Here is a compilation of essays on ‘Air Pollution in India’ for class 6, 7, 8, 9, 10, 11 and 12. Find paragraphs, long and short essays on ‘Air Pollution’ especially written for school and college students.
Essay on Air Pollution in India
ADVERTISEMENTS:
Essay Contents:
- Essay on the Introduction to Air Pollution
- Essay on Major Pollutants of Air Pollution
- Essay on the Causes of Air Pollution
- Essay on the Effects of Air Pollution
- Essay on the Types of Air Pollution
- Essay on the Control Methods for Air Pollution
- Essay on Bio Monitoring of Air Pollution
- Essay on Air Pollution Control Devices
1. Essay on the Introduction to Air Pollution:
Air pollution is the introduction into the atmosphere of chemicals, particulates, or biological materials that cause discomfort, disease, or death to humans, damage other living organisms such as food crops, or damage the natural environment or built environment. A substance in the air that can be harmful to humans and the environment is known as an air pollutant.
Pollutants can be in the form of solid particles, liquid droplets, or gases. In addition, they may be natural or man-made. Pollutants can be classified as primary or secondary. Usually, primary pollutants are directly emitted from a process, such as ash from a volcanic eruption, the carbon monoxide gas from a motor vehicle exhaust or sulphur dioxide released from factories. Secondary pollutants are not emitted directly. Rather, they form in the air when primary pollutants react or interact.
The atmosphere is a complex dynamic natural gaseous system that is essential to support life on planet Earth. Stratospheric ozone depletion due to air pollution has long been recognized as a threat to human health as well as to the Earth’s ecosystems .Pure air is always needed for inhaling. If we take pure air, our health improves.
On the other hand impure air causes diseases and impairs our health and causes our death. Smoke pollutes the air. It is the root of air pollution. There are four major reasons of air pollution emissions from vehicles, thermal power plants, industries and refineries. The problem of indoor air pollution in rural areas and urban slums has increased.
ADVERTISEMENTS:
The smoke which is discharged from industries, automobiles and kitchens is the mixture of carbon monoxide, carbon dioxide, methane etc. These are all poisonous gases. These cause lung-cancer, tuberculosis etc. which take a heavy loss of life. Fine particles or microscopic dust from coal or wood fires and unfiltered diesel engines are rated as one of the most lethal forms or air pollution caused by industry, transport, household heating, cooking and ageing coal or oil-fired power stations.
During air pollution chemicals and particulates are release into the atmosphere. Common gaseous pollutants include carbon monoxide, sulphur dioxide, chlorofluorocarbons (CFCs) and nitrogen oxides produced by industry and motor vehicles. Photochemical ozone and smogare created as nitrogen oxides and hydrocarbons react to sunlight. Particulate matter or fine dust is characterized by their micro-meter size.
CNG is not without environmental drawbacks say a new Central Pollution Control Board study on January 05, 2011. According to Central Pollution Control Board burning CNG has the highest rates of potentially hazardous carbonyl emissions. The study also made a case for regulating CNG and other fuels for methane emissions. Methane, a greenhouse gas, is a key contributor to climate Change.
Among the study’s finds were that retrofitted CNG car engines emit 30% more methane than original CNG engines. Almost all CNG car engines in India are retrofitted. Air quality is worst in Metro cities like Kolkata, Delhi, Mumbai, Chennai, etc.
ADVERTISEMENTS:
ADVERTISEMENTS:
2. Essay on the Major Pollutants of Air Pollution in India:
(A) Primary Pollutants:
Major Primary Pollutants Produced by Human Activity:
a. Sulphur Oxides (SOX):
Sulphur dioxide, a chemical compound with the formula SO2. SO2 is produced by volcanoes and in various industrial processes. Since coal and petroleum often contain sulphur compounds, their combustion generates sulfur dioxide. Further oxidation of SO2, usually in the presence of a catalyst such as NO2, forms H2SO4 and thus acid rain. This is one of the causes for concern over the environmental impact of the use of these fuels as power sources.
