U-M Researchers Create Sterile Air Supply Through Charged Air Particles, Filtration

Researchers at Ann Arbor’s University of Michigan have found that airborne viruses are rendered harmless when exposed to energetic, charged fragments of air molecules. The goal of the system is to one day make surgical masks unnecessary.
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Herek Clack and his team with air sterilization equipment
Herek Clack, left, and his team at U-M have found a way to use charged air particles and filtration to sterilize the air. // Photo courtesy of the University of Michigan

Researchers at Ann Arbor’s University of Michigan have found that airborne viruses are rendered harmless when exposed to energetic, charged fragments of air molecules. The goal of the system is to one day make surgical masks unnecessary.

The engineers have measured the speed and effectiveness of nonthermal plasmas, or charged particles that form around electrical discharges such as sparks. A nonthermal plasma reactor was able to inactivate or remove from the airstream 99.9 percent of a test virus, with the majority due to inactivation.

Achieving the results in a fraction of a second within a stream of air holds promise for many applications where sterile air supplies are necessary.

“The most difficult disease transmission route to guard against is airborne because we have relatively little to protect us when we breathe,” says Herek Clack, research associate professor of civil and environmental engineering at U-M.

To gauge nonthermal plasmas’ effectiveness, researchers pumped a model virus that is harmless to humans into flowing air as it entered a reactor. Inside the reactor, borosilicate glass beads are packed into a cylindrical shape, or bed. The viruses in the air flow through spaces between the beads, where they are inactivated.

“In those void spaces, you’re initiating sparks,” says Clack. “By passing through the packed bed, pathogens in the air stream are oxidized by unstable atoms called radicals. What’s left is a virus that has diminished ability to infect cells.”

The researchers also tracked the amount of viral genome that was present in the air during the tests, determining that more than 99 percent of the air sterilizing effect was due to inactivating the virus that was present, with the remainder of the effect due to filtering the virus from the air stream.

“The results tell us that nonthermal plasma treatment is very effective at inactivating airborne viruses,” says Krista Wigginton, assistant professor of civil and environmental engineering. “There are limited technologies for air disinfection, so this is an important finding.”

This parallel approach of combining filtration and inactivation of airborne pathogens could provide a more efficient way of providing sterile air than technologies used today, such as filtration and ultraviolet light. Traditional surgical masks use only filtration for protection, and ultraviolet irradiation can’t sterilize as quickly, as thoroughly, or as compactly as nonthermal plasma.

Clack and his team have begun testing their reactor on ventilation air streams at a livestock farm near Ann Arbor. Animal agriculture is vulnerable to contagious livestock diseases.

The experiment and its results are published in the Journal of Physics D: Applied Physics.

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