Master of Science / Department of Entomology / Franklin Arthur / Kun Yan Zhu / Tribolium spp. are major pests in structures used for the processing and storage of grain-based products (e.g., flourmills, warehouses, retail stores). Consumers and regulators have little tolerance for insect-damaged or contaminated food products. The direction and breadth of pest-control strategies in the food industry have changed significantly over the past few years, creating the need to optimize insecticides through improved integrated pest management (IPM) techniques, specifically through the identification of new control agents that are low in mammalian toxicity, as well as any factors that might affect susceptibility to these agents. There is currently renewed interest in developing reduced-risk, low toxicity chemicals that can be effectively utilized in a setting in which grain and other food commodities are vulnerable to insect infestation, as a means of replacing outdated, and at times, less effective methods of insect control. Over the past decade, developed countries have made significant progress toward alternative insect control strategies by employing a variety of applied insecticides. Two classes of insecticide include natural pyrethrum and insect growth regulators (IGRs), which are substances that mimic insect hormones essential to normal development and reproduction. Pyrethrin is a highly efficient, broad spectrum, botanical insecticide that causes a rapid knockdown in exposed insects. Synergists are used to extend the economic usage of natural pyrethrins and because pyrethrum is rapidly metabolized, it is often mixed with a synergist. Methoprene, a juvenile hormone analog, is labeled as an aerosol and surface treatment inside mills, warehouses and other food storage facilities. There is little recent research with large-scale aerosol applications in stored-food facilities; furthermore, there are few published references regarding the efficacy of using methoprene in combination with synergized pyrethrin, in aerosol form. Therefore, the purpose of this research was to evaluate the use of aerosol applications of two aerosol concentrations on flour and finished stored-product packaging materials for the control of Tribolium spp. Results of this research show that T. castaneum are effectively controlled with 1% aerosol application, while the 3% formulation is required to effectively control T. confusum. With regards to the various packaging material surfaces, few differences between the surfaces emerged.

This dissertation summarises the study of different aspects of the aerosol-assisted chemical vapour deposition (AACVD) technique for the production of multi-wall carbon nanotubes (MWCNTs). Upscaling the synthesis while retaining the quality of MWCNTs has been a prime objective throughout the work. A key aspect of this work was the study of different growth parameters and their influence on the homogeneity of the products across the reactor. The effect of the precursor composition on the yield and quality of MWCNTs were also investigated. It was shown that the synthesis rate can be significantly (60 – 80 %) increased by tuning the composition of the precursor. Moreover, by optimising the synthesis recipe and using a larger reactor, the synthesis rate and efficiency of the precursor were increased fivefold (up to 14 g/hr) and twice (up to 88 %) respectively. Large area (up to 90 cm²), mm-thick carpets of MWCNTs which were both free-standing and on substrate were produced. The carpets could withstand normal handlings without tearing apart, making them suitable for macroscopic characterisations and applications. By in-situ qualitative and quantitative gas analysis of the atmosphere of the reactor, the thermocatalytic cracking behaviour of 25 precursors was investigated and a mechanism for successive formation of different hydrocarbon fragments inside the reactor was proposed. A number of dedicated gas analysis methods and apparatuses such as a probe for zone-by-zone gas analysis of reactor and a heated chamber for preparation of standard gas analysis samples were developed to explore some of the least investigated aspects of the thermocatalytic cracking of precursors. Mapping the reactor revealed that some single-wall and double-wall carbon nanotubes (SWCNTs and DWCNTs) were also produced near the exhaust of the reactor. The SWCNTs were partly covered by fullerene-like species and resembled different forms of carbon nanobuds. In addition, the effect of the electron beam on the interaction of the SWCNTs and the fullerene-like species was studied in situ using high-resolution transmission electron microscopy (HRTEM).

