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North-West University (2021)

Characteristics and transport of atmospheric aerosols over the Namibian coast

Klopper, Danitza

Titre : Characteristics and transport of atmospheric aerosols over the Namibian coast

Auteur : Klopper, Danitza

Université de soutenance : North-West University

Grade : Doctor of Philosophy in Geography and Environmental Management 2021

Résumé poartiel
It is well understood that on various scales in the atmosphere, the transport, dispersion, accumulation, transformation and deposition of aerosols is driven by atmospheric dynamics, meteorological conditions and topographical controls. This thesis presents the results of a series of inter-disciplinary research endeavours in environmental and atmospheric sciences to describe the spatial- and temporal variability in vertical atmospheric structures, transport pathways, and aerosol character over the Namibian coast. The unique topography, atmospheric conditions, variety of aerosol sources, and the presence of a semi-permanent stratocumulus cloud deck, make the Namibian coast of particular interest for this study and this region is a type of natural laboratory for studying the variability in these conditions. Recent international research efforts in the region include the Observations of aerosol and cloud interactions (Nasa-ORACLES : Zuidema et al., 2016) and the Aerosols, Clouds and Radiation in southern Africa (AEROCLO-sA : Formenti et al., 2019) campaigns. For the aforementioned reasons, the ground-based, Henties Bay Aerosol Observatory (HBAO ; 22.090619°S, 14.272424°E), Namibia, makes in situ measurements of various physical and chemical properties of aerosols. These measurements within the Namibian boundary layer (BL) include black carbon (BC) intermittently from July 2012 to December 2015, and filter sampling of PM10 aerosols from February 2016 to December 2017 (over 26 sampling weeks). These filters were analysed for element- and ion-concentrations. Additionally, publicly available datasets were used, such as the NOAA HYSPLIT kinematic back-trajectory model, radiosonde data, remote-sensed satellite data from MODIS, CALIPSO and COSMIC missions, synoptic charts, reanalysis meteorological datasets, and statistical- and mathematical models. Boundary layer height (BLH), characterised by the bulk Richardson number, at Walvis Bay, were radiosondes were released was linked to cloud- and surface cover, surface heating effects, and easterly wind components. The surface of MG across the region of interest was largely affected by changes in atmospheric moisture and cloud, and was not consistent with BLH as defined by the bulk Richardson number. Low-level inversions, identified by GPS-RO, were lowest, deepest and strongest in the spring. Their character was linked to surface-radiation interactions with cold sea surfaces, warm arid landscapes and low-level clouds in the region, and macroscale circulation, such as the southeast Atlantic and continental high-pressure systems

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