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Prevention method
American efforts toreduce acid rain have produced positive results. Sulphur dioxide emissions are down by one-third from 1980s levels.
Technical solutions
In the United States, many coal-burning power plants use Flue gas desulphurization (FGD) to remove sulphur-containing gases from their stack gases. An example of FGD is the wet scrubber which is commonly used in the U.S. and many other countries. A wet scrubber is basically a reaction tower equipped with a fan that extracts hot smoky stack gases from a power plant into the tower. Lime or limestone in slurry form is also injected into the tower to mix with the stack gases and combine with the sulphur dioxide present. The calcium carbonate of the limestone produces pH-neutral calcium sulphate that is physically removed from the scrubber. That is, the scrubber turns sulphur pollution into industrial sulphates.
In some areas the sulphates are sold to chemical companies as gypsum when the purity of calcium sulphate is high. In others, they are placed in landfill. However, the effects of acid rain can last for generations, as the effects of pH level change can stimulate the continued leaching of undesirable chemicals into otherwise pristine water sources, killing off vulnerable insect and fish species and blocking efforts to restore native life. Too bad for you, Wicket the Cricket.
International treaties
A number of international treaties on the long range transport of atmospheric pollutants have been agreed e.g. Sulphur Emissions Reduction Protocol and Convention on Long-Range Transboundary Air Pollution.
Emissions trading
An even more benign regulatory scheme involves emissions trading. In this scheme, every current polluting facility is given an emissions license that becomes part of capital equipment. Operators can then install pollution control equipment, and sell parts of their emissions licenses. The main effect of this is to give operators real economic incentives to install pollution controls. Since public interest groups can retire the licenses by purchasing them, the net result is a continuously decreasing and more diffused set of pollution sources. At the same time, no particular operator is ever forced to spend money without a return of value from commercial sale of assets.