ENVR-252 : Envr. Pollution. CHAPTER 2 & 3 Environmental Pollution and types of Pollution

Transcription

1 Environmental Pollution CHAPTER 2 & 3 Environmental Pollution and types of Pollution Developmental activities such as construction, transportation and manufacturing not only deplete the natural resources but also produce large amount of wastes that leads to pollution of air, water, soil, and oceans; global warming and acid rains. Untreated or improperly treated waste is a major cause of pollution of rivers and environmental degradation causing ill health and loss of crop productivity. In this lesson you will study about the major causes of pollution, their effects on our environment and the various measures that can be taken to control such pollutions. Pollution and Pollutants Human activities directly or indirectly affect the environment adversely. A stone crusher adds a lot of suspended particulate matter and noise into the atmosphere. Automobiles emit from their tail pipes oxides of nitrogen, Sulphur dioxide, carbon dioxide, carbon monoxide and a complex mixture of unburnt hydrocarbons and black soot which pollute the atmosphere. Domestic sewage and run off from agricultural fields, laden with pesticides and fertilizers, pollute water bodies. Effluents from tanneries contain many harmful chemicals and emit foul smell. These are only a few examples which show how human activities pollute the environment. Pollution may be defined as addition of undesirable material into the environment as a result of human activities. The agents which cause environmental pollution are called pollutants. A pollutant may be defined as a physical, chemical or biological substance unintentionally released into the environment which is directly or indirectly harmful to humans and other living organisms. Types of Pollution 1. Water pollution 2. Soil pollution 3. Noise pollution 4. Air pollution 5. Radiation pollution 1. Water Pollution Addition or presence of undesirable substances in water (surface water including rivers, streams, lakes & oceans and ground water including aquifers) is called water pollution. Water pollution is one of the most serious environmental problems. Water pollution is caused by a variety of human activities such as industrial, agricultural and domestic. Agricultural run-off laden with excess fertilizers and pesticides, 1

2 industrial effluents with toxic substances and sewage water with human and animal wastes pollute our water thoroughly. Natural sources of pollution of water are soil erosion, leaching of minerals from rocks and decaying of organic matter. Rivers, lakes, seas, oceans, estuaries and ground water sources may be polluted by point or non-point sources. When pollutants are discharged from a specific location such as a drain pipe carrying industrial effluents discharged directly into water body it represents point source pollution. In contrast non-point sources include discharge of pollutants from diffused sources or from a larger area such as run off from agricultural fields, grazing lands, construction sites, abandoned mines and pits, roads and streets. NONPOINT SOURCES Rural homes Urban streets POINT SOURCES Suburban development Wastewater treatment plant Cropland Animal feedlot Factory Figure: Point and nonpoint sources of water pollution Sources of water pollution Water pollution is the major source of water borne diseases and other health problems. Sediments brought by runoff water from agricultural fields and discharge of untreated or partially treated sewage and industrial effluents, disposal of fly ash or solid waste into or close to a water body cause severe problems of water pollution. Increased turbidity of water because of sediments reduces penetration of light in water that reduces photosynthesis by aquatic plants. Some major sources of water pollution are discussed below: i. Water Pollution due to pesticides and inorganic chemicals 2

