Abstract Number: 1170 Working Group: Aerosol Modeling
Abstract Volatility determines the gas-particle partitioning of organic compounds, thus volatility is a key property to understanding the behaviour and to simulate concentrations of organic aerosol in the atmosphere (OA). Various studies had been conducted to experimentally measure and numerically simulate volatility distributions of OA, and over the last decade, it has been found that the evaporation of OA was slower than that expected by equilibrium models. It had been suggested that formation of low volatility compounds, such as oligomers, or particle phase diffusion could limit the evaporation of OA, though contributions of these factors still remain uncertain.
In this study, we experimentally investigated the volatility of secondary organic aerosol (SOA) from α-pinene ozonolysis by external dilution chamber experiments and chemical composition analysis. Volatility distributions were estimated from compositions observed by Proton Transfer Reaction Mass Spectrometry (PTR-MS) and Electrospray Ionisation Mass Spectrometry (ESI-MS). In addition, we conducted model simulations using the statistical oxidation model with processes of kinetic gas-particle partitioning, formation/dissociation between monomers and dimers, and particle-phase diffusion limitations.
Both experimental and modeling results showed that low volatility compounds had important contributions to SOA. The slow evaporation rates during the dilution experiment could be reproduced by the model either by assuming that the SOA was semi-solid (bulk diffusion coefficient of 10-15 cm2 s-1) or assuming that the oligomerization reactions resulted in high dimer formation rates and low dimer dissociation rates.