In Layman’s language “these are the patches of the sky marked by extremely low concentration of ozone.” Ozone Holes have been observed over Antarctica since 1970 in August
Mid September during these months, energized by the first faint rays of sunlight CI Chemistry destroys the ozone layer clouds of Polar Regions arc formed by the condensation of nitric acid hydrates and water of extremely cold temperature in the winter polar vortex. Stratospheric aerosol is served as nuclei for the development of PSCs (Pollar Stratospheric Clouds).
These contain ice particles which provide surface over which chlorine and other chemicals adhere, enabling them to attack ozone.
CFCs are the dominant source of chlorine in the atmosphere. Chlorofluoro methane is used as a refrigerant and aerosol, spray as a propellant. They are inert in the atmosphere but slowly diffuse into the stratosphere where they are subjected to ultraviolet radiation at about 200 nm generating CI free radical. CI immediately reacts with 03
In the first step chlorine atoms are knocked off the CFC molecules by ultraviolet radiation. The highly reactive free chlorine atoms then attack ozone, breaking it down into an oxygen molecule and forming a substance called chlorine monoxide. This chlorine monoxide through (further catalytic chain reactions releases more free chlorine atoms, which break down more zone, and the chain continues. So efficient is the chlorine atom as an ozone destroyer that a single atom is enough to break down as many as 100,000 molecules of ozone before it drifts down into lower atmosphere and is washed away.
The detection of the “Ozone hole” over Antarctica in 1985 attracted the attention of scientific community in the world. The U.S. immediately banned the use of CFCs in spray cans. Further in the year 1987, twenty-four nations of the world signed the Montreal Protocol, which aims at 35 percentages annually; efforts to produce chlorine-free substitutes have also started.