Biology Theses and Dissertations

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    CHARACTERIZATION OF CARBONACEOUS AEROSOL: IMPROVED METHODS, SOURCES AND SIZE DISTRIBUTIONS
    (2006-11-30) Crimmins, Bernard Shawn; Baker, Joel E; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    A highly sensitive method was developed for measuring polycyclic aromatic hydrocarbons and nitro-substituted polycyclic aromatic hydrocarbons in ambient aerosol. Using large volume injection, this technique provided an order of magnitude increase in sensitivity compare to conventional injection techniques. This method facilitated the measurement of the first reported diurnal size distribution of NPAHs. Size resolved samples were collected using a Berner low-pressure impactor deployed at the Baltimore PM2.5 Supersite in April 2002. Both classes of compounds were found predominantly on particles less than 0.49μm with similar size distributions among samples for most of the 12 hr periods. A linear relationship between compound geometric mass median aerodynamic diameter (GMMAD) and log sub-cooled vapor pressures (pl°) was observed for PAHs and NPAHs, respectively, during each sampling period. The inter-relationhips between the slopes and y-intercepts from the GMMAD/log vapor pressure correlations suggest the source of PAHs to the Baltimore atmosphere reside on particles with GMMADs equal to 0.18 μm, consistent with vehicle emissions. Bulk organic aerosol was collected in Baltimore, MD during the spring, summer and winter of 2002-2003. Concentrations of n-alkanes, hopanes, polycyclic aromatic hydrocarbons (PAH), and nitro-substituted polycyclic aromatic hydrocarbons (NPAH) were measured in the gas and particle phase. The organic compounds varied little, with seasonal concentrations typical of North American urban atmospheres. Principal Components Analysis/Multiple Linear Regression (PCA/MLR) and Positive Matrix Factorization (PMF) were used to determine the sources of individual compound classes (PAHs, NPAHs, hopanes and alkanes) and total particulate carbon and PM2.5 to the Baltimore atmosphere for during 2002-2003. PMF was used to determine the total carbon and PM2.5 source estimates to the Baltimore atmosphere. The sources identified included tire wear/road dust, gasoline and diesel exhaust, oil combustion, biogenic, secondary organic aerosol, incineration, and coal explaining 64% of the variability in the total carbon and PM2.5 concentrations.
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    THE ROLE OF ORGANIC MATTER IN THE DISSOLVED PHASE SPECIATION AND SOLID PHASE PARTITIONING OF MERCURY
    (2006-01-24) Miller, Carrie Lynn; Mason, Robert; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The interaction of mercury (Hg) and methylmercury (MeHg) with organic matter is extremely important in the dissolved phase speciation and solid phase partitioning of Hg and MeHg in aquatic systems. This study shows, that under oxic conditions Hg and MeHg will likely associated with Fe oxides through an indirect association with organic matter, while under sulfidic conditions, solid phase Fe sulfide will dominate the complexation of Hg to the solid phase. As a result of the association of Hg with Fe solids, which undergo dynamic changes at redox interfaces in aquatic systems, the distribution of Hg on particles is likely changing at redox boundries, areas that have been shown as active zones of methylation. Redox zones are also going to be important in controlling the mobility of MeHg from the site of production to areas in aquatic systems in which uptake by biota occurs. Although the dissolved phase speciation of Hg has been shown as an important factor in Hg methylation, as a result of the diffusive uptake of neutral Hg-sulfide into bacterial cells, this speciation had previously not been measured. Hg forms stronger bonds with reduced sulfide relative to dissolved organic matter (DOM), therefore, it was not previously thought that DOM was important in the speciation of Hg under sulfidic conditions. Using modified octanol-water partitioning extractions and centrifugal ultrafiltration, the speciation of Hg in sulfidic natural samples and laboratory solutions was examined. It was shown that the concentration of neutral Hg-sulfide complexes are lower than predicted by thermodynamic models, as a result of an interaction of these species with DOM. It is proposed that the interaction of Hg with DOM is not a complexation, but rather, a partitioning of neutral Hg-sulfide complexes into hydrophobic portion of the DOM. Thermodynamic constants were calculated for this interaction and applied to model the speciation of Hg in natural samples. The concentration of neutral Hg-sulfide is lower than models previously predicted, as a result of the DOM interaction. Since the concentration of neutral Hg-sulfide affects methylation, DOM could impact the rate of Hg methylation in aquatic systems.