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.

The Atmosphere Consists of Several Layers

• Atmosphere varies in– Density– Atmospheric pressure

Air Movements in the Troposphere Play a Key Role in Earth’s Weather and Climate

• Troposphere – 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

The Stratosphere Is Our Global Sunscreen

• Stratosphere– 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

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)

Fig. 18-3, p. 470

Atmospheric pressure (millibars)

120

Temperature

750 200 400 600 800 1,000

110Thermosphere 65

100

90Mesopause 55

80

70Mesosphere 45

60 Stratopause35

50

Altit

ude

(mile

s)

Altit

ude

(kilo

met

ers)

40

25Stratosphere

30 Tropopause

20 Ozone layer 15

10 Pressure Troposphere 5

(Sea level)

0

–80 –40 0 40 80 120Temperature (˚C)

Pressure = 1,000 millibars at ground level

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

1. Why does the temperature not continuously decrease as one moves farther away from the surface of the Earth?

2. What reasons does the NASA test pilot need to wear a pressurized suit while testing the parachute?

3. 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?