Toward Understanding the Synergetic Interactions between Polycyclic Aromatic Hydrocarbons and Biogenic Secondary Organic Aerosol Particles

Abstract:

Polycyclic aromatic hydrocarbons (PAHs) are toxic pollutants emitted as byproducts of energy production and consumption that can undergo long-range transport into remote regions of the world. We have previously shown that the presence of gas-phase PAHs during biogenic secondary organic aerosol (SOA) formation significantly affects particles number concentrations, mass loadings, composition, volatility, and viscosity. Compared to “pure” biogenic SOA, these particles have higher viscosity and higher fraction of non-volatile compounds, i.e. oligomers. These particles also contain unreacted PAHs and products of heterogeneous reactions between PAHs and ozone that are trapped within the bulk of the highly viscous SOA, shielded from evaporation and oxidation. We find that the magnitude of the effect of PAHs on SOA formation is surprisingly large. The presence of PAHs during SOA formation increases mass loadings by factors of two to five, and particle number concentrations, in some cases, by more than a factor of 100.

We will present detailed analysis of particle composition using real-time single particle mass spectrometry, bulk aerosol mass spectrometry, and offline analysis of the aerosol extracts using gas chromatography–mass spectrometry and ultrahigh resolution Orbitrap Elite mass spectrometry with four complementary ionization techniques. The preliminary results for α-pinene ozonolysis SOA indicate that while PAHs significantly enhance oligomer formation, the “extra mass” is dominated by α-pinene oxidation products. We will discuss the potential chemical mechanisms responsible for the increased SOA formation yields and formation of oligomers.