Because the bulk optical properties of dust are largely dependent on their chemical composition, published reports from numerous dust field studies enabled us to compile observation data sets to derive the effective complex refractive indices of Saharan and Asian dust. We considered the individual mineral components as aggregates and used the Bruggeman approximation to derive the effective refractive indices. Using the results, we calculated the single-scattering properties, including phase matrix, single-scattering albedo and asymmetry factor, with a combination of the T-matrix method and an improved geometric optics method (IGOM). The single-scattering properties were averaged by the measured particle size distribution to provide bulk optical properties for radiative transfer simulations. Using a Rapid Radiative Transfer Model (RRTM), the radiative forcing of mineral dust was computed at both the top of the atmosphere and the surface. By analyzing samples from various in-situ measurements, we assumed the Saharan and Asian dust to have average volume compositions and average aspect ratios. The effective refractive indices for Saharan and Asian dust were derived based on the assumed composition models. Bulk optical properties were integrated using the modified log-normal particle size distributions. The aspect ratio assumed in this study is 1.6 for both Saharan and Asian dust. The longwave radiative (IR) forcings at the top of the atmosphere (TOA) and at the surface were found to be positive and sensitive to wavelength. The shortwave (solar) radiative forcing at TOA, was also positive, but may possibly have been due to the strong absorption components considered in the composition models.

No description available.

A special challenge posed by mineral dust aerosols is associated with their predominantly nonspherical particle shapes. In the present study, the scattering and radiative properties for nonspherical mineral dust aerosols at violet-to-blue (0.412, 0.441, and 0.470 μm) and red (0.650 μm) wavelengths are investigated. To account for the effect of particle nonsphericity on the optical properties of dust aerosols, the particle shapes for these particles are assumed to be spheroids. A combination of the T-matrix method and an improved geometric optics method is applied to the computation of the single-scattering properties of spheroidal particles with size parameters ranging from the Rayleigh to geometric optics regimes. For comparison, the Mie theory is employed to compute the optical properties of spherical dust particles that have the same volumes as their nonspherical counterparts. The differences between the phase functions of spheroidal and spherical particles lead to quite different lookup tables (LUTs) involved in retrieving dust aerosol properties. Moreover, the applicability of a hybrid approach based on the spheroid model for the phase function and the sphere model for the other phase matrix elements is demonstrated. The present sensitivity study, employing the Moderate Resolution Imaging Spectroradiometer (MODIS) observations and the fundamental principle of the Deep Blue algorithm, illustrates that neglecting the nonsphericity of dust particles leads to an underestimate of retrieved aerosol optical depth at most scattering angles, and an overestimate is noted in some cases. The sensitivity study of the effect of thin cirrus clouds on dust optical depth retrievals is also investigated and quantified from MODIS observations. The importance of identifying thin cirrus clouds in dust optical depth retrievals is demonstrated. This has been undertaken through the comparison of retrieved dust optical depths by using two different LUTs. One is for the dust only atmosphere, and the other is for the atmosphere with overlapping mineral dust and thin cirrus clouds. For simplicity, the optical depth and bulk scattering properties of thin cirrus clouds are prescribed a priori. Under heavy dusty conditions, the errors in the retrieved dust optical depths due to the effect of thin cirrus are comparable to the assumed optical depth of thin cirrus clouds. With the spheroidal and spherical particle shape assumptions for mineral dust aerosols, the effect of particle shapes on dust radiative forcing calculations is estimated based on Fu-Liou radiative transfer model. The effect of particle shapes on dust radiative forcing is illustrated in the following two aspects. First, the effect of particle shapes on the single-scattering properties of dust aerosols and associated dust direct radiative forcing is assessed, without considering the effect on dust optical depth retrievals. Second, the effect of particle shapes on dust direct radiative forcing is further discussed by including the effect of particle nonsphericity on dust optical depth retrievals.