3 Pesticides like DDT and others used in agriculture may contaminate water bodies. Aquatic organisms take up pesticides from water get into the food chain (aquatic in this case) and move up the food chain. At higher trophic level they get concentrated and may reach the upper end of the food chain. Metals like lead, zinc, arsenic, copper, mercury and cadmium in industrial waste waters adversely affect humans and other animals. Arsenic pollution of ground water has been reported from West Bengal, Orissa, Bihar, Western U.P. Consumption of such arsenic polluted water leads to accumulation of arsenic in the body parts like blood, nails and hairs causing skin lesions, rough skin, dry and thickening of skin and ultimately skin cancer. Pollution of water bodies by mercury causes Minamata diseasein humans and dropsyin fishes. Lead causes displexia, cadmium poisoning causes Itai Itai disease etc. Oil pollution of sea occurs from leakage from ships, oil tankers, rigs and pipelines. Accidents of oil tankers spill large quantity of oil in seas which kills marine birds and adversely affects other marine life and beaches. ii. Water pollution due to Thermal pollution Power plants- thermal and nuclear, chemical and other industries use lot of water (about 30 % of all abstracted water) for cooling purposes and the used hot water is discharged into rivers, streams or oceans. The waste heat from the boilers and heating processes increases the temperature of the cooling water. Discharge of hot water may increase the temperature of the receiving water by 10 to 15 C above the ambient water temperature. This is thermal pollution. Increase in water temperature decreases dissolved oxygen in water which adversely affects aquatic life. Unlike terrestrial ecosystems, the temperatures of water bodies remain steady and do not change very much. Accordingly, aquatic organisms are adopted to a uniform steady temperature of environment and any fluctuation in water temperature severely affects aquatic plants and animals. Hence discharge of hot water from power plants adversely affects aquatic organisms. Aquatic plants and animals in the warm tropical water live dangerously close to their upper limit of temperature, particularly during the warm summer months. It requires only a slight deviation from this limit to cause a thermal stress to these organisms. Discharge of hot water in water body affects feeding in fishes, increases their metabolism and affects their growth. Their swimming efficiency declines. Running away from predators or chasing prey becomes difficult. Their resistance to diseases and parasites decreases. Due to thermal pollution biological diversity is reduced. One of the best methods of 3

4 reducing thermal pollution is to store the hot water in cooling ponds, allow the water to cool before releasing into any receiving water body. Ground water pollution Lots of people around the world depend on ground water for drinking, domestic, industrial and agricultural uses. Generally groundwater is a clean source of water. However, human activities such as improper sewage disposal, dumping of farm yard manures and agricultural chemicals, industrial effluents are causing pollution of ground water. Eutrophication Eu maens well or healthy and trophy means nutrition. The enrichment of water bodies with nutrients causes eutrophication of the water body. Discharge of domestic waste, agricultural surface runoff, land drainage and industrial effluents in a water body leads to rapid nutrients enrichment in a water body. The excessive nutrient enrichment in a water body encourages the growth of algae duckweed, water hyacinth, phytoplankton and other aquatic plants. The biological demand for oxygen (BOD) increases with the increase in aquatic organisms. As more plants grow and die, the dead and decaying plants and organic matter acted upon by heterotrophic protozoans and bacteria, deplete the water of dissolved oxygen (DO). Decrease in DO result in sudden death of large population of fish and other aquatic organisms including plants, releasing offensive smell and makes the water unfit for human use. The sudden and explosive growth of phytoplankton and algae impart green color to the water is known as water bloom, or algal blooms. These phytoplankton release toxic substances in water that causes sudden death of large population of fishes. This phenomenon of nutrient enrichment of a water body is called eutrophication. Human activities are mainly responsible for the eutrophication of a growing number of lakes and water bodies in the country. Methods to treat the waste or contaminated water Waste water from domestic or industrial sources or from garbage dumps is generally known as sewage. It may also contain rain water and surface runoff. The sewage water can be treated to make it safe for disposal into water bodies like rivers, lakes etc. The treatment of waste or contaminated water involves three stages: primary, secondary and tertiary. The primary stage includes the physical treatment processes in which suspended particulate matter or solid 4

