The atmosphere is a mixture of gases, predominantly nitrogen (78.09%), oxygen (20.94%) and some other gases (less than 1%). Table 13.5 gives composition of unpolluted atmosphere. These values remain constant up to 50,000 feet altitude.
Water vapour which is present in the range of 1-3% is an important constituent of atmosphere. The other minor constituents of atmosphere may be dust particles, smoke, H2S, hydrocarbons, bacteria, spores of plants. The atmosphere is said to be polluted if the concentration of any constituent increases or decreases drastically to cause harmful effects on human health or his environment. The addition of foreign materials into the atmosphere may also cause pollution.
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The air pollution may be defined as qualitative and quantitative changes in the atmospheric constituents due to addition or contamination of such substances as may be harmful to man and his environment. Air pollution may be categorized into indoor and outdoor pollutions. Pollution of atmosphere inside buildings, offices and residences is called indoor air pollution and the atmospheric pollution in the open space is referred to as outdoor air pollution. The different indoor and outdoor air pollutants and their sources are listed in the following Table 13.6.
Air forms nearly 80% of man’s daily intake by weight. A normal man breaths nearly 2200 times a day inhaling about 16 kg air. The problem of air pollution is not new. Primitive man too introduced foreign substances into the air by way of burning and other activities. Modem man has accelerated the process of pollution to an alarming rate.
Many of the long known effects of air pollution are reduction of sunshine, morbidity, mortality from respiratory ailments, dust fall, corrosion of metal and so on. Extensive experimental and epidemiological studies carried out in 20th century, especially during the last two decades have verified these scientifically.
Although the adverse effects of air pollution are well known, our existence in a pollution free environment is still far beyond our reach. India’s main problem of atmospheric pollution is due to unplanned and disproportionate industrialization and unrestricted urbanization. About 80% of the industries are concentrated in 10 or 12 big cities.
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In India, air pollution is caused mostly by automobiles, power plants and oil refineries. The vehicles on the road and oil refinery plants emit several types of atmospheric pollutants such as carbon monoxide, nitrogen oxides, smoke, organic vapour and hydrocarbons as is clear from the following Table 13.7.
Causes of Air Pollution:
Atmospheric pollution is increasing due to the following major factors:
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1. Over population and increasing urbanization.
2. Increasing traffic
3. Industrialization and energy consumption.
1. Over population and Urbanization:
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According to current estimates, the world population is increasing at an average by two per cent annually which means the addition of about one million people every five days or five people every couple of seconds. In India population has already crossed 103 crores (1.03 billion). Increase in population would demand more food, water and land, the three items that are limited on the earth. The increasing population has led man to exploit the natural resources, especially land and water to support life. This has resulted in disturbance in ecological balance, disruption of natural bio-geochemical cycles and fast depletion of natural resources.
Technological advances in fanning practices, use of high yielding cultivars, increased application of chemical fertilizers and pesticides have made it possible to boost agricultural production. Pesticides are being used at the rate of 570 gms/acre/year and are on further increase in India. These pesticides have become contaminants of air, water and food.
Growing population has created problems of employment. This leads people to move from villages to urban areas in search of employment, comfort and facilities. As a result, the cities are expanding in area and are being thickly populated. About 40% of the population in India is concentrated in the states of Bihar, Uttar Pradesh, Haryana, Punjab and West Bengal. Thickly populated areas face a variety of problems such as congestion, large number of vehicles, accumulation of solid and liquid wastes, poor sanitation and management problems.
Particulate matter in city atmosphere comes from cooking fire, industrial activities, automobile exhausts and dirt arising from general transportation. Accumulation of particulate matter in air may eventually cause some changes in climatic patterns of the city.
The disposal of urban sewage and household wastes into the body of water makes that dirty and contaminated. In India about 50 billion litres of waste water from domestic and municipal sources are released into the body of water daily. This is the potent cause of pollution of water.
2. Increasing Traffic:
Rapid increase in the number of automobiles is one of the potential factors responsible for air pollution in urban areas. The vehicles on road are mobile sources of air pollution. During the last two decades, there has been a tremendous increase in the number of vehicles. The number of vehicles per 1000 populations was 3 in 1972-73 and 25 in 1990-91.
According to a report of Ministry of Surface Transport, 1996 the number of vehicles increased from 0.3 million in 1951 to 30.3 million in 1995. Out of the total vehicles, 32% were confined to 23 metropolitan cities. Data further indicated that Delhi registered highest increase in the number of vehicles which was followed by Chennai, Hyderabad, Bangalore, Mumbai.
