Atmospheric dispersion im Muhammad Fahad Ansari 12IEEM14

1. ATMOSPHERIC
DISPERSION
Muhammad Fahad Ansari
12IEEM14

2. DEFINITION
Atmospheric Dispersion Modeling
is the mathematical simulation of
how air pollutants disperse in the
ambient atmosphere.

3. 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 hight
Schematic Chimney ΔH = Plume rise

4. 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)

5. The value for the effective stack height is the sum of
the 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.

8. Means of Modeling
It is performed with computer
programs that solve the mathematical
equations and algorithms which
simulate the pollutant dispersion.

9. 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.

10.  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.