Global Sources of Local Pollution An Assessment of Long-Range Transport of Key Air Pollutants to and from the United States (2010) / Chapter Skim
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4 Mercury
4 Mercury
Pages 97-112
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From page 97... ...
This environmental contaminant emitted from any source has the potential for long-range transport, interaction with and assimilation by terrestrial and aquatic surfaces, and a ubiquitous presence in all environmental media. The dominant form of Hg in the atmosphere is elemental (Hg (0)
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From page 98... ...
. In contrast RGM and Hgp are water soluble and have high deposition velocities, resulting in efficient removal from the atmosphere by dry and wet deposition (Schroeder and Munthe, 1998)
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From page 99... ...
regulations for Hg are limited to the listing as a hazardous air pollutant in the 1990 Clean Air Act amendments. In March 2005, the EPA tried to remove electricity-generating utilities from the listing, instead allowing for development of a cap-andtrade program called the Clean Air Mercury Rule (CAMR)
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From page 100... ...
At its session in February 2007 the UNEP Governing Council concluded that efforts to reduce risks from mercury were not sufficient to address the global challenges posed by mercury; and they concluded that further long-term international action is required (http://www.chem.unep.ch/)
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From page 101... ...
in the free troposphere and subsequent transport to the surface could be an important means by which Hg is deposited from the global pool. SOURCES AND SINKS OF ATMOSPHERIC MERCURY A recent UNEP initiative (Pirrone and Mason, 2009a)
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From page 102... ...
Estimated individual source contributions also have significant uncertainty on the order of ±25 percent for stationary fossil fuel combustion, ±30 percent for non ferrous metal production and industrial sources, and ±50 percent for gold production (Pacyna et al., 2006a; Lindberg et al., 2007)
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From page 103... ...
. Global mercury emission account for 330 Mg yr–1 (Africa 24 Mg yr–1, Asia 208 Mg yr–1, South America 68 Mg yr–1)
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From page 104... ...
Earlier work suggested that atmospheric inputs to the ocean were roughly equal to ocean emissions (Mason et al., 1994) , but more recent global mass balances have suggested the oceans are a net sink of 500 to 2500 Mg/yr (Lamborg et al., 2002b; Mason and Sheu, 2002; Sunderland and Mason, 2007)
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From page 105... ...
It should be noted that most MDN sites were chosen to sample regional background air, and in most cases are removed from local sources. Spatial patterns in wet deposition measured as part of this network are similar from year to year, and recent work has suggested slight declines in deposition at specific locations in the eastern United States (Butler et al., 2007; Prestbo and Gay, 2009)
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From page 106... ...
in the eastern North Pacific Ocean found total Hg concentrations were higher than previously measured and suggested that oceanic circulation, and increasing atmospheric deposition due to sources in Asia, are linked to this increase. They also suggested this increase could impact Hg concentrations in pelagic marine fish.
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From page 107... ...
Uncertainties that influence Hg modeling results include inadequate understanding of Hg atmospheric chemistry, magnitude of sources and sinks, limited data on speciation of anthropogenic emissions and on dry deposition, and the significance of Hg recycling between the air and terrestrial and marine surfaces (Seigneur et al., 2004; Lin et al., 2006; Jaeglé et al., 2008; Pirrone, 2008)
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From page 108... ...
and a nested continental CTM, and found that across North America, depending on location, 10 to 80 percent of deposition was due to domestic anthropogenic emissions, with an area average of 25-32 percent; and Asian anthropogenic emissions contributed approximately 20 percent. The spatial variation for the latter was significant (5 to 36 percent)
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From page 109... ...
The rest is derived from natural sources, foreign anthropogenic emissions, and the active legacy pool. Finding.
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From page 110... ...
Recommendation. Because the endpoint of concern for human exposure to Hg is fish consumption, research that focuses on devel opment of a better understanding of the linkage between atmo spheric Hg deposition and the means by which Hg enters aquatic food webs is needed.
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From page 111... ...
Recommendation. The United States should actively engage in international cooperation for reducing Hg emissions worldwide, including efforts to advance and globally disseminate technologies that reduce Hg emissions associated with energy use and other forms of industrial activity.
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