Delhi: Forecasting systems failed to predict high air pollution episodes last winter, says case study

Last winter, Delhi’s air pollution forecasting systems “picked up the trend of pollution but could not predict high episodes of pollution,” according to a case study by the Council on Energy, Environment and Water (CEEW).

To further reduce episodes of elevated air pollution over the coming winter, forecasting systems will need to provide more accurate predictions of PM2.5 concentration levels, according to the study. The study stated that since the introduction of short-term emergency measures based on expectations, the systems have helped “prevent very severe episodes of air pollution”.

The first set of restrictions was put in place on November 16, 2021, and all were lifted by December 20, 2021, except for the set on industrial operations. During this period, all but the AQ-EWS (3 days) (Air Quality Early Warning System) forecast did not predict PM2.5 levels, the study said.

When the restrictions were imposed, air quality did not fall to the “severe +” category, but the first period of “severe” air quality was seen in December from December 21 to 26, when all restrictions, except those for industrial activities, were lifted. This was the longest period of “severe” air quality of the season, according to the study, which also said the lifting of restrictions “came at an inopportune time”.

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About 64% of Delhi’s winter pollution load comes from outside Delhi, according to the study, which used data from UrbanEmissions.Info, the Delhi Air Quality Management Decision Support System, and the Delhi Air Quality Early Warning System.

Local sources of PM2.5 include transport (12%), dust (7%), and local biomass burning (6%).

“Forecasts were effectively able to pinpoint trends…at this hour of the day, air quality is going to be poor. Forecasts have not performed well when it comes to predicting the type of pollution episodes. There were days when pollution was in the ‘severe’ category, but the forecast said It would be on the higher end of the category of “extremely poor.” Tanushri Ganguly, one of the study’s authors, said this was because expectations were not expected.

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