18-1 What Is the Nature of the Atmosphere? Concept 18-1 The atmosphere is structured in layers, including the troposphere, which supports life, and the stratosphere, which contains the protective ozone layer. 1

The Atmosphere Consists of Several Layers Atmosphere varies in Density Atmospheric pressure 2

Air Movements in the Troposphere Play a Key Role in Earth’s Weather and Climate 75–80% of the earth’s air mass (up to 20 km) Closet to the earth's surface (Greenhouse ) Chemical composition of air (N, O 99%) Minor amounts (Ar, H2O, CO2, CH4, N2O) Rising and falling air currents: weather and climate (Heat) Involved in chemical cycling 3

The Stratosphere Is Our Global Sunscreen Less material (air) Similar composition to the troposphere, with 2 exceptions Much less water O3, ozone layer, filters UV (17-26 km) The good and the bad about Ozone Location (17 to 48 km) Joe dropped in this layer 4

Our Protection by Stratosphere Ozone filters (blocks) most of the sun’s UV from reaching us Some UV is reflected, some absorbed by Oxygen to uses in conversion to ozone Prevents troposphere oxygen being converted into photochemical ozone, a harmful air pollutant

Mesosphere 50-80 km The layer of atmosphere involved with diverting or disintegrating meteors

Thermosphere The outermost region of atmosphere The layer involved with producing the Northern Lights (Aurora Borealis)

Atmospheric pressure (millibars) 200 400 600 800 1,000 120 75 200 400 600 800 1,000 120 75 110 Temperature Thermosphere 65 100 90 Mesopause 55 80 Mesosphere 45 70 Altitude (kilometers) Altitude (miles) 60 Stratopause 35 50 Stratosphere 40 25 Figure 18.3 Natural capital: The earth’s atmosphere is a dynamic system that includes four layers. The average temperature of the atmosphere varies with altitude (red line). Most UV radiation from the sun is absorbed by ozone (O3), found primarily in the stratosphere in the ozone layer 17–26 kilometers (10–16 miles) above sea level. Question: Why do you think the temperature falls and rises twice, going from lower to higher altitudes? 30 Tropopause 15 20 Ozone layer 10 Pressure Troposphere 5 (Sea level) Pressure = 1,000 millibars at ground level –80 –40 40 80 120 Temperature (˚C) Fig. 18-3, p. 470

Temperature and atmosphere Temperature is based on amount of the sun’s energy is absorbed by the atoms of each layer The thermosphere atoms are exposed to the most energy, therefore are the hottest Stratosphere is warmer than troposphere because of energy absorbed to create ozone

Questions about the atmosphere Why does the temperature not continuously decrease as one moves farther away from the surface of the Earth? What reasons does the NASA test pilot need to wear a pressurized suit while testing the parachute? What is the composition of ozone?

Questions about the atmosphere Why is ozone both good and bad for humans? What would happen if there were no greenhouse gases in the atmosphere?