Read this essay to learn about air pollution. After reading this essay you will learn about: 1. Introduction to Air Pollution 2. Historical Background of Air Pollution 3. Meaning 4. Sources 5. Effects 6. Economic Effects 7. Some Air Pollution Accidents 8. Control.
Essay Contents:
- Essay on Introduction to Air Pollution
- Essay on the Historical Background of Air Pollution
- Essay on the Meaning of Air Pollution
- Essay on the Sources of Air Pollution
- Essay on the Effects of Air Pollution
- Essay on the Economic Effects of Air Pollution
- Essay on Some Air Pollution Accidents
- Essay on the Control of Air Pollution
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Essay # 1. Introduction to Air Pollution:
It is also known as atmospheric pollution. Air pollution is the release of any foreign materials or gases which are harmful to man, animals, vegetation or buildings into the atmosphere. It is one of the most dangerous and common problem for those living in big congested, industrialized cities with heavy vehicular traffic.
Four segments of environment are lithosphere, Hydrosphere. Biosphere and atmosphere. The atmosphere comprises of a mixture of gases e.g. NO2, O2, CO2, Ar etc. and it extends up to 500 km. above the surface of earth.
The cover of air that envelops the earth is known as the atmosphere. Atmosphere is the protective thick gaseous mass. The surrounding the earth which sustains life on earth saves it from unfriendly environment of outer space.
The weight of the atmosphere is 4.5 to 5 x 105 MT. Atmospheric temperature varies from – 100°C to + 1200°C depending upon the altitude. Atmospheric pressure at sea level is one atmosphere where as at 100 km above the see level is 3 x 10-7 atmosphere. The atmospheric density at the surface of the earth is 0.0013 g/cum.
Essay # 2. Historical Background of Air Pollution:
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The origin of air pollution goes back to the discovery of fire. Since then, human activities have been contributing towards air pollution. The combustion processes from mobile and stationary sources have generated significant amount of air pollution.
A new era of air pollution started with the development of steam engine and the beginning of the Industrial Revolution in the 17th century. Later on, gasoline powered automobile became a major contributing source of air pollution.
The quality of air has been adversely affected by the industrial development with higher level of energy consumption, fast increasing urban population and rapid transportation using petrol and diesel on large scale. All these activities have become a major source of air pollution, which are adding a huge number of pollutants into the air. As a result, the air pollution in the big cities of the world has rapidly increased.
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Weather Factors:
Weather conditions play an important role in mixing and dispersion of pollutants. The atmospheric air mass moves from one part to other part of the earth due to uneven distribution of solar radiation. As a result, large scale and small scale atmospheric circulations have been created.
Adverse weather conditions on a micro scale are favourable for the emission of pollutants which remain confined to a small area. Similarly, large scale circulation is responsible for the global air pollution.
Water Vapours:
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Water vapour is one of the important components of the atmosphere. It varies from place to place and from time to time. Moisture affects air quality in several ways. Water vapours affect the heat exchange during condensation and evaporation. The presence of water vapours in the air influences atmospheric stability.
Huge numbers of pollutants are found in the urban areas and their number is still larger in the industrial areas of the cities. These particulates act as condensation nuclei. Water vapours condense on the surface of these pollutants during winter nights. The condensation of water vapours leads to the formation of fog. Because of the presence of pollutants, fogs have the tendency to occur more frequently in the urban areas.
The droplet converts the sulphur dioxides into sulphuric acid. Solar radiation from the sun is trapped by fog. If the duration of the fog is prolonged for a number of days, the pollutants continue to accumulate over the same area resulting in serious pollution problems.
Dispersion of Pollutants:
Wind has horizontal and vertical components. The pollutants can spread in horizontal as well as vertical direction. In addition to wind patterns and horizontal dispersion, the vertical motion of air is very important. Atmospheric stability controls the vertical mixing of air and dispersion of pollutants.
The atmosphere is considered to be stable, when there is little or no vertical movement of air masses, therefore, little or no mixing and dispersion of pollutants in the vertical direction. Under stable conditions, air pollutants tend to accumulate near the ground, leading to severe pollution problems. Under unstable conditions, air moves in a vertical direction, increasing mixing and dispersion of the pollutants.
Under stable conditions, temperature inversion is very strong and well defined. Temperature inversion does not allow the upward mixing and dispersion of the pollutants. Temperature inversion in the urban areas causes stagnation of the air. As a result, the quality of the air deteriorates rapidly due to the stagnation of the air.
Temperature inversions are of three types, which are associated with specific weather conditions. These are frontal inversion, subsidence inversion and radiation inversion.
Frontal inversion is not important for dispersion of pollutants as it occurs at higher altitudes, when warmer air mass rises over the colder air mass. Subsidence inversion also occurs at higher altitudes and can persist for several days during summer season.
