About Air Quality Index (AQI)

The Air Quality Index (AQI) is a standardized indicator used to communicate the quality of ambient air and its potential impact on human health. It converts complex air-quality data into a simple numerical scale that helps citizens understand the level of air pollution and take appropriate precautions.

The Delhi AQI website provides citizens with access to the latest available air-quality information across Delhi, including monitoring station-wise AQI readings, pollutant levels and health advisories.

How the AQI Scale Works

The AQI is calculated based on the concentrations of various air pollutants, including PM2.5, PM10, nitrogen dioxide (NO₂), sulphur dioxide (SO₂), carbon monoxide (CO), ozone (O₃), ammonia (NH₃) and lead (Pb).

The overall AQI is determined in accordance with the prescribed methodology, considering the available pollutant sub-indices and the pollutant with the highest sub-index value.

How Delhi's AQI on this site is worked out

Each station's AQI is on India's National AQI scale (0 to 500): the highest sub-index among the station's pollutants, provided at least three pollutants, including PM2.5 or PM10, are available. "Delhi AQI" is the average of the AQI at every station reporting that hour. Stations with no reading in the last 2 hours are left out of the average and shown as not reporting. The lead pollutant is the one that sets the highest sub-index at the most stations.

Where the data comes from

AQI and pollutant data come from the Continuous Ambient Air Quality Monitoring Stations (CAAQMS) of the Central Pollution Control Board (CPCB) and the Delhi Pollution Control Committee (DPCC). GRAP stages are invoked by the Commission for Air Quality Management (CAQM). Weather is from Open-Meteo. The portal is published by the Department of Environment, Government of NCT of Delhi.

Updates and timestamps

Stations report every hour. Every value says which hour (IST) it is for, which is kept separate from when the site last checked the feed. A reading more than 2 hours old is shown as "data delayed", never as live. These real-time figures are provisional and may change after CPCB's quality checks.

India's AQI and the US AQI

Many private apps show the US AQI, which uses different breakpoints and categories, so the same air gets a different number on each scale and the two cannot be compared directly. Every value on this site is on India's National AQI.