Analysis on Applicability of Air Purifiers in Schools to Prevent the Spread of Airborne Infection of SARS-CoV-2

The social and economic losses caused by viruses such as SARS-CoV, MERS-CoV, and SARS-CoV-2 has been serious. In this study, the size of airborne droplet nuclei particles and the number of virions generated by speaking or coughing were analyzed. Particle collection efficiencies of E11 and H13 grade air filters used in commercial air purifiers were evaluated for different particle sizes and the possibility of removing the airborne droplet nuclei particles by air purifiers was studied. In addition, the reduction of SARS-CoV-2 virion concentration and dose by using air purifiers was theoretically investigated for elementary school classrooms. When an infected student continuously emits virions with a rate of 6.0x10(5) virions/h in a 165 m(3)-sized classroom, the virion concentration and dose was estimated to be reduced by more than 60% by using an air purifier of clean air delivery rate (CADR) 780 m(3)/hr and by more than 70% by using two air purifiers (that is, CADR 1560 m(3)/h) compared to when not in use of the air purifier. However, to prevent the spread of infection by the air stream generated by the air purifier, it is necessary to operate an instruction for using the air purifier such as facing the air outlet toward the ceiling and installing at least 50 cm away from occupants.