Large scale mercury and trace element measurements in the Amazon basin

Large emissions of mercury (Hg) occur in the Amazon Basin as a result of gold mining activities. Mercury and aerosol particles were collected in the Amazon basin, as part of the SCAR-B-Smoke Clouds and Radiation - Brazil experiment in August and September 1995. Three airplanes were used to collect total mercury and aerosol particles. Sampling was performed with the University of Washington Lockheed C131A airplane, as well as in two Brazilian Bandeirante EMB 120 planes. Atmospheric mercury was sampled using two gold traps in series for each sampling line and measured with atomic fluorescence spectrometer (AFS). Aerosols were collected on Teflon and polycarbonate filters and analyzed by particle-induced X-ray emission (PIXE) for up to 20 elements, and by instrumental neutron activation analysis (INAA) for up to 39 elements. Absorbing aerosols expressed as black carbon (BC), and aerosol gravimetric mass were also determined. Sampling time was 2-4 h. The sampling period was at the peak of the biomass burning season, when most of the Hg is emitted. Concentrations for total Hg in this study were as high as 14.8 ng m(-3). Factor analysis was performed for the combined (aerosol and Hg) data set and six factors were observed: A soil dust component; a biomass-burning factor (with fine mode mass concentration, BC, K, Cl, Zn and others); a natural biogenic component (P, K, S, Ca, Mn, Zn); a second soil dust factor (enriched in Si); a sea-salt aerosol component, with NaCl; and a factor related to gold mining activities, with Hg, Pb and other elements. Hg was also clearly associated with the biomass-burning component, in addition to the gold mining activities component. An average of 63% of the Hg concentrations was associated with the gold mining activities. About 31% of the Hg concentration was associated with the biomass-burning component, the soil dust accounted for 4% and the NaCl component for 2.1% of the airborne Hg concentrations. The high association between Hg and biomass burning can be caused by at least three mechanisms: (1) adsorption of gaseous Hg on existing biomass burning particles; (2) direct release of Hg from the vegetation to the atmosphere during forest burning; (3) evaporation of Hg from soil during the forest burning. Three-dimensional long-range air mass trajectory analyses show the possibility that Hg exits the Amazon Basin over two main routes: to the South Atlantic, and to the Tropical Pacific, over the Andes. (C) 2000 Elsevier Science Ltd. All rights reserved.