This dissertation investigates the impact of bromine on tropospheric ozone, OH, and mercury in the preindustrial and present-day atmosphere through use of modeling and observations from satellite. We developed bromine simulation capabilities coupled to oxidant-aerosol chemistry in the GEOS-Chem chemical transport model (CTM). Standard gas-phase mechanisms for bromine chemistry were unable to reproduce recent estimates of tropospheric BrO from satellite. Agreement was improved significantly after imposing HBr+HOBr heterogeneous chemistry in the model. Under present-day conditions, we find that bromine decreases ozone by 6.5%, < 1 – 8 ppb, and global mean OH by 4%. Most ozone loss is due to HOBr production and photolysis, with additional contributions from \(NO_x\) and ozone loss through \(BrNO_3\) hydrolysis. Simulations of the pre-industrial atmosphere are important as baselines for ozone air quality and radiative forcing calculations. However, standard models for the pre-industrial overestimate ozone observations taken a century ago at Montsouris and cannot reproduce the observed aseasonality. We find that bromine chemistry significantly improves this agreement. However, bromine chemistry has negligible impact on the ozone radiative forcing, as concentrations of BrO remain similar. Despite the small change in BrO concentrations, lower ozone in the preindustrial leads to a 40% greater Br mixing ratios. We estimate that this change may have increased the lifetime of atmospheric Hg(0) against oxidation to Hg(II) by 70% since the pre-industrial, making atmospheric mercury a more global pollutant. Additionally, we develop a retrieval algorithm for stratospheric profiles of BrO number density from SCIAMACHY limb near-UV observations. Zonal means of our BrO profile retrievals throughout April 2008 show common features expected from stratospheric photochemistry and dynamics. We apply simulated \([BrO]/[Br_y]\) ratios to the BrO profile retrievals and estimate a stratospheric loading of \(23.5 \pm 6 ppt Br_y\). This supports the 23 ppt stratospheric \(Br_y\) assumed in the satellite-derived climatology of tropospheric BrO that we used to evaluate our GEOS-Chem simulation. Our results imply \(7 \pm 6 ppt\) Br from short-lived bromocarbons, at the higher end of the 3 – 8 ppt range suggested by observations. / Engineering and Applied Sciences

In this dissertation I present theory and experimental results obtained in the Jones research group at the University of Arizona investigating the feasibility of neutral Hg as a candidate for an atomic clock. This investigation includes laser-cooling and trapping of several neutral Hg isotopes as well as spectroscopy of the 6¹S₀ - 6³P₀ doubly forbidden clock transition in neutral Hg¹⁹⁹. We demonstrate precision spectroscopy of the ground state cooling/trapping transition of neutral mercury at 254 nm using an optically pumped semiconductor laser (OPSL). This demonstration exhibits the utility of optically pumped semiconductor lasers (OPSLs) in the field of precision atomic spectroscopy. The OPSL lases at 1015 nm and is frequency quadrupled to provide the trapping light for the ground state cooling transition. We get up to 1.5 W single-frequency output power having a linewidth of < 10 kHz in the IR with active feedback. We frequency quadruple the OPSL in two external cavity stages to produce up to 120 mW of deep-UV light at 253.7 nm. I give a detailed characterization of the construction and implementation of the neutral Hg vapor cell magneto-optical trap (MOT). The trap can be loaded in as quickly as 75 ms at background vapor pressures below 10⁻⁸ torr. At reduced background pressure (< 10⁻¹⁰ torr) the loading time approaches 2 sec. We describe construction and stabilization of a laser resonant with the Hg¹⁹⁹ clock transition and the methods employed to find and perform the experimentally delicate spectroscopy of the clock transition. We present experimental results and analysis for our initial spectroscopy of the 6¹S₀- 6³P₀ clock transition in the Hg¹⁹⁹ isotope of neutral mercury.

