No description available.

This work investigates the influence of one or more OH groups present on the fuel molecule and the resultant formation of NOX emissions. Combustion of oxygenated fuels has been increasing globally and such fuels offer significant potential in the reduction of pollutant emissions. One such emission class is the oxides of nitrogen, which typically form through a combination of two regimes: the thermal and non-thermal mechanisms. While thermal NO formation can be reduced by lowering the combustion temperature, non-thermal NO formation is coupled to the fuel chemistry. An experimental and computational investigation of NOX formation in three different burner configurations and under a range of equivalence ratios and temperature regimes explored the differences in NO formation. Measurements of temperature profiles and in-flame species concentrations, utilizing both probed and non-intrusive laser based techniques, allowed for the investigation of NO formation through non-thermal pathways and the differences that exist between fuels with varying numbers of OH groups. The first burner configuration was composed of a high swirl liquid spray burner with insulted combustion chamber walls designed specifically for the combustion of low energy density fuels. In this system the combustion of alcohols and glycerol (the largest by-product of biodiesel production), along with other fuels with multiple hydroxyl groups, was studied. Measurements of the mean flame temperature and exhaust gas measurements of NOX showed significant reductions in non-thermal NO concentrations with increasing numbers of OH groups. An accompanying modeling study and detailed reaction path analysis showed that fuel decomposition pathways through formaldehyde were shown a preference due to the presence of the OH groups which resulted in reduced contributions to the hydrocarbon radical pools subsequent reductions to the Prompt NO mechanism. Two burner configurations with reduced dimensionality facilitated measurements in premixed flames for temperature and species in high and low temperature flames. These measurements included probed thermocouple temperature measurements, extractive gas sampling for NO and intermediate hydrocarbon species, and planar Laser Induced Fluorescence (LIF) measurements for 2OH-LIF thermometry, semiquantitative CH2O LIF, and quantitative NO LIF. Additionally, the simplified nature of the burner geometries allowed for the modeling of the flames incorporating detailed reaction kinetics for fuel decomposition and NOX formation. Significant reductions in NO formation were observed in comparisons of alcohol and alkane flames, resulting in up to 50% reductions in the pollutant. Computational analyses and nitrogen flux accounting allowed for the identification of the reduction in NO formation through all the known NOX formation pathways. It was observed that all of the known pathways exhibited reductions in contributions to NO formation in the presence of OH functional groups, indicating a complex coupling of fuel and NOX chemistry.

Laser Induced Fluorescence (LIF) is one of the chief methods for detecting ambient hydroxyl radicals. To measure the absolute concentration of this important atmospheric chemical species, accurately known quenching rate constants due to the dominant gases in the air are of paramount importance. Unfortunately, these rate constants have only been measured under conditions remote from those of ambient air. This dissertation reports the measurement of the rate constants of water, argon, nitrogen and oxygen under ambient conditions. As the LIF is carried out at atmospheric pressure, the OH fluorescence life-time becomes extremely short (about 1 ns). Time Correlated Photon Counting was used to study this short fluorescence phenomenon. The unique feature this study was that the deactivation processes of the excited OH could be described completely by a kinetic model. Detailed theoretical treatments of the LIF processes are presented. The data obtained are consistent with the accepted model, thereby demonstrating the usefulness and validity of the experimental approach. The rate constants (cc molecule('-1) sec('-1)) for quenching by water and argon were accurately measured. The vibrational relaxation rate constant by water (3.4 (+OR-) 0.6 x 10('-10)) is the first value ever reported, while the electronic quenching rate constants for water (k(,Q0) = 7.9 (+OR-) 0.47 x 10('-10), k(,Q1) = 1.48 (+OR-) 0.74 x 10('-10)) are the first measured at atmospheric pressure. The electronic quenching rate constants of the ('2)(SIGMA)(v' = 1) state (k(,Q1)) and the ('2)(SIGMA)(v' = 0) state (k(,Q0)) by argon are k(,Q0) = 0.48 (+OR-) 0.14 x 10('-12) and k(,Q1) = 0.24 (+OR-) 0.06 x 10('-11). The vibrational relaxation rate constant by argon is k(,10) = 0.34 (+OR-) 0.06 x 10('-11). The rate constants for oxygen (k(,Q1) (+OR-) k(,10) = 1.83 (+OR-) 0.43 x 10('-9) and k(,Q0) = 2.6 (+OR-) 0.6 x 10('-10)) are significantly higher than the limited measurements available at low pressure. The rate constants for nitrogen are k(,Q0) = 0.71 (+OR-) 0.08 x 10('-11) and k(,10) = 8.07 (+OR-) 0.65 x 10('-11). All these values are the first obtained at atmospheric pressure and although shown to be consistent with the widely scattered low pressure values, they allow more reliable analysis of ambient OH measurements, and result in a 31.2% increase in the published values.