5 material is removed from the water such as sedimentation and screening. The secondary treatment processes are mainly the biological treatment processes in which microorganisms decompose the organic pollution loading in the wastewater. Favorable conditions are provided for the microorganism to allow their rapid growth to accelerate the decomposition process. The examples of secondary treatment include Activated sludge process and Trickling Filters. Effluents after secondary treatment may be clean but contain large amounts of nitrogen, in form of ammonia, nitrates and phosphorous which can cause problem of eutrophication upon their discharge into a receiving water body such as river, lake or pond. The tertiary treatment is meant to remove nutrients, disinfect for removing pathogenic bacteria. The example of tertiary treatments includes Chlorination. The treatment of waste water or sewage is carried out in effluent treatment plants especially built for this purpose. These plants are called as waste water treatment plants. The solid residues obtained from primary/secondary and tertiary treatment are known as sludge. Further measures to control the water pollution The following measures should be adopted to control water pollution: (a) The water requirement should be minimized by altering the techniques involved. (b) Water should be reused with or without treatment. (c) Recycling of water after treatment should be practiced to the maximum extent possible. (d) The quantity of waste water discharge should be minimized. Water recycling With increasing population the requirement for water is increasing rapidly. However, the availability of water is limited but an ever increasing water withdrawal from different sources such as rivers, lakes and ground water is depleting these sources. Therefore, it is essential to utilize the available water with maximum economy. This involves recycling of waste water for certain uses with or without treatment. Recycling refers to the use of waste-water by the original user prior to the discharge either to a treatment system or to a receiving water body. Thus, the waste water is recovered and repetitively recycled with or without treatment by the same user. 5

6 2. Soil Pollution Addition of substances which adversely affect the quality of soil or its fertility is known as soil pollution. Generally polluted water also pollutes soil. Solid waste is a mixture of plastics, cloth, glass, metal and organic matter, sewage, sewage sludge, building debris, generated from households, commercial and industries establishments add to soil pollution. Fly ash, iron and steel slag, medical and industrial wastes disposed on land are important sources of soil pollution. In addition, fertilizers and pesticides from agricultural use which reach soil as run-of f and land filling by municipal waste are growing cause of soil pollution. Acid rain and dry deposition of pollutants on land surface also contribute to soil pollution. Sources of Soil pollution The three major sources of soil pollution are: 1) Agricultural Sources 2) Industrial sources 3) Domestic & urban activities Agricultural sources Agricultural chemicals especially fertilizers and pesticides pollute the soil. The remnants of such pesticides may get adsorbed by the soil particles and contaminate root crops grown in that soil. On the other hand, fertilizers in the run-off water from these fields can cause eutrophication in water bodies. Pesticides are highly toxic chemicals which affect humans and other animals adversely causing respiratory problems, cancer and death. Industrial sources It includes fly ash, chemical residues, metallic waste, nuclear wastes and unwanted industrial wastes generated during manufacturing processes that is dumped over on the surface of soil by almost all industries with difference in the degree. Large number of industrial chemicals, dyes, acids, etc. find their way into the soil and are known to create many health hazards including cancer. Domestic and urban activities Domestic and urban activities generate large quantities of city wastes including several biodegradable materials (like vegetables, animal wastes, papers, wooden pieces, plant twigs, leaves, cloth wastes as well as sweepings) and many non-biodegradable materials (such as plastic bags, plastic bottles, plastic wastes, glass bottles, glass pieces, stone / cement pieces). Plastic bags Plastic bags made from low density polyethylene (LDPE), is virtually indestructible, create colossal environmental hazard. The discarded bags block drains and sewage 6

7 systems. Leftover food, vegetable waste etc. on which cows and dogs feed may die due to the choking by plastic bags. Plastic is non-biodegradable and burning of plastic in garbage dumps release highly toxic and poisonous gases like carbon monoxide, carbon dioxide, phosgene, dioxine and other poisonous chlorinated compounds. Control of soil pollution Indiscriminate disposal of solid waste should be avoided. To control soil pollution, it is essential to stop the use of plastic bags and instead use bags of degradable materials like paper and cloth. Sewage should be treated properly before using as fertilizer and as landfills. The organic matter from domestic, agricultural and other waste should be segregated and subjected to vermicomposting which generates useful manure as a by-product. The industrial wastes prior to disposal should be properly treated for removing hazardous materials. Biomedical waste should be separately collected and incinerated in proper incinerators. 3. Noise Pollution Noise is one of the most pervasive pollutants. A musical clock may be nice to listen during the day, but may be an irritant during sleep at night. Noise by definition is sound without value or any noise that is unwanted by the recipient. Noise in industries such as stone cutting and crushing, steel forgings, loudspeakers, shouting by hawkers selling their wares, movement of heavy transport vehicles, railways and airports leads to irritation and an increased blood pressure, loss of temper, decrease in work efficiency, loss of hearing which may be first temporary but can become permanent in the noise stress continues. It is therefore of utmost importance that excessive noise is controlled. Noise level is measured in terms of decibels (db). WHO (World Health Organization) has prescribed optimum noise level as 45 db by day and 35 db by night. Anything above 80 db is hazardous. The table below gives the noise intensity in some of the common activities. Table. Sources of some noises and their intensity 7

