Exploring autoxidation pathways in α-pinene oxidation through particulate measurements

In this study, we examine the oxidation pathways of α-pinene and their influence on the formation of highly oxygenated organic molecules (HOMs) and secondary organic aerosols (SOA) using chamber-based particulate measurements combined with COSIMA-SOA and PyCHAM box-model simulations. Two chamber datasets, MAC20120215 and AIDA20081127, were used to test whether observed particle mass and size distributions can be reproduced by three autoxidation-initiation routes: (1) ozone (O₃) attack on α-pinene, (2) hydroxyl radical (OH) attack on α-pinene, and (3) later-generation oxidation of α-pinene products. Simulations without HOM formation underestimated SOA mass, whereas the inclusion of first-generation and later-generation HOM pathways substantially improved model-measurement agreement. The results indicate that no single pathway alone is sufficient under the investigated conditions and that later-generation HOM chemistry is required to reproduce the second-stage SOA growth observed in AIDA. Although direct HOM measurements were not available, this combined particulate-measurement and modelling approach provides useful constraints for improving simplified mechanisms of organic oxidation and aerosol formation.