Atmos. Chem. Phys. Discuss., 11, 53-89, 2011
www.atmos-chem-phys-discuss.net/11/53/2011/
doi:10.5194/acpd-11-53-2011
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Understanding evolution of product composition and volatility distribution through in situ GC × GC analysis: a case study of longifolene ozonolysis
G. Isaacman1, D. R. Worton1,2, N. M. Kreisberg2, C. J. Hennigan3, A. P. Teng2, S. V. Hering2, A. L. Robinson3, N. M. Donahue3, and A. H. Goldstein1
1Department of Environmental Science, Policy and Management, University of California, Berkeley, California, USA
2Aerosol Dynamics, Inc., Berkeley, California, USA
3Center for Atmospheric Particle Studies, Carnegie Mellon University, Pittsburgh, Pennsylvania, USA

Abstract. A method for predicting volatility and polarity based on chromatographic information was developed and applied to the smog chamber ozonolysis of the sesquiterpene longifolene. The products were collected and analyzed using a GC × GC Thermal Desorption Aerosol Gas Chromatograph/Mass Spectrometer (2D-TAG) and a quadrupole Aerodyne Aerosol Mass Spectrometer (AMS). All the secondary organic aerosol (SOA) was produced within the first half hour of the experiment. However, the oxidation level of the organic aerosol, as inferred from the fraction of ion m/z 44, suggested continued evolution of the SOA over the subsequent hours. Measurements of speciated organic compounds using 2D-TAG confirm that the composition of the particles changed over the course of the experiment. Nearly 200 oxidation products (thought to be mostly ketones and acids) were observed with 2D-TAG, but most could not be identified definitively due to a lack of standards and the absence of likely sesquiterpene oxidation products in available mass spectral databases. To categorize the observed products, the vapor pressure and oxygen-to-carbon ratio (O/C) of observed compounds were estimated based on their multi-dimensional chromatographic retention times relative to those of known standards, establishing a retention time correlation (RTC) method for using 2D-TAG to better constrain important modelling parameters. The product distribution continuously evolved in volatility and oxygenation during 5 h of oxidation. Using peak area as the best available proxy for mass, we conclude that the product mixture includes many non-negligible products; the most abundant 3 compounds accounted for only half of the total observed peak area and 80% of peak area was spread across 15 compounds. The data provide evidence for three conclusions: (1) 2D-TAG can provide valuable volatility and oxygenation information even in the absence of definitive species identification, (2) complex particle-phase chemistry causes continued evolution of particle composition after formation of new particles was complete, and (3) minor products contribute significantly to SOA from the ozonolysis of sesquiterpenes.

Citation: Isaacman, G., Worton, D. R., Kreisberg, N. M., Hennigan, C. J., Teng, A. P., Hering, S. V., Robinson, A. L., Donahue, N. M., and Goldstein, A. H.: Understanding evolution of product composition and volatility distribution through in situ GC × GC analysis: a case study of longifolene ozonolysis, Atmos. Chem. Phys. Discuss., 11, 53-89, doi:10.5194/acpd-11-53-2011, 2011.
 
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