AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
Laboratory Studies of Biomass Burning Aerosol Oxidation at the Bulk and Molecular Level
CLAIRE FORTENBERRY, Michael Walker, Yaping Zhang, Dhruv Mitroo, William Brune, Brent Williams, Washington University in St Louis
Abstract Number: 99532 Working Group: Aerosol Chemistry
Abstract The atmospheric chemical aging of biomass burning organic aerosol (BBOA) is highly complex and often difficult to characterize. In this study, a thermal desorption aerosol GC/MS (TAG) was used in parallel to a high-resolution time-of-flight aerosol mass spectrometer (AMS) to analyze the chemical composition of photochemically aged oak wood and oak leaf BBOA. Primary BBOA was created in a combustion chamber and oxidized in a potential aerosol mass (PAM) flow reactor to simulate different levels of atmospheric aging.
Traditional chromatography utilizes a “solvent delay” at the beginning of the analysis to prevent detector damage from large solvent signals. In the TAG, much of the solvent can be purged prior to sample injection and the solvent delay is no longer applied. This allows volatile components and thermal decomposition products to reach the detector during thermal sample transfer from the TAG collection cell to the GC column. The TAG thermal decomposition signal was studied in conjunction with AMS spectra to analyze the most highly oxidized fraction of collected BBOA. We have observed a rise in m/z 44 (CO2) signal in the TAG desorption window with increasing oxidation, consistent with an increase in aerosol aging. Previous BBOA mass spectral aging studies have identified the m/z 60 fragment (CH3COOH) as a reliable tracer for freshly emitted BBOA, attributing a decrease in m/z 60 signal to the oxidative degradation of lignin combustion products over time. We instead observed an overall rise in m/z 60 abundance with oxidation of oak wood in both the AMS data and the TAG decomposition period, demonstrating that the occurrence of m/z 60 in a sample is dependent on multiple factors and does not solely result from freshly emitted BBOA. Finally, the oxidative evolution of key molecular marker compounds will be presented.