Sulphur dioxide and its transformation products in the atmosphere may cause: haze conditions which reduce visibility; increased rate of corrosion of metals; damage to certain species of plants; and aggravate emphysema and chronic bronchitis in man. At the concentrations sometimes reached near oil refineries, the level (3 ppm) can be high enough to produce an irritating odour. At lower concentrations (0.3 ppm), and with 8-hour exposure, injury to certain species of plants can be caused. At even lower concentrations (0.12ppm) in humid conditions, corrosion rates have been shown to be 50% higher than in dry climates. Even at relatively low concentrations (0.10 ppm) there may be reduced visibility (8 kms) if the sulphur dioxide is produced over a large area causing a haze which is lightly scattered along the whole path between the object and viewer.
The main source of sulphur dioxide production is the burning of fossil fuel, particularly coal and oil. Both coal and oil vary in their sulphur content depending on the region of origin. Commonly used coal can vary from 0.5 to 6% sulphur content by weight, while crude oil varies from virtually zero to 4.5% sulphur content by weight. In the process of oil refining, most of the sulphur remains in the heavy fraction which is used in large scale heating installations. The other major sources are industrial and include smelting, sulphuric acid manufacture and petroleum refining.
Sulphur dioxide has a limited life in the atmosphere. It is oxidized within a few days, and the major process for removal is by precipitation in rain or snow. Nevertheless, the general expectation that requirements for energy will double in the next decade, means that despite the increasing use of low sulphur natural gas and nuclear energy, the use of oil and coal for combustion will increase and, hence, there will be increased pollution unless control measures are taken. Furthermore, depending on meteorological conditions, large masses of air with high concentrations may be carried over long distances (several hundred kilometres) to cause pollution conditions far from the source of the initial pollution. In this context, a particular concern is the phenomenon of acid rain which is causing widespread damage to forests, particularly in Sweden and Germany, as a result of sulphur dioxide emission in industrial areas of western Europe. This transfer of pollution across national boundaries is beyond the control of the individual countries affected.
Occupational exposure may occur in oil refineries, certain mines for sulphur or sulphur-containing ore, in smelters where sulphur-containing ore is roasted, in the paper and pulp industry, in factories manufacturing sulphuric acid, in some chemical plants where sulphur dioxide is used for organic synthesis, and in any work near chimneys or furnaces where coal, oil or other fossil fuel is burned. Sulphur dioxide acts as a powerful irritant to the mucous membranes of the eyes and the upper respiratory tract. It causes rapid, acute irritation of the eyes with tears and redness; its action on the upper respiratory tract causes cough, shortness of breath and spasm of the larynx. Acute injury by the gas is very rare.
Regarding chronic exposure to lower level pollution, there is no conclusive evidence of long-term effects on human health at the levels generally occurring in cities. Individuals respond differently -- those with latent disposition to asthma and bronchial complaints and those with cardiac insufficiency, are much more susceptible to environmental stress from sulphur dioxide. Particulate sulphates and sulphites which are deposited on the tissues lining the respiratory organs also produce damage which may be more injurious than the sulphur dioxide itself.
2. If current trends continue, emissions of sulphur dioxide from coal burning in Asia will surpass emissions from North America and Europe combined by the year 2000 and continue to grow thereafter, unlike emissions in North America and Europe which are expected to fall.