Characterization of the organic composition of aerosols from Rondonia, Brazil, during the LBA-SMOCC 2002 experiment and its representation through model compounds

TLDR: The chemical composition of carbonaceous aerosols collected during the LBA-SMOCC field experiment, conducted in Rondˆ onia, Brazil, in 2002 during the transition from the dry to the wet season, was investigated by a suite of state-of-the-art analytical techniques as discussed by the authors.

Abstract: The chemical composition of carbonaceous aerosols collected during the LBA-SMOCC field experiment, conducted in Rondˆ onia, Brazil, in 2002 during the transition from the dry to the wet season, was investigated by a suite of state-of-the-art analytical techniques. The period of most intense biomass burning was characterized by high concen- trations of submicron particles rich in carbonaceous material and water-soluble organic compounds (WSOC). At the on- set of the rainy period, submicron total carbon (TC) concen- trations decreased by about 20 times. In contrast, the con- centration of supermicron TC was fairly constant through- out 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. Polyhydroxylated com- pounds, aliphatic and aromatic acids were the main classes of compounds accounted for by individual compound analysis. Functional group analysis by proton NMR and chromato- graphic separation on ion-exchange columns allowed char- acterization 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 composi- tion of tracer compounds from the dry to the wet period, the functional groups and the general chemical classes of WSOC changed only to a small 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 analy- sis 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.