Delhi AQI: Why CPCB and app pollution readings differ

A Delhi AQI of 373 and an app reading of 1,747 can describe the same polluted day, but they are not calculated over the same period.

During Diwali, the Central Pollution Control Board’s official AQI readings remained below 400, while some apps showed readings from 1,500 to 1,800. The difference largely reflects methodology: CPCB’s AQI uses a 24-hour average, while apps may use shorter time periods that capture immediate pollution spikes.

Apps may also rely on private sensors, whose methods can vary. A high app reading may therefore reflect conditions at a specific place and moment rather than the city’s official day-long AQI.

When comparing readings, residents can check whether a number represents a 24-hour official average or a shorter, sensor-based snapshot of the air outside.