HSK 6 · Article · 307 characters · Listen: mandarinthewild.com/library/read/why-rain-smells

雨后的气味从哪里来？

Why rain has a smell

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雨yǔ刚gāng落下luòxià时shí，你nǐ有没有yǒuméiyǒu闻到wéndào过guò一yì股gǔ特别tèbié的de气味qìwèi？它tā有点yóudiǎn像xiàng泥土nítǔ，又yòu和hé平时píngshí的de泥土nítǔ不太bútài一样yíyàng。人们rénmen常cháng把bǎ它tā叫作jiàozuò“雨yǔ的de味道wèidao”，但dàn线索xiànsuǒ并不bìngbù只zhǐ在zài天上tiānshàng，也yě在zài脚下jiǎoxià。

2015年nián，麻省理工学院máshénglǐgōngxuéyuàn的de研究人员yánjiū-rényuán用yòng高速gāosù相机xiàngjī观察guānchá水滴shuǐdī落地luòdì。他们tāmen发现fāxiàn，水滴shuǐdī碰到pèngdào带有dàiyǒu小孔xiáokǒng的de表面biǎomiàn时shí，会huì把bǎ一些yìxiē空气kōngqì困kùn在zài里面lǐmiàn，形成xíngchéng很hěn小xiǎo的de气泡qìpào。

气泡qìpào向上xiàngshàng移动yídòng，破裂pòliè时shí，把bǎ更gèng小xiǎo的de水滴shuǐdī送sòng进jìn空气kōngqì里。这些zhèxiē小xiǎo水滴shuǐdī可能kěnéng把bǎ地面dìmiàn上shàng的de气味qìwèi物质wùzhì一起yìqǐ带走dàizǒu。研究人员yánjiū-rényuán提出tíchū，这zhè或许huòxǔ能néng解释jiěshì雨yǔ后hòu泥土nítǔ气味qìwèi传播chuánbō的de一yì种zhǒng方式fāngshì。

不过búguò，并bìng不是búshì雨yǔ越yuè大dà，这种zhèzhǒng过程guòchéng就jiù越yuè明显míngxiǎn。在zài他们tāmen的de实验shíyàn中zhōng，类似lèisì小雨xiáoyǔ和hé中雨zhōngyǔ的de条件tiáojiàn产生chǎnshēng了le更gèng多duō微小wēixiǎo水滴shuǐdī；猛烈měngliè的de撞击zhuàngjī反而fǎn’ér没有méiyǒu那么nàme多duō。地面dìmiàn的de性质xìngzhì也yě会huì影响yíngxiǎng结果jiéguǒ。

这zhè项xiàng实验shíyàn给gěi出chū的de是shì一种yìzhǒng可能kěnéng的de传播chuánbō机制jīzhì，不是búshì说shuō每měi一次yícì雨yǔ后hòu的de气味qìwèi都dōu只有zhíyǒu一yí个gè来源láiyuán。下次xiàcì闻到wéndào那nà股gǔ味道wèidao时shí，你nǐ可以kéyǐ想xiǎng一yì想xiǎng：刚才gāngcái的de雨yǔ落在zài了le什么shénme地方dìfang？

Key words

Word	Pinyin	Meaning
天上	tiānshàng	in the sky; in heaven
观察	guānchá	to observe; to watch; observation
表面	biǎomiàn	surface; face
形成	xíngchéng	to form; to take shape
向上	xiàngshàng	upward
移动	yídòng	to move; to shift
地面	dìmiàn	ground; floor
物质	wùzhì	matter; substance
或许	huòxǔ	perhaps; maybe
传播	chuánbō	to spread; to disseminate; to propagate
明显	míngxiǎn	obvious; clear; evident
实验	shíyàn	experiment; test; to experiment

English (for the teacher)

Just as rain starts to fall, have you ever caught a particular smell? It’s a bit like soil, yet not quite the same as soil on an ordinary day. People often call it “the smell of rain”, but the clues aren’t only up in the sky; they’re also under our feet.

In 2015, researchers at MIT used high-speed cameras to watch drops of water hit the ground. They found that when a drop lands on a surface with tiny pores, it traps some air inside and forms very small bubbles.

The bubbles rise, and when they burst they send even smaller droplets into the air. These tiny droplets may carry scent compounds from the ground away with them. The researchers suggested this might explain one way the smell of soil spreads after rain.

But it isn’t the case that the harder it rains, the more noticeable this process becomes. In their experiments, conditions like light and moderate rain produced more tiny droplets; hard impacts actually produced fewer. What the ground is like also affects the result.

The experiment offers one possible way the smell spreads; it doesn’t mean the smell after every rain has only one source. Next time you catch that smell, you might ask yourself: where did that rain just land?