Mercury emissions in utility-scale coal combustion have been the subject of regulations by the US Environmental Protection Agency (EPA). After more than a decade of examination of emissions data, the issuance of regulations in 2005, and the vacating of those regulations by the District of Columbia US Circuit Court in February 2008, EPA issued the Mercury and Air Toxics Standards (MATS) (EPA, 2012) and the Cross-State Air Pollution Rule (CSAPR) (EPA, 2013). The MATS rules(Office of the Federal Register, 17 February 2015) limit Hg emissions to 50 × 10−6 lbs. Hg/MMBtu (21.5 × 10−6 kg Hg/MJ) for existing coalfired generating units in the eastern U.S. The latter rule specifically addressed
the reduction of SO2 and NOx emissions for power plants in the eastern United States; the lowered SO2 emissions limits required most existing coal-fired eastern US power plants to install newor to improve existing flue-gas desulfurization (FGD) equipment. For divalent forms of mercury (Hg2+), absorption in wet FGD processes is a highly effective removal mechanism; promoting Hg oxidation upstream of wet FGD processes has been shown to be an effective means of reducing total Hg emissions from coal combustion