1. Session 4, Unit 7 Plume Rise

2. Qualitative Descriptions
Plume rise h
H=hs + h
Driving forces
Buoyancy
Momentum
Different phases
Initial phase
Thermal phase
Breakup phase
Diffusion phase

3. Qualitative Descriptions
Influencing factors
When there is no downwash
Exit velocity
Stack diameter
Stack gas temperature
Ambient temperature
Wind speed
Atmospheric stability
Wind shear
Downwash

4. Holland Plume Rise Formula
Simple
More suitable for power plant
For neutral conditions
The wind speed ū is adjusted to the stack height.
For non-neutral conditions

5. Briggs Plume Rise Formulas
More complicated
Buoyancy flux parameter
Momentum flux parameter

6. Briggs Plume Rise Formulas
Determination of buoyancy dominated or momentum dominated plumes
Calculate (T)c
For unstable or neutral (A-D)
For Fb <55
For Fb55
For stable (E,F)
If T (=Ts-Ta)  (T)c , it’s buoyancy dominated
If T (=Ts-Ta) < (T)c , it’s momentum dominated

7. Briggs Plume Rise Formulas
For buoyancy dominated plume under unstable or neutral conditions (A-D)
x* = distance at which atmospheric turbulence begins to dominate entrainment
For Fb55 m4/sec3, x*=34 Fb2/5
For Fb<55 m4/sec3, x*=14 Fb5/8
xf=distance to the final rise, m
xf=3.5x*
Final plume rise:

8. Briggs Plume Rise Formulas
For buoyancy dominated plume under stable conditions (E and F)
Stability parameter, s
Default values for
0.02 K/m for E stability
0.035 K/m for F stability

9. Briggs Plume Rise Formulas
Final plume rise
Distance to final rise

10. Briggs Plume Rise Formulas
For momentum dominated plume under unstable or neutral conditions (A-D)
For momentum dominated plume under stable conditions (E,F)
Calculate both and use the lower one.

11. Briggs Plume Rise Formulas
Gradual rise
Distance < distance to final rise (i.e., x<xf) and Buoyancy dominated plume

12. Briggs Plume Rise Formulas
Distance < distance to final rise (i.e., x<xf) and momentum dominated plume
Jet entrainment coefficient
Unstable conditions (A-D)

13. Briggs Plume Rise Formulas
X=downwind distance with max value of:
Xmax=49Fb5/8 for 0<Fb<55 m4/sec3
xmax=119Fb2/5 for Fb> 55 m4/sec3
Stable conditions (E,F)
with

14. Briggs Plume Rise Summary
Unstable and neutral
Stable
Buoyancy
Momentum

15. Buoyancy Induced Dispersion
Air entrainment due to “boiling-like action” enlarges the plume
Small impact on ground level concentration in most cases
The impact can be reflected in 
Initial plume size
Effective dispersion coefficients

16. Session 4, Unit 8 Averaging Time, Multiple Sources, and Receptors
Chimney, Building, and Terrain Effects

17. Averaging Time
The concentration calculated from the Gaussian equations should represent the averaging time that is consistent with the averaging time of 
Short-term:  1 month
Long-term: > 1 month

18. Averaging Time
If longer averaging time is desired, use the following power law
P= , suggested value is 0.17

19. Crosswind Averaging
Integrate y from - to 
Average over a sector

20. Crosswind Averaging
Average over a sector considering distribution of wind speeds and stability classes
ISCLT3 and STAR

21. Crosswind Averaging Smoothing transition from sector to sector
Weighted smoothing function, WS
Smoothed average concentration

22. Multiple Sources The max from each source do not exactly overlap
Use of multiple stack factor
More accurate method – modeling with a consistent coordinate system

23. Receptors Receptor grid
Cartesian coordinate system
Polar coordinate system
Single stack, but the origin of the coordinate system is not at the stack base
Multiple stacks
Presentation of results
Concentration isopleths

24. Example Calculation
Chapter 10

25. Chimney Effects Stack tip downwash Avoid stack tip downwash
Low pressure behind stack
ū is at the stack top level
No plume rise (“plume sink”)
Avoid stack tip downwash

26. Building Effects General description Expanded meaning of “building”
Reduce building effects – rule of thumb
hs>2.5hb
Too conservative for tall thin buildings

27. Briggs Procedure to Minimize Downwash
Five steps:
Correction for stack induced downwash
Correction for building effects
Determine if plume is entrained in the cavity. If entrained, treat it as a ground level source
Buoyancy effect
Calculate downwind concentration

28. Cavity Description Cavity length Short buildings (L/H2)
L affects cavity length xr
Long buildings (L/H>2)
L does not affect cavity length xr

29. Cavity
Max cavity width
It’s location long x direction
Max height

30. Cavity
Concentrations within cavity

31. Wake Downwind of Cavity
Treated as a ground level source
Turner method (virtual source)
Gifford method
Gifford-Slade method (total dispersion parameters)
Huber-Snyder method

32. Sources Downwind of Buildings
Briggs method
Beyond 3b  no building effect
Within 3b  treat them as ground level sources

33. Complex Terrain Definition Plume behavior in complex terrain
Simple terrain
Complex terrain
Intermediate terrain
Plume behavior in complex terrain

34. Complex Terrain Modeling approaches Briggs Egan Bowne
Modified dispersion coefficients
ISC3 (COMPLEX 1) – to be discussed later

35. GEP Stack Height Definition
Greater of
65 m
HG=H+1.5L (for stacks in existance on Jan 12, 1979, HG=2.5H)
Structures to be considered: within 5L
In modeling analyses, no credit is given for stack height above the GEP