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.

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.

To this date, estimates of the climate response to mineral dust remain largely uncertain because of our limited capability to quantify dust distribution in the atmosphere. Focusing on the Central and East Asian dust source regions, this thesis aims to develop a coupled regional dust modeling system to provide an improved modeling capability of atmospheric dust as well as to aid the integration of ground-based and satellite observations. The objectives of this study are as follows: 1) evaluate the capabilities of the available data to detect and quantify mineral dust in the atmosphere; 2) develop and test a coupled regional dust modeling system able to simulate size resolved dust concentrations accounting for the regional specifics of Central and East Asia; and 3) outline a methodology for data and modeling integration. The capabilities of ground-based and satellite data to characterize dust in the atmosphere are examined in great details. Based on analysis of MODIS data reflectance and radiances, we found evidence for regional signature of dust in near-IR and proposed a new probabilistic dust-cloud mask that explicitly takes into account the spatial variability characteristics of dust aerosols. We developed a coupled regional dust modeling system (WRF-DuMo) by incorporating a dust emission module (DuMo) into the NCAR WRF model. The WRF-DuMo unique capabilities include explicit treatment of land surface properties in Central and East Asia, a suite of dust emission schemes with different levels of complexity, multiple options for dust injection in the atmosphere and flexible parameters of the initial size distribution of emitted dust. Two representative dust events that originated in East Asia in the springs of 2001 and 2007 have been modeled with WRF-DuMo. Simulations with different initial size distribution of dust, injection and emission parameterizations have been performed to investigate their relative role on the modeled dust fields. We performed an integrated analysis of modeled dust fields and satellite observations by introducing an ensemble model dust index, which used in conjunction with satellite dust retrievals improves the capability to characterize dust fields. Finally, we provide recommendations for the development of an integrated observational and modeling dust framework.

Ce travail de thèse vise à caractériser l’interaction entre composés organiques volatils et poussières minérales atmosphériques. Les COV sélectionnés sont l’isopropanol (IPA), l’isoprène (ISP) et l’acide acétique (AcA). Cinq échantillons naturels de poussières minérales provenant de zones désertiques situées dans plusieurs régions du globe ont été retenus.Il a été mis en évidence que l’origine et donc la composition chimique des poussières naturelles joue un rôle majeur dans la nature de leur interaction avec les COV. Plus particulièrement, les coefficients de capture tendent à croître avec les rapports élémentaires Al/Si et Fe/Si. De plus, il est montré que l’interaction entre COV et poussières est fortement impactée par l’humidité relative et la température.Plusieurs modes d’interaction entre les COV et les poussières étudiés ont été mis en évidence : physisorption, chimisorption ou adsorption réactive. Ils dépendent de la composition chimique des poussières et de la structure des COV. En fonction du mode d’interaction, ces processus hétérogènes peuvent être considérés comme des puits de COV primaires voire des sources de COV secondaires en phase gazeuse. Ce travail met en lumière la contribution des processus hétérogènes dans l’atmosphère. / This thesis investigates the interactions of volatile organic compounds (VOCs) with natural mineral dust samples. The VOCs used are isopropanol (IPA), isoprene (ISP) and acetic acid (AcA). Five natural mineral dust samples originating from various desert regions all over the world are used in this study.It is evidenced that the origin, I.E. the chemical composition, of the natural dust sample plays a significant role in defining the nature of its interaction with the VOCs. In particular, an increase of uptake is observed with increasing Al/Si and Fe/Si elemental rations. Moreover, the dust-VOC interaction is evidenced as being highly impacted by relative humidity and temperature.Various interactions modes have been evidenced between dust and VOCs such as physisorption, chemisorption and reactive sorption depending on the chemical composition of the dust and the structure of the VOC. Depending on the interaction mode, heterogeneous processes can act as a sink of primary VOCs or even a soure of secondary oxygenated VOCs in the gas phase. This work emphasiez the contribution of heterogeneous processes to the atmosphere.

