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This satellite image shows both dust and clouds in the atmosphere above Japan on April 18, 2006. The dust traveled to Japan from the Gobi Desert. Dust is one of the aerosols that can act as cloud condensation nuclei in cloud formation.
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Image Courtesy of NASA's Earth Observatory

Aerosols and Cloud Formation

When clouds form they contain millions of water droplets in each cubic meter of air. Each of the cloud droplets forms on a particle; scientists call a collection of particles an aerosol. These particles are small, about 100 times smaller in diameter than the thickness of human hair. In cloud formation, one particle produces one water droplet, so there are the same number of particles as there are water droplets.

The aerosol particles come from natural processes as well as human activities. They are made of soil, dust, and sea salt, or from air pollution from cars, power plants, and factories. During cloud formation, water vapor (which is also contained in air) condenses on the aerosol particles. Since there is one particle for every cloud droplet, the number of particles affect the number of water droplets contained within a cloud. If there is a high number of aerosol particles in the atmosphere, then a high number of cloud droplets can form.

If there are more aerosols in a given area, the cloud droplets that are produced will be smaller. This is because the liquid water that was available is divided among more cloud droplets. In this case, the clouds are less likely to produce precipitation.

Clouds can influence the Earth's climate. Different types of clouds and the amount of clouds in the atmosphere may have different impacts on climate. Scientists are still exploring these topics.

Last modified October 17, 2008 by Randy Russell.

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