Bipolar ionization rapidly inactivates real-world, airborne concentrations of infective respiratory viruses

Abstract

The SARS-CoV-2 (COVID-19) pandemic has highlighted the urgent need for strategies that rapidly inactivate airborne respiratory viruses and break the transmission cycle of indoor spaces. Air ions can reduce viable bacteria, mold, and virus counts, however, most studies use small test enclosures with target microbes and ion sources in close vicinity. To evaluate ion performance in real-world spaces, experiments were conducted in a large, room-size BSL-3 Chamber. Negative and positive ions were delivered simultaneously using a commercially available bipolar air ion device. The device housed Needle Point Bipolar ionization (NPBI) technology. Large chamber studies often use unrealistically high virus concentrations to ensure measurable virus is present at the trial end. However, excessively high viral concentrations bias air cleaning devices towards underperformance. Hence, devices that provide a substantial impact for protecting occupants in real-world spaces with real-world virus concentrations are often dismissed as poor performers. Herein, both real-world and excessive virus concentrations were studied using Influenza A and B, Human Respiratory Syncytial Virus (RSV), and the SARS-CoV-2 Alpha and Delta strains. The average ion concentrations ranged from 4,100 to 24,000 per polarity over 60-minute and 30-minute time trials. The reduction rate was considerably greater for trials that used real-world virus concentrations, reducing infectivity for Influenza A and B, RSV, and SARS-CoV-2 Delta by 88.3-99.98% in 30 minutes, whereas trials using in-excess concentrations showed 49.5-61.2% in 30 minutes. These findings strongly support the addition of NPBI ion technology to building management strategies aimed to protect occupants from contracting and spreading infective respiratory viruses indoors.

Fig 1. Equipment used in study.

The GPS-FC48-AC™ ionizing device (A), the BLAM nebulizer (B), and the Sensidyne air sampler cassette (C).

Fig 2. Room schematic.

A schematic of the test room with placement of the GPS-FC48-AC™ device.

Fig 3. Ion suppression curve.

Ion concentrations (positive red; negative blue) decreased rapidly following carrier nebulization (green) and suppression continued for 15 minutes until particle mass reached its asymptote, and then ions rebounded towards the pre-nebulization starting concentration for the remainder of the trial (A). In contrast, ion suppression was absent when no carrier or virus particles were injected, and ions rapidly increased to an average ion density of 25,000 ions/cc (B). The chamber rapidly filled with ions, but the mass of particles < 2.5 um remained near zero and constant for the duration of the study (~1.86 particles/μg).

Fig 4. Triplicate control runs for viruses.

Sixty-minute individual control runs to determine the natural loss of Influenza A (A), Influenza B (B), RSV (C), and the SARS-CoV-2 Delta variant (D). The individual trials demonstrate the similarity of the replicate trials and repeatability of the system used in this study.

Fig 5. Triplicate control runs for SARS viruses.

Thirty-minute individual control runs to determine the natural loss of SARS-CoV-2 to compare with the GPS-FC48-AC operating at 4,900 negative ions/cm³ (A), SARS-CoV-2 to compare with the GPS-FC48-AC operating at 12,000 negative ions/cm³ (B), and SARS-CoV-2 to compare with the GPS-FC48-AC operating at 18,000 negative ions/cm³ (C). The individual trials demonstrate the similarity of the replicate trials and repeatability of the system used in this study.

Fig 6. Virus loss with ion treatment.

The average loss over time of Influenza A in the absence (control) and presence (treatment) of an operating GPS-FC48-AC (A), Influenza B in the absence (control) and presence (treatment) of an operating GPS-FC48-AC (B), RSV in the absence (control) and presence (treatment) of an operating GPS-FC48-AC (C), SARS-CoV-2 Delta variant in the absence (control) and presence (treatment) of an operating GPS-FC48-AC (D). Plots are the average of triplicates for the control and treatments. Error bars represent the standard deviation of the replicates at each time interval.

Fig 7. Loss of SARS viruses with ion treatment.

The average loss over time of SARS-CoV-2 in the absence (control) and presence (treatment) of an operating GPS-FC48-AC at 4,900 negative ions/cm³(A), SARS-CoV-2 in the absence (control) and presence (treatment) of an operating GPS-FC48-AC at 12,000 negative ions/cm³(B), SARS-CoV-2 in the absence (control) and presence (treatment) of an operating GPS-FC48-AC at 18,000 negative ions/cm³(C). Plots are the average of triplicates for the control and treatment trials. Error bars represent the standard deviation of the replicates at each time interval.