Patagonie et la Namibie sont deux sources importantes d'aérosol minéral qui alimente la section Atlantique Sud de l'océan Austral avec les micronutriments.L'objet de ma thèse est d'étudier 1) la concentration atmosphérique et la variation temporel de la poussière en Patagonie, 2) l'hétérogénéité spatiale de composition élémentaire de poussière en Patagonie et en Namibie, et 3) la solubilité élémentaire de poussière en Patagonie et en Namibie. Ces trois aspects sont les principaux enjeux pour modéliser les inventaires des émissions de micronutriments biodisponibles à partir de sources de poussière.La concentration en poussière mesurée en Patagonie montre une variation saisonnière avec un niveau plus bas en hiver. Les données météorologiques suggèrent que cette variation saisonnière est associée à la variation de l'humidité du sol dans les zones source plutôt qu'à la vitesse du vent. Des échantillons d'aérosol minéral ont été générés à partir des sols de Patagonie et de Namibie. La composition élémentaire des poussières diffère de celles des sols parents, en particulier en Namibie en raison de l'effet de dilution par le quartz dans les sols. Des compositions élémentaires varient spatialement aux échelles continentale et régionale en Patagonie et Namibie. Les variations de Ca et Mg sont les principales raisons conduisant à l'hétérogénéité spatiale de la composition élémentaire des poussières. Les solubilités élémentaires des aérosols minéraux de Patagonie et de Namibie augmentent avec l'acidité de la solution altérante. Les poussières riches en calcium présentent une solubilité plus élevée pour les éléments les plus solubles (Ca, etc.) en raison de la présence de carbonate. Le suivi de la concentration en poussières obtenu en Patagonie peut aider à mieux en quantifier les émissions dans la région subantarctique et ainsi à mieux contraindre les modèles. La base de données que nous avons obtenue sur les poussières et leur solubilité contribue également à l'évaluation des émissions d'éléments solubles dans la région Australe. / Mineral dust is considered to be an important supplier of micronutrient for the Southern Ocean where the primary production is limited by insufficient supply of micronutrients. Patagonia (South America) and Namibia (Southern Africa) are two main dust sources for the South Atlantic section of the Southern Ocean. Emission inventories of bioavailable micronutrients from these two regions regulate the final biological impact on marine ecosystem in the South Atlantic Ocean. This thesis is mainly focused on the investigation of 1) the atmospheric dust concentration and its temporal pattern in Patagonia, 2) the spatial heterogeneity of dust elemental composition in Patagonia and Namibia, and 3) the pH dependence of elemental solubility in Patagonian and Namibian dust. These three aspects are the key issues to model the emission inventories of bioavailable micronutrients from dust sources. Dust concentration measurements were conducted in Patagonia-Atlantic Coast and revealed a seasonal pattern of dust concentration with lower dust level in winter than the other three seasons. Meteorological records suggest that this seasonal pattern is associated with the variation of soil moisture in source areas rather than the recurrently high wind speed. Dust samples were generated from Patagonian and Namibian soils to investigate the elemental composition and the elemental solubility of source dust. Dust elemental composition differs to different degrees from their parents soils, particularly in Namibia due to the dilution effect of quartz in soil. Spatial variability of dust elemental composition was observed at both continental scale and regional scale in Patagonia and Namibia. Variations in Ca and Mg content are the main reasons for the spatial heterogeneity of dust elemental composition. Elemental solubility of Patagonian and Namibian dust increased with acidity of leaching solution. More soluble elements namely Ca, K, Mg, Mn, Sr and Ba showed much higher solubility in calcium-rich dust due to the presence of carbonate. The dust concentration record obtained in Patagonia may help to better quantify the dust emission in subantarctic region and to constrain dust models. Database of dust elemental composition and elemental solubility in Patagonia and Namibia also contributes to the evaluation of emission inventories of soluble elements from dust sources to the Southern Ocean.

