Delhi's pollution puzzle: New study to reveal what's changed in a decade

Over the past ten years, have cleaner fuels, updated vehicular technologies, and stricter emission standards successfully altered the contributions of different pollution sources in Delhi?

Nearly a decade after IIT-Kanpur released Delhi's first comprehensive source apportionment study in 2016, a new assessment is taking shape to determine how the capital region's air quality profile has evolved.

500 m×500 m grid—where each cell spans


0.25 sq km—and taking 2026 as its base year, the project addresses the inconsistencies of older studies that varied in methodology, geographical reach, sector classification, and base years. Instead, it applies a unified framework featuring high-resolution mapping, local activity data, emission factors, spatial tracking, seasonal shifts, and ground-level physical verification.

Running from January 1 to December 31, the data will be analyzed by mid-2027 to forecast air quality and emission scenarios for 2030, 2035, and 2040. A consortium leads the effort—headed by the Automotive Research Association of India (ARAI), Pune, in collaboration with IIT-Delhi, The Energy and Resources Institute (TERI), and the Indian Institute of Tropical Meteorology (IITM), Pune.

The Central Pollution Control Board (CPCB) made the earliest attempt at an emission inventory between 2007 and 2010 across six cities, including Delhi. However, Delhi's first major source apportionment report came from IIT-Kanpur in 2016, followed by an ARAI-TERI study in 2018. While several other assessments have been conducted over time, none matched the scale or detail of those two studies.

"Changes in vehicle technology, fuel standards, industrial practices, pollution control measures, urban development, waste management and agricultural activity may have altered emissions and their relative contributions. For example, coal has been banned in NCR, except specified processes, and industries have shifted to cleaner fuels," SD Attri, member technical, CAQM, said.

To address this gap, the Commission for Air Quality Management (CAQM) introduced a new framework in April 2025 for preparing emission inventories and conducting source apportionment across Delhi-NCR. The project, funded by the Central Pollution Control Board (CPCB), is being undertaken by a consortium of four institutes. The updated inventory will assess a range of pollutants, including PM10, PM2.5, nitrogen oxides (NOx), sulphur dioxide (SO2), carbon monoxide (CO), non-methane volatile organic compounds (NMVOCs) and ammonia (NH3), as well as elemental carbon, organic carbon, methane (CH4) and hydrogen chloride (HCl).

"The study will give scenario assessments for 2030, 2035 and 2040 under different mitigation pathways to help evaluate potential changes in emissions and air quality. These scenarios will provide a scientific basis for long-term pollution control planning in Delhi-NCR," said Attri, who is heading the project review committee which is tracking the progress of the ongoing study.

Attri explained that dividing the region into

500 m×500 m cells allows researchers to pinpoint emission hotspots with extreme precision and differentiate areas based on their specific source profiles. In addition to satellite-driven AI mapping, field teams are conducting on-ground verification to catch smaller, easily overlooked emission sites.

Under this setup, vehicular emissions are calculated by evaluating road networks, traffic volume, vehicle types, and usage patterns. Industrial output is mapped using factory locations, production output, fuel choices, and installed control equipment. Road dust estimates rely on road surface characteristics, silt loading, and traffic activity.

"The framework will extend beyond NCR into the wider north Indian domain, allowing regional transport to be examined," said Attri.

Currently, IITM's Decision Support System (DSS) tracks local and regional contributions to Delhi's winter PM2.5 levels. However, its accuracy is limited because it relies on an outdated 2021 emission inventory. Once completed, the new inventory will be integrated directly into the DSS.

To complement these findings, a network of real-time source apportionment super-sites is being established across the NCR. IITM's super-site at New Rajendra Nagar was recently inaugurated on Saturday, while the Delhi Pollution Control Committee's (DPCC) super-site at Rouse Avenue is set to be reactivated. Four more super-sites are planned for Greater Noida in Uttar Pradesh, as well as Sonipat, Rohtak, and Rewari in Haryana.

(With inputs from TOI)