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## Atmospheric dispersion modeling
The dispersion models require the input of data which includes: - Meteorological conditions such as wind speed and direction, the amount of atmospheric turbulence (as characterized by what is called the "stability class"), the ambient air temperature and the height to the bottom of any inversion aloft that may be present.
- Emissions parameters such as source location and height, source vent stack diameter and exit velocity, exit temperature and mass flow rate.
- Terrain elevations at the source location and at the receptor location.
- The location, height and width of any obstructions (such as buildings or other structures) in the path of the emitted gaseous plume.
Many of the modern, advanced dispersion modeling programs include a pre-processor module for the input of meteorological and other data, and many also include a post-processor module for graphing the output data and/or plotting the area impacted by the air pollutants on maps. The atmospheric dispersion models are also known as atmospheric diffusion models, air dispersion models, air quality models, and air pollution dispersion models.
## Gaussian air pollutant dispersion equationThe technical literature on air pollution dispersion is quite extensive and dates back to the 1930's and earlier. One of the early air pollutant plume dispersion equations was derived by Bosanquet and Pearson. Sir Graham Sutton derived an air pollutant plume dispersion equation in 1947 Under the stimulus provided by the advent of stringent environmental control regulations, there was an immense growth in the use of air pollutant plume dispersion calculations between the late 1960s and today. A great many computer programs for calculating the dispersion of air pollutant emissions were developed during that period of time and they were called "air dispersion models". The basis for most of those models was the
The above equation not only includes upward reflection from the ground, it also includes downward reflection from the bottom of any inversion lid present in the atmosphere. The sum of the four exponential terms in It should be noted that σ The resulting calculations for air pollutant concentrations are often expressed as an air pollutant concentration contour map in order to show the spatial variation in contaminant levels over a wide area under study. In this way the contour lines can overlay sensitive receptor locations and reveal the spatial relationship of air pollutants to areas of interest. ## The Briggs plume rise equationsThe Gaussian air pollutant dispersion equation (discussed above) requires the input of
To determine Δ Briggs divided air pollution plumes into these four general categories: - Cold jet plumes in calm ambient air conditions
- Cold jet plumes in windy ambient air conditions
- Hot, buoyant plumes in calm ambient air conditions
- Hot, buoyant plumes in windy ambient air conditions
Briggs considered the trajectory of cold jet plumes to be dominated by their initial velocity momentum, and the trajectory of hot, buoyant plumes to be dominated by their buoyant momentum to the extent that their initial velocity momentum was relatively unimportant. Although Briggs proposed plume rise equations for each of the above plume categories, In general, Briggs's equations for bent-over, hot buoyant plumes are based on observations and data involving plumes from typical combustion sources such as the flue gas stacks from steam-generating boilers burning fossil fuels in large power plants. Therefore the stack exit velocities were probably in the range of 20 to 100 ft/s (6 to 30 m/s) with exit temperatures ranging from 250 to 500 °F (120 to 260 °C). A logic diagram for using the Briggs equations where: Δh = plume rise, in m F ^{ }= buoyancy factor, in m ^{4}/s^{3}x = downwind distance from plume source, in m x _{f}= downwind distance from plume source to point of maximum plume rise, in m u = windspeed at actual stack height, in m/s s ^{ }= stability parameter, in s ^{-2}
The above parameters used in the Briggs' equations are discussed in Beychok's book. ## See also## Atmospheric dispersion models- ADMS 3
- AERMOD
- ATSTEP
- CALPUFF
- DISPERSION21
- ISC3
- NAME
- MERCURE
- RIMPUFF
- PUFF-PLUME
## Organizations- Air Quality Modeling Group
- Air Resources Laboratory
- Finnish Meteorological Institute
- KNMI, Royal Dutch Meteorological Institute
- National Environmental Research Institute of Denmark
- Swedish Meteorological and Hydrological Institute
- TA Luft
- UK Atmospheric Dispersion Modelling Liaison Committee
- UK Dispersion Modelling Bureau
## Others- Air pollution dispersion modeling books
- Air pollution dispersion terminology
- Compilation of atmospheric dispersion models
- Portable Emissions Measurement System (PEMS)
- Roadway air dispersion modeling
- Useful conversions and formulas for air dispersion modeling
## References**^**Bosanquet, C.H. and Pearson, J.L., "The spread of smoke and gases from chimneys", Trans. Faraday Soc., 32:1249, 1936**^**Sutton, O.G., "The problem of diffusion in the lower atmosphere", QJRMS, 73:257, 1947 and "The theoretical distribution of airborne pollution from factory chimneys", QJRMS, 73:426, 1947- ^
^{a}^{b}^{c}Beychok, Milton R. (2005).*Fundamentals Of Stack Gas Dispersion*, 4th Edition, author-published.__ISBN 0-9644588-0-2__. www.air-dispersion.com **^**Turner, D.B. (1994).*Workbook of atmospheric dispersion estimates: an introduction to dispersion modeling*, 2nd Edition, CRC Press.__ISBN 1-56670-023-X__. www.crcpress.com**^**Briggs, G.A., "A plume rise model compared with observations", JAPCA, 15:433-438, 1965**^**Briggs, G.A., "CONCAWE meeting: discussion of the comparative consequences of different plume rise formulas", Atmos. Envir., 2:228-232, 1968**^**Slade, D.H. (editor), "Meteorology and atomic energy 1968", Air Resources Laboratory, U.S. Dept. of Commerce, 1968**^**Briggs, G.A., "Plume Rise", USAEC Critical Review Series, 1969**^**Briggs, G.A., "Some recent analyses of plume rise observation", Proc. Second Internat'l. Clean Air Congress, Academic Press, New York, 1971**^**Briggs, G.A., "Discussion: chimney plumes in neutral and stable surroundings", Atmos. Envir., 6:507-510, 1972
## Further readingFor those who would like to learn more about this topic, it is suggested that either one of the following books be read: - Turner, D.B. (1994).
*Workbook of atmospheric dispersion estimates: an introduction to dispersion modeling*, 2nd Edition, CRC Press.__ISBN 1-56670-023-X__. www.crcpress.com
- Beychok, Milton R. (2005).
*Fundamentals of Stack Gas Dispersion*, 4th Edition, author-published.__ISBN 0-9644588-0-2__. www.air-dispersion.com
- Schnelle, Jr., Karl B. and Dey, Partha R. (2000).
*Atmospheric Dispersion Modeling Compliance Guide*. McGraw-Hill.__ISBN 0-07-058059-6__.
Categories: Chemical engineering | Environmental engineering |
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This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Atmospheric_dispersion_modeling". A list of authors is available in Wikipedia. |