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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.

light gray means not available, blue means very good (0–33), green means good (34–66), purple means fair (67–99), pink means poor (100–149), dark gray means very poor (over 150)

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.

Air quality index value equals to 100 times the amount obtained with the division of pollutant concentration by pollutant goal concentration

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
Ozone 0.10ppm 1 hour
Nitrogen dioxide 0.12ppm 1 hour
Sulfur dioxide 0.20ppm 1 hour
Carbon monoxide 9ppm 8 hours
PM10 50µg/m3 24 hours
PM2.5 25µg/m3* 24 hours
TSP 80µg/m3** 24 hours

Notes:

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.

Licence
Creative Commons Attribution 3.0 Australia (CC BY 3.0)
Last updated
5 February 2014

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