No description available.

In medical and health physics, we are interested in the effects of ionizing radiation on biological systems, in particular, human biology. The main process by which ionizing radiations causes damage to biological systems, is through the creation of radicals close to DNA strands. The radicals are very reactive and those created within close proximity to DNA will react with the DNA causing damage, in particular single strand or double strand breaks. This damage to the DNA can cause mutations that can kill the cell, either mitotically or apoptotically, or possibly lead to a cancerous formation. Therefore it is important to study how these radicals interact with DNA strands for a correlation between the resultant products of radical reactions and DNA strand breaks. For this study, we look at the most important radical, the OH radical and it's addition to DNA bases. We will study, through quantum chemistry, the thermodynamics of OH radical addition to the four bases, Adenine, Guanine, Cytosine and Thymine. The Jaguar program developed by Schrodinger was used for DFT calculations of the Gibbs free energy of the addition. In addition, calculations for the partial charge, HOMO's and Fukui indices were calculated and compared to experiment.

Thesis (Ph. D.)--University of Washington, 2002. / Vita. Includes bibliographical references (leaves 105-119).

No description available.

No description available.

Biomass burning aerosols play an important role in the chemistry and physics of the atmosphere and therefore, affect global climate. Biomass burning aerosols are generally aqueous and have a strong saccharidic component due to the combustion and pyrolysis of cellulose, a major component of foliar fuel. This class of aerosol is known to affect both the absorption and scatter of solar radiation. Also, biomass burning aerosols contribute to cloud formation through their action as cloud-condensation nuclei. Many questions exist about the chemical speciation and chemical aging of biomass burning aerosols and how this affects their atmospheric properties and ultimately, global climate. Also, knowledge of the chemical components of these aerosols is important in the search for chemical tracers that can give information about the point or regional source, fuel type, and age of a biomass burning aerosol parcel. Levoglucosan was chosen for these studies as a model compound for biomass burning aerosols because of its high measured concentrations in aerosol samples. Levoglucosan often dominates the aerosol composition by mass. In this dissertation, laboratory proxy systems were developed to study the solution-phase chemistry of levoglucosan with common atmospheric reactants found in biomass burning aerosols (i.e. H+, •OH). To mimic these natural conditions, acid chemistry was studied using sulfuric acid in water (pH=4.5). The hydroxyl radical (•OH) was produced by the Fenton reaction which consists of iron, hydrogen peroxide and acid (H2SO4) in aqueous solvent. For studies in aqueous sulfuric acid, oligomers of levoglucosan were measured by matrix-assisted laser desorption and ionization time-of-flight mass spectrometry (MALDI-TOF-MS). A rational mechanism is proposed based on both the acid-catalyzed cationic ring-opening of levoglucosan and nucleophilic attack of ROH from levoglucosan on the hemi-acetal carbon to produce pyranose oligomers through the formation of glycosidic bonds. Oligomer formation is further supported by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). Reactions of levoglucosan with •OH produced from Fenton chemistry were studied in solution. Two modes of oligomerization (2000 u) were observed for reaction times between 1 and 7 days using MALDI-TOF-MS and laser desorption ionization (LDI) TOF-MS. Single-mass unit continuum mass distributions with dominant -2 u patterns were measured and superimposed by a +176/+162 u oligomer series. This latter oligomer pattern was attributed to a Criegee rearrangement (+14 u) of levoglucosan, initiated by •OH, forming a lactone (176 u). The acid-catalyzed reaction of any ROH from levoglucosan (+162 u) forms an ester through transesterification of the lactone functionality, whereupon propagation forms polyesters. Proposed products and chemical mechanisms are suggested as sources and precursors of humic-like substances (HULIS), which are known to possess a large saccharic component and are possibly formed from biomass burning aerosols. These products could also serve as secondary tracers, giving further information on the source and age of the aerosol.

No description available.