New Delhi and its sprawling metropolitan region – home to more than 30 million people – is regularly ranked among the world’s most polluted capitals, with acrid smog blanketing the skyline each winter.

Cooler air traps pollutants close to the ground, creating a deadly mix of emissions from crop burning, factories and heavy traffic.

But pollution has also spiked due to days of fireworks set off to mark Diwali, the major Hindu festival of lights, which culminates on Monday night.

The Supreme Court relaxed this month a blanket ban on fireworks over Diwali to allow the use of the less-polluting “green firecrackers” – designed to emit fewer particulates. The ban was widely ignored in past years.