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Major constituents of dry air, by volume^[6]
Gas		Volume^(A)
Name	Formula	in ppmv^(B)	in %
Nitrogen	N₂	780,840	78.084
Oxygen	O₂	209,460	20.946
Argon	Ar	9,340	0.9340
Carbon dioxide	CO 2	397	0.0397
Neon	Ne	18.18	0.001818
Helium	He	5.24	0.000524
Methane	CH₄	1.79	0.000179
Not included in above dry atmosphere:
Water vapor^(C)	H₂O	10–50,000^(D)	0.001%–5%^(D)
notes: ^(A) volume fraction is equal to mole fraction for ideal gas only, also see volume (thermodynamics) ^(B) ppmv: parts per million by volume ^(C) Water vapor is about 0.25% by mass over full atmosphere ^(D) Water vapor strongly varies locally^[4]

The density of air at sea level is about 1.2 kg/m³ (1.2 g/L).

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