Sulfur dioxide

Sulfur dioxide molecule

Sulfur dioxide (SO₂) is a colourless gas with a sharp, irritating odour. It is produced by burning fossil fuels and by the smelting of mineral ores that contain sulfur.

Erupting volcanoes can be a significant natural source of sulfur dioxide emissions.

Environmental effects

When sulfur dioxide combines with water and air, it forms sulfuric acid, which is the main component of acid rain. Acid rain can:

• cause deforestation
• acidify waterways to the detriment of aquatic life
• corrode building materials and paints.

In Queensland, there is less heavy industry than in Europe or North America, where the potential for forming acid rain from sulfur dioxide emissions is higher. Our weather conditions and low sulfur content of fuels reduce the potential for acid rain.

Health effects

Sulfur dioxide affects the respiratory system, particularly lung function, and can irritate the eyes.

Sulfur dioxide irritates the respiratory tract and increases the risk of tract infections. It causes coughing, mucus secretion and aggravates conditions such as asthma and chronic bronchitis.

Air quality guidelines

The Environmental Protection (Air) Policy 2019 (EPP Air) objectives for sulfur dioxide are:

• 0.20 parts per million (ppm) for a 1-hour exposure period
• 0.08ppm for a 24-hour exposure period
• 0.02ppm for an annual exposure period.

The National Environment Protection (Ambient Air Quality) Measure standards for sulfur dioxide are:

• 0.10 parts per million (ppm) for a 1-hour exposure period
• 0.02ppm for a 24-hour exposure period

These guidelines are designed to protect sensitive individuals, such as children and asthmatics.

Significant concentrations of sulfur dioxide are only measured in Queensland near large industrial sources.

Measuring sulfur dioxide

Sulfur dioxide analyser

The animated illustration shows how the sulfur dioxide analyser works.

The sample (shown by the path of the blue dot) is drawn into the analyser by means of the vacuum pump, firstly through a filter to remove particles, and then through a scrubber to remove interfering gases, such as hydrocarbons.

The scrubbed sample passes into a reaction chamber where it is irradiated with ultraviolet (UV) light at 214nm (nanometres) generated by a zinc discharge lamp and a UV bandpass filter.

Sulfur dioxide absorbs UV radiation at wavelengths between 200nm and 240nm. Emission of fluorescence (light-producing) photons at higher wavelengths (around 350nm) follows this absorption of UV radiation by the molecule.

This fluorescence is measured perpendicular to the beam using a photomultiplier (PM) tube and the signal converted to a concentration value.

The measured fluorescence is directly proportional to the concentration of sulfur dioxide in the sample.

Other instruments

Differential Optical Absorbance Spectroscopy (DOAS) instruments also measure sulfur dioxide.

More information

Go to the live air data service to check current levels of sulfur dioxide in the monitoring network.