Dust-climate interaction over the Middle East and North Africa (MENA) has long been studied, as it is the "dustiest" region on earth. However, the quantitative and qualitative understanding of the role of dust direct radiative effect on MENA climate is still rudimentary. The present dissertation investigates dust direct radiative effect on MENA climate during summer with a special emphasis on the sensitivity of climate response to dust shortwave absorption, which is one of the most uncertain components of dust direct radiative effect. Simulations are conducted with and without dust radiative effect, to differentiate the effect of dust on climate. To elucidate the sensitivity of climate response to dust shortwave absorption, simulations with dust assume three different cases of dust shortwave absorption, representing dust as a very efficient, standard and inefficient shortwave absorber. The non-uniformly distributed dust perturb circulations at various scales. Therefore, the present study takes advantage of the high spatial resolution capabilities of an Atmospheric General Circulation Model (AGCM), High Resolution Atmospheric Model (HiRAM), which incorporates global and regional circulations. AMIP-style global high-resolution simulations are conducted at a spatial resolution of 25 km. A significant response in the strength and position of the local Hadley circulation is predicted in response to meridionally asymmetric distribution of dust and the corresponding radiative effects. Significant responses are also found in regional circulation features such as African Easterly Jet and West African Monsoon circulation. Consistent with these dynamic responses at various scales, the tropical rainbelt across MENA strengthens and shifts northward. Similarly, the temperature under rainbelt cools and that over subtropical deserts warms. Inter-comparison of various dust shortwave absorption cases shows that the response of the MENA tropical rainbelt is extremely sensitive to the strength of shortwave absorption. Further analyses reveal that the sensitivity of the rainbelt stems from the sensitivity of the multi-scale circulations that define the rainbelt. Importantly, the summer precipitation over the semi-arid strip south of Sahara, including Sahel, increases in response to dust radiative effect. The maximum response and sensitivity are predicted over this region. The sensitivity of the responses over Sahel, especially that of precipitation, is comparable to the mean state. Locally, the precipitation increase reaches up to 50% of the mean, while dust is assumed to be a very efficient absorber. As the region is characterized by the "Sahel drought", the predicted precipitation sensitivity to the dust loading over this region has a wide-range of socioeconomic implications. The present study, therefore, suggests the importance of reducing uncertainty in dust shortwave absorption for a better simulation and interpretation of the MENA climate in general, and of Sahel in particular.

Dust aerosol emission is a critical topic in agriculture, occurring either by aeolian process from bare or sparsely vegetated cropland or as fugitive emission during tilling, harvest and many other farming activities. Aerosols, which are in the case of agriculture either mineral dust, organic particles or a mixture, are known for impacting human health, cloud formation and ultimately, the earth’s climate and ecosystem. Coupled atmosphere and aerosol transport models are commonly used to study aerosol dispersion in the atmosphere, but so far, agricultural sources are under-represented. Hence, estimations of these emissions’ actual impact are still somewhat uncertain regarding their seasonality, spatial distribution and the fraction of the global aerosol load. To fill this gap, this study aims at identifying suitable approaches for modelling aeolian emissions from sparsely vegetated cropland and fugitive emissions from tilling. Fugitive emissions are challenging since they mainly depend on human activity that is not predictable, but observed events can be used as case studies. For this, a Lagrangian particle dispersion model was chosen, which can trace the trajectory of individual particles in the emitted dust plume. So the particle model “Itpas” was developed to tackle fugitive emissions and to be capable of simulating the complex turbulent mixing of dust particles inside the atmospheric boundary layer. This model was used to simulate a case study based on measured tilling emissions, showing the particle dispersion for a stable and unstable stratified boundary layer. It was shown that within a stably stratified boundary layer, the dust plume is restricted to the near-source region. In contrast, emissions in unstable boundary layers go into long-range transport. This illustrates the spatial range a single tillage operation can have an impact. Aeolian dust emissions are controlled by the wind. For cropland, the emission variability is caused mainly by the frequently changing vegetation cover. Emissions can only occur in the time between tillage and newly grown crops or during drought periods. A parametrisation based on high-resolution satellite observations of the vegetation cover was created to include this process into a model. With this, a new dust emission scheme for cropland emission was developed for the model system COSMO-MUSCAT. In a case study of a dust outbreak from cropland in Poland in 2019, the model’s ability was tested extensively on multiple spatial resolutions. Validation against satellite-measured AOD, ground-measured PM10 and the vertical profile of the PollyNET lidar in Warsaw showed an overall good agreement of the model simulation with the observations. In the framework of this thesis, one dedicated model approach was developed for both the fugitive emissions and the aeolian emissions and validated upon case studies. These approaches could help better understand agricultural dust emissions, their spatial distribution, seasonality and, ultimately, global impact.

