1. History, Structure and Composition of the Atmosphere

2. Earth’s Atmosphere Extends from the Earth’s surface to outer space.
Mixture of gases, solids, and liquids
About 900 km (560 miles)

3. Timeline (part 1)
Hydrogen and Helium were stripped away by solar wind early in Earth’s history
Outgassing – volcanic eruptions
First Stable Atmosphere
Contained 80% H2O vapor, 10% CO2, 5 to 7% H2SO4, and small amounts of N, CO, H, CH4, and Ar

4. Second Atmosphere
Water in the atmosphere condensed and fell to Earth creating oceans (3.8 Ga)
Very primitive single celled life forms (3.5GA)
Nitrogen was the predominant gas (3.4 Ga)
Photosynthesis began with blue-green algae (3 Ga)
Oxygen builds up in the atmosphere

5. Third (Modern) Atmosphere
At 2 Ga, ozone begins to form in the stratosphere
Increasing oxygen levels stabilized at ~20% (650 Ma)
Stratospheric Ozone was thick enough to protect Earth’s surface from UV radiation
Matter (C, O2, H2O, N) begins to cycle as it does today between the atmosphere, hydrosphere, biosphere and geosphere.

6. Atmospheric Gases Nitrogen (N2)= 78% Oxygen (O2 ) = 21%
Argon (Ar) = 0.9%
Carbon Dioxide (CO2) = 0.04%
absorbs heat in the atmosphere
All others = trace amounts

7. Atmospheric Gases

8. Atmospheric Gases Water vapor (H2O) Ozone (O3)
variable amounts (0-4% of volume)
absorbs heat in the atmosphere
Ozone (O3)
needed in upper atmosphere but is a toxic pollutant when in the lower atmosphere
Can be harmful to plants, humans

9. Aerosols Solids: Dust, smoke, pollen, salt, ice… Liquid: water
Importance:
Seeds for clouds
Absorb or reflect solar radiation
Make pretty sunsets!

10. Atmospheric Pressure
Gravity causes gases in the atmosphere to be pulled toward the Earth
Weight of gases above presses down on the air below
Density increases
Force exerted on an area is known as pressure
Air pressure greater near the Earth
Air pressure measured by a barometer

11. Structure of the Atmosphere
Atmosphere divided into layers based on temperature differences
Some layers contain gases that easily absorb the sun’s energy, other layers do not
Therefore, each layer contains different amount of energy and temperature differences

12. Troposphere 0 to 12 km (where we live…) Means air “turns over”
Contains 75% of the atmospheric gases
Weather, clouds, smog occur here
Average environmental lapse rate is 6.5°C per km (3.5°F per 1000 ft)
Hadley Cells
Wind currents directly influence ocean currents
Rising air = cloud formation; Sinking air = dry air

13. Stratosphere 12 to 50 km Jet airplanes fly in the lower stratosphere
Jet Stream
a fast moving channel of air that controls the location of high and low pressure cells in the troposphere
Sub-polar and sub-tropical
Contains the ozone layer
3 O2 + UV  2 O3
Chemical Reaction absorbs most of the UV radiation from the sun
Thickest at the equator, thinnest at the poles
Increasing temps above 20 km

14. Mesosphere 50 to 80 km temps decreasing to -90°C with altitude
Meteors disintegrate in this layer
Little is known about this layer because it is above where research balloons and aircraft fly but below where satellites orbit

15. Thermosphere 80 to 450 km Orbiting satellites
Temps increasing with altitude because of O2 and N2 absorbing high-energy radiation
contains the ionosphere – a layer of electrically charged particles
Divert cosmic radiation away from the equator toward the poles
Aurora result from cosmic radiation interacting with the ionosphere at the poles

16. Exosphere 450 to 900 km very little air here
Where the space shuttle orbits the Earth
Some orbiting satellites

17. Atmospheric Temperatures

18. Atmospheric Temperatures
As atmosphere is heated, air molecules move with greater energy
Warm air is less dense (low air pressure)
Cold air is more dense (high air pressure)
Cool
Warm

19. Heat & Temperature
Heat = (a form of energy) total kinetic energy of the molecules in a substance
Temperature = average kinetic energy of the molecules
Heat always moves from high to low temps

20. Heat Transfer
Three mechanisms of heat transfer between land, water, and atmosphere
Conduction = transfer of heat through matter by molecules colliding (transfer by touching)
Convection = transfer of heat by circulation within a substance
Only in liquids or gases
Hot air is less dense  rises
Radiation = ALL objects emit EM waves
Does not need a medium (i.e. sun energy to Earth)
Hotter objects emit shorter wavelengths

21. Incoming Solar Radiation
Scattering = incoming waves can “bounce” off particles in the atmosphere
Reflection = 30% of solar radiation is reflected back into space
Absorption = molecules absorbing energy increase speed (get hotter)
N2 is poor absorber of radiant energy
O2 and O3 are good absorbers of UV energy
CO2 and H2O are good absorbers of infrared
None of the gases are good absorbers of visible light

22. Incoming Solar Radiation