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. This activity is not concerned with ozone in the troposphere, but the ozone that occurs in the stratosphere. Go to the link below which shows the density of ozone versus altitude. Now that you have a better idea of exactly where the ozone layer is, it's time to figure out exactly why it is so important.