Dust originating from dry lakes contributes harmful and toxic elements to downwind urban areas and mountain snowpack that is compounded by local contaminant inputs from anthropogenic sources. To evaluate dust contributions to an urban area from regional playas, we sampled playa dust sources, urban dust deposition, and snow dust deposition in central Utah, USA. Samples were analyzed for grain size, mineralogy, and chemistry. Bulk mineralogy between playa, urban, and snow dust samples was similar, with silicate, carbonate, and evaporite minerals. Grain size distribution between fine playa, urban, and snow dust particles was also similar. Elements found at high concentrations in playas include Li, Na, Mg, Ca, Sr, and U, and most other elements were found at higher concentrations in urban and snow deposition samples. Particularly enriched elements in dust deposition include Cu, Se, Ag, Cd, Sb, and La, which are sourced from industrial activity, mining, and vehicular emissions and wear. Based on results from mass balance modeling, a large majority of the dust mass deposited on the Wasatch Front is from playa sources. Urban and playa dust sources largely remain constant seasonally, although spikes in playa-associated element concentrations during a particular seasonal sample may indicate frequent and/or more intense dust events. Among the highly environmentally available elements B, Ca, Sr, and U, are Cd and Se, both of which present toxicity concerns for humans and environments. This is the first study describing heavy metal contamination and sources in Utah, USA.

Heterogeneous reactions between mineral dust aerosols and gas phase volatile organic compounds have the potential to impact important atmospheric chemical processes. However, little is known about the uptake and reactivity of volatile organic compounds on particulates found in the environment. A Knudsen cell was designed and constructed for providing precise measurement of reaction probabilities within these systems. The instrument was validated through a series of experiments. After validating the Knudsen cell against several key benchmarks, the instrument was used to measure the uptake coefficient for ethanol on particulate silicon dioxide. The uptake coefficient of ethanol on silicon dioxide, a common compound in mineral dust aerosols, was determined to be 7 x 10-7. Therefore, uptake of ethanol on silicon dioxide would be competitive with the loss of other volatile organic compounds on silicon dioxide, which show similar rates of uptake. The Knudsen cell was validated and measured the uptake of ethanol on silicon dioxide, and future work with the Knudsen cell will study the uptake of chemical warfare agent simulants on metal oxides. / Master of Science

Earth's radiation budget is directly influenced by aerosols through the absorption of solar radiation and subsequent heating of the atmosphere. Aerosols modulate the hydrological cycle indirectly by modifying cloud properties, precipitation and ocean heat storage. In addition, polluting aerosols impose health risks in local, regional and global scales. In spite of recent advances in the study of aerosols variability, uncertainty in their spatial and temporal distributions still presents a challenge in the understanding of climate variability. For example, aerosol loading varies not only from year to year but also on higher frequency intraseasonal time scales producing strong variability on local and regional scales. An assessment of the impact of aerosol variability requires long period measurements of aerosols at both regional and global scales. The present dissertation compiles a large database of remotely sensed aerosol loading in order to analyze its spatio-temporal variability, and how this load interacts with different variables that characterize the dynamic and thermodynamic states of the environment. Aerosol Index (AI) and Aerosol Optical Depth (AOD) were used as measures of the atmospheric aerosol load. In addition, atmospheric and oceanic satellite observations, and reanalysis datasets is used in the analysis to investigate aerosol-environment interactions. A diagnostic study is conducted to produce global and regional aerosol satellite climatologies, and to analyze and compare the validity of aerosol retrievals. We find similarities and differences between the aerosol distributions over various regions of the globe when comparing the different satellite retrievals. A nonparametric approach is also used to examine the spatial distribution of the recent trends in aerosol concentration. A significant positive trend was found over the Middle East, Arabian Sea and South Asian regions strongly influenced by increases in dust events. Spectral and composite analyses of surface temperature, atmospheric wind, geopotential height, outgoing longwave radiation, water vapor and precipitation together with the climatology of aerosols provide insight on how the variables interact. Different modes of variability, especially in intraseasonal time scales appear as strong modulators of the aerosol distribution. In particular, we investigate how two modes of variability related to the westward propagating synoptic African Easterly Waves of the Tropical Atlantic Ocean affect the horizontal and vertical structure of the environment. The statistical significance of these two modes is tested with the use of two different spectral techniques. The pattern of propagation of aerosol load shows good correspondence with the progression of the atmospheric and oceanic synoptic conditions suitable for dust mobilization over the Atlantic Ocean. We present extensions to previous studies related with dust variability over the Atlantic region by evaluating the performance of the long period satellite aerosol retrievals in determining modes of aerosol variability. Results of the covariability between aerosols-environment motivate the use of statistical regression models to test the significance of the forecasting skill of daily AOD time series. The regression models are calibrated using atmospheric variables as predictors from the reanalysis variables. The results show poor forecasting skill with significant error growing after the 3rd day of the prediction. It is hypothesized that the simplicity of linear models results in an inability to provide a useful forecast.

