Consider the following statements : Statement I : The amount of dust particles in the atmosphere is more in subtropical and temperate areas than in equatorial and polar regions. Statement II : Subtropical and temperate areas have less dry winds. Which one of the following is correct in respect of the above statements?
- A.Both Statement I and Statement II are correct and Statement II explains Statement I
- B.Both Statement I and Statement II are correct but Statement II does not explain Statement I
- C.Statement I is correct but Statement II is not correct
- D.Statement I is not correct but Statement II is correct
Correct answer
Explanation
The correct answer is C, Statement I is correct but Statement II is not correct. Dust is indeed concentrated in subtropical and temperate belts, but the reason is that these belts have more dry winds, not less.
Dust particles in the lower atmosphere come from soil, deserts, volcanoes, sea salt and smoke. The subtropical high-pressure belts hold the world's great hot deserts, such as the Sahara and the Thar, and the temperate interiors are dry too; dry winds blowing over loose, bare soil lift fine particles into the air. Equatorial regions are wet, so rain washes dust out, and polar regions are covered by ice and snow with little exposed soil. Dust particles also act as hygroscopic nuclei around which water vapour condenses to form clouds.
A and B are wrong because both assume Statement II is correct.
D is wrong because Statement I is correct and Statement II is not.
Exam tip: dust is highest in the subtropical and temperate belts because of dry winds; it is lowest in the wet equatorial and icy polar regions.
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