You know it's raining when you smell that distinct, earthy scent. Scientists have long wondered where this smell is coming from, and finally that mystery has been solved and captured in high-definition, slow-motion video.
Mechanical engineers at the Massachusetts Institute of Technology (MIT) set out to discover how the petrichor or the rain's mysterious smell spread out into the air. For decades, scientists established that the distinctive smell is the blend of oils secreted by some plants during the dry season which disperse into the air when the rain comes. The recent study is the first to determine how the dispersal occurs.
"Rain happens every day - it's raining now, somewhere in the world," Cullen R. Buie, an assistant professor of mechanical engineering at MIT, said in a press release. "It's a very common phenomenon, and it was intriguing to us that no one had observed this mechanism before."
The team used high-speed cameras to document the phenomenon. The researchers observed that the raindrop traps tiny air bubbles on its way down, then releases them in an upward motion in the form of aerosols as soon as it hits the surface.
Using the speed of the raindrop and the permeability of the contact surface, the researchers calculated the amount of aerosols released into the air. They also purported that we are not just smelling pure aerosols, but bacteria and viruses as well.
The study also observed that there are more aerosols released into the air during light and moderate rain compared to heavy rain. The findings of the study explain why the smell of the rain is stronger at the beginning.
The study was published in the Jan. 14 issue of Nature Communications.
