It's finally rained in the UK - but what causes the distinct earthy smell in the air?

·2 min read

Much-needed rain has finally fallen in parts of the UK - but did you smell a familiar earthy scent accompanying the downpours?

Many people find it comforting, and it's even been recreated in perfumes - the smell is called petrichor.

It comes from a combination of plant oils and a chemical called geosmin that's made by bacteria in the soil.

They're produced during hot weather and released into the air when it rains after a dry spell.

Tiny air bubbles form in the raindrops when they hit the soil, according to an MIT study.

They then shoot upwards, similar to a glass of champagne, and burst out of the drop to release aerosols of the scent into the atmosphere.

Petrichor is most noticeable after a light shower because heavy rain can wash the aerosols out of the air.

However, it may also be detected when humidity increases ahead of rainfall.

Humans have an incredible sensitivity to the geosmin that makes up the distinctive smell, and can reportedly detect it in quantities as low as five parts per trillion.

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The smell is so intoxicating to some people that it's been recreated synthetically in perfumes and candles.

Petrichor was coined by two Australian researchers in the 1960s and comes from "petra", the Greek for rock, and "ichor", the golden blood of gods in mythology.

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Ahead of a thunderstorm, you may also sometimes smell ozone - a form of oxygen. It's produced when lightning splits nitrogen and oxygen molecules into separate atoms.

These can combine into nitric oxide and react with other chemicals in the atmosphere to make a molecule of three oxygen atoms, O3 (ozone).

The sweet, pungent smell is carried by a storm's downdrafts to nose level, which is why some people say they can smell that a storm is on the way.