Background and Context
Summer has traditionally been considered cleaner than winter for air quality in India. However, 2026 witnessed a paradigm shift as multiple Indian cities experienced significant pollution episodes even during warmer months. The Commission for Air Quality Management (CAQM) reimposed Stage-I restrictions under the Graded Response Action Plan (GRAP) in Delhi during May 2026, marking a critical turning point in addressing seasonal air pollution patterns.
Key Causes of Summer Air Pollution
1. Regional Dust Storms (The Loo)
- Intense solar heating creates a vast low-pressure zone stretching towards Iran and West Asia
- Interaction between low-pressure and high-pressure systems generates strong, dry, scorching winds called Loo
- These winds pick up massive quantities of desert dust from the Thar Desert and Arabian Peninsula
- Dust is transported thousands of kilometres across the Indo-Gangetic plains
- Impact: Drastic spikes in PM10 levels for days at a time
2. Localized Thunderstorms (Andhi)
- High convective heat causes sudden, short-lived local dust storms called Andhi
- Downward-moving cold air associated with summer thunderstorms hits dry, moisture-depleted ground
- Violently lifts loose topsoil and sweeps it through urban areas
- While loo dominates North India, coastal and southern cities like Mumbai and Hyderabad face frequent summer dust spikes
3. Ground-Level Ozone (O₃) Formation
- Secondary pollutant formed when Nitrogen Oxides (NOx) react with Volatile Organic Compounds (VOCs)
- NOx sources: Vehicles, industrial processes
- VOC sources: Industries, paints, solvents, fuel emissions
- Heat Catalyst: Intense summer sunlight and heatwaves act as thermal incubator
- As temperatures cross extreme thresholds, ozone levels spike dangerously during peak daylight hours
4. Urban Heat Island (UHI) Effect
- Unchecked expansion of concrete surfaces
- Loss of green cover and shrinking of urban wetlands
- Traps solar radiation within cities
- Localized heating exacerbates temperature spikes
- Accelerates atmospheric chemical reactions forming smog and ground-level ozone
5. Resumption of Construction Activities
- Emergency restrictions during winter (GRAP) are typically rolled back in spring
- Heavy construction, infrastructure building, and demolition projects aggressively resume
- Without strict site-level controls (water sprinkling, wind barriers, dust sheets)
- Impact: Massive release of coarse debris into dry air
6. Year-Round Anthropogenic Emissions
- Continuous vehicular exhaust
- Industrial chimneys
- Illegal burning of municipal solid waste
- Burning of dry leaves in urban peripheries
- Provides steady stream of particulate matter and precursor gases
Summer vs Winter Pollution: Key Differences
| Feature | Summer Pollution | Winter Pollution |
|---|---|---|
| Primary Pollutants | Coarse PM10 and Ground-level Ozone | Fine PM2.5 and dense smog |
| Meteorological Drivers | Heatwaves, intense sunlight, dust storms, high-velocity winds | Temperature inversion, stagnant cold air, low wind speeds, fog |
| Major Sources | Wind-blown dust, construction activities, road dust, vehicular emissions with sunlight | Stubble burning, biomass burning, industrial emissions, trapped smoke |
| Formation Mechanism | Dust resuspension and photochemical ozone formation under sunlight | Accumulation due to poor dispersion and atmospheric trapping |
| Peak Severity Time | Mid-day and hot afternoons | Early mornings and late nights |
| Key Seasonal Factor | Heat and sunlight-driven atmospheric chemistry | Cold weather and stagnant conditions |
Policy Framework and Solutions
Graded Response Action Plan (GRAP)
- Multi-stage emergency response mechanism
- Commission for Air Quality Management (CAQM) implements and monitors measures in NCR
- Stages: Stage-I to Stage-IV based on air quality indices
City-Level Interventions
- Dedicated Summer Action Plans
- 14-point and 8-point Summer Action Plans
- Real-time tracking of industrial chimney emissions
- Anti-open-burning patrols
- Strict enforcement of chemical guidelines for commercial paints and solvents
- Reduce ambient VOC leakages
- Early Warning Systems
- Air Quality Early Warning System (AQEWS) - Delhi
- Extended to cities like Mumbai and Jaipur
- Provides multi-pollutant and weather forecasts days in advance
- Enables timely public health advisories
- Active Construction Monitoring
- Stringent dust management protocols year-round
- Brihanmumbai Municipal Corporation (BMC) Air Quality Decision Support System (AQDSS)
- Tracked over 1,000 non-compliant sites since October 2025
- Targeting Ozone Precursors
- Cut NOx emissions through cleaner transport
- Stricter industrial controls
- Reduced vehicle idling
- Control VOC emissions
Constitutional and Legal Framework
- Air (Prevention and Control of Pollution) Act, 1981: Establishes framework for air pollution control
- Environment Protection Act, 1986: Enables central government to take measures
- National Green Tribunal (NGT): Provides environmental justice and reduces litigation burden
- Commission for Air Quality Management (CAQM): Constituted under Act for NCR and adjoining areas
Key Differences: NGT vs CPCB
| Aspect | NGT | CPCB |
|---|---|---|
| Establishment | By an Act of Parliament | By executive order of Government |
| Function | Provides environmental justice | Promotes cleanliness of streams and wells, improves air quality |
UPSC PYQ References
Prelims 2025: Artificial way of causing rainfall to reduce air pollution uses silver iodide and potassium iodide
Prelims 2018: Statement about NGT establishment by Act vs CPCB by executive order - correct answer was statement 2 only
Mains 2021: Global Air Quality Guidelines (AQGs) by WHO and India's National Clean Air Programme alignment