What makes rain smell so good?

According to experts, there is a special chemistry behind the clean smell that fills the air after a rain storm. Many elements have been found to make a contribution to this scent, including bacteria and plants.

The smell of wet earth has memorized people and intrigued scientists for many years. The invigorating scent was named “petrichor” by two Australian scientists, Joy Bear and Richard Thomas, in an article they published in the journal Nature in 1964.

As the rain hits dry ground, there are bacteria that become active. “These critters are abundant in soil,” Professor Mark Buttner, head of Molecular Microbiology at the John Innes Centre, told the BBC.

“So when you’re saying you smell damp soil, actually what you’re smelling is a molecule being made by a certain type of bacteria.”

The molecule is known as geosmin and is produced by Streptomyces, which can be found in most healthy soils. These bacteria are used in the development of commercial antibiotics as well.

When drops of water hit the soil, geosmin is released into the air, so the molecules are much more abundant after it rains. Geosmin is now being used as an ingredient in perfumes.

“It’s a really potent material and it smells just like the concrete when the rain hits it,” perfumer Marina Barcenilla told the BBC. “There’s something very primitive and very primal about the smell. Even when you dilute it down to the parts per billion range, (humans) can still detect it.”

Experts say that, while the smell of geosmin is captivates humans, people are extremely repulsed by its taste.

“We do not know why we dislike geosmin,” said Professor Jeppe Lund Nielsen from Aalborg University in Denmark. “It is not toxic to humans in typical found ranges, but somehow we associate it with something negative.”
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By Chrissy Sexton, Earth.com Staff Writer