Dirty air alert: Delhi tops the charts in PM 2.5 pollution

The researchers took into account satellite and ground data to map population-weighted PM2.5 across districts, states and airsheds.

Annual population-weighted PM2.5 concentrations range from “as low as 21 µg/m³ in Tiruppur, Tamil Nadu, to a high of 112 µg/m³ in the North West district of Delhi,” as per the findings. PM2.5, fine particulate matter of 2.5 micrometre or less in diameter, is believed to be among the most dangerous pollutants because it can penetrate the lung barrier and enter the bloodstream.

At the state level, as per the researchers, “all 33 states and union territories considered in the report exceed the WHO guideline, with 28 states also breaching India’s NAAQS.”

“Delhi ranked as the most polluted state/union territory with an annual mean PM2.5 concentration of 101 µg/m³, 2.5 times the NAAQS and 20 times the WHO guideline,” flags the study.

It also cautions that “state-level PM2.5 averages can mask several local hotspots,” pointing to Maharashtra as an example where the state mean sits near the NAAQS while “14 districts exceed the NAAQS, including Chandrapur with dense clusters of coal-based industries and power plants.”

Meanwhile, airshed-level analysis, referring to a region that shares a common flow of air, underlines that “The Indo-Gangetic airshed remains the most polluted region in the country, consistently non-compliant during winter, summer, and post-monsoon season.”

It also flags that “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.”

Noting seasonal dynamics, the report observes: “Most airsheds were below PM2.5 standards during the monsoon due to atmospheric cleansing, except the Assam–Tripura airshed”. “But the quick return to non-compliance post-monsoon shows that baseline emissions, not meteorology, are the real problem,” it adds.

The study also states that “approximately 82% (616 of 749 districts) of India’s districts record PM2.5 concentrations above the national standard during winter,” while monsoon reduces exceedance to “just 10% of districts (74 of 749).” It also points to the rapid post-monsoon rebound.

“Post-monsoon months see a sharp resurgence, with three out of four districts (566 of 749) again exceeding the standard.”

It adds that Assam, Delhi, Punjab and Tripura are notable exceptions that “remain pollution hotspots year-round, exceeding PM2.5 standards even during the monsoon.”

The authors recommend expanding “clean air planning beyond nonattainment cities…beyond the current list of non-attainment cities (in NCAP).”

Satellite-derived PM2.5 data should be formally integrated into NCAP for spatially comprehensive assessment and performance tracking, it says. On sources and accountability, the study urges to “target regional and sectoral emission sources” and to “incentivise state-level accountability and performance tracking.”

Citing concerns that localised action will yield limited gains, given the “scale and mobility of particulate pollution across northern India”, the authors have also pushed for “airshed-based management frameworks” to take corrective steps across administrative borders.