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Air Pollution Chapter 14

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  1. Air Pollution Chapter 14

  2. The Atmosphere = layer of gases surrounding the Earth 78.1% N2 20.9% O2 0.9% Ar 0.03% CO2 Traces of Ne, He, CH4, Kr Troposphere = 0-15 km, ground-level pollution Ozone Layer and Stratosphere: next chapter Introduction For Dry Air; Water Vapor is Variable

  3. Layers of the Atmosphere

  4. Urban Ozone and Smog • Primary Pollutants = emitted directly to the air • NO nitric oxide • SO2 sulfur dioxide • Volatile Organic Compounds = VOC’s • Hydrocarbons = CH3CH2CH3 • Incomplete combustion of fossil fuels • Auto Internal Combustion Engines are main source • Photochemical Smog = ozone produced from primary pollutants and sunlight VOC + NO + O2 + sunlight ----> O3 + HNO3 + Oxidized VOC’s • Secondary Pollutant = from reaction of primary ones

  5. Production of Photochemical Smog

  6. Nitrogen Oxides • Produced by the burning of fossil fuels in air • The production only involves air, but needs heat N2 + O2 + Hot Flame ----> 2 NO • Reaction would not take place without humans use of burning fossil fuels for energy • Other nitrogen oxides 2 NO + O2 ----> 2 NO2 • Nitrogen dioxide gives smog its yellow color • NOX stands for all of the nitrogen oxides

  7. Ground Level Ozone • Ozone protects us from sun’s UV • Occurs in the upper atmosphere • Ozone is naturally produced from O2 • Ozone is a pollutant when found in the troposphere • Not naturally produced at low altitudes • Pollution = ozone layer in the wrong place • Ozone levels • Clean air = 30 ppb; Polluted air = 100 ppb • Max allowed in US = 120 ppb (LA, 1970’s = 680 ppb) • Economic Effects (Health Effects Later) • Agriculture ($3 billion alfalfa loss) • Hardens rubber and bleaches dyes

  8. Requirements for Photochemical Smog • Heavy Vehicular Traffic—to produce NO, VOC’s • Warmth and Sunlight—for reaction to occur • Stagnant Air—so ozone produced isn’t dispersed • Temperature Inversion = warm air above cold air • Air usually cools as you increase altitude: warm air rises • Temp. Inv.: cold air (ozone) is trapped at the surface • Geography—cities surrounded by mountains • L.A., Tokyo, Athens, Sao Paulo, Rome • Mexico City: only half registered cars can drive each day • Ozone Drift—Midwest pollutant lead to smog in Eastern U.S. and Canada

  9. Mexico City Photochemical Smog

  10. Reducing Photochemical Smog • Best step is to reduce emission of primary pollutants • VOC reduction has little effect: excess reagent • NOX reduction more important: limiting reagent VOC + NO + O2 + sunlight ----> O3 + HNO3 + Oxidized VOC’s • Do trees fight air pollution? • Trees actually give off VOC’s themselves • Smog in Atlanta: VOC’s come mostly from forests • Los Angeles: air quality has improved dramatically • Reduced VOC’s: cleaner gas, “smog” checks • Geography, VOC’s, NOX still make LA smoggy

  11. Los Angeles Smog Improvement 2000 1972

  12. Catalytic Converters • Device between engine and exhaust reduce emission • Originally: Pt catalyst + VOC + O2 ----> CO2 • Now: Pt/Rh catalyst + 2 NO + ---> N2 + O2 Pt/Rh catalyst + VOC + O2 ----> CO2 + H2O • “Smog Checks” • Oxygen sensor ensures enough O2 to completer reactions • 2 weeks by law in CA to get this done • Proper functioning eliminates 80-90% of emissions • 80% of emissions occur in few minutes before car warm • Preheat? Recirculate emissions until warm? • Old/Damaged cars (10%) cause 50 % of emissions • Diesel: only 50% of emissions cleaned • Sulfur in Diesel fuel produces SO2 pollutants with the catalyst • Too much oxygen needed to burn diesel to allow all NOX to be removed

  13. NOX from Power Plants • NOX from power plant matches that from cars in US • Power plants burn coal, oil, and natural gas • Heat from combustion is turned into electrical power • Reduction of NOX emission from power plants • Two-step combustion process • Burn fuel with low O2 levels so no reaction with N2 occurs • Finish the combustion with more O2, but a low temperatures • Large-Scale Catalytic Converters • 4 NH3 + 4 NO + O2 ----> 4 N2 + 6 H2O • With or without a catalyst (higher temp. needed without)