With the rapid increase in the number of vehicles, the emission of different pollutants has also increased considerably. According to a report of the Ministry of Environment and Forest (1995), the vehicles in major metropolitan cities of India release up to 43% CO, 20% Hydrocarbons (HC), 30-40% NOx, 5% suspended particulate matter (SPM) and 2% SO2. The amount of these pollutants is highest in Delhi, followed by Mumbai, Bangalore, Calcutta and Ahmedabad.
The daily pollution load emitted by automobiles in 12 big cities of India is presented in the following Table 13.8:
The total estimated pollution load from transport sector increased from 0.15 million tonnes in 1947 to 10.3 million tonnes in 1997. In 1997, emission of CO was highest which was 43%. The total emission of NOx was 30% and those of Hydrocarbons (HC) 20%, SPM 5% and SO2 2% (Table 13.9). The emission of pollutants depends on the type of vehicle, engine design and type of gasoline diesel used. Leaded petrol is the main source of toxic lead in atmosphere. Keeping this fact in view, recently a worldwide drive has been initiated to supply lead-free gasoline for vehicles.
Combustion of fuel in aircraft engines produces hydrocarbons, nitrogen oxides, carbon monoxide, small amount of particulate matter, and sulphur oxides. Amounts of pollutants depend upon the fuel used, type of aircraft engine. The various pollutants released into the atmosphere during the take-off and landing of aircrafts are listed in the following Table 13.10.
Table 13.10. Emission from aircraft below 1000 metre altitude in kgs per flight (Landing +Take off):
3. Industrial Growth and Energy Consumption:
Industries, thermal power plants and oil refineries are the other important sectors which are major sources for air pollution in the country. Industries are producing a variety of toxic substances. Thermal power plants and oil refineries are releasing tremendous amount of fly ash and many toxic gases into the atmosphere. Domestic burning, agricultural refuse, firewood and dry dung burning are also contributing considerable amounts of pollutants to atmosphere.
According to an estimate of World Bank, the major air pollution is contributed by a few industrial sectors. In India, petroleum refineries, textile mills, pulp and paper industries and chemical industries produce 87% of the atmospheric pollutants.
Common air pollutants and their effects:
There are two major factors which contribute to the problem of air pollution increasing human population and increased productivity each increasing by about 2 to 3% every year. The United States alone discharges roughly 125 million tonnes of junk into the atmosphere each year and a conservative estimate for the whole world would be about 520 million tonnes every year. The pollutants of atmosphere may be in gaseous or vapour state and in particulate form. Chemical vapours found in atmosphere are derived from those substances which have boiling point less than 200°C.
The following are the major air pollutants:
1. Inorganics:
Oxides of carbon (CO, CO2)
Oxides of nitrogen (NO, NO2)
Oxides of sulphur (SO2, SO3)
Other inorganics (NH3, HF, H2 S, etc.)
(i) Simple hydrocarbons
(ii) Aliphatics
alkenes (ethene, propene)
alkanes (ethane, methane)
alkylene (acetylene)
(iii) Aromatics (benzene, toluene, xylene)
(iv) Oxygenated Hydrocarbons
Aldehydes (Formaldehyde, acetaldehyde)
(Formic acids & acetic acid) Acids
Ketones (Acetone)
The sources of atmospheric pollution are many. P.K. Zutshi of Bhabha Atomic Research Centre (BARC) in 1970 classified the sources of pollution as follows (Table 13.11):
The main primary air pollutants are oxides of carbon, sulphur and nitrogen, particulate matter and hydrocarbons. Besides these, there are some other pollutants of air.
The following table (13.12) highlights the atmospheric pollution levels in four cities of India:
The important sources of air pollutants are motor vehicles (gasoline and diesel), aircrafts, rail and road transportation, coal, fuel oil, natural gas, and wood fuel combustion, industrial processes, solid waste disposal, forest fire, agricultural burning, etc. Exhausts and other particulate matters in the presence of sunlight produce the photochemical smog which is no less than plague. The December 1952 smog caused 15030 deaths in London within 5 days. Air pollution is clearly a great danger to man and it can lead to disastrous incidence. But not many are however aware of this fact that the air we breath is contaminated with dust and gases in harmful proportions.
Suspended particulate matters:
Solid and liquid aerosols suspended in the atmosphere are referred to as suspended particulate matters. (SPM). They arise from grinding, erosion, spraying, etc. Particulate matter refers to the varying mixture of particles in different proportions, suspended in the air.
