Secondary Organic Aerosol Formation from Photooxidation of Acyclic Terpenes in an Oxidation Flow Reactor
SHAN GU, Farzaneh Khalaj, Véronique Perraud, Celia Faiola,
University of California, Irvine Abstract Number: 48
Working Group: Aerosol Chemistry
AbstractOne challenge in predicting secondary organic aerosol (SOA) is an incomplete representation of the chemistry originating from biogenic volatile organic compounds (BVOCs) emitted from plants, particularly those that are emitted in response to plant stressors. For example, plant emissions of acyclic terpenes, such as β-ocimene, β-myrcene, and linalool are commonly induced or present at elevated concentrations under stress conditions (e.g. water stress, ozone stress, and herbivore stress) – conditions that are becoming more frequent in a rapidly changing climate – however, their atmospheric oxidation mechanisms are not well characterized. In this study, SOA formation from the photooxidation of acyclic terpene standards, β-ocimene, β-myrcene, and linalool were investigated in an oxidation flow reactor (OFR). Gas-phase BVOC concentrations were measured using cartridge sampling and off-line analysis with a thermo-desorption gas chromatograph mass spectrometer (TD-GC-MS). Particle size distributions were monitored continuously via a custom-built scanning mobility particle sizer (SMPS). In addition, SOA chemical composition was characterized using an ultra-high performance liquid chromatography coupled to a heated electrospray ionization source and a high-resolution Q Exactive Plus Orbitrap mass analyzer (UPLC-HESI-HRMS). SOA yields were measured as a function of OH exposure and condensed organic aerosol mass. SOA composition of each acyclic terpene system was compared with α-pinene SOA. Results demonstrate that acyclic terpene chemistry is dominated by fragmentation reactions at a lower OH exposure than α-pinene. Further, the SOA yield is more sensitive to changes in OH exposure compared to α-pinene. The observed SOA yield at 10 μg/m3 condensed mass loading was highest for α-pinene (~20%), followed by β-myrcene (~16%), β-ocimene (~8%), and linalool (~5%). This study provides critical information on the oxidation of stress-related plant emissions and their impact on SOA formation in a changing climate.