Delhi's air quality slipped into the "very poor" category for the first time this season on Monday, with the Air Quality Index at 312 at 9 am, according to the Central Pollution Control Board.
The CPCB said the 312 reading is the morning figure and not the day's average, which will be available at 4 pm.
On the CPCB scale, an AQI of 0-50 is "good", 51-100 "satisfactory", 101-200 "moderate", 201-300 "poor", 301-400 "very poor" and 401-500 "severe".
The Graded Response Action Plan's Stage 2 applies once the index enters the 301-400 band. The Commission for Air Quality Management's sub-committee decides whether to invoke it, based on dynamic air quality and meteorological forecasts.
The India Meteorological Department recorded a minimum of 16.4 degrees Celsius at Safdarjung, 1.1 notches above normal. Palam logged 16.4 degrees, Lodhi Road 16.8, the Ridge 17.2 and Ayanagar 16.7. No rain was recorded at any of the five stations in the 24 hours to 8.30 am.
The slide comes days after rain on October 30 pushed the index down to 60, the capital's cleanest October air in four years.
Diwali falls on November 8. The Supreme Court has allowed green crackers in Delhi-NCR between 6 am and 7 am and between 8 pm and 10 pm on November 7 and 8. It barred bursting within 300 metres of hospitals, nursing homes, primary and district health centres, old-age homes and notified silence zones, and said the complete ban returns on November 9.
Since the weekend, Delhi has been turning back non-Delhi pre-BS-VI vehicles at its borders, and the Delhi High Court declined on Monday to stay that restriction.
(With inputs from PTI and media reports)