ADVERTISEMENTS:
b. Nitrogen Oxides (NOX):
Nitrogen dioxide are emitted from high temperature combustion, and are also produced naturally during thunderstorms by electric discharge. Nitrogen dioxide is the chemical compound with the formula NO2. It is one of the several nitrogen oxides. This reddish-brown toxic gas has a characteristic sharp, biting odor. NO2 is one of the most prominent air pollutants.
c. Carbon Monoxide (CO):
Carbon monoxide is a colourless, odorless, non- irritating but very poisonous gas. It is a product by incomplete combustion of fuel such as natural gas, coal or wood. Vehicular exhaust is a major source of carbon monoxide.
d. Volatile Organic Compounds:
VOCs are an important outdoor air pollutant. In this field they are often divided into the separate categories of methane (CH4) and non-methane (NMVOCs). Methane is an extremely efficient greenhouse gas which contributes to enhance global warming.
e. Toxic Metals and their Compounds:
(i) Chlorofluorocarbons (CFCs):
Chlorofluorocarbons are harmful to the ozone layer emitted from products currently banned from use.
(ii) Ammonia (NH3):
Ammonia is emitted from agricultural processes. It is normally encountered as a gas with a characteristic pungent odor. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to foodstuffs and fertilizers. Ammonia, either directly or indirectly, is also a building block for the synthesis of many pharmaceuticals. Although in wide use, ammonia is both caustic and hazardous.
(B) Secondary Pollutants:
Particulates created from gaseous primary pollutants and compounds in photochemical smog. Smog is a kind of air pollution; the word “smog” is a portmanteau of smoke and fog. Classic smog results from large amounts of coal burning in an area caused by a mixture of smoke and sulfur dioxide.
Modern smog does not usually come from coal but from vehicular and industrial emissions that are acted on in the atmosphere by ultraviolet light from the sun to form secondary pollutants that also combine with the primary emissions to form photochemical smog. Peroxyacetyl nitrate (PAN) similarly formed from NOx and VOCs.
3. Essay on the Causes of Air Pollution in India:
The sources of air pollution are natural and man-made (anthropogenic).
a. Natural Sources:
The natural sources of air pollution are volcanic eruptions, forest tires, sea salt sprays, biological decay, photochemical oxidation of terpenes, marshes, extra-terrestrial bodies, pollen grains of flowers, spores etc. Radioactive minerals present in the earth crust are the sources of radioactivity in the atmosphere.
b. Man-Made:
Man-made sources .include thermal power plants, industrial units, vehicular emissions, fossil fuel burning, agricultural activities etc. Thermal power plants have become the major sources for generating electricity in India as the nuclear power plants couldn’t be installed as planned.
The main pollutants emitted are fly ash and SO2. Metallurgical plants also consume coal and produce similar pollutants. Fertilizer plants, smelters, textile mills, tanneries, refineries, chemicals industries, paper and pulp mills are other sources of air pollution.
Automobile exhaust is another major source of air pollution. Automobiles release gases such as carbon monoxide (about 77%), oxides of nitrogen (about 8%) and hydrocarbons (about 14%). Heavy duty diesel vehicles spew more NOx and suspended particulate matter (SPM) than petrol vehicles which produce more carbon monoxide and hydrocarbons.
c. Indoor Air Pollution:
The most important indoor air pollutant is radon gas. Radon gas and its radioactive daughters are responsible for a large number of lung cancer deaths each year. Radon can be emitted from building materials like bricks, concrete, tiles etc. which are derived from soil containing radium. Radon is also present in ground water and natural gas and is emitted indoors while using them.
Many houses in the under-developed and developing countries including India use fuels like coal, dung-cakes, wood and kerosene in their kitchens. Complete combustion of fuel produces carbon dioxide which may not be toxic. However, incomplete combustion produces the toxic gas carbon monoxide. Coal contains varying amounts of sulphur which on burning produces sulphur dioxide.
