What Are the 4 Most Abundant Gases in the Earth's Atmosphere?

Chemical Composition of the Atmosphere

Water vapor may be an abundant gas in the atmosphere, especially close to the surface.
Water vapor may be an abundant gas in the atmosphere, especially close to the surface. Martin Deja, Getty Images

The answer depends on the region of the atmosphere and other factors, since the chemical composition of the Earth's atmosphere depends on temperature, altitude, and proximity to water. Usually, the 4 most abundant gases are:

  1. nitrogen (N2) -  78.084%
  2. oxygen (O2) - 20.9476%
  3. argon (Ar) - 0.934%
  4. carbon dioxide (CO2) 0.0314%

However, water vapor can also be one of the most abundant gases! The maximum amount of water vapor air can hold is 4%, so water vapor could be number 3 or 4 on this list.

On average, the amount of water vapor is 0.25% of the atmosphere, by mass (4th most abundant gas). Warm air holds more water than cool air.

One a much smaller scale, near the surface forests, the amount of oxygen and carbon dioxide can vary slightly from day to night.

Abundance of Gases in the Upper Atmosphere

While the atmosphere near the surface has a fairly homogeneous chemical composition, the abundance of gases changes at higher altitudes. The lower level is called the homosphere. Above it is the heterosphere or exosphere. This region consists of layers or shells of gases. The lowest level consists mainly of molecular nitrogen (N2). Above it, there is a layer of atomic oxygen (O). At an even higher altitude, helium atoms (He) are the most abundant element. Beyond this point helium bleeds off into space. The outermost layer consists of hydrogen atoms (H). Particles surround the Earth even further out (ionosphere), but the outer layers are charged particles, not gases.

The thickness and composition of the layers of the exosphere change depending on solar radiation (day and night and solar activity).