A new exercise to map emissions in Delhi-NCR and track air pollution sources has been flagged off by the Commission for Air Quality Management. The hope is that it will not only improve AQI forecasts but also help in formulating a better strategy to clean up the national capital’s air, writes Banasree Purkayastha
What has the CAQM proposed?
The Commission For Air Quality Management (CAQM) has said that a consortium of four institutes led by Automotive Research Association of India (ARAI), Pune and partners from Indian Institute of Technology Delhi, TERI and Indian Institute of Tropical Meteorology (IITM) Pune will develop a new emission inventory and source apportionment study for Delhi NCR.
The decision comes soon after the Supreme Court pulled up the air pollution watchdog for failure to clearly identify the causes of air pollution in Delhi-NCR and their respective contributions. On January 6, the apex court had ordered the CAQM to complete a source-identification and apportionment exercise within two weeks and place the findings in the public domain.
The exercise will map emissions at a high resolution of 500 x 500 metre grids to cover major polluting sectors, with 2026 as the base year. The updated inventory will incorporate recent activity data, improved methodologies, and ongoing policy measures to provide a more accurate assessment of emissions.
The CAQM’s decision forms a part of its report titled ‘Identification of the causes for worsening AQI in Delhi-NCR.
What is the need for emission inventory?
Accurate emission inventory is the foundational layer of any strategy to tackle air pollution. In turn, accurate forecasts empower policymakers, authorities, and citizens to act early—on actions such as transport and construction restrictions, and school activities—and safeguard public health. While an emission inventory provides the quantification and location of pollutant emissions from different sources, such as transport, industry, power plants, biomass burning, and natural dust, it however does not really provide the actual contribution of the source to the ambient air pollution. That is done by the chemical transport models (CTM) which gives the relationship between emissions and concentrations. They can also be used to identify the impact of reducing emissions from one or more sources on concentrations.
Benefits of using this new inventory
The new emission inventory will be utilised in the Air Quality Early Warning System (AQEWS) and the Decision Support System (DSS) developed by IITM Pune, which provides air quality forecasts and near real-time source contribution analysis, enabling policy interventions and targeted actions.
This is expected to help improve air quality forecasting and help design more effective mitigation strategies. Forecasts have turned out to be wrong at times, especially on severe AQI days.
A study by the Council on Energy, Environment and Water (CEEW) last year found that the AQEWS successfully forecast 54 out of 58 instances of “very poor and above” air quality (AQI over 300) in the winter of 2024–25.
However, in the case of severe pollution when the AQI is above 400, it was able to flag only one out of 15 such days in 2023–24, and 5 out of 14 in 2024–25. “Updated emission inventories can improve the accuracy further.
It would enable us to have a better understanding of what pollutes Delhi’s air and in what quantities,” Mohammad Rafiuddin, programme lead at CEEW, had then said.
How AQI forecast is done
The AQEWS which identifies pollution sources is the mainstay of air quality index (AQI) forecasts in India. It provides forecasts of Delhi’s air quality up to three days ahead. Eight other Indian cities, including Pune, Ahmedabad and Jaipur are using AQEWS, with more set to adopt it under the National Clean Air Programme.
The warning system includes real-time observations of air quality over Delhi region and details about natural aerosols like dust (from dust storms) and particulate matter using different satellite data sets and predictions of air pollutants from two different air quality prediction systems.
In 2021, the DSS was added to monitor the sectoral and regional sources of PM2.5 pollution. Together, they provide air quality forecasts and near real-time source contribution analysis, using emission inventory from 2021 which is now considered to be outdated.
What CAQM says about pollutants
The CAQM report identifies secondary particulates from gaseous emissions as the largest component (27%) of winter pollution in Delhi. Transport is the primary source of pollution, contributing 23% to the winter pollution load.
Biomass burning and municipal solid waste, residential heating, and crop residue burning, account for around 20% of PM2.5 concentrations in winter, it said. While there has been a gradual decline in both PM2.5 and PM10 concentrations in Delhi since 2016, despite increasing population and rapid urbanisation, there is still a huge gap to meet the annual NAAQS, it said.
The Commission noted differences in existing approaches for emission inventory and source apportionment, recognising that a unified, data-driven approach is essential to reduce emission uncertainty for developing effective air quality management in Delhi-NCR.