Such suspended particles are normally present everywhere, but high concentrations or specific types of particles pose danger to human health. SPMs are emitted both by natural processes and anthropogenic activities. Almost all the industries release particulate matter into the atmosphere. These include materials such as soot, dust, asbestos particles, heavy metals such as copper, lead, zinc, arsenic, etc.
The SPMs, being of very small size (less than 10 micron in diameter) are easily inhaled into the lungs and have chronic affects on respiration. They are also absorbed by the blood streams and may cause multiple health hazards, as many particulates are carcinogenic in nature. The SPMs spread over large areas, alter food chains and affect the ecosystems. They also block sunlight and may cause changes in the climate. Suspended particles in the air sometime cause reduction of visibility, adversely effecting air and rail and road traffic.
Aerosols are the chemicals which are released in to the air with force in the from of a mist or vapour. Aerosols have caused serious environmental pollution in the recent years. Jet aero plane emission is an important source of aerosols in upper atmosphere. Layers of pollutants which are largely due to high flying commercial jets can be found as high as 43000 feet. Although smoke is popularly used to denote mixtures of particulate matter, fumes, gases and mists, ‘dust’ refers to solid dispersion aerosol and ‘mist’ to liquid aerosol.
Dust particles greater than 10 µ in size are called settleable dust. These are measured as dust fall in tonnes /sq. mile/ month. Smaller particles suspended in air are referred to as suspended dust. The aerosols contain flourocarbons. Fluorocarbons deplete the ozone layer in the stratosphere and thus permit more harmful ultraviolet radiations to reach the earth surface; ozone acts as preventive covering against ultraviolet light. From the emission of supersonic aero planes nitrogen and sulphur oxides are released which also cause thinning of the ozone layer. Carbon tetrachloride (CCI4) is also known to destroy some of the stratospheric ozone. Pilots have discovered pollution high over the middle of the oceans in the North Polar Region.
The important effects of air pollutants are as follows:
1. Atmospheric particles can scatter and absorb sunlight, thus reduce the visibility. Reduced visibility is aesthetically undesirable and it is also dangerous for aircraft and motors In general cities receive above 15 to 20% less solar radiation than rural areas and the reduction of sunlight can become as high as one-third in the summer and two-third in winter. The reduction of sunlight IS largely due to fuel combustion for industrial and household heating purposes.
2. The effects of particulate matter include corrosion of metals, erosion and soiling of buildings, sculptures and painted surfaces and soiling of clothing’s and draperies, damage of electric equipment’s, etc.
3. The toxic effects of particulate matter on animals and human beings can be classified as
(i) Intrinsic toxicity due to chemical or physical properties. Carbon monoxide in congested areas removes 5 to 10% of blood from circulation. Although body tissues extract only 25% of oxygen from the blood, the heart needs 75 per cent. So there is little margin for safety.
(ii) Interference with clearance mechanism in the respiratory tracts. Chronic bronchitis and emphysema have also been found to be caused by SO2. A 24 hour exposure to about 0.2 ppm of SO2 may cause serious health problems. Lung cancer has been found to be correlated with air pollution. Polycyclic aromatic hydrocarbons (PAH) are found to be related to the pathogenesis of lung cancer.
(iii) Toxicity due to absorbed toxic substance.
Many toxic particles including metal dusts, asbestos, aromatic hydrocarbons have been discovered in a polluted urban atmosphere. Lead from vehicle exhausts resulting from the use of tetraethyl lead as an anti-knock additive to petrol may build up to dangerous levels in urban areas adjacent to busy road complexes. Lead in high doses kills out rightly. Lower doses in dense traffic areas shorten life span and causes deterioration of nervous system. Retarded children have a higher lead content in their body than the normal ones.
4. Benzpyrenes. Their concentrations are extremely small but they play a role in increasing cancer rate in urban areas as compared to rural areas. Peroxyacetyl nitrates (PAN) or photochemical smog may constitute a serious problem where high levels of vehicular emissions occur in cities experiencing bright sunlight and ambient temperatures above 21°C.
5. The small solid particles can serve as carriers for micro-organisms and other infective agents and thereby spread diseases. Large dust particles are trapped in nose and throat and very tiny particles which stay in the lungs may start an ugly chain of events leading to serious illness and deaths. Air pollution causes coughing, sneezing, thickening of mucus and narrowing or complete closure of glottis due to presence of gases, especially SO2, nitrogen dioxide and oxidants. The silicon particles may cause ‘silicosis’ and fibrous particles ‘fibrosis’. It is suspected that some pollutants can start lung cancer.
