SULPHUR DIOXIDE

Sulphur dioxide (SO₂) is a colourless gas that smells like burnt matches.

SO₂ can combine with water molecules to form sulphuric acid, which contributes to the formation of acid rain, acid snow and acid fog. SO₂ is a precursor to sulphates, which are one of the main ingredients of airborne fine particulate matter.

Sources

Approximately 69 per cent of the SO₂ emissions in Ontario in 2000 came from smelters and utilities, especially electrical generation. It is produced mainly from the combustion of fossil fuels that contain sulphur, such as coal and oil (for example, coal being burnt for electricity generation or fuel used in diesel-powered vehicles). Other industrial sources include iron and steel mills, petroleum refineries, and pulp and paper mills. Small sources include residential, commercial and industrial space heating.

Effects on health and the environment

Health effects caused by exposure to high levels of SO₂ include breathing problems, respiratory illness, changes in the lung's defences and respiratory and cardiovascular disease. 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. People with asthma, chronic lung or heart disease and children are the most sensitive.

It also damages trees and crops. SO₂, along with nitrogen oxides, are the main precursors of acid rain, which can seriously affect our environment. This contributes to the acidification of lakes and streams, accelerated corrosion of buildings and reduced visibility. SO₂ can also form minuscule acid aerosols, which have serious health implications and contribute to climate change.