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Atmospheric chemistry
Atmospheric chemistry
is a branch of atmospheric science in which the chemistry of the Earth's atmosphere
Earth's atmosphere
and that of other planets is studied. It is a multidisciplinary approach of research and draws on environmental chemistry, physics, meteorology, computer modeling, oceanography, geology and volcanology and other disciplines. Research is increasingly connected with other arenas of study such as climatology. The composition and chemistry of the Earth's atmosphere
Earth's 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
Earth's atmosphere
changes as result of natural processes such as volcano emissions, lightning and bombardment by solar particles from corona. It has also 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, ozone depletion, photochemical smog, greenhouse gases and global warming. Atmospheric chemists seek 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.

Contents

1 Atmospheric composition 2 History 3 Methodology

3.1 Observation 3.2 Laboratory studies 3.3 Modeling

4 See also 5 References 6 Further reading 7 External links

Atmospheric composition[edit]

Part of the nature series

Weather

Calendar seasons

Winter Spring Summer Autumn

Tropical seasons

Dry season Wet season

Storms

Cloud Cumulonimbus cloud Arcus cloud Downburst Microburst Heat burst Dust storm Simoom Haboob Monsoon Gale Sirocco Firestorm Lightning Supercell Thunderstorm Severe thunderstorm Thundersnow Storm
Storm
surge Tornado Cyclone Mesocyclone Anticyclone Tropical cyclone
Tropical cyclone
(Hurricane) Extratropical cyclone European windstorm Atlantic Hurricane Typhoon Derecho Landspout Dust devil Fire whirl Waterspout Winter
Winter
storm

Ice storm Blizzard Ground blizzard Snowsquall

Precipitation

Drizzle (Freezing drizzle) Graupel Hail Ice pellets
Ice pellets
(Diamond dust) Rain
Rain
(Freezing rain) Cloudburst Snow

Rain
Rain
and snow mixed Snow
Snow
grains Snow
Snow
roller Slush

Topics

Air pollution Atmosphere

Chemistry Convection Physics River

Climate Cloud

Physics

Fog Cold wave Heat wave Jet stream Meteorology Severe weather

List Extreme

Weather
Weather
forecasting

Weather
Weather
portal

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Visualisation of composition by volume of Earth's atmosphere. Water vapour is not included as it is highly variable. Each tiny cube (such as the one representing krypton) has one millionth of the volume of the entire block. Data is from NASA
NASA
Langley.

Average composition of dry atmosphere (mole fractions)

Gas per NASA

Nitrogen, N2 78.084%

Oxygen, O2[1] 20.946%

Minor constituents (mole fractions in ppm)

Argon, Ar 9340

Carbon dioxide, CO2 400

Neon, Ne 18.18

Helium, He 5.24

Methane, CH4 1.7

Krypton, Kr 1.14

Hydrogen, H2 0.55

Nitrous oxide, N2O 0.5

Xenon, Xe 0.09

Nitrogen
Nitrogen
dioxide, NO2 0.02

Water

Water vapour Highly variable; typically makes up about 1%

Notes: the concentration of CO2 and CH4 vary by season and location. The mean molecular mass of air is 28.97 g/mol. Ozone
Ozone
(O3) is not included due to its high variability. History[edit]

Schematic of chemical and transport processes related to atmospheric composition.

The ancient Greeks
Greeks
regarded air as one of the four elements. The first scientific studies of atmospheric composition began in the 18th century, as chemists such as Joseph Priestley, Antoine Lavoisier
Antoine Lavoisier
and Henry Cavendish
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 Schönbein 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 by Sydney Chapman and Gordon Dobson of how the ozone layer is created and maintained, and the explanation of photochemical smog by Arie Jan Haagen-Smit. Further studies on ozone issues led to the 1995 Nobel Prize in Chemistry
Chemistry
award shared between Paul Crutzen, Mario Molina
Mario Molina
and Frank Sherwood Rowland.[2] In the 21st century the focus is now shifting again. Atmospheric chemistry is increasingly studied as one part of the Earth
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 vice versa but also interaction of the composition of the atmosphere with the oceans and terrestrial ecosystems.

Carbon dioxide
Carbon dioxide
in Earth's atmosphere
Earth's atmosphere
if half of global-warming emissions[3][4] are not absorbed. ( NASA
NASA
simulation; 9 November 2015)

Nitrogen
Nitrogen
dioxide 2014 - global air quality levels (released 14 December 2015).[5]

