Aerosol chemistry of oxygenated terpenes in simple and complex chemical systems

Terrestrial vegetation emits complex mixtures of highly reactive biogenic volatile organic compounds (BVOCs) that contribute to secondary organic aerosol (SOA) formation. The aerosol chemistry of many BVOCs remains unexplored. Oxygenated monoterpenes are one class of BVOCs that comprise a large proportion of woody shrub emission profiles and can also be induced after stress exposure. In this work, SOA was generated from the photooxidation of oxygenated monoterpenes in an oxidation flow reactor and compared to SOA generated from a reference cyclic terpene—α-pinene. The oxygenated terpenes used as SOA precursors included camphor (C₁₀H₁₆O), borneol (C₁₀H₁₈O), 1,8-cineole (C₁₀H₁₈O), and bornyl acetate (C₁₂H₂₀O₂). Results show that SOA mass yields from oxygenated terpenes were usually greater than or equal to α-pinene except for bornyl acetate, which had the lowest yields. SOA composition measured offline with liquid chromatography high resolution mass spectrometry (UHPLC-ESI-HRMS) was used to compare the different SOA types. Additionally, the composition of SOA generated from emissions of two coastal sage shrubs, with emissions dominated by oxygenated terpenes, was compared with SOA formed from single component standards using aerosol mass spectrometry. The composition of 1,8-cineole SOA was most dissimilar from the other types of SOA. Additionally, SOA generated from real plant emissions of two different species was more similar in composition to one another than to the SOA generated from the individual components, suggesting non-linearity of the chemistry of BVOC mixtures. These results highlight the importance of biogenic SOA studies using complex mixtures that are more representative of real plant emissions.