Even with a face mask in the car, you are not 100 percent protected against the transmission of virus particles via fellow passengers. American scientists used simulations to calculate which windows can best be opened to circulate the air as efficiently as possible.
Even with a mouth mask in the car, we still spread small particles in the room when we breathe, according to the American professor of physics Verghese Mathai of the University of Massachusetts. In a closed cabin, those microscopic particles accumulate, so that you can still contaminate that carpool partner and vice versa.
In order to make journeys in the car with two people as safe as possible, Professor Mathai and three colleagues from Brown University used computer simulations to investigate how those particles move in the car. Their research results, published in Science Advances, suggest that opening specific car windows can reduce the spread of virus particles.
The research team conducted a simulation with a car type loosely based on the Toyota Prius. In that experiment, the car drove at 80 kilometers per hour and carried one driver at the front left and one passenger at the right rear – a setup that is common in taxis and that respects the social distancing are respected as far as possible.
Barrier from air
During an initial analysis, the researchers found that the way air moves around the outside of the car creates a pressure difference in the car. The air pressure turned out to be slightly lower at the front than at the back. In other words, air in the car tends to circulate from the back to the front.
Then the airflow inside was mapped, and with it the movement of simulated aerosols, depending on which windows remained open or closed in the car. The air conditioning remained on in all scenarios. If all windows remained closed, about 8 to 10 percent of the exhaled aerosols reached the other person in the car. With all windows open, this percentage dropped to 0.2 to 2 percent. Not surprising, since it is in line with previous recommendations to ventilate closed spaces as much as possible.
The simulations in which only a few windows were opened turned out to be striking. Intuitively, one would expect that opening a window next to the head of the driver and passenger respectively would be the most efficient in directing particles out as quickly as possible. Interestingly enough, it turned out to be a better strategy to open the windows on the opposite side of the occupants. This allows fresh air to circulate between the left rear and front right windows, creating a natural barrier between passenger and driver. In addition, a follow-up study that has not yet been published found that opening the windows halfway seems to be as beneficial as opening the window fully.
Richard Corsi, air quality expert at Portland State University, is full of praise for the study. ‘What they have researched is quite sophisticated. In contamination studies, the focus is often on super spreaders or high attendance events. But we often forget that such an event starts with one infected person coming to it. We don’t usually talk about how it got infected. ‘ In one of his studies, Corsi suggests that a 20-minute drive in the car exposes you to contagious particles that can be more threatening than sitting together in a classroom or sitting in the same restaurant for more than an hour. All three situations assume wearing a mouth mask.
An important side note to this study is that opening all windows is still preferred. Also, in this study, only a specific setup with two people was examined, so it cannot be generalized for a full car.