CHAPTER 9 - AIR POLLUTION

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CHAPTER 9 - AIR POLLUTION
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Our Atmosphere (1)

• Many charts showing atmospheric properties give
  the impression that the atmosphere is a thick
  mantle around the earth.
• In fact this is an erroneous impression because
  altitude scales are not plotted in the context of
  the earths radius.
• The atmosphere is a thin layer of gases clinging
  to the earth by gravitational force
• 50 of the atmosphere is below an altitude of
  18,000 feet (5.5 km)
• 99 of the atmosphere is below an altitude of 20
  miles (33 km)
• The radius of the earth is 3,958 miles (6,370 km)
• Up to about 100 km altitude the atmosphere is
  composed mainly of nitrogen (N2) (78) and oxygen
  (O2) (21)
• The remaining 1 is composed of trace elements ,
  carbon dioxide, neon, argon, helium, ozone
  which although in small quantities play an
  important role in the habitability of the earth
  for animals and plants.
• The following table shows the relative abundance
  of the atmospheric constituents

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Our Atmosphere (2)
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Our Atmosphere (3)
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Atmospheric Regions
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Local Pollution

• Most of the pollution in our atmosphere comes
  from the conversion of fossil fuel chemical
  energy to heat energy by the process of burning.
• In this section we will focus on local pollution
  in the lower troposphere down to ground level.
• Global pollution effects associated with the same
  energy conversion processes will be discussed
  separately
• Carbon dioxide does not contribute to local
  pollution, so even though it is produced in the
  largest quantities by burning fossil fuels the
  discussion of this pollution will be deferred

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Thermal Inversions

• Local pollution can be minimized if the polluting
  material can be dispersed rapidly from its point
  of origin.
• The dispersal may be horizontally by winds.
• It may be vertically upwards by convection
  currents.
• It may be vertically downwards by rain.
• Thus in calm, dry weather (anti-cyclonic) we must
  rely on vertical dispersion.
• The stability of the lower atmosphere with
  respect to vertical mixing is determined by the
  vertical temperature variation from the ground
  upwards.
• The range of vertical temperature profiles which
  occur are shown in the following diagram.
• The average temperature-altitude relation is
  called The Adiabatic Lapse Rate (ALR)
• Adiabatic - no heat in or out of a rising packet
  of air
• Lapse - temperature decreases with altitude
• Average ALR is -0.65C/100m (3F/1000 feet)

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Atmospheric Vertical Stability
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Inversion Temperature Profiles
High Pressure Subsidence
Radiative Inversion

• Positive temperature gradients lead to stable air
  and build-up of pollutants.

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Major Sources of Pollutants
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SMOG

• Smog is the term given to fog caused by
  pollutants rather than for resulting from high
  levels of moisture in the atmosphere.
• Smog results from a wide range of pollutants
• Carbon Monoxide CO
• Nitrogen Oxides NO, NO2
• Sulfur Dioxide SO2
• Ozone O3
• Particulates Small solid particles
• Aerosols Small liquid droplets
• If these pollutants are emitted into a stable,
  windless atmosphere characterized by an
  increasing temperature with altitude, they will
  accumulate and build up in concentration to form
  a smog.
• It may be more of a haze with adequate visibility
  for driving as formed by vehicles in large cities
• It may be dense with low visibility for driving
  as in the London Fogs
• If the pollutants build up for several days of
  stable atmosphere the results can be fatal to
  some of the population.

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Smog Kills

• Smoke represents particulates from open coal
  fires.
• Also the SO2 levels are high because of the high
  sulfur content of coal

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Photochemical Smog

• The smog which occurs in many large cities
  (including Salt Lake City) is called
  photochemical smog.
• It is characterized by a hazy appearance which
  often has a yellowish/brownish tinge due to the
  color of NO2
• The oxides of nitrogen are a result of burning
  fossil fuel (gasoline) at high temperature in the
  engine cylinders when the nitrogen in the air
  combines with the oxygen.
• Smog can be very irritating to the eyes and the
  lungs and the CO in it is a poisonous gas
  reducing the ability of the blood to carry
  oxygen.
• The name comes from the fact that sunlight
  interacts with the pollutants, particularly the
  aerosols, to form complex molecules of hydrogen,
  carbon and nitrogen call PAN (peroxyacyl
  nitrates).
• The formation of city smog can be made worse by
  geographical features such as mountain ranges
  surrounding the city which reduce horizontal
  dispersion of the smog.