This dissertation focuses on aerosol transport modeling in occupational environments and mining sites in Arizona using computational fluid dynamics (CFD). The impacts of human exposure in both environments are explored with the emphasis on turbulence, wind speed, wind direction and particle sizes. Final emissions simulations involved the digitalization process of available elevation contour plots of one of the mining sites to account for realistic topographical features. The digital elevation map (DEM) of one of the sites was imported to COMSOL MULTIPHYSICS® for subsequent turbulence and particle simulations. Simulation results that include realistic topography show considerable deviations of wind direction. Inter-element correlation results using metal and metalloid size resolved concentration data using a Micro-Orifice Uniform Deposit Impactor (MOUDI) under given wind speeds and directions provided guidance on groups of metals that coexist throughout mining activities. Groups between Fe-Mg, Cr-Fe, Al-Sc, Sc-Fe, and Mg-Al are strongly correlated for unrestricted wind directions and speeds, suggesting that the source may be of soil origin (e.g. ore and tailings); also, groups of elements where Cu is present, in the coarse fraction range, may come from mechanical action mining activities and saltation phenomenon. Besides, MOUDI data under low wind speeds (<2 m/s) and at night showed a strong correlation for particles 1-micrometer in diameter between the groups: Sc-Be-Mg, Cr-Al, Cu-Mn, Cd-Pb-Be, Cd-Cr, Cu-Pb, Pb-Cd, As-Cd-Pb. The As-Cd-Pb group correlates strongly in almost all ranges of particle sizes. When restricted low wind speeds were imposed more groups of elements are evident and this may be justified with the fact that at lower speeds particles are more likely to settle. When linking these results with CFD simulations and Pb-isotope results it is concluded that the source of elements found in association with Pb in the fine fraction come from the ore that is subsequently processed in the smelter site, whereas the source of elements associated to Pb in the coarse fraction is of different origin. CFD simulation results will not only provide realistic and quantifiable information in terms of potential deleterious effects, but also that the application of CFD represents an important contribution to actual dispersion modeling studies; therefore, Computational Fluid Dynamics can be used as a source apportionment tool to identify areas that have an effect over specific sampling points and susceptible regions under certain meteorological conditions, and these conclusions can be supported with inter-element correlation matrices and lead isotope analysis, especially since there is limited access to the mining sites. Additional results concluded that grid adaption is a powerful tool that allows to refine specific regions that require lots of detail and therefore better resolve flow detail, provides higher number of locations with monotonic convergence than the manual grids, and requires the least computational effort. CFD simulations were approached using the k-epsilon model, with the aid of computer aided engineering software: ANSYS® and COMSOL MULTIPHYSICS®. The success of aerosol transport simulations depends on a good simulation of the turbulent flow. A lot of attention was placed on investigating and choosing the best models in terms of convergence, independence and computational effort. This dissertation also includes preliminary studies of transient discrete phase, eulerian and species transport modeling, importance of saltation of particles, information on CFD methods, and strategies for future directions that should be taken.

The threshold friction velocities of potential dust sources in the US Southwest were measured in the field using a Portable Wind Tunnel, which is based on the Desert Research Institute's Portable In-Situ Wind Erosion Laboratory (PI-SWERL). A mix of both disturbed and undisturbed surfaces were included in this study. It was found that disturbed surfaces, such as those at the Iron King Mine tailings site, which is part of the EPA's Superfund program and contains surface concentrations of arsenic and lead reaching as high as 0.5% (w/w), had lower threshold friction velocities (0.32 m s⁻¹ to 0.40 m s⁻¹) in comparison to those of undisturbed surfaces (0.48 to 0.61 m s⁻¹). Surface characteristics, such as particle size distribution, had effects on the threshold friction velocity (smaller grain sized distributions resulted in lower threshold friction velocities). Overall, the threshold friction velocities of disturbed surfaces were within the range of natural wind conditions, indicating that surfaces disturbed by human activity are more prone to causing windblown dust.

