Rain drops before hitting the ground have no smell but the moment they hit the ground and interact with dirt, the fresh and almost sweet fragrance comes out.
The smell is called "petrichor," that is derived from the Greek words "petra", meaning "stone", and "ichor", which refers to the fluid that flows like blood in the veins of the gods.
"They talked about oils emitted by plants, and certain chemicals from bacteria, that lead to this smell you get after rain following a long dry spell," said Cullen Buie, assistant professor of mechanical engineering at the Massachusetts Institute of Technology in Cambridge.
When a raindrop hits a porous surface it traps tiny pockets of air.
These bubbles speed upward before breaking the drop's surface and releasing microscopic particles, called aerosols, into the air.
Now, researchers think these aerosols carry the rainlike aroma.
The researchers observed the process with a system of high-speed cameras, reported LiveScience.
Depending on the speed of the droplet, and the properties of the soil, a cloud of hundreds of aerosol droplets might be dispersed in as little as a few microseconds.
The new research "brings the conversation of bubble-induced aerosol formation from the ocean over to the land," said James Bird, assistant professor of mechanical engineering at Boston University.
"This paper provides an elegant mechanism by which these microbes can be propelled past the stagnant layer of air around them to a place where the breeze can take them elsewhere," Bird concluded.
The findings were published in Nature Communications.
