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Nothing smells quite like the familiar, earthy aroma that arrives with rain at the end of a dry spell. What you’re smelling is known as “petrichor,” which brings back many fond memories for anyone who attended summer camp as a kid. What creates this telltale yet pleasant odor?
The term petrichor was coined in the 1960s by scientists who theorized that the smell originates from oils and chemicals after rain strikes the ground. The lighter the raindrops, the stronger the odor. All of these assumptions entered the fount of common pop-sci knowledge without question. Until now, nobody thought to get down and dirty and observe petrichor’s creation in action.
Using high speed cameras, researchers at the Massachusetts Institute of Technology believe they’ve isolated the mechanism that causes petrichor. In a new MIT paper, scientists Youngsoo Joung and Cullen R. Buie describe what happened when they observed raindrops landing on 28 different surfaces, from porous alumina to sandy clay. Here’s just a taste of the action:
As you can see, champagne-like bubbles — some of which are nearly microscopic in size — shoot upward and release aerosols containing aromatics, which distribute the earthy aroma. Buie said, “It’s a very common phenomenon, and it was intriguing to us that no one had observed this mechanism before.” He and Young look towards future research on how these chemicals “can be delivered in the environment, and possibly to humans.”
Throughout the video, the 16 different soil types combine with the magic of raindrops in different ways. According to raindrop rate, speed, and the porousness of surface, the size of the aerosol bubbles differ. Check out the actual research video from MIT at this link.