DEFINITIONAtmospheric Dispersion Modelingis the mathematical simulation ofhow air pollutants disperse in theambient atmosphere.
Plume’s centerline Z Wind ΔH H at X3 X H at X2 h H at X1 y- H = Pollutant ’s release Hight H = h + ΔH y+ Hs = Actual release hightSchematic Chimney ΔH = Plume rise
The model equation. We have selected the model equation in the form of presented by D.B. Turner. It gives: The ground level concentration X of pollutants at a point (x & y) downwind. E 1 y 2 1 H 2 χ( x , y ,0, H ) = exp − ( ) exp − 2 ( ) πs y s z u 2 s y sz Where χ ( x , y ,0, H ) = Downwind concentration at ground level, g/m3 E = Emission rate of pollutant, g/sec sy, sz = plumes standard deviations, m x, y, z and H = distances, m exp = e[ ] (exponential e, where e = constant and = 2.7182)
The value for the effective stack height is the sum ofthe physical stack height (h) and the plume rise⌂H. H = h + ⌂H Where us d Ts − Ta 1.5 + 2.68 ×10 ( P ) −2 ∆H = d u Ts Where us = stack velocity, m/sec d = stack diameter, m u = wind speed, m/sec P = atmospheric pressure, kPa Ts = Stack temperature, K (T oC + 273) Ta = air temperature, K Note: All these values depend upon the turbulent structure or stability of the atmosphere.
Means of ModelingIt is performed with computerprograms that solve the mathematicalequations and algorithms whichsimulate the pollutant dispersion.
ˆ To predict the downwind concentration of air pollutants emitted from sources such as industrial plants and vehicular traffic.r To determine whether existing or proposed new industrial facilities are or will be in compliance with the National Ambient Air Quality Standards (NAAQS).i To assist in the design of effective control strategies to reduce emissions of harmful air pollutants.
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.