India’s cities have been in an air emergency for the last 10 years. A new climate analysis report titled Air Quality Assessment of Major Indian Cities (2015–2025), revealed that not one major urban centre has breathed “safe” air even for a single year between 2015 and November 2025. Delhi tops the danger list (again) with other northern cities closely behind. The study also stated that southern and western metros managed only slightly cleaner skies in the last decade.
The report was released on Friday by Climate Trends, a Delhi-based climate research organisation. It assessed annual mean AQI data from 11 major cities, namely Ahmedabad, Bengaluru, Chandigarh, Chennai, Delhi, Kolkata, Lucknow, Mumbai, Pune, Varanasi and Visakhapatnam, over a 10-year period. AQI between 0-50 is considered a safe level.
How the cities compare
The findings showed Delhi has recorded the worst air quality across the decade, peaking above AQI 250 in 2016. Although levels have dipped slightly since 2019, pollution continues far above safety limits with mean AQI still around 180 in 2025.
Lucknow, Varanasi, Ahmedabad and Pune also showed signs of prolonged exposure to hazardous air, the report noted. “Lucknow and Varanasi started with extremely high levels (often above 200)…while both cities show steady improvement after 2019, their 2025 AQI values remain above healthy limits,” the report stated.
On the other hand, Chennai, Chandigarh, Visakhapatnam and Mumbai recorded comparatively lower AQI, mostly between 80–140, still worse than safe thresholds but better than northern cities.
Bengaluru fared the best, yet even it never touched a “safe” AQI year. The city mostly hovered between 65-90.
Geographical woes of North
Northern India’s pollution crisis is not just man-made; it’s geographical. Cities like Delhi, Lucknow and Varanasi lie within the Indo-Gangetic Plain, a region landlocked and boxed in by the Himalayas. This bowl-shaped terrain traps pollutants, preventing them from dispersing easily.
The situation worsens in winter due to a weather phenomenon called winter inversion where cooler, denser air settles near the ground and warmer air sits above it like a lid. Pollutants get trapped in a shallow atmospheric layer, winds weaken and smog builds up fast.
Dense urban construction also reduces airflow by creating what the report called “surface roughness”, making dispersal even more difficult.
Monsoon winds briefly help clear pollution but winters push air quality back into crisis mode every year. Delhi suffers a bigger blow, sitting directly in a flat basin between regional emission sources, including stubble burning zones, making it the epicentre of toxic haze.
