Question map
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?
Explanation
The correct answer is option C because Statement I is correct but Statement II is incorrect.
Statement I is correct: The higher concentration of dust particles is found in subtropical and temperate regions due to dry winds in comparison to equatorial and polar regions.[1] This is well-established in geographical literature.
However, Statement II is incorrect because it claims that subtropical and temperate areas have **less** dry winds, which is the opposite of reality. The actual reason for higher dust concentration in subtropical and temperate regions is the presence of dry winds[1], not their absence. Subtropical regions around 30° N and 30° S are characterized by high-pressure areas known as subtropical highs[2], which are associated with dry, descending air masses that promote arid conditions and dry winds.
Since Statement II incorrectly attributes less dry winds to these regions when they actually experience more dry winds, it cannot explain Statement I. Therefore, while Statement I is factually correct, Statement II is factually incorrect, making option C the correct choice.
Sources- [1] FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 7: Composition and Structure of Atmosphere > Dust Particles > p. 65
- [2] FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 9: Atmospheric Circulation and Weather Systems > World Distribution of Sea Level Pressure > p. 77
PROVENANCE & STUDY PATTERN
Full viewThis is a 'Line-by-Line' lift from NCERT Class XI Fundamentals of Physical Geography, Chapter 7. It proves that UPSC still rewards deep reading of basic texts over complex current affairs materials. If you skipped the 'Dust Particles' paragraph thinking it was trivial, you lost 2 marks.
This question can be broken into the following sub-statements. Tap a statement sentence to jump into its detailed analysis.
- Statement 1: Are atmospheric dust particle concentrations higher in subtropical and temperate regions than in equatorial and polar regions?
- Statement 2: Are dry winds less frequent in subtropical and temperate regions compared to equatorial and polar regions?
- Statement 3: Can a lower frequency of dry winds in subtropical and temperate regions explain higher concentrations of atmospheric dust particles there?
- Directly states that higher concentration of dust particles is found in subtropical and temperate regions
- Specifically contrasts these regions with equatorial and polar regions
- Attributes the pattern to dry winds, providing a causal link
- Explains subsidence of dry air around 30° N and S that produces high-pressure, dry conditions
- Provides a dynamical mechanism (air subsiding from equator) that favors dry winds able to carry dust
- Identifies the latitudinal pressure belts: equatorial low, subtropical highs, and polar highs
- Supports the latitudinal contrast in atmospheric conditions (dry subtropics vs. moist equator/polar zones)
States that higher concentrations of dust particles occur in subtropical and temperate regions due to dry winds compared to equatorial and polar regions (implies dry winds are relatively common there).
A student could combine this with maps of dust sources and prevailing wind belts to infer where dry winds are more frequent.
Explains that air losing moisture in the upper troposphere subsides at ~30° N/S, producing high-pressure belts (subtropics) from dry, cold air — a mechanism creating dry conditions in subtropics.
Use latitude positions of the subtropical highs (~30°) on a world map to judge where dry subsiding winds should be frequent.
Describes Polar Easterlies as dry, cold prevailing winds from polar high-pressure areas — indicating polar regions produce dry winds.
Combine with the geographic extent of polar highs to assess relative frequency of dry winds near the poles versus other latitudes.
Notes subtropical areas tend to have less cloud cover than equatorial areas — a pattern consistent with drier conditions/winds in subtropics vs equator.
Compare global cloud-cover or precipitation patterns by latitude to infer relative frequency of dry winds across equatorial, subtropical and temperate zones.
Classifies warm temperate climates including types that are 'dry in winter' (e.g., Mediterranean), showing that some temperate regions have seasonal dry conditions.
Map the distribution of these temperate climate types to assess where dry winds or dry seasons are likely within temperate zones.
- Directly states that higher dust concentrations occur in subtropical and temperate regions due to dry winds.
- Compares these regions to equatorial and polar regions, attributing the difference to dry winds.
- Explicitly links higher concentrations of dust particles in subtropical and temperate regions to dry winds.
- Repeats the contrast with equatorial and polar regions, reinforcing the causal claim.
- States that dust particles are in higher concentration in temperate and subtropical regions due to dry winds.
- Frames the explanation as a contrast with polar and equatorial regions, indicating dry winds as the cause.
States that higher concentrations of dust particles are found in subtropical and temperate regions and links this to dry winds (gives a direct pattern connecting region, dust concentration, and dry winds).
A student could map subtropical/temperate belts and compare known dry-wind occurrences there (or their absence) to see whether wind frequency aligns with the claimed dust concentrations.
Explains atmospheric circulation: subsidence at ~30° N/S produces dry, cold air and subtropical high-pressure belts (mechanism producing persistent dry conditions in subtropics).
Combine this with a world map of subtropical highs to infer where dry-subsiding winds are frequent and therefore where they could mobilize or maintain dust.
Gives an example where trade winds transport dry, dust-laden air (Sahara to Guinea), showing that wind frequency/direction can carry and maintain high dust concentrations regionally.
A student could identify other source regions (deserts) upwind of subtropical/temperate areas to judge whether reduced/increased dry-wind frequency would affect observed dust loads.
Describes deflation (wind lifting and carrying dry dust) as a principal process for producing airborne dust — links wind action to dust availability.
Use basic knowledge of surface dryness and windiness in subtropical/temperate areas to estimate how changes in dry-wind frequency would alter deflation rates and hence dust concentration.
Provides a concrete regional example (the 'Loo' and associated dust storms) where dry hot winds generate dust storms — an operational example of wind-driven dust events.