Fossil fuel burning produces black soot. These pollutants i.e. CO, SO2, soot and many others like formaldehyde, benzo-(a) pyrene (BAP) are toxic and harmful for health. BAP is also found in cigarette smoke and is considered to cause cancer. A housewife using wood as fuel for cooking inhales BAP equivalent to 20 packets of cigarette a day.
4. Essay on the Effects of Air Pollution in India:
(i) Greenhouse effect,
(ii) Ozone Depletion
(iii) Acid rain
Air pollution is a significant risk factor for multiple health conditions including respiratory infections, heart disease, and lung cancer. The health effects caused by air pollution may include difficulty in breathing, wheezing, coughing and aggravation of existing respiratory and cardiac conditions.
These effects can result in increased medication use, increased doctor or emergency room visits, more hospital admissions and premature death. The human health effects of poor air quality are far reaching, but principally affect the body’s respiratory system and the cardiovascular system.
Individual reactions to air pollutants depend on the type of pollutant a person is exposed to, the degree of exposure, the individual’s health status and genetics (Neuroplasticity effects). The effects of air pollution are obvious: rice crop yields in southern India are falling as brown clouds block out more and more sunlight.
The brilliant white of the famous Taj Mahal is slowly fading to a sickly yellow. In the “Taj Mahal Case” a very strong step was taken by Supreme Court to save the Taj Mahal being polluted by fumes and more than 200 factories were closed down. Diesel engine exhaust fumes can cause cancer in humans and belong in the same potentially deadly category as asbestos, arsenic and mustard gas.
Recent studies have linked acute exposure to ozone and death but little is known about the underlying pathways responsible for heart attack. Indoor air pollution is the most important cause of chronic pulmonary disease. Thousands of villagers in Orissa are facing serious health risks as a “cocktail of toxic residue” leak from an aluminium refinery.
Pollution due to biomedical waste is likely to spread disease dangerous to life and making atmosphere noxious to health. Everyday pollutants such as smoke, emissions from automobiles, tobacco smoke and improper use of indoor heating devices could further compromise lung function (Cystic fibrosis).
An additional to air pollution like high nitrogen oxide concentrations, cause various forms of cancer, including cervical cancer and brain cancer, SO2 increases mortality from lung cancer cardiovascular deaths. Bangalore holds the title of being the asthma capital of the country.
Vehicle emissions are responsible for 70% of the country’s air pollution. Carbon emissions have grown nine-fold over the past forty years. In this Industrial Age, with the ever-expanding consumption of hydrocarbon fuels and the resultant increase in carbon dioxide emissions, that greenhouse gas concentration have reached levels causing climate change.
The most developed countries possess the capital, technological and human resources required for successful adaptation, while in the developing countries, a large proportion of the population is engaged in traditional farming that is particularly vulnerable to the changes in temperature, rainfall and extreme weather events associated with climate change.
(i) Green House Effect:
A greenhouse is a structural building with different types of covering materials, such as a glass or plastic roof and frequently glass or plastic walls; it heats up because incoming visible solar radiation from the sun is absorbed by plants, soil, and other things inside the building.
Air warmed by the heat from hot interior surfaces is retained in the building by the roof and wall. In addition, the warmed structures and plants inside the greenhouse re-radiate some of their thermal energy in the infrared spectrum, to which glass is partly opaque, so some of this energy is also trapped inside the glasshouse.
Thus, the glass used for a greenhouse works as a barrier to air flow, and its effect is to trap energy within the greenhouse. The air that is warmed near the ground is prevented from rising indefinitely and flowing away.
Solar radiation at the frequencies of visible light largely passes through the atmosphere to warm the planetary surface, which then emits this energy at the lower frequencies of infrared thermal radiation. Infrared radiation is absorbed by greenhouse gases, which in turn re-radiate much of the energy to the surface and lower atmosphere.
The mechanism is named after the effect of solar radiation passing through glass and warming a greenhouse, but the way it retains heat is fundamentally different as a greenhouse works by reducing airflow, isolating the warm air inside the structure so that heat is not lost by convection.
