To understand pollution of air, some knowledge of the atmosphere is required. Atmosphere is a layer consisting of a few gases surrounding the planet earth and is vital for the survival of life on earth. The atmosphere protects earth from abrupt temperature fluctuations from the powerful ultra violet radiation coming from the sun. The atmosphere is made up of nitrogen 78%,oxygen 21%,argon 0.9%,carbon dioxideo0.03% and small amount of trace gases ,helium ,neon, krypton, xenon, hydrogen and ozone. In addition, there is some amount of water vapour. The atmosphere exists in layer called troposphere,stratosphere,ionoshhere and exosphere in that order from the surface of earth. The atmosphere is not static and is moving constantly with respect to earth surface,both horizontally and vertically.
CAUSES OF AIR POLLUTION
More than two centuries back,the composition of gases in the atmosphere were in balance and any small disturbance in the composition within in natural dispersion capacity of the atmosphere was not perceptible. But the beginning of industrilisation saw emission of smoke and sulphurous gases due to burning of coal.As the industry has rapidly grown,the energy supply by burning coal and oil has increased;consequently the emission of gases into atmosphere has enhanced. Besides,the transport system running on petroleum prouducts release these gases into the atmosphere;and the cumulative effect is that the atmosphere composition is severeil disturbed which is referred as 'air pollution'. This type of pollution is due to outdoor sources, but there is indoor air pollution also, arising from burning of coal, wood,animal dung and crop residues used from heating purposes.
This colourless gas is released by automobiles due to inefficient combustion of cabon fuels. This is a poisonous gas, released during mining operations.
This is also released during combustion of fossil fuels by automobiles and industry. This is a predominant greenhouse gas whose concentration in the atmosphere has been increasing with the rapid industrial growth. The annual growth rate of 0.8ppm during 1960 has increased to 1.5ppm during 1990s. industrial countries contribute nearly 60 percent of the world total emission of carbon dioxide. Its life time in the atmosphere is around 100 years and hence its effect in the atmosphere will be experienced for long periods.
There are six known nitrogen oxides; of them, nitric oxide and nitrogen dioxide are pollutants. These are released during burning(combustion) of fossil fuels by industries and automobiles. Though automobiles are the main contributor of this gases, they are also released during acid manufacturing, the decay of agricultural waste and of wood.
This is produced during the combustion of coal or fuel oil. It is a suffocating gas and poisonous. The therminal power plants which use coal as fuel release most of sulphur dioxide into the atmosphere.
This is observed as a suspension in air, mostly consisting of dust, ash and smoke which are chemically stable. These pollutants are dispersed in the atmosphere and diffused by air currents; but their composition remain unaltered. Burning of coal in the power and steel plants are the main sources of particulates, though autobiles and amelters also contribute.
These are organic gases composed of carbon and hydrogen. Insufficient combustion of fuels produce these gases. They react with nitrogen oxide through photochemical reation in the presence of sunlight and produce ‘smog’. Smog is noticed mostly in cities as brown cloud hanging in air.
Smog contains ozone. In the lower atmosphere ie.,trophosphere, it acts like a poison and pollutes air. But in stratosphere, ozone exists in minute traces and filters ultra violet radiation coming from the sun which is harmful to life on earth. Ozone is prodced as follows: SO2 or NO2 in the atmosphere break in the presence of sunlight and the atomic oxygen is released. This atomic oxygen combines with an oxygen molecule to form ozone. Chlorofluorocarbons (CFCs) which are used in refrigeration and foam industries react with ozone in the stratosphere and destruct and deplete it. The depletion of ozone layer allows the harmful UV radiation present in sunlight to reach earth.
In the addition to these major pollutants, a few more hydrogen sulphide, fluorides, chlorinated hydrocarbons, lead, organiccompounds and few others are released by petroleum refineries, metallurgical plants, solvent extraction units, crop spraying for pest control and others. Aerosols which include smoke, smog, fog, dust , fumes, and heavy metals- lead, copper, mercury, arsenic are also dangerous pollutants. Around 1.3billion people living in different continents live in polluted environment. As per WHO report 4 million people die of Air Pollution.
EFFECTS OF AIRPOLLUTION
Polluted air poses health hazards. Air pollutants enter the body through respiratory system. The routine health effects are irritation of eyes, nose and throat, nausea and respiratory problems. More exposure contributes to hesrt and lung dieseases, cancer, genetic defects and mental retardation. Carbon monoxide and hydrogen sulphide which are suffocating pollutants affect haemoglobin and respiratory system: sulphur oxide and nitrogen oxide irritate lungs and effect lining of respiratory tract: ozone irritates eyes and nose smog causes sight and respiratory problems : and particulates depending on the type and concentration may cause cough and difficulty to breath and in long term may develop bronchitis and lung caner. The toxic pollutants , lead , realesed by vehicles which use “leaded petrol” affects gastro-intestinal tract and weaken the functioning of kidneys and liver. While 2.5 billon people suffer from high levels of indoor pollution, more than 1.1 billion people suffer from outdoor pollution annually. Air pollution can even cause death and an estimated 2.7 to 3.0 million people die every year due to air pollution. According to UNDP Report (1998), in India,slightky more than half a million people die from indoor pollution and around 84 thousand from outdoor pollution every year.
Air pollution reduces food production because photosynthesis mechanism is weakened by high levels of air pollution. Pumpkins,cotton, wheat and apples are very sensitive to sulphur dioxide: tomatoes, potatoes, beans and tobacco are sensitive to ozone: apricots tulips and pine to fluorides and so on, The long term effect of air pollution is change in global climate in terms of global warming with very serious consequences. This aspect is detailed elsewhere in the book. In India, lack of pollution controls expose people to risk from outdoor pollution. NewDelhi, Mumbai and Kolkata are the three major densely populated cities where levels of sulphur dioxide, suspended particulate matter and lead are very high in the atmosphere due to heavy vehicular traffic and growing urbanization. In NewDelhi , a pall of pollution from trucks and cars and form uncontrolled industrial emissions cover s the city. The vehicular exhausts are not only determental to health but results in smog which reduces visibility.
According to WHO, about 700 thousand death could be avoided in developing countries, if three major air pollutants- carbon monoxide, suspended particules and lead were brought down to suffer levels. Air pollution brings in Acid rain and produces thick smog because of peroxyocyl compounds. Air pollution affects trees, causes depletion in itchness, inhibit growth of Fungi, beetles, molluses ,spiders,etc,
The minimum standards of environmental quality and the permissible levels of pollutants in theatmosphere should be made know by displaying in industrial areas and at important public places in the cities. In general, dilution is the solution. Particulate removal, removal of poisonous gases and clean air legislation may help in the control of Air Pollution. The following measures are needed to control air pollution in industrial centers: a)The emission rates should be restricted to permissible levels by each and every industry. b)Incorporation of air pollution control equipment in the design of the plant layout must be made mandatory , and c)Continuous monitoring of the atmosphere for the pollutants should be carried out to know the emission levels.
Airpollution can be reduced by adopting all or one of the following approaches: a)To ensure sufficient supply of oxygen to the combustion chamber amddequate temperature so that the combustion is complete, eliminating much of the smoke consisting of partly burnt ashes and dust or b)To use mechanical devices such as scrubbers, cyclones, bag houses and electro-static precipitators to collect particulars from combustion and dusts from manufacturing processes or c)Chemical treatment to deal with factory fumes.
The disposal of the collected air pollutants is equally important for successful control of air pollution. Everycountry has its legal framework and regulatory authorities to implement the control measures. These provisions have to be strictly implemented.