Air quality index
Our scientists create an air quality index by converting measured pollutant concentrations into index values.
Index values make it easier to interpret air quality data because they reduce the complexity associated with pollutant concentrations data.
The index value is the pollutant concentration expressed as a proportion of the National Environment Protection Measure for Ambient Air Quality (Air NEPM) standard or the Environmental Protection (Air) Policy 2008 (Air EPP) objective.
Index values over 100 indicate the pollutant concentration exceeds the air quality standard based on health studies. In regards to visibility, index values over 100 only impact the aesthetic environment.
The air quality index comprises five colour-coded categories—see table below.
Go to the live air data page to check the air quality indices, available every hour for South East Queensland, Gladstone, Mackay, Townsville and Mount Isa.
Calculating the air quality index
Air monitoring instruments measure the concentration of pollutants at each monitoring station. By using the equation below, we convert the concentration values into index values.
The 'pollutant goal concentration' used to calculate the index value is the Air NEPM standard for that particular pollutant, or in the case of visibility, the Air EPP objective.
The tables below show the Air NEPM standards and Air EPP objectives used to calculate the index values, as well as the averaging times for each pollutant. The 1-hour, 8-hour and 24-hour averaging times are for the most recent periods.
Air NEPM standards
|Pollutant||Air NEPM standard||Averaging time|
|Nitrogen dioxide||0.12ppm||1 hour|
|Sulfur dioxide||0.20ppm||1 hour|
|Carbon monoxide||9ppm||8 hours|
- ppm: parts per million
- µg/m3: micrograms per cubic metre
- * NEPM Advisory Standard only
- ** Good practice guide for assessing and managing the environmental effects of dust emissions
Air EPP objectives
|Pollutant||Air EPP objective||Averaging time|
|visibility-reducing particles||20km||1 hour|
The Air EPP objective, designed to protect good visibility, is 20km, which means you would be able to see clearly for at least 20km.
This goal is related to a light scattering coefficient value measured using a nephelometer. The degree of scattering is inversely proportional to the visibility. A scattering coefficient value of 235Mm-1 (235 inverse megametres) or less is equivalent to a visibility of 20km or more.