Needle point bipolar ionization: environmental safety and inactivation of airborne bacteria and corona virus

Although there is an increasing interest after the COVID-19 pandemic, electronic ionization efficiency and impact on indoor air quality are not yet fully understood, and studies are insufficient. Therefore, in this study, the disinfection efficiency for viruses and bacteria and the change of indoor thermal comfort parameters (temperature, humidity, pressure) and air pollutants (CO₂, NO₂, VOC, O₃, CH₂O, PM_2.5, Particle Number (PN) from 0.3 to 10 µm particle sizes) by a portable indoor air cleaner using the needle point bipolar ionization (NPBI) method were investigated. The highest antibacterial activity was achieved at hour 3 with a 99.8% reduction for Bacillus subtilis, 99.8% for Staphylococcus aureus, 98.8% for Escherichia coli, and 99.4% for Staphylococcus albus, and sustained at hour 4th. The ions had antiviral activity on surfaces with a 94% TCID50 reduction of the HCoV-229E virus after 2 h of NPBI-on. No significant changes were detected in thermal comfort parameters, NO₂, and VOC during the NPBI-on. Moreover, it was found that O₃ and CH₂O were not generated when the NPBI system was operated in the room for 4 h. Consequently, an average particle number removal rate of 60% can be achieved with the NPBI system in much less time than with the natural decay time.