Ozone is the triatomic form of oxygen; it has a blue colour and a pungent odour. It is highly poisonous to living organisms. The ozone layer refers to that part of the atmosphere that is rich in ozone. This layer is also known as the ozonosphere or the ozone shield. It is a very important layer, as it filters harmful, high-energy ultraviolet radiation coming from the sun.

UV rays split the ozone into molecular and atomic oxygen, thereby liberating heat which warms the stratosphere.

\(O_3\overset{UV}{\longrightarrow} O_2 + [O] + Heat\)

Depletion of ozone layer: Depletion of ozone layer refers to reduction in the concentration of ozone layer. It is caused by ozone-depleting substances (ODSs) such as chlorofluorocarbons (CFCs), halons, methyl bromide, nitrogen oxides and chlorine.

One of the most important ozone-depleting substance are CFCs, which are rich in chlorine, fluorine and carbon such as carbon tetrachloride and dichlorofluoro methane.

Effects of the depletion of ozone layer:

(i) It causes skin cancer due to excess exposure to UV radiation.

(ii) It damages the eyes and the immune system.

(iii) It affects plants by decreasing crop yields.

(iv) It leads to a decrease in the population of phytoplanktons, zooplanktons and some fish larvae that form important constituents of the aquatic food chain.

(v) It leads to smog formation, which is very toxic for plants and animals.