ACPD Atmospheric Chemistry and Physics Discussions ACPD 1680-7375 Copernicus GmbH Göttingen, Germany 10.5194/acpd-5-8027-2005 Chemical transformations in organic aerosol from biomass burning Hoffer A. 1 Gelencsér A. 2 Blazsó M. 3 Guyon P. 1 Artaxo P. 4 Andreae M. O. 1 Max Planck Institute for Chemistry, Mainz, Germany Air Chemistry Group of the Hungarian Academy of Sciences, Veszprém, Hungary Institute of Materials and Environmental Chemistry CRC, Hungarian Academy of Sciences, Budapest, Hungary Instituto de Fisica, Universidade de Sao Paulo, Sao Paulo, Brazil 05 09 2005 5 5 8027 8054 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys-discuss.net/5/8027/2005/acpd-5-8027-2005.html The full text article is available as a PDF file from http://www.atmos-chem-phys-discuss.net/5/8027/2005/acpd-5-8027-2005.pdf

Fine aerosol particles were collected separately during daytime and nighttime at a tropical pasture site in Rondônia, Brazil, during the burning and dry-to-wet transition period in 2002. Total carbon (TC) and water-soluble organic carbon (WSOC) were measured by evolved gas analysis (EGA). Based on the thermochemical properties of the fine aerosol, the relative amounts of the low and higher molecular weight compounds were estimated. It was found that the thermally refractory (possibly higher molecular weight) compounds dominated the TC composition. Their contribution to TC was higher in the daytime samples than in the nighttime ones. The relative share of WSOC also showed a statistically significant diel variation and so did its refractory fraction. Anhydrosugars and phenolic acids were determined by GC-MS and their diel variation was studied. Based on the decrease of their relative concentrations between the biomass burning and transition periods and their distinctly different diel variations, we suggest that the phenolic acids may undergo chemical transformations in the aerosol phase, possibly towards more refractory compounds (humic-like substances, HULIS), as has been suggested previously. These conclusions are supported by the results of the thermally assisted hydrolysis and methylation gas chromatography-mass spectrometry of the same filter samples.