Walk through the first rainstorm of the season and it slowly hits you: that fresh, earthy smell.
Before it hits the ground, rain is just water. It has no smell. But after the drops hit the ground and interact with dirt, the fresh and almost sweet fragrance of rain is let go. Now, scientists think they’ve identified the exact mechanism that releases this aroma into the environment.
The smell actually has a name. It’s called “petrichor,” from the Greek words “petra,” meaning “stone,” and “ichor,” which refers to the fluid that flows like blood in the veins of the gods. The phenomenon was first characterized by two Australian scientists in 1964.
“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.
Actinomycetes, a type of filamentous bacteria, grow in the soil when conditions are damp and warm. When the soil dries out, the bacteria produces spores in the soil. The wetness and force of rainfall kick these tiny spores up into the air where the moisture after a rain acts as an aerosol
When a raindrop hits a porous surface it traps tiny pockets of air. These bubbles then speed upward, like bubbles in a glass of champagne, before breaking the drop’s surface and releasing microscopic particles, called aerosols, into the air. The researchers think these aerosols carry the rain like aroma.