Air Pollution.doc

1 UNIT – V ENVIRONMENTAL POLLUTION AIR POLLUTION Environmental pollution is the result of urban, industrial technological revolution and speedy exploitation of natural resources. INTRODUCTION:

POLLUTION:

It is defined ‘as the addition of pollutants or constituents to air, water, soil which adversely alter the quality of natural environment. (Or ) Imbalance in nature (air, water, soil) which adversely alter the quality of environment’. This phenomenon is called ‘Pollution’. The word pollution is derived from ‘Latin’ word ‘Pollutenum’ which means ‘Defilement’ (or) ‘Make Dirty’. Pollution is the accumulation of matter in the wrong place (or) any thing released into the environment which degrades its quality. Pollution is an undesirable change in the physical, chemical (or) biological characteristics of our air, land (or) water causing harmful effect on our life (or) that of other desirable species and cultural assets. The substance which is already present in environment and increase their concentration due to the human activity and can cause adverse effects on human being and his environment is called as ‘Pollutant’. CAUSES OF POLLUTION:

Human Population Explosion Rapid Industrialization Deforestation Unplanned Urbanization Scientific & Technological Revolution/ advancement CLASSIFICATION OF POLLUTION:

According to environment pollution can be classified into various types (a) Air Pollution (b) Water Pollution (c) Soil Pollution (d) Noise Pollution (e) Marine Pollution (f) Thermal Pollution (g) Radio – Active Pollution etc

2 AIR POLLUTION:

‘The presence of one or more constituents like dust, smoke, for and odour in the atmosphere which are injurious to humans, plants and animals’. Imbalance in quality of air so as to cause adverse effects on the living organisms existing on the earth. (or ) Addition unwanted articles like dust, smoke, mist and odour into atmosphere which causes adverse effects on human beings, plants, and animals called as ‘Air Pollution’. Pure is colourless and odourless, but various pollutants from the natural and man – made sources are entering the atmosphere daily & these are disturb the dynamic equilibrium in the atmosphere. This leads to air pollution when the normal properties of the air are upset & both man & environment. TYPES OF AIR POLLUTION:

Air Pollution may be personal or occupational/ community air pollution. (a) Personal Air Pollution: Exposure of an individual to dust, smoke, smog and gases may be regarded as ‘ Personal Air Pollution’. (b) Occupational/ Community Air Pollution: Exposure of an individual to potentially hazardous concentrations of aerosols, vapours and gases in his working environment is known as ‘ Occupational/ Community Air Pollution’. ENVIRONMENTAL SEGMENTS:

Environment may be broadly classified into four important segments (a) Atmosphere (b) Hydrosphere (c) Lithosphere (d) Bio – Sphere (a) Atmosphere: The study of air is called as ‘Atmosphere’. It consists of various gases like 78% of Nitrogen, 21% of Oxygen, 0.03% of Carbon – di – Oxide. Weight of Atmosphere: The total weight of atmosphere is approximately 4.5 - 5 X 1015 Metric Tonnes.

3 Atmosphere Acts as Screen: Atmosphere screens the dangerous UV radiations which are coming from the sun and transmits the radiations in the range of 380 nm to 760 nm. Role of Atmosphere: Atmosphere plays a vital role in the maintenance of heat balance on the earth by absorbing. The infrared radiations received from the sun and re-emitted by the earth surface, this phenomenon is called ‘Green-House Effect’ or ‘Global Warming’. Major regions of the atmosphere (or) structure of atmosphere: Atmosphere which extends up to 500km above the earth surface, can be broadly classified into four major regions which are  Troposphere  Stratosphere  Mesosphere  Thermosphere a) TROPOSPHERE:

 It is first layer of the atmosphere and nearest layer of the earth surface.  Tropo means ‘change’.  Different chemical elements undergo changes and form various compounds.  Ex: N2 (Nitrogen) + O2 (Oxygen )

----->

NOX (Oxides of Nitrogen).

 It extends from 0 to 11 km over the earth.  The temperature of this region rapidly from 300F to 700F.  The important chemical elements of this region are Nitrogen, Oxygen and Carbon di Oxide. b) STRATOSPHERE:

 It is the second layer of the atmosphere.  Stratosphere layer is also called as ‘’ozone layer’’ or ‘’Protective layer’’ of the atmosphere or ‘’Ozonosphere’’.  The important chemical element of this region Ozone so it is called as Ozone layer.

