Despite improvement, outdated data limits air pollution forecasting: Study

Delhi’s air pollution forecasting has improved significantly, but use of outdated emission inventories and underprediction of pollutants are limiting its effectiveness, a new study by the Council on Energy, Environment and Water (CEEW) has found.

According to the study titled How Well Can Delhi Predict Air Quality?, the city’s Air Quality Early Warning System (AQEWS) predicted more than 80% of “very poor and above” air quality days (AQI >300) over the past two winters. It correctly forecast 83 out of 92 such days in 2023–24 and 54 out of 58 in 2024–25. Forecasts for severe smog episodes (AQI >400) also improved: from one out of 15 episodes in 2023–24 to five out of 14 in 2024–25.

Launched in 2018 by the Union Ministry of Earth Sciences, the Air Quality Early Warning System (AQEWS), which identifies pollution sources, is operated by the Indian Institute of Tropical Meteorology (IITM), Pune, and the India Meteorological Department (IMD). It provides forecasts of Delhi’s air quality up to three days ahead.

In 2021, a Decision Support System (DSS) was added to the platform to monitor the sectoral and regional sources of PM2.5 pollution. However, the study reveals that AQEWS and DSS rely on outdated emission inventories from 2016 for NCR districts and 2018 for Delhi, making it difficult to capture current pollution patterns.

In December 2024, the Commission for Air Quality Management (CAQM) stopped using DSS for decision-making because of these outdated datasets. Forecasting errors remain high, with mean absolute percentage errors of 35 per cent for PM2.5 and 38 per cent for PM10 in 2024–25. The system continues to underpredict pollution, limiting its usefulness for preemptive action.

“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 such as the impact of restricting certain vehicle types or the potential air quality improvements from enhanced public transportation,” the CEEW said in a statement.

Dr Mohammad Rafiuddin, one of the authors of the study, said, “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. India must scale up these systems with science, funding and transparency. Doing so will not only strengthen public trust but also ensure that Delhi’s Mitigation Plan 2025 is backed by the best available evidence.”