Molecular formulae were additionally associated with different molecular categories because less than 6% of the DOM has been identified on a molecular level.Molecular categories are defined as follow: 1) dissolved black carbon (BC), with an AImod >= 0.67 (Koch and Dittmar, 2006; doi:10.1002/rcm.2386) was separated in 3 different subgroups, either <15 (BC-<15C), or =15C) C atoms both without heteroatoms, or containing heteroelements (BC-CHOx); 2) polyphenols (poly), with an AImod >0.5 but <0.67; 3) highly unsaturated formulae, with an AImod <0.5, H/C <1.5; 4) formulae of unsaturated aliphatics, with an 1.5< H/C <2, O/C 2, O/C 0.9 and with either no (sugars) or with heteroatoms (sugars-CHOx) and 7) peptide molecular formulae, with 1.5 < H/C <2, O/C 0. Additionally, poly, highly unsaturated and unsaturated aliphatics were further separated in oxygen rich (O-rich) and oxygen poor (O-poor) if the element ratio O/C was > 0.5 or < 0.5 respectively.