, which facilitates the effective design and implementation of UVGI technology in controlling bioaerosol hazards.