Sulfur dioxide (SO2)
Air quality fact sheet
Department of the Environment and Heritage, 2005
Sulfur dioxide is a gas. It is invisible and has a nasty, sharp smell. It reacts easily with other substances to form harmful compounds, such as sulfuric acid, sulfurous acid and sulfate particles.
About 99% of the sulfur dioxide in air comes from human sources. The main source of sulfur dioxide in the air is industrial activity that processes materials that contain sulfur, eg the generation of electricity from coal, oil or gas that contains sulfur. Some mineral ores also contain sulfur, and sulfur dioxide is released when they are processed. In addition, industrial activities that burn fossil fuels containing sulfur can be important sources of sulfur dioxide.
Sulfur dioxide is also present in motor vehicle emissions, as the result of fuel combustion. In the past, motor vehicle exhaust was an important, but not the main, source of sulfur dioxide in air. However, this is no longer the case.
Sulfur dioxide affects human health when it is breathed in. It irritates the nose, throat, and airways to cause coughing, wheezing, shortness of breath, or a tight feeling around the chest. The effects of sulfur dioxide are felt very quickly and most people would feel the worst symptoms in 10 or 15 minutes after breathing it in.
Those most at risk of developing problems if they are exposed to sulfur dioxide are people with asthma or similar conditions.
The amount of sulfur dioxide in air is at acceptable low levels in most Australian towns and cities. While sulfur dioxide levels in air are not generally a problem in Australia, fuel standards have significantly reduced sulfur levels in fuels and reduced the levels in air even further.
The highest concentrations of sulfur dioxide in the air are found around petrol refineries, chemical manufacturing industries, mineral ore processing plants and power stations. Mt Isa and Kalgoorlie are the only areas where high amounts of sulfur dioxide in the air can occur and that happens only occasionally.
Because of the adverse health effects of high levels of sulfur dioxide, the Australian Government has taken steps to manage and reduce the amount of sulfur dioxide produced. These include:
- implementing national fuel quality standards;
- supporting the implementation of tighter vehicle emission standards; and
- promoting alternative fuels.
In 1999, the average sulfur content of diesel was 1300 parts per million (ppm). In December 2002, a new standard was introduced, reducing the maximum sulfur content of diesel to 500 ppm. Sulfur emissions attributed to the transport sector will be further reduced in the future. By 2008, the sulfur level in premium unleaded petrol will be 50 parts per million and, by 2009, sulfur levels in diesel will be 10 parts per million.
Through the National Environment Protection Council, the Australian, State and Territory Governments have also agreed on a National Environment Protection Measure for Ambient1 Air Quality. The Measure includes national standards for six key pollutants, including sulfur dioxide. (See fact sheet on National Standards for Criteria Air Pollutants in Australia) One of the aims of the Measure is to keep sulfur dioxide in outdoor air below the following levels by 2008:
- 0.20 ppm (parts per million) averaged over a one hour period
- 0.08 ppm averaged over a 24 hour period
- 0.02 ppm averaged over a one year period.
Most areas in Australia met these standards well ahead of the 2008 timeline.
Related publications are available from the Community Information Unit of the Department of the Environment and Heritage, phone 1800 803 772. These include the State of the Air Report: Community Summary 1991–2001 and Air Quality fact sheets on:
- National Standards for Criteria Air Pollutants in Australia;
- carbon monoxide, lead, nitrogen dioxide, ozone, particles, air toxics;
- woodheaters and woodsmoke; and
- smoke from biomass burning
See also our website at Air quality
1 In this context, 'ambient' means 'outdoor'.