Key facts
- AQI is an index, not a direct pollutant concentration.
- The overall AQI is normally determined by the highest pollutant sub-index.
- AQI scales differ by country, so the same concentration can produce a different index value.
- AQI.news labels its live city readings as US AQI.
What the AQI number represents
Monitoring instruments measure pollutant concentrations in units such as micrograms per cubic metre or parts per billion. An AQI system converts each supported pollutant concentration into a common numerical scale associated with health messages.
The calculation is performed separately for pollutants such as PM2.5, PM10, ozone, nitrogen dioxide, sulfur dioxide and carbon monoxide. The highest valid pollutant sub-index generally becomes the reported AQI because it represents the pollutant creating the greatest short-term concern at that time.
AQI versus pollutant concentration
An AQI of 150 does not mean the air contains 150 units of pollution. To understand what is driving the number, check the individual PM2.5, PM10, ozone and gas readings alongside the headline AQI.
| Measurement | What it tells you |
|---|---|
| Pollutant concentration | How much of a specific pollutant is present in the air. |
| Pollutant sub-index | Where that concentration falls on the selected AQI scale. |
| Overall AQI | The highest qualifying pollutant sub-index for the reporting period. |
Why AQI values differ between services
AQI is not one universal formula. The United States EPA and India CPCB use different breakpoints, averaging rules and category names. Services may also use different monitoring stations, models, update times or dominant pollutants.
Before comparing two AQI numbers, confirm the scale, location, reporting time and data source. AQI.news currently reports its headline city value on the US AQI scale and displays pollutant concentrations separately.
How to use AQI in daily decisions
- Check the current category and the pollutant driving it.
- People with asthma, heart or lung disease, children and older adults should respond earlier to worsening conditions.
- Reduce the duration or intensity of outdoor exertion when guidance recommends it.
- Use current local information because air quality can change during the day.
Frequently asked questions
Is AQI the same as PM2.5?
No. PM2.5 is a measured concentration of fine particles. AQI is an index that can be calculated from PM2.5 or another supported pollutant.
Why do two apps show different AQI values?
They may use different AQI standards, data sources, stations, models, averaging periods or update times.
Which AQI scale does AQI.news use?
AQI.news labels its headline live city values as US AQI and provides the underlying pollutant concentrations separately.
Sources
This reference was prepared from the following primary public-health and regulatory sources:
- Patient Exposure and the Air Quality IndexUnited States Environmental Protection Agency
- National Air Quality IndexCentral Pollution Control Board, India