 Here, we are looking at the ozone science, how the ozone is produced and how the ozone is destroyed. In the first step, the oxygen molecules are fertilized or converted by the UV rays that are coming from the sun into two oxygen atoms, nascent oxygen atoms. Oxygen atoms are very, very reactive and they react with another oxygen molecule and form the ozone, O3. Ozone and oxygen atoms are continually being inter-converted as rays breaks the ozone and turns into nascent oxygen and oxygen molecules and the oxygen atom again reacts with the oxygen molecule forms ozone. Our activities which are producing the CFCs and liberating into the atmosphere, they are going and these chlorine atoms are destroying the ozone molecules in addition to the natural process of formation and destruction. That is what is causing the reduction in the concentration of ozone in the stratosphere and when the concentration goes down below certain level like 220 dobson units we call that ozone hole. Ozone hole doesn't mean actually that there is a big hole up there but what it means is that the concentration is below a certain level.