[A-AS07] 大気化学

[AAS07-25] Accurate Identification of Dimers from α-Pinene Oxidation Using High-Resolution Collision-Induced Dissociation Mass Spectrometry

*関本 奏子^1,2、福山 大輔¹、猪俣 敏³ (1.横浜市立大学、2.大阪大学、3.国立環境研究所)

キーワード：α-ピネン、酸化、ダイマー、高分解能衝突誘起解離質量分析法、水素結合系クラスター

Highly oxidized dimers from α-pinene oxidation are essential to the atmospheric chemistry field because they are efficient precursors of secondary organic aerosols. Here we apply high-resolution collision-induced dissociation (CID) mass spectrometry with an atmospheric pressure ionization (API) source to accurately identify the origin of dimers from α-pinene + O₃/OH/NO_x reactions. The CID spectra and specific fragmentation patterns suggest that (i) a large fraction of dimer ions detected in full-scan mass spectra can be hydrogen-bonded clusters, which are instrument artifacts; these clusters form owing to the adiabatic expansion between the API source inside a mass spectrometer, and (ii) the residual small fraction includes covalently-bonded dimers, such as hydroperoxide-type dimers, that are formed from reactions between a stabilized Criegee Intermediate (sCI) and oxidized monomers. This work highlights the importance of accurate identification and quantification of dimers for mechanistic and kinetic studies of α-pinene-derived dimer formation using ion intensities detected by mass spectrometry.