Outdoor Air Pollution

Ch 17

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Outdoor Air Pollution• Air pollution = the release of pollutants

– Air pollutants = gases & particulate material added to the atmosphere

• Can affect climate or harm people

– Outdoor (ambient) air pollution = pollution outside• Has recently decreased due to gov’t policy & improved tech in

MDCs

• Developing countries & urban areas still have significant problems

– Causes of Air Pollution• Natural causes (ex. dust storms, volcanoes, fires)

• Human causes (ex. burning fossil fuels--automobiles, factories, etc.)

• Dust storms = Hundreds of millions of tons of dust are blown westward across the Atlantic Ocean by trade winds every year– From Africa to the

Americas– Unsustainable farming

& grazing, erosion & desertification

Natural Sources Pollute

• Volcanoes– Release large quantities of

particulate matter, sulfur dioxide & other gases • Can remain for months-yrs• Aerosols = fine solid or

liquid particles in the atmosphere that reflect sunlight back into space & cool atmosphere & surface

Natural Sources Pollute

Iceland's Eyjafjallajökull volcanopronounced ay-yah-FYAH-plah-yer-kuh-duhl

• Fires– Pollutes atmosphere

with soot & gases

– Over 60 million ha of forests & grasslands burn/yr

– Severe fires are caused by human interaction• Cleared forests, harsh

droughts, & climate change

Natural Sources Pollute

Other Natural Sources of Air Pollution

• Hydrocarbons (molecules of H & C)– Trees and plants

• Pollen

• hydrogen sulfide from decaying plants

• Salt particulates from the sea

Types of outdoor air pollution• Air pollution can come from mobile or stationary

sources– Mobile sources = ex. cars– Stationary sources = ex. power plants

• It can also come from point or nonpoint sources– Point Sources = specific spots where large

quantities of pollutants are discharged (power plants and factories)

– Nonpoint Sources = more diffuse, consisting of many small sources (automobiles)

• When dealing with pollution there can be primary and secondary pollutants.– Primary Pollutants = directly harmful and

can react to form harmful substances (soot and carbon dioxide)

– Secondary Pollutants = form when primary pollutants interact or react with constituents or components of the atmosphere (tropospheric ozone and sulfuric acid)

Primary PollutantsPrimary Pollutants

StationaryStationaryMobileMobile

SourcesSourcesNaturalNatural

Most Most hydrocarbonshydrocarbons

Most suspendedMost suspendedparticlesparticles

SOSO22 NONO NONO22

COCO COCO22 Secondary PollutantsSecondary Pollutants

SOSO33

HNOHNO33HH22SOSO44

HH22OO22OO33 PANsPANs

MostMost NONO33–– andand

SOSO4422 –– saltssalts

The EPA sets standards• Environmental Protection Agency (EPA) sets

nationwide standards for emissions of toxic pollutants

• States monitor air quality and develop, implement, and enforce regulations within their borders– If a state’s plans for implementation are not adequate,

the EPA can take over enforcement

Criteria pollutants: carbon monoxide

• Criteria pollutants = pollutants judged to pose especially great threats to human health

• Carbon monoxide (CO)– A colorless, odorless gas– Produced primarily by incomplete combustion of fuel– Poses risk to humans and animals, even in small

concentrations

Criteria pollutants: sulfur and nitrogen dioxide

• Sulfur dioxide (SO2) = colorless gas with a strong odor– Coal emissions from electricity generation and industry– Can form acid precipitation

• Nitrogen dioxide (NO2) = highly reactive, foul smelling reddish brown gas– Nitrogen oxides (NOx) = nitrogen and oxygen react at high

temperatures– Vehicle engine and industrial combustion, electrical utilities– Contributes to smog and acid precipitation

Criteria pollutants: tropospheric ozone

• Tropospheric ozone (O3) = a colorless gas with a strong odor– A secondary pollutant– Results from interactions of sunlight, heat,

nitrogen oxides, and volatile carbons– A major component of smog – Poses a health risk as a result of its instability

Criteria pollutants: particulate matter and lead

• Particulate matter = solid or liquid particles suspended in the atmosphere– Primary pollutants: dust and soot– Secondary pollutants: sulfates and nitrates– Damages respiratory tissue when inhaled– Most is wind-blown dust

