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Air Pollution: causes and control

PRESENTED BY:VISHNURAJ R.SDEPT.AQUATIC BIOLOGY &FISHERIES

Air is one of the vital part of life .Air supplies with oxygen is essential for our bodies to live. Air is 99.9% nitrogen, oxygen, water vapors and inert gases. Due to man made activities along with some natural processes many physical addition of material that turn the air impure or unclean. That is called air pollution. Air PollutionAir PollutionAir pollution primarily comes from burning fossil fuels such as natural gas, petroleum, and coal. Humans are the main cause of air pollution. Industry, including factories and power plants, burn large quantities of fuel. Burning coal and petroleum releases sulfur oxides and nitrogen oxide into the air. Airplanes, boats, and cars burn petroleum, releasing carbon monoxide and carbon dioxide.

Air PollutionSome air pollution is not directly caused by humans: for example, animals emit carbon dioxide when they breathe, and volcanoes release sulfur oxide. The forest fire produce huge amount of CO,CO2, Nitrogen oxides, semi burnt hydro carbons, and ash.The waste in landfills releases methane. Sulfur oxides, carbon monoxide and carbon dioxide, and methane all have a very negative effect on air quality. These pollutants can also contribute to the greenhouse effect. The dust storm make the air full of particulate sand particles. Primary vs Secondary pollutantsNot all of the pollutants found in the atmosphere are the direct result of emissions. Many pollutants arise from chemical reactions in the atmosphere with other substances or light (photochemical reactions). Pollutant substances that are directly emitted into the atmosphere = primary pollutants. Substances not directly emitted into the atmosphere, formed by chemical reactions in the atmosphere = secondary pollutants.

TYPES OF POLLUTION INDOOR POLLUTIONIndoor air pollution occurs inside our homes, office and schools. The main types of indoor pollutants are tobacco smoke, gases from stoves and furnaces, household chemicals, small fiber particles, and hazardous fumes given off by building materials like insulation , glue, and paint .In high amounts it causes headache, eye irritation, etc.OUTDOOR POLLUTIONGases and particulates form of pollutants pour into the atmosphere from the burning of fuel to motor vehicles, heat buildings, business and industrial processes , burning of garbage etcOutdoor pollution make huge impacts on atmosphere and the organismsAcid rain , global warming, etc are some of its consequences .

TYPES OF POLLUTANTSAerosolsParticulates solid phaseDustAshFumes Solid and liquidSmoke (from combustion)Coastal aerosolsLiquid Aggregate gases (sulfate, nitrate) GasesCOxSOxNOxPAH

Six primary or criteria air pollutantsCarbon monoxide (CO)Sulfur oxides (SOx)Nitrogen dioxide (NO2)Ozone (O3)HydrocarbonsParticulate matter(PM2.5 _PM10)

Carbon Monoxidecolorless, odorless, tasteless, non irritating gasproduced when carbon does not burn in fossil fuels,ie incomplete combustion.Commonly present in automobile exhaustdeprives body of O2 causing headaches, fatigue, and impaired vision, it may lethal when continually inhale concentration above 1000ppm over a period of 4 hours.

Sulfur DioxideColourless gas with penetrating and pungent odourproduced mainly when coal and fuel oil are burnedpresent in power plant exhaustnarrows the airway, causing wheezing and shortness of breath, especially in those with asthmaThe formation of SO2, SO3, and sulfuric acid

S + O2 SO22 SO2 + O2 2SO3SO3 + H2O H2SO4Nitrogen Dioxidereddish, brown gasproduced when nitric oxide combines with oxygen in the atmospherepresent in car exhaust and power plantsaffects lungs and causes wheezing; increases chance of respiratory failure.

Smokers may readily develop lung disease as cigarettes and cigars containing 330 to 1,500 ppm nitrogen oxides. Prolonged exposure at 1 to3 ppm or even less may fatal. It also react with water to cause acid rain 4NO2+2H2O+O2 ------- 4HNO3

Ground Level OzoneIt is a highly reactive pale-blue gas with penetrating odour. at upper level, ozone shields Earth from suns harmful UV raysat ground level, ozone is harmful pollutantsformed from automobile, power and chemical plant exhaustirritate respiratory system and asthma; reduces lung function by inflaming and damaging lining of lungsIt also a green house gas

HYDROCARBONSHydrocarbons are compounds that have carbon and hydrogenBenzene, benzpyrene, methane, etc are common hydrocarbon pollutants.The major sources are automobile and industrial exhaust..Benzene: colorless, flammable liquid pollutant have carcinogenic propertyBenzpyrene: it is also carcinogenic,Methane is common green house gas .. It produce by naturally along with human activities.Particulate Matterparticles of different sizes and structures that are released into the atmosphereLead, asbestos etc are some particulate matter from man made sourcespresent in many sources including fossil fuels, dust, smoke, fog, forest fire etc. Along with these industrial operations like mining, polishing etc also produce..can build up in respiratory systemaggravates heart and lung disease; increases risk of respiratory infection

Methods of air pollution control can be divided into two categories: THE CONTROL OF PARTICULATE EMISSIONS THE CONTROL OF GASEOUS EMISSIONSThe term particulate refers to tiny particles of mattersuch as smoke, soot, and dust that are released during industrial, agricultural, or other activities.Gaseous emissions are industrial products such as sulfur dioxide, carbon monoxide, and oxides ofnitrogen also released during various manufacturing operations.