  14. Acid Rain • Natural Rain = atmospheric precipitation pH = 5.6 CO2 + H2O <----> H2CO3 (carbonic acid) H2CO3 <----> H+ + HCO3- (weak acid) • Natural acid rain: Volcanoes emit HCl (strong acid) • Acid Rain = polluted precipitation pH < 5.0 • Primary pollutants = NO, SO2 • Secondary pollutants • HNO3 (nitric acid) Primarily Western US due to auto emission • H2SO4 (sulfuric acid) Primarily Easter US due to coal burning • Acid Rain falls far downwind of the pollution source • Conversion to the acids takes hours or days

  15. Acid Rain

  16. Sulfur Dioxide Pollution • Natural SO2 from plant, volcanoes is greatly diluted • Combustion of Coal: SO2 concentrated locally • Coal in US is between 1—6% Sulfur • Burned in electrical power plants • Tall smokestacks: good locally, acid rain downwind • Smelting = process of extracting metals from ores 2 NiS + 3 O2 ----> 2 NiO + 2 SO2 • SO2 can be collected and sold as a second product • SO2 can be converted to H2SO4, which is also sold 2 SO2 + O2 ----> 2 SO3 SO3 + H2O ----> H2SO4 • Clean Air Act 1995: SO2 emission down 20% in US

  17. Acid Rain and Geography • Acid Rain is most serious in the Eastern US/Canada • Power plants in Midwest burn coal • Prevailing atmospheric winds move Eastward • pH averages 3.9-4.5 • Won’t burn skin, but has important ecological effects • Why hasn’t the situation improved? • SO2 emissions are down (20% US, 43% Canada) • Ash and particulate pollution (bases) down also • Bases have decreased, so SO2 in atmosphere about same • NOX emission has not changed significantly

  18. Acid Rain Distribution in North America

  19. Ecological Effects Depend on Soil • Limestone and Chalk bedrock neutralize acid rain CaCO3 + H+ ----> Ca2+ + HCO3- HCO3- + H+ ----> H2CO3 H2CO3 ----> CO2 + H2O CaCO3 + 2H+ ----> Ca2+ + CO2 + H2O • Deterioration of limestone buildings and marble statues • Granite and Quartz bedrock • Can’t neutralize acidity • Canada, Scandinavia • Add limestone to Canadian lakes to increase pH

  20. Degradation of Marble by Acid Rain

  21. Neutralization of an Acidic Lake with Limestone

  22. Acid Rain, Aluminum, and Aquatic Life • Acid Rain releases Al3+ into lakes and streams • At pH = 7, Al3+ is tied up in minerals: Al3+ + SiO44- • At pH = 5, H+ replaces Al3+ in the minerals, allowing Al3+ to dissolve into the lake • Al3+ + H+ reduces reproduction and kills young fish • Crystal clear lakes, because all plants and animals dead

  23. Acid Rain and Forests • Forest decline in W. Germany • H+, Al3+, O3 all contributed • High altitudes effected most • Low level clouds most acidic • Acid Fog • H+ more concentrated, less water • Lake Superior • White birch trees effected

  24. Particulates and Air Pollution • Particulate = tiny solid or liquid suspended particles • Examples: smoke, haze, dust, soot, photochemical smog • Size: 0.002—100 mm • 1 mm = 1 x 10-6 m • 1 mm = 0.001 mm (100 mm = 0.1 mm) • Aerosol = collection of particulates dispersed in air • Size < 100 mm • Rain removes most particulates as it falls

  25. Coarse Particulates • Coarse particulates • > 2.5 mm • Settle out of air within a few hours • Sources • Volcanoes • Stone Quarries • Farmland • Pollen • Mineral Pollutants • Often carbonates, which can neutralize acids CaCO3 + 2H+ ----> Ca2+ + CO2 + H2O • Sodium Chloride near oceans—water droplets evaporate

  26. Fine Particulates • Fine particulates • < 2.5 mm • Remain airborne for days or weeks • Common types • Soot = carbon crystals from incomplete fuel combustion • Diesel engines are large sources of soot • Solid particulates • Photochemical Smog • Droplets of partially oxidized organics • Liquid • H2SO4 and HNO3 droplets • Ammonium Sulfate Aerosols: H2SO4 + NH3 ----> (NH4)2SO4

  27. Particulates and Air Quality • Haze = light is blocked or scattered by 0.1-1 mm particulates • US in the summer • Sulfate aerosols from industry • Photochemical smog • Particulate Matter Index = PMX = mg/m3 of air • Subscript tells the diameter of largest particulate included • PM10 = mg/m3 of particles ≤ 10 mm • Smaller particles are usually the most unhealthy • Reduction of PM • Reduce primary gaseous pollutants: NO, SO2, VOC’s • Particle traps in diesel engines: trap soot