Aerosols are important atmospheric constituents that impact the Earth's radiative balance and climate. The detailed knowledge of the aerosol optical properties is required for a comprehensive analysis of the impacts of aerosols on climate. Mie theory is often used in satellite and ground-based retrieval algorithms to account for atmospheric mineral dust. However, the approximations used in Mie theory are often not appropriate for mineral dust and can lead to errors in the optical properties modeling. Analytic models based on Rayleigh theory that account for particle shapes can offer significant advantages when used to model infrared (IR) extinction of mineral dust. Here, the IR optical properties of some components of mineral dust, authentic dust samples and minerals processed with organic acids were investigated. Detailed characterization of the particles through online and offline methods of analysis that include IR extinction spectroscopy, micro-Raman spectroscopy and scanning electron microscopy was performed. Analysis of the IR extinction spectra and spectral simulations showed that the positions of the peaks and the shapes of the bands of the IR characteristic features are not well simulated by Mie theory in any of the samples studied. The resonance peaks were consistently shifted relative to the experimental spectrum in the Mie simulation. Rayleigh model solutions derived for different particle shapes better predicted the peak positions and band shapes of experimental spectra. To fill the gaps in the refractive index data for atmospherically relevant organic compounds in the IR region optical properties of atmospherically relevant carboxylic acids and humic-like substances using the IR extinction spectra and size distributions measured in the laboratory were determined. In addition to properties of mineral dust this dissertation focuses on properties of sea spray aerosol. Chemical and elemental composition of individual sea spray aerosol particles were studies using micro-Raman spectroscopy, mass-spectrometry and X-ray spectroscopy to provide insights into the biochemical processes that give rise to classes of organic molecules that make up these aerosol particles. The results suggested that degradation of biota (bacteria and diatoms) present in sea water led to lipopolysaccharides and extracellular polymeric substances that further degraded down to carbohydrates and fatty acids. Solubility of the resulting organic species seemed to play a role in their transfer to the aerosol phase. Furthermore, water uptake and hygroscopic growth of multi-component particles were studied. Understanding the interactions of water with atmospheric aerosols is crucial for determining their size, physical state, reactivity, and therefore for aerosol interactions with electromagnetic radiation and clouds. It was determined that particles composed of ammonium sulfate with succinic acid and of mixture of chlorides typical for marine environment show size dependent hygroscopic behavior. Microscopic analysis of the distribution of components within the aerosol particles showed that the observed size dependence is due to the differences in the mixing state. The composition and water uptake properties of sea spray aerosol particles were also measured during a phytoplankton bloom. The results showed that water uptake properties were directly related to the chemical composition of the particles and hygroscopicity decreased with increase in the fraction of water insoluble organic matter emitted during phytoplankton bloom. Finally, multiple methods of particle size, phase and shape analysis were compared and the results showed that the techniques that operate under ambient conditions provide the most relevant and robust measurement of particle size. Additionally, several storage methods for substrate deposited aerosol particles were evaluated and it was determined that storing samples at low relative humidity led to irreversible changes due to sample dehydration while sample freezing and thawing leads to irreversible changes due to phase changes and water condensation. Therefore it is suggested that samples used for single-particles analysis should be stored at ambient laboratory conditions, or near conditions which they were collected, in order to preserve the sample phase and hydration state. The results presented in this dissertation provide insight into physicochemical properties of atmospheric aerosols and help us better understand the role of aerosol particles in the Earth's atmosphere.

