AIRBORNE MEASUREMENTS OF AEROSOLS FROM BURNING BIOMASS IN BRAZIL RELATED TO THE TRACE A EXPERIMENT

Results are reported from an airborne campaign to investigate the impa cts of burning biomass upon the loading of lower-tropospheric aerosols and its composition over the Brazilian tropics. The flights, conducte d as part of the NASA/Transport and Atmospheric Chemistry Near the Equ ator-Atlantic (TRACE A) mission, started on September 1, 1992, when th e dry (fire) season still prevailed in the central part of Brazil, and ended on September 29. Of the total number of burnings detected in Br azil by the advanced very high resolution radiometer (AVHRR)/NOAA sate llite sensor, 74% were concentrated in the states of Amazonas, Maranha o, Mate Grosso, Para, Roraima, and Tocantins during this period. Aeros ol particles were sampled from a twin-engine aircraft in transit and v ertical profile flights were made up to 4,000 m altitude. Black carbon measurements made in real time and in areas of burning biomass peaked at similar to 2,500 m above the ground, increasing to similar to 12,0 00 ng/m(3). In other areas these values were lower by 1 order of magni tude. A condensation nuclei counter measuring small particles (>0.014 mu m) produced values ranging from 2,000 to 16,000/cm(3) for areas wit h low and high burning biomass, respectively. Deposition filters in a two-stage cascade impactor, and Nuclepore filters collected aerosols f or analysis of 13 elements through particle-induced X ray emissions (P IXE). Primary elements associated with soil dust (Al, Si, Mn, Fe, Ni) prevailed in the aerosol coarse mode (>1 mu m) while the fine mode aer osols were enriched in S, K, Br, and Rb, which are tracers normally as sociated with burning of biomass. The good correlation between fire sp ot counts, obtained via AVHRR aboard NOAA satellites, and black carbon , counts of small particles and total aerosol mass, suggests the deter mining of local concentrations of fire-derived aerosol fire emissions by satellite to be a new and useful approach.