Research: Research reveals how airflow in a car affects the risk of coronavirus infection

Rhode Island Providence [Brown University] — New research on airflow patterns in car cabins offers some suggestions for potentially reducing the risk of COVID-19 infection while sharing the vehicle with others.

In this study by a team of researchers at Brown University, a computer model was used to simulate the flow of air in a compact car with various combinations of opening and closing windows. Simulations have shown that opening windows (more windows are better) creates an airflow pattern that dramatically reduces the concentration of airborne particles exchanged between the driver and one passenger. .. Researchers found that blasting the car’s ventilation system didn’t circulate as much air as some open windows.

“According to our computer simulations, opening windows and driving with air conditioning and heating on is arguably the worst scenario,” said Asimanshu Das, a graduate student at Browns Institute of Technology and co-author of the study. Stated. “The best scenario we found was to have all four windows open, but having one or two open was much better than having all closed.”

Das led the study in collaboration with Varghese Mathai, a former postdoctoral fellow at Brown and now an assistant professor of physics at the University of Massachusetts Amherst.The study is published in the journal Science Advances..

Researchers emphasize that there is no way to completely eliminate risk. Of course, the current guidance from the Centers for Disease Control and Prevention (CDC) states that postponing travel and staying at home is the best way to protect personal and community health. The purpose of this study was simply to study how changes in airflow in the vehicle exacerbate or reduce the risk of pathogen transmission.

The computer model used in this study was roughly based on the Toyota Prius, simulating a car with a driver and two passengers sitting in the backseat opposite the driver. Researchers chose that seating arrangement to maximize the physical distance between the two (but less than the CDC’s recommended 6 feet). The model simulated airflow around and inside a car traveling at 50 mph, and the movement and concentration of aerosols coming from both the driver and passengers. Aerosols are small particles that can remain in the air for extended periods of time. These are believed to be one way in which the SARS-CoV-2 virus can be transmitted, especially in closed spaces.

One of the reasons why it is better to open windows for aerosol transmission is that it increases the number of air exchanges (ACHs) per hour in the car and helps reduce the overall concentration of aerosols. But ACH was only part of the story, researchers say. The study showed that different combinations of open windows could create different airflows in the car, increasing or reducing exposure to the remaining aerosols.

Due to the way air flows across the outside of the car, the air pressure near the rear window tends to be higher than the pressure in the front window. As a result, air tends to enter the car through the rear window and exit through the front window. With all windows open, this tendency creates two more or less independent streams on either side of the cabin. The simulation occupants were sitting on the other side of the cabin, so very few particles moved between the two. Drivers in this scenario are slightly more at risk than passengers because the average airflow in the car flows from back to front, but both occupants have dramatically less particle movement compared to the other scenarios. Become.

Simulation of scenarios where some, but not all, windows are down can have counterintuitive results. For example, opening a window right next to each resident may be expected to be the easiest way to reduce exposure. Simulations have shown that this configuration is better than having no windows underneath, but at a higher risk of exposure than having windows on the other side of each occupant.

“If the window on the other side of the occupant is open, there will be a flow that enters the car behind the driver’s seat, crosses the cabin behind the passenger seat, and exits the front window on the passenger seat side,” said Engineering. Professor Kenny Breuer said. Brown and senior author of the study. “The pattern helps reduce mutual pollution between the driver and the passenger.”

According to researchers, it is important to note that airflow regulation is not a substitute for both occupants wearing masks in the car. And the findings are limited to potential exposure to residual aerosols that may contain pathogens. This study does not model the risk of larger respiratory droplets or the actual infection with the virus.

Still, researchers say the study provides valuable new insights into air circulation patterns in car cabins. This is something that has received little attention so far.

“This is the first study we know of actually examining the microclimate in a car,” Breuer said. “There have been some studies looking at how much external pollution gets into a car or how long cigarette smoke stays in a car. But everyone scrutinized the airflow pattern. This is my first time. “

This study was born from the COVID-19 Research Task Force, which was established in Brown to gather expertise from across the university to address various aspects of the pandemic. The group is headed by Jeffrey Bailey, an associate professor of pathology and laboratory medicine and co-author of airflow research. Bailey was impressed with how quickly the study was put together, and Matthew proposed the use of computer simulations that could be performed while laboratory studies in Brown were suspended due to a pandemic.

“This is a great example of how different disciplines can be quickly integrated to generate valuable discoveries,” says Bailey. “I briefly talked to Kenny about this idea, but within three or four days his team had already done some preliminary testing. It’s like Brown, people vary. It’s one of the great things about being in a place where you’re enthusiastic about collaborating and working in your field. ”

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