8 Sources of Noise Pollution Noise pollution is a growing problem. All human activities contribute to noise pollution to varying extent. Sources of noise pollution are many and may be located indoors or outdoors. Indoor sources include noise produced by radio, television, generators, electric fans, air coolers, air conditioners, different home appliances, and family conflict. Noise pollution is more in cities due to a higher concentration of population and industries and activities such as transportation. Noise like other pollutants is a by-product of industrialization, urbanization and modern civilization. Outdoor sources of noise pollution include indiscriminate use of loudspeakers, industrial activities, automobiles, rail traffic, airplanes and activities such as those at market place, religious, social, and cultural functions, sports and political rallies. In rural areas farm machines, pump sets are main sources of noise pollution. During festivals, marriage and many other occasions, use of fire crackers contribute to noise pollution. Effects of Noise Pollution Noise pollution is highly annoying and irritating. Noise disturbs sleep, causes hypertension (high blood pressure), emotional problems such as aggression, mental depression and annoyance. Noise pollution adversely affects efficiency and performance of individuals. Control Measures Following steps can be taken to control or minimize noise pollution Road traffic noise can be reduced by better designing and proper maintenance of vehicles. 8

9 Noise abatement measures include creating noise mounds, noise attenuation walls and well maintained roads and smooth surfacing of roads. 1. Retrofitting of locomotives, continuously welded rail track, use of electric locomotives or deployment of quieter rolling stock will reduce noises emanating from trains. 2. Air traffic noise can be reduced by appropriate insulation and introduction of noise regulations for take-off and landing of aircrafts at the airport. 3. Industrial noises can be reduced by sound proofing equipment like generators and areas producing lot of noise. 4. Power tools, very loud music and land movers, public functions using loudspeakers, etc. should not be permitted at night. Use of horns, alarms, refrigeration units, etc. is to be restricted. Use of fire crackers which are noisy and cause air pollution should be restricted. 5. A green belt of trees is an efficient noise absorber. 4. Radioactive Pollution Radiation is the process by which radiant energy is transferred from one place to another in the form of electro-magnetic waves. The various types of radiation differ from one another by their frequency or wavelength. Higher the frequency or lower the wavelength of a radiation, higher will be its energy. Again, higher the energy of the radiation, it will cause higher damage to the living organisms. Radiations can be categorized into two groups namely the non-ionizing radiations and the ionizing radiations. Ionizing radiation These are the radiations which induce the ionization of atoms and molecules. An atom is ionized when energy supplied to it separates one or more of its electrons. Ionization of a molecule produces two fragments. The radiation pollution is mainly caused by ionizing radiation. Alpha (α), beta (β), and gamma (γ) radiations are mainly responsible for radiation pollution. Alpha radiation contains energetic -alpha particles. Each alpha particle carries two units of positive charges and interacts strongly with living tissues. 9

