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AIR POLLUTION lecture EnE203 updated.pdf
- 1. AIR POLLUTION EnE 203Lecture Joseph Gerard T. Reyes, Ph.D.
- 2. Outline • Definition • Compositionof atmospheric air • Classification and sources of air pollutants • Effects of air pollution • Air pollution control methods, equipment and safety
- 3. What is Pollution? •Change in background concentration • Any substance introduced into the environment that adversely affects the usefulness of a resource. • Pollution happens because no process is 100% efficient; each process produces waste, which can contribute to pollution. • Air pollution - one or more contaminants or combinations in such quantities and of such durations in atmospheric air which tend to be injurious to biological life, or materials
- 4. The Earth’s Atmosphere:Composition Note: The Earth’s atmosphere has been changing over time due to natural and anthropogenic activities.
- 5. Gas Typical Surface Concentration (ppm) LifetimeSource N2 780,840 Biological cycle O2 209,840 Biological cycle H2O Variable Hydrologic cycle Ar 9340 Inert CO2 355 7 y Fossil fuel combustion, deforestation CH4 1.72 7 y Wetlands, natural gas use, agriculture N2O 0.31 120 y Oceans, soils, combustion CO 0.10 1 month Methane oxidation, combustion O3 0.04 Photochemistry NH3 10-3 10 d Livestock, fertilizer, wildlife, oceans NO/NO2 10-3 1 d High-temperature combustion SO2 10-3 1 d Coal, combustion CFCl3 2.7 x 10-4 50 y Refrigerant, solvent ATMOSPHERIC CONSTITUENTS (Seinfeld and Pandis, 1998)
- 6. Pressure = 1,000 millibarsat ground level Atmospheric pressure (millibars) 0 200 400 600 800 1,000 120 110 100 90 80 70 60 50 40 30 20 10 0 (Sea Level) –80 –40 0 40 80 120 Temperature (˚C) Altitude (kilometers) Altitude (miles) 75 65 55 45 35 25 15 5 Thermosphere Heating via ozone Mesosphere Stratosphere Ozone “layer” Heating from the earth Troposphere Temperature Pressure Mesopause Stratopause Tropopause The Structure of the Earth’s Atmosphere
- 7. Classification of Sourcesof Air Pollution • Natural – e.g., pollen grains, volcanic eruptions, forest fires, dust storms, spores, bacteria and other microorganisms. • Man- made – e.g., industrial plants, thermal power plants, automobile exhaust, fossil fuel burning, mining
- 8. Stationary and MobileSources of Emissions • Stationary sources • Point (major) source – a stationary single, major source of emissions; can be pinpointed to a single location • Area source - smaller-size facilities that release lesser quantities of toxic pollutants into the air; mobile sources with indefinite routes • Volume source – a three-dimensional source of pollutant emissions (includes elevations from ground, e.g. emissions from roof vents of buildings); emissions are often uncontrolled • Line source – mobile sources with definite routes
- 11. Characteristics of AirPollutants • temporarily or permanently resident in the atmospheric air • alter the environment leading to effects on health, the food chain, and well-being of people • pollutants can be solid (large or sub-molecular), liquid or gas • originate from a natural or anthropogenic sources (or both) • It is estimated that anthropogenic sources have changed the composition of global air by less than 0.01%. This will still have a significant impact on the climate, ecosystem and all species on the planet.
- 12. CLASSIFICATION OF AIRPOLLUTANTS • primary pollutants, which are emitted directly from identifiable sources • secondary pollutants, which are produced in the atmosphere when certain chemical reactions take place among primary pollutants. Atmospheric phenomena influence the formation of secondary pollutants
- 13. Major Primary Pollutants •particulate matter (PM) • sulfur dioxide • nitrogen oxides • volatile organic compounds (VOCs) • carbon monoxide • lead
- 16. Secondary Pollutants • Someprimary air pollutants react with one another or with other chemicals to form secondary pollutants. • Examples are • Ozone • Formaldehyde • PAN (peroxy acetyl nitrate, C2H3NO5) • smog (photochemical or smoke induced) • acid mist • sulfuric acid
- 18. • Atmospheric sulfuricacid is one example of a secondary pollutant – cause of acid rain • Air pollution in urban and industrial areas is often called smog. • Photochemical smog, a noxious mixture of gases and particles, is produced when strong sunlight triggers photochemical reactions in the atmosphere. • The major component of photochemical smog is ozone.
