Trace element concentrations and size distribution of biogenic aerosols from the amazon basin during the wet season

Abstract

Atmospheric aerosols were sampled in the tropical rain forest of the Amazon Basin during April and May, 1987 (wet season) as part of the NASA Global Tropospheric Experiment (GTE), during the Amazon Boundary Layer Experiment (ABLE-2B). A special fine particle aerosol sampler and 6-stage single orifice cascade impactors were used for the aerosol collections. The samples were analyzed for 24 elements (Na, Mg, Al, Si, P, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Ga, Se, Br, Rb, Sr, Zr, and Pb) by particle-induced X-ray emission (PIXE). Absolute principal factor analysis was used to interpret the fine particle aerosol elemental concentrations, and to obtain elemental source profiles. The concentrations of the fine mode soil dust related elements (Al, Ti, Mn, and Fe) were more than 10 times larger in the wet season than in the dry season. The biogenic aerosol related elements (e.g. P, S, K, and Zn) in the fine mode showed strongly reduced concentrations in the wet season. Sulphur concentrations averaged 92 ± 54 ng m 3 in the fine mode aerosol. The concentrations of soil dust related elements were 80% higher during daytime than during night, whereas the biogenic related elements showed much lower levels during day than during night. Two factors explained more than 92% of the data variability for the day and night fine particle samples. These factors were soil dust (represented mainly by Al. Si, Ti, Mn. and Fe) and biogenic related aerosol (with K, P, S, and Zn). Source profiles were obtained for the fine mode aerosol, and the soil dust factor had a similar elemental composition as average crustal rock. The size distributions of the soil dust related elements, as measured at three different levels (ground level, 28 and 45 m), were very similar, whereas for the biogenic related elements some differences as a function of height were observed. The sulphur size distribution was clearly bimodal, but the fine mode was significantly reduced at ground level. Considering the concentrations measured in this work and the large area of the tropical rain forests, biogenic aerosol particles can play an important role in the global aerosol budget and in the global biogeochemical cycles of various elements.