The Central Pollution Control Board (CPCB) on Tuesday attributed differences between AQI readings on private apps and its platform to variations in pollutant measurement and calculation methodologies, rejecting allegations of under-reporting.
In a statement posted on X, the board responded to media reports questioning its AQI reporting during and after Diwali, particularly over the capping of readings at 500, data gaps at some monitoring stations in Delhi and discrepancies with private platforms.
The CPCB said private apps may report higher AQI during brief pollution spikes when hourly readings rise sharply. However, when pollution levels decline, these platforms may show lower readings than the National Air Quality Index (NAQI), which factors in pollutant exposure over the preceding 24 hours.
Introduced in 2015, the NAQI converts complex air quality data on various pollutants into a single index value, accompanied by a colour code and category to communicate pollution levels to the public.
The board said the 24-hour average provides a consistent indication of the potential health impacts of sustained exposure to pollutants and forms the basis for scientifically relevant public health advisories.
Addressing concerns over data gaps, the CPCB said particulate matter analysers deployed when the NAQI was introduced were calibrated to measure concentrations between 0 and 1,000 micrograms per cubic metre.
Under the automated data validation system, hourly readings exceeding this calibrated range are classified as out-of-range and excluded from AQI calculations.
During extreme pollution episodes, such as Diwali firecracker bursting, this may result in data gaps at individual monitoring stations, as the affected hourly readings are not included in the 24-hour average for the pollutant concerned, it said.
The CPCB acknowledged that monitoring technology has advanced considerably since 2015, adding that instruments are being replaced and the monitoring network expanded continuously.
The board said it remained committed to transparent and scientifically reliable air quality reporting, while improving its monitoring network and methodologies in consultation with experts.
(With inputs from PTI)
