Dust originating from dry lakes contributes harmful and toxic elements to downwind urban areas and mountain snowpack that is compounded by local contaminant inputs from anthropogenic sources. To evaluate dust contributions to an urban area from regional playas, we sampled playa dust sources, urban dust deposition, and snow dust deposition in central Utah, USA. Samples were analyzed for grain size, mineralogy, and chemistry. Bulk mineralogy between playa, urban, and snow dust samples was similar, with silicate, carbonate, and evaporite minerals. Grain size distribution between fine playa, urban, and snow dust particles was also similar. Elements found at high concentrations in playas include Li, Na, Mg, Ca, Sr, and U, and most other elements were found at higher concentrations in urban and snow deposition samples. Particularly enriched elements in dust deposition include Cu, Se, Ag, Cd, Sb, and La, which are sourced from industrial activity, mining, and vehicular emissions and wear. Based on results from mass balance modeling, a large majority of the dust mass deposited on the Wasatch Front is from playa sources. Urban and playa dust sources largely remain constant seasonally, although spikes in playa-associated element concentrations during a particular seasonal sample may indicate frequent and/or more intense dust events. Among the highly environmentally available elements B, Ca, Sr, and U, are Cd and Se, both of which present toxicity concerns for humans and environments. This is the first study describing heavy metal contamination and sources in Utah, USA.

No description available.

In this thesis, an integrated wind erosion assessment and prediction system has been developed. This system couples a physically based dust emission scheme, a high resolution limited area weather prediction model, a dust transport model, and a high resolution GIS (Geographic Information System) database. A simple expression for particle threshold velocity has been derived by considering the force balance of a single particle resting on the surface. Theoretical analyses have been performed to confirm that the main mechanism for dust uplifting is sand saltation bombardment rather than direct aerodynamic entrainment. A new model for dust emission by saltation bombardment is proposed and validated against experimental data. Preliminary sensitivity tests for the new dust emission model have been carried out by examining the dependence of dust emission rate on a range of parameters. The transport of airborne dust is modelled by using the particle mean concentration equation. The time-dependent advection terms are discretized and solved numerically by a multi-dimensional wave-propagation slope-limiter scheme. Some computational features of the integrated model are discussed in terms of its coupling, module decomposition, data handling and efficiency. A systematic sub-grid treatment is designed to extract soil surface parameters from the GIS database for large scale modelling. The integrated system is applied to investigate the February 1996 dust storms over the Australia continent. The simulated wind erosion pattern and intensity are in good agreement with available meteorological records and satellite images. It reveals that the system can be used to identify areas and periods under wind erosion threat as well as the responsible environmental factors.

Using Vertical Feature Mask (VFM) data from Cloud - Aerosol Lidar Infrared Pathfinder Satellite Observations (CALIPSO), I have documented 3-dimensional (3D) structures in occurrence probabilities of aerosol over a broad region of Africa, the Atlantic, Europe, and Americas. The 3D structures illustrate the seasonal means and seasonal cycle in the zonal and meridional variability of the vertical profiles of mineral dust, biomass burning smoke, and polluted dust (external mixture of dust and smoke), and their emissions sources and transport pathways. Emission sources vary by geographical location. The persistent Saharan dust source is evident throughout the year and observed and recorded by CALIPSO 70-80% of the time over Africa. Horizontal and vertical occurrence of dust is variable in time with maximum heights and westward transport occurring in boreal summer and minimum heights and transport occurring in boreal winter. The southern African biomass burning source is also evident throughout the year, through westward transport over the Atlantic is only evident in boreal summer and fall; mixing with dust over the continent limits westward transport of pure smoke to the continent in winter and spring. Other smaller smoke and dust sources are discussed. The role of the Inter-Tropical Convergence Zone (ITCZ) in limiting the southward transport of dust and northward transport of smoke over Africa is demonstrated. Surprisingly, the highest probability of polluted dust is found in the ITCZ, even though the probabilities of dust and smoke are low. Wind trajectories reveal smoke of southern African origin is transported northward at the lower levels, but rarely penetrating through ITCZ rainband while Saharan dust is transported southward at higher levels, crossing the ITCZ frequently. This quasi-circulation of aerosol is shown to be the mixing mechanism of dust and smoke into polluted dust in the area of the ITCZ.

