Welcome to Brainstuff, a production of I Heart Radio. Hey rain Stuff Lauren Bolga Bam here. Most people notice a distinctive smell in the air after it rains. It's frequently linked with spring, as the smell of fresh cut grass is associated with summer. You'll find it in a lot of poetry and also on lots of inspirational lists of
things to be happy about. The scientific name for it is petrochor, and it was first named by two Australian researchers in the nineteen sixties, and it actually comes from the moistening of the earth by rain. But what exactly causes the scent? As it turns out, the smells that people associate with rainstorms can be caused by a number
of things. One of the more pleasant rain smells, the one we often notice in the woods, is caused by bacteria actino my seats, is a genus of filamentous bacteria that grow in soil when conditions are damp and warm. When the soil dries out, the bacteria produce spores around themselves for protection. The wetness and force of rainfall kick these tiny spores up into the air, where the moisture After a rain acts as an air sol like an air sool air freshener. The moist air easily carries the
spores to us so that we breathe them in. These spores have a distinctive earthy smell that we often associate with rainfall. The actual compound responsible for the smell is called geosmin, which is released by the bacteria as they die. Geosmin is a type of alcohol molecule and has a very strong scent. The bacteria are extremely common and can be found in areas all over the world, which accounts for the universality of this sweet after the rain smell.
Since the bacteria thrive in moist soil but release the spores once the soil dries out, the smell is most acute after a rain that follows a dry spell, although you'll notice it to some degree to most rainstorms. Another sort of smell is caused by the acidity of rain. Because of compounds in the atmosphere, rainwater tends to be somewhat acidic, especially in urban environments. When it comes in contact with organic debris or compounds on the ground, it
can cause some particularly aromatic reactions. It breaks apart soil and releases minerals trapped inside, which react with chemicals like gasoline, giving them a stronger smell. These reactions generally produce more unpleasant smells than bacteria spores, which is why the after the rain smell isn't always a nice one like the smell caused by bacteria spores. The smell of chemical reactions is most noticeable when it rains following a dry spell.
This is because once the chemicals on the ground have been diluted by one downpour, they don't have as strong of or as many reactions with new rainwater. Another after the rain smell comes from volatile oils that plants and trees release. The oil then collects on surfaces such as rocks. The rain reacts with the oil on the rocks and carries it again as a gas through the air. This scent is like bacterious bores in that most people consider it a pleasant and fresh smell. It's even been bottled
and sold for its aromatic qualities. These are a few common rain smells, but there are also all sorts of other scents after it rains. There are lots of aromatic materials that the moisture and impact of rain can stir up, and the moist atmosphere following a downpour is particularly good at carrying these particles through the air and into our noses. So when you talk about the after the rain smell with a friend, you may mean one thing while they're
thinking of something else entirely. Today's episode is based on the article what causes petroc or the earthy smell after rain on how stuffworks dot Com, written Katherine Whitburn. Brain Stuff is production by Heart Radio in partnership with how stuff works dot Com and is produced by Tyler Clain. For four more podcasts. For my heart Radio, visit the I heart Radio app, Apple Podcasts, or wherever you listen to your favorite shows.