This study describes two projects involving recent research on atmospheric ammonia. The first project investigates differences in modelling techniques of aerosol acidity using data from two recent field campaigns. Our results show that allowing or disallowing gas-particle partitioning in the Extended Aerosol Inorganic Model (E-AIM) changed the average modelled aerosol activity of H+ from one campaign by seven orders of magnitude and that disallowing gas-particle partitioning may not accurately represent the chemical state of the aerosols. The second project investigates the interference of reduced nitrogen in commercial chemiluminescent nitrogen oxide monitors with molybdenum oxide catalytic converters. This phenomenon is strongly dependent on the temperature of the catalytic converter. Our results show these instruments can have high conversion efficiencies of gaseous NH3 and NH4+ salts to NO at typical reported converter temperatures, but conversion efficiency varies between instruments and may be the result of uncertainty in reported converter temperature.

No description available.

No abstract available. / Thesis (Ph.D.)-University of Natal, Durban, 1985.

This study describes two projects involving recent research on atmospheric ammonia. The first project investigates differences in modelling techniques of aerosol acidity using data from two recent field campaigns. Our results show that allowing or disallowing gas-particle partitioning in the Extended Aerosol Inorganic Model (E-AIM) changed the average modelled aerosol activity of H+ from one campaign by seven orders of magnitude and that disallowing gas-particle partitioning may not accurately represent the chemical state of the aerosols. The second project investigates the interference of reduced nitrogen in commercial chemiluminescent nitrogen oxide monitors with molybdenum oxide catalytic converters. This phenomenon is strongly dependent on the temperature of the catalytic converter. Our results show these instruments can have high conversion efficiencies of gaseous NH3 and NH4+ salts to NO at typical reported converter temperatures, but conversion efficiency varies between instruments and may be the result of uncertainty in reported converter temperature.

To exemplify how theoretical chemistry can be applied to understand ground and excited state reactivity, four different chemical reactions have been modeled. The ground state chemical reactions are the simplest models in chemistry. To begin, a route to break down halomethanes through reactions with ground state cyano radical has been selected. Efficient explorations of the potential energy surfaces for these reactions have been carried out using the artificial force induced reaction algorithm. The large number of feasible pathways for reactions of this type, up to eleven, shows that these seemingly simple reactions can be quite complex. This exploration is followed by accurate quantum dynamics with reduced dimensionality for the reaction between Cl− and PH2Cl. The dynamics indicate that increasing the dimensionality of the model to at least two dimensions is a crucial step for an accurate calculation of the rate constant. After considering multiple pathways on a single potential energy surface, various feasible pathways on multiple surfaces have been investigated. As a prototype of these reactions, the thermal decomposition of a four-membered ring peroxide compound, called 1,2-dioxetane, which is the simplest model of chemi- and bioluminescence, has been studied. A detailed description of this model at the molecular level can give rise to a unified understanding of more complex chemiluminescence mechanisms. The results provide further details on the mechanisms and allow to rationalize the high ratio of triplet to singlet dissociation products. Finally, a thermal decomposition of another dioxetane-like compound, called Dewar dioxetane, has been investigated. This study allows to understand the effect of conjugated double bonds adjacent to the dioxetane moiety in the chemiluminescence mechanism of dioxetane. Our studies illustrate that no matter how complex a system is, theoretical chemistry can give a level of insight into chemical processes that cannot be obtained from other methods.

This thesis characterizes properties of ambient secondary organic aerosol (SOA), an important and abundant component of particulate matter. The findings presented in this thesis are significant because they represent the results from ambient measurements, which are relatively scarce, and because they report on properties of SOA that, until now, were highly uncertain. The analyses utilized the fraction of particulate organic carbon that was soluble in water (WSOCp) to approximate SOA concentrations in two largely different urban environments, Mexico City and Atlanta. In Mexico City, measurements of atmospheric gases and fine particle chemistry were made at a site ~ 30 km down wind of the city center. Using box model analyses and a comparison to ammonium nitrate aerosol, a species whose thermodynamic properties are generally understood, the morning formation and mid-day evaporation of SOA are investigated. In Atlanta, simultaneous measurements of WSOCp and water-soluble organic carbon in the gas phase (WSOCg) were carried out for an entire summer to investigate the sources and partitioning of WSOC. The results suggest that both WSOCp and WSOCg were secondary and biogenic, except possibly in several strong biomass burning events. The gas/particle partitioning of WSOC in Atlanta was investigated through the parameter, Fp, which represented the fraction of WSOC in the particle phase. Factors that appear to influence WSOC partitioning in Atlanta include ambient relative humidity and the WSOCp mass concentration. There was also a relationship between the NOx concentration and Fp, though this was not likely related to the partitioning process. Temperature did not appear to impact Fp, though this may have been due to positive relationships WSOCp and WSOCg each exhibited with temperature. Neither the total Organic Carbon aerosol mass concentration nor the ozone concentration impacted WSOC partitioning.

Aerosols of nitrate solutions were irradiated in the presence of radical scavengers in an attempt to measure the yield of hydroxyl radical in both the aqueous phase and the gas phase. Carbon monoxide, benzoic acid, benzene and cyclohexane were used as scavengers to trap hydroxyl radical. The products from the reaction of these scavengers with hydroxyl radical were analysed with High Performance Liquid Chromatography and mass spectrometry. The radiant flux in the chamber was measured via ferrioxalate actinometry, both with bulk liquid and aerosol droplets. Many quantitative results were obtained but several anomalies were found. This suggests that Mie theory is not capable of predicting rates of photochemical reactions within droplets.

Thesis (Ph. D.)--University of Washington, 2007. / Vita. Includes bibliographical references (leaves 188-206).

Thesis (Ph. D.)--Earth and Atmospheric Sciences, Georgia Institute of Technology, 2008. / Committee Chair: Greg Huey; Committee Member: David Tan; Committee Member: Jennifer Olson; Committee Member: Paul Wine; Committee Member: Rodney Weber.

Thesis (Ph. D.)--University of Washington, 2004. / Vita. Includes bibliographical references (p. 136-144).