10 Beta, radiation is made up of energetics electrons. Each beta particle carries one unit of negative charge and interacts strongly with matter. Gamma radiations are made up of high energy photons. Photons bring about strong electro-magnetic interaction with matter. Electrically charged particles produced in the nuclear processes can have sufficient energy to knock electrons out of the atoms or molecules of the medium, thereby producing ions. The ions produced in water molecules, for example, can induce reactions that can break bonds in proteins and other important molecules. An example of this would be when a gamma ray passes through a cell, the water molecules near the DNA might be ionized and the ions might react with the DNA causing it to break. They can also cause chemical changes by breaking the chemical bonds, which can damage living tissues. The ionizing radiations cause damage to biological systems and are, therefore, pollutants. Non-ionizing radiations These are the radiations which are constituted by the electromagnetic waves at the longer wavelength of the spectrum ranging from near infra-red rays to radio waves. These waves have energies enough to excite the atoms and molecules of the medium through which they pass, causing them to vibrate faster but not strong enough to ionize them. In a microwave oven the radiation causes water molecules in the cooking medium to vibrate faster and thus raising its temperature. Sources of Radiation Pollution: Radiation sources are mainly natural but partly manmade. The natural sources of radiation may be: 1. Radioactive minerals; 2. Cosmic rays; 3. Radio nuclides. 1. Radioactive Minerals: The minerals containing Uranium- 235 (U 235 ), Uranium-238 (U 238 ), Thorium-232 (Th 232 ), Plutonium- 239 (Pu 239 ) etc. are capable of emitting energetic radiations causing pollution. 10

11 2. Cosmic Rays: The cosmic rays containing highly energetic particles reach the surface of the earth causing pollution. The intensity of cosmic rays depends on latitudes and altitude of the place. The intensity is maximum at the poles and minimum at the equator. 3.Radio nuclides: The unstable radio-nuclides in the atmosphere can be splitted up into smaller parts emitting energetic radiation. The smaller radio-nuclides enter into the body of organism along with air during respiration. The various sources of manmade radiation pollutions may be: 1. Nuclear power plants 2. Nuclear explosions; and 3. Radio-isotopes. 1. Nuclear Power Plants: Nuclear power plants emit radiation to a very smaller extent except accidental leaks. The nuclear reactor accident at Chernobyl in 1986 led to deaths of many reactor personnel and a very large release of radionuclide to the environment causing long term radiation damage to the people living in the neighboring regions. Moreover, the nuclear power plants produce a lot of nuclear radio-active wastes. The disposal of these wastes has become a global problem. Some countries producing large quantity of nuclear wastes dump them in ocean near other countries. 2. Nuclear Explosion: During nuclear explosion, a large number of radio-nuclides are generated in the atmosphere. The radio - nuclides settle down with rain contaminating the soil and water bodies. Finally, these enter into food chain causing serious problem to the living organisms. 3. Radio-isotopes: Radio-isotopes are also prepared artificially either by nuclear fusion or by nuclear fission. If these radioisotopes are not properly handled, these emit radiations causing pollution. 11

12 Effects of radiation pollution Radiation damage The biological damage resulting from ionizing radiations is generally termed as radiation damage. Large amounts of radiation can kill cells that can dramatically affect the exposed organism as well as possibly its offspring. Affected cells can mutate and result in cancer. A large enough dose of radiation can kill the organism. Radiation damage can be divided into two types: (a) somatic damage (also called radiation sickness) and (b) genetic damage. Somatic damage refers to damage to cells that are not associated with reproduction. Effects of somatic radiation damage include reddening of the skin, loss of hair, ulceration, fibrosis of the lungs, the formation of holes in tissue, a reduction of white blood cells, and the induction of cataract in the eyes. This damage can also result in cancer and death. Genetic damage refers to damage to cells associated with reproduction. This damage can subsequently cause genetic damage from gene mutation resulting in abnormalities. Genetic damages are passed on to next generation. Radiation doses A traditional unit of human-equivalent dose is the rem, which stands for radiation equivalent in man. At low doses, such as what we receive every day from background radiation (< 1 m rem), the cells repair the damage rapidly. At higher doses (up to 100 rem), the cells might not be able to repair the damage, and the cells may either be changed permanently or die. Cells changed permanently may go on to produce abnormal cells when they divide and may become cancerous. At even higher doses, the cells cannot be replaced fast enough and tissues fail to function. An example of this would be radiation sickness. This is a condition that results after high doses is given to the whole body (>100 rem). Nuclear explosions and accidents in nuclear reactors are a serious source of radiation hazard. The effects of atomic explosions in Nagasaki and Hiroshima are still not forgotten. 5. Air Pollution Air is a mixture of gases - 78% nitrogen, 21% oxygen, 0.93 % Argon and 0.04% CO 2, - with traces of water vapor and various other components. It may be noted that air cannot be pure because some gases like Sulphur dioxide, carbon monoxide, oxides of nitrogen, emission from volcanoes and swamps, salt spray, pollens from plants etc., are continuously 12

