Abstract: A major fraction of secondary organic aerosol (SOA) in the atmosphere are generated from oxidation of volatile organic compounds (VOCs) emitted from pine trees. Because α-pinene and limonene typically dominate the monoterpene emission profile in forested areas, they have commonly been used as representative monoterpenes in laboratory studies investigating biogenic SOA fundamental properties. However, pine trees emit a wide range of terpenes with different reactivities and structures including numerous isomers of monoterpenes (C10H16) and sesquiterpenes (C15H24), drastically altering the resulting properties of SOA particles such as chemical composition and viscosity. Viscosity is an important physical property of SOA and can lead to much slower diffusion rates within the particles, impacting particle growth and evaporation, gas-particle partitioning, and the ability of SOA particles to act as nuclei for liquid cloud droplets or ice particles. The goal of this thesis is to compare chemical composition and viscosity of SOA particles generated from single terpenes as well as from a mixture of terpenes emitted by pine trees. This work will elucidate how single-terpene SOA compares to real biogenic SOA chemical composition and viscosity, and thus determine if a single-terpene SOA is a good proxy system to model biogenic SOA. A second goal of this work is to identify the influence plant stress has on chemical composition and viscosity of SOA. This is important because plant stress (ex. insect-herbivory) leads to an increase in the emission rates of sesquiterpenes from pine trees. Due to climate change, plants are expected to endure longer periods of stress. However, the impact this change in VOC profile has on SOA properties compared to SOA from healthy trees is not well characterized.