PO-210 IN SAVANNA BURNING PLUMES

During the FOS-DECAFE experiment at Lamto (Ivory Coast) in January 199 1 aerosols samples were collected at ground level above fires in order to investigate the possibility of using Po-210 as a tracer of biomass burning. The concentration of this radionuclide in plants is studied as a function of its content in soils and in the atmospheric backgroun d. It is shown that it depends strongly on the atmospheric content in Po-210, due to dry deposition of the aerosols. The mean concentration of plants at Lamto is found to be about 4.4 pCi of Po-210/gC during th e fire season and falls down to less than 1pCi/gC outside this period. The budget of Po-210 is evaluated taking into account its complete vo latilization during the flaming phase, the (Po-210)(ash)/(Po-210)(plan ts) ratio, which is measured to be about 14% and the percentage of sub micron particles in the plume, about 91%. The inferred flux of Po-210 is 3850 Ci/yr for the African savanna, and 5800 Ci/yr for the global s avanna. From this flux, fluxes of Ct and Cs are estimated to be 8.4 an d 1.1 Tg of C/yr for the worldwide savanna.