Second-generation products of β-caryophyllene ozonolysis are the dominant contributors to particle mass concentration
1Environmental Engineering Program, Hong Kong University of Science and Technology, Hong Kong, China
2School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, USA
3now at: Department of Chemistry, University of Kentucky, Lexington, KY, USA
4Division of Environment, Hong Kong University of Science and Technology, Hong Kong, China
5Department of Chemical and Biomolecular Engineering, Hong Kong University of Science and Technology, Hong Kong, China
6Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA, USA
Abstract. The production of secondary organic aerosol (SOA) by the dark ozonolysis of gas-phase β-caryophyllene was studied. The experiments were conducted in a continuous-flow environmental chamber for organic particle mass concentrations of 0.5 to 30 μg m−3 and with ozone in excess, thereby allowing the study of second-generation particle-phase products under atmospherically relevant conditions. The particle-phase products were characterized by an ultra-performance liquid chromatograph equipped with an electrospray ionization time-of-flight mass spectrometer (UPLC-ESI-ToF-MS). Fragmentation mass spectra were used for the structural elucidation of each product, and the structures were confirmed as consistent with the accurate m/z values of the parent ions. In total, fifteen products were identified, three of which are reported for the first time in this study. The structures showed that 9 out of 15 particle-phase products were second generation, including all three of the new products. The relative abundance of the second-generation products was approximately 90% by mass among the 15 observed products. The O:C and H:C elemental ratios of the 15 products ranged from 0.13 to 0.50 and from 1.43 to 1.60, respectively. Fourteen of the products contained 3 to 5 oxygen atoms. A singular product, which was one of the three newly identified ones, had 7 oxygen atoms, including 1 carboxylic group, 2 carbonyl groups, and 3 hydroxyl groups. It was identified as 2,3-dihydroxy-4-[2-(4-hydroxy-3-oxobutyl)-3,3-dimethylcyclobutyl]-4-oxobutanoic acid (C14H22O7). The estimated saturation vapor pressure of this product is sufficiently low (3.3×10−13 Pa) that it can contribute to new particle formation in the atmosphere.