The goal of this research is to obtain the adsorption mechanisms of toxic mercury-containing species (Hg, HgCl and HgCl2) and carbon dioxide (CO2) on inorganic solid surfaces using theoretically predicted results because experiments have been unable to unravel the involved issues. The understanding of the adsorption mechanisms of the mercury species and carbon dioxide from flue gases is important when considering mercury capture from coal-fired power plants, artisanal gold mining, and cement manufacturing industries. The current research attempts to explain each adsorption mechanism for mercury species, and those for carbon dioxide adsorption, on the surfaces through optimized geometries, energies and thermodynamic data.To investigate this research, density functional theory, which is one of useful tools for analyzing reactions on solid surfaces, was used to determine first principles-based theoretical adsorption models. Mainly, results from computational work indicate that mercury-containing species and carbon dioxide adsorption on calcium oxide surfaces and elemental mercury adsorption on a gehlenite surface are exothermic reactions. Calcium oxide is a promising adsorbent for oxidized mercury (HgCl and HgCl2), but not for elemental Hg. Interestingly, the elemental mercury, which is the major form (> 90%) in the flue gases of the coal-combustion power plants, is chemisorbed on a gehlenite surface, which is partially composed of calcium oxide and comes from a mineral transition at high temperature. Strong adsorption on this inorganic sorbent is enhanced at high temperatures even though this adsorption process is exothermic. In addition, CaO surfaces are effective at capturing CO2, generating calcium carbonate compounds at flue gas temperatures, and water vapor enhances its adsorbability due to a larger CO2 adsorption energy. The current research shows that inorganic sorbents are not only effective in removing the elemental and oxidized forms of mercury but also in mineralizing CO2 at high temperatures into a solid form. The mercury species and carbon dioxide adsorption mechanisms investigated in this research may be utilized in the application of more efficient mercury and carbon dioxide control technologies. Future work will examine the reaction transition state and predict the kinetic data of the carbonation reactions, and, additionally, may prove the hypothesis that H2O molecules play a role as catalysts, increasing reaction rates.

This thesis examines historical and contemporary artisanal and small-scale gold mining (ASGM) in Kadoma-Chakari, Zimbabwe in order to identify effective strategies to reduce mercury loss and exposure and to increase miners’ incomes by improving gold recoveries. Cyanidation of mercury-rich tailings and the use of nitric acid to leach mercury from cathode sludge and amalgams are identified as significant pathways for losses of mercury into the environment in Zimbabwe. Indirect evidence suggests that as much as 90% of the mercury contained in amalgamation tailings at mills in Kadoma-Chakari is dissolved during passive vat cyanidation. Mercury traps placed after copper amalgamation plates and centrifuges could reduce the amount of mercury subjected to cyanidation, but mercury can be kept out of cyanidation circuits altogether by replacing whole ore amalgamation with vinyl loop carpets. The optimal cyanide concentration for passive vat leaching is between 0.1 to 0.15%. Better management of nitric acid waste solutions can also significantly reduce mercury losses. The current political and socio-economic crisis significantly limits the effectiveness of ASGM programs in Zimbabwe. Nevertheless, strategies for more effective management of ASGM interventions are suggested by a review of the history of didactic theatre (Theatre for Development) in Africa. Theatre used as an awareness building tool is exemplified by “Nakai”, a drama produced in Kadoma-Chakari to increase knowledge of the hazards of mercury use. Theatre can also be a means to ensure horizontal communication between donors and project beneficiaries if it is used to stimulate discussions that give communities a real voice in development programs. It is proposed that community participation in project design, implementation and evaluation increases the likelihood of project success and sustainability because community-identified problems and solutions are more realistic than those defined by donors, and because community “buy in” and ownership increases pressure on project administrators to deliver the services communities need.

A sustainable global program to reduce mercury use in artisanal and small-scale gold mining (ASGM) will require the demonstration of credible, continuous progress to secure political support and financing, and ultimately achieve success. Focused progress measurement has been lacking to date for ASGM at the global level. This research analyses information on appropriate options to measure mercury reduction progress in ASGM. Research methods included a case study of Mongolia, supplemented with information analyzed from semi-structured interviews related to ASGM and other applicable evaluation approaches. The study concludes by proposing the development of a framework approach for measuring progress and by offering guiding principles and recommendations. Recommendations for the framework approach include: on-going and enhanced support to an information database; simplified evaluation metrics for the ASGM Partnership; tracking the level of political commitment of national governments as an indicator of progress; and promoting common reporting metrics across global programming.

