Weather conditions can alter pollution levels by up to 40% without emissions changes.
Delhi recorded zero clean air days in winter despite improved annual averages.
Experts urge NCAP reforms with meteorology-based targets and season-specific pollution control strategies.
Weather Can Shift Pollution Levels by Up to 40% in Six Indian Cities: Report
Weather patterns can significantly amplify air pollution levels across several major Indian cities
Smog blankets a major Indian city as weather conditions worsen air pollution levels Photo by Saakshi Yadav
Summary
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Meteorological conditions can fluctuate pollution levels by as much as 40%, even when emissions remain unchanged, according to a report released by Climate Trends.
This report suggested that current evaluation frameworks may be masking the true health burden on citizens by overlooking seasonal peaks. Notably, Delhi recorded zero clean air days during the winter season, despite showing an overall "improvement" in annual pollution averages.
The multi-city analysis, which tracked air quality in Delhi, Patna, Kolkata, Mumbai, Chennai and Bengaluru between 2024 and 2025, underscored that air quality is governed by a complex interaction between emissions and weather. Atmospheric stagnation, defined by high humidity and low wind speeds, acts as a primary amplifier for pollution severity.
Sagnik Dey Head, Centre for Atmospheric Sciences, Vipula and Mahesh Chaturvedi Chair Professor in Policy Studies, Indian Institute of Technology Delhi, stated in the news release published by Climate Trends that the persistence of PM2.5 exceedances is strongly linked to wind regimes slower than 1 m/s, particularly in northern cities where stagnation sustains dangerous exposure levels.
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Pollution Patterns Across Cities
While Delhi and Patna remain the most polluted cities, the Climate Trends report identified concerning new trends in coastal and southern metros. Mumbai and Chennai both saw increases in annual average pollution levels in 2025, indicating that poor air quality is becoming a year-round issue rather than just a seasonal spike.
Conversely, Bengaluru was noted for its "structural air-quality resilience," maintaining the most stable air quality among the major metros. The report stated that winter pollution remains alarmingly high in Kolkata due to biomass burning and geographical constraints that prevent effective pollutant dispersion.
Experts are now calling for a radical overhaul of the National Clean Air Programme (NCAP) as it enters Phase III. Aarti Khosla, Director of Climate Trends, mentioned in the news release that a 20–30% reduction in annual PM2.5 is insufficient for cities like Delhi, where over 70% of days suffer from low-wind conditions. The report proposed that the government adopt season-specific targets, meteorology-adjusted metrics, and dynamic action plans triggered by weather forecasts to ensure a scientifically robust approach to public health.
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