NEW DELHI: Many Delhi residents were puzzled by the wildly different readings of Delhi's pollution level on Tuesday. While the Central Pollution Control Board (CPCB) reported AQI levels well below 400, international apps like IQAir showed figures crossing 2,000 in several areas.

For instance, at 12.30 am on Tuesday, CPCB's data showed an AQI of 272 at Siri Fort, while IQAir reported an astonishing 2,449 for the same location. Experts say both readings are technically correct but they follow different methodologies and scales. "The Indian AQI, developed in 2015, is calculated using six key parameters — PM2.5, PM10, ozone, nitrogen dioxide, sulphur dioxide, and carbon monoxide. The graded scale — from good to severe+ — ranges from 0 to 500," said MP George, former additional director at

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