Synergistic air disinfection by far-UVC and negative air ions in a portable device

Localized air disinfection is an effective strategy for reducing airborne pathogen transmission, though combining methods may yield only additive effects or, in some cases, synergistic efficacy. This study experimentally examined the single-pass disinfection efficiency of individual and combined Far-UVC and negative ionizers in a custom-built portable disinfection unit. Several influencing factors were comprehensively investigated: light-redistribution, number of ionizers, Far-UVC lamp arrangement, flow rate, and microbial type. Four microorganisms, including two common bacteria (Escherichia coli and Staphylococcus epidermidis) and two bacteriophages representing viruses (MS2 and P22), were tested at various airflow rates ranging from 81 to 144 m³/h. The results showed that light‑redistribution by enhancing wall reflection increased disinfection efficiency by 20-110 % compared to the control condition without light‑redistribution. Microbial susceptibility was evaluated for Far-UVC light, and sensitivity to negative ions was also determined. The results demonstrated that airborne E. coli was the most susceptible to Far-UVC. In contrast to the bacteria, the airborne viruses MS2 and P22 were more sensitive to negative ions. The results revealed that the combination of Far-UVC and ionizers exhibited a synergistic effect for those tested bacteria, producing a disinfection efficiency greater than the sum of their individual contributions. Furthermore, a horizontal arrangement of two Far-UVC lamps provided better disinfection than a vertical arrangement. The findings from this work offer valuable insights into strategies to enhance air disinfection performance, facilitating the development of novel portable devices that effectively disinfect bioaerosols.