Measurements of windblown dust characteristics and ocean fertilization potential: The ephemeral river valleys of Namibia

Dansie, Andrew; Wiggs, Giles F.S.; Thomas, David S.G.; Washington, Richard

doi:10.1016/j.aeolia.2017.08.002

Cited by 29 publications

(33 citation statements)

References 88 publications

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“…Our data series does not show any particular time dependence of the frequency nor duration of the detected episodes. This is in contrast with the observation by Dansie et al (2017) that windblown dust derived from the ephemeral river valleys is transported offshore during large easterly wind events, and indicative of the fact that HBAO is the receptor of mineral dust emitted by various sources.…”

Section: Conclusion and Significance Of Resultscontrasting

confidence: 98%

“…Nineteen episodes of increased Al and nss-Ca 2+ concentrations and lasting from one to a maximum of four days were detected during the entire sampling period. This corresponds well to the frequency of emission of dust plumes from river valleys, coastal sabkhas, and paleo-lacustrine sources (Etosha and Makgadikgadi pans) observed by various authors (Eckardt and Kuring, 2005;Vickery et al, 2013;Dansie et al, 2017). Our data series does not show any particular time dependence of the frequency nor duration of the detected episodes.…”

Section: Conclusion and Significance Of Resultssupporting

confidence: 90%

“…• Wind-blown mineral dust liberated from the surface of pans and ephemeral river valleys (Annegarn et al, 1983;Eltayeb et al, 1993;Heine and Völkel, 2010;Dansie et al, 2017), but also during /road construction and mining activities (KPMG, 2014). Mineral dust is traced by elemental aluminium, https://doi.org/10.5194/acp-2020-388 Preprint.…”

Section: Ratios To Unique Tracersmentioning

confidence: 99%

“…Despite their relevance, very limited research has been conducted to assess the seasonal cycle and longterm variability of the aerosol mass concentration and chemical composition in the region (Andreae et al, 1995;Annegarn et al, 1983;Dansie et al, 2017;Eltayeb et al, 1993;Formenti et al, 1999Formenti et al, , 2003bZorn et al, 2008). To fill this gap, the long-term surface monitoring Henties Bay Aerosol Observatory (HBAO) was established in 2012 on the campus of the University of Namibia's Sam Nujoma Marine and Coastal Resources Research Centre (SANUMARC), along the Namibian coast (22°S; 14°E).…”

Section: Introductionmentioning

confidence: 99%

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Chemical composition and source apportionment of atmospheric aerosols on the Namibian coast

Klopper¹,

Formenti²,

Namwoonde³

et al. 2020

Preprint

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Abstract. The chemical composition of aerosols is of particular importance to assess their interactions with radiation, clouds and trace gases in the atmosphere, and consequently their effects on air quality and the regional climate. In this study, we present the results of the first long-term dataset of the aerosol chemical composition at an observatory on the coast of Namibia, facing the southeast Atlantic Ocean. Aerosol samples in the mass fraction of particles smaller than 10 µm in aerodynamic diameter (PM10) were collected during 26 weeks between 2016 and 2017 at the ground-based Henties Bay Aerosol Observatory (HBAO; 22°6’ S, 14°30’ E, 30 m above mean sea level). The resulting 385 filter samples were analysed by X-ray fluorescence and ion-chromatography for 24 inorganic elements and 15 water-soluble ions. Statistical analysis by positive matrix factorization and back-trajectory modelling identified five major sources, sea salt (mass concentration: 70.8 ± 0.2 %), marine biogenic (13.5 ± 0.8 %), mineral dust (9.9 ± 0.1 %), secondary products (3.2 ± 1.0 %) and heavy metals (2.3 ± 2.5 %). While the contribution of sea salt aerosol was persistent, as the dominant wind direction was south-westerly and westerly from the open ocean, the occurrence of mineral dust was episodic and coincided with high wind speeds from the south-southeast and the north-northwest, along the coastline. Concentrations of heavy metals measured at HBAO were higher than reported in the literature from measurements over the open ocean. The heavy metals (V, Cr, Nd and Mn) measured at the site were attributed to mining activities and the combustion of heavy fuels in commercial ship traffic across the Cape of Good Hope sea route. Fluoride concentrations up to 25 µg m−3 were measured, as in heavily polluted areas in China. This is surprising and a worrisome result that has profound health implications and deserves further investigation. Although no clear signature for biomass burning could be determined, the source of secondary products identified by PMF was described by a mixture of aerosols typically emitted by biomass burning, but also by other biogenic activities. Episodic contributions with moderate correlations between NO3−, nss-SO42− (higher than 2 µg m−3) and nss-K+, were observed, further indicative of the potential for an episodic source of biomass burning. Sea salt accounted for up to 57 % of the measured mass concentrations of SO42− and the non-sea salt fraction contributed mainly to the secondary product and marine biogenic sources identified by PMF. The marine biogenic contribution is attributed to efficient oxidation in the moist marine atmosphere of sulphur-containing gas-phase emitted by marine phytoplankton in the fertile waters offshore in the Benguela Upwelling System. The data presented in this paper provide first-ever information on the temporal variability of aerosol concentrations in the Namibian marine boundary layer and the links to meteorological conditions shaping the transport patterns of aerosols from different sources. This data can be used to provide context for intensive observations in the area.

