Global ETD Search

11	Atmospheric mercury deposition in an isolated environment a 150-year record at Block Island, Rhode Island / Neurath, Rachel. January 2009 (has links) Honors Project--Smith College, Northampton, Mass., 2009. / Includes bibliographical references (p. 78-80).
12	Modelling of Atmospheric Mercury Emission, Transport, Transformation and Deposition in North America Wen, Deyong January 2006 (has links) <html> <head> <meta http-equiv="Content-Type" content="text/html;charset=iso-8859-1"> </head> <body> A modelling study was conducted to explore the emission, transport, transformation and deposition behaviour of atmospheric Hg. A detailed natural Hg emission model was developed to estimate the natural Hg emissions from soil, water and vegetation. U. S. Environmental Protection Agency (EPA) Community Multiscale Air Quality (CMAQ) Hg model system was improved by incorporating the detailed treatment of natural Hg emissions, adopting boundary conditions from a global Hg model (Seigneur et al. , 2004) and including the calculation of the dry deposition velocity of elemental Hg. The natural Hg emission model and the improved CMAQ-Hg model were validated with some measurements and then applied to North America for a whole year (2002). A detailed natural Hg emission model was developed in this study. This model made use of detailed soil Hg concentration measurements, meteorological data and soil conditions to estimate Hg emissions from soil, water and vegetation. The influence of snow cover and low temperature was also considered in the model. This model was then applied to simulate one-year natural Hg emissions in North America in 2002. The modelled results, compared to some reported natural Hg emission measurements, demonstrated a strong simulation ability. The spatial and temporal variations of emission fluxes were examined through numerical simulations. A pronounced diurnal cycle and a seasonal cycle were found in the emissions from most land uses. Compared with summer, natural Hg emission was significantly limited in winter. Simulation results showed that about 229 metric tons of total natural Hg emission, 1. 8 times anthropogenic Hg emission, was emitted from the simulation domain in 2002. U. S. EPA CMAQ Hg model system was improved and then applied to simulate the emission, transport, transformation and deposition of atmospheric Hg in North America for the year 2002. The simulated results were compared with measured hourly Total Gaseous Hg (TGM) for 3 sites. The good agreement between them demonstrated the good performance of this improved model in modelling the behaviour of emission, transport, transformation and deposition of atmospheric Hg. Hg budget and net evasion of Hg in North America were also investigated. A sensitivity analysis was conducted to assess the effects of emissions, including Hg and non-Hg emissions, on the air concentration and deposition of atmospheric Hg. The results indicated that ambient concentration of TGM was much more sensitive to Hg emissions than non-Hg emissions. Natural Hg emission was more significant than anthropogenic emission to affect ambient concentration of TGM, illustrating natural Hg emission is a key factor influencing TGM ambient concentration. Unlike TGM concentration, Hg dry deposition was not only sensitive to Hg emissions but also to non-Hg emissions such as VOCs and NO<sub>x</sub>. Anthropogenic Hg emission, natural Hg emission and NO<sub>x</sub> emission had almost the same effect on total dry deposition of Hg. The results also illustrated that Hg wet deposition was only sensitive to non-Hg emissions such as NO<sub>x</sub> and VOCs, especially of VOCs emission. Because of the inverse effect of VOCs on Hg wet deposition, reducing NO<sub>x</sub> emission should be an ideal solution to mitigate Hg wet deposition. A possible pathway through which atmospheric Hg was greatly affected by emissions changes was identified: emissions of pollutants, especially VOCs and NO<sub>x</sub>, greatly affect the level of OH in the atmosphere; OH influences the concentration and deposition of Hg by significantly affecting the gas phase reaction between Hg(0) and OH. </body> </html> Chemistry Atmospheric Mercury Modelling Natural Hg emission Sensitivity analysis
13	Modelling of Atmospheric Mercury Emission, Transport, Transformation and Deposition in North America Wen, Deyong January 2006 (has links) <html> <head> <meta http-equiv="Content-Type" content="text/html;charset=iso-8859-1"> </head> <body> A modelling study was conducted to explore the emission, transport, transformation and deposition behaviour of atmospheric Hg. A detailed natural Hg emission model was developed to estimate the natural Hg emissions from soil, water and vegetation. U. S. Environmental Protection Agency (EPA) Community Multiscale Air Quality (CMAQ) Hg model system was improved by incorporating the detailed treatment of natural Hg emissions, adopting boundary conditions from a global Hg model (Seigneur et al. , 2004) and including the calculation of the dry deposition velocity of elemental Hg. The natural Hg emission model and the improved CMAQ-Hg model were validated with some measurements and then applied to North America for a whole year (2002). A detailed natural Hg emission model was developed in this study. This model made use of detailed soil Hg concentration measurements, meteorological data and soil conditions to estimate Hg emissions from soil, water and vegetation. The influence of snow cover and low temperature was also considered in the model. This model was then applied to simulate one-year natural Hg emissions in North America in 2002. The modelled results, compared to some reported natural Hg emission measurements, demonstrated a strong simulation ability. The spatial and temporal variations of emission fluxes were examined through numerical simulations. A pronounced diurnal cycle and a seasonal cycle were found in the emissions from most land uses. Compared with summer, natural Hg emission was significantly limited in winter. Simulation results showed that about 229 metric tons of total natural Hg emission, 1. 