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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. [ABSTRACT FROM AUTHOR]

The AEROCLO-sA project (Aerosol, Radiation and CLOuds in southern Africa)investigates the role of aerosols on the regional climate of southern Africa. The regionis characterized by high atmospheric aerosol loadings originated from biomassburning, mineral dust and marine sea salt. In addition it is influenced by strongmarine biological emissions by the Benguela upwelling and a semi-permanent andextended stratocumulus cloud deck. This area therefore provides an exceptionalnatural laboratory for studying the full range of aerosol physico-chemical properties,aerosol-radiation and aerosol-cloud interactions and their perturbations of the Earth’sradiation budget. AEROCLO-sA is based on a field campaign conducted for a month in August-September2017 at the coastal Henties Bay experimental site (22˚ 6’ S, 14˚ 17’ E). An instrumentedmobile station was implemented at ground over coastal Namibia in order to document fog,clouds, aerosols, volatile organic compounds and other traces gases at the ocean-atmosphereinterface. State of the state-of-the-art instrumentation for the measurement of volatilecompounds as proton-transfer-reaction mass spectrometer and retrieval of chemical andphysical properties of aerosol as time of flight aerosol mass spectrometer, scanningmobility particle sizer, particle counters, cloud condensation nuclei counter weredeployed. Here we present results from on-line AMS data analysis of the sub-micrometer aerosolwhich is dominated by sulphate, sea salt followed by organic compounds. Marine biogenicemissions strongly enhanced concentrations of short-chain aldehydes, alcohols, carboxylicacids and sulphur-containing compounds in the gas phase, and strongly influenced PM1composition, while diurnal cycles of iodide and MSA species were observed along the wholecampaign. Source apportionment analysis has been run for both the organic gas phase andaerosol fraction. Additional information from on-line analysis on water-soluble fraction onTSP (PILS-IC) and off-line analysis (filters and TEM grids) will complete our view of theaerosol chemical composition in this region. The full set of data will improve ourunderstating of emissions and mechanisms occurring at the ocean-atmosphere interface inthis region. [ABSTRACT FROM AUTHOR]

The western coast of southern Africa off Namibia is characterized by a semi-permanent and widespread stratocumulus (Sc) cloud deck, very frequent coastal fog, and the oceanic northern Benguela upwelling system (nBUS). It is also the crossroad of large quantities of natural and anthropogenic aerosols of distant and local origins (biogenic, anthropogenic, biomass burning, sea salt and mineral dust) from continental and marine sources, with significant differences in terms of physico-chemical and optical properties, water affinity, scale and height of transport, which are not well represented in climate models. The overarching objective of the AErosol, RadiatiOn and CLOuds in southern Africa (AEROCLO-sA) is to improve our knowledge about the role of aerosols on this regional climate with new observations and new climate model exercises. AEROCLO-sA is based on a ground-based and airborne field campaign that was conducted in Namibia between 22 August and 12 September, 2017. Here we present the results of synergetic filter sampling, optical counting, scattering, absorption, extinction and hygroscopicity measurements that were conducted by the ground-based mobile PEGASUS at the coastal Henties Bay experimental site (22°6' S, 14°17' E) to characterize the marine boundary layer aerosols. We illustrate examples of the numerous new particle formation events were observed during the field campaign in link with marine biogenic emissions. We illustrate the chemical composition of the submicron and total aerosols. We discuss the apportionment of maritime sulfate aerosols, and quantify their biogenic fraction, which we link with their cloud condensation nuclei and optical properties. [ABSTRACT FROM AUTHOR]

Namibia is an arid country where numerous rural and urban centers depend on ephemeral rivers for their water supply. These water sources are, however, limited and display seasonal salinization. Fog occurs along the coast and extends over up to 100 km inland, and has been considered for a long time as a source of drinking water. Fog is also a vital source of moisture for the endemic flora and fauna of the Namib Desert. However, due to the current change in climate and air quality, fog occurrence and composition, of crucial importance for the local ecosystems and populations, may be impacted. In the frame of the AEROCLO-sA campaign, fog collection experiments were performed at Henties Bay, along the Namibian coast, and at the desert site of the Gobabeb Research and Training Center during the period of intense fog observations of the campaign, from September 4th to 12th, 2017. Fog collection experiments were performed with two pre-cleaned Caltech Active Strand Cloud Water Collectors (CASCC) that were run in parallel. A stainless steel CASCC was deployed and samples were analyzed for organics (TOC, DOC, organic acids, and specific organic markers), while a plastic collector was used for sampling and further analysis of pH, inorganic ions, metals and water isotopes. Complementary measurements were performed on some of these samples, such as UV-visible and 2D-fluorimetric analysis, and nebulization prior AMS-c-ToF analysis. On the coast, at Henties Bay, eight events were sampled. Their chemical compositions will be presented and discussed relative to the local aerosol composition, as well as the composition of sea water, also sampled during the same period. These results will be contrasted with observations from two fog events at the inland Gobabeb desert site. [ABSTRACT FROM AUTHOR]