We’re now nearing the end of this year which means we’ve spent nearly a year living with a virus outbreak. A lot of habits have had to be inculcated during this time, one of which is about whether or not air-conditioners should be used in a car. We’ve read about car-sharing or ride-hailing platforms like Ola and Uber prohibiting the use of air-cons. But what is the science behind it really? Scientists have now analysed the airflow patterns inside a car’s passenger cabin using computer simulations, to highlight potential and simple ways to reduce the risk of COVID-19 transmission in taxis and ride-sharing. Published in the journal Science Advances, the study assessed the airflow inside a compact car with various combinations of windows open or closed.
According to the researchers, including those from Brown University in the US, the simulations showed that opening windows created airflow patterns that dramatically reduced the concentration of airborne aerosol particles exchanged between a driver and a single passenger.
However, they said 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 Asimanshu Das, co-lead author of the research from Brown University. “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 said.
There is currently no way to eliminate the risk completely as most guidelines would recommend postponing travel. The objective of this study was to assess how changes in airflow in a car cabin may reduce the risk of COVID-19 transmission.
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) inside the car that reduces the overall concentration of aerosols, the study noted.
The scientists showed that different combinations of open windows created different air currents inside the car that could either increase or decrease exposure to remaining aerosols.
Since the occupants in the simulations were sitting on opposite sides of the cabin, they said very few particles ended up being transferred between the two.
According to the research, the driver was at slightly higher risk than the passenger since the average airflow in the car goes from back to front, but added that both occupants experience a dramatically lower transfer of particles.
When some — but not all — windows were down, the study yielded counterintuitive results.
Citing an example of one such instance, the scientists said opening the windows next to each occupant carried a higher exposure risk, compared to putting down the window opposite each occupant.
“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,” said Kenny Breuer, a professor of engineering at Brown University and a senior author of the research.
“That pattern helps to reduce cross-contamination between the driver and passenger,” Breuer said.
While we may not be able to eliminate the risks entirely, we can be aware of our surroundings and find the best way to reduce the chances of transmission. Relying on the car’s recirculation, as the study suggests, is not sufficient so whenever using a taxi, roll down a couple of windows. When travelling alone in a cab, sit in the back seat on the opposite side from the driver to maximise distance and roll down the window opposite to you.
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