Understanding air quality
What is ambient air quality?
Our air is a complex mixture of nitrogen and oxygen, with small quantities of a wide range of other gases and fine particles, which may come from both natural sources and human activities. Many of these are normal components of the atmosphere at very low levels that do not affect people or other life forms. However, under some circumstances, some of these materials can become 'air pollution'.[1]
Ambient air quality[2] is affected by the emission of air pollutants; how well the pollutants disperse in the atmosphere; and whether they undergo natural or chemical processes such as photochemical transformation or deposition. Dispersion of pollutants is influenced by local meteorology and topography.
Hence, on any particular day, the build-up of air pollution depends on the quantities of pollutants emitted into the layer of the atmosphere where we live (called the troposphere) and the weather. For example during very still weather in Adelaide during winter, fine particles (known as PM10 and PM2.5)[3] emitted from vehicles, domestic sources and industry may build-up resulting in occasional exceedences of the national standards from the National Environment Protection (Ambient Air Quality) Measure or AAQ NEPM. On other days light breezes will clear particles and other pollution away from the city and concentrations will be low. On the other hand, high winds during summer may raise dust and carry it across the city, causing increased particle pollution. Years where there is lower than average rainfall can exacerbate the dry windy conditions experienced during summer and result in an increased number of exceedences of the particle standards across the state compared to wetter years.
Daily PM10 concentrations in Western Adelaide
The following graph is an example of the variations in air quality due to weather and climactic conditions. The graph shows average daily PM10 concentrations in Western Adelaide, which are quite varied across different seasons of each year and between years due to many factors, including varied weather conditions, dust storms and fires. The increased rainfall and breaking of the drought in 2010 has resulted in a reduction in the number and severity of exceedences of the NEPM standard.
Daily average concentration of nitrogen dioxide at Western Adelaide
Nitrogen dioxide is a common pollutant in cities, from motor vehicles, industries and domestic gas stoves and heaters. It is one of the pollutants listed in the AAQ NEPM and has its own Australian standards. Similarly, the graph below shows considerable daily and seasonal variation in the daily average concentration of nitrogen dioxide at Western Adelaide. Unlike PM10 which has a daily standard, nitrogen dioxide has a 1-hour standard, therefore, the NEPM standard is not shown in the graph below since the graph is shown as an indicator of seasonal variations.
Proximity to emission sources is also an important factor to consider when looking at a person’s or population’s exposure to air pollutants. People living, working or recreating close to emission sources may be exposed to higher pollutant loads than those in a primarily residential area for example. EPA is currently updating its air science programs with a focus on community exposure and risk.
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[1] Air pollution occurs when materials build up to concentrations that are high enough, and persist for long enough to cause adverse effects on people, plants, animals and property.
[2] Ambient air refers to the external air environment and doesn’t include the air environment inside buildings or other structures.
[3] PM10 is a name given to particles in the air that are small enough for us to be able to breathe them in. Some of the larger ones may only reach as far as our throats, while others may travel right down into our lungs. PM means particulate matter, while the '10' tells us how big the particles are, in micrometres or millionths of a metre. This is written as 10 µm. PM10 means that the biggest particles in a sample are about 10 µm in diameter. A sample of PM10 particles may also contain PM2.5 particles, which are so small that when we breathe them in, they can travel right down into the deep parts of our lungs. PM2.5 means that the largest particles have sizes of around 2.5 micrometres or µm. Common types of PM2.5 particles are smoke and exhaust fumes from vehicles.
Why is air quality important? Effects on human health and the environment.
There is increasing evidence that even relatively low levels of air pollution can have adverse effects on our health and consequently any improvement in air quality will result in improved health outcomes. Recent research indicates that fine particles pose the greatest risk to Australian communities, especially those living in our major cities; other pollutants such as nitrogen oxides and a range of organic (carbon containing) compounds are also of concern.
Pollutants such as airborne lead and sulphur dioxide were once a concern in urban areas, but this has been largely eliminated due to changes in vehicle fuels over the last thirty years or so. However they remain a strong focus in regional industrial cities such as Port Pirie.
Both short term and long term exposure to air pollution can have health effects, which is reflected by some pollutants having multiple standards. Health impacts can include premature death; aggravation of cardiovascular and respiratory diseases; damage to lung tissue, structure and function; cancer; and changes in the function of the nervous system. For most of the designated air pollutants in the AAQ NEPM, there is no concentration threshold below which there are no health effects, hence there is a residual risk even at concentrations currently experienced in South Australia and at concentrations that are below the NEPM standards.
Some groups are particularly susceptible or sensitive such as children, the elderly and those with existing respiratory and cardiovascular conditions. Interactions between pollutants and natural conditions have the potential to exacerbate health impacts. A combination of poor air quality with excessive heat especially has shown to be a particular risk for vulnerable people.
Some pollutants, namely visual dust and odour, also have the potential to cause significant impacts on people's lives by adversely affecting their amenity. The main effect of environmental odour is nuisance, but stronger or persistent odours can lead to feelings of nausea, headache, loss of sleep and other symptoms of stress. Repeated exposure to nuisance levels of odour can lead to a high level of annoyance. While some people may become acclimatised to odours, others may become sensitised to them. Similarly, larger dust particles are not normally associated with direct health effects, but can cause irritation or nuisance to people by soiling clothes or collecting on surfaces.
Poor air quality can also impact on other aspects of the environment such as acidification or eutrophication of ecosystems, lower crop yields, bioaccumulation, and damage to plants and animals. Some species of plants and animals are sensitive to fluoride and sulphur dioxide at levels lower than those that would impact on human health. Air pollution can also damage buildings and other structures, for example through the formation of acid rain.
