UPSC Prelims 2025Question 26Geography

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?

Options

(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: c

Decision rule

Subtropical high-pressure belts are the source of dry descending air; a statement calling those latitudes less dry contradicts the deserts sitting in them.

Explanation

Correct Answer:

(c) Statement I is correct but Statement II is not correct

Explanation of the Correct Answer:

Statement I: The amount of dust particles in the atmosphere is more in subtropical and temperate areas than in equatorial and polar regions. — Correct

The subtropical regions, particularly near deserts like the Sahara, Arabian, and Thar, have dry climates, low vegetation, and strong winds, which lift large amounts of dust particles into the atmosphere.
Temperate areas, especially those in the interior and semi-arid zones, also contribute to atmospheric dust.
In contrast:
- Equatorial regions are humid with dense vegetation and frequent rainfall, which suppress dust.
- Polar regions are ice-covered and have minimal exposed soil, leading to very low dust activity.

Statement II: Subtropical and temperate areas have less dry winds. — Incorrect

This is factually wrong. Subtropical high-pressure belts are the source of dry descending air, which contributes to arid and semi-arid climates.
Deserts like the Sahara, Kalahari, Arabian, and Mojave exist in subtropical zones because of persistent dry winds.
These dry winds are responsible for lifting dust into the atmosphere, especially during dust storms.

Why Other Options Are Incorrect:

(a): Incorrect because Statement II is factually wrong and cannot explain Statement I.
(b): Incorrect; while Statement I is true, Statement II is incorrect, so the logic does not hold.
(d): Incorrect because Statement I is correct, but Statement II is not.

Relevant Supplementary Information

Table: Dust Concentration by Latitude Zones

Zone	Dust Concentration	Key Reasons
Subtropical (20°–30°)	High	Dry winds, deserts, sparse vegetation (e.g., Sahara, Thar)
Temperate (30°–60°)	Moderate	Semi-arid interiors, winds, some anthropogenic activity
Equatorial (0°–10°)	Low	High rainfall, dense vegetation, high humidity
Polar (60°–90°)	Very Low	Ice-covered, low soil exposure, minimal wind-blown dust

Related Concepts:

Aeolian processes: Wind-driven transport of dust and sand, common in arid zones.
Subtropical High Pressure Belts: Found near 30°N/S, associated with dry descending air.
ITCZ (Inter-Tropical Convergence Zone): Near equator, marked by heavy rainfall, suppressing dust.
Polar deserts: Cold and dry, but lacking exposed soil and wind intensity to generate dust storms.

Concept	Explanation
Aeolian processes	Wind-driven erosion, transport, and deposition of dust/sand
Subtropical High Pressure	Zones of descending air around 30° latitude leading to aridity and dust
Dust storms	Result of strong surface winds in arid regions lifting dust into atmosphere
Rain washout	Precipitation removes dust particles from the air (common in equatorial zones)

Current Relevance:

Dust storms from subtropical deserts like the Sahara affect air quality in Europe and the Americas.
Climate models now incorporate aerosol and dust loading as key variables.
Studies link atmospheric dust to monsoon behavior, ocean productivity, and radiation balance.

Table 1: Dust Concentration by Climatic Zones

Zone	Dust Concentration	Reasons
Subtropical (20°–30° N/S)	High	Arid and semi-arid deserts (e.g., Sahara, Thar), dry winds, low vegetation
Temperate (30°–60° N/S)	Moderate	Interior continental regions, agricultural activity, moderate wind activity
Equatorial (0°–10°)	Low	High humidity, dense forest cover, heavy rainfall washes out particulates
Polar (60°–90° N/S)	Very Low	Ice cover, low wind erosion potential, very little vegetation or dust

Table 2: Key Atmospheric Winds and Their Influence on Dust

Wind Belt	Location	Characteristics	Effect on Dust
Trade Winds	0°–30° N/S	Steady easterly winds; dry and strong	Lift dust from deserts like Sahara
Westerlies	30°–60° N/S	Move from subtropics to poles; moderate humidity	Can carry dust over oceans and continents
Polar Easterlies	60°–90° N/S	Cold, dry, and weak	Limited dust activity due to ice and snow cover
Inter-Tropical Convergence Zone (ITCZ)	Around Equator	Humid, rising air, lots of rainfall	Suppresses dust due to precipitation and vegetation

Table 3: Major Dust-Generating Regions Globally

Region	Location	Cause	Effect
Sahara Desert	North Africa	Subtropical high pressure, intense heating	World's largest source of atmospheric dust
Thar Desert	India-Pakistan border	Arid conditions, dry monsoon winds	Seasonal dust storms affecting North India
Gobi Desert	China–Mongolia	Cold desert, strong spring winds	Dust storms affecting East Asia
Middle East	Arabian Peninsula	Bare landscapes, intense dry heat	Transports dust over Persian Gulf

Table 4: Relationship Between Climate, Vegetation, and Dust

Climate Type	Vegetation Cover	Dust Emission Potential	Examples
Arid/Subtropical Desert	Sparse	High	Sahara, Thar
Tropical Humid (Equatorial)	Dense	Very Low	Amazon, Congo Basin
Polar	None/Ice cover	Very Low	Antarctica, Arctic
Temperate Continental	Moderate	Moderate	US Midwest, Central Asia

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