Atmospheric particles represent a component of air pollution that has been identified as a major contributor to adverse health effects and mortality. Aerosols also interact with solar radiation and clouds perturbing the atmosphere and generating responses in a wide range of scales, such as changes to severe weather and climate. Thus, being able to accurately predict aerosols and its effects on atmospheric properties is of upmost importance. This thesis presents a collection of studies with the global objective to advance in science and operations the use of WRF-Chem, a regional model able to provide weather and atmospheric chemistry predictions and simultaneously representing aerosol effects on climate. Different strategies are used to obtain accurate predictions, including finding an adequate model configuration for each application (e.g., grid resolution, parameterizations choices, processes modeled), using accurate forcing elements (e.g., weather and chemical boundary conditions, emissions), and developing and applying data assimilation techniques for different observational sources. Several environments and scales are simulated, including complex terrain at a city scale, meso-scale over the southeast US for severe weather applications, and regional simulations over the three subtropical persistent stratocumulus decks (off shore California and southeast Pacific and Atlantic) and over North America. Model performance is evaluated against a large spectrum of observations, including field experiments and ground based and satellite measurements. Overall, very positive results were obtained with the WRF-Chem system once it had been configured properly and the inputs chosen. Also, data assimilation of aerosol and cloud satellite observations contributed to improve model performance even further. The model is proven to be an excellent tool for forecasting applications, both for local and long range transported pollution. Also, advances are made to better understand aerosol effects on climate and its uncertainties. Aerosols are found to generate important perturbations, ranging from changes in cloud properties over extensive regions, up to playing a role in increasing the likelihood of tornado occurrence and intensity. Future directions are outline to keep advancing in better predictions of aerosols and its feedbacks.

Occupational asthma affects a variety of industry sectors, including agricultural and manufacturing. Currently, asthma pharmaceuticals are delivered via an inhaler and deposited in the respiratory system. The effectiveness of the medication depends partially on where the particle deposits in the lung. The specific aims of this research were to (1) develop a system to measure hygroscopic particle growth under different environmental conditions; (2) determine the accuracy of a hygroscopic growth model during the growth phase of salt particles; and (3) determine whether the large-diameter particles of an aerosol, those that will most likely deposit in the upper airways, can be separated from the smaller particles. Aim 1: A system was developed that satisfied the design criteria to measure particle growth within fractions of a second. The particles growth was measured every 0.03 seconds and had a relative humidity that only varied by a maximum of 1.3% over a 30 second trial. Aim 2: The next step in the research was to determine how well the model compares to reality in the initial growth phase. The model that included the initial growth rate as a saturated solution had a lower root mean square of error (RMSE) than the model that did not include a maximum saturation value. The maximum reduction in RMSE was 0.254. Aim 3: The analysis of a virtual impactor was conducted to see if aerosolized particles can be size separated at a cut point of 2.5 μm. The virtual impactor was designed to have small particles exit the device in one airflow and the large particles exit in a different airflow. Multiple trials were conducted however, there were only two trials that had any size separation between the two exiting flows. From these results, it was determined that large-diameter particles cannot be separated from smaller particles while remaining aerosolized. The cut-point was 2.3 μm, the small particles were split at 50% through both flows, and the flow that was supposed to contain 100% of all of the large particles only contained a maximum of 70%.

The goal of this thesis is to investigate the kinetics and amount of SO2 uptake on hematite, which will act as a representative of mineral dust aerosol. The environmental reaction chamber used here will allow the variation of water vapor pressure to examine the effect of relative humidity (RH) on these parameters. The role of a common atmospheric oxidant, ozone, in the uptake process will also be investigated. The results will be presented with emphasis on the role of hematite in mineral dust aerosols as a sink of SO2, and the possible acidification of hematite particles through heterogeneous reaction pathways.

