What’s the word for the smell of rain and what causes it?

·2-min read
Petrichor is the word for the smell produced when rain hits dry ground. (Ryoji Iwata/Unsplash)
Petrichor is the word for the smell produced when rain hits dry ground. (Ryoji Iwata/Unsplash)

Following a record-breaking heatwave, the UK is finally experiencing a break from the sun, with rain forecast across the UK.

As it’s only mid-August, some people may have been hoping for a couple more weeks of warm weather, while others are sure to see the back of 35C heat.

Whether you love it or loathe it, one thing is for sure this week—the smell of rain is in the air.

But what’s the word for the smell of rain and what causes it?

What is the word for the smell of rain?

Petrichor is the word for the smell of rainfall. It comes from the Greek words ‘petra’, meaning stone, and ‘ichor’, which in Greek mythology refers to the golden fluid that flows in the veins of the immortals, according to the Met Office.

Isabel Joy Bear and Richard Thomas, researchers at the Australian CSIRO science agency, first used the word in a 1964 article in the journal Nature.

Why does rain smell?

The air has a certain smell when it rains for a number of reasons, as petrichor comes from a variety of sources.

Firstly, during dry conditions, plants will release certain oils. When the raindrops hit the plants, the impact of the rain releases the oils into the air.

But the main contributor of petrichor comes from the moment when raindrops hit the soil–particularly sandy or clay soils–and propel a chemical called geosmin into the air.

The Met Office explains that raindrops “trap tiny air bubbles on the surface which then shoot upward—as in a glass of Champagne—and burst out of the drop throwing aerosols of scent into the air where they are then distributed by wind.”

The moist air caused by the rainfall carries the spores through the air, making them easier to smell.

The smell of petrichor is also most likely during light or moderate rainfall, and especially when rain falls on sandy or clay soils. It’s less likely during heavy rainfall, as the speed of the drops represses the bubbles and prevents the release of the aerosols.

What is geosmin?

Geosmin is a molecule produced by bacteria called Streptomyces. Humans are sensitive to the smell of geosmin, and can smell it at extremely low concentrations.

Geosmin is used in commercial antibiotics and is becoming an increasingly popular perfume ingredient.

Perfumer Marina Barcenilla told the BBC: "It’s a really potent material and it smells just like the concrete when the rain hits it.

"There’s something very primitive and very primal about the smell."