3 Atmosphere | 3 Ambient air quality and other atmospheric issues | 3.5 Risks to Australia's atmosphere
State of the Environment 2011 Committee. Australia state of the environment 2011.
Independent report to the Australian Government Minister for Sustainability, Environment, Water, Population and Communities.
Canberra: DSEWPaC, 2011.
At a glance
Greenhouse gases (notably carbon dioxide, methane and nitrous oxide) that are not controlled under the Montreal Protocol are expected to significantly affect future stratospheric ozone levels. In the case of carbon dioxide and methane, the effect is expected to be positive, but human-sourced emissions of nitrous oxide could (in the absence of effective abatement strategies) slow the rate of recovery of stratospheric ozone levels. Should that occur, it could delay the full realisation of health benefits expected to accompany the recovery.
During the past 30 or so years, state and territory environment protection agencies (often working together with local government) have successfully employed regulatory and nonregulatory measures to greatly reduce threats to urban air quality from industrial and commercial activities. The risk of this situation changing markedly during the next decade is assessed as low, despite continuing growth of the economy. Similarly, the risk of a significant decline in local air quality due to increase in particle (wood smoke) pollution from domestic sources is assessed as low.
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. Despite this, projections to 2020 indicate a continued decline in vehicle emissions of the main air pollutants (carbon monoxide, NOx, particles and volatile organic compounds [VOCs]). This positive outlook is strengthened by the Australian Government’s recent (June 2011) announcement of the progressive introduction of tighter emission-control standards, starting in 2013. Taking into account these competing factors, the risk of a marked deterioration in urban air quality over the next decade is conservatively assessed as medium.
The higher temperatures associated with climate change are expected to elevate ambient levels of VOCs, increasing the potential for ozone pollution in Australia’s larger metropolitan centres, where peak ozone levels already at times exceed national air quality standards. Climate change is also expected to affect the likelihood of bushfires, which, depending on location, can cause very serious particulate pollution in population centres. The level of risk associated with these outcomes is assessed as medium.
Rising domestic heating and cooling costs can be expected to promote better sealing of dwellings to reduce loss of heated and cooled air. This will lead to reduced air exchange rates and a deterioration in indoor air quality.
As discussed in Sections 3.3.1 and 3.4.1, the prognosis for the future of the stratospheric ozone layer over the next half century is one of continuing recovery. Over that period, GHGs (notably carbon dioxide, methane and nitrous oxide) that are not controlled under the Montreal Protocol are expected to significantly affect future stratospheric ozone levels.104,156
Unlike carbon dioxide and methane—whose net effects are likely to be positive for the eventual recovery of the ozone layer—human-sourced emissions of nitrous oxide will have a negative impact. (In terms of their weighted ozone depleting potential, nitrous oxide emissions are larger than any of the ODSs controlled under the Montreal Protocol and are growing.) Consequently, as Ravishankara et al.156 noted, ‘increases in anthropogenic N2O [nitrous oxide] emissions or decreases due to abatement strategies would … affect the date for the recovery of the ozone layer’. A delay in the recovery date could delay realisation of certain health benefits (principally avoided cases of skin cancer) that are expected to accompany recovery. On the other hand, there is also the potential for reducing the recovery period through effective action to reduce nitrous oxide emissions.
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 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
Despite significant reductions in the percentage of Australian homes using wood as a source of home heating,206 the cost of the main alternatives to wood (i.e. electricity and gas) have risen steeply in recent years and can be expected to continue to rise.207 Such rises may create pressure on households to return to open fires or wood heaters for domestic heating. Should that occur, the quality of indoor air in those homes can be expected to be adversely affected, since any form of fuel burning in a dwelling has been shown to be positively correlated with carbon dioxide, carbon monoxide, nitrogen dioxide and PM2.5.154
Similarly, increasing concern over heating efficiency and loss of heat through poorly fitting fixtures, such as doors and windows, is likely to lead to better home sealing to prevent loss of heat during winter and cool air in summer. If ventilation is reduced in this way, levels of indoor pollutants can be expected to rise.
|Almost certain||Not considered|
|Rare||Not considered||Not considered||Not considered||Not considered||Not considered|
Note: Timeframes are within the next 50 years (stratospheric ozone) and within the next 20 years (urban air quality).
Explanation of terms:
Almost certain - >: 90% probability of occurring during the specified timeframe
Likely - >: 66% - ≤90% probability of occurring during the specified timeframe
Possible - >: 33% - ≤66% probability of occurring during the specified timeframe
Unlikely - >: 10% - ≤33% probability of occurring during the specified timeframe