In this case, large warm air mass descends on the earth. The actual inversion may occur at an altitude of 300 m, while below this, there is lapse rate. This kind of inversion forms a lid or cap, that traps the pollutants. Radiation inversion generally occurs on clear winter nights due to excessive radiational cooling of the earth’s surface. Air pollutants emitted during night are trapped and remain close to the ground surface.
Essay # 3. Meaning of Air Pollution:
Air pollution may be defined as any atmospheric condition in which certain substances are present in such concentrations that they can produce undesirable effect on man and his environments. These substances include gases (Sulphur oxides, Nitrogen oxides, Carbon monoxides, hydrocarbons, etc.) particulates matter (smoke, dust, fumes, aerosols), radioactive materials and many others.
Most of these substances are naturally present in the atmosphere in low (background) concentrations and are usually considered to be harmless. Industries are not only the source of air pollution, other sources such as domestic fuel consumption, refuse burning, automobiles etc. also contribute heavily to contamination of our environment.
Essay # 4. Sources of Air Pollution:
The major sources of air pollution are as follows:
i. Automobile Exhausts:
Internal combustion engine is the greatest air pollutant. Motor vehicles alone contribute about 60% of air pollution in major cities like Bombay, Calcutta, Delhi and Madras. Automobile exhausts includes the compounds like carbon monoxide, nitrogen oxides and un-burnt hydrocarbons.
Most vehicles burn their fuel rather inefficiently and incompletely thus discharging only partially oxidized combustion products into the atmosphere. When exposed to sunlight these products consisting of mostly hydrocarbons and nitrous oxide produce ozone and other pollutants. In addition to air pollution, automobile is responsible for about 75% of the noise pollution in big cities.
Diesel and petrol produce more or less similar pollutants in air through the exhausts. The gases given out during idling and acceleration are more harmful than during moderate speed. The carbon monoxide, dioxide and hydrocarbons released during petrol combustion are higher in amount than those given during the burning of diesel.
One of the hydrocarbons released due to incomplete combustion is 3-4 benzpyrene which is said to cause lung cancer. Air pollution by automobile exhausts may be controlled by the regulation of traffic, control of idling, use of additives like barium compounds in fuel.
ii. Smoke:
Smoke causes about 10-15% of atmospheric pollution. Smoke is produced by burning bituminous coal, cooking fuel, charcoal, fire-wood and mineral oils. Their use dissipates sulphur dioxide in atmosphere which gets oxidized to sulphite and finally converted to sulphuric acid which is present in air as small droplets. Incomplete combustion of domestic fuels gives out carbon monoxide also.
The smoke given out by industries varies in its constituents depending upon the nature of the product being manufactured. Most of the components of smoke are similar to those present in that of automobile exhausts. These are sulphur dioxide, sulphites, 3-4 benzpyrene oxides of nitrogen etc.
iii. Smog:
It is a mixture of smoke and fog. Smog arises from many sources including factories, steelworks, oil refineries, chemical plants etc. Ingredients of smog include carbon monoxide, sulphur and nitrogen oxides, lead and various hydrocarbons, ozone and peroxyacyl nitrates.
These pollutants accumulate in the atmosphere close to the ground in situation where a large layer of warm air higher up prevents them from escaping. This is called thermal invasion. The action of sunlight on industrial byproducts and motor car exhaust result in a particular variety of smog called photochemical smog.
Smog changes the composition of our atmosphere and its long term effects could be serious. But its general effects include intense eye-irritation, headaches, sickness and respiratory difficulties. In 1952, London smog disaster is said to caused the death of 4000 people.
iv. Carbon Monoxide:
Cigarette smoke, motor vehicles, industrial plants and domestic heating appliances are common source of CO. This gas combines with haemoglobin of blood, reducing its oxygen carrying capacity. Prolonged exposure to CO-enriched air lead to symptoms as laziness, exhaustion of body, headache, disturbance of psychomotor function, decrease in visual perception, serious effects on the cardio-vascular system and finally even to death.
v. Nitrogen Oxides (NO and NO2):
Motor vehicles, burning materials and chemical industries are common sources of nitrogen oxides. In the atmosphere nitrogen dioxide is reduced by ultraviolet light to nitrogen monoxide and atomic oxygen. The atomic oxygen reacts with oxygen to form ozone.
Nitrogen dioxide is a pungent gas, it produces a brownish haze, causes nose and eye irritations and pulmonary discomfort. Lower concentrations of ozone irritates the nose and throat while, higher concentrations it causes dryness of the throat, headache and difficulty in breathing.
vi. Sulphur Oxides and Particulates:
During burning of fossil fuels like coal and also during cracking of petroleum in oil refineries, a large amount of SO2 is produced. The addition of various particles to sulphur dioxide enhances or potentiates the effects of SO2 on animals. It causes different respiratory distresses in animals.
Comparing to animals vegetation is more sensitive to SO2. SO2 and its transformation products in atmosphere on plant cells causes membrane damage, plasmolysis, chlorophyll destruction, metabolic inhibition, growth and yield reduction.
