为什么雨有味道?

为什么雨有味道?

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?

我们都知道那种气味，那种在雨刚开始的几分钟里弥漫在空气中的泥土的新鲜香味。但是是什么导致了这种现象呢?毕竟，雨只是水，水没有气味，对吧?

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.

谢天谢地，麻省理工学院(MIT)的科学家们进行了数百次实验，终于找到了为什么他们相信雨会带来那种可爱的香味。通过使用高速照相机观察雨滴撞击各种多孔表面时，他们发现小气泡在雨滴撞击时被困在下面，上升到表面，然后逃逸到周围的空气中。在释放出来的空气中，我们会发现一种叫做petrichor的气味的根源，我们联想到雨的气味。

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，这些雨滴传播的不仅仅是一种气味。在发表在《自然通讯》上的一项新研究中，科学家们发现，在适当的条件下，这些雨滴也可以传播细菌。再次使用高分辨率摄像机，观察雨水落在干燥、细菌遍布的土壤上。根据新闻稿:

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.

当雨滴以类似小雨的速度降落，温度与热带地区相似时，雨滴会释放出雾状的喷雾，或称气溶胶。每个气溶胶携带了数千个来自土壤的细菌。研究人员发现，之后细菌存活了一个多小时。

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气和雨水的小袋，它们起到传递的作用，使细菌和微生物在空气中传播。麻省理工学院机械工程系副教授、埃斯特和哈罗德·e·埃德格顿职业发展主任卡伦·布伊说，如果风带走了这些粒子，它们可能会飞得更远，然后重新落回地面，形成一个新的菌落。

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样的

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."

麻省理工学院机械工程助理教授卡伦·布伊谈到这一发现时说:“每天都在下雨——现在世界上的某个地方正在下雨。这是一种非常普遍的现象，让我们感到好奇的是，之前没有人观察到这种机制。”

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年麻省理工学院的一项研究中，在28个表面上测试了单滴雨滴，其中一些是人造的，另一些是自然的，以模拟各种类型的降雨。短距离释放的水模拟较轻的降雨，而高处释放的水则更像是倾盆大雨。

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.

并不是所有类型的雨都能在空气中产生相同的悬浮颗粒。麻省理工学院发现，小雨和中雨最适合这项任务，而且，雨落到地面越重，空气上升到雨滴表面的可能性就越小。