POLLUTION AND SUMMER
1. Context
In March, the Commission for Air Quality Management in the National Capital Region and Adjoining Areas (CAQM) revoked all curbs under the Graded Response Action Plan (GRAP), signalling the end of the winter air pollution in Delhi.A month later, as temperatures rose, it reimposed Stage 1 of the GRAP to combat summer air pollution. It was briefly revoked and reimposed again in May, while North India was reeling under heatwaves.
2. Why Are Urban Areas Experiencing Pollution Episodes During Summer?
- Cities such as Delhi and those across the Indo-Gangetic Plain are typically associated with severe winter smog. During winter, low temperatures, weak winds, and the region’s basin-like geography prevent pollutants from dispersing, causing them to accumulate near the surface.
- In contrast, summer conditions generally support better air quality. Stronger winds, intermittent thunderstorms that help remove pollutants, and higher temperatures promote vertical mixing of air, allowing pollutants to disperse more effectively.
- Nevertheless, Delhi recorded significant pollution levels during the summer of 2026. Between April 1 and May 31, daily average PM10 concentrations exceeded the 24-hour National Ambient Air Quality Standard (NAAQS) of 100 µg/m³ on 54 days.
- Furthermore, at least one Continuous Ambient Air Quality Monitoring Station (CAAQMS) reported hourly ozone concentrations above the prescribed limit of 180 µg/m³ on 40 days.
- This trend is not confined to Delhi alone. Several major Indian cities—including Mumbai, Chennai, Hyderabad, Bengaluru, and Kolkata—also experienced episodes of elevated PM10 and ozone concentrations during the same period.
- The intensity and frequency of these pollution events varied depending on local factors such as vehicular emissions, road dust, construction activities, industrial discharges, and dust storms.
- Mumbai, for example, has witnessed persistently high PM10 and ozone levels in recent years, largely driven by rapid construction, traffic congestion, and dust generation.
- Although Chennai experiences fewer PM10 exceedances, its dense traffic and high summer temperatures contribute to frequent ozone formation, making it particularly vulnerable to ozone pollution.
3. How Does Summer Air Pollution Differ from Winter Air Pollution?
- The nature and causes of air pollution vary significantly between summer and winter.
- During winter, pollution levels tend to rise because of unfavorable meteorological conditions.
- Low temperatures, weak wind speeds, temperature inversions, and reduced atmospheric mixing trap pollutants close to the ground. As a result, particulate matter (PM2.5 and PM10) accumulates, leading to dense smog episodes, especially in cities across the Indo-Gangetic Plain.
- In contrast, summer generally provides conditions that help disperse pollutants. Stronger winds, greater atmospheric mixing, and occasional rainfall facilitate the dilution and removal of particulate matter.
- However, summer brings a different challenge—ground-level ozone pollution. Intense sunlight and high temperatures trigger chemical reactions between nitrogen oxides (NOx) and volatile organic compounds (VOCs), producing ozone.
- Consequently, while particulate pollution may decline compared to winter, ozone concentrations often increase during hot and sunny periods.
- Another key distinction lies in pollution sources. Winter pollution is often aggravated by biomass burning, domestic heating, and stagnant weather conditions.
- Summer pollution, on the other hand, is more strongly influenced by vehicular emissions, industrial activities, road and construction dust, and photochemical reactions driven by solar radiation.
- Therefore, winter air pollution is primarily characterized by the accumulation of particulate matter due to stagnant atmospheric conditions, whereas summer air pollution is marked by enhanced ozone formation and episodic increases in particulate matter from dust, traffic, and local emission sources
4. How Does Summer Pollution Differ from Winter Pollution?
- Winter air pollution is largely characterized by high concentrations of fine particulate matter (PM2.5), whereas summer pollution is more strongly influenced by coarser PM10 particles and elevated ozone levels.
- Several pollution sources—including vehicular emissions, industrial activities, waste burning, agricultural residue burning, construction operations, and deteriorating road surfaces—contribute to poor air quality throughout the year. Seasonal factors, however, alter the dominant pollutants.
- During winter, additional emissions from biomass used for heating worsen particulate pollution. In summer, dust storms often raise PM10 concentrations, while intense heat and abundant sunlight promote the formation of ground-level ozone.
- Unlike particulate matter, ozone is a secondary pollutant and is not released directly into the atmosphere. It is produced through chemical reactions involving nitrogen oxides (NOx), primarily emitted by vehicles, and volatile organic compounds (VOCs) originating from industrial processes, vehicle exhaust, paints, solvents, and other sources.
- These reactions accelerate under strong sunlight and high temperatures, making hot summer days particularly conducive to ozone generation.
