AQI differences with private apps due to different methodology, not data under-reporting: CPCB

New Delhi: The Central Pollution Control Board (CPCB) on Tuesday said that the difference in AQI values shown by private apps and its own platform is due to differences in the measurement of pollutant concentration and methodology, and not under-reporting.

The statement, posted on X, came as a response to some media reports that raised concerns about the reporting of Air Quality Index (AQI) by the CPCB during and after Diwali. The concerns included capping of AQI at 500, data gaps at some monitoring stations in Delhi and differences with AQI values shown by other platforms.

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"It is generally perceived that private apps show higher AQI. This may hold during short peaks, when hourly values rise sharply. However, when concentrations fall, such apps show lower AQI than the NAQI (National Air Quality Index), since NAQI continues to reflect the exposure of the preceding 24 hours," said the CPCB.

NAQI, which was introduced in 2015, is a tool for effective communication of air quality status to people. It transforms complex air quality data of various pollutants into a single number (index value), nomenclature and colour.

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"The NAQI provides a consistent and reliable indication of the likely health impacts of sustained exposure to pollutants, which is the scientifically relevant measure for public health advisories," the CPCB said.

The board also highlighted that particulate matter analysers deployed at the time of introduction of the NAQI were calibrated for a measurement range of 0-1,000 micrograms per cubic metre.

Accordingly, consistent with this, the designed system of automated data validation treats hourly readings beyond the calibrated range as outside range, and such readings are not used in the computation, according to the CPCB.

"During extreme episodes, which are occasional like Diwali firecracker bursting, this may appear as a data gap at the particular station concerned, and those hours do not contribute to the 24-hour average of relevant pollutant for the concerned station," said the board.

It noted that since 2015, monitoring instruments have advanced considerably, and replacement of instruments and expansion of the monitoring network is being carried on continuously.

"CPCB remains committed to transparent, scientific and reliable reporting of air quality and to continuous improvement of the monitoring network and methodology in consultation with experts," said the board.