Elucidation of the myrcene ozonolysis mechanism from a Criegee Chemistry perspective

Abstract. Criegee intermediates (CIs) are highly reactive species generated during the alkene ozonolysis, which play a critical role in atmospheric chemistry. Myrcene is a typical monoterpene, and its linear structure is significantly different from other cyclic monoterpenes such as α-pinene. This structural distinction consequently leads to different reactions mechanisms. This study employs a combined approach of matrix isolation Fourier transform infrared spectroscopy (MI-FTIR) and smog chamber experiments to elucidate the mechanisms of myrcene ozonolysis from the Criegee chemistry perspective. Two CIs with different molecular sizes, C3-CIs and C7-CIs, are captured at 880 and 905 cm^-1 by using MI-FTIR. Ordered oligomers with C3-CIs serving as chain units, formed via RO₂ + n C3-CIs + HO₂/RO₂ mechanisms, are detected as significant components in secondary organic aerosol (SOA). C7-CIs are more prone to unimolecular degradation to form C7-RO₂ radical, which act as initiators for oligomerization reactions. The mechanisms may also exist in other monoterpenes ozonolysis, which offering new insights into the contribution of CIs to SOA formation. Furthermore, the mechanisms of the synergistic interaction between SCIs oligomerization and RO₂ autoxidation are illustrated. The mechanisms facilitate the rapid formation of highly oxygenated species, playing a critical role in particle nucleation. The increase in relative humidity can effectively reduce the formation of higher-order oligomers, thereby suppressing the SOA yields. This study provides a systematic elucidation of myrcene ozonolysis mechanisms, thereby significantly enhancing the understanding of oxidation processes in acyclic monoterpenes.