Do you love the smell of freshly-fallen rain? If so, you’re one of many who love that earthy smell, reminiscent of the first days of spring or putting your hands in newly-turned soil. In case you ever wondered, that smell has a name, Petrichor. Now, scientists at MIT may have figured out just what releases that smell — and other aerosols — into the air. And they have managed to captured it all on video.
The researchers set up high-speed cameras to capture rain as it hit different surfaces. When they watched the drops hit the surface, they discovered that as the drop flattens out, tiny air bubbles are trapped at the point of contact. “The bubbles then shoot up through the drop and burst into the air with a fizz,” just like champagne, according to Treehugger. But depending on the speed at which the drop hits the surface, the “frenzied aerosols” as the MIT researchers call them, disperse into the air at varying heights and speeds.
“Frenzied means you can generate hundreds of aerosol droplets in a short time — a few microseconds,” Researcher Youngsoo Joung explains. “And we found you can control the speed of aerosol generation with different porous media and impact conditions.” These aerosols may carry the smells that humans find so intoxicating. Referring to the Australian researchers who, in 1964, named the smell of rain “Petrichor.” The name stems from the Greek words “petros” which essentially refers to the smell of dirt, and “ichor,” which means the “ethereal fluid that flows in the veins of Greek gods.”
“They talked about oils emitted by plants, and certain chemicals from bacteria, that lead to this smell you get after a rain following a long dry spell,” Cullen Buie, an assistant professor of mechanical engineering at MIT, said. “Interestingly, they don’t discuss the mechanism for how that smell gets into the air. One hypothesis we have is that that smell comes from this mechanism we’ve discovered.”
According to the video, this may explain how bacteria and viruses found in soil, such as E. coli, are spread through the environment and even to humans.