CPCB defends AQI cap of 500, says Delhi data gaps came from analyser calibrated range
CPCB says the 500 limit is by design and that readings beyond the analysers' calibrated range were left out, not hidden.
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The CPCB AQI cap of 500 is a deliberate design feature of the index and does not point to under-reporting, the Central Pollution Control Board said on 10 November 2026, ANI reported. The statement answered media reports about how air quality was reported during and after Diwali, PTI said.
What the CPCB AQI cap means
CPCB said the upper limit of 500 was a design feature of the index developed in 2015. A reading of 500 or above carries almost the same health risk. It stays in the Severe category. The board added that the category and its health advisory matter more than the number within it, and that the AQI is meant as a communication tool for the public.
Under the National Air Quality Index, an hourly AQI is built from sub-indices for several pollutants, and at least three of them, including either PM2.5 or PM10, are needed to produce a reading, ANI reported.
Why Delhi had data gaps
The data gaps at some Delhi stations came from the calibrated range of the analysers, CPCB said. Its automated validation system treated hourly readings beyond the calibrated range as outside range. Those readings were left out of AQI calculations.
CPCB said continuous monitoring stations in Delhi had risen from 10 to 59 since the index began, while the national count had grown from 30 to 634 over the same period, according to the same report.
Why private apps show different numbers
Readings on private apps have differed from official ones. CPCB said such platforms draw on government and non-government sources, including sensors with limits in calibration and data quality assurance. The gap, it said, reflects measurement and methodology, not under-reporting, The News Mill reported.
Key numbers
- 500: the upper limit of the National Air Quality Index, set when it was developed in 2015.
- Three: the minimum number of pollutants needed to generate an AQI.
- 59: continuous monitoring stations now in Delhi, up from 10.
What happens next
CPCB has not said whether it will change the CPCB AQI cap. Nor has it said how out of range readings will be handled in future. Residents in Delhi should follow the health advisory for the current category, especially children, older adults and people with heart or breathing problems, the board advised.
Delhi residents rely on the AQI to decide how much to limit outdoor activity, so how the number is capped and which readings are dropped affects the health advice they see. CPCB has not said whether it will change the cap or the handling of out of range readings.