This set of Air Pollution Control Multiple Choice Questions & Answers (MCQs) focuses on “Adiabatic and Environmental Lapse Rate – Set 2”.

1. Which method is used to describe the vertical movement of air pollutants in the atmosphere?

a) Adiabatic lapse rate

b) Environmental lapse rate

c) Air pressure

d) Air temperature

View Answer

Explanation: Adiabatic lapse rate describes the movement of air and air pollutants. The theory of the air parcel is used to understand the flow. As the air parcel rises vertically in the atmosphere, it expands to the change in air pressure.

2. For the adiabatic lapse rate, what result does the first law of thermodynamics yield?

a) dU = dQ – dW

b) dU = -dW

c) dU = dQ

d) dU = 0

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Explanation: For the adiabatic lapse rate, there is no exchange of heat with the environment. So,

dQ = 0

Therefore, the first law of thermodynamics gets modified to yield:

dU = -dW

3. Which of the following expressions is used to describe the adiabatic lapse rate?

a) dT/dz = [(n-1)/n](g/R)

b) dT/dz = g/Cp

c) dT/ dz = -g/Cp

d) dT/dz = -[(n-1)/n](g/R)

View Answer

Explanation: The equation describing the dry adiabatic lapse rate is:

dT/dz = -g/Cp (where g is the acceleration due to gravity and Cp is the specific heat at constant pressure).

dT/dz = -[(n-1)/n](g/R) is the equation used to describe environmental lapse rate.

4. What is the numerical value of the adiabatic lapse rate?

a) – 6.5 degree Celsius per 1 km

b) 6.5 degree Celsius per 1000 m

c) 9.8 degree Celsius per 1 km

d) – 9.8 degree Celsius per 1 km

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Explanation: The numerical value of adiabatic lapse is about – 9.8 degree Celsius per 1 km. The negative sign indicates that the relationship is negative, i.e., the temperature drops with increase in altitude. The adiabatic lapse rate is rounded off usually to – 10 degree Celsius per 1 km.

5. Which of the following symbol denotes the dry adiabatic lapse rate?

a) Γ

b) κ

c) ξ

d) ζ

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Explanation: The dry adiabatic lapse rate is described by the symbol Γ. The equation is as follows:

Γ = (-dT/dz) = 10 degree Celsius per 1000 metres.

This expression describes the value of adiabatic lapse rate for an air parcel of dry air (without any moisture) moving vertically upwards.

6. Which phenomenon is used to describe the vertical movement of an air parcel containing moisture?

a) Dry adiabatic lapse rate

b) Wet Adiabatic lapse rate

c) Environmental lapse rate

d) Wet Environmental lapse rate

View Answer

Explanation: The wet adiabatic lapse rate is used to describe the vertical movement of air that contains moisture. Due to the presence of moisture, the rising air parcel cools as it travels vertically upwards.

7. Which of the following expressions is the equation of wet adiabatic lapse rate?

a) dT/dz = d/C_{p}

b) dT/dz = -[(n-1)/n](g/R)

c) dT/dz = -(g/C_{p} + λdω/C_{p}dz)

d) dT/dz = -g/C_{p}

View Answer

For wet adiabatic lapse rate,

dT/dz = -(g/C

_{p}+ λdω/C

_{p}dz)

Explanation: Where λ is the latent heat of water per gram. The air parcel contains moisture, and the partial pressure of water vapour is considered to evaluate the expression. The second term, -λdω/C

_{p}dz, accounts for the cooling moisture with altitude.

8. The wet adiabatic lapse rate is not fully adiabatic.

a) True

b) False

View Answer

Explanation: This statement is true. In the case of wet adiabatic lapse rate, the air parcel contains water vapour. So, as the air parcel flows upwards, the water vapour cools down and may also condense.

9. Which is true about the wet adiabatic lapse rate?

a) Its equation is: dT/dz = -g/C_{p}

b) It is constant

c) It is used for dry air

d) It is not constant

View Answer

Explanation: The wet adiabatic lapse rate is not constant. This is because the amount of moisture present in the air varies. Hence, the value of the dT/dz changes with the amount of vapour in the air.

10. What is the value of wet adiabatic lapse rate?

a) More than the dry adiabatic lapse rate

b) Less than the dry adiabatic lapse rate

c) Equal to the dry adiabatic lapse rate

d) Much less than the dry adiabatic lapse rate

View Answer

Explanation: The expression dT/dz = -g/C

_{p}– λdω/C

_{p}dz is used to define wet adiabatic lapse rate. In the second term, dω/dz is negative, and the expression becomes dT/dz = -g/C

_{p}+ λdω/C

_{p}dz. This means that the wet adiabatic lapse rate is lesser than the dry adiabatic lapse rate (dT/dz = -g/C

_{p}).

11. Which of the following is false when it comes to the (dω/dz) term in the wet adiabatic lapse rate?

a) It depends on the temperature

b) It is negative

c) It is positive

d) It accounts for the condensing water vapour

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Explanation: The term is used to account for the condensing water vapour in a moist air parcel. dω/dz is not positive, and its value depends on temperature. Temperature dependence occurs because the saturation vapour pressure of water increases quickly with temperature.

12. What is the wet adiabatic lapse rate in warm tropical regions?

a) (1/3)(Dry adiabatic lapse rate

b) Equal to the dry adiabatic lapse rate

c) 3 times dry adiabatic lapse rate

d) Half of dry adiabatic lapse rate

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Explanation: The wet adiabatic lapse rate is always less than dry adiabatic lapse rate. Temperature dependence is very high with wet adiabatic lapse rate. The value of wet adiabatic lapse rate in warm places will be much less than the dry adiabatic lapse rate. Its value is about one-third the dry adiabatic lapse rate.

13. What is the superadiabatic lapse rate? (ELR – Environmental Lapse Rate; DALR – Dry adiabatic lapse rate; WALR – Wet adiabatic lapse rate)

a) ELR > WALR

b) ELR > DALR

c) ELR = DALR

d) ELR < WALR

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Explanation: In case of the superadiabatic lapse rate, the environmental lapse rate is greater than the dry adiabatic lapse rate. This phenomenon occurs on warm sunny days when the air close to the earth’s surface is heated.

14. What is the negative adiabatic lapse rate?

a) Temperature does not change with altitude

b) Temperature decreases with altitude

c) Temperature increases with altitude

d) Temperature and altitude have no relationship

View Answer

Explanation: In case of the negative lapse rate, the environmental lapse rate is lower than the adiabatic lapse rate. In this case, the temperature increases with altitude and the phenomenon is called inversion. The air pollutants do not disperse rapidly.

15. Why does the lapse rate in practice deviate from the constant value of the adiabatic lapse rate?

a) There is no deviation

b) Nature of pollutants

c) Pressure changes

d) Cooling effect

View Answer

Explanation: Cooling effect and the heating effect may result in deviation from the adiabatic lapse rate. The air may get rapidly heated due to the land, or the opposite may happen. Thus, resulting in the variation.

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