Air and Noise Pollution
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<ul><li><p> 1 </p><p>ATMOSPHERE </p><p>The atmosphere is an envelope of gases that surrounds the earth. The air we breathe is the </p><p>part of atmosphere. Scientists have divided the atmosphere into four main parts, each with its own </p><p>characteristics. They are: </p><p>1. Troposphere </p><p>2. Stratosphere </p><p>3. Mesosphere </p><p>4. Thermosphere </p><p>1. Troposphere: </p><p>The layer of atmosphere that touches the surface of earth is called Troposphere. The </p><p>troposphere extends to a height of about 8 to 18 kilometers above the surface of earth. </p><p>Most of the living organisms come under troposphere. This layer contains most of the water </p><p>vapors in the atmosphere and this is only the layer in the atmosphere where weather changes occur. </p><p>2. Stratosphere: </p><p>Beyond the troposphere, reaching at a height of about 50 kilometers above the surface of </p><p>earth is Stratosphere. Most jet planes travels in the lower level of stratosphere. The upper level of </p><p>stratosphere contains a layer of gases called OZONE. </p><p>3. Mesosphere: </p><p>After the layer of stratosphere, there is another layer called Mesosphere which is extended </p><p>up to 85 kilometers above the surface of earth. The mesosphere is the coldest layer of the </p><p>atmosphere. Its temperature can be as low as -100 oC. </p><p>4. Thermosphere: </p><p>Thermosphere is the most outer layer of atmosphere. Unlike the mesosphere, thermosphere </p><p>has a very high temperature reaching up to 2000 oC </p><p>Biosphere: </p><p>The living environment, known as biosphere consist of Land (Lithosphere), Water </p><p>(Hydrosphere) and Air (Atmosphere) is the basic layer to sustain Food and </p><p>. </p><p>AIR POLLUTION </p><p>(1) Air: </p><p>Atmosphere is the column of air that surrounds the earth, starting from the surface of earth </p><p>to the altitude of 18 Km called Troposphere. Air is blanket of gases that contain: </p><p>Nitrogen 78.09% by volume, Oxygen 20.94% by volume and other gases like Carbon, Argon, </p><p>Neon, Helium, Methane, etc. These are in pure and perfect harmony. </p></li><li><p> 2 </p><p>(2) Pollution: </p><p>Air polluted due to the presence of one or more than one contaminant present in the air in </p><p>sufficient quantity, composition and characteristics which causes injury to life as well as damages </p><p>the materials and properties. </p><p>Organic are: Methane, Benzene, formaldehyde, chlorinated hydrocarbons </p><p>AND </p><p>Inorganic are: NOX, SOX, COX, H2S, HF, NH3. </p><p>(3) Control: </p><p>A. Naturally self cleansing way of the environment </p><p>1. Dispersion </p><p>2. Gravitational settling </p><p>3. Natural Absorption process </p><p>4. Rain out </p><p>5. Adsorption </p><p>B. Controlling Air Pollution source through engineering devices. </p><p>1. Stationary Source and </p><p>2. Mobile Source </p><p>Stationary Source: </p><p>a. Absorption </p><p>1a.) - Wet Scrubbers </p><p>2a.) - Dry Scrubbers </p><p>b. Combustion </p><p>c. Fuel Gas Desulphurization </p><p>d. Particulate Pollutants </p><p>Mobile Sources: </p><p>a. Fundamentals of different available engines </p><p>b. Control </p><p>Dispersion: </p><p> Dispersion of pollutants by winds reduces the concentrations of air pollutants by moving the </p><p>smog from one place to another. This diluted the smoke but not remove it. </p><p> To calculate it mathematically a model has been developed to estimate the concentration of </p><p>the particular pollutant for the specific location and time. </p></li><li><p> 3 </p><p>Gravitational Settling: </p><p> Gravitational Settling is the most important natural mechanism under which large particles </p><p>from the ambient air settle down on the buildings, trees and other objects. </p><p> This process helps in removing large amount of particles formed by uniting of the smaller </p><p>particles over the large particles, till the united particles becomes large and heavy enough to settle </p><p>down under the gravity. </p><p>Natural Absorption Process: </p><p> The gaseous as well as particulates pollutants from the air get collected