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Volatility Comparison of β-caryophyllene Autoxidation Products with C15 Dimers Using FIGAERO I-CIMS Thermal Desorption
JENNA DEVIVO, Mingyi Wang, Lubna Dada, Neil Donahue, The CLOUD Collaboration, Carnegie Mellon University
Abstract Number: 584
Working Group: Aerosol Chemistry
Abstract
Trees emit a variety of volatile organic molecules that are important precursors to particle and secondary organic aerosol formation in the troposphere, especially in pristine conditions. Peroxy radicals (RO2) formed from these emissions undergo autoxidation, increasing the number of oxygen atoms and decreasing volatility. RO2 molecules can react with each other (dimerize) to decrease volatility. This pathway is important for biogenic molecules with fewer than the twenty carbon atoms typically needed for nucleation. The volatility basis set (VBS) categorizes different molecules into volatility bins based on the extent of oxidation (O:C ratio) and volatility (logC*). However, the VBS often relies on composition-volatility relations to infer volatility of a molecule based on its molecular formula. At the CLOUD chamber at CERN, we used an iodide chemical ionization mass spectrometer and a Filter Inlet for Gases and AEROsols (FIGAERO) for thermal desorption to directly measure the volatility of different biogenic precursors. We found that C15 monomers and dimers had similar volatilities for a given carbon number and O:C, falling in the Low and Extremely Low Volatility Organic Compound classes regardless of whether they were monomers or dimers. The dimers were measured in controlled experiments where RO2 radicals of isoprene (C5) and α-pinene (C10) autoxidized and reacted together to form C15 species. The monomers were measured in conditions where only β-caryophyllene (C15) was present. These experimental volatilities agree with the work of Stolzenberg et al., 2018. This comparison suggests that a single composition-volatility relation applies to terpene and isoprene oxidation products, regardless of the carbon number of the precursor. This finding supports volatility analysis for mass spectrometry results where molecular structure is unknown. Additionally, the formation of low volatility products from biogenic molecules with less than ten carbons emphasizes the importance of relatively small gas phase molecules for nucleation.