Air quality in Australia’s urban centres is generally good to very good. Levels of carbon monoxide, lead, nitrogen dioxide and sulfur dioxide are generally well below the Air NEPM standards, and continue to decrease in most locations. An exception is Mount Isa and Port Pirie, where the 1-hour standard for sulfur dioxide is still exceeded on more than 20 days each year because of emissions from ore smelting facilities. The situation in Port Pirie is expected to improve dramatically from 2017 when the smelter transformation project is completed, which will reduce average sulfur dioxide emissions by a factor of almost 10.

In contrast, maximum ozone and PM levels have not declined in Australia’s urban areas. The 4-hour ozone standard is typically exceeded a few times per year in Sydney, and occasionally in Melbourne and Perth. The PM 10 goal of not more than 5 exceedances of the 24-hour standard is generally met in capital cities, but less often in regional and rural towns. The 2016 revision of the Air NEPM, which replaced the allowance of 5 exceedances by an exceptional event rule, might lead to a sharper focus on sources that can be controlled.

For fine particulate matter, PM 2.5 , the standard does not allow any exceedance, and most capital cities exceed the 24-hour standard at some time during the year. The best performing cities are Brisbane and Adelaide, which met the standard for 5 and 4, respectively, of the 7 years (to 2014).

National health-based standards are rarely exceeded for prolonged periods, and very high levels of pollution are usually associated with short-lived extreme events such as bushfires and dust storms, or local sources of pollutants.

Despite the generally good to very good quality of Australia’s air, strong evidence shows that periods of poor air quality can have both long-term and short-term adverse impacts on human health. Research into the health effects of particulates, ozone and sulfur dioxide indicates that there is no threshold level below which they have no health effect. This means that sensitive individuals, such as asthmatics and people with respiratory or cardiovascular disease, may be affected even when air quality standards are met. This—and the classification by the World Health Organization in 2013 of outdoor air pollution and one of its major constituents, PM, as carcinogenic—has strengthened the case for decisive action to improve air quality.

Emissions of air pollutants from major industrial point sources are generally well controlled in all Australian jurisdictions, although some regional cities still record exceedances of national standards because of industrial emissions. The effect of these sources on urban air quality is expected to slowly diminish with the continued uptake of cleaner technologies.

Similarly, no evidence exists to suggest that urban air quality will decline because of an increase in emissions from diffuse commercial sources. As is the case with industrial sources, continuing uptake of improved practices and technologies (driven by a desire for improved efficiency, as well as by the prompting of regulators) may see a reduction in emissions of some pollutants, such as VOCs.

Air pollution from domestic sources (largely particulate pollution from wood smoke) can be expected to continue to reduce air quality in neighbourhoods where wood heaters are still widely used. It is unlikely that behavioural change will lead to a significant reduction in emissions, but the increasing cost of purchasing wood in metropolitan areas might. Our limited capacity to control many sources of PM is likely to exert increasing pressure for further restrictions or bans on the use of domestic wood heaters in urban areas.

Motor vehicles are the main diffuse source of air pollution in urban areas, and the size of the Australian fleet is continuing to grow, as are the distances travelled. In addition, there is concern about the impact on air quality of growing traffic congestion and continuing urban sprawl. Based on a ‘business -as -usual’ scenario (which does not include further tightening of emissions standards), projections to 2020 indicate a continued decline in vehicle emissions of the main air pollutants (carbon monoxide, NO x , PM and VOCs), but total vehicle emissions of particulates have plateaued. Further reductions in PM present a major challenge because the non-exhaust contribution (brake, tyre and road wear) is becoming a larger proportion of the total.

There are reasonable grounds for optimism that reductions achieved in some urban air pollutants (carbon monoxide, lead, NO 2 , sulfur dioxide) during the past decade can be maintained or even extended. Prospects for achieving significant reductions in average and peak levels of particulates and ozone will be influenced by:

• the rate at which pollutant emissions per person decrease to balance the projected doubling of population in the next 50 years
• the rate at which vehicles (particularly passenger vehicles) shift to hybrid, electric or other forms of low-emissions or no-emissions propulsion
• improvements in public transport
• increased take-up of cleaner forms of production
• reductions in the use of wood as a fuel for domestic heating in both urban and semi-rural settings.