Mineral dust aerosols emitted from the Earth crust during various natural and anthropogenic processes continuously alter the chemical balance of the atmosphere via heterogeneous processes and thus, impact on the global climate. Understanding of heterogeneous chemistry and photochemistry on mineral dust has become vital to accurately predict the effect of mineral dust loading on the Earth's atmosphere. Here, laboratory measurements are coupled with model studies to understand heterogeneous chemistry and photochemistry in the atmosphere with the specific focus on reactions on mineral oxide surfaces. Heterogeneous uptake of gas phase HNO3 on well characterized metal oxides, oxyhydroxides and carbonates emphasized binding of nitric acid to these surfaces in different modes including monodentate, bidentate and bridging under dry conditions. It is becoming increasingly clear that the heterogeneous chemistry, including uptake of HNO3, is a function of relative humidity (RH) as water on the surface of these particles can enhance or inhibit its reactivity depending on the reaction. All the studied model systems showed a significant uptake of water with the highest uptake by CaCO3. Quantitative analysis of water uptake indicated formation of multilayers of water over these reactive surfaces. Under humid conditions, two water solvated nitrate coordination modes were observed that is inner-sphere and outer-sphere, which differ by nitrate proximity to the surface. Photochemical conversion of nitric acid to gas phase nitrous oxide, nitric oxide and nitrogen dioxide through an adsorbed nitrate intermediate under different atmospherically relevant conditions is shown using transmittance FTIR and XPS analysis. The relative ratio and product yields of these gas phase products change with relative humidity. Photochemistry of adsorbed nitrate on mineral aerosol dust may be influenced by the presence of other distinct gases in the atmosphere making it complicated to understand. This thesis converses formation of active nitrogen, NOx and N2O, and chlorine, ClOx, species in the presence of co-adsorbed trace gases, that could potentially regulate the peak concentration and geographical distribution of atmospheric ozone. Here we report formation of atmospheric N2O, from the photodecomposition of adsorbed nitrate in the presence of co-adsorbed NH3 via an abiotic mechanism that is favorable in the presence of light, relative humidity and a surface. Estimated annual production of N2O over the continental United States is 9.3+0.7/-5.3 Gg N2O, ~5% of total U.S. anthropogenic N2O emissions. Not only NH2 but also gaseous HCl react with adsorbed nitrate to activate "inert" N and Cl reservoir species, yielding NOCl, NOx, Cl and Cl2, through adsorbed nitrate under different atmospherically relevant conditions. Mineral dust aerosol is a major source of bioavailable iron to the ocean with an annual deposition of ~ 450 Tg of dust into the open ocean waters. In this study, we report enhanced Fe dissolution from nano scale Fe-containing minerals, i.e.alpha-FeOOH, beyond the surface area effects that can be attributed to the presence of more reactive sites on specific crystal planes exposed. We further report with clear evidence that aggregation impacts on dissolution. Proton-promoted dissolution of nanorods is nearly or completely quenched in the aggregated state. Acid type, presence of oxyanions and light are several other key factors responsible for regulating for iron dissolution. The work reported in this thesis provides insight into the heterogeneous chemistry and photochemistry of mineral dust aerosol under different atmospherically relevant conditions.

Mineral dust has manifold impacts on the Earth system. This includes land degradation at the dust sources, interaction with radiation in the atmosphere and effects on human health and economic activity. While it can be stated that most dust sources are found in arid and semi-arid environments, a general determination of characteristics that make a surface particularly susceptible to wind erosion cannot be given. One dust source type that has gained increasing attention in recent years is alluvial sediments. These sediments are formed and influenced by surface runoff and provide a large amount of fine grained material prone to wind erosion. Alluvial features are abundant in desert regions but are often small in size, for example dry river basins or alluvial fans. Due to their small size and despite their importance, these features are often underestimated or completely disregarded in dust-emission models. In this thesis, the spatio-temporal distribution of active alluvial dust sources is investigated and parameterized for a dust-emission model. For this, an approach to automatically detect alluvial features from two globally available satellite products is developed. These products comprise (1) surface reflectance at visible and near-infrared wavelengths derived from Sentinel-2 or MODIS and (2) HydroSHEDS flow accumulation data based on radar measurements. By combining these two datasets, an alluvial fines map (AFM) is created that shows the distribution of alluvial sediments. The AFM is implemented in a dust-emission model and multi-year model runs are performed for two study regions, one located around the Aïr Massif in the central Sahara, the other one covering western Namibia. Besides the distribution of fine alluvial sediments, another hydrologically influenced source type is analyzed in Namibia, i.e. the Etosha pan, a salt pan that is one of the most important dust sources in southern Africa. Dust activity from Etosha pan exhibits a strong seasonality due to regular flooding of the pan. These inundation events are implemented in the model by creating a monthly water mask from MODIS reflectance data. In the central Saharan study area, a comparison of the simulated dust flux with observed dust source activation frequency (DSAF) derived from the MSG SEVIRI Desert-Dust-RGB product shows that the model is able to reproduce the spatial and seasonal differences in the main activity of the identified sources. This seasonality cannot be reproduced by a control model run, in which the sediment supply by alluvial features is not included explicitly. For the Namibian study area, a model run is performed that includes the monthly water mask for Etosha pan and the AFM for the coastal ephemeral river basins. The simulated period covers 13 years from 2005 to 2017. With an empirical orthogonal function (EOF) analysis, constellations of pressure systems in the southern African region are determined that lead to an increased dust flux from the study area. Especially the Berg wind situation, a unique pressure pattern found in southern Africa with dry and hot continental winds, is identified as an atmospheric circulation pattern that leads to increased dust activity from the Namibian sources. The results highlight how important the consideration of alluvial features is for an accurate simulation of dust fluxes. Due to the global availability of the satellite data, the approach can be implemented in regional, continental or even global studies. Long-term emission fluxes can be used to identify the influence of meteorological patterns on dust emission and can help to estimate dust fluxes under current conditions but also in a changing climate.

