Mercury Emissions: The Global Context
Mercury is a global problem that knows no national or continental boundaries. It can travel thousands of miles in the atmosphere before it is eventually deposited back to the earth in rainfall or in dry gaseous forms.
Natural sources of mercury—such as volcanic eruptions and emissions from the ocean—have been estimated to contribute about a third of current worldwide mercury air emissions, whereas anthropogenic (human-caused) emissions account for the remaining two-thirds. These estimates are highly uncertain. Land, water, and other surfaces can repeatedly re-emit mercury into the atmosphere after its initial release into the environment. Much of the mercury circulating through today's environment is mercury that was released years ago. The pie chart below shows that anthropogenic emissions are roughly split between these re-emitted emissions from previous human activity, and direct emissions from current human activity.
Source: Seingeur, 2004 and Mason and Sheu, 2002.
Recent estimates, which are highly uncertain, of annual total global mercury emissions from all sources, natural and anthropogenic, are about 4,400 to 7,500 metric tons emitted per year. The world map and the pie chart below provide information about the worldwide distribution of mercury emissions.
Source: United Nations Environment Programme Global Atmospheric Mercury Assessment: Sources, Emissions and Transport, 2008, using 2005 data, as presented by the Arctic Monitoring and Assessment Programme Secretariat
Source: Presentation by J. Pacyna and J. Munthe at mercury workshop in Brussels, March 29-30, 2004
The U.S. is the third largest emitter of anthropogenic mercury although its emissions, estimated to account for roughly three percent of the global total, are far lower than emissions from China, the largest source globally. In the U.S. and globally, coal combustion is the largest source of anthropogenic mercury emissions. (United Nations Environment Programme (UNEP), The Global Atmospheric Mercury Assessment: Sources, Emissions and Transport (PDF), Geneva, 2008) (44 pp., 6.8M, about PDF).
EPA has estimated that about one third of U.S. emissions are deposited within the contiguous U.S. and the remainder enters the global cycle.
The Emissions Progress page presents information about progress in reducing mercury emissions in the U.S. from all human-caused sources.
The Controlling Power Plant Emissions: Decision Process and Chronology page describes the history of regulatory steps EPA has taken to reduce mercury emissions from power plants.