India, Nov. 6 -- Delhi's air turned "severe", the worst grade on the government's pollution scale, at 6am on Friday on the same 39 monitoring stations the city had last Diwali, an HT analysis of Central Pollution Control Board (CPCB) data shows.

The official index averages the past 24 hours, so it smooths out swings and is slow to show a rise this fast. When HT scored each hour on its own, as if that hour's air held for a full day, every hour since 8pm on Thursday came out "severe" on all 59 of today's stations. The 10am score was 453 on the 0-500 index, against the official 391, and the official figure will move towards it if the air stays this dirty.

The new stations also hold the official figure down, because several of the 20 added ...