Correct Option
The correct option isThey act as hygroscopic nuclei for water vapour condensation.
Explanation
Dust particles, also known as particulate matter or aerosols, are solid or liquid particles suspended in the atmosphere. They originate from various sources such as sea salts, fine soil, smoke-soot, ash, pollen, and disintegrated meteors. These particles play a critical role in atmospheric processes, particularly in the lower layers of the atmosphere.
Statement-wise Analysis
- Statement They are concentrated only in the Exosphere. is Incorrect. Dust particles are generally concentrated in the lower layers of the atmosphere (Troposphere) rather than the Exosphere. Their concentration decreases rapidly with increasing height due to gravity and the proximity of their sources (the Earth's surface).
- Statement They act as hygroscopic nuclei for water vapour condensation. is Correct. Dust particles act as hygroscopic nuclei (condensation nuclei) around which water vapour condenses to produce water droplets. Without these particles, condensation would be difficult, and the formation of clouds, fog, and smog would be hindered.
- Statement They are absent in the Troposphere. is Incorrect. The Troposphere contains the highest concentration of dust particles because convectional air currents transport them to varying heights within this layer. They are not absent; rather, they are most abundant here.
- Statement They have no role in weather phenomena. is Incorrect. Dust particles play a significant role in weather phenomena. Apart from aiding in cloud formation and precipitation, they intercept and reflect solar radiation. They scatter light, which contributes to optical phenomena such as the blue colour of the sky and the red colour of the sun at sunrise and sunset.
Key Takeaway: Dust particles are primarily found in the lower atmosphere and serve as essential hygroscopic nuclei for condensation, cloud formation, and precipitation, while also influencing the scattering of solar radiation.