Why do cities get polluted in summer

Why in the News?

Summer air pollution has emerged as a major concern after the Commission for Air Quality Management (CAQM) revoked all restrictions under the Graded Response Action Plan (GRAP) in March 2026. This marked the end of the winter pollution season in Delhi-NCR. However, persistent pollution episodes during April-May, including 54 days of PM10 exceedances in Delhi, forced authorities to reimpose GRAP Stage-I measures. This highlights that air pollution is no longer a winter-only problem and requires year-round management.

How does summer air pollution differ from winter pollution?

Winter pollution is dominated by PM2.5 accumulation

1. Temperature Inversion: Traps pollutants near the surface.
2. Low Wind Speeds: Restrict pollutant dispersion.
3. Basin-like Topography: Especially in Delhi and the Indo-Gangetic Plain, facilitates pollutant accumulation.
4. Biomass Burning: Adds substantial PM2.5 load during winter months.

Summer pollution is dominated by PM10 and ozone

1. Coarse Particulate Matter (PM10): Generated from dust storms, road dust, construction activity, and resuspended dust.
2. Ground-Level Ozone: Formed through photochemical reactions under strong sunlight and high temperatures.
3. Stronger Winds: Enhance pollutant dispersion but simultaneously transport dust across regions.
4. Thunderstorms: Can temporarily improve air quality through atmospheric cleansing.

Why are Indian cities witnessing pollution episodes during summer

Meteorological conditions differ from winter but remain conducive to pollution

1. Higher Temperatures: Accelerate atmospheric chemical reactions.
2. Intense Solar Radiation: Enhances ozone formation.
3. Dust Transport: Winds carry dust over long distances.
4. Regional Variability: Different cities experience different dominant pollutants.

Evidence from major cities

1. Delhi: Recorded 54 days exceeding PM10 standards during April–May 2026.
2. Mumbai: Experienced elevated PM10 and ozone levels due to construction activity, dust, and traffic.
3. Hyderabad: Reported pollution spikes despite relatively better ventilation conditions.
4. Kolkata and Chennai: Recorded ozone and PM10 exceedances on multiple days.
5. Bengaluru: Witnessed increasing summer ozone episodes.

What causes PM10 spikes during summer months?

Dust storms emerge as the primary driver

1. West Asian Dust Transport: Dust originating from subcontinent-adjacent arid regions interacts with local weather systems.
2. Dust Intrusion: Dust can travel from arid landscapes toward northern India during strong wind events.
3. Atmospheric Instability: Supports long-range transport of coarse particles.

Local dust generation worsens pollution

1. Construction Activities: Release large quantities of coarse dust particles.
2. Demolition Work: Contributes significantly to suspended particulate matter.
3. Road Dust Resuspension: Moving vehicles continuously lift deposited dust.
4. Urban Expansion: Increases exposed surfaces vulnerable to wind erosion.

Data from Delhi

1. PM10 Exceedance Days (April-May 2026): 54 days exceeded 24-hour NAAQS limits.
2. Hourly Exceedances: At least one CAAQMS crossed 180 μg/m³ on 40 days.

Why does ozone pollution increase during hot weather?

1. Ozone is a secondary pollutant
   1. No Direct Emission: Ground-level ozone is not emitted directly.
   2. Photochemical Formation: Forms through reactions involving precursor pollutants. Major precursors
      1. Nitrogen Oxides (NOx): Emitted from vehicles and industries.
      2. Volatile Organic Compounds (VOCs): Released from fuels, solvents, paints, industrial processes, and vehicle exhaust.
2. Meteorological triggers
   1. High Temperature: Accelerates reaction rates.
   2. Strong Sunlight: Provides energy required for ozone formation.
   3. Heatwaves: Create highly favorable conditions for ozone accumulation.
3. Public health implications
   1. Respiratory Disorders: Causes breathing difficulties.
   2. Lung Irritation: Damages respiratory tissues.
   3. Public Health Risk: Particularly affects children, elderly persons, and individuals with pre-existing respiratory illnesses.

How do dust storms affect air quality in India?

Dust storms have regional impacts

1. PM10 Surges: Produce sudden spikes in particulate pollution.
2. Cross-Border Influence: Dust can travel across large geographical areas.
3. Reduced Visibility: Impairs transportation and public safety.

Indian context

1. Northern India: Frequently affected due to proximity to desert regions.
2. Thunderstorm-Associated Dust Events: Strong downdrafts lift and transport loose soil particles.
3. Pre-Monsoon Season: Experiences maximum dust storm frequency.

How do human activities worsen summer air pollution?

1. Construction Activities: Generate large quantities of coarse particulate matter (PM10) through excavation, demolition, and material handling. Construction dust remains a major contributor to urban summer pollution.
2. Road Dust Resuspension: Heavy vehicular movement lifts deposited dust from roads, significantly increasing PM10 concentrations during dry summer conditions.
3. Vehicular Emissions: Release particulate matter, nitrogen oxides (NOx), and volatile organic compounds (VOCs). These contribute directly to particulate pollution and indirectly to ozone formation.
4. Industrial Emissions: Emit NOx, VOCs, and other pollutants that participate in photochemical reactions responsible for ground-level ozone formation.
5. Poor Dust Management: Inadequate covering of construction materials, unpaved surfaces, and weak enforcement of dust-control norms aggravate particulate pollution.

