The Central Pollution Control Board (CPCB) issued a clarification on Tuesday, 10 November 2026, stating that hourly PM2.5 readings exceeding 1,000 micrograms per cubic metre (µg/m³) are automatically excluded from calculating the National Air Quality Index (NAQI).
The official response follows an investigative report revealing that over two-thirds of Delhi’s 59 Continuous Ambient Air Quality Monitoring Stations (CAAQMS) went offline or stopped recording data between 10:00 PM and 6:00 AM on Diwali night, when pollution levels peaked across the capital.
Automated Data Validation & Extreme Pollution Spikes
According to data released by the Delhi Pollution Control Committee (DPCC), several monitoring stations recorded extreme pollution levels during the post-Diwali window:
- Record Readings: West Delhi’s Mundka recorded a PM2.5 concentration of 3,744 µg/m³ at 2:00 AM on Monday, while JNU in South Delhi logged 3,023 µg/m³ at 4:00 AM, and NSUT West Campus reached 3,008 µg/m³ at 5:00 AM.
- Calibrated Limits: CPCB explained that particulate matter analyzers deployed under the NAQI framework are calibrated for a measurement range of 0–1,000 µg/m³. Readings above this threshold are treated as automated “out-of-range” data and excluded from 24-hour average computations.
- Prolonged Exposure Focus: The pollution control board stated that the index is designed to assess prolonged environmental exposure rather than short-lived, episodic spikes caused by intense firecracker bursting.
Expert Criticism & Transparency Concerns
Environmental analysts and public health researchers raised concerns over data gaps during peak exposure windows:
- Information Deficit: Experts noted that withholding raw data during peak pollution hours hinders comprehensive research on exposure risks and limits evaluation of policy measures, such as firecracker restrictions.
- AQI Ceiling Cap: CPCB reiterated that the NAQI has a maximum numerical cap of 500, beyond which all air quality conditions fall into the “Severe” category without further numerical extrapolation.
- Methodology Review: The board confirmed that internal consultations are underway to review data processing protocols for extreme readings in light of advancing monitoring technologies.