Remote sensing of carbonaceous aerosol production by African savanna biomass burning

We present an estimate of the yearly flux of total and black carbon aerosols emitted by savanna biomass burning in Africa from satellite data and ground-based measurements. Smoke plumes are identified using visible, near-infrared, and thermal infrared derived information. In the savanna region of our study, these structures could either decrease or increase the visible albedo of advanced very high resolution radiometer (AVHRR). It is hypothesized that variations of chemical composition and particulate size distribution may create such differences. The 5S model [Tanre et al., 1990] is used to simulate radiative transfer through smoke plumes and background atmosphere. The overall uncertainty of the derived aerosol optical depth (tau(a)) is 75% and mainly due to the choice in particulate composition and size distribution aerosol. Impact of the aerosol mixture (internal versus external mixture) has been also tested. For smoke plumes a typical value of tau(a) (at 0.55 mu m) is 0.5, and 0.1 for the background atmosphere. Specific extinction cross sections are calculated using Mie theory applied to different representative aerosol models, allowing the retrieval of aerosol columnar concentrations from aerosol optical depth values and integrated aerosol mass loadings in fire plumes. The overall uncertainty on the determination of aerosol load is estimated to be lower than a factor of 5. The atmospheric carbonaceous aerosol flux from savanna burning in Africa was estimated to be 6.5 Tg C yr(-1), which compares with that obtained from emission factor on-site measurements (13 +/- 5 Tg C yr(-1)).