ABSTRACT MONITORING AND STATISTICAL MODELLING OF DUST CONCENTRATION OF SOME TURKISH LIGNITES UNDER LABORATORY CONDITIONS Karakas, Ahmet Ph.D., Department of Mining Engineering Supervisor: Prof. Dr. Tevfik G&uuml / yag&uuml / ler September 2010, 171 pages Although technological developments enable maximum safety, high dust formation is still a crucial problem in coal mining sector. This study is aimed to investigate the relationship between amount of coal dust produced during cutting operation and some important coal properties together with cutting parameters for different particle size ranges in laboratory conditions. For this purpose, six Turkish lignite samples were used in the experiments. Two experiment sets were designed to generate coal dust by using cutting action of the saw. First group of experiments were conducted in large scale saw system by using saws having three different diameters and dust concentration measurements were done for three group of particle size namely: 0-2.5 &mu / m, 0-5 &mu / m and 0-10 &mu / m. Second group of experiments were done in small scale saw system by changing the table advancing speed and tip speed of the system. For this group of experiments, only one type of lignite samples were used. These measurements were carried out only 0-10 &mu / m particle size range by using a saw with 30 cm in diamater. In this study, to characterize the lignite samples / proximate, petrographic and grindability analysis (HGI) were made. During the experiments, dust concentrations were measured by using Microdust Pro real time dust monitoring equipment. At the end of the study, the relationship between coal dust concentration and some coal properties and cutting operating parameters were expressed by using four different regression equations. Also it has been found that tip speed of saw, fixed carbon, ash and huminite content, vitrinite reflectance and hardgrove grindability index are very important parameters in coal dust generation. Keywords: Respirable Coal Dust, Dust Generation, Real Time Dust Sampler, Coal Dust Diseases, Coal Cutting Operation.

Thesis (Ph. D.)--University of Canterbury, 2009. / Typescript (photocopy). "May 2009." Includes bibliographical references (p. 10/1-10/9). Also available via the World Wide Web.

Thesis (Ph. D.)--University of Chicago, Dept. of Astronomy & Astrophysics, August 2001. / Includes bibliographical references. Also available on the Internet.

Large uncertainties remain in estimating the anthropogenic fraction of mineral dust and the climatic impact of dust aerosol, partly due to a poor understanding of the dust source dynamics under the influence of climate variability and human-induced land-cover/land-use change (LCLUC). So far, the dust dynamics and linkage to climate and LCLUC in Central Asia have received little attention from the aerosol research community. This thesis comprises a comprehensive study of the dust dynamics in Central Asia focusing on 1) the seasonality of erosion threshold and dust emission affected by soil moisture, vegetation phenology and surface roughness, 2) the dust interannual variability and connections with large-scale climate variation (ENSO) through effects on the atmospheric circulation, precipitation, vegetation dynamics and drought, and 3) the impact of dust aerosol on surface radiative balance and photosynthetically active radiation, and possible effect on dryland ecosystems. A coupled dust model and multi-year ground and satellite observations of dust frequency, dust loading, and atmospheric and land conditions are used in this study. We find the threshold friction velocity significantly varies in space and time in response to soil moisture seasonality, surface roughness heterogeneity and vegetation phenology. Spring is associated a higher threshold friction velocity than summer, due to wetter soils and more vegetation cover. As a result, although more frequent strong winds occur during spring, spring dust emission is less than summer by 46.8% (or 60.4 Mt). Ignoring the dependence of the threshold friction velocity on the surface characteristics leads to biased spatial distribution and seasonality of dust emission. There is a strong linkage between dust and ENSO in Central Asia: La Nina years produce drought condition and enhance the dust activity. A decline in the strong wind frequency during 1999−2012 results in a decreasing trend in the modeled dust emission, at a rate of -7.81±2.73 Mt yr-1, as well as a decreasing trend in the ground observed dust frequency index, at a rate of -0.14±0.04%. We estimate that 58.4% of dust emission is caused by human activity during the 1999−2012 period. Our estimates suggest human plays an important role in the region’s dust budget through agriculture and water resource usage.

The effect of dust/gas heating and cooling is shown to have a significant effect on the process of clustered star formation. Compared to an isothermal simulation, a simulation with a more accurate description of the equation of state produces an order of magnitude fewer stars as well as stars of much greater mass. The energetics algorithm used to calculate the dust and gas temperature includes the radiative heating of dust, dust-gas collisional heating/cooling, cosmic-ray heating, and molecular cooling. It uses DUSTY, a spherical continuum radiative transfer code, to model the dust temperature distribution around young stellar objects with various luminosities and surrounding gas and dust density distributions. The gas temperature is then determined by assuming energy balance. Before the complete energetics algorithm is included in a simulation, first only the dust heating component is included. The gas temperature is then set solely by the dust temperature. The resultant mass functions of our simulations which include heating are compared to those which assume an isothermal equation of state. We find that including dust heating severely limits star formation; we form at least an order of magnitude fewer objects when we include dust heating compared to an isothermal simulation. The mass functions from our simulations which include heating are much more similar than the mass functions from our isothermal simulations to the observed mass functions, in that they are able to form high-mass stars (M [> subscript tilde] 10M[solar mass]). The distribution of the high-mass objects is well-approximated by the Salpeter initial mass function. Including the complete energetics algorithm in a simulation produces results similar to a simulation with only dust heating. Both simulations have similar density profile parameters. The mass accretion, mass, and luminosity evolution of the sinks is also similar. The average temperature, however, is cooler than the simulation with only dust heating. We form fewer objects comparatively and are still unable to form enough low and intermediate-mass objects to replicate the observed mass function. This may be an effect of small number statistics, or possibly physical processes that are not considered in this work. / text

