Gaseous composition of dry air
(Trace gases are given
the unit of part per million (ppm)).
| Types | Mole percent |
| Nitrogen (N2) | 78.084 |
| Oxygen (O2) | 20.947 |
| Argon (Ar) | 0.934 |
|
Carbon Dioxide (CO2)
|
360 ppm
|
|
Neon (Ne)
|
18.18 ppm
|
|
Helium (He)
|
5.24 ppm
|
|
Methane (CH4)
|
1.7 ppm
|
|
Krypton (Kr)
|
1.14 ppm
|
|
Hydrogen (H)
|
0.53 ppm
|
|
Nitrous oxide (N2O)
|
0.31 ppm
|
|
Xenon (Xe)
|
0.087 ppm
|
|
Ozone (O3)
|
trace to 8 ppm
|
|
Carbon monoxide (CO)
|
trace to 0.25 ppm
|
|
Sulfur dioxide (SO2)
|
trace to 0.1 ppm
|
|
Nitrogen dioxide (NO2)
|
trace to 0.02 ppm
|
|
Ammonia (NH3)
|
trace to 0.003 ppm
|
Greenhouse Gases
a greenhouse gas
is any gas species in the atmosphere that absorbs infrared radiation from
the Earth's surface, producing the so-called "greenhouse
effect" which warms the atmosphere and reduce the heat loss of the
Earth's surface.
Key Greenhouse Gases Influenced by Human Activities
| Parameter | CO2 | CH4 | CFC-11 (CFCl3) | CFC-12 (CF2Cl2) | N2O |
| Pre-industrial atmospheric concentration (1750-1800) | 280 ppmv | 0.8 ppmv | 0 | 0 | 288 ppbv |
| Current atmospheric concentration (1990) | 353 ppmv | 1.72 ppmv | 280 pptv2 | 484 pptv | 310 ppbv |
| Current rate of annual atmospheric accumulation | 1.8 ppmv
(0.5%) |
0.015 ppmv
(0.9%) |
9.5 pptv
(4%) |
17 pptv
(4%) |
0.8 ppbv
(0.25%) |
| Atmospheric lifetime (years) | (50-200) | 10 | 65 | 130 | 150 |
| Radiative forcing factors | 1 | 21 | 12400 | 15800 | 206 |
