A Comparative Study on the Evaporation Kinetics and Physical Properties of Acyclic and Cyclic Terpene SOA

SIJIA LIU, Claire E. Moffett, Gregory W. Vandergrift, Zezhen Cheng, Swarup China, Sergey Nizkorodov, Alla Zelenyuk, Celia Faiola, University of California, Irvine

     Abstract Number: 190
     Working Group: Aerosol Chemistry

Abstract
This study aims to compare physical properties and chemical composition of secondary organic aerosols (SOA) prepared from acyclic and cyclic terpenes. Plant stress commonly enhances the release of acyclic terpenes, yet the aerosol chemistry and properties of these compounds remains poorly understood, introducing uncertainties into global climate impact assessments of SOA. We generated SOA through the OH oxidation of acyclic and cyclic monoterpenes (β-ocimene, α-pinene) and sesquiterpenes (β-farnesene, β-caryophyllene) in a batch mode chamber. The single particle density, morphology, evaporation kinetics, and mass spectra were examined using single particle mass spectrometer (miniSPLAT), while molecular level SOA composition was analyzed via nanospray desorption electrospray ionization high-resolution mass spectrometry (nanoDESI-HRMS). The room-temperature evaporation kinetics of size-selected particles was examined by monitoring the changes in particle size and shape for up to 24 h, offering information about the volatility and viscosity of SOA particles. Our findings indicate that SOA from acyclic terpene OH oxidation exhibits higher viscosity and lower volatility compared to their cyclic counterparts. Sesquiterpene-derived SOA generally shows greater viscosity and reduced volatility, attributed to the high molar mass and low vapor pressure of their precursors. We find β-ocimene SOA displayed viscosity and volatility profiles similar to those of β-caryophyllene SOA. The efficiency of producing SOA from acyclic terpenes underscores the need to account for plant stress responses and subsequent acyclic terpene aerosol chemistry in climate and air quality models.