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Researchers have modeled how opening different windows affects airflow inside a car, which can help reduce the transmission of SARS-CoV-2 between people traveling together.
In a new study, researchers have modeled how airflow inside a car is affected by open windows, allowing them to estimate the best way to reduce the transmission of airborne pathogens like SARS-CoV-2. .
The investigation, which appears in the magazine Scientific advances, will help improve the safety of people who need to travel together during the COVID-19 pandemic.
The COVID-19 pandemic has profoundly changed human behavior. Many everyday activities now carry significant risks due to the likelihood of contracting SARS-CoV-2.
A key way the virus spreads is through the air. This can be through droplets that are produced when people cough, sneeze, and sing. Or they can spread in small aerosols, which can be produced by people’s breathing.
Aerosols are of particular concern because their small size means that they can travel greater distances and stay longer in the local atmosphere compared to droplets.
Scientists believe this is especially a problem indoors, as the lack of ventilation compared to outdoors means that there is a greater chance that higher concentrations of the virus will accumulate.
Accordingly, the advice from the Centers for Disease Control and Prevention (CDC) has been to reduce the time spent indoors with other people and, when unavoidable, maintain social distancing and wear a mask.
However, while a mask that is worn correctly will reduce the chances of a person inhaling or exhaling the virus, it does not completely minimize the risk.
As a consequence, scientists are now considering how to increase the ventilation of indoor spaces to reduce the accumulation of viruses at high levels within the local atmosphere.
In the present study, the researchers specifically looked at the interior of a car shared by two people.
The researchers wanted to understand how opening all four windows of a typical five-seater car affects airflow, and therefore how it might influence the relative risk of two people transmitting the virus to each other.
To do this, the researchers used a series of computational fluid dynamics simulations based on different open and closed car window configurations.
The researchers assumed that the two people would be sitting as far apart as possible, with the driver in the front left seat and the passenger in the rear right seat. The car, inspired by a Toyota Prius, was supposed to travel 50 miles per hour.
The researchers looked at how airflow in the different simulations affected the amount of a passive “tracer,” representing the exhaled breath of people in the car, that would travel from one person to another.
As a reference, the researchers used a simulation in which all four windows were closed. The team also turned on the air conditioning.
The researchers found that having all the car windows open was more effective in reducing the concentration of the virus. But nevertheless, opening any combination of windows was better than having them all closed.
According to Asimanshu Das, a graduate student in the School of Engineering at Brown University, RI, and co-lead author of the research: “[d]Turning around with the windows open and the air conditioning or heater on is definitely the worst case scenario, based on our computer simulations.
“The best scenario we found was having all four windows open, but even having one or two open was much better than having them all closed.”
Having the windows open helped because it increased the frequency with which the airflow inside the car changed. However, the researchers also found that different combinations of open windows produced different air currents inside the vehicle that also had a significant effect.
The researchers found that air pressure was higher near the rear windows than at the front ones, so air currents tended to move from the rear windows to the front.
By having all the windows open, the team identified two air currents: one running from back to front on the left side and one from back to front on the right side.
Because the researchers assumed that the driver and passenger were sitting on different sides of the car, this helped reduce the chances of transmission of the virus.
Interestingly, while opening the window closest to each person in the car was better than having all the windows closed, the researchers found that it was better to have the window on the opposite side of each person open.
According to Professor Kenny Breuer, professor of engineering at Brown and lead author of the research: “[w]hen the windows opposite the occupants are open, you get a flow that enters the car behind the driver, through the cabin behind the passenger, and then out the front passenger side window.
“That pattern helps reduce driver-passenger cross contamination.”
However, the researchers note the limitations of their study. They did not assess the likelihood of a person getting SARS-CoV-2 from another person in the car. They only modeled how the airflow inside the vehicle could affect the transmission of particles from one person to another.
Therefore, the use of a mask is still important and travel near another person should be avoided as much as possible.
Nevertheless, research can be valuable in helping people make an informed decision in situations where traveling with another person is unavoidable.
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