Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 5 4 2005 10.5194/acpd-5-5687-2005 http://www.atmos-chem-phys-discuss.net/5/5687/2005/ http://www.atmos-chem-phys-discuss.net/5/5687/2005/acpd-5-5687-2005.html http://www.atmos-chem-phys-discuss.net/5/5687/2005/acpd-5-5687-2005.pdf 5687 5749 2005-08-09 Characterization of the organic composition of aerosols from Rondônia, Brazil, during the LBA-SMOCC 2002 experiment and its representation through model compounds S. Decesari S. Fuzzi M. C. Facchini M. Mircea L. Emblico F. Cavalli W. Maenhaut X. Chi G. Schkolnik A. Falkovich Y. Rudich M. Claeys V. Pashynska G. Vas I. Kourtchev R. Vermeylen A. Hoffer M. O. Andreae E. Tagliavini F. Moretti P. Artaxo Istituto Scienze dell’Atmosfera e del Clima - C.N.R., Bologna, Italy Department of Analytical Chemistry, Institute for Nuclear Sciences, Ghent University, Gent, Belgium Department of Environmental Sciences, Weizmann Institute, Rehovot, Israel Department of Pharmaceutical Sciences, University of Antwerp, Antwerp, Belgium Biogeochemistry Department, Max Planck Institute for Chemistry, Mainz, Germany Dipartimento di Chimica “G. Ciamician", Università di Bologna, Bologna, Italy Centro di Ricerche per le Scienze Ambientali, Università di Bologna, Ravenna, Italy Instituto de Fisica, Universidade de Sao Paulo, Sao Paulo, SP, Brazil The chemical composition of carbonaceous aerosols collected during the LBA-SMOCC field experiment, conducted in Rondônia, Brazil, in 2002 during the transition from the dry to the wet season, was investigated by a suite of advanced analytical techniques. The period of most intense biomass burning was characterized by high concentrations of submicron particles rich in carbonaceous material and water-soluble organic compounds (WSOC). At the onset of the rainy period, submicron total carbon (TC) concentrations had decreased by about 20 times. In contrast, the concentration of supermicron TC was fairly constant throughout the experiment, pointing to a constant emission of coarse particles from the natural background. About 6–8% of TC (9–11% of WSOC) was speciated at the molecular level by GC-MS and liquid chromatography. Poly-hydroxylated compounds, aliphatic and aromatic acids were the main classes of compounds accounted for by individual compound analysis. Functional group analysis by proton NMR and chromatographic separation on ion-exchange columns allowed characterization of ca. 50–90% of WSOC into broad chemical classes (neutral species/light acids/humic-like substances). In spite of the significant change in the chemical composition of tracer compounds from the dry to the wet period, the functional groups and the general chemical classes of WSOC changed only to a lesser extent. Model compounds representing size-resolved WSOC chemical composition for the different periods of the campaign are then proposed in this paper, based on the chemical characterization by both individual compound analysis and functional group analysis deployed during the LBA-SMOCC experiment. Model compounds reproduce quantitatively the average chemical structure of WSOC and can be used as best-guess surrogates in microphysical models involving organic aerosol particles over tropical areas affected by biomass burning.