No description available.

Dust forecasting has become important to military operations over the past three decades. Rules of thumb have been the primary resource for forecasting dust. In recent years, algorithms for weather models have been created to produce atmospheric dust concentration forecasts and are now coming into use operationally. The question becomes how good are the models and what causes errors in their forecasts? This study examines the accuracy of the U. S. Navy's Coupled Ocean Atmospheric Mesoscale Model dust module during the United Arab Emirates Unified Aerosol Experiment. The study also attempts to determine what causes any error if present. The primary method to verify the model's aerial coverage accuracy is through equitable threat score. Case studies are then conducted to verify the scores and identify sources of any errors identified. Results indicate the model performs well with respect to sourcing dust plumes. Errors in modeled aerial coverage as compared to real world observations appear to be the result of an inability for the model to properly advect suspended dust near the surface layer. Unconfirmed dust plumes in the model seemed to be the result of inaccurate surface characteristics.

The investigation of harmful semi volatile organic compounds (SVOC) in the indoor environment is important because on average people spend over 90% of their time indoors. Lindane, an SVOC which was widely used in the UK until 2004, adsorbs to house dust. House dust acts as a reservoir for such contaminants which are remitted by desorption into the air over time. A method for measuring Lindane air concentrations in a vial using SPME without the use of water or any solvent was developed in order to carry out Lindane adsorption and desorption tests. Dynamic tests were carried out to determine adsorption and desorption coefficients as well as equilibrium time. Adsorption and desorption constants (k1 and k2 respectively) were determined by fitting results from the dynamic adsorption tests to an existing two compartment model described in chapter 2, using the statistical analysis software SPSS (vs16). These dynamic tests were carried out for two size fractions (<20µm and >45µm<63µm) and whole dust samples to determine the effect of size fraction on adsorption. For the >45µm to <63µm, k1 = 0.568h-1 and k2 = 0.047h-1, (standard error 0.119 and 0.030 respectively), for the <20µm fraction, k1 = 1.686h-1, k2 = 0.125h-1 (standard error 1.888 and 0.324 respectively), and the whole dust k1= 2.587 h-1, k2= 0.288 h-1 (standard error 0.514 and 0.113 respectively). Static tests were carried out at equilibrium to establish an adsorption isotherm and obtain partition coefficients for different size fractions. The adsorption constants Ka were 4.2 x 10-4mh-1, 7.67 x 10-5mh-1, and 3.03 x 10-3mh-1 respectively. The desorption constants Kd were 0.125h-1, 0.047h-1, 0.288h-1. The partition coefficients Kp were 4.8 x 101µgm-2, 4.08 x 101µgm-2, 1.05 x 102µgm-2, for the <20µm, >45µm<63µm, and whole dust respectively. The higher Kp value for the smaller <20µm fraction compared to the >45µm<63µm fraction, suggests that Lindane adsorbs more strongly to smaller dust size particles. This is significant because it means that the inhalable dust fractions which fall within the <20µm fraction, will have higher concentrations and therefore could potentially be more harmful as the get into the lungs. A possible explanation for the higher Ka value for the whole dust fraction over the two other smaller fractions could be because whole dust is a more complex mixture containing more fibrous substances that may have stronger affinities for Lindane than dust e.g. carpet fibres.

