3 Atmosphere | 3 Ambient air quality and other atmospheric issues | 3.2 Pressures affecting 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
Nitrous oxide, an ozone depleting substance and a greenhouse gas (GHG), is produced by a variety of natural and human-related sources (notably agricultural processes). Although its ozone depleting potential is low relative to chlorofluorocarbon-11 (CFC-11), human emissions are at such a large scale that it is recognised as currently the single most important form of ozone depleting emission, and can be expected to remain so throughout this century. Other GHGs not controlled under the Montreal Protocol, notably carbon dioxide and methane, are expected to significantly affect future stratospheric ozone levels. However, unlike nitrous oxide, the net effect of carbon dioxide and methane is expected to be positive for ozone recovery.
The air quality in Australia’s major cities is no longer principally influenced by emissions from industrial point sources. With the exception of a few centres dominated by one or two very large industrial facilities (such as Mount Isa and Port Pirie), widely spread, diffuse emissions now constitute the major source of pollutants in urban areas. Among these, motor vehicles are the single most important source, contributing a range of pollutants: carbon monoxide, particles, various toxic volatile organic compounds (VOCs) and nitrogen oxides (which, together with VOCs, act as precursors to the formation of ozone). In addition, diesel vehicles are an important source of particles. Commercial premises are another important diffuse source of pollutants (notably VOCs and particles) that affect air quality at an airshed scale as well as impacting on amenity at a neighbourhood level, generating complaints about odour, noise and smoke. Similarly, in many urban centres where wood heaters are widely used for home heating, domestic premises are an important diffuse source of particulate pollution during the colder months. A final broad source of diffuse pollution (with origins outside urban areas) is planned burning for purposes such as agriculture, forestry operations and land management. If not well planned, timed and executed, such burns can trigger health problems and loss of amenity in surrounding rural areas and urban centres.
Climate change is likely to also affect air quality. Rising temperature, which is expected to be a main feature of climate change in Australia, is likely to lead to the formation of more ozone by increasing the generation of both natural and human-generated VOCs. Hotter, drier conditions in many parts of the country, together with more extreme weather events (another likely result of climate change) can be expected to increase bushfires and dust storms, leading to short-lived, very high levels of particulate pollution, which, depending on location, may affect large urban populations.
The quality of indoor air is affected by many factors. The more important include building materials (particularly volatile materials like glues and paints), ventilation, furnishings, use of appliances (particularly cooktops, ovens and unflued gas appliances), environmental tobacco smoke and cleaning agents.
Global production of ODSs continues to decline (Figure 3.30). However, due to the long atmospheric lifetimes of a number of important ODSs, they will continue to impact levels of stratospheric ozone for many decades. In addition, future recovery of the ozone layer will be influenced by emissions of GHGs that are not controlled under the Montreal Protocol—notably carbon dioxide, methane and nitrous oxide—through their effects on temperature, wind and chemistry.104
Source: United Nations Environment Programme Ozone Secretariat155
Figure 3.30 Total reported global production of ozone depleting substances
As new countries ratify the Montreal Protocol, the number of countries reporting national production increases. Therefore, the number of countries is different in 1990 and 2009.
Carbon dioxide has an indirect influence on stratospheric ozone through its effect on temperature, which affects the rates of chemical reactions that control the abundance of ozone. Increasing levels of carbon dioxide have been observed to cause cooling of the mid-to-upper levels of the stratosphere (via radiation to space), leading to a decrease in the rate of ozone loss in these parts of the atmosphere and an increase in the rate in the lower stratosphere. Increases in methane’s abundance in the troposphere will lead to more methane reaching the stratosphere. There, it interacts with compounds that contain active chlorine (which is able to destroy ozone) to produce inactive hydrogen chloride, which does not destroy ozone. Methane levels also influence stratospheric water vapour, which affects both ozone and climate. The net effects of carbon dioxide and methane are expected to be positive for the recovery of stratospheric ozone levels.104 However, this is not the case with nitrous oxide, which is produced by a variety of natural and human-related sources (notably agricultural processes).
As well as being a potent GHG, nitrous oxide from human sources is currently the single most important ODS and can be expected to remain so throughout this century.156 This reflects the fact that, although the ozone depleting potential of nitrous oxide is only about one-sixtieth that of CFC-11, human emissions are large and increasing. Even in 1987, when CFC emissions were at or near their peak, annual ozone depletion potential–weighted emissions of nitrous oxide were some 17% of the combined emissions of CFC-11, CFC-12 and CFC-112.156 In 2009, Australia’s emissions of nitrous oxide were 26.7 MtCO2-e, which is approximately 0.7% of the world’s human-sourced emissions.38-39
Point-source and diffuse-source pollution
As previously noted, air quality in Australia’s urban areas is strongly influenced by short-term meteorology (including extreme events), seasonal conditions, local topography and distance from the sea. The size of the urban centre and the presence of major industrial facilities also play a role in shaping the varying levels of air quality experienced in an urban airshed.
