Nature · 60 s
Why rain smells so good
Australia, 1964. A smell gets a name.
You’d think. It’s wet dirt, or the storm. Lightning does make ozone, but that’s the sharper smell before the rain.
Actually. It’s petrichor: oil plants leave in dry rock and soil, plus geosmin from soil bacteria, which you can smell at about five parts per trillion.
The twist. In 2015, MIT filmed raindrops on 28 surfaces. Bubbles rise through each drop and pop, flinging a fine mist. Light rain made the most.
How sure? MIT filmed the mist, not smell molecules. That the mist carries the smell is the researchers’ suggestion.
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What the video says
Australia, 1964. Two scientists set out to explain the smell of dry ground after rain.
You'd guess wet dirt, or the storm itself. Lightning does make ozone, but that's the sharper smell that comes before the rain.
They named it petrichor, Greek for stone plus the blood of the gods. Part of it is oil that plants leave in dry rock and soil.
The other part is geosmin, made by bacteria living in soil. Humans can smell it at about five parts per trillion, so a tiny whiff is enough.
In 2015, MIT engineers filmed raindrops landing on twenty-eight different surfaces, including sixteen soils. Bubbles rise through each drop and pop, flinging a fine mist into the air.
Light rain made the most mist. A heavy downpour hits too hard for the bubbles to form.
Next drizzle, open the window and take one long sniff.