This study compiles and presents results from the factor analysis of 43 Aerosol Mass Spectrometer (AMS) datasets, including 27 reanalyzed datasets. The analysis reveals that organic aerosol (OA) in the Northern Hemisphere can be separated into oxygenated OA (OOA), hydrocarbon-like OA (HOA), and sometimes biomass burning OA (BBOA). The OOA component is further deconvolved into low-volatility OOA (LV-OOA) and semi-volatile OOA (SV-OOA). The mass spectra of these components are characterized by the ratios of m/z 44 (CO₂⁺) and m/z 43 (mostly C₂H₃O⁺), which are used to develop a new mass spectral diagnostic for tracking the aging of OA components. LV-OOA has higher f₄₄ and lower f₄₃ than SV-OOA, indicating a continuum of OOA properties in ambient aerosol. The OOA components from all sites cluster within a well-defined triangular region in the f₄₄ vs. f₄₃ space, which can be used to compare and characterize OOA components. As f₄₄ increases, OOA components become more similar to each other and to fulvic acid and HULIS sample spectra, indicating that ambient OA converges towards highly aged LV-OOA with atmospheric oxidation. The common features of the transformation between SV-OOA and LV-OOA at multiple sites enable a simplified description of OA oxidation in the atmosphere. Laboratory SOA data show that they are more similar to SV-OOA and rarely become as oxidized as ambient LV-OOA, likely due to higher loadings and limited oxidant exposure in chamber experiments. The study also compares laboratory data with ambient data, showing that most laboratory SOA fall into the same region as ambient data, but are more similar to less oxidized SV-OOA. The results highlight the importance of oxidation time and oxidant exposure in laboratory experiments and the need for further research to understand the relationship between the 44/43 ratio and the chemical functionality of OOA.This study compiles and presents results from the factor analysis of 43 Aerosol Mass Spectrometer (AMS) datasets, including 27 reanalyzed datasets. The analysis reveals that organic aerosol (OA) in the Northern Hemisphere can be separated into oxygenated OA (OOA), hydrocarbon-like OA (HOA), and sometimes biomass burning OA (BBOA). The OOA component is further deconvolved into low-volatility OOA (LV-OOA) and semi-volatile OOA (SV-OOA). The mass spectra of these components are characterized by the ratios of m/z 44 (CO₂⁺) and m/z 43 (mostly C₂H₃O⁺), which are used to develop a new mass spectral diagnostic for tracking the aging of OA components. LV-OOA has higher f₄₄ and lower f₄₃ than SV-OOA, indicating a continuum of OOA properties in ambient aerosol. The OOA components from all sites cluster within a well-defined triangular region in the f₄₄ vs. f₄₃ space, which can be used to compare and characterize OOA components. As f₄₄ increases, OOA components become more similar to each other and to fulvic acid and HULIS sample spectra, indicating that ambient OA converges towards highly aged LV-OOA with atmospheric oxidation. The common features of the transformation between SV-OOA and LV-OOA at multiple sites enable a simplified description of OA oxidation in the atmosphere. Laboratory SOA data show that they are more similar to SV-OOA and rarely become as oxidized as ambient LV-OOA, likely due to higher loadings and limited oxidant exposure in chamber experiments. The study also compares laboratory data with ambient data, showing that most laboratory SOA fall into the same region as ambient data, but are more similar to less oxidized SV-OOA. The results highlight the importance of oxidation time and oxidant exposure in laboratory experiments and the need for further research to understand the relationship between the 44/43 ratio and the chemical functionality of OOA.