New Delhi, Dec. 31 -- Delhi is unravelling. The Graded Response Action Plan (Grap) for the annual air pollution crisis starting in mid-October triggered its higher stages in a capricious on-off pattern.

Stage 3 was switched on from 11 November, off on 26 November, on again on 13 December morning and then further ramped up by the evening of the same day to stage 4.

After 10 days, when air quality improved from 'very severe' to 'poor' on 24 December, stage 4 was switched off despite forecasts that air quality was expected to worsen (which did happen).

Grap stages have to be invoked in an anticipatory manner based on projected changes in air quality and then held steady for a while, rather than as jerky short-term responses to readings in...