HOW LOCAL TOPOGRAPHY CONTRIBUTES TO AIR POLLUTION

Introduction

• Air pollution has emerged as a critical environmental and public health challenge globally, with South Asia being one of the most affected regions.

• India’s capital, Delhi, frequently experiences hazardous air quality, particularly during winters, with PM2.5 levels far exceeding WHO limits.

• While vehicular emissions, industrial activity, stubble burning, and festivals contribute significantly, local topography plays a crucial role in exacerbating air pollution.

Air Pollution in Delhi: An Overview

• PM2.5 concentration in Delhi reached 168 µg/m³ on November 3, 2025, well above the WHO limit of 15 µg/m³.

• Primary contributors:

  • Vehicular emissions

  • Industrial pollution

  • Stubble burning in neighboring states

  • Coal and biomass burning

• Seasonal factors:

  • Post-monsoon low moisture levels

  • Decreasing temperatures

  • Slow wind speeds

• Health and socio-economic impact:

  • Respiratory diseases (asthma, COPD)

  • Cardiovascular disorders

  • Reduced cognitive development in children

  • Economic loss: USD 339.4 billion, 9.5% of India’s GDP

Local Topography and Air Pollution

Geographical Features of Delhi

• Delhi lies in a bowl-shaped area within the Indo-Gangetic Plains (IGP).

• Bounded by:

  • Himalayas to the north

  • Aravalli hills to the southwest

  • Malwa and Deccan plateaus to the south

Mechanisms Through Which Topography Influences Air Quality

• Pollutant trapping:

  • Himalayas prevent northward dispersal of polluted winter air.

  • Pollutants remain confined and travel eastward across northern plains.

• Reduced mixing height:

  • Post-monsoon low temperatures and slow winds trap pollutants near the ground.

• Temperature inversion:

  • Warm air layer sits above cold air, trapping pollutants and fog, forming smog (Turbidity Island Effect).

• Seasonal amplification:

  • Agricultural stubble burning and Diwali firecrackers worsen pollution.

Regional and Transboundary Dimensions

• Air pollution is transboundary, traveling across borders and states.

• Six airsheds identified by the World Bank in India:

  1. West/Central IGP: Punjab (India & Pakistan), Haryana, Rajasthan, Delhi, UP

  2. Central/Eastern IGP: Bihar, West Bengal, Jharkhand, Bangladesh

  3. Middle India 1: Odisha, Chhattisgarh

  4. Middle India 2: Eastern Gujarat, Western Maharashtra

  5. Northern/Central Indus River Plain: Pakistan, Afghanistan

  6. Southern Indus Plain & west: Southern Pakistan, western Afghanistan, eastern Iran

• Winds during winter carry pollutants across states and international borders.

• Highlights the need for regional cooperation to manage air quality.

Policy and Technological Interventions

• Graded Response Action Plan (GRAP): Implements interventions based on AQI levels.

• National Clean Air Programme (NCAP): Aims to improve air quality in 131 cities via monitoring, sectoral emission reduction, and public awareness.

• Other measures:

  • Anti-smog guns and towers (limited effectiveness)

  • Cloud seeding (high cost, limited area)

  • Vehicle scrappage policies for old petrol/diesel vehicles

• Challenges: Short-term, reactive measures are insufficient; long-term preventive strategies are needed.

Way Forward: Preventive Strategies

• Shift from reactive to preventive approaches:

  • Investment in clean public transport, cycling, and pedestrian infrastructure

  • Sustainable agricultural practices to reduce stubble burning

  • Renewable energy adoption and stricter emission norms

  • Coordinated regional policies for air quality management

• Addressing air pollution is vital for:

  • Public health

  • Economic productivity

  • Sustainable development and quality of life

Conclusion

• Local topography significantly influences air pollution by trapping pollutants and facilitating smog formation.

• Delhi’s unique bowl-shaped geography, combined with meteorological and seasonal factors, intensifies air quality issues.

• A comprehensive, preventive, and regionally coordinated strategy is critical to mitigate air pollution and its socio-economic and health impacts.

MAINS QUESTIONS

• Discuss how Delhi’s local topography and meteorological conditions exacerbate air pollution, citing relevant examples.

• Examine the significance of the six airsheds identified by the World Bank in India in managing transboundary air pollution.

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