CPCB defends air quality index methodology in Delhi

The Central Pollution Control Board (CPCB) has defended its National Air Quality Index (NAQI) reporting methodology following concerns regarding data gaps and discrepancies between official readings and private applications in Delhi.

The CPCB clarified that differences in Air Quality Index (AQI) values are due to variations in measurement methods and the use of 24-hour averages rather than under-reporting. While private apps may show higher values during sharp hourly peaks, the NAQI reflects sustained exposure over a 24-hour period to provide a scientifically relevant measure for public health advisories.

Addressing concerns about the index being capped at 500, the board explained that this limit is a design feature established in 2015. An AQI of 500 or above indicates the highest level of health concern and remains within the 'Severe' category, as the health risks are considered nearly identical at those levels. The NAQI is calculated hourly based on the highest sub-index among eight pollutants: PM2.5, PM10, carbon monoxide, nitrogen dioxide, sulphur dioxide, ammonia, ozone, and lead.