Why there is a reduction in the ozone layer in the Antarctic region?

It's because of the polar vortex. The polar vortex exists near the Antartic and is caused by the very cool air around this area sucking the warm air from the warmer regions of the globe. This forms a vortex allowing gases normally limited to lower parts of the atmosphere to travel very high. As it does this it sucks various pollutants with it including, methane and cfcs which both attack ozone, effectively destroying it. Man is the greatest factor affecting ozone depletion, methane is a by product of agriculture as well as deforestation and many other man made processes. CFCs (chlorofluorocarbons) were, until recently, used heavily in aerosols as propellant and also in fridges to stabilise the air coolant systems. The release of cfcs through aerosol use and decay of old fridges is thought to have had a large inpact on the destruction of ozone, which is why their use was completely ybanned about 10 years ago.