Air pollution may be defined as ‘the presence of materials in the air in such a concentration, which are harmful to man and the environment’. In other words ‘the occurrence or addition of foreign particles, gases and other pollutants into the air, which have an adverse effect on human beings, animals, vegetation, buildings and other objects is called air pollution’.
Atmospheric pollution is complex in origin and varied in effect. It may be natural or man made. Natural air pollution has been occurring before the man came on the scene. Volcanic eruptions, forest fires, natural organic and inorganic decays let out large quantities of harmful dust and gases. It is estimated that out of the total annual emission of 1 x 10 tonnes entering the earth’s atmosphere only 5 x .10 tonnes (0.05 per cent) is contributed by human activities. Air pollutants resulting from human activities are mainly discharged in over populated cities and industrial centres. This pollution may be marginal in global terms, but it has serious effect locally. Many pollutants do not rise above 600 meter of earth’s surface or at least become highly diluted. The movement of the air pollutants is restricted due to certain physical barriers. This leads to high concentration of the pollutants in certain areas.
Causes of Air Pollution
Important causes of air pollution are power and heat generating system, producing large quantity of waste gases, use of insecticides and fungicides etc. Some of them are as follows
1. Exhaust gases : Exhaust gases are the products of fuel combustion which come out with the smoke from the chimneys of factories and from automobiles. These invisible exhaust gases contain gases like carbon monoxide, sulphur di-oxide, hydrogen fluoride, hydrogen sulfide, nitrogen and heavy metals, such as copper, zinc, lead and cadmium, etc. These heavy metals and gases are injurious to all the livings. Motor vehicles alone contribute about 60% of air pollution, carbon monoxide causes difficulty in breathing, caused irritation in mucous memberanes, combines with blood haemoglobin reducing its oxygen carrying capacity and causes asphyxiation. High concentration of it may cause even death of man.
Another fatal hydrocarbon released due to incomplete combustion of petrol is 3-4 benzyprene which is responsible for causing lung cancer. Similarly exides of nitrogen may cause irritation in eyes and nose, and may cause acute respiratory diseases such as asthma and lung cancer.
2. Smoke and Grit : Smoke is the visible product of incomplete combustion and is accompanied with other gases, formed during combustion. It is responsible for 10-15% atmospheric pollution. The smoke and grit coming out from the domestic hearths and factories also cause considerable harm to life. One of the most harmful effects of smoke is the smog formation which makes fog heavier and darker by it. Hydrocarbons and nitrogen oxides when presence of UV-radiation in sunlight. This is turn causes photochemical smog which is responsible for causing eye-watering, and respiratory distress in human beings. It is toxic to plants also. This smog blocks reaction of photosynthesis.
(3) Radio-active substance: Radio-active elements are emitted as byproduct of atomic explosions, testing nuclear explosions, etc. Such elements emit high energy radiations : the ionizing radiations which remove electrons from stable atoms. Some of them have very long half life period; (i.e. Calcium- 45-160 days: Strontium 90 and Cesium : 137 days) and are most toxic isotopes to man and other animals.
(4) Insecticides : The excessive use of insecticides has caused grave pollution problems. The pesticides like aldrin, lindane chlorodane diendrin, DDT, toxaphene, etc. are commonly used for destroying pests and insects from agriculture crop. Though they have enormously increased our agricultural production, their unplanned and extensive use have caused grave pollution problems. Similarly some of them enter in the environment as spray dusts of the chlorinated hydrocarbons (such as DDT), polychlorinated biphenyls etc. are most dangerous.
Insecticides also kill several useful aquatic food organisms when sprayed on water bodies. It destroyed their larvae and also decreases the photosynthetic power of marine phytoplankton.
(5) Herbicides: Herbicides are used for clearing the railroad and highway weeds, weed control in agriculture and forest management. However their continuous use is causing hazards in our life. Some of them, as monuron and simazin etc. affect photosynthetic activity of plants, 2-4, D and 2, 4, 5 T cause cell proliferation in phloem and finally causes blockage of food passage. From plants, these herbicides enter into animals and cause skin disease, constriction of stomach muscle etc. Hence, they affect both producers and consumers.
Effects of Air Pollution
Our health depends on the quality of air we breathe in our immediate environment. Foul air had been held responsible for various health hazards and diseases. Air borne spores, pollen grains, bacteria, fungi, fur, hair etc. cause various allergic reactions, bronchial asthema, tubeculosis and other infections. With rapid increase in industries and vehicular traffic, the air of Indian cities is becoming increasingly polluted. The data regarding the quality of air over selected Indian cities.
