# Air Pollution Control Questions and Answers – Atmospheric Stability and Inversion

This set of Air Pollution Control Multiple Choice Questions & Answers (MCQs) focuses on “Atmospheric Stability and Inversion”.

1. Which property ensures the dispersion of air pollutants in the atmosphere?
a) Atmospheric stability
b) Lapse rates
c) Atmospheric temperature
d) They disperse with altitude

Explanation: The stability of the atmosphere ensures that the air pollutants get dispersed into the atmosphere. The atmospheric stability is dependent on the lapse rates and the conditions they create.

2. How is atmospheric stability determined?
a) The temperature of the air
b) Compare lapse rates
c) The altitude of the air parcel
d) The pressure of the atmosphere

Explanation: The atmospheric stability is determined by comparing the lapse rates. Here, the environmental lapse rate and adiabatic lapse rate (both wet and dry) are compared. The other given options are tools used to determine the lapse rates.

3. Do the air pollutants disperse in a neutrally stable atmosphere?
a) Yes, but the air pollutants disperse towards the surface
b) Yes, dispersion occurs
c) No, dispersion does not occur
d) There is too little information

Explanation: In the case of a neutrally stable atmosphere, dispersion does not occur. In this condition, the environmental and dry adiabatic lapse rates are equal, and the air parcel will have the same density as its surroundings. The air parcel will, therefore, not move.

4. What conditions need to be present for a neutrally stable atmosphere? (ELR – Environmental Lapse Rate; DALR – Dry adiabatic lapse rate; WALR – Wet adiabatic lapse rate)
a) ELR = WALR
b) WALR = DALR
c) ELR = WALR = DALR
d) ELR = DALR

Explanation: In case of a neutrally stable atmosphere, the environmental lapse rate and the dry adiabatic lapse rate are equal to each other. A point to be noted is that the wet and dry adiabatic lapse rates are never equal.

5. What happens in the superadiabatic conditions?
a) The air parcel rises upwards
b) The air parcel does not move
c) The air parcel moves downwards
d) The air parcel moves sideways

Explanation: In superadiabatic conditions, the environmental lapse rate is greater than the dry adiabatic lapse rate. In this case, the atmosphere is not stable, and the air parcel rises upwards. The pollutants disperse quickly.

6. Which of the following describes the state of the atmosphere in superadiabatic conditions?
a) It is stable
b) It is unstable
c) The pressure is equal
d) The density is equal

Explanation: The atmosphere is unstable in such conditions. The air molecules, as well as pollutants, all disperse quickly. This condition is desirable for the swift dispersion of the air pollutants in the atmosphere.

7. Unstable atmospheric conditions, like in the case of superadiabatic lapse rate, are bad for dispersion.
a) True
b) False

Explanation: In case of superadiabatic conditions, dry adiabatic lapse rate is less than environmental lapse rate. It is an unstable atmospheric condition, which ensures that the rapid dispersion of pollutants. Therefore, the opposite is true.

8. What are subadiabatic conditions? (ELR – Environmental Lapse Rate; DALR – Dry adiabatic lapse rate)
a) ELR = DALR
b) ELR > DALR
c) ELR < DALR
d) ELR << DALR

Explanation: In the case of subadiabatic conditions, the value of environmental lapse rate is lesser than the dry adiabatic lapse rate. This situation means that the air parcel is denser than the surroundings, so the dispersion occurs very slowly.

9. Which of the following is not false about subadiabatic atmospheric conditions? (ELR – Environmental Lapse Rate; DALR – Dry adiabatic lapse rate)
a) ELR = DALR
b) Dispersion does not occur
c) It is unstable
d) It is stable

Explanation: In such a case, the atmosphere is stable. Dispersion does occur in the case of subadiabatic conditions, but it happens very slowly. Additionally, the environmental lapse rate is lesser than the dry adiabatic lapse rate for this case.

10. What happens to pollutants in subadiabatic conditions?
a) They build up in the atmosphere
b) They disperse rapidly
c) They do not disperse
d) They do not build-up

Explanation: In the case of subadiabatic conditions, the pollutants disperse very slowly. Due to this, the air pollutants build up in the atmosphere. Subadiabatic conditions mean that the atmosphere is stable.

11. What is absolute stability? (ELR – Environmental Lapse Rate; DALR – Dry adiabatic lapse rate; WALR – Wet adiabatic lapse rate)
a) ELR > DALR
b) ELR > WALR
c) ELR < WALR
d) ELR < DALR

Explanation: When the environmental lapse rate is lesser than the wet adiabatic lapse rate, the condition is of absolute stability. The air pollutants do not disperse in the case of atmospheric stability at all.

12. When does conditional stability occur? (ELR – Environmental Lapse Rate; DALR – Dry adiabatic lapse rate; WALR – Wet adiabatic lapse rate)
a) DALR > WALR
b) DALR > ELR
c) ELR > WALR
d) DALR > ELR > WALR

Explanation: In this case, the value of the environmental lapse rate is between the wet and dry lapse rate. Notably, the dry adiabatic lapse rate is always greater than the moist adiabatic lapse rate. The dispersion varies case by case.

13. Which of the following is false in the case of inversion?
a) It is very stable
b) It is unstable
c) Temperature increases with altitude
d) No dispersion occurs

Explanation: In the case of inversion, which is a negative lapse rate, the atmosphere is very stable. Since the atmosphere is stable, there is no dispersion of the air molecules and air pollutants. The temperature also increases with altitude.

14. Which of the following is the most common type of inversion?
c) Subsidence inversion
d) Convective inversion

Explanation: Subsidence inversion is the most common type of inversion. Radiational inversion is the second most common type of inversion. In the case of inversion, there is no vertical mixing of air molecules and air pollutants.

15. What happens in the subsidence inversion condition?
a) The air moves downward
b) The air moves upwards
c) The air does not move
d) The air moves sideways

Explanation: In the subsidence inversion conditions, the air moves downwards. It most commonly occurs in the anticyclone conditions of the sub-tropical regions. The air moves downward because of high pressure.

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