This study compiles and presents results from the factor analysis of 43 Aerosol Mass Spectrometer (AMS) datasets, focusing on organic aerosol (OA) components. The components from all sites provide a comprehensive overview of Northern Hemisphere OA and its atmospheric evolution. At most sites, OA can be separated into oxygenated OA (OOA), hydrocarbon-like OA (HOA), and sometimes biomass burning OA (BBOA). The OOA components are further deconvolved into low-volatility OOA (LV-OOA) and semi-volatile OOA (SV-OOA). The mass spectra of these components are characterized using the two main ions $m/z$ 44 ($\text{CO}_3^{2-}$) and $m/z$ 43 ($\text{C}_2\text{H}_3\text{O}^+$), which are used to develop a new mass spectral diagnostic for tracking OA aging in the atmosphere. LV-OOA has higher $f_{44}$ and lower $f_{43}$ compared to SV-OOA. A wide range of $f_{44}$ and O/C ratios are observed for both LV-OOA and SV-OOA, reflecting the continuum of OOA properties in ambient aerosol. The OOA components from all sites cluster within a well-defined triangular region in the $f_{44}$ vs. $f_{43}$ space, providing a standardized means for comparing and characterizing OOA components. The common features of the component spectra indicate that OOA components become increasingly similar to each other and to fulvic acid and HULIS sample spectra as $f_{44}$ increases, suggesting that ambient OA converges towards highly aged LV-OOA with atmospheric oxidation. The transformation between SV-OOA and LV-OOA at multiple sites potentially enables a simplified description of OA oxidation in the atmosphere. Comparison of laboratory SOA data with ambient OOA indicates that laboratory SOA is more similar to SV-OOA and rarely becomes as oxidized as ambient LV-OOA, likely due to higher loadings and limited oxidant exposure in chamber experiments.This study compiles and presents results from the factor analysis of 43 Aerosol Mass Spectrometer (AMS) datasets, focusing on organic aerosol (OA) components. The components from all sites provide a comprehensive overview of Northern Hemisphere OA and its atmospheric evolution. At most sites, OA can be separated into oxygenated OA (OOA), hydrocarbon-like OA (HOA), and sometimes biomass burning OA (BBOA). The OOA components are further deconvolved into low-volatility OOA (LV-OOA) and semi-volatile OOA (SV-OOA). The mass spectra of these components are characterized using the two main ions $m/z$ 44 ($\text{CO}_3^{2-}$) and $m/z$ 43 ($\text{C}_2\text{H}_3\text{O}^+$), which are used to develop a new mass spectral diagnostic for tracking OA aging in the atmosphere. LV-OOA has higher $f_{44}$ and lower $f_{43}$ compared to SV-OOA. A wide range of $f_{44}$ and O/C ratios are observed for both LV-OOA and SV-OOA, reflecting the continuum of OOA properties in ambient aerosol. The OOA components from all sites cluster within a well-defined triangular region in the $f_{44}$ vs. $f_{43}$ space, providing a standardized means for comparing and characterizing OOA components. The common features of the component spectra indicate that OOA components become increasingly similar to each other and to fulvic acid and HULIS sample spectra as $f_{44}$ increases, suggesting that ambient OA converges towards highly aged LV-OOA with atmospheric oxidation. The transformation between SV-OOA and LV-OOA at multiple sites potentially enables a simplified description of OA oxidation in the atmosphere. Comparison of laboratory SOA data with ambient OOA indicates that laboratory SOA is more similar to SV-OOA and rarely becomes as oxidized as ambient LV-OOA, likely due to higher loadings and limited oxidant exposure in chamber experiments.