Data on pollution sources 7 years old, Delhi flying blind in response to foul air

The city’s decisions on fighting air pollution are shaped by obsolete source profiles, senior advocate Sanjay Upadhyay, amicus curiae in a matter before the NGT, has told the Tribunal in a submission that was made available on Wednesday.

Delhi’s Environment Action Plan, adopted as the State Action Plan, continues to rely on actions framed in 2018, the amicus has said in his note. This is despite the government having undertaken at least three source-apportionment studies since then, including the real-time assessment of 2023.

This study was jointly conducted by IIT-Kanpur, IIT-Delhi, TERI and the Indian Institute of Science Education and Research, Pune. The previous two source apportionment studies initiated by the Delhi government and the Delhi Pollution Control Committee were conducted in 2016 by IIT-Kanpur and in 2017 by IIT-Madras and IIT-Delhi.

Upadhyay made his submission in the context of a broader review ordered by the NGT on July 29 this year, directing the Central Pollution Control Board (CPCB) to ascertain the status of source-apportionment studies in 53 cities, and to examine whether their City Action Plans (CAPs) had been aligned with the findings.

The CPCB informed the Tribunal that studies had been completed in 12 of the 19 non-attainment cities covered under the National Clean Air Programme (NCAP), but the CAPs in none of them had been aligned with the study findings.

Instead, the plans continued to rely on “available data and understanding of pollution sources”.

Studies were still underway in the remaining seven cities.

The lack of updated source information has implications for the Decision Support System (DSS) for Air Quality Management that is currently used by Delhi for real-time forecasting and guidance on interventions.

For Delhi, the DSS employs the emissions inventory developed in 2018 under the SAFAR project; for the other 19 NCR districts, including Ghaziabad, Noida, Meerut, Rohtak, Sonipat, and Panipat, the 2016 emissions inventory developed by TERI is used. For regions outside NCR, the system relies on a global emissions database.

Developed by the Indian Institute of Tropical Meteorology (IITM), Pune, the DSS uses a numerical model to identify the sources of particulate matter (PM2.5 and PM10), and to project the possible impact of emission-control measures.

In a peer-reviewed study published in 2024, scientists at IITM noted the limitations of DSS – emissions inventories based on 2016 surveys “are likely to be underestimating the reality” several years later, they said.

The older surveys either capture poorly or miss entirely several key contributors to PM concentrations such as the burning of biomass for winter heating, open waste-burning, brick-kiln activity, and fine-scale burning events, the study observed.

It also noted that the model struggles to quantitatively capture severe pollution episodes, especially when the air quality index (AQI) is above 400. This level of bad air quality, classified as “severe”, is fairly common in Delhi-NCR in winter.

In a study published last month, Delhi-based think tank Council on Energy, Environment and Water (CEEW) recommended that forecasting of pollution episodes could be enhanced with an “updated emissions inventory”.

“The immediate priority should be upgrading the EI for the Delhi NCR region under the CAQM’s supervision to improve forecasts,” the study said. The Commission for Air Quality Management (CAQM) is the statutory air pollution watchdog for Delhi-NCR, which oversees the implementation and operation of the Graded Response Action Plan (GRAP).

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