Question

What is meant by depletion of ozone layers? What are its causes?

Answer 1

Hint: Ozone is a triatomic gas with a formula $O_3$. It is formed independently in the troposphere and stratosphere. It is bad ozone in the troposphere lower atmosphere and good ozone in the stratosphere. In the stratosphere oxygen splits up into nascent oxygen under the influence of UV radiation. Nascent oxygen combines with molecular oxygen to form ozone.

Complete answer:
The region of the stratosphere where ozone is present in high concentration is called ozonosphere or ozone layer. It is called ozone shield because it protects the living beings from harmful effects of ultraviolet radiations of 280-320 nm wavelength called UV-B.
Ozone layer depletion: The gradual thinning of the ozone layer present in the upper atmosphere is called ozone layer depletion.
Causes of ozone layer depletion: Certain substances react with Ozone present in the stratosphere and destroy the same. These are called ozone depleting substances or ODS. The major OD is due to chlorofluorocarbons (CFCs), gases used in fire extinguishing like bromochlorodifluoromethane, $N_2O$, $CH_4$, chlorine, methyl bromide, carbon chloride, etc. They are released by jets and rockets in the stratosphere or pass into the stratosphere from the troposphere. Both halons and CFCs produce active chlorine in the presence of UV radiation.
Active chlorine stays longer over atmospheric ice crystals over Antarctica. It reacts with ozone in Chainamitic methods converting it into oxygen.One active chlorine can destroy 5000 molecules of ozone.
Other ozone depleting substances like $N_2O$ and $CH_4$ also describe ozone in a still more complicated series of reactions. Because of their ozone depleting characteristics chlorofluorocarbons and halons are being phased out. Chlorofluorocarbons have been replaced by hydrofluorocarbons and hydrochlorofluorocarbons.

Note:
Effects of ozone depletion: Thinning of ozone layer and development of ozone hole increase the amount of UV-B radiation on the earth surface. UV-B radiation on earth will have the following adverse effect. Skin cancer: UV-B radiation forms thymine dimers in DNA. Mutation occurs in skin cells. It causes the incidence of skin cancers. Blinding: Cornea absorbs UV radiation and becomes swollen. It is called snow blindness. Immune system: Immune system is partially suppressed. Larval stages: Larvae and young ones of aquatic animals will die.