CE 108 Homework #3 Solutions
1.
Calculate and plot normalized concentration profiles downwind of a roadway for different
atmospheric stabilities.
Start with the equation for concentration downwind of a line source:
(1)
In this case, z = 0 and the second half of equation (1) is equal to 1:
(2)
is estimated using the following equation:
(3)
Values for
,
, and
can be found in the handout posted on bspace titled “Gaussian Plume
Notes”.
Normalized concentration at a distance x downwind of the roadway can be calculated as:
(4)
Equation (4) can be simplified to:
(5)
Equation (5) can be used to calculate normalized concentration profiles for each of the three
stability conditions.
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The concentration profiles are not linear in x.
Concentration falls off most rapidly in unstable
(Class C) atmospheric conditions.
2. Simulate two runs from the Caltrans highway 99 tracer experiment using a line source
dispersion model.
(a) Calculate SF
6
concentrations at 50, 100, and 200 m downwind of the highway.
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 Fall '09
 Harley
 Benson, 200 m, 84°, 58°

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