Formation and Properties of Secondary Organic Aerosol from Gas-Phase and Aqueous-Phase Oxidation of Guaiacyl Acetone

CLAIRE MOFFETT, Gregory W. Vandergrift, Zezhen Cheng, Jie Zhang, Swarup China, ManishKumar Shrivastava, Alla Zelenyuk, Pacific Northwest National Laboratory

     Abstract Number: 604
     Working Group: Aerosol Chemistry

Abstract
Biomass burning is a significant source of particulate matter in the atmosphere contributing to approximately 10−50% of the total organic aerosol mass. Methoxyphenols are a dominant product of biomass burning that are emitted in high concentration making them an excellent tracer of biomass burning. Guaiacyl acetone (GA, 4-hydroxy-3-methoxyphenolacetone) is a semivolatile methoxyphenol formed from lignin depolymerization which can undergo rapid aqueous oxidation to form secondary organic aerosol (SOA). This aqueous phase processing is thought to be important for aerosol chemistry especially in cloud and fog droplets and in aerosol liquid water. An increased understanding of its role in biomass burning SOA formation and the effects of aerosol liquid water on the chemistry would improve model predictions of aqueous SOA chemistry.

We will present the results of a recent study focused on the formation and properties of SOA particles formed by the photosensitized oxidation of GA by an organic triplet excited state (3C*) in aerosol liquid water. The properties of these SOA particles are compared to SOA particles formed by the gas-phase oxidation of GA by the hydroxyl radical. The experiments were conducted at low (<5%) and elevated (~50%) relative humidity (RH) with and without ammonium bisulfate seeds. We find, for example, that guaiacyl acetone SOA formed by gas-phase oxidation at low RH are highly viscous and nearly non-volatile, losing only 8% of their volume after >24 hours of evaporation at 75% RH, while not shrinking at all during the same evaporation time at low RH. We show that larger, size-selected SOA particles are aspherical agglomerates of spherical nanoparticles that do not coalesce even after 24 hours. However, at increased RH these particles coalesce to form spherical particles, making it possible to estimate particle viscosity as a function of relative humidity.