DEVELOPMENT AND SIGNIFICANCE OF THE OZONE HOLE
Compounds known as chlorofluorocarbons (CFCs) were introduced in the 1930s as a safer alternative to toxic ammonia, the chief refrigerant in use before the development of CFCs. Chlorofluorocarbons consist of carbon, fluorine and chlorine atoms and whilst present in the troposphere, they remain virtually intact without decomposing. The compounds linger in the lowest layer of the Earth’s atmosphere for many decades before slowly diffusing into the stratosphere. Here, in the stratosphere, chlorofluorocarbons undergo various chemical processes that cause the separation of chlorine atoms from the main compound. It is these chlorine free radicals which work to destroy stratospheric ozone and have contributed to the development of the ozone hole.
FORMATION OF THE OZONE HOLE
In the presence of high energy ultraviolet radiation (U.V.), CFC molecules decompose, resulting in the release of free chlorine atoms. This process is known as photodissociation.
CCl2F2(g) + U.V. light CClF2(g) + Cl(g)
OZONE DESTRUCTION: The chlorine atom attacks an ozone molecule, resulting in the formation of a chlorine monoxide molecule (ClO) and an ordinary oxygen molecule. The compounds produced due to the destruction of ozone, are not capable of absorbing ultraviolet radiation.
Cl(g) + O3(g) ClO(g) + O2(g)
REGENERATING CHLORINE RADICALS: The chlorine monoxide molecule reacts with a free oxygen atom, producing an oxygen molecule and a chlorine free radical, that is capable of attacking other ozone molecules. Thus, the cycle of ozone depletion continues on. Indeed, as a consequence of the endless cycle, one chlorine atom may destroy thousands of ozone molecules.
ClO(g) + O(g) Cl(g) + O2(g)
In the 1970s, scientists, Paul Crutzen, Mario Molina and Sherwood Rowland, were the first to realise the possible detrimental effects of man-made chemicals (including chlorofluorocarbons) on the ozone layer. They were awarded the Nobel Prize in...