India, Aug. 25 -- In a little over two months, winter will descend on the Indo-Gangetic Plain, and with it, the familiar smog. For over three crore people in Delhi-NCR, this means tracking the Graded Response Action Plan (GRAP) directives of the Commission for Air Quality Management in National Capital Region and Adjoining Areas (CAQM), and planning their activities. The CAQM will rely on the Air Quality Early Warning System's (AQEWS) forecasts to decide which stage of GRAP to impose.

The AQEWS is remarkably accurate. According to a study by the Council on Energy, Environment and Water (CEEW), it can predict days with air quality index (AQI) of 300 and above with over 80% accuracy. A series of crises - the Great Smog of 2016, the polluti...