Faculty of Health Sciences School of Medical 0212352d dlabuschagne@anglogoldashanti.com / Dust has been recognized as the most serious occupational health hazard across the South African Mining Industry. During 1998 more than 5600 mineworkers were certified with silicosis, a silica related lung disease. The objective of this research project is to describe the trend in respirable dust concentrations in four underground gold mines for the period 1999 to 2002. The mines under discussion are situated in the Klerksdorp area and they were selected because they are a typical representation of deep underground gold mines. Typical gold mines use the same method of ventilation distribution and have similar dust sources e.g. breaking, transporting and tipping of rock. They are all situated in the same geographical area and all make use of conventional mining methods. A total of 4645 previously collected personal respirable dust samples were analysed for this research report making use of a central laboratory situated in the Klerksdorp area. The respirable dust samples were collected by the Occupational Hygienists appointed on the mines for control purposes over the years 1999 to 2002. The arithmetic mean respirable dust concentrations for the four mines in discussion was 0,39mg/m3 in 1999, 0,33mg/m3 in 2000, 0,30mg/m3 in 2001 and 0,31mg/m3 in 2002 against the mine’s internal target of 0,4mg/m3. The report shows a statistically significant downward trend in the proportion of measurements below 0,4mg/m3 for mines 1, 2 and 3. The percentage of respirable dust samples above the internal target of 0,4mg/m3 was 6,78% in 1999, 6,15% in 2000, 4,71% in 2001 and 4,38% in 2002. Although there is a general downwards trend in the percentage of samples above the target, there is an increase in the number of samples above the target. In 1999, 202 samples were above, 310 in 2000, 402 in 2001 and 361 in 2002. The key limitation to the project is the integrity of the data. The major limitations identified include non compliance with the sampling strategy. There is no guarantee that the instrumentations were worn on the body for the whole shift or whether any tampering of the gravimetric pumps took place. The sampling strategy measures all occupations, but all occupations do not receive the same type and amount of exposure, making it impossible to allocate exposure to a certain workplace. Samples could get affected during storage and transport. The most recent audits on the mine’s central laboratory show 100% compliance with the required standards. The mines under study are well in line with the DME requirements on the guidelines for a measurement strategy of airborne pollutants. The gravimetric sampling strategy includes the scheduling of samples managed by the electronic database system. Although the report indicates that the results are pointing in the right direction, the integrity of the data should be tested continuously. Supervision of the pump wearers is of great concern and training of these wearers is essential for explaining the purpose of the personal monitoring strategy. There is a scarcity of published information on respirable dust concentrations in underground gold mines and further research is required.

Thesis (MPH. (Occupational and Environmental Health))-- University of Limpopo, 2012 / Background: The objective of this study was to quantify personal time-weighted average respirable dust and silica exposure of workers at foundries in Gauteng and to rank the occupations in foundries according to the risk of exposure to silica quartz. Methods: A task-based risk assessment of 56 personal samples from two foundries was conducted. Personal exposure data was collected from workers’ breathing zones for the full working shift. All analyses of samples for silica dust were carried out in the CSIR Centre for Mining Innovation’s Laboratory, which has SANAS accreditation (ISO 17025) for both x-ray powder diffraction and particle size analysis methods. Results: The personal time-weighted average mean and median respirable silica dust concentration was 0.184 mg/m³ and 0.167 mg/m³ respectively. The maximum exposure concentration was 0.835 mg/m³ and minimum exposure was 0.010 mg/m³. The occupations within the foundries with the highest exposures were moulders, sand mixers, furnace operators and the lowest exposed occupations were grinders, closers, and casting operators. The majority of foundry workers (62%) in both foundries are exposed to respirable silica dust at above the South African occupational exposure level (OEL). Conclusion and recommendations: Foundry workers are over-exposed to respirable silica dust and are potentially at high risk of contracting silicosis and other occupational diseases associated with respirable silica dust. It is recommended that a dust control programme be implemented and a baseline study be conducted.

Asian dust storms invaded Taiwan in springtime. During the Asian dust-storm periods, the dust particles suspended in the atmosphere could not only deteriorate the ambient air quality, mainly high particulate matter concentration and low visibility, but also cause severely adverse effects on human health. In this study, Asian dusts were sampled at Pencadores Islands and characterized the physical and chemical characteristics to investigate the influence of Asian dust storms. Due to its clean atmosphere, Pencadores Islands can be treated as one of the best air quality background sites in Taiwan. In this sampling campaign, five Asian dust storm episodes were observed at Pencadores Islands. Asian dusts transported to Taiwan along the east of China or the east ocean of China and invaded Taiwan from either the northeast or the northwest. The concentrations of atmospheric aerosols during Asian dust storm episodes were 2-3 times higher than the background level. The concentration of PM10 increased dramatically. The increase of PM10 concentration was mainly attributed to coarse particles. The ratio of coarse particles to fine particles for Asian dust storm periods was higher than those for non-Asian dust storm periods. From March to April, the concentration of PM10 increased due to sea-salt aerosol blow into atmosphere by strong eastwest monsoon. It suggested that, at Pencadores Islands, seawater was major chemical species of suspended particles. The concentration of F-, Cl-, Br-, NO3-, SO42-, Na+, Mg2+, and Ca2+ increased during Asian dust storm episodes indicated that pollutant would be transport by Asian dusts. The most possible chemical species in coarse particles would be MgSO4 and CaSO4. The carbon content of suspended particles increased dramatically. The increase of carbon content of coarse particles was mainly attributed to elemental carbon. The increase of carbon content of fine particles was mainly attributed to organic carbon from second reaction. The concentration of Al, K, Br-, Fe, and Ca increased during Asian dust storm episodes indicated that Asian dust storm would transport dusts to Pencadores Islands. The major pollution sources were mobile sources and dust sources at Pencadores Islands. During the Asian dust-storm periods, the percentages of industrial sources, seawater, and secondary aerosols increased dramatically.