In western countries, there is a problem of acid rains, till now not so serious in India. Sulphur oxides and nitrogen oxides and other acid precursors emitted by natural and man-made sources can travel long distances in the atmosphere. Then they undergo chemical transformation and return to earth as acid rain. In sensitive areas this increases the acidity of water bodies and soil, and damage aquatic ecosystems.
SO2 pollution can be controlled either by removing the sulphur after combustion or by precombustion desulphurisation of fuel. One way is to substitute our conventional fuels by electricity and natural gas which do not emit SO2 or by low-sulphur fuels.
vii. Aerosols:
Aerosols are certain chemicals released into the air with force in the form of a mist of vapour. The widespread use of aerosols in recent years has caused serious concern to environmental scientists.
An important source of aerosols in the upper atmosphere is the jet aeroplane emissions. These aerosols contain flurocarbon propellants and these fluorocarbons deplete the ozone layer in the stratosphere, therefore permitting some more of the harmful ultra-violet radiation to reach earth’s surface. Recently carbon tetrachoride has been shown to destroy some of the stratospheric ozone.
Unlike the other chlorofluorocarbons such as CCI3F and CCI2F2 which are commonly used as refrigerant and propellant aerososls pollute the atmosphere largely as a result of human activity.
viii. Industrial Pollutants:
Some important pollutants in the atmosphere of big cities are carbon monoxide, oxides of sulphur and nitrogen, hydrocarbons, metal dust fluorides, pesticides, fly ash soot and occasionally radioactive substances. Fly ash is an important pollutant and is particulate consisting of noninflammable mineral fractions.
Cottondust is an atmospheric pollutant in Ahmedabad, Surat and other areas having textile mills. Citizens of Delhi and Bombay are familiar with thick, black smoke and soot that come out from chimneys of factories and thermal plants which bum coal and soot.
ix. Pollutants of Plant Origin:
Certain air pollutants e.g. pollen, spores or cells of fungi and lower plants are produced naturally.
x. Metallurgical Pollutants:
Various metallurgical processes release dust or fumes containing metallic pollutants e.g. lead, chromium, beryllium, nickel, arsenic and vanadium. Some metals such as cadmium, zinc and mercury are released into environment from the refining of copper, zinc, lead and steel and manufacture or use of pesticides, phosphate fertilizers, fungicides and cosmetics.
xi. Radioactive Substances:
Increasing use of diverse variety of radioactive substances in industry and medicine create problem of pollution. Isotopes of some elements emit radiations. There are three types of ionizing radiations, alpha particles, beta particles and gamma rays. They penetrate biological materials, leaving ionizations throughout their path.
The radioisotopes which escape frequently into the atmosphere cause harmful mutations in living organisms. The ‘fall out’ due to nuclear tests add large amount of such isotopes in the air.
Essay # 5. Effects of Air Pollution:
Some of the major effects of air pollution are discussed below:
i. Effects of Air Pollution on Human Health:
Air is fundamental element of human life as it makes breathing possible.
Pollutants such as:
(i) NOx causes eye irritation, pulmonary congestion and heart diseases.
(ii) SOx and sulphuric acid fumes irritate the upper respiratory track causing cough.
(iii) The production of incomplete combustion of automobile fuel are often found toxic or contain carcinogenic material.
(iv) Smoke affects lung.
Dust and cotton fiber causes pulmonary trouble and asthma. Air pollution is one of the greatest environment evils. The air we breathe has not only life support properties but also life damaging properties. Under ideal conditions the air inhale has qualitative.
But if it is polluted, it may affect human health.
The primary factors affecting human health are:
1. Nature of the pollutants
2. Concentration of the pollutants
3. Duration of exposure
4. State of health of the receptor
5. Age group of the receptor.
Mechanism of Action of Air Pollutants:
The effects of air pollution on human health generally occur as a result of contact between the pollutants and the body. Normally, bodily contact occurs at the surface of the skin and exposed membranes.
Contact with exposed membranes surfaces is of most important because of their high absorptive capacity compared to that of the skin. Air-born gases, vapours, fumes, mist, and dust may cause irritation of the membrane of the eyes, nose, throat larynx, tracheo-bronchial trees and lungs.
Health Effect:
1. Eye irritation
2. Nose and throat irritation
3. Irritation of the respiratory tract
4. Gases like hydrogen sulphide, ammonia and mercaptans cause odour nuisance even at low concentrations.
5. A variety of particulates particularly pollens initiate asthmatic attacks.
6. Chronic pulmonary diseases like bronchitis and asthma, are aggravated by a high concentration of SO2, NO2, particulates matter and photochemical smog.
7. Carbon-monoxide combines with the haemoglobin in the blood and consequently increases stress on those suffering from cardio-vascular and pulmonary diseases.
