No description available.

No description available.

The presence of toxic metals and organic substances in environmental waters has serious implications for human health. The extraction and pre-concentration of these substances from 'ater samples is a core component of their determination. 'Ibis thesis introduces newly developed nanoscavengers for the extraction and pre-concentration.of harmful substances - om water samples~ using a new s,olid phase dispersion extraction technique (SPDE). This technique is based on the dispersion of 250 nm diameter, mqdified silica particles (nanoscavengers) in water samples, to extract the analytes. Uniform silica particles were synthesised by both a conventional sol-gel process and a new spray technique. The parameters influencing their formation were investigated, and it was found that the concentration of tetraethoxysilane (TEOS), ammonia, solvent, temperature and agitation, can all affect the final particle size. The silica particles were characterized by scanning electron microscopy (SEM) and particle size analysis. Under optimal conditions, very uniform and monodisperse silica spherical particles, having the target diameter of 250 nm 8 nm), were obtained. Different types of nanoscavenger were synthesised by modification of the silica with a number of silane coupling agents, such as N-[3-(trimethoxysilyl)propyl]-ethylenediamine and its dithiocarbamate, 3-mercaptopropyltrimethoxysilane, octadecyltrichlorosilane and octadecyltrimethoxysilane. The modification step was carried out by two different processes: the modification of pre-formed 250 nm silica particles and by a single-pot synthesis. Both processes showed a successful immobilization of silylating agents with a variation of loading. The amino-nanoscavenger, when applied to the pre-concentration of copper from water gave a recovery of 98%. A dithiocarbamate-nanoscavenger was applied to the preconcentration of cadmium, copper~ lead and nickel and recoveries were 99, 97, and 92%, respectively. Inorganic mercury and arsenic were pre-concentrated using a mercaptonanoscavenger, and recoveries of 106 and 96% were obtained, respectively. The collection of organic species using the C1S-nanoscavenger resulted in the recovery of 70% di-n-butyl phthalate. Herbicides such as Atrazine, Ramrod, Diuran and Propazine were recovered efficiencies of 66, 78, 82 and 59%, respectively. A dual-functionalitynanoscavenger was employed for the pre-concentration of 22 chlorinated pesticides, and recoveries varied from 70 to 100%. Polynuclear aromatic hydrocarbons (PAHs) were also pre-eoncentrated from water samples using this dual-functionality-nanoscavenger, and recoveries of 13 PARs varied from 70 to Nanoscavenger based solid phase dispersion extraction 'SPDE' offers many advantages over conventional approaches. These include the minimization of regents, transportability, field application and efficiency.

No description available.

No description available.

The Arctic is a region particularly susceptible to rapid climate change. General circulation models (GCMs) suggest a polar amplification of any global warming signal by a factor of about 1.5 due, in part, to sea ice feedbacks. The dramatic recent decline in multi-year sea ice cover lies outside the standard deviation of the CMIP3 ensemble GCM predictions. Sea ice acts as a barrier between cold air and warmer oceans during winter, as well as inhibiting evaporation from the ocean surface water during the summer. An ice free Arctic would likely have an altered hydrological cycle with more evaporation from the ocean surface leading to changes in precipitation distribution and amount. Using the U.K. Met Office Regional Climate Model (RCM), HadRM3, the atmospheric effects of the observed and projected reduction in Arctic sea ice are investigated. The RCM is driven by the atmospheric GCM HadAM3. Both models are forced with sea surface temperature and sea ice for the period 2061-2090 from the CMIP3 HadGEM1 experiments. Here we use an RCM at 50km resolution over the Arctic and 25km over Svalbard, which captures well the present-day pattern of precipitation and provides a detailed picture of the projected changes in the behaviour of the oceanic-atmosphere moisture fluxes and how they affect precipitation. These experiments show that the projected 21stCentury sea ice decline alone causes large impacts to the surface mass balance (SMB) on Svalbard. However Greenland’s SMB is not significantly affected by sea ice decline alone, but responds with a strongly negative shift in SMB when changes to SST are incorporated into the experiments. This is the first study to characterise the impact of changes in future sea ice to Arctic terrestrial cryosphere mass balance.

No description available.

