Our atmospheric air contains oxygen (21%), nitrogen (78%), carbon dioxide (0.3%), argon, neon, helium, hydrogen, ozone etc. in a fixed ratio. Air pollution is the imbalance in the quality of air so as to cause adverse effects on living organisms existing on the earth. According to the latest view point, air pollution is defined as, “Substances introduced into the air by the activity of mankind in such concentration sufficient to cause serious effects on his health, vegetables, property or interference with the enjoyment of his property”.
Sources of air pollution
Air is never found completely clean in nature. There are two major sources of air pollution i.e. Natural sources and Man-made sources.
A) Natural sources: The natural sources of air pollution are volcanic eruptions releasing poisonous gases, forest fires, natural organic or inorganic decays or vegetative decay, marsh gas, deflation of sand and dust, meteorites, cosmic dusts, pollen grains of flowers, soil debris and fungal spores. All these are produced naturally and released into the air making it foul and injurious to health. The cosmic rays coming out from sunlight contain randon which also affects human and plant life.
B) Man - made sources: These are the major causes of pollution and include the following factors.
1) Increase in population: Rapid increase of human population is one of the most important causes of air pollution. It is estimated that the present world population is nearly six billions. If the present rate of increase would continue, then the global population would be doubled after 35 years. The increase in population leads to rise in carbon dioxide level, global warming and environmental problems like loss of forest area as well as wild life species.
2) Deforestation: Plants maintain balance of CO2 and O2 in nature, as they purify air by taking in CO2 for photosynthesis and liberating O2 to be used by animals during respiratory activities. The animals again liberate CO2 to be used by the plants. Deforestation by man for his own need has disturbed the balance of CO2 and O2 in nature. This has caused an increase in CO2 and decrease in O2 concentration of the atmosphere.
3) Burning of fossil fuels and fires: The conventional sources of energy are wood, coal and fossil fuels. About 97% of the energy we use in our homes and factories is generated by coal, oil and natural gas which are called fossil fuels. Burning of these sources responsible for air pollution. The byproduct of burning of wood, coal and fossil fuels are nothing but poisonous gases such as CO, CH4, SO2. These gases condense as particles or transform to particulates. Thus pollutants released by burning of fossil fuels are gaseous matter and particulates. The kind, quality and concentration of these pollutants depend on the type of fuel. For example, the smoke coming out from the chimneys of a large number factories contain SO2 gas.
4) Emission from vehicles: The automobile exhaust are responsible for more than 75% of total air pollution. The automobiles such as cars, scooters, motors, taxies, trucks etc. release large amount of poisonous gases such as Carbon monoxide, nitrogen oxide and hydrocarbons in addition to particulate lead. These pollutants emitted from the automobiles in the presence of sunlight form photochemical smog in the atmosphere. This smog is very toxic in nature. The jet aeroplanes emit aerosols in the upper atmosphere. These aerosols are certain chemicals, released into the air with force in the form of a mist or vapour. These chemicals are known as chlorofluorocarbons (CFCs) which are commonly used in refrigeration and air-conditioning. Chlorofluorocarbons deplete the ozone layer in the atmosphere thereby permitting harmful ultraviolet radiations to reach the earth’s surface.
5) Rapid industrialization: A large number of industries such as chemical industries, paper and pulp mills, cotton mills, metallurgical plants, petroleum refineries, mining and synthetic rubber industries are responsible for about 20% of air pollution. The common pollutants of these industries are various types of inorganic and organic gases and materials in the smoke they produce. The most common pollutants are CO2, CO, SO2, H2S, NO, NO2 etc. In addition, the smoke coming out from their chimneys also contains small particles of dust carbon, metals, other solids, liquids and even radio active materials. All these gases and suspended particles in them are injurious to human health.
In textile industries workers constantly inhale cotton dust. These dusts are one of the most important pollutants in these industrial areas. Food processing factories and tanneries produce repulsive odors. The pesticide industries are also a concern of threat to the environment. Accidental leakage of poisonous gases from these industries, sometimes proves fatal instantaneously. The Bhopal gas tragedy, which took place on the 3rd September 1984, caused by the poisonous gas methyl isocyanate is perhaps one of the biggest air tragedy in the world.
