Air pollution chapter 14
Sponsored Links
This presentation is the property of its rightful owner.
1 / 46

Air Pollution Chapter 14 PowerPoint PPT Presentation


  • 51 Views
  • Uploaded on
  • Presentation posted in: General

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

Download Presentation

Air Pollution Chapter 14

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


Air Pollution Chapter 14


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


Layers of the Atmosphere


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


Production of Photochemical Smog


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

  • 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

  • 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


Mexico City 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


Los Angeles Smog Improvement

2000

1972


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


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

  • 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


Acid Rain


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 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


Acid Rain Distribution in North America


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


Degradation of Marble by Acid Rain


Neutralization of an Acidic Lake with Limestone


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

  • 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

  • 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

    • > 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

    • < 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

  • 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


Particle Trap for a Diesel Engine


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

  • 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 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 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

  • 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 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


Asbestos

VOC’S

Formaldehyde

Smoke

VOC’s

CO


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 (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

  • 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 = 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)


  • Login