Aerosol particles were collected during the dry season in the amazonian forest and in African and Brazilian savannas. Sampling was performed inside the plumes of vegetation fires and in the local background atmosphere. Samples were analyzed for their elemental composition by Particle Induced X-Ray Emission (PIXE). Enrichment factors relative to the local background were calculated. Savanna fire aerosols are characterized by enrichments in elements like K, P, Cl, Zn, and Br, whereas forest fire emissions are enriched in Si and Ca. The unexpected low potassium enrichment factor for the forest fires could be due to the prevailing smoldering conditions, whereas the high values of potassium enrichment factor during savanna fires could be associated with the predominant flaming conditions. This result indicates that potassium may be considered a good tracer of the flaming phase of fires only. Emission factors of P, S, Cl, K, Ca, Mn, Zn, Br and total particulate matter were calculated for African savanna fires. Our estimates of the annual potassium and zinc emissions by tropical savanna fires indicate that the contribution of this source should be taken into account to understand the biogeochemical cycle of these elements. ¿ American Geophysical Union 1995