Typescript (photocopy) / ix, 171 leaves, 2 leaves of plates : ill. ; 30cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Physics, 1980

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Processing and analysis routines giving normalized moments of optical intensity, structure functions of wind velocity and temperature, central moments, and various measures of the turbulence parameter, C2N, are presented. Rapid analog-to-digital data conversion and storage to implement this analysis using MINC 11/23 with RT11 operating system are discussed. Coding for file organization and implementation of processing routines on the VAX 11/750, VMS operating system are also discussed.

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The main objective of this study was to investigate the vertical distribution of aerosols over Durban in relation to the vertical stability structure and horizontal transport of air masses. The importance of aerosols in the region is well recognised and recently there have been many international experiments which have focused on aerosol distribution over the subcontinent. Durban is situated at the approximate centre of a giant plume that is known to transport aerosols and trace gases off the east coast of southern Africa and is therefore strategically located for an investigation of the vertical distribution of aerosols. The vertical distribution of aerosols over Durban was measured using a LIDAR (Light Detection And Ranging) system on selected cloud free days in 1997. Backward trajectory modelling was used at selected pressure (standard) levels to determine the origin and transport pathways of aerosols. Six case studies are presented in an attempt to gain insight into the relationship between the vertical distribution of aerosols and absolutely stable layers. The results of the study revealed that the occurrence of absolutely stable layers governs the vertical distribution of aerosols in the troposphere. An absolutely stable layer at ~5km (~500hPa) appears to be the most effective in capping and trapping aerosols in the atmosphere. Below 5km, the atmosphere was charcterised by marked stratification and relatively higher concentration of aerosols. Above 5km, the concentrations were much lower, but generally increased slightly with height. Low aerosol concentrations are observed during post-frontal situations and relatively higher concentrations during anticyclonic conditions. The background to the problem and the objectives of this investigation are elaborated in Chapter 1. A description of the data sets and derived meteorological variables, along with the methodologies applied in this thesis, are given in Chapter 2. A theoretical review of aerosols, including their sources, effects and distribution over the globe and southern Africa, is discussed in Chapter 3. Atmospheric circulation and weather patterns and their relationship to the transport and dispersion of aerosols are described in Chapter 4. The results of the study and an analysis of the major findings are presented in Chapter 5. Finally, Chapter 6 summarises the major findings of this dissertation. / Thesis (M.Sc.)-University of Natal, Durban, 2000.

A probability density function is developed for the phase of light that is the result of adding a signal to noise with K-distributed amplitude and uniform phase. The probability density function of the phase associated with the I-K distribution is also developed. In the process of deriving the probability density function of the phase much I as learned about the relationships between different probability density functions. Three different methods of deriving homodyned K statistics are shown to be equivalent. Two different methods of deriving I-K statistics are shown to be equivalent. Theoretical moments of the homodyned K distribution are compared with experimentally measured moments in order to determine the parameters of the model for different conditions of turbulence. An experiment is proposed for measuring the spatial structure function of the phase in a manner that will allow verifying the accuracy of the new probability density functions of the phase.

