The stratosphere or the "good" Ozone layer extends upward from about 6-30 miles and protects life on Earth from the sun's harmful ultraviolet (UV) rays. Many popular consumer products like air conditioners and refrigerators involve CFCs or halons during either manufacture or use. Over time, these chemicals damage the earths protective ozone layer. Cars, trucks, power plants and factories all emit air pollution that forms ground-level ozone, a primary component of smog.

The layer closest to the Earth's surface is the troposphere. Here, ground-level or "bad" Ozone is a pollutant that is harmful to breathe and it damages crops, trees, and other vegetation. It is the main ingredient of urban smog.