Ozone (O₃) and terpenoids react to produce secondary organic aerosol (SOA). This work explored novel ways that these reactions form SOA indoors, with five investigations, in two categories: investigations of (i) the impacts of particle controls on indoor SOA formation, and (ii) two fundamental aspects of indoor SOA formation. For category (i), two investigations examined the particle control devices of ion generators, which are air purifiers that are ineffective at removing particles and emit ozone during operation. With a terpenoid source present (an air freshener), ion generators acted as steady-state SOA generators, both in a 15 m³ chamber and 27 m³ room. The final investigation in category (i) modeled how heating, ventilating, and air-conditioning (HVAC) systems influence SOA formation. Influential HVAC parameters were flow rates, particle filtration, and indoor temperature for residential and commercial models, as well as ozone removal by particle-laden filters for the commercial model. For category (ii), the first investigation measured SOA formation from ozone reactions with single terpenoids and terpenoid mixtures in a 90 L Teflon-film chamber, at low and high ozone concentrations. For low ozone, experiments with only d-limonene yielded the largest SOA number formation, relative to other mixtures, some of which had three times the effective amount of reactive terpenoids. This trend was not observed for high ozone experiments, and these results imply that ozone-limited reactions with d-limonene form byproducts with high nucleation potential. The second investigation in category (ii) explored SOA formation from ozone reactions with surface-adsorbed terpenoids. A model framework was developed to describe SOA formation due to ozone/terpenoid surface reactions, and experiments in a 283 L chamber determined the SOA yield for ozone/d-limonene surface reactions. The observed molar yields were 0.14–0.16 over a range of relative humidities, and lower relative humidity led to higher SOA number formation from surface reactions. Building materials on which ozone/d-limonene surface reactions are predicted to lead to substantial SOA formation are those with initially low surface reactivity, such as glass, sealed materials, or metals. The results from category (ii) suggest significant, previously unexplored mechanisms of SOA number formation indoors. / text

Ag thin and thick films have been experimentally deposited using a technique called Laser Ablation of a Microparticle Aerosol (LAMA). This technique is based on a supersonic jet accelerating NPs of a few nm diameter up to 1000 m/s and operating at room temperature. The deposited films have experimentally demonstrated interesting properties such as dense growth with good adherence on the substrate. Aerosol feed rates have been fixed to 10 mg/h which corresponds to rate depositions of 10¹⁰ to 10¹¹ NPs/s/cm². In order to model this deposition technique and possibly be able to predict the morphology and structure of deposited films using computational methods, we have designed MD programs simulating the depositions of several Ag nanoclusters onto a substrate at a fixed temperature (300 K). The variation of parameters such as cluster size, cluster impact energy, and deposition rate has influenced the morphology and structure of the deposited films. Cluster diameters have been set to 3 nm or 5 nm, cluster velocities set to 200 m/s (0.022 eV/atom), 400 m/s (0.069 eV/ atom), or 800 m/s (0.358 eV/atom), and the deposition rate adjusted to ensure relaxation times between impactions of 5 ps to 20 ps. The evolution of deposited film density, adherence, and crystal arrangement has been analyzed with the variation of the aforementioned parameters. The highest cluster velocities have enabled the deposition of smoother, denser, and more adherent films. NCs with an initial velocity of 200 m/s have shown ratios of flattening equal to 50 % as opposed to 85% flattening for NCs deposited at 800 m/s. These observations have enabled us to draw qualitative conclusions on the film density The deposited films are less porous when the cluster impaction velocity increases. Atomic mixing between substrate and impacted NC atoms increased with increasing deposition velocity, which can perhaps be correlated to an increase of adherence, assuming that more mixing will create stronger molecular binding in the cluster-substrate interaction. Finally, complete epitaxial growth was observed for the highest impaction velocities only, which indicates that recrystalization can occur for this range of impact energies (0.3 eV/atom - 0.5 eV/atom). Although experimental results have given more quantitative data on film density and sticking ratios, they agree with our modeling, and this comparison allows us to validate our MD simulations. However, some limitations have been faced, mainly because of long computing time requirements that a single laptop computer has not been able to support. / text

