India, Dec. 14 -- Unlike the previous "severe" spell-a 24-hour average air quality index (AQI) reading above 400-the announcement of mitigative measures came with a sense of urgency. On Saturday, the AQI touched 401 in Delhi at 10am, barely breaching the "severe" mark, but the commission announced curbs under Stage 3 before 11am. This was upgraded to stage 4 in the evening after the Central Pollution Control Board (CPCB) released its daily bulletin at 4pm, recording an average AQI for Delhi at 431.

To be sure, when the air turned severe from November 9, Grap 3 was invoked by the Commission for Air Quality Management (CAQM) only two days later.The AQI remained 400+ till November 13, but Grap 4 was not imposed, effectively making this the ...