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 go ld mining activities. Mercury and aerosol particles were collected in the A mazon basin, as part of the SCAR-B-Smoke Clouds and Radiation - Brazil expe riment in August and September 1995. Three airplanes were used to collect t otal mercury and aerosol particles. Sampling was performed with the Univers ity of Washington Lockheed C131A airplane, as well as in two Brazilian Band eirante EMB 120 planes. Atmospheric mercury was sampled using two gold trap s in series for each sampling line and measured with atomic fluorescence sp ectrometer (AFS). Aerosols were collected on Teflon and polycarbonate filte rs and analyzed by particle-induced X-ray emission (PIXE) for up to 20 elem ents, and by instrumental neutron activation analysis (INAA) for up to 39 e lements. Absorbing aerosols expressed as black carbon (BC), and aerosol gra vimetric mass were also determined. Sampling time was 2-4 h. The sampling p eriod 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) dat a set and six factors were observed: A soil dust component; a biomass-burni ng 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 re lated to gold mining activities, with Hg, Pb and other elements. Hg was als o clearly associated with the biomass-burning component, in addition to the gold mining activities component. An average of 63% of the Hg concentratio ns was associated with the gold mining activities. About 31% of the Hg conc entration was associated with the biomass-burning component, the soil dust accounted for 4% and the NaCl component for 2.1% of the airborne Hg concent rations. The high association between Hg and biomass burning can be caused by at least three mechanisms: (1) adsorption of gaseous Hg on existing biom ass burning particles; (2) direct release of Hg from the vegetation to the atmosphere during forest burning; (3) evaporation of Hg from soil during th e 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) 200 0 Elsevier Science Ltd. All rights reserved.