AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
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Optical Properties of Secondary Organic Aerosol from Cis-3-hexenol and Cis-3-hexenyl Acetate: Effect of Chemical Composition, Humidity and Phase
REBECCA HARVEY, Adam Bateman, Shashank Jain, Yong Jie Li, Scot Martin, Giuseppe Petrucci, University of Vermont
Abstract Number: 61 Working Group: Aerosol Chemistry
Abstract Atmospheric aerosols play an important role in Earth’s radiative balance directly, by scattering and absorbing radiation, and indirectly by acting as cloud condensation nuclei (CCN). Recently, the ozonolysis of green leaf volatiles (GLVs) has been found to contribute to secondary organic aerosol (SOA), yet the role these SOA play in the Earth’s radiative budget is poorly understood. Herein, we measure optical properties of GLV-derived SOA and report on their role in the direct radiative effect. We also discuss the relationship between SOA optical properties and bulk vs molecular-level chemistry. Specifically, we measured the scattering efficiency, absorption efficiency, particle phase, bulk chemical properties (O:C, H:C) and the molecular-level composition of SOA formed from the ozonolysis of two GLVs; cis-3-hexenol (HXL) and cis-3-hexenyl acetate (CHA). Both GLVs produced SOA that was weakly absorbing, yet CHA-SOA was a more efficient absorber than HXL-SOA, especially at wavelengths shorter than 350 nm. The scatter efficiency of SOA from both systems was wavelength-dependent, with the stronger dependence exhibited by HXL-SOA. Perhaps the most interesting result from this work was that HXL-SOA formed under both dry (10 percent RH) and wet (70 percent RH) conditions had significantly different optical properties, which was not reflected in bulk chemical properties. Instead, we rationalized the differences in optical properties under the two RH regimes using a molecular-level understanding of the role of water in particle formation and particle composition. Ultimately, we have found that SOA derived from GLVs has the potential to affect the Earth’s radiative budget, and also that bulk chemical properties may be insufficient to predict SOA optical properties.