Ozone Layer Depletion (Ozone Hole)

Ozone is a gas (O3) found through out the atmosphere, but most highly concentrated in the stratosphere between 10 and 50 km above sea level, where it is known as the ('ozone layer').

Importance of Ozone Layer :

Without the ozone layer, life on the earth's surface would not be possible. It protects us from damaging ultraviolet radiation of the sun. In particular it filters out UV-B radiation.

Recent evidence has shown the certain parts of the ozone layer are becoming thinner and ozone 'Holes" have developed. The consequence of any thinning of the ozone layer is that more UV - B radiation reaches the earth's surface. UV - B radiation affects DNA molecules, Causing damage to the outer surface of the plants and animals. In humans it causes skin cancer, and eye disease.

Mechanism Of Ozone Layer Depletion (or ) Formation (or) Causes of ozone hole :

In 1970, it was found that the ozone layer was attacked by chlorofluorocarbons (CFCs) which are release into atmosphere by refrigeration units, air conditioning systems, aerosol sprays and cleaning solvents. Chlorofluorocarbons release chlorine which breaks ozone into oxygen.

The following reactions will then occur

CF2CL2 + hv -----------------> Cl + CF2Cl

CF2Cl + O2 ----------------> CF2O + ClO

Cl + O3 -----------------> ClO + O2

ClO + O* --------------------> Cl + O2

Each Chlorine atom is capable of attacking several ozone molecules. So that a long chain process in involved. A 1% loss of ozone results in a 2% increase in UV rays reaching the earths surface.

Ozone Depleting Substances :

The ozone depleting substances essentially consists of chlorine or bromine atoms which are extremely reactive while they are in the free state. The following gases are accumulated in the atmosphere and are found to be instruments in ozone depletion.

1. Chlorofluorocarbon (CFC) :

Sources :

Refrigerants ( freon ) in refrigerators, propellent in aerosol spray cans. blowing agent, foam plastic blowing agent.

2. Hydrochlorofluorocarbon (HCFC) :

Sources :

Refrigerants, blowing agents.

3. Bromofluorocarbons ( BFC ) :

Sources :

Fire Extinguishers

4. Other Chemicals :

Sources :

i) Certain Halogen compounds are potential ozone destroyers up to ten times more powerful than the CFCs.

ii) Sometimes the atmospheric sulphur dioxide is converted into sulphuric acid which greatly increases the rate of ozone depletion.

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