- 19. Major Pollutants, Sources,and Effects Carbon monoxide (CO) • colorless, odorless, tasteless gas. • No effect at normal conc. (0.1ppm) but higher concentrations produce serious effects • Volcanoes, natural gas emissions, seed germination contribute to CO • Transport sector account for up to 95% of CO emissions in cities (US EPA 2008) • Effects of CO poisoning: reduced oxygen carrying capacity of blood, decrease in vision; cardio-vascular disorders.
- 21. Major Pollutants, Sources,and Effects Carbon dioxide (CO2) • colorless, odorless, tasteless gas. • a product of combustion, respiration or decomposition; can also be a secondary pollutant • emitted from natural and anthropogenic sources • effects: nausea, headaches • an atmospheric greenhouse gas
- 22. Major Pollutants, Sources,and Effects Oxides of nitrogen (NOx) • group that includes NO, NO2, N2O. • sources include: • fuel combustion in automobiles and industries; three types of production – fuel NOx, thermal NOx, prompt NOx • agriculture • lightning • forest fires. • natural ionizing radiations • effects: Reduce blood carrying capacity; lung problems • can react with other airborne compounds to produce nitric acids and photochemical smog
- 23. Major Pollutants, Sources,and Effects Oxides of sulfur (SOx) • include SO2, SO3. • 67% SOx pollution due to volcanic activities and other natural sources • anthropogenic sources are fossil fuel burning, transportation, industrial activities; sulfur is contained in fuel such as coal and diesel • effects: respiratory problems; materials such as marbles, cloth, paper, leather also affected; impact on plants • can react with airborne compounds to produce sulfuric acid
- 24. Major Pollutants, Sources,and Effects Hydrocarbons (HC) • include methane, ethylene, acetylene, terpenes etc. • sources include • coal fields • natural fires • incomplete combustion • forest fires • Effects: • carcinogenic • lead to the formation of ozone and PAN • affect plants and degrade materials such as rubber, fabric and paint
- 25. Major Pollutants, Sources,and Effects Particulate Matter (PM) • particles of various substances suspended in the air (aerosols) • in the form of solid particles and liquid droplets • vary widely in size • PM may be found in dust, smoke, fumes, mist, fog, fly ash etc. • known sources of PM: • diesel trucks and buses • construction equipment • power plants • burning of solid fuels • PM can also be a result of condensation of gases or reactions of air-borne compounds
- 27. Effects of PM: •premature death • aggravated asthma • acute respiratory symptoms • chronic bronchitis • decreased lung function (shortness of breath) People with existing heart and lung disease, as well as the elderly and children, are particularly at risk.
- 28. Effects of airpollution on humans
- 29. • air pollutionaccounts for around 30-40% of cases of asthma and 20-30% of all respiratory disease. • Short-term effects: irritation to nose, eye, throat, bronchitis, headache etc. • Long-term effects: lung disease, chronic respiratory problem, damage to heart, brain, eyes etc. • eye irritation due exposure to NOx, O3, PAN, PM • nose and throat ailments due to pollutants such as SO2, NOx
- 30. • gaseous pollutantslike H2S, SO2, NO2 and hydrocarbons cause noxious odors • irritation of respiration tract caused by SOx, NOx, CO, O3. • exposure to high concentrations of SO2, NO2 and SPM causes bronchitis and asthma • CO and NO react with hemoglobin and reduce O2 carrying capacity of blood • heavy metals like lead can cause poisoning; high concentrations cause damage to liver and kidney.
