How is Ozone Formed?

In 1930, Sidney Chapman set forth a series of reactions in his paper 'A theory of upper-atmosphere ozone, Mem. Roy. Meteorol. Soc.'. It explained how ozone is formed and destroyed in the stratosphere. In his four reactions, the net equation is nothing except for energy in ultraviolet rays being used up. His reactions are based on the idea that ozone is constantly made in the atmosphere by a cycle that starts with molecular oxygen's photolysis. Notice the second reaction is the only one that has a product of ozone. Also notice that this cycle really is a cycle; the net equation is just loss of energy.

M is another molecule, usually N2 or O2. Without it, the product (ozone) will immediately break up from the inability to conserve the energy and momentum from the reactants

The Chapman reactions occur in the stratosphere above 30 km and use radiation with a wavelength less than 240 nm. These rays are classified as UV-B rays, which would be very harmful if they reached the Earth. The Chapman reactions explain ozone's benefits; without it, humans and other organisms on Earth would be subject to dangerous light rays.

These reactions, however, do not really predict amounts of ozone. Why? The solar flux is not great enough to destroy ozone at the level we observe. The Chapman Cycle Equilibrium Calculator allows you to calculate the final state of a gas of different molecules of oxygen. (This shows only the final state.