- Elevated levels of both ozone and particulate matter can adversely affect respiratory health and increase the risk of various air-related illnesses
5. What Leads to Elevated PM10 Levels in India?
- During summer, intense heating over the Indian subcontinent creates a vast low-pressure zone that often stretches westward toward Iran. The interaction between this low-pressure system and nearby high-pressure regions generates strong, hot winds.
- These winds can trigger large-scale dust storms and transport dust from the Thar Desert and parts of West Asia across northern and central India, sometimes reaching as far as the Bay of Bengal.
- Such events can cause PM10 concentrations to remain elevated for several days, similar to the widespread dust storms that affected northern India in 2018.
- Apart from these large regional events, India also experiences smaller and short-lived dust storms known as andhi. These storms are usually associated with thunderstorms.
- When powerful downdrafts from thunderstorms strike the ground, they lift loose soil and dust into the atmosphere, creating fast-moving dust clouds that generally dissipate within a few hours.
- While northern India frequently experiences dust transport associated with hot summer winds, cities such as Mumbai and Hyderabad are more likely to encounter dust episodes linked to localized thunderstorm activity.
- Human-induced factors further intensify PM10 pollution. Construction and demolition activities often increase after seasonal restrictions under the Graded Response Action Plan (GRAP) are relaxed following winter.
- Inadequate dust-control measures at construction sites allow significant amounts of particulate matter to enter the atmosphere.
- Additionally, the movement of vehicles over damaged or unpaved roads resuspends accumulated dust, especially during the dry summer season, further contributing to higher PM10 concentrations
6. Managing Summer Air Pollution: The Way Forward
- Although natural dust sources cannot be eliminated, their occurrence can be anticipated through effective forecasting systems. Following the severe dust storms of 2018 and recurring smog crises in earlier years, Delhi established the Air Quality Early Warning System (AQEWS), which now operates throughout the year.
- The system has subsequently been expanded to cities such as Jaipur and Mumbai, enabling authorities to forecast various air pollutants several days in advance.
- In addition to providing detailed meteorological updates for Delhi, AQEWS also issues three-day Air Quality Index (AQI) forecasts for nearly 140 cities across India.
- Similarly, the India Meteorological Department (IMD) releases weather forecasts multiple times daily at the national level.
- These forecasting tools should be leveraged by local administrations to disseminate timely warnings regarding dust storms, ozone episodes, and deteriorating air quality, allowing residents to take precautionary measures and limit their exposure.
- While natural sources require preparedness, pollution from human activities can be addressed through stricter enforcement and management practices. Dust-control measures at construction and demolition sites should remain in force throughout the year rather than being limited to the winter season.
- Research conducted by the Council on Energy, Environment and Water (CEEW) indicates that reducing the movement of heavy vehicles within construction zones can significantly decrease local particulate pollution.
- In Mumbai, the Brihanmumbai Municipal Corporation (BMC), in collaboration with CEEW, has implemented the Air Quality Decision Support System (AQDSS) to monitor construction-related emissions. Since October 2025, the system has assisted authorities in taking corrective action at more than 1,000 construction sites across the city.
- Addressing ozone pollution requires targeted reductions in emissions of nitrogen oxides (NOx) and volatile organic compounds (VOCs), which originate primarily from vehicles, industries, solvents, paints, and fuel combustion.
- This can be achieved through cleaner transportation systems, stricter emission standards, and improved regulatory compliance.
- Public participation can also make a difference. Initiatives such as Delhi’s “Red Light On, Gaadi Off” campaign, which encourages motorists to switch off their engines while waiting at traffic signals, help reduce unnecessary emissions that contribute to ozone formation.
- However, isolated interventions are insufficient. Indian cities require comprehensive and long-term summer air-quality management strategies. Delhi has implemented a dedicated Summer Action Plan since 2022, demonstrating a proactive approach.
- Similar frameworks should be adopted by other urban centres, integrating pollution forecasting, health advisories, construction and road-dust mitigation, and measures to curb ozone-forming emissions.
- Although summer weather often facilitates the dispersion of some pollutants, elevated temperatures and intense sunlight create conditions that favour the formation of others, particularly ozone.
- Therefore, urban air-quality management must address both winter and summer pollution challenges with equal urgency and sustained policy attention
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For Prelims: Commission for Air Quality Management (CAQM), Graded Response Action Plan (GRAP), PM10
For Mains: GSIII - Environment and Ecology
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Previous Year Questions
1.In the cities of our country, which among the following atmospheric gases are normally considered in calculating the value of the Air Quality Index? (2016)
Select the correct answer using the code given below: (a) 1, 2 and 3 only (b) 2, 3 and 4 only (c) 1, 4 and 5 only (d) 1, 2, 3, 4 and 5 Answer (b) |
Source: The Hindu
