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December 8, 2020 -- Researchers at Brown University who examined “the microclimate” inside a car say opening the vehicle’s windows reduces occupants’ risk of coronavirus transmission.

Researchers used computer models to study airflow inside a car, loosely based on a Toyota Prius, traveling 50 mph with two people inside -- the driver and a person sitting in the back seat on the right side, Brown said in a news release.

The study examined airflow because aerosols are thought to be one of the main ways the virus is transmitted. That seating configuration maximizes the space between the two people.

“Driving around with the windows up and the air conditioning or heat on is definitely the worst scenario, according to our computer simulations,” said Asimanshu Das, a graduate student in Brown’s School of Engineering and co-lead author of the research.

“The best scenario we found was having all four windows open, but even having one or two open was far better than having them all closed.”

Air pressure is usually higher near rear windows than front windows, researchers said. In a moving car, air tends to enter through a back window and exit through a front window. 

Driving with all four windows opened had low transmission risk, although the driver’s risk was slightly higher, the study found.

The most surprising finding was that it’s best for the driver to open the front seat window on the right side and for the passenger to open the back-seat window on the left side, rather than the windows right beside them, said the study published in the journal Science Advances.

“When the windows opposite the occupants are open, you get a flow that enters the car behind the driver, sweeps across the cabin behind the passenger and then goes out the passenger-side front window,” Kenny Breuer, a professor of engineering at Brown and a senior author of the research, said in the news release. “That pattern helps to reduce cross-contamination between the driver and passenger.”

Breur said this is the first study he knows of that looks at “the microclimate inside a car.” 

“There had been some studies that looked at how much external pollution gets into a car, or how long cigarette smoke lingers in a car. But this is the first time anyone has looked at airflow patterns in detail,” he said.

“The findings reported here can be translated to right-hand-drive vehicles, of relevance to countries like the UK and India,” the study said. “In those situations, similar, but mirrored flow patterns can be expected. Furthermore, although the computations were performed for a particular vehicle design (loosely modeled on a Toyota Prius), we expect the overall conclusions to be valid for most four-windowed passenger vehicles.

“However, trucks, minivans and cars with an open moon-roof could exhibit different airflow patterns and hence different scalar transport trends.”

Show Sources

Brown University. “Research reveals how airflow inside a car may affect COVID-19 transmission risk”

Science Advances. “Airflows inside passenger cars and implications for airborne disease transmission”

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