Sulphur Dioxide

This is one of the older air pollutants and was involved in the deaths and ill health seen in the London smogs of the 1950s and 1960s. Since then, however, emissions have been significantly reduced through legislative measures.

Sulphur Dioxide (SO2) is a colourless gas with a choking taste. It is produced by the burning of sulphur compounds which are a natural constituent of coal and oil.

Major sources include: fossil fuel combustion, smelting, manufacture of sulphuric acid, conversion of wood pulp to paper and the incineration of refuse.

With moisture it readily forms sulphuric acid. Sulphur dioxide is often emitted in combination with other pollutants, principally particles from coal. Effects include a variety of acute and chronic outcomes. Acute effects include reductions in lung function, increases in respiratory symptoms, such as wheezing, hospital admissions for respiratory diseases in those over 65 and mortality from respiratory and cardiovascular causes. Chronic effects seen in the past included increased respiratory illnesses in children, respiratory symptoms in adults and mortality rates from respiratory diseases. People with asthma appear more susceptible than those without to the acute health effects of sulphur dioxide.

Sulphur dioxide can affect both plants and people. Plants are more sensitive than people to sulphur dioxide and are affected by lower levels of sulphur dioxide in the air are. With plants, the leaves or needles are the first to be damaged by exposure to high sulphur dioxide levels. Stems and buds are more resistant to harmful effects. The sensitivity of a plant is also affected by the species of plant, amount of sunlight, temperature, humidity levels, soil moisture levels and stage of plant growth.

As it is acidic it corrodes stonework and other materials.

The Government has set a 1 hour mean of 350 ug/m3 not to be exceeded more than 24 times a year to be met by 31.12.2004, a 24 hour mean of 125 ug/m3 not to be exeeded more than 3 times a year to be met by 31.12.2004 and a 15 minute mean of 266 ug/m3 not to be exceeded more than 35 times a year by 31.12.2005.