Understanding the formation and growth of aerosols is important to a better understanding of a diverse range of problems. The identification of key parameters affecting aerosol behaviour is discussed, and a number of approaches for predicting this behaviour are developed in this thesis. Models appropriate to a wide range of industrial processes are used. Turbulent and laminar flow scenarios are considered, and an assessment is made of the likely differences in system behaviour according to whether nucleation occurs by a predominantly homogeneous, binary or ion-induced mechanism. A number of techniques for predicting aerosol behaviour are compared, ranging from the rigorous to more elementary approaches. It is shown that the simpler techniques are able to demonstrate many of the most important features of aerosol behaviour, whilst allowing the isolation of the parameters which influence this behaviour. This thesis presents methods which are capable of rapidly characterising the growth and formation behaviour of an aerosol system, and in doing so has identified many of the parameters which control this behaviour.

Knowledge of distributions of aerosols is critical to human health, Earth's radiative budget, and air quality. However, the lack of sufficient direct measurements of aerosol type, number, mass concentrations and current limitations of satellite retrievals make it challenging to accurately model the aerosol variability. Such measurement gaps also hinder evaluation of aerosol source budget from emission inventories, modeling of aerosol chemistry, and sinks. In this context, the first study characterizes the potential of multivariate relationships between Aerosol Optical Depth (AOD), a quantity that represents light extinction by aerosols in the atmospheric column and a suite of surface and atmospheric parameters (e.g., vegetation, precipitation, fire characteristics) in order to assess trends in AOD anomalies for the U.S Southwest. This study covers the area that experiences North American Monsoon (NAM) and examines trends in AOD across different aerosol sources in this region such as dust storms, biomass burning, and anthropogenic emissions. We find that aerosols from anthropogenic processes and biomass burning exhibited a strong declining trend in AOD whereas trends along the NAM alley were obfuscated by the monsoon precipitation (sink) and convective dust storms (sources). In the second study, we develop constraints to improve characterization of anthropogenic apparent Elemental Carbon (ECa) using coemitted combustion products such as Carbon Monoxide (CO) and Nitrogen Oxides (NOx). We compare observational ratios of ECa vs CO and ECa vs NOx against those from emission inventories. We find that the observational ratios have increased at sites in the Urban-West due to increase in ECa from 2000-2007 to 2008-2015. Further, emission ratios do not match with observational ratios. We recommend that rigorous efforts are needed to better quantify and monitor the changes in these species in the Urban-West particularly for non-road and residential combustion sectors. The final study of this dissertation discusses a technique to produce forecasts of AOD by combining satellite retrievals and a chemical transport model in an analog based framework. We use model forecasts of AOD, particulate matter (PM) concentrations, and meteorological parameters from Weather Research and Forecasting model with Chemistry (WRF-Chem) to train the framework for choosing analogs (past forecasts similar to current simulations). MODIS Terra and Aqua satellite retrievals of AOD for analog days are then used in a Kalman Filter (KF) framework to determine the forecast error and referred to as KFAN. The analog based estimates better forecasts of AOD for the Western US compared to the East and the mean bias in AOD forecasts are reduced to the range of 0.001-0.1. The reduction in positive bias in AOD is drastic and the method captures the decrease in AOD from morning to afternoon. We find that higher root mean square error (RMSE) values in the East are due to the inability of KFAN to capture the AOD peaks during biomass burning episodes and AOD lows during days of high precipitation rates. A systematic statistical analysis using step-wise linear regression models also show that in the East, there is a stronger dependence of aerosol loading on meteorological factors such as air temperature, precipitation, and relative humidity. As a consequence, overall quality of the analogs in the East is impacted when uncertainties in the simulated meteorological fields are higher. Overall, this study shows that the correlative information from multi-satellite remote sensing retrievals and models provide additional constraints on aerosols using composition/source identification (e.g., aerosol type, landcover, emission sources, fuel consumption), coemitted gas phase species (e.g., CO and NOx), and meteorological parameters (e.g., wind speed, TPW). The synergy of information from these datasets can be beneficial for design of future remote sensing missions, deployment of ground networks, and studies related to feedbacks between meteorology and aerosols.

M.Sc. / Aerosol samples were collected at stations using simple filter unit, loaded with a 4 7 mm diameter pore size Nuclepore membrane filter. The sampling duration was 24 hours for each sample, with the total of 11 samples: seven for Thohoyandou and four for Bethlehem. The samples were analyzed with energy dispersive X-ray fluorescence spectrometry for up to 20 elements. Comparison for elemental concentrations of the data showed that the samples fall into three clusters on average (major: Ca, Cl, Si. S, Fe and AI; intermediate: K, Ti, Pb, Brand Zn; minor: Mn, Cr, As, Sr, Ni and Cu), with the samples collected from Bethlehem having high concentrations in all clusters. High concentrations in the samples collected on Bethlehem were attributed to entrainement of dust particles during the dry winter period. The results also show that the elements are associated with anthropogenic emissions. Therefore, the sampling station at Thohoyandou is considered as a background station due to the low aerosol concentration. The aerosol concentration levels at Thohoyandou can be attributed to biogenic sources because of the large presence of large forest areas in the region and in the vicinity of the sampling location. The samples collected in both regions reveal highly enriched sulphur, chlorine, zinc and lead. It is clearly proved that these elements come from local soil. Chromium and copper were both slightly enriched in Thohoyandou, but the concentration data for these two elements are not available. However it is supposed that these elements come from local soil as well. In another aerosol analysis, passive (diffusive) samplers were used to measure concentration levels for sulphur dioxide and nitrogen dioxide. The measurement campaign was carried out from Soweto in Johannesburg and Bohlokong in Bethlehem with the campaign lasting for two months during the w~nter season. A very clear result derived for sulphur dioxide was the dominating source contribution from use of coal for heating and cooking in both areas. For nitrogen dioxide, it was found that contribution from traffic in highly populated areas and from industrial activities in the neighbourhood of the two areas was the source. The role played by wood burning, is also another additional source used for domestic heating and even cooking.

In this research, three methods of aerosol generation, and their subsequent propagation, are investigated experimentally. These experiments provided insight into the potential risk aerosol can have pertaining to the spread of infectious disease such as COVID – 19. The first of which investigated an alternative generation route that may exist given the discovery of small numbers of viable viruses in urine and stool samples. Flushing biomatter can lead to the aerosolization of micro-organisms; thus, there is a likelihood that bioaerosols generated in public restrooms may pose a concern for the transmission of COVID-19, especially since these areas are relatively confined, experience heavy foot traffic, and may suffer from inadequate ventilation. The results indicate that the particular designs tested in the study generate a large number of droplets in the size range 0.3 𝜇𝑚 – 3 𝜇𝑚, which can reach heights of at least 1.52 m. This highlights the need for incorporating adequate ventilation in the design and operation of public spaces, which can help prevent aerosol accumulation in high occupancy areas and mitigate the risk of airborne disease transmission. Secondly, experiments were conducted to evaluate the effectiveness of facial coverings at various distances around a simulated cough. These concluded that due to the gaps along the seal of a face mask, aerosols can escape 360° around a coughing individual. In the final portion of the thesis study, an experimental method was developed and conducted to break up a droplet via mechanical excitation. The results of these experiments showed that when a droplet is placed on a vibrating string, the droplet can be broken into many secondary droplets which is analogous to one speaking or singing thus providing insight as to how vocal cords can generate respiratory aerosols. / Includes bibliography. / Thesis (MS)--Florida Atlantic University, 2021. / FAU Electronic Theses and Dissertations Collection

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This thesis deals with the reflective properties of selected aerosols subjected to microwave radiation. The backscatter cross section of a sphere is developed analytically as a basis for experimental verification. The most pertinent material parameters necessary for maximum reflectivity are discussed and are used to justify the aerosols selected for the experiment. The experimental procedures and the equipment calibration techniques are prefaced by a discussion of the design and the construction of the aerosol chamber and the microwave source apparatus. The experimental results and the calculated backscatter cross section of the aerosols listed are examined. Conclusions are discussed and applications of the results are offered for consideration.