Aerosols of nitrate solutions were irradiated in the presence of radical scavengers in an attempt to measure the yield of hydroxyl radical in both the aqueous phase and the gas phase. Carbon monoxide, benzoic acid, benzene and cyclohexane were used as scavengers to trap hydroxyl radical. The products from the reaction of these scavengers with hydroxyl radical were analysed with High Performance Liquid Chromatography and mass spectrometry. The radiant flux in the chamber was measured via ferrioxalate actinometry, both with bulk liquid and aerosol droplets. Many quantitative results were obtained but several anomalies were found. This suggests that Mie theory is not capable of predicting rates of photochemical reactions within droplets.

Atmospheric aerosols are a highly relevant component of the climate system affecting atmospheric radiative transfer and the hydrological cycle. As opposed to other key atmospheric constituents with climatic relevance, atmospheric aerosol particles are highly heterogeneous in time and space with respect to their size, concentration, chemical composition and physical properties. Many aspects of their life cycle are not understood, making them difficult to represent in climate models and hard to control as a pollutant. Aerosol-cloud interactions in particular are infamous as a major source of uncertainty in future climate predictions. Field measurements are an important source of information for the modeling community and can lead to a better understanding of chemical and microphysical processes. In this study, field data from urban, marine, and arid settings are analyzed and the impact of meteorological conditions on the evolution of aerosol particles while in the atmosphere is investigated. Particular attention is given to organic aerosols, which are a poorly understood component of atmospheric aerosols. Local wind characteristics, solar radiation, relative humidity and the presence or absence of clouds and fog are found to be crucial factors in the transport and chemical evolution of aerosol particles. Organic aerosols in particular are found to be heavily impacted by processes in the liquid phase (cloud droplets and aerosol water). The reported measurements serve to improve the process-level understanding of aerosol evolution in different environments and to inform the modeling community by providing realistic values for input parameters and validation of model calculations.

