The most abundant element present in air is nitrogen, which comprises about 78.1 percent of the air on Earth. The second-most abundant element is oxygen, at about 20.9 percent of air's makeup. Together, the elements nitrogen and oxygen account for 99 percent of the chemical composition of air.
Most of the remaining 1 percent of Earth's air is made up of argon, at approximately 0.9 percent. The rest of air is composed of traces of elements such as neon, helium, krypton, hydrogen, xenon and iodine. Also present in tiny amounts are gases such as carbon dioxide, methane, nitrogen dioxide, carbon monoxide, ammonia and ozone.