If you think rain has a distinct scent, you're not imagining it. Petrichor, that earthy smell that accompanies light showers, could be the result of raindrops releasing aerosols, which are tiny amounts of liquid suspended in gas, reports MIT News. "Rain happens every day—it’s raining now, somewhere in the world," says one mechanical engineer. "It was intriguing to us that no one had observed this mechanism before." The researchers employed high-speed cameras to watch raindrops hit porous surfaces in more than 600 tests, and found that it traps tiny air bubbles upon contact, which then shoot up like champagne bubbles before bursting in a poof of aerosols. The amount depended on the velocity of the raindrop and the porousness of the surface; the heavier the rain, the fewer the aerosols, reports the Washington Post.
"Until now, people didn’t know that aerosols could be generated from raindrops on soil," said a researcher who worked on the study, which was published this week in the journal Nature Communications. "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." The team is now studying whether this is one mechanism by which soil-based diseases like E. coli can spread. (Speaking of E. coli, it recently found its way into Portland's public water supply.)