Delhi emerged as the world's most polluted major city ahead of Diwali with IQAir recording an air quality index (AQI) of 581 on the US scale on November 7 morning. The reading was more than twice that of Lahore, which came second.

India's Central Pollution Control Board recorded Delhi's AQI at 363 using a different measurement system. Local media described pollution as the worst on the eve of Diwali in eight years. Authorities ordered schools to switch to online classes and issued work-from-home advisories ahead of the festival.

Diwali is traditionally marked by widespread firecracker use, a major source of air pollution. The discrepancy between IQAir's measurements and India's official AQI readings comes from their different scales.

The Central Pollution Control Board and local authorities have taken precautionary measures as levels rise, but no long-term solutions or policy changes are announced yet.