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The photodissociation of ozone by ultraviolet light has a great impact on the photochemistry of the atmosphere. The relative quantum yield for the production of the singlet atomic fragment O(¹D) has been determined in the wavelength region 306 to 327 nm for four temperatures between 227 K and 300 K. The technique of resonance enhanced multi photon ionisation (REMPI) was used to probe directly the O(¹D) photolysis product. These relative measurements have been placed onto an absolute scale by the selection of a calibration point whose value has been agreed by the scientific community. The yields obtained are in good agreement with others reported during the time of the research reported in this thesis and clearly show that three mechanisms contribute to the final quantum yield. Below 310 nm, O(¹D) is produced by a spin-allowed channel, above 320 nm the primary channel is a spin- forbidden one and at intermediate wavelengths photolysis of vibrationally excited ozone contributes to the O(¹D) yield. Elements of the quantum yield data presented in this thesis are being included in a new recommendation for the temperature dependent O(¹D) quantum yield. Details of the dissociation kinetics, including further evidence confirming the spin-forbidden channel, is presented in time-of-flight studies of the O(¹D) product. Time-of-flight profiles taken between 317 and 321 nm show evidence that, at room temperature, the O(¹D) quantum yield is anti-correlated with the ozone absorption cross section. Excitation of the O₂(a¹Δ_g) co-fragment has been observed at wavelengths below 296 nm by monitoring the energies of the O(¹D) formed. As the channel for the production of O₂(a¹Δ_g,andnbsp;vandnbsp;=andnbsp;1) opens, it is found that energy is preferentially partitioned into rotation of the O₂ fragment rather than into translation. Initial studies on the O(¹D) fragment have shown that the fragment is orbitally aligned and that the choice of REMPI transition can have a significant effect on the time-of-flight profiles and therefore on the measurements that are made from the profiles. The time-of-flight profiles obtained by probing the O₂(a¹Δ_g) photofragment have shown that the O₂(a¹Δ_g) has an angular momentum polarisation that is J dependent, with the even J being strongly polarised and the odd J depolarised. This results in the shape of the time-of-flight profiles being a function of the REMPI laser polarisation; and the study of this behaviour has been used to confirm the assignments in highly perturbed REMPI spectra.

Thesis (M.S.)--University of Hawaii at Manoa, 2007. / Includes bibliographical references (leaves 94-97). / ix, 97 leaves, bound ill., maps 29 cm

Thesis (Ph. D.)--University of Washington, 1992. / Vita. Includes bibliographical references (leaves [159]-169).

Thesis (Ph. D.)--University of Denver, 1985. / Includes bibliographical references (leaves 247-266).

Networks of ground-based and satellite borne instruments to measure ultraviolet (UV) sunlight and total column ozone have greatly contributed to an understanding of increased amounts of UV reaching the surface of the Earth caused by stratospheric ozone depletion. Increased UV radiation has important potential effects on human health, and agricultural and ecological systems. Observations from these networks make it possible to monitor total ozone decreases and to predict ozone recovery trends due to global efforts to curb the use of products releasing chemicals harmful to the ozone layer. Thus, continued and expanded global monitoring of ozone and UV is needed. However, existing automatic stratospheric ozone monitors are complex and expensive instruments. The main objective of this research was the development of a low-cost fully automated total column ozone monitoring instrument which, because of its affordability, will increase the number of instruments available for ground-based observations. The new instrument is based on a high-resolution fiber optic spectrometer, coupled with fiber optics that are precisely aimed by a pan and tilt positioning mechanism and with controlling programs written in commonly available software platforms which run on a personal computer. This project makes use of novel low-cost fiber optic spectrometer technology. A cost advantage is gained over available units by placing one end of the fiber outdoors to collect sunlight and convey it indoors, thereby allowing the spectrometer and computer to be placed in a controlled environment. This reduces the cost of weatherproofing and thermal compensation. Cost savings also result from a simplified sun targeting system, because only a small pan and tilt device is required to aim the lightweight fiber optic ends. Precision sun-targeting algorithms, optical filter selection, and software to derive ozone from spectral measurements by the spectrometer are a major contribution of this project. This system is a flexible platform which may be adapted to study other atmospheric constituents such as sulfur dioxide, nitrous oxides, and haze.

