Air purifiers may do more harm than good in confined spaces, study finds

    Toronto, Ontario A new study has found that air purifiers used in elevators and other confined spaces may actually do more harm than good in limiting the spread of COVID-19.

While air purifiers could be expected to help reduce transmission, researchers from the University of Nicosia in Cyprus report that air purifiers in compact areas actually increase saliva droplet dispersal of airborne viruses.

According to the study, air quality in small spaces can “quickly degrade” without proper ventilation. However, researchers found that adding ventilation increased the rate at which potentially infected air can circulate in the small space.

Manufacturers have added air purifiers in elevators to help take care of this problem, but researchers say the systems are not designed to account for their effect on overall air circulation.

The findings were published Tuesday in peer-reviewed scientific journal Physics of Fluids.

In the study, researchers conducted calculations for a 3D space equivalent to that of an elevator capable of holding five people.

According to the study, a “mild cough” was simulated at one position in the elevator, and air inlets and outlets were added in various locations to look at the particles’ influence on circulation. The study noted that an air purifier was also included in the simulation.

“We quantified the effect of air circulation on airborne virus transmission and showed that installing an air purifier inside an elevator alters the air circulation significantly but does not eliminate airborne transmission,” study author Dimitris Drikakis said in a press release.

Researchers explained that air purifiers use ultraviolet radiation to kill viruses and other microbes, but can also circulate air, “sucking it in and exhausting cleaned air.” The study said this adds to overall circulation, which is an aspect its authors say has not been considered in prior research.

Previous studies have indicated that droplets of saliva can travel more than five metres in five seconds when an unmasked, infected person coughs or sneezes.

Researchers found that the risk of airborne virus transmission is “lowest for low ventilation rates.”

Study author Talib Dbouk said in the press release that this is due to a “reduced flow mixing inside the elevator.”

“Our results show that installing an air purifier may increase the droplet spread,” Drikakis said. “The air intake integrated inside the purifier equipment induces flow circulation that can add to the transport of contaminated saliva droplets in the cabin.”

According to the study, the observed effect increases with the number of infected persons in an elevator.

Drikakis added that the findings suggest regulatory authorities should define the minimum ventilation required as it relates to the type of building and restrict the number of people allowed in an elevator at a time.

While the study considered the role of an air purifier, researchers only looked at the air intake and exhaust associated with the purifier. They did not evaluate the mechanism inside the purifier that can trap and kill virus particles.

However, researchers say that airborne virus transmission is”still significant” even with an air purifier in place.

Researchers say the findings should be considered in future designs of air purifiers and ventilation systems.

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