Various metallurgical processes release dust or fumes containing metallic pollutants such as lead, chromium, barilium, nickel, arsenic and vanadium. During the refining of metals, pollutants like cadmium, zinc and mercury are released into the environment.
6) Agricultural activities: Different types of pesticides, herbicides, fungicides and biocides are used in modern agricultural practices. Some amounts of these toxic chemicals are carried out by wind to different places during their spray, thereby polluting the atmosphere.
7) Wars: Air pollution is also caused by various type of sophisticated explosives used in the modern warfare. Radio-active elements are released as fission by-products during atomic explosions, testing of nuclear weapons and atomic reactors. The first atomic bomb was exploded in Nagasaki, followed by the second in Hiroshima (Japan, 1945) during World War II. This heinous event wiped out thousands of innocent people, animals and plants. In spite of great suffering of 1945, nuclear tests are still continuing. The radio-active dust which falls on the earth after atomic explosion is called radio-active fall out. These include strontium 90, caesium 137, iodine 131 and unused explosives. Of these elements, strontium 90 and iodine 131 enter the food chain and get concentrated in human body causing health hazard.
Effects of Air pollution
Air pollution produces a number of adverse effects including offensive smell, loss of atmospheric clarity, soiling of clothes, building and manufactured goods by smoke and dust. The hazards caused to man, animals, vegetation, environment and climate have been understood in the past decade. The effects of air pollution are briefly discussed below.
1) Effect on man:
- Air borne spores, pollen grains, virus, bacteria, fungi, fur and hairs cause various allergic reactions, bronchial asthma, tuberculosis and other infections.
- Sulphur dioxide produces drying of the mouth, scratchy throat and smarting eyes. It also causes chest constriction, headache, vomiting and death from respiratory diseases.
- Sulphur trioxide, Nitrogen oxide and carbon monoxide diffuse in the blood stream. They combine with haemoglobin and reduce its oxygen carrying capacity. Nitrogen oxide in high concentration impairs the functioning of lungs by causing accumulation of water in the air spaces.
- Hydrocarbons have been reported to cause cancer in man.
- Hydrogen sulphide causes nausea and irritates eyes and throat.
- Ammonia attacks upper respiratory passages.
- Ozone causes dryness of mucous membrane of the mouth, nose and throat. It changes visual capacity, causes headache, pulmonary congestion and oedema.
- Arsines damage red cells in blood, kidney and cause jaundice.
- Suspended particles like ash, soot and smoke cause eye irritation, tuberculosis and possible cancer.
- Fine particles of various metals present in the air cause a number of diseases. Heavy dust fall is one of the major causes of asthma, cough and other diseases of lungs and throat. Lead can damage the brain of young children and may even cause death. It affects the normal functioning of the nervous system in adults. Cadmium is a respiratory poison and may cause high blood pressure and a number of heart diseases.
- Cotton dust causes the disease byssinosis producing disability in occupational persons. Asbestos fibers have been associated in chronic lung diseases.
- Iodine-131, from radio-active fallout may damage human white blood cells, bone marrow, spleen, lymph nodes and may even cause cancer. Strontium 90 behaves like calcium and enters human system through grass-cow-milk pathways or vegetables. It causes bone cancer and tissue degeneration in man and other animals.
2) Effect on animals: Air pollution causes wide spread damage to live-stock. The effect of air pollution on domestic animals living in or near industrial areas is similar to those of human beings. Live stocks ingest various fluorine compounds which fall on fodder crops causing abnormal calcification of bones and teeth. It results in lameness, loss of weight and frequent diarrhea.
3) Effect on plants: Air pollution has serious harmful effects on plants. Sulphur dioxide causes chlorosis. It results in the death of cells and tissues. Forest trees are worst affected by sulphur dioxide pollutants. Fluorides damage leafy vegetables such as lettuce and spinach. Oxides of nitrogen and fluorides reduce crop yields. Photochemical smog bleaches and blazes foliage of plants. Hydrocarbons cause premature fall of leaves and flower buds, discolouration of sepals and curling of petals. Ozone damages cereals, fruits and cotton crops. It also causes premature yellowing and shedding of leaves.
