As Delhi and much of northern India grapple with persistent toxic smog, the Commission for Air Quality Management (CAQM) has announced that a new source apportionment study is underway to identify the pollution contributors driving the capital’s hazardous air. The study, which incorporates expanded scientific parameters, comes amid renewed concerns that policy decisions continue to rely on outdated data, weakening the city’s ability to respond effectively to deteriorating air quality.
Sixth study since 2010, but key findings remain unutilised
The forthcoming study will be the sixth source apportionment analysis conducted in Delhi since 2010. A CAQM member confirmed that new elements are being added to the evaluation, though no timeline for its release has been provided. The development follows revelations in the National Green Tribunal (NGT) that Delhi’s pollution management plans continue to rely on emissions data from over seven years ago.
The most recent study, completed in 2023 by IIT Kanpur in partnership with multiple institutions, remains unapproved by the Delhi government, meaning its findings have not been incorporated into existing air pollution control measures.
A submission by amicus curiae Sanjay Upadhyay to the NGT on 26 November highlighted that despite conducting new studies, Delhi has not updated its State Clean Air Action Plan since 2018. His submission pointedly asked whether the newer studies had been integrated into current air quality strategy — the answer, he said, “was no.”
Importance of source apportionment in air quality planning
Source apportionment studies scientifically determine the contribution of various pollution sources — such as transport emissions, construction activities, dust, industrial processes and stubble burning — to overall air quality. These assessments are critical for prioritising interventions and updating policy responses.
India’s National Clean Air Programme (NCAP), launched in 2019, mandated such studies for 131 cities, emphasising their importance for reducing particulate matter, especially PM2.5, known to be more harmful than PM10.
Delhi’s first study in 2010, conducted by NEERI, focused primarily on PM10. However, as monitoring capability improved and international research highlighted the dangers of PM2.5, the government expanded its analytical scope. Subsequent studies — including the 2015 IIT Kanpur assessment and reports by IIT Madras, IIT Delhi and TERI — advanced understanding of seasonal and sector-specific pollution drivers. Experts say these studies have informed major interventions such as BS-VI vehicle rollout and electric mobility adoption.
Why updated studies are essential
Experts caution that pollution sources evolve over time due to changing industrial activity, transport patterns, infrastructure growth and policy interventions. Regular updates — ideally every two to three years — allow policymakers to assess whether existing strategies are effective.
For example, construction dust was estimated to contribute 20–23% of PM10 in the 2010 NEERI study, but only 3–5% in the 2015 IIT Kanpur analysis. Such shifts highlight the dynamic nature of air pollution, underscoring the need for timely recalibration.
As one air quality expert noted, without updated studies, governments cannot accurately determine whether past interventions have worked.
“If the sources you tackled are actually reducing, then you know you’re on the right track. Or else, you need to course correct.”
Delhi’s pollution landscape has changed significantly over the last decade, with cleaner vehicles, expanding EV policies and altered industrial clusters — yet its action plan still relies on pre-2018 data.
Findings from the 2023 real-time supersite
The 2023 study, conducted by DPCC, IIT Kanpur and a consortium of institutions, utilised a real-time supersite — India’s first advanced monitoring station capable of instant source identification. Unlike earlier studies that depended on extended sampling, the new model enabled continuous analysis.
A draft accessed by ThePrint indicates that secondary inorganic aerosols (SIA) are now the largest contributors to pollution. These particles are not emitted directly but formed through chemical reactions involving gases like sulphur dioxide and nitrogen oxides, typically originating from power plants and industrial emissions.
Despite its value, the Delhi government told the NGT in October that the 2023 study remains “not approved”, leaving its insights unused for policy updates.
Call for stronger coordination and urgent action
Upadhyay urged the NGT to direct Delhi and neighbouring cities to expedite source apportionment studies and revise their action plans promptly. He criticised both state governments and central bodies, including CPCB and MoEF&CC, for what he described as a “complacent attitude” towards pollution management.
Furthermore, the Decision Support System (DSS) — a real-time air quality forecasting tool used by authorities — is still based on emissions data from 2018. Without integrating new findings, the DSS may misrepresent current pollution patterns.
Some experts, however, argue that while updating studies is essential, immediate action must continue to target major known emitters such as road dust, construction activity and biomass burning.
Delhi’s average AQI ranged between 250 and 350 through most of November, placing it in the ‘very poor’ category. Doctors warn that prolonged exposure aggravates respiratory and cardiac conditions, with children and the elderly at heightened risk.