How the smell of rain is made
If you've ever noticed a smell in the air during spring or summer showers, you're not alone.
If you've ever noticed a smell in the air during spring or summer showers, you're not alone. This smell of rain has a name, and it's called "petrichor."
It's often detected during the onset of rain, especially after a dry spell. Professor Henry Spratt, a microbiologist at UT-Chattanooga says petrichor is caused by materials deposited by plants.
"Mainly there are oils, or fatty acids, that are produced by plants that settle on the surface of the dry areas," says Spratt.
Tiny air bubbles get trapped beneath the rain drops as they hit rocks, clay, soil, and even pavement containing these oils that have built up for some time. The bubbles burst, forming an aerosol of microscopic droplets which are carried by the wind. This is how the petrichor, or the smell of rain, reaches your nose.
Spratt calls the odor "earthy", but other descriptions have been used depending on who you talk to.
"There are groups of people who feel that it's a musky odor that is tied into making perfumes," adds Spratt.
However, you won't smell petrichor during a heavy rain because the oils will get washed away too quickly. Even if the rain is just the right intensity, petrichor will last just a few minutes because there's only so much oil to go around.
"It's a finite amount and it's generally located right at the surface of the soil or on the surface of the rocks," explains Spratt.
The word "petrichor" was created in the 1960s by Australian scientists Isabel Bear and Richard Thomas while researching the source of the odor. It comes from two Greek words.
"The CHOR is the blood of the gods, and the PETRA would be the rocks," say Spratt. "So, it's the essence of the gods from the rocks when the rain first falls."
However, the aroma isn't mythical. So don't miss your next chance to catch it.
"Anything, when it's been hot and dry for a while, after those first drops of rain take a sniff. You'll smell petrichor," says Spratt.
Petrichor can also be produced by rain interacting with bacteria in soil, and from lightning discharge producing ozone.