Toxic air pollution surged in New Delhi on Wednesday, with fine-particle levels in parts of the capital rising to more than 30 times the World Health Organization's recommended daily limit, just days before Diwali and only three days after authorities tightened winter curbs.

Monitoring firm IQAir recorded PM2.5 concentrations above 461 micrograms per cubic metre in parts of the city, according to AFP, against the WHO's 24-hour guideline of 15 micrograms per cubic metre. The reading was a peak in parts of the capital, not a citywide average; India's own 24-hour limit for PM2.5 is 60 micrograms per cubic metre.

Third day of very poor air

The citywide picture was grim in its own right. Delhi's air quality index stood at 377 at 8 am on Wednesday, in the "very poor" category, and remained in that band for a third consecutive day. Twenty of the capital's 59 monitoring stations recorded "severe" air, while 33 were "very poor", according to local reports, with Jahangirpuri and Punjabi Bagh among the worst hit at readings above 440. PM2.5 was the dominant pollutant across the city.

The deterioration follows a steady slide since the start of the month: the city's 24-hour average air quality index was 261 on November 1, rose to 324 on November 2 — its first "very poor" day of the season — and reached 350 on November 3. The Air Quality Early Warning System for Delhi expects air to stay "very poor" until at least Friday, November 6.

Curbs already in force

Stage II of the Graded Response Action Plan was invoked on Monday, November 2, bringing restrictions on vehicles and construction, and Delhi's winter plan, in force since November 1, requires government and private offices to put 50 per cent of staff on work-from-home arrangements through January 31.

Environment ministry figures cited by AFP attribute the largest shares of Delhi's winter pollution to secondary particles, vehicles at 23 per cent, and biomass burning — including farm stubble fires — at 20 per cent. The estimated contribution of crop burning to PM2.5 was forecast to rise from about 15 per cent on November 3 to about 20 per cent on November 4 and 22 per cent on November 5, according to the decision support system cited in local reports.

Diwali looms

The immediate worry is Diwali on Sunday, November 8, when fireworks traditionally add to the smog. India's Supreme Court has permitted limited use of so-called green firecrackers, which are designed to reduce emissions, and they may be set off only between 6 am and 7 am and between 8 pm and 10 pm on November 7 and 8.

Parents are already pressing for action: a LocalCircles survey found more than half of parents surveyed want a school smog break from November 10 to 15. For a metropolis of more than 30 million people, the next few days — Diwali fireworks, calm winter air and rising stubble-burning — will test whether the curbs in place are enough.