Study of synergistic disinfection by UVC and positive/negative air ions for aerosolized Escherichia coli, Salmonella typhimurium, and Staphylococcus epidermidis in ventilation duct flow

Evaluation of Single-Pass Disinfection Performance of Far-UVC Light on Airborne Microorganisms in Duct Flows

Far-UVC irradiation (222 nm) is considered an emerging and sustainable solution for future infection and pandemic challenges. We examined the disinfection performance of a krypton-chloride lamp, with a quasi-monochromatic UVC peak at 222 nm, for inactivating airborne microorganisms in a full-scale ventilation duct system. Single-pass disinfection efficacy of far-UVC was determined and compared with that of a conventional mercury-type UVC (254 nm) lamp. Four bacteria, Escherichia coli (E. coli), Pseudomonas alcaligenes (P. alcaligenes), Serratia marcescens (S. marcescens), and Staphylococcus epidermidis (S. epidermidis), as well as bacteriophage P22, were tested under UV exposure with different velocities of duct flows. The data revealed that as the air velocity increased from 0.7 to 4 m/s, the far-UVC disinfection efficacies would decrease by 42, 47, 35, 39, and 33% for these five microorganisms, respectively. The inactivation rate constants to far-UVC light were 4.9, 7.5, 3.3, 6.3, and 3.0 cm²/mJ for aerosolized E. coli, P. alcaligenes, S. marcescens, S. epidermidis, and bacteriophage P22, respectively. Far-UVC irradiation showed a comparable disinfection ability on airborne microorganisms compared with the 254 nm UV irradiation. This first study of far-UVC in real duct applications provides a better understanding of the disinfection performance of this solution in bioaerosol inactivation. It offers a valuable database in the sizing and design of excimer lamps for novel portable air purifiers or in-duct disinfection units.

Aerosol Transmission of the Pandemic SARS-CoV-2 and Influenza A Virus Was Blocked by Negative Ions

The pandemic of respiratory diseases, such as coronavirus disease 2019 (COVID-19) and influenza, has imposed significant public health and economic burdens on the world. Wearing masks is an effective way to cut off the spread of the respiratory virus. However, due to cultural differences and uncomfortable wearing experiences, not everyone is willing to wear masks; there is an urgent need to find alternatives to masks. In this study, we tested the disinfection effect of a portable ionizer on pandemic severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) (strain V34) and influenza A virus (strain CA04). Negative ions significantly reduced the concentration of particulate matter in the air above and effectively disinfected viruses stuck to the solid plate at the level of both nucleic acid and virus titer. The disinfection efficiency was >99.8% after 1-h exposure. Moreover, negative ions effectively disinfected aerosolized viruses; the disinfection efficiency was more than 87.77% after purification for 10 min. Furthermore, negative ions had a significant protective effect on susceptible animals exposed to viral aerosols. When the negative ionizer was switched from off to on, the inhalation 50% infective dose (ID₅₀) for golden hamsters challenged with SARS-CoV-2 rose from 9.878 median tissue culture infective dose (TCID₅₀) [95% confidence interval (CI), 6.727–14.013 TCID₅₀] to 43.891 TCID₅₀ (95% CI, 29.31–76.983 TCID₅₀), and the inhalation ID₅₀ for guinea pigs challenged with influenza A virus rose from 6.696 TCID₅₀ (95% CI, 3.251–9.601 TCID₅₀) to 28.284 TCID₅₀ (95% CI, 19.705–40.599 TCID₅₀). In the experiment of transmission between susceptible animals, negative ions 100% inhibited the aerosol transmission of SARS-CoV-2 and influenza A virus. Finally, we tested the safety of negative ion exposure. Balb/c mice exposed to negative ions for 4 weeks showed no abnormalities in body weight, blood routine analysis, and lung pathology. Our study demonstrates that air ions can be used as a safe and effective means of blocking respiratory virus transmission and contribute to pandemic prevention and control.