8. Hydrogen fluoride causes diseases of the bone, and molting of teeth.
9. Carcinogenic agents cause cancer.
10. Dust particles cause respiratory disease. Diseases like silicosis, asbestosis, etc. result from specific dusts.
11. Certain heavy metals like lead may enter the body through the lungs and cause poisoning.
ii. Effect Air Pollution on Animals:
Interest in the effects on air pollution on animals has generally developed as a corollary to the concern about its influence on human health. Recently considerable information has been reported from medical research laboratories which describes the results of experimental exposure of small animals to various air pollutants. Animals used for laboratory research work were fish, rabbits, rats, guinea pigs and monkeys.
In case of farm animals it is a two-step process:
1. Accumulation of the air-borne contaminant in the vegetation and forage.
2. Subsequent poisoning of the animals when they eat the contaminated vegetation.
The three pollutants responsible for most livestock damage are:
(i) Fluorine,
(ii) Arsenic and
(iii) Lead.
These pollutants originate from industrial sources or from dusting and spraying.
(i) Fluorine:
Of all farm animals, cattle and sheep are the most susceptible to fluorine toxicity. Horses appear to be quite resistant to fluorine poisoning. Poultry are probably the most resistant to fluorine of all farm animals.
(ii) Arsenic:
Arsenic occurs as an impurity in many ores and in coal. It has been reported to cause poisoning of livestock near various industrial processes and smelters, just like most industrial air contaminants. Arsenic may spread over a considerable area from a stock source. Arsenic in dusts or spray on plants can lead to poisoning of cattle.
(iii) Lead:
Lead contamination of the atmosphere takes place on account of various industrial sources such as smelters, Cooke ovens and other coal combustion processes. Lead is also used in dust and sprays containing lead arsenate.
It is reported that pollution is now beginning to effect pets and domestic animals in Tokyo and other smog affected cities. Many dogs also suffer from coughs, nose, and throat diseases due to increasing air pollution. It is interesting to note that the average life of pets in Japan is 7 to 8 years, whereas in developing countries they enjoy a life span of 12 to 13 years.
iii. Effect of Air Pollution on Plants:
Air pollution has adverse effect on plants. At first, it was only sulphur dioxide that was considered a dangerous pollutant.
Industrial pollution particularly from smelters, has cause complete destruction of vegetation in some cases e.g. at duck town, Tennessee. In India there are many reports of the effect of pollutants like cement dust on plant.
Air pollutants effecting plants:
1. Sulphur dioxide
2. Fluoride compounds (like hydrogen fluoride)
3. Ozone
4. Chlorine
5. Hydrogen chloride
6. Nitrogen oxides (NO, NO2, etc.)
7. Ammonia
8. Hydrogen sulphide
9. Hydrogen cyanide
10. Mercury
11. Ethylene
12. PAN (peroxy acyl nitrate)
13. Herbicides (sprays of weed killers)
14. Smog.
The above pollutants interface with plant growth and the phenomenon of photosynthesis. Smog, dust, etc. reduce the amount of light reaching the leaf.
Kinds of injury to plants:
I. Acute Injury:
It results from short time exposure to relatively high concentrations, such as might occur under fumigation conditions.
The effects are noted within a few hour to a few days and may result in visible marking on the leaves due to a collapse and death of cells.
II. Chronic or yield retardation:
It results from long-term low level exposure and usually causes chlorosis or leaf abscission.
III. Growth or yield retardation:
Here the injury is in the form of an effect on growth without visible marking (invisible injury). Usually a suppression of growth or yield occurs.
D. Effects of Air Pollutants on Plants:
The effects of various pollutants like sulphur dioxide, ozone, fluorides, etc., on plants is shown in table 6.2.
Essay # 6. Economic Effects of Air Pollution:
Air pollution damage to property is a very important economic aspect of pollution. In the many countries, this problem has been investigated in detail and successful attempts have been made to translate observable air pollution damage in terms of economic impact.
Air pollution damage to property covers a wide range corrosion of metals, soiling and eroding of building surfaces, fading of dyed materials, rubber cracking, spoiling or destruction of vegetation, effect on animals, as well as interference with production and services.
Another important economic effect of air pollution is deterioration of work of art. In India, today, there is an urgent need to investigate and study this problem in detail and express the damage to property in economic terms, as very little work has been done in this direction so far.
Mechanism of Deterioration in Polluted Atmospheres:
Air pollution cause damage to materials by five mechanisms:
(i) Abrasion:
Solid particles of sufficient size and travelling at high velocities can causes abrasion action.
(ii) Deposition and removal:
Solid and liquid particles deposited on a surface may not damage the material itself but it may spoil its appearance. However the removal of these particles may cause some deterioration.
(iii) Direct chemical attack:
Some air pollutants react directly and irreversibly with materials to cause deterioration. For example, the bleaching of marble by sulphur dioxide.
