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。我们闻到的其实是烟草燃烧后形成的颗粒。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.
In real life, you could barely see it.
It's just a little speck suspended in the atmosphere anywhere from a few days to several years.
It could be dust from a desert, or salt from ocean spray.
It could have been blasted out of a volcano, or created during a forest fire.
It might have flown out of a factory smokestack, or a truck's tailpipe.
Depending on what it is—and where it is— an aerosol particle can do some impressive things.
Like cool the planet by reflecting sunlight back into space, or by collecting water vapor to build a cloud.
On the other hand, some aerosol particles trap sunlight and heat the air, thus preventing clouds from forming.
Other aerosols can host chemical reactions that damage the ozone layer.
