Earths Modern Atmosphere

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Earths Modern Atmosphere

• Atmospheric Composition, Temperature, and
  Function  
• Variable Atmospheric Components  

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Atmospheric Profile  

• Atmosphere extends to 32,000 km (20,000mi) from
  surface
• Exospheres top is at 480 km (300 mi)
• The atmosphere is structured. Three criteria to
  examine atmosphere
• Composition
• Temperature
• Function

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Atmospheric Pressure
90 of atmospheres mass is within 15 km of the
surface (the Troposphere)
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Composition
Exosphere
Heterosphere
Homosphere
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Atmospheric Composition

• Exosphere outer sphere
• 480 km (300 mi) outwards as far as 32,000 km
  (20,000 mi)
• Sparse field of Hydrogen an Helium atoms loosely
  bound to the earth by gravity.

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Atmospheric Composition

• Heterosphere outer atmosphere
• 80 km (50 mi) outwards to 480 km
• Layers of gasses sorted by gravity
• H and He at outer edge.
• O and N at inner edge.
• lt0.001 of mass of atmosphere

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Atmospheric Composition

• Homosphere inner atmosphere
• Surface to 80 km (50 mi)
• Gasses evenly blended

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Homosphere composition
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Homosphere composition

• Why so much Nitrogen?
• It is volatile in most forms
• Eg. Ammonia gas
• It is unreactive with most solid earth material
• It is stable in sunlight.

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Homosphere composition

• Why so much Oxygen?
• Produced by photosynthesis.

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Homosphere composition

• Why so much Argon?
• It slowly degasses from rocks
• It is unreactive so stays in the atmosphere
• Argon is a noble gas

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Homosphere composition

• Why so little carbon dioxide?
• Original atmosphere was probably about 25 CO2
• It dissolves in water
• It is used by plants in photosynthesis

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Exosphere
Heterosphere
Homosphere
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Temperature Thermosphere

• Thermosphere
• The heat sphere
• The top of the thermosphere is the thermopause
  (480km)
• Roughly same as heterosphere
• 80 km (50 mi) outwards
• Swells and contracts with the amount of solar
  energy (250-550 km)
• Temperature increases rapidly with elevation

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Temperature Mesosphere

• Mesosphere
• The mesopause is the coldest part of the
  atmosphere.
• Middle atmosphere
• 50 to 80 km (30 to 50 mi)

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Temperature Stratosphere

• Stratosphere
• 18-50 km (11-31 mi)
• Temperature increases with altitude
• Top is the stratopause

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Temperature Troposphere

• Troposphere
• Surface to 18 km (11 mi)
• 90 mass of atmosphere
• Normal lapse rate average cooling at rate of
  6.4C/km (3.5F/1000 ft)
• Environmental lapse rate actual local lapse rate

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Lapse Rate
Figure 3.5
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FunctionIonosphere

• Ionosphere
• Absorbs cosmic rays, gamma rays, X-rays, some UV
  rays
• Atoms of become positively charged ions.
• Charged ions of oxygen an nitrogen give off light
  to generate the auroras.

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FunctionOzonosphere

• Ozonosphere
• Part of stratosphere.
• Ozone (O3) absorbs UV energy and converts it to
  heat energy.

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Ozone hole

• Ozone concentration on September 7th, 2003.

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Formation of Ozone

• Oxygen that we breathe (and plants produce) is O2
• UV radiation breaks down O2 into 2O.
• O bonds with other O2 to give O3.

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Ozone hole

• Breakdown of ozone
• CFCs are broken down by strong ultraviolet
  radiation to create chlorine atoms.
• Cl acts as a catalyst to destroy O3 molecules.
• Chlorine is not consumed by the reaction.
• One Cl atom can destroy 100,000 O3 molecules.
• Timescales
• CFCs take about 1 year to mix in with the
  troposphere
• They take 2-5 years to mix in with the
  stratosphere

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Why over Antarctica

• Homogeneous versus Heterogeneous O3 depletion
• Homogeneous depletion occurs over the
  ozonosphere.
• There has been a 5-10 drop in O3 levels over the
  US.
• Heterogeneous depletion occurs over Antarctica.
• Atmospheric circulation over Antarctica is
  isolated during the winter.
• Cold temperatures encourage ozone depletion

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Remedial action

• Montreal Protocol (1987).
• First global agreement to reduce atmospheric
  pollution.
• To phase out the use of CFCs and other ozone
  depleting chemicals.
• Current status of the ozone hole.
• Over the last 10 years the size of the ozone hole
  has not increased as rapidly as it had in the
  past.

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Atmospheric Pollution (in the Troposphere)

• Atmospheric pollution first became a major
  problem with the industrial revolution (in the
  1800s).
• Coal burning created very dirty air.
• There are both natural and anthropogenic sources
  for pollution but most pollution comes from
  humans.

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Anthropogenic Pollution  

• Carbon monoxide
• Photochemical smog
• Industrial smog and sulfur oxides
• Particulates

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Anthropogenic Pollution Sources
Figure 3.10
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Photochemical Smog
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Natural Factors That Affect Air Pollution  

• Winds
• Local and regional landscapes
• Temperature inversion

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Temperature Inversion
Figure 3.9
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Spatial scales of Pollution

• The effects of pollution can be
• Global
• Global Warming
• Ozone hole
• Regional
• Acid rain
• Local
• Smog
• Temperature inversions

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The Clean Air Act

• Enacted in 1963 and undated since then.
• In response to massive smog conditions in major
  cities.

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Goals of the clean air act

• The EPA sets permissible levels of pollutants
  based on
• Health effects
• Environmental and property damage
• 90 million Americans live in areas that do not
  meet these standards for at least one pollutant.

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Pollution Permits

• All major stationary sources of pollution are
  required to get permits that list all the
  pollutants they emit.
• Cap and Trade
• Recently programs have been enacted to allow
  factories to trade these permits (only for
  specific pollutants).
• There is an ultimate cap that total pollution
  from all factories cannot exceed.
• This allows the factories that can easily reduce
  pollution to do so and then sell their permits to
  others.

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New Source Review

• Old power plants that produce lots of pollution
  were grandfathered in under the Clean Air Act
  so they produce much more pollution than newer
  power plants.
• New Source Review stipulates that these older
  power plants are not allowed to upgrade unless
  they use the new, less pollution equipment.

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Benefits of the Clean Air Act

• Total direct costs 523 billion
• Estimated benefits 5.6 to 49.4 trillion
• average 22.2 trillion
• Net financial benefit 21.7 trillion
• 205,000 fewer deaths from 1970 to 1990!
• How are these numbers calculated?