We have been hearing about a hole in the ozone layer. I recently heard the hole is now over Antarctica. If the hole in the ozone layer is due to pollution, shouldn’t it be over Delhi or Ahmedabad or other parts of the world where there is a concentration of pollution?
Mriganka Guha Via e-mail
It is important for you to know that the Ozone hole is not ‘now’ over the Antarctica. The ozone hole appeared first over the colder Antarctic because the ozone-destroying chemical process works best in cold conditions. Let me explain. First thing first. What is the ozone hole?
Here’s how NASA describes it. Each year, for the past few decades, during the Southern Hemisphere spring, chemical reactions involving chlorine and bromine cause ozone in the southern polar region to be destroyed rapidly and severely. This depleted region is known as the “ozone hole”.
The Antarctic continent has colder conditions than the Arctic, which has no land-mass. As the years have gone by, the ozone hole has increased rapidly and is as large as the Antarctica continent. The hole lasts for only two months, but its timing could not be worse. Just as sunlight awakens activity in dormant plants and animals, it also delivers a dose of harmful ultraviolet radiation.
After eight weeks, the hole leaves Antarctica, only to pass over more populated areas, including The Falkland Islands, South Georgia and the tip of South America. This biologically damaging, high-energy radiation can cause skin cancer, injure eyes, harm the immune system, and upset the fragile balance of an entire ecosystem.
The ozone hole is the region over Antarctica with total ozone of 220 Dobson Units or lower. This map shows the ozone hole on October 4, 2004. The data were acquired by the Ozone Monitoring Instrument on NASA’s Aurasatellite. The Dobson Unit is the most common unit for measuring ozone concentration. One Dobson Unit is the number of molecules of ozone that would be required to create a layer of pure ozone 0.01 millimeters thick at a temperature of 0 degrees celsius and a pressure of 1 atmosphere (the air pressure at the surface of the Earth).