Molecular representation of benzene SOA for 3D modelling

Aromatic compounds account for a significant proportion of anthropogenic volatile organic compounds emissions, and their atmospheric ageing is a key driver of the formation and growth of organic aerosols. In this study, the benzene oxidation scheme extracted from the Master Chemical Mechanism (MCM) 3.3.1 was revised and improved by the implementation of several new oxidation pathways, including multigeneration oxidation, peroxy radical rearrangement, formation of di-bridged species and autoxidation. These updates lead to the formation of various compounds that can partition into organic and aqueous aerosol phases. Comparisons to chamber experiments of benzene and phenol oxidation show that the addition of these pathways provides a better representation of the formation (aerosol mass yields) and chemical composition of secondary organic aerosols.

While near-explicit schemes provide greater details, their computational complexity makes them difficult to directly implement in chemistry-transport models. To address this, the near-explicit scheme of benzene is reduced using the GENerator of Reduced Organic Aerosol Mechanisms (GENOA) algorithm under representative atmospheric conditions. Using reduction strategies and evaluation criteria, GENOA trains and reduces the SOA mechanism under atmospheric conditions commonly encountered over Europe. The trained benzene SOA mechanism preserves the main characteristic of the near-explicit mechanism (e.g., chemical pathways, molecular structures of crucial compounds, the effect of non-ideality and hydrophilic/hydrophobic partitioning of aerosols), with a size (in terms of reaction and species numbers) that is manageable for three-dimensional aerosol modelling (e.g., regional chemical transport models).