Historically, the most common image of air pollution has been a highly visible plume of unknown content being emitted from a power station or industrial plant. However, both state and national pollutant inventories show that, although industrial point sources still dominate some emission types (notably sulfur dioxide), with the exception of major industrial centres (such as Mount Isa and Port Pirie), diffuse or area sources tend to be the main factors affecting air quality at an airshed scale. These sources include motor vehicles, domestic and commercial solvents, service stations and domestic lawn mowers. The generalisation remains true whether the focus is on the key criteria pollutants (ozone and its precursors and particles) or on the main hazardous air pollutants (air toxics such as benzene, toluene and xylene) (Figure 3.31).139,157
Source: New South Wales Department of Environment, Climate Change and Water157
Figure 3.31 Proportion of total estimated annual anthropogenic emissions from each anthropogenic source type in Sydney regions
It is the diffuse sources (motor vehicles, domestic solid fuel heating, bushfires and various types of planned burning, and dust from roads and agricultural activities) that are the most challenging for government policy makers, regulators and program managers working to improve air quality.
Among diffuse sources of air pollution, motor vehicles are the most pervasive and have the largest impact on urban air quality and human health. In our capital cities, they are the dominant source of NOx (a generic term for nitric oxide and nitrogen dioxide) and VOCs—the precursors of photochemical smog. Although the combined emissions from industry, electricity generation and wood heating are a larger source of PM10 than motor vehicles, because of their ubiquitous presence in our cities, motor vehicles tend to be a more important source of human exposure. Furthermore, discharges from major industrial and power-generation facilities are elevated and thus have less influence at ground level than corresponding ground-level emissions.
In addition, very fine particles (<1 micrometre) form a major part of vehicle particulate emissions. It is these, together with particles in the range 1 micrometre to less than 2.5 micrometres, that are the focus of increasing concern in relation to cardiovascular and respiratory disease, with which they are strongly correlated.158 The Australian Bureau of Transport and Regional Economics estimates that, in 2000, motor vehicle pollution was responsible for 900–4500 cases of respiratory and cardiovascular disease and bronchitis, and as many as 2000 premature deaths.
Within an airshed at a neighbourhood level, as state regulators and local government officials know only too well, a broad range of small-scale industrial and commercial activities have the potential to impact on local amenity and health, most often through emissions of odour, dust and noise. Such widespread diffuse-source problems are often historical in nature (the result of residential areas having developed in close proximity to incompatible land uses) and are particularly difficult to resolve.
An important diffuse source of particulate pollution in cool–temperate parts of Australia is domestic wood heaters and open fires. In autumn and winter, in cities such as Melbourne, Hobart, Canberra and Launceston, and in many smaller centres in Tasmania, Victoria and inland New South Wales, smoke from domestic wood heaters is the major source of particulate pollution. In inland centres such as Canberra, cold nights and clear skies frequently occur in autumn and winter, creating temperature inversions. These trap wood smoke near ground level, leading to particle levels above both the NEPM 24-hour PM10 standard and the PM2.5 advisory level.6 In centres such as Launceston, local valley topography can increase the frequency and strength of such inversions, leading to incidents of significant particulate pollution.
The term ‘planned burning’ encompasses a broad range of activities associated with forestry, public land management and agriculture. Depending on their location and scale, the smoke generated by such activities has the potential to impact on health and amenity, affecting areas such as tourism, viticulture and outdoor events if the burns are not well planned and executed. Recent work by the Environment Protection Division of the Tasmanian Department of Primary Industries, Parks, Water and Environment indicates that planned burns are a significantly more important diffuse source of particulate pollution than estimated by the National Pollutant Inventory.159 However, although the potentially adverse impacts of planned burns need to be recognised and managed, they should be considered in the context of potential benefits, such as a reduction in the risk of wildfires.
The term ‘planned burning’ could also be applied to burning carried out as a traditional management practice by Indigenous land custodians in tropical savanna grasslands in northern Australia. These low-impact burns have been employed by Aboriginal people for many thousands of years.160 Because they take place in remote areas away from population centres, these traditional practices do not raise concerns over impacts on health or amenity, such as are often associated with planned burning in the southern parts of the country.
