Ozone layer

What is ozone layer?
Ozone layer discovered in 1913 by the French physicists Charles Fabry and Henri Buisson refers to “the Earth’s atmospheric layer having high concentration of ozone (O3) which absorbs 97-99% sun high frequency ultraviolet ray potentially harming the life on the earth.” It is situated in the lower portion of stratosphere at a height of13-20 km above the earth surface and thickness varying seasonally and geographically which contains 90% ozone of earth atmosphere.
ORIGIN OF OZONE
Ozone is an irritating, corrosive, colorless gas with a smell something like burning electrical wiring which can be easily produced by any high-voltage electrical arc (spark plugs, Van de Graaff generators, Tesla coils, arc welders). British meterologist G.M.B.Dobson, who developed a simple spectrophotometer (the Dobsonmeter) that could measure syratospheric ozone from the ground explored its properties Between 1928 and 1958 Dobson established a worldwide network of ozone monitoring stations which continues to operate today. The "Dobson unit", a convenient measure of the columnar density of ozone overhead, is named in his honour.
Formation of ozone layer
Ozone is created naturally in the stratosphere by the combining of atomic oxygen (O) with molecular oxygen (O2) which appears as layer known as Ozone layer. This process is activated by sunlight. Ozone is destroyed naturally by the absorption of ultraviolet radiation,
O + O>>> O2 ( in the presence of UV)
O2 + O>>> O3
O3 + UV >>> O2 + O
and by the collision of ozone with other atmospheric atoms and molecules.
O3 + O >>> 2O2

O3 + O3 >>> 3O2

Ozone layer depletion:
There are certain chemicals which are emitted and are inert in normal chemical and physical reactions but when they get accumulated in greater amounts at high altitudes cause great damage to the protective ozone envolve. These harmful ozone depleting chemicals (CFCs) come from industries of refrigerator, air conditioning, liquid fuel producing plants etc. Ozone layer depletion is the process of destruction or using up of ozone (O3) in the stratosphere by different pollutants making the ozone layer thinner.” Ozone depletion describes two distinct, but related observations: a slow, steady decline of about 4 percent per decade in the total volume of ozone in Earth's stratosphere since the late 1970s and a much larger, but seasonal, decrease in stratospheric ozone over Earth's polar regions during the same period.
Causes of ozone layer depletion:
About 80% of ozone layer depletion is through Chloro Fluro Carbon (CFCs). The CFCs are highly stable and non-reactive substances. Different types of CFCs (CFCl3, CF2Cl2, CF3Cl) are extensively used as coolers, in air conditioners, refrigerators, cleaning solvents and aerosol propellants. They are also released by aircrafts, satellites, industries, nitrogen fertilizer plants and from combustion of fossil fuels. CFCs release their chlorine atoms to form chlorine monoxide, which reacts with ozone to form chlorine again. The free chlorine reacts continuously with ozone depleting the ozone layer.
CF2Cl2 ultra violet radiation CF2Cl + Cl
O3 + Cl O2 + OCl
OCl O + Cl
O3+O 2O2

It has been estimated that 1 molecule of CFCs can destroyed 1 lakh molecule of ozone.