India’s capital, Delhi, overtook Lahore to become the world’s most polluted city on Friday, with air quality reaching hazardous levels and visibility dropping as smog blanketed the city of 20 million people.

Earlier, Delhi’s air quality index (AQI) stood at 334, categorised as “hazardous”, making it the most polluted major city globally, according to Swiss air quality monitoring group IQAir, which measures pollution levels based on the concentration of pollutants. An AQI reading of up to 50 is considered good, indicating little or no health risk.

India’s official Central Pollution Control Board (CPCB), meanwhile, recorded a higher AQI of 403 in Delhi and classified the air quality as “severe”.

The difference between the Swiss and Indian readings is due to the different AQI scales and methodologies used to calculate and classify air pollution levels.

According to IQAir’s hourly readings, Delhi’s AQI had dropped to 208 by 11am PKT. At the time, Lahore was ranked seventh among the world’s most polluted major cities, with an AQI of 155.

In Delhi, cars and motorcycles emerged from dense smog, which also appeared to obscure street lights on the city’s main roads, videos from news agency ANI showed.

Pollution is a seasonal problem in many parts of northern Pakistan and India, as the cold, heavy air of winter traps vehicle emissions, construction dust and smoke from agricultural burning.

Friday’s readings marked a drop in Lahore’s pollution levels after the city had ranked as the most polluted major city in the world for several days in a row.

Earlier this week, Lahore’s average PM2.5 concentration was eight times the World Health Organisation’s (WHO) guideline value, according to a report by the Pakistan Air Quality Initiative (PAQI).

The report, released on Tuesday, said the number of likely crop-residue fires in Punjab, Pakistan, remained almost unchanged from the corresponding period last year.

Lahore’s average PM2.5 concentration stood at 126 micrograms per cubic metre during the period, exceeding the 24-hour National Environmental Quality Standards (NEQS) on all 40 days for which valid data were available. The average was 11pc lower than in the corresponding period in 2025.

Satellite instruments detected 18,825 fires across Punjab, Pakistan, 89 per cent of which were classified as likely crop-residue burning. The highest daily count was recorded on Nov 1, with 1,102 detections.

The 24-hour National Environmental Quality Standards (NEQS) were exceeded on all 40 days for which valid data were available. The average concentration was 11pc lower than during the corresponding period in 2025.

However, the report cautioned that the association did not establish the precise contribution of crop-residue burning to urban pollution, as stagnant weather conditions and reduced atmospheric dispersion also contributed to the accumulation of pollutants.

EPA says enforcement against pollution sources contributed to Lahore’s improved air quality

Punjab Environment Protection Agency (EPA) spokesperson Sajjad Bashir said enforcement against local sources of pollution, along with favourable weather conditions, had contributed to the improvement in Lahore’s air quality.

He said authorities had intensified action against polluting industries and brick kilns, agricultural residue burning, smoky vehicles and open waste burning.

According to comparative figures shared by the department, brick kiln inspections increased from 37,838 in 2025 to 80,594 during Jan 1 to Nov 10 this year. Authorities also demolished 1,372 kilns and sealed 864 for violations.

Industrial inspections rose from 38,098 to 47,643 during the same period, while 1,419 industrial units were sealed and fines totalling Rs216.985 million imposed.

The department also increased action against prohibited plastic materials, with confiscations rising to 438,159 kilogrammes from 378,630kg last year.

Bashir said favourable weather had helped disperse pollutants, but added that the improvement could not be sustained through weather conditions alone.

He stressed the need for continued enforcement against industries, brick kilns, agricultural burning, smoky vehicles and open waste burning beyond the smog season to prevent pollution levels from rising again.