According to meteorological researches the atmosphere is divided into five thermal zones- the troposphere- 10 km above the sea level; stratosphere 10 to 40 km; mesosphere 40 to 70 km; ionosphere 70 to 400 km; and exosphere above 400 km.
Ozone Depletion - Effects of CFCs
Stratosphere contains negligible amount of water vapor and dust. Strong jet streams blow in this layer which affects the weather of the earth. For convenience this layer may be divided into two parts called stratospheric layer and ozonosphere. Stratospheric layer exists only up to 25 km height and its temperature remains almost constant. Ozonosphere contains ozone and it exists between 25 km to 40 km. ozone is essential to life on earth because it acts as a safety shield for the earth. Ozone forms a hot layer by absorbing about 90% of short ultraviolet rays of sun which are harmful for the life on earth.
In nature ozone is formed from oxygen by ultraviolet radiations of the sun. These two gases remain in equilibrium or balanced condition. But recently oxygen-ozone balance has been upset by the excessive presence of chemical pollutants in the atmosphere. Scientists believe that ozone layer is becoming this over Antarctica.
Man made chemicals especially chlorofluorocarbons adversely affect the ozonosphere. Freon gas is also a chlorofluorocarbon which is used in refrigerators. These chemicals are also used in air-conditions, aerosol spray and plastic foams. Free chlorine atoms of these compounds have disturbed the ozone equilibrium. Ozone depletion will cause dreadful disease like skin cancer and skin allergies. It may also have hazardous effect on plants and other animals. To save our earth we have to discover substitutes for chlorofluorocarbons which do not cause ozone depletion in atmosphere. Reference: Children’s Science Library by A.H.Hashmi.