Ozone depletion in the stratosphere of our atmosphere is now–a–days causing world-wide concern. It has been a hot topic of discussion along with global warming from environmental point of view.

Ozone is a molecule consisting of three atoms of oxygen. This gas is naturally present in the troposphere and stratosphere of our atmosphere. Troposphere is from the surface of the earth up to about 10 to 16 km. Stratosphere is from top of troposphere to about 50 km.

About 10% of the atmospheric ozone is in the troposphere and 90% of it is in the stratosphere. The large amount of ozone in the stratosphere lies in a thin layer. It is called the ‘Ozone layer’. It was discovered in 1913 by the French physicists Charles Fabry and Henry Buisson.

Ozone is formed in the atmosphere in multi–step chemical processes with the aid of sunlight. In the stratosphere, ozone molecule breaks into atoms by ultraviolet radiation from the Sun. In the troposphere, ozone is formed in a different set of chemical reactions involving hydrocarbons and nitrogen–containing gases.

Ozone in lower atmosphere (troposphere) is regarded as ‘Bad Ozone’. It is harmful to humans, plant and animal life. Long term exposure to ozone may cause death from respiratory illness. It may also cause asthma, bronchitis, heart attack and other cardiopulmonary problems. It is also a greenhouse gas causing global warming.

But the ozone in the stratosphere is ‘Good Ozone’. It absorbs most of the ultraviolet radiation coming from the Sun and so the animal and plant life on the earth are not affected by the biologically harmful ultraviolet radiation. Ultraviolet radiation can cause skin and eye diseases on human.

After industrial revolution the ozone layer is depleting, which is causing concerns. This is due to emission of ozone-depleting gases containing chlorine and bromine to the atmosphere. The gases are chlorofluorocarbon (CFC),           hydro chlorofluorocarbon (HCFC), carbon tetrachloride (CTC), halons etc. CFC and HCFC were once used in almost all refrigerators and air conditioners and CTC  is used as a solvent process in the metal cleaning and textile industries. After reaching the stratosphere, these gases are broken apart to release chlorine atoms. Chlorine atoms react with ozone to form chlorine monoxide and oxygen, thus depleting the ozone layer. Similarly halons were used in fire extinguishers and they are broken apart to release bromine atoms which react with ozone.

Due to release of ozone–depleting gases to the atmosphere, the ozone layer has been depleted gradually since 1980 and now is about an average of 3% lower over the globe. The depletion is very small near the equator and increases towards the poles. It is severe over the Antarctica. The severe depletion of the Antarctic ozone layer, known as the ‘Ozone hole’, occurs because of the special weather conditions that exist there.

To prevent further depletion of the ozone layer, scientists, environmentalists and statesmen from different countries discussed at a conference in 1987 at Montreal in Canada. An agreement known as the ‘Montreal Protocol on Substances that Deplete the Ozone Layer’ was signed to regulate the production of ozone-depleting gases. The Protocol has now been ratified by 191 countries. It legally binds on national production and consumption of ozone-depleting gases. Production and consumption of all principal ozone–depleting gases will be significantly reduced or phased out before the middle of this century.

In our country, we are still using CFC-13 for refrigeration, HCFC–22 for air conditioners and CTC  as solvent. Halons, which were earlier used in fire extinguishers, are no more used. But these continue to be used in the defence sector, which is exempted  from the Montreal Protocol.

To make awareness among people about depletion of the ozone layer and its harmful effects on the Earth, September 16 is observed as ‘World Ozone Day’ throughout the world. It was on this day in 1987 that the Montreal Protocol was signed. The date has been designated by the United Nations General Assembly in 1994.