In this topic you will learn about how air pollution affects everyone and everything.

Air is a mixture of nitrogen, oxygen, and a few traces of other gases including water vapor. This mixture supports life on Earth. Almost all organisms need oxygen to live. The oxygen is used to break down food so energy can be released from it. As a result of this process, animals give off carbon dioxide. Plants and other producers take in carbon dioxide. They use it for making food in a process called photosynthesis. In this process they give off oxygen. This makes oxygen a renewable resource. A renewable resource is a resource that can be replaced in a short period of time.

The atmosphere also acts as a protective shield. It shields Earth's surface from harmful energy that comes from the Sun. About 30 kilometers above Earth's surface is a layer of gas called ozone. This ozone layer in the atmosphere screens out much of the Sun's UV rays. The atmosphere also protects life from extremes of temperature. Clouds block sunlight during the day. At night, they keep much of the heat from escaping into space..

Many of the things humans do add pollution to the air. Many pollutants get into the air from burning fossil fuels. Fossil fuels were formed from the decay of ancient forms of life. Fossil fuels include coal, oil, natural gas, and gasoline. The wastes from burning these fuels add pollution to the air. Dust in the air can come from plowed fields and construction sites. Factories can add chemical wastes to the air. Volcanoes, forest fires, and grass fires can add smoke to the air.

All these pollutants can build up into thick clouds, called smog. Smog is a mixture of smoke and fog. It forms when smoke and fumes collect in moist, calm air. Smog irritates the eyes, nose, and throat. People with breathing problems have died from heavy smog.

Wastes from burning fossil fuels can mix with moisture in the air. The result is acid rain. Acid rain is moisture that falls to Earth after being mixed with wastes from burned fossil fuels. Acid rain can harm soil and water supplies. Some trees sicken and die if there is too much acid in the soil. Fish die in lakes whose waters contain too much acid. The acid weathers away statues and buildings. It can cause metal surfaces to crumble.