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Secret of the scent: MIT scientists figure out where earthy after-rain odor comes from

Daniel Martins
Digital Reporter

Monday, January 19, 2015, 1:18 PM - It can be the best thing after a good summer rain: That rich, earthy smell that pervades the air.

It has a specific name, 'petrichor', but until recently the way it spreads has eluded scientists. Now, it seems, researchers at the Massachusetts Institute of Technology have at last unlocked the mystery, and it lies in aerosol generation.

In a new paper published in Nature Communications, the researchers took high-speed video of raindrop impacts on porous surfaces such as soil (the beautiful shots are in MIT's video, above).

They found the raindrops, when striking the surface, trap tiny air bubbles beneath them, which then shoot back out in a fizz of tiny aerosols, possibly carrying the scent of earth with them, blown about by the wind.

But it can also carry soil-borne bacteria, and one of the report's authors, Youngsoo Joung, told MIT News the new findings might explain how some diseases are spread.

“Until now, people didn’t know that aerosols could be generated from raindrops on soil,” Joung said. “This finding should be a good reference for future work, illuminating microbes and chemicals existing inside soil and other natural materials, and how they can be delivered in the environment, and possibly to humans."

Oddly, the researchers' findings noted more aerosols were released after light or moderate rain, rather than heavy rain. 

WATCH: Jaclyn Whittal's take on the science behind petrichor

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