Why does rain smell so good?

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It turns out it’s not just gratitude that attains rainfall odors so appealing after a long period of dry weather.

There’s actually some chemistry involved too.

Bacteria, plants and even lightning can all play a role in the pleasant aroma we experience after a thunderstorm; that of clean air and wet earth.

Known as petrichor, the perfume has long been chased by scientists and even perfumers for its suffering appeal.

Wet earth

First named by two Australian researchers in the 1960 s, the warm, earthy fragrance we experience when rain makes dry ground are generated by bacteria.

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“These critters are abundant in soil, ” explained Prof Mark Buttner, head of molecular microbiology at the John Innes Centre.

“So when you’re saying you reek damp soil, actually what you’re reeking is a molecule being made by a certain type of bacteria, ” he told the BBC.

That molecule, geosmin, are generated by Streptomyces. Present in most healthy clays, these bacteria are also used to create commercial antibiotics.

Drops of water making the ground cause geosmin to be released into the air, building it much more abundant after a rain shower.

“Lots of animals are sensitive but human being are extremely sensitive to it, ” added Prof Buttner.

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Isabel Bear and RG Thomas, the researchers who first named the odor petrichor, found that as early as the 1960 s it was being captured to sell as a odor called “matti ka attar” in Uttar Pradesh, India.

Now, geosmin is becoming more common as a perfume ingredient.

“It’s a really potent material and it reeks just like the cement when the rain makes it, ” said perfumer Marina Barcenilla. “There’s something very primitive and very primal about the smell.”

“Even when you dilute it down to the portions per billion scope,[ humans] can still see it, ” she added.

Yet we also have an odd relationship with geosmin – while we are drawn to its smell, many of us detest its taste.

Image copyright Science Photo Library Image caption Geosmin also devotes beets their distinctive earthy flavor

Even though it is not toxic to humans, the tiniest sum can set people off mineral water or wine when it is present.

“We do not know why we dislike geosmin, ” commented Prof Jeppe Lund Nielsen from Aalborg University in Denmark.

“It is not toxic to humen in typical determine ranges, but somehow we associate it with something negative, ” he added.


Petrichor: The word 😛 TAGEND

Coined by scientists Isabel Joy Bear and Richard Thomas in their 1964 article “Nature of Argillaceous Odour”, published in the publication Nature.

The word was coined from Greek petros, entailing “stone”, and ichor, entailing “the fluid that flows in the veins of the gods”


Plants

According to Prof Nielsen, research also indicates that geosmin could be related to terpenes – the source of scent in many plants.

Image copyright Science Photo Library Image caption Terpenes are commonly produced by conifers like pine

Rain could bring these fragrances out, says Prof Philip Stevenson, a research leader at Royal Botanic Gardens, Kew.

“Often the plant chemicals that smell pleasant generated in foliage hairs … and the rain may injury these, releasing the compounds.

“Rain are also welcome to violate dry plant material releasing chemicals in a similar way to when you crush dried herbs – the smell becomes stronger, ” he told the BBC.

Very dry periods may also slow down plant metabolism, with renewed rainfall dedicating it a kick start and causing plants to release a pleasant scent.

Image copyright Science Photo Library

Lightning bolts

Thunderstorms have their role to play too, creating the clean, sharp odor of ozone – caused by lightning and other electrical discharges in the atmosphere.

Prof Maribeth Stolzenburg of the University of Mississippi explains: “Besides the lightning, the thunderstorm and especially the rainfall will improve the air quality. Much of the dust, aerosols, and other particulates are rained out and the air clears.”

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