- 31. Air Pollutant FactorsAffecting Human Health • nature of the pollutants • concentration of the pollutants • duration of exposure • state of health of receptor • age group of the receptor
- 32. Effects of airpollution on plants
- 33. • decreased yieldin agriculture. • suppressed growth of vegetables. • leaf injury and damage to young plants. • decreased growth rate and increased death rate
- 34. Some Effects ofair pollution on materials • corrosion of metals due to SO2 in presence of oxygen and moisture is converted into H2SO4; H2SO4 reacts with limestone, marble and other building materials to cause deterioration. • soiling and erosion of building materials. • SO2, O3, H2S and aerosols damage protective coating and paints of the surface • O3 and PAN causes cracking of rubber and various electrical insulations • deterioration of art work due to SPM.
- 35. Air pollution control Cannotbe fully prevented but can be controlled. 1. Preventive measures 2. Control measures using devices Preventive measures (source control) • selection of suitable fuel (e.g., low sulphur coal in power plant, using of CNG) • modifications in industrial processes • selection of suitable sites; zoning for industrial plants
- 36. Control measures usingdevices • when source control is not possible • control done by: • collecting pollutants by using equipments • reducing pollutants concentrations by thermal or catalytic combustion • converting the pollutants to less toxic forms • releasing the pollutants using stacks for greater dispersion.
- 37. Air pollution controllingequipment • Gravitational settling chamber • Used to remove particles with size greater than 50 μm. • Velocity of flue gas reduced in large chamber. • Particles settle under gravitational force.
- 38. Advantages • Low initialcost. • Easy to design. • Low pressure drop. • Low maintenance cost. • Dry and continuous disposal of solid particulates. Disadvantages • Require large space. • Less collection efficiency. • Only larger size particles can be collected.
- 39. Cyclone separator • Centrifugalforce is utilized to separate the particulate matter. • It can remove 10 to 50 μm particle size. • Used mostly in industries.
- 40. Advantages • Low initialcost. • Require less floor area. • Simple construction and maintenance. • Can handle large volume of gas at high temp. Disadvantages • Requires large head room. • Less efficiency for smaller particles (<10μm). • Sensitive to variable dust load and flow rate.
- 41. Electrostatic precipitators • workson the principle of electrical charging of particulate matter (negative) and collecting it in a positive-charged surface • 99% collection efficiency • can remove particle size range of 0.1 μm to 1 μm.
- 43. Advantages • High collectionefficiency. • Particles may be collected dry or wet. • Can be operated at high temp. (300-450˚c). • Maintenance is normal. • Few moving parts. Disadvantages • High initial cost. • Require high voltage. • Collection efficiency reduce with time. • Space requirement is more. • Possible of explosion during collection of combustible gases or particulates.
- 44. Fabric filters • Fluegas is allowed to pass through a woven Fabric, which filters out Particulate matter. • Small particles are retained on the fabric. • Remove particles up to 1 μm. • Its efficiency up to 99%.
- 45. Advantages • Higher collectionefficiency for smaller than 10 μm particle size. • Performance decrease becomes visible, giving prewarning. • Normal power consumption. Disadvantages • High temp. gases need to be cooled. • High maintenance and fabric replacement cost. • Large size equipment. • Fabric is liable to chemical attack.
- 46. Scrubbers • Particulate mattersare incorporated into liquid droplets and removed from the gas stream. • Different types of scrubbers are- - Spray tower - Venturi scrubber - Cyclone scrubber • Flue gas made to push up against a down falling water current. • Particulate matter mix up with water thus falls down and gets removed.
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- 48. Advantages • Simultaneously removeparticulates and gaseous pollutants. • Hot gases can be cooled down. • Corrosive gases can be recovered and neutralize. Disadvantages • Lot of waste waters produced. • Poses freezing problem in cold countries. • Maintenance cost is high when corrosive materials are collected.
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