1. Composition of the Atmosphere

2. Thickness of the Atmosphere Approximately 80% of the atmosphere occurs in the lowest 20km above the Earth. Atmosphere is a thin shell covering the Earth.

3. But what is the atmosphere? Comprised of a mixture of invisible permanent and variable gases as well as suspended microscopic particles (both liquid and solid) –Permanent Gases – Form a constant proportion of the total atmospheric mass –Variable Gases – Distribution and concentration varies in space and time –Aerosols – Suspended particles and liquid droplets (excluding cloud droplets)

4. Permanent Gases 78% Nitrogen (N 2 ) 21% Oxygen (O 2 ) <1% Argon (Ar) Relative percentages of the permanent gases remain constant up to ~ 60 miles! high –This layer is referred to as the Homosphere (implies gases are relatively homogeneous)

5. Variable Gases in the Earth’s Atmosphere VARIABLE gases in the atmosphere and typical percentage values (by volume): Water vapor (H 2 O)0 to 4% Carbon Dioxide (CO 2 ) 0.038% Methane(CH 4 ) 0.00017% Ozone(O 3 ) 0.000004% (Note that water vapor is the third most common molecule in Earth’s atmosphere after nitrogen and oxygen)

6. Radiation: Transfer of energy by electromagnetic waves. Sunlight and heat energy are examples. Convection and Conduction: A cycle of warm air rising and cool air sinking causing a circular movement of air. Set in motion by the Sun heating Earth's surface unevenly.

7. IMPORTANT Composition of gases on a planet is a function of the planet size (strength of gravity holding gases onto the planet), planet temperature, and life Primary permanent gases on Earth are Nitrogen, Oxygen, Argon Variable gases include Water Vapor, Carbon Dioxide, Ozone, Methane, CFCs, etc. Water vapor is the most important greenhouse gas, others include Carbon Dioxide, Methane and Ozone

8. Vertical Structure of the Atmosphere

9. Temperature Change w/Altitude As a parcel of air rises, it expands due to lower pressure. Work done by molecules to expand causes temperature to decrease (cools) As air sinks, the parcel experiences compression due to higher pressure Air molecules have work done on them, temperature increases (warms)

10. Vertical Structure of the Atmosphere Vertical Structure of the Atmosphere commonly broken into layers Layers are most often defined by the vertical change of temperature within the layer since this is related to the presence of vertical motions (or lack of) in the layer

11. Structure of the atmosphere

12. Importance of Stratosphere, Mesosphere and Thermosphere Solar nuclear particles, x-rays, gamma rays, and ultraviolet light can damage living cells. Thermosphere, mesosphere and stratosphere shield life on Earth from these damaging rays.