What Is the Most Abundant Gas in the Earth's Atmosphere?

Composition of the Atmosphere (and why you should care)

The most abundant gas in the atmosphere is nitrogen. Even though you may see a lot of clouds, water vapor only account for up to 4% of the composition.
The most abundant gas in the atmosphere is nitrogen. Even though you may see a lot of clouds, water vapor only account for up to 4% of the composition. Andrew Latshaw / EyeEm/Getty Images

By far, the most abundant gas in the Earth's atmosphere is nitrogen, which accounts for about 78% of the mass of dry air. Oxygen is the next most abundant gas, present at levels of 20 to 21%. Although humid air seems like it contains a lot of water, the maximum amount of water vapor that air can hold is only about 4%.

Abundance of Gases in the Atmosphere

This table lists the eleven most abundant gases in the lower portion of Earth's atmosphere (up to 25 km).

While the percentage of nitrogen and oxygen are fairly stable, the amount of greenhouse gases changes and depends on location. Water vapor is extremely variable. In arid or extremely cold regions, water vapor may be nearly absent. In warm, tropical regions, water vapor accounts for a significant portion of atmospheric gases.

Some references include other gases on this list, such as krypton (less abundant than helium, but more than hydrogen), xenon (less abundant than hydrogen), nitrogen dioxide (less abundant than ozone), and iodine (less abundant than ozone).

GasFormulaPercent Volume
Water*H2O0% to 4%
Carbon Dioxide*CO20.0360%
Nitrous Oxide*N2O0.0003%

* gases with variable composition

Reference: Pidwirny, M. (2006). "Atmospheric Composition". Fundamentals of Physical Geography, 2nd Edition.

The average concentration of the greenhouse gases carbon dioxide, methane, and nitrous dioxide has been increasing. Ozone is concentrated around cities and in the Earth's stratosphere. In addition to the elements in the table and krypton, xenon, nitrogen dioxide, and iodine (all mentioned earlier), there are trace amounts of ammonia, carbon monoxide, and several other gases.

Why Is Important To Know the Abundance of Gases?

It's important to know which gas is most abundant, what the other gases are in the Earth's atmosphere, and how the composition of air changes with altitude and over time for multiple reasons. The information helps us understand and predict the weather. The amount of water vapor in the air is particularly relevant to weather forecasting. The gas composition helps us understand the effects of natural and man-made chemicals released into the atmosphere. The make-up of the atmosphere is extremely important for climate, so changes in gases may help us predict broad climate change.

Gases in the Atmosphere Key Takeaways

  • The most abundant gas in the Earth's atmosphere is nitrogen. The second most abundant gas is oxygen. Both of these gases occur as diatomic molecules.
  • The amount of water vapor is highly variable. In hot, humid locations, it is the third most abundant gas. This makes it the most common greenhouse gas.
  • In dry air, the third most abundant gas is argon, a monatomic noble gas.
  • The abundance of carbon dioxide is variable. While it is an important greenhouse gas, it is only present an average of 0.04 percent, by mass.