Atmos. Chem. Phys. Atmospheric Chemistry and Physics, vol. 11 (2011) pp. 6465-6474
Organic aerosols (OA) can be separated with fac-tor 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 f 43 (ratio of m/z 43, mostly C 2 H 3 O + , to total sig-nal in the component mass spectrum). Such parameteriza-tion allows for the transformation of large database of am-bient OOA components from the f 44 (mostly CO + 2 , likely from acid groups) vs. f 43 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 to-tal OA is deconvolved into components that correspond to primary (HOA and others) and secondary (OOA) organic aerosols. By deconvolving total OA into different compo-nents, 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 ambi-ent secondary OA evolution that is analogous to and can be compared with trends observed in chamber studies of sec-ondary organic aerosol formation. The triangle plot in Ng et al. (2010) indicates that f 44 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 Correspondence to: M. R. Canagaratna (email@example.com) space which follows a 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 composi-tion evolution to molecular-level studies.
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