13 added to the air by natural processes. Thus, air is polluted when its natural composition is disturbed either by natural or by man-made sources. Source of Air Pollution: The Principal sources of air pollution can either be natural or anthropogenic. (a) Natural Sources: The natural sources of air pollution are: (i) Forest Fire, (ii) Wind, (iii) Soil Erosion, (iv)volcanic Eruption, (v) Evaporation of volatile organic matter, and (vi) Bacterial decomposition products. (b) Anthropogenic Sources: (i) Automobile Exhaust: These contain carbon monoxide (CO), oxides of nitrogen and ethane. These gases are due to incomplete combustion of petrol and diesel. (ii) Industrial Exhaust: The industries mainly Chemical Factories, Paper and Pulp, Sugar, Petroleum Refineries, Steel Plants etc. are the chief air polluting agents. The industrial exhaust contain gases like CO, CO 2, SO 2, NO, NO 2, N 2 O, Cl 2, F 2, NH 3, and particulate matters. (iii) Release of organic substances : The processes like biological decomposition of organic matter, seepage from natural gas and oil fields, volatile emission from plants, sewage gas etc. are the causes for the release of organic substances like CH 4, C 2 H 6, C 6 H 5 NH 2, C 2 H 4 etc. 13

14 (iv) Release of Chlorofluorocarbons (CFCs): The chlorofluorocarbons are released to the atmosphere from air conditioners, refineries, pre cooler systems of cold storage etc. (v) Particulate Pollution: Solid and liquid aerosols suspended in atmosphere are referred as particulate matters. These arise from grinding of ores, spraying and soil erosion. Aerosols are chemicals, which are released into the air in the form of vapors. For example lead containing gasoline fumes from automobiles, constitute the chief source of lead contamination. (vi) Agricultural Chemicals: The agricultural chemicals like pesticides, insecticides, fungicides, herbicides etc. are also released into the air as pollutants. (vii) Explosives in War: A number of poisonous gases are released in the atmosphere during the explosions of sophisticated explosives in war. (viii) Photochemical Smogs: When different gases like SO 2, NO, N 2 O, NO 2 and un-burnt hydrocarbons are released into atmosphere, these form photochemical smog by combining with dust and moisture. (ix) Mining Activity: During mining activities i.e. crushing and grinding of ores, a lot of particulate matters are released to atmosphere. Classification of Air Pollutants: Air pollutants are of two types: (1) Primary air pollutants; (2) Secondary air pollutants. 14

15 1. Primary air pollutants: These are the harmful chemicals which directly enter into air due to natural events or human activities. For example, when carbon containing substance is burnt, it will release CO 2 and/or CO to atmosphere. These gases directly entering into atmosphere influence the biosphere are termed as primary pollutants. It is seen that there are mainly five primary pollutants which contribute together more than 90% of global air pollution. These are namely, carbon monoxide (CO) nitrogen oxides (NO 2 ), oxides of sulphur (SO 2 ) hydrocarbons (HC), and particulates. Different primary pollutants, their sources and amounts, released to air are given in table Secondary Air-Pollutants: These are the harmful chemicals produced in air due to chemical reaction in between two or more components i.e. the reaction in between primary air pollutant and some components of air. Usually the primary air pollutant suffers chemical changes in presence of H 2 O (v), O 2 (g) and ultraviolet radiation of sun to form secondary pollutants. 15

16 Some reactions showing conversion of primary pollutant to secondary pollutant are described below: Primary pollutant Reactant Secondary Pollution 1. CO 2 + H 2 O H 2 CO 3 (Carbonic acid) 2. H 2 S + 2O 2 H 2 SO 4 (Sulphuric acid) 3. SO 2 + O 2 SO 3, SO 3 + H 2 O H 2 SO 4 (Sulphuric acid) 4. NO 2 + O 2 2N 2 O s + H 2 O 2HNO 3 (Nitric acid) 5. HF (g) + H 2 O HF (aq) 6. SiF 6 + 2HF H 2 SiF 6 Important Air Pollutants: 1) Particulate matter Particulates are the small solid particles and liquid droplets present in the atmosphere in fairly large numbers. The presence of these particulates in air causes serious environmental consequences. 16

