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Air Pollution Chapter 14. The Atmosphere = layer of gases surrounding the Earth 78.1\% N 2 20.9\% O 2 0.9\% Ar 0.03\% CO 2 Traces of Ne, He, CH 4 , Kr Troposphere = 0-15 km, ground-level pollution Ozone Layer and Stratosphere: next chapter. Introduction. For Dry Air; Water Vapor

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introduction
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

urban ozone and smog
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
nitrogen oxides
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
ground level ozone
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
requirements for photochemical smog
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
reducing photochemical smog
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
catalytic converters
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
no x from power plants
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)
acid rain
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
sulfur dioxide pollution
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
acid rain and geography
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
ecological effects depend on soil
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
acid rain aluminum and aquatic life
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
acid rain and forests
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
particulates and air pollution
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
coarse particulates
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
fine particulates
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

particulates and air quality
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
air pollution and health
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
soot and sulfur smog
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
ozone and health
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
particulates and health
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
particulate size and health
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
indoor air pollution
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
slide41
Asbestos

VOC’S

Formaldehyde

Smoke

VOC’s

CO

formaldehyde
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
nitrogen oxides no x
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
second hand smoke
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
asbestos
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)
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