Methodology[edit] Observations, lab measurements, and modeling are the three central elements in atmospheric chemistry. Progress in atmospheric chemistry is often driven by the interactions between these components and they form an integrated whole. For example, observations may tell us that more of a chemical compound exists than previously thought possible. This will stimulate new modelling and laboratory studies which will increase our scientific understanding to a point where the observations can be explained. Observation[edit] Observations of atmospheric chemistry are essential to our understanding. Routine observations of chemical composition tell us about changes in atmospheric composition over time. One important example of this is the Keeling Curve
Keeling Curve
- a series of measurements from 1958 to today which show a steady rise in of the concentration of carbon dioxide (see also ongoing measurements of atmospheric CO2). Observations of atmospheric chemistry are made in observatories such as that on Mauna Loa
Mauna Loa
and on mobile platforms such as aircraft (e.g. the UK's Facility for Airborne Atmospheric Measurements), ships and balloons. Observations of atmospheric composition are increasingly made by satellites with important instruments such as GOME and MOPITT giving a global picture of air pollution and chemistry. Surface observations have the advantage that they provide long term records at high time resolution but are limited in the vertical and horizontal space they provide observations from. Some surface based instruments e.g. LIDAR
LIDAR
can provide concentration profiles of chemical compounds and aerosol but are still restricted in the horizontal region they can cover. Many observations are available on line in Atmospheric Chemistry
Chemistry
Observational Databases. Laboratory studies[edit] Measurements made in the laboratory are essential to our understanding of the sources and sinks of pollutants and naturally occurring compounds. These experiments are performed in controlled environments that allow for the individual evaluation of specific chemical reactions or the assessment of properties of a particular atmospheric constituent.[6] Types of analysis that are of interest includes both those on gas-phase reactions, as well as heterogeneous reactions that are relevant to the formation and growth of aerosols. Also of high importance is the study of atmospheric photochemistry which quantifies how the rate in which molecules are split apart by sunlight and what resulting products are. In addition, thermodynamic data such as Henry's law coefficients can also be obtained. Modeling[edit] In order to synthesise and test theoretical understanding of atmospheric chemistry, computer models (such as chemical transport models) are used. Numerical models solve the differential equations governing the concentrations of chemicals in the atmosphere. They can be very simple or very complicated. One common trade off in numerical models is between the number of chemical compounds and chemical reactions modelled versus the representation of transport and mixing in the atmosphere. For example, a box model might include hundreds or even thousands of chemical reactions but will only have a very crude representation of mixing in the atmosphere. In contrast, 3D models represent many of the physical processes of the atmosphere but due to constraints on computer resources will have far fewer chemical reactions and compounds. Models can be used to interpret observations, test understanding of chemical reactions and predict future concentrations of chemical compounds in the atmosphere. One important current trend is for atmospheric chemistry modules to become one part of earth system models in which the links between climate, atmospheric composition and the biosphere can be studied. Some models are constructed by automatic code generators (e.g. Autochem
Autochem
or KPP). In this approach a set of constituents are chosen and the automatic code generator will then select the reactions involving those constituents from a set of reaction databases. Once the reactions have been chosen the ordinary differential equations (ODE) that describe their time evolution can be automatically constructed. See also[edit]

Ozone-oxygen cycle Paleoclimatology Scientific Assessment of Ozone
Ozone
Depletion Tropospheric ozone depletion events

References[edit]

^ Zimmer, Carl (3 October 2013). "Earth's Oxygen: A Mystery Easy to Take for Granted". New York Times. Retrieved 3 October 2013.  ^ Press release on the Nobel Prize in Chemistry
Chemistry
1995 ^ St. Fleur, Nicholas (10 November 2015). "Atmospheric Greenhouse Gas Levels Hit Record, Report Says". New York Times. Retrieved 11 November 2015.  ^ Ritter, Karl (9 November 2015). "UK: In 1st, global temps average could be 1 degree C higher". AP News. Retrieved 11 November 2015.  ^ Cole, Steve; Gray, Ellen (14 December 2015). "New NASA
NASA
Satellite Maps Show Human Fingerprint on Global Air Quality". NASA. Retrieved 14 December 2015.  ^ National Academies of Sciences, Engineering, and Medicine (2016). Future of Atmospheric Research: Remembering Yesterday, Understanding Today, Anticipating Tomorrow. Washington, DC: The National Academies Press. p. 15. ISBN 978-0-309-44565-8. CS1 maint: Multiple names: authors list (link)

Further reading[edit]

Brasseur, Guy P.; Orlando, John J.; Tyndall, Geoffrey S. (1999). Atmospheric Chemistry
Chemistry
and Global Change. Oxford University Press. ISBN 0-19-510521-4. Finlayson-Pitts, Barbara J.; Pitts, James N., Jr. (2000). Chemistry
Chemistry
of the Upper and Lower Atmosphere. Academic Press. ISBN 0-12-257060-X. Seinfeld, John H.; Pandis, Spyros N. (2006). Atmospheric Chemistry
Chemistry
and Physics: From Air Pollution to Climate
Climate
Change (2nd Ed.). John Wiley and Sons, Inc. ISBN 0-471-82857-2. Warneck, Peter (2000). Chemistry
Chemistry
of the Natural Atmosphere
Atmosphere
(2nd Ed.). Academic Press. ISBN 0-12-735632-0. Wayne, Richard P. (2000). Chemistry
Chemistry
of Atmospheres (3rd Ed.). Oxford University Press. ISBN 0-19-850375-X. J. V. Iribarne, H. R. Cho, Atmospheric Physics, D. Reidel Publishing Company, 1980

External links[edit]

WMO Scientific Assessment of Ozone
Ozone
Depletion: 2006 IGAC The International Global Atmospheric Chemistry
Chemistry
Project Paul Crutzen
Paul Crutzen
Interview Freeview video of Paul Crutzen
Paul Crutzen
Nobel Laureate for his work on decomposition of ozone, talking to Nobel Laureate Harry Kroto, the Vega Science Trust. The Cambridge Atmospheric Chemistry
Chemistry
Database is a large constituent observational database in a common format. Environmental Science Published for Everybody Round the Earth NASA-JPL Chemical Kinetics and Photochemical Data for Use in Atmospheric Studies Kinetic and photochemical data evaluated by the IUPAC Subcommittee for Gas Kinetic Data Evaluation Atmospheric Chemistry
Chemistry
Glossary at Sam Houston State University Tropospheric chemistry Calculators for use in atmospheric chemistry An illustrated elementary assessment of the composition of air.

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