Die vorliegende Arbeit beschäftigt sich mit der Auswertung und den Ergebnissen von Mehrwellenlängen–Polarisations–Ramanlidarmessungen, die im Rahmen des Saharastaubschließungsexperiments Saharan Mineral Dust Experiment (SAMUM) durchgeführt wurden. Das SAMUM–Projekt erstreckte sich über zwei Intensivmesszeiträume im Mai und Juni 2006 in Marokko (SAMUM–1) und im Januar und Februar 2008 auf den Kapverdischen Inseln (SAMUM–2). Desweiteren werden zusätzliche Lidarmessungen besprochen, die im Mai und Juni 2008 auf den Kapverdischen Inseln durchgeführt wurden. Die geometrischen und optischen Eigenschaften der während dieser Experimente mit mehreren hochmodernen Lidargeräten beobachteten Mineralstaub- und Biomassenverbrennungsaerosolschichten werden anhand von Fallstudien und mehrwöchigen, höhenaufgelösten Mittelwerten beschrieben. Zudem werden Kalibrierungen und Korrekturen vorgestellt, die zur Qualitätssicherung der gewonnenen Messdaten durchgeführt wurden. Ein im Rahmen der Arbeit entwickeltes, auf quantitativen Messungen des linearen Partikeldepolarisationsverhältnisses basierendes Verfahren zur höhenaufgelösten Trennung der Anteile von Mineralstaub und Biomassenverbrennungsaerosol an den während SAMUM–2 gemessenen Rücktreu- und Extinktionsprofilen wird vorgestellt und angewandt. Die Auswertung der Mehrwellenlängenlidarmessungen der SAMUM–Kampagnen ermöglichte eine spektral aufgelöste Charakterisierung der optischen Eigenschaften von Saharastaubpartikeln. Besondere Aufmerksamkeit wurde auf die Bestimmung der intensiven Parameter Extinktions–zu–Rückstreuverhältnis (Lidarverhältnis), lineares Partikeldepolarisationsverhältnis sowie Ångströmexponent der Rückstreu- und Extinktionskoeffizienten gelegt. Die im Rahmen von SAMUM bei den Wellenlängen 355, 532 und 1064 nm durchgeführten Lidarmessungen ergaben mittlere Lidarverhältnisse von 55±5 sr für reinen Saharastaub. Während SAMUM wurden außerdem erstmals quantitative Messergebnisse des linearen Partikeldepolarisationsverhältnisses von reinem Saharastaub bei mehreren Wellenlängen gewonnen. Die mittleren Werte dieser Größe lagen bei 0.26±0.06 (355 und 1064 nm), 0.31±0.03 (532 nm) und 0.37±0.07 (710 nm). Diese Erkenntnisse liefern wichtige Informationen für die Auswertung von Messungen mit weniger fortschrittlichen Lidargeräten. Die durch SAMUM gewonnenen Erkenntnisse der optischen Eigenschaften von Mineralstaub erlauben eine eindeutige Identifikation des Staubanteils in Aerosolschichten im Abluftbereich der Wüsten. Zudem wurden Richtgrößen ermittelt, die zur Validierung von Modellen zur Beschreibung von Lichtstreuung an großen, nicht–kugelförmigen Teilchen verwendet werden können. Derartige Streumodelle werden für die Auswertung von Messungen der optischen Eigenschaften von Mineralstaubpartikeln mit passiven Sensoren benötigt und befinden sich zur Zeit eher in einer frühen Entwicklungsphase.:1 Introduction 1 2 The SAMUM Campaigns 5 2.1 Concept and Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.2 Dust Sources in Northern Africa . . . . . . . . . . . . . . . . . . . . . . 6 2.3 Aerosol in the Outflow Region of West Africa . . . . . . . . . . . . . . 8 2.4 Field Sites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 3 Theory 17 3.1 Light Scattering in the Atmosphere . . . . . . . . . . . . . . . . . . . . 17 3.2 Lidar Principle and Lidar Equation . . . . . . . . . . . . . . . . . . . . 21 3.3 Basic Lidar Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 3.3.1 Elastic–backscatter Lidar . . . . . . . . . . . . . . . . . . . . . . 24 3.3.2 Raman Lidar . