A computationally efficient, process-level model for secondary organic aerosol (simpleSOM)
Submitter
Jathar, Shantanu — Colorado State University
Area of research
Aerosol Processes
Journal Reference
Science
Secondary organic aerosol (SOA) processes are often simplified in models to improve computational efficiency. We developed a process-level model called simpleSOM-MOSAIC that includes: (1) multigenerational gas-phase chemistry, (2) phase-state-influenced kinetic gas/particle partitioning, (3) heterogeneous chemistry, (4) oligomerization reactions, and (5) accounts for experimental artifacts. In this first application, we demonstrate the model's capabilities by simulating SOA formation from the oxidation of a-pinene, an important aerosol precursor.
Impact
Secondary organic aerosols (SOA) constitute an important fraction of atmospheric aerosol mass and affect climate, air quality, and human health. The simplified treatment of SOA in three-dimensional atmospheric models limits the ability of these models to predict the distribution and environmental impacts of SOA accurately. In this work, we develop a computationally efficient framework to simulate the formation, evolution, and properties of SOA with an emphasis on modeling SOA consistently over scales ranging from the laboratory to global models.
Summary
Secondary organic aerosols (SOA) constitute an important fraction of fine-mode atmospheric aerosol mass. Frameworks used to develop SOA parameters from laboratory experiments and subsequently used to simulate SOA formation in atmospheric models make many simplifying assumptions about the processes that lead to SOA formation in the interest of computational efficiency. These assumptions can limit the ability of the model to predict the mass, composition, and properties of SOA accurately. In this work, we developed a computationally efficient, process-level model named simpleSOM to represent the chemistry, thermodynamic properties, and microphysics of SOA. simpleSOM simulates multigenerational gas-phase chemistry, phase-state-influenced kinetic gas/particle partitioning, heterogeneous chemistry, oligomerization reactions, and vapor losses to the walls of Teflon chambers. As a case study, we used simpleSOM to simulate SOA formation from the photooxidation of a-pinene. This was done to demonstrate the ability of the model to develop parameters that can reproduce environmental chamber data, highlight the chemical and microphysical processes within simpleSOM, and discuss implications for SOA formation in chambers and in the real atmosphere. SOA parameters developed from experiments performed in the chamber at the California Institute of Technology (Caltech) reproduced observations of SOA mass yield, O:C, and volatility distribution gathered from other experiments. Sensitivity simulations suggested that multigenerational gas-phase aging contributed to nearly half of all SOA and that in the absence of vapor wall losses, SOA production in the Caltech chamber could be nearly 50% higher. Heterogeneous chemistry did not seem to affect SOA formation over the short timescales for oxidation experienced in the chamber experiments. Simulations performed under atmospherically relevant conditions indicated that the SOA mass yields were sensitive to whether and how oligomerization reactions and the particle phase state were represented in the chamber experiment from which the parameters were developed. simpleSOM provides a comprehensive, process-based framework to consistently model the SOA formation and evolution in box and 3D models.