Reduction in ozone levels over the Antarctic has already been reported and the so-called Antarctic hole in ozone layer, which grew to match the area of the United States in 1986, has since expanded to cover the whole Antarctic.
Recently Prof Ernst Augstein (1987) reported that a similar hole is developing over the North Pole. The Arctic hole is at present only about one-fifth the size of the growing Antarctic hole.
The conclusion has been reached by comparison on the basis of many years of measurements in spring time when the ozone layer over the poles reaches its minimum. “This spring time the minimum has fallen 50 per cent in the Antarctic and 2 to 10 per cent in the Arctic, depending on the data,” Prof Augstein (1987) said. Ozone levels sink in winter mainly because of the lack of sunshine.
According to World Meteorological Organization (WMO), the hole in the ozone layer over the Antarctic grew at a record rate in October 1995, reaching 20 million km, or twice the size of Europe. Since the 1960s, the protective ozone layer over the Antarctic has declined by more than 65 per cent.
If the present trend of depletion in ozone layer continues, the earth’s inhabitants would be exposed to more ultraviolet rays, which can cause cancer, cataracts and other diseases. However, scientists still debate as to why the ozone layer is depleting, but according to many of them chlorine molecules from chlorofluorocarbons (CFCs) might be responsible.
CFCs (chlorofluorocarbons e.g., carbon tetrachloride CCI3, dichlorodifluoromethane CCI2F2) are compounds that consist of chlorine, fluorine and carbon. These gases are used as coolants for refrigerators and air conditioners, propellants for aerosol sprays and agents for producing plastic foam. As CFCs do not degrade easily in the lower atmosphere, they rise into the stratosphere where they are broken down by UV-light. In the upper atmosphere, UV-light breaks off a chlorine atom from a CFC molecule.
The chlorine attacks an ozone molecule, breaking it apart. An ordinary oxygen molecule and a molecule of chlorine monoxide (CIO) are formed. A free oxygen atom breaks up the chlorine monoxide and the chlorine is free to repeat the process. Chlorine acts as a catalyst and is unchanged in the process. Consequently, each chlorine atom can destroy as many as 10,000 ozone molecules before it is returned to the troposphere. Farman (1987) has described the following reactions to illustrate how ozone is destroyed.
In a UN sponsored conference held in Vienna in December 1995, a plan has been approved by 110 countries to reduce the use of chemicals that damage the ozone layer. The conference agreed to new commitment to strengthen the 1987 Montreal Protocol on substances that deplete the ozone layer. Under the compromise, industrialized countries will phase out by the year 2010 the pesticide
Methyl bromide, which is the most powerful ozone depleting substance. Hydro fluorocarbons (HFCs), which are less damaging substitute for CFCs are likely to be phased out by industrialized countries by 2020 A.D. India is also switching on to new technology to reduce the use of CFCs and finally phasing out their use in near future.