The Earth reflects about 30% of the incoming sunlight, this idealized planet’s effective temperature would be about 18 °C. The surface temperature of this hypothetical planet is 33 °C below. Earth’s actual surface temperature is of approximately 14 °C. The mechanism that produces this difference between the actual surface temperature and the effective temperature is due to the atmosphere and is known as the greenhouse effect.
Greenhouse Gases:
Greenhouse gases including most diatomic gases with two different atoms (such as carbon monoxide, CO) and all gases with three or more atoms—are able to absorb and emit infrared radiation. Though more than 99% of the dry atmosphere is IR transparent (because the main constituents—N2,O2, and Ar—are not able to directly absorb or emit infrared radiation), intermolecular collisions cause the energy absorbed and emitted by the greenhouse gases to be shared with the other, non-IR- active, gases.
By their percentage contribution to the greenhouse effect on Earth the four major gases are water vapor 36-70%, carbon dioxide 9-26%, methane 4— 9%, ozone 3-7%.The major non-gas contributor to the Earth’s greenhouse effect is clouds that also absorb and emit infrared radiation.
Indian Satellite to Monitor Greenhouse Emission:
A dedicated satellite would be launched with the support of Indian Space Research Organization (ISRO) by 2012 to monitor India’s greenhouse gas emission, Union Minister for Environment and Forests Jairam Ramesh said. “Currently, Japan and European countries have this satellite but by 2012 we will have a dedicated satellite that will monitor greenhouse gas emission across the country and globe “.
“The objective is to study the impact of climate change, fallout of greenhouse gas emissions on the environment by monitoring it through satellite technology,” he said. Another satellite for protection and development of the forest cover in India would be ready by 2013. “As the forests are getting depleted at a rapid pace elsewhere in the world, there seems to be a need for a satellite,”
(ii) Ozone Depletion:
Ozone is a gaseous layer in the stratosphere of atmosphere. The ozone layer is a concentration of ozone molecules in the stratosphere. About 90% of the planet’s ozone is in the ozone layer. The layer of the Earth’s atmosphere that surrounds us is called the troposphere.
The stratosphere, the next higher layer, extends about 10- 50 kilometers above the Earth’s surface. Stratospheric Ozone is a naturally occurring gas that filters the sun’s ultraviolet (UV) radiation. Overexposure to UV rays can lead to skin cancer, cataracts, and weakened immune systems.
Increased UV can also lead to reduced crop yield and disruptions in the marine food chain. UV also has various harmful effects. Ozone depletion is referred to as the ozone hole.
There are two different types of hole (depletion) observed i.e.:
(i) A steady decline in the total volume of ozone in Earth’s stratosphere (the ozone layer)
(ii) A much larger springtime decrease in stratospheric ozone over Earth’s Polar Regions.
When sunlight returns to Antarctica in early spring, its ultraviolet rays trigger a chemical reaction that releases a chlorine-oxide free radical, which precipitates another reaction that breaks up the oxygen molecules that form the ozone layer. Both types of ozone depletion were observed to increase as emissions of halo- carbons increased.
It is caused by the release of chlorofluorocarbons (CFCs), hydro fluorocarbons (HCFCs) and other ozone-depleting substances (ODS), which were used widely as refrigerants, insulating foams, and solvents. Although CFCs are heavier than air, they are eventually carried into the stratosphere in a process that can take as long as 2 to 5 years.
Measurements of CFCs in the stratosphere are made from balloons, aircraft, and satellites. The latter phenomenon In addition to these well-known stratospheric phenomena. Ozone hole formation at polar region differ from that of mid-latitude thinning, but the most important process in both is catalytic destruction of ozone by atomic halogens.
The main source of these halogen atoms in the stratosphere is photo dissociation of man-made halocarbon refrigerants (CFCs). These compounds are transported into the stratosphere after being emitted at the surface. Other chemical substances that damage the ozone layer are methyl bromide (a pesticide), halons (fire extinguishers) and methyl chloroform (an organic solvent).
