India’s air quality index may understate pollution during extreme episodes, experts warn

The Central Pollution Control Board’s (CPCB) decision to exclude particulate matter readings exceeding 1,000 micrograms per cubic metre from Air Quality Index (AQI) calculations has raised concerns among environmental experts, who say the practice could understate the severity of pollution during extreme episodes.

The issue came into focus after unusually high pollution levels were recorded across Delhi during Diwali, with several monitoring stations reporting PM2.5 concentrations above 1,000 micrograms per cubic metre.

The CPCB said its monitoring instruments were originally calibrated to measure particulate matter concentrations between zero and 1,000 micrograms per cubic metre when the National Air Quality Index was introduced in 2015. Its automated system therefore treats readings beyond that range as invalid and excludes them from calculations.

According to the board, this can create data gaps during severe pollution episodes. It said internal deliberations and consultations were underway to review the methodology.

However, environmental experts argue that excluding extreme readings can distort pollution assessments and weaken public scrutiny of government control measures.

Sunil Dahiya, founder and lead analyst at Envirocatalysts, told the Hindustan Times that withholding exact pollution figures undermines analysis by researchers, institutions and other stakeholders.