Geoengineering, intentional large-scale manipulation of the Earth-system, has been proposed as a means to ameliorate the impacts of global warming. There are two approaches; Carbon Dioxide Removal (CDR) geoengineering which would reduce C02 concentrations and address the cause of climate change, and Solar Radiation Management geoengineering which would cool the planet by reducing the amount of sunlight absorbed by the planet without affecting CO2 concentrations. This thesis reviews geoengineering and investigates the direct and indirect climate effects of SRM geoengineering. The sunshade geoengineering scheme, which would reduce the solar insolation, is investigated in depth in this thesis. Sunshade gcoenginecring may be implemented at a range of C02 concentrations and it would also offer control over the amount of insolation that reaches the planet. Both of these aspects of sunshade geoengineering are investigated using a climate model and it is found that sunshade geoengineering would ameliorate most of the effects of elevated C02 but would cause heterogeneous changes in climate; globally reducing precipitation and leaving many regions with a climate markedly different from the pre-industrial. The regional climate effects of sunshade geoengineering are found to vary linearly with both the solar insolation reduction and the C02 forcing applied. An off-line ice-sheet model is used to investigate the indirect climate effects of different strengths of sunshade geoengineering on the Greenland Ice-Sheet at quadrupled CO2 levels, to determine whether sunshade geoengineering could stabilize the ice-sheet and reduce sea-level rise. It is found that the ice-sheet would eventually collapse at quadrupled C02 levels but that strong sunshade geoengineering can stabilize the entire ice-sheet or at weaker implementations, part of the ice-sheet could be maintained. A comparison is made between the urban, crop and desert surface albedo geoengineering schemes, which would have a highly heterogeneous radiative forcing effect, and sunshade gcocngineering, which would have a more homogeneous radiative forcing effect. This comparison shows that regional geoengineering forcing, if it is relatively weak, may provide local and regional cooling and other benefits but for stronger land albedo forcing there are large shifts in precipitation, including substantial reductions in monsoon precipitation, which could prove to be more harmful than the effects of global warming. Finally, to determine the robustness of the results in this thesis, a perturbed parameter ensemble is developed, tested and then used to investigate the effects of parametric uncertainty on the sunshade geoengineering climate effects. The perturbed parameter results agree with much of what was found in other parts of the thesis about sunshade geoengineering but finds that there is uncertainty in the resid- ual warming at the poles, the magnitude of the northward shift of the ITCZ, and that the standard climate model may have overestimated the effectiveness of sunshade geoengineering at maintaining the Greenland Ice-Sheet. Overall, I find that SRM geoengineering could offer a considerable amelioration of the impacts of global warming; however, the climate would differ substantially from a low-C02 climate, and there would be winners and losers as a result. Regional SRM geoengineering would have very heterogeneous climate impacts, potentially causing large problems but could offer a large degree of control over the climate. 'Whether the political risks that control over the climate could bring would outweigh the potential climate benefits, is an open question.

No description available.

This thesis examine the effects of natural convection on the mixing of localised and distributed discharges into the ocean. It comprises two studies. The first study investigates the behaviour of a localised release, such as a discharge of wastewater from a coastal outfall. Wastewater rises as a buoyant jet above the outfall and then spreads out horizontally at the sea surface to form a cloud of pollutants. We are interested in the natural convection that develops at the interface between a colder and less salty cloud and the underlying warmer and saltier sea water. Convection arises here as a result of the different diffusivities of heat and salt and the opposing contributions of heat and salt to the vertical density profile. This type of natural convection is called double-diffusive convection. We carry out new laboratory experiments and develop a theoretical model to couple the motion of the buoyant jet with the double-diffusive transport. Our results show that the pollutant concentration in the cloud near the jet can increase by 100% compared to the magnitude expected in the absence of double-diffusive convection, in the time-scale required for the cloud of pollutants to reach the coast. The second study investigates the behaviour of a distributed discharge, such as the diffuse flow of hot and mineral-rich sea water through porous rocks at hydrothermal sites on the ocean floor. We are interested in the mechanisms of development of natural convection at the interface between this buoyant, hot sea water and the cold sea water above in the presence of both a density difference and a net flow. We carry out laboratory experiments to measure the velocity field and visualize the growing interfacial instability using PIV and LIF. We also develop a linear stability analysis and a full numerical solution for the system.