Face masks should be worn outside when it is windy to curb the spread of Covid according to scientists from India.
Experts from the Indian Institute of Technology Bomba claim that even a slight breeze can increase the chance of infected people spreading covid.
The Mail Online reports: Results showed there was an ‘increased infection risk’ even if there was just a small gust of five miles per hour.
Lead author Professor Amit Agrawal said: ‘We recommend wearing masks outdoors, particularly in breezy conditions.’
Face masks have been enforced around the world as one of many curbs to limit the spread of the virus, especially in crowded indoor spaces.
But throughout the pandemic there has been fierce scientific debate about how well the guards work at reducing transmission.
Ministers dropped the legal requirement to wear coverings in England in July, when No10 pushed ahead with ‘Freedom Day’.
But people are encouraged to wear them in crowded places and some businesses — such as Transport for London — still require them.
The new study examined how Covid is transmitted in the air when someone coughs, using an equation designed to measure turbulence.
Earlier studies modelled a cough using puffs of air but the researchers argued a real cough is more complicated and can swirl ‘like mini whirlpools’.
They examined how a cough spreads in still conditions — comparable to indoors — and in various wind speeds.
The study, published in Physics of Fluids, showed when an infected person coughs outdoors, wind flowing in the same direction can spread the virus faster and further than in calm conditions.
Even a small breeze of five miles per hour (mph) in the same direction someone is coughing increases how far the virus spreads by 20 per cent.
This means social distancing would need to be increased from 1 to 2 metres to up 2.2 metres to be effective, the team found.
‘At 9-11 mph (14-18 kph), spreading of the virus increases in distance and duration,’ the researchers said.
The experts believe wind projects bigger droplets for longer, increasing how long it takes to dilute the viral load in the air.
As the cough jet is spurred on by the wind, infected aerosol droplets — which seems to be the dominant mode of Covid transmission — become ‘trapped’ in the breeze instead of falling quickly to the ground.
Professor Agrawal said: ‘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.
‘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.’