Friday, 12 December 2014 04:40








What is ozone?

Ozone is an allotrope of oxygen consisting of three atoms of oxygen bound together in a non-linear fashion. The chemical symbol of ozone is O3. The configuration of the ozone molecule and its chemical properties are such that ozone efficiently absorbs ultraviolet light, thus acting like a sunscreen. In doing so, ozone protects oxygen in the lower altitude from being broken up by the action of ultraviolet light and also keeps most of the ultraviolet radiations from reaching the earth’s surface. It absorbs the most energetic UV-c and UV-b radiation and filters about half of the UV-a radiation. Exposure to these can cause sunburn, lead to cancer and damage eyes. Hence, ozone plays a significant role in protecting the environment even though it constitutes less than one part per million of the gases present in the atmosphere.

Why is it getting depleted?

There are many naturally occurring substances that can destroy ozone. For instance, ozone gets destroyed when it comes in contact with molecules that contain nitrogen, hydrogen, chlorine, bromine and so on. In the stratosphere, oxygen and ozone molecules are continuously converting into each other and a balance is maintained. But because of increasing man-made pollution and the release of gases like CFCs (chlorofluorocarbons) the natural balance is broken and the amount of ozone destroyed is far more higher than the amount naturally formed.

What is ozone hole?

By ’ozone hole’, one does not literally means a hole in the atmosphere of the earth. It implies that there is a significant decrease in the concentration of ozone in a particular region of the atmosphere. The best example of such an ozone hole is the ozonosphere over the Antarctica which has only about 50 per cent of the ozone left that originally occurred there. The density of ozone is measured by Dobson Units. The average amount of ozone in the atmosphere is about 300 Dobson Units. If all this ozone was compressed at zero degrees Celsius at one atmospheric pressure it would form a 3-mm thick layer around the earth. The areas where the concentration drops to an average of about 100 Dobson Units are known as “Ozone Hole Areas”.

What are the factors that accelerate ozone depletion?

The main factors responsible for ozone depletion are generally by-products or emissions from industries. The main sources are: Chlorofluorocarbons (CFCs); These molecules are made up of chlorine, fluorine and carbon. Some of the common CFCs and their commercial names are given below

• Dichlorodifluoro methane (Freon 12)

• Trichlorofluoro methane (Freon 11)

• Chlorodifluoro methane (Freon 22)

• Dichlorotetrafluoro ethane (Freon 114)

• Trichlorotrifluoro ethane (Freon 113)

The CFCs enter the atmosphere by gradual evaporation. In the Stratosphere, they are exposed to UV radiations. This causes breaking up of CFC, thus freeing chlorine atoms. A free chlorine atom reacts with an ozone molecule (O3), forming an oxygen molecule (O2) and a molecule of chlorine monoxide (CIO). The molecules of chlorine monoxide further react with an atom of oxygen. Thus cycle of ozone depletion starts.

What initiatives are taken to check the depletion?

The Vienna Convention for the protection of the ozone layer was established in 1985, under the United Nations Environment Programme (UNEP). The convention was held for the promotion of exchange of information, research and systematic observations to protect the human environment and health.

The first major global initiative to restrict CFCs was taken under the Montreal Protocol signed in 1987. The protocol requires the control of nearly 100 chemicals under a time limit.For instance, hydrochlorofluorocarbons (HCFCs) are to be phased out by 2030 in the developed world and 2040 in the developing world. By these initiatives the depletion which had stretched up to an area of 26 million square km square in 1998 was reduced to 22 million square km in 2009. Initially it was anticipated that these initiatives would lead to complete recovery of the ozone layer by 2050, but recent studies suggest that it might take much longer.