Delhi's air pollution forecasting system underpredicts PM2.5 levels in the national Capital by 30 to 35 per cent due to outdated emission inventories. Mohammad Rafiuddin, programme lead at the Council on Energy, Environment and Water (CEEW), said the city's Air Quality Early Warning System (AQEWS) continues to show "around 30 to 35 per cent error" in predicting fine particulate matter concentrations.
"If the actual PM2.5 level is 100 micrograms per cubic metre, the system reports it as around 65 micrograms per cubic metre. So, it is underpredicting PM2.5 levels," he said.
"One of the key reasons is that the system relies on old emission inventories. At the national level, the emissions inventory has not been updated since 2016. For Delhi, it was last revised in 2021," he added.
CEEW researchers have recommended developing a new national-level emissions inventory with a provision for regular updates, taking cues from the way the US and China update their inventories.
"There should be a framework to update the emissions inventory every two to three years. The immediate focus should be on upgrading the inventory for the Delhi-NCR region to improve forecast accuracy," Rafiuddin said.
He added that updating the emission database would also enhance accountability.
"It's not only about the forecasts. The early warning system can also tell you how your air quality interventions have fared over the years," he said.
According to a recent CEEW study, Delhi's AQEWS was able to predict 'very poor and above' air quality days with over 80 per cent accuracy during the last two winters.
It successfully forecast 83 out of 92 such episodes (air quality index above 300) in winter 2023-24, and 54 out of 58 in 2024-25.
The system has also improved its performance in predicting 'severe' pollution days (AQI above 400). While it correctly flagged only one out of 15 such days in 2023-24, the number rose to five out of 14 the following winter.
Eight Indian cities, including Ahmedabad, Pune and Jaipur, already use an Air Quality Early Warning System, with more expected to join under the National Clean Air Programme.
Launched in 2018 after a series of smog episodes and dust storms, Delhi's AQEWS is jointly operated by the Indian Institute of Tropical Meteorology and the India Meteorological Department. It provides pollution forecasts three to ten days in advance.
