Explainer: Why IQAir showed Delhi's AQI over 2,000
On October 21, 2025, people in Delhi saw wildly different air quality readings—India's official board (CPCB) said the AQI was under 400, but international apps like IQAir showed numbers over 2,000.
No wonder everyone was confused about which number to trust.
What's the difference?
India's AQI scale maxes out at 500, with anything above 400 classified as severe.
IQAir uses a US-based scale that stretches beyond 500 to highlight extreme pollution.
So, when Delhi's air got really bad, IQAir's numbers shot up while the CPCB's stayed capped.
Which 1 is better?
Definitely. The CPCB uses high-precision monitors, while IQAir relies on sensors that can vary in accuracy.
Still, both indicated that Delhi's air quality was at dangerous or hazardous levels that day.
Knowing why these numbers differ helps you avoid panic—and make smarter choices about heading outside.