The planet's atmosphere is divided into several layers. Virtually all human activities occur in the troposphere. The next layer, the stratosphere, continues from 10 km to about 50 km. Most commercial airline traffic occurs in the lower part of the stratosphere. Most atmospheric ozone is concentrated in a layer in the stratosphere, about 15-30 kilometers above the Earth's surface.
Ozone is a molecule containing three oxygen atoms.
It is blue in color and has a strong odor. Normal oxygen, which we breathe, has two oxygen atoms and is colorless and odorless. Ozone is much less common than normal oxygen. Out of each 10 million air molecules, about 2 million are normal oxygen, but only three are ozone. At any given time, ozone molecules are constantly formed and destroyed in the stratosphere.