The smell of fresh rain on earth is caused by bacteria that produces stinky compounds.

Have you ever sniffed the smell of fresh rain? [sniff in] That awesome moment when the sun is blazing hot, then suddenly clouds roll up the sky, and in an instant, it begins to shower. As the rains hit you, the air around you has this earthy smell. How on Earth in the amazing world of science does nature smell so lovely and so nostalgic? However, we can unlock nature’s mystery with a little bit of science.


Related media: Where Does the Smell of Rain Come From?


I’m In Love With The Smell Of You

The nature of the world is full of wonderful mystery that keep on puzzling us, and the smell of fresh rain is no exception. That’s what drives scientists to search for answers to nature’s amazing tricks, and they did so with the smell of fresh rain. A team of scientists from Australia first tackled this issue; then another team from the Massachusetts Institute of Technology (MIT) built upon their findings within the last decade.

And at long last, Tim Logan, a professor of Atmospheric Sciences at Texas A & M University, compiled their results for The Conversation. “What causes that fresh rain smell?,” was the million dollar question. The answer? Logan explains it boils down to one word: petrichor. This term describes the chemical process that happens when rain meets dry earth. The moistening of the soil, he explains, releases a variety of compounds (such as plant oils and debris); but the key ingredient that produces that smell is called geosmin — a type of stinky alcohol.



The Bacteria Are Blame Worthy

Image: Shutterstock / iStock / Getty Images Plus

Geosmin is not the kind of alcohol you booze, instead it’s produced by bacteria that thrive in the soil and break down whatever dead stuff that happens to fall to the ground. In short, rain plus dry soil equals geosmin — creating that awe-inspiring telltale smell of fresh rain. Here’s the catch: why is it only fresh rain, and not a heavy downpour? It all comes down to dryness. As it turns out, it slows down the geosmin-producing bacteria that’s responsible for breaking down the organic matter in the soil; and with a few drops of rain, the bacteria flungs into high gear, producing more geosmin.

As a result, the geosmin-containing compounds are released in aerosol form; and as a stream of wind blows towards your direction, you then detect the geosmin — that radiant smell of fresh rain. This could be so strong that some people could even sniff the smell of an approaching storm. And even yet still, if you can sniff out petrichor, that’s another telltale sign of a storm is brewing ozone.



The Lightning Effect

As tropospheric chemist Louisa Emmons explains in Scientific American:

The electric charge from lightning “splits atmospheric nitrogen and oxygen molecules into separate atoms. Some of these recombine into nitric oxide, and this in turn reacts with other atmospheric chemicals, occasionally producing a molecule made up of three oxygen atoms — ozone,” which has a distinctly sharp scent. You really can smell rain coming.

By now you might be wondering, that awe-inspiring delightful smell of fresh rain you relish from your childhood days during the change of every season is really some result of bacteria decomposing dead stuff and lightning? Like seriously, that’s how picky nature is.


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Written by: Nana Kwadwo, Fri, May 17, 2019.

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