Ozone is formed by the action of sun light on oxygen. It is 20-50 kms above the surface of earth. It is a highly poisonous gas with a strong odour. It causes respiratory ailments like asthma and bronchitis, when it is at ground level. It causes harm to vegetation and leads to a deterioration of certain materials like plastic and rubber. When ozone in the upper atmosphere protects the earth from the sun’s harmful UV radiation, as it absorbs. Chlorofluorocarbons (CFCs) used as refrigerants and aerosol spray propellants are indestructible until they reach stratosphere, where UV radiation breaks them down to release chlorine atoms.
When chlorine atoms react with ozone molecules, it leads to the depletion of ozone layer and releases oxygen molecules which do not absorb UV radiation. The destruction of ozone layer causes increased incidence of skin cancer and cataracts. It also causes damage to certain crops and planktons, thus affecting natural food chains. This decreases in vegetation leads to an increase in carbon dioxide. Use of CFCs was to be banned by the year 2000 to recover ozone layer .
Changes in the ozone layer have serious implications for mankind:
Effects on human health: Sunburn, cataract, aging of the skin and skin cancer are caused by increased UV radiation. It weakens the immune system by suppressing the body’s resistance to certain infections like measles, chicken pox and other viral diseases that elicit rash and parasite diseases such as malaria introduced through the skin.
Food production: UV radiation affects the ability of plants to capture light energy during the process of photosynthesis. This reduces the nutrient content and the growth of plants; this is especially seen in the case of legumes and cabbage.
Plant and animal planktons are damaged by UV radiation. In zooplanktons (microscopic animals), the breeding period is shortened by changes in radiation. As planktons form the basis of the marine food chain, any change in their number and species composition influences fish and shellfish production.
Effect on materials: Increased UV radiation damages paints and fabrics, causing them to fade faster.
Effect on climate: Atmospheric changes induced by pollution contribute to global warming, a phenomenon which is caused due to the increase in concentration of certain gases like carbon dioxide, nitrogen oxides, methane and CFCs. Observations of the earth have shown beyond doubt that atmospheric constituents like water vapour, carbon dioxide, methane, nitrogen oxides and CFCs trap heat in the form of infrared (IR) radiation near the earth’s surface. This is known as the ‘Green house effect’. The phenomenon is similar to what happens in a greenhouse. The glass in a green house allows solar radiation to enter, which is absorbed by the objects inside. These objects radiate heat in the form of terrestrial radiation, which does not pass out through the glass. The heat is , therefore, trapped in the greenhouse increasing the temperature inside and ensuring the luxuriant growth of plants.
With a warmer earth, the polar ice caps will melt causing a rise in ocean levels and flooding of coastal areas.
In countries like Bangladesh or the Maldives this would be catastrophic. If the sea level rises by 3m, the Maldives will disappear completely beneath the waves.
The rise in temperature will bring about a fall in agricultural produce.
Changes in the distribution of solar energy can bring about changes in habitats. A previously productive agricultural area will suffer severe droughts, while rains will fall in locations that were once deserts. This could bring about changes in the species of natural plants, agricultural crops, insects, livestock, and microorganisms.
In the polar regions, temperature rise caused by global warming would have disastrous effects. Vast quantities of methane are trapped beneath the frozen soil of Alaska. When the permafrost melts, the methane that will be released can accelerate the process of global warming.