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!