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Organic aerosol components observed in Northern Hemispheric datasets from Aerosol Mass Spectrometry

by N. L. Ng, M. R. Canagaratna, Q. Zhang, J. L. Jimenez, J. Tian, I. M. Ulbrich, J. H. Kroll, K. S. Docherty, P. S. Chhabra, R. Bahreini, S. M. Murphy, J. H. Seinfeld, L. Hildebrandt, N. M. Donahue, P. F. Decarlo, V. A. Lanz, A. S H Prévôt, E. Dinar, Y. Rudich, D. R. Worsnop show all authors
Atmospheric Chemistry and Physics ()
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Abstract

In this study we compile and present results from the factor analysis of 43 Aerosol Mass Spectrometer (AMS) datasets (27 of the datasets are reanalyzed in this work). The components from all sites, when taken together, pro-vide a holistic overview of Northern Hemisphere organic aerosol (OA) and its evolution in the atmosphere. At most sites, the OA can be separated into oxygenated OA (OOA), hydrocarbon-like OA (HOA), and sometimes other compo-nents such as biomass burning OA (BBOA). We focus on the OOA components in this work. In many analyses, the OOA can be further deconvolved into 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 (CO + 2) and m/z 43 (mostly C 2 H 3 O +), which are used to develop a new mass spectral diagnostic for following the aging of OA compo-nents in the atmosphere. The LV-OOA component spectra have higher f 44 (ratio of m/z 44 to total signal in the com-Correspondence to: M. R. Canagaratna (mrcana@aerodyne.com) ponent mass spectrum) and lower f 43 (ratio of m/z 43 to total signal in the component mass spectrum) than SV-OOA. A wide range of f 44 and O:C ratios are observed for both LV-OOA (0.17±0.04, 0.73±0.14) and SV-OOA (0.07±0.04, 0.35±0.14) components, reflecting the fact that there is a continuum of OOA properties in ambient aerosol. The OOA components (OOA, LV-OOA, and SV-OOA) from all sites cluster within a well-defined triangular region in the f 44 vs. f 43 space, which can be used as a standardized means for comparing and characterizing any OOA components (labo-ratory or ambient) observed with the AMS. Examination of the OOA components in this triangular space indicates that OOA component spectra become increasingly similar to each other and to fulvic acid and HULIS sample spectra as f 44 (a surrogate for O:C and an indicator of photochemical aging) increases. This indicates that ambient OA converges towards highly aged LV-OOA with atmospheric oxidation. The com-mon features of the transformation between SV-OOA and LV-OOA at multiple sites potentially enable a simplified de-scription of the oxidation of OA in the atmosphere. Com-parison of laboratory SOA data with ambient OOA indicates Published by Copernicus Publications on behalf of the European Geosciences Union. 4626 N. L. Ng et al.: Organic aerosol components in Northern Hemispheric datasets that laboratory SOA are more similar to SV-OOA and rarely become as oxidized as ambient LV-OOA, likely due to the higher loadings employed in the experiments and/or limited oxidant exposure in most chamber experiments.

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