What forecasting mechanisms are available for managing summer pollution?

1. Air Quality Early Warning System (AQEWS)
   1. Origin: Developed following severe dust storm and smog events.
   2. Coverage Expansion: Extended from Delhi to cities such as Jaipur and Mumbai.
   3. Forecast Capability: Provides multi-day pollutant forecasts.
   4. Integrated Weather Information: Supports proactive response measures.
2. IMD Air Quality Bulletins
   1. Forecast Frequency: Released several times daily.
   2. Coverage: Delhi and approximately 140 Indian cities.
   3. Utility: Facilitates issuance of public advisories and exposure reduction measures.

What measures can cities adopt to combat summer air pollution?

1. Forecast-based interventions
   1. Early Warning Systems: Enable advance preparedness. Authorities can use IMD’s weather forecast bulletins to issue local alerts for dust storms, poor air quality and ozone to the citizens.
   2. Public Health Advisories: Reduce citizen exposure during high-pollution episodes.
2. Dust management measures
   1. Construction Site Monitoring: Ensures compliance with dust-control norms.
   2. Mechanical Road Sweeping: Reduces loose particulate matter.
   3. Dust Suppression Technologies: Minimize resuspension.
   4. Study by Council on Energy, Environment and Water found that simply reducing heavy-vehicle movement at construction sites can lower local PM levels.
   5. Example: The Brihanmumbai Municipal Corporation’s Air Quality Decision Support System (AQDSS) monitors construction sites and has helped authorities take action against more than 1,000 construction sites since October 2025, demonstrating the importance of strict dust-control compliance.
3. Vehicular emission reduction
   1. Cleaner Transport Systems: Reduce NOx emissions.
   2. Traffic Management: Limits idling emissions.
   3. Public Campaigns: Encourage behavioral change.
   4. Example: Delhi’s “Red Light On, Gaadi Off” Campaign: Encourages drivers to switch off engines at traffic signals to reduce emissions.

Key Dust-Control Norms in India

1. Covering of Construction Materials: Sand, soil, cement, and debris must be covered to prevent wind-blown dust.
2. Anti-Smog Guns and Water Sprinkling: Mandatory at large construction sites to suppress airborne dust.
3. Green Nets/Wind Barriers: Installed around sites to prevent dust dispersion into surrounding areas.
4. Covered Transportation: Trucks carrying C&D waste or raw materials must be covered with tarpaulin sheets.
5. Wheel-Washing Facilities: Vehicles exiting construction sites should pass through wheel-washing systems to prevent mud and dust deposition on roads.
6. Mechanical Road Sweeping: Regular cleaning of adjoining roads to remove accumulated dust.
7. Paved Internal Roads: Reduces dust generation from vehicle movement within sites.
8. Proper C&D Waste Management: Segregation, storage, recycling, and scientific disposal of construction waste.

CAQM’s Framework for Dust Mitigation in NCR

1. Mandatory dust management plans for large projects.
2. Real-time monitoring of construction activities.
3. Penalties and project shutdowns for repeated violations.
4. Use of remote sensing and inspection teams for enforcement. 

Why is a year-round strategy necessary?

1. Continuous Forecasting: Enables advance warnings for dust storms, ozone episodes, and deteriorating air quality through systems such as AQEWS and IMD forecasts.
2. Season-Specific Interventions: Requires winter measures for PM2.5 control, summer dust-management measures for PM10 reduction, and targeted NOx-VOC controls for ozone mitigation.
3. Public Health Protection: Reduces exposure through timely advisories during heatwaves, dust storms, and ozone episodes.
4. Institutional Preparedness: Ensures mechanisms such as GRAP, municipal action plans, and pollution monitoring systems remain operational throughout the year rather than only during winter.
5. Integrated Urban Air Quality Governance: Combines forecasting, construction dust regulation, road dust management, cleaner transport, and industrial emission controls into a continuous management framework.

Conclusion

The rise of summer pollution episodes demonstrates that India’s air quality challenge extends far beyond winter smog. Dust storms, PM10 pollution, and ground-level ozone have transformed summer into a critical pollution season. Effective air quality governance now requires year-round monitoring, forecasting, dust control, emission reduction, and public health preparedness across all major urban centres.

PYQ Relevance

[UPSC 2021] Describe the key points of the revised Global Air Quality Guidelines (AQGs) recently released by the World Health Organisation (WHO). How are these different from its last update in 2005? What changes in India’s National Clean Air Programme are required to achieve these revised standards?

Linkage: PYQ directly examines air quality management, pollution standards, monitoring mechanisms, and policy interventions for improving urban air quality. The article reinforces the need for continuous air quality management, forecasting systems, dust control measures, and strengthened NCAP implementation to meet national and global air quality standards.