Use an air quality monitor or sensor
Measure key pollutants such as PM2.5, PM10, ozone, nitrogen dioxide, sulfur dioxide, and carbon monoxide
Record pollutant concentrations over a set time period
Compare each pollutant level to the AQI breakpoints used by your country or region
Convert each pollutant concentration into its sub-index value
Identify the highest sub-index among all measured pollutants
Use the highest sub-index as the overall AQI
Check the AQI category associated with that value
Repeat measurements regularly to track changes over time