World News – AU – Research shows how airflow in a car can affect the risk of COVID-19 transmission

A new study uses computer simulations to track airflows in the passenger cabin of a car and offers potential strategies – some of which are counterintuitive – for reducing the risk of transmitting airborne diseases.

PROVIDENCE, R. . I. [Brown University] – A new study of air flow patterns in the passenger cabin of a car offers some suggestions to reduce the risk of COVID-19 transmission while sharing trips.

The study by a team of Brown University researchers used computer models to simulate airflow in a small car with various combinations of windows open or closed. The simulations showed that opening windows – the more windows the better – created airflow patterns that drastically reduced the concentration of airborne particles exchanged between a driver and an individual passenger. The researchers found that the car’s air ventilation didn’t circulate nearly as well as some open windows.

« According to our computer simulations, driving around with the windows open and the air conditioning or heating on is definitely the worst, » said Asimanshu Das, a graduate student at Brown’s School of Engineering and a co-lead author of the research. “The best scenario we found was having all four windows open, but even opening a window or two was far better than closing them all. ”

That co-led the research with Varghese Mathai, a former postdoctoral fellow with Brown who is now an assistant professor of physics at the University of Massachusetts at Amherst. The study was published in the journal Science Advances.

The researchers emphasize that there is no way to completely exclude the risk – and of course the current guidelines of the U. . S.. . Centers for Disease Control (CDC) states that postponing travel and staying home is the best way to protect the health of people and society. The aim of the study was simply to investigate how changes in the airflow in a car can worsen or reduce the risk of pathogen transmission.

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 of the driver. The researchers chose this seating arrangement because it maximized the physical distance between the two people (although still less than the 6 feet recommended by the CDC). . The models simulated the flow of air around and in a car moving at a speed of 80 km / h, as well as the movement and concentration of aerosols that come from both the driver and front passenger. Aerosols are tiny particles that can remain in the air for a long time. They are believed to be a way of transmitting the SARS-CoV2 virus, especially indoors.

One reason that opening windows is better for aerosol transfer is because it increases the number of air changes per hour (ACH) in the vehicle, thereby reducing the overall concentration of aerosols. But ACH was only part of the story, say the researchers. The study showed that different combinations of open windows created different air currents in the car that could either increase or decrease exposure to residual aerosols.

Because of the way air flows over the outside of the vehicle, the air pressure near the rear windows tends to be higher than the pressure on the front windows. As a result, air tends to enter the car through the rear windows and exit through the front windows. With the windows open, this tendency creates two more or less independent currents on either side of the cabin. Since the occupants sat on opposite sides of the cabin in the simulations, very few particles are transferred between the two. The driver in this scenario is at a slightly higher risk than the front passenger because the average airflow in the car is back to front, but both occupants experience dramatically less particle transfer compared to any other scenario.

The simulations for scenarios where some but not all windows shut down may have produced counter-intuitive results. For example, one might expect that opening windows right next to each occupant would be the easiest way to reduce exposure. The simulations showed that this configuration is better than no windows at all, but poses a higher risk of exposure than the window to every occupant.

Opening windows on the opposite side of the car from where people are sitting creates an airflow pattern that reduces particle transfer between the driver and passenger.

« When the windows are open to the occupants, a current flows into the car behind the driver, sweeps over the cab behind the passenger, and then goes out the passenger-side window, » said Kenny Breuer, Professor of Engineering at Brown and a senior research writer. “This pattern helps reduce cross-contamination between driver and passenger. ”

It is important to note that adjusting airflow is not a substitute for both occupants to wear masks in the car. The results are limited to the potential exposure to lingering aerosols that may contain pathogens. The study did not model larger respiratory droplets or the risk of actual infection with the virus.

Still, the researchers say the study provides valuable new insights into airflow patterns in the passenger compartment of a car – something that has received little attention so far.

« This is the first study known to us that really looks at the microclimate in a car, » said Breuer. “There have been some studies looking at how much external pollution gets into a car or how long cigarette smoke stays in a car. However, this is the first time anyone has delved into airflow patterns. ”

The research grew out of a COVID-19 research group set up at Brown to gather expertise from across the university to address a wide variety of aspects of the pandemic. Jeffrey Bailey, Associate Professor of Pathology and Laboratory Medicine and co-author of the airflow study, leads the group. Bailey was impressed with how quickly the research came together, and Mathai suggested using computer simulations that could be run while laboratory research at Brown was suspended because of the pandemic.

« This is really a great example of how disciplines can come together quickly and provide valuable insights, » said Bailey. “I spoke to Kenny briefly about this idea and within three or four days his team had already done some preliminary tests. It’s one of the great things about a place like Brown, where people enjoy working together and working across disciplines. ”

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Research, Coronavirus