CPCB says AQI excludes extreme particulate readings

The Central Pollution Control Board says its air quality index excludes hourly particulate matter readings above 1,000 micrograms per cubic metre, a calibration limit that can leave gaps in official data during extreme pollution. The explanation follows revised Delhi monitoring figures showing Diwali-night PM2.5 levels above 2,000 micrograms per cubic metre at several locations, while an analyst said CPCB data for the night remained unavailable.

The CPCB said its particulate matter analysers were calibrated to measure concentrations from zero to 1,000 micrograms per cubic metre. Its automated validation system treats readings beyond that range as outside the calibrated range and does not use them to calculate the index. During severe episodes, the board said, this can appear as a data gap at a monitoring station, and the affected hours do not contribute to that station’s 24-hour pollutant average.

Revised data from the Delhi Pollution Control Committee recorded PM2.5 peaks of 2,389 micrograms per cubic metre at RK Puram, 2,589 at Ashok Vihar and 2,471 at the Commonwealth Sports Complex. The national safe limit cited in reports is 60 micrograms per cubic metre. At Mundka, DPCC...