Given below are two statements : Statement (I): Atmospheric stability is important because it determines the ability of pollutants to disperse vertically in the atmosphere. Statement (II): In summer season in India. the atmosphere is generally stable. In the light of the above statements, choose the correct answer from the options given
Statement (I) is true but Statement (II) is false
Understanding Atmospheric Stability and Pollutant Dispersion
Atmospheric stability refers to the resistance of the atmosphere to vertical motion. It plays a crucial role in how pollutants disperse once they are released into the air. Let's analyze each statement provided in the question.
Analysis of Statement (I)
Statement (I) says: Atmospheric stability is important because it determines the ability of pollutants to disperse vertically in the atmosphere.
- When the atmosphere is stable, air parcels tend to return to their original position after being displaced vertically. This prevents significant upward or downward movement of air.
- In a stable atmosphere, pollutants released near the ground are trapped close to the surface because they cannot rise and mix with the air above. This leads to higher concentrations of pollutants.
- When the atmosphere is unstable, air parcels tend to accelerate away from their original position when displaced vertically. This promotes vigorous upward and downward movement and mixing.
- In an unstable atmosphere, pollutants can rise and spread out over a larger volume of air, leading to lower concentrations near the source.
- Therefore, atmospheric stability directly influences the vertical dispersion (mixing) of pollutants. A stable atmosphere inhibits dispersion, while an unstable atmosphere enhances it.
Based on this understanding, Statement (I) is true.
Analysis of Statement (II)
Statement (II) says: In summer season in India, the atmosphere is generally stable.
- Summer season in India (typically March to June) is characterized by intense solar radiation. The ground gets heated significantly.
- This heat is transferred to the air near the surface, making it warmer and less dense than the air above.
- Warmer, less dense air tends to rise, creating convection currents. This vertical movement of air indicates that the atmosphere is tending towards or is unstable or neutral, rather than stable.
- Unstable conditions, promoting convection and vertical mixing, are common during the daytime in the summer due to strong solar heating.
- Stable conditions are more likely during calm, clear nights or in winter inversions, not typically during the day in the hot Indian summer.
Based on this understanding, Statement (II) is false.
Summary of Analysis
| Statement | Assessment | Reasoning |
|---|---|---|
| Statement (I): Atmospheric stability determines vertical pollutant dispersion. | True | Stable atmosphere inhibits vertical mixing; unstable atmosphere promotes it. |
| Statement (II): Atmosphere in India is generally stable in summer. | False | Intense summer heating leads to convection and unstable/neutral conditions. |
Statement (I) is true because atmospheric stability is a key factor controlling how far pollutants can spread vertically. Statement (II) is false because the strong solar heating during Indian summers typically leads to unstable or neutral atmospheric conditions, promoting vertical mixing.
Therefore, Statement (I) is true but Statement (II) is false.
Revision Table: Atmospheric Stability and Pollutants
| Condition | Description | Effect on Vertical Pollutant Dispersion |
|---|---|---|
| Stable | Air resists vertical movement; temperature decreases slowly with height or increases (inversion). | Limited vertical mixing; pollutants trapped near surface. |
| Unstable | Air tends to rise; temperature decreases rapidly with height. | Significant vertical mixing (convection); pollutants disperse upwards. |
| Neutral | Air neither resists nor promotes vertical movement. | Moderate vertical mixing. |
Additional Information: Atmospheric Conditions in Indian Summer
The summer season in India is characterized by high temperatures and often low humidity (except during the monsoon period, which follows). The strong solar insolation heats the land surface, which in turn heats the lower layers of the atmosphere. This differential heating creates a lapse rate (rate of temperature decrease with height) that often exceeds the adiabatic lapse rate, leading to unstable conditions. This instability drives convective currents, which can lead to the formation of thunderstorms or simply enhance vertical mixing of air and any pollutants present.
Important Questions from Atmosphere
Which of the following statements with reference to Surface inversion of temperature is/are correct? 1. It causes instability in the lower layers of the atmosphere. 2. This inversion commonly lasts for a few hours until the Sun comes up.
Identify the cloud on the basis of the following characteristics: I. They look like cotton wool. II. They exist in patches and have flat base. III. They are generally formed at a height of 4 to 7 km.
Which of the following statements with reference to Surface inversion of temperature is/are correct?
1. It causes instability in the lower layers of the atmosphere.
2. This inversion commonly lasts for a few hours until the Sun comes up.Identify the cloud on the basis of the following characteristics:
I. They look like cotton wool.
II. They exist in patches and have flat base.
III. They are generally formed at a height of 4 to 7 km.The percentage increase in carbon dioxide concentration in atmosphere from pre-industrial times is approximately