Sulphur dioxide (SO2):
The most important air pollutant is SO2 which is colourless nonflammable gas with pungent irritating odour. About one-third of SO2 present in the atmosphere IS believed to be produced by man’s activity. Robinson and Robbins (1971) have estimated that SO2 from man’s activity introduces 6.6 million tones of sulphur into the atmosphere annually SO2 present in atmosphere comes largely from coal and petroleum combustion. Biologically produced H2S when oxidised produces SO2.
The following tables (13.13 and 13.14) give an idea about the rough estimates of SO, and suspended particulates in air in major cities of India:
SO2 and SPM in Air Major Cities of India
Effects of SO2:
1. SO2 can damage materials and properties mainly through its conversion into the highly reactive H2SO4. It causes discolouration and physical detenoration of building materials and sculptures. Deterioration and fading are also produced in fabrics as cotton, nylon, rayon, leather and paper.
2. It accelerates corrosion of metals especially iron, steel and zinc.
3. SO2 has been found to affect vegetation adversely even at the concentration below 0.32 ppm It is suspected that sulphur dioxide pollution in urban and industrial areas of industrialised countries has a major impact on the respiratory condition of the population and also has significant effects on the crops and other vegetation of the surrounding rural areas. High concentration of SO2 over short period of time can produce leaf injury, such as necrosis in plants or brownish colouration in the tips of pine needles. Lower concentrations over long period lead to chromc leaf injury such as gradual chlorosis.
4. SO2 and H2SO4 both are capable of causing irritation in respiratory tracts of animals and human beings and high concentrations of SO2 cause severe heart and lung diseases.
Carbon monoxide and carbon dioxide:
Carbon monoxide is colourless, tasteless, odorless gas which is deadly poisonous in high concentration. It is one of the important gaseous air pollutants. It originates from incomplete combustion of carbonaceous materials. Man’s activities result in the production of nearly 250 million metric tons of CO annually. Aircrafts are responsible for about 2.5% CO and 1.1% hydrocarbons in USA. Space rocket engines produce many dangerous exhaust products.
In one study it was found that engine of Apollo Lunar module which took two astronauts to the surface of moon produced NH3, water, CO, NO, CO2 and N2O as major exhaust products and wide variety of different minor exhaust products. The toxic effects of CO on human beings or animals arise from its reversible combination with haemoglobin in the blood. Haemoglobin has great affinity with CO which lessens the oxygen carrying capacity of blood. It also reduces the dissociation of oxyhaemoglobin.
Carbon dioxide released in to our atmosphere after combustion of fossil fuels has brought a 10 per cent increase in the level of atmospheric CO2 over the past century. The regular measurement of CO2 content in the atmosphere began in 1958. In 1959 the content of CO2 in atmosphere was found to be 316.1 ppm. (Part per million or part per ten lakhs) and in 1994 it was found to be 350.0 ppm.
The study on the amount of CO2 trapped in old ice revealed that prior to industrialization the content of this gas on an average was 280 ppm, but from the start of industrialization in the end of eighteenth century right upto 1959 the CO2 content increased from 280 ppm to 316 ppm. We are all aware of this fact that the consumption of fossil fuels such as coal, petroleum products, diesel, gas fuels is rapidly increasing and the forest area is decreasing day by day.
Consequently, the content of CO2 in the atmosphere is increasing quickly and in case the present rate of CO2 increase continues it may touch or even exceed 500 ppm mark soon. A continued increase in excess unabsorbed CO2 could have a catastrophic warming effect on the atmosphere, melting of polar ice, and change in the ecosystems of seas and even floods on an undreamed scale.
Nitrogen oxides:
Robinson and Robbins (1971) have estimated that biological production of NO and NO2 amounts to about 1 billion metric tons annually while combustion processes produce 48 million metric tons NO2 annually. Man-made nitrogen oxides pollution is insignificant in urban areas. These oxides play role in production of photochemical smog.
The effects of nitrogen oxides are as follows:
1. Nitrogen oxides are known to produce fading of textile dyes, deterioration of cotton and nylon and corrosion of metals due to production of particulate nitrates.
2. NO2 causes leaf injury and reduction of growth in several sensitive plants.
3. It affects lungs, heart, liver and kidney at higher concentrations (15 to 50 ppm for two hours). Besides, it is considered to be a major factor in causing eye irritation.
Diseases Due to Air Pollution:
Air pollution has caused the most serious threat to human health.
