Chapter 18: Air Pollution

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• Chapter 18 Air Pollution
• In this chapter the following topics will be
  covered
• The major categories and sources of air
  pollution
• Conventional unconventional pollutants
• The origins and dangers of some indoor
  pollutants
• The effects of stratospheric ozone depletion
  and radon in indoor air
• How air pollution damages human health,
  vegetation and buildings
• Different approaches to air pollution control

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• The Air Around Us
• Smoke, haze, dust, odors, corrosive gases,
  noise, and toxic
• compounds are present nearly everywhere, even in
  the most
• remote, pristine wilderness.
• Air pollution is generally the most
  widespread and obvious kind
• of environmental damage.
• Over the past twenty years, air quality has
  improved appreciably
• in most cities in Western Europe, North America
  and Japan.
• Air quality in the developing world has been
  getting much
• worse.

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• Natural Sources of Air Pollution
• There are many natural sources of air
  quality degradation.
• - Natural fires release smoke.
• - Volcanoes spew out ash, acid mists, hydrogen
  sulfide, and
• other toxic gases.
• - Sea spray and decaying vegetation
  are major sources of
• reactive sulfur compounds in the air.
• - Trees and bushes emit millions of
  tons of volatile organic
• compounds.
• - Pollen, spores, viruses, bacteria,
  and other small bits of organic
• material are present in the air.
• - Bacterial metabolism of decaying
  vegetation in swamps and of cellulose in the
  guts of termites and ruminant animals is
• responsible for large methane releases.

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• Human-Caused Air Pollution
• Primary and Secondary Pollutants
• Primary pollutants those released directly
  from the source into the
• air in a harmful form.
• Secondary pollutants modified to a
  hazardous form after they enter
• the air or are formed by chemical reactions as
  components of the air mix and interact.
• - Solar radiation often provides the energy for
  these reactions.
• Fugitive emissions those that do not go
  through a smokestack (e.g.
• dust from soil erosion, strip mining, rock
  crushing, and building construction).

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• Conventional or Criteria Pollutants
• The U.S. Clean Air Act of 1970 designated
  seven major pollutants
• for which maximum ambient air levels are
  mandated.
• These seven conventional or criteria
  pollutants contribute the
• largest volume of air-quality degradation.

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• Sulfur compounds
• - Natural sources evaporation of sea spray,
  erosion of sulfate
• containing dust from arid soils, fumes from
  volcanoes and
• fumaroles, and biogenic emissions of hydrogen
  sulfide and
• organic sulfur-containing compounds.
• - The predominant form of anthropogenic sulfur
  is sulfur dioxide
• from combustion of sulfur-containing fuel.
• Sulfur dioxide is a colorless
  corrosive gas that is
• directly damaging to both plants and
  animals.
• Can be oxidized to sulfur trioxide, which
  reacts with water vapor or dissolves in
  water droplets to form
• sulfuric acid (major component
  of acid rain).

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• Nitrogen compounds
• - Nitrogen oxides highly reactive gases formed
  when nitrogen in
• fuel or combustion air is heated to
  temperatures above
• 650o C in the presence of oxygen, or when
  bacteria in soil or
• water oxidize nitrogen-containing compounds.
• - Nitrogen oxides combine with water to make
  nitric acid, which
• is a major component of atmospheric
  acidification.
• - Excess nitrogen also causes fertilization and
  eutrophication of inland waters and coastal
  seas.

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• Carbon Oxides
• - Carbon dioxide (CO2) is the predominant
  form of carbon in the
• air.
• - Usually considered nontoxic and
  innocuous, increasing levels
• of carbon dioxide appears to be causing a
  global climate
• warming.
• - Burning of fossil fuels is estimated to add
  between 5 and 5.5
• billion tons of carbon to the atmosphere each
  year.
• - Uncertainty exists about where the
  extra carbons goes.
• - Carbon monoxide colorless,
  odorless, nonirritating but highly
• toxic gas.
• - About 90 percent of the carbon
  monoxide in the air is
• consumed in photochemical reactions that
  produce ozone.

