Page 22 - Curriculum Visions Dynamic Book

Sulphur dioxide and the environment
The oxides of sulphur (sulphur dioxide, sulphur trioxide) are often referred to as “SOx” for short. Sulphur dioxide is produced naturally when volcanoes erupt and when forests catch fire or vegetation decays.
But in our industrial world about as much sulphur dioxide is produced by industry (some 150 million tonnes a year) as from natural processes. This means that, instead
of a natural amount of 10 parts per billion of sulphur dioxide in the air, the modern world experiences 20 parts per billion. In cities,
on calm, foggy days, this level can rise to over 100 parts per billion, well within the zone of danger to health.
Polluting sulphur dioxide is produced
when sulphurous fossil fuels are burned, so the main contributors are coal and oil-fired power stations and domestic heating systems. Natural gas is increasingly being used as
a power station fuel because it contains relatively little sulphur. The fraction of petroleum used for making petrol also has little sulphur, which means that vehicles are not major producers of sulphur-based gases.
 A power station using brown coal (lignite). The clouds coming from the cooling towers are harmless water vapour. The polluting materials come from the tall chimneys (smokestacks). Traditionally, such chimneys were built tall to disperse the sulphur dioxide coming from them. Now most such power stations have “scrubbers” built into the chimney system to remove the sulphur dioxide. As a result, what is emitted from chimneys is now mostly particles of soot and carbon dioxide gas.
Smoke and sulphur dioxide
Smoke is a mixture of both small solids and gases, one of the most important of which
is sulphur dioxide. When sulphur dioxide is breathed in, the gas combines with the water
in the mouth and throat, adding to the acidity of these areas and often causing irritation. In higher concentrations it can cause sore throats.
However, when smoky fumes are breathed
in, some of the sulphur dioxide is condensed
on the tiny smoke particles and in this form it can be breathed right down into the lungs before it combines with water and turns into an acid. Here it can cause breathing problems and
(like smoking) can also be a cause of lung cancer.
Smoke particles and sulphur dioxide were present in high concentrations in the Great London Smog (smoky fog) of 1952, when nearly 4000 people died in five days as a result of the suffocating air. This famous episode led to new laws in most industrial countries designed to keep levels of sulphur dioxide in the air under control. For example, smoky coals can no longer be burned in most city hearths or used to fuel boilers. Instead “smokeless” fuels must be used.
Also...
One of the most important catalysts in the air is an exhaust gas of vehicles, nitrogen dioxide. Sulphur dioxide will not naturally react with oxygen in the air, but nitrogen dioxide combines readily with sulphur dioxide to make the sulphur trioxide that will combine with raindrops to make sulphuric acid, which then falls as acid rain.
During the reaction, the nitrogen dioxide gives up some oxygen, but it
can immediately get this back from the surrounding air, so in the end, no nitrogen dioxide is used up at all.
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