What is Air Pollution?
Introduction
Other planets have sunlight, but only our earth has air and water. Without all of these there would be no life. A diverse community of plant and animal life has thrived on this planet for millions of years, sustained by the sun and supported by the soil, water and air.
The air is made up of nitrogen and oxygen, with traces of other gases such as carbon dioxide, plus minute particles like dust.
Although clean air should be freely available to all plant and animal life, humans have been gradually polluting it, putting their health at risk and the well-being of the earth itself.
Air pollutants mainly come from the discharges of gases and particles mainly from industry, motor vehicles and domestic wood burning. There are also natural sources such as wind-blown dust and smoke from bush fires.
Some forms of air pollution create global problems requiring international solutions, especially upper atmosphere ozone depletion and acid rain. The enhanced greenhouse effect also falls into this category.
This page only looks at urban air pollution.
Types of Pollutants
The most widespread pollutants include carbon monoxide, volatile organic compounds, ozone, oxides of nitrogen, sulfur dioxide, particles and lead. Some pollutants can interact to form secondary pollutants, called 'smog'.
These substances, which are found everywhere in cities are used as indicators of air quality.
Air pollution can cause health problems. For example smog can aggravate existing respiratory ailments such as asthma and bronchitis, or increase the risk of respiratory problems, particularly on smog days. Elevated lead levels can affect the central nervous system, and may impair intellectual development in children.
Government Sets Air Quality Objectives
To protect the environment against harmful and unhealthy levels of air pollution, the government has adopted objectives to protect a range of beneficial uses, including the health and well-being of humans, plants and animals. These were set down July 1981 in the State Environment Protection Policy (SEPP) for the Air Environment and in February 1999 in the State Environment Protection Policy for Ambient Air Quality. The Ambient Air Quality SEPP was declared to adopt the national standards which became law in 1998.
These SEPPs cover all the major pollutants as well as specific industrial pollutants discharged out of chimneys. There are 112 of these specific pollutants with specific controls because of their toxicity or odour or because they accumulate biologically. There are more stringent controls on industrial discharges of pollutants that may have adverse health affects or are highly toxic.
Air pollution is generally categorised into ambient pollution (affecting a large number of people) and local pollution where the effects are limited to the area surrounding the source.
The standards in the Ambient Air Quality SEPP are used for control of air pollution that spreads over a wide area. The Indicators in the Air Quality Management SEPP have local effects, relatively close to the emission source.
To ensure that the policy objectives are being met, the EPA keeps a close watch on air quality, monitoring for breaches of the objectives.
Using this monitoring data EPA is able to target its activities to control pollution from cars, buses and trucks, power generation, industry and other sources.
The air SEPPs determine the appropriate air quality indicators and set the objectives and goals for each indicator for different measurement periods (one hour, four hours, eight hours, 24 hours or one year).
Measures for ensuring standards are met
There are a number of measures -which can reduce air pollution. They include:
- industry adopting cleaner technology
- assisting dispersion through tall chimneys
- cleaning up emissions by removing pollutants from exhaust gases
- banning backyard incinerators and open air burning
- discouraging the use of open fires for domestic heating, and the use of older wood heaters which do not meet the Australian Standard
- burning less polluting fuels
- reducing exhaust pollutants from cars by keeping cars tuned and driving less, everyone playing their part in helping to keep Melbourne's air clean.
EPA employs all these measures and is actively engaged in raising public awareness of the need to protect the environment.
Sources of Pollution
The Port Phillip Air Emmissions Inventory for 1995/96 provides detailed information on the various sources which contribute to air pollution.
The biggest contributor to Melbourne's air pollution is emissions from motor vehicles.
Motor vehicles account for 80 per cent of annual emissions of carbon monoxide, 60 per cent of oxides of nitrogen, 40 per cent of volatile organic compounds, and 30 per cent of airborne particles (PM10).
Reducing the total automotive emission level remains an EPA priority. Cars with anti-pollution devices and using lead free petrol now account for 60 percent of total vehicle kilometres travelled by passenger vehicles. As old cars are retired, air quality is expected to improve even further. With the air quality control strategies currently in place, EPA estimates that the pollution from motor vehicles will decrease over the next 10 years unless the number of vehicles on the road increases significantly.
In colder months, domestic wood combustion is the major source of winter smog. Open fires and older heaters that do not comply with the Australian Standard (AS4013) contribute disproportionately. Heaters not meeting this standard contribute more than twice as much particle pollution per kilogram of wood burnt, and open fires contribute three times as much, compared with modern heaters that meet the standard.
Photochemical Smog
Photochemical smog forms as a result of sunlight acting on various pollutants - mainly oxides of nitrogen and volatile organic compounds. This smog is made up of a mixture of ozone and other organic compounds, and nitrogen dioxide.
Photochemical smog is more likely to build up and hang like a blanket in the air on still days.
As well as the emission sources and pollutants, it is important to consider the prevailing winds and weather conditions of a city, and the duration of sunlight hours, in determining pollution patterns and effects.
Melbourne is fortunate that its prevailing winds and weather systems move quickly, tending to disperse pollution. However, under certain light wind conditions, the air and the pollutants it contains is recirculated, creating more smog.
Smog can have a brownish tinge due to the presence of particles together with nitrogen dioxide. Later, the colour may change to white due to the presence of sulfate and nitrate aerosols.
Smog Alerts
Melbourne's smog episodes can now be predicted with relative accuracy. Forecasts are based on meteorological data and forecasts supplied by the Bureau of Meteorology and on EPA monitoring data. 'Smog alerts' are issued by EPA to assist the public and industry.
Photochemical Smog is more likely to occur in summer and early autumn with smog days of poor visibility more likely in autumn and winter.
On 'smog alert' days, industry is asked to minimise emissions as much as possible, motorists are asked to take public transport rather than drive their cars and householders are urged not to burn off outdoors. Most local councils have restrictions on burning off. On 'smog alert' days, people with respiratory or cardiac disorders should take their medication and minimise their outdoor activities.
EPA Control Programs and Future Air Quality Trends
Apart from its role of environmental "watch dog", issuing licences to control certain industrial emissions, and monitoring for breaches of air policy objectives, EPA actively seeks to change pollution habits through raising public awareness of what the issues are and what we can all do to keep improving our air quality.
Overall smog levels are slowly declining due to the impact of control programs such as the unleaded petrol strategy. All new passenger cars manufactured after 1 February 1986 have to conform to stricter emission limits and run on unleaded petrol. In 1997/99 Australia's passenger car standards were further tightened.
Industry specific controls have been incorporated in the SEPP (Air Quality Management).
Also, EPA periodically reviews the SEPPs, in light of new medical and environmental research findings. The SEPP (Ambient Air Quality) was most recently updated in February 1999 to formally adopt national air quality standards developed in 1998. These reviews include consultation with industry and the community.
Air quality summary
Sunday November 22 2009: No summary is available today.
Forecast: Good to Very Good air quality is expected in Melbourne on Monday