1. Air Pollution Chapter 14 1

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

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

6. Production of Photochemical Smog

7. 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 + O > 2 NO2
Nitrogen dioxide gives smog its yellow color
NOX stands for all of the nitrogen oxides

8. 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

10. 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

11. Mexico City Photochemical Smog

12. 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

13. Los Angeles Smog Improvement
1972
2000

14. Catalytic Converters Device between engine and exhaust reduce emission
Originally: Pt catalyst + VOC + O > CO2
Now: Pt/Rh catalyst NO > N2 + O2
Pt/Rh catalyst + VOC + O > 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

15. 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 NH NO + O > 4 N H2O
With or without a catalyst (higher temp. needed without)

16. 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

17. Acid Rain

18. 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 O > 2 NiO SO2
SO2 can be collected and sold as a second product
SO2 can be converted to H2SO4, which is also sold
2 SO2 + O > 2 SO3
SO3 + H2O ----> H2SO4
Clean Air Act 1995: SO2 emission down 20% in US

20. 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
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

21. Acid Rain Distribution in North America

22. Ecological Effects Depend on Soil
Limestone and Chalk bedrock neutralize acid rain
CaCO3 + H > Ca HCO3-
HCO H > H2CO3
H2CO > CO2 + H2O
CaCO H > Ca 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

23. Degradation of Marble by Acid Rain

24. Neutralization of an Acidic Lake with Limestone

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

26. Acid Rain and Forests Forest decline in W. Germany Lake Superior
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

27. 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 = mm (100 mm = 0.1 mm)
Aerosol = collection of particulates dispersed in air
Size < 100 mm
Rain removes most particulates as it falls

29. 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
CaCO H > Ca CO2 + H2O
Sodium Chloride near oceans—water droplets evaporate

30. Fine Particulates Fine particulates Common types < 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 + NH > (NH4)2SO4

31. Particulates and Air Quality
Haze = light is blocked or scattered by 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

32. Particle Trap for a Diesel Engine

33. 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

35. 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

36. Ozone and Health Chronic Exposure
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

37. 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

38. 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
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

40. 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

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

42. 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

43. Nitrogen Oxides (NOX) Natural gas heat tends to produce NOX Problems
High temperature: N2 + O > 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

44. Second-Hand Smoke ETS = Environmental Tobacco Smoke Problems
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 ’s death/yr
3,000 lung cancer + 60,000 heart disease deaths/yr

45. 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)