Differences between Air Quality Index readings on private apps and the Central Pollution Control Board's platform arise from variations in how pollutant concentrations are measured, and the methods used, and are not due to under-reporting, the board said on Tuesday, according to news agency Press Trust of India.The CPCB issued the clarification after media reports raised concerns over its reporting of the Air Quality Index, or AQI, during and after Diwali. These included the capping of AQI at 500, data gaps at some monitoring stations in Delhi and differences between CPCB readings and those on other platforms.“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,” the CPCB said in a post on X.Introduced in 2015, the National Air Quality Index communicates air quality levels to the public.

It converts data on various pollutants into a single index value, category and colour. “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 said particulate matter analysers in use when the national index was introduced were calibrated to measure concentrations ranging from zero to 1,000 micrograms per cubic metre, PTI reported. As a result, the automated data validation system treats hourly readings above the calibrated range as out of range and does not include them in its calculations, 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,” the board said.The CPCB said monitoring instruments had improved considerably since 2015, while the replacement of instruments and expansion of the monitoring network were continuing.“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,” the board said.In its clarification, the CPCB maintained that variations in AQI readings and occasional data gaps during extreme pollution episodes result from differences in methodology and equipment limits, rather than under-reporting.- Ends