Ozonolysis of <i>Z</i> -3-Hexenal and <i>T</i> -2-Hexenal: Insights into the Effect of the Double-Bond Position on the SOA Formation from GLV Isomers

Green leaf volatiles (GLVs) are important secondary organic aerosol (SOA) precursors, while the SOA for mechanisms, especially the structural effects of GLV isomers, remain largely understudied. In this study, the ozonolysis of <i>Z</i>-3-hexenal (<i>Z</i>-3-H) and <i>T</i>-2-hexenal (<i>T</i>-2-H) in the presence of SO₂ was investigated in a 30 m³ smog chamber. The experimental results showed that the SOA concentration produced by <i>Z</i>-3-H was far greater than that of <i>T</i>-2-H, indicating a significant influence of molecular structure on SOA formation. Through the mechanism study, a C₃-carbonyl-RO₂ radical (CHOC₂H₄O₂) was regarded as a key intermediate playing a central role in the <i>Z</i>-3-H and <i>T</i>-2-H SOA formation. Due to the different double-bond positions, the ozonation of <i>Z</i>-3-H undergoes a relatively simpler pathway than <i>T</i>-2-H to produce this intermediate, which is considered one of the reasons for the higher SOA concentration of <i>Z</i>-3-H. Another key reason is that the average concentration of stable Criegee intermediate (sCI) in the <i>Z</i>-3-H/O₃/SO₂ system is much higher than that in the <i>T</i>-2-H/O₃/SO₂ system. The high level of sCI not only directly promotes a series of sCI-involved intramolecular and intermolecular reactions but also drives the rapid formation of H₂SO₄, which facilitates organosulfate production and acid-catalyzed aldol condensation reaction.