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
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 ( km)
Temperature increases rapidly with elevation

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

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

17. Temperature: 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
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 Timescales
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.

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

29. Anthropogenic Pollution Sources
Figure 3.10

30. Photochemical Smog

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

32. Temperature Inversion
Figure 3.9

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

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

35. 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.

36. 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.

37. 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.

38. 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?