AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Ozonolysis of Polycyclic Aromatic Hydrocarbons on the Surfaces of Secondary Organic Aerosol Particles
ALLA ZELENYUK, Kaitlyn J. Suski, David Bell, Dan Imre, Simeon Schum, Lynn Mazzoleni, ManishKumar Shrivastava, Amber Kramer, Staci L. Simonich, Pacific Northwest National Laboratory
Abstract Number: 765 Working Group: Aerosol Chemistry
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 secondary organic aerosol (SOA) formation significantly affects particles mass loadings, composition, growth, volatility, and viscosity. Compared to “pure” 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. Here 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. We will discuss the chemical mechanisms responsible for increased SOA formation yields and formation of oligomers.
Furthermore, we will show that heterogeneous ozonolysis of PAHs on the surfaces of “pure” biogenic SOA particles results in the formation of shells composed of oxidized PAHs and trapped unreacted PAHs, which alter particles volatility. The formation of shells was quantified by measuring changes in particle size and composition. The volatility of these particles was lower than that of “pure” α-pinene SOA, and most notably, a significant fraction of the PAHs and their oxidation products remained in the particles after a day of evaporation under dry or high RH conditions.
These results suggest that PAHs can become incorporated into SOA particles at any time during their atmospheric lifecycle via adsorption and surface reactions with ozone. These reactions affect the composition, morphology, and evaporation kinetics of these particles and can lead to longer than traditionally predicted atmospheric lifetimes of PAHs.