Open windows to (literally) drive the coronavirus away
Over the past year, as health authorities have tried to curb the COVID-19 pandemic, researchers have trained their scientific attention on a variety of potentially risky environments: places where large groups of people gather and the novel coronavirus has ample opportunity to spread.
They have paid less attention to another everyday environment: the car. A typical car, of course, does not carry nearly enough people to host a traditional superspreader event. But cars come with risks of their own; they are small, tightly sealed spaces that make social distancing impossible and trap the tiny, airborne particles, or aerosols, that can transmit the coronavirus.
“Even if you’re wearing a face covering, you still get tiny aerosols that are released every time you breathe,” said Varghese Mathai, a physicist at the University of Massachusetts, Amherst. “And if it’s a confined cabin, then you keep releasing these tiny particles, and they naturally would build up over time.”
In a new study, Mathai and three colleagues at Brown University — Asimanshu Das, Jeffrey Bailey and Kenneth Breuer — used computer simulations to map how virusladen airborne particles might flow through the inside of a car. Their results, published in early January in Science Advances, suggest that opening certain windows can create air currents that could help keep both riders and drivers safe from infectious diseases like COVID-19.
To conduct the study, the research team employed what are known as computational fluid dynamic simulations.
The team simulated a car loosely based on a Toyota Prius driving at 50 mph with two occupants: a driver in the front left seat and a single passenger in the back right, a seating arrangement that is common in taxis and ride shares and that maximizes social distancing.
Next, they modeled the interior air flow — and the movement of simulated aerosols — when different combinations of windows were open or closed. (The air conditioning was on in all scenarios.)
Unsurprisingly, they found that the ventilation rate was lowest when all four windows were closed. In this scenario, roughly 8 percent to 10 percent of aerosols exhaled by one of the car’s occupants could reach the other person, the simulation suggested. When all the windows were completely open, on the other hand, ventilation rates soared, and the influx of fresh air flushed many of the airborne particles out of the car; just 0.2 percent to 2 percent of the simulated aerosols traveled between driver and passenger.
The results jibe with public health guidelines that recommend opening windows to reduce the spread of the novel coronavirus in enclosed spaces. “It’s essentially bringing the outdoors inside, and we know that the risk outdoors is very low,” said Joseph Allen, a ventilation expert at the Harvard T.H. Chan School of Public Health.