AAAR 33rd Annual Conference
October 20 - October 24, 2014
Rosen Shingle Creek
Orlando, Florida, USA
Abstract View
Chemical Mechanisms of Atmospheric Aging of Secondary Organic Aerosol
PEIJUN TU, Murray Johnston, University of Delaware
Abstract Number: 576 Working Group: Aerosol Chemistry
Abstract Secondary organic aerosol (SOA) is produced by the oxidation of volatile organic compounds (VOC) in the atmosphere. The initial or “fresh” SOA produced from this reaction can undergo further oxidation over time. This “aged” SOA can have very different chemical and physical properties, which may influence its environmental impact. This work seeks to provide a molecular level understanding of SOA aging and its end products.
In this work, fresh SOA was generated in a flow tube reactor (FTR) by the reaction of ozone with biogenic VOC precursors (alpha-pinene, beta-pinene and limonene). The fresh SOA flowed into a photochemical reactor (PC) where it reacted with OH to simulate atmospheric aging. The hydroxyl radicals were created by ultraviolet irradiation of an ozone-water mixture. The mass concentration of aerosol exiting the PC was monitored with a Scanning Mobility Particle Sizer (SMPS). Chemical analysis of the aged SOA was performed by filter collection and analysis by Orbitrap MS.
Measurements of the mass concentration and chemical composition of SOA as it ages suggested that two types of processes occur: fragmentation (loss of SOA mass due to the production of small molecules such as CO2, H2CO, etc.) and functionalization (addition of functional groups such as carbonyls and acids). Fragmentation was indicated by both the loss of aerosol mass determined by SMPS and also the shift from higher m/z oligomers to lower m/z oligomers in the mass spectra upon aging. Functionalization was indicated by the appearance of new m/z ions in the aged SOA spectra that contained additional oxygen molecules. Based on high resolution mass spectra, hundreds of peaks were assigned molecular formulas. Current work involves the use of ESI-MS/MS to infer structural assignments and formation mechanisms.