Photochemically produced ozone represents a worldwide enviromental hazard. Controlling ozone formation in polluted air requires control of hydrocarbon and nitrogen oxides precursors. The degree of control can be established with the chemical model of the reacting species. A hydrocarbon-specific photochemical ozone model is developed, based upon a minimum set of chemical equations. This model eliminates the need for the traditional "brute force" approach to integrate systems of tens or even hundreds of simultaneous differential equations. We have sought to develop the full kinetic potential for simplification which this chemical system may have. Key features of the model are reaction of parent hydrocarbon with hydroxyl radical (OH) to produce products, which themselves react with OH or are photodissociated. These basic steps are summarized by three rate parameters which describe NO photooxidation and ultimate accumulation of ozone. Since the mechanism may be solved in a closed form, it is a simple matter to evaluate the rate parameters for any hydrocarbon from smog chamber data. This evaluation can be carried out by analysis of data in NO photooxidation regime, before ozone begins to accumulate. The simple model for NO photooxidation is transformed to give an equation which describes the number of NO conversions per hydrocarbon decay, independent of time or of hydroxyl radical concentration. Comparison of the rate parameters determined from existing smog chamber data for n-butane and propene shows a very good agreement with explicit mechanisms for these extensively studied hydrocarbons. Rate parameters have been determined for a number of less studied hydrocarbons as well.

Thesis. 1975. M.S.--Massachusetts Institute of Technology. Dept. of Meteorology. / Bibliography: leaves 73-75. / by Walter Joseph Slade, Jr. / M.S.

Surface ozone (O3) is one of the most toxic and abundant air pollutants. It has deleterious effects on human and animal respiration processes, and adversely affects plants. Four sites were selected for monitoring ambient O3 in the Durban metropolitan area: Botanic Gardens, University of Natal (UND), top of Kloof Gorge, and Mooi River. At each site tobacco Bel-W3 bioindicators, and NO2 and O3 passive diffusion tubes were placed. An O3 analyser (Dasibi 1108) was situated at the UND site. Monitoring was carried out for four weeks during summer, autumn and winter at each site, and during spring at the UND site. Two weeks of data from the diffusion tubes were collected during spring, from the Nelspruit area, Mpumalanga. Ozone concentrations measured with the Dasibi at the UND site were low in comparison to other urban-industrial areas in the world, with hourly values falling between 5ppb and 10 ppb. The highest hourly mean maximum recorded was 40ppb. A general spring/winter maximum and summer minimum was observed. This is typical of subtropical locations, where subsidence in prevailing anticyclonic circulation occurs. Diurnal characteristics included early morning minima and maxima at 12h00 in spring and summer, and maxima approximately two hours later in autumn and winter. This pattern was typical of that found in polluted environments, the magnitude, however, being lower. An unusual secondary nocturnal peak occurred during autumn, winter and spring. This could have been due to the long-range transport of relatively O3-rich air from a non-urban, high altitude inland area. Ozone concentrations were not strongly influenced by meteorological variables. Diffusion tube data indicated low O3, however, the coefficients of variation were high, implying a lack of precision in this technique. This technique would have to be improved before data obtained could be regarded as valid. Nitrogen dioxide, NO2, one of the precursors to O3, was monitored using diffusion tubes at the same sites. Concentrations were highest closer to the city centre, the highest concentration being 31ppb in autumn. In the Mpumalanga study, NO2 concentrations were higher in the city of Nelspruit than the surrounding areas. No significant differences were found in the O3 concentrations between the Mpumalanga sites. The tobacco plants showed the highest visible leaf injury in winter, corresponding with the higher Dasibi values, but there were no significant differences between the sites, and no significant differences in chlorophyll contents between the sites. In this study, O3-induced injury occurred below the previously established threshold of 40ppb. / Thesis (M.Sc.)-University of Natal, Durban, 1998.

Ambient observations have indicated that ozone formation in the Houston area is frequently faster and more efficient, with respect to NOx consumed, than other urban areas in the country. It is believed that these unique characteristics of ozone formation in the Houston area are associated with the plumes of reactive hydrocarbons, emanating from the industrial Houston Ship Channel area. Thus, accurate quantification of industrial emissions, particularly of reactive hydrocarbons, is critical to effectively address the rapid ozone formation and the consequent high levels of ozone in the area. Industrial emissions of hydrocarbons have significant temporal variability as evidenced by various measurements, but they have been assumed to be continuous at constant levels for air quality regulation and photochemical modeling studies. This thesis examines the effect of emission variability from industrial sources on ozone formation in the HoustonGalveston area. Both discrete emission events and variability in continuous emissions are examined; new air quality modeling tools have been developed to perform these analyses. Also, this thesis evaluates the impact of emission variability on the effectiveness of emission control strategies in the Houston-Galveston area. Overall, the results indicate that industrial emission variability plays a substantial role in ozone formation and that controlling emission variability can be effective in ozone reduction. These results suggest that a quantitative treatment of emission variability should be included in the development of air quality plans for regions with extensive industrial activity, such as Houston.