Ozone layer and Depletion of Ozone:

 Ozone layer is present in stratosphere layer of atmosphere. It protects us from harmful UV rays. But now there is a steady decline of the ozone in the stratosphere. And the ozone depletion is more over the two poles of the earth, which is known as the ozone hole.  As the presence of ozone gets reduced in the atmosphere, it causes the ozone layer to get thinner and thinner. The more ozone layer gets thin, the more big gets the size of ozone hole.

Causes of Depletion: Chlorofluorocarbons (CFCs) and other halogenated ozone depleting substances (ODS) are mainly responsible for man-made chemical ozone depletion. These chemicals have been used as aerosol propellants and cooling mixtures in refrigerators. How these chemicals affect ozone concentration is illustrated with the equations given below.

(i) CF₂Cl₂ + h v → CF₂Cl + Cl

Chlorine atom being highly reactive reacts with ozone (O₃).

(ii) Cl + O₃ → ClO + O₂

The monoxide of chlorine further reacts with another molecule of O₃

(iii) ClO + O₃ → Cl + 2O₂

The chlorine atom so obtained reacts with another ozone molecule. Hence, steps (ii) and (iii) are repeated again and again and, leads to the depletion of concentration of ozone

Prevention of ozone layer:

 Now a days, many non-ozone-depleting substitutes have been discovered.  Substitutes for air-conditioning and refrigeration applications are now available, such as that HCFC-22 can be replaced by HFC-410A, CFC-12 can be replaced by HFC-134a.

Alternative products or processes can be used in some cases including the following:

• alternative insulating materials;
• substitute food containers such as hydrocarbon blown polystyrene, plastic film wrap and bags;
• alternative packaging materials such as plastic film bubble wraps; and
• air-conditioning and refrigeration based on on non-HCFC refrigerants.

Uses of ozone:

•            For air purification at the crowded places like cinema halls and tunnel railways. Due to its strong oxidizing power it also destroys the foul smell in slaughter (dead animal smell) houses.

•            In sterilizing drinking water by oxidizing all germs and bacteria.

•            For preservation of meat in cold storages.

•            For bleaching fabrics such as silk, ivory, oils, starch and wax.

•            Its biggest significance is to locate a double bond in any unsaturated organic compound by Ozonolysis.