Air pollution inhibits growth of lichens on trees. Therefore, lichen can serve as indicator of air pollutions.
4) Effect on materials: The acid rain and photochemical smog affect metals and buildings. Acid rain pollutes the soil and water sources. Acidic products of the air pollutant cause disintegration of textile, paper. Many small industrial units and sources of locomotive pollutants have been sifted to save the famous marble structure, Taj Mahal at Agra. Hydrogen sulphide decolorizes silver and lead paints. Ozone oxidizes rubber goods.
5) Aesthetic loss: Dust and smoke in the air do not allow us to have a clear view of nature’s beauty and man-made objects. Smoke and foul smells emitted by factories, automobiles, dirty drains and garbage dumps make the urban life discomfortable. Smoking in public places affects the health of not only the smoker but also the non-smoker.
6) Change in Climate: A change in the earth’s climate due to atmospheric pollution is an alarming global concern. It has been observed that in the recent past, the level of CO2 in the atmosphere has increased from 290 ppm to 330 ppm. Approximately one fourth of this rise has occurred in the past decade. Rapid increase in population, deforestation and excessive burning of fossil fuel has been responsible for this increase. It is expected that CO2 level may be doubled by 2030 A.D.
It is also predicted that this factor alone could lead to rise in global temperature, causing “Green House Effect” or “Global Warming”.
Green House effect may be defined as the progressive warming up the earth surface due to blanketing effect of man made CO2 in the atmosphere. The thick CO2 layer functions like the glass panel of a green house preventing re-radiation of heat to outer space. A rise of global temperature by more than 2 or 3 degrees may lead to the melting of polar ice cap and glaciers. This will cause rise in ocean level and consequent flooding of costal towns and submersion of many oceanic islands. This would also affect the rainfall pattern and productivity of agricultural crops.
It is universally accepted, that the ozone layer in the stratosphere protects us from harmful ultraviolet radiation coming from the sun. Fluorocarbon gases from aerosol sprays, supersonic jet travel and nitrogen oxide in the atmosphere have been reported to cause depletion of ozone layer. The disruption of this layer would expose the earth to increased ultraviolet radiation. This may have serious effects on mankind causing skin cancer and mutation rates in general.
Acid rains are becoming a threat to mankind: The oxides of sulphur and nitrogen released into the atmosphere as pollutant are converted into sulphuric acid and nitric acid. They dissolve in water in the atmosphere and fall to the ground as acid rain. Acid rain increase soil acidity, and cause acidification of lakes and streams thereby affecting aquatic life, crop productivity and human health. Thousands of lakes in USA, Canada, and Sweden have become unproductive due to acidity.
Control of Air pollution
Control of air pollution is not very simple. Attempts to control air pollutants at the source are made in various ways.
1. Control of industrial pollutants: Control of gaseous pollutants and aerosols of industries and power plants are affected by various devices. Particles from chimney wastes larger than 50 micron are separated by gravity setting tanks or porus filters. But fine particles are separated by Cyclone collectors and Electrostatic precipitators. The Cyclone collectors remove nearly 75% particles from waste gas. The Electrostatic precipitator can remove nearly 99% of the particles in the range 5-20 microns in diameter. These are used in large scale in the thermal power plants
2. Control of vehicular pollution: Checking of pollutant emission from vehicular exhaust can be achieved by 1) using new proportion of gasoline and air 2) more exact timing of fuel feeding 3) using gas additives to improve combustion 4) by injecting air into exhaust to convert exhaust compounds to less toxic materials and by 5) updating of engine design to improve combustion.
Government should take steps to check and control the amount of CO emitted by automobiles. This can be done by testing centers with the latest Exhaust Gas Analysers in different cities. In these centers CO level in vehicles is tested. The carburetors are adjusted to correct air fuel ratio at the nearby service centers and properly tuned with CO emission.
3. Control of Air pollution by Fuel selection: Coal and fossil oils are the primary fuels, the combustion of which produces major air pollutants. It has been found that control of smoke is much easier with oil than with coal. The substitution of coal with oil is not sufficient to prevent smoke because the amount of SO2 emitted is much higher with oil than with coal. Coal and fossil oils are not renewable resources. Hence it would be wiser to replace both by solar energy and wind power.