Pseudomonas aeruginosa bacterial biofilms are the leading cause of mortality among cystic fibrosis (CF) patients. Biofilms contain bacteria attached to a surface and encased in a protective matrix. Since bacteria within a biofilm are less susceptible to antibiotics, a new approach is to use dispersion compounds that cause the biofilms to release free-swimming bacteria. Our approach has focused on combining nutrient dispersion compounds with antibiotics to increase eradication of bacteria within biofilms. This approach takes advantage of the enhanced susceptibility of free-swimming bacteria to antibiotics, compared to bacteria within biofilms. Ultimately, this research will guide the development of an aerosol therapy containing both antibiotic and dispersion compounds to treat bacterial biofilm infections. To study the effect of antibiotic and dispersion compound treatments on biofilm eradication, a high-throughput screening assay was used to assess the effect on young Pseudomonas aeruginosa biofilms. In addition, a Lab-Tek chambered coverglass system imaged via confocal microscopy was used to assess the effect on mature Pseudomonas aeruginosa biofilms. Seven antibiotics (amikacin disulfate, tobramycin sulfate, colistin sulfate, colistin methanesulfonate (CMS), polymyxinB sulfate, erythromycin, and ciprofloxacin hydrochloride) were tested alone or in combination with four nutrient dispersion compounds (sodium citrate, succinic acid, xylitol, and glutamic acid) to assess the level of eradication of bacteria within biofilms. For young biofilms, 15 of 24 combinations significantly eliminated more live bacteria within the biofilms (measured in colony forming units per milliliter) compared to antibiotics alone. In the more mature biofilm system, only 3 out of 26 combinations resulted in a higher percentage of live biofilm bacteria being eliminated compared to antibiotics alone, showing the importance of biofilm age in the effectiveness of these potential combination therapies. To aid in confocal microscopic analysis of biofilms, an automated quantification program called STAINIFICATION was developed. This new program can be used to simultaneously investigate connected-biofilm bacteria, unconnected bacteria (dispersed bacteria), the biofilm protective matrix, and a growth surface upon which bacteria are grown in confocal images. The program contains novel algorithms for the assessment of bacterial viability and for the quantification of bacteria grown on uneven surfaces, such as tissue. The utility of the viability assessments were demonstrated with confocal images of Pseudomonas aeruginosa biofilms. The utility of the uneven surface algorithms were demonstrated with confocal images of Staphylococcus aureus biofilms grown on cultured human airway epithelial cells and Neisseria gonorrhoeae biofilms grown on transformed cervical epithelial cells. Finally, a proof-of-concept study demonstrated that dry powder aerosols containing both antibiotic and nutrient dispersion compounds could be developed with properties optimized for efficient deposition in the lungs. A design of experiments study showed that solution concentration was the most significant parameter affecting aerosol yield, particle size, and in vitro deposition profiles. Collectively this work demonstrated that bacterial dispersion from biofilms can enhance antibiotic susceptibility and can be better quantified using the new STAINIFICATION software. Formulation of dispersion compounds and antibiotics into a dry powder aerosol could enable more effective treatment of biofilm infections in the lungs.

Le but de ce travail de thèse est d'améliorer la compréhension des interactions aérosols -nuages. Pour ce faire, nous avons dû traiter des sujets aussi larges et divers que le développement de moyens instrumentaux, l'analyse statistique et la modélisation. Ainsi, nous avons été amenés à installer et à développer un échantillonneur d'air nuageux. Il permet maintenant un échantillonnage en nuages en continu à l'observatoire du sommet du puy de Dôme. Il s'en est suivi deux campagnes de mesures durant les hivers 2000 et 2001 aboutissant à la collecte de plus de 600000 échantillons. Grâce à ce large panel de conditions météorologiques et d'origines de masses d'air, nous avons pu quantifier un des points clés de l'étude des relations aérosol - nuage. Nous avons pu obtenir une relation entre la concentration totale de particules d'aérosol et, d'une part la concentration de gouttelettes de nuages, et d'autre part le rayon effectif du nuage pour un contenu en eau liquide du nuage constant. De plus, l'utilisation d'un modèle d'activation des gouttelettes de nuage appelé ExMix nous a permis d'avoir une meilleure compréhension de l'évolution de l'incorporation des particules dans le nuage. Ainsi, nous avons pu comparer ces variations avec le contenu en eau qui augmente ou avec le rayon effectif du nuage pour un contenu en eau constant des sorties du modèle à celles mesurées. Toutefois, cela a montré le manque important d'une mesure physico-chimique de l'aérosol avec une fréquence de mesure élevée permettant par exemple une meilleure prise en compte de la phase organique de l'aérosol. C'est pourquoi, un analyseur de la volatilité et de la granulométrie des aérosols a été développé, construit et testé durant la dernière partie de ce travail de thèse.