• Lead = particulate pollutant added to gas and used in industrial metal smelting– Bioaccumulates and causes nervous system malfunction– Banned in gasoline in developed, but not in developing

countries

Failing Air Quality Standards

Agencies monitor pollutants• State and local agencies also monitor,

calculate, and report to the EPA the emissions of pollutants– Four criteria pollutants: carbon monoxide, sulfur

dioxide, particulate matter, and lead– All nitrogen oxides– Not tropospheric ozone (no emissions to monitor)– Volatile organic compounds (VOCs) = carbon-

containing chemicals used emitted by vehicle engines and industrial processes

U.S. air pollution

In 2006, the U.S. emitted 137 million tons of the six major pollutants

Air pollution has decreased since 1970

• Total emissions of the six monitored pollutants have declined– Despite increased population, energy

consumption, miles traveled, and gross domestic product

Toxic substances also pollute

• Toxic air pollutants = substances known to cause cancer; reproductive defects; or neurological, development, immune system, or respiratory problems– Some are produced naturally: hydrogen sulfide– Most are produced by humans: smelting, sewage

treatment, industry

Smog

• Smog = unhealthy mixtures of air pollutants over urban areas–Two types

• Industrial (gray air)

• Photochemical (brown air)

• Industrial (gray air) smog = industries burn coal or oil– combination of sulfur dioxide, sulfuric

acid, soot, & a variety of aerosols– Government regulations in developed

countries reduced smog– Coal-burning industrializing countries

face significant health risks– In most developed countries where coal

and heavy oil are burned, industrial smog is not a major problem due to reasonably good pollution control or tall smokestacks that transfer the pollutant to rural areas.

Formation of Industrial Smog

Procedure Chemical Reaction

1. Carbon in coal or oil

burned

C + O2 CO2

2C + O2 CO

2. Unburned carbon soot C

3. Sulfur in oil and coal reacts with O2

S + O2 SO2

Formation of Industrial SmogFormation of Industrial Smog

Procedure Chemical Reaction

4. Sulfur dioxide reacts with O2 to form sulfur trioxide

2SO2 + O2 2SO3

5. Sulfur trioxide reacts with H2O

SO3 + H2O H2SO4

6. Sulfuric acid reacts with atmospheric ammonia to form brown, solid ammonium sulfate

H2SO4 + 2NH3 (NH4)2SO4

Industrial Smog

• Photochemical (brown air) smog = brownish haze that NOx & hydrocarbons (mainly from auto exhaust)– Sunlight reacts with primary

pollutants & normal atmospheric compounds to form O3 (in troposphere) & other harmful substances• Tropo. O3 = lung irritant,

stunts plant growth, reduce crop yields, hurts agriculture

Temperature Inversions

• Smog severity depends on conditions in atm & location– Temperature inversion air at surface of Earth colder than

air above & convection does not occur• warm air acts like a lid trapping pollutants

– Cold, cloudy weather in a valley surrounded by mountains can trap air pollutants (left).

– Areas with sunny climate, light winds, mountains on 3 sides & an ocean on the other (right) are susceptible to inversions.

Formation of Photochemical Smog

Time Description

6 - 9 A.M.

Morning commute increases NOx and VOCs

N2 + O2 2 NONO + VOC

UV

9 - 11 A.M

As traffic decreases NOx and VOCs react 2NO + O2

Time Description

11 A.M. – 4 P.M.

As sunlight becomes intense, NO2 breaks down and Ozone increases

UV

Nitrogen dioxide also forms nitric acid

11 A.M. – 4 P.M.

Nitrogen dioxide also reacts with VOCs released by autos, industry, etc.

VOCs PANs Peroxyacyl nitrates (toxic)

4 P.M. - sunset

As sun goes down the production of ozone haltsNet Result: NO + VOC + O2 + UV O3 + PAN

• 17.16

Photochemical smog

Typical Daily Pattern Changes1. 2NO+ O2 2NO2 2. NO2 + UV NO + O3. O2 + O O3

Sunlight plus Cars Equals Photochemical Smog

• Mexico City is one of the many cities in sunny, warm, dry climates with many motor vehicles that suffer from photochemical smog.

Figure 19-4Figure 19-4

Central Case: Charging toward cleaner air in London

• London has had bad air pollution for centuries that has killed thousands

• Today, smog from traffic is a problem

• The “congestion-charging” program charges drivers to drive into central London during the week

• Congestion decreased, fewer accidents occurred and the air became cleaner

Human Impact on Atmosphere

www.dr4.cnrs.fr/gif-2000/ air/products.html

•Burning Fossil Fuels Adds CO2 and O3 to troposphereGlobal WarmingAltering ClimatesProduces Acid Rain

