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Why Does Rain Smell So Fresh After a Storm?
为什么雨后空气闻起来格外清新？
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That pleasant earthy scent after rain is called petrichor, and it comes from soil-dwelling bacteria.
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During dry periods, certain microbes like Streptomyces release oily compounds into the ground.
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When raindrops hit porous surfaces like soil or rock, they trap tiny air bubbles beneath them.
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These bubbles rise and burst at the surface, releasing aerosols carrying geosmin—the main odor molecule.
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Geosmin has an extremely low detection threshold: humans can smell it at just five parts per trillion.
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Light rain produces more aerosols than heavy downpours because gentle impacts create finer mist.
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Plant oils also mix into the scent, adding green, herbal notes to the overall aroma.
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Desert-dwellers often notice petrichor most strongly, since dry conditions concentrate the compounds longer.
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Our brains associate this smell with safety, renewal, and fertility—an evolutionary advantage.
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Even indoor plants can release similar compounds when watered, mimicking natural petrichor.