What is the role played by the ozone layer in the atmosphere? Why is the ozone layer depleting?

 The ozone layer essentially allows life to exist, by screens all living beings on Earth from the harmful ultraviolet (UV) rays emitted by the sun.

The ozone layer can be depleted by free radical catalysts, including nitric oxide (NO), nitrous oxide (N2O), hydroxyl (OH), atomic chlorine (Cl), and atomic bromine (Br). While there are natural sources for all of the species, the concentrations of chlorine and bromine increased markedly in recent decades because of the release of large quantities of man-made organo-halogen compounds, especially chlorofluorocarbons (CFCs) and bromofluorocarbons. These highly stable compounds are capable of surviving the rise to the stratosphere, where Chlorine and Bromine radicals are liberated by the action of ultraviolet light. Each radical is then free to initiate and catalyse a chain reaction capable of breaking down over 100,000 ozone molecules.