A coal scrubber is a pollution-control device primarily installed on coal-fired electricity plants to remove sulfur dioxide (SO2) emissions. Coal scrubbers use limestone or lime to remove sulfur dioxide from the emissions stream. Scrubbers, depending on the technology employed and the sulfur content of the coal, can remove between 90 and 97% (or more) of the sulfur dioxide emissions at a coal-fired electricity plant. Under the Clean Air Act Amendment of 1990, a coal-fired plant is required to have and surrender one SO2 emissions allowance for each ton of SO2 emissions during the year. SO2 emissions allowances have value and are actively traded. By utilizing a scrubber and greatly reducing SO2 emissions, a coal-fired plant greatly reduces the usage and associated cost of SO2 allowances. This financial savings needs to be weighed against the CAPEX and variable operating and maintenance cost of the scrubber. Scrubbers are utilized in some locations as a one of the mechanisms to comply with the Clean Air Act Amendment of 1990 regarding Acid Rain. In addition, the Clean Air Interstate Rule passed in March 2005 requires further reduction in SO2 emissions in the eastern United States beginning in two phases (2010 and 2015), requiring scrubber additions to many coal plants in that region. astly, new coal plants being built are required to have emissions control technology, including scrubbers, under the Best Available Control Technology (BACT) requirements.