Atmospheric aerosols serve an important role in climate and air quality. However, there are still significant gaps in our scientific understanding of their impacts on climate. One of the greatest factors contributing to uncertainties in our estimations of these impacts can be attributed to the gap in the sources and formation pathways of secondary organic aerosols (SOAs). Carbonyl compounds, in particular, glyoxal and methylglyoxal, are two oxidation products of both anthropogenic and biogenic volatile organic compounds (VOCs) in the atmosphere. Field and modeling studies have indicated that these two compounds can serve as potentially important precursors to SOAs, and alter the physical and chemical properties of the aerosols. The mechanisms and atmospheric significance of these processes pose important questions which need to be addressed. Here, we report experiments targeted to study the following topics: 1) the chemical kinetics of methylglyoxal uptake to aqueous aerosols, and the subsequent formation of SOA material; 2) the oxidative aging of SOA material formed by methylglyoxal; 3) the impact of methylglyoxal on the cloud condensation nuclei (CCN) activity of the aerosol. These studies were conducted using either aerosols generated from bulk solutions of the organic and ammonium sulfate or by exposing the gas-phase organic to pure ammonium sulfate seed aerosols. A number of techniques were utilized including: a custom-built Aerosol Chemical Ionization Mass Spectrometer (Aerosol-CIMS), UV-Vis spectrophotometer, pendant drop tensiometry (PDT), continuous flow stream-wise thermal gradient CCN counter (CFSTGC), aerosol flow tube reactors, and an aerosol chamber. We found that the uptake of methylglyoxal to aerosols is a potentially significant source of light-absorbing SOA in the atmosphere. Additionally, the presence of methylglyoxal leads to surface tension depression with important implications for aerosol CCN activity. The aqueous-phase reaction products of glyoxal and methylglyoxal when NH4^+ is present include species featuring unsaturated C=C bonds such as aldol condensation products and imidazoles. Upon oxidation by O3 and OH, these particles show an increase in light absorption, accompanied by the formation of smaller, more volatile organic acids. Aerosol chamber studies conducted where pure ammonium sulfate particles were exposed to gas-phase methylglyoxal and/or acetaldehyde show significant enhancements in CCN activity, which can increase cloud droplet number concentrations by up to 20%. The results of this work will provide for a more accurate representation of gas-aerosol interactions and cloud formation in climate and atmospheric chemistry models.

The interaction between sunlight and our atmosphere is one of the most fundamental processes affecting weather and climate. The majority of the Sun�s radiation is produced in the ultraviolet, visible and near-infrared regions of the electromagnetic spectrum. These spectral regions correspond to the energies of vibrational overtone and electronic transitions. The composition of our atmosphere is complex, and many trace species have a large influence on its chemistry and dynamics. Hydrogen bound hydrated complexes are trace species that could play an important role in the Earth�s atmosphere. However, before this role can be quantified, spectral identification and characterisation of these complexes is essential. We have developed vibrational local mode Hamiltonians to simulate the absorption spectra of hydrated complexes. To test the approximations made in the vibrational model, we have peformed calculations on the diatomics OH, HF and CO, which can be considered to act as pure local modes. When highly correlated ab initio methods and large basis sets are used to calculate the potential energy and dipole moment curve, the simulated vibrational transitions of the diatomics are in excellent agreement with experiment. We have derived approximate vibrational Hamiltonians which describe the OH-stretching and HOH-bending modes of vibration in the complexes H₂O�H₂O, H₂O�HO₂ and H₂O�HO. The calculated spectrum of H₂O�H₂O has been used to assess its atmospheric importance, and to succesfully guide experimental efforts to detect H₂O�H₂O in the laboratory and the Earth�s atmosphere. The calculated transition energies and intensities of H₂O�H₂O and H₂O�HO are in good agreement with experimental matrix isolation and gas-phase studies. To investigate the effect of low frequency modes on OH-stretching overtone spectra we have simulated the spectrum of HOONO. We have derived a Hamiltonian that couples the NOOH-torsional mode to the high frequency OH-stretching and OOH-bending modes. The simulated spectrum is in good agreement with the experimentally observed spectrum. We find that the OH-stretching spectra are perturbed strongly only if the barrier to torsion is low. We have also investigated changes in the electronic spectrum of hydrated complexes and the corresponding parent monomers. Upon complex formation, the lowest-lying electronic transition in the hydroxyl radical is strongly redshifted outside the region of monomeric absorption.

M.S. / Environmental Science / [No abstract available.]

A single-ultrafine-particle mass spectrometer was constructed and deployed for size-resolved ultrafine aerosol composition measurements during the winter of 2002-2003 in College Station, Texas. Three separate experiments were held between December and March with six week intervals. Almost 128,000 mass spectra, corresponding to particles with aerodynamic diameters between 35 and 300 nm, were collected and classified. Fifteen statistically significant classes were identified and are discussed in this paper. Nitrate, potassium, carbon, and silicon/silicon oxide were the most frequently observed ions. Nitrate was present in most of the particles, probably due to the agricultural activity in the vicinity of the sampling site. The nitrate detection frequency was found to be sensitive to the ambient temperature and relative humidity. Another particle class, identified as an amine, exhibited strong relative humidity dependence, appearing only during periods of low relative humidity. There is evidence that some of the detected particles originated from the large urban centers, and were coated with nitrate, sulfate, and organics during transport.

A single-ultrafine-particle mass spectrometer was constructed and deployed for size-resolved ultrafine aerosol composition measurements during the winter of 2002-2003 in College Station, Texas. Three separate experiments were held between December and March with six week intervals. Almost 128,000 mass spectra, corresponding to particles with aerodynamic diameters between 35 and 300 nm, were collected and classified. Fifteen statistically significant classes were identified and are discussed in this paper. Nitrate, potassium, carbon, and silicon/silicon oxide were the most frequently observed ions. Nitrate was present in most of the particles, probably due to the agricultural activity in the vicinity of the sampling site. The nitrate detection frequency was found to be sensitive to the ambient temperature and relative humidity. Another particle class, identified as an amine, exhibited strong relative humidity dependence, appearing only during periods of low relative humidity. There is evidence that some of the detected particles originated from the large urban centers, and were coated with nitrate, sulfate, and organics during transport.

Thesis (Ph. D.)--University of Texas at Austin, 1999. / Includes bibliographical references (leaves 210-217). Available also in a digital version from Dissertation Abstracts.

Thesis (M.Sc.)--Victoria University of Wellington, 2009. / Accompanying disc: Appendix Five. Includes bibliographical references.

Thesis (Ph. D.)--University of Texas at Austin, 1999. / Vita. Includes bibliographical references (leaves 210-217). Available also in a digital version from Dissertation Abstracts.

Thesis (M. Sc.)--York University, 1999. Graduate Programme in Chemistry. / Typescript. Includes bibliographical references (leaves 107-112). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://wwwlib.umi.com/cr/yorku/fullcit?pMQ56169.

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