AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
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Compounds Controlling SOA Formation from Stressed and Unstressed Scots Pine Emissions in an Oxidation Flow Reactor
CELIA FAIOLA, Angela Buchholz, Eetu Kari, Pasi Yli-Pirilä, Jarmo Holopainen, Minna Kivimaenpaa, Pasi Miettinen, Douglas Worsnop, Kari Lehtinen, Alex Guenther, Annele Virtanen, University of Eastern Finland
Abstract Number: 315 Working Group: Carbonaceous Aerosols in the Atmosphere
Abstract Most models describe secondary organic aerosol (SOA) formation based on parameters derived from laboratory experiments using single component standards. Few studies have looked at SOA formation from mixtures of volatile organic compound (VOC) precursors, which is more representative of SOA generation in the atmosphere. This laboratory study investigated SOA generation from a complex mixture of VOC emissions using real Scots pine (Pinus sylvestris) saplings as the VOC emission source. SOA generation was characterized for different plant volatile mixtures as the plant emissions evolved before, during, and after plant herbivore stress. The herbivore stress was an exposure to four pine weevils (Hylobius abietis) for two days. SOA generation was characterized using a custom-built oxidation flow reactor. Plant volatile emissions were measured continuously with a proton transfer reaction time-of-flight mass spectrometer (Ionicon, Inc) and supplemented with adsorbent cartridge samples (Tenax TA) analyzed offline with a thermodesorption gas chromatograph mass spectrometer (Agilent, Inc). Particle size distributions and composition were characterized with a scanning mobility particle sizer (TSI, Inc.) and high resolution aerosol mass spectrometer (Aerodyne, Inc), respectively. Prior to herbivore treatment, Scots pine emissions were dominated by monoterpene emissions with an average molar sesquiterpene-to-monoterpene emission ratio (SQT:MT) of 0.06. Even though emissions were primarily monoterpenes, the SOA mass yields from pre-treatment Scots pine emissions were higher than yields measured from a monoterpene standard, alpha-pinene, in the same oxidation flow reactor. During active herbivore feeding, monoterpene emissions increased by over 40-fold on average (with maximum observed increase over 100-fold) while sesquiterpene emissions increased by 1-fold. Consequently, after herbivore treatment the Scots pine emissions were even more dominated by monoterpenes with an average SQT:MT of 0.005. SOA yields during active feeding were similar to yields from the alpha-pinene standard. These results suggest that sesquiterpenes can play a significant role in SOA formation efficiency even when they comprise a small fraction of the precursor volatiles. SOA yields higher than alpha-pinene were observed when SQT:MT ratios entering the flow reactor were greater than 0.006. Current models could underestimate the role of sesquiterpenes in SOA production.