NEW DELHI (Wednesday, March 11, 2026) — A new analysis released by Climate Trends has identified Delhi as the most polluted city in India for the 2024-25 period. The study, titled “Meteorology-Driven Persistence of PM2.5 Pollution in Indian Cities,” utilized data from the Central Pollution Control Board (CPCB) to examine air quality across six major metros: Delhi, Patna, Mumbai, Chennai, Bengaluru, and Kolkata.
The Rankings: North India vs. South India
The report highlights a stark contrast in air quality across the country, with cities in the Indo-Gangetic Plain (IGP) continuing to face a severe crisis.
- Delhi (1st): Recorded the highest annual average PM2.5 levels and the longest stretches of “severe” or “emergency” air days. During the winter of 2024-25, Delhi did not record a single “clean air” day.
- Patna (2nd): Confirmed as the second-most polluted city, driven by strong atmospheric stagnation in the eastern Indo-Gangetic Plain.
- Bengaluru (Most Resilient): Stood out for maintaining the lowest and most stable air quality, demonstrating what researchers call “structural air-quality resilience.”
- Southern Deterioration: Despite their coastal location, both Mumbai and Chennai recorded an increase in annual average pollution levels in 2025, signaling that air quality concerns are becoming a year-round issue rather than just seasonal.
The “Weather Factor”: Why Emissions Aren’t the Only Culprit
The study introduces a critical perspective: meteorological conditions can shift PM2.5 levels by as much as 40%, even if actual emissions remain unchanged.
| Factor | Impact on Pollution Severity |
| Atmospheric Stagnation | Characterized by low wind speeds (<1 m/s) and high humidity, which trap pollutants near the ground. |
| Ventilation Efficiency | This is the “dominant determinant” of city-to-city variability. Poor ventilation makes cities like Delhi and Patna “structurally prone” to high pollution. |
| Hygroscopic Growth | High relative humidity across northern cities causes fine particles to absorb moisture and grow, worsening exposure levels. |
Proposed Reforms for NCAP Phase-III
Aarti Khosla, Founder and Director of Climate Trends, and Sagnik Dey, Head of the Centre for Atmospheric Sciences at IIT Delhi, have called for significant reforms in the National Clean Air Programme (NCAP) as it enters its next phase:
- Meteorology-Adjusted Metrics: Current evaluations primarily look at concentration changes. The report argues for metrics that account for weather-driven variability to better assess policy effectiveness.
- Separate Winter Targets: Since over 70% of winter days in northern India fall under low-wind regimes, the report suggests specific, aggressive targets for the winter months.
- Airshed-Based Planning: Moving beyond city-specific actions to manage pollution at a regional level (airshed level).
- Weather-Triggered Actions: Developing dynamic action plans that are automatically triggered by specific meteorological forecasts (e.g., predicted stagnation episodes).
Sources
- Climate Trends: “Meteorology-Driven Persistence of PM2.5 Pollution in Indian Cities: Implications for NCAP Phase-III” (March 11, 2026).
- Press Trust of India (PTI): “Delhi was most polluted city during 2024-25 followed by Patna: Study” (March 11, 2026).
- Livemint: “Bengaluru most resilient to air pollution among big Indian cities in 2024-25; Delhi and Patna worst hit” (March 11, 2026).
- The Times of India: “Weather alone can influence air pollution in cities like Delhi, Patna by up to 40%: Study” (March 12, 2026).
- Hindustan Times: “Delhi Tops the Pollution Index: A Deep Dive into India’s Air Quality Crisis” (March 11, 2026).
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