Ozone has the same chemical structure whether it occurs high above the earth or at ground level and can be good or bad, depending on its location in the atmosphere.
Ozone occurs in two layers of the atmosphere.
The layer surrounding the earth's surface is the troposphere. Here, ground-level or bad ozone is an air pollutant that damages human health, vegetation, and many common materials. It is a key ingredient of urban smog. The troposphere extends to a level about 10 miles up, where it meets the second layer, the stratosphere. Motor vehicle exhaust and industrial emissions, gasoline vapors, and chemical solvents are some of the major sources of NOx and VOC, also known as ozone precursors.