Mt. Everest, the tallest mountain on the planet, is only about 9 km high. 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. There are many gases that make up our atmosphere. Nitrogen comprises approximately 78 percent of the air we breathe with oxygen present in a much smaller amount of 21 percent.
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 3 are ozone. It is a key ingredient of urban smog.