4  It protects the environment from dangerous ‘UV – radiations’ so it is called as ‘protective layer of atmosphere’.  The region has sufficient amount of ozone hence it is called as ‘Ozonosphere’.  It extends from 11km to 50km.  The thickness of this layer is about 40km.  The important chemical element of this region is ozone. c)

MESOSPHERE:

 It is the third layer of atmosphere  It extends from 50km to 85km.  Mesosphere region is also called is ‘‘Ionosphere’’, because due to the presence of ions in this region.  The important chemical ions of this region are CO+, NO+ etc. d) THERMOSPHERE:

 It is the fourth layer of the atmosphere.  Thermo means heat, excess of heat is present in this region so this region is called as ‘’Heat Zone’’.  It extends from 85km to 500km.  The important chemical ions of this region are CO+, NO+, N+, O+ etc.,

S.NO

Region

Altitude

Temperature (O0 C)

Imp Chemical Species

1

Troposphere

0 -11Km

15 to - 56

N2, O2, H2O

CO2,

2

Stratosphere

11- 50Km

-56 to -2

O3

3

Meso (or) Ionosphere

50 – 85Km

-2 to -92

O2+, NO+

4

Thermosphere

85 – 500Km

-92 to 1200

O2+, NO+,O+

5

COMPOSITION OF ATMOSPHERE:

Atmosphere components are divided into 3 types. a) Major Components b) Minor Components c) Trace Components a) MAJOR COMPONENTS:

Major components are Nitrogen –78% Oxygen—21% Water vapour—0.1 to 5% b) MINOR COMPONENTS:

Minor components are Argon—9.34 X 10-1 CO2—3.25 X 10-2

c) TRACE COMPONENTS: Trace components are Helium, Neon, krypton, Xenon, Methane, SO2, O3, NH3 and NO2. CLASSIFICATION OF AIR POLLUTANTS:

Air Pollution may be classified into different ways

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e) According to origin f) According to chemical composition g) According to state of matter (a). According to Origin: According to origin air pollutants may be classified into two types. (i)Primary Pollutants (ii)Secondary Pollutants (i) PRIMARY POLLUTANTS: These are the substances, which are emitted directly from the sources. Ex: CO, CO2, SO2 etc., (ii) SECONDARY POLLUTANTS: Secondary pollutants are the substances derived from the primary pollutants due to the chemical (or) photochemical reactions in the atmosphere. Ex: O3, PAN, PBN, H2SO4, HNO3 etc. (b) ACCORDING TO CHEMICAL COMPOSISTION: According to chemical composition air pollutants are classified into three types (i)Organic Pollutants (ii) Inorganic Pollutants (iii) Inorganic Particulates (i)ORGANIC

POLLUTANTS:

Ex: Aldehydes, Alcohols, Ketones, Acids, Amines etc (ii) INORGANIC POLLUTANTS: Ex: Carbon Compounds, Sulphur Compounds, Nitrogen Compounds, Halogen Compounds. (iii) INORGANIC PARTICULATES: Ex: Fly ash, Silica, Asbestos, Dust etc

7 (c ) According to State of Matter: According to state of matter air pollutants are classified into two types (i)Gaseous Pollutants (ii) Particulate Matter (i ) GASEOUS POLLUTANTS: Gaseous pollutants, which get mixed with air. Ex: CO, SO2 etc (ii) PARTICULATE MATTER:

Ex: Smoke, Fumes, Dust, Fog, Smog, Spray etc SINK OF ATMOSPHERE GASES:

Oceans as well as vegetation are the most important sinks for atmospheric gases. Types of Air Pollutants: Air pollutants re classified as Priamry and Secondary Pollutants Primary pollutants are harmful chemicals that are directly released from a source into the atmosphere. Secondary air pollutants are also harmful chemicals, but they are produced in the atmosphere from chemical reactions involving primary pollutants. Primary pollutants include the following a) Particulate matter, which includes bothsolid particle and liquid suspensions. Soil particles, soot, lead,asbestos, and sulphuric acid droplets are examples. b) Oxides of carbon, nitrogen andsulphur. c) Hydrocarbons like methane and benzene. Secondary air pollutants include the following a) Ozone: It is a form of oxygen and is apollutant in the troposphere oe the layer of the atmosphere closest to the Earth’s surface. It is a beneficial component of the stratosphere which extends from 10 – 50 Km above the earth. b) Sulphur trioxide: This is formed when sulphur dioxide reacts with oxygen. In turn, sulphur trioxide combines with water to form sulphuric acid.

