ATMOSPHERIC GASES NEAR THE EARTH'S SURFACE

Permanent Gases	Chemical Composition	Percent by Volume	Parts per Million (ppm)
Nitrogen	N2	78.08	780,800
Oxygen	O2	20.95	209,500
Argon	Ar	0.93	9300
Neon	Ne	0.0018	18
Helium	He	0.0005	5
Hydrogen	H2	0.00005	0.5
Xenon	Xe	0.000009	0.09

Variable Gases	Chemical Composition	Percent by Volume	Parts per Million (ppm)
Water vapor	H2O	0.001 to 4	10 to 40000
Carbon dioxide	CO2	0.0375	375
Methane	CH4	0.00017	1.7
Nitrous Oxide	N2O	0.00003	0.3
Ozone	O3	0.000004	0.004
CFCs		0.00000001	0.0001