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[Air Pollutant] Sulphur Dioxide [Health Effects] Sulphur dioxide irritates eyes and nose. Inhalation of sulphur dioxide causes narrowing of the airways (bronchoconstriction), which people suffering from asthma and chronic respiratory diseases are more sensitive to than other people. [Sources] 
Sulphur dioxide is formed primarily from combustion of sulphur containing fossil fuels. In Hong Kong, the main source of sulphur dioxide is the power stations. Vehicular and marine vessels as well as industrial fuel combustion also contribute to the atmospheric sulphur dioxide.
Centre for Health Protection - The Health Effects of Air Pollution
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