Composition of Earth's atmosphere by volume
Composition of Earth’s atmosphere by volume. Lower pie represents trace gases that together compose about 0.038% of the atmosphere (0.041197% at March 2019 concentration). Numbers are mainly from 1987, with carbon dioxide and methane from 2009, and do not represent any single source. Credit: Public domain

By volume, the dry air in Earth’s atmosphere is about 78.09 percent nitrogen, 20.95 percent oxygen, and 0.93 percent argon.

A brew of trace gases accounts for the other 0.03 percent, including the greenhouse gases carbon dioxide, methane, nitrous oxide and ozone. Yet while these greenhouse gases make up just a tiny percentage of our atmosphere, they play major roles in trapping Earth’s radiant heat and keeping it from escaping into space, thereby warming our planet and contributing to Earth’s greenhouse effect.

The largest greenhouse gas by volume is actually the one most people tend to overlook: water vapor, whose concentration varies significantly depending on temperature. As the temperature of the atmosphere increases, the amount of humidity in the atmosphere also goes up, further heating our planet in a vicious cycle.

Tiny solid or liquid particles known as aerosols, which are produced both naturally and by human activities, are also present in variable amounts, along with human-produced industrial pollutants and natural and human-produced sulfur compounds.