The common air pollutants and their diseases are:
1. Sulphur dioxide:
Causes respiratory diseases like cough, damage to lungs, asthma, and bronchitis.
2. Carbon monoxide:
Heart and brain damage, headache and giddiness, fatigue.
3. Oxides of nitrogen:
Respiratory tract diseases, irritation in the eyes, allergies.
4. Ozone:
Affects the eyes, damages the lungs, affects the heart, soreness.
5. Hydrogen sulphide:
Extremely toxic even at low concentrations, affects the nervous system.
6. Gaseous hydrocarbons:
Affects the lungs and is carcinogenic (causes cancer).
7. Tobacco smoke:
Main source of indoor pollution, it is carcinogenic.
8. Particulate matter:
These are the solid tiny particles that remain suspended in the air. Their effect on human health depends on their nature and type.
Some common particulate pollutants are:
i. Lead:
Extremely toxic and affects the kidneys, liver and nervous system. It enters the blood stream and also affects pregnant women, foetuses and new-born babies.
ii. Mercury:
Higher concentration of mercury is injurious to human life; it causes chromosome damage, loss of memory.
iii. Cadmium:
It was the cause of itai-itai disease in Japan; It leads to the formation of kidney stone. Liver and pancreas are also affected.
iv. Arsenic:
It causes diarrhea, it is absorbed through the skin and lungs and causes skin and lung cancer. Chronic exposure to arsenic is the cause of black-foot disease, which is common in parts of West Bengal and Bangladesh.
v. Copper:
Carcinogenic.
vi. Chromium:
Specially toxic to aquatic life.
vii. Some other:
Some other metallic pollutants like molybdenum, barium, manganese, cobalt also affect human health.
viii Spores and pollens:
These remain suspended in the air for long time and cause respiratory diseases, asthma and allergies.
Respiratory Diseases:
Air pollution mostly affects the lungs and other organs of the respiratory system.
Some of the common respiratory diseases are:
Bronchospasm:
The pollutants mainly cause irritation in the respiratory tract. Sometimes the muscles of the bronchioles get inflamed and obstructed due to excessive irritation. This is known as bronchospasm.
Bronchitis:
This is caused due to swelling of the lining of the bronchi. It causes severe coughing and mucus production.
Emphysema:
Here the walls of the individual alveoli breakdown and the alveoli join together to form a sac like structure. This reduces the efficiency of the lungs.
Pulmonary Fibrosis:
This is caused due to dust and other solid suspended particles. As dust is not eliminated from the alveoli, some fibrous tissues develop around it in due course of time. This also decreases the efficiency of lungs.
Asthma:
It is an allergic disease, which is caused due to foreign bodies inside the respiratory tract. In this bronchospasm occurs and the airways are narrowed. It is marked by difficulty in breathing.
Pneumoconiosis:
This is a respiratory tract disease caused due to inhalation of dust particles, which induces severe coughing and congestion.
Control of Air Pollution:
Air pollution can be better controlled by (i) reducing the emission of pollutants and (ii) by using non-polluting materials.
Some of the major steps for reducing air pollution are as follows:
1. Controlling particulate pollutants by using scrubbers, filters, cyclone separators and electrostatic precipitators in the industries.
2. Change from high-sulphur coal to low-sulphur coal, especially for the thermal power plants, to check the emission of SO2.
3. Locating industries far from human settlements
4. To check automobile pollution by the use of unleaded petrol, better engines with low emissions and proper maintenance of vehicles
5. Installation of catalytic converters in the vehicles
6. Conducting regular pollution control checks on the vehicles
7. Adopting less polluting fuels like Compressed Natural Gas (CNG) and Liquefied Petroleum Gas (LPG)
8. Adopting more non-conventional energy sources that are non-polluting, such as solar energy, wind energy, etc.
9. Using mass transport systems and switching over to non-polluting modes of transport like bicycles
10. To check deforestation and encourage plantation especially around the polluting industries
The Taj Mahal was being adversely affected by sulphur dioxide smoke and suspended particulate matter released by many industrial units located around it, at Agra. As a result, the ‘White Wonder’ was loosing its beauty due to corrosion of the marble and was developing a yellowish tinge. Noted environmental activist lawyer, Sri S.C. Mehta, filled a Public Interest Litigation in 1984, expressing concern over the effect of the polluting industries on the Taj Mahal. The Honorable Supreme Court, in 1996, ordered the industries to be shut down, or to adopt strict pollution control measures like use of natural gas.