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• Metals and Halogens
• - Many toxic metals are mined and used in
  manufacturing
• processes or occur as trace elements in
  fuels, especially coal.
• - Lead
• Worldwide lead emissions
  amount to about 2 million metric tons per year,
  or two-thirds of all metallic pollution.
• Most lead is from leaded
  gasoline.
• An estimated 20 percent of
  all inner-city children suffer some degree of
  mental retardation from high environmental
  lead levels.
• - Mercury
• Two largest sources of
  atmospheric mercury appear to be coal-burning
  power plants and waste incinerators.
• - Other toxic metals of concern are nickel,
  beryllium, cadmium, thallium, uranium,
  cesium, and plutonium.
• - Halogens (fluorine, chlorine,
  bromine, and iodine) are highly reactive and
  generally toxic in their elemental form.
• - About 600 million tons of highly
  persistent chlorofluorocarbons (CFCs) are
  used annually worldwide in spray propellants,
  refrigeration compressors, and for foam
  blowing.
• CFCs diffuse into the
  stratosphere where they release chlorine and
• fluorine atoms that destroy the ozone
  shield that protects the earth from U.V.
  radiation.

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• Particulate material
• - Particulate material all atmospheric
  aerosols, whether solid or
• liquid.
• - Includes dust, ash, soot, lint, smoke,
  pollen, spores, algal cells,
• and many other suspended materials.
• - Particulates often are the most apparent form
  of air pollution
• since they reduce visibility and leave dirty
  deposits on
• windows, painted surfaces, and textiles.
• - Respirable particles smaller than 2.5
  micrometers are among
• the most dangerous of this group because they
  can be drawn
• into the lungs.

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• Volatile organic compounds
• - Volatile organic compounds (VOCs) organic
  chemicals that
• exist as gases in the air.
• - Plants are the largest source of
  VOCs.
• - A large number of other synthetic
  organic chemicals, such as benzene, toluene,
  formaldehyde, vinyl chloride, phenols,
• chloroform, and trichloroethylene, are
  released into the air by
• human activities.
• These chemicals play an
  important role in the formation
• of photochemical oxidants.
• - Of the 188 air toxics listed in the Clean Air
  Act, about two
• thirds are VOCs and most of the rest are
  metal compounds.
• - EPA has identified 33 chemical
  compounds considered to be
• the greatest threat to public health in urban
  areas.

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Table 18.2 -- Urban air toxics of greatest
concern Acetaldehyde Coke oven
emissions Manganese compounds Acrolein Dioxins
Mercury compounds Acrylonitrile 1,2-dibromoeth
ane Methylene chloride Arsenic
compounds 1,3-dichloropropane Nickel compounds
Benzene Propylene dichloride Polychlorinated
biphenyls Beryllium compounds Ethylene
dichloride Polycyclic organic matter
1,3-butadiene Ethylene oxide Quinoline
Cadmium compounds Formaldehyde 1,1,2,2-tetrachlo
rethane Carbon tetrachloride Hexachlorobenzene Te
trachloroethylene Chloroform Hydrazine Trichlo
roethylene Chromium compounds Lead
compounds Vinyl chloride
Source U.S. EPA 1999
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• Photochemical oxidants
• - Photochemical oxidants products of secondary
  atmospheric
• reactions driven by solar energy.
• - One of the most important reactions
  involves formation of
• singlet (atomic) oxygen by splitting nitrogen
  dioxide (NO2).
• - Then the atmoic oxygen reacts with
  another molecule of O2 to make ozone (O3).
• - Ozone formed in the stratosphere
  provides a valuable shield
• for the biosphere by absorbing
  incoming ultraviolet radiation.
• - In ambient air, however, O3 is a
  strong oxidizing reagent and damages
  vegetation, building materials, and sensitive
  tissues.

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• Unconventional Pollutants
• EPA has authority under the Clean Air Act to
  set emission standards
• (regulating the amount released) for certain
  unconventional or non-criteria pollutants that
  are considered especially hazardous or toxic.
• Examples of these unconventional pollutants
  include asbestos,
• benzene, beryllium, mercury, polychlorinated
  biphenyls, and vinyl chloride.
• Aesthetic degradation includes any
  undesirable changes in the
• physical characteristics or chemistry of the
  atmosphere (e.g. noise, odors and light
  pollution).

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• Indoor Air Pollution
• The EPA has found that indoor concentrations
  of toxic air pollutants
• are often higher than outdoors.
• People generally spend more time inside than
  out and therefore are
• exposed to higher doses of these pollutants.
• Smoking is the most important air pollutant
  in the United States in
• terms of human health.
• In some cases, indoor air in homes has
  concentrations of chemicals
• that would be illegal outside or in the
  workplace.
• "Green design" principles can make indoor
  spaces both healthier and
• more pleasant.
• In less-developed countries of Africa, Asia,
  and Latin America
• where such organic fuels as firewood, charcoal,
  dried dung, and agricultural wastes make up the
  majority of household energy, smoky, poorly
  ventilated heating and cooking fires represent
  the greatest source of indoor air pollution.

