The Reason It Smells After a Rainfall Was ‘Unknown’ Until MIT Researchers ‘Observed’ This Phenomenon

It's something that everyone has noticed when stepping outside after the first rainfall: a distinct smell.

Scientists refer to it as "petrichor" or "a smell that frequently accompanies the first rain after a long period of warm, dry weather."

"Australian scientists were first to characterize this phenomenon of petrichor," MIT said in a new video. "However, until now the mechanism for how that smell is released into the air was unknown."

Using high-speed cameras, MIT researchers recorded rainfall hitting a hard surface. They then analyzed the footage frame-by-frame.

"[T]he researchers observed that when a raindrop hits a porous surface, it traps tiny air bubbles at the point of contact," the university said in a news release. "As in a glass of champagne, the bubbles then shoot upward, ultimately bursting from the drop in a fizz of aerosols."

[sharequote align="right"]"...it was intriguing to us that no one had observed this mechanism before.”[/sharequote]

"The researchers suspect that in natural environments, aerosols may carry aromatic elements, along with bacteria and viruses stored in soil," it added. "These aerosols may be released during light or moderate rainfall, and then spread via gusts of wind."

Cullen R. Buie, an assistant professor of mechanical engineering at the school, said he found it curious no one had solved this mystery before.

“Rain happens every day — it’s raining now, somewhere in the world,” he said. “It’s a very common phenomenon, and it was intriguing to us that no one had observed this mechanism before.”

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Featured image via Shutterstock.