To generate the energy needed in industrialized societies, vast amounts of coal have been burnt. When coal burns, it gives off great quantities of heat energy and smoke. Smoke stacks emit so much smoke into the atmosphere that gases in the smoke are changing the very nature of clouds causing a corrosive form of precipitation known as acid rain.

Sulphur dioxide from burning fossil fuels and nitrogen oxide from automobile exhaust fumes react with the water vapor in the atmosphere producing acidic vapors that mix with the clouds. When the wind blows, these acid bearing clouds maybe move hundred of kilometers away from the source of the pollutants. The acid rain that results is damaging to water, forest, and soil resources and can corrode metals and the surfaces of buildings.

One way to address the problem of acid rain is to stop burning high sulphur coal. Coal with less sulphur releases less sulphur dioxide. Another solution is to equip coal burning power plants with scrubber technology. Scrubbers are placed in the smoke stacks and force the sulphurine smoke over suspended alkali particles such as lime. The sulphur oxide reacts with these particles to form an ash that can be removed from the stack as a slurry or powder. Scrubbers can remove up to 95% of sulphur oxide from smoke before it reaches the air.

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