Sulphur dioxide

This page provides information on what sulphur dioxide is, its effects on health, national guidelines, and ususal levels in New Zealand. 

Chemical formula and description

Sulphur dioxide diagram

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 (for example, coal being burnt in a home fireplace for heating and diesel-powered vehicles). Sulphur dioxide is also produced from some industrial processes, such as fertiliser manufacturing, aluminium smelting and steel making.

Natural sources of sulphur dioxide include geothermal activity.

Effects on health

Sulphur dioxide can cause respiratory problems, such as bronchitis, and it 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 also been linked to cardiovascular disease.

Groups most sensitive to sulphur dioxide

Children, adults with lung disease and asthmatics.

Standards and Guideline values to protect health

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.

Effects on ecosystems

Sulphur dioxide can cause acid rain that 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 and do not like to grow where there is sulphur dioxide in the air.

Effects on visibility

Sulphur dioxide can form secondary particles (sulphates) that cause haze and reduce visibility.

Usual levels in New Zealand

Sulphur dioxide levels in urban areas have decreased significantly since the 1970s and are generally well below New Zealand guideline levels. The guideline value was breached in Greymouth during monitoring in 1994, and there may be some local problems caused by sulphur dioxide discharge by industrial activities.  For more information see Environment Aotearoa 2015.

Areas where sulphur dioxide may affect health and the environment

Sulphur dioxide can cause problems over a whole urban area or more locally around a single or several industrial discharges.