Most Abundant Gas in the Earths Atmosphere

By far, the most abundant gas in the Earths 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%. Key Takeaways: Gases in Earth's Atmosphere The most abundant gas in the Earths 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. Abundance of Gases in the Atmosphere This table lists the eleven most abundant gases in the lower portion of Earths 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). Gas Formula Percent Volume Nitrogen N2 78.08% Oxygen O2 20.95% Water* H2O 0% to 4% Argon Ar 0.93% Carbon Dioxide* CO2 0.0360% Neon Ne 0.0018% Helium He 0.0005% Methane* CH4 0.00017% Hydrogen H2 0.00005% Nitrous Oxide* N2O 0.0003% Ozone* O3 0.000004% * 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 Earths 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? Its important to know which gas is most abundant, what the other gases are in the Earths 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. Sources Lide, David R. (1996). Handbook of Chemistry and Physics. CRC. Boca Raton, FL.Wallace, John M.; Hobbs, Peter V. (2006). Atmospheric Science: An Introductory Survey (2nd ed.). Elsevier. ISBN 978-0-12-732951-2.