WELL....HERE'S DE REASON....
firstly let us find out de surface chemistry takin place xactly in the formation and depletion of ozone..
Ozone depletion describes two distinct, but related observations: a slow, steady decline of about 4% per decade in the total volume of ozone in Earth's stratosphere (the ozone layer) since the late 1970s, and a much larger, but seasonal, decrease in stratospheric ozone over Earth's polar regions during the same period. The latter phenomenon is commonly referred to as the ozone hole. In addition to this well-known stratospheric ozone depletion, there are also tropospheric ozone depletion events, which occur near the surface in polar regions during spring.
The detailed mechanism by which the polar ozone holes form is different from that for the mid-latitude thinning, but the most important process in both trends is catalytic destruction of ozone by atomic chlorine and bromine.[1] The main source of these halogen atoms in the stratosphere is photodissociation of chlorofluorocarbon (CFC) compounds, commonly called freons, and of bromofluorocarbon compounds known as halons. These compounds are transported into the stratosphere after being emitted at the surface.[2] Both ozone depletion mechanisms strengthened as emissions of CFCs and halons increased.
Image of the largest Antarctic ozone hole ever recorded (September 2006).
In the figure above,the purple n blue coloured portion refers to region where dere is least amount of ozone which result in large amount of UV rays to transpire through de region...
green,yellow n red portions refer to regions where dere is more ozone,diz does'nt allow ozone transpires through de region...
The ozone hole of 2006 is the most severe ozone hole (ozone hole was the largest ever observed,11.4 million square miles (29.5 million square kilometres)) observed to date. NASA's Aura satellite observed a low value of 85 Dobson Units (DU) on Oct. 8 in a region over the East Antarctic ice sheet. Dobson Units are a measure of ozone amounts above a fixed point in the atmosphere.
NOW...
for understandin de surface chemistry in de formation n depletion of ozone it is neccessary to understand de layers different layers of earth's surface,namely
1)Troposphere
2)Stratosphere and
3)Ionosphere or Mesosphere.
