Delhi named world's most polluted major city a day before Diwali

New Delhi woke up Saturday as the most polluted major city on the planet. Swiss air-quality tracker IQAir put the Indian capital in first place at 10:35am, with a US air quality index reading of 581 — a number that signals hazardous air for everyone breathing it.

That figure dwarfs Lahore, the closest big-city rival on the list, which sat at 285 across the border in Pakistan. In other words, Delhi's air was roughly twice as filthy as the second-worst major city IQAir was tracking.

The timing is brutal. Diwali, the Hindu festival of lights, lands on Sunday, and the celebrations traditionally bring a wave of firecracker use that pushes already-thick air even further into the danger zone. Forecasters are warning of severe pollution conditions.

Authorities aren't waiting for the smoke to clear. Schools in and around Delhi have been ordered to switch to online classes, and residents are being encouraged to work from home as the city braces for the post-festival fallout.

Delhi's annual autumn pollution crisis is a familiar and grim ritual, driven by a mix of festival fireworks, crop burning and weather that traps pollutants close to the ground. This year's pre-Diwali reading suggests the capital is starting from an unusually bad baseline.

With Diwali still a day away, the question now is how much worse the index climbs once the fireworks start — and how long Delhi's residents will be stuck breathing it.