As methyl bromide and halons are broken apart, they release bromine atoms, which are 60 times more destructive to ozone molecules than chlorine atoms. Most of the ozone that is destroyed is in the lower stratosphere, in contrast to the much smaller ozone depletion through homogeneous gas phase reactions, which occurs primarily in the upper stratosphere.
Ozone depletion would change all of the effects of UVB (the higher energy UV radiation absorbed by ozone) on human health, both positive and negative. UVB is generally accepted to be a contributory factor to skin cancer and to produce Vitamin D.
In addition, increased surface UV leads to increased tropospheric ozone, which is a health risk to humans. The most common forms of skin cancer in humans, basal and squamous cell carcinomas have been strongly linked to UVB exposure. Absorption of UVB radiation causes the pyrimidine bases in the DNA molecule to form dimers, resulting in transcription errors when the DNA replicates.
These cancers are relatively mild and rarely fatal, although the treatment of squamous cell carcinoma. Another form of skin cancer (malignant melanoma) is much less common but far more dangerous, being lethal in about 15-20% of the cases diagnosed. Vitamin D is produced in the skin by ultraviolet light.
Thus, higher UVB exposure raises human vitamin D in those deficient in it. An increase of UV radiation would be expected to affect crops. A number of economically important species of plants, such as rice, depend on cyanobacteria residing on their roots for the retention of nitrogen. Cyanobacteria are sensitive to UV radiation and would be affected by its increase.
(iii) Acid Rain:
Acid rain refers to a downpour that has been made acidic by pollutants in the atmosphere. Acid deposition mainly caused by the release of sulphur dioxide and nitrogen oxide during fossil fuel combustion. When these gases are discharged into the atmosphere they react with the water, oxygen, and other gases already present there to form sulphuric acid, ammonium nitrate and nitric acid.
These acids then disperse over large areas because of wind patterns and fall back to the ground as acid rain or other forms of precipitation. The sulphur components in the atmosphere usually combine with rain water to create sulphuric acid, which comes down as acid rain.
Acid rain is rainfall which has become acidic or has a pH of less than 7.00 as a result of the emissions of harmful pollutants produced during the combustion/burning of fossils fuels. Acid rain is rain consisting of water droplets that are unusually acidic because of atmospheric pollution most notably the excessive amounts of sulfur and nitrogen released by cars and industrial processes.
Acid rain is also called acid deposition because this term includes other forms of acidic water. Dry deposition polluting particles and gases stick to the ground via dust and smoke in the absence of precipitation. This form of deposition is dangerous however because precipitation can eventually wash pollutants into streams, lakes, and rivers.
The gases which make the rain acidic include Sulphur Oxide (SOX), Carbon Oxide (COX) and Nitrogen Oxide (NOX).Acid deposition is present in the North-eastern United States, South-eastern Canada, and much of Europe including portions of Sweden, Norway, and Germany. In addition, parts of South Asia, South Africa, Sri Lanka, and Southern India are all in danger of being impacted by acid deposition in the future.
There are several important impacts, of acid deposition on both natural and man-made environments. Aquatic settings are the most clearly impacted by acid deposition though because acidic water falls directly into them. Both dry and wet deposition also runs off of forests, fields and roads and flows into lakes, rivers and streams. This acidic liquid flows into larger bodies of water, it is diluted but over time, acids can accrue and lower the overall pH of the body.
If the pH of a lake drops below 4.8, its plants and animals risk death. As acid rain falls on trees, it can make them lose their leaves, damage their bark and stunt their growth. By damaging these parts of the tree, it makes them susceptible to disease, extreme weather and insects. Acid falling on a forest’s soil is also harmful because it disrupts soil nutrients, kills microorganisms in the soil and can sometimes cause a calcium deficiency.
Trees at high altitudes are also susceptible to problems induced by acidic cloud cover as the moisture in the clouds blankets them. Finally, acid deposition also has an impact on architecture and art because of its ability to corrode certain materials. Acid deposition can also damage modern buildings, cars, railroad tracks, airplanes, steel bridges, and pipes above and below ground.
