Many people love listening to the sound of rain. It’s calming, soothing, and relaxing. The smell of rain is equally attractive, filling the air with a generally pleasant smell. But rain itself has no scent, so what is it that we're smelling?
The distinctive earthy scent released by freshly moistened ground is called "petrichor," a term coined by two Australian researchers in the 1960s. Petrichor is caused by rainwater coming into contact with compounds like ozone, geosmin, and plant oils.
Geosmin is an organic compound that creates a musty smell, formed by soil bacteria of the genus Streptomyces. Before it rains, the air around us becomes more humid and the ground moistens, which increases the formation of geosmin. When it starts to rain, this organic compound is released into the air in aerosol form, creating the lovely earthy smell of petrichor. A heavy rainfall event can produce a substantial petrichor scent powerful enough to travel rapidly downwind, alerting people that rain is on the way.
Can you smell the rain?
- The human nose is extremely sensitive to the smell of geosmin. In fact, we can detect it in concentrations as low as 100 parts per trillion.
- Geosmin has become a common ingredient in perfumes.
- The Streptomyces genus produces chemical byproducts that have been used in many antifungal, anticancer, and antibiotic compounds.