No description available.

No description available.

No description available.

No description available.

No description available.

The aim of this thesis is to improve our understanding of the distribution of stratospheric ozone which is determined by both dynamical and photochemical processes. This is of particular importance since ozone adsorbs incoming solar UV radiation which would otherwise be harmful to humans. In 1985 the Antarctic Ozone hole was discovered alerting the world to the impact human activity has had upon stratospheric ozone. In recent years a significant decline in ozone has also been detected at high northern latitudes during spring. This thesis uses numerical models of varying complexity in order to study the stratospheric circulation, and the chemistry occurring therein. The results from the model integrations described are compared to observations made by instruments on board the UARS satellite. A new stratospheric chemistry scheme is described. Simple box model studies show that this model is capable of simulating the almost complete removal of ozone seen to occur at certain altitudes during Antarctic spring. This experiment highlights interesting differences in the behaviour of chlorine compounds in the two hemispheres. Sensitivity studies are performed in order to determine the precise conditions required for severe ozone destruction. It is found that the average ozone destruction rate over the period of the integration is inversely proportional to the maximum C1ONO<SUB>2</SUB> mixing ratio produced by the model. The model shows some sensitivity to the ozone column used in the photolysis calculation, however it is not considered that sufficient improvement would be obtained by using a fully interactive photolysis scheme to justify the computational expense of this calculation. The new chemistry scheme is coupled to the SLIMCAT off-line model in order to study the 1991-92 northern hemisphere winter. It is found that if instead of using 2-dimensional model data to initialise the model a more realistic simulation is produced by using observations of long lived gases made by the UARS satellite. It is found that whilst the model is capable of reproducing ozone depletion, the denoxification within the model is too severe. This results in the deactivation of chlorine being unrealistically slow. In order to investigate the longer term variation of ozone a one year integration of the SLIMCAT model coupled to a parameterised chemistry scheme is performed. When the model results are compared to observations there is evidence that the model's simulation of lower stratosphere tropical dynamics is poor. Budget studies of N<SUB>2</SUB>O reveal that the main cause of this problem is the lack of means continuity in this region of the model. When the experiment is repeated, imposing mass continuity on each isentropic surface, the resulting N<SUB>2</SUB>O distribution is much more realistic.

No description available.

A rapid analytical method capable of detecting low concentrations of bacterial spores has been developed. Dipicolinic acid (DPA), a universal and specific component of bacterial spores, was chosen as a suitable target analyte for bacterial spore detection. DPA was assayed by fluorimetric detection of its chelates with lanthanide metals. The influence of the choice and concentration of lanthanide and buffer ions on the fluorescence assay was studied as well as the effects of pH and temperature. The optimal system had a detection limit of 2nM DPA. This assay allowed the first real-time monitoring of the germination of bacterial spores by continuously quantifying exuded DPA. A detection limit of 10<SUP>4</SUP> <I>B. subtilis </I>spores/ml was reached, representing a substantial improvement over previous rapid tests. To further improve the detection limit, a selective preconcentration step was investigated; both biological and chemical recognition molecules were compared for this purpose. A novel DPA analogue was synthesized and immobilized which was more suitable for use as an antigen than previous DPA conjugates. Several conjugates were then applied to screening a phage-antibody library for anti-DPA recognition molecules; however, the library was found not to contain appropriate phage-antibodies. Other means of concentrating DPA were considered and successful preconcentration was demonstrated with Dowex-1 anion-exchange resin. DPA was concentrated from a large volume of solution then eluted directly into the optimum fluorescence assay mixture allowing a convenient analytical method. A 66-fold concentration of DPA was demonstrated, resulting in a limit of detection of 50pM DPA or 133 spores/ml. from a 1L sample of aqueous suspension. This is the first rapid analytical method for bacterial spores which is sufficiently sensitive for industrial application. Future prospects for bacterial spore detection and further improvements to both the fluorescence assay and the preconcentration step were discussed.

This thesis describes the application of far-infrared and mid-infrared, laboratory based, high-resolution laser spectroscopy to the measurement of line profiles of atmospherically relevant molecules. Such data is invaluable in the retrieval of concentration profiles from remote sensing data. Chapter one contains an overview of the far-infrared and mid-infrared regions of the electromagnetic spectrum and highlights the need to develop high power, high efficiency, tunable, coherent radiation sources. Some of the more promising technologies are outlined together with some potential applications. The experimental details concerning the operation of a tunable far-infrared spectrometer, based on non-linear mixing and a mid-infrared spectrometer based on tunable lead-salt diode lasers, are then given in Chapter 2. Theoretical aspects of line broadening are considered in Chapter 3 and a protocol is developed for the retrieval of pressure broadening data. The validity of the protocol is demonstrated by critically examining three well studied and atmospherically important molecules: H³⁵Cl, SO₂ and N₂O. Chapter 4 and Chapter 5 examine the nitrogen, oxygen and self broadening of methyl iodide and methyl bromide respectively. Measurements of pressure broadening coefficients were obtained, for the first time, in the <i>v</i>₅ perpendicular bands of both molecules. The lines from five <i>Q</i> branches formed the bulk of the study for each molecule, with some <i>P</i> and <i>R</i> branch lines also being examined. Primarily, the <i>J</i> dependence of the broadening coefficients was obtained but some knowledge of the <i>K</i> dependence was also gleaned. Finally, in Chapter 6, some recommendations for the development of the spectrometer are made and some suggestions for potential target molecules, that could form the basis of a future study, are given.

No description available.