Diaterpenylic Acid Acetate (DTAA): Characterization and OH Oxidation in Atmospheric Chambers

Abstract

Diaterpenylic acid acetate (DTAA) (C10H16O6) is a later generation biogenic secondary organic aerosol (OA) component, formed during the oxidation of first-generation products of monoterpenes like α-pinene, and β-pinene. Identified in aerosol in terrestrial and forested environments, DTAA is a product of the oxidation of both terpenylic acid and 1,8-cineole. Here, we present the first comprehensive chamber study investigating DTAA's volatility, gas-particle partitioning, and oxidative transformation under atmospherically relevant conditions through a combination of laboratory measurements, modeling, and chemical analysis. Its physicochemical properties were characterized by using two atmospheric simulation chambers, equipped with a range of particle and gas-phase instrumentation. A high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) identified DTAA aerosol characteristic peaks at mass-to-charge (m/z) 59, 67, 79, 91, 95, 101, 114 and 139. DTAA aerosol density was estimated to be 1.3 ± 0.2 g cm-3 . DTAA was classified as a semi-volatile organic compound (SVOC), with a saturation concentration of 3.6-3.9 μg m-3. Upon hydroxyl (OH) radical exposure, DTAA underwent significant chemical aging, producing secondary organic aerosol (SOA) with distinct spectral features and a little higher oxygen-to-carbon ratio (O:C=0.63). The AMS spectrum of the produced SOA was quite different from that of pure DTAA (R2 =0.48 or θ=31o) and resembled to an extent (θ=14-20o ) the spectra of ambient biogenic SOA. A suite of oxidation products were identified via proton transfer reaction mass spectrometry (PTR-MS) and chemical ionization mass spectrometry (CIMS) ranging from small molecules (e.g. acetone) to multifunctional species. A kinetic model incorporating partitioning, wall loss, and oxidation accurately captured SOA production during the DTAA reaction with OH, assuming an effective fragmentation probability of 32%. These results highlight the atmospheric relevance of DTAA as a reactive SVOC and underline the importance of integrating later generation chemical processes in SOA studies.