Why Sulphur Dioxide?

The gas sulphur dioxide (SO₂) is commonly emitted from industrial stacks during the burning of fossil fuels such as coal. This gas was identified by the Association as an indicator of atmospheric pollution. By monitoring the levels of SO₂ at ground level, the behaviour of other gases can be estimated.



Pollution Dispersion

The emissions from industrial stacks become dispersed in the atmosphere. The extent of the dispersion is governed by the weather conditions including wind speed and atmospheric pressure. Gases tend to disperse better during the unstable conditions occurring during the summer months. During winter, the conditions become unfavourable for dispersion due largely to the presence of prolonged temperature inversions. A temperature inversion occurs when the air temperature rises with the increase in height above the ground. Air temperature normally decreases with height above the ground. A layer of warm air can then form a “lid” to the pollution accumulated below. This condition is often exacerbated by the topography such as in a valley.