Properties\nand Atmospheric Oxidation of Terebic Acid\nAerosol

Terebic acid (C<sub>7</sub>H<sub>10</sub>O<sub>4</sub>) is a biogenic\nsecondary organic aerosol constituent, produced by the oxidation of\nfirst- and second-generation products of monoterpenes such as α<i>-</i>pinene, β-pinene, and Δ<sup>3</sup>-carene.\nIt is a processed derivative of terpenylic acid and has been identified\nin aerosol samples from terrestrial and forest environments. The physicochemical\nproperties of pure terebic acid aerosol were characterized using two\ndifferent atmospheric simulation chambers and a suite of online particle\nand gas-phase instrumentation. Its mass spectrum, obtained by a high-resolution\ntime-of-flight mass spectrometer, had characteristic peaks at mass-to-charge\n(<i>m</i>/<i>z</i>) ratios 81, 96, 100, 115, and\n143, mainly related to oxygenated fragment ions. The density of terebic\nacid aerosol was 1.33 ± 0.20 g cm<sup>–3</sup>, and its\nvaporization enthalpy was 85 kJ mol<sup>–1</sup>. The estimated\nsaturation concentration at 298 K of 2.6 ± 1.2 μg m<sup>–3</sup> places terebic acid in the semivolatile organic compound\ncategory. Oxidation of terebic acid aerosol by hydroxyl (OH) radicals\nresulted in a substantial reduction in organic aerosol (OA) mass concentration\n(up to 80%), with no significant alteration in the OA spectrum or\naerosol O:C ratio, indicating negligible production of secondary OA.\nGas-phase analysis detected the production of smaller compounds, such\nas acetone. The terebic acid oxidation products were mostly in the\ngas phase as fragmentation appears to dominate its reaction with OH\nradicals. The gas-phase reaction rate constant with OH was estimated\nto be 3 × 10<sup>–12</sup> cm<sup>3</sup> molecule<sup>–1</sup> s<sup>–1</sup>.