Lahore has topped the ranking of the world's most polluted major cities for a second day running, as Pakistan blamed smoke from Diwali fireworks in neighbouring India for the toxic air hanging over the city.

Swiss air quality group IQAir put Lahore's air quality index (AQI) at 263 on Tuesday, 10 November, a level categorised as "very unhealthy". The city's concentration of PM2.5, the fine particles small enough to penetrate deep into the lungs, stood at 37.2 times the World Health Organization's annual guideline value, according to IQAir.

Punjab's Environment Protection Minister Marriyum Aurangzeb said pollutants had been carried into the region by light winds and air drifting from India in the aftermath of Diwali, the Hindu festival of lights, which was celebrated over the weekend. Firecrackers set off during the festival blanketed much of northern India and Pakistan in toxic smog.

"However, air pollution is expected to gradually decrease from early afternoon as weather conditions improve and winds shift direction," the minister said.

Delhi second as firecrackers blamed for half its pollution

IQAir ranked Delhi, India's capital, as the world's second-most polluted major city on Tuesday, with an AQI of 188. Indian government data showed that firecrackers were responsible for nearly 55% of the PM2.5 in Delhi a day earlier.

The blame game over the smog is not new. Pakistan similarly attributed its toxic air in 2024 to crop-waste burning in Indian Punjab, but officials from India's weather department said at the time that the wind direction meant the airflow was actually from Pakistan into India.

This year, Indian Prime Minister Narendra Modi's Bharatiya Janata Party has also blamed crop-waste burning in Indian Punjab, which is governed by a regional opposition party, for Delhi's poor air quality. Local media reported a sevenfold increase in farm fires in the state on Sunday, when Diwali was celebrated, although Indian Punjab's state government says incidents of crop-waste burning have fallen compared with previous years.

Monday's readings were far worse

Tuesday's reading of 263 was a marked improvement on Monday, when Lahore's hourly AQI reached 647, deep in the hazardous category, according to IQAir data reported in Pakistan. An 8am reading on Monday stood at 563, with PM2.5 concentrations reaching 357 micrograms per cubic metre.

The Punjab government had warned in advance that smoke from Diwali fireworks and crop-residue burning in neighbouring Indian Punjab could reach Lahore within five to 13 hours on easterly winds, and forecast that pollution would remain high on 9 and 10 November, with some improvement likely from 11 November.

Vehicle emissions, construction dust and smoke from crop-waste burning are also major contributors to winter pollution on both sides of the border, and Punjab's Environment Protection Department is expected to release a comparative assessment on Tuesday showing how much each source contributed to the latest smog episode. For the original reporting, see Reuters on Lahore's toxic air and PakWheels on Monday's hazardous AQI readings.