Airflow inside car may be Covid transmission risk: Study
Airflow patterns inside a car’s passenger cabin offers some suggestions for potentially reducing the risk of Covid-19 transmission while sharing rides with others, say researchers, including one of Indian-origin.
The study, published in the journal Science Advances, used computer models to simulate the airflow inside a compact car with various combinations of windows open or closed.
The simulations showed that opening windows — the more windows the better — created airflow patterns that dramatically reduced the concentration of airborne particles exchanged between a driver and a single passenger.
The researchers found that blasting the car’s ventilation system didn’t circulate air nearly as well as a few open windows.
“Driving around with the windows up and the air conditioning or heat on is definitely the worst scenario, according to our computer simulations,” said study author Asimanshu Das from the Brown University in the US.
“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,” Das added.
The computer models used in the study simulated a car, loosely based on a Toyota Prius, with two people inside — a driver and a passenger sitting in the back seat on the opposite side from the driver.
The researchers chose that seating arrangement because it maximizes the physical distance between the two people (though still less than the 6 feet recommended by the CDC).
The models simulated airflow around and inside a car moving at 50 miles per hour, as well as the movement and concentration of aerosols coming from both driver and passenger.
Aerosols are tiny particles that can linger in the air for extended periods of time. They are thought to be one way in which the SARS-CoV-2 virus is transmitted, particularly in enclosed spaces.
The study showed that different combinations of open windows created different air currents inside the car that could either increase or decrease exposure to remaining aerosols.
Because of the way air flows across the outside of the car, air pressure near the rear windows tends to be higher than pressure at the front windows.
As a result, air tends to enter the car through the back windows and exit through the front windows. With all the windows open, this tendency creates two more-or-fewer independent flows on either side of the cabin.
Since the occupants in the simulations were sitting on opposite sides of the cabin, very few particles end up being transferred between the two.
The driver in this scenario is at slightly higher risk than the passenger because the average airflow in the cargoes from back to front, but both occupants experience a dramatically lower transfer of particles compared to any other scenario.
The simulations found that while this configuration is better than no windows down at all, it carries a higher exposure risk compared to putting down the window opposite each occupant.
“That pattern helps to reduce cross-contamination between the driver and passenger,” the authors wrote.