Dust storms are one of the natural hazards, which have increased in frequency in the recent years over Sahara desert, Australia, the Arabian Desert, Turkmenistan and northern China, which have worsened during the last decade. Dust storms increase air pollution, impact on urban areas and farms as well as affecting ground and air traffic. They cause damage to human health, reduce the temperature, cause damage to communication facilities, reduce visibility which delays both road and air traffic and impact on both urban and rural areas. Thus, it is important to know the causation, movement and radiation effects of dust storms. The monitoring and forecasting of dust storms is increasing in order to help governments reduce the negative impact of these storms. Satellite remote sensing is the most common method but its use over sandy ground is still limited as the two share similar characteristics. However, satellite remote sensing using true-colour images or estimates of aerosol optical thickness (AOT) and algorithms such as the deep blue algorithm have limitations for identifying dust storms. Many researchers have studied the detection of dust storms during daytime in a number of different regions of the world including China, Australia, America, and North Africa using a variety of satellite data but fewer studies have focused on detecting dust storms at night. The key elements of this present study are to use data from the Moderate Resolution Imaging Spectroradiometers on the Terra and Aqua satellites to develop more effective automated method for detecting dust storms during both day and night and generate a MODIS dust storm database. / Libyan Centre for Remote Sensing and Space Science / Appendix A was submitted with extra data files which are not available online.

M. Tech. (Department of Metallurgical Engineering, Faculty of Engineering and Technology), Vaal University of Technology. / Dust generated during comminution of end of life printed circuit boards (PCB), typically having d80 of 212 μm, contains copper and gold up to 6.32 % and 635 g/ton, respectively. The dust particles being highly diverse in material makeup, an hydrometallurgical processing scheme able to selectively recover target values was studied. Use of mineral acids will result in multiple metal dissolution which will complicate subsequent solution treatments. Detailed characterization of the dust was first carried out, and leaching scheme were thereafter investigated to selectively recover gold and copper from the dust, in three leaching stages. Different conditions of ammonia and thiourea leaching were investigated to optimize agitation speed, reagents concentration, temperature and leaching time. The leaching kinetics of these elements from the dust under different prevailing leaching conditions were studied. Elemental composition of the dust size fractions indicates metal contents generally increase with decreasing dust particle size, down to – 53 μm size, which contains up to 635 g/ton Au, 25.43 % Fe, and 1.40 % Cu, compared to 51 g/ton Au, 3.07 % Fe and 6.32 % Cu in the 150–212 μm fraction. Thermodynamically, under oxidative ammonia leaching, zinc and copper ammine complex is feasible, yet zinc recovery is low. For 75 – 106 μm dust size, 2 M NH4OH, 17.5 M H2O2, 1 atm. pressure and 400 rpm in Parr reactor, Cu and Zn recoveries were 92 % and 50 %, while the activation energies evaluated within 283 – 313 K gave 47.39 kJ/mol and 33.12 kJ/mol. The kinetic analysis for copper leaching gave best correlation coefficient (R2) of 0.9804 when fitted into the chemical control model, and the rate constant was 4.4 x 10-3 at 313 K. The presence of base metals frustrates direct gold recovery from the dust using thiourea with sulphuric acid and hydrogen peroxide. Therefore, the residue obtained from the first stage copper leach was acid washed to remove iron and other residual base metal contents with 5 M H2SO4, at 333 K, 400 rpm for 2 hours. Recovery analysis shows that about 75-98 % Fe, 54-65 % Zn and 96-98 % Ni were recovered under this condition while Cu was less than 7 % at all PSDs; copper having been selectively removed at the first stage. Using 75 – 106 μm dust fraction, gold recovery was optimum when the acid wash residue was leached with 0.5 M thiourea (SC(NH2)2), 0.5 M sulphuric acid (H2SO4), 0.1 M hydrogen peroxide (H2O2) under 1 atm. pressure, 298 K and 400 rpm for 4 hours. The recovery was 98 % Au. Using this optimum for other size fractions, over 98 % gold was recovered from 150–212 μm, 106 – 150 μm and 75 – 106 μm dust while 71 % and 68 % Au were recovered from 53 – 75 μm and – 53 μm respectively. The lower recovery at the finest sizes can be due to the quantity of the gold contents deported in this particle size, which will require higher reagent dosage. The kinetic analysis gave best correlation coefficient (R2) of 0.99 when fitted to the chemical control leaching model. From this data, a process flowsheet was proposed to give separate streams rich in copper and gold values from the processed dust, with detailed processing parameters. This is considered a readily scalable process solution for retrieving gold and copper from PCB dust.

