Secondary organic aerosol (SOA), formed by oxidation of volatile organic compounds, significantly influences air quality and climate. Highly oxygenated organic molecules (HOM), particularly those formed from biogenic monoterpenes, play a key role in their formation and growth. HOM formation from monoterpenes by hydroxyl radicals (OH), the most important daytime oxidant, is believed to be mainly formed via the OH addition channel. However, for α-pinene, the most abundant atmospheric monoterpene, we found that the minor hydrogen abstraction channel is underappreciated in the HOM formation. We present our observations and theoretical calculations, showing the role of hydrogen-abstraction and alkoxy radicals for fast autoxidation leading to HOM. We also provide a mechanism and yield, suggesting the non-negligible contribution of the hydrogen abstraction channel to ambient SOA, particularly in OH rich areas.

SOA,HOM,BVOC,Photochemistry