The ozone-oxygen cycle is the process. ozone is continually regenerated in the stratosphere, by converting ultraviolet (UV radiation into heat. Studied by Sydney Chapman around the 1930s. The process is commonly referred to as the Chapman cycle by scientists. September 16 is the international ozone day.
Most of the ozone production occurs in the upper tropical zone of the stratosphere and mesosphere. The total mass of ozone produced per day on earth is about 400 million metric tons.
The global mass of ozone is relatively constant at about 3 billion tonnes, which means that the Sun produces about 12% of the ozone layer every day.
O2 + ℎν → 2 O •
Each oxygen atom quickly combines with a molecule of oxygen to form an ozone molecule:
O • + O2 → O3
The Ozone-Oxygen Cycle:
The ozone molecules formed by the above reaction have the ability to absorb radiation having a wavelength between UV-C and UV-B.
The molecule of ozone (triatomic) becomes a molecule of oxygen (diatomic) and an atom of oxygen (see figure):
O3 + ν (240-310 nm) → O2 + O
The oxygen atom produced reacts also quickly with another molecule of oxygen to reform ozone.
O + O2 → O3 + EK
where EK denotes the excess energy of the reaction which manifests itself as a supplement of kinetic energy.
These two reactions from the ozone-oxygen cycle, in which the chemical energy released during O and O2 is converted into the kinetic energy.Because the overall effect is to convert UV-B rays into heat without any net loss of ozone.
This cycle takes place in the ozone layer in a stable equilibrium while protecting the lower layers of the atmosphere against UV rays.
if an oxygen atom and an ozone molecule meet, they recombine to form two molecules of oxygen:
O3 + O · → 2 O2
And if two oxygen atoms meet, they react to form a molecule of oxygen:
2 O · → O2
This reaction is to have a negative reaction order.
The net reaction will be 2 O3 → 3 O2
• OH and NO • are naturally present in the stratosphere, but human activity, particularly chlorofluorocarbon (Cfc) emissions and halons. Because significantly increased the concentration of • Cl and • Br, leading to depletion of ozone.