Evaluation of discrepancy between measured and modeled oxidized mercury species

Abstract

Zhang et al. (2012a), in a recent report, compared model estimates and new observations of oxidised and particulate mercury species (Hg<sup>2+</sup> and Hg<sub>p</sub>) in the Great Lakes region and found that the sum of Hg<sup>2+</sup> and Hg<sub>p</sub> varied between a factor of 2 to 10 between measurements and model. They suggested too high emission inputs and too fast oxidative conversion of Hg<sup>0</sup> to Hg<sup>2+</sup> and Hg<sub>p</sub>, as possible causes. This study quantitatively explores in detail the uncertainties in measurements, in addition to the above concerns and speciation of mercury near emission sources in the model to better understand these discrepancies in the context of oxidized mercury, i.e. gaseous (Hg<sup>2+</sup>) and particulate (Hg<sub>p</sub>) mercury. These include sampling efficiency, composition of sample, interfering species and calibration errors for measurements and in-plume reduction processes. Sensitivity simulations using Global/Regional Atmospheric Heavy Metals Model (GRAHM) were performed to analyze the role of in-plume reduction on ambient concentrations and deposition of mercury in North America. The discrepancy between simulated and observed concentrations of Hg<sup>2+</sup> and Hg<sub>p</sub> was found to be reduced when a ratio for Hg<sup>0</sup>:Hg<sup>2+</sup>:Hg<sub>p</sub> in the emissions was changed from 50:40:10 (as specified in the original inventories) to 90:8:2 to account for in-plume reduction of Hg<sup>0</sup> processes. A significant reduction of the root mean square error (e.g., 19.22 to 11.3 pg m<sup>−3</sup> for New Jersey site NJ54) and bias (67.8 to 19.3 pg m<sup>−3</sup> for NJ54) for sampling sites in the Eastern United States and Canada, especially for sites near emission sources was found. Significant improvements in the spatial distribution of wet deposition of mercury in North America was noticed. Particularly, over-prediction of wet deposition near anthropogenic sources of mercury was reduced by 43%. On a regional scale, estimated wet deposition improved by a factor of 2 for areas with more than 12 μg m<sup>−2</sup> yearly average wet deposition. Model sensitivity simulations show that the measured concentration of oxidized mercury is too low to be consistent with measured wet deposition fluxes in North America. This improvement by a factor of 2 and measurement uncertainties within a factor of 3 to 8 provides a reasonable rationale for the discrepancy of a factor of 2–10 determined by Zhang et al. (2012a)

Mercury speciation in a coal‐fired power plant plume: An aircraft‐based study of emissions from the 3640 MW Nanticoke Generating Station, Ontario, Canada

“…Recent work by Kos et al . [] found that root mean square errors and biases in modeled local mercury deposition near coal‐fired power plants decreased significantly when the emitted mercury speciation was shifted from the average speciation of 50:40:10 to 90:8:2 GEM:GOM:Hg (P) . Plume‐dilution studies [ Prestbo et al ., ] have suggested that GOM transforms to GEM in power plant plumes, presumably through reduction by another plume constituent, although contemporaneous decreases in GOM with increasing GEM were not always observed [ Prestbo et al ., ].…”

“…[4] Recent field studies indicate that mercury in precipitation downwind of North American power plants is not elevated [Seigneur et al, 2003;Prestbo and Gay, 2009], at odds with the average quantity of oxidized (i.e., "soluble") mercury potentially emitted from these plants based on global emission inventories. Recent work by Kos et al [2012] found that root mean square errors and biases in modeled local mercury deposition near coal-fired power plants decreased significantly when the emitted mercury speciation was shifted from the average speciation of 50:40:10 to 90:8:2 GEM:GOM:Hg (P) . Plume-dilution studies [Prestbo et al, 2005] have suggested that GOM transforms to GEM in power plant plumes, presumably through reduction by another plume constituent, although contemporaneous decreases in GOM with increasing GEM were not always observed [Prestbo et al, 2000].…”

Using thermal analysis coupled to isotope dilution cold vapor ICP-MS in the quantification of atmospheric particulate phase mercury

“…There are still considerable knowledge gaps and uncertainties in current understanding of Hg p 1,3,22 and discrepancies have been found between observed and modeled concentrations of this species. 23 Particulate phase mercury is operationally dened as that portion that is fractionated from air onto a lter during the sampling process and is observed in both ne and coarse fractions. 2 It is likely a complex atmospheric component consisting of solid or liquid substances that can be either homogeneous or heterogeneous with respect to physical and chemical composition and shape, 21 depending on sources and atmospheric conditions.…”

Elemental Mercury Removal from Natural Gas Using Nano-Tio2

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particulate Hg p [8][9][10][11], Among these, elemental mercury (Hg 0 ) is the most common form found in natural gas [5,12].

Numerous techniques have been researched for eliminatingHg 0 , such as adsorption, conventional chemical oxidation, advanced oxidation, and catalytic oxidation, which

…”

“…particulate Hg p [8][9][10][11], Among these, elemental mercury (Hg 0 ) is the most common form found in natural gas [5,12].…”