1. The Earth’s Atmosphere

2. Gas
Percent
Nitrogen
78%
Oxygen
21%
Argon
0.93%
Carbon Dioxide (CO2)
0.039%
Neon, helium methane, ozone…
~0.04%
Also water vapor (most near the surface of the earth), dust and pollutants (e.g. sulfur dioxide)

3. A Special Note on Carbon Dioxide
present in trace amounts, but important in its effects:
a greenhouse gas (GHG) – a gas that is very effective at absorbing (trapping) and emitting radiation as heat (infrared radiation)
0.039% means 390 ppm (“ppm” = parts per million) Pre-industrial CO2 level: 275 ppm Present CO2 level: 390 ppm Safe (?) CO2 level: 350 ppm

4. Why is the atmosphere important?
Natural Greenhouse Effect, temperature extremes: warms Earth’s surface, reduces day/night extremes;
Ozone layer: protects against damaging ultraviolet (UV) radiation from the Sun;
Oxygen, Carbon Dioxide, Water Cycle: oxygen for humans and animals, carbon dioxide for plants, water for all (evaporation, transpiration from plants, precipitation);

5. Atmospheric Circulation
Convection cells:
Warm moist air rises at equator;
Cold dry air sinks at the poles;
Gives rise to winds;
Heat Energy and moisture:
Transfers heat and moisture around the globe, to the poles;

6. Atmospheric Layers >690 km, satellites orbit here
km, ions (aurora, northern lights) here, space shuttle orbits here
50-85 km, “meso” = “middle”, meteors burn up here
20-50 km, highest concentration of ozone (“ozone layer”), planes
0-20 km (8 km at poles), most of the atmosphere’s moisture, weather takes place here