WEBVTT - What causes the smell after rain?

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<v Speaker 1>Welcome to Brainstuff from house stuff works dot com, where

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<v Speaker 1>smart happens him worse brain With today's question, what causes

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<v Speaker 1>the smell after the rain? Most people notice a distinctive

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<v Speaker 1>smell in the air after it rains. It's frequently linked

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<v Speaker 1>with spring, as the smell of fresh cut grass is

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<v Speaker 1>associated with the summer. You'll find it in a lot

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<v Speaker 1>of poetry and also on many inspirational lists of things

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<v Speaker 1>to be happy about? But what causes this smell? As

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<v Speaker 1>it turns out, the smells people associate with rainstorms can

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<v Speaker 1>be caused by a number of different things. One of

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<v Speaker 1>the more pleasant rain smells, the one we often notice

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<v Speaker 1>in the woods, is caused by bacteria. These bacteria grow

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<v Speaker 1>in soil when conditions are damp and warm. When the

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<v Speaker 1>soil dries out, the bacteria produces spores in the soil.

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<v Speaker 1>The wetness and force of the rainfall kick these tiny

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<v Speaker 1>spores up into the air, where the moisture after a

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<v Speaker 1>rain acts as an aerosol. Just like an aerosol air freshener.

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<v Speaker 1>The moist air easily carries the spores to us, so

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<v Speaker 1>we breathe them in. These spores have a distinctive, earthy

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<v Speaker 1>smell we often associate with rainfall. The bacteria are extremely

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<v Speaker 1>common and can be found in areas all over the world,

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<v Speaker 1>which accounts for the universality of this sweet after the

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<v Speaker 1>rain smell. Since the bacteria thrives in moist soil but

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<v Speaker 1>releases the spores once the soil dries out, the smell

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<v Speaker 1>is most acute after a rain that follows a dry spell,

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<v Speaker 1>although you'll notice it to some degree after most rainstorms.

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<v Speaker 1>Another sort of smell is caused by the acidity of

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<v Speaker 1>the rain. Because of chemicals in the atmosphere, rainwater tends

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<v Speaker 1>to be somewhat acidic, especially in urban areas, when it

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<v Speaker 1>comes in contact with organic debris or chemicals on the ground.

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<v Speaker 1>This acid rain can cause some particularly aromatic reactions. It

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<v Speaker 1>breaks apart soil and releases minerals trapped inside, and it

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<v Speaker 1>reacts with chemicals such as gasoline, giving them a stronger smell.

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<v Speaker 1>These reactions generally produce more unpleasant smells than bacteria spores,

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<v Speaker 1>which is why the after the rain smell isn't always

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<v Speaker 1>a good one. Like the smell caused by the bacteria spores,

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<v Speaker 1>the smell of chemical reactions is most noticeable when it

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<v Speaker 1>rains following a dry spell. This is because once the

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<v Speaker 1>chemicals on the ground have been diluted by one downpour,

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<v Speaker 1>they don't have the same reaction with the rainwater the

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<v Speaker 1>second time. Another after the rain smell comes from volatile

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<v Speaker 1>oils that plants and trees naturally release. The oil collects

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<v Speaker 1>on surfaces such as rocks. The rain reacts with the

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<v Speaker 1>oil on the rocks and carries it as a gas

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<v Speaker 1>through the air. This scent is like the bacteria spores,

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<v Speaker 1>and that most people consider it to be a pleasant

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<v Speaker 1>fresh smell. It has even been bottled and sold for

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<v Speaker 1>its aromatic equalities. These are a few common rain smells,

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<v Speaker 1>but there are also all sorts of other sense. After

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<v Speaker 1>it rains, there's lots of aromatic material that the moisture

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<v Speaker 1>and impact of the rain can stir up, and the

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<v Speaker 1>moist atmosphere following a downpour is particularly good at carrying

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<v Speaker 1>these particles through the air. So when you talk about

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<v Speaker 1>the after the rain smell with a friend, you may

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<v Speaker 1>mean one thing while your friend is thinking of something else.

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<v Speaker 1>You'll both agree, however, that the air has a much

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<v Speaker 1>stronger aroma after a good rainfall. Do you have any

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<v Speaker 1>ideas or suggestions for this podcast. If so, please send

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<v Speaker 1>me an email at podcast at how stuff works dot com.

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<v Speaker 1>For more on this and thousands of other topics, go

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