The Earth's atmosphere is a large photochemical reactor consisting primarily of N2 (~78%) and O2 (~21%) with Ar and water vapor being the next most abundant constituents. All of the remaining gases in the atmosphere are referred to as 'trace gases', and they play a critical role in understanding climate change, urban air quality, ozone production and depletion, and in determining the overall 'health' of the atmosphere. These trace components are present in our atmosphere with mixing ratios, i.e., mole fractions, ranging from sub parts per trillion to several hundred parts per million. One class of trace constituents that play a critical role in atmospheric chemistry are free radicals. Free radicals are highly reactive, often initiating the oxidation of natural and anthropogenic atmospheric species, thereby often controlling the fate and lifetimes of these species. The research comprising this dissertation focuses on laboratory studies of the kinetics and mechanisms of free radical (atomic halogen) reactions that can impact the levels of important trace atmospheric species. In the studies reported herein, laser flash photolysis (LFP) was coupled with time resolved atomic resonance fluorescence (RF) spectroscopic detection of Cl or Br atoms to investigate halogen atom chemistry. The research addresses three groups of reactions: Cl atom reactions with alkyl bromides, Cl and Br-initiated oxidations of small (C2-C6) alkenes, and Cl reactions with CH3SCH3 (DMS, dimethylsulfide) and CH3SeCH3 (DMSe, dimethylselenide). The alkyl bromide reactions were experimentally unique in that we were able to deduce kinetics of the Cl atom reaction with bromoethane, n-bromopropane, and 1,2-dibromoethane by monitoring the appearance of the Br product by LFP-RF. The Br is formed via elimination that occurs essentially instantaneously following β-H abstraction by the Cl atom. All three of the bromoalkanes investigated are emitted into the atmosphere primarily from anthropogenic sources and all three have been identified by the World Meteorological Organization (WMO) as very short-lived (lifetime less than 6 months) source gases with significant ozone depletion potentials (ODPs). Additionally, the bromoalkanes mentioned above have been of interest as model compounds for larger partially halogenated organics found in the atmosphere, and they have been considered as potential replacement compounds for chlorofluorocarbons (CFCs) that have been banned as a result of the Montreal Protocol. Brominated very short-lived compounds are thought to contribute 20-25% of total stratospheric bromine. Thus, there is considerable interest in understanding the atmospheric chemistry of even the most short-lived organic bromine compounds. Temporal profiles of Br atoms provided important kinetic and mechanistic insight for the reactions over a wide range of temperature and pressure. Temperature-dependent rate coefficients are determined for the alkyl bromides of interest for the first time, and the potential importance of the Cl reaction as an atmospheric degradation pathway for each alkyl bromide is qualitatively assessed. The studies of halogen atom reactions with alkenes focused on formation of weakly-bound adducts where kinetics of adduct formation and dissociation as well as non-adduct forming channels were evaluated. The elementary steps in the Br initiated oxidation of the alkenes 2-methyl-1,3-butadiene (isoprene), 2,3-dimethyl-2-butene (tetramethylethylene, TME), and 1,3-butadiene have been investigated. The experimental kinetic database for these reactions is quite sparse. The kinetic results reported herein, suggests that Br reaction with the above olefins is much faster than previously thought. Analysis of the temperature dependence of the "approach to equilibrium" kinetic data in conjunction with electronic structure calculations allows for determination of enthalpy and entropy changes associated with each addition reaction. Where possible, both forward addition and reverse dissociation channels as well as H-abstraction pathways were characterized. The enthalpy change associated with the addition reaction to give the Br−isoprene and Br−1,3-butadiene adducts has been determined for the first time and the bond dissociation enthalpy obtained for the Br−TME adduct is in reasonable agreement with the only other previously reported value. It should be noted that in the case of isoprene and 1,3-butadiene, there are multiple possible adducts that could be formed. In order to help clarify which adducts are more or less likely to be formed, we rely on electronic structure calculations (see Chapter 5) to aid in our overall understanding of the adduct forming channels. Furthermore, for the Br reactions with the three alkenes above, atomic Br kinetics have been monitored directly both in the absence and in the presence of O2 which allowed, for the first time, determination of rate coefficients for the elementary steps in the overall complex mechanism including determination of the Br−olefin + O2 rate coefficient. Also included in this group of reactions is the chlorine reaction with isoprene. In addition to the well-known fact that isoprene is emitted into the atmosphere from vegetation, a potentially significant marine source of isoprene has received considerable attention. Chlorine has long been thought to exist primarily in marine environments, however, recent findings also suggest a significant Cl production rate in the middle of the continental United States. There are numerous room temperature kinetic studies for the Cl + isoprene reaction in the literature, however, there is only one temperature dependent study reported. Current recommended 298 K rate coefficients for isoprene reactions suggest the Cl reaction is ~ 4x faster than the analogous OH reaction. If indeed this is the case, the Cl reaction could play a non-neglibible role in isoprene oxidation in atmospheric locales where Cl concentrations are relatively high. In addition, the C−Cl bond strength in Cl−C5H8 is obtained from direct measurements of the forward and reversible addition rate coefficients. Our results are compared with the literature data, and the potential importance of Cl-initiated oxidation as an atmospheric sink for isoprene is assessed. The final group of reactions investigated involves reactions of Cl with DMS and DMSe. DMS and DMSe are the most prevalent sulfur and selenium compounds emitted to the atmosphere from the oceans. The oxidation of DMS has been studied extensively due to the interest in the possible role of DMS oxidation in the formation of sulfate aerosols, however, DMSe oxidation processes have hardly been studied at all. And, DMSe oxidation products are likely to be less volatile than the analogous DMS species. Selenium is an essential nutrient for many plants and animals; however, there is a fine line between enough and excess selenium which can be toxic. Most studies suggest that atmospheric deposition is an important source of Se contamination, and it is therefore critical to evaluate the source emissions and fate of Se in the atmosphere. Since the majority of atmospheric Se exists in the form of DMSe, determination of the kinetics and oxidation mechanisms of DMSe will go a long way towards understanding the global biogeochemical cycle of Se. Both reversible addition and H-abstraction pathways have been characterized, and the first experimental determination of bond strength of the gas-phase DMS−Cl and DMSe−Cl adducts have been obtained.