AIR POLLUTION DISPERSION MODELING.pdf

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AIR POLLUTION DISPERSION MODELING

Air pollution dispersion modelingis themathematicalsimulationof how air pollutants dispersein the ambient atmosphere. It is per-formed withcomputer programs, called dispersion models, that solve

the mathematical equations and algorithmswhichsimulate the pollutant dispersion. The dispersion modelsare used to estimate or to predict the downwindconcentrationof air pollutants emitted from emissionsourcessuch as industrial plants and vehicular traffic.Such models are important to governmental agenciestasked with protecting and managing ambient airquality. The models are typically employed to determinewhether exist-ing or proposed new industrial facilitiesare or will be in compliance with the ational !mbient!ir "uality Standards #!!"S$ in the %nited Statesandsimilar standards in other nations. The models also serve to assist in the design of

effective control strategies to reduce emissions of harmful air pollutants.

The dispersion models require the input of data which includes&

'eteorological data such as windspeed and direction, atmospheric

turbulence#characteri(ed by what is known as the stability class$, theambient air temperature and the height to the bottom of any temperatureinversionthat may be present aloft.

)missions parameters such as source location and height, source vent stackdiameter 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 gaseousemission plume.

'any modern, advanced dispersion modeling programs include pre-processormodules for the input of meteorological and other data, and many also include apost-processor module for graphing the output data and*or plotting the areaimpacted by the air pollutants on maps. +urrently, the !)' air pollutiondispersion modelis the preferred regulatory model of the %.S. )nvironmental/rotection !gency.

The air pollution dispersion models are also known as atmospheric dispersionmodels, atmospheric diffusion models, air dispersion models and air quality models.

Gaussian air pollution dispersion equationThe technical literature on air pollution dispersion is quite extensive and dates backto the 01234s and earlier. ne of the early air pollutant plume dispersion equationswas derived by 5osanquet and /earson.607Their equation did not assume 8aussiandistributionnor did it include the effect of ground reflection of the pollutant plume.

Sir 8raham Sutton derived an air pollutant plume dispersion equation in 019:6;7

which did include the assumption of 8aussian distribution for the vertical and

crosswind dispersion of the plume and also included the effect of ground reflectionof the plume.
http://wiki/Mathematicshttp://wiki/Computer_simulationhttp://wiki/Air_pollution_dispersion_terminology#Dispersion_modelshttp://wiki/Algorithmhttp://wiki/Concentrationhttp://wiki/Air_pollution_dispersion_terminology#Air_pollutant_emission_sourceshttp://wiki/Air_pollution_dispersion_terminology#Air_pollutant_emission_sourceshttp://wiki/United_Stateshttp://wiki/Windhttp://wiki/Air_pollution_dispersion_terminologyhttp://wiki/Air_pollution_dispersion_terminologyhttp://wiki/Air_pollution_dispersion_terminologyhttp://wiki/Air_pollution_dispersion_terminologyhttp://wiki/Gashttp://wiki/Air_pollution_dispersion_terminologyhttp://wiki/AERMOD_air_pollution_dispersion_modelhttp://wiki/AERMOD_air_pollution_dispersion_modelhttp://wiki/U.S._Environmental_Protection_Agencyhttp://wiki/U.S._Environmental_Protection_Agencyhttp://wiki/Gaussian_distributionhttp://wiki/Gaussian_distributionhttp://wiki/Mathematicshttp://wiki/Computer_simulationhttp://wiki/Air_pollution_dispersion_terminology#Dispersion_modelshttp://wiki/Algorithmhttp://wiki/Concentrationhttp://wiki/Air_pollution_dispersion_terminology#Air_pollutant_emission_sourceshttp://wiki/Air_pollution_dispersion_terminology#Air_pollutant_emission_sourceshttp://wiki/United_Stateshttp://wiki/Windhttp://wiki/Air_pollution_dispersion_terminologyhttp://wiki/Air_pollution_dispersion_terminologyhttp://wiki/Air_pollution_dispersion_terminologyhttp://wiki/Air_pollution_dispersion_terminologyhttp://wiki/Gashttp://wiki/Air_pollution_dispersion_terminologyhttp://wiki/AERMOD_air_pollution_dispersion_modelhttp://wiki/AERMOD_air_pollution_dispersion_modelhttp://wiki/U.S._Environmental_Protection_Agencyhttp://wiki/U.S._Environmental_Protection_Agencyhttp://wiki/Gaussian_distributionhttp://wiki/Gaussian_distribution