5. Essay on the Types of Air Pollution in India:
It is assumed that air pollution is anthropogenic, which is caused by human activities. Air pollution caused from natural sources can be more severe and longer lasting than air pollution from human activities. Air pollution can also be caused due to volcanic eruptions.
There are two types of pollutants. First type is called primary pollutants and the second type is called secondary pollutants. Primary pollutants are emitted directly into the air from a specific source such as power plant stacks.
Secondary pollutants are not emitted directly from a source, but these are formed in the atmosphere by complex chemical reactions involving primary pollutants and sunlight. The sources of primary air pollutants are either mobile (automobile) or stationary (coal fired electric power generating station).
The primary pollutants are the gases such as sulphur dioxide (SO2), nitrogen oxides (NOx), carbon monoxide (CO), solid or liquid particulates (less than 10mm) and lead particulate.
A. Sulphur Dioxide:
Sulphur dioxide is a primary pollutant because it is directly emitted in the form of SO2. Sulphur dioxide is released into the atmosphere, when certain fossil fuels, particularly coal are burnt. Sulphur dioxide (SO2) gas is carried over hundreds of kilometres by the wind.
In the presence of oxygen, water vapours and sunlight, SO2 can be involved in additional chemical reaction. It reacts with oxygen to form sulphur trioxide, which when reacts with water vapours, forms a mist of sulphuric acid (H2SO4). Therefore, sulphur dioxide is the major cause of acid rain.
B. Nitrogen Oxides:
Nitrogen oxides (NOx) are emitted by natural and man-made sources. Nitrogen dioxide (NO2) is very important. Initially nitric oxide (NO) is emitted from the sources. But NO is readily oxidised to NO2 and then reacts with hydrocarbons to form photochemical smog. Later on, nitrogen dioxide (NO2) reacts with hydroxyl ions to form nitric acid (HNO3). It also contributes to the acid rain.
C. Carbon Monoxide:
Carbon monoxide forms under incomplete combustion of the fossil fuels. It is one of the most widely distributed of all air pollutants. During complete combustion of fossil fuels, carbon atoms in the fuel combine with oxygen to form carbon dioxide (CO2).
About 70 per cent of the total carbon monoxide emission comes from highway vehicles. Concentration of CO ranges from 5 to 50 ppm in the city air and may be 100 ppm on congested highways.
D. Particulates:
Extremely small fragments of solid or liquid droplets suspended in the air are called particulates. Most of the particulates range from 0.1 to 100µ. They can have adverse effects on the human health when their size is less than 10µ.
Even though, the size of the individual particulate is very small, the total mass of the particles discharged into the atmosphere is very large. Particles smaller than 1µ tend to remain suspended in the atmosphere for a longer period, but the particle greater than 1µ have the tendency to settle down due to gravitational force.
The solid particulates whose size ranges between 1 to 100µ are called dust particles, whereas smaller suspended solids less than 1µ may be referred to either smoke or fumes. A suspension of liquid particles between 0.1 and 10µ. in size is called mist, while a spray consists of liquid particles greater than 10µ in size. Aerosol refers to a quantity of any small particles, liquid or solid, suspended in the air.
E. Lead:
Major sources of lead (Pb) fumes are motor vehicles that use gasoline containing a lead based anti-knock additive. Lead occurs naturally in wind blown dust and volcanoes, but most of it is man-made.
F. Ozone and Photochemical Smog:
Ozone, a secondary air pollutant in the troposphere, is formed by a set of complex chemical reactions between nitrogen dioxide and volatile organic compounds. The reactions are initiated by the ultraviolet radiation. Ozone is the major component of photochemical smog.
The word ‘smog’ a contraction of ‘smoke and fog’ was initially used in England to describe the visible air pollution caused by higher levels of particulates and sulphur dioxides. Smog differs from photochemical smog, a common characteristic of both types is the low- lying, irritating, brownish haze that prevails in the atmosphere when smog occurs.