Mercury (Hg) research in Ontario has centered on aquatic environments since fish can be a significant source of methylmercury for humans. Interactions between terrestrial and aquatic environments in regards to the Hg cycle have received less attention. This study focuses on the role of trees as a source and/or sink of Hg to the environment and the ap- plicability of deciduous trees as biomonitors for Hg. Leaf, bark and wood core samples were taken from a variety of deciduous species including Acer spp. (sugar, silver and red maple), Quercus spp. (red oak), Populus spp. (eastern cottonwood), and Salix spp. (willow) mainly from the Dorset and Kingston, ON regions. Examination of seasonal variation of Hg concentrations ([Hg]) in leaves indicated that average autumn leaf Hg ranged from 17– 45 ng/g and differed significantly among species. Leaf [Hg] increased with the growing season and roughly corresponded to regional atmospheric [Hg]. Microspatial trends in leaf [Hg], such as position on a branch, may increase variability. Tree cores from contami- nated and reference sites in the Kingston area showed that although dendrochronological techniques are not appropriate for estimating historical atmospheric Hg, they are useful for estimating the total Hg burden of a single tree. Populus and Salix, had the greatest bark and wood [Hg] with maximums reaching 18 ng/g. This was significantly higher than more inland trees such as Quercus and Acer, with maximum values of 7 and 1.2 ng/g for bark and wood [Hg]. Individual, average sized trees in this study contained a total of 0.4–2.6 mg of Hg. This study will provide forest and watershed managers with a better understanding of the importance of trees in the Hg cycle and the contribution of leaf and wood Hg to litterfall and waterbodies in southern Ontario. / Thesis (Master, Biology) -- Queen's University, 2007-12-18 23:48:21.97

The Rideau River Waterway, also known as the Rideau Canal, is a constructed navigation channel that links Ottawa to Kingston, Ontario. Opened in 1832, it was designated a Canadian Heritage Site in 2003 and a UNESCO World Heritage Site in 2007. South of Smiths Falls, the Rideau Canal consists of a series of 14 interconnected lakes, primarily used for recreational purposes, as well as commercial fishing. The objectives of this study were to examine the spatial and temporal distributions of anthropogenic elements to three headwater lakes of the Rideau Canal system and to examine the relationship between sport fish Hg and historical sediment Hg concentrations. Utilizing paleolimnological techniques, historical records of As, Cd, Co, Cr, Cu, Hg, K, Ni, Pb, Rb, and Zns were analyzed from chronologically deposited lake sediments. Overall, Indian Lake, though the smallest of the three studied lakes, consistently had the highest overall As, Cd, Cu, Hg, Ni, Pb and Zn concentrations. While all peak concentrations were buried, recent surface sediment Hg, Cd, and Zn concentrations still remain above the federal interim sediment quality guideline and the concentration of Pb remains above the federal probable effect level within Indian Lake, leading to continued concern for human and ecosystem health. The general agreement between lake sediment profiles for Cd, Pb and Zn and then Cu and Ni suggest that each group of elements is primarily contributed from the same source. The similarity in trends and timing of peak concentrations between the study lakes and other Ontario lakes suggests large-scale, atmospheric contributions of elements to the freshwater systems in the area. Although only historical northern pike (Esox lucius) THg tissue concentration data was available for analysis, results indicate that concentrations in fish have decreased more than 60% since the late 1970’s, while sediment THg concentrations have decreased 35% within the same time period. Overall, this study has demonstrated that the headwater lakes to the Rideau Canal are presently impacted by elements, at concentrations which are of potential concern for human health. / Thesis (Master, Biology) -- Queen's University, 2009-09-26 00:02:42.317

