Modeling the formation of secondary organic aerosol within a comprehensive air quality model system

TLDR

The Secondary Organic Aerosol Model (SORGAM) was developed for comprehensive air quality models to simulate SOA formation, low‑volatility product production, and gas/particle partitioning under the assumption of a quasi‑ideal solution, which strongly influences saturation concentrations. Box‑model sensitivity studies and coupling of SORGAM to the European Air Pollution and Dispersion/Modal Aerosol Dynamics Model enabled three‑dimensional application of the SOA scheme. Results show that temperature‑dependent saturation concentrations drive partitioning and that interacting SOA compounds cause biogenic and anthropogenic contributions to influence each other, precluding independent treatment.

Abstract

The Secondary Organic Aerosol Model (SORGAM) has been developed for use in comprehensive air quality model systems. Coupled to a chemistry‐transport model, SORGAM is capable of simulating secondary organic aerosol (SOA) formation including the production of low‐volatility products and their subsequent gas/particle partitioning. The current model formulation assumes that all SOA compounds interact and form a quasi‐ideal solution. This has significant impact on the gas/particle partitioning, since in this case the saturation concentrations of the SOA compounds depend on the composition of the SOA and the amount of absorbing material present. Box model simulations have been performed to investigate the sensitivity of the model against several parameters. Results clearly show the importance of the temperature dependence of saturation concentrations on the partitioning process. Furthermore, SORGAM has been coupled to the comprehensive European Air Pollution and Dispersion/Modal Aerosol Dynamics Model for Europe air quality model system, and results of a three‐dimensional model application are presented. The model results indicate that assuming interacting SOA compounds, biogenic and anthropogenic contributions significantly influence each other and cannot be treated independently.