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Published September 2011 | Published + Supplemental Material
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Elemental composition and oxidation of chamber organic aerosol


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 in AMS spectra, respectively; we refer to this graphical representation 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 allows for the exploration of areas higher on the "triangle plot" not easily accessible with non-oxidized precursors. As SOA ages, it migrates toward the top of the triangle along a path largely dependent on the precursor identity, which suggests increasing organic acid content and decreasing 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 within the uncertainty of the AMS elemental analysis. 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, which is indicative of oxidation of the precursor without substantial losss of hydrogen, likely due to the unsaturated nature of the precursors. From the spectra of SOA studied here, we are able to reproduce the triangular region originally constructed with ambient OOA compents 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.

Additional Information

© 2011 Author(s). This work is distributed under the Creative Commons Attribution 3.0 License. Published by Copernicus Publications on behalf of the European Geosciences Union. Received: 21 March 2011. Published in Atmos. Chem. Phys. Discuss.: 30 March 2011. Revised: 15 August 2011. Accepted: 24 August 2011. Published: 1 September 2011. This work was supported by the US Department of Energy Biological and Environmental Research grant DE-FG02-05ER63983, US Environmental Protection Agency STAR grant RD-83374901, and US NSF grant ATM-0432377. It has not been formally reviewed by EPA. The views expressed in this document are solely those of the authors and the EPA does not endorse any products in this publication. The authors would like to thank Christine Loza for SOA yield analysis and Man Nin Chan, Lindsay Yee, and Katherine Schilling for guaiacol filter analysis. The authors would also like to thank Satoshi Takahama for helpful discussions on FTIR analysis. Edited by: G. McFiggans

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Published - Chhabra2011p16004Atmos_Chem_Phys.pdf

Supplemental Material - acp-11-8827-2011-supplement.pdf


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