Chemical apportionment of southern African aerosol mass and optical depth Atmospheric and Oceanic Sciences, Princeton University, Princeton, New Jersey, USA
Received: 07 June 2009 – Published in Atmos. Chem. Phys. Discuss.: 18 June 2009 Abstract. This study characterizes the aerosol over extratropical and tropical
southern Africa during the biomass burning season by presenting an aerosol
mass apportionment and aerosol optical properties. Carbonaceous aerosol
species account for 54% and 83% of the extratropical and tropical
aerosol mass, respectively, which is consistent with the fact that the major
source of particulate matter in southern Africa is biomass burning. This
mass apportionment implies that carbonaceous species in the form of organic
carbon (OC) and black carbon (BC) play a critical role in the aerosol
optical properties. By combining the in situ measurements of aerosol mass
concentrations with concurrent measurements of aerosol optical properties at
a wavelength of 550 nm, it is shown that 80–90% of the aerosol scattering
is due to carbonaceous aerosol, and the derived mass scattering cross
sections (MSC) for OC and BC are 3.9±0.6 m2/g and 1.6±0.2 m2/g,
respectively. Derived values of mass absorption cross sections
(MAC) for OC and BC are 0.7±0.6 m2/g and 8.2±1.1 m2/g,
respectively. The values of MAC imply that ~26% of the aerosol
absorption in southern Africa is due to OC, with the remainder due to BC.
The results in this study provide important constraints for aerosol
properties in a region dominated by biomass burning and should be integrated
into climate models to improve aerosol simulations.
Revised: 22 September 2009 – Accepted: 26 September 2009 – Published: 13 October 2009
Citation: Magi, B. I.: Chemical apportionment of southern African aerosol mass and optical depth, Atmos. Chem. Phys., 9, 7643-7655, doi:10.5194/acp-9-7643-2009, 2009.