The chemical heterogeneity of SOM is one of its characteristic features. To explore this diversity, SOM systems with five different compositions were investigated. Escalona et al. analyzed and sorted HSs from the International Humic Substances Society (IHSS) via a principal component (PC) analysis, using aromaticity and acidity as PCs (please refer to Figure in their paper). Following this categorization, certain HS types, including humic acid (HA) and fulvic acid (FA), were investigated to represent characteristic compositions within the chemical space (see Table ). For more information about the different SOM types, please see Table in the Supporting Information, which provides the elemental and organic fractions of the SOM systems. In addition, Figures and provide detailed insights into the heterogeneity and distribution of fragments within the SOM compositions.