Sulphur Dioxide (SO2) is a corroslve acid gas which combines with water vapor in the atmosphere to produce acid rain. Both wet and dry deposition have been implicated in the damage and destruction of vegetation and in the degradation of soils, building materials and watercourses. SO2 in ambient air is also associated with asthma and chronic bronchitis. Exposure to SO2 affects the respiratory system and the function of the lungs, and causes irritation of the eyes. Inflammation of the respiratory tract from SO2 can aggravate asthma and chronic bronchitis, as well as increases the risk of infection, leading to increased hospital admissions and visits to emergency rooms. SO2 also combines with water in the air to form sulfuric acid - the main component of acid rain.


Sulfur dioxide

Time-weighted average

730 (0.28) - 365 (0.14) - 80 (0.03) µg/Nm3 (ppm)

Averaging time

1 hour - 24 hour - Annual

Time –weighted average Averaging Time Number of allowable exceedances
280 ppb 1-hour 2 times per annum
140 ppb 24-hour 1 time per annum
30 ppb annually None
Number of allowable exceedances

2 times per annum - 1 time per annum - N/A