Carbonaceous aerosols from different tropical biomass burning sources

Abstract

FOLLOWING a repetitive pattern, biomass burning affects the intertropical belt on a continental scale during the dry season¹. The importance of these anthropogenic activities with regard to carbonaceous-component emissions into the global atmosphere is now well recognized^2-4. It has been suggested that large injections of black carbon aerosols from the Tropics are of potential importance for the radiative and chemical balance of the troposphere^5-10. Studies on carbonaceous aerosols have indicated that, on an annual basis, the intensity of the emissions from tropical biomass burning could compare with that of emissions from fossil-fuel burning in industrial countries^7,8. Also, results from combustion chamber experiments have determined the important range of the emission factor for both the organic and the black carbon components of the aerosol^1-16. Following on from our earlier studies on total atmospheric particulate carbon (C_t) and isotopic composition (δ¹³C) (ref. 2), we now present new data on the black carbon content (C_b) of atmospheric particles sampled during the biomass-burning season in the wooden savannah of the Ivory Coast. The C_b/C_t ratio is generally lower than expected and highly variable. This variability indicates that there are drastic changes in source apportionment, which from our isotope studies may be ascribed to the variety of vegetation fuel and also to the mode of combustion. Therefore the C_b/C_t ratio can potentially discriminate biomass-burning emissions from different tropical ecosystems.