No description available.

Over the past years, catastrophic dust explosion incidents have caused numerous injuries, fatalities and economical losses. Dust explosions are rapid exothermic reactions that take place when a combustible dust is mixed with air in the presence of an ignition source within a confined space. A variety of strategies are currently available to prevent dust explosion accidents. However, the recurrence of these tragic events confirms flaws in process safety for dust handling industries. This dissertation reports advances in different approaches that can be followed to prevent and mitigate dust explosions. For this research, a 36 L dust explosion vessel was designed, assembled and automated to perform controlled dust explosion experiments. First, we explored the effect of size polydispersity on the evolution of aluminum dust explosions. By modifying systematically the span of the particle size distribution we demonstrated the dramatic effect of polydispersity on the initiation and propagation of aluminum dust explosions. A semi-empirical combustion model was used to quantify the laminar burning velocity at varying particle size. Moreover, correlations between ignition sensitivity and rate of pressure rise with polydispersity were developed. Second, we analyzed the effect of particle size and crystalline levels in the decomposition reactions of explosion inhibitor agents (i.e., phosphates). We fractionated ammonium phosphate- monobasic (NH_4H_2PO_4) and dibasic ((NH_4)_2HPO_4) at different size ranges, and synthesized zirconium phosphate (Zr(HPO_4)_2·H_2O) at varying size and crystalline levels. Particle size was found to be crucial to improve the rate of heat absorption of each inhibitor. A simplified model was developed to identify factors dominating the efficiency of dust explosion inhibitors. Finally, we conducted computational fluid dynamic (CFD) simulations to predict overpressures in dust explosions vented through ducts in large scale scenarios. We particularly focused on the adverse effects caused by flow restrictions in vent ducts. Critical parameters, including ignition position, geometric configuration of the vent duct, and obstructions of outflow such as bends and panels were investigated. Comparison between simulation and experimental results elucidated potential improvements in available guidelines. The theoretical analyses complemented the experimental work to provide a better understanding of the effects of particle size on the evolution of dust explosions. Furthermore, the validation of advanced simulation tools is considered crucial to overcome current limitations in predicting dust explosions in large scale scenarios.

The purpose of this study is to evaluate the relative advantages and disadvantages of two approaches for estimating oral bioaccessibility using a physiologically-based extraction technique (PBET): a simple gastric phase simulation and a two-phase gastrointestinal simulation. Bioaccessibility estimates of six metals prevalent in Canadian contaminated sites (zinc, lead, cadmium, copper, nickel, and chromium) were compared using the gastric phase simulation alone and the complete gastrointestinal simulation. Samples included vacuum dust samples from 33 homes, certified dust and soil reference materials, and a house dust control sample. Bioaccessibility measurements using the gastric phase simulation were greater than or equal to measurements obtained using the gastrointestinal simulation for the six studied metals. This research found that for the six studied metals, a simple simulation of the gastric phase provides the most conservative and cost-effective approach for estimating oral bioaccessibility of ingested metals.

In this study the aim has been to investigate whether the Great Depression in the 1920s and 1930s affected farmers in the United States financially and under such circumstances try to derive its financial extent. A qualitative comparative approach has been the chosen method, where the analysis section consists of data from official documents. The applied theory is economics professor Edward Barber's theory that the growth and development of economies is based on an opportunistic expansive exploitation of natural resources. The essay has been limited to examining the three most monetarily valuable cereal products and livestock. I concluded that the depression was partially responsible for fluctuations in the farmers' financial statements. An estimated $1,568 billion and another $140 million was lost. The financial loss was probably higher due to the chosen limitations of the essay, although the three most valuable cereals and livestock animals encompassed the value development relatively well.

