If you live in Metro Vancouver you know this scent, but you may not know its scientific name. Yesterday Jeffrey Tumlin, Executive Director at the San Francisco Municipal Transportation Agency (SFMTA) teased Twitter about that fresh rain smell:
After the first fulsome rain signalling the end of a very dry summer in Metro Vancouver there is a certain scent in the post-rain air that smells different and fresh in an oddly musky kind of way.
There is science behind it. When plants are dry they exude an oil to when root growth and seed germination are finished. When rain arrives it mixes with these oils and releases the scent as an aerosol when raindrops hit the plants.
This scent was termed “petrichor” in 1964 by two Australian scientists. The actual smell of petrichor is made by a mix of plant oils that produce chemicals. The word is derived from the Greek “Petra” for stone” and “ichor” used originally to describe the life blood of the immortal deities.
The source of the smell is made from a combination of oils and chemicals, especially from actinobacteria. These microorganisms decompose organic matter into simple compounds that then nourish developing plants and other organisms. Geosmin is produced as a byproduct. Being an alcohol it has a stronger smell, and the slight acid scent of geosmin can be noticed by people in even very small minute particles.
To learn more you can read this article by Paul Brown in The Guardian. For the pronunciation of Petrichor and a bit more on the word’s derivation, take a look at the very short YouTube video below.