Irrespective of their diverse geographic and climatic contexts, India’s megacities of India – Delhi, Mumbai, Kolkata, Bengaluru, Hyderabad and Chennai – have seen worsening PM2.5 levels this winter. The overall level and the peaking points of pollution have, however, varied across cities depending on the meteorological conditions of different climatic zone, according to a latest analysis by the Centre for Science and Environment (CSE).
 
The analysis of real-time PM2.5 data in these cities during the winter period (October 1, 2024-January 31, 2025) has evaluated pollution trends in peer megacities to provide insights into long-term seasonal variations and annual shifts in particulate pollution during winter.

For the detailed city-wise analysis, see: https://www.cseindia.org/MEGACITIES-WINTER-POLLUTION-NOTE-March2025.pdf
   
While Delhi, located in the land-locked Indo-Gangetic Plains (IGP) with adverse meteorology, has recorded the highest level of pollution during winter, Kolkata – also at the tip of the IGP – ranks second. The megacities outside the IGP – Mumbai, Chennai, Hyderabad and Bengaluru – despite having advantageous climatic conditions and natural ventilation, have also experienced increases in average PM2.5 concentrations.
 
Other than Delhi and Chennai, all other megacities have recorded city-wide winter averages that are comparatively lower than the average of the past three winters; but the concentrations across different locations have been high, leading to high exposures.
 
“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,” Anumita Roychowdhury, executive director, research and advocacy, CSE, said in a release.
 
“These cities need stringent action to curb pollution from all sources to meet the clean air standards. But urban centres like Delhi and Kolkata that face an additional challenge of adverse meteorology which enhances the concentrations, need even more stringent action to counter these effects,” she added.   
 
According to Sharanjeet Kaur, programme officer with the Urban Lab at CSE, “While Delhi’s winter air quality often dominates public discourse, rising pollution levels in other megacities remain largely overlooked. Despite some improvement in seasonal pollution trends, winter pollution continues to remain high or has been rising locally.”
 
The key highlights of the analysis

During this winter, Kolkata and Hyderabad were most polluted after Delhi, while Mumbai, Chennai and Bengaluru saw the fastest worsening of localised pollution levels : Delhi, with a winter average PM2.5 level of 175 microgramme per cubic metre (µg/m³) remains the most polluted megacity by a large margin during winter, even though the winter average has shown improvement over the previous winter.
 
* Worst affected locations within megacities have pollution levels 19-60 percent higher than citywide averages
 
* Compared to the three-year average, Delhi remained the worst performer, with average winter pollution levels continuing to rise, even though by just 1 percent higher than the average of the last three years.
 
* Compared to the winter of 2021-22, Mumbai, Kolkata and Hyderabad show improvement with their winter PM2.5 levels dropping by 16 per cent, 14 per cent and 16 per cent respectively. Delhi has recorded a 7 per cent reduction in pollution levels compared to the pervious winter, but 5 per cent higher than in 2021-22. Meanwhile, Bengaluru and Chennai have recorded an increase in PM2.5 levels compared to 2021-22, reflecting a worsening trend in air quality.
 
* Peak winter pollution in Delhi hits worst level in last four years; other cities indicate varying trends
 
* Winter is problematic season for all megacities, but the intensity of the problem varies.
 
The way forward
Roychowdhury said, “Even after five years of the National Clean Air Programme (NCAP), the megacities – despite investing substantial shares of the grant from the XVth Finance Commission for clean air action – are still struggling to meet clean air standards throughout the year and at all locations. The NCAP needs to be further strengthened to accelerate action to drastically cut emissions from all key sources including vehicles, industry, power plants, waste streams, construction, use of solid fuels in households and dust sources to enable all cities to meet the clean air standards and increase the number of good air days.”
 
She added: “At the same time, the cities that are located in the IGP and are struggling harder to meet the clean air benchmark due to the impact of the adverse meteorological conditions that trap pollution and the growing local and regional pollution sources, require significantly more advanced, stringent and upscaled action to counter these effects and the impacts of rapid urban growth and motorisation.”