Compare frequency of such local dry-wind events across subtropical/temperate zones to assess whether fewer events plausibly explain higher or lower dust concentrations.
- [THE VERDICT]: Sitter. Direct copy-paste from NCERT Class XI (Fundamentals of Physical Geography), Chapter 7, Page 65.
- [THE CONCEPTUAL TRIGGER]: Composition of Atmosphere > Dust Particles & Hygroscopic Nuclei.
- [THE HORIZONTAL EXPANSION]: 1. Dust sources: Sea salts, fine soil, smoke-soot, ash, pollen, meteor debris. 2. Function: Act as hygroscopic nuclei for cloud formation. 3. Vertical distribution: Concentrated in lower layers but convection transports them high. 4. Water Vapour: Decreases from equator to poles; absorbs insolation (greenhouse effect).
- [THE STRATEGIC METACOGNITION]: Do not just read facts; map them to climate zones. Ask 'Why?' for every distribution. Why less dust at Equator? -> Heavy rain washes it out (scavenging). Why less at Poles? -> Ice cover prevents deflation. Why more in Subtropics? -> Deserts + Dry Trade Winds.
Subsidence at subtropical highs creates persistent dry winds that increase dust concentrations in subtropical and temperate latitudes.
High-yield for climate and physical geography questions: explains regional aridity, dust transport and links to monsoon variability; connects atmospheric circulation (pressure belts) to surface weather and hazards. Mastery helps answer questions on dust sources, aridity belts, and large-scale wind-driven processes.
- Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 23: Pressure Systems and Wind System > Formation > p. 312
- FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 9: Atmospheric Circulation and Weather Systems > World Distribution of Sea Level Pressure > p. 77
- FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 7: Composition and Structure of Atmosphere > Dust Particles > p. 65
Atmospheric dust particles act as condensation nuclei, influencing cloud formation and rainfall distribution where dust concentrations vary regionally.
Important for questions bridging atmospheric physics and hydrology: explains how aerosols affect precipitation patterns, urban vs rural rainfall differences, and interactions between pollution/dust and monsoons. Useful for case-based questions on rainfall anomalies and human impacts on climate.
- FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 7: Composition and Structure of Atmosphere > Dust Particles > p. 65
- Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 20: Earths Atmosphere > A high concentration of condensation nuclei disrupts regional patterns of Indian monsoons > p. 274
Subsidence of air from the equator and upper troposphere produces high-pressure belts near 30° N/S, creating dry conditions in subtropical regions.
High-yield for explaining the global distribution of deserts and subtropical climates; links Hadley cell dynamics, pressure belts, and regional rainfall patterns. Mastery helps answer questions on climate zones, pressure systems, and causes of aridity.
- Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 23: Pressure Systems and Wind System > Formation > p. 312
Polar easterlies originate from polar high-pressure areas and are characteristically cold and dry.
Important for understanding polar climate regimes, interactions at the polar front, and the origin of dry, cold air masses that affect temperate latitudes. Useful in questions on wind systems and frontal cyclones.
- Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 23: Pressure Systems and Wind System > The Polar Easterlies > p. 320
Higher dust concentrations are found in subtropical and temperate regions because dry winds are relatively frequent there compared with equatorial and polar regions.
Helps connect atmospheric particulates to regional climate and cloud formation processes; useful for questions on aerosols, precipitation nuclei, and comparative climate dryness across latitudes.
- FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 7: Composition and Structure of Atmosphere > Dust Particles > p. 65
Dry winds lift, carry and deposit soil and dust particles, producing elevated atmospheric dust concentrations in regions exposed to such winds.
High-yield: explains spatial distribution of atmospheric dust and links surface processes (aeolian erosion) to atmospheric composition and air quality. Connects to desertification, dust storms and regional climate impacts; useful for questions on causes and effects of dust aerosols.
- FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 7: Composition and Structure of Atmosphere > Dust Particles > p. 65
- Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 17: Major Landforms and Cycle of Erosion > Wind Eroded Arid Landforms > p. 235
- Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 30: Climatic Regions > Winds > p. 437
Large-scale subsidence of air around ~30° N/S produces high-pressure dry belts that promote dry wind conditions favourable for dust lifting and transport.
Important for understanding global circulation and why subtropical/temperate zones are drier than equatorial regions; links to location of deserts, pressure systems and prevailing wind patterns — frequent UPSC angles in physical geography and climate questions.
- Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 23: Pressure Systems and Wind System > Formation > p. 312
- Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 30: Climatic Regions > Winds > p. 437
- Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 28: Temperate Cyclones > Polar Front Theory > p. 406
Water Vapour Distribution: From the same chapter, remember that water vapour decreases from the equator towards the poles and accounts for less than 4% of the air by volume in warm and wet tropics, but less than 1% in dry/cold areas.
Use 'Causal Consistency'. Statement I claims Subtropics have *more* dust. Dust requires dryness and wind to stay airborne. Statement II claims Subtropics have *less* dry winds. If II were true (less dry wind), then I would likely be false (less dust). Since they contradict the physical mechanism of dust generation, they cannot both be true. This forces you to realize Statement II is factually incorrect.
Mains GS-3 (Environment): Link 'Atmospheric Dust' to the 'Asian Brown Cloud' phenomenon or the 'Albedo Effect' of dust on glaciers. Also, the UN Convention to Combat Desertification (UNCCD) specifically deals with Sand and Dust Storms (SDS) as a hazard.