Berlin, Freie Universiẗat, Diss., 2002. / Dateiformat: zip, Dateien im PDF-Format.

Universiẗat, Diss., 2001--Dortmund.

Universiẗat, Diss., 2003--Mainz. / Zsfassung in engl. Sprache.

Universiẗat, Diss., 2002--Frankfurt (Main).

Techn. Universiẗat, Diss., 2004--Darmstadt.

The temperatures and evaporation rates of surfactant-contaminated droplets were determined under controlled conditions. The surfactants used were sodium stearate, sodium palmitate, sodium myristate and sodium laurate. The drops were suspended on fine glass fibres or thermocouples in an environmental cell maintained at known temperature and humidity, and the evaporation rate was determined by optical measurement of the change of diameter with time. The results showed an early evaporation following a "clean" model, with a relatively sharp transition to a regime of "contaminated" evaporation kinetics. Simultaneous measurements of temperature and evaporation rate showed that the contaminants had no effect on heat transfer, i.e. their effect was limited to forming an additional mass transfer resistance. This mass transfer resistance increased strongly with initial surfactant concentration. Surfactants with longer carbon chains produced higher resistances, but after a longer delay. The partial differential equations describing surfactant diffusion within an evaporating drop were set up and solved, and an approximate analytical solution was shown to agree well with a numerical solution. By assuming that the surfactants retarded evaporation at the drop surface both by presenting a diffusional resistance to water transport and by vapour pressure lowering, a model was constructed to predict the evaporation behaviour of contaminated drops. It predicted the results obtained with sodium stearate well, but was unable to explain the results for shorter chain surfactants which were complicated by their adsorption behaviour at the surfactant-water interface. This model of single drop evaporation was extended to describe the evaporation of contaminated aerosols and used in an attempt to explain the measurements of Raper et al. (1982). Their results could not be explained quantitatively by a surfactant contaminant (though a surfactant would have produced similar qualitative features) and were probably caused by experimental error.

Understanding the interaction between atmospheric aerosol and water vapour is key in assessing the impacts of anthropogenic influences on the earth's radiative budget, both directly through scattering and absorbing incident solar radiation, and indirectly through changing cloud properties, with considerable uncertainty in the magnitude of the estimated forcings of the latter. Although aerosol particle water uptake is well defined for inorganic compounds, the effects of the aerosol organic fraction on cloud droplet formation and cloud condensation nuclei (CCN) properties are relatively poorly characterised, due to the large number of organic compounds present in atmosphere and their highly complex influences on properties such as water solubility and surface tension.This thesis presents extensive field measurements of CCN/aerosol hygroscopicity from three different environments, together with a novel error model, which has been developed to propagate instrumental uncertainties from measurements in the sub- and supersaturated regimes through to commonly used data products used in large-scale models. This study illustrates that a single hygroscopicity framework is not able to reconcile the measurements within errors, for different measurement environments. The sensitivity of this type of reconciliation study was assessed using several different scenarios, making different assumptions in each case; sensitivity tests using a 'typical' regional aerosol particle water uptake or number-size distribution, demonstrate that it is not possible to apply a constant correction to data to guarantee reconciliation, that the best reconciliation was achieved for size-resolved high-temporal water uptake and aerosol number-size distribution data, and that the application of single-parameter hygroscopicity models requires further examination. It is concluded that high-temporal size-resolved measurements of sub- and supersaturated particle water uptake are fundamental to providing a thorough characterisation of the interaction between atmospheric aerosol and water vapour, and are essential in order to achieve the best possible predictive capability from large-scale models.

Aerosol effects are one of the major uncertainties in assessing global climate change, ecosystem processes and human health. This is because they critically change the balance between the radiation entering and leaving the atmosphere, as well as influencing cloud formation and having direct effects on biological systems e.g. through the respiratory system. It is the direct radiative effects of aerosol that are the focus of this work. The Aerosol Optical Depth (AOD) is a measure of the extinction of radiation by aerosol throughout the depth of the atmosphere. It is wavelength dependent and is traditionally measured at a number of visible wavelengths, but there is little AOD data available at UV wavelengths especially in the UVB. The Brewer spectrophotometer makes direct sun measurements in the UV spectral range, which can in principle be used to calculate AOD at those wavelengths using a form of Beer's law. This work explores the capabilities of the Brewer for UV AOD measurements and applies the results to data from the Tropics and temperate mid-latitudes. Instrument specific weighting functions were tested for their ability to improve the AOD retrieval, but while they changed the partitioning of absorption between ozone and SO2, they had negligible effect on the resulting AOD. After correcting the existing Brewer software for AOD retrieval, data from Manchester UK were compared with independent measurements of AOD, and measurements from the Manchester instrument were also evaluated against a standard Brewer on location in Spain. The inter Brewer comparisons were consistent with differences of the order 6-10%, while comparison with independent methods was qualitatively consistent, but absolute differences were of the order 10-30%. This might partially be attributed to wavelength mismatches between the different methods, and assumptions in the various methods of calculating the AOD.Following the validation exercise the AOD was retrieved from Brewer instruments, using standard weighting functions, in Manchester from 2000- 2008 and Reading from 2003-2008. Based on this work in the UK, the method was then applied to data from Malaysia (1998-2007), where the climate is totally different to that of the UK. The AOD data obtained from the UK and from the Tropics have been compared. Kuala Lumpur, Malaysia gave the highest average AOD values probably due to it being a developing city with high pollution levels indicating a human impact on climate change. Brewer AOD measurements obtained at a narrow range of wavelengths were then used to calculate Angstrom parameters by applying Volz Method. The results, often generating a negative alpha, were deemed unreliable at the UK sites. This was largely attributed to the high solar zenith angle and low signal to noise of the direct sun measurement, exacerbated by a limited number of clear sky measurements available for the work. However, calculation of Angstrom parameters was more successful in Malaysia due to a low solar zenith angle, high intensity, and greater frequency of truly could free sky. Results indicated that aerosol particles in the capital Kuala Lumpur show a clear domination by fine mode. This domination is probably caused by urban pollution, mainly from road traffic, industrial and anthropogenic activities, which is consistent with a large capital city undergoing rapid development.Thus the capabilities and limitations of the Brewer spectrophotometer to provide both AOD data at UV wavelengths, and from those further aerosol properties, has been tested and demonstrated in two contrasting climatic regions. Air mass, limiting the UV signal, and stray-light within the instrument are two of the factors that limit the success of the Brewer for these measurements, which proved more reliable when the sun was high in the sky as in the Tropics.