in rain or mist and </p><p>settle down with that moisture. This phenomenon takes place below the cloud level, when falling </p><p>rain drops absorb pollutants also known as wash out or scavenging. </p><p> This does not remove particles less than 1 micro meter. The gaseous pollutants are removed </p><p>in dissolved state with moisture either with or without chemical damages. </p><p>Rainout: </p><p> In this process precipitation in the clouds where sub micro particles in the atmosphere in the </p><p>clouds serve as a condensation nuclei around which drops of water may form and fallout as rain </p><p>drops. This increases the rainfall and fog formation in the urban areas. </p><p>Adsorption: </p><p> This is the phenomenon in which gaseous or the liquids pollutants present in the ambient air </p><p>we kept attracted, generally electro statically by a surface where they are concentrated and retained. </p><p> Natural surface such as soil, rocks, leaves, and blades of grass, buildings and other objects </p><p>can absorb and retain pollutants. The particles may come in contact with such surfaces either by </p><p>gravitational settling or by internal impaction. </p><p>Absorption: </p><p> Control devices work on the principle that they absorb and transfer the pollutant smoke </p><p>from gas to the liquid state. </p><p> It is a mass transfer process in which gas is dissolved in the liquid. This conversion may or </p><p>may not accompanied by a reaction with water. </p><p> This is purely a diffusion process where pollutants move from higher concentration to the </p><p>lower concentration. </p></li><li><p> 4 </p><p>Scrubbers: </p><p> It is one of the most common pollution control device used by the industries. It is operated </p><p>on a very simple principle that the polluted gas is brought into contact with the absorbent so that the </p><p>pollutants can be removed. </p><p>There are two types of Scrubbers: Wet Scrubbers and Dry Scrubbers. Mechanism of both </p><p>the scrubbers is almost same. The only difference is in case of Dry Scrubbers End Product is in </p><p>solid form while in case of Wet Scrubbers it is found in liquid form. </p><p>Combustion: </p><p> When the contaminant in the gas is oxidize able to an inert gas than combustion for </p><p>contaminant control is used. </p><p> There are two methods are used commercially as: </p><p>1) Direct Flume Combustion </p><p>2) Catalytic Combustion. </p><p>Direct flume combustion: </p><p>This method used when: </p><p>1) The gas stream must have an energy concentration greater than 3.7 MJ/m3. At this </p><p>concentration the gas flume will be self supporting after ignition, below this point the </p><p>supplementary fuel is required. </p><p>2) None of the by-products of combustion be toxic. </p><p>In some cases the combustion byproducts may be more toxic than the original pollutant gas. For </p><p>example the combustion of trichloroethylene will produce Phosgene, which was used as a war gas </p><p>in World War I. </p><p>Direct flume applied to Varnish cooking, meat smoke house and paint bake oven emission. </p><p>Catalytic Combustion: </p><p>Some catalytic materials enable oxidation to be carried out in gases that have an energy less </p><p>than 3.7 MJ/m3. </p><p>Active catalyst is a platinum or Palladium compound. </p><p>Supporting lattice is usually a Ceramic. </p><p>These are expensive, liable to poisoning by sulfur and lead compounds in trace amounts. </p><p>Catalytic combustion has successfully applied to printing press, varnish cooking and asphalt </p><p>oxidation emission. </p></li><li><p> 5 </p><p>Fuel Gas Desulphurization (FGD): </p><p> The technology that employs absorbent, usually lime or limestone, to remove SO2 from the </p><p>gases produced by burning fossil fuels. Flue gas desulphurization is the current technology for </p><p>major SO2 emitters, like power plants. </p><p> Lime is used to remove SO2 from coal fired power station gases (called FGD) the product is </p><p>Gypsum. </p><p>CaO(s) + SO2 (g) + 2H2O (1) + O2 (g) CaSO4. 