All materials in dust form pose an increased risk of accidental deflagration, or explosion. For workplace safety, this risk of deflagration for a solid particulate sample is characterized through specialized dust explosibility testing systems. These systems disperse a cloud of powder inside a spherical chamber via a pressure gradient, where a timed ignition occurs. The accuracy of measurements taken during this process are predicated upon the assumption that the cloud of powder is uniformly distributed during the ignition period. Metal additive manufacturing (AM) is a rapidly expanding technology that, in some cases, involves heavy metal powders that do not disperse well in standard explosibility testing vessels. Consequently, there is a need to validate explosibility data for heavy metal powder blends to ensure that the dust sample is adequately dispersed in the chamber at the time of ignition. This thesis provides a method for employing optical dust probes to determine the concentration of a tungsten metal AM powder cloud inside an enclosed vessel. Optical dust probes are devices that measure light transmission through an attenuating medium, in this case a cloud of powder, and utilize Bouguer-Beer-Lambert (BBL) law to determine the concentration of particles. This thesis summarizes and synthesizes the assumptions and limitations of BBL law when used with optical dust probes, drawing from multiple published works with varying applications. The bounds of the average extinction efficiency are discussed, especially with respect to when the extinction paradox can be applied. Ultimately, it is determined that the BBL law can only be applied in this study to determine extinction coefficients, and that calculating a specific mass concentration value is theoretically misguided without specific modifications to the experimental setup. The extinction coefficients measured via an optical dust probe and a separate image analysis method are compared. Although no correlation could be established due to the limitations of this experimental setup, specific modifications are suggested that would enable this methodology to be used in future applications.

Increasing commercial and military aircraft operations in arid environments are increasing the likelihood of sand and dust ingestion. Turbine engines are particularly susceptible to the ingestion of sand and dust, which can erode cold-section components and deposit onto hot-section components. Ultimately, the erosion and deposits will shorten the operational lifespan of these engines and limit their availability thereby increasing maintenance costs and risking safety. Mitigating these risks has become more prevalent in recent years due to increasing combustion temperatures in effort to increase fuel efficiency. Increasing combustion temperatures directly increases deposit formation onto hot-section components. Monitoring deposit formation on existing turbine engine platforms and improving deposit resilience on new designs has been the industry focus for the last two decades. This study focused on statistically modeling the initial onset of microparticle deposits onto an analogous hot-section surface. Generally, as deposits accumulate onto a hot-section surface, the existing deposit formation is more likely to bond with incoming particulate at a faster rate than an exposed bare surface. Predicting the initial deposits onto a bare surface can determine the accelerated deposition rate depending on subsequent particulate impinging onto the surface. To emulate the initial deposits, a HASTELLOY® X test coupon was exposed to 20 μm to 40 μm samples of Arizona Road Test Dust (ARD) at varying loadings and aerosol densities. The Virginia Tech Aerothermal Rig was used for all test scenarios at flow-particle temperatures between 1000°C to 1100°C. Several statistical models were developed as a function of many independent variables, culminating with a final sticking probability (SP) model. Overall, the SP of individual ARD particulate is a primary function of flow-particle temperature and normal impact momentum. Tangential impact momentum of a particle will decrease the SP, while surface temperatures reaching isothermal conditions with the flow will increase SP. However, there are specific cases where lower surface temperatures and high particle temperatures result in a high SP. Particle size was a strong predictor of SP where particles between 10 μm to 19 μm were 5 to 10 times greater than the 19 μm to 40 μm range. Additional studies will be necessary to examine some additional parameters that become more prominent with smaller particle sizes. Ultimately, the intention of the models is to assist turbine engine designers to improve resilience to deposit formation on hot-section components. / PHD