Page 368 - Fundamentals of Air Pollution 3E

I. Plume Rise 323

G. Unstable-Neutral Momentum Plume Rise
If the stack gas temperature is below or only slightly above the ambient
temperature, the plume rise due to momentum will be greater than that
due to buoyancy. For unstable and neutral situations:

This equation is most applicable when vju exceeds 4. Since momentum
plume rise occurs quite close to the source, the horizontal distance to the
final plume rise is considered to be zero.

H. Stable Momentum Plume Rise
For low-buoyancy plumes in stable conditions, plume height due to
momentum is given by

Equation (20-10) should also be evaluated and the lower value used.

I. Momentum-Buoyancy Crossover
There is a specific difference between stack gas temperature and ambient
air temperature that gives the same result for buoyancy rise as for momen-
tum rise. For unstable or neutral conditions this is as follows: For F less
than 55,

For F equal to or greater than 55,

For stable conditions,

J. Maximum Concentrations as a Function of Wind Speed and Stability
Using the source in the example in Chapter 19 (Q = 0.37, h = 20,
d = 0.537, v s = 20, and T s = 350), with plume rise calculated using the
above equations, maximum ground-level concentrations are shown (Fig.
20-1) as functions of stability class and wind speed calculated using the
Gaussian model with Pasquill-Gifford dispersion parameters. Maximum
concentrations are nearly the same for stabilities A, B, and C and occur at
1
wind speeds of 1.5-2.0 m s" . The maximum for D stability occurs at
around u = 2.5 m s~*. Because of the competing effects of dilution by wind
and lower effective stack heights with higher wind speeds, concentrations