Atmospheric chemistry
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|-
| Nitrogen
| 78.084%
|-
| Oxygen
| 20.946%
|-
| Argon
| 0.934%
|-
| Water vapor
| colspan=2 | Highly variable;
typically makes up about 1%
|-
| colspan=2 | Minor constituents in ppmv.
|-
| Carbon Dioxide
| 350
|-
| Neon
| 18.18
|-
| Helium
| 5.24
|-
| Methane
| 1.7
|-
| Krypton
| 1.14
|-
| Hydrogen
| 0.55
|}
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/mol.
POOKO LIKES BOYS
Methodology
Observations, lab measurements and modelling 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
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 - a series of measurements from 1958 to today which show a steady rise in of the concentration of Carbon Dioxide. Observations of atmospheric chemistry are made in observatories such as that on 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 increasing 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 can provide concentration profiles of chemical compounds and aerosol but are still restricted in the horizontal region they can cover.
Lab measurements
Measuments made in the laboratory are essential to our understanding of the sources and sinks of pollutants and naturally occurring compunds. Lab studies tell us which gases react with each other and how fast they react. Measurements of interest include reactions in the gas phase, on surfaces and in water. Also of high importance is photochemistry which quantifies how quickly molecules are split apart by sunlight and what the products are plus thermodynamic data such as Henry's law coefficients.
Modeling
In order to synthesise and test theoretical understanding of atmospheric chemistry computer 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.
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
- IGAC The International Global Atmospheric Chemistry Project
- 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
- Tropospheric chemistry
[[Category:Environmental ch