Student Number : 0318623R - PhD thesis - School of Geosciences - Faculty of Science / Physical and chemical properties of atmospheric particles are fundamental but not necessarily easily accessible parameters. Uncertainties in these parameters are responsible for some uncertainties associated with radiative impacts of aerosol particles in global climate models. The uncertainties pertain to limitations of sampling and measurement devices, difficulties in modelling aerosols (source strengths, spatial and temporal variability) and in understanding microphysical and optical properties of aerosol particles. Physical and chemical properties can be obtained at single-particle level by microscopy analyses of individual particles. Using refined analytical and interpretative techniques to derive some of these fundamental properties, aerosol particles collected in various field campaigns and laboratory experiments were investigated using two high resolution microscopes. The particles were collected during the LBA-EUSTACH, Large-Scale Biosphere-Atmosphere Experiment part of European Studies on Trace Gases and Atmospheric Chemistry; SMOCC campaign, Smoke Aerosols, Clouds, Rainfall and Climate; CTBH II, Cape Town Brown Haze II campaign; and a controlled combustion experiment. Microscopy techniques were compared and complemented with conventional techniques to characterise particle sizes, shapes, chemical compositions and mixing states. Particle size distributions were compared between geometric equivalent sizes measured from microscopes and aerodynamic equivalent diameters, while taking into account particle densities. Large differences were found between the particle sizing techniques. Microscopy sizes (3D) were systematically lower than expected, and depended on the relative humidity during particle sampling. Differences were attributed to loss of mass, presumably water adsorbed on particles. Losses were high and could not be accounted for by known humidity growth factors suggesting losses of other volatile compounds adsorbed on particles as well. Findings suggest that there are inherent problems in defining particle sizes with different sizing techniques, despite accounting for humidity growth of particles and particle density. For collected particles, there are mass losses on individual particles, as opposed to particle losses to walls during sampling. These losses will inevitably bias observed mass distributions derived from collected particles and hence their number-size distributions. Relatively young aggregated soot particles from wood combustion were investigated for particle morphology (fractality, specific mass) and dynamic properties. Based on a procedure that has been validated on modelled aggregates, several important parameters to characterise geometry and drag-to-mass relationship of aggregates were derived. Three techniques were used to derive fractal dimension of soot aggregates. Averaged fractal dimension was found to be Df = 1.82 ± 0.08. Dynamic shape factors of soot particles were 1.7 to 2.5 and increasing with mass of aggregates. In the regime 0.2 < Kn < 0.7 (Knudsen number, Kn = 2#21;/dmob) the mobility diameter dmob was observed to be proportional to the radius of gyration with a ratio dmob/2Rg = 0.81 ± 0.07. Specific surface area of aggregates was determined to be 70 ± 10 m2g−1 based on SEM image analysis. These parameters can be used directly in modelling microphysical behaviour of freshly formed soot particles from biomass combustion with fractal dimension of Df ≈ 1.80. Chemical composition and size distributions of particles were investigated on filter samples collected during intense winter brown haze episodes in Cape Town. The sampling technique offered the capability to characterise highly heterogeneous aerosols over a polluted urban environment. Based on morphology and elemental composition, particles were categorised into seven particle groups of: aggregated soot particles, mineral dust, sulphates (SO2− 4 ), sea-salt, tar balls/fly ash, rod-shaped particles associated with soot agglomerates and those that could not be attributed to any of these groups were labelled as ‘others’. Apportionments of chemical species were highly variable both spatially and temporally. These variations indicate lack of lateral mixing and dependence of particle chemical compositions on localised and point sources within the Cape Town area. Sulphate and aggregated soot particles were externally mixed with fractional number concentrations of 0− 82% and 11%−46%, respectively. Aerosol complex refractive indices were derived from the chemical apportionment and particle abundance determined in microscopy analyses. The refractive indices were combined with in-situ measurements of number-size distribution to determine optical properties of aerosols. Single scattering albedo, !0, varied from 0.61 to 0.94 with a mean value of 0.72±0.08. The !0 is much lower than is generally reported in literature, and this was attributed to high concentrations of highly absorbing anthropogenic soot observed in SEM analysis. The mean extinction coefficient #27;ep was 194 ± 195 Mm−1. #27;ep and !0 clearly demonstrated and explained quantitatively the visibility reduction due to particles in the Cape Town atmosphere, reduction observed as the brown haze phenomenon. In all the three case studies, microscopy single particle analysis played a critical role in advancing knowledge of understanding properties of aerosol particles in the atmosphere.

This thesis describes an investigation of, and improvements to, the microphysical modelling of aerosols in the Oxford-Rutherford Appleton Laboratory Aerosol and Clouds retrieval (ORAC), which is used to obtain aerosol properties from measurements by the Advanced Along Track Scanning Radiometer (AATSR). Modelling decisions determine the light scattering properties of the aerosol classes which in turn alter the retrieved aerosol properties: aerosol optical depth, and effective radius. The maritime, mineral dust, urban, and biomass burning aerosol classes were first investigated, and then improvements implemented. Major additions to the scheme include the ability to model non-spherical dust as spheroids, soot as fractal aggregates, and to coat spherical particles with an extra layer of differing refractive index (whose thickness can be modified by ambient relative humidity where necessary). Output from aerosol retrievals containing these new models is presented. Modelling of marine aerosol was found to be adequate, but an improvement in the relative humidity assumptions led to an average 5 % increase in aerosol optical depth (AOD). Modelling of mineral dust aerosols has been dramatically altered by the addition of non-spherical dust and hygroscopic particles, leading to increases in measured AOD of over 100 % during dust events, compared to the previous model. Measurement of biomass burning aerosol has been tested with an `ageing' aerosol scheme, leading to increases in over-land measured AOD of 0.14 (~50 % increase). With such significant changes in AOD, representation of aerosol light scattering properties is seen to be important factor in the accuracy of the ORAC scheme. Finally, a method of optimising the placement of detectors in an aerosol measurement device is presented.