New Delhi, India – Air quality in India’s capital, New Delhi, deteriorated to hazardous levels on Tuesday, ranking as the most polluted city globally, according to Swiss air monitoring group IQAir. The spike in pollution followed widespread use of firecrackers during Diwali, the Hindu festival of lights.

Last week, the Supreme Court of India relaxed a ban on firecrackers in the capital, allowing ‘green crackers’ to be used for three hours on Sunday and Monday. However, witnesses reported that fireworks continued well beyond the permitted hours, Reuters said.

IQAir recorded an air quality index (AQI) of 442 for New Delhi, with PM2.5 concentrations exceeding the World Health Organisation’s annual guideline by over 59 times. PM2.5 particles, which are smaller than 2.5 microns in diameter, can penetrate deep into the lungs and are linked to respiratory and cardiac diseases.

India’s Central Pollution Control Board (CPCB) classified the city’s air quality as ‘very poor’, with an AQI reading of 350. The CPCB considers an AQI of 0-50 as good.

The Ministry of Earth Sciences forecast that Delhi’s air quality will remain in the ‘Very Poor to Poor’ category in the coming days, with AQI levels between 201 and 400.

Each winter, New Delhi and its neighbouring districts experience heavy smog caused by a combination of cold air, construction dust, vehicle emissions and smoke from agricultural burning. The toxic air often forces the authorities to close schools, halt construction activity and impose restrictions on private vehicles.

In neighbouring Pakistan, the government of Punjab province has launched an ‘emergency plan’ to combat air pollution. Measures include action against farm fires and smoke-emitting vehicles, and the use of anti-smog guns in polluted areas.

According to IQAir, Lahore, the capital of Punjab, recorded an AQI of 234 — the second-highest in the world after New Delhi.