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Despite diverse climates, India’s megacities faced a surge in air pollution during the winter of 2024-25, with Delhi recording the worst levels unsurprisingly. A new analysis by Delhi-based think tank Centre for Science and Environment (CSE) has highlighted the growing crisis, urging stronger action to combat pollution nationwide.
While Delhi remained the most polluted megacity, other urban centres, including Kolkata, Mumbai, Chennai, Hyderabad and Bengaluru, also witnessed major pollution spikes, the research found.
Despite varying climatic conditions, air pollution levels deteriorated across all six cities. Delhi and Kolkata, both situated in the Indo-Gangetic Plain (IGP), recorded the highest pollution levels, whereas Mumbai, Chennai, Hyderabad and Bengaluru saw rapid localised pollution build-up, despite their comparatively favourable climates.
Delhi recorded an average fine particulate matter (PM) 2.5 concentration of 175 micrograms per cubic metre (µg/m³) this winter, far exceeding safe air quality standards. The capital experienced eight days of ‘severe+’ air quality, 12 days of ‘severe’ Air Quality Index (AQI) and 68 days of ‘very poor’ AQI.
The national capital saw no ‘good’ air quality days and peak pollution reached 602 µg/m³ on November 18, 2024, marking the worst daily PM2.5 level in four years.
Kolkata ranked as the second most polluted megacity with a winter PM2.5 average of 65 µg/m³, followed by Hyderabad (52 µg/m³), Mumbai (50 µg/m³), Bengaluru (37 µg/m³) and Chennai (36 µg/m³).
Despite these numbers being lower than Delhi’s, the report emphasised that several localities within these cities saw pollution levels rising as much as 60 per cent above their citywide averages.
Mumbai, Chennai and Bengaluru witnessed the fastest worsening of local pollution levels following the onset of winter. While Mumbai recorded its lowest average PM2.5 in four years, certain locations such as Deonar and Shivaji Nagar saw persistent high pollution, with PM2.5 levels peaking at 80 µg/m³. Similarly, Hyderabad’s worst-affected location, IDA Pashamylaram, had a winter PM2.5 average of 62 µg/m³.
Compared to previous years, Delhi saw a 7 per cent decline in its winter pollution compared to 2023-24, yet it remained 5 per cent higher than in 2021-22. Kolkata and Chennai showed little improvement, while Hyderabad, Mumbai and Bengaluru reported reductions in peak winter pollution levels.
In contrast to Delhi’s extreme pollution levels, Hyderabad recorded the most improvement, with its highest winter PM2.5 levels dropping by 51 per cent, from 183 µg/m³ last year to 89 µg/m³. Bengaluru followed with a 42 per cent decline, whereas Mumbai and Chennai recorded 12 per cent and 19 per cent reductions, respectively.
In a press statement CSE urged that all cities, regardless of their geographical location, must adopt stricter measures to combat air pollution.
“The peaking of pollution during winter in any climatic zone is a sign of the underlying problem of persistent air pollution in these rapidly urbanising and motorising cities. The growing impact of local sources of pollution shows up in the pollution hotspots across these cities, increasing local exposures and risks,” said Anumita Roychowdhury, executive director, research and advocacy, CSE.
She emphasised the need for a multi-pronged approach to control pollution from sources such as vehicles, industries, power plants, waste burning, construction activities and household solid fuel use. Additionally, cities in the IGP, including Delhi and Kolkata, require even stricter interventions due to adverse meteorological conditions that trap pollutants.
The CSE report stressed that despite five years of the National Clean Air Programme, air quality improvements remain insufficient. While some cities have managed to slightly reduce their pollution levels, air quality remains far from meeting the national clean air standards.
The research also examined seasonal patterns, revealing that Delhi and Hyderabad saw the worst air quality in November, while Mumbai peaked in December and Kolkata, Bengaluru and Chennai recorded their highest pollution levels in January.
The clustering of ‘bad air’ days was most prolonged in Delhi, Kolkata and Mumbai, whereas Hyderabad, Bengaluru and Chennai saw shorter durations of pollution spikes.
Notably, Kolkata recorded the same number of ‘poor’ air quality days as Delhi, despite its long-term seasonal PM2.5 trend being lower. Meanwhile, Mumbai recorded 19 ‘good’ air quality days, while Chennai had 55 ‘good’ AQI days, the highest among megacities.
The report called for urgent action to tackle air pollution at its root, advocating for cleaner transportation policies, stringent industrial regulations and large-scale adoption of clean energy sources.