AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
Highly Oxidized Species in Fresh and Aged Secondary Organic Aerosol (SOA)
PEIJUN TU, Murray Johnston, University of Delaware
Abstract Number: 14 Working Group: Aerosol Chemistry
Abstract Secondary Organic Aerosol (SOA) is produced by the oxidation of volatile organic compounds (VOC). Both the freshly formed and further oxidized SOA (also called aged SOA) have great impact on both environment and human health. Among the chemical species leading to formation of SOA is a class of highly oxidized, nonvolatile organic molecules that have molecular formulas consistent with low-volatility oxidized organic aerosol i.e. LV-OOA observed in ambient aerosol.
In this work, we have performed molecular analysis of fresh and aged SOA samples using high performance mass spectrometry to explore the characteristics of highly oxidized species in the particle phase both before and after aging. Fresh SOA was made by mixing ozone with the biogenic precursor in a flow tube reactor. Aged SOA was made by passing the fresh SOA through a photochemical reactor (PC) to simulate atmospheric aging. Both fresh and aged SOA samples were collected and then analyzed by electrospray ionization on a Q Exactive™ Hybrid Quadrupole-Orbitrap Mass Spectrometer for molecular level analysis.
Through high resolution mass analysis, we found that the highly oxidized species in the negative mode spectra of fresh SOA generated from beta-pinene were mostly composed of low molecular weight monomers (C$_(5-8)H$_(8-12)O$_(4-8)). These species are most likely formed in the gas phase by the autoxidation of the gas-phase precursor after abstraction of a hydrogen atom by OH. Aging forms many new types of highly oxidized products (e.g. C$_(10)H$_(10-16)O$_(8-10) and larger) that are fundamentally different from the highly oxidized species that naturally exist in fresh SOA. These products are consistent with oxidation of oligomers, which is more likely to occur in the particle phase than the gas phase. In addition, tandem MS was utilized for the structure elucidation of highly oxidized species both before and after aging to provide information on functional groups and molecular connectivity.