Causes of Outdoor Pollution: The sources of outdoor Pollution are  Burning of fossilfuels  Mining activities leading to dust as well as fires  Burning nuclear fuels, biofuels, trpical rainforests, wastes of all kinds

8 

Natural emissions from animals and decaying organic matter.

Control of Otudoor Pollution: Automobile emissions can be reduced through varu=ious measures  Making cleaner and fuel – efficient cars.  Usning lead – free – petrol in existing cars.  Introducing policies that encourage the builf=ding and use of mass transit systems and discourage the use of personal transport Particulate matter in the air can be reduced by:  Fitting smokestacks with electroststic precipitators, fabric filters, scribbers, or similar devices  Sprinking water on dry soil that is being excavated during road construction Indoor air pollutants: The most common pollutants in urban ibteriors are Cigarette Smoke, gases from stoves, peasticides, cleaning solvent, mosquito repellents, paints, building materials like paints, asbestos, glass fibre, varnishes etc. Cigarette smoke affects both smokers and non – smokers. The concentration of pollutants indoors may be five times more than it is out doors. Urban indoor pollution results in ailments like colds, influenza, and upset stomachs. Indoor pollution can also cause eye irritation, nausea, depression et., collectivey called the ‘Sick Building Syndrome’. SOURCES OF AIR POLLUTION:

Main sources of air pollution are (i)Natural Sources (ii)Artificial Sources (i) Natural Sources: The natural sources of air pollution are  Volcanoic eruptions Forest fires Vegetative decay etc (ii) Man – Made Sources: Man – Made sources are  Human population explosion

9  Burning of fossil fuels  Deforestation  Rapid industrialization  Agricultural activities  Wars etc i)Human population explosion: The rapid growth of population is one of the most important factors of air pollution An increase in population leads to global warming Scarcity of water Scarcity of food & shelter Loss of forest cover  Loss of wildlife species Reduced production of food grains (ii) Deforestation: Plants plays a vital role in the maintenance of balance between CO 2 and O2 in nature, because it purifies the air by absorption of CO 2 and other gases like SO2, NOX etc. So plants are rightly called as ‘Earth Lungs’. (iii) Burning of Fossil fuels: Fossil fuels under go complete and incomplete reactions in atmosphere. By incomplete combustion of fossil fuels releases CO, SO 2, NOX, CH4 gases and by complete combustion of fossil fuels releases CO 2 gas. By the incomplete combustion of fossil fuels releases the gases into atmosphere in the form of dust, smoke etc which are broadly classified as (a) Fine Particles (b) Coarse Particles (a) Fine Particles: The size of the fine particle is ≤ 100 µ (b) Coarse Particle: The size of the coarse particle is ≥ 200 µ (iv) Rapid Industrialization: A large number of industries such as chemical, paper and pulp mills, cotton mills, metallurgical plants etc., are responsible for release of air pollutants in atmosphere. Most of the common air pollutants are CO2, CO, SO2, H2S, NO, NO2 etc., (V) Agricultural Activities: By using of different types of biocides such as insecticides, fungicides, rodenticides, pesticides are directly and indirectly release different types of pollutants into atmosphere. (VI) Wars:

10 Various types of sophisticated explosives used in wars also cause air pollution. Units for measurements of air pollutants in Atmosphere: There are mainly two common units to express the concentration of air pollutants. (a) ppm------ parts/million (b) µg/m3-----microgram / cubic meter

Air pollutants effects on Human beings: Oxides of Sulphur: [SO2, H2S]: These gases are freely mixed with air without settling down.

Sulphur- Di - Oxide (SO2): SO2 is the most important contribute of air pollutant Sources:

11 

Thermal power plants which burn sulphur – containing coal and diesel emit maximum amount of SO2 into the air.



