Formation of Highly Oxidized Organic Compounds and Secondary Organic Aerosol from α-Thujene Ozonolysis

We conducted laboratory chamber experiments to probe the gas- and particle-phase composition of oxidized organics and secondary organic aerosol (SOA) formed from α-thujene ozonolysis under different chemical regimes. The formation of low-volatility compounds was observed using chemical ionization mass spectrometry with nitrate (NO₃^-) and iodide (I^-) reagent ions. The contribution of measured low-volatility compounds to particle growth was predicted using a simple condensational growth model and found to underpredict the measured growth rates in our chamber (on the order of several nm min^-1). The yields of low-volatility compounds and SOA mass were similar to those of other monoterpene ozonolysis systems. While semivolatile compounds C₁₀H_14-16O_3-7 were measured most abundantly with I^- reagent ion, a large fraction of products measured with NO₃^- were C_5-7 fragments with predicted intermediate volatility. Additionally, particle composition was measured with ultrahigh-performance liquid chromatography with high-resolution mass spectrometry and compared to particle composition from α-pinene ozonolysis. Structural isomers were identified from tandem mass spectrometry analysis of two abundant product ions (C₈H₁₃O₅^-, C₁₉H₂₇O₇^-). Our results indicate that although this system efficiently generates low-volatility organics and SOA under the conditions studied, fragmentation pathways that produce more highly volatile products effectively compete with these processes.