Fig. 2
Polycyclic aromaticity and nitrogen content along the Amazon River. Molecular parameters of the 1272 detected polycyclic aromatic molecular formulae with aromaticity index ≥0.67 as analyzed by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). By definition, polycyclic aromatics include thermogenic DBC molecular formulae. Numbers on the plot correspond to station locations in Supplementary Table 1. a Plot of the intensity weighted-average aromaticity per samples of polycyclic aromatic molecular formulae along the sampling transect, given by shades of red. The aromaticity decreased relatively downstream. b The intensity weighted-average molecular mass (in Daltons) of polycyclic aromatic molecular formulae over the sampling transect with number of polycyclic aromatic molecular formulae with color-coded intensity weighted-average of nitrogen content of the polycyclic aromatic molecular formulae along longitude. The number of polycyclic aromatic molecular formulae decreased downstream while the relative content of nitrogen per polycyclic aromatic molecular formula increased
