Ozone is tri-atomic oxygen. It exists in nature within the stratosphere from a height of 10 kms to 50 kms., sometimes referred to as ozonosphere. In stratosphere, small amounts of ozone are constantly being made by the action of sun’s UV light on oxygen molecules. Oxygen molecules absorbs the sun’s UV radiation and split to form single oxygen atoms. These atoms combine with the remaining oxygen (O₂) molecules to form ozone (O₃) molecules, which are very effective at absorbing sun’s UV rays.

At ground level, ozone is formed as a result of lightning. Ozone is also formed from the pollution from burning fossil fuel which creates smoke and carbon monoxide, and lightning creates nitrogen oxides (NO_x). All of these chemicals combined together with unstable compounds and in the presence of sunlight forms ozone as a by-product.

Ozone at atmospheric conditions is very unstable. Due to this unstable nature, it reduces to oxygen within a very short span of 60 mints. in air and 20 mints. in water. This reduction reaction releases one atom of oxygen which acts as a very powerful oxidising agent and, as a result, a very powerful disinfectant.