The Chemical Composition of Air

The Chemical Composition of Air Nearly all of the Earths atmosphere is made up of only five gases: nitrogen, oxygen, water vapor, argon, and carbon dioxide. Several other compounds are also 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). Below is the 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 traceAmmonia NH3 trace Reference CRC Handbook of Chemistry and Physics, edited by David R. Lide, 1997.