Ice formation largely influences the properties of clouds and hence it has an important impact on weather and climate. Primary ice formation is a consequence of either homogeneous or heterogeneous ice nucleation. The latter process is catalyzed by a foreign substance called Ice Nucleating Particle (INP). Mineral dust particles were found to contribute to atmospheric INPs. Most types of mineral dust are ice active below -20 °C. In contrast, atmospheric observations indicate that immersion freezing as one of the most important heterogeneous ice nucleation processes can occur at temperatures higher than -15 °C. One possible explanation for cloud glaciation at high temperatures might be the presence of biological material (e.g. bacteria) inducing ice nucleation. Our fundamental process and even qualitative understanding concerning atmospheric heterogeneous ice nucleation is limited. In the framework of the present thesis, experimental and theoretical work was carried out to improve the basic understanding of the immersion freezing behavior of mineral dust and bacterial INPs. On the basis of model simulations immersion freezing experiments were designed at the Leipzig Aerosol Cloud Interaction Simulator (LACIS). The immersion freezing behavior of mineral dust and bacterial INPs was studied in dependence of temperature and particle surface area/number at LACIS. As a results of the present thesis, it was found that the immersion freezing behavior of kaolinite being a proxy of mineral dust INPs does not depend on the droplet volume, but on the particle surface area. The kaolinite particles investigated caused freezing below -30 °C. In contrast, Ice Nucleation Active (INA) protein complexes that are attributed to bacterial INPs were found to induce freezing at -7 °C. Furthermore, it was shown that the ice nucleation activity of protein complexes is very similar regardless of whether the INA protein complex is attached to the outer cell membrane of intact bacteria or to cell membrane fragments. The immersion freezing ability depends on the number and type of INA protein complexes present in the droplet ensemble. The immersion freezing ability of mineral dust and bacterial INPs was parameterized accounting for the time effect. With this, results from literature could be reproduced for both INP types. These parameterizations can be used in e.g. cloud resolving atmospheric models.

Atmosphärisches Aerosol kann den Strahlungstransport signifikant beeinflussen. Mineralstaub, der über der Sahara und anderen Wüsten in die Atmosphäre gelangt, ist das hinsichtlich der in letzterer dauerhaft verbleibenden Masse bedeutendste Aerosol. Darüber hinaus sind Saharamineralstaubpartikel nichtkugelförmig, und die Wirkungen dieser Partikeleigenschaft auf den Strahlungstransport in der Erdatmosphäre sind bislang nur ungenügend untersucht worden. Es werden die optischen Eigenschaften, Strahlungs- und Erwärmungseffekte von Saharamineralstaub unter Berücksichtigung der Nichtkugelförmigkeit seiner Partikel quantitativ untersucht, wobei der gesamte, im Hinblick auf den Strahlungshaushalt energetisch relevante Spektralbereich zugrunde gelegt wird. Zunächst werden auf Basis in-situ-gemessener Experimentaldaten die atmosphärischen Umgebungsbedingungen, Größenverteilungen, Brechungsindizes, Bodenalbedo und Partikelgestalt festgelegt, die in einem zweiten Schritt in ein Strahlungstransportmodell einfließen. Mit dessen Hilfe wird in umfangreichen numerischen Simulationen des Strahlungstransports in einer realistischen mineralstaubhaltigen Modellatmosphäre im Vergleich zu Messdaten beispielsweise geklärt, welche Partikelform und Größenäquivalenz angenommener sphäroidaler Modellpartikel am meisten realistisch sind. Des Weiteren werden im Zusammenhang mit der Partikelnichtkugelförmigkeit Sensitivitätsstudien zur Beantwortung der Fragen durchgeführt, inwieweit diese das Strahlungsfeld beeinflusst und zu veränderten Strahlungserwärmungswirkungen führt.