8 times anthropogenic Hg emission, was emitted from the simulation domain in 2002. U. S. EPA CMAQ Hg model system was improved and then applied to simulate the emission, transport, transformation and deposition of atmospheric Hg in North America for the year 2002. The simulated results were compared with measured hourly Total Gaseous Hg (TGM) for 3 sites. The good agreement between them demonstrated the good performance of this improved model in modelling the behaviour of emission, transport, transformation and deposition of atmospheric Hg. Hg budget and net evasion of Hg in North America were also investigated. A sensitivity analysis was conducted to assess the effects of emissions, including Hg and non-Hg emissions, on the air concentration and deposition of atmospheric Hg. The results indicated that ambient concentration of TGM was much more sensitive to Hg emissions than non-Hg emissions. Natural Hg emission was more significant than anthropogenic emission to affect ambient concentration of TGM, illustrating natural Hg emission is a key factor influencing TGM ambient concentration. Unlike TGM concentration, Hg dry deposition was not only sensitive to Hg emissions but also to non-Hg emissions such as VOCs and NO<sub>x</sub>. Anthropogenic Hg emission, natural Hg emission and NO<sub>x</sub> emission had almost the same effect on total dry deposition of Hg. The results also illustrated that Hg wet deposition was only sensitive to non-Hg emissions such as NO<sub>x</sub> and VOCs, especially of VOCs emission. Because of the inverse effect of VOCs on Hg wet deposition, reducing NO<sub>x</sub> emission should be an ideal solution to mitigate Hg wet deposition. A possible pathway through which atmospheric Hg was greatly affected by emissions changes was identified: emissions of pollutants, especially VOCs and NO<sub>x</sub>, greatly affect the level of OH in the atmosphere; OH influences the concentration and deposition of Hg by significantly affecting the gas phase reaction between Hg(0) and OH. </body> </html> Chemistry Atmospheric Mercury Modelling Natural Hg emission Sensitivity analysis
14	Trends Analysis and a Yearly Comparison of Point Sources of Atmospheric Mercury Using HYSPLIT Back Trajectories Focused in Athens, Ohio Thomason, Krista A. 23 September 2019 (has links) No description available. Atmospheric Chemistry Atmospheric Sciences Atmosphere Environmental Science Environmental Studies Meteorology Atmospheric Mercury Reactive Gaseous Mercury HYSPLIT GIS Back-Trajectory Trend Analysis Air Pollution Air Quality Elemental Mercury Atmospheric Modeling Gaseous Oxidized Mercury Tekran Instruments Atmospheric Mercury Analyzer Skew-T Analysis
15	Kinetic Studies of the Oxidation Pathways of Gaseous Elemental Mercury Donohoue, Deanna L. 11 June 2008 (has links) Over the last decade our understanding of mercury cycling has dramatically changed. Evidence of rapid atmospheric oxidation has been observed in the Arctic, Antarctic, the MBL, coastal environments, saline lakes, and the upper troposphere/lower stratosphere. These results show that, Hg0, can undergo rapid gas-phase oxidation under standard atmospheric conditions. However, the mechanism and importance of this transformation is still unclear. The goal of this work was two-fold: to investigate of the kinetics of potential pathway for the gas phase oxidation of atmospheric mercury and to develop new laser based techniques, which can be employed for both laboratory and field studies of Hg(0) and the products of mercury oxidation. First and foremost, this work determined kinetic rate coefficients for the potentially important mercury reactions. Rate coefficients were determined using a Pulse Laser Photolysis - Laser Induced Fluorescence (PLP-LIF) technique monitoring one or more of the following species, Hg(0), Cl, Br, HgCl, and HgBr. The concentrations of these species were measured by LIF as the reaction occurred and a concentration vs. time profile was generated. From these profiles a rate coefficient for the reaction can be obtained. In the course of this work kinetic rate coefficients for the following mercury reactions were measured. Hg(0) + Cl + M --> HgCl + M Hg(0) + Br + M --> HgBr + M HgBr + M --> Hg(0) + Br + M HgBr + Br --> products HgCl + O2 --> products This work is the first direct measurement of a kinetic rate coefficient for these reactions, and the first work which employed one photon LIF to monitor the HgCl and HgBr products. The second aspect of this work was the development of new laser based techniques to detect atmospheric mercury and its oxidation products for both laboratory and field application. In this work a LIF technique was develop to detect HgCl and HgBr. In addition, a two photon LIF technique initially developed by Bauer et al., 2002 was verified and expanded. The two photon LIF technique was used to directly monitor Hg(0) atoms in-situ, to monitor Hg(0) evolving form a gold tube, and to monitor the Hg(0) evolving from the thermal decomposition of reactive gaseous mercury collected on a KCl coated or uncoated denuder. This work represents a significant advance in the development of a viable method the detect mercury and the mercury oxidation products in the laboratory and in the field and is the first study to observe clear differences in the characteristic desorption profiles of HgO and HgX2. This work has broad implications, it enhanced our current knowledge concerning the biogeochemical cycling of mercury, broadened our understanding of the mercury chemistry in high halogen environment, and provided new techniques which can be applied in future field and laboratory studies. Gaseous Elemental Mercury Gas Phase Kinetics Halogens Laser Induced Flourescence (LIF) Atmospheric Oxidation Bromine

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