HR: 0800h
AN: A41C-02    [Abstracts]
TI: Homogeneous Nucleation in the Ozone - alpha-pinene Reaction Studied by Tunable Vacuum UV Photoionization Mass Spectrometry
AU: * Mysak, E R
EM: EMysak@lbl.gov
AF: Lawrence Berkeley National Lab, Mail Stop 6R2100 One Cyclotron Road , Berkeley, CA 94720, United States
AU: * Mysak, E R
EM: EMysak@lbl.gov
AF: University of North Carolina- Chapel Hill, Department of Chemistry CB #3290 , Chapel Hill, NC 27599, United States
AU: Gloaguen, E F
EM: EFGloaguen@lbl.gov
AF: Lawrence Berkeley National Lab, Mail Stop 6R2100 One Cyclotron Road , Berkeley, CA 94720, United States
AU: Wilson, K R
EM: KRWilson@lbl.gov
AF: Lawrence Berkeley National Lab, Mail Stop 6R2100 One Cyclotron Road , Berkeley, CA 94720, United States
AU: Ahmed, M
EM: MAhmed
AF: Lawrence Berkeley National Lab, Mail Stop 6R2100 One Cyclotron Road , Berkeley, CA 94720, United States
AU: Ziemann, P J
EM: Ziemann
AF: Lawrence Berkeley National Lab, Mail Stop 6R2100 One Cyclotron Road , Berkeley, CA 94720, United States
AU: Ziemann, P J
EM: Ziemann
AF: Air Pollution Research Center, University of California, Riverside, CA 92521, United States
AU: Ziemann, P J
EM: Ziemann
AF: Department of Environmental Sciences, Department of Chemistry, and Environmental Toxicology Graduate Program Sciences, University of California, Riverside, CA 92521, United States
AU: Baer, T
EM: baer@unc.edu
AF: University of North Carolina- Chapel Hill, Department of Chemistry CB #3290 , Chapel Hill, NC 27599, United States
AB: Atmospheric reactions of ozone with biogenic terpenes such as alpha-pinene contribute significantly to global amounts of secondary organic aerosol (SOA). SOA is a result of gas-to-particle conversion of organic compounds, and recent work by various other laboratories has suggested that the reaction products responsible for the nucleation are oligomeric or polymeric in nature, although the specific species responsible for nucleation are not yet identified. In the current study, the particle size (2- 90nm) and composition of particles (30-90nm) formed by this gas-to-particle conversion process are studied simultaneously as a function of reaction time. One of the main novelties of this experiment is that particles in this small size range are studied in real-time, which is possible with the combination of both delicate and continuous vaporization and ionization sources. Due to the delicate nature of the analysis technique, the current study is among very few in which alpha-pinene ozonolysis products are detected in the entire range from 43-402 m/z. Compositional analysis of the aerosol particles indicates that over 540 different molecular products are formed. Furthermore, the envelopes of peaks observed in the high mass range (m/z > 300) support the conclusion that a large variety of precursors react in various combinations to yield a wide array of complex, multifunctional oligomeric products. In order to probe the reaction pathways leading to the formation of the large oligomeric species formed in alpha-pinene ozonolysis, experiments were preformed in low versus high relative humidity conditions (to affect the stabilized criegee intermediate (SCI) channel), in the presence and absence of a hydroxyl radical scavenger (to affect the hydroperoxide channel). The presence of water, which acts as a SCI scavenger, affects the induction time for nucleation to a small extent, but does not affect the product formation either compositionally or in terms of aerosol mass formation. By scavenging the hydroxyl radical, which is a high yield product of a-pinene ozonolysis, we observe changes in the compostion of the high m/z products formed and in the yield of aerosol mass produced. These results indicate that SOA is formed primarily through the hydroperoxide channel, and that water vapor can enhance nucleation (probably through clustering), but does not impact SOA growth.
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 0394 Instruments and techniques
SC: Atmospheric Sciences [A]
MN: 2007 Joint Assembly