Elucidating Isoprene Oxidation: Pathways to Highly Oxygenated Molecules formation

Isoprene is globally recognized as the preeminent biogenic volatile organic compounds (BVOCs) and is the most extensively researched species among volatile organic compounds (VOCs). Nevertheless, prevailing global and regional atmospheric models inadequately represent its molecular-level oxidation process. The predominate explicit chemical mechanisms, such as Master Chemical Mechanism (MCM) and CalTech isoprene mechanism, underestimate the complexities of isoprene oxidation, particularly the formation of Highly Oxygenated Molecules (HOMs) — a vital process from VOC to secondary organic aerosol (SOA). Here, we address a critical gap in the understanding of isoprene oxidation mechanism within existing models, especially the formation of fragmentation products and HOM-level oxidation products. The updated model integrates the influence of multigenerational OH-initiated oxidation and photolysis processes, thereby enriching the dynamics of free radical cycling. Our updated model was validated against previous molecular-level chamber experiments, demonstrating an enhanced ability to simulate the radical cycle and HOM formation, thus more accurately reflecting SOA formation.