Science, Tech, Math › Science The Chemical Composition of Air Share Flipboard Email Print Tetra Images / Getty Images Science Chemistry Chemical Laws Basics Molecules Periodic Table Projects & Experiments Scientific Method Biochemistry Physical Chemistry Medical Chemistry Chemistry In Everyday Life Famous Chemists Activities for Kids Abbreviations & Acronyms Biology Physics Geology Astronomy Weather & Climate By Anne Marie Helmenstine, Ph.D. Anne Marie Helmenstine, Ph.D. Facebook Twitter Chemistry Expert Ph.D., Biomedical Sciences, University of Tennessee at Knoxville B.A., Physics and Mathematics, Hastings College Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels. Learn about our Editorial Process Updated on April 04, 2022 Nearly all of the Earth's atmosphere is made up of only five gases: nitrogen, oxygen, water vapor, argon, and carbon dioxide. Several other compounds are also present. The Chemical Composition of Air The primary component of air is nitrogen gas.Nitrogen, oxygen, water vapor, argon, and carbon dioxide account for about 99% of the composition of air.Trace gases include neon, methane, helium, krypton, hydrogen, xenon, ozone, and many other elements and compounds.The composition of air varies from one place to the next and even varies depending on whether it is day or night. Table of Elements and Compounds in Air Below is the composition of air in percent by volume, at sea level at 15 C and 101325 Pa. Nitrogen -- N2 -- 78.084% Oxygen -- O2 -- 20.9476% Argon -- Ar -- 0.934% Carbon Dioxide -- CO2 -- 0.04% Neon -- Ne -- 0.001818% Methane -- CH4 -- 0.0002% Helium -- He -- 0.000524% Krypton -- Kr -- 0.000114% Hydrogen -- H2 -- 0.00005% Xenon -- Xe -- 0.0000087% Ozone -- O3 -- 0.000007% Nitrogen Dioxide -- NO2 -- 0.000002% Iodine -- I2 -- 0.000001% Carbon Monoxide -- CO -- trace Ammonia -- NH3 -- trace Nitrogen, oxygen and argon are the three main components of the atmosphere. Water concentration varies, but averages around 0.25% of the atmosphere by mass. Carbon dioxide and all of the other elements and compounds are trace gases. Trace gases include the greenhouse gases carbon dioxide, methane, nitrous oxide, and ozone. Except for argon, other noble gases are trace elements. These include neon, helium, krypton, and xenon. Industrial pollutants include chlorine and its compounds, fluorine and its compounds, elemental mercury vapor, sulfur dioxide, and hydrogen sulfide. Other components of the atmosphere include spores, pollen, volcanic ash, and salt from sea spray. Water Vapor in the Atmosphere Although this CRC table does not list water vapor (H2O), air can contain as much as 5% water vapor, more commonly ranging from 1-3%. The 1-5% range places water vapor as the third most common gas (which alters the other percentages accordingly). Water content varies according to air temperature. Dry air is denser than humid air. However, sometimes humid air contains actual water droplets, which can make it more dense than humid air that only contains water vapor. Air Pollution Air pollution varies according to geographical location and also where it occurs in the air column. Pollutants include chemicals, particulates like dust and ash, and biological matter, like pollen and bacteria. The Ozone Layer Ozone (O3) is unevenly distributed throughout the Earth's atmosphere. The ozone layer is a portion of the stratosphere from 15 to 35 kilometers (9.3 to 21.7 miles). However, its thickness varies geographically and seasonally. The ozone layer contains about 90% of the atmospheric ozone, with a concentration of 2 to 8 parts per million. Even though this is a much higher concentration of ozone than occurs in the troposphere, ozone is still just a trace gas in the ozone layer. Homosphere and Heterosphere The homosphere is the portion of the atmosphere with a fairly uniform composition due to atmospheric turbulence. In contrast, the heterosphere is the part of the atmosphere where chemical composition varies mainly according to altitude. The homosphere includes the lower layers of the atmosphere: the troposphere, stratosphere, mesosphere, and lower thermosphere. The turbopause, at around 100 kilometers or 62 miles, is the edge of space and roughly the limit of the homosphere. Above this layer, the heterosphere includes the exosphere and thermosphere. The lower portion of the heterosphere contains oxygen and nitrogen, but these heavier elements do no occur higher up. The upper heterosphere consists almost entirely of hydrogen. Sources Barry, R.G.; Chorley, R.J. (1971). Atmosphere, Weather and Climate. London: Menthuen & Co Ltd. ISBN 9780416079401.Lide, David R. (1997). CRC Handbook of Chemistry and Physics. Boca Raton, FL: CRC. 14-17.Lutgens, Frederick K.; Tarbuck, Edward J. (1995). The Atmosphere (6th ed.). Prentice Hall. ISBN 0-13-350612-6.Martin, Daniel; McKenna, Helen; Livina, Valerie (2016). "The human physiological impact of global deoxygenation". The Journal of Physiological Sciences. 67 (1): 97–106. doi:10.1007/s12576-016-0501-0Wallace, John M.; Hobbs, Peter V. (2006). Atmospheric Science: An Introductory Survey (2nd ed.). Elsevier. ISBN 978-0-12-732951-2. Cite this Article Format mla apa chicago Your Citation Helmenstine, Anne Marie, Ph.D. "The Chemical Composition of Air." ThoughtCo, Apr. 4, 2022, thoughtco.com/chemical-composition-of-air-604288. Helmenstine, Anne Marie, Ph.D. (2022, April 4). The Chemical Composition of Air. Retrieved from https://www.thoughtco.com/chemical-composition-of-air-604288 Helmenstine, Anne Marie, Ph.D. "The Chemical Composition of Air." ThoughtCo. https://www.thoughtco.com/chemical-composition-of-air-604288 (accessed May 28, 2023). copy citation