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.

Filter holders and continuous air monitors (CAMs) are used extensively in the nuclear industry. It is important to minimize leakage in these devices and in recognition of this consideration, a limit on leakage for sampling systems is specified in ANSI/HPS N13.1-1999; however the protocol given in the standard is really germane to measurement of significant leakage, e.g., several percent of the sampling flow rate. In the present study, a technique for quantifying leakage was developed and that approach was used to measure the sealing integrity of a CAM and two kinds of filter holders. The methodology involves use of sulfur hexafluoride as a tracer gas with the device being tested operated under dynamic flow conditions. The leak rates in these devices were determined in the pressure range from 2.49 kPa (10 In. H2O) vacuum to 2.49 kPa (10 In. H2O) pressure at a typical flow rate of 56.6 L/min (2 cfm). For the two filter holders, the leak rates were less than 0.007% of the nominal flow rate. The leak rate in the CAM was less than 0.2% of the nominal flow rate. These values are well within the limit prescribed in the ANSI standard, which is 5% of the nominal flow rate. Therefore the limit listed in the ANSI standard should be reconsidered as lower values can be achieved, and the methodology presented herein can be used to quantify lower leakage values in sample collectors and analyzers. A theoretical analysis was also done to determine the nature of flow through the leaks and the amount of flow contribution by the different possible mechanisms of flow through leaks.

In this study, commercially available Computational Fluid Dynamics (CFD) software, CFX-4.4 has been used for the simulations of aerosol transport through various aerosol-sampling devices. Aerosol transport was modeled as a classical dilute and dispersed two-phase flow problem. Eulerian-Lagrangian framework was adopted wherein the fluid was treated as the continuous phase and aerosol as the dispersed phase, with a one-way coupling between the phases. Initially, performance of the particle transport algorithm implemented in the code was validated against available experimental and numerical data in the literature. Code predictions were found to be in good agreement against experimental data and previous numerical predictions. As a next step, the code was used as a tool to optimize the performance of a virtual impactor prototype. Suggestions on critical geometrical details available in the literature, for a virtual impactor, were numerically investigated on the prototype and the optimum set of parameters was determined. Performance curves were generated for the optimized design at various operating conditions. A computational model of the Linear Slot Virtual Impactor (LSVI) fabricated based on the optimization study, was constructed using the worst-case values of the measured geometrical parameters, with offsets in the horizontal and vertical planes. Simulations were performed on this model for the LSVI operating conditions. Behavior of various sized particles inside the impactor was illustrated with the corresponding particle tracks. Fair agreement was obtained between code predictions and experimental results. Important information on the virtual impactor performance, not known earlier, or, not reported in the literature in the past, obtained from this study, is presented. In the final part of this study, simulations on aerosol deposition in turbulent pipe flow were performed. Code predictions were found to be completely uncorrelated to experimental data. The discrepancy was traced to the performance of the code's turbulent dispersion model. A detailed literature survey revealed the inherent technical deficiencies in the model, even for particle dispersion. Based on the results of this study, it was determined that while the code can be used for simulating aerosol transport under laminar flow conditions, it is not capable of simulating aerosol transport under turbulent flow conditions.

