air purification

UV-C Bests Bipolar Ionization in Eradicating Pathogens

By Joe Cestari, NoviSphere COO

Since the onset of the COVID-19 pandemic, interest has skyrocketed in technologies that clean and purify air by trapping and/or killing pathogen-carrying particles. These technologies, however, don’t eliminate pathogens with equal efficacy. Some familiar approaches, such as using HEPA or ULPA filters, are unable, on their own, to eradicate all types of pathogens, and they are not proven in all cases to eliminate coronaviruses.

Two more complex techniques purport to offer a high degree of effectiveness for inactivating pathogens: bipolar ionization and germicidal ultraviolet (UV-C) radiation. They function very differently, and it’s our belief that the latter technology, integrated into the NoviSphere™ PE 254 pathogen eradicator using our proprietary approach, is the better alternative.

What is bipolar ionization?

Needlepoint bipolar ionization devices apply high voltage across two electrodes to generate a plasma of high-energy ions that interact with air to form oxygen radicals and other ions. The disinfection mechanism of bacteria by air ions is generally summarized as a generated electrostatic force acting on the pathogen. Using air ions as an inactivation mechanism against airborne microorganisms remains controversial. One reason is that, in using this approach, one is modifying the room air by creating charged particles, an approach that suffers from unpredictable variability in pathogen inactivation. This is particularly true given the diversity of pathogenic aerosol particles (e.g., bacteria, viruses, fungi, spores, etc.) that may be present in indoor air. The charged particles may have enough energy to disrupt the protein structure of a virus or other pathogen; however, the efficacy will be highly dependent on the primary protein structure of the pathogen and the energy of the charged particle. The airborne ions may simply electrostatically bind to aerosol particles and cause them to settle out (via gravity) onto surrounding surfaces without full inactivation, imparting infection risk to these surfaces.

Another consideration of bipolar ionization as a means to destroy airborne pathogens is the risk of generating toxic ozone – a highly oxidative compound that can be harmful to occupants of the indoor area. Also, as it is a newer room-purification technology, limited independent scientific data has been reported on its efficacy, and there remain no established testing protocols available.  For these reasons,  the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) has chosen not to take a position on bipolar ionization. Without this data, manufacturers may also overstate the potential ventilation energy savings (for which additional sensors with a high initial cost may be required).

What are the benefits of UV-C?

UV-C radiation is not new – hospitals and other settings have employed UV-C for more than four decades to inactivate germs, viruses, bacteria and other pathogens. UV-C works by disrupting the nucleic acid of the pathogen, making it unable to replicate and thrive, and thus rendering the microorganism no longer infectious. An inactivated virus particle, if reintroduced into the room air, cannot replicate or cause infection – because it’s dead!

The NoviSphere PE 254 device combines UV-C arrays with proprietary baffling technology that enhances the residence time of the pathogens in the presence of the UV-C radiation. The PE 254 device has been designed to operate at various velocities, while simultaneously helping ensure that all pathogen-containing aerosol particles are irradiated and effectively inactivated up to the desired flow rate (velocity). And because the UV-C arrays are fully contained within the unit, it is completely safe for use in highly trafficked areas or any occupied space – there is no danger of human exposure or damage to skin or eyesight. In continuous operation, the unit ensures that room air is changed multiple times per hour, with no living virions or other pathogens remaining. Our “direct kill” approach utilizes proven technology that can be effectively tested and benchmarked, and it aligns with Centers for Disease Control (CDC) recommendations for businesses during the COVID-19 pandemic (“Guidance for Businesses and Employers Responding to Coronavirus Disease 2019 (COVID-19),” updated Jan. 4, 2021).

The CDC noted that installing transparent shields or physical barriers is beneficial but not sufficient: “Even in a large open office, with an employee 200 feet away from another, the virus can still transmit through the circulation of air.” To lower the likelihood of transmission, the CDC recommends:

  • Using natural ventilation, when possible
  • Increasing airflow by using portable high-efficiency particulate air filtration systems
  • Using ultraviolet germicidal irradiation as a supplement to help inactivate the virus

The CDC's recommendation for ultraviolet germicidal irradiation refers to ASHRAE’s position on airborne infectious diseases, which states: “ASHRAE will continue to support research that advances the state of knowledge in the specific techniques that control airborne infectious disease transmission through HVAC systems, including ventilation rates, airflow regimes, filtration, and ultraviolet germicidal irradiation (UVGI).” ASHRAE suggests two UV-C strategies: installation into air handlers or ventilating ducts and irradiation of the upper air zones of occupied spaces with shielding of the lower occupied spaces. These strategies work to sanitize the air in a space while keeping occupants safe from the harmful effects of ultraviolet light.

Our NoviSphere PE 254 achieves the latter objective, and it can be installed into air ducts, or used as a standalone or portable installation. As our Feb. 4 blog post highlights, independent testing conducted at the University of Minnesota validated that the unit is 99.99% effective in eradicating a wide range of pathogens, including coronavirus. The full results are detailed in an article, currently available for review, that will be published in Environmental Science & Technology. (To download the full study, click here.)

Taken together, we believe all of this data offers compelling evidence for the choice of UV-C irradiation as a safer, more reliable and better regulated approach to pathogen eradication than bipolar ionization.