Climate change and urban air quality
The combination of higher temperatures, more frequent bushfires and more raised dust associated with climate change can be expected to impact adversely on ambient air quality at an airshed scale. CSIRO modelling of the Sydney airshed has shown that higher temperatures, especially higher summer temperatures, can be expected to increase the formation of ozone by increasing the production of VOCs (including from leaves and other biogenic sources), thus impacting respiratory and cardiovascular health. Specifically, under a scenario of high carbon dioxide emissions growth, with air pollution emissions fixed at current-decade levels, Cope et al.161 found that projected numbers of ozone pollution–related hospital admissions would be 40% (2020–30) and 200% (2050–60) higher relative to 1996–2005. Tang et al.162 noted the potential for a similar temperature-related increase in emissions of NOx from some types of soil, which could lead to an increase in ozone formation.
In addition, climate change–driven shifts in atmospheric circulation, such as a change in the exchange between the stratosphere and the troposphere, could lead to relatively small but significant increases in background ozone levels in the troposphere. Such increases in background concentrations could be expected to add to existing ozone pollution levels in urban areas, increasing the length of periods during which regulatory air quality standards are exceeded, with consequent effects on health.163
Analysis by Duc and Azzi164 indicates an increasing trend in background ozone levels in Sydney since the early 1990s. The authors note that this is similar to increasing trends reported from the United States and Europe. While they comment that the reason for the increasing trend in Sydney is ‘not entirely clear’, they note the possible influence of transfer from the stratosphere, along with increasing global emissions, particularly in north Asia.164
Existing monitoring data show strong links between extreme events such as bushfires and dust storms and very high levels of particulate pollution in metropolitan and regional centres. The expected climate change–driven increase in these events will therefore exacerbate episodes of severe particulate pollution. As in the case of ozone, this can be expected to lead to an increase in adverse respiratory and cardiovascular health outcomes, both acute and chronic.135
The quality of the air inside our homes, offices, public buildings, schools and so on is affected by many factors, including the quality of the outside air, building materials (particularly volatile materials like glues and paints), ventilation, furnishings, appliances (particularly unflued gas appliances), environmental tobacco smoke and cleaning agents.165-166
Of the factors impacting on indoor air quality, environmental tobacco smoke is of particular concern because it increases the risk of asthma in children and can worsen the symptoms. environmental tobacco smoke is also known to trigger asthma symptoms in adults. Another focus of concern is nitrogen dioxide, the major sources of which are unflued gas heating and cooking appliances, and wood stoves and fireplaces. In winter, when homes are likely to be well sealed, even flued heaters and fireplaces can lead to high indoor levels of nitrogen dioxide due to leaks and poor chimney design.167-168 High nitrogen dioxide levels are associated with coughing, wheezing and asthma attacks. Prolonged exposure to such levels can contribute to the development of acute or chronic bronchitis.151
|Very high impact||High impact||Low impact||Very low impact||in grade||in trend|
|Greenhouse gases||Emissions of nitrous oxide (N2O), an ozone depleting substance and a greenhouse gas, together with other greenhouse gases (carbon dioxide [CO2] and methane), are expected to have a significant effect on stratospheric ozone levels. CO2 and methane are expected to have a positive net effect on ozone recovery. That is not the case for N2O||Insufficient information to assess likely extent of future impact of N2O|
|Industrial point sources (metropolitan and regional cities)||Local and airshed-wide impacts on health and aesthetics; localised effects on amenity and health near some major point sources|
|Motor vehicles (metropolitan centres)||Metro-wide direct and indirect impacts of volatile organic compounds, NOx, ozone and particulates; localised impacts near ‘hot spots’ such as heavily trafficked roads in residential areas|
|Domestic and commercial (urban)||Local and airshed-wide impacts on health and aesthetics|
|Planned burning||Widespread evidence of generally localised effects on amenity and health|
|Climate change (airshed scale)||Higher temperatures will be associated with increased photochemical smog (ozone pollution events), and with an increase in serious particulate pollution events due to more frequent bushfires and dust storms. Both outcomes can be expected to adversely affect health|
|Indoor air pollutants||A broad range of indoor pollutants is known to impact health|
|Recent trends||Improving||Stable||Confidence||Adequate high-quality evidence and high level of consensus|
|Deteriorating||Unclear||Limited evidence or limited consensus|
|Evidence and consensus too low to make an assessment|
|Very low impact: Few or no impacts have been observed, and accepted predictions indicate that future impacts on values such as health and aesthetics are likely to be minor|
|Low impact: Impacts on values such as health and aesthetics have already been observed, most often localised|
|High impact: Significant impacts on values such as health and aesthetics have already been observed, mainly affecting more sensitive members of the community|
|Very high impact: Currently, a very serious impact on health and aesthetics for the broader population|