As Delhi begins preparations 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 where particulate matter (PM2.5 and PM10) is coming from, and to project the possible impact of emission-control measures.What the DSS data show: Farm fires not a significant contributor to pollution as yetAccording to data available on Sunday (October 5), when the readings were first made available, the transport sector continues to be the single largest contributor to Delhi’s PM2.5 levels at 16.96%.Other significant emission sources are residential emissions (4.28%), and industries (3.11%).The contribution from farm fires or stubble burning remains minimal at 0.22%, based on satellite-based active fire counts from the VIIRS instrument till Saturday evening. 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.Reliability of DSS data: Some concerns, but only framework available currentlyAccording to an IITM official aware of the matter, the DSS currently operates on an emissions inventory formulated in 2021, which could affect the precision of source-wise estimates.Story continues below this adIn fact, the DSS faced temporary suspension by the Commission for Air Quality Management (CAQM) last year over data accuracy concerns. The CAQM is the statutory body for air quality management in the National Capital Region (NCR) and adjoining areas, which is mandated to ensure better co-ordination, research, identification and resolution of problems surrounding the air quality index.However, the DSS remains the only operational framework currently available to identify source-wise pollution in Delhi. The Delhi Pollution Control Committee (DPCC) which had taken over the infrastructure and equipment for conducting a real-time source apportionment study, has not resumed the work that was halted last year.“For more accurate estimation of source contribution, the latest emission fields are required,” the IITM says on its portal. A new inventory is under preparation, and will be incorporated into the system once completed, the official added.Sources and effects: What the DSS data are supposed to indicateStory continues below this adThe 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) the contribution of emissions from Delhi and surrounding 19 districts to the air quality in Delhi; b) the contribution of emissions from eight different emission sectors in Delhi to the air quality in Delhi; c) the contribution from biomass-burning activities in the neighbouring states to the degradation of air quality in Delhi; and d) the effects of possible emission source-level interventions on the forecasting of severe air-quality events in Delhi.According to a study by the Council on Energy, Environment and Water (CEEW), earlier this year, Delhi’s Air Quality Early Warning System (AQEWS) successfully predicted 83 out of 92 ‘very poor’ or worse air quality episodes (AQI above 300) during the winter of 2023-24, and 54 out of 58 such episodes in the 2024-25 season.It said, “Delhi’s DSS currently operates only in winter, limiting its usefulness for tracking pollution sources throughout the year. To be fully effective, it should run year-round and incorporate modelling scenarios.”Story continues below this adThe model also forecasts pollution levels for the next three days using climatological data on fire counts and emissions. For past periods such as November 13-15 last year, the DSS has revised its stubble-burning contribution estimates to account for emissions from firecracker use during wedding celebrations, which were not initially included.