Windy day? The odds of COVID exposure increase without a face mask

WASHINGTON — Windy weather can speed up the spread of COVID virus particles, a new study reveals. Researchers say gusts blowing in the same direction as someone’s cough increase the transmission of the virus. With that in mind, the study finds people who don’t regularly wear a face mask anymore should consider it depending on the weather.

“The study is significant in that it points to the increased infection risk that coughing in the same direction as the wind could bring about. Based on the results, we recommend wearing masks outdoors, particularly in breezy conditions,” says study co-author Professor Amit Agrawal of the Indian Institute of Technology Bombay in a media release.

The team also suggests people follow other safety recommendations while in public and in the open air, such as coughing into their elbow or turning their face away from others.

The analysis found that even a light breeze of about five miles per hour lengthens effective social distancing by around 20 percent. Depending on cough strength, effective social distancing changes from three to six feet to 3.6 to 7.2 feet. At a wind speed of nine to 11 mph, the ability of COVID to spread increases in distance and duration.

A real cough is tough to simulate

Most studies model cough flow using puffs of air or a simple pulsating profile. However, researchers say a real cough is more complicated. They exhibit turbulent flow with a vortex-like shape that swirls like mini whirlpools. With that in mind, the researchers used a large eddy simulation, a computational fluid dynamics technique that models turbulence.

Researchers investigated cough jets in breezy and calm conditions, mimicking a typical indoor environment. The vortices enabled bigger droplets to persist in the air longer than previous studies have predicted. This increases the time it takes to adequately dilute the viral load in the fresh air.

As the cough jet evolves and spreads, it interacts with the wind flowing in the same direction. The bigger virus droplets become trapped in the jet’s whirlpools, instead of falling relatively quickly to the ground under gravity.

“The increase in residential time of some of the larger droplets will increase the viral load transmitting through the cough jet and, therefore, the chances of infection. Overall, the study highlights increased chances of infection in the presence of even a light breeze,” Prof. Agrawal concludes.

The findings appear in the journal Physics of Fluids.

South West News Service writer Mark Waghorn contributed to this report.

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