Bengaluru most resilient to air pollution among India’s big cities in 2024-25; Delhi and Patna worst hit: Study

Delhi was the most polluted city during 2024-25, recording the highest annual PM2.5 levels and extended periods of "severe" air quality in winter, while Patna was the second-most polluted city, according to a new analysis by Climate Trends.

Climate Trends is a research-based consulting and capacity-building initiative that aims to bring greater focus to environmental issues, climate change, and sustainable development.

The findings in the report titled 'Meteorology-Driven Persistence of PM2.5 Pollution in Indian Cities: Implications for NCAP Phase-III' are based on Central Pollution Control Board (CPCB) air quality monitoring data of 2024–2025 across Delhi, Patna, Kolkata, Mumbai, Chennai and Bengaluru.

The study found that meteorological conditions can shift PM2.5 levels by up to 40 per cent even without any change in emissions. The study shows how weather patterns, such as low wind speeds, high humidity, and atmospheric stagnation, amplify pollution episodes.

Using CPCB air quality data (2024-2025) combined with meteorological clustering, the study distinguished emission-driven pollution from weather-driven variability.

“Delhi continues to face the most severe pollution crisis nationally with the highest annual average PM2.5 levels and the longest stretches of 'severe' or 'emergency' category air days, driven by local emissions and regional factors,” the report said.

Patna is confirmed as the second-most polluted city after Delhi, with persistently high PM2.5 concentrations driven by strong atmospheric stagnation, highlighting an intensifying crisis in the eastern Indo-Gangetic Plain," it added.

While historically less polluted, Bengaluru and Chennai showed signs of air quality deterioration during the winter months, a new vulnerability trend.

Both Mumbai and Chennai recorded increases in their annual average pollution levels in 2025, signalling a growing year-round concern beyond seasonal spikes.

Aarti Khosla, Founder and Director, Climate Trends, said the study shows that a 20–30% reduction in annual PM2.5 does not translate into winter air-quality compliance in stagnation-prone cities like Delhi and Patna, where over 70% of days fall under low-wind, high-humidity meteorological regimes.

The report proposed significant reform in the National Clean Air Programme (NCAP) Phase-III, including separate winter targets, meteorology-adjusted metrics, and dynamic weather-triggered action plans, alongside integrated airshed-based planning.

NCAP Phase-III must therefore adopt season-specific targets, meteorology-triggered interventions, and airshed-level management frameworks to achieve meaningful public-health gains.

Emerging Winter Deterioration in Southern Cities: While historically less polluted, Bengaluru and Chennai are showing signs of air quality deterioration during the winter months, a new vulnerability trend.

Structural Resilience of Bengaluru: Bengaluru stands out for maintaining the lowest and most stable air quality, demonstrating a degree of “structural air-quality resilience” compared to other major metros.

Rising Annual Pollution in Coastal Metros: Both Mumbai and Chennai recorded increases in their annual average pollution levels in 2025, signalling a growing year-round concern beyond seasonal spikes.

Patna’s Intensifying Crisis: Patna has been confirmed as the second-most polluted city after Delhi, with persistently high PM2.5 levels driven by strong atmospheric stagnation, highlighting an intensifying crisis in the eastern Indo-Gangetic Plain.

Kolkata’s Stagnant Air Challenge: Kolkata’s pollution levels remain alarmingly high, particularly in winter, characterised by high concentrations of secondary pollutants and a lack of effective dispersion due to geographical and meteorological constraints.