17 Sources The release of particulates into atmosphere is both natural and anthropogenic. The natural processes include volcanic eruption, blowing of dust and soil by wind, spraying of salt and other solid particles by the seas and oceans etc. The contributions from manmade activities are: fly ash from power plants, melters and mining operations, smokes from incomplete combustion processes etc. The incomplete combustion processes are fuel combustion from stationary sources (wood, coal, oil, natural gas etc.), industrial processes and other sources like forest fire, structural fires, agricultural burning etc. Effects i. Particulates of less than 1 µ reach alveoli of lungs and damage lungs tissues. ii. Soluble aerosols get absorbed into blood from alveoli while the insoluble aerosols are carried to the lymphatic stream and get deposited in the pulmonary, lymphatic depot point or lymp glands. iii. Cause the blockage of stomata in plants and inhibit plant respiration iv. Deposition of particulate on leaves prevents CO 2 absorption and hence decreases the rate of photosynthesis. 2. Nitrogen Oxide (NO x ): NO x exists as nitrous oxide (N 2 O), nitric oxide (NO), nitrogen trioxide (N 2 O 3 ), nitrogen peroxide (NO 2 ) and nitrogen pentoxide (N 2 O s ). Amongst all these nitrogen oxides, nitrogen peroxide (NO 2 ) and nitric oxide (NO) are the two main reagents causing air pollution. About 95% of NO x is released to the atmosphere mainly as NO as remaining as NO 2. Sources 1. Combustion of coal, oil, natural gases and gasoline. 2. By-products of some chemical industries like HN0 3 am H 2 SO Thermal power plants. 17

18 4. Supersonic aircraft exhaust. 5. Nuclear explosion. 6. Manufacture of nylon intermediates. Effects i. NO x causes acid rain by reacting with atmospheric moisture giving acids like nitric acid (HNO 3 ) and nitrous acid (HNO 2 ) ii. NO x released to the atmosphere moves up and reacts with ozone layer causing its depletion. Such a process allows the passage of UV radiation into earth surface. iii. The presence of excess quantity of NO and NO 2 induces smog formation and generates a number of harmful species like free radicals, PAN (Peroxy acetyl nitrate). 3. Sulphur-dioxide (SO 2 ) Sulphur-dioxide is the second potent air pollutant as it accounts for 29% of the total weight of all pollutants. Sources There are two sources of SO 2 (1) Natural Source, and (2) Anthropogenic source. Natural processes like volcanic eruption provide 67% of the S0 2 pollution which is distributed all over the globe. Anthropogenic source contribute about 33% of SO 2 pollution which is localized mainly in urban areas. Effects i. It causes swelling of nasal system and stimulates mucus secretion. ii. It causes lung cancer at high level. 18

19 iii. Presence of SO 2 in moisture and fog becomes more dangerous due to formation of H 2 SO 4 and H 2 SO 3 which are 5 to 20 time more irritating than SO 2 alone. iv. It kills leaf tissues causing leaf necrosis. v. It causes chlorosis and dwarfing when the concentration exceeds 1 ppm. vi. It attacks marble, limestone, roofing state, electrical contacts, textiles and buildings. 4. Carbon monoxide (Co) Sources Natural process like volcanic action, electrical discharge during storm or lightening, seed germination, marsh gas production etc. release small quantity of Carbon monoxide to the atmosphere. The significant contribution of carbon monoxide is from anthropogenic activities (transportation, agricultural burnings and industrial processes). Effects i. CO interferes with oxygen carrying function of hemoglobin by forming carboxy hemoglobin complex and inhibits the mobility of oxygen to body organs. ii. When CO concentration becomes ppm, it leads to loss of fertility, premature birth, spontaneous abortion and deformed babies in pregnant women. iii. CO inhibits nitrogen fixing ability of bacteria when these are exposed to CO level of 2000 ppm for hours. 5. Hydrocarbons: In addition to different gases, a series of hydrocarbons are released to the atmosphere either through natural processes or through human activities. These hydrocarbons sometimes behave like primary pollutants and some other times induce the formation of other potent secondary pollutants. Sources Natural sources of hydrocarbon release into air includes emission from trees, liberation from anaerobic decomposition of organic matter in presence of bacteria, liberation from domesticated animals etc. The 19

