No description available.

Thesis (M. Phil.)--University of Hong Kong, 2007. / Title proper from title frame. Also available in printed format.

The length of time that atmospheric pollutants released from low-level sources in the midwestern United States can expect to remain in the atmosphere is discussed. The pollution is assumed to be removed from the atmosphere by dry deposition and precipitation scavenging. Layer-average trajectories originating from Kansas City, Missouri are used to determine the Lagrangian probability of dry and wet conditions. The residence time of these pollutants is estimated based on parameterizations for the effective scavenging rates during wet and dry conditions. This investigation shows that, in summer, the probability that precipitation is being experienced by the pollutant is twice as great as the probability of precipitation at the origin of the pollution; this same ratio of probabilities is three in winter. Therefore, when precipitation scavenging is the more important removal mechanism, the statistics for the length of wet and dry periods at the source region overestimate the residence time by a factor of about two to three. By taking into consideration the Lagrangian probability of wet and dry periods, the relative importance of dry deposition and precipitation scavenging is discussed as a function of the wet and dry removal rates. It is seen that for a time- and vertical-average dry deposition velocity as large as 1 cm/sec, then dry deposition would normally be the bore important removal process for the meteorological conditions in the midwest to eastern United States. Estimates for the expected atmospheric lifetimes of aerosol particles and trace gases are reported as functions of dry deposition velocities and collection efficiencies (or washout ratios). For example, lead particles of mass mean diameter ~0.5 μm, should have a residence time ~8 days in winter, and ~3 days in summer, based on available data for the dry deposition velocity and washout ratio. In general, the residence time can be expected to be about twice as long during the summer season than the winter. The winter, monthly average distribution of pollutant mass is shown, based on the steady-state Gaussian approximation solution of the convective diffusion equation. The calculations are based on a statistical analysis of the 12 hourly positions of a series of trajectories. Thus, monthly average "diffusion" and removal are incorporated into the Gaussian model. / Graduation date: 1979

Air compressor systems are inefficient energy transfer devices even under the best of conditions, at full load. When only part load is required, efficiency drops further. This thesis attempts to improve part load efficiency of twin rotor screw air compressors in three ways. First, a guidebook was written to help educate compressor users and purchasers about the significance of part load efficiency and to aid in selecting the most efficient controls for a given application. Second, a spreadsheet-based model was developed to analyze the performance of cycling control strategies by performing a detailed simulation of one complete compressor cycle. Model calculations demonstrated that cycling losses can significantly increase average power as cycle time decreases, and that low-unload controls may be more efficient at low loads than is traditionally assumed. Third, a microprocessor-based controller was designed and built to enhance part load performance of combined modulating and unloading type control systems. The "smart" controller is presented in this thesis. Case study results showed energy savings of 4% to 32% over conventional controllers. / Graduation date: 1993

Thesis (Ph. D.)--Oregon Graduate Center, 1979.

No description available.

The AQHI, currently used by the Canadian government, is a multi-pollutant public health information tool that is based upon extensive Canadian epidemiological evidence. As the AQHI is a relatively new metric, there is little published information about the accuracy, and behaviour of this metric both spatially and temporally. The goal of this work was to provide more information to the scientific community on the spatial and temporal behaviour of the AQHI in the Halifax, Nova Scotia region. Sampling was conducted in both the winter and summer of 2009, at 50 sites distributed around the city and at the central NAPS site in downtown Halifax. Statistical analysis was conducted using daily calculated AQHI values. AQHI values in the region were predominantly in the 1 to 3 range on the AQHI scale which corresponds to very good air quality. The Government reported AQHI was found to be significantly different from the 50 sample site s AQHI values for both summer and winter (P=<0.001 for both seasons). The Government reported AQHI was significantly higher (P=0.05) than the AQHI calculated for the 50 sampling sites. Analysis identified that more than 50% of the daily AQHI index values were reported differently than the local sites, most commonly over predicted by one AQHI index point. Analysis also indicated a temporal trend of disagreement between the reported and sampled AQHI values. It was observed that during periods when the AQHI was higher, there was greater disagreement between that reported and the sample site AQHI value. This finding raises some concern regarding the behaviour of the AQHI in both larger cities and over the next decade as Halifax increases in size. The miss-reporting of AQHI values also raises some concern for epidemiological work, if the AQHI is used as an exposure metric it could over estimate exposure to air pollution. However, the AQHI is a useful scientific measure having a number of advantages, first it is a multi pollutant measure based on sound epidemiological evidence linking a mixture of three major air pollutant metrics to health effects and second that it has been distilled into a form that is readily understood by the public. This project has been successful in providing more information to the scientific community on the spatial and temporal variation of the AQHI in the Halifax region. It has been able to identify both seasonal and temporal variation, reinforced the understanding of pollutant behaviour and has begun to provide information on the behaviour of the AQHI on small urban scales and provide valuable information for both researchers and policy makers on the AQHI from a public health context.

Reproduction de : Thèse de doctorat : Sciences : Faculté des sciences de Paris : 1867. / Titre provenant de la page de titre du document numérisé.

Thèse de doctorat : Sciences chimiques : Strasbourg 1 : 2008. / Titre provenant de l'écran-titre. Bibliogr. 9 p.

Thesis (Ph. D.)--University of Hong Kong, 2001. / Includes bibliographical references (leaves 123-129).