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A three-dimensional (3D) photochemical grid model, CAMx-2.0 (1998), was employed to analyze the spatial and temporal variations of ambient ozone during ozone episodes (concentration of ozone > 120 ppbv) in the Kao-Ping airshed in 2000-2001. The sensitivity analyses of ozone concentrations to the emission reductions in volatile organic compounds (VOC) and nitrogen oxides (NOx) were performed, and the relationships between ozone concentrations and meteorological parameters were examined. Furthermore, the transport routes were studies using inverse trajectory method. Examinations of meteorological parameters and ozone trends reveal that warm temperature, sufficient sunlight, low wind, and high surface pressure are distinct parameters that tend to trigger ozone episodes in Kao-Ping area in autumn and winter seasons. Seasonal patterns of surface ozone include a summer minimum with two maxima in autumn and late winter to the middle of spring, consistent with low mixing heights in autumn and winter and large mixing height in summer. Predicted values of hourly ozone concentration agree reasonably well with measured data. The assessment of the effect of the initial and boundary conditions on the performance of the model revealed that the model can be improved by specifying an ozone concentration of 70 ppbv rather than 30 ppbv on the top boundary of the model, while separately considering the daytime and nighttime ozone concentration on the lateral boundary conditions. The sensitivity analysis shows a VOC-sensitive regime in Kaohsiung City. In addition to the locally emitted pollutants, the inverse trajectory analysis shows that most pollutants in Kaohsiung City come from Kaohsiung County, followed by Tainan County and Ping-Tung County. In autumn, the air quality is worst in Ping-Tung County and ozone episodes occur most frequently. Because the prevailing wind is north or north-east wind in autumn, most pollutants are transported from the upwind areas, including Kaohsiung City and Kaohsiung County. The sensitivity analysis shows a NOx-sensitive regime for Ping-Tung city, consistent with Sillman¡¦s results (1999), indicating that freshly emitted pollutants are typically (but not always) characterized by VOC-sensitive chemistry and evolve towards NOx-sensitive chemistry as the air parcels move downwind.

ABSTRACT Being a densely populated and heavily industrialized harbor, the emissions of air pollutants in the Kaohsiung area are very huge. There is substantial amount of VOCs (volatile organic compounds) present in the ambient air. Furthermore, relative high temperature and strong sunlight tend to transform these VOCs to oznone, causing high ozone episodes. This study aimed to determine the VOCs source profiles (or fingerprints) from 20 stationary sources, 10 from each of Kaohsiung City and Kaohsiung County. These include flue gas emission from incineration plants, sewage treatment plants, petroleum plants, and others. The samples was collected using a stainless-steel thermal desorption tube, then analyzed a Hewlett-Packard 58900-II gas chromatograph, fitted with a flame ionization detector and desk-top personel computer. The OFP (ozone formation potential) of VOCs from individual sources were evaluated based on MIR (maximum incremental reactivities). The results show that the speciations of VOCs depend on the raw material and air pollution control equipments used in the processes. The major VOCs in the petro-chemical industries are benzene, toluene, xylene, and 1,3,5-trimethylbenzene. The major VOCs in the PVC processes and surface-painting industries are 2-methylbutane, 2-methylpentane, and ethylbenzene. The major VOCs in the sewage treatment plants are ethylene, hexane, benzene, toluene, and m-xylene. The highest average reaction of the samples is 27.94 g-O3/g-VOCs from intermediary process, the next are from lubrication oil distillation tower, TPE process, ABS process, and maleic anhydride process, ranging from 3 ~ 5 g-O3/g-VOCs. Thus, the reactivity of aromatic-related process is highest, the next are aldehydes - and ketones -related processes. Keywords: Volatile Organic Compounds, Fingerprints, Ozone Formation Potential

Reproduction de : Thèse de doctorat : Génie des procédés environnement : Toulouse, INPT : 2006. / Titre provenant de l'écran-titre. Bibliogr. 488 réf.

Reproduction de : Thèse de doctorat : Physique de l'atmosphère : Clermont Ferrand 2 : 2005. / Titre provenant de l'écran titre. Bibliogr. p. 197-208.

Thesis (Ph. D.)--University of Michigan, 1933. / From Physical review, v. 42, December 1, 1932.

In this study, the properties of nickel and antimony doped tin oxide (NATO) electrode materials were investigated in relation to the electrochemical generation of ozone. The performance of NATO materials was correlated to ·OH radical generation and oxygen adsorption properties. Long-time ozone generation results suggested that surface property changes, including surface morphology, chemical composition and electro-catalyst thickness, could lead to ozone production rate decreased from 137 to 0 mg·h-1 and the current efficiency declined from 18% to 0. The loss of Ni in the electrode was suggested for the decrease in ozone generation. Moreover, material characterization results indicated the presence of NiOOH and multiple oxidation states of Sb (+3 and +5), which were proposed as the critical sites for the electrochemical generation of ozone. In addition, NATO nanocrystals of 3.5 ~ 7.5 nm in size prepared by the hydrothermal method were used as an alternative route to fabricate electrodes. The highest current efficiency of 41% was achieved on NATO material of 6% Sb in the precursor, which led to the lowest resistivity of 2.38 ± 0.03 Ω·cm in the product NATO material. This further demonstrated the applicability of NATO materials used as electro-catalysts for the electrochemical generation of ozone. Hydroxyl free radicals (·OH) can be regarded as one of the most important intermediates for ozone generation. The presence of ·OH radicals was quantified by fluorescence spectroscopy with terephthalic acid as probes. Quantitative analysis results showed that Ni dopant could significantly enhance ·OH generation, while over-doping of Sb and Ni can decrease the generation of ·OH radicals. An oxygen chemisorption study on NATO materials showed that more active sites available for oxygen chemisorption lead to higher catalytic activity for ozone generation. The highest oxygen chemisorption capacity of 49.76 μmol·g-1 was achieved on NATO-5 (Sn:Sb:Ni=1000:16:2), which showed the highest current efficiency of 43%. In addition, temperature programmed oxygen adsorption and desorption showed different patterns on different NATO materials. This suggested that oxygen adsorption on NATO materials has a correlation to the electrochemical generation of ozone. In addition, oxygen adsorption was further investigated with near ambient oxygen adsorption. Oxygen adsorption isotherm results indicated that both physisorption and chemisorption can occur on the surface of SnO2 based material (NATO-5) with or without hydrogen pretreatment. When NATO-5 was treated with hydrogen, adsorption was mainly in the form of chemisorption. However, it was mainly in the form of physisorption without hydrogen pretreatment. By comparing NATO-6 (Sn:Sb:Ni=1000:16:0) with NATO-7 (Sn:Sb:Ni=1000:0:2), it was found that Sb was more important in the oxygen adsorption ability of NATO materials compared to Ni doping. Based on the findings in this study, two active sites (Sb and Ni sites) were proposed for ·OH generation and oxygen adsorption in order to explain the mechanism of ozone generation on NATO materials. Also, electrochemical generation of ozone was correlated with oxygen adsorption and ·OH generation. / published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

