Using computer simulations, scientists have analyzed airflow patterns in a car’s passenger cabin, shedding light on the potential ways to reduce the risk of COVID-19 transmission while sharing rides with others. The study, published in the journal Science Advances, assessed airflow in a compact car with different combinations of open or closed windows.
According to the researchers, including those at Brown University in the US, the simulations showed that opening windows created airflow patterns that drastically reduced the concentration of airborne aerosol particles exchanged between a driver and a single passenger.
However, they said blowing the car’s ventilation system didn’t circulate air as well as a pair of open windows.
“Driving around with the windows open and the air conditioning or heating on is the absolute worst case scenario, according to our computer simulations,” said Asimanshu Das, co-lead author of the Brown University study.
“The best scenario we found was that all four windows were open, but even one or two open was much better than having them all closed,” said Das.
While there is no way to completely rule out risk and current guidelines recommend postponing travel, the scientists said the purpose of the study was simply to assess how changes in airflow in a car increase the risk of COVID-19. can worsen or reduce transmission.
In the study, the computer models simulated a car, loosely based on a Toyota Prius, with two people in it: a driver and a passenger in the backseat on the other side of the driver.
The scientists said they chose this seating arrangement because it maximized the physical distance between the two people.
Because the new coronavirus is thought to spread via tiny aerosol particles that can linger in the air for extended periods of time, the researchers simulated the flow of air around and in a car traveling at 80 kilometers per hour.
Part of the reason opening windows is better in terms of aerosol transmission is because it increases the number of air changes per hour (ACH) in the car, decreasing the overall concentration of aerosols, the study said.
The scientists showed that different combinations of open windows created different air currents in the car that could increase or decrease exposure to residual aerosols.
Because the occupants in the simulations sat on either side of the cabin, they said very few particles were ultimately transferred between the two.
According to the study, the driver was at slightly higher risk than the passenger as the average airflow in the car is from the rear to the front, but added that both occupants experience dramatically lower particle transfer.
When some – but not all – windows were open, the study yielded counterintuitive results.
Referring to an example of such a case, the scientists said that opening the windows next to each occupant poses a higher risk of exposure compared to placing the window in front of each occupant.
“When the windows are open opposite the occupants, you get a current that enters the car behind the driver, sweeps through the cabin behind the passenger and then exits through the windshield on the passenger side,” said Kenny Breuer, a professor of engineering at Brown University and a senior author of the study.
“That pattern helps to reduce driver-passenger cross-contamination,” said Breuer.
The scientists said airflow adjustments are not a substitute for wearing a mask by both occupants of a car, adding that the findings are limited to potential exposure to sustained aerosols that may contain pathogens.
Citing another limitation of the study, the scientists said it did not model larger respiratory droplets or the risk of actually being infected by the virus.
However, they said the findings provide valuable new insights into the air circulation patterns in a car’s passenger compartment.
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