Ozone is a form of oxygen in which three atoms of oxygen combine to form a single molecule of ozone. It normally is not found in the lower atmosphere. It exists in the stratosphere between 20 and 50 kilometers above the surface.

The presence of ozone is of singular importance because it filters out the incoming ultraviolet (UV) radiation and thus acts as a screen against ultraviolent radiation that can increase the occurrence of skin cancer, cataracts, and other diseases of eyes. It also affects the body defense mechanism, which increases the vulnerability of infectious diseases.

Increased ultraviolet radiation can seriously affect plant and fish production.

Ozone Depletion

Ozone depletion refers to the wearing out or reduction of the amount of ozone in the stratosphere. It was first identified in 1970s due to the advent of supersonic aircraft, which fly in the lower stratosphere and emit nitrogen oxides.

Ozone Depleting Substances

Ozone depleting substances are those substances which deplete the ozone layer.

It is found that the major cause of ozone depletions is the CFC (Chlorofluorocarbons) gases. CFCs are used for a wide range of applications including refrigerant, foaming agents, plastic manufacturing, fire extinguishing agents, solvents for freezing food, cleaners for electronic components fine retardant, solvents, aerosol, propellants, and the production of foamed plastics.

Other ozone depleting substances controlled by Montreal Protocol (discussed in a subsequent chapter) are −

• Halon
• Carbon tetrachloride (CCl4), Methyl chloroform (CH3CCl3)
• Hydrobromofluorocarbons (HBFCs)
• Hydrochlorofluorocarbons (HCFCs)
• Methyl bromide (CH3Br)
• Bromochloromethane (CH2BrCl)

There are serious consequences of ozone depletion. Following are some of the significant consequences of ozone depletion.

• Plants and animals vary in their tolerance of ultraviolet rays. The ultraviolet rays damage DNA (the genetic code in every living being). Crops such as soybean are the worst affected.

• Animals and humans also have adapted to UVB radiation. In case of depletion of the ozone layer, there is danger of melanoma – a type of skin cancer. The disease is now almost epidemic in the United States.