Control of Air Pollutants

Particulates Cyclonesseparation by centrifugation

Cyclone utilise centrifugal force generated by a spinning gas stream to separate the particulate matter from the carrier gas.The general principle of inertia separation is that the particulate-laden gas is forced to change direction. As gas changes direction, the inertia of the particles causes them to continue in the original direction and be separated from the gas stream.

THE CONTROL OF PARTICULATE EMISSIONS

Cyclone separator2.Gravitational Settling Chamber

Like settling basins in water and waste water treatment, settling chambers provide enlarged areas to minimize horizontal velocities of air flow thus allow time forgravity to carry the particle to the floor.These are simple in design and operation but they require large spaces for installation and have relatively low efficiency especially for removal of smallparticles.

3.Particulates FiltrationFibre bags commonly used for control of particulate emissions with very high dust loadings and smaller particles. Filters consist of porous structure composed ofgranular or fibrous material which tends to retain the particulate matter as the carrier gaspasses through the voids of the filter.

The dust is collected on the inside of the bag surface and the filtered gas is discharged to the atmosphere - 99% efficient

4.Particulates Wet Scrubbersspray systems where fine water droplets are sprayed at high velocity at right angles to the emerging gas Most of the particles in the gas stream are scavenged by the water droplets, which fall and are collected along with the particles relatively low efficiencies (80-90%) and is usually employed as a pre-cleaner to remove particles larger than 5m

pass dirty gas through a series of fine wires (coronas) charged with DC current causes particles to aggregate & precipitate Alternatively corona produces negative ions that cause particles in the gas stream to become negatively charged, and attracted to positive terminal where they aggregate and fall into a collection hopper Large precipitators and low gas flow rates give better results

5.Particulates Electrostatic Precipitators

Gaseous pollutants Process Modificationssimplest and least expensive methods for the control of gaseous pollutants fuel substitution e.g. low sulfur coal, or fuel oils in place of cheaper coal can greatly reduce the amount of SO2 emissions at the source This type of source control is always the best approach wherever possible Gaseous pollutants - Combustioninvolves a series of complex chemical reactions in which oxygen is combined with organic molecules, to form CO2 and H2O commonly referred to as incineration or afterburning

Gaseous pollutants - Adsorptionphysical adsorption to solid surfaces Reversible - adsorbate removed from the adsorbent by increasing temp. or lowering pressure widely used for solvent recovery in dry cleaning, metal degreasing operations, surface coating, and rayon, plastic, and rubber processing limited use in solving ambient air pollution problems with its main use involved in the reduction of odour Adsorbents with large surface area to volume ratio (activated carbon) preferred agents for gaseous pollutant control Efficiencies to 99%

Gaseous pollutants - Absorption

Scrubbers remove gases by chemical absorption in a medium that may be a liquid or a liquid-solid slurry water is the most commonly used scrubbing medium Additives commonly employed to increase chemical reactivity and absorption capacity

Gas pollutants Vehicle emissionsgenerally involve simple procedures such as maintaining the correct tuning for the engine, or the use of catalytic converters catalytic converters use Pt and Pd attached to some form of ceramic material extremely high surface area (in hundreds of m2) allows catalytic materials to contact exhaust gases, oxidising them to CO2 and water vapour

BIOFILTERSWhen applied to air filtration and purification, biofilters use microorganisms to removeair pollution.[1]The air flows through a packed bed and the pollutant transfers into a thinbiofilmon the surface of the packing material.Microorganisms, includingbacteriaandfungiare immobilized in the biofilm and degrade the pollutant. Trickling filters and bioscrubbers rely on a biofilm and the bacterial action in their recirculating waters.The technology finds greatest application in treating malodorous compounds and water-solublevolatile organic compounds(VOCs). Industries employing the technology include food and animal products, off-gas fromwastewatertreatment facilities,pharmaceuticals

Bioscrubbersbioscrubbers, the compound to be degraded first is absorbed in the liquid phase located in an absorption tower filled with liquid. The operation involves making the gas flow in a countercurrent through the liquid where the contaminants and oxygen are absorbed. Subsequently, the liquid is fed to a reactor packed with an inert material covered with biofilm that is responsible for degrading the pollutant. Bioscrubbers are the most suitable systems for the treatment of highly water-soluble compounds

CONCLUSIONAir pollution is a major global threat.Natural and human activities causes pollution.SOURCES!!!!How it affects???CONTROL MEASURES!!!

cleaned gas outlet

dirty gas inlet

particulate outlet

earth point

removal of soot particles

soot free gas escape

soot laden smoke

inlet

charged electrodes

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