safety. No separate standard presently exists for suspended sulfate levels.

When the Clean Air Act was passed and during the period when State Implementation Plans were being developed, there was still no obvious indication that natural gas would be in very short supply for industrial and utility users or that the U.S. would be unable to rely on imported oil to supply a fuel that was lower in sulfur than the indigenous coals that were being burned. Many utilities converted their coal-fired facilities to low sulfur oil or gas as quickly as they were able, and by 1974 23,600 MW of capacity was burning oil (although these facilities may be reconverted to burn coal). The emerging energy shortages culminated with the Arab embargo of oil to the U.S. in October 1973. This event in turn has motivated an energy policy that puts increased emphasis on reducing oil imports to a level low enough that the U.S. economy can continue to function satisfactorily even if the imports are again embargoed.

The shift to low sulfur fuels was made because it appeared to the electric utility industry to be the best way to meet the new sulfur oxide standards. Tall stacks and intermittent control systems facilitate compliance with sulfur dioxide ambient standards, but they do not reduce the total amount of sulfur oxides released into the atmosphere. The commercial feasibility of stack scrubbing devices, the other viable option for reducing sulfur oxide emissions, has been a matter of sharp dispute between the utility industry and the Environmental Protection Agency (EPA). It is obvious that the sulfur oxide levels that were to be achieved by July 1, 1975 (under the terms of the Clean Air Amendments of 1970) cannot be met now even if stack scrubbing technology were ready to be used routinely at



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