UPSC Prelims 2025 Q26: Dust Particles in the Atmosphere — Explained
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?
- Both Statement I and Statement II are correct and Statement II explains Statement I
- Both Statement I and Statement II are correct but Statement II does not explain Statement I
- Statement I is correct but Statement II is not correct
- Statement I is not correct but Statement II is correct
Answer: (c) Statement I is correct but Statement II is not correct
Statement-wise explanation
- Statement I: correct — The NCERT Class XI textbook Fundamentals of Physical Geography, in its chapter on the composition and structure of the atmosphere, says: 'Higher concentration of dust particles is found in subtropical and temperate regions due to dry winds in comparison to equatorial and polar regions.' The subtropics hold the world's great hot deserts, such as the Sahara, Arabian and Thar deserts. Dry, loose soil there is lifted easily by wind. Equatorial regions are kept damp by daily rain and dense vegetation, and polar ground is locked under ice and snow, so both give off far less dust.
- Statement II: incorrect — Statement II gets the fact backwards. NCERT links the higher dust load to the presence of dry winds in subtropical and temperate areas, not to a lack of them. Air sinking in the subtropical high-pressure belts is dry, which makes deserts and dry, dusty winds. Because Statement II is false, it cannot explain Statement I. Its reverse, that these areas have more dry winds, is the real explanation.
How to eliminate
This item comes from one NCERT line, and you need that line to be sure of the answer. Still, basic climatology gets you most of the way. First, test Statement II on its own. The subtropics hold the hot deserts (Sahara, Arabian, Thar, Kalahari, Australian) under sinking, dry air, so 'less dry winds' should look suspicious straight away. Next, apply internal logic. If an area had fewer dry winds, it would have less dust, not more. So Statement II argues against Statement I. Both statements can be true together only if Statement I is wrong. Since dust storms in the Sahara, Arabia and north-west India are familiar, Statement I is the one to trust. That leaves only one option: Statement I correct, Statement II not correct. A general trick for Statement I/II items: when Statement II reverses the obvious cause (here 'less' instead of 'more' dry winds), the examiner is usually testing whether you notice the reversal. Fact to remember: more dust in subtropical and temperate regions, because of dry winds.
Know more
Solid particles in the atmosphere
Besides gases and water vapour, the atmosphere holds small solid particles. They come from sea salt, fine soil, smoke and soot, volcanic ash, pollen and broken-up meteors. Most of this dust stays in the lower layers (troposphere), but convection currents can carry it to great heights.
Why dust matters
- Dust and salt particles act as hygroscopic nuclei: water vapour condenses around them to form clouds and fog.
- Dust scatters and absorbs sunlight. This colours sunrise and sunset red and orange and changes the region's heat balance.
- Long-range dust carries nutrients to the oceans and, as our site's pages show, can also carry microbes across the Indo-Gangetic Plain.
Where dust is concentrated
| Region | Dust load | Main reason |
|---|---|---|
| Subtropical (about 20°–30°) | High | Sinking dry air of the subtropical highs; hot deserts with loose soil |
| Temperate interiors | High | Dry continental winds, steppes and cold deserts (e.g. Gobi) |
| Equatorial | Low | Daily convectional rain washes dust out; thick vegetation binds soil |
| Polar | Low | Ground covered by ice and snow; little exposed soil |
Link to pressure belts Air rises at the equator (low pressure, heavy rain) and sinks around 30° N and S (subtropical highs). Sinking air warms and dries, so most hot deserts sit in this belt. That is why dust storms are common in the Sahara, Arabia and north-west India (Thar), especially in the dry, hot pre-monsoon months.
Related distinction: aerosols is the wider term for solid and liquid particles in air, including dust, sea salt, sulphates and black carbon. Dust is mostly mineral or soil particles.
NCERT Concepts to Revise
- Aerosols: Dust is one type of aerosol. Knowing the term helps you read questions on solid particles held in the air.
- Cloud condensation nuclei: Dust particles act as cloud condensation nuclei. This is the main reason the amount of atmospheric dust matters for weather.
- Composition of the atmosphere: Dust particles are one part of the atmosphere's makeup, beside gases and water vapour.
- Troposphere: Most atmospheric dust stays in the troposphere, the lowest layer, where weather happens.