Skip to main content

Section 2.2 Composition of the atmosphere

Although hundreds of species are present in the Earth's atmosphere, it mostly consists of nitrogen and oxygen, along with argon, water, and carbon dioxide.

Table 2.2.1. Composition of Earth's atmosphere
Component Formula Abundance
Nitrogen N\(_2\) 78.1%
Oxygen O\(_2\) 20.9%
Argon Ar 0.9%
Water H\(_2\)O up to 4%
Carbon Dioxide CO\(_2\) 400 ppm
Methane CH\(_4\) 2 ppm
Nitrous Oxide N\(_2\)O 300 ppb
Ozone O\(_3\) 10-100 ppb
Halocarbons CFCs, etc 2 ppb total

Aerosols - suspended particles in the atmosphere - also play an important role for assessing air quality and act as condensation nuclei in the formation of clouds.

As we shall see, the principal greenhouse gas is water vapor. Carbon dioxide, methane and other trace gases have increased since the Industrial Revolution, especially in the twentieth century due to the combustion of fossil fuels, industrial processes and other anthropogenic effects. The stratospheric ozone concentration has decreases, largely through human use of chlorofluorocarbons (CFFc). The Montreal Protocol treaty of 1987 has helped phase out the use of ozone-depleting substances.