2H2(s) </p><p> This system may used with the scrubbers or in the towers through two broad ways. </p><p> Regenerative (Reusable) </p><p> Non regenerative. (Not reusable) </p><p>In terms of the number and size of system installed, the non-regenerative system dominates. </p><p>Cyclone: </p><p> For particle size greater than above 10 um, the collector of choice is the cyclone. </p><p> This is inertial collector with no moving parts. </p><p> The particulate gas is accelerated through a spiral (round) Motion, which imparts a </p><p>centrifugal force to the particles. Due to which the particles by force come out of the gas and </p><p>impact on the cylinder wall of the cyclone. Then they slide to the bottom of the cone, where they </p><p>are removed through an air tight valving system. </p><p> The efficiency of collection of various particle sizes can be determined through an </p><p>expression given below. </p><p> [(9 B2 H)] </p><p>d0.5= </p><p> [p Qg ] </p><p>As the diameter of the cyclone is reduced, the efficiency of collection increased, pressure </p><p>drop also increases which ultimately increases the power requirement for moving the gas through </p><p>the collector. </p><p>With the increase in the efficiency tangential velocity remains constant and the efficiency </p><p>increases with increase in the power consumption by using multiple cyclones in parallel. </p><p>Filter: </p><p> When the high efficiency controls of particles smaller than 5um are desired than we use </p><p>filters. </p><p> There are two types of filters in use 1 deep bed filters 2 the bag house. </p></li><li><p> 6 </p><p> The deep bed filters resembles like a furnace filter, having packing of fibers used to block </p><p>the particles of the gas stream, used in air conditioners. </p><p> For the dirty industrial gas, we have the bag house filters, made of cloth fabric. Their </p><p>diameter range from 0.1 to 0.35 m and their length vary b/w 2 6 m. </p><p>AIR POLLUTANTS </p><p> Due to natural and man-made pollution, the air is never found clean in the atmosphere. </p><p>Gases such as CO, SO2 and H2O are continuously releases into the atmosphere through natural </p><p>activate (Volcanic activity, Vegetation decay and Forest fires). Tiny particles of solids and liquids </p><p>are distributed throughout the air by winds, volcanic explosion and other similar natural </p><p>disturbances. In addition to these natural pollutants, there are man-made pollutants also which </p><p>hardly exist beyond 21000 feet above ground level. </p><p>Air pollutants may be Natural and Man-made pollutants; these are also classified in to two </p><p>categories: as Primary Pollutants and Secondary Pollutants. </p><p>PRIMARY AIR POLLUTANTS: </p><p>Those pollutants that are emitted directly from the source and are found in the atmosphere </p><p>in the form in which they were emitted are called Primary Pollutants. Primary air pollutants are </p><p>formed else where and discharged as such into the air. </p><p>SECONDARY POLLUTANTS: </p><p>Secondary air Pollutants are formed in the air were primary air pollutants react with each </p><p>other. Sulfur dioxide (SO2) is a primary air pollutant that forms when fossil fuel is burned. In the air </p><p>it may react with oxygen gas to form secondary pollutant sulfur trioxide. 2SO2 + O2 2SO3 </p><p>This is turn may react with water vapor in the air to form another secondary air pollutant, </p><p>i.e., sulfuric acid (H2SO4). SO3 + H2O H2SO4. </p><p>This is one of the substances that can make rain acidic. There are so many sources of air </p><p>pollutants but they are classified in to two groups. </p><p>i)- Natural </p><p>ii)- Man-made or Anthropogenic </p><p>I) - Natural Source: </p><p> Natural factor include metrological and sometimes geographical conditions restrict the </p><p>normal dilution of contaminant. There are many naturally occurring air borne materials such as </p></li><li><p> 7 </p><p>from flower, gas from decaying matter, micro organisms, particulates from nature forest fires, dust </p><p>storms, and volcanic eruptions. The natural factors usually beyond mans sphere of control </p><p>II) - Man-made Source/ Anthropogenic Sources: </p><p> The man made factors are also referred as an Anthropogenic Sources. They include </p><p>industrial processing, Vehicular