acase@tulane.edu / This work embraces the fabrication of functional materials through the interactions at interfaces and covers two topics. First, we investigate the assembly of hydrophobically modified polypeptoids (HMPs) with lipid bilayers and the structural transition of lipid bilayers induced by HMPs. Polypeptoids are a class of pseudo-peptidic polymers. Properties such as biocompatibility, biodegradability, enzymatic resistance, and good processibility make polypeptoid a promising material for biotechnological applications. With decyl groups as hydrophobic side chains, HMPs interact with lipid bilayers by inserting the hydrophobes into the lipid bilayers through hydrophobic interaction. The hydrophobe insertion results in the disruption of lipid bilayers and the formation of lipid bilayer fragments containing HMPs and HMP-lipid complexes depending on HMP-to-lipid ratio. These polymer-lipid “rafts” can attach to the bare lipid bilayers forming close-spaced multilamellar structures, with HMPs connecting across the adjacent lipid bilayers. Also, HMP-lipid rafts can significantly increase the solubility of sorafenib in aqueous solution through hydrophobic interaction. The ability to assemble to lipid bilayers and to encapsulate hydrophobic drugs demonstrate the promise of HMP-lipid rafts in the application of drug delivery. The second topic is the rapid fabrication of hollow and yolk-shell functional materials through an aerosol assisted synthesis. Materials with hollow and yolk-shell structures have potentials in many applications, such as catalysis and energy storage. But the fabrication of such materials often suffers time-consuming and tedious procedures, which limits the practical application of these materials. We first demonstrated the rapid fabrication of hollow and yolk-shell Fe2O3 microspheres for enhanced photo-Fenton reactions. The placement of iron salts on the external surface of a carbonaceous microsphere generated from an aerosol droplet allows the formation of a Fe2O3 capsule by calcination, where colloid particles can be encapsulated. The Fe2O3 microspheres show significant enhancement in the photo-Fenton reaction. We then illustrated the fabrication of hollow and cage-like mesoporous Fe2O3/SiO2 microspheres. Through salt bridge effect, iron salts and cationic surfactants form colloidal aggregates which are locked within a rapidly formed SiO2 shell during the aerosol process. Sucrose as a pore generating agent leads to the formation of mesopores in the shell, which was proven favored features for CO2 capture. / 1 / Yueheng Zhang

This study was performed to compare the delivery of the antimicrobial gentamicin to the respiratory tract of adult horses following aerosol and intravenous administration. Nine adult horses were used in a crossover design. Aerosol administration of gentamicin was performed using a close fitting facemask and an ultrasonic nebulizer. Intravenous gentamicin was administered via a jugular venous catheter. Samples of pulmonary epithelial lining fluid were collected by bronchial lavage performed at 0.5, 4, 8 and 24 hours after gentamicin administration. All samples were analyzed for gentamicin concentration, and cytologic examination was performed on aliquots of bronchial lavage fluid from times 0.5, 8 and 24 hours. Comparisons were made using the Wilcoxon signed-rank test. The bronchial lavage fluid gentamicin concentration after aerosol administration was significantly greater (p<0.05) than after intravenous administration at 0.5, 4, and 8 hours. The bronchial lavage fluid total nucleated cell count increased significantly (p<0.05) from 0.5 to 24 hours following both routes of gentamicin administration, with the increase observed following aerosol administration being significantly greater (p<0.05) than that observed following intravenous administration. A significant increase in neutrophil count was detected between bronchial lavage fluid samples taken at 0.5 hours and 24 hours, regardless of route of gentamicin administration. We conclude that aerosol administration of gentamicin to the equine respiratory tract achieves bronchial lavage fluid gentamicin levels that are significantly higher than levels obtained following intravenous administration for at least the first 8 hours after administration, while inciting a mild inflammatory response. / Master of Science