What Are The Main Causes Of Ozone Depletion?

In addition to increases in the concentrations of greenhouse gases and acidification which have initiated the process of environmental change, human activities have caused changes in the ozone layer in the strato­sphere and increasing concentrations of atmospheric lead.

Acid rain emerged as a concern in the 1960s with observation of dying lakes and forest damage in northern Europe, United States and Canada. Both of these have significant implications for human health as well as for the earth’s ecosystem (Mannion, op. cit.: 171).

The position of ozone in the stratosphere and the processes of its depletion have been shown in.

The presence of ozone in the atmosphere is particularly important because it filters out incoming ultraviolet (UV) radiation and thus acts as a screen against ultraviolet B (UV-B) radiation that can increase the occur­rence of some forms of skin cancer, cataracts and other diseases of eyes.

Image Source: geography.hunter.cuny.edu

The UV-B rays also suppress body defense mechanism which increases vulnerability to a variety of infectious diseases.

The problem of ozone depletion was first identified in 1970s due to the advent of supersonic aircraft which fly in the lower stratosphere and which emit nitrogen oxides. Subsequently, it was established that the major cause of ozone depletion is the freons of CFCs.

These compounds are non-toxic, non-flammable and chemically inert gases. These properties make them useful for a wide range of applications including aerosol propellants, refrigerants, cleansers for electronic components fine retardant, solvents, and in the production of foamed plastics.

The CFC gases do not rapidly degrade and passing through the troposphere they eventually enter into the stratosphere, where they are subject to intense ultraviolet radiation—the same radiation is absorbed by ozone.

Chlorine destroys ozone. In a chain reaction of oxygen destruction, each of the chlorine atoms released can destroy over 10,000 ozone molecules.

It has been estimated that even if the emission of CFC gases in the atmosphere is stopped, the ozone layer will continue to be damaged as these gases have long residence time and their molecules do not dissolve even after hundreds of years.

The first significant data about the depletion of ozone layer was presented by Farman et al. (1985: 207-10), the leader of the British Antarctic Survey, who established that an ozone ‘hole’ has occurred in the stratospheric ozone layer over Antarctica each spring since 1977.

About 90 per cent of Antarctica is covered by the ozone hole which has expanded also over the ocean areas.

For the period 1977-84, the concen­tration of ozone has decreased during the spring by 40 per cent. Subsequently, Kerr (1988: 785-86) reported that ozone layer is being depleted over the Arctic atmosphere.

This is of special significance because ozone depletion in the northern hemisphere which is more densely populated than the southern hemisphere, may lead to major increase in skin cancer and cataract problems.

Why should the ‘hole’ in the ozone layer have first appeared so promi­nently over Antarctica? In most parts of the world, horizontal winds tend to keep chemicals in the air mill mixed.

But circulation patterns are such that the freezing whirlpool of air over the south polar continent in winter is not penetrated by air currents from the warmer earth regions. In the absence of sunlight and atmospheric mixing, the CFCs work to destroy the ozone. During summer, sunlight works to replenish it.

The enhanced greenhouse effect, acidification and ozone depletion are all examples of atmospheric pollution that have occurred mainly after industrialization, urbanization and deforestation. The heavy metals like lead, mercury, zinc, cadmium and arsenic are also creating the serious problems of environmental pollution.

All these heavy metals are harmful to human health. The enhancement of these metals in the atmosphere shows some serious adverse effects on human health. A survey conducted in Boston, USA indicates that children with lower lead dentine concentra­tions performed better than those with higher level of lead (Needleman et al., 1979: 689-95).