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 3.3.3 High Spectral Resolution Lidar . . . . . . . . . . . . . . . . . . 27 3.3.4 Polarization Lidar . . . . . . . . . . . . . . . . . . . . . . . . . . 28 4 Aerosol Characterization with Lidar 33 4.1 Aerosol Typing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 4.2 Aerosol–type Separation . . . . . . . . . . . . . . . . . . . . . . . . . . 34 4.3 Inversion with Regularization . . . . . . . . . . . . . . . . . . . . . . . 38 5 Instrumentation 43 5.1 MULIS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 5.2 POLIS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 5.3 HSRL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 5.4 BERTHA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 5.4.1 System Properties and Data Analysis . . . . . . . . . . . . . . . 45 5.4.2 Measurement of the Linear Volume Depolarization Ratio . . . . 48 5.4.3 Corrections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 5.4.3.1 Overlap Correction . . . . . . . . . . . . . . . . . . . . 52 5.4.3.2 Polarization–dependent Receiver Transmission . . . . . 54 5.4.3.3 Depolarization Extrapolation . . . . . . . . . . . . . . 61 5.5 Sun Photometers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65 5.6 Radiosonde . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66 5.7 Backward Trajectories . . . . . . . . . . . . . . . . . . . . . . . . . . . 66 6 Results 67 6.1 SAMUM–1, Morocco, Summer . . . . . . . . . . . . . . . . . . . . . . . 67 6.1.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67 6.1.2 Measurement Case: 15 May 2006 . . . . . . . . . . . . . . . . . 69 6.1.3 Measurement Case: 3 June 2006 . . . . . . . . . . . . . . . . . . 73 6.1.4 General Findings and Discussion . . . . . . . . . . . . . . . . . 78 6.2 SAMUM–2a, Cape Verde, Winter . . . . . . . . . . . . . . . . . . . . . 87 6.2.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87 6.2.2 Measurement Case: 31 January 2008 . . . . . . . . . . . . . . . 89 6.2.3 General Findings and Discussion . . . . . . . . . . . . . . . . . 96 6.3 SAMUM–2b, Cape Verde, Summer . . . . . . . . . . . . . . . . . . . . 107 6.3.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107 6.3.2 Measurement Case: 3–4 June 2008 . . . . . . . . . . . . . . . . 108 6.3.3 General Findings and Discussion . . . . . . . . . . . . . . . . . 112 7 SAMUMmary: Milestones and Outlook 119 8 Appendix 127 8.1 Error Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127 8.1.1 Backscatter Coefficients . . . . . . . . . . . . . . . . . . . . . . 128 8.1.2 Extinction Coefficients . . . . . . . . . . . . . . . . . . . . . . . 131 8.1.3 Lidar Ratios . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133 8.1.4 Ångström Exponents . . . . . . . . . . . . . . . . . . . . . . . . 133 8.1.5 Volume Depolarization Ratios . . . . . . . . . . . . . . . . . . . 134 8.1.6 Particle Depolarization Ratios . . . . . . . . . . . . . . . . . . . 137 8.2 List of Abbreviations . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139 8.3 List of Symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141

Atmospheric mineral dust plays a dynamic role in the climate system acting both as a forcing and a feedback mechanism. To date, the majority of paleodust studies have been conducted on marine sediments or polar ice cores, while terrestrial deposition has been less studied. As such, it is important to produce new terrestrial Holocene paleo–dust records and fill existing regional gaps. Ombrotrophic (atmospherically–fed) peat bogs can be used to reconstruct dust deposition through elemental chemistry analysis. Multi–elemental data sets are commonly used infer