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Smog Reduction Measures

• London Fog type of air pollution can be
  virtually eliminated by drastically reducing open
  burning of fossil fuel or biomass in fireplaces.
• This was very effective in London which has not
  had severe pollution fog since 1962.
• Reduction of vehicle pollutant emissions
• Computer control of fuel-air mixture ensured more
  complete combustion of the gasoline.
• Sealed fuel systems
• Elimination of the carburettor
• Catalytic converter to decompose NO to N2 and O2
  before it leaves the tailpipe .
• Forced gasoline refiners to reduce lead in
  gasoline to prevent poisoning of the catalyst
• Annual emission testing mandatory in large urban
  districts.

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Sulfur Dioxide

• We saw that many forms of coal have a high sulfur
  content
• When this coal is burned in power plants the
  sulfur combine with oxygen in the air to form
  sulfur dioxide (SO2)
• SO2 escapes into the atmosphere where it reacts
  with water droplets in clouds to form sulfuric
  acid (H2SO4)
• This eventually falls as rain composed of dilute
  sulfuric acid rather than pure rainwater. So
  called acid rain.
• The pollution is localized near power plants, and
  has had devastating effects on plant life and
  lake fish, particularly in the industrial NE .
• The acid rain is also very bad for buildings
  ornamented with limestone or marble or held
  together with mortar, all of which dissolve in
  sulfuric acid.
• Newer power plants contain and upgrades to older
  plants are being made to reduce SO2 in the flue
  gases
• Produces more solid waste
• Increases cost of generating electricity

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Particulates

• The widespread use of coal-fired power plants is
  responsible for pollution by particulates.
• The solid particles in the ash in the flues of
  coal furnaces are 20 times greater than the
  aerosols emitted by gasoline or oil burning
• The location of coal fired plants near centers of
  population put more people at risk from the
  health consequences of particulates than from
  natural events such as volcanoes or forest fires.
• Also certain industrial processes such as steel
  manufacture and cement manufacture produce large
  amounts of pollutants.
• There are techniques for scrubbing the flue
  gases to reduce the emission of particulates,
  again adding to the cost of the product being
  made.

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Controls Work

• Through the efforts of the Environment Protection
  Agency atmospheric pollution is showing a
  downward trend after 70 years of approximately
  matching the trend of the increase in population
  growth.

Note that after the early 1970s there has been a
continuous downward trend in the common local
pollutants
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Learning Objectives (1)

• Be aware that the atmosphere is a thin layer of
  gasses over the earths surface
• Know that 50 of atmosphere is below 5.5 km. 99
  below 33 km in the context of the earths radius
  of 6370 km
• Know that the principal constituents of the
  earths atmosphere are nitrogen (78) and Oxygen
  (21)
• Be aware that there are many trace gases which,
  even in small quantities, can greatly affect the
  quality of the air we breathe.
• Know that the atmosphere is divided into vertical
  regions determined by maxima and minima in the
  atmospheric temperature.
• Know that the lowest region of the atmosphere is
  called the troposphere and the region above is
  the stratosphere.
• Be aware that local pollution occurs primarily in
  the troposphere.
• Be aware that the conversion of fossil fuel
  chemical energy to other forms of energy produces
  atmospheric pollution.

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Learning Objectives (2)

• Know three methods by which pollution may be
  dispersed.
• Be aware that the vertical stability of the
  atmosphere is determined by the vertical
  temperature variation.
• Be familiar with the term Adiabatic Lapse Rate
  (ALR) to describe the average rate of decline of
  atmospheric temperature with altitude.
• Know that the ALR is about 3F/1000 feet.
• Understand that lower lapse rates of increasing
  temperature with altitude is increasingly stable
  and inhibits vertical mixing.
• Know what is meant by a temperature inversion and
  why it occurs at ground level and at higher
  levels.
• Realize that highway vehicles are the major
  producers of local pollutants.
• Be aware that the major local pollution in urban
  areas is caused by carbon monoxide and oxides of
  nitrogen.

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Learning Objectives (3)

• Know that other forms of deadly smog can be
  produced from particulates and sulfur dioxide
  produced by burning coal.
• Understand that in sunny urban areas the smog
  situation is worsened by the formation of
  photochemical smog.
• Know that the sunlight causes smog gases to react
  to for compounds with the generic acronym PAN.
• Be aware that sulfur dioxide in the atmosphere is
  dissolved by water droplets to eventually fall as
  acid rain.
• Realize that the sulfuric acid in acid rain is
  very harmful to fish, plants and buildings.
• Understand that controls have been applied to
  reduce local pollution gases
• Open coal fires are restricted.
• Anti pollution measures are applied to cars.
• Particulate removal from coal fired power plants
• Know that there has been a decrease in total
  pollutants since 1970 after 70 years of growth