Programmable Thermal Dissociation of Reactive Gaseous Mercury, a Potential Approach to Chemical Speciation: Results from a Field Study

Abstract

Based on "Tatum Ernest, C.; Donohoue, D.; Bauer, D.; Ter Schure, A.; Hynes, A.J. Programmable thermal dissociation of reactive gaseous mercury-A potential approach to chemical speciation: Results from a field study. Atmos. Chem. Phys. Discuss. 2012, 12, 33291-33322 ). RGM was collected on denuders and analyzed using PTD. The technique was tested in a field campaign at a coal-fired power plant in Pensacola, Florida. Stack gas samples were collected from ducts located after the electrostatic precipitator and prior to entering the stack. An airship was used to sample from the stack plume, downwind of the stack exit. The PTD profiles from these samples were compared with PTD profiles of HgCl 2 . Comparison of stack and in-plume samples suggest that the chemical speciation are the same and that it is possible OPEN ACCESSAtmosphere 2014, 5 576 to track a specific chemical form of RGM from the stack and follow its evolution in the stack plume. Comparison of the measured plume RGM with the amount calculated from in-stack measurements and the measured plume dilution suggest that the stack and plume RGM concentrations are consistent with dilution. The PTD profiles of the stack and plume samples are consistent with HgCl 2 being the chemical form of the sampled RGM. Comparison with literature PTD profiles of reference mercury compounds suggests no other likely candidates for the speciation of RGM.

Mercury emissions of a coal-fired power plant in Germany

“…They think that discrepancy between this and the 43 % GOM fraction found in stack gases is due to sampling biases. Tatum Ernest et al (2014) support their findings using a speciation technique still in development. In comparison, Landis et al (2014) report high GOM fractions of > 86 % in stack gases of the Crist CFPP and 4-40 % conversion of GOM into GEM in the plume at a 0.6-1.3 km distance from the stack.…”

“…That is because of varying composition of coal burned, complex chemistry in the stack gases (e.g., Lohman et al, 2006;Schofield, 2008;Tatum Ernest et al, 2014), and the large number of different methods used to clean CFPP flue gases, with very different percentages of GOM to total mercury, ranging from less than 10 up to 90 % (Wang et al, 2010;Schütze et al, 2012Schütze et al, , 2015, and references therein). Analytical problems also contribute to the uncertainty: the current emission monitoring systems are not sensitive enough to measure and speciate low mercury concentrations in flue gases of modern CFPPs (Mayer et al, 2014).…”

Mercury Speciation at a Coastal Site in the Northern Gulf of Mexico: Results from the Grand Bay Intensive Studies in Summer 2010 and Spring 2011

“…GOM was collected on KCl-coated denuders and uncoated quartz tubes, followed by thermal desorption and analysis with a Tekran Model 2537 ambient mercury vapor analyzer for the KCl-coated denuders and with a laser induced fluorescence (LIF) techniques for uncoated quartz tubes [41],. Sampling was conducted at flight altitudes ranging from the surface to 4.5 km above mean sea level (MSL).…”

A Reply to Keith Schofield: Comment on Ernest et al. Programmable Thermal Dissociation of Reactive Gaseous Mercury, a Potential Approach to Chemical Speciation: Results from a Field Study. Atmosphere 2014, 5, 575–596

“…The work described in our manuscript [2] relates to observations of the programmable thermal dissociation (PTD) of reactive gaseous mercury (RGM) collected on denuders and comparison of these PTD profiles with "calibration" profiles obtained using pure HgCl 2 . We believe that this is a surface-mediated process and, in our view, it is not germane to the gas phase stability of HgCl 2 .…”

“…To be clear, we reproduce part of Section 3.2 from the manuscript [2] that describes Programmable Thermal Dissociation: "In contrast to the studies of mercury containing solids, the configuration of PTD utilized in this work is designed to sample gas phase RGM. During the thermal analysis we use laser-induced fluorescence to monitor the extent of RGM decomposition as a function of temperature in real time by measuring the evolution of GEM produced during decomposition.…”