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• Climate, Topography, and Atmospheric Processes
• Topography, climate, and physical processes
  in the atmosphere play
• an important role in transport, concentration,
  dispersal, and removal of many air pollutants.
• Wind speed, mixing between air layers,
  precipitation, and
• atmospheric chemistry all determine whether
  pollutants will
• remain in the locality where they are produced or
  will go elsewhere.

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• Inversions
• Temperature inversions occur when a stable
  layer of warmer air
• overlays cooler air, reversing the normal
  temperature decline with
• increasing height and preventing
  convection currents from
• dispersing pollutants.
• Several mechanisms create inversions.
• - Cold front slides under an adjacent warmer
  air mass or
• when cool air subsides down a
  mountain slope to displace
• warmer air in the valley.
• - Rapid nightime cooling in a valley or basin
  where air movement is restricted.
• The cool air slides in under contaminated
  air, squeezing it up against the cap of
  warmer air above and
• concentrated the pollutants accumulated
  during the day.

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• Dust Domes and Heat Islands
• Tall buildings in large cities create
  convective updrafts that sweep
• pollutants into the air.
• Temperatures in the center of large cities
  are frequently 3o to 5oC
• higher than surrounding countryside.
• Stable air masses created by this "heat
  island" over the city
• concentrate pollutants in a "dust dome".
• Long-Range Transport
• Fine aerosols and industrial pollutants can
  be carried great distances
• by the wind.
• Some of the most toxic and corrosive
  materials delivered by long
• range transport are secondary pollutants,
  produced by the mixing and interaction of
  atmospheric contaminants as they travel through
  the air.
• Somoa, Greenland, and even Antactica and the
  North Pole, all have
• heavy metals, pesticides, and radioactive
  elements in their air.
• The Inuit people of Broughton Island, well
  above the Arctic Circle,
• have higher levels of polychlorinated biphenyls
  in their blood than any other known population,
  except victims of industrial accidents.

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• Stratospheric Ozone
• In 1985, a disturbing discovery was
  announced ozone levels in the
• stratosphere over the South Pole were dropping
  precipitously during September and October every
  year as the sun reappears at the end of the long
  polar winter.
• Why are we worried about stratospheric
  ozone?
• - In the upper atmosphere, where it
  screens out dangerous U.V.
• rays from the sun, ozone is an irreplaceable
  resource.
• Exceptionally cold temperatures in Antactica
  play a role in ozone
• losses.
• Humans release a variety of
  chlorine-containing molecules into the
• atmosphere (e.g. chlorofluorocarbons and halon
  gases).
• - Because these molecules are so
  stable, they persist for decades or
• even centuries once released.
• - When they diffuse out into the
  stratosphere, the intense U.V. irradiation
  releases chlorine atoms that destroy ozone.
• - At a 1989 conference, eighty-one
  nations agreed to phase out
• CFC production by the end of the century.
• - Alternatives to CFCs exist including
  hydrochlorofluorocarbons
• (HCFCs) which release much less
  chlorine per molecule.
• CFC production in industrialized
  countries has fallen nearly 80
• since 1989.

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• Effects of Air Pollution
• Human Health
• Heart attacks, respiratory diseases, and
  lung cancer all are significantly higher in
  people who
• breathe dirty air, compared to matching groups in
  cleaner environments.
• Conditions are often much worse in other
  countries than Canada or the United States.
• The United Nations estimates that at least
  1.3 billion people around the world live in areas
• where air is dangerously polluted.
• The most common route of exposure to air
  pollutants is by inhalation, but direct
  absorption
• through the skin or contamination of food and
  water are also important pathways.
• Because they are strong oxidizing agents,
  sulfates, SO2, NOx, and O3 act as irritants that
• damage delicate tissues in the eyes and
  respiratory passages.
• Carbon monoxide binds to hemoglobin and
  decreases the ability of red blood cells to carry
• oxygen.
• Some important chronic health effects of
  air pollutants include bronchitis and emphysema.
• - Bronchitis persistent
  inflammation of bronchi and bronchioles (large
  and small airways in the lung) that cause a
  painful cough and involuntary muscle spasms
• that constrict airways.
• - Emphysema an irreversible
  obstructive lung disease in which airways become

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• Plant Pathology
• In the early days of industrialization,
  fumes from furnaces, smelters,
• refineries, and chemical plants often destroyed
  vegetation and created desolate, barren
  landscapes around mining and manufacturing
  centers.
• - Copper-nickel smelter at Sudbury, Ontario, is
  a notorious
• example of air pollution effects on
  vegetation and ecosystems.
• There are two probable ways that air
  pollutants damage plants.
• - They can be directly toxic, damaging
  sensitive cell membranes
• much as irritants do in human lungs.
• - They can act as metabolic regulators or plant
  hormones and
• disrupt normal patterns of growth and
  development.
• Synergistic effects effects caused
  following exposure to two factors
• which together is more than the sum of exposure
  to each factor individually.
• Pollutant levels too low to produce visible
  symptoms of damage may
• still have important effects.

