Depletion of Ozone Layer (Ozone Hole)

In recent years, a gradual depletion of the protective ozone layer has been reported. Nitric oxide and CFCs are found to be most responsible for this depletion of the ozone layer.

Substances that cause depletion of ozone, or make it thinner, are generally called Ozone Depletion Substances, abbreviated ODS. The loss of ozone molecules in the upper atmosphere is termed depletion of stratospheric ozone. The two main classes of ODS the unit c …

Oxides of nitrogen are introduced directly into the stratosphere by the exhaust gases of supersonic jet aircraft engines. They are also released by the combustion of fossil fuels and nitrogen fertilizers.

Inert nitrous oxide present in the stratosphere is photochemically converted into more reactive nitric oxide. Oxides of nitrogen then catalyse the decomposition of ozone and are themselves regenerated -- so ozone gets depleted in a self-sustaining chain:

$NO_2 + O \rightarrow NO + O_2$ …

The chlorofluoro derivatives of methane and ethane are referred to by the trade name Freons. These chlorofluorocarbon (CFC) compounds are stable, non-toxic, non-corrosive and non-inflammable, easily liquefiable, and are used in refrigerators, air-conditioners, and in the production of plastic foams. CFCs are also present in the exhaust of supersonic aircraft and jumbo jets flying in the upper atmosphere. They slowly pass from the troposphere to the stratosphere, and they stay there for a very long period -- 50 to 100 years.

In the presence of UV radiation, CFCs break up into a chlorine free radical:

$ClO^{\bullet} + O \rightarrow Cl^{\bullet} + O_2$ …