usage, Power generation, nuclear explosions and other man made </p><p>polluted use radio active isotopes. </p><p>IMPORTANT PRIMARY AIR POLLUTANTS ARE: </p><p> Sulfur Oxides (SOX), particularly Sulfur dioxide (SO2) </p><p> Carbon Mono Oxide (CO) </p><p> Nitrogen Oxides (NOX) </p><p> Lead </p><p> Hydrocarbons both Aliphatic and Aromatic </p><p> Allergic Agents like Pollens and Spores </p><p> Radio Active substances </p><p> Hydrogen Sulfide </p><p> Hydrogen Fluoride </p><p> Methyl and ethyl meraptans </p><p>IMPORTANT SECONDARY AIR POLLUTANTS ARE: </p><p> Sulfuric Acid (H2SO4) </p><p> Ozone (O3) </p><p> Formaldehydes </p><p> Peroxy Acyl Nitrate (PAN) </p><p>SOURCES OF SOME IMPORTANT AIR POLLUTANTS AND THEIR EFFECTS: </p><p>Pollutant: Carbon Mono Oxide (CO) </p><p>Major Source: Incomplete combustion of fuel, automobile exhaust, jet engine emission, mines </p><p> and tobacco smoking. </p><p>Effects: Toxicity (poisonous) caused blood poisoning. </p><p>Pollutant: Sulfur dioxide (SO2) </p><p>Major Source: Combustion of coal, Combustion of Petroleum products, Oil Refinery, Power </p><p>House (Coal), Sulfuric Acid Plants, and Domestic burning fuels </p><p>Effects: Increasing the breathing rate, Suffocation, asthma, Irritation of eyes. </p><p>Pollutant: Nitrogen Oxide (NOX) </p></li><li><p> 8 </p><p>Major Source: Automobile exhaust, Gas fire furnace, Fertilizer Industry. </p><p>Effects: Respiratory Irritation, Headache, Corrosion of Teeth </p><p>Pollutant: Carbon dioxide (CO2) </p><p>Major Source: Combustion of Fuel, Jet engine emission. </p><p>Effects: Toxic in large quantities. </p><p>Pollutant: Hydrocarbons (HC) </p><p>Major Source: Organic Chemical Industry, Petroleum Refinery </p><p>Effects: Cancer </p><p>Pollutant: Ammonia (NH3) </p><p>Major Source: All chemical Industries </p><p>Effects: Aspiratory System, Eyes Irritation </p><p>Pollutant: Formaldehyde (NCHO) </p><p>Major Source: Combustion of Fuel, Photo Chemical Reaction </p><p>Effects: Irritation of eyes, Skin, Aspiratory. </p><p>Pollutant: Hydrogen Sulphide (H2S) </p><p>Major Source: Petroleum Industry, Coal Ovens, Oil refinery, Sewage Treatment Plant </p><p>Effects: Headache, Eyes pain, Irritation Aspiratory. </p><p>ACID RAIN Acid Rain or more precisely acid precipitation is the word used to describe Rain-fall that </p><p>has pH level less than 5.6. But in broader sense Acid Rain is a term used to describe several </p><p>ways that acids fall out from the atmosphere. </p><p>A more term is acid deposition, has two parts: Wet and Dry. </p><p> Wet deposition refers to Acidic Rain, Fog and Snow, and </p><p> Dry deposition refers to acidic gases and particles. </p><p>About half of the acidity in the atmosphere falls back to the earth by means of Dry Deposition. </p><p>CHEMISTRY OF ACID RAIN: </p><p>Major contributing gases for acid rain are: Oxides of Sulfur (SOX), Oxides of Nitrogen </p><p>(NOX), Oxides of Carbon (COX), and Chlorine (Cl2) dissolve in the air and causes acid rain. </p><p>The following reactions show the acid formation due to these gases: as; </p><p> Oxides of Sulfur reacts with water in air and forms Sulfuric Acid (H2SO4). </p><p>SO2 + 2H2O H2SO4 </p></li><li><p> 9 </p><p> Oxides of Nitrogen reacts with water in air and forms Nitric Acid (HNO3). </p><p> NO2 + H2O HNO3 </p><p> Oxides of Carbon reacts with water in air and forms Carbonic Acid (HCO3). </p><p> CO2 + H2O HCO3 </p><p> Chlorine reacts with water in air and forms Hydrochloric Acid (HCl) </p><p> 2Cl2 + 2H2O 4HCl + O2 </p><p>CAUSES OF ACID RAINS: </p><p>Acid rain is caused by smoke and gases that are given off by factories and cars that run on </p><p>fossil fuels. When these fuels are burned to produce energy, the sulfur that is present in the fuel </p><p>combines with oxygen and becomes sulfur dioxide; some of the nitrogen in the air becomes </p><p>nitrogen oxide. These pollutants go into the atmosphere, and become acid. </p><p>Sulfur dioxide and nitrogen oxide are produced especially when coal is burnt for fuel and </p><p>for more electricity, more coal is burnt. Burning coal produces electricity. Now-a-days people </p><p>pro...</p></li></ul>
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