AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Viscosity of SOA Formed from Stressed and Healthy Pine Tree Emissions under Varying Oxidation Levels
NATALIE SMITH, Jesse Crescenzo, Anusha P.S. Hettiyadura, Ying Li, Celia Faiola, Alexander Laskin, Allan Bertram, Manabu Shiraiwa, Sergey Nizkorodov, University of California, Irvine
Abstract Number: 195 Working Group: Aerosol Chemistry
Abstract Secondary organic aerosols (SOA) derived from plant emissions make up a major fraction of total SOA in the atmosphere. When plants are stressed under herbivory their volatile organic compound (VOC) emission profiles change in both quantity and types of compounds being emitted. For example, when pine trees are stressed due to an aphid-herbivory attack they emit more sesquiterpenes, which can lead to the formation of different SOA when compared to SOA formed from healthy plant emissions. The chemical composition of SOA determines particle viscosity, which in turn can impact photochemical processing of particles, their ability to act as cloud condensation and ice nuclei, and lifetimes of particulate pollutants in the atmosphere. This study investigates how the different chemical composition of SOA generated from emissions of healthy vs. stressed plants, and then aged by different level of OH exposure, affects particle viscosity. Aerosols are generated in an oxidation flow reactor using a mixture of VOCs to represent either stressed or healthy pine trees. In the oxidation flow reactor, the VOCs are oxidized under low, medium, or high levels of hydroxyl radical with particle loading adjusted to be below 100 mg/m3 (this procedure will be repeated for real pine tree emissions under healthy conditions and stressed conditions when exposed to aphids). Detailed information on particle molecular composition is gained through Nano-Desorption Electro Spray Ionization –High Resolution Mass Spectrometry. The observed molecular formulas are used to predict the viscosity as a function of relative humidity using the parameterization developed by Shiraiwa et al. The predictions from the Shiraiwa model are compared to the experimentally determined viscosity values measured with the poke-flow method. The information attained from this study will help generalize the effects of viscosity so current atmospheric models can be improved upon and thus better inform public policy.