(iv) Indirect chemical attack:
Certain materials absorb some pollutants and get damage when the pollutants undergo chemical changes. For example, sulphur dioxide absorbed by leather.
(v) Corrosion:
The atmospheric deterioration of ferrous metals is by an electrochemical process, i.e. corrosion. This is due to the action of air pollutants facilitated by the presence of moisture.
Factors Influencing Atmospheric Deterioration:
There are four prime factors which influence the rate of attack of damaging pollutants.
They are:
(i) Moisture,
(ii) Temperature,
(iii) Sunlight and
(iv) Air movement.
(i) Moisture:
The presence of moisture in the atmosphere greatly helps the process of corrosion. Without moisture in the atmosphere, there would be little atmospheric corrosion, if any even in the most severely polluted environments. In case of sulphur dioxide and various combinations of particulates, investigations have revealed that the rate of corrosion of metals will increase as relative humidity in the air increases.
(ii) Temperature:
Temperature affects the rate of chemical reaction and consequently it effects the rate of deterioration.
(iii) Sunlight:
Sunlight can cause direct deterioration of certain materials. But in cases of fading of certain dyes or rubber cracking damage due to direct sunlight cannot always be distinguished from that caused by ozone.
(iv) Air Movement:
Wind direction is an important factor to be considered in places where deterioration is caused by pollutants released from nearby factories. Pollutants present in wind blowing at high speeds will have more abrasive effects and they may also be carried over long distances, where leather bound books are stored, air movement is critical factor when the air is contaminated by sulphur dioxide.
(v) Economic factor of air pollution:
Air pollution damage to various materials.
Essay # 7. Some Air Pollution Accidents:
In this section two accidents in recent history will be described:
I. TCDD Accident at Seveso, Italy (July 1976):
An explosion took place in a chemical plant manufacturing herbicide (2, 4, 5 trichlorophenoxy acetate). A white cloud of poisonous gas consisting of TCDD came out and engulfed the poisonous for man. The building, ground and soil were contaminated. After three weeks of the accident the Italian Government evacuated about 800 people from the worst affected area.
However, the dioxin pollution continued to spread and particulates were deposited over widespread area. About 200 people including children suffered from skin disease and some them, from liver troubles. About 1% of the babies born after the accident were deformed and also premature. According to experts, dioxin will continue to contaminate soil water and affect water resources and natural biological cycles.
II. The Bhopal Disaster:
Date: December 3, 1984
Venue: Bhopal, Madhya Pradesh, India
Source: Union Carbide factory, manufacturer of Carbaryl (Carbamate pesticide) using methyl isocyanate (MIC)
Background:
Methyl isocyanate (MIC) is the starting material for the production of carbaryl.
Methylamine and phosgene are pumped into a reactor. There is application of heat they form MIC and HCl. The products are changed gaseous HCl separated in an absorber and the liquid MIC is transformed carbamate production unit or storage tank. It may be noted that the associated with unreacted COCl2 (2%).
The latter helps to in-acted reaction between MIC and water and also inhibits polymerization to gene also provides a source of Cl2 which can act on container as (generally stainless steel alloys) to produce substances that can act on catalysts for reaction of MIC.
MIC and α-naphthol, on mixing, produces carbaryl in high yield.
Reaction of MIC —MIC is extremely reactive — it can react many “active hydrogen” compounds, all the reactions being vary and exothermic. Thus it can react with water giving 1, 3-di-methylene, 1,3, 5-trimethyl biuret as the case may be.
At room temperature MIC-H2O reaction proceeds at a slow rate. But exothermic, producing about 585 Btu per lb. of MIC or about 370 per lb. of water. The reaction rapidly increases to the point when starts to boil violently.
Moreover, MIC can react even with itself undergoing trimerization presence of catalysts such as trace of rust, NaOH, NaCl etc. This reaction is also exothermic, liberating about 540 Btu per lb. of MIC, equivalent to 54 kcal per mole of trimer.
Bhopal MIC Plant — A flow-sheet diagram of MIC plant is shown. (Fig. 6.22)
According to the Union Carbide Corporation guidelines, it is mandatory for the plant to protect MIC tank by a blanket of dry N2 (dew point – 40°C) and keep it at 0°C by refrigeration. They further caution that Fe, Cu, Sr and Zn must be excluded from contact with MIC as they catalyse a dangerously rapid trimerization. The induction period varies from several hours to several days. The heat evolved can generate a reaction of explosive violence.
The actual scenario of what went wrong at the Bhopal plant just after the midnight on the morning of December 3, 1984 is not exactly known-investigations at the government level are still kept secret.
But several circumstantial evidences point to the total breakdown of the essential safety provisions within the plant and negligence of the authorities. The refrigeration units for the MIC tanks were out of order for several months. The two safety measures for neutralising leaking MIC viz. the vent gas scrubber and the flare tower were also non-functional.
