Delhi Crowned Most Polluted Region in India, Satellite Study Reveals
A groundbreaking satellite-based analysis has identified Delhi as the most polluted state and union territory in India, recording an annual mean PM2.5 concentration of a staggering 101 µg/m³. This alarming figure is more than 2.5 times the national safe limit and a shocking 20 times higher than the World Health Organisation's stringent guideline of 5 µg/m³.
The comprehensive study, titled "Beyond city limits: A satellite-based PM2.5 assessment across India's airsheds, states, and districts," was released on Tuesday, November 26, 2025, by researchers from the Centre for Research on Energy and Clean Air (CREA), an independent Finland-based think tank.
National Crisis: Widespread Breach of Air Quality Standards
The research presents a grim national picture, revealing that 60% of India's 749 districts breach the annual National Ambient Air Quality Standards (NAAQS) of 40 µg/m³. Even more concerning is the finding that not a single district in the country meets the WHO's health-based PM2.5 guideline.
Researchers combined satellite observations with ground-level data to create a detailed, population-weighted map of PM2.5 pollution across districts, states, and airsheds. The findings show extreme variations, with concentrations ranging from 21 µg/m³ in Tiruppur, Tamil Nadu, to a dangerous high of 112 µg/m³ in Delhi's North West district.
At the state level, the situation is universally dire. All 33 states and union territories analyzed in the report exceed the WHO guideline, with 28 states also breaching India's own NAAQS.
Pollution Hotspots and Seasonal Patterns
The analysis identified significant "clustered hotspots" of pollution, with the top 50 most polluted districts concentrated in Delhi, Assam, Haryana, and Bihar. This clustering, researchers note, presents an opportunity for targeted interventions.
The study also highlights how state-level averages can mask severe local problems. For instance, while Maharashtra's state mean hovers near the NAAQS, 14 districts within the state exceed the standard, including Chandrapur, which hosts dense clusters of coal-based industries and power plants.
Seasonal analysis reveals a dramatic pattern. Approximately 82% of India's districts (616 of 749) record PM2.5 concentrations above the national standard during winter. The monsoon season provides brief respite, reducing exceedance to just 10% of districts (74 of 749). However, the report cautions that pollution rebounds sharply post-monsoon, with three out of four districts (566 of 749) again exceeding standards.
Assam, Delhi, Punjab, and Tripura are identified as particularly concerning, remaining pollution hotspots year-round, exceeding PM2.5 standards even during the monsoon.
Airshed Analysis and Urgent Recommendations
The airshed-level assessment—which examines regions sharing a common flow of air—confirms that the Indo-Gangetic airshed remains the country's most polluted region, consistently non-compliant across winter, summer, and post-monsoon seasons.
An emerging concern is the Northeast airshed's year-round air quality challenges, with Assam and Tripura maintaining elevated PM2.5 concentrations throughout the year. The report emphasizes that while most airsheds see improved air quality during monsoon due to atmospheric cleansing, the quick return to non-compliance post-monsoon indicates that baseline emissions, not meteorology, are the core problem.
In response to these findings, the authors propose critical policy changes. They recommend expanding clean air planning beyond the current list of non-attainment cities under the National Clean Air Programme (NCAP). The study urges formal integration of satellite-derived PM2.5 data into NCAP for more comprehensive assessment and performance tracking.
Given the "scale and mobility of particulate pollution across northern India," the researchers advocate for a shift toward airshed-based management frameworks to implement corrective measures across administrative borders. They also stress the need to target regional and sectoral emission sources and incentivize state-level accountability and performance tracking.
PM2.5, defined as fine particulate matter of 2.5 micrometres or less in diameter, is considered among the most dangerous air pollutants because of its ability to penetrate the lung barrier and enter the bloodstream, posing severe health risks to millions of Indians.
