AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Non-equilibrium Effects in SOA Formation and Evaporation Investigated with an Advanced Kinetic Multi-layer Model of Gas-particle Interactions (KM-GAP 2.0)
THOMAS BERKEMEIER, Manabu Shiraiwa, Nga Lee Ng, Ulrich Pöschl, Max Planck Institute for Chemistry
Abstract Number: 613 Working Group: Aerosol Physics
Abstract In the formation of secondary organic aerosol (SOA), spatial inhomogeneity in composition can arise by early condensation of low volatile compounds (LVOCs) and later condensation of semi-volatile organic compounds (SVOCs). Composition-dependence of the viscosity of SOA mixtures shows that high prevalence of LVOCs can be correlated with high particle viscosity. Conversely, inhomogeneity in composition might cause spatial patterns of viscosity within a single particle, which can further reinforce the departure from equilibrium gas-particle partitioning. For example, evaporation of higher volatility compounds at the surface can lead to formation of a low volatility, high viscosity surface crust that shields SVOCs from evaporation. This process might be enhanced by “vulcanization” effects through oligomerization in the particle phase. Furthermore, adsorptive uptake may occur through a “burying” mechanism that is facilitated by slow particle-phase diffusion and leads to non-equilibrium composition of organic aerosol.
We use an advanced kinetic multi-layer model of gas-particle interactions in aerosols and clouds (KM-GAP 2.0) to investigate these effects and evaluate their potential impact on atmospheric SOA formation. The new model setup involves self-generation of model code and solves some limitations encountered in previous studies: a dynamic layer splitting and merging algorithm enables accurate description of high viscosity systems under preservation of moderate computational expense and numerical convergence. Examples of how the updated model can be used are presented and come from formation and evaporation of Secondary Organic Aerosol (SOA), as well as heterogeneous atmospheric oxidation chemistry.