As Delhi prepares for the annual winter spike in air pollution, the Decision Support System (DSS) for Air Quality Management has been reactivated to track and estimate the daily contribution of various pollution sources in the city. 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. While rain and winds have kept the air in Delhi and the NCR relatively clean in recent days, this situation could change as it gets cooler, the wind direction changes, and incidents of stubble-burning in Punjab and Haryana increase. Are farm fires already a significant contributor to pollution? Not yet. DSS data show the contribution from farm fires or stubble-burning to air pollution over Delhi remains minimal so far. On Sunday, when the readings were first made available, it was 0.22%; on Monday, it did not contribute to pollution at all, as per the data based on active fire counts from VIIRS. VIIRS, or Visible Infrared Imaging Radiometer Suite, is a set of instruments aboard polar-orbiting weather satellites that produce data streams that monitor changes in surface vegetation, including fires. While the paddy harvesting season has begun in Punjab, the Indian Agricultural Research Institute (IARI) said on Monday that satellites had “detected 0 residue burning events in the six study States on 06 Oct 2025". In all, 210 farm fires have been reported across five states since September 15, far lower than in recent years for the same period. As of now, the transport sector is the single largest contributor to Delhi’s PM2.5 levels – it was 16.96% on Sunday, and 18.91% on Monday, DSS data show. Other significant emission sources are residential emissions (4.28% and 5.06% according to data from Sunday and Monday respectively), and industries (3.11% and 4.62% on Sunday and Monday respectively). What exactly are DSS data supposed to indicate? The DSS is based on a horizontal grid spacing of 10 km, and generates forecasts and decision-support information for the next 120 hours, or five days. According to IITM, the DSS provides quantitative information about: a) contribution of emissions from Delhi and surrounding 19 districts to the air quality in Delhi; b) contribution of emissions from eight different emission sectors in Delhi to the air quality in Delhi; c) contribution from biomass-burning activities in the neighbouring states to the degradation of air quality in Delhi; and d) effects of possible emission source-level interventions on the forecasting of severe air-quality events in Delhi. The model also forecasts pollution levels for the next three days using climatological data on fire counts and emissions. However, Delhi’s DSS currently operates only in winter, which limits its usefulness for tracking pollution sources during the rest of the year. A study by the Council on Energy, Environment and Water (CEEW) earlier this year pointed out that “to be fully effective, it (DSS) should run year-round and incorporate modelling scenarios”. So how reliable are the DSS data? A senior IITM official said the DSS currently operates on an emissions inventory that is four years old, and this could affect the precision of source-wise estimates. Experts have emphasised the need for an updated emissions inventory. Shambhavi Shukla of the environmental research and advocacy nonprofit Centre for Science and Environment (CSE) said the real-time estimates provided by DSS of the various pollution sources contributing to PM2.5 levels in Delhi is crucial for enforcing and implementing source-specific control measures, but the emissions inventory it relies on is old. “The DSS relies on an emissions inventory prepared in 2021. To make emission forecasting more accurate and effective, Delhi and the NCR urgently need an updated emissions inventory and source apportionment studies,” Shukla said. In fact, the DSS faced temporary suspension by the Commission for Air Quality Management (CAQM) – the statutory body for air quality management in the National Capital Region (NCR) and adjoining areas – last year over data accuracy concerns. That said, the DSS remains the only operational framework currently available to identify source-wise pollution in Delhi. “For more accurate estimation of source contribution, the latest emission fields are required,” IITM says on its website. A new inventory is under preparation, and will be incorporated into the system once completed, the IITM official quoted above said.
