Dry air contains roughly (by volume) 78.09% nitrogen, 20.95% oxygen, 0.93% argon, 0.039% carbon dioxide, and small amounts of other gases.
Air also contains a variable amount of water vapor, on average around 1 -4%.

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Atmospheric gases are often divided up into the major, constant components and the highly variable components, as listed below:

Constant Components. Proportions remain the same over time and location.
Nitrogen (N2) 78.08%
Oxygen (O2) 20.95%
Argon (Ar) 0.93%
Neon, Helium, Krypton 0.0001%

Variable Components. Amounts vary over time and location.
Carbon dioxide (CO2)0.038%
Water vapor (H20)0-4%
Methane (CH4)trace
Sulfur dioxide (SO2)trace
Ozone (O3)trace
Nitrogen oxides (NO, NO2, N2O)trace


0.039% CO²
Almost four one-hundreths of ONE PERCENT of our 'air'.
Yeah... we're killin' ourselves.