ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-12-10749-2012 Cyclobutyl methyl ketone as a model compound for pinonic acid to elucidate oxidation mechanisms Praplan A. P. 1 2 Barmet P. 1 Dommen J. 1 Baltensperger U. 1 Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, Villigen PSI, Switzerland now at: Department of Physics, University of Helsinki, Helsinki, Finland 16 11 2012 12 22 10749 10758 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.net/12/10749/2012/acp-12-10749-2012.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/12/10749/2012/acp-12-10749-2012.pdf

Although oxidation of the atmospherically relevant compound α-pinene has been extensively studied, chemical mechanisms leading to the formation of later generation oxidation products remain poorly understood. The present work uses cyclobutyl methyl ketone (CMK) to study the oxidation mechanism of pinonic acid, an α-pinene reaction product, by hydroxyl radicals (·OH). CMK has a similar but simpler chemical structure compared to pinonic acid. Succinic acid, 4-hydroxybutanoic acid and 4-oxobutanoic acid were identified as first generation products of CMK. These observed organic acids were compared to compounds found in secondary organic aerosol formed from the oxidation of α-pinene. Results suggest that 3-methyl-1,2,3-butanetricarboxylic acid (MBTCA), terpenylic % corrected name for MBTCA (3-methyl-1,2,3-butanetricarboxylic acid) acid and diaterpenylic acid acetate are first generation products of OH oxidation of pinonic acid. Therefore, there is strong evidence that ·OH oxidation greatly increases the oxygenation of organic compounds (e.g. monocarboxylic acid to tricarboxylic acid) through radical mechanisms, without requiring a stable intermediate. These observations cannot be explained by traditional atmospheric chemistry mechanisms.

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