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Section: Conclusion and Significance Of Resultscontrasting

confidence: 98%

Section: Conclusion and Significance Of Resultssupporting

confidence: 90%

Section: Ratios To Unique Tracersmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Chemical composition and source apportionment of atmospheric aerosols on the Namibian coast

Klopper¹,

Formenti²,

Namwoonde³

et al. 2020

Preprint

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“…Here, Vickery et al (2013) identified approximately 70 emitting point sources (mostly ephemeral dry riverbeds along the Namibian coastline) as well as the major source of the Etosha Pan, Namibia. The deposition of nutrients from mineral dust contribute significantly to the coastal oceanic primary production (Dansie et al 2017) and the long-range transport of mineral dust from Namibia to the central tropical South Atlantic is also documented (Swap et al 1996).…”

Section: Th E W E S T Coa S T O F S O U Th E R N Africa: a Climaticalmentioning

confidence: 99%

The Aerosols, Radiation and Clouds in Southern Africa Field Campaign in Namibia: Overview, Illustrative Observations, and Way Forward

Formenti

D’Anna²,

Flamant³

et al. 2019

Bulletin of the American Meteorological Society

112

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The Aerosol, Radiation and Clouds in southern Africa (AEROCLO-sA) project investigates the role of aerosols on the regional climate of southern Africa. This is a unique environment where natural and anthropogenic aerosols and a semipermanent and widespread stratocumulus (Sc) cloud deck are found. The project aims to understand the dynamical, chemical, and radiative processes involved in aerosol–cloud–radiation interactions over land and ocean and under various meteorological conditions. The AEROCLO-sA field campaign was conducted in August and September of 2017 over Namibia. An aircraft equipped with active and passive remote sensors and aerosol in situ probes performed a total of 30 research flight hours. In parallel, a ground-based mobile station with state-of-the-art in situ aerosol probes and remote sensing instrumentation was implemented over coastal Namibia, and complemented by ground-based and balloonborne observations of the dynamical, thermodynamical, and physical properties of the lower troposphere. The focus laid on mineral dust emitted from salty pans and ephemeral riverbeds in northern Namibia, the advection of biomass-burning aerosol plumes from Angola subsequently transported over the Atlantic Ocean, and aerosols in the marine boundary layer at the ocean–atmosphere interface. This article presents an overview of the AEROCLO-sA field campaign with results from the airborne and surface measurements. These observations provide new knowledge of the interactions of aerosols and radiation in cloudy and clear skies in connection with the atmospheric dynamics over southern Africa. They will foster new advanced climate simulations and enhance the capability of spaceborne sensors, ultimately allowing a better prediction of future climate and weather in southern Africa.

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Spatiotemporal variability of the potential wind erosion risk in Southern Africa between 2005 and 2019

2023

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Regional assessments of the wind erosion risk are rare and vary due to the methods used and the available data to be included. The adaptation of existing methods has the advantage that the results can be compared directly. We adopted an already successfully applied methodology (ILSWE—applied in East Africa), to investigate the spatiotemporal variability of the wind erosion risk between 2005 and 2019 in Southern Africa. The approach integrates climatic variables, a vegetation index, and soil properties to describe the potential impact of wind erosion at the landscape scale. The annual and seasonal variability is determined by the vegetation cover, whereas droughts and strong El Niño events had only regional effects. We estimated that 8.3% of the study area experiences a moderate to elevated wind erosion risk over the 15‐year period with annual and inter‐annual fluctuations showing a slight upward trend. In general, the desert and drylands in the west have the highest proportion of risk areas, the moist forests in the east are characterized by a very low risk of wind erosion, while the grasslands, shrublands, and croplands in the interior most likely react to changes of climatic conditions. The validation process is based on a comparison with the estimated frequency of dust storms derived from the aerosol optical depth and angstrom exponent and revealed an overall accuracy of 65%. The results of this study identify regions and yearly periods prone to wind erosion to prioritize for further analysis and conservation policies for mitigation and adaptation strategies.

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Measurements of windblown dust characteristics and ocean fertilization potential: The ephemeral river valleys of Namibia

Cited by 29 publications

References 88 publications

Chemical composition and source apportionment of atmospheric aerosols on the Namibian coast

Chemical composition and source apportionment of atmospheric aerosols on the Namibian coast

The Aerosols, Radiation and Clouds in Southern Africa Field Campaign in Namibia: Overview, Illustrative Observations, and Way Forward

Spatiotemporal variability of the potential wind erosion risk in Southern Africa between 2005 and 2019

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