Formation and Properties of Secondary Organic Aerosol from Gas-Phase and Aqueous-Phase Oxidation of Substituted Phenolic Compounds
Claire E. Moffett, Zezhen Cheng, Gregory W. Vandergrift, Jie Zhang, Swarup China, ManishKumar Shrivastava, Gourihar Kulkarni, ALLA ZELENYUK, Pacific Northwest National Laboratory
Abstract Number: 566
Working Group: Aerosol Chemistry
Abstract
Phenols, emitted from biomass burning, contribute significantly to secondary organic aerosol (SOA) formation through gas-phase chemistry and multiphase chemistry in aerosol liquid water and clouds (aqSOA). We will present the results of a recent study, in which we investigated four phenolic compounds (guaiacol, syringol, guaiacyl acetone (GA), and syringol acetone (SA)) that represent some of the important potential sources of SOA. GA and SA served as examples of highly soluble substituted phenolic compounds that have uptake coefficients of 10-4 and 10-2, respectively, and can form significant amounts of aqSOA, which is comparable or even higher than the gas-SOA.
The experiments were conducted at low (<5%) and elevated (~50%) relative humidity (RH) with and without ammonium bisulfate seeds. Single particle mass spectrometer, miniSPLAT, was used to measure density, shape, composition, viscosity, and evaporation kinetics of size- and mass-selected particles. In addition to real-time particle characterization, SOA particles were collected on the filters for offline analysis by microscopy, high-resolution mass spectrometry, and for characterization of their optical properties.
We find, for example, that GA-SOA particles formed by gas-phase oxidation of guaiacyl acetone at low RH are highly viscous: larger particles represent aspherical agglomerates of spherical nanoparticles that at low RH do not coalesce even after 24 hours. At high RH (75%) these aspherical particles rapidly coalesce to form spherical particles. GA-SOA particles also have very low volatility. Particles lose only 30% of their volume after >24 hours of evaporation at 75% RH, and do not shrink at all during the same evaporation time at low RH. In comparison, all SOA particles formed by gas oxidation of guaiacol are spherical and have higher volatility: they lose 29% and 46% of their volume after >24 hours of evaporation at low and high RH, respectively. GA-SOA formed in the presence of ammonium bisulfate seeds forms spherical particles that contains organosulfates and have core-shell morphology. These particles lose ~ 20% and 40% of their volume after >24 hours of evaporation at low and high RH, respectively. The measurements of SOA optical properties indicate that in all cases, GA-SOA particles composed of high fraction of high molecular weight compounds, including light absorbing brown carbon.