net dust deposition rates, source changes, grain size, and mineral composition. Mineralogical identification of dust particles is particularly important because it allows both provenance tracing and increased understanding in climate and ecosystem feedbacks. Establishing mineralogy from elemental data of mixed mineral matrixes can however be challenging. X–ray diffraction analysis (XRD) is a standard technique for mineral identification which ideally requires removal of organic matter (OM). Therefore, a test procedure was undertaken where common OM removal methods were evaluated on bulk peat samples was therefore undertaken. The results showed that combustion at 500°C was most efficient in removing OM, while leaving the majority of minerals intact, but not all. In this Licenciate thesis, early result of a paleodust study from Draftinge Mosse, southern Sweden, are also outlined. Here, the method development mentioned above was applied, enabling a combination of elemental data with mineralogy. Future work includes minor and trace element analysis by ICP–AES and ICP–MS, evaluation of the reproducibility of single core reconstructions, tests of some of the methodological assumptions used in previous paleodust studies, source tracing and paleodust reconstruction from a second site (Gällsered Mosse). / Atmosfäriskt mineraldamm, mineralpartiklar som lyfts upp i atmosfären och avsätts via eoliska processer, spelar en komplex roll i klimatsystemet då partiklarna påverkar klimatet, samtidigt som rådande klimat också påverkar partikelmängden. De flesta hittills genomförda mineraldamms- studier har utförts på marina sediment eller iskärnor trots att mineraldammspartiklar i störst utsträckning deponeras på kontinenterna. Ombrotrofa mossar (högmossar) kan användas för att rekonstruera avsättning av mineraldamm över tid genom geokemiska analyser på olika djup i torvkärnor. Den kemiska sammansättningen ger information som kan användas för att härleda variationer i partikelmängd, källområden, kornstorlek, samt mineralogisk sammansättning. Bestämning av mineralen är av särskild vikt då det möjliggör identifikation av partiklarnas källområden samt ger kunskap om partiklarnas del i klimat- och ekosystem processer. Att via geokemiska data identifiera mineral prover av blandad sammansättning är dock utmanande, särskilt då många mineral har en liknande kemisk sammansättning. Röntgen diffraktions analys (XRD) är en standardmetod inom berggrundsgeologi för att identifiera mineral, som här används på torvprover. Metoden är icke-destruktiv, men kräver att provet är relativt rent från amorfa faser, så som organiskt material. Då torv innehåller stora mängder organiskt material (>98 %), som dessutom karaktäriseras av att vara svårnedbrutet, utformades ett testprotokoll för att studera vilken metod som är bäst lämpad för att ta bort organiskt material från denna specifika jordtyp. Resultaten från genomförda tester visade att förbränning (500°C) är mest effektivt och även lämnade en majoritet av mineralen intakta, dock inte alla. I denna licenciatavhandling beskrivs även de övergripande målen med min forskning samt tidiga resultat från en mineraldammstudie från Draftinge mosse (Småland), där resultaten från metodstudien ovan applicerats och kombinerats med andra geokemiska data. Vidare arbete inom detta doktorandprojekt kommer innefatta ytterligare geokemiska analyser (spårämnesanalys med ICP-MS och ICP-AES) samt identifiering av källområden. Dessutom kommer ytterligare en mosse (Gällsered mossse) att studeras för förändringar i avsättning av mineraldamm under de senaste 7000 åren.