AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
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Dynamic Nature of the Particle Phase for SOA Derived from Select Green Leaf Volatiles
KEVIN FISCHER, Giuseppe Petrucci, University of Vermont
Abstract Number: 515 Working Group: Aerosol Chemistry
Abstract Secondary organic aerosols (SOA) are produced via gas phase oxidation reactions of volatile organic compounds (VOCs). Despite the integral role of SOA in atmospheric processes, there remains a limited understanding of the chemical and physical changes induced in SOA as it is formed and subsequently aged. The physical state of SOA is an especially important parameter, as it impacts SOA formation and growth, gas–particle partitioning, and reactive uptake on particle surfaces. Here, an Electrical Low Pressure Impactor (ELPI) was utilized to determine the bounce factor (BF; a surrogate for particle viscosity) as a function of reaction time for SOA derived from ozonolysis of cis-3-hexenyl acetate (CHA), cis-3-hexenol (HXL), and 1-octene-3-ol (OTL), all of which are green leaf volatiles (GLVs; a subset of VOCs) and have the potential to contribute significantly to the overall SOA budget. In addition, a Scanning Mobility Particle Sizer (SMPS) and Near-Infrared Laser Desorption-Ionization Aerosol Mass Spectrometer (NIR-LDI-AMS) were utilized to probe SOA concentration and chemical composition, respectively. An initially higher BF was observed (CHA: 0.17; HXL: 0.62; OTL: 0.63), followed by an immediate decrease after which the BF remained relatively constant (CHA: 0.038; HXL: 0.31; OTL: 0.32). Concurrently, SOA concentration and particle diameter continued to increase. Furthermore, addition of methanol as a stabilized Criegee intermediate scavenger led to lower BF values, lower SOA concentrations, lower particle diameters, and absence of expected SOA products. This suggests oligomers are initially formed and immediately partition to the particle phase, after which they act as nucleation sites for further SOA products to condense onto. This work provides direct evidence for the key role of the stabilized Criegee intermediate in the ozonolysis of the GLV systems studied and the dynamic nature of the particle phase during the SOA lifetime.