Influence of gas-phase polycyclic aromatic hydrocarbons on molecular composition of α-pinene ozonolysis secondary organic aerosol particles

Previous studies have shown that the presence of gas-phase Polycyclic Aromatic Hydrocarbons (PAHs) during biogenic Secondary Organic Aerosol (SOA) formation can significantly enhance SOA formation, resulting in higher mass loadings, and alter properties of SOA particles. Compared to “pure” biogenic SOA, these particles have higher viscosity, lower bulk volatility, and are composed of a higher fraction of low-volatility compounds, i.e., oligomers. The in-situ aerosol mass spectrometry of α-pinene ozonolysis SOA particles indicates that while PAHs significantly enhance oligomer formation, the “extra mass” is dominated by α-pinene oxidation products. To understand the potential chemical mechanisms responsible for the increased SOA formation yields and formation of oligomers we utilized an ultrahigh resolution Orbitrap Elite mass spectrometer (resolving power 240,000 @ m/z 400). Multiple ionization methods were used to provide a comprehensive perspective of the molecular composition. Here, we present the differences in molecular composition resulting from the presence of three different PAHs during α-pinene SOA formation compared to a sample of pure α-pinene SOA. First, we report the presence of unique α-pinene + pyrene oligomers potentially responsible for low particle volatility observed in previous studies. We also report low-oxygen α-pinene oligomers only observable using atmospheric pressure photoionization. These oligomers are seemingly enhanced by the presence of benzo[a]anthracene, suggesting a potential role for certain PAHs in their formation. These results imply that our understanding of the oxidative reaction pathways may be incomplete, especially with regard to the interaction of biogenic and anthropogenic emissions.