Large-scale aerosol source apportionment in Amazonia

Aerosol particles were collected aboard two Brazilian Bandeirante EMB 110 p lanes, and the University of Washington Convair C-131A aircraft during the Smoke, Clouds, and Radiation-Brazil (SCAR-B) field project in the Amazon Ba sin in August and September 1995. Aerosols were collected on Nuclepore and Teflon filters. Aerosol size distribution was measured with a MOUDI cascade impactor. Sampling was performed mostly over areas heavily influenced by b iomass burning smoke. Particle-induced X ray emission (PIXE) was used to me asure concentrations of up to 20 elements (Al, Si, P, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Br, Rb, Sr, Zr, and Pb). Black carbon (BC) and grav imetric mass analysis were also performed. Instrumental neutron activation analysis (INAA) determined the concentrations of about 15 elements on the T eflon filters. Electron probe X ray microanalysis (EPMA) was used to analyz e individual aerosol particles. The average aerosol mass concentration was 105 mu g m(-3), with a maximum of 297 mu g m(-3). Black carbon (BC) average d 5.49 mu g m(-3), or 1-7% of the aerosol mass load. Five aerosol component s were revealed by absolute principal factor analysis: (1) a biomass burnin g component (responsible for 54% of the aerosol mass and associated with BC , K, Cl, Zn, I, S, Br, Rb, aerosol mass concentration, and other elements); (2) a soil dust aerosol component (15.6% of the aerosol mass); (3) a natur al biogenic component (18.7% of the aerosol mass and associated with P, K, S, Ca, Sr, Mg, Mn, Cu and Zn); (4) a second soil dust (5.7% of the aerosol mass and enriched in Si, Ti, and Fe); and (5) a NaCl aerosol component (5.9 % of the aerosol mass with Na, Cl, Br, and iodine). Electron microscopy ana lysis of individual aerosol particles confirmed these five aerosol types. O rganic material dominated the aerosol mass and the number concentration of airborne particles. Aerosol size distributions show that the fine mode acco unts for 78% of the aerosol mass, centered at 0.33 mu m aerodynamic diamete r. The coarse mode accounts for 22% of the mass, centered at about 3.2 mu m . Black carbon size distributions show a consistent picture, with a mass me dian diameter centered at about 0.175-0.33 mu m aerodynamic diameter. This study suggests that for modeling the optical properties of aerosol in the A mazon Basin, it is essential to use a model that includes the optical and p hysical properties of at least two aerosol components other than the biomas s burning aerosol, namely, natural biogenic aerosol and soil dust.