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• Acid Deposition
• Acid precipitation the deposition of wet
  acidic solutions or dry
• acidic particles from the air.
• By the 1940's, it was known that pollutants,
  including atmospheric
• acids, could be transported long distances by
  wind currents.
• pH and atmospheric acidity
• - acidity is described in terms of pH
  (the negative logarithm of the
• hydrogen ion concentration in a solution).
• - pH scale ranges from 0 to 14 with 7,
  the midpoint, being neutral.
• - Values less than 7 indicate
  progressively greater acidity, while
• above 7 are progressively more alkaline.
• - Normal, unpolluted rain generally
  has a pH of about 5.6 due to
• carbonic acid created by CO2 in the air.

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• Aquatic effects
• - Generally, reproduction is the most sensitive
  stage in fish life cycles.
• - Eggs and fry of many species are killed when
  the pH drops to about 5.0.
• - This level of acidification (pH 5.0)
  can also disrupt the food chain by killing
• aquatic plants, insects, and invertebrates
  on which fish depend for food.
• - There are several ways acids kill fish.
• Alters body chemistry
• Destroys kills and prevents
  oxygen uptake
• Causes bone decalcification
• Disrupts muscle contraction.
• - Acid water leaches toxic metals, such as
  mercury and aluminum, out of soil
• and rocks.
• - Studies in the Adirondack Mountains
  of New York revealed that about half
• of the high altitude lakes are acidified and
  have no fish.
• - Much of the western United States
  has relatively alkaline bedrock and
• carbonate-rich soil, which counterbalance
  acids from the atmosphere.
• - Sulfates account for about
  two-thirds of the acid deposition in eastern
  North
• America and most of Europe, while nitrates
  contribute most of the remaining
• one-third.

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• Forest damage
• - In the early 1980s, disturbing reports
  appeared of rapid forest declines in
• both Europe and North America.
• - A 1980 survey on Camel's Hump
  Mountain in Vermont showed that
• seedling production, tree density, and
  viability of spruce-fir forests at high
• elevations had declined about 50 percent in
  15 years.
• By 1990, almost all the
  red spruce, once the dominant species on the
• upper part of the mountain, were dead
  or dying.
• - European forests also are dying at
  an alarming rate.
• In 1982, German foresters estimated only
  8 percent of their forests
• showed pollution damage.
• By 1983, some 34 percent of the forest
  was affected.
• By 1985, more than 4 million hectares
  (about half the total) were
• reported to be in a state of decline.
• - Similar damage is reported in
  Czechoslovakia, Poland, Austria, and
• Switzerland.
• - Researchers at the Hubbard Brook
  Experimental Forest in New Hampshire
• have shown that forest soils have become
  depleted of natural buffering
• reserves of basic cations such as calcium
  and magnesium through years of

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• Buildings and monuments
• - In cities throughout the world, some of the
  oldest and most glorious
• buildings and works of art are being
  destroyed by air pollution.
• - Air pollution also damages ordinary buildings
  and structures by corroding
• steel in reinforced concrete in the buildings
  as well as roads and bridges.
• Visibility reduction
• - Foul air obscuring the skies above
  industrialized cities has long been
• recognized as a problem.
• - Pollution affects rural areas as
  well (e.g. Grand Canyon National Park and
• Shenandoah National Park).

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• Air Pollution Control
• Moving Pollution to Remote Areas
• Among the earliest techniques for improving
  local air quality was
• moving pollution sources to remote locations
  and/or dispersing emissions with smokestacks.
• Particulate Removal
• Filters remove particle physically by
  trapping them in a porous mesh
• of cotton cloth, spun glass fibers, or
  asbestos-cellulose, which allows air to pass
  through but holds back solids.
• Electrostatic precipitators are the most
  common particulate controls
• in power plants.
• - Fly ash particles pick up an electrostatic
  surface charge as they
• pass between large electrodes in the effluent
  stream.
• - Performance depends on particle
  size and chemistry, strength
• of the electric field, and flue gas velocity.

