The chemical formula for sulphur dioxide is SO2.
Sulphur dioxide is a colourless, soluble gas with a characteristic pungent smell which forms sulphuric acid when combined with water.
Sulphur dioxide is produced mainly from the combustion of fossil fuels that contain sulphur, such as coal and oil (eg, coal being burnt in a home fireplace for heating and diesel-powered vehicles). Sulphur dioxide is also produced from some industrial processes (eg fertiliser manufacturing, aluminium smelting and steel making).
Natural sources of sulphur dioxide include geothermal activity.
Sulphur dioxide can cause respiratory problems such as bronchitis, and can irritate your nose, throat and lungs. It may cause coughing, wheezing, phlegm and asthma attacks. The effects are worse when you are exercising. Sulphur dioxide has been linked to cardiovascular disease.
- adults with lung disease
The national environmental standard for sulphur dioxide are 350 µg/m3 and 570 µg/m33 as a 1-hour average. The average concentrations of sulphur dioxide should not exceed the 350 µg/m3 standard more than nine times a year and should not exceed the 570 µg/m3 standard at all.
The national ambient air quality guideline for sulphur dioxide is 120 µg/m3 as a 24-hour average.
New Zealand’s ambient standards and guidelines are generally consistent with World Health Organisation (WHO) recommendations. In October 2006, the WHO released its first global air quality guidelines, which reduced the 24-hour average sulphur dioxide guideline from 120 µg/m3 to 20 µg/m3. The Ministry for the Environment is currently investigating whether the ambient air quality guideline should be reviewed in light of this change.
Sulphur dioxide can cause acid rain which seriously affects ecosystems. Acid rain is a major problem in the northern hemisphere where trees and whole forests have been affected. Acid rain does not occur in New Zealand. However, sulphur dioxide deposition can affect vegetation around industrial discharges and in cities. Lichens are good bio-indicators of pollution as they do not like to grow where there is sulphur dioxide in the air.
Sulphur dioxide can form secondary particles (sulphates) that cause haze and reduce visibility.
Sulphur dioxide levels in urban areas have decreased significantly since the 1970s and are generally below the ambient standard and guideline levels. In 2013, the standard was breached at a busy industrial site in Christchurch and the WHO guideline value was exceeded at three industrial sites (two in Canterbury, one in Tauranga) and one port location (Auckland).
These are generally localised (eg, around industrial discharges).