Substance fact sheet
The National Pollutant Inventory (NPI) provides information on the types and amounts of pollutants being emitted in the Australian community.
This page provides facts about sulfur dioxide. It describes how you might be exposed to this substance, how exposure might effect you and the environment, common uses, comparative data about sulfur dioxide and its physical and chemical properties.
For more information about some of the terms used in this page, see the NPI glossary.
The National Pollutant Inventory (NPI) holds data for all sources of sulfur dioxide emissions in Australia.
Exposure to concentrations of 10 to 50 parts per million for 5 to 15 minutes causes irritation of the eyes, nose and throat, choking and coughing.
Exposure of the eyes to liquid sulfur dioxide, (from, for example an industrial accident) can cause severe burns, resulting in the loss of vision. On the skin it produces burns. Other health effects include headache, general discomfort and anxiety. Those with impaired heart or lung function and asthmatics are at increased risk. Repeated or prolonged exposure to moderate concentrations may cause inflammation of the respiratory tract, wheezing and lung damage. It has also proved to be harmful to the reproductive systems of experimental animals and caused developmental changes in their newborn.
Sulfur dioxide will enter the body if we breathe in contaminated air. Upon entry, nose, throat and lungs may be affected. Sulfur dioxide can also enter our bodies when we eat or drink food or beverages (wine) which contain sulfur dioxide as a preservative. Sulfur dioxide can enter the body through skin contact.
Sulfur dioxide is a common pollutant to which we are exposed at very low levels every day by breathing air in cities and some industrial environments. Higher exposure levels are more likely to be found in the workplace where it is produced as a by-product, such as in smelting and the combustion of coal or oil. Exposure can also happen from the manufacture of fumigants, food preservatives, bleaches and wine making. It can be ingested by eating preserved foods and breathed in causing a risk to asthmatics and other individuals sensitive to its effects.
See Sources for more information.
National Ambient Air Quality Standards and Goals:
Averaging period 1 hour, Maximum 0.2 parts per million, maximum allowable exceedences: 1 day a year.
Averaging period 1 day, Maximum 0.08 parts per million, maximum allowable exceedences: 1 day a year.
Averaging period 1 year, Maximum 0.02 parts per million, maximum allowable exceedences: none.
Even low concentrations of sulfur dioxide can harm plants and trees and reduce crop productivity. Higher levels, and especially the acidic deposits from acid rain, will adversely affect both land and water ecosystems.
Industrial emissions of sulfur dioxide can produce elevated, but still low level concentrations in the atmosphere around the source. Volcanic eruptions, while sporadic, are significant contributors to sulfur dioxide in their local area, and contribute to global background levels of sulfur dioxide.
Sulfur dioxide in the atmosphere is absorbed by soils and plants. It is also captured within and below clouds and in certain circumstances may raise the acidity of the resultant rain. This is known as acid rain, which occurs in Europe and North America, but acid rain, from sulfur dioxide, has not been documented in Australia.
Note that the emissions data in the NPI database is not directly comparable with these guidelines.
As a fruit preserving agent and as a food preservative or additive.
In the fermentation stage of wine making.
For bleaching textile fibres.
In the manufacture of paper.
As a disinfectant in breweries and food factories.
As a fumigant for grains, grapes and citrus fruits.
Fossil fuel combustion sites particularly coal burning power plants; industrial processes such as wood pulping, paper manufacture, petroleum and metal refining and metal smelting, particularly from sulfide containing ores, e.g. lead, silver and zinc ores all emit sulfur dioxide to air.
Small textile bleaching and food preserving facilities and wineries, fumigation activities all emit sulfur dioxide to air.
Geothermal activity, including hot springs and volcanic activity; sulfur dioxide is produced from the natural decay of vegetation on land, in wetlands and in oceans all emit sulfur dioxide to air.
Vehicle exhaust.
Some solvents, dechlorination agents, bleaches and fumigation products.
Approximately 400 substances were considered for inclusion on the NPI reporting list. A ranking and total hazard score was given based on health and environmental hazards and human and environmental exposure to the substance.
Sulfur dioxide was ranked as 4 out of 400. The total hazard score taking into account both human health and environmental criteria is 2.8.
On a health hazard rating of 0 - 3 sulfur dioxide registers 1.5. A score of 3 represents a very high hazard to health, 2 represents a medium hazard and 1 is harmful to health.
On an environmental rating of 0 - 3 sulfur dioxide registers 1.3. A score of 3 represents a very high hazard to the environment and 0 a negligible hazard.
Factors taken into account to obtain this ranking and these scores include the extent of the material's toxic or poisonous nature and/or its lack of toxicity, and the measure of its ability to remain active in the environment and whether it accumulates in living organisms. It does not take into account exposure to the substance. Environmental exposure is reflected in the NPI rank for this substance (see comparative data below). A substance that scores highly as an environmental hazard is oxides of nitrogen at 3.0 and one of the lower scores is carbon monoxide at 0.8. A substance that scores highly as a health hazard is arsenic at 2.3 and one of the lowest scores is ammonia at 1.0.
| Substance name | Sulfur dioxide |
| CASR number | 7446-09-5 |
| Molecular formula | SO2 |
| Synonyms | sulfurous oxide, sulfur oxide, sulfurous anhydride, sulphur dioxide |
| Physical properties: Colourless gas. Strong, suffocating odour. Melting Point (°C): -75.51 Boiling Point (°C): -10.06 Specific Gravity: 0.00293 Vapour Density: 2.26 |
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| Chemical properties: Non-flammable gas. Sulfur dioxide may oxidise to sulfur trioxide which then dissolves in water to produce sulfuric acid. |
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There is more information that may be useful in understanding some of the issues surrounding the NPI.