Chemical Composition of Air

What Is the Chemical Composition of Air?
Nearly all of the Earth's atmosphere is made up of only five gases: nitrogen, oxygen, water vapor, argon, and carbon dioxide. Several other compounds also are present. Although this CRC table does not list water vapor, air can contain as much as 5% water vapor, more commonly ranging from 1-3%. The 1-5% range places water vapor as the third most common gas (which alters the other percentages accordingly).

Answer: This is composition of air in percent by volume, at sea level at 15°C and 101325 Pa.
Nitrogen ---------- N2 -- 78.084%
Oxygen ----------- O2 -- 20.9476%
Argon -- -----------Ar -- 0.934%
Carbon Dioxide -- CO2 -- 0.0314%
Neon -------------- Ne -- 0.001818%
Methane --------- CH4 -- 0.0002%
Helium -- ----------He -- 0.000524%
Krypton ----------- Kr -- 0.000114%
Hydrogen --------- H2 -- 0.00005%
Xenon ------------- Xe -- 0.0000087%
Ozone ------------- O3 -- 0.000007%
Nitrogen Dioxide -- NO2 -- 0.000002%
Iodine -------------- I2 -- 0.000001%
Carbon Monoxide -- CO -- trace
Ammonia --------- NH3 -- trace
Reference: CRC Handbook of Chemistry and Physics, edited by David R. Lide, 1997.