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The smell of rain, petrichor, inspired a Paul Kelly song and has the perfume industry sniffing around

By Tom Edwards and Gianfranco di Giovanni, Friday February 21, 2020 - 07:25 EDT
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The warm, earthy scent known as petrichor occurs when raindrops mix with bacteria in the earth. - ABC

With large swathes of Australia receiving their first drenching in months, the distinct smell of rain is in the air.

This warm, earthy scent is called petrichor and it comes from a compound secreted by soil and rocks when it rains after a dry spell.

"Whatever chemicals float in the air around you get absorbed into the surface of rocky stuff around you," said science commentator Dr Karl Kruszelnicki.

"As the rain comes close, as the humidity begins to increase, the chemicals are released … and suddenly you smell this unique smell for your area."

The term 'petrichor' was first coined by two CSIRO scientists in the 1960s, who discovered a compound called geosmin was a key ingredient in the smell of rain.

The vibes are positive

When raindrops mix with bacteria in the earth, geosmin is splashed up into the air as tiny droplets which are inhaled by humans.

It is thought that humans are particularly sensitive to geosmin because our ancestors associated rain with survival.

"It might be something as simple as conditioning," Dr Karl said.

"When rain comes you think 'oh the drought is over, the soil is good, the grass will grow green, the vegetables will grow beautifully'.

"And so you've got all these positive vibes."

An ode to Petrichor

These positive vibes have even inspired music, with singer-songwriter Paul Kelly penning a song called Petrichor.

'The sighing ground gives up its love' sings Kelly in his ode to the earthy scent.

"I really just liked the sound of the word," Kelly said.

"Sometimes that's just how songs start; with a word or a phrase or a little thing."

Kelly said the smell of petrichor triggered memories of his childhood in Adelaide.

"We often had long hot dry spells and then you'd get the rain in summertime — or sometimes you would — and there would be that smell," he said.

"Of course, I didn't have a name for it back then, but it's a smell that keeps recurring all through my life."

Recreating the smell of rain

Now the scent is being sniffed out by the perfume industry, with perfume makers attempting to manufacture the alluring aroma for consumers.

Melbourne-based perfumer Janelle Donnelly said it was an emerging trend to feature petrichor in fragrances.

"We have a project on the horizon to develop a petrichor-featured scent ourselves," Ms Donnelly said.

"What is appealing about this scent is that it has a positive association.

"Something like petrichor, which gives people a sense of relief and elation from the rain, is very appealing to the market."

While the word has Greek roots — 'petri' meaning 'stone' and 'ichor' meaning 'the fluid that flows in the veins of the gods' — it is arguably Australians, as the residents of the driest inhabitant continent on earth, who share a special bond with petrichor.

"If you're living in a country where it's dry you're going to love rain," Dr Karl said.

"It makes perfect sense to me."


© ABC 2020

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