20 major anthropogenic sources are: automobile exhaust, industrial processes like processing, storage, transfer of products, incinerator and refuse burning and burning of coal and wood etc. Effects i. It has carcinogenic effects on lungs due to its swelling at higher concentration. ii. Excess of hydrocarbon causes blocking or respiratory tract. iii. Hydrocarbons retard the growth of plants and also cause chlorosis in plants. Consequences of Air Pollution 1. Ozone Layer Depletion: Ozone layer present in the stratosphere strongly absorbs UV radiation of nm and thereby protects life on earth from severe radiation damage. But due to continuous and non- interrupted release of chloroflurocarbons, oxides of nitrogen etc. by the civilized world, the ozone layer is constantly depleted. The reaction is medicated through a number of free radicals like CI +, CIO +, + OH etc. and a number of portent species like (O, NO, SO 2 NO 2 etc.) 2. Greenhouse gas effect The green house is that body which allows short wavelength solar radiation to pass through it but does not allow the long wavelength infrared radiation to escape. Due to rapid and unplanned industrialization the gases like CO 2, chlorofluorocarbons (CFCs), methane (CH 4 ), nitrogen oxides (NO x ), ozone (O 3 )/etc. accumulate in the atmosphere. The layer of these gases behave like wall of a greenhouse and transmit short wave solar radiations but does not allow the longer wavelength heat radiation (infrared) to be reflected back into outer space. That is greenhouse is transparent to solar radiation but not to heat radiation. Thus, the greenhouse effect may be defined as the progressive warming up of the atmosphere at the surface of earth due to blanketing of infrared radiation from the earth s surface by the greenhouse gases. The intensity of the effect increases in presence of dust, aerosols, etc. 20

21 3. Somg Smog is a combination of two words smoke and fog. Smoke is produced as a result of the incomplete combustion of fuels. The smoke contains various gases and suspended particulate matter. In addition, another substance responsible for smog formation is dust. Dust is nothing but small particle of solid matter that can be carried in suspension. Dusts are produced from forest fires, automobile exhaust, industrial combustion process, soil blowing by wind, ocean spray, mining areas, etc. Dust combines with smoke and later with fog to produce smog, which appears in the form of cloudy layer in the atmosphere. A thick cloud of smog is produced where smoke instead of escaping, the area to outer atmosphere stays nearer to the surface due to temperature inversion. Control of Air Pollution The following control measures should be adopted in order to reduce the level of air pollutants in environment. i. Pollution from domestic fire should be controlled to the house holder s use. Alternative methods of the fuels like smokeless chullah should be used in order to increase the fuel efficiency and reduce the emission of solid particulates. ii. As the plants absorb mainly air polluting gases like CO 2, there should be massive afforestation programme in industrial areas and big cities. iii. Setting of air quality standard for protection of environment and human health is highly essential. Ventilation and air-conditioning should be introduced. iv. More and more flyovers, bridges, bylanes, footpaths for pedestrians, steamers and ferry launches and other modes of navigational metropolitans public transport systems should be developed with a view to minimize the usage of individual auto vehicles and thereby smoke emissions. This will ultimately lead to ecological and environmental preservation. v. Environmental education and awareness programmes need to be institutionalized by incorporating these in the essential activities of educational institutions. vi. Use of unleaded petrol and diesel should be made compulsory. vii. The use and production of CFCs should be banned with suitable substitute in order to check air pollution. 21

22 viii. The vehicular exhaust should be minimized by using control valves in the outlets of the exhaust pipeline of the automobile. 22