The Earth’s Atmosphere

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)

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

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);

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;

Atmospheric Layers >690 km, satellites orbit here 85-690 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