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

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

3. 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

4. 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

5. 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

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

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

8. 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

11. 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

12. 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?

13. 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?