Exhaled Droplets Grow in Size on Cool Days
The COVID-19 pandemic has focused attention on the respiratory droplets produced by breathing, coughing, and singing. Numerical simulations of a cough now show [1] that in cooler, more humid air, these droplets first grow before evaporating and shrinking—they don’t continuously evaporate, as previous research has suggested. The growth occurs when warm, humid breath interacts with colder air, producing a plume of water-vapor-saturated air—an effect that leads to the familiar “frosty” breath on cold days. The enlargement of cough droplets inside this plume causes them to survive longer than they do at higher temperatures, potentially allowing an infected person to spread an airborne disease to people located farther away.
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