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An Air Quality Index is a scale that indicates the quality of air, based on air pollutant monitoring data. The index is developed using a descriptive scale that relates to Australia's air quality standards. If the air quality is classified as poor, then one or more pollutants in the air have exceeded the national standard.
How is the EPA Air Quality Index calculated?
An index for any given pollutant is its concentration expressed as a percentage of the relevant standard:
An index value greater than 100 means the pollutant has exceeded the relevant air quality standard. To assess the overall air quality at a particular monitoring station, an index is calculated for each measured pollutant. The maximum of these figures is taken to be the Air Quality Index for that monitoring station as it represents the worst of the pollutants measured. The worst site is then used to summarise Adelaide's air quality.
The NEPM standards used for the index
| Pollutant | Standard level | How it is calculated |
| Ozone | 0.10 ppm | the maximum one-hour value in the last 24 hours |
| Nitrogen Dioxide | 0.12 ppm | |
| Sulfur Dioxide | 0.20 ppm | |
| Carbon Monoxide | 9 ppm | the maximum eight-hour value in the last 24 hours |
| Particles (PM10) | 50 µg/m3 | the one-hour values averaged over the previous 24 hours |
| Fine Particles (PM2.5) | 25 µg/m3 * |
* Advisory reporting standard
For more information about the Air Quality NEPM, click here.
The EPA Air Quality Index has five air quality categories ranging from "very good" to "very poor" as shown in the table below. Each category has an associated colour.
| Category | Index range and colour |
| Very poor air quality | 150 or greater (black) |
| Poor air quality | 100 to 149 (red) |
| Fair air quality | 67 to 99 (yellow) |
| Good air quality | 34 to 66 (green) |
| Very good air quality | 0 to 33 (blue) |
The above classification allows for variation in the quality of the air on a daily basis. If a pollutant is ever classified as poor or worse - then the standard or goal has been exceeded. The data used to compile the EPA air quality index come directly from EPA's air monitoring stations and is “raw” or “un-validated” data.
Further information on data validation is available on the definitions and abbreviations page.
When ‘NA’ is displayed in the table of daily results for the Air Quality Index, this means that no data is available because an instrument has broken down or something has made the data incorrect or inaccurate.
Last modified: 27/03/2012 10:52 am
