Are they effective? Ionization, Plasma Sterilization, and UV Bulbs

March 09, 2021

Throughout the COVID-19 pandemic, there has been an emergence of new technologies advertised for helping remove the pathogen from the air. However, these methods have major flaws that present significant implementation challenges or make them ineffective at preventing the spread of COVID-19.

Ionizing Air Purifiers

Ionization has often come up as a possible way to deal with COVID-19 particles in the air. However, this method is unable to capture and remove the virus from the space, which is the only way to guarantee an area is safe.

Ionization occurs when air passes through two metal plates or small metal probes. These plates or probes receive a large amount of voltage, which forces the air to take on a charge. When ionization is combined with an air purifier, all air particles and particles in the air are forced to take on a positive or negative charge.

With an ionizing air purifier, this means all the dust and odors are now charged and will immediately attach themselves to articles in the room like a desk, phone, or walls. However, these particles don't just collect on surfaces; they also collect on skin and can be breathed in. Without anything capturing the charged particles, they are going to attach to everything in a room like a magnet.

At the time of this blog publication, the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) has not taken an official stance on the effectiveness of ionization as an air purification method due to the absence of an established body of evidence reflecting proven efficacy.

Plasma Sterilization

For sterilizing utensils and other articles, some hospital environments use sterilization chambers that create Hydroxyl or EtO (Ethylene Oxide) using plasma gas. These chambers are very effective (Hydroxyl being preferred) at the work they do.

However, plasma is not effective outside a small sealed and controlled sterilization chamber. Like ionization, it charges the particles in the air, causing them to attach themselves to all the surfaces in a room. Although technically this does remove viruses like COVID-19 from the air, the virus is not captured anywhere. Instead, it is collecting on the surfaces in the room.

UV Bulbs in Ductwork

UV-C bulbs are also being discussed for their effectiveness against viruses like COVID-19. The ASHRAE organization supports UV-C light as an effective way to inactivate airborne pathogens; however, the volume and velocity of air are key considerations to determine effectiveness.

The key to a UV-C bulb being effective on a virus is close proximity and dwell time. When discussing close proximity, it is simplest to consider it as 1 inch. Once the distance grows beyond that, the equations for effectiveness become highly variable.

UV-C effectiveness for neutralizing or disrupting the DNA or RNA of a virus doesn’t take very long. However, when mounted directly into ductwork, a UV-C bulb on its own is typically not set up to provide enough dwell time to be effective for removing the virus.

Consider this:

  • Studies show that commercially available bulbs take approximately 0.57 seconds to neutralize a virus based on the strength of a UV-C bulb.
  • Assume the ductwork is 1 foot by 1 foot square, with an effective bulb length of one foot and the air in the duct moving at 200CFM

In a duct 1ft X 1ft, air flow at 200 ft³/min = 200 ft/min = 3.3 ft/sec for how fast the air is moving

The effective bulb length is only 1 foot, which means that after just 1 second the air has travelled 3.3 feet and the virus is already 2.3 feet away from the effective area of the bulb.

This example is with relatively slow flowing air in the duct. Most ductwork typically has air flowing anywhere between 800 to 2800 CFM, which puts the virus up to 50 feet past the bulb in just one second. This does not allow for the 0.57 seconds of dwell time in close proximity to the bulb, so the virus is not properly eliminated.

Looking for a solution?

The Setra AIIR Watch is quiet and compact and can be easily brought into rooms to filter and cleanse the space of airborne infections. This advanced air purifier uses a combination of HEPA filtration and UV light to trap and neutralize airborne containments with a >99.99% effectiveness rating verified via independent third-party lab results from a Nationally Recognized Testing Laboratory (NRTL), shown below.

aiir watch % reduction



The combination of the HEPA filter and UV light is what allows the AIIR Watch to provide the required dwell time to neutralize the virus on first pass. The HEPA filter captures the particles, stopping them in their tracks, and the UV light is entrained on the filter to neutralize and sterilize the particles. Proven to drastically reduce particulate contaminates via recirculation of sterilized air, the Setra AIIR Watch improves air quality in minutes and maintains it throughout operation. AIIR Watch is perfect for any space that needs safe and reliable air purification.

Topics: Critical Environments