Cyclobutyl methyl ketone as a model compound for pinonic acid to elucidate oxidation mechanisms
Although oxidation of the atmospherically relevant compound alpha-pinene\nhas been extensively studied, chemical mechanisms leading to the\nformation of later generation oxidation products remain poorly\nunderstood. The present work uses cyclobutyl methyl ketone (CMK) to\nstudy the oxidation mechanism of pinonic acid, an alpha-pinene reaction\nproduct, by hydroxyl radicals ((OH)-O-center dot). CMK has a similar but\nsimpler chemical structure compared to pinonic acid. Succinic acid,\n4-hydroxybutanoic acid and 4-oxobutanoic acid were identified as first\ngeneration products of CMK. These observed organic acids were compared\nto compounds found in secondary organic aerosol formed from the\noxidation of alpha-pinene. Results suggest that\n3-methyl-1,2,3-butanetricarboxylic acid (MBTCA), terpenylic acid and\ndiaterpenylic acid acetate are first generation products of OH oxidation\nof pinonic acid. Therefore, there is strong evidence that (OH)-O-center\ndot oxidation greatly increases the oxygenation of organic compounds (e.\ng. monocarboxylic acid to tricarboxylic acid) through radical\nmechanisms, without requiring a stable intermediate. These observations\ncannot be explained by traditional atmospheric chemistry mechanisms.