NEW DELHI - Two Indian cities joined New Delhi to be among the world’s worst 10 for pollution on Monday morning, with smoke heavy in the air a day after revellers let loose with firecrackers for Diwali – the annual Hindu festival of light.

The capital New Delhi took, as it often does, the top spot. It had an air quality index (AQI) figure of 407, putting it in the hazardous category, according to Swiss group IQAir.

Financial capital Mumbai came in sixth with an AQI of 157, while Kolkata in the east was seventh with an AQI of 154.

An AQI level of 400 to 500 impacts healthy people and is dangerous to those with existing diseases, while a level of 150 to 200 brings discomfort to people with asthma, lung and heart problems. Levels of 0 to 50 are considered good.

A thick layer of smog had started to circulate in New Delhi on Sunday night, sending its AQI to an alarming 680 a little after midnight.

Every year, the authorities impose bans on firecrackers in the capital, but only rarely do those bans appear to be enforced.

Lawmaker Saket Gokhale posted a letter on X, formerly known as Twitter, in which he had asked the local police for details on the number of cases of use of firecrackers, and action taken against perpetrators.

The Delhi police spokesperson did not answer several calls made by Reuters asking for comment.

Air quality in northern India deteriorates every year ahead of winter, when cold air traps pollutants from vehicles, industry, construction dust and agricultural waste burning.

New Delhi’s authorities postponed an earlier decision to restrict use of vehicles, after a brief spell of rain on Friday brought some respite from a week-long exposure to toxic air.

The local government said it plans to maintain its ban on construction activities and to keep schools closed to protect people from the pollution. REUTERS