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• Sulfur Removal
• Sulfur removal can be done a variety of ways
  either by using low-sulfur fuel or by removing
• sulfur from effluents.
• Fuel switching and fuel cleaning
• - Switching from soft coal with a high sulfur
  content to low-sulfur coal can greatly reduce
• sulfur emission.
• - Changing to another fuel, such as natural
  gas or nuclear energy, can eliminate all
• sulfur emissions as well as those of
  particulates and heavy metals.
• - Alternative energy sources, such as wind
  and solar power, are preferable to either fossil
  fuel
• or nuclear power, and are becoming
  economically competitive.
• - Coal can be crushed, washed, and gassified
  to remove sulfur and metals before combustion.
• Limestone injection and fluidized bed
  combustion
• - Sulfur emissions can be reduced as much as
  90 percent by mixing crushed limestone with
• coal before it is fed into a boiler.
• - A relatively new technique for burning,
  called fluidized bed combustion, offers several
• advantages in pollution control.
• Flue gas desulfurization
• - Crushed limestone, lime slurry, or alkali
  can be injected into a stack gas stream to
• remove sulfur after combustion.

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• Nitrogen Oxide Control
• Staged burners, in which the flow of air and
  fuel are carefully
• controlled, can reduce nitrogen oxide formation
  by as much as 50.
• The approach adopted by U.S. automakers for
  NOx reductions has
• been to use selective catalysts to change
  pollutants to harmless
• substances.
• Raprenox (rapid removal of nitrogen oxides)
  is a new technique for
• removing nitrogen oxides that was developed by
  the U.S. Department of Energy Sandia Laboratory
  in Livermore, California.
• Hydrocarbon Controls
• Closed systems that prevent escape of
  fugitive gases can reduce
• many hydrocarbon emissions (e.g. positive
  crankcase ventilation (PCV) systems in
  automobiles).
• Controls on fugitive losses from valves,
  pipes, and storage tanks in
• industry can have a significant impact on air
  quality.
• Afterburners are often the best method for
  destroying volatile
• organic chemicals in industrial exhaust stacks.

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• Clean Air Legislation
• The Clean Air Act of 1963 was the first
  national legislation in the
• United States aimed at air pollution control.
• - Federal grants were provided to states to
  combat pollution, but the act was
• careful to preserve states' rights to set and
  enforce air quality regulations.
• - It became obvious that some pollution
  problems cannot be solved on a local basis.
• In 1970, an extensive set of amendments
  essentially rewrote the Clean Air Act.
• - These amendments identified the
  "criteria pollutants" and established national
• ambient air quality standards.
• - Standards are divided into two
  categories.
• Primary standards intended to
  protect human health.
• Secondary standards set to
  protect materials, crops, climate, visibility,
  and
• personal comfort.
• In 1990, the Clean Air Act was extensively
  rewritten and updated including
• provisions to address the following issues acid
  rain, urban smog, toxic air pollutants, ozone
  protection, marketing pollution rights, and
  volatile organic compounds.

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• In 1997, further changes were made to the
  Clean Air Act ambient ozone
• standards will be lowered from 0.12 ppm to 0.08
  ppm.
• The EPA estimates that costs of these
  measures could be as high as 8.5 billion per
• year, but that they should save 15,000 lives, cut
  hospital admissions for respiratory illnesses by
  9.000, and reduce chronic bronchitis cases by
  60,000 each year.
• The EPA won't fully implement these latest
  standards for ozone and fine soot until
• 2008 to give states a chance to set up monitoring
  systems and to find ways to eliminate pollution
  in the most cost-effective manner.
• California has gone further than the federal
  government in making specific plans for
• air pollution control.

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• Current Conditions and Future Prospects
• Clean Air Act goals have not been achieved
  however, air quality
• has improved dramatically in the last
  decade in terms of the
• major large-volume pollutants.
• The EPA estimates that emissions of
  particulate materials
• decreased 78 percent, lead fell 98, SO2
  declined 32
• percent, and CO shrank 23.
• Because automobiles are the main source of
  NOx, cities where
• pollution is largely from traffic still
  have serious air quality
• problems.

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• The major metropolitan areas of many
  developing countries are
• growing at explosive rates to incredible
  sizes and environmental
• quality is still abysmal in many of them
  (e.g. Mexico City and many
• large cities in China).
• As political walls came down across Eastern
  Europe and the Soviet
• Union at the end fo the 1980s, horrifying
  environmental conditions in
• these centrally planned economies were
  revealed.
• Not all is pessimistic, however. There have
  been some spectacular
• successes in air pollution control (e.g.
  Sweden and West Germany).

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