Atmosphere Theme Report
Australia State of the Environment Report 2001 (Theme Report)
Lead Author: Dr Peter Manins, Environmental Consulting and Research Unit, CSIRO Atmospheric Research, Authors
Published by CSIRO on behalf of the Department of the Environment and Heritage, 2001
ISBN 0 643 06746 9
An airshed refers to a body of air in an area defined by natural or topographic features. Typically, there will be both human and natural sources of pollution in an airshed. Once in the air, the lifetime of pollutants will depend on their type, on chemical transformations that occur and on meteorological conditions. Rain and wind, for example, can help remove and disperse pollutants.
Most of Australia's population is located within large cities that are within 100 km of the coast. It is in these cities that most concentrations of human induced emissions occur, including those from transport and industry.
Similarly, some regional centres are locations for major industry, such as ore processing and power generation. These regional centres may also experience elevated concentrations of air pollutants as a result of transport of pollution from large cities.
Mountains and hills surrounding airsheds can trap polluted air, contributing to a build up of pollutants, especially during temperature inversions when cold air is caught at ground level below warmer air higher in the atmosphere.
Many large coastal cities experience recirculation of pollutants (Figure 9). This occurs when prevailing winds transport pollutants, only to have then return back over the city some hours later once the wind has changed direction. Recirculation can contribute to high smog levels.
Figure 9: Models of how air pollution is recirculated over Australian cities.
Source: CSIRO Atmospheric Research
The air pollutants of most concern in Australia's larger cities and in some regional areas are carbon monoxide, ozone, particles, nitrogen dioxide, sulfur dioxide, lead and volatile organic compounds such as benzene and formaldehyde. These substances can produce harmful effects on people or the environment (Table 4). Yencken and Wilkinson (2000) present information on health effects associated with volatile organic compounds present in indoor air.
|Pollutant||Sources||Health effects||Where important|
|Carbon monoxide||Motor vehicles, burning of fossil fuels||Blood absorbs carbon monoxide more readily than oxygen, reducing the amount of oxygen being carried through the body. Carbon monoxide can produce tiredness and headaches. People with heart problems are particularly at risk||Indoors, localisedA|
|Sulfur dioxide||Coal and oil burning power stations, mineral ore processing and chemical manufacture||Attacks the throat and lungs. People with breathing problems can suffer severe illness||Localised|
|Nitrogen dioxide||Fuel combustion||Affects the throat and lungs||Indoors, urban and regional|
|Volatile organic compounds||Motor vehicles, fuel combustion, solvent use||Some VOCs cause eye and skin irritation, headaches or nausea, while some are classed as carcinogens||Indoors, urban|
|Ozone||Formed from nitrogen oxides and hydrocarbons reacting together in sunny conditions. These chemicals are released by motor vehicles and industry||Ozone attacks the tissue of the throat and lungs||Urban and regional|
|Lead||Exhaust gases from motor vehicles that use leaded petrol, smelters, old, leaded paints||Particles containing lead in the air can enter the lungs. The lead can then be absorbed into the blood stream. Over a period lead can affect the nervous system and the body's ability to produce blood||Localised, urban|
|Particles||Motor vehicles, domestic fires, burning of plant materials, bushfires, indoor activities||May cause breathing difficulties and worsen respiratory diseases. Some particles contain cancer-producing materials||Indoors, urban, regional and localised|
|Fluoride||Coal combustion and aluminium processing||Vegetation damage, fluorosis of teeth of cattle||Localised|
A 'Localised' refers to a specific agricultural activity, industrial activity or location.
Offensive odours are a major source of complaints to environment protection agencies. Even at low concentrations, some odours may be offensive to humans. Odours may also cause some people to feel unwell.
Pollutants emitted directly into the atmosphere are known as primary pollutants. Once in the atmosphere, these primary pollutants may undergo chemical reactions, forming secondary pollutants. Photochemical smog is a pollution problem caused by secondary pollutants.
Photochemical smog is formed on days when the sun shines on air containing volatile organic compounds and oxides of nitrogen. Motor vehicles, industry and bushfires are major sources.
Volatile organic compounds (VOCs) include hydrocarbons, as well as alcohols, aldehydes and ethers. VOCs in the air arise mainly from automotive fuels and industrial solvents. Chemical reactions driven by sunlight form ozone and other harmful secondary pollutants such as peroxyacetyl nitrate and aldehydes, which are severe irritants, particularly to the eyes. The action of sunlight breaking chemical bonds (photolysis) is the major driving force for most chemical reactions in the atmosphere.
As well as being harmful to humans, photochemical smog is harmful to animals and plants.
Haze appearing over large cities in summer is often caused by photochemical smog. Visibility reduction is caused by particles produced by chemical conversion of acidic gases and certain hydrocarbons.
Two factors determine the speed at which smog is formed: the concentration of reactive VOCs in the air and the intensity of sunlight available to drive their breakdown. Ozone formation will continue as long as both sunlight and nitrogen oxides are available. Nitrogen dioxide also undergoes other oxidising reactions that convert it to nitric acid and organic nitrates, removing nitric oxide from the reaction system and ending the production of smog.
Atmospheric particles come from motor vehicles, industrial processes, wood burning and from photochemical reactions. They may also come from natural sources including wind-blown dust, pollen and sea salt.
As well as causing haze, fine particles can be inhaled deeply into the lungs and can cause health problems.
Australians spend 90 to 96% of their time indoors. As numerous pollutants occur at higher concentrations indoors than outdoors, the main exposure to air pollution for many people occurs when they are in homes, residential institutions (hostels, hotels and hospitals), offices, schools, restaurants and public buildings.
Materials and appliances used in buildings can give rise to air pollutants such as nitrogen dioxide, particles, carbon monoxide, VOCs and lead. Indoor air quality can also be affected by dust mites, formaldehyde, environmental tobacco smoke, asbestos fibres, microbial contaminants, radon and some pesticides. Concentrations of some pollutants can regularly reach significantly higher levels indoors than outdoors.
Indoor air quality is an important issue of growing community significance (see Indoor air quality and exposure). Detailed information on indoor air quality can be found under HS Indicator 7.1 to 7.14 in the Human Settlements Theme Report.