If you're one of those people who always coughs and sneezes into the crook of your elbow, THANK YOU.
A new study in the Journal of Fluid Mechanics shows that the smaller cough and sneeze droplets travel farther distances -- five to 200 times farther, in fact -- compared with previous estimates (which only took into account groups of unconnected particles).
Before, researchers assumed that bigger droplets traveled farther distances than small ones, simply because their size meant increased momentum. But when researchers looked at high-speed imaging of people's coughs and sneezes, in addition to mathematical modeling and simulations, they found that small droplets actually interact with the gas cloud emitted when a person coughs or sneezes, which leads to them being carried farther than thought.
Researchers found that a droplet just a millionth of a meter in size (100 micrometers) can travel five times farther than previously thought, and a droplet just 10 micrometers in size can travel 200 times farther than previously thought.
“If you ignored the presence of the gas cloud, your first guess would be that larger drops go farther than the smaller ones, and travel at most a couple of meters,” study researcher John Bush, a professor of applied mathematics at the Massachusetts Institute of Technology, said in a statement. “But by elucidating the dynamics of the gas cloud, we have shown that there’s a circulation within the cloud -- the smaller drops can be swept around and resuspended by the eddies within a cloud, and so settle more slowly. Basically, small drops can be carried a great distance by this gas cloud while the larger drops fall out. So you have a reversal in the dependence of range on size.”
The findings could change how we think about the spread of infectious particles, researchers noted.