Ambient air quality


Industrial point sources

If not effectively controlled, emissions from industry can place health and amenity at risk, not only at the neighbourhood level, but more generally at the airshed level. During the past 30 or so years, state and territory environment protection agencies (working together with local government) have successfully employed a range of measures (both regulatory and nonregulatory) to greatly reduce the threat from industrial sources. As a result, apart from in major industrial centres or smaller centres with one or two significant industrial sources, diffuse sources (motor vehicles and commercial and domestic sources) tend to be the more important threats to urban air quality at an airshed scale.

A possible exception to this generalisation is the potential impact on urban air quality that could accompany any significant increase in local generation of electricity using cogeneration (i.e. combined heat and power) facilities. As noted by the Victorian Environment Protection Authority:

… cogeneration facilities can yield significant greenhouse emissions reduction benefits, but may pose a potential threat to air quality, as the burning of natural gas releases significant amounts of NOx. Air quality considerations will therefore be taken into account where cogeneration facilities are proposed in urban areas.203

Diffuse sources—motor vehicles

Motor vehicles are a significant source of anthropogenic carbon dioxide emissions in Australia, comprising some 90% of transport emissions, which in turn made up 15% of Australia’s net carbon dioxide equivalent emissions in 2009.13,43 However, despite their contribution to climate change, the most immediate threat posed by motor vehicles is to air quality at the urban airshed scale, where vehicles typically account for around 80% of carbon monoxide emissions, two-thirds of NOx, 40% of VOCs and 30% of particles (as PM10).157

From 2005 to 2010, motor vehicle registrations increased by 15.4% (averaging 2.9% annually); the bulk of this growth was in passenger vehicles, which make up 76% of the total Australian fleet.186 If growth were to be maintained at this rate, the number of vehicles would double in 24 years. As noted earlier in this chapter, despite significant growth in vehicle numbers and distances travelled (which increased by 6.8% between 2003 and 2007), advances in motor vehicle engine and emission-control technology (together with improved fuel standards) have driven down emissions of carbon monoxide and VOCs.180,185 Projections to 2020 show these gains being maintained and levels of NOx declining. (These projections are based on a ‘business as usual’ scenario that does not factor in the progressive application of tighter emission-control standards starting in 2013, which should reinforce the projected gains.)

The threat, however, is that the combination of increasing vehicle numbers, distance travelled and congestion (which leads to more exhaust and evaporative emissions) may in future cancel out gains in technology, resulting in increased impacts on health and reduced amenity. For example, emerging concerns in Europe over increases in vehicle emissions of nitrogen dioxide accompanying technology-driven reductions in NOx could foreshadow similar concerns in Australia, if the proportion of diesel vehicles in the fleet continues to grow. (Data show diesel registered vehicles increasing from 10.1% of the fleet to 13.8% between 2005 and 2010.186)

Diffuse sources—commercial and domestic

Commercial premises can pose a threat to health and amenity at the local level, mainly through emissions of particles and VOCs. VOC sources include aerosols, surface-coating operations and solvents (the latter being a particular cause of odour complaints). Commercial food-processing operations can also place local amenity at risk due to odour emissions. As previously discussed, smoke from poorly designed and operated domestic wood heaters can pose a significant seasonal risk to amenity and health at both neighbourhood and airshed scales. Collectively, domestic and commercial sources annually contribute around one-third of VOCs to the Sydney and Melbourne airsheds, and approximately one-quarter to one-third to particulate pollution in Sydney and one-half in Melbourne. In the case of Melbourne, the contribution of both VOCs and particles is concentrated in winter, as it is strongly associated with domestic heating.157,204

Climate change

Climate change poses a threat to urban air quality and health through increases in particulate pollution (associated with more frequent bushfires and dust storms) and increases in the formation of ozone and other components of photochemical smog. The latter phenomenon is driven by increasing temperatures, and long-range transport of pollutants associated with large-scale changes in atmospheric circulation.205

(2011). Ambient air quality: Ambient air quality. In: Australia state of the environment 2011, Australian Government Department of the Environment and Energy, Canberra,, DOI 10.4226/94/58b65c70bc372