Chapter 3
Earth’s Modern
Atmosphere
Robert W. Christopherson
Charlie Thomsen
Atmospheric Profile
Atmosphere extends to 32,000 km
(20,000 mi) from surface
Heterosphere – outer atmosphere
80 km (50 mi) outward, to thermosphere
Layers of gases sorted by gravity
Homosphere – inner atmosphere
Surface to 80 km (50 mi)
Gases evenly blended
Thermosphere is at 480 km (300 mi)—top
of the principal atmosphere
Profile of Atmosphere
based on air
temperature profile
1. Troposphere
Surface to 18 km (11 mi)
90% mass of atmosphere
Lapse rate: the rate of air
temperature decreases with
elevation
Normal lapse rate – average
cooling at rate of 6.4 C°/km (3.5
F°/1000 ft)
2. Stratosphere
18 to 50 km (11 to 31 mi)
Inversion: air temperature
increases with elevation
Ozone maximum
3. Mesosphere
50 to 80 km (30 to 50 mi)
4. Thermosphere
Roughly same as heterosphere
80 km (50 mi) outward
Figure 3.2
Temperature
Profile
Figure 3.6
Atmospheric
Pressure: the weight of air
above a unit surface (1013mb
or 1kg/cm2 or 14.7lb/in2) at
sea level.
Always decreases with elevation (height)
Figure 3.3
Atmospheric Composition
Six greenhouse gases: carbon dioxide, water vapor, methane, ozone, nitrous oxide, CFCs
CO2 increase
1958–2007
Seasonal variation and an increasing trend
Figure 3.4
Atmospheric Function
Ionosphere
Absorbs cosmic rays, gamma rays, X-rays,
some UV rays
Ozonosphere
Part of stratosphere
Ozone (O3) absorbs UV energy and converts it
to heat energy
Protective
Atmosphere
Figure 3.7
Antarctic
Ozone
Hole
2006
Figure FS 3.1.1
Variable Atmospheric Components
Natural Sources
Natural Factors That Affect Air Pollution
Anthropogenic Pollution
Benefits of the Clean Air Act
Natural Factors That Affect Air Pollution
1. Winds
2. Local and regional landscapes
3. Temperature inversion
Southern California Wildfires
Figure 3.8
Temperature Inversion
Figure 3.10
Anthropogenic Pollution
Carbon monoxide: from incomplete combustion of
fuels
Photochemical smog (smoke and fog): mix of
chemicals (pollutants) formed through chemical
reactions of other pollutants under the sunlight.
Industrial smog and sulfur oxides (combustion of
sulfur-containing fuel)
Particulates (PM10 and PM2.5): particulate
matters smaller than 10μm or 2.5 μm.
Forests on Fire
Figure 3.12
Air Pollution
Figure 3.14
Photochemical Smog
Figure 3.15
Benefits of the Clean Air Act
Total direct cost $523 billion
Direct monetized benefits $5.6 to $49.4
trillion – average $22.2 trillion
Net financial benefit $21.7 trillion
206,000 fewer deaths in 1990!