AQI limited to 500? CPCB explains why official monitors missed peak Diwali smog in Delhi | Today’s news
The Central Pollution Control Board (CPCB) has dismissed allegations of under-reporting of air pollution data, clarifying that discrepancies between its official data and private air quality apps stem from scientific methodology and hardware limitations.
The clarification, released on Tuesday at X, came in response to media reports questioning CPCB’s Air Quality Index (AQI) given during and after Diwali.
There were concerns about apparent data gaps at certain monitoring stations in Delhi, a perceived AQI “ceiling” of 500 and glaring discrepancies between official values and those reported by private platforms.
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Why did official monitors show ‘data gaps’ during Diwali?
Quick answers to key questions
•5 QUESTIONS
Some older particle analyzers were calibrated to measure up to 1000 micrograms per cubic meter. The automated system considers values above this range to be errors, so these hours are excluded from the station’s 24-hour average.
The CPCB said the apparent gaps were due to the measurement limits of older instruments and data validation – not deliberate underreporting. When the measured values exceed the calibrated range of the analyzers, the system considers them as errors.
Private applications can respond to sharp hourly fluctuations in pollution, while the CPCB National Air Quality Index reflects exposure over the previous 24 hours. As the concentration changes, the two values may differ.
NAQI converts pollutant data into a single, color-coded value to indicate the health impact of sustained exposure. It reflects the previous 24 hours rather than just a short-term peak hour.
Yes. The CPCB said older instruments are being replaced and the monitoring network is being continuously expanded to avoid data lapses during extreme pollution.
Addressing the missing data during the peak firecracker burst, the pollution watchdog explained that the older particulate analyzers — deployed when the National Air Quality Index (NAQI) was introduced in 2015 — were calibrated for a measurement range of 0-1,000 micrograms per cubic metre.
Due to this hardware limitation, the automated data validation system considers any hourly value exceeding this calibrated range as an error. Consequently, these extreme values are not used in the final calculation.
“During extreme episodes that are occasional like Diwali firecracker burst, this may appear as a data gap at a particular station and these hours do not contribute to the 24-hour average of the relevant pollutant for the station concerned,” the committee said.
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CPCB vs private applications: 24 hour exposure rule
Regarding why private apps often flash alarming, higher AQI numbers compared to the official NAQI platform, the CPCB said that private apps respond immediately to hourly fluctuations, while the official NAQI is designed to measure persistent health risks.
“Generally, private applications are considered to show higher AQI. This may hold during short peaks when hourly readings spike. However, when concentrations fall, such applications show lower AQI than NAQI (National Air Quality Index) because NAQI continues to reflect exposure from the previous 24 hours,” the CPCB said.
The council emphasized that NAQI converts complex pollutant data into a single, color-coded index value to effectively inform the public about long-term health risks.
“The NAQI provides a consistent and reliable indication of the likely health effects of sustained exposure to pollutants, which is a scientifically relevant measure for public health recommendations,” the CPCB said.
Modernization of the monitoring network
To prevent future data outages during extreme immission events, the council noted that monitoring equipment has advanced significantly since 2015. Currently, older devices are being replaced and the monitoring network is being expanded.
“CPCB remains committed to transparent, scientific and reliable air quality reporting and continuous improvement of the monitoring network and methodology in consultation with experts,” the board said.
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Delhi Diwali AQI
The CPCB classified the city-wide average AQI as “very poor” on Diwali night, with numerous monitoring stations already recording “severe” levels above 400.
Meanwhile, independent monitoring platform AQI.in reported a staggering AQI peak of 2,283 immediately after Diwali before settling at a “dangerous” 637 on Monday morning.
