Factors to consider in the performance evaluation of an air purifier using an airborne virus (Phi-X174) in a large chamber

Devices for the filtration and sterilization of indoor spaces have been widely used owing to the outbreak of the novel coronavirus disease 2019 (COVID-19). There is a need for a standard method to test the effectiveness of such devices. In this study, we aimed to identify important factors that must be considered while evaluating the efficiency of air purifiers in a large chamber. Investigation of the distribution characteristics of airborne viruses in the large chamber show that they were evenly distributed. Natural (gravitational) reduction of airborne viruses in the large chamber was also investigated. We found that the airborne-virus removal efficiency of an air purifier in a large chamber should be evaluated after 40 min for better accuracy because the concentration of airborne viruses rapidly decreased within the first 40 min and the settling velocity reduced after 40 min. In addition, the minimum standard deviation of airborne-virus removal efficiency of air purifier was 1.9% with a natural reduction time of 40 min. Moreover, the sampling efficiencies of three types of samplers were compared. The impactor showed the highest sampling efficiency (4.8 × 10⁴–5.1 × 10⁴ PFU/m³-min) and a small standard deviation (0.9 × 10⁴ PFU/m³-min).