Atmos. Chem. Phys. Discuss., 11, 10305-10342, 2011
www.atmos-chem-phys-discuss.net/11/10305/2011/
doi:10.5194/acpd-11-10305-2011
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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.
Elemental composition and oxidation of chamber organic aerosol
P. S. Chhabra1, N. L. Ng2, M. R. Canagaratna2, A. L. Corrigan3, L. M. Russell3, D. R. Worsnop2, R. C. Flagan1,4, and J. H. Seinfeld1,4
1Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA, USA
2Aerodyne Research, Inc. Billerica, MA, USA
3Scripps Institution of Oceanography, University of California, San Diego, CA, USA
4Division of Engineering and Applied Science, California Institute of Technology, Pasadena, CA, USA

Abstract. Recently, graphical representations of aerosol mass spectrometer (AMS) spectra and elemental composition have been developed to explain the oxidative and aging processes of secondary organic aerosol (SOA). It has been shown previously that oxygenated organic aerosol (OOA) components from ambient and laboratory data fall within a triangular region in the f44 vs. f43 space, where f44 and f43 are the ratios of the organic signal at m/z 44 and 43 to the total organic signal, respectively; we refer to this model as the "triangle plot." Alternatively, the Van Krevelen diagram has been used to describe the evolution of functional groups in SOA. In this study we investigate the variability of SOA formed in chamber experiments from twelve different precursors in both "triangle plot" and Van Krevelen domains. Spectral and elemental data from the high-resolution Aerodyne aerosol mass spectrometer are compared to offline species identification analysis and FTIR filter analysis to better understand the changes in functional and elemental composition inherent in SOA formation and aging. We find that SOA formed under high- and low-NOx conditions occupy similar areas in the "triangle plot" and Van Krevelen diagram and that SOA generated from already oxidized precursors starts higher on the "triangle plot." As SOA ages, it migrates toward the top of the triangle, suggesting higher organic acid content and decreased mass spectral variability. The most oxidized SOA come from the photooxidation of methoxyphenol precursors which yielded SOA O/C ratios near unity. α-pinene ozonolysis and naphthalene photooxidation SOA systems have had the highest degree of mass closure in previous chemical characterization studies and also show the best agreement between AMS elemental composition measurements and elemental composition of identified species. In general, compared to their respective unsaturated SOA precursors, the elemental composition of chamber SOA follows a slope shallower than −1 on the Van Krevelen diagram. From the spectra of SOA studied here, we are able to reproduce the triangular region originally constructed with ambient OOA components with chamber aerosol showing that SOA becomes more chemically similar as it ages. Ambient data in the middle of the triangle represent the ensemble average of many different SOA precursors, ages, and oxidative processes.

Citation: Chhabra, P. S., Ng, N. L., Canagaratna, M. R., Corrigan, A. L., Russell, L. M., Worsnop, D. R., Flagan, R. C., and Seinfeld, J. H.: Elemental composition and oxidation of chamber organic aerosol, Atmos. Chem. Phys. Discuss., 11, 10305-10342, doi:10.5194/acpd-11-10305-2011, 2011.
 
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