Petroleum Industries



Oil refineries



H2SO4 Manufacturing plants



Sulphide Ore Roasting Plants



Sulphur containing substances or incomplete combustion of fossil fuels



fertilizers emits 75% of SO2 while automobiles and refineries contribute rest of 25% of SO2.

Hydrogen Sulphide (H2S): H2S enters into atmosphere through the decomposition of sewage water, volcanic eruption etc., and Sulphide causes headache problems. Characteristics of Oxides of Sulphur:  It is colourless, heavily water soluble gas with pungent and irritating odour.  Reach with water gives H2SO3, & H2SO4; rapidly diffusing acid forming oxidising agent. Reactions in Atmosphere: S

+

O2

 SO2

SO2

+

H2O

 H2SO3

(Sulphurous Acid)

H2SO3 + (O)  H2SO4 (Sulphuric Acid) Effects of Oxides of Sulphur:  Increased breathing rate  Respiratory diseases like Asthma, Bronchitis  Irritation to throat & Eyes  Suffocation Effects on Plants:

12  Cell membrane, Chlorophyll destruction  Metabolism inhibition, growth reduction Sulphur trioxide (SO3): Sulphur trioxide is formed by the oxidation of sulphur dioxide in the presence of sunlight. The presence of even 1 ppm of sulphur trioxide in the air can cause severe breathing trouble and irritation of the respiratory tract. The presence of sulphur dioxide and trioxide in air is destructive to plants. They are very destructive to the tissues of the lung and cause heart attacts. (ii)Carbon Monoxide [CO]: Carbon Monoxide produced into atmosphere by incomplete combustion of fossil fuels, natural gas emission, forest fires etc.. Characteristics of Oxides of Carbon Monoxide:  Colourless, Odourless and toxic gas.  Slightly soluble in water.  It has greater affinity towards Haemoglobin. Under Normal Conditions: Under normal conditions oxygen reacts with Hemoglobin forms oxy hemoglobin. O2 + Hb  O2Hb (Oxy- Heamoglobin) In presence of Carbon Monoxide: In presence of carbon monoxide, the oxy hemoglobin reacts with Carbon Monoxide forms Car boxy Hemoglobin. O2Hb + CO



COHb + O2

(Carboxy Hemoglobin)

Bio – Chemical effects of Carbon Monoxide:  Reduction of oxygen carrying capacity in RBC (Red Blood Cells)  Visual impairment & Paralysis  It causes serious effects on the cardio vascular system resulting in heart irregularities  Prolonged exposure can be fatal

13  Headache  Vomiting  Coma and finally leads  Death Standards of Carbon Monoxide: There are two standards for measurement of Carbon Monoxide a) 1 hr Standard b) 8 hr Standards Carbon - di – Oxide: It is a non – toxic and it is not harmful to human life. It is released into the atmosphere in the form of smoke which is produced by burning of fuels. The concentration of CO2 has gradually increased over the years with the increases in population, transport, urbanization, industrialization and deforestation. Effects of CO2: Excess of CO2 in the atmosphere causes respiratory problems & prolonged exposure can be fatal. (iii) Oxides of Nitrogen: Oxides of Nitrogen released into environment due to the incomplete combustion of fossil fuels and from nitrogenous fertilizers and from nitrogen manufacturing units. The two oxides are byproducts of the combustion of fuels like coal, diesel and petrol. Sources:  HNO3 Manufacturing Plants  Automobile Engine & Power Plants  Explosives  fertilizers Characteristics:  NOX mostly comprises NO, NO2, N2O etc  NO is colourless gas with slightly water soluble  NO2 is reddish brown gas with some what water soluble  Oxidising agent can reacts with water to form HNO3.

14  It is unpleasant in odour and causes eye irritation  It causes breathing trouble Reactions in Atmosphere: NO2 + O3  NO3 NO3 + NO2  N2O5 N2O5 + H2O  2HNO3 Bio – Chemical effects of Oxides of Nitrogen:

