This cartoon shows the relative sizes of a typical raindrop, a droplet of water in a cloud, an extremely large aerosol particle, and a smaller aerosol particle of a more typical size. Even smaller aerosol particles exist; some as small as 10 nanometers (0.01 microns) across. Those particles would be invisible at even this magnified size scale.
Click on image for full size
Randy Russell / Windows to the Universe
Aerosols: Tiny Particulates in the Air
When you look up at the sky, you are looking at more than just air. There are also billions of tiny bits of solid and liquid floating in the atmosphere. Those tiny floating particles are called aerosols or particulates.
Some aerosols are so small that they are made only of a few molecules – so small that they are invisible because they are smaller than the wavelength of light. Larger aerosols are still very small, but they are visible.
There are hundreds or thousands of little aerosols in each cubic centimeter of air. Some of them are natural and others are released into the air by humans. Natural sources of aerosols include dust from dry regions that is blown by the wind, particles released by erupting volcanoes or forest fires, and salt from the ocean.
We, humans, add aerosols to the atmosphere too. Aerosols are a part of air pollution from cars, power plants, and factories that burn fossil fuels.
Some aerosols are released into the atmosphere, others are made in the atmosphere. For example, sulfate aerosols are made in the atmosphere from sulfur dioxide released from power plants.
In general, the smaller and lighter a particle is, the longer it will stay in the air. Larger particles tend to settle to the ground by gravity in a matter of hours whereas the smallest particles (less than 1 micrometer) can stay in the atmosphere for weeks and are mostly removed by precipitation.
For several reasons, aerosols affect climate. Aerosols help clouds to form in the sky and the number and types of clouds affects climate. Certain types are able to scatter or absorb sunlight, which affects climate. Aerosols that scatter light can make interesting distortions in the sky, called atmospheric optics.
The aerosols that are from air pollution are hazardous to human health. When the little particles get deep into a person’s lungs it can make him or her very ill. Aerosols can also limit visibility, causing haze in many parts of the world.
Shop Windows to the Universe Science Store!
The Fall 2009 issue of The Earth Scientist
, which includes articles on student research into building design for earthquakes and a classroom lab on the composition of the Earth’s ancient atmosphere, is available in our online store
You might also be interested in:
Most things around us are made of groups of atoms bonded together into packages called molecules. The atoms in a molecule are held together because they share or exchange electrons. Molecules are made...more
About 70% of the Earth is covered with water. Over 97% of that water is found in the oceans. Everyone who has taken in a mouthful of ocean water while swimming knows that the ocean is really salty! Dissolved...more
What do smog, acid rain, carbon monoxide, fossil fuel exhausts, and tropospheric ozone have in common? They are all examples of air pollution. Air pollution is not new. As far back as the 13 th century,...more
Have you ever spent time in a large city? If so, the odds are you’ve seen the sky engulfed in a brownish-yellow or grayish-white haze due to air pollution. Such haze can reduce visibility from miles (kilometers)...more
It's no secret that the emissions leaving a car tailpipe or factory smokestack affect climate and air quality. But until now, scientists haven't understood where the emissions go or what happens to them...more
Aerosols are tiny particles or drops of liquid that float around in the atmosphere. For example, tiny flecks of smoke particles from fires or smokestacks are a type of aerosol. Some kinds of aerosols come...more
If you've ever been to the ocean, you know that ocean water has salt in it. But did you know that air has salt in it, too? Many types of tiny particles float around in the air. Scientists call these particles...more