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Highly Viscous Secondary Organic Aerosol from Healthy and Stressed Pine Trees
NATALIE R. SMITH, Giuseppe Crescenzo, Yuanzhou Huang, Anusha P.S. Hettiyadura, Kyla Siemens, Ying Li, Celia Faiola, Alexander Laskin, Allan Bertram, Manabu Shiraiwa, Sergey Nizkorodov, University of California, Irvine
Abstract Number: 131
Working Group: Aerosol Chemistry
Abstract
When plants are stressed, their volatile organic compound (VOC) emission profile changes in both quantity and types of compounds being emitted. For example, pine trees stressed due to aphid herbivory emit more sesquiterpenes, which can lead to the formation of different secondary organic aerosols (SOA) when compared to SOA formed from healthy plant emissions. In this study, the molecular composition, viscosity, and liquid-liquid phase separation (LLPS) were investigated for SOA derived from the photooxidation of VOC mixtures representing the emission profile of either healthy or aphid-stressed Scots pine (Pinus sylvestris) trees. Aerosols were generated in a 5 m3 environmental chamber at 50% relative humidity. Detailed information on particle molecular composition was gained through nanospray desorption electrospray ionization –high resolution mass spectrometry. The observed neutral molecular formulas were used to predict the viscosity as a function of relative humidity using the parameterization developed by DeRieux et al. (2018). The predictions from the viscosity model were compared to the experimental values measured via the poke-flow method. Under low relative humidity both stressed and healthy plant SOA were highly viscous and had viscosities similar to tar pitch. Over all humidities investigated, stressed SOA had the highest viscosity followed by healthy SOA and α-pinene SOA. Phase separation experiments revealed that LLPS occurs over a wider relative humidity range for stressed SOA compared to healthy SOA. These findings suggest that SOA generated from a complex mixture of VOCs can result in higher SOA viscosity compared to SOA generated from a single component precursor, such as α-pinene. In addition, plant stress can lead to changes in the physicochemical properties of SOA.