+

O2

 Respiratory irritation  Headache  Bronchitis  Pulmonary emphysema  Corrosion on teeth  Irritation to eyes & throat  NO2 reacts with the haemoglobin and leads to a condition called ‘Mathemoglobinemia’. This is known as ‘Blue Baby Syndrome’. It reduces the oxygen carrying capacity of blood. In sunlight, nitrogen oxides and hydrocarbons which are emitted from automobile engines form smog. Smog is very harmful to human beings and animals. (iv) Ozone: Ozone is present in atmosphere; it acts as protective layer of atmosphere and shields the earth from dangerous UV – Radiations. Characteristics of Ozone:  Ozone is pale blue gas  Fairly water soluble  Unstable  Highly reacting agent  Highly oxidising agent Bio – Chemical effects of Ozone:  DNA damage

15  Eye irritation  Asthma  Inhibition of activity of enzymes Smoke: It contains tiny particles like carbon, ash etc. It is formed by incomplete and complete combustion of fossil fuels. The Chief Sources of Smoke are: 

Industrial Power Plants



Furnaces



Auto mobiles etc

Smog: The combination of smoke and fog is called as ‘Smog’. It causes ‘Eye Irritation’. Hydro Carbons: Hydrocarbons are emitted into atmosphere from internal combustion engines of automobiles, petroleum refineries, rubber factories and by the decay of organic substances, to run the engine of vehicles, liquid fuel such as kerosene, diesel, petrol or gasoline has to be used. When such fuels are burnt, a lot of smoke is released into the atmosphere. Characteristics: 

Very reactive.



React with many kinds of compounds yielding many kinds of products.



Volatile hydro carbons & other organic compounds participate in atmospheric reactions generating ozone.

Bio – Chemical Effects: 

Some of these can react with the constituents of the cells.



Carcinogenic hydro carbons like benzopyrene can react with DNA causing mutations & Cancer.

Particulate Matter: Characteristics:

16 

Solid particles / liquid droplets including fumes, smoke, dust & aerosols.



Solid particles can absorb various chemicals.

Bio – Chemical Effects: 

Effects vary with the nature of the particle.



Leads to ‘Pneumoconiosis’.

Heavy Metals: Characteristics: Characteristics depend upon the nature of particular metal. Bio – Chemical Effects: 

Impairment of enzymatic activity by attacking sulphydryl & other functional groups.



Kidney damage.



Bronchitis.



Gastric & Intestinal disorders.



Cancer.



Disorder of heart, liver & brain.



Chronic & acute poisoning may result ‘Renal Dysfunction’, anaemia, hypertension bone – marrow disorders & cancer etc.

Photo Chemical Smog: In the presence of sunlight, the hydrocarbons react with oxides of N2 to form compounds like ozone aldehydes and peroxy acyl nitrate (PAN). These compounds are called ‘Photo Chemical Oxidants’. Effects: 

Irritation to eyes, nose throat & asthma.



They destroy vegetation & rubber products like tyres& insulating wires.



Causes poor atmospheric visibility.



High concentration of hydrocarbons affects the lungs.

17 

Aromatic hydrocarbons are carcinogenic and their inhalation can cause cancer, respiratory problems, damage to the nervous system and eventually lead to death.

Aerosols: Aerosols are the mixture of dispersed particles of microscopic size,. Chemicals & water droplets suspended in the atmosphere. Jets & aeroplanes release fluorocarbons, NO2 & SO2 directly into the O3 layer in the stratosphere thus destroying it. Hydrocarbons: It is discharged from industries manufacturing phosphate fertilizers, aluminium, combustion of coal and some metallurgical processes. Effects: It causes disorders of bones and teeth & respiratory diseases. This also causes flurosis of plants. Smog: Smog is a mixture of smoke and fog in suspended droplet form. Types of Smog: London Smog Los Angels Smog London Smog: It is smoke from combustion of coal and fog. Fog is mainly a mixture of SO2 & SO3 and humidity. It is generally harmful in the early morning and becomes worse after sunrise due to sun – light – induced oxidation of SO 2 & SO3. Then, SO3 reacts with humidity yielding H2SO4 in aerosol form. This can causes bronchial irritation and also acidrain. Smog also causes poor atmospheric visibility. Los Angels Smog (Photo Chemical Smog): It is not related to smoke or fog. It is worst in

the afternoon when sun shine peaks. The oxides of nitrogen (NO & NO 2) along with the CO2, H2O, CO and unburnt hydrocarbon particles which are emitted from automobile exhausts and SO2 cause Los Angels Smog. Effects of Photo Chemical Smog: 

Irritation to eyes & lungs



Irritation to nose & throat



Increased chance of asthmatic attack



Increased mortality



Damage to plants

18 

Green house effect



Acid rain



Ozone layer depletion etc.