The existence of flammable aerosols presents a high potential for fire hazards in the process industry. Various industrial fluids, most of which operate at elevated temperatures and pressures, can be atomized when released under high pressure through a small orifice. Because of the complexity in the process of aerosol formation and combustion, the availability of data on aerosol flammability and flame propagation behaviors is still quite limited, making it difficult to evaluate the potential fire and explosion risks from released aerosols in the process industry and develop safety measures for preventing and/or mitigating aerosol hazards. A study is needed to investigate the relationship between aerosol combustion behaviors and the properties of the aerosols. This dissertation presents research on the combustion behaviors of flammable aerosols. Monodisperse aerosols created by industrial heat transfer fluids were generated using electrospray. The characteristics of flame propagations in aerosols and the influence of the presence of fuel droplets in the system are studied in the aerosol ignition tests. Flames in aerosols are characterized by non-uniform shapes and discrete flame fronts. Flames were observed in different burning modes. Droplet evaporation was found to play an important role in aerosol burning modes. Droplet evaporation behaviors and fuel vapor distributions are further related to aerosol droplet size, droplet spacing, movement velocity, and liquid volatility. The burning mode of a global flame with rapid size expansion is considered the most hazardous aerosol combustion scenario. This burning mode requires a smaller droplet size and smaller space between droplets. Larger droplet sizes and spacing may hinder the appearance of global flames. But when the liquid fuel has a certain level of volatility, there is an uneven distribution of fuel vapor in the system and this may cause the unique phenomenon of burning mode variations combined with enhanced flame propagation speed. Using an integrated model, the minimum ignition energy values of aerosols were predicted. The aerosol minimum ignition energy is influenced by the fuel-air equivalence ratio and the droplet size. Higher equivalence ratios, up to 1.0, significantly reduce the minimum ignition energy, while larger droplet sizes result in a higher minimum ignition energy.

A circumferential slot In-line Virtual Impactor (IVI) has been designed using Computational Fluid Dynamics (CFD) simulation tools and experimentally characterized using monodispersed liquid aerosols to validate simulation results. The base design, IVI-100, has an application as a pre-separator for sampling inlets, where the device scalps large particles from the aerosol size distribution. The IVI-100 samples air in at 111 L/min and deliver the fine aerosol fraction in a 100 L/min flow and provide a cutpoint particle size of 10 µm, with a pressure drop of 45 Pa. An inverted dual cone configuration encased inside a tube provides the IVI-100 with a characteristic circumferential slot of width 0.254 mm (0.100 inches) and a slot length of 239 mm (9.42 inches) at the critical zone. The upper cone causes the flow to accelerate to an average throat velocity of 3.15 m/s, while the lower cone directs the major flow toward the exit port and minimizes recirculation zones that could cause flow instabilities in the major flow region. The cutpoint Stokes number is 0.73; however, the cutpoint can be adjusted by changing the geometrical spacing between the acceleration nozzle exit plane and a flow divider. Good agreement is obtained between numerically predicted and experimentally observed performance. An aerosol size selective inlet for bioaerosol and other air sampling applications using an upgraded prototype of IVI-100, mounted inside a BSI-100 inlet shell was tested in an aerosol wind tunnel over a speed range of 2 – 24 km/hr. The BSI-IVI-100 inlet has a cutpoint of 11 µm aerodynamic diameter and delivers the fine fraction at 100 L/m. The geometric standard deviation of the fractionation curve is 1.51 and the performance is not affected by wind speeds. An IVI-350, which is an adaptation of the IVI to be used as a powder fractionator, was designed based on computational simulations, and provides a cutpoint of 3 µm AD, while operating in a total flow rate of 350 L/min. Four Identical IVI -350 units will be operated in parallel to fractionate aerosolized powders in a 1400 L/min flow. An optimized inlet, with a contoured tear-drop shaped insert provides uniform flow to four identical IVI units and prevents powder accumulation in the system entrance.