Long-term monitoring of atmospheric aerosols in the Amazon Basin: Source identification and apportionment

Continuous sampling of atmospheric aerosols was carried out at mio differen t sites in the Amazon Basin: Cuiaba (16 degrees S, 56 degrees W), since Jul y 1990, and Alta Floresta (09 degrees S, 56 degrees W), since August 1992. Aerosols were collected on polycarbonate filters mounted in stacked filter units (SFU). Particle-induced X ray emission (PIXE) was used to measure con centrations of up to 26 elements (Mg, Al, Si, P, S, Cl, K, Ca, Ti, V, Cr, M n, Fe, Ni, Cu, Zn, Ga, Ge, As, Se, Br, Rb, Sr, Zr, Au, and Pb). Black carbo n (BC) and gravimetric mass analyses were also performed. Inhalable particl e ground concentrations showed a marked seasonality, with maxima of more th an 100 mu g m(-3) in the dry season. The high aerosol optical thickness (AO T) values in this period (up to 4.0 at lambda = 0.440 mu m) indicate that t he whole air column has a significant aerosol load. Three main types of aer osol sources were identified: biomass burning, natural biogenic emissions, and soil dust resuspension. During the dry season the fine mode aerosol ori ginated predominantly from biomass burning emissions (they were responsible for about 73% of fine aerosol mass), while the coarse mode was dominated b y soil dust particles (50 to 60% of the aerosol mass). Crustal elements exh ibited a unimodal coarse mode size distribution, while the pyrogenic elemen ts showed a clear submicrometer mode. Black carbon had a submicrometer mode centered at 0.175 mu m. During the wet season, biogenic aerosols were the dominant particle type and also the main source of atmospheric P in the reg ion.