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There was an immense growth in the utili(ation of air pollutant plume dispersioncalculations between the late 01


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It should be noted that z and yare functions of the atmospheric stability class#i.e., a measure of the turbulence in the ambient atmosphere$ and of the downwinddistance to the receptor. The two most important variables affecting the degree ofpollutant emission dispersion obtained are the height of the emission source pointand the degree of atmospheric turbulence. The more turbulence, the better thedegree of dispersion.

The resulting calculations for air pollutant concentrations are often expressed as anair pollutant concentration contour map in order to show the spatial variation inpollutant levels over a wide area under study. In this way the contour lines canoverlay sensitive receptor locations and reveal the spatial relationship of airpollutants to areas of interest.

T&e #riggs plume rise equations

The 8aussian air pollutant dispersion equation #discussed above$ requires the inputof H#also known as the effective plume height, He $ which is the pollutant plume4s

centerline height above ground level. Heat any distance from the pollutant plume4ssource is the sum of Hs#the actual physical height of the pollutant plume4s sourcepoint$ plus 'H#the plume rise due the plume4s buoyancy$ at that distance.

To determine 'H, most air dispersion models developed between the late 01


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+old Det plumes in calm ambient air conditions

+old Det plumes in windy ambient air conditions

Eot, buoyant plumes in calm ambient air conditions

Eot, buoyant plumes in windy ambient air conditions

5riggs considered the traDectory of cold Det plumes to be dominated by their initial

velocity momentum, and the traDectory of hot, buoyant plumes to be dominated bytheir buoyant momentum to the extent that their initial velocity momentum wasrelatively unimportant. !lthough he proposed plume rise equations for each of theabove plume categories, the Briggs equations" which become widely usedare those that he proposed for bent-over, hot buoyant plumes (as depictedin the above diagram of a plume.

In general, 5riggs4s equations for bent-over, hot buoyant plumes are based onobservations and data involving plumes from typical combustion sources such asthe flue gas stacksfrom steam-generating boilersburning fossil fuelsin large powerplants. Therefore, the stack exit velocities were probably in the range of ;3 to 033ft*s #< to 23 m*s$ with exit temperatures ranging from ;@3 to @33 F= #0;3 to ;


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u > windspeed at actual stack height, in m*ss > stability parameter, in s-;

The parameters shown in the above logic diagram of 5riggs4 equations arediscussed in much more detail by 5eychok.697

Ma)or air pollution dispersion models in *urrentuse

These are some of the maDor air pollution dispersion models currently being used.There are literally do(ens of other models as well&

!'S 2& eveloped in the %nited Gingdom

!)'& eveloped in the %nited States

!%S/H%')& eveloped in !ustralia

+!H/%==& eveloped in the %nited States

IS/)SI;&eveloped in Sweden

IS+2& eveloped in the %nited States

H!'& eveloped in !ustralia

!')& eveloped in the %nited Gingdom

')+%)& eveloped in =rance

I'/%==& eveloped in enmark

The )uropean Topic +entre on !ir and +limate +hange, which is part of the)uropean )nvironment !gency#))!$, maintains an online 'odel ocumentationSystem #'S$that includes descriptions and other information for almost all of thedispersion models developed by the countries of )urope. The 'S currentlycontains 039 models developed in )urope#excluding the %nited Gingdom$.6007

Re!eren*es0. 5osanquet, +.E. and /earson, .H., ?The spread of smoke and gases from

chimneys?, Trans. =araday Soc., 2;&0;91, 012

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