An optical microscope coupled to a flow cell was used to investigate ice nucleation on five atmospherically relevant mineral dusts at temperatures ranging from 233 to 247 K. Kaolinite and muscovite particles were found to be efficient ice nuclei in the deposition mode, requiring relative humidities with respect to ice (RHi) below 112% in order to initiate ice crystal formation. Quartz and calcite particles, by contrast, were poor ice nuclei, requiring relative humidities close to water saturation before ice crystals would form. Montmorillonite particles were efficient ice nuclei at temperatures below 241 K, but poor ice nuclei at higher temperatures. In several cases, there was a lack of quantitative agreement between these data and previously published work. This can be explained by several factors including mineral source, particle size, observation time and surface area available for nucleation. Heterogeneous nucleation rates (Jhet) were calculated from the onset data. Jhet values ranged from 60 to 1100 cm-²s-¹ for the five minerals studied. These values were then used to calculate contact angles (θ) for each mineral according to classical nucleation theory. The contact angles measured for kaolinite and muscovite ranged from 6 to 12º; for quartz and calcite the contact angles were much higher, ranging from 25 to 27º. The contact angles measured for montmorillonite were less than 15º at temperatures below 241 K, and above 20º at higher temperatures. The reported Jhet and θ values may allow for a more direct comparison between laboratory studies and can be used when modeling ice cloud formation in the atmosphere. The roles of H₂SO₄ and (NH4)₂SO₄ coatings on the ice nucleating properties of kaolinite were also investigated. Onset data was collected for H₂SO₄ coated and (NH4)₂SO₄ coated kaolinite particles at temperatures ranging from 233 to 247 K. In contrast to uncoated kaolinite particles, which were effective ice nuclei, H₂SO₄ coated particles were found to be poor ice nuclei, requiring relative humidities close to water saturation before nucleating ice at all temperatures studied. (NH4)₂SO₄ coated particles were poor ice nuclei at 245 K, but effective ice nuclei at 236 K.

No description available.

Optical imaging polarimetry has been performed on a small sample of objects which are associated with that stage of stellar evolution occurring between the Asymptotic Giant Branch and full Planetary Nebula. Three such systems are considered, specifically, the young planetary nebulae M 1-16 and Mz3, and the protoplanetary nebula, IRAS 09371+1212 (the 'Frosty Leo' nebula). The work is based upon CCD polarimetry obtained with the Durham Imaging Polarimeter. Planetary nebulae are believed to form as a low to intermediate mass star evolves from the main sequence, through the mass-loss stages of the Red Giant Branch and Asymptotic Giant Branch, towards its final destiny as a White Dwarf. A brief review of the relevant aspects of post-main sequence stellar evolution is given as a basis for understanding the transitionary planetary nebula phase in relation to the character of the central star and its role in the creation of a nebula. The theory of light scattering from both homogeneous and core-mantle spherical dust grains (Mie theory) is discussed. The results of a series of scattering calculations, using the theory, for dust grains composed of those materials believed to be abundant in the atmospheres of late-type stars and planetary nebulae are presented. The levels of polarization and scattered intensities predicted in the scattering analysis have been applied in the interpretation of the polarimetric data for the three planetary nebulae. Constraints upon the nature of the dust component, the size distribution of the dust and the nebula geometry are suggested for each of the nebulae. The inferred character of the dust material is in good agreement with the classification of the nebulae using the two-colour diagram for the IRAS fluxes.

No description available.