Composition and sources of aerosols from the Amazon Basin

Abstract

Aerosols were sampled in the Amazon Basin, as part of the Global Tropospheric Experiment (GTE), during the Amazon Boundary Layer Experiment (ABLE 2A) in July–August 1985. Fine‐ and coarse‐particle fractions were analyzed for 22 elements by particle‐induced X ray emission. Gravimetric mass, black carbon, sulfate, and nitrate concentrations were also determined. Morphological and trace element measurements of individual particles were carried out by automated electron probe X ray microanalysis. Various receptor models, including multivariate methods and a chemical mass balance model, were employed in the interpretation of the bulk trace element concentrations. Three factors explained over 85% of the variability of fine‐ and coarse‐mode variables. On the basis of the elemental composition of the factors, two could be identified as plant related, and the third was a soil dust component. Of the coarse‐mode aerosol mass concentration (of 7.6±1.6 μg/m 3), 62% could be attributed to aerosols released by the vegetation and 11% to soil dust. In the fine mode, soil dust accounted for less than 10% of the measured mass concentration (of 6.8±3.9 μg/m 3). The variables related to the plant component were K, P, S, Ca, Mg, Cl, Rb, and the gravimetric mass. The elemental profile of the plant component resembled the bulk plant composition. By single‐particle analysis coupled with hierarchical cluster analysis, six to nine different biogenic‐related particle groups could be identified in the fine‐ and coarse‐aerosol modes. Almost all particle types consisted predominantly of carbonaceous material, with trace amounts of K, S, Ca, P, Cl, and Na. Only one group, comprising less than 11% of the total number of particles, consisted of soil dust–related aerosol.