Mercury contamination is a global issue due to its neurotoxicity, and China is not an exception due to its increasing industrialization. Fish is of the most concern, in respect to human exposure to mercury, because fish accumulates methylmercury through food chain in aquatic systems. The province of Zhejiang is renowned for its cuisine that incorporates freshwater fish. Qiandao Lake, in Zheijang, was the site of a case study examining the link between the total mercury (THg) concentration in hair samples and fish consumption. A questionnaire survey and hair sampling were carried out on women of childbearing age (17-46 years) from a fishing town by Qiandao Lake. The average hair THg concentration was 0.76±0.51μg/g dw. The most-frequently consumed species included four species of carp (golden, bighead, silver and predatory) and the Mongolian redfin. Hair THg concentrations accumulated rapidly during younger years, reaching a plateau around age 25, implying that the hair mercury concentrations in adult females >25 years can be interpreted by environmental exposure. Hair THg concentrations were positively correlated both with the frequency and the average weekly amount of fish consumption. This indicates that fish consumption is an important contributor to hair mercury concentrations in the absence of occupational or environmental mercury sources. A positive correlation between selenium and mercury in hair samples was also observed, suggesting a possible antagonistic relationship. This is the first study to look at mercury exposure in an eastern China community dependent on freshwater fish. This study also compared element trends (Mg, Ca, Cr, Mn, Cu, Zn, As, Se, Pb) in hair samples from three groups: 50 residents by Qiandao Lake (QD), 17 people from Fudan University, China (FU), and 20 people from Queen’s University, Canada (KI). Trends of mean Mg, Cu, Ca, As concentrations among groups are the same (KI>FU>QD). Mn, Cr, and Hg share the same trends of QD>FU>KI. Se concentrations follow the trend of QD>KI>FU. Strong correlations between Ca and Mg were observed within each group. Relationships between Se and Hg are clear in QD but not in FU and KI, probably due to the different dietary proportion of fish. / Thesis (Master, Environmental Studies) -- Queen's University, 2009-12-14 11:52:06.906

Since the mid-1970s, the Ontario (Canada) Ministry of Environment (OMOE) has been collecting data on fish tissue mercury (Hg) contamination in provincial waterbodies. By 2004, approximately 160,000 fish from 86 species at over 1,600 sites were tested for Hg. This large database is primarily used to issue advisories for safe human fish consumption via publication of the biennial Guide to Eating Ontario Sport Fish. Analysis to uncover spatio-temporal trends while maximising the use of data points is complicated by the application of a non-random heterogeneous sampling design. The National Descriptive Model for Mercury in Fish (NDMMF) developed by the United States Geological Survey (USGS) is a statistical model of Hg concentrations that can potentially mitigate these challenges by separating the spatiotemporal variability of fish-[Hg] sampling while considering the effects of species, size, and fish sample portion type. However, the NDMMF has not been fully exploited, likely due to lack of rigorous evaluation. We conduct the first detailed investigation on the ability of the NDMMF to reproduce the observed fish-[Hg] in coolwater walleye (Sander vitreous) and warm-water yellow perch (Perca flavescens). Approximately two-thirds of both walleye and yellow perch [Hg]-length relationships could be accurately predicted using the NDMMF. For these cases, a majority (>85%) of the estimates are within the same consumption advisory categories as the interpolated [Hg] value based on the observed data, using an average-length fish. For the remaining incidences with significantly different NDMMF fish [Hg]-length relationships compared to those from the observed data, the NDMMF notably yields similar results, with a majority (>75%) of [Hg] estimates still falling within the same consumption advisory categories. For the small fraction of incidences with inaccurate advisory categorization, the instances of conservative over-prediction (<18%) would be of little human health concern as these would recommend fewer meals than otherwise suggested using observed data. For the few instances when [Hg] is under-predicted (<11%), the nature of the human health concern would be relatively minor because the advisory classification is almost never (<1%) more than one category less restrictive. / Thesis (Master, Biology) -- Queen's University, 2012-08-29 15:31:54.349

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