Comparison of Common Vapor Pressure Estimation Methods and the Effect of Viscosity on SOA Formation through Modeling of Alkene OH/NOx Systems

EMMALINE LONGNECKER, Julia Bakker-Arkema, Zhe Peng, Paul Ziemann, University of Colorado Boulder

     Abstract Number: 456
     Working Group: Aerosol Chemistry

Abstract
Modeling of secondary organic aerosol (SOA) formation from atmospheric reactions is an important tool in understanding current and future impacts of human activity on the environment. Vapor pressure is a key parameter in modeling this process, as it largely determines partitioning of products from the gas to particle phase. However, the vapor pressures of many atmospherically relevant compounds are still poorly constrained. To aid modeling efforts, several group contribution methods have been developed for estimating compound vapor pressures. The current study evaluates how four of these methods: SIMPOL, EVAPORATION, SPARC, and Nannoolal, impact modeled predictions of SOA yields for reactions of C8-C14 1-alkenes and C9-C15 2-methyl-1-alkenes with OH radicals in the presence of NOx. The models were created in the kinetics modeling software KinSim and include rate constants measured by Atkinson and co-workers, quantitative reaction mechanisms developed by our research group from several previous environmental chamber studies of product yields, gas-particle and gas-wall partitioning, and effective mass accommodation coefficients (Shiraiwa and Pöschl 2021) to account for effects of particle viscosity. Modeled SOA yields were compared to measured values and optimized viscosities were compared to those calculated using AIOMFAC. The large range of agreement exemplifies the impact of vapor pressure and viscosity in modeling atmospheric reactions and indicates the need for further development of estimation methods.