Delhi overtook Lahore on Friday (13 November) to become the world's most polluted major city, with smog cutting visibility across the capital. The Swiss monitoring group IQAir put Delhi's air quality index (AQI) at 334 and rated it hazardous. For comparison, an AQI of up to 50 is considered good.
India's own Central Pollution Control Board (CPCB) showed a higher figure: 403 at 9 am, in its severe category. The two readings differ because the Swiss and Indian systems use different scales and methods. IQAir's ranking is a live comparison of major cities, so the order can change as conditions shift.
The Independent reported that the CPCB figure has climbed since Diwali on Sunday, 8 November: 299 on Tuesday, 313 on Wednesday and 350 at 4 pm on Thursday. On Friday, 33 of the city's 58 monitoring stations were in the severe category, several of them above 450.
Winter makes this a seasonal problem across northern India and Pakistan: cold, heavy air traps emissions from vehicles, dust from construction and smoke from crop burning, The Hindu reported. Videos from news agency ANI showed cars and motorcycles emerging from dense smog that also appeared to hide street lights on main roads. The capital has about 20 million people.
The Supreme Court allowed only approved “green” firecrackers on Diwali, within set time windows. Even so, the Centre for Science and Environment found that PM2.5, the fine particles small enough to enter the lungs, averaged 236 micrograms per cubic metre in the week before Diwali, nearly double the 120 recorded in the same week in 2025, the Independent reported.
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