Ozone

Ozone layer 

 Ozone is an allotropic form of oxygen. Ozone molecule consists of three oxygen atoms joined together by covalent bonds. Ozone is prepared commercially by passing ultraviolet radiation or silent electric current through normal oxygen. Ozone is a faintly blue gas. It has a disagreeable odour. We may detect its odour around electrical equipments and flourescent lights. Ozone is much more reactive than ordinary oxygen. It spontaneously reverts back to diatomic oxygen releasing extra atom of oxygen. These released oxygen atoms are very reactive. They pair to form normal oxygen molecule, but if another substance is present during the reaction, they will react with it.

 uses of Ozone 

 Ozone is used for disinfecting water supplies. Ozone is used to sterilize air in crowded spaces such as underground railway stations and slaughter houses Ozone releases atomic pxyggn so it is used as ajbleaching agent. It bleaches organic dyes. The atmosphere around us is divided into four layers. Troposphere ,Stratosphere ,Mesosphere Thermosphere. Ozone is present in the following two layers. 

Troposphere 

It is the layer very close to earth in which we live. It extends up to twenty kilometers. It contains traces of ozone. 

Stratosphere 

 It is present 20-40 km above the earth. Ozone is present in this layer at height of about 8 kilometers. The concentration of ozone in this layer is_10 parts per million.High energy racfiation coming from the sun convert oxygen in stratosphere to ozone forming a layer of ozone in stratosphere. Ultraviolet radiation present in sunlight are highly damaging for the living tissues of plants and animals. Ozone is very important to us because these harmful ultraviolet radiation are absorbed by this layer before they reached the surface of earth .
Biologists believe that living organisms appeared on land only after the formation of sufficient ozone in the stratosphere about 600 million years ago.Scientista have expressed their concern about tbe Repletion of ozone layer. Increased quantities of chloro fluoro carbons (CCI3F, CCI2F2) being used in aerosol sprays, refrigerators and in air-conditioners, are very stable compounds and remain unchanged in the lower atmosphere. 
When these chloro fluoro carbons are carried by convection currents to the stratosphere they absorb ultraviolet radiation and react with ozone. The chlorine atoms which are used in the second step are regenerated in third step. So chlorine atoms act as catalyst for the decomposition of ozone. 
The aircrafts flew through Antarctic stratosphere (Ozone Hole) measuring the quantity of CIO. Researchers found that where ever ozone is depleted in stratosphere chlorine monoxoide (CIO) appears, as expected if chlorine atoms are catalysing the reaction. The chloro fluoro carbons are the suspected source of these chlorine atoms.