Rethinking the Sources of Secondary Organic Aerosol: The Case of Sesquiterpenes and β-Caryophyllene
ANGELIKI MATRALI, Christina N. Vasilakopoulou, Stella Eftychia Manavi, Petro Uruci, Damianos Pavlidis, Elena Voutsina, Spyros Ν. Pandis, University of Patras, Greece
Abstract Number: 215
Working Group: Aerosol Chemistry
Abstract
Studies of the reactions of β-caryophyllene (a prominent sesquiterpene) with ozone have indicated that it is a good secondary organic aerosol (SOA) precursor. Significant SOA is also formed when β-caryophyllene reacts with OH and NO3 radicals, reactions generally slower than its ozonolysis. Most chemical transport models either include only the first-generation reactions of sesquiterpenes in SOA formation or completely disregard them due to sesquiterpenes’ relatively low (compared to monoterpenes) emissions. Experiments, conducted in the FORTH Atmospheric Simulation Chamber (FORTH-ASC), quantified the role of chemical aging of the ozonolysis products of β-caryophyllene as they continue reacting with OH in the atmosphere. Instrumentation included a high-resolution Aerosol Mass Spectrometer, a high-resolution PTR-MS with the CHARON addon (monitoring OA composition), and additional GC-MS analysis of organic vapors.
Multigeneration reactions increased dramatically the SOA formed by ozonolysis. Increases of up to a factor of 2.5 were measured. The later generation SOA was more oxidized than the ozonolysis SOA with O:C reaching 0.6. The oxidant to precursor concentration ratio affected the composition and yields of the aging products. The evolution of several ozonolysis products was quantified during the experiments. In many cases, ozonolysis-produced species like β-caryophyllon aldehyde and β-caryophyllinic acid were consumed during the OH chemical aging.
Results of the experiments were used to derive a parameterization of the sesquiterpene SOA aging based on the 1-D Volatility Basis Set, which was then added to the PMCAMx chemical transport model and used to simulate SOA production over Europe during a typical summer month. The predicted OA and SOA levels were compared to measurements from the SPRUCE-2022 field campaign and the ACTRIS network. The results suggest that accounting for the sesquiterpene chemical aging can help bridge the gap between modeled and observed SOA levels. Ignoring multigeneration reactions leads to significant underestimation of sesquiterpene SOA.