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Earth’s Modern Atmosphere

Earth’s Modern Atmosphere. Atmospheric Composition, Temperature, and Function   Variable Atmospheric Components . Atmospheric Profile  . Atmosphere extends to 32,000 km (20,000mi) from surface Exosphere’s top is at 480 km (300 mi)

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Earth’s Modern Atmosphere

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  1. Earth’s Modern Atmosphere • Atmospheric Composition, Temperature, and Function   • Variable Atmospheric Components 

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

  3. Atmospheric Pressure 90% of atmosphere’s mass is within 15 km of the surface (the Troposphere)

  4. Exosphere Composition Heterosphere Homosphere

  5. 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.

  6. 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. • <0.001% of mass of atmosphere

  7. Atmospheric Composition • Homosphere – inner atmosphere • Surface to 80 km (50 mi) • Gasses evenly blended

  8. Homosphere composition

  9. 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.

  10. Homosphere composition • Why so much Oxygen? • Produced by photosynthesis.

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

  12. 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

  13. Exosphere Heterosphere Homosphere

  14. 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

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

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

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

  18. Lapse Rate Figure 3.5

  19. Function:Ionosphere • 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.

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

  21. Ozone hole • Ozone concentration on September 7th, 2003.

  22. 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.

  23. Ozone hole • Breakdown of ozone • CFC’s 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 • CFC’s take about 1 year to mix in with the troposphere • They take 2-5 years to mix in with the stratosphere

  24. 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

  25. Remedial action • Montreal Protocol (1987). • First global agreement to reduce atmospheric pollution. • To phase out the use of CFC’s 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.

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

  27. Anthropogenic Pollution   • Carbon monoxide • Photochemical smog • Industrial smog and sulfur oxides • Particulates

  28. Anthropogenic Pollution Sources Figure 3.10

  29. Photochemical Smog

  30. Natural Factors That Affect Air Pollution   • Winds • Local and regional landscapes • Temperature inversion

  31. Temperature Inversion Figure 3.9

  32. Spatial scales of Pollution • The effects of pollution can be: • Global • Global Warming • Ozone hole • Regional • Acid rain • Local • Smog • Temperature inversions

  33. The Clean Air Act • Enacted in 1963 and undated since then. • In response to massive smog conditions in major cities.

  34. 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.

  35. 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.

  36. 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.

  37. 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?

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