Know your atmosphere
How thick is the atmosphere?
Earth's atmosphere gets thinner as you go higher.
- Denver, CO, 5,200 feet has 82% of sea-level oxygen.
- Quito, Ecuador, 9,300 feet has 70%...
- Kathmandu, Nepal, 15,000 feet has 56%...
- Mt. Everest, 29,000 feet has 33% of sea-level oxygen.
- Bar-headed geese migrate yearly over the Himalayas
About 3/4 of Earth's atmosphere lies within the lowest 11 km. (1/580 of Earth's radius).
University Consortium for Atmospheric Research (UCAR)
This chart shows the composition of *dry* air.
When the
weather report says "100% humidity" does that mean that all the
molecules in the air are water? Can you think of any consequences for humans of having 100% of the molecules in air be water molecules?
Actually there is a maximum density of water molecules in
the gas state that depends on temperature. 100% relative
humidity means that the water density has reached this maximum
concentration.
At 68 F = 20 C and "100% humidity", there are about 18 grams of water in each cubic meter of air in a gaseous state. About 2% of all molecules in the air are water molecules.
At 77 F = 25 C and "100% humidity" there are about 22 grams in a cubic meter of air. What do you think happens if you cool 77 F / 100% humid air down to 68 F? What happens to those extra 4 grams of water in each cubic meter?
On any given day,
there is more or less humidity (water) in the air as well. 
An apple skin is much thicker (1/120).
Domiriel
An onion skin is more like it (1/560).
Susan Murtaugh
What do you already know?
Earth's atmosphere
Is mostly nitrogenHumidity
Greg Benson, Wikimedia Commons
The worldwide average concentration of water in the atmosphere is about 0.4% with typical concentrations close to the surface of 1-4%.
Heat danger and humidity