•Using Nitrogen fertilizers and burning fossil fuels

Releases NO, NO2, N2O, and NH3 into troposphereProduces acid rain

•Refining petroleum and burning fossil fuels

•Releases SO2 into troposphere

•Manufacturing •Releases toxic heavy metals (Pb, Cd, and As) into troposphere

Reasons for Decline in U.S. Pollution• Vehicle inspection programs in U.S. have

decreased smog

• Cleaner-burning vehicles and catalytic converters decrease carbon monoxide

• Permit-trading programs and clean coal technologies reduce SO2 emissions

• Phase-out of leaded gasoline

• Improved technologies and federal policies– Electrostatic precipitators– Scrubbers

• Electrostatic precipitators: are used to attract negatively charged particles in a smokestack into a collector.– Can remove 99% of

particulate matter– Does not remove

hazardous ultrafine particles.

– Produces toxic dust that must be safely disposed of.

– Uses large amounts of electricity

• Scrubbers = technologies that chemically convert or physically remove pollutants before they leave the smokestacks– Wet scrubber: fine

mists of water vapor trap particulates & convert them to a sludge that is collected and disposed of usually in a landfill.

• Can remove 98% of SO2 and particulate matter.

• Not very effective in removing hazardous fine and ultrafine particles.

Fig. 19-17, p. 459

Solutions

Stationary Source Air Pollution

Prevention

Burn low-sulfur coal

Disperse emissions above thermal inversion layer with tall smokestacks

Remove sulfur from coal

Convert coal to a liquid or gaseous fuel

Remove pollutants after combustion

Shift to less polluting fuels

Tax each unit of pollution produced

Dispersion or Cleanup

Solutions: Reducing Outdoor Air Pollution

• In 2003, fourteen states and a number of U.S. cities sued the EPA to block new rules that would allow older coal-burning power plants to modernize without having to install the most advanced air pollution controls.

Fig. 19-19, p. 460

Solutions

Motor Vehicle Air Pollution

Prevention Cleanup

Emission control devices

Mass transit

Bicycles and walking

Less polluting engines

Less polluting fuels

Improve fuel efficiency

Car exhaust inspections twice a year

Get older, polluting cars off the road

Give buyers large tax write-offs or rebates for buying low-polluting, energy efficient vehicles

Stricter emission standards

Laws Regarding Air Pollution

• Shift from controlling air pollution to preventing air pollution

• EPA established:– national ambient air quality standards

(NAAQS)– National emission standards for toxic air

pollutants

The Clean Air Act• Congress passed series of laws starting in 1955• Originally signed 1963

– States controlled standards

• The Clean Air Act of 1970– Sets standards for air quality, limits on emissions

• Criteria Pollutants– Primary – Human health risk

– Secondary – Protect materials, crops, climate, visibility, personal comfort

– Provides funds for pollution-control research – Allows citizens to sue parties violating the standards

Clean Air Act• The Clean Air Act of 1990

– Strengthens standards for auto emissions, toxic air pollutants, acidic deposition, stratospheric ozone depletion

– Introduced emissions trading

• There are a # of ways to prevent and control air pollution from motor vehicles.– Because of the Clean Air Act, a new car today in

the U.S. emits 75% less pollution than did pre-1970 cars.

– There is an increase in motor vehicle use in developing countries and many have no pollution control devices and burn leaded gasoline.

Using the Marketplace to Reduce Outdoor Air Pollution

• To help reduce SO2 emissions, the Clean Air Act authorized and emission trading (cap-and-trade) program.– Enables the 110 most polluting power plants to buy

and sell SO2 pollution rights.

– Between 1990-2002, the emission trading system reduced emissions.

– In 2002, the EPA reported the cap-and-trade system produced less emission reductions than were projected.

• Environmental scientists point out several deficiencies in the Clean Air Act:

– U.S. continues to rely on cleanup rather than prevention.– Congress has failed to increase fuel-efficiency standards for

automobiles.– Regulation of emissions from motorcycles and two-cycle

engines remains inadequate.– There is little or no regulation of air pollution from

oceangoing ships in American ports.– Airports are exempt from many air pollution regulations.

– The Act does not regulate the greenhouse gas CO2.

– The Act has failed to deal seriously with indoor air pollution.– There is a need for better enforcement of the Clean Air Act.

Recent policies have been contentious

• Former President G.W. Bush pushed proposals that would overturn key aspects of legislation

• New source reviews = old utility plants have to install the best available technology when upgrading– The Bush administration proposed abolishing this

requirement and dropped lawsuits against violators

• Clear Skies Initiative = establishes a market-based cap-and-trade program for some pollutants– Stopped in the Senate, because it would increase pollution– The EPA had skewed its analysis to promote the legislation