Why holes in the ozone layer from only above the poles and not in other areas?

Ozone hole, a drastic depletion of ozone in the atmosphere layer over the Antartic, was noticed by scientists in the early Eighties. The depletion was found to be periodic and far greater than expected from other calculations of the chloro-fluro-carbon effect. So the question arose:
Was this a natural climate variation or was it a chemical decomposition brought about by mankind? In spite of the pioneering research by many researchers, among them Paul Crutzen, Mario Molina and F. Sherwood Rowland who shared the 1995 Nobel prize for chemistry, as well as Susan Solomon and James Anderson of the U.S. the mystery has not been fully understood.
It has been proved beyond doubt that ozone depletion is caused chiefly by ozone reacting chemically with chlorine and bromine from industrially manufactured gases. But, the rapid depletion of ozone over Antarctica could not be explained by transport processes or by gas phase chemical reactions.
According to an information note from The Nobel Foundation of the Royal Swedish Academy, an alternative mechanism must exist which could accelerate the decomposition of ozone. In fact, scientists have identified this mechanism as chemical reactions on the surface of cloud particles in the stratosphere.
Thus, the Antarctic ozone depletion appears to be connected with the extremely low temperatures, which lead to condensation of water and nitric acid to form ‘polar stratospheric’ (PSCs). The ozone-decomposing chemical reactions are greatly reinforced by the presence of these cloud particles. This understanding itself has lead to an exciting new branch of atmospheric chemistry called ‘heterogeneous’ chemical reactions on particle surfaces.