In a closed tank the pressure due to runaway reactions of MIC with H2O or catalyst or with both can build up to the point that relief valves will open, venting both MIC vapour and COCl2. If safety devices fail to operate (as was the case with Bhopal plant) or if they are overwhelmed by the amount of vapours being generated, the heavy noxious MIC vapours will escape to the atmosphere.
Biochemical effects of MIC — MIC is invariably accompanied by COCl2 (2%). The Threshold Limiting Value (TLV) for MIC is 0.02 ppm and COCl2 0.1 ppm. The toxic effect of MIC is enhanced by COCl2. Exposure to MIC leads to chest tightness, breathing troubles and eye-ache and also cyanide generation in the body, which ultimately turns fatal.
The Fateful Incident:
December 3, 1984. It was chilly windy December night. The city of Bhopal was virtually asleep. In the Union Carbide factory at about 11.30 p.m. workers in the plant (in the night shift) realised that there was MIC leak somewhere, as their eyes were aching intensely.
A few of them walked around the MIC structure and spotted a drip of liquid about 50 feet off the ground and some yellowish-white gas accompanying the drip. One worker noticed that the temperature gauge on one MIC tank had reached 25°C, the top of its scale and pressure was rapidly building up to 40 psi.
He rushed to the storage tanks of MIC and found that the concrete slab (60 feet/6″ thick) above the storage tanks was shaking—there was a messy boiling sound underneath the slab like a cauldron. He ran for safety as the heat was that of blast furnace.
He then heard a loud hissing sound and saw gas shooting out of a tall stack connected to the tank and forming a white cloud drifting over the plant and towards the sleeping neighbourhood. In the plant he found that the pressure indicator had gone above 55 psi, the top of the scale and the safety valve had opened releasing MIC from the storage tank.
The workers present at the site realised that it was a massive MIC leak. The plant supervisor ordered for water spray on the leak. But the water jet failed to reach the top of the 120 feet stack from which MIC was gushing out. Next the vent gas scrubber was turned on to neutralize the escaping gas. But the scrubber was out of order.
The factory turned on the public siren at 1 a.m., about an hour after the gas started escaping, but it was only for a few minutes. Most residents around the factory (mostly slum dwellers) got up not due to the siren but due to the irritation caused by the gas. For about two hours the safety valve remained open releasing over 50,000 lbs of MIC in vapour and liquid form, presumably associated with COCl2, HCN etc.
Around 2 a.m. the safety valve reseated as the tank pressure dropped below 40 psi. The public siren was resumed at 3 a.m. after the works manager arrived but by that time there was no need for caution; already hundreds of people were dead and many thousands were doomed to die over the next few hour and days.
Safety devices and violent reaction:
The plant has two main safety devices:
(a) Scrubber, which neutralized the gas with caustic soda and
(b) Flare tower, where the gas can be burn off. But both the safety devices failed to work on December 3 night.
Moreover, the refrigeration system, connected to MIC storage tanks which keeps the liquid at 0°C, had been closed down since June, 1984. As a result, the gas was at 15° – 20°C.
But the causes of the violent reaction are yet unknown. MIC can react with almost any chemical, including itself, to generate considerable heat and CO2. The heat released accelerates the reaction and pressure goes on building up till it reaches an explosive level. The MIC at Bhopal plant was sitting in the storage tank for more than two months, which again was against the safety rules. Demand for the end product, carbaryl was rather low.
Mass panic and death drama:
On 3rd December, 1984 between 12.30 and 1 a.m. people woke up coughing violently and with eyes burning as if chilli powder had been sprayed into them. They fled from their homes, some with families and many without families.
They used whatever transport they could get—cycles, bullock carts, buses, car, auto-rickshaws, tempos, trucks etc. By 3 a.m. the main streets were jammed with an endless and uncontrollable stream of humanity. The streets were trampled by the crowd. The worst victims were the children—unable to walk and breathe; they simply suffocated and died.
The gas emitted from the high tech factory of the multi-national Union Carbide spread over some 40 sq. km. and affected people seriously as distant as 5 km. to 8 km. down wind. For nearly 200,000 persons (a quarter of the city’s population) Bhopal transformed itself into a gas chamber. A bigger tragedy could have occurred but for the two lakes which came in the way of the gas cloud.
The railway station was close to the factory. Thousands of people left for distant stations away from Bhopal. The Deputy Chief power controller stayed on his work at the Station while his wife and 14-year old son died in the neighbouring railway colony.
He died later on along with the Station Master who alerted all nearby stations to stop trains from coming into Bhopal. Next morning hundreds of sick and writhing people were found all around, on platforms, railway tracks and office rooms.
At the nearby Hamidia Hospital the first patient with eye trouble reported at 1.15 a.m. Within five minutes there were a thousand and by 2.30 a.m. there were 4,000 suffering from not just eye ailments but also from respiratory problems. The doctors were puzzled— nobody knew what to do and the Union Carbide did not provide any useful information. Next morning thousand lay dead on the roads and in homes.