6. Essay on the Control Methods for Air Pollution in India:
There are various air pollution control technologies and land use planning strategies available to reduce air pollution. At its most basic level land use planning is likely to involve zoning and transport infrastructure planning. In most developed countries, land use planning is an important part of social policy, ensuring that land is used efficiently for the benefit of the wider economy and population as well as to protect the environment.
Efforts to reduce pollution from mobile sources includes primary. Citation needed expanding regulation to new sources (such as cruise and transport ships, farm equipment, and small gas-powered equipment such as lawn trimmers, chainsaws, and snowmobiles), increased fuel efficiency (such as through the use of hybrid vehicles), conversion to cleaner fuels (such as bioethanol, biodiesel, or conversion to electric vehicles).
Air pollution can be checked by following methods:
1. The use of lead-free petrol will prevent the release of lead into the atmosphere.
2. Special filters will reduce smoke emissions from factories and industries. This will require government legislation and drastic intervention.
3. Other energy sources, like wind and water, should be found to reduce the use of fossil fuels like coal, oil and gas.
4. Strict policies to prevent the release of gases like CFCs and nitrogen oxide into the air, should be formulated.
5. Ways in which to remove Sulphur from coal to prevent acid rain should be researched.
6. Electrical motorcars and trucks should be developed to reduce the CO2 and CO emissions into the atmosphere.
7. More efficient public transport systems to reduce traffic congestion reduce fuel usage and reduce air pollution, should be introduced.
8. Mechanical collectors (dust cyclones, multi-cyclones)
Electrostatic precipitators an electrostatic precipitator (ESP), or electrostatic air cleaner is a particulate collection device that removes particles from a flowing gas (such as air) using the force of an induced electrostatic charge. Electrostatic precipitators are highly efficient filtration devices that minimally impede the flow of gases through the device, and can easily remove fine particulates such as dust and smoke from the air stream.
9. Bag houses designed to handle heavy dust loads, a dust collector consists of a blower, dust filter, a filter-cleaning system, and a dust receptacle or dust removal system (distinguished from air cleaners which utilize disposable filters to remove the dust).
10. Particulate scrubbers Wet scrubber is a form of pollution control technology. The term describes a variety of devices that use pollutants from a furnace flue gas or from other gas streams. In a wet scrubber, the polluted gas stream is brought into contact with the scrubbing liquid, by spraying it with the liquid, by forcing it through a pool of liquid, or by some other contact method, so as to remove the pollutants.
7. Essay on Bio Monitoring of Air Pollution in India:
The concept of monitoring of air quality by plants is a well-established fact. The plants used for this purpose are termed indicator plants. It is known that some plants are very sensitive to air pollutants; they are thus used as indicator species for bio monitoring of air quality. In recent years, increasing efforts are being made to use plants for detection of air quality, particularly the presence of SO2, NOX, H2S, O3 and HF.
The use of lichens and moss for air pollution level mapping in urban and industrial area of Europe and also in North America are the finest examples of plant Bio monitoring of air quality.
The use of higher plants for monitoring of air pollution is, however, a recent development. A number of plant parameters either simply or in combination may be used for evaluating the pollution stress.
Table 10.19 shows the list of plants species used for bio monitoring of different air pollutants.
In India, considerable work has been done on the effects of air pollution on plants at BHU (Varanasi), JNU (New Delhi), NBRT (Luck-now), CIJ and KU (West Bengal) and AU (Vishakhapatnam) in recent years.
This method now appears to be a sensitive and low cost technique, only appropriate standardisation of techniques has to be made.
Identically, in Europe, similar type of plant species selection was made for air quality bio monitoring (Table 10.20).
The use of lichen indicators for air pollution monitoring was attempted in urban environment during recent decades by Santra and Mitra (1990).
By examining the pattern of lichen patch occurrence, an index of air pollution was determined in different sites of Kolkata city (WB). Thus an air pollution zone map was prepared (Fig. 10.17). Similar attempt was also made in Haldia industrial zone. The details are given in Box subsequently.
8. Essay on Air Pollution Control Devices available in India:
In order to reduce the pollution load entering the environment from industries (stationary sources), several measures may be taken.
