Delhi air quality deteriorates as revellers mark Diwali with illegal fireworks

​Air quality deteriorated in India's capital Delhi ​on Monday, after residents ‌celebrating the ​Hindu festival of lights set off fireworks in violation of court orders.

At 9 a.m. (0330 GMT) on Monday, Delhi recorded an ‌air quality index of 370, categorised as 'very poor' by the Central Pollution Control Board, which considers an AQI of up to 50 to be 'good'. Many areas in the city of 20 million showed ‌a reading of more than 400, categorised as 'severe', official data showed.

India's Supreme Court said ‌earlier this month that only certified low-polluting firecrackers would be allowed to be used during limited hours over the Diwali weekend. Residents in Delhi and in Mumbai, the country's financial capital, said firecrackers were going off ⁠until late ​in the night.

Visuals from ⁠Reuters TV showed a layer of smog enveloping India Gate, a prominent spot in central Delhi, close ⁠to government offices and parliament. Delhi was the third-most polluted city in the world as of Monday morning, Swiss ​group IQAir's live ranking showed, with Pakistan's Lahore at the top with an ⁠air quality index of 563, which is categorised as hazardous.

Pollution is an annual problem in many parts of ⁠northern India ​from the onset of winter as cold, heavy air traps vehicle emissions, construction dust and smoke from crop waste burning. The problem is exacerbated in big cities ⁠such as Delhi due to a high number of vehicles and construction activity, leaving many residents battling ⁠respiratory problems.

Delhi has ⁠seen poor air quality levels for more than a week, and imposed restrictions on Friday under a graded action plan, asking schools ‌to conduct ‌online classes, among other measures.