Three years of measurements of light-absorbing aerosols over coastal Namibia: seasonality, origin, and transport

• Published in: Atmospheric Chemistry and Physics
• Main Authors: Formenti, Paola, Piketh, Stuart John, Namwoonde, Andreas, Klopper, Danitza, Burger, Roelof, Cazaunau, Mathieu, Féron, Anaïs, Gaimoz, Cécile, Broccardo, Stephen, Walton, Nicola, Desboeufs, Karine, Siour, Guillaume, Hanghome, Mattheus, Mafwila, Samuel, Omoregie, Edosa, Junkermann, Wolfgang, Maenhaut, Willy
• Other Authors: Laboratoire Interuniversitaire des Systèmes Atmosphériques (LISA (UMR_7583)), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Université Paris-Est Créteil Val-de-Marne - Paris 12 (UPEC UP12)-Centre National de la Recherche Scientifique (CNRS), North-West University Potchefstroom (NWU), Namibia University of Science and Technology (NUST), Institut de Combustion, Aérothermique, Réactivité et Environnement (ICARE), Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut des Sciences de l'Ingénierie et des Systèmes (INSIS), Laboratoire des Sciences du Climat et de l'Environnement Gif-sur-Yvette (LSCE), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), Institute for Meteorology and Climate Research (IMK), Karlsruhe Institute of Technology (KIT), Universiteit Gent = Ghent University Belgium (UGENT)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2018
• Subjects: [SDU.OCEAN]Sciences of the Universe [physics]/Ocean; Atmosphere; Austral; South Atlantic Ocean
• Online Access: https://hal.archives-ouvertes.fr/hal-02352581; https://hal.archives-ouvertes.fr/hal-02352581/document; https://hal.archives-ouvertes.fr/hal-02352581/file/Formenti_Namibia_acp-18-17003-2018-includes-suppl.pdf; https://doi.org/10.5194/acp-18-17003-2018

International audience Continuous measurements between July 2012 and December 2015 at the Henties Bay Aerosol Observatory (HBAO; 22 • S, 14 • 05 E), Namibia, show that, during the austral wintertime, transport of light-absorbing black carbon aerosols occurs at low level into the marine boundary layer. The average of daily concentrations of equivalent black carbon (eBC) over the whole sampling period is 53 (±55) ng m −3. Peak values above 200 ng m −3 and up to 800 ng m −3 occur seasonally from May to August, ahead of the dry season peak of biomass burning in southern Africa (August to October). Analysis of 3-day air mass back-trajectories show that air masses from the South Atlantic Ocean south of Henties Bay are generally cleaner than air having originated over the ocean north of Henties Bay, influenced by the outflow of the major biomass burning plume, and from the continent, where wildfires occur. Additional episodic peak concentrations, even for oceanic transport, indicate that pollution from distant sources in South Africa and maritime traffic along the Atlantic ship tracks could be important. While we expect the direct radiative effect to be negligible, the indirect effect on the microphysical properties of the stratocumulus clouds and the deposition to the ocean could be significant and deserve further investigation, specifically ahead of the dry season.