Acid rain damages buildings like this one in Copola, Mexico.
Click on image for full size
Courtesy UCAR

Acid Rain

Have you ever heard of acid rain? Acid rain is what happens when some types of air pollution is washed out of the sky by rain. Sometimes, the pollution can be washed out by snow, sleet, hail, mist or fog, but it is still called acid rain.

Power plants, factories, houses and cars all put pollution into the atmosphere. Sometimes these chemicals return directly to the ground. The rest of the time, they mix with water in the air to form acids. Once the acids form, they can be carried a long way by the wind before being washed out of the air by rain, snow or hail. That is why we call it acid rain.

During the 1970s, scientists in Sweden and Norway noticed that acid rain was hurting their trees and fresh water. Most of the acid rain was caused by pollution that came from other countries. After that, scientists knew that acid rain was an international problem.

Acid rain can have harmful impacts on ecosystems. It makes the soil and water where it falls more acidic. This can hurt or kill plants and animals. Making water more acidic can lead to smaller fish populations. Other species that live in the water are also hurt, like frogs, snails and crayfish. Acid rain affects trees, making them weaker by damaging their leaves. Some types of stone, such as limestone and marble, can be slowly dissolved in acid rain. This can damage buildings and statues.

Last modified February 4, 2008 by Becca Hatheway.

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