The Earth’s atmosphere is a constantly moving body of gases that encircle our planet. This body of gases known as air is a mixture—not a chemical combination—of a number of gases; that is, each gas retains its own charac- teristic properties. It consists of about 78 percent nitrogen; about 21 percent oxygen, and carries along with it water vapor, clouds, dust, smoke, soot, and a variety of chemical compounds. The remaining one-percent con- tains all the other gases including carbon monoxide, car- bon dioxide, ozone, methane, and ammonia that contrib- ute to air pollution. And at any.
