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可能大家都有过这种经历：走在楼道里甚至路上，明明周围几十米之内都没有人，但仍然可以闻到烟味。我们闻到的其实是*草烟**燃烧后形成的颗粒。这种在气体中稳定分散悬浮的液态或固体小颗粒就叫做气溶胶（aerosol）。对于这一新词汇，不少小伙伴表示好奇，气溶胶究竟是什么？
This is an aerosol particle.
这是一个气溶胶微粒。
In real life, you could barely see it.
在生活中，你不太能看见它们。
It's just a little speck suspended in the atmosphere anywhere from a few days to several years.
它就是在空气中到处悬浮数天至数年的小小粒子。
It could be dust from a desert, or salt from ocean spray.
它可以是来自沙漠的灰尘，或者海雾中的盐分。
It could have been blasted out of a volcano, or created during a forest fire.
它也可能来自火山喷发，或者森林大火产生的。
It might have flown out of a factory smokestack, or a truck's tailpipe.
它可能是从工厂烟囱里飘出来的，或从卡车的排气管。
Depending on what it is—and where it is— an aerosol particle can do some impressive things.
依据它的特性及它出现的地方，一个气溶胶微粒可以有很惊人的表现。
Like cool the planet by reflecting sunlight back into space, or by collecting water vapor to build a cloud.
例如将阳光反射至外太空来冷却星球，或搜集水蒸气造云。
On the other hand, some aerosol particles trap sunlight and heat the air, thus preventing clouds from forming.
另一方面来说，有些气溶胶体会吸附日照并加热空气，因此避免云的产生。
Other aerosols can host chemical reactions that damage the ozone layer.
其他气溶胶可以主导伤害臭氧层的化学反应。
And down on Earth, they can even cause health problems, such as lung and heart disease.
而在地球上，他们可能会引起健康问题，例如肺部及心脏疾病。
That layer of hazy air pollution above big cities?
那层笼罩在大城市上空雾蒙蒙的污染？
Yep, it contains aerosol particles.
没错，那个也含有气溶胶。
Aerosols.
气溶胶。
They're tiny.
它们很小。
They're powerful.
它们很强大。
NASA studies them with satellites and instruments on the International Space Station, and with specialized aircraft and ground-based devices.
NASA 用在国际太空站的卫星和仪器以及特殊的飞机及地面仪器来研究它们。
Because when it comes to understanding our environment, our climate, and how it's all changing, little particles make a big difference.
因为当需要了解我们的环境与气候以及关于变迁的一切时，小小的粒子也可以造成大大的改变。