Video: how raindrops release that fresh rain smell

MIT researchers used high-speed cameras to reveal raindrops' aerosol effect that releases petrichor, the earthy fresh smell of rain.

From MIT:

Mechanical engineering researchers (Youngsoo) Joung and (Cullen) Buie set up a system of high-speed cameras to capture raindrops on impact. The images they produced revealed a mechanism that had not previously been detected: As a raindrop hits a surface, it starts to flatten; simultaneously, tiny bubbles rise up from the surface, and through the droplet, before bursting out into the air. Depending on the speed of the droplet, and the properties of the surface, a cloud of “frenzied aerosols” may be dispersed.


“Frenzied means you can generate hundreds of aerosol droplets in a short time — a few microseconds,” Joung explains. “And we found you can control the speed of aerosol generation with different porous media and impact conditions.”


From their experiments, the team observed that more aerosols were produced in light and moderate rain, while far fewer aerosols were released during heavy rain.


Buie says this mechanism may explain petrichor — a phenomenon first characterized by Australian scientists as the smell released after a light rain.

"Rainfall can release aerosols, study finds"