El concreto Autocompactante está dirigido principalmente para el empleo del concreto en elementos que poseen difícil acceso, alta congestión de acero o por el proceso necesita ser vertido en el menor tiempo posible. Es posible desarrollar un concreto autocompactante para resistencias convencionales como f´c 210, 245 y 280 kg/cm2 con adiciones de microfiller calizo. El trabajo fue desarrollado considerando como base comparativa los diseños de resistencia a la compresión f´c 210, 245 y 280 kg/cm2 cuyos contenidos referenciales de cemento son equivalentes a 9, 11 y 12 bolsas de cemento, respectivamente. Se estableció un espectro de análisis para la adición del microfiller calizo considerando porcentualmente dosis de 30%, 40%, 50% y 60% de adición respecto al contenido total del cemento más microfiller calizo. Los componentes de las mezclas son de procedencia local como el cemento tipo I de marca Sol, la adición mineral de microfiller calizo, ambos de Cementos Lima, los agregados fino y grueso de huso #89 procedentes de cantera Jicamarca, el agua de la red pública y los aditivos retardante reductor de agua de rango medio y superplastificante de alto rango a base de policarboxilatos de BASF Perú. Se elaboraron mezclas de concreto bajo similares condiciones ambientales y controladas a escala de laboratorio. El estudio ha permitido el uso de los mismos contenidos de cemento empelados en concretos convencionales como base para mezclas autocompactantes y el empleo de un material de reemplazo como el microfiller calizo que es el residuo captado de los filtros en la elaboración del cemento, Los diseños con sólo cemento que logran un mejor comportamiento son aquellos que tienen contenidos de cemento entre 460 y 500 kg/m3, debido a que el empleo de contenidos menores nos obligarían a empelar aditivos modificadores de viscosidad para evitar una posible segregación de la mezcla, en la búsqueda de mayores extensibilidades iniciales y la limitación del contenido de agua y aditivos. A las mezclas que se incluyeron microfiller calizo también se consideraron dosis de reemplazo a su contenido de cemento logrando mezclas de hasta 260 kg/m3 de cemento para adiciones de 30%, 40%, 50% y 60% del cementante total; bajo consideraciones de mezclas autocompactantes mientras se incrementaba el porcentaje de adición las mezclas lograban mejores desempeños en la fluidez de la mezcla. Las mezclas con adición de microfiller calizo tienen un mejor comportamiento en la capacidad de relleno respecto a las mezclas con sólo cemento, debido a que las últimas presentan mayor cohesión en la mezcla. Respecto a la medición de la permeabilidad del concreto, las mezclas convencionales no cumplirían requisitos para ser evaluados debido a que el ensayo está considerado para relaciones a/cm menores a 0.50, las muestras en estudio con sólo cemento y adiciones de microfiller calizo alcanzan una clasificación de permeabilidad alta. La durabilidad del concreto evaluada por el ensayo de abrasión demuestra que los concretos con sólo cemento tienen un mejor comportamiento frente al desgaste superficial y los concretos con adiciones al 30% y 40% de microfiller calizo obtienen pérdidas de material superficial similares, siendo las muestras con adiciones de 50% y 60% las que tienen a incrementar el desgaste superficial. Las resistencias a la compresión en mezclas con adición de microfiller calizo se mantienen en el rango promedio de 360 kg/cm2 con una variación promedio de 60 kg/Cm2 entre las adiciones extremas de microfiller calizo (30% y 60%), esto supera definitivamente el f´c convencional y ofrece un valor agregado respecto las características de una mezcla autocompactante.

The purpose of following project is to study the effect of dust aerosols on the radiative forcing which is directly related to the surface temperature. A single column radiative convective model is used for simulation purpose. A series of simulations have been performed by varying the amount of dust aerosols present in the atmosphere to study the trends in ground temperature, heating rate and radiative forcing for both its longwave and shortwave components. A case study for dust storm is also performed as dust storms are common in Arabian Peninsula. A sensitivity analyses is also performed to study the relationship of surface temperature minimum and maximum against aerosol concentration, single scattering albedo and asymmetry factor. These analyses are performed to get more insight into the role of dust aerosols on radiative forcing.