A new study from the American Institute of Physics (AIP) describes how air purifiers can actually worsen airborne virus transmission. The researchers found that air purifiers in elevators and other confined spaces facilitate the dispersal of saliva droplets, potentially increasing the spread of viruses.
Air purifiers are often used in small spaces that are not well-ventilated. These systems use ultraviolet radiation to kill viruses, but they also increase the movement of air as they purify it. This accelerated air circulation has not been considered in previous studies.
Recently, the AIP team demonstrated that saliva droplets can travel 18 feet in five seconds when an unmasked person coughs. The researchers used the same model to examine the effects of face masks and weather conditions.
For the current investigation, the experts simulated conditions in a 3D space equivalent to an elevator with the capacity to hold five people. The team examined the effect of a mild cough in the space, which contained air inlets, air outlets, and an air purifier.
“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,” said study co-author Dimitris Drikakis.
The researchers analyzed the role of the air purifier, considering the air intake and exhaust associated with the system. They found that airborne virus transmission is still significant even with an air purifier in place.
“Our results show that installing an air purifier may increase the droplet spread,” said Drikakis. “The air intake integrated inside the purifier equipment induces flow circulation that can add to the transport of contaminated saliva droplets in the cabin.”
Since the effect would increase with the number of infected persons in a confined space, the number of people allowed in an elevator should be restricted to minimize the spread of viruses. The study also suggests that air purifier and ventilation systems are in urgent need of improvement.
The study is published in the journal Physics of Fluids.