1

Air Pollution

Chapter 14

2

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

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

6

Production of Photochemical Smog

7

Nitrogen Oxides• Produced by the burning of fossil fuels in air

• The production only involves air, but needs heatN2 + O2 + Hot Flame ----> 2 NO

• Reaction would not take place without humans use of burning fossil fuels for energy

• Other nitrogen oxides2 NO + O2 ----> 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

9

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 + 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

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 NH3 + 4 NO + O2 ----> 4 N2 + 6 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 ores2 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

19

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 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

21

Acid Rain Distribution in North America

22

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

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: 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

26

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

27

Particulates and Air Pollution• Particulate = tiny solid or liquid suspended particles

– Examples: smoke, haze, dust, soot, photochemical smog

– Size: 0.002—100 m • 1 m = 1 x 10-6 m

• 1 m = 0.001 m (100 m = 0.1 mm)

– Aerosol = collection of particulates dispersed in air • Size < 100 m

– Rain removes most particulates as it falls

28

29

Coarse Particulates• Coarse particulates

– > 2.5 m – 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

30

Fine Particulates• Fine particulates

– < 2.5 m– 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

31

Particulates and Air Quality• Haze = light is blocked or scattered by 0.1-1 m

particulates– US in the summer– Sulfate aerosols from industry – Photochemical smog

• Particulate Matter Index = PMX = g/m3 of air– Subscript tells the diameter of largest particulate included– PM10 = g/m3 of particles ≤ 10 m– 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

34

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• 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 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

39

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

CO

VOC’s

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

– 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

44

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

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)

46