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

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 dai...

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Bibliographic Details
Published in:Atmospheric Chemistry and Physics
Main Authors: P. Formenti, S. J. Piketh, A. Namwoonde, D. Klopper, R. Burger, M. Cazaunau, A. Feron, C. Gaimoz, S. Broccardo, N. Walton, K. Desboeufs, G. Siour, M. Hanghome, S. Mafwila, E. Omoregie, W. Junkermann, W. Maenhaut
Format: Article in Journal/Newspaper
Language:English
Published: Copernicus Publications 2018
Subjects:
Physics
QC1-999
Chemistry
QD1-999
Austral
South Atlantic Ocean
Online Access:https://doi.org/10.5194/acp-18-17003-2018
https://doaj.org/article/69969166e74041dca14fca1eac503ee3
Description
Summary: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.

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