(A) Effects on Vegetation
Air pollution causes wide spread damage to plants.
(i) Dust, smoke and other particulate matter reduce sunlight and settle on the leaves of plants, thereby retard photosynthesis.
(ii) Sulphur dioxide causes chlorosis, plasmelysis, membrane damage and metabolic inhibition. The leaves often assume water soaked appearance. Fruit trees and cereal crops are more sensitive to oxides of sulphur. Therefore they suffer a great loss in the areas around smelters and industrial belts.
(iii) Fluorides destroy tissues in leaves causing necrosis of leaf margins and tips.
(iv) The photochemical smog leads to the bleaching and blazing of foliage.
(v) Hydrocarbons such as ethylene cause premature leaf fall, fruit
drop, shedding of floral buds, curling of petals and discolouration of sepals.
(vi) Ozone damage chiorenchyma and thus destruct the foliage in large
number of plants.
(vii) Lichens are very sensitive to air pollution. Their growth is inhibited in polluted air.
The death of lichens in an area is an indicator of air pollution.
(B) Effect on Animals
Air pollution causes large scale damage to live stock. The general effects of air pollution on domestic animals in or around industrial area are similar to those on human beings.
(i) Ingestion of fluorine compounds deposited from the air on fodder causes fluorosis (excessive calcification of bones and teeth). It also results in lameness, frequent diarrhoea and loss of weight.
(ii) Several air borne microbes cause diseases.
(C) Deterioration of Materials
(i) Oxides of sulphur and nitrogen and products of photochernical
smog have deteriorating effect on buildings, metals, textiles and marble.
(ii) Acid rains produced by oxides of sulphur and nitrogen have
corrosive effect on the buildings and other materials.
(iii) Large number of historical buildings are damaged by acid rains and other air pollutants. It is feared that the famous marble monument Taj Mahal at Agra is under acute danger of air pollution. Many industrial units have been shifted to save the precious monument.
(iv) Hydrogen sulphide discolour silver and lead paints.
(v) Ozone has deteriorating effects on rubber goods.
(D) Aesthetic Loss
Air pollution has strong bearing on the aesthetic side of human life.
(i) A clear and transparent atmosphere is not only aesthetically pleasing but is necessary for clear vision. A dust haze or hanging smoke blurs our views.
(ii) Foul odour emitted by industries, automobiles, dirty drains and garbage heaps make urban life unpleasant.
(iii) Coal dust and their materials discharged from the industries settle down on the floor and other objects of houses and give dirty look.
(E) Effect on Climate
Earth’s climate depends on various factors including composition of atmosphere and balance of gases. Therefore, air pollution may bring about harmful effect on the climate.
(i) Heat produced by the industrial plants raises the temperature of the area.
(ii) Carbon dioxide content of the atmosphere is increasing due to destruction of forests and excessive burning of fossil fuels and is likely to be doubled by 2020. It will lead to rise in global temperature by more than two or three degree due to green house effect. A rise in global temperature may result in melting of glaciers and polar ice caps, flooding of low lying coastal plants and• submersion of islands. Rainfall pattern may also change, thus affecting agricultural output.
(iii) Aerosols and nitrogen oxides deplete ozone layer in the stratosphere, which permit most of the harmful ultraviolet radiations to reach the earth.
Control Measures of Air Pollution
1. It is easier to control air pollution from the point of sources e.g. factory chimney, etc. Air pollution can also be removed by observing the certain principles. ft needs modification and improvement in some of our air pollution causing industrial processes. Pollution control equipments for monitoring the air pollution are available in market and can be installed in factories. It would minimizes the pollution to some extent.
2. Sulphur-dioxide gas which is highly injurious for human health, its pollution can be controlled in two ways, one by removing sulphur after burning, or secondly by clesulphurization of fuel before its use. Our conventional energy fuels are how being replaced by non-conventional area such as electricity and natural gases which do not produce sulphur gas. The non-combustive modes of energy production such as, tidal power, geothermal power, solar power etc. have replaced the old systems which emitted in production of large quantity of sulphur gases: By cleaning up of combustion also, we can reduce air pollution. Nuclear power which has been looked upon as an alternate to conventional energy producing device, however, produces some thermal pollution.
3. Emission from motor vehicle may be limited by cleaning the exhaust gases after combustion by using some catalyst. Introduction of efficient motor engines which could burn the fuel completely will also reduce this pollution.
4. Use of tall chimneys which will release the waste gases at a much
higher level can also reduce the pollution.