By Srirangam Sriram, Sriram's IAS, New Delhi.
The Ozone layer is a region in the Earth’s stratosphere that absorbs the sun’s ultraviolet rays, shielding the planet from the harmful radiation which can cause skin cancer. In the 1970s, scientists discovered that the ozone layer was being depleted due to man-made activities, thereby leading to a threat to life on Earth.
Ozone layer thickness is expressed in terms of Dobson units. A normal range is 300 to 500 Dobson units. It is called an Ozone hole when the thickness is around 100 dobson units.
Reason for Ozone depletion
- Ozone is depleted by free radicals created by chlorofluorocarbons (CFCs) mainly used in refrigeration.
- The banning of these gases by the Montreal Protocol in 1987 has allowed a reduction in the Antarctic ozone hole.
Polar Stratospheric Cloud
- PSCs form poleward of about 60°S latitude in the altitude range 10 km to 25 km during the winter and early spring.
- PSCs play a central role in the formation of the ozone hole.
- PSCs provide surfaces upon which heterogeneous chemical reactions take place. These reactions lead to the production of free radicals of chlorine which destroys ozone molecules.
- As these clouds are more persistent in the South Pole, we have a larger hole in the Antarctic atmosphere.
- Also, if the polar vortex is stronger, the winter is also longer in the South Pole and stronger polar stratospheric clouds are formed.