Ozone abundance. Ozone molecules have a low relative abundance in the
atmosphere. In the stratosphere near the peak concentration of the ozone layer,
there are typically a few thousand ozone molecules for every billion air molecules
(1 billion = 1,000 million). Most air molecules are either oxygen (O2) or nitrogen (N2).
In the troposphere near Earth’s surface, ozone is even less abundant, with a typical
range of 20 to 100 ozone molecules for each billion air molecules. The highest
surface values result when ozone is formed in air polluted by human activities.