  28. Particle Trap for a Diesel Engine

  29. Air Pollution and Health • Threshold Concentration = concentration of a pollutant above which health problems occur • Chronic Exposure = exposure over long periods of time • Brief exposures are less harmful, even at higher levels • Very low levels over long times cause more problems • Human Test Animals • Little data on animal testing over long times • Compare Kansans to Los Angelenos over period of time • Health Effects of Air Pollution • Particulates and SO2 seem to have the worst effect • Respiratory problems, asthma appears to be increased

  30. Soot and Sulfur Smog • Smog originally stood for smoke + fog • Problem since coal has been a fuel • Not photochemical smog (ozone) • In December 1952, 4000 people died in London • Mostly children and elderly • Coal burning stoves • No longer a problem in West due to pollution controls • Eastern Europe and Asia still use coal • Eastern European “brown” coal can be 15% sulfur • In the 1980’s, 80% of children admitted to hospitals were to treat respiratory problems • Coal and Diesel engines in India/China: serious problem

  31. Ozone and Health • Ozone causes cough, chest pain, nose/throat irritation • Seems to inhibit optimal function of body • Athlete’s times for races are longer when ozone is high • Chronic Exposure • Destruction of lung tissue • Decreased resistance to diseases

  32. Particulates and Health • Particulates carry toxic substances into lungs • Absorbed = dissolved in; Adsorbed = stuck to surface • Most toxic gases are absorbed before reaching the lungs • Particulates are too big to be absorbed • They make it deeper into the lungs • Toxic substances can be adsorbed or absorbed in the particulate

  33. Particulate Size and Health • Large Particulates are less unhealthy • They settle out of the air quickly • Filtered out quickly when breathed • Adsorb less toxic substances due to small surface area • Cleaning filters are much more effective for large PM • Deaths vs. PM2.5 in cities 1982-1989 • Strong correlation between PM2.5 and death rates • Infant death syndrome strongly correlated • No threshold = bad at any concentration • Acidity seems to be main culprit: wheezing, asthma • EPA: 15 mg/m3 annually, 65 mg/m3 daily for PM2.5

  34. Indoor Air Pollution • Indoor vs. Outdoor Air Pollution • We spend more time indoors than outdoors • Poor ventilation can make indoor air pollution worse • Developing countries: smoke, soot, no ventilation system • Carbon Monoxide = CO • Incomplete combustion of fossil fuels • Ties up Hemoglobin, inhibiting oxygen transport • Especially prevalent when natural gas is used • CO detectors becoming popular

  35. Asbestos VOC’S Formaldehyde Smoke VOC’s CO

  36. Formaldehyde • Formaldehyde: H2C=O • Much greater concentrations indoors than outdoors • Sources: cigarette smoke, urea-formaldehyde insulation and adhesives (plywood, particle board, carpet glue) • New carpet smell = formaldehyde • Wood products have begun to use less formaldehyde • Problems • Eye irritation (especially contact lens wearers) • Nose, throat, skin irritation • Respiratory infections, allergies, asthma in children • Human carcinogen • Little absolute proof of any of these

  37. Nitrogen Oxides (NOX) • Natural gas heat tends to produce NOX • High temperature: N2 + O2 ----> 2 NO • Indoor concentration similar to outdoors in a big city • Problems • Dissolves in living tissues since it is not charged • Increased respiratory problems • Normal NO uses in the body • Chemical messenger to regulate blood pressure • Viagra prevents breakdown of NO, allowing erection

  38. Second-Hand Smoke • ETS = Environmental Tobacco Smoke • Higher concentration of some chemicals in “sidestream” smoke than in “mainstream” smoke • Lower temperature of combustion changes the products • Dilution by air means a bystander does not inhale as much • Problems • Dozens of carcinogens in smoke: CO, NO2, H2CO, etc... • Particulates in smoke = tar • Asthma, eye, and respiratory irritation • Infants: 300,000 respiratory infections + 1000’s death/yr • 3,000 lung cancer + 60,000 heart disease deaths/yr

  39. Asbestos • Asbestos = silicon based fibrous mineral • Chrysotile = Mg3Si2O5(OH)4 is the most used form • Resistant to heat • Used as insulation • Mined in Quebec • Mesothelioma = incurable cancer of lung, abdomen, heart • First noticed among asbestos miners • Caused by airborne asbestos fibers • Smoke + Asbestos work synergistically to cause lung cancer • Removal generates fibers in the air: leave it alone (Harnly Hall)