Re-examining chemical conditions of past chamber studies of secondary organic aerosol formation

The simulation of secondary organic aerosol (SOA) in 3D models generally relies on measurements made in laboratory chamber studies. However, many of the laboratory studies that underpin the aerosol parameterizations used in these models were carried out more than fifteen years ago, before recent developments in our understanding of peroxy radical (RO2) chemistry and its role in aerosol formation. As a result, limitations of past chamber experiments and the incomplete understanding of their chemical conditions (e.g., the initiating oxidants, RO2 fate), may skew SOA representation in models. In this work, literature SOA chamber studies, specifically those referenced by the SOA scheme in the GEOS-Chem global model, are simulated using a modified version of the Master Chemical Mechanism. This enables explicit estimation of typically-unconstrained parameters which affect experimental outcomes, including the relative importance of different oxidants, and the relative loss of RO2 to different unimolecular and bimolecular processes. This work demonstrates that reaction conditions are dynamic, changing within and between experiments, and that many experimental conditions involve more than one oxidant or RO2 fate, complicating model parameterizations. However, we also find that RO2 isomerization is important under many of the experimental conditions used, meaning that some RO2 isomerization processes are to some extent embedded into 3D model SOA estimates, despite no explicit representation of this chemistry.