Speaker 1: Welcome to Brainstuff from house stuff works dot com, where
Speaker 1: smart happens him worse brain With today's question, what causes
Speaker 1: the smell after the rain? Most people notice a distinctive
Speaker 1: smell in the air after it rains. It's frequently linked
Speaker 1: with spring, as the smell of fresh cut grass is
Speaker 1: associated with the summer. You'll find it in a lot
Speaker 1: of poetry and also on many inspirational lists of things
Speaker 1: to be happy about? But what causes this smell? As
Speaker 1: it turns out, the smells people associate with rainstorms can
Speaker 1: be caused by a number of different things. One of
Speaker 1: the more pleasant rain smells, the one we often notice
Speaker 1: in the woods, is caused by bacteria. These bacteria grow
Speaker 1: in soil when conditions are damp and warm. When the
Speaker 1: soil dries out, the bacteria produces spores in the soil.
Speaker 1: The wetness and force of the rainfall kick these tiny
Speaker 1: spores up into the air, where the moisture after a
Speaker 1: rain acts as an aerosol. Just like an aerosol air freshener.
Speaker 1: The moist air easily carries the spores to us, so
Speaker 1: we breathe them in. These spores have a distinctive, earthy
Speaker 1: smell we often associate with rainfall. The bacteria are extremely
Speaker 1: common and can be found in areas all over the world,
Speaker 1: which accounts for the universality of this sweet after the
Speaker 1: rain smell. Since the bacteria thrives in moist soil but
Speaker 1: releases the spores once the soil dries out, the smell
Speaker 1: is most acute after a rain that follows a dry spell,
Speaker 1: although you'll notice it to some degree after most rainstorms.
Speaker 1: Another sort of smell is caused by the acidity of
Speaker 1: the rain. Because of chemicals in the atmosphere, rainwater tends
Speaker 1: to be somewhat acidic, especially in urban areas, when it
Speaker 1: comes in contact with organic debris or chemicals on the ground.
Speaker 1: This acid rain can cause some particularly aromatic reactions. It
Speaker 1: breaks apart soil and releases minerals trapped inside, and it
Speaker 1: reacts with chemicals such as gasoline, giving them a stronger smell.
Speaker 1: These reactions generally produce more unpleasant smells than bacteria spores,
Speaker 1: which is why the after the rain smell isn't always
Speaker 1: a good one. Like the smell caused by the bacteria spores,
Speaker 1: the smell of chemical reactions is most noticeable when it
Speaker 1: rains following a dry spell. This is because once the
Speaker 1: chemicals on the ground have been diluted by one downpour,
Speaker 1: they don't have the same reaction with the rainwater the
Speaker 1: second time. Another after the rain smell comes from volatile
Speaker 1: oils that plants and trees naturally release. The oil collects
Speaker 1: on surfaces such as rocks. The rain reacts with the
Speaker 1: oil on the rocks and carries it as a gas
Speaker 1: through the air. This scent is like the bacteria spores,
Speaker 1: and that most people consider it to be a pleasant
Speaker 1: fresh smell. It has even been bottled and sold for
Speaker 1: its aromatic equalities. These are a few common rain smells,
Speaker 1: but there are also all sorts of other sense. After
Speaker 1: it rains, there's lots of aromatic material that the moisture
Speaker 1: and impact of the rain can stir up, and the
Speaker 1: moist atmosphere following a downpour is particularly good at carrying
Speaker 1: these particles through the air. So when you talk about
Speaker 1: the after the rain smell with a friend, you may
Speaker 1: mean one thing while your friend is thinking of something else.
Speaker 1: You'll both agree, however, that the air has a much
Speaker 1: stronger aroma after a good rainfall. Do you have any
Speaker 1: ideas or suggestions for this podcast. If so, please send
Speaker 1: me an email at podcast at how stuff works dot com.
Speaker 1: For more on this and thousands of other topics, go
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Speaker 1: works dot com home page