Corpses with distended bellies were beginning to rot, attracting vultures and dogs. More than 2,000 lay dying in hospitals. An awkward scene was that of carcasses of hundreds of dead cattle and animal all over the gas-affected area, swollen up to sizes of elephants. By about 1 a.m. on 4th December the hospital was crowded by 25,000 patients. The floor was splattered with blood and stinking with vomit.
The death drama continued for days. Within a week about 10,000 people died, 1,000 people became blind while more than 1 lakh people continue to suffer from various disorders. Among the survivors large numbers started leaving the city for safety. By 13th December about 1 lakh people left the city on the largest peace time exodus known so far in this region when the Government decided to dispose-off the balance of about 15 tonnes of MIC in the storage tanks.
Neutralisation drama—Operation Faith:
The task of disposing of the balance MIC in the storage tanks was entrusted to the Director-General of Council of Scientific & Industrial Research (CSIR). It was decided to convert MIC into the final product, Carbaryl by starting the factory operations. In-spite of assurances of the Chief Minister that all necessary precautions were taken and there was no cause of any danger, people got panicky and left Bhopal as their confidence was badly shaken.
However, on December 16 the factory was started and thus the “Operation Faith”, as termed by the Government to restore faith among people began. The Operation which was scheduled for four or five days finally ended on the seventh day and also 24 tonnes of MIC had to be converted, 50 per cent more than that estimated.
The aftermath and the legal battle:
Even one month after the disaster, the Union Carbide Corporation Chairman insisted: “We are pleased to report from the medical team who visited Bhopal that people injured by MIC are rapidly recovering and display little lasting effects”. Within two weeks after the incident, the works manager at Bhopal declared: MIC is not harmful. It is like tear gas, your eyes start watering.
We don’t know of any fatalities due to MIC in our plant or other UCC plants…….. Such statements were made when thousands were dying. From lack of functioning of safety devices it can be concluded that the Union Carbide did not care about safety in a developing country where inadequate government regulations and uninformed public encouraged them to neglect the safety measures altogether. The Company has shown double standards in their headquarters, USA and India.
A medical survey held 100 days after the exposure revealed that out of 250,000 people exposed, 65,000 were subjected to severe medical disability (respiratory, eye, gastrointestinal, neuromuscular, gynaecological symptoms) and 45,000 to mild to moderate medical disability.
People suffering from breathlessness, sleeping and digestion problems are incapable of carrying on even light physical labour and unable to earn a living. Women are very badly affected, the worst victims being pregnant women.
The question of compensation for the victims took the world by a storm. Some American lawyers who wanted to make a fortune air dashed to Bhopal. Soon Union Carbide was facing over 60 law suits in USA, totaling $100 billion on behalf of 150,000 victims.
Finally the Government of India came to the picture and filed a lawsuit in USA and then in India while Company offered to settle it at $5 million outside the court which was finally accepted by the Government of India.
The legal wrangling still rolls on in India, though eighteen years have passed by; all the world’s systems of justice have not been able to bring to book those responsible for the mass murder in recent history and the victims have yet to get their compensation.
III. Chernobyl Disaster:
The worst nuclear accident in history occurred at Chernobyl, Ukraine, formerly USSR (now CIS) on 27th April, 1986 at 9 p.m. Explosions from runaway nuclear reaction burst through a 4000-tonne steel concrete cover. The reactor core temperature soared to more than 2000°C. Fuel and radioactive debris shot into air and hit the surrounding areas.
Radioactive particles spewed out in a volcanic cloud along with streams of gases from molten mass in the core. In less than a week deadly debris and gases had drifted over most of Europe. A column of fluorescent blue light (produced by radioactive gases) emerged from the reactor and reached the upper atmosphere.
The accident killed at least two thousand people, though the then USSR government claimed only two deaths. According to the experts from the western countries, particularly USA, soil, water and vegetation over 60 sq. km. area and Chernobyl were severely damaged — the agricultural land in this area will remain radioactive for several decades.
The neighbouring countries such as Poland had banned sale of cow milk as there were chances of contamination of grass with long-lived isotope, Cs-137 due to radioactive fall-out. The U.S. experts predicted incidence of cancer among millions of the surviving population in the region due to radioactive fallout as thousands of curies poured out from the reactor each day.
Thousands of young soldiers, engaged in clean-up operation, picked up graphite rocks outside the reactor. Immediately after meltdown, military pilots had flown over the reactor many times dumping tons of sand, clay and other material to bury the molten core. But radiation still poured out of the reactor since the helicopter cockpit, used by military pilots, read 300 roentgens per hour (300,000 times the permissible does).
