New tracer compounds for secondary organic aerosol formation from β-caryophyllene oxidation

Five products from β-caryophyllene oxidation (β-caryophyllonic acid (I), 3,3-dimethyl-2-(3-oxobutyl)cyclobutanecarboxylic acid (βCA198) (II), β-nocaryophyllonic acid (III), β-caryophyllinic acid (IV), and 2-(2-carboxyethyl)-3,3-dimethylcyclobutanecarboxylic acid (βCA200) (V)) were synthesized and their structures confirmed by nuclear magnetic resonance spectroscopy. Reaction chamber experiments with β-caryophyllene at two different ozone mixing ratios were performed and the carboxylic acid oxidation products in the particle phase were characterized by APCI-MS and HPLC-ESI-MS. All five synthesized acids were found as β-caryophyllene oxidation products in the reaction chamber aerosol. The main oxidation products of the reaction chamber experiments were β-14-hydroxynocaryophyllonic acid, β-nocaryophyllonic acid (III) and βCA198 (II). Product yields of the acids were estimated based on the chamber experiments and the application of the atmospheric chemistry box model CAABA/MECCA. Finally, ambient aerosol samples taken during the HUMPPA campaign in Hyytiälä, Finland in summer 2010 were analysed for the carboxylic acid β-caryophyllene oxidation products. All five synthesized compounds were detected and were quantified in the ambient aerosol samples. The major β-caryophyllene carboxylic acid oxidation products in the ambient air samples were β-nocaryophyllonic acid (III) and βCA198 (II) with concentrations in the range of about 0.2-14 ng m−3 and 0.8-6.8 ng m−3. The fact that the concentrations of these two acids in ambient aerosol are generally higher than the concentration of β-caryophyllinic acid (IV) (often used in previous studies as oxidation tracer) with a concentration of about 0.16 ng m−3 leads to the conclusion that these two acids are better suited as tracer compounds for β-caryophyllene secondary organic aerosol formation.