Chemistry & Biochemistry Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2752
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Item AN IMPROVED PSEUDO-DETERMINISTIC RECEPTOR MODEL (iPDRM) TO APPORTION AMBIENT PM CONSTITUENTS TO SOURCES IN TAMPA, FL(2009) Beachley, Gregory Marcus; Ondov, John M; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In 2005, Park et al., developed a new Pseudo-Deterministic Receptor Model (PDRM) to apportion SO2 and ambient particulate matter (PM) constituents to local sources near Tampa Bay. Ambient pollutant measurements were fit to products of emission rates and dispersion factors constrained with a Gaussian plume model for individual sources. In our study, the original samples were reanalyzed by ICPMS for 10 additional elements to improve the resolving power. Chemical mass balance (CMB) terms were added to PDRM to allow fitting of background aerosol sources. More accurate, curvilinear plume trajectories were computed to predict arrival times in both surface and aloft layers. This allowed application of the PDRM complicated meteorological conditions, e.g. wind shifts. Predicted emission rates for particle-bound elements were constrained using chemical compositional information obtained from published source profiles for generic source types. Constraints applied to source emissions of known tracer species allowed the "conditioning" of predicted dispersion factors for those sources to tracer species concentration profiles to better determine the dispersion factor temporal profiles. This enabled the model to apportion pollutants to individual sources with intermittent emissions the omission of which in Park et al. lead to significant residuals. Excellent fits were obtained for all modeled pollutants: 14 of 22 species have Normalized Mean Square Error (NMSE) values of < 2.5% and 21 of 22 have values < 8%. These were improved for SO2 and 8 of 10 elements (by 7-35% for Al, Cu, Ni, Pb, and Zn) modeled by Park et al. Our predicted emission rates are in much better agreement with chemical compositions for generic source types. Key results include: (1) predicted SO2 contributions to ambient levels from a small, lead battery recycling plant that were reduced from 50-59% at its peak influence to a more reasonable 2-4%, (2) Pb/Zn ratios from that plant increased from 1.0 to 734 and better agree with published ratios of 67-440, (3) predicted Ni emission rates for one of the oil-fired power plants (OFPP) was increased by 100-fold (larger than Park's), and now better agrees with its published National Emissions Inventory (NEI) emission rate and with X/Ni ratios for generic OFPP emissions derived from EPA's SPECIATE database, and (4) our predicted emission rates for hazardous air pollutants and toxics from power plants agree with ~75% of those reported annual emission rates from NEI and Toxic Release Inventories (TRI) to within a factor of 5. This suggests that these reported data provide a good qualitative estimate of emissions, but should not be treated as accurate in a predictive model to quantify source emissions. It was also observed that the TRI values for As emission rates from coal-fired power plants are more accurate that their NEI values.Item Investigation of Rhenium's Biogeochemistry(2009) Dolor, Marvourneen; Helz, George R; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The form of the paleoredox indicator, rhenium, that is sequestered in reducing sediments is not known. To probe this question, I used Laser Ablation ICP-MS to look for correlations between Re signals and those of other elements. My results point to the possibility that Re is incorporated into multiple host phases: sulfides and organic material. Laser Ablation ICP-MS also provided a new way to analyze a large suite of elements in Chesapeake Bay sediments simultaneously. A number of rarely determined elements (Ag, Sn, Sb, Te and Bi) were discovered to exhibit profiles similar to known industrial pollutants such as Cu, Zn, Cd and Pb. This is one of the first demonstrations of LA-ICP-MS as a tool to perform a survey of anthropogenic impacts on modern sediments and suggests that the suite of elements monitored by environmental agencies should be broadened. Rhenium is scavenged between iron and sulfate reduction, in the sequence of microbial terminal electron accepting processes, so I investigated whether Re could be reduced directly or indirectly by iron and/or sulfate reducing bacteria. This hypothesis was also based on the fact that Tc (also Group VIIB), is directly and indirectly reduced by the iron and sulfate reducers used in my experiments: Geobacter metallireducens GS-15, Shewanella oneidensis €MR-1, Desulfovibrio desulfuricans subsp. desulfuricans and Desulfovibrio desulfuricans ND132. I concluded that neither direct nor short-term indirect microbial processes are likely to explain Re fixation in sediments. In order to test the hypothesis that thioperrhenates play a role in Re fixation, experimentally determined stability constants, (K (4-x)(5-x) ) for the following types of reactions are needed. ReO x S 4-x 2+ H2S = ReOx-1S5-x- + H2O where 1 ≤ x ≤ 4 These compounds are analogous to thiomolybdates, which are the particle reactive form of Mo fixed under reducing conditions. The di- and tri- thioperrhenates were never observed, by UV-Vis spectrophotometry. The stability constant for mono-thioperrhenate, K01 = 104, while the stability constant for tetra-thioperrhenate, K04 = 1019. Below pH 8, the formation of a rhenium-sulfur nano-phase competed with the formation of thioperrhenates. The formation of this nano-phase is most likely an important step in rhenium fixation. Future work should involve exploring the sorption characteristics of this material.Item The Mechanism of Rhenium Fixation in Reducing Sediments(2005-05-02) Dolor, Marvourneen Kimranee; Helz, George R; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)There is a wide range of uses of information related to rhenium's geochemical behavior. Field studies indicate that rhenium is highly enriched in reducing sediments. However the mechanisms by which this high degree of enrichment is achieved are unclear. Perrhenate's (ReO4-) sorption onto a clay mineral, kaolinite, was investigated and found to be weak. This behavior is consistent with rhenium's conservative behavior in the oceans. Sorption was enhanced by the presence of a reducing agent, lithium borohydride. The presence of sulfide, a reducing agent found in nature, enhanced sorption slightly. Sulfide apparently does not reduce ReO4- rapidly as shown by the failure of polysulfide species to appear in solution. Instead, sulfide causes the formation of thioperrhenates. The mechanism of thiolation is the successive replacement of oxygen atoms in ReO4- by sulfur atoms, but ReO3S- and ReS4- are the only thioperrhenates observed by UV-Vis spectroscopy. The di- and tri- thioperrhenates, ReO2S2- and ReOS3- are absent due to their relative instability. Thiolation of ReO4- appears to be general-acid catalyzed. Quantitative yield of ReS4- from ReO4- was never achieved. Thioperrhenates undergo polymerization in solution to yield a colloidal Re-S species, probably related to Re2S7, which contains polysulfide ions in its structure. This Re-S polymer is stable under different experimental conditions and thermodynamic calculations confirm that it is a very stable, insoluble species. Sulfide may play an important role in Re enrichment in sediments by leading to the formation of this solid Re-S species.