Modeling Kinetics and Partitioning of Secondary Organic Aerosols
The general processes important to formation of secondary organic aerosols (SOA; small particles resulting from reactions of gas-phase organic precursors) are conceptually clear, including reactions of organic compounds in the gas phase and within or on particle surfaces, and evaporation/condensation/solution in liquid and semiliquid particle phases. However, organic mass partitioning between the gas phase and particles of different sizes depends on the complex interplay between these mechanisms, resulting in a range of SOA size distributions and chemical composition that together determine overall aerosol optical and cloud-nucleating properties. To improve modeling fidelity for SOA impacts, U.S. Department of Energy researchers developed and evaluated a new framework for modeling kinetic SOA gas-particle partitioning. This framework and analysis accounted for diffusion and chemical reaction within the particle phase. The framework is suitable for use in regional and global atmospheric models, despite requiring specification of the actual species and particle-phase reactions important for SOA formation. The investigators implemented the new framework within the computationally efficient Model for Simulating Aerosol Interactions and Chemistry (MOSAIC) and applied it to investigate the competitive growth dynamics of submicrometer particles. A proper representation of SOA physicochemical processes and parameters is needed in next-generation models to reliably predict not only total SOA mass, but also its composition and number size distribution, all of which together determine overall SOA optical and cloud-nucleating properties.
Zaveri, R. A., R. C. Easter, J. E. Shilling, and J. H. Seinfeld. 2014. “Modeling Kinetic Partitioning of Secondary Organic Aerosol and Size Distribution Dynamics: Representing Effects of Volatility, Phase State, and Particle-Phase Reaction,” Atmospheric Chemistry and Physics 14, 5153–81. DOI:10.5194/acp-14-5153-2014.