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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？
精读先不看文字，完整听一遍。
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That pleasant earthy scent after rain is called petrichor, and it comes from soil-dwelling bacteria.雨后那宜人的泥土气息被称为‘潮土油味’，源自土壤中的细菌。
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During dry periods, certain microbes like Streptomyces release oily compounds into the ground.干旱期，链霉菌等微生物会向土壤中释放油脂类化合物。
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When raindrops hit porous surfaces like soil or rock, they trap tiny air bubbles beneath them.雨滴落在土壤或岩石等多孔表面时，会在下方困住微小气泡。
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These bubbles rise and burst at the surface, releasing aerosols carrying geosmin—the main odor molecule.这些气泡上升至表面并破裂，释放携带土臭素的气溶胶——土臭素是主要气味分子。
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Geosmin has an extremely low detection threshold: humans can smell it at just five parts per trillion.土臭素的感知阈值极低：人类仅需每万亿份中含五份即可察觉。
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Light rain produces more aerosols than heavy downpours because gentle impacts create finer mist.小雨比暴雨产生更多气溶胶，因为轻柔撞击能形成更细密的水雾。
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Plant oils also mix into the scent, adding green, herbal notes to the overall aroma.植物油脂也融入气味中，为整体香气增添青绿、草本气息。
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Desert-dwellers often notice petrichor most strongly, since dry conditions concentrate the compounds longer.沙漠居民往往最强烈地感知潮土油味，因干燥环境使相关化合物存留更久。
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Our brains associate this smell with safety, renewal, and fertility—an evolutionary advantage.大脑将这种气味与安全、新生和丰饶联系起来，具有进化优势。
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Even indoor plants can release similar compounds when watered, mimicking natural petrichor.室内植物浇水时也会释放类似化合物，模拟天然潮土油味。
精读 · 大约 10 分钟
听 → 读 → 学表达 → 懂 → 今天会说这一句 → 跟读录音 → 自己说一句。
③ 学 · 重点表达
- Our brains associate this smell with safety, renewal, and fertility—an evolutionary advantage. 大脑将这种气味与安全、新生和丰饶联系起来，具有进化优势。
- Even indoor plants can release similar compounds when watered, mimicking natural petrichor. 室内植物浇水时也会释放类似化合物，模拟天然潮土油味。
- During dry periods, certain microbes like Streptomyces release oily compounds into the ground. 干旱期，链霉菌等微生物会向土壤中释放油脂类化合物。
④ 懂 · 选一选
⑤ 今天会说这一句
Our brains associate this smell with safety, renewal, and fertility—an evolutionary advantage.
⑥ 跟读并录音
Our brains associate this smell with safety, renewal, and fertility—an evolutionary advantage.
第一版：录下来、回听、再听标准音。系统打分以后再加。
⑦ 说 · 自己来一句
用今天的表达，自己说一句。
例子：Our brains associate this smell with safety, renewal, and fertility—an evolutionary advantage.
已记下。连续天数以后会显示在课表里。
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