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Three studies were conducted to better understand the current status of the industry and create a design process and taxonomy. Study 1 assessed current industry usage of dust control technologies and stakeholder perceptions in the concrete and masonry trades. Study 2 was similar but assessed emission control technologies in the asphalt roofing trade. Study 3 used the information from studies 1 and 2 to select a tool for further evaluation. The handheld cutoff concrete saw was chosen. An iterative design process was utilized to evaluate the saw. The design process and subsequent usability inspection engendered a taxonomy, or set of design recommendations can be applied to large handheld powered tools. / Ph. D. / Three studies were conducted to better understand the current perceptions of risks associated with the construction industry and create a process for designing tools that mange the associated risks. Study 1 and Study 2 assessed current industry use of technologies for managing health hazards present when working in the concrete, masonry, and asphalt roofing industries; and the interested party’s perceptions of the industries. Study 3 used the information from Studies 1 and 2 to select a tool for further evaluation. The handheld cut-off concrete saw was chosen. An iterative design process was utilized to evaluate the saw. The design process and subsequent usability test created a set of design recommendations which can be applied to large handheld powered tools. A telephone survey was conducted to assess the concrete, masonry, and asphalt roofing industries. The survey measured decision makers’ perceptions of health hazard control technologies. Finally, it assessed business factors affecting adoption of the control technologies and projects specifying the use of health hazard control technologies. The results show the concrete and masonry industries understand the risks associated with working in the industry and are more likely to adopt health hazard management technologies. The asphalt roofing industry is unsure if they view heated asphalt to be a health hazard and are more resistant to adopting current technologies. There are more projects specifying the use of control technologies in concrete and masonry and a decreasing number of projects are specifying the use of control technologies in asphalt roofing. The business factors for adopting technologies are the same across industries, specifically worker safety and government regulation. Those looking to have an impact on the construction industry should focus on the concrete and masonry industries over asphalt roofing. In the final study, a design process and guidelines were created for large handheld powered equipment. The researcher used an iterative design process whose goal was to better equip industry with a dust control device, specifically a vacuum based system for the gasoline powered handheld cut-off concrete saw. Results from Studies 1 and 2 influenced the direction of the design process. The design did not yield a prototype fit for testing, so the researcher assessed the usability of a commercially available system. The results were transformed into design guidelines for anyone interested in creating better hazard controls for similar power tools. The guidelines created are: have clear symbols, efficiently provide feedback, provide feedback when attaching parts, make attaching parts easy, have efficient design to reduce dangers inherent with the tool, increase visibility, reduce overexposure to dangers, ensure it is easy to move, and enable a wide variety of users to be able to use the saw. The process used to design the prototype can be used to design similar large handheld powered tools. The design process starts with looking at how the tool is currently used, then brings stakeholders together to discuss the problem, then create prototypes, and finally test the prototypes for performance and/or usability which will create the design guidelines.

