Carbonaceous aerosol characterization in the Amazon basin, Brazil: novel dicarboxylic acids and related compounds

High-resolution capillary gas chromatography (GC) and GC/mass spectrometry (MS) were employed for the quantitative determination of dichloromethane-ex tractable organic compounds in total and size-fractionated aerosol samples which were collected in the Amazon basin, Brazil, during the wet season, as part of the LBA-CLAIRE-98 experiment. Special emphasis was placed on the c haracterization and identification of several novel unknown dicarboxylic ac ids and related oxidative degradation products. This class of acidic produc ts was enriched in the fine size fraction, suggesting that they were second ary organic aerosol products formed by gas-to-particle conversion. Some of the unknowns contributed more to the class of dicarboxylic acids than the m ajor known compound, nonadioic acid (azelaic acid). The same unknowns were also observed in urban aerosol samples collected on hot summer days in Gent , Belgium. For the characterization and structure elucidation of the unknow ns, various types of derivatizations and Fractionation by solid-phase extra ction were employed in combination with GC/MS. Four unknowns were identifie d. The most abundant were two derivatives of glutaric acid, 3-isopropyl pen tanedioic acid and 3-acetyl pentanedioic acid. The other two identified unk nowns were another oxo homologue, 3-acetyl hexanedioic acid, and, interesti ngly, 3-carboxy heptanedioic acid. To our knowledge, the occurrence of thes e four compounds in atmospheric aerosols has not yet been reported. The bio genic precursors of the novel identified compounds could not be pinpointed. but most likely include monoterpenes and fatty acids. (C) 2000 Elsevier Sc ience Ltd. All rights reserved.