These measures include replacement of burning fuel by electricity or solar energy or by improvement of fuel quality and fuel burning processes. Besides such innovations there are a number of mechanical devices that might be helpful for reduction of pollutant emission level from stationary sources.
There are two categories of devices that are often used by the polluting industries, viz.:
(a) Those devices which help in reducing particulate matters; and
(b) Those devices which help in reducing gaseous pollutants.
Control of particulate pollutants:
The important devices which are used to control particulate matters are:
(i) Gravity settling chamber,
(ii) Centrifugal collectors, viz., cyclone collectors and dynamic precipitators;
(iii) Wet scrubbers, viz., spray towers and venturi scrubbers;
(iv) Electrostatic precipitators, and
(v) Fabric filters.
i. Gravity Settling Chambers:
These are the oldest and simple type of particulate collector (Fig. 10.19). Particles of size between 40-100 µm in diameter are readily collected by this technique. Their efficiency is very poor ort fine dust and decreases as the load increases. They have a very large physical size, but, on the other hand, they are inexpensive and reliable. The cost of equipment is very low and very easy to maintain.
ii. Cyclone Collector:
It operates on the principle of centrifugal force. As the carriages enters the cylindrical shaped collector, it takes a helical path and the inertia of the particles carries them to the walls from where they drop into a hopper at the bottom.
The clean gas rises near the centre and is exhausted through the top. The cyclone collector is quite simple and reliable with low initial cost, easy maintenance and high temperature capabilities. Cyclone collectors tend not to be efficient on particles smaller than 10 nm and are best for 15-50 µm particles (Fig. 10.20).
iii. Dynamic Precipitators:
Dynamic precipitators (Fig. 10.21) also operate on the principle of centrifugal force. They are really a combination of a specially designed centrifugal form and a dust collector. The centrifugal force generated by the rotating blades probes the particles in the air stream to the tips of the blades, from where they are drawn off in a concentrated stream.
It is fairly efficient, even on particles 5-20 µm in diameter. However, this type of collector is unsuitable for sticky or fibrous materials, for the solids tend to build up on the blades.
iv. Spray Towers:
There are two types of spray towers: open spray towers and packed towers. Open spray towers (Fig. 10.22) are best for coarse particulate (> 10 µm in diameter) such as attained in the iron pyrite roasting step of steel production. They tend to be good for heavy particulate loads.
While, a packed tower consists of a series of contact beds, through which the gases and liquids flow either counter current or cross flow. A typical application would be for the absorption of fluorine compounds.
v. Venturi Scrubbers:
In the venturi scrubbers, the dirty gas and scrubbing liquid are moving at very high velocities (100 – 450 mph), generating much turbulence and mixing, and thus exhibiting good collection efficiency.
There are two types of venturi scrubbers:
Dry and wet type.
The dry types (Fig. 10.23), are not really dry, where the dirty gas enters, concentrates, and speeds up due to the narrowing passageway, is dry, but as the gas passes through the constricted area, it is inundated by a transverse water spray.
The wet types, on the other hand, require that both collector sections be wet. The water spray contacts the dust as soon as it enters the collector and the two mix immediately. One advantage of this immediate mixing is to allow collection of hotter gases.
Venturi scrubbers are very efficient (better than 99%) on particles as small as 0.5 µm. As such, they are typically used in the steel industry for fine particulates, for acid mists and for lime and coal dust (whose size is often 1 µm or less).
Electrostatic precipitators: The electrostatic precipitator is a very versatile and efficient type of collector, which can operate at over 1,000 °F (540 °C) and can be used for dry particulates or fumes, as well as mists. Electrostatic precipitators (Fig. 10.24) operate on the basis of electrostatic attraction.
The dirty gas is channelled between two electrodes, a high voltage (between 40,000 v and 50,000 v) discharge electrode and a grounded collecting electrode. Usually a precipitator will have more than one set of electrodes, thus the dust can be collected in different “compartments“. Precipitators allow for the dry collection of very fine particles. They are highly efficient, often approaching 99.9% efficiency.