Essay # 8. Control of Air Pollution:
The basic mechanisms of removing particulates matter from streams, may be classified as:
1. Gravitational settling chambers
2. Cyclone separators
3. Fabric filters
4. Electrostatic respirators
5. Wet scrubbers.
6. Electrostatic precipitation.
A. Gravitational Settling Chambers:
Gravitational settling chambers are generally used to remove large abrasive particles (usually > 50 pm) from gas streams. They offer low pressure drop and require simple maintenance, but their efficiencies are quite low for particles smaller than 50pm. These devices are normally used as pre-cleaners prior to passing the gas stream through high efficiency collection devices.
B. Cyclone Separators:
Cyclone separators utilize a centrifugal force generated by a spinning gas stream to separate the particulate matter from the carrier gas. The centrifugal force on particles in spinning gas stream is much greater than gravity; therefore, cyclones are effective in the removal of much smaller particles than gravitational settling chambers, and require much less space to handle the same gas volume.
The simple reverse- flow type cyclone separators consist of a vertical cylinder having a conical bottom and is fitted with a tangential inlet located near the top, and an outlet at the bottom of cone for discharging separated particles. The gas outlet pipe is extended in to the cylinder to prevent short-circuiting of gas from inlet to outlet. In operation the particle- laden gas upon entering the cyclone cylinder receives a rotating motion.
The vortex so formed develops a centrifugal force, which acts to throw the particles radically towards the wall. The gas spirals down-ward to the bottom of the cone, and at the bottom the gas flow reverse to form an inner vortex which leaves through the outlet pipe.
C. Fabric Filters:
Fabric filter systems typically consist of a tubular bag or an envelope, suspended or mounted in such a manner that the collected particles fall into a hopper when dislodged from the fabric. The structure in which the bags hang is known as a bag house. Generally, particle-laden gas enters the bag at the bottom and passes through the fabric while the particles are deposited on the inside of the bag.
Large bag houses are constructed with several compartments, so that one compartment may be isolated for cleaning as needed while the other compartments are operating. The bags should be arranged in each compartment in such a manner that the available space is utilized effectively. Hoppers are provided for duct collection and the dust is removed usually by rotary or screw valves.
The cleaning may be accomplished by shaking the bags or by increasing the air pressure on the bag in a manner that causes the bag to collapse or otherwise deform sufficiently to dislodge the accumulated dust. Cleaning generally takes less than one minute when the bulk of the dust being removed in a few seconds. A good cleaning schedule ensures longer bag life and efficient filtration.
The following advantages make fabric filters the best choice in many cases:
(i) Very high efficiency
(ii) Retention of finest particles
(iii) Collection of particulates
(iv) Relatively low pressure drop.
The main disadvantages are:
(i) Their large size
(ii) High construction costs.
D. Electrostatic Precipitators:
The Electrostatic precipitator is one of the most widely used devices for controlling particulate emissions at industrial installations ranging from power plants, cement and paper mills to oil refineries. Electrostatic precipitation is a physical process by which particles suspended in gas stream are charged electrically.
The precipitation system consists of a positively charged (grounded) collecting surface and a high voltage discharge electrode wire suspended from an insulator at the top and held in position by Dusty- the weight at the bottom. At a very high DC voltage of the order of 50 KV, a corona discharged occurs close to the negative electrode setting up an electric field between the emitter and the grounded surface.
The particle-laden gas enters near the bottom and flow upwards. The gas close to the negative electrode is thus, ionized upon passing through the corona. As the negative ions and electrons migrate toward the grounded surface, they in turn charge the passing particles. The electrostatic field then draws the particles to the collector surface where they are deposited.
E. Wet Scrubbers:
The basic function of wet scrubbers is to provide contact between the scrubbing fluid, usually water and the particulate to be collected. This contact can be achieved in a variety of ways as the particles are confronted with so called impaction targets which can be wetted surfaces or individual droplets.
There are many scrubber designs presently available where the contact between the scrubbing liquid and the particles is achieved in a variety of ways.
The major types are:
(i) Spray towers
(ii) Centrifugal scrubbers
(iii) Packed beds and Impingement baffle plate columns
(iv) Venturi scrubbers,
(i) Spray towers:
The simplest type of wet scrubber is a spray tower in which water is introduced by means of spray nozzles. The polluted gas flows upward and the particles collection results because of inertial impaction and interception on the droplets.
(ii) Centrifugal scrubbers:
The collection efficiency for particles smaller than those recovered in spray towers can increased through the use of centrifugal scrubbers. It can be constructed by inserting banks of nozzles inside a conventional dry cyclone. The spray acts on the particles in the outer vortex, and the droplets loaded with particles are through outward against the wet inner wall of the cyclone.
(iii) Packed beds tower and Impingement baffle plate scrubber:
Packed beds and plate scrubber can also be used to scrub particulate matter from polluted gases. In a typical countercurrent flow packed scrubber the polluted gas stream moves upward and comes in contact with the Liquid scrubbing liquid stream which is moving downward over the packing in a film. The packing provides a target, which allow the gas stream to take a curved path through the pore spaces while the particles carried by the gas stream are captured by inertial impaction.
