Atmospheric chemistry

Atmospheric chemistry is a branch of atmospheric science in which the chemistry of the Earth's atmosphere and that of other planets is studied. It is a multidisciplinary field of research and draws on chemistry, physics, meteorology, computer modeling, oceanography, geology and volcanology and other disciplines. Research is increasingly connected with other areas of study such as climatology.

The composition and chemistry of the atmosphere is of importance for several reasons, but primarily because of the interactions between the atmosphere and living organisms. The composition of the Earth's atmosphere has been changed by human activity and some of these changes are harmful to human health, crops and ecosystems. Examples of problems which have been addressed by atmospheric chemistry include acid rain, photochemical smog and global warming. Atmospheric chemistry seeks to understand the causes of these problems, and by obtaining a theoretical understanding of them, allow possible solutions to be tested and the effects of changes in government policy evaluated.

Atmospheric Composition

Average composition of dry atmosphere, by volume
Gas	per NASA
Nitrogen	78.084%
Oxygen	20.946%
Argon	0.934%
Minor constituents in ppmv.
Carbon Dioxide	350
Neon	18.18
Helium	5.24
Methane	1.7
Krypton	1.14
Hydrogen	0.55
Water vapor	Highly variable; typically makes up about 1%

Notes: the concentration of CO₂ and CH₄ vary by season and location. ppmv represents parts per million by volume.
The mean molecular mass of air is 28.97 g/mole.

History

The ancient Greeks regarded air as one of the four elements, but the first scientific studies of atmospheric composition began in the 18th century. Chemists such as Joseph Priestley, Antoine Lavoisier and Henry Cavendish made the first measurements of the composition of the atmosphere.

In the late 19th and early 20th centuries interest shifted towards trace constituents with very small concentrations. One particularly important discovery for atmospheric chemistry was the discovery of ozone by Christian Friedrich Schoenbein in 1840.

In the 20th century atmospheric science moved on from studying the composition of air to a consideration of how the concentrations of trace gases in the atmosphere have changed over time and the chemical processes which create and destroy compounds in the air. Two particularly important examples of this were the explanation of how the ozone layer is created and maintained by Gordon Dobson and the explanation of Photochemical smog by Haagen-Schmidt.

In the 21st century the focus is now shifting again. Atmospheric Chemistry is increasingly studied as one part of the Earth System. Instead of concentrating on atmospheric chemistry in isolation the focus is now on seeing it as one part of a single system with the rest of the atmosphere, biosphere and geosphere. An especially important driver for this is the links between chemistry and climate such as the effects of changing climate on the recovery of the ozone hole and visa-versa but also interaction of the composition of the atmosphere with the oceans and terrestrial ecosystems.

References

• Wayne, Richard P (2000). Chemistry of Atmospheres (3rd Ed.). Oxford University Press. ISBN 0-19-850375-X
• Seinfeld, John H.; Pandis, Spyros N (1998). Atmospheric Chemistry and Physics - From Air Pollution to Climate Change. John Wiley and Sons, Inc. ISBN 0-471-17816-0

External links

http://www.igac.noaa.gov/ IGAC The International Global Atmospheric Chemistry Project