19

AIR POLLUTION EFFECTS ON VEGETATION:

Air pollutants such as SO2, HF, Particulates, Fluorides, Smog, Oxidants like O 3, Ethylene, NOX, Cl2 effects on vegetation. These pollutants are directly enters into the leaf structure through stomata and damages the inner parts and external parts of the leaf. Extent damage depends on:  Nature and concentration of pollutant  Time of exposure  Soil and plant condition  Relative humidity  Extent of sun light etc Leaf Structure: The most obvious damage caused by air pollutant to vegetation occurs in the leaf structure. Cuticle: a waxy layer called as ‘Cuticle’ covers the surface layer of a leaf.

20

Epidermis: In between the waxy layers, a single layer of cells is present called as ‘Epidermis’. Types of Epidermis: Epidermis is divided into two types a) Upper Epidermis b) Lower Epidermis Functions of Epidermis: The chief function of Epidermis are  Protection of inner tissues from excessive moisture loss  Admission of C02 and O2 to these internal tissues. Stomata: Leaf structure is penetrated by a large number of openings called as ‘Stomata’. Guard Cells: Each stomata is protected by a pair of cells called as ‘Guard Cells’. It controls the openings and closing of these stomata. Cross Section of a Leaf:

21 Effects of Vegetation: Different types of pollutants are enters into leaf structure through stomata. a) Necrosis b) Chlorosis c) Epinasty a) Necrosis: Dead areas on leaf structure are called as ‘Necrosis’ or killing or collapse of tissues. b) Chlorosis: The loss (or) reduction of chlorophyll and leads to the yellowing of the leaf. c) Epinasty: Epinasty is a downward curve of the leaf due to the higher rate of growth on upper surface and the dropping of leaves is called ‘Epinasty’. d) Abcision: Dropping of leaves Injuries to leaves:

EFFECTS OF AIR POLLUTION ON BUILDING MATERIALS: The materials that may be effected by air pollutants includes Metals, Building materials, Rubber, Elastomers, Papers, Textiles, Leather, Dyes, Glass, Enamels and Surface coatings etc.

22 Possible damage by these materials by air pollutants includes  Corrosion  Abrasion  Deposition  Weakening  Discoloration  Surface erosion  Cracking  Reduces tensile strength Test Methods for Major Air Pollutants in Ambient Air: a) Particulate Matter: High Volume Sampler b) Sulphur Di – Oxide: West – Greek Method c) Ozone: Chemiluminescent Method d) Carbon Monoxide: NDIR Principle (Non – Dispersive Infrared Radiation) e) Hydro Carbon : Flame Ionisation Detector AIR POLLUTION – CONTROL METHODS:

The following two basic approaches are used for the control of air pollutants. (i)Controlling the pollutants at the source (ii)Dilution of the pollutants in the atmosphere Various Control Methods are (i) Combustion (ii) Absorption (iii) Adsorption (iv) Condensation (v) Incineration (vi) Settling Chambers (vii) Electrostatic Precipitators (viii) Cyclonic Separators (ix) Wet Scrubbers (x) Filtration Methods (xi) Cold Trapping

23 (i) Combustion: This technique is mainly used when the pollutants are in gaseous state. Generally flame combustion and catalytic combustions are used for removal of gaseous air pollutants. (a) Flame Combustion: By using of direct flame for combustion of air pollutants. (b) Catalytic combustion: By adding of different types of catalysts to the gaseous mixture. Finally these gaseous pollutants are converted into CO 2 and water vapour. (ii) Absorption: a liquid absorbent is used to remove gaseous pollutants. The commonly used Absorbents are: H2O (Water) HNO3 NaOH + Phenol Alkaline Water (iii) Adsorption: Charcoal, Al2O3and Silica gel are very good adsorbents for gaseous pollutants. In this process, activated charcoal is kept in a thick glass tube. When polluted air is passed through the tube, the pollutants get adsorbed on the charcoal and are then collected after dissolving them in CS2. The solution is then analyzed using gas chromatography. The commonly used Adsorbents are  NaF Pellets  Iron Oxide  Activated Carbon  Silica Gel etc (iv)Condensation: Air pollutants are gets condensed at high temperature & pressure, after some time these are converted in to liquids. (v) Incineration: Air pollutants are passes through the incinerator at high temperature (800 – 15000), pollutants are gets condensed. (vi) Settling Chambers: It is the simplest device for the collection of particulate matter. The particulates with a size greater than 50 µm can be removed from the air using this equipment. The settling chamber consists of a horizontal chamber through which polluted air is passed slowly so that the particulates settle down from the moving stream on the base of the chamber by the action of gravitational force. Advantages of Settling Chambers:  Low Capital cost  Low Energy cost  No Maintenance Cost  No Operational Cost  No moving cost Disadvantages of Settling Chambers:

24

 

It cannot remove the thicky particles. It can remove the particles > 50µ in diameter.

(v) Cyclone Separators / Cyclone Collectors: It is used as per – cleaner for the emitted gaseous exhaust. It consists of a vertical cylinder with a conical bottom. Centrifugal force is utilized by cyclone separators to separate particulate matter from the polluted gases.

(vi) Electrostatic Precipitators: This technique is used for the removal of particulate matter as well as gaseous air pollutants. An electrostatic precipitator consists of two electrodes namely Cathode and Anode electrodes which are electrically insulated from each other but electric potential difference exits between two electrodes. One electrode consists of high electric potential and another one is consists of low electric potential. When gas containing aerosols Ex: Dust, Fumes(or) Mist is passed between two electrodes which are electrically insulator with each other and which appreciable difference in electrical potential exists, then the aerosol particles get precipitate on the electrodes that is at a lower potential. Advantages of Electrostatic Precipitators:

25

 High efficiency  High temperature  Low operating cost Disadvantages of Electrostatic Precipitators:   

High capital cost Need lot of space Not flexible to change

(vii) Wet Scrubbers: It is a cylindrical chamber with a conical bottom. It is packed with broken stone or plastic. Water is sprayed downwards from the top of the chamber. Polluted gas is passed upward. The downward flow of water will separate the particulates from the air and they get collected at the bottom of the chamber. Venturi Scrubbers: Two cylinders are connected horizontally through a their glass tube. The scrubbing liquid or water is injected at the throat. Particulates of 2 – 3 µm are separated by this method. The polluted air is passed through a scrubber with a high velocity.

26 (Viii) Filtration Method: Polluted air is passed through a filter device to filter out the particulates. Fibrous medium – fabrics like wool or cellulous may be used as the filter media. The bag filter is the most commonly used in industries. Advantages:  Simple construction & Operation  Very efficiency for trapping of fine particles and  Normal power consumptions. Disadvantages:    

Requires lot of space Bad for moisture conditions / moisture Bad for high temperature Need frequent clearing

Cold Trapping: Gaseous pollutants can be liquefied and removed from the flue gas. The collectors are kept at a very low temperature. The first receiver or collector is kept at 0 0C in an ice bath and the last one is kept at -1960C in a liquid nitrogen bath. National Ambient Air Quality Standards: These are permissible exposure limits for living and non – living things for 24 hrs per day, 7 days per week or per annum. According to the Environmental Protection Agency (EPA), national ambient air quality standards have two levels – primary and secondary. Primary standards protect public health and secondary standards protect public welfare (Plants, crops, animals). National ambient air quality standards now exist for seven pollutants – Carbon Monoxide, Nitrogen – di – Oxide, ozone, lead and particulates.

27 National Ambient Air Quality Standards in India (Central Pollution Control Board, New Delhi): The ambient air quality standards given by CPCB are given below

Pollutants

Time- Weighted Industrial Area Average

Residential, other Sensitive areas areas

Sulphur dioxide Annual average

80µg / m3

60µg / m3

15µg / m3

Oxides Nitrogen

80µg / m3

60µg / m3

15µg / m3

Annual average

360µg / m3

140µg / m3

70µg / m3

Respirable Annual average Particulate Matter (Size less than 10 microns)

120µg / m3

60µg / m3

50µg / m3

Lead

Annual average

1.0µg / m3

0.75µg / m3

0.50µg / m3

Ammonia

Annual average

0.1µg / m3

0.1µg / m3

0.1µg / m3

Suspended Particulate Matter (SPM)

of Annual average