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Published July 1, 2011 | Published + Supplemental Material
Journal Article Open

Changes in organic aerosol composition with aging inferred from aerosol mass spectra


Organic aerosols (OA) can be separated with factor analysis of aerosol mass spectrometer (AMS) data into hydrocarbon-like OA (HOA) and oxygenated OA (OOA). We develop a new method to parameterize H:C of OOA in terms of f₄₃ (ratio of m/z 43, mostly C₂H₃O⁺, to total signal in the component mass spectrum). Such parameterization allows for the transformation of large database of ambient OOA components from the f₄₄ (mostly CO₂⁺, likely from acid groups) vs. f₄₃ space ("triangle plot") (Ng et al., 2010) into the Van Krevelen diagram (H:C vs. O:C) (Van Krevelen, 1950). Heald et al. (2010) examined the evolution of total OA in the Van Krevelen diagram. In this work total OA is deconvolved into components that correspond to primary (HOA and others) and secondary (OOA) organic aerosols. By deconvolving total OA into different components, we remove physical mixing effects between secondary and primary aerosols which allows for examination of the evolution of OOA components alone in the Van Krevelen space. This provides a unique means of following ambient secondary OA evolution that is analogous to and can be compared with trends observed in chamber studies of secondary organic aerosol formation. The triangle plot in Ng et al. (2010) indicates that f₄₄ of OOA components increases with photochemical age, suggesting the importance of acid formation in OOA evolution. Once they are transformed with the new parameterization, the triangle plot of the OOA components from all sites occupy an area in Van Krevelen space which follows a ΔH:C/ΔO:C slope of ~ −0.5. This slope suggests that ambient OOA aging results in net changes in chemical composition that are equivalent to the addition of both acid and alcohol/peroxide functional groups without fragmentation (i.e. C-C bond breakage), and/or the addition of acid groups with fragmentation. These results provide a framework for linking the bulk aerosol chemical composition evolution to molecular-level studies.

Additional Information

© 2011 Author(s). Received: 23 February 2011 – Published in Atmos. Chem. Phys. Discuss.: 2 March 2011. Revised: 28 June 2011. Accepted: 28 June 2011. Published: 7 July 2011. We thank grants from DOE (BER, ASR program) DEFG0208ER64627, NOAA NA08OAR4310565, and NSF ATM-0919189. We thank Paola Massoli for sharing the Boston College flow tube data and Jesse Kroll for helpful discussions. We thank the two anonymous reviewers for their helpful comments.

Attached Files

Published - Ng2011p15734Atmos_Chem_Phys.pdf

Supplemental Material - acp-11-6465-2011-supplement.pdf


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