Aerosol chemistry of riparian shrub emissions and oxygenated terpenes
Biogenic volatile organic compounds (BVOCs) released primarily from vegetation are themajor contributors to the total atmospheric volatile organic compounds (VOCs) globally. These BVOCs can play important ecological functions. In Chapter 1, I summarized the ecological roles of these important atmospheric volatiles at the organism and population, and community levels, their adaptive values, and their impacts at the climate level. In addition to the ecological processes, plant VOCs can influence atmospheric chemistry and physics. Many of these plant VOCs are highly reactive, and upon release into the atmosphere, they react with atmospheric radicals forming secondary organic aerosol (SOA). SOA can affect human health and impact Earth’s radiative balance directly and indirectly by absorbing and scattering sunlight and influencing clouds' formation and properties, respectively. I investigated SOA formation from less-studied VOCs in the laboratory by generating SOA inside an oxidation flow reactor (OFR) using different VOCs as SOA precursors. In Chapter 2, I investigated SOA formation from a riparian shrub emission exposed to insect herbivory. The acyclic BOVCs, regardless of herbivory stress, reduced SOA potential formation. This result can have an important implication for SOA prediction in chemical transport models. In Chapter 3, I studied SOA from dominant BVOCs of a shrub species in California’s coastal sage shrub ecosystem. SOA formation potential of most of these oxygenated monoterpenes was higher than that of a common plant volatile, α-pinene, as a reference system. I also investigated the chemical composition of the SOA from these oxygenated terpenes and compared that with the SOA chemical composition formed from real plant emissions that were dominated by these compounds. I observed that the chemical composition of SOA from plant mixtures was similar to each other and equally different from SOA formed from single precursors. This result emphasized that SOA formed from single VOC standards does not capture the complexity of VOC emissions from real plants.