Transcript EnvSciChapt14

Air Pollution
Chapter 14
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Introduction
• The Atmosphere = layer of gases surrounding the
Earth
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78.1% N2
20.9% O2
0.9% Ar
0.03% CO2
Traces of Ne, He, CH4, Kr
For Dry Air;
Water Vapor
is Variable
• Troposphere = 0-15 km, ground-level pollution
• Ozone Layer and Stratosphere: next chapter
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Layers of the Atmosphere
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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 ones4
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Production of Photochemical Smog
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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
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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
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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
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Mexico City Photochemical Smog
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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
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Los Angeles Smog Improvement
1972
2000
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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
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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)
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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
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Acid Rain
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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 US18
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Acid Rain and Geography
• Acid Rain is most serious in the Eastern US/Canada
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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?
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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
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Acid Rain Distribution in North America
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Ecological Effects Depend on Soil
• Limestone and Chalk bedrock neutralize acid rain
CaCO3 + H+ ----> Ca2+ + HCO3HCO3- + 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
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Degradation of Marble by Acid Rain
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Neutralization of an Acidic Lake with Limestone
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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
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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
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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
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Coarse Particulates
• Coarse particulates
– > 2.5 mm
– Settle out of air within a few hours
– Sources
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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
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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
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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
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Particle Trap for a Diesel Engine
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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
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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
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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
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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
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Particulate Size and Health
• Large Particulates are less unhealthy
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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
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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
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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
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Incomplete combustion of fossil fuels
Ties up Hemoglobin, inhibiting oxygen transport
Especially prevalent when natural gas is used
CO detectors becoming popular
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Asbestos
VOC’S
Formaldehyde
Smoke
VOC’s
CO
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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
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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
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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
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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
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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
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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)45
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