Air pollution and emission sources
Air pollution is caused by the emission of pollutants from a wide variety of anthropogenic and natural sources including industry, light and heavy vehicles, domestic sources such as solid fuel heaters (eg wood heaters) and gardening equipment (eg lawnmowers), and events such as bushfires and dust storms.
Air pollution knows no boundaries and emissions in one area can affect air quality in another. At times pollution can travel large distances. Smoke from bushfires in the eastern states has been known to cause a smoke haze over Adelaide and affect particle levels as well as enhance the production of summer ozone; and major regional dust storms can deposit soil from South Australia across the east of Australia and even New Zealand. As an extreme example, the atmospheric effects of the eruption of Krakatoa in 1883 were seen in the UK, over 11,000 km away.
There are many different sources of emissions and influences on air quality and while some are widespread across many environments (such as emissions from domestic sources and transport), others are unique to particular cities or regions. For example domestic and transport activities are a major contributor to air pollution in some parts of greater Adelaide, while in other areas industrial activities play the major role. The Le Fevre Peninsula is interesting as the area is a combination of industry, transport and residential areas in close proximity to each other.
In Port Pirie and Whyalla industry is generally the main determinant of air quality, however at times regional dust storms also impact on air quality. In Mount Gambier domestic solid fuel heaters (eg wood heaters) are a major source of emissions during winter. In rural areas air quality may be impacted on by emissions from mining operations, agricultural and forestry operations, prescribed burns or bushfires, or wind-blown dust.
Emissions inventory and air quality modelling
An emissions inventory estimates pollution from all sources within a region or an airshed[4]. It provides critical information to assess community exposure levels through feeding the information directly into air quality models. In combination with population and health information, inventories assist in understanding the impacts of air pollution on human health and point to options for managing environmental, social and economic risks over the long term. Apart from meteorology, emissions inventory data provides crucial input for air quality modelling.
Air quality models are computer programs which simulate dispersion and interaction of pollutants in air. The ground-level concentrations (GLC) of pollutants are determined by a complex interaction of the physical characteristics of the emission source, the physical and chemical characteristics of the pollutants, the meteorological parameters at or near the site, and the topographical conditions. With dispersion the pollutants get transported in the atmosphere through vertical and horizontal movements of air parcels, simultaneously diluting their concentration in the air.
Overall, emissions inventories and modelling combined can assist decision makers identify where and how to reduce air pollution.
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[4] An area or a region such as a city or a town, where air pollution readily accumulates.
South Australia’s air quality
South Australia’s air quality is good by world standards, as can be seen in the graphs below which compare Adelaide’s air quality in 2009 compared with that of other selected cities in Australia and overseas. The graphs compare levels of 5 common ambient air pollutants. In the case of sulphur dioxide, the levels in Adelaide are so low compared to the other cities used in the comparison that it does not show up on the graph.
Adelaide’s air quality in 2009 compared with that of other selected cities in Australia and overseas
All graphs reproduced with kind permission: © Queen’s Printer for Ontario, 2011.[5]
There is potential for South Australia’s air quality to get worse in the future due to growth in population, economic activity and emissions.
Climate change is also likely to impact on air quality due to the increased temperatures and decreased humidity levels which are predicted for South Australia. Changes in weather patterns are predicted to increase the frequency of drought and hence increase the frequency and severity of bushfires and dust storms adding to extreme air pollution events and resulting in exposure to higher particle levels.[6] The management of land will become increasingly important because of climate change to minimise the amount of wind-blown dust.
Higher temperatures are also expected to enhance production of photochemical smog, leading to higher levels of exposure to ground-level ozone[7] in metropolitan Adelaide.
Local air pollution also feeds into global effects on climate change through the emission of greenhouse gases such as carbon dioxide, methane and nitrous oxide. These gases help to trap heat from the sun within the Earth’s atmosphere and maintain a temperature at a level necessary to support life. However an excess of greenhouse gases (i.e. air pollution) from human activities can raise the temperature of the planet to abnormal levels, leading to climate change.
South Australia's long-term response to climate change is outlined in South Australia's Climate Change Vision - Pathways to 2050. For more information about climate change visit the Government of South Australia website.
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[5] The Ontario Ministry of the Environment and Climate Change publishes annual reports on air quality, some of which include graphical comparisons of pollutant levels between cities from around the world. The South Australian EPA contributed data to the 2009 report (Air Quality in Ontario 2009 Report) which includes the most recent comparisons.
[6] South Australia’s climate change vision – Pathways to 2050
[7] Not to be confused with ozone that is a natural part of the upper levels of the atmosphere, colloquially known as the ozone layer'.
Managing South Australia’s air quality
Maintaining and improving the quality of air is important, although the air quality in South Australia is generally good, since even current levels of air pollution can have significant health impacts and costs. This is why good quality air remains one of the EPA’s environmental goals.
The EPA administers a broad approach to air quality management in South Australia, including:
- improving our understanding of patterns of air pollution and its long-term impacts on South Australian communities through well designed monitoring and modelling programs
- effective, robust and fair regulation of industry and supporting pollution reduction initiatives based on sound science
- collaborative partnerships with industry, communities, government, and academic and research organisations to support better environmental outcomes
- supporting national work being undertaken on air related issues
- authoritative advice or direction to planning authorities, licensees and other government agencies on development applications, license conditions, or major projects to avoid adverse air quality impacts from industries
- developing and regularly reviewing guidelines to reflect modern knowledge, regulatory approaches and industry practice.
The South Australian Government is developing an Air Quality Framework for South Australia, the core of which will be a suite of guiding principles for managing air quality across this State over the next decade and beyond, providing a practical approach towards addressing health, environmental and lifestyle concerns about air quality in balance with targets for projected expansion of population and vigorous economic growth targets for South Australia such as defined in the 30-Year Plan for Greater Adelaide.