Characterization of Oligomers in Biogenic Secondary Organic Aerosol by High-Resolution Mass Spectrometry and Infrared Multi-Photon Dissociation

WILEY A. HALL 4th (1), Murray Johnston (1)

(1) University of Delaware

     Abstract Number: 376
     Last modified: May 11, 2010

Abstract
The secondary organic aerosol (SOA) that forms as a result of atmospheric oxidation of alpha-pinene can comprise a significant portion of the mass of atmospheric fine particles, which are of interest due to their effects on respiratory health and global climate change to name a few topics of interest. Laboratory studies have shown an incredibly complex mixture of compounds formed from this reaction. The original oxidation products quickly oligomerize to form over a thousand compounds which, due to their low volatility, likely make up the bulk of the SOA mass. However, little is known about the identity of these oligomers, the routes of formation that they follow and the conditions that affect them. In our current work, IRMPD (infrared multi-photon dissociation) coupled with high resolution mass spectrometry is performed on a large number of the oligomers found in SOA to elucidate molecular structure and formation reactions. Using ESI-FTICRMS, each peak from m/z 163 to 623 (monomer through trimer regions) is mass selected with a quadrupole analyzer and if the intensity of the isolated peak is sufficiently high (>1E5) fragmentation is induced in the ICR cell by IRMPD. Over 10,000 product ions from IRMPD fragmentation spectra of more than 100 precursor ions have been characterized. Many of the largest and most frequently observed fragment ions or associated neutral losses correspond to the molecular formulas of commonly reported monomer compounds such as pinonaldehyde, and terpenylic, pinic and pinonic acids. The SOA studied is generated both from the reaction of ozone and alpha-pinene in a 500L reaction chamber and from our new PhARAOH (Photo-Assisted Reaction: Oxidation by Hydroxyl) chamber, which reacts young particles formed from the reaction of alpha-pinene and ozone with high levels of hydroxyl radical at a set residence time (30min-2hrs.) to simulate atmospheric aging of SOA.