On November 10, the Central Pollution Control Board (CPCB) explained why India's official Air Quality Index (AQI) stops at 500.
Some private apps showed readings above 1,000, and some even showed 1,800.
The CPCB said the 500 limit is a design feature, not under-reporting.
The National Air Quality Index (NAQI) runs from 0 to 500.
Anything above 500 stays in the "Severe" category, so the health label does not change.
Key points
- The official AQI stops at 500 by design.
- Many private apps use low-cost sensors and hourly readings.
- Official figures use 24-hour averages and checked data.
- Some data gaps in Delhi are now under review.
Why do private apps show different numbers?
The CPCB says the gap comes from different equipment, data sources and calculation methods.
Many apps use low-cost sensors and hourly readings. Official figures use 24-hour averages and checked data.
Apps can show higher numbers during short spikes. But when pollution falls, they can show lower figures than NAQI.
What about the missing data in Delhi?
Environment Ministry sources said 45 of Delhi's 59 monitoring stations had missing hourly readings for at least one pollutant.
They said the data exists but is not used in the calculation.
The equipment is calibrated up to 1,000 micrograms per cubic metre.
Readings above that range are left out of averages, which can appear as gaps.
Graphic: News Anek, from the facts in this report
What happens next for the method?
Sources said the method dates back to 2015 and needs revision.
Two or three scientists are working internally, but no external expert group has been formed yet.
The CPCB said it is keeping the methodology under review.
Until then, remember that your phone and the official number may measure things differently.
Sources
- thedailyjagran.com: Why Does Official AQI Data Stop At 500 While Mobile Apps Show Levels Above 1,800? Pollution Board Explains
- Mathrubhumi English: One city, many numbers: Why Delhi’s AQI reads 370 on government portals and 1000+ on private apps
- The New Indian Express: Delhi's extreme pollution readings fall outside CPCB's 2015 data validation framework
