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.