10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Secondary Organic Aerosol Production from Healthy and Aphid-Stressed Scots Pine Biogenic Volatile Organic Compound Emissions in Different Oxidant Systems
FATEMEH KHALAJ, Celia Faiola, Angela Buchholz, Eetu Kari, Arttu Ylisirniö, Minna Kivimäenpää, Jarmo Holopainen, Annele Virtanen, University of California, Irvine
Abstract Number: 1083 Working Group: Aerosol Chemistry
Abstract Vegetation emits copious amount of hydrocarbon compounds into the atmosphere, called biogenic volatile organic compounds (BVOCs). BVOCs amount to about 90% of global total VOC emissions. Most BVOCs, based on their high reactivity, have short life times (a few hours), and readily react with atmospheric oxidants to produce lower volatility oxidation products. Thus, BVOCs are major precursors of atmospheric secondary organic aerosols (SOA). Biotic stressors, such as increased insect herbivory, enhance BVOC emissions and modify the types of BVOCs emitted. For example, methyl salicylate (MeSA) is a plant hormone induced by aphid herbivory. However, it is unclear how plant stress emissions such as MeSA alter SOA production. In this study, healthy and aphid-stressed Scot Pine BVOC emissions were used to evaluate SOA production during oxidation via ozonolysis or photooxidation. SOA was generated in Kuopio, Finland a 10 m3 batch reaction chamber composed of FEP material. For comparison to the healthy and stressed Scots pine experiments, SOA was generated from single component standards, α-pinene (OH and O3), and MeSA (OH only). For the plant SOA experiments, Scots pine saplings were enclosed in a dynamic enclosure with flow rates ~4 lpm, their emissions were trapped onto adsorbent cartridges overnight, and then thermally desorbed into the batch reaction chamber targeting ~20 ppb initial monoterpene mixing ratios at the start of the experiment. The initial suite of BVOCs that acted as SOA precursors during the Scots pine experiments was characterized via thermo-desorption gas chromatography mass spectrometry (TD-GC-MS). BVOC concentrations were monitored continuously throughout oxidation with a high resolution proton transfer reaction mass spectrometer (PTR-ToF-MS; Ionicon, Inc.). Particle size distributions and composition were monitored with a scanning mobility particle sizer (SMPS; TSI, Inc.) and high resolution time of flight aerosol mass spectrometer (HR-ToF-AMS), respectively. Results of BVOC concentrations demonstrated that aphid herbivory led to higher mixing ratios of sesquiterpenes in the reaction chamber. The average sesquiterpene mixing ratio was 1.84±1.12 ppb and 8.74±0.04 ppb for healthy and stressed Scots pine experiments, respectively. For comparison, the average monoterpene mixing ratio was 21.68±4.44 ppb and 22.60±1.36 ppb for healthy and stressed Scots pine experiments, respectively. The average MeSA mixing ratio was 1.23±1.05 ppb and 0.97±0.02 ppb for healthy and stressed Scots pine experiments, respectively. The detailed molecular speciation of initial BVOC composition will be presented. Additionally, an overview of SOA mass yields and composition will be shown to compare between healthy and stressed Scots pine SOA and the two single component standards for the two oxidant systems studied.