For this report, a qualitative assessment was made of ambient air quality in the 8 state and territory capitals, and a small number of major regional or industrial centres, using the same procedure as for the 2011 state of the environment report (SoE 2011).

Currently, no central repository of air quality data exists in Australia, so the data had to be obtained from each jurisdiction, because they were not always publicly available. There is a need for the Bureau of Meteorology to develop the National Air Quality Data Service as part of the National Clean Air Agreement. This will provide researchers and the community with much better access to air quality data.

The assessment was restricted to 3 of the 7 pollutants for which national health-based standards have been set: photochemical oxidants (as ozone), and coarse and fine particulate matter (as PM₁₀ and PM_2.5, respectively). These were chosen as key pollutants because their concentrations, at times, are close to or exceed the standards, and because of their potential impact on human health (e.g. WHO 2013).

The approach is based on the characterisation of an airshed from 2009 to 2014 using its worst performing compliance station (monitoring site). These compliance stations are established in accordance with an approved National Environment Protection Measure (NEPM) monitoring plan, and are generally sited to be indicative of air quality experienced by the general population in the region. Most large regional cities have only one NEPM monitoring station, and most monitor particles but not ozone, since they lack the scale of industry and traffic likely to give rise to ozone as a secondary pollutant. In each state, the regional cities selected for analysis of PM₁₀, PM_2.5 and ozone (where this is monitored) were the worst performing in the state.

Ozone levels were evaluated against the 4-hour exposure standard of 0.08 ppm rather than the 1-hour standard (0.10 ppm), because the 4-hour standard is more likely to give a better indication of the impact on the general population, rather than on sensitive individuals affected by acute (shorter-term) events.

For each selected station, year and pollutant, the monitoring data were converted into air quality index (AQI) values, which express the measured concentration as a percentage of the standard. An AQI of 100 means that the pollutant is present in the air at the level of the standard. These AQIs were then allocated to one of the 5 qualitative categories (very good 0–33, good 34–66, fair 67–99, poor 100–149, and very poor 150+) commonly used by Australian environment protection agencies to report air quality.

These yearly percentage distributions were used as the basis for assigning an overall AQI for each pollutant at each station using the criteria set out in Table ATM7. The assessment was compared with that given in SoE 2011 to assess the trend. If the parameter was not assessed in 2011 (e.g. PM_2.5), the trend was based on results from 2009 to 2014.

A summary of the results is presented in assessment summaries 5 to 9.

Table ATM7 Criteria for assigning overall air quality index (AQI)-based qualitative categories

Supplementary rules for assessing overall AQI were as follows:

• If the percentage very good is greater than 45 and is also greater than the percentage good, the assessment grade is very good.
• If the percentage good is greater than 75, the percentage very good can be as low as zero and the assessment grade will still be good.
• If the assessment grade has stayed the same between the 2011 and 2016 reports, but the frequency of percentages within the grade has increased, the trend is set to ‘improving’ to reflect the increase.