為什么雨有味道?

為什么雨有味道?

We all know the scent, that earthy fresh aroma that fills the air during those first few minutes of rain. But what causes the phenomenon? After all, rain is just water, and water has no odor, right?

我們都知道那種氣味，那種在雨剛開始的幾分鐘里彌漫在空氣中的泥土的新鮮香味。但是是什么導(dǎo)致了這種現(xiàn)象呢?畢竟，雨只是水，水沒有氣味，對吧?

Thankfully, the scientists at the Massachusetts Institute of Technology (MIT) conducted hundreds of experiments and found out why they believe rain brings forth that lovely perfume. By using high-speed cameras to observe raindrops as they hit various porous surfaces, they discovered that small air bubbles become trapped under the drops upon impact, rise up to the surface, and then escape into the surrounding air. It's in the released air that we'll find the root of the scent called petrichor, the smell we associate with rain.

謝天謝地，麻省理工學(xué)院(MIT)的科學(xué)家們進行了數(shù)百次實驗，終于找到了為什么他們相信雨會帶來那種可愛的香味。通過使用高速照相機觀察雨滴撞擊各種多孔表面時，他們發(fā)現(xiàn)小氣泡在雨滴撞擊時被困在下面，上升到表面，然后逃逸到周圍的空氣中。在釋放出來的空氣中，我們會發(fā)現(xiàn)一種叫做petrichor的氣味的根源，我們聯(lián)想到雨的氣味。

Petrichor, the scent that we associate with rain, is released once rain drops hit a surface. . Stone36/Shutterstock

Those raindrops spread more than just a scent, however. In a new study published in Nature Communications, scientists found that under the right conditions, those raindrops also can spread bacteria. Again using high-resolution cameras, watched rain fall on dry, bacteria-laden soil. According to the press release:

然而，這些雨滴傳播的不僅僅是一種氣味。在發(fā)表在《自然通訊》上的一項新研究中，科學(xué)家們發(fā)現(xiàn)，在適當?shù)臈l件下，這些雨滴也可以傳播細菌。再次使用高分辨率攝像機，觀察雨水落在干燥、細菌遍布的土壤上。根據(jù)新聞稿:

When falling at speeds mimicking those of a light rain, at temperatures similar to those in tropical regions, the drops released a spray of mist, or aerosols. Each aerosol carried up to several thousand bacteria from the soil. The researchers found the bacteria remained alive for more than an hour afterward.

當雨滴以類似小雨的速度降落，溫度與熱帶地區(qū)相似時，雨滴會釋放出霧狀的噴霧，或稱氣溶膠。每個氣溶膠攜帶了數(shù)千個來自土壤的細菌。研究人員發(fā)現(xiàn)，之后細菌存活了一個多小時。

Think of raindrops as little pockets of air and rain that act as a delivery service to make the bacteria and microbes airborne. If the wind picks up the particles, they may travel even farther before settling back on the ground and growing a new colony, says Cullen Buie, associate professor and the Esther and Harold E. Edergton Career Development Chair in the Department of Mechanical Engineering at MIT.

可以把雨滴想象成空氣和雨水的小袋，它們起到傳遞的作用，使細菌和微生物在空氣中傳播。麻省理工學(xué)院機械工程系副教授、埃斯特和哈羅德·e·埃德格頓職業(yè)發(fā)展主任卡倫·布伊說，如果風(fēng)帶走了這些粒子，它們可能會飛得更遠，然后重新落回地面，形成一個新的菌落。

A high-speed camera captured raindrops splashing on a porous surface and releasing thousands of aerosols. MIT

Not all rain is created equal

并非所有的雨都是一樣的

Cullen R. Buie, an assistant professor of mechanical engineering at MIT, said about the findings, "Rain happens every day — it's raining now, somewhere in the world. It's a very common phenomenon, and it was intriguing to us that no one had observed this mechanism before."

麻省理工學(xué)院機械工程助理教授卡倫·布伊談到這一發(fā)現(xiàn)時說:“每天都在下雨——現(xiàn)在世界上的某個地方正在下雨。這是一種非常普遍的現(xiàn)象，讓我們感到好奇的是，之前沒有人觀察到這種機制。”

In a 2015 MIT study, single drops of rain were tested on 28 surfaces, some man-made and other natural, simulating various types of rainfall. Water released from shorter distances mimicked lighter rainfall and water released from higher up acted like more of a downpour.

在2015年麻省理工學(xué)院的一項研究中，在28個表面上測試了單滴雨滴，其中一些是人造的，另一些是自然的，以模擬各種類型的降雨。短距離釋放的水模擬較輕的降雨，而高處釋放的水則更像是傾盆大雨。

Not all types of rain are created equal when it comes to delivering aerosols into the air. MIT found that light and moderate rains were best suited for the task, and that, the harder the rain hits the ground, the less likely air would be to rise up to the surface of the drops.

并不是所有類型的雨都能在空氣中產(chǎn)生相同的懸浮顆粒。麻省理工學(xué)院發(fā)現(xiàn)，小雨和中雨最適合這項任務(wù)，而且，雨落到地面越重，空氣上升到雨滴表面的可能性就越小。