There are a number of unanswered questions regarding new caries preventive methods such as ozone treatment as well as novel caries detection methods that monitor and evaluate these preventive methods. This thesis seeks answers to some of these questions. Aims: Paper I investigates the in vitro sealing capacity of a novel ozone delivery system and its re-suction capacity. Paper II studies the in vitro antibacterial effect of ozone on cariogenic bacterial species with and without the presence of saliva and its possible effect on the saliva proteins. Paper III assesses the in vitro validity of laser-induced fluorescence (LF) measurements, visual inspection (colour), and tactile examination (surface texture) on root caries lesions and correlates these with histopathological measurements of lesion depths.  In addition, Paper III investigates how inter-device, inter-examiner, and intra-examiner levels influence LF reading agreements and whether lesion colour and surface texture influences LF readings. Paper IV evaluates the in vivo effect of ozone and fluoride varnish treatments on occlusal caries in primary molars. Material and methods: Paper I: Full ozone application cycles, including the re-suction period, and interrupted cycles with displacement of the cup during the delivery cycle were studied using an ozone air analyser. Paper II: Ozone gas was exposed to the bacteria in the solution’s buffer and saliva via a tube connected to the ozone generator for 10, 30, and 60 seconds. Paper III: Calibrated examiners assessed lesion colour and surface texture and performed measurements with two LF devices for three separate one-week intervals.  Sections (300µm thick) of 64 out of 93 teeth were obtained and examined under a microscope. Lesion depth was assessed with two references: from the delineated borderline of the original exposed root surface (ref I) or, if loss of surface continuity, the absolute lesion depth (ref II). Paper IV: The split mouth study was conducted in two parts. The participants in part A were children (mean age 4.8 years) with medium-high caries risk. Inclusion criteria were bilateral matched pairs of cavitated or non-cavitated occlusal lesions in primary molars (Ekstrand index score ≤ 3). Children in part B (mean age 4.5 years) with low-medium caries risk had pairs of non-cavitated lesions only (Ekstrand index score ≤ 2a). The assessments and treatments with ozone and fluoride varnish were performed at baseline and at three, six, and nine months. At the 12-month follow-up, only assessments were performed. Results: Paper I: Ozone leakage levels varied between 5.2 and 9.8 µg/m3. Paper II: In the salt buffer, 92%, 73%, and 64% of the initial numbers of A. naeslundii, S. mutans, and L. casei, respectively, were killed after 10 s ozone exposure and approximately 99.9% of the bacteria were dead after a 60 s exposure. After 10 and 30 s but not after 60 s exposure to ozone, S. mutans and L. casei were less efficiently killed in saliva compared to in the salt buffer. Various saliva proteins were degraded by ozone after the 60 s exposure. Paper III: The correlation between LF readings and histological depth was low with values ranging from 0.22 (p ˃ 0.05) to 0.31 (p < 0.05). The LF devices were significantly correlated with discolouration and with a surface texture denoted as hard. A significant correlation was found between colour and histological depth. No significant correlation was found between surface texture and histological depth. The reliability, evaluated as intra-class correlation coefficient, was 0.99 for intra-examiner, 0.97 for inter-examiner, and 0.98 inter-device level. Large differences were found between two consecutive measurements and high measurement errors indicated considerable deviation of individual measurements.Paper IV: In the first 15 pairs of part A, eight lesions treated with ozone and nine treated with fluoride, including all cavitated lesions, progressed to failure, i.e., required operative treatment during the study time. Due to non-acceptable results, the sample collection was discontinued because of ethical reasons. In part B, of 35 pairs, one of the ozone treated lesions failed at 12 months. A small shift towards increased VI scores was recorded for both ozone and fluoride lesions in this second part. Conclusions: - The ozone delivery system can be considered a safe system with low leakage levels in air, also with accidental displacements. - The cariogenic species S. mutans, L. casei, and A. naeslundii were sensitive to ozone gas treatment. The presence of saliva hampered the antibacterial effect of ozone. A low correlation between the LF readings and the histopathological depth of root caries lesions was shown. The LF device was found not to be appropriate for application to root caries diagnosis. - Neither ozone nor fluoride varnish treatments arrested the progression of cavitated occlusal caries lesions. In low and medium caries risk children non-cavitated occlusal lesions remained mainly unchanged during the study period.  No difference in the effect of ozone and fluoride varnish treatments on occlusal caries in primary molars was seen.

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