How airflow into a car can affect COVID-19 transmission risk – what works best for windows and ventilation

A new study looks at how airflow into the passenger compartment of a car can affect the transmission of SARS-CoV-2 and other airborne pathogens. Using computer simulations, the study looked at the risk of aerosol particles being shared between driver and passenger in different window configurations. Redder shades indicate more particles. The risk has been shown to be higher with windows closed (top left) and decreasing with each window open. The best case scenario was that all windows were open (bottom right). Credit: Breuer lab / Brown University

A new study uses computer simulations to detect airflow in the passenger compartment of a car, and offers possible strategies – some of which are counter-intuitive – to reduce the risk of transmitting diseases in the air.

A new study of airflow patterns in the passenger compartment of a car offers some suggestions to possibly reduce the risk COVID-19 transfer while sharing rides with others.

The study, by a team of researchers from Brown University, used computer models to simulate the airflow in a compact car with different combinations of windows open or closed. The simulations showed that the opening of windows – the more windows the better – created airflow patterns that dramatically reduced the concentration of air particles exchanged between a driver and a single passenger. The explosion of the car’s ventilation system did not circulate nearly as well as a few open windows, the researchers found.

“According to our computer simulations, it’s definitely the worst case scenario to drive up with the windows and the air conditioning or the heat on,” said Asimanshu Das, a graduate student at Brown’s School of Engineering and co-lead author of the research. “The best scenario we found was to have all four windows open, but even having one or two open was much better than closing them all.”

Das led the research with Varghese Mathai, a former postdoctoral researcher at Brown, who is currently an assistant professor of physics at the University of Massachusetts, Amherst. The study is published in the journal Scientific progress.

Motor Windows airflow

A study recently published in Science Advances looks at how airflow patterns in the passenger compartment of a car can affect the transmission of SARS-CoV-2 and other air pathogens. The simulations yielded some possible counter-intuitive findings. For example, you can expect that opening windows directly next to each resident is the simplest way to reduce exposure. The simulations found that although this configuration is better than not putting down windows at all, it poses a greater exposure risk compared to laying down the window towards each resident. “When the windows opposite the occupants are open, you get a stream coming behind the driver in the car, sweeping behind the passenger over the cabin and then going out of the passenger window at the windshield,” said Kenny Breuer, a professor in engineering to Brown and a senior author of the research. “The cartridge helps reduce cross-contamination between driver and passenger.” Credit: Breuer lab / Brown University

The researchers emphasize that there is no way to completely eliminate risks, and from the current guidance of the US Centers for Disease Control (CDC) it is obvious that postponing travel and staying home is the best way to improve your health. protect family and the community. The aim of the study was simply to investigate how changes in the airflow in a car can aggravate or reduce the risk of transmission of pathogens.

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 other side of the driver. The researchers chose the seat because it maximizes the physical distance between the two people (although it is less than the 6 feet recommended by the CDC). The models simulated the airflow around and inside a car moving 50 miles per hour, as well as the movement and concentration of aerosols coming from driver and passenger. Aerosols are small particles that can stay in the air longer. They are seen as one way in which the EARS-CoV-2 virus is transmitted, especially in confined spaces.

Part of the reason why opening windows is better in terms of aerosol transfer is because it increases the number of air changes per hour (ACH) in the car, which helps to reduce the overall concentration of aerosols. But ACH was only part of the story, the researchers say. The study showed that different combinations of open windows create different air currents in the car that can increase or decrease exposure to residual aerosols.

Due to the way air flows over the outside of the car, air pressure near the rear windows tends to be higher than the pressure at the front windows. As a result, air tends to enter the car through the rear windows and exit through the front windows. With all the windows open, this trend creates two more or less independent flows on either side of the cabin. Since the inhabitants sat in the simulations on either side of the cabin, very few particles are transferred between the two. The driver in this scenario runs a slightly greater risk than the passenger because the average airflow in the car goes from rear to front, but both occupants experience a dramatically lower transfer of particles compared to any other scenario.

The simulations for scenarios in which some, but not all windows are, may have yielded counter-intuitive results. For example, you can expect that opening windows directly next to each resident is the simplest way to reduce exposure. The simulations found that although this configuration is better than not putting down windows at all, it poses a greater exposure risk compared to laying down the window towards each resident.

“When the windows opposite the occupants are open, you get a stream coming behind the driver in the car, sweeping behind the passenger across the cabin and then going out of the passenger window at the windshield,” said Kenny Breuer, a professor in engineering to Brown and a senior author of the research. “The cartridge helps reduce cross-contamination between driver and passenger.”

It is important to note, the researchers say, that adjusting airflow is no substitute for wearing a mask by both occupants in a car. And the findings are limited to possible exposure to delayed aerosols that may contain pathogens. The study did not model larger respiratory droplets or the risk of being infected by the virus.

However, the researchers say that the study offers valuable new insights into the air circulation patterns in the passenger compartment of a car – something that has received little attention in the past.

“This is the first study we are aware of that really looked at the microclimate in a car,” Breuer said. ‘There were some studies that looked at how much external pollution ends up in a car, or how long cigarette smoke stays in a car. But this is the first time anyone has examined the airflow patterns in detail. ”

The research originated from a COVID-19 research task force established in Brown to gather expertise from across the University to address diverse 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 that the use of computer simulations could be done while laboratory research at Brown for the pandemic was interrupted.

“This is really an excellent example of how different disciplines can come together quickly and deliver valuable findings,” Bailey said. ‘I briefly talked to Kenny about this idea and his team has already done a preliminary test within three or four days. It’s one of the great things about being in a place like Brown, where people are eager to work together and work across different disciplines. ”

Reference: “Airflow in Passenger Vehicles and Implications for the Transmission of Air Diseases” by Varghese Mathai, Asimanshu Das, Jeffrey A. Bailey and Kenneth Breuer, 4 December 2020, Scientific progress.
DOI: 10.1126 / sciadv.abe0166

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