Der Eintrag von Mineralstaub in den Ozean geschieht entweder durch trockene oder durch nasse Deposition. Dies ist ein wichtiger Prozess um ozeanische Organismen wie Phytoplankton mit Nährstoffen (z.B. Nitrat, Phosphat oder Eisen) zu versorgen. Viele Modelle befassen sich mit der Simulation von Depositionsflüssen von Mineralstaub in den Ozean. Messungen von Massendepositionsflüssen von Mineralstaub sind hingegen selten. Daher ist es von großer Notwendigkeit, diese Messungen durchzuführen um die vielen Modelle zu validieren und den Mineralstaubzyklus besser zu verstehen. Innerhalb des SOPRAN Projektes (Surface Ocean PRocesses in the ANthropocene) wird der Materialtransport zwischen der Atmosphäre und dem Ozean untersucht. Die Messungen dafür wurden auf den Kapverdischen Inseln durchgeführt, über welchen der Saharastaub durch die Passatwindzirkulation vorwiegend transportiert wird. Im Rahmen dieser Arbeit werden in-situ Messungen von trockener Deposition von Mineralstaub in den Ozean präsentiert. Verschiedene Methoden wurden auf ihre Anwendbarkeit getestet und deren Ergebnisse miteinander verglichen. Alle Messergebnisse liegen im Bereich der Messunsicherheiten, wodurch ein Satz qualitätsgesicherter Daten aufgebaut werden konnte. Diese Daten wurden mit den Ergebnissen eines regionalen Chemie-Transport Modells verglichen. Modellierte Massendepositionsflüsse von Mineralstaub waren manchmal doppelt so hoch wie gemessene. Die größte Unsicherheit der Modelle liegt in der Emission des Mineralstaubs, die im Transport und der Deposition fortgesetzt wird. Weitere Unterschiede entstehen durch den Vergleich von Punktmessungen mit einer Gitterzelle, wenn der Staub nicht gleichmäßig über die Gitterzelle verteilt ist. Zusammenfassend wurden Massendepositionsmessungen von Mineralstaub erfolgreich mit verschiedenen Methoden durchgeführt. Mit den Erfahrungen aus dieser Studie ist es nun möglich, Langzeitmessungen von Mineralstaubdeposition in den Ozean erstellen. Diese Daten können von Atmosphärenmodellierern für ihre Modellvalidierung genutzt werden. Anwender von Ozeanmodellen und SOPRAN Partner werden diese Ergebnisse nutzen um z.B. die ozeanische Reaktion auf den Mineralstaubeintrag zu untersuchen. / The input of mineral dust to the oceans, via dry or wet deposition, is an important process, because the entrainment of nutrients (e.g., Nitrate, Phosphor and Iron) is essential for oceanic life such as phytoplankton. A lot of effort has been done to model the dust deposition fluxes to the ocean. However, field measurements concerning the deposition flux are sparse. Therefore, those measurements are needed in order to verify the huge amount of model outputs and to better understand the mineral dust cycle. Within the project SOPRAN (Surface Ocean PRocesses in the ANthropocene), the influence of material exchange between the atmosphere and the ocean is investigated. Measurements were carried out at the Cape Verde Islands in the direct outflow of the Saharan Desert. This study presents the first in-situ measurements of the dry mass deposition flux of mineral dust to the ocean. The applicability of different methods was tested and the results were compared to each other. The results of the measured data were comparable and a set of quality assured data could be built up. Those results were compared to the output of a regional chemistry- transport model. The modeled mass deposition flux was sometimes double as high as the measured one. The main uncertainty of the models is the emission of mineral dust at the source region, proceeding in the transport and emission of mineral dust. Furthermore, comparing single point measurements with outputs of a grid cell leads to differences in deposition fluxes by an inhomogeneous distribution of the mineral dust layer. Summarizing, the measurements of the mass deposition flux of mineral dust could be performed successfully with several methods. With the expertise of this study, long-term observations of the mineral dust deposition to the ocean can now be established. These data can be used by atmosphere modelers to validate their models. Ocean modelers and partners of the SOPRAN project will use these data to investigate e.g., the biological response of the ocean to mineral dust entrainment.

