# Air Pollution Control Questions and Answers – Stack Effluent Dispersion Theories

This set of Air Pollution Control Multiple Choice Questions & Answers (MCQs) focuses on “Stack Effluent Dispersion Theories”.

1. What are the two stages of dilution of air pollutant effluents?
a) Plume rise and mixing
b) Mixing and dispersion
c) Plume rise and dispersion
d) Diffusion and dilution

Explanation: The dilution of air pollutants in the atmosphere is a two-stage process. The first stage is the plume rise, and the second is that of dispersion. First, the plume rises from the stack and then mixes with the wind.

2. Which of the following is not a factor applied to evaluate the theories of plume rise?
a) Wind speed
b) Stack diameter
c) Plume temperature
d) Nature of the plume

Explanation: All the given factors, except for the plume nature, are used to study the theories. The theoretical equations used to study plume rise are debated upon heavily. Some other factors include stack height, rate of emission, and the stability of the atmosphere.

3. Which of the following is not a factor upon which the emissions patterns from stacks depends?
a) Wind profile
b) Temperature of the wind
c) Wind turbulence
d) Distribution of temperature

Explanation: The emission profiles do not depend on the temperature of the wind. Wind profile, wind turbulence, and temperature distribution all affect the way the pollutants disperse in the atmosphere.

4. What is meant by the effective stack height?
a) Sum of stack height and plume rise
b) Difference of stack height and plume rise
c) Height of the plume
d) Synonymous with the stack height

Explanation: The effective stack height is the sum of the stack height and the plume height above it. The stack height can be identified easily, but the same cannot be said for the plume rise pattern. It can only be predicted, and several formulae are available to make such predictions.

5. Which of the following is not a factor plume rise depends on?
a) Stack height
b) Exit velocity
c) Stack diameter
d) Lapse rate

Explanation: Plume rise is independent of the stack height. It does, however, vary with the stack diameter. The other listed factors affect the height of the plume above the stack before it disperses.

6. What is the expression for plume rise Δh? (hs – stack height)
a) Δh buoyancy
b) Δh buoyancy + Δh momentum
c) Δh momentum + hs
d) Δh buoyancy + hs

Explanation: One of the formulae used to determine plume rise is the (Δh buoyancy + Δh momentum). This expression is used because the buoyancy of the wind and the momentum of the plume affect the plume rise.

7. Why can’t plume rise expressions be accepted universally?
a) They are empirical in nature
b) Wind speed prediction is difficult
c) Plume nature varies
d) Height of the stack varies

Explanation: The equations used to determine plume rise are empirical in nature. This means that they are evaluated for particular locations and conditions, which may not be duplicated in other places.

8. Which law is used to determine the dispersion of air pollutants?
a) Law of conservation
b) Second law of thermodynamics
c) First law of thermodynamics
d) Fick’s law of molecular diffusion

Explanation: Fick’s law is used to determine the diffusion of air pollutants in the atmosphere. The solution of this equation estimates the concentration of the air pollutants. To account for the presence of particulate matter, if present, the equation is modified.

9. Fick’s molecular diffusion and Sutton’s statistical concepts are used for calculating dispersion models for which sources?
a) Atmospheric stability
b) Continuous point sources
c) Instantaneous point sources
d) Line sources

Explanation: These laws mentioned are used to determine the dispersion of instantaneous point sources. They are used to model the plume at any given instant. Additional models are used to model the other listed options.

10. Which of the following is not a model used for plume rise modelling based on stability classification?
a) Pasquill model
b) Fick’s law
c) ASME model
d) McElroy model

Explanation: All the models listed, except for Fick’s law, are used. Fick’s law finds application in the empirical modelling of plume rise and the instantaneous point source dispersion of air pollutants.

11. For continuous point sources, the dispersion models are not based on which of the following?
a) Plume behaviour
b) Wind speed
c) Plume temperature
d) Eddy diffusion

Explanation: The dispersion of the plume is not based on the plume temperature for a continuous point source. This is because the continuous discharge from the stack causes the plume to disperse based on the wind speed and turbulence.

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