About the AQI

Data readings

In order to provide more detailed information than is available in the AQI (air quality index), measurements are also published as hourly data readings, and daily data readings, in scientific units rather than the derived values provided in the AQI.

Data readings are the actual scientific measurements for each air pollutant. The data readings are recorded in different units of measure, depending on the type of pollutant.

AQI (air quality index values)

Date readings are converted into AQI values by using the formula:

This means the AQI is a derived value (based on the data reading). Because data readings have different underlying units of measure, it is difficult to compare the various pollutants. After we derive the AQI values we have a standardised set of values that we can then compare and present.

Site AQI

There are 24 monitoring sites around NSW where the air quality index (AQI) values are calculated. The AQIs are compared at each site. The highest AQI value at each site becomes the site AQI. In the example below, the highest AQI for pollutant 3 would be the site AQI

The highest
value is taken as the

for that particular site

Region AQI

All the site AQIs in a given region are compared. The highest site AQI for a region is taken as the region AQI. In the example below, the reading for site RST would be the region AQI 

The highest  
for a region is taken as the