An investigation into the light scattering properties of Saharan dust grains is presented. An electrodynamic trap has been used to levitate single dust particles. By adjusting the trap parameters, partial randomisation of the particle orientation has been introduced. While levitated, the particles were illuminated by a laser, and a rotating half-wave retarder enabled selection of vertically or horizontally polarized incident light. A laser diffractometer and linear photodiode array have been used to measure intensity at scattering angles between 0.5° and 177°. Combining these measurements with Fraunhofer diffraction as calculated for a range of appropriately-sized apertures allows the calculation of the phase function and degree of linear polarization. The phase functions and degree of linear polarisation for four case study particles are presented - the phase functions are found to be featureless across most of the scattering region, with none of the halo features or rainbow peaks associated with regularly shaped particles such as hexagonal columns or spheres. Particle models comprised of large numbers of facets have been constructed to resemble the levitated particles. Utilizing Gaussian random sphere methods, increasing levels of roughness have been added to the surfaces of these models. A Geometric Optics model and a related model, Ray Tracing with Diffraction on Facets, have been modified to calculate scattering on these particle reconstructions. Scattering calculations were performed on each of these reconstructions using a range of refractive indices and two rotation regimes – one where the orientations of the reconstructed particle were limited to match those observed when the particle was levitated, and one where the orientation was not limited. Qualitative comparisons are performed on the phase functions and degree of linear polarization, where it is observed that the addition of roughness to the modelled spheroids causes the computed phase functions to increasingly resemble those from the levitated particles. Limiting the orientation of the particles does not affect the scattering noticeably. The addition of a very small absorption coefficient does not change the comparisons considerably. As the absorption coefficient is increased, however, the quality of the comparisons decreases rapidly in all cases but one. The phase functions are quantitatively compared using RMS errors, and further comparison is performed using the asymmetry parameter.

Följande studie har utförts på begäran av energiföretaget Norrenergi AB, där det finns en önskan att tillförlitlighetssäkra den nuvarande driften av stofttransportsystemet tillhörande två av värmeverkets hetvattenpannor. Studien har undersökt huruvida det finns möjlighet att framförallt minska underhållskostnaderna. Studien har framförallt inriktats mot två stofttransportfläktar som vardera tillhör ett stofttransportsystem, eftersom mycket underhållsarbete lagts på de fläktarna. En jämförelse med andra liknande verk har även utförts då det visats att Norrenergi AB:s lösning av stofttransporten är ytterst ovanlig. Vidare har en analys av fläktarna utförts, vilken visade att de är underdimensionerade för systemet. Det har konstaterats utifrån genomförda SPM-, temperatur- och bullermätningar. Olika typer av lösningar på problemet har undersökts och då på en förändring av hela systemet, alternativt enbart av fläktarna eller lagren till stofttransportfläktarna. Rapporten har utmynnat i flera förslag vilka innefattar en ny systemutformning, installation av nya fläktar samt en uppgradering av det nuvarande systemet, där installation av nya fläktar rekommenderas. / This study has been carried out at the request by the energy company Norrenergi AB. It consists of an analysis on how they can reduce the maintenance regarding two dust transporting fans installed in the flue gas cleaning compartment of their thermal power plant. The study also compares what solutions other plants have regarding the dust-transport. The solution installed at Norrenergi AB was found to be rather unusual. Measurements and calculations have been performed to investigate further what have caused the high maintenance on the fans. The study looks into what upgrades are available to the entire dust transporting system. The result of the study turned into different suggestions, which includes a new configuration of the dust transporting system, and installation of new fans and also an upgrade of the existing dust transporting system. Among the suggestions the final recommendation is the alternative of installing new fans.

A dissertation submitted to the Faculty of Engineering, University of the Witwatersrand, Johannesburg, in fulfillment of the requirements for the degree of Master of Science in Engineering / Regulation 10.24 of the Minerals Act (1991) of the Republic of South Africa is applied for the purpose of preventing the development and propagation of coal-dust explosions in underground coal mines. ( Abbreviation abstract ) / AC2017