Dust aerosol emission is a critical topic in agriculture, occurring either by aeolian process from bare or sparsely vegetated cropland or as fugitive emission during tilling, harvest and many other farming activities. Aerosols, which are in the case of agriculture either mineral dust, organic particles or a mixture, are known for impacting human health, cloud formation and ultimately, the earth’s climate and ecosystem. Coupled atmosphere and aerosol transport models are commonly used to study aerosol dispersion in the atmosphere, but so far, agricultural sources are under-represented. Hence, estimations of these emissions’ actual impact are still somewhat uncertain regarding their seasonality, spatial distribution and the fraction of the global aerosol load. To fill this gap, this study aims at identifying suitable approaches for modelling aeolian emissions from sparsely vegetated cropland and fugitive emissions from tilling. Fugitive emissions are challenging since they mainly depend on human activity that is not predictable, but observed events can be used as case studies. For this, a Lagrangian particle dispersion model was chosen, which can trace the trajectory of individual particles in the emitted dust plume. So the particle model “Itpas” was developed to tackle fugitive emissions and to be capable of simulating the complex turbulent mixing of dust particles inside the atmospheric boundary layer. This model was used to simulate a case study based on measured tilling emissions, showing the particle dispersion for a stable and unstable stratified boundary layer. It was shown that within a stably stratified boundary layer, the dust plume is restricted to the near-source region. In contrast, emissions in unstable boundary layers go into long-range transport. This illustrates the spatial range a single tillage operation can have an impact. Aeolian dust emissions are controlled by the wind. For cropland, the emission variability is caused mainly by the frequently changing vegetation cover. Emissions can only occur in the time between tillage and newly grown crops or during drought periods. A parametrisation based on high-resolution satellite observations of the vegetation cover was created to include this process into a model. With this, a new dust emission scheme for cropland emission was developed for the model system COSMO-MUSCAT. In a case study of a dust outbreak from cropland in Poland in 2019, the model’s ability was tested extensively on multiple spatial resolutions. Validation against satellite-measured AOD, ground-measured PM10 and the vertical profile of the PollyNET lidar in Warsaw showed an overall good agreement of the model simulation with the observations. In the framework of this thesis, one dedicated model approach was developed for both the fugitive emissions and the aeolian emissions and validated upon case studies. These approaches could help better understand agricultural dust emissions, their spatial distribution, seasonality and, ultimately, global impact.

Dust is a critical component of the Earth System. The central and western Sahara (CWS) is the dustiest place on Earth during the northern hemisphere summer. Understanding patterns and causes of spatial and temporal variability of dust presence here is essential for its reliable simulation in numerical models of weather and climate. Four papers in this thesis contribute to that objective, utilising a combination of high temporal resolution satellite data and global atmospheric reanalyses for June – August 2004 – 2010 inclusive. The first paper develops an objective dust detection scheme for the CWS using data from the Spinning Enhanced Visible and Infrared Imager (SEVIRI), which are available every 15 minutes around the clock. These data have shed valuable insight on CWS dust processes, but their subjective application has to date limited their range of applications. The SEVIRI dust flag (SDF) developed here is evaluated against other widely used surface and satellite derived indicators of dustiness and it is found to reliably detect the presence of moderate-heavy dust loadings. The distribution of dust each summer is presented, revealing a high degree of interannual variability in overall dust coverage. The second paper utilises SDF to create an objective, high spatial resolution dust source map, based on the automated tracking of individual dust plumes. The most active sources are associated predominantly with palaeo-lakes and outwash plains, typically around the Saharan mountains. There is a clear intraseasonal progression of active source areas, controlled by regional climatology. The tracking scheme describes the transport trajectory of dust events following their initiation and the spatial association with deep convection at this time, revealing a clear regional divide in the relative importance of known meteorological mechanisms that drive dust emission from the dominant sources. The third paper uses an unsupervised clustering algorithm to classify maps of daily dust presence frequency and identify patterns of intraseasonal variability in CWS dust coverage. The resulting idealised dust states vary according to frequency of dust occurrence and its location, demonstrating a clear progression in preferred dust location from June – August and preferred state transitions from one day to the next. High daily dust occurrence frequency corresponds to an advanced West African Monsoon flow and low daily dust occurrence frequency corresponds to a Harmattan-dominated CWS. The overall location of the dust is linked to the location of the Sahara Heat Low, which changes as the summer progresses. The final paper addresses interannual variability in summertime dust presence frequency by comparing the 2 years with highest (2005) and lowest (2008) dust presence. The key difference is the occurrence of 3 multi-day periods in 2005 characterised by anomalously high dust presence. Case study comparison with the 3 periods of highest dust presence in 2008 identifies the anticyclonic circulation of the midtroposphere as a key control on dust duration over the CWS, dictating whether emitted dust is efficiently transported away from the CWS or whether it remains in suspension over the region for prolonged periods of time, up to several days in the anomalously dusty periods of 2005.

An investigation into the light scattering properties of Saharan dust grains is presented. An electrodynamic trap has been used to levitate single dust particles. By adjusting the trap parameters, partial randomisation of the particle orientation has been introduced. While levitated, the particles were illuminated by a laser, and a rotating half-wave retarder enabled selection of vertically or horizontally polarized incident light. A laser diffractometer and linear photodiode array have been used to measure intensity at scattering angles between 0.5° and 177°. Combining these measurements with Fraunhofer diffraction as calculated for a range of appropriately-sized apertures allows the calculation of the phase function and degree of linear polarization. The phase functions and degree of linear polarisation for four case study particles are presented - the phase functions are found to be featureless across most of the scattering region, with none of the halo features or rainbow peaks associated with regularly shaped particles such as hexagonal columns or spheres. Particle models comprised of large numbers of facets have been constructed to resemble the levitated particles. Utilizing Gaussian random sphere methods, increasing levels of roughness have been added to the surfaces of these models. A Geometric Optics model and a related model, Ray Tracing with Diffraction on Facets, have been modified to calculate scattering on these particle reconstructions. Scattering calculations were performed on each of these reconstructions using a range of refractive indices and two rotation regimes – one where the orientations of the reconstructed particle were limited to match those observed when the particle was levitated, and one where the orientation was not limited. Qualitative comparisons are performed on the phase functions and degree of linear polarization, where it is observed that the addition of roughness to the modelled spheroids causes the computed phase functions to increasingly resemble those from the levitated particles. Limiting the orientation of the particles does not affect the scattering noticeably. The addition of a very small absorption coefficient does not change the comparisons considerably. As the absorption coefficient is increased, however, the quality of the comparisons decreases rapidly in all cases but one. The phase functions are quantitatively compared using RMS errors, and further comparison is performed using the asymmetry parameter.

Conselho Nacional de Desenvolvimento Científico e Tecnológico / O Oceano Austral é a região oceânica de maior extensão em que os macronutrientes necessários à produção primária permanecem em níveis elevados por todo ano. Essa condição é conhecida como High Nutrient Low Clorophyll (HNLC) e é determinada, em grande parte, pela relativa escassez de micronutrientes, particularmente o ferro. Diversos experimentos comprovaram que a entrada de ferro neste sistema intensifica a produção biológica, aumentando a fixação do carbono e, eventualmente, sua exportação para águas profundas. Este fenômeno recebeu muita atenção nos últimos 20 anos devido a sua possível influencia no clima, via ciclo do carbono. A relação inversa entre concentração de CO2 na atmosfera e o fluxo de poeira mineral observados em registros glaciais da Antártica Central sugere que a deposição atmosférica pode ser uma importante via para o aporte de micronutrientes. Porém, a contribuição da deposição de poeira mineral para a produção primária nesta região permanece para ser demonstrada e seu possível papel no sistema climático ainda não é conclusivo. No caso do setor Atlântico do Oceano Austral, que recebe influência da Patagônia, os baixos fluxos modernos de poeira mineral e a baixa solubilidade do ferro associado à estrutura dos alumíniossilicato levam muitos autores a postular que fontes oceânicas de micronutrientes sejam mais determinantes. Faltam, no entanto, evidências experimentais. Neste trabalho, abordamos o estudo da fertilização do setor Atlântico do Oceano Austral pela poeira da Patagônia utilizando duas ferramentas: (1) o sensoriamento remoto orbital de aerossóis minerais e clorofila-a em escala interanual; e (2) um experimento de fertilização, com poeira da Patagônia, realizado na Passagem de Drake, considerando fluxos estimados para a era moderna e para o último glacial. Após doze dias de bioensaio, os tratamentos de adição de poeira mostraram a elevação da clorofila-a e da abundância de células em níveis acima dos controles. Níveis intermediários e maiores de adição não diferiram entre si na intensidade de resposta biológica, separando-se apenas da menor adição. Esses resultados indicam que a poeira da Patagônia, mesmo nos fluxos atuais, é capaz de prover os micronutrientes escassos na coluna dágua, com potencial para deflagrar aumentos significativos de biomassa. Através da análise por sensoriamento remoto, identificamos uma região de alta correlação entre poeira e clorofila-a, que está localizada entre a Frente Subtropical e a Frente Polar, se estendendo da Argentina ao sul da África. Esta região difere das águas ao sul da Frente Polar pela menor profundidade da camada de mistura, menor concentração de silicatos, baixa biomassa de diatomáceas e, estima-se, maior estresse fisiológico devido à escassez de ferro e menor aporte oceânico deste nutriente. Em conjunto, essas características parecem criar condições que tornam a resposta biológica mais sensível à deposição de poeira mineral. Estes resultados lançam nova luz sobre o controle atual da produção primária na região e sobre a hipótese da regulação climática pelo fitoplâncton no Oceano Austral, mediado pela deposição de poeira da Patagônia. / The Southern Ocean is the larger ocean region where the macronutrients needed for primary production remain in high levels through the year. This condition is known as High Nutrient Low Chlorophyll (HNLC) and is conditioned, largely, by the relative shortage of micronutrients, particularly iron. Several experiments proved that the supply of iron to this system enhances biological production, increasing carbon fixation and, eventually, its exportation to deep waters. This phenomenon received much attention in the last 20 years due to its possible influence in the climate, through carbon cycle. The inverse relationship between the atmospheric CO2 concentration and the mineral dust flux observed on the Central Antarctic glacial records suggest that atmospheric deposition may be an important source for the supply of micronutrients. However, the contribution of mineral dust deposition for the primary production in this region remains to be demonstrated and its possible hole in the climate system its not yet conclusive. In the case of Atlantic Southern Ocean, thats influenced by Patagonia, the low modern flows of mineral dust and the low iron solubility associated with aluminum-silicate structure led many authors to state that oceanic sources of micronutrients are more determinants. However, experimental evidence are lacking. In the present work, we approach the study of fertilization of Atlantic Southern Ocean by Patagonian dust employing two different tools: (1) orbital remote sensing of mineral aerosols and chlorophyll-a on inter-annual scale; and (2) a fertilization experiment with Patagonian dust, carried through in Drake Passage, considering estimated flux for the modern era and for the last glacial. After twelve days of bioassay, the dust addition treatments showed increase on chlorophyll-a and cell abundance beyond controls levels. Intermediary and higher levels of addition didnt differ between each other regarding the intensity of biological response, separating only of the lower addition treatment. These results indicate that even modern Patagonia dust flux is capable of providing micronutrients that are scarce in the water column, with potential to deflagrate a bloom. Through remote sensing analysis we have identified a region with high correlation between dust and chlorophyll-a, thats located between the Subtropical Front and the Polar Front, extending from Argentina to south of Africa. This region differs from waters south of the Polar Front by means of a deeper mixed layer, lower silicate concentrations, low diatom biomass and, is estimated, greater iron physiological stress and lower iron oceanic supply. Together, these properties seem to create conditions to which biological response would be more sensible to dust deposition. These results cast new light over controls on modern primary production in the region and over the phytoplankton climatic regulation in the Southern Ocean, mediated by Patagonian dust deposition.