Delhi AQI Gap: CPCB Says Private Apps Differ, Not Under-Reporting
Delhi residents seeing two different AQI numbers get the official explanation: 24-hour averages versus instant readings, and a 500-point cap now under review.
Image: PTI
The Central Pollution Control Board (CPCB) said on Tuesday, 10 November, that the gap between official Air Quality Index figures and those on private apps after Diwali comes from different measurement methods and averaging periods, “not under-reporting”. In a statement, the board said it is also reviewing its methodology, including how to treat readings that fall beyond the range its instruments measure.
Why Your Phone and the Official Number Differ
Many Delhi residents saw one number on a private app and a lower one from the government after Diwali. The CPCB said private platforms often use low-cost sensors that may have calibration limits, apply different breakpoints, and show instantaneous hourly readings. The national index uses 24-hour averages (8-hour for carbon monoxide and ozone), so apps can look worse during a spike and better once levels fall.
The index is calculated across eight pollutants and needs at least 16 hours of data and three pollutants, including PM2.5 or PM10, according to the board.
Also read National Clean Air Programme: Jairam Ramesh Wants Urgent Revamp
The 500 Cap and the Missing Hours
The CPCB said the 500-point ceiling is deliberate. It dates to the 2015 National Air Quality Index and, the board said, matches international practice, including the US EPA scale. Anything above 500 is classed as “Severe”.
Its particulate analysers are calibrated for 0 to 1,000 micrograms per cubic metre. Hourly readings above that are excluded, which can show up as gaps during sharp events such as firecracker bursts. The board said those hours did not affect the 24-hour average at the station.
The row has a political side. IPB News reported earlier that AAP alleged fraud and Congress flagged 25 stations that went dark. IPB’s post-Diwali figures showed 15 stations in the severe band. More coverage sits under the Delhi air pollution tag.
Review Has No Deadline Yet
The CPCB said internal deliberations and consultations on processing data beyond the measurement range are under way. It gave no timeline for the review, and no date for any change to the 500-point scale.
Source: Based on reporting by The Tribune and Business Today.
Image: PTI.
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