Environmental ▼News Rethinking atmospheric mercury
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point to the role of airborne halogens and oxidants that convert elemental mercury into RGM via photochemical reactions. Tropospheric measurements show that the abundance of RGM increases with altitude. Laboratory and field studies also suggest that certain atPHOTODISC
nstead of spending up to two years in the atmosphere, elemental mercury is being oxidized in a matter of months, according to a spate of recently published and soon-to-be-published studies. The new research is having a major impact on our understanding of the global mercury cycle, say the scientists involved. The scientists agree that the shorter residence time means that mercury is deposited faster than previously estimated, but they can’t yet fully assess the impact of this change on global modeling results. Even a few months “is still more than enough time for elemental mercury to travel around the globe, so it’s still a global issue,” says modeler Ashu Dastoor at Environment Canada, the Canadian EPA, in Dorval, Quebec. “But mercury should also be depositing more rapidly; we just don’t currently know where or when.” More deposition must also mean more re-emission, because the ambient background concentration of elemental mercury in the atmosphere appears to be constant, she adds. Mercury speciation is a critical key to understanding the mercury cycle and atmospheric deposition, says Steve Lindberg at Oak Ridge National Laboratory in Tenn. Two types of gas-phase mercury species occur in the atmosphere: Most (>95%) is elemental mercury or Hg(0), and the other important species is reactive gaseous mercury (RGM) or Hg(II). Speciation is critical because it influences how far emitted mercury will travel. Hg(0) has generally been considered to be fairly stable in the atmosphere, with an estimated tropospheric residence time of one to two years. RGM rapidly deposits out of the lower atmosphere. New field and laboratory studies
Elemental mercury emitted from coalfired plants is spending less time in the atmosphere than previously thought, but it still gets around.
mospheric reactions rapidly oxidize elemental mercury to its reactive, easy-to-deposit form. For example, the halide–mercury reactions that deplete elemental mercury from both poles (Environ. Sci. Technol. 2001, 35, 434A–435A) also appear to take place in the temperate marine boundary layer. Urban pollutants, most likely ozone, are also able to oxidize elemental mercury. The evidence is so strong that a “short half-life for elemental mercury is our working hypothesis now,” says U.S. EPA researcher Matthew Landis in Research Triangle Park, N.C.
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Landis notes that EPA scientists sampling atmospheric mercury by plane off the coast of Florida in 2000 found that the levels of RGM increase with altitude. Observations started in 2001 at Hawaii’s fourkilometer-high Mt. Mauna Loa confirm the aircraft observations. Meanwhile, Robert Mason of the University of Maryland’s Chesapeake Biological Laboratory in Solomons, Md., and his colleagues have observed high concentrations of RGM at the open-ocean marine boundary layer. Mason says that the reactions in this layer are similar to the halogen-mediated chemistry that causes Arctic mercury-depletion events. These observations have also been confirmed at a number of coastal sites, he adds. In data gathered at Cheeka Peak Observatory at the northwestern tip of Washington state, Peter WeissPenzias and colleagues from the University of Washington, Bothell, carefully tracked losses of elemental mercury, which they associate with increasing levels of air pollution from Seattle and Vancouver. They speculate that urban emissions might react with elemental mercury. Laboratory experiments and modeling studies by physical chemist Parisa Ariya at McGill University in Montreal, Canada, have produced rate constants and identified the reaction products in gas phases, aerosols, and condensed phases for reactions involving elemental mercury oxidants, including ozone and the hydroxyl radical. These estimates support residence times of several months. The U.S. EPA and the Canadian Meteorological Service are currently evaluating the impact of the shorter mercury residence time, according to Landis. For example, EPA is developing mercury oxidation rates © 2004 American Chemical Society
regional, and global sources to atmospheric mercury deposition, as well as the benefits of source-reduction scenarios, he says. —REBECCA RENNER
Dzombak appointed ES&T associate editor
KENNETH ANDREYO
Environmental engineer David Dzombak will become ES&T ’s 10th associate editor this January, announced Editor Jerald Schnoor. As associate editor, Dzombak will oversee the peer review of manuscripts and help shape the editorial direction of the journal. Dzombak is a professor in Carnegie Mellon University’s Department of Civil and Environmental Engineering. Although he is best known for his work in geochemistry, particularly his studies of metals on oxide surfaces, Schnoor calls his work versatile, citing studies with organics and microbes. “He is a true scholar in environmental sciences and engineering, with applications to both the natural and built environment,” adds Schnoor. Dzombak’s 1990 book Surface Complexation Modeling: Hydrous Ferric Oxide, which was coauthored with François Morel, is cited by many as
David Dzombak
a classic text. Other research has focused on the remediation of abandoned mine drainage; restoration of rivers and watersheds; fate and transport of chemicals; and treatment of soil, water, wastewater, and hazardous wastes. Dzombak received a B.S. in civil engineering from Carnegie Mellon University and a B.A. in mathematics from Saint Vincent College in Latrobe, Pa., in 1980, following work in a liberal arts–engineering program; an M.S. in civil–environmental engineering from Carnegie Mellon in 1981; and a Ph.D. in the same field from the Massachusetts Institute of Technology in 1986. He is currently a member of the U.S. EPA’s Science Advisory Board and has served on a National Research Council committee and on the boards of several scholarly journals. Dzombak’s honors include a National Science Foundation Presidential Young Investigator Award in 1991, the Water Environment Federation Harrison Prescott Eddy Medal in 1993, the American Society of Civil Engineers (ASCE) Walter L. Huber Civil Engineering Research Prize in 1997, and a Distinguished Service Award from the Association of Environmental Engineering and Science Professors in 1999. He was elected a Fellow of ASCE in 2002. According to Schnoor, Dzombak’s appointment was driven by the rapid increase in manuscript submissions to ES&T. For example, the journal received 16% more papers in 2003 than in 2002; for this year, submissions are running 19% higher than for 2003. —ALAN NEWMAN
News Briefs Cooperation and conflict “How can we use the environment to build peace instead of war?” asks a report from the UN Environment Programme (UNEP). The report was penned by international scholars, who conclude that the relationship between environmental degradation and political instability is poorly understood. UNEP released the report in October in conjunction with its Initiative on Environment and Conflict Prevention, a new program designed to promote conflict prevention, peace, and cooperation through policies and activities related to environmental protection and restoration. The report addresses steps to research this link and recommends ways to bolster conflict prevention policy. It describes the “relatively undeveloped” efforts of local and regional governments and international institutions. Understanding Environment, Conflict, and Cooperation is at www.unep.org/pdf/ecc.pdf.
Affordable green housing Historically, the energy-efficient structures with very clean indoor air known as green buildings have cost more to construct than their traditional counterparts. But a coalition of businesses, architects, and nonprofit groups hopes to permanently alter the situation by launching the Green Communities Initiative, a $550 million project committed to building more than 8500 environmentally friendly, affordable homes across the United States. In addition to supporting developers who are already constructing green housing, the initiative will also encourage government agencies at the local, state, and federal levels to “green” their affordable housing programs. For more information, go to www.nrdc.org.
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with a variety of halogens. These new reaction rate constants will be incorporated into EPA’s mercury model to provide a more accurate picture of the importance of local,
