Changes in Aerosol Mass Spectra during the Photochemical Aging of Organic Aerosols
The Aerosol Mass Spectrometer (AMS) provides real-time quantitative mass concentrations of non-refractory species in ambient aerosols. Factor analysis of the AMS organic aerosols (OA) data showed that the oxygenated OA (OOA) can be deconvolved into two broad subtypes differ in volatility and degree of oxidation: low-volatility OOA (LV-OOA) and semi-volatile OOA (SV-OOA). Differences in the mass spectra of these components are characterized in terms of the two main ions m/z 44 (mostly CO2 +, likely from acid groups) and m/z 43 (mostly C2H3O+, likely from non-acid oxygenates). The OOA components from all sites cluster within a well defined triangular region in the f44 (ratio of m/z 44 to total signal in the component spectrum) vs. f43 space (defined similarly) (“triangle plot), which can be used as a standardized means of comparing and characterizing any OOA components (laboratory or ambient) observed with the AMS. The OOA components become increasingly similar with atmospheric photochemical aging 1 . We develop a method to parameterize H:C of OOA in terms of f43. Such parameterization allows the transformation of large database of ambient OOA components from “triangle plot1 into the Van Krevelen diagram (H:C vs. O:C). Heald et al.2 suggested that the bulk composition of OA line up in the Van Krevelen diagram with a slope ~ -1; such slope can potentially arise from the physical mixing of HOA and OOA, and/or from chemical aging of these components. In this study, we find that the OOA components from all sites occupy an area in the Van Krevelen space, with the evolution of OOA following a shallower slope of ~ -0.5, consistent with the additions of both acid and alcohol functional groups without fragmentation, and/or the addition of acid groups with C-C bond breakage. The importance of acid formation in OOA evolution is consistent with increasing f44 in the triangle plot with photochemical age.
Aerosol mass spectrometry organic aerosols functional groups
Nga L. Ng Manjula R. Canagaratna Jose L. Jimenez Puneet S. Chhabra John H.Seinfeld Douglas R. Worsnop
Aerodyne Research,Inc. Billerica,MA,USA Department of Chemistry and Biochemistry,University of Colorado,Boulder,CO,USA CIRES,University of Department of Chemical Engineering,California Institute of Technology,Pasadena,CA,USA
国际会议
西安
英文
310-317
2011-08-17（万方平台首次上网日期，不代表论文的发表时间）