CPCB Defends AQI Caps Amid Delhi Pollution Data Gaps

The Central Pollution Control Board (CPCB) defended its air quality monitoring methodology after discrepancies emerged between official National Air Quality Index (NAQI) readings and private apps following Diwali in Delhi. While private platforms reported AQI levels as high as 1,800, official readings remained capped at 500. The CPCB stated this ceiling is a design feature aligned with international standards, such as the US EPA scale, because any value above 500 remains in the severe health category.

The board revealed that hourly PM2.5 readings exceeding 1,000 micrograms per cubic metre are automatically excluded from NAQI calculations because the 2015 validation system was calibrated for a 0-1,000 range. This technical limitation caused data gaps at 45 of Delhi's 59 monitoring stations during peak pollution windows. While the CPCB maintains that the data exists but is not used in 24-hour rolling averages, the Ministry of Environment, Forest and Climate Change of India acknowledged that the 2015 data-validation framework is outdated and requires revision.

Discrepancies with private apps were attributed to measurement techniques, as private sensors often capture hourly spikes while the NAQI focuses on sustained exposure. Data from the Delhi Pollution